CA1138723A - Developing method for developer transfer under electrical bias and apparatus therefor - Google Patents
Developing method for developer transfer under electrical bias and apparatus thereforInfo
- Publication number
- CA1138723A CA1138723A CA000332015A CA332015A CA1138723A CA 1138723 A CA1138723 A CA 1138723A CA 000332015 A CA000332015 A CA 000332015A CA 332015 A CA332015 A CA 332015A CA 1138723 A CA1138723 A CA 1138723A
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- CA
- Canada
- Prior art keywords
- developer
- electric field
- bearing member
- image bearing
- clearance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
- G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
- G03G15/09—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush
- G03G15/0914—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush with a one-component toner
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
- G03G15/065—Arrangements for controlling the potential of the developing electrode
Abstract
TITLE OF THE INVENTION
DEVELOPING METHOD FOR DEVELOPER TRANSFER UNDER
ELECTRICAL BIAS AND APPARATUS THEREFOR
ABSTRACT OF THE DISCLOSURE
This specification discloses a method of toner transfer development in which a low frequency alternating electrical bias is applied to the space between a latent image bearing member and a developer carrying member to develop the latent image on the latent image bearing member, and an apparatus for carrying out the same method.
This bias has a first process in which reciprocal move-ment of developer particles is effected also between the non-image area of the latent image bearing member and the developer carrying member, and a second process in which the intensity of the bias is adjusted so that one-sided movement of developer particles from the developer carrying member to the image area and one-sided movement of developer particles from the non-image area to the developer carrying member may take place. .
DEVELOPING METHOD FOR DEVELOPER TRANSFER UNDER
ELECTRICAL BIAS AND APPARATUS THEREFOR
ABSTRACT OF THE DISCLOSURE
This specification discloses a method of toner transfer development in which a low frequency alternating electrical bias is applied to the space between a latent image bearing member and a developer carrying member to develop the latent image on the latent image bearing member, and an apparatus for carrying out the same method.
This bias has a first process in which reciprocal move-ment of developer particles is effected also between the non-image area of the latent image bearing member and the developer carrying member, and a second process in which the intensity of the bias is adjusted so that one-sided movement of developer particles from the developer carrying member to the image area and one-sided movement of developer particles from the non-image area to the developer carrying member may take place. .
Description
Field of the Invention This invention relates to a developing method for developing a latent image by the use of a developer and an apparatus therefor, and more particularly to a develop-ing method using a one-component developer, especially a developing method which enables obtainment of fogless visible images excellent in sharpness and tone reproduction, and an apparatus therefor.
Description of the Prior Art Various types of developing method using a one-component developer are heretofore known such as the powder cloud method which uses toner particles in cloud condition, the contact developing method in which a uniform toner layer formed on a toner supporting member comprising a web or a sheet is brought into contact with an electrostatic image bearing surface to effect develop-ment, and the magnedry method which uses a conductive magnetic toner formed into a magnetic brush which is brought into contact with the electrostatic image bearing surface to effect development.
Among the above-described various developing methods using one-component developer, the powder cloud method, the contact developing method and the magnedry method are such that the toner contacts both
Description of the Prior Art Various types of developing method using a one-component developer are heretofore known such as the powder cloud method which uses toner particles in cloud condition, the contact developing method in which a uniform toner layer formed on a toner supporting member comprising a web or a sheet is brought into contact with an electrostatic image bearing surface to effect develop-ment, and the magnedry method which uses a conductive magnetic toner formed into a magnetic brush which is brought into contact with the electrostatic image bearing surface to effect development.
Among the above-described various developing methods using one-component developer, the powder cloud method, the contact developing method and the magnedry method are such that the toner contacts both
- 2 -1 the image area (the area to which the toner should adhere) and the non-image area~(the background area to which the toner should not adhere) and therefore, the toner more or less adheres to the non-image area as well, 5 thus unavoidably creating the so-called fog.
To avoid such fog, there has been proposed the transfer development with space between toner donor and image bearing member in which a toner layer and an electrostatic image bearing surface are disposed in opposed relationship with a clearance therebetween in a developing process so that the toner is caused to fly to the image area by the electrostatic field thereof and the toner does not contact the non-image area.
Such development is disclosed, for example, in U.S.
Patents Nos. 2,803,177; 2,758,525; 2,838,997; 2,839,400;
2,862,816; 2,996,400; 3,232,190 and 3,703,157.
This development i9 a highly effective method in prevent-ing the fog. Nevertheless, the visible image obtained by this method generally suffers from the following disadvantages because it utilizes the flight of the toner resulting from the electric field of the electro-static image during the development.
A first disadvantage i9 the problem that th0 sharpness of the image is reduced at the edges of the image. The state of the electric field of the electro-.
` ~ 113Ei7Z3 1 static image at the edge thereof is such that ifan electrically conductive member is used as the developer supporting member, the electric lines of force which emanate from the image area reach the toner supporting member so that the toner particles fly along these electric lines of force and adhere to the surface of the photo-sensitive medium, thus effecting development in the vicinity of center of the image area. ~t the edges of the image area, however, the electric lines of force do not reach the toner supporting member due to the charge induced at the non-image area and therefore, the adherence of the flying toner particles is very unreliable and some of such toner particles barely adhere while some of the toner particles do not adhere.
Thus, the resultant image is an unclear one lacking sharpness at the edges of the image area, and line images, when developed, give an impression of having become thinner than the original lines.
To avoid this in the above-described toner transfer development, the clearance between the electro-static image bearing surface and the developer supporting member surface must be sufficiently small (e.g. smaller than 100 ~) and actually, accidents such as pressure contact of the developer and mixed foreign substances are liable to occur between the two surfaces. Also, 113E~7Z3 1 maintaining such a fine clearance often involves difficulties in designing of the apparatus.
A second problem is that images obtained by the above-described toner transfer development usually lack tone reproducibility. In the toner transfer development, the toner does nct fly until the toner overcomes the binding power to the toner supporting member by the electric field of the electrostatic image.
This power which binds the toner to the toner supporting member is the resultant force of the Van der Waals force between the toner and the toner supporting member, the force of adherence among the toner particles, and the reflection force between the toner and the toner supporting member resulting from the toner being charged. Therefore, flight of the toner takes place only when the potential of the electrostatic image has become greater than a predetermined value (hereinafter referred to as the transition threshold value of the toner) and the electric field resulting therefrom has exceeded the aforementioned binding force of the toner, whereby adherence of the toner to the electrostatic image bearing surface takes .
place. But the binding power of the toner to the supporting member differs in value from particle to particle or by the particle diameter of the toner even if the toner has been manufactured or prepared in accord-,' ', ' '' ',' , ~ 113~17Z3 1 ance with a predetermined prescription, and therefore,it is considered to be distributed narrowly around a substantially constant value and correspondingly, the threshold value of the electrostatic image surface potential at which the flight of toner takes place also seems to be distributed narrowly around a certain constant value. Such presence of the threshold value during the flight of the toner from the supporting member causes adherence of the toner to that part of the image area which has a surface potential exceeding : such threshold value, but causes little or no toner to adhere to that part of the image area which has a surface potential lower than the threshold value, with a result that there are only provided images which lack the tone gradation having steep y (the gradient of the character-istic curve of the image density with respect to the electrostatic image potential).
In view of such problems, a developing device in which a pulse bias of very high frequency is introduced across an air gap to ensure movement of charged toner particles flying through the air gap, whereby the charged toner particles are made more readily available to the charged image is disclosed in U.S. Patents Nos.
To avoid such fog, there has been proposed the transfer development with space between toner donor and image bearing member in which a toner layer and an electrostatic image bearing surface are disposed in opposed relationship with a clearance therebetween in a developing process so that the toner is caused to fly to the image area by the electrostatic field thereof and the toner does not contact the non-image area.
Such development is disclosed, for example, in U.S.
Patents Nos. 2,803,177; 2,758,525; 2,838,997; 2,839,400;
2,862,816; 2,996,400; 3,232,190 and 3,703,157.
This development i9 a highly effective method in prevent-ing the fog. Nevertheless, the visible image obtained by this method generally suffers from the following disadvantages because it utilizes the flight of the toner resulting from the electric field of the electro-static image during the development.
A first disadvantage i9 the problem that th0 sharpness of the image is reduced at the edges of the image. The state of the electric field of the electro-.
` ~ 113Ei7Z3 1 static image at the edge thereof is such that ifan electrically conductive member is used as the developer supporting member, the electric lines of force which emanate from the image area reach the toner supporting member so that the toner particles fly along these electric lines of force and adhere to the surface of the photo-sensitive medium, thus effecting development in the vicinity of center of the image area. ~t the edges of the image area, however, the electric lines of force do not reach the toner supporting member due to the charge induced at the non-image area and therefore, the adherence of the flying toner particles is very unreliable and some of such toner particles barely adhere while some of the toner particles do not adhere.
Thus, the resultant image is an unclear one lacking sharpness at the edges of the image area, and line images, when developed, give an impression of having become thinner than the original lines.
To avoid this in the above-described toner transfer development, the clearance between the electro-static image bearing surface and the developer supporting member surface must be sufficiently small (e.g. smaller than 100 ~) and actually, accidents such as pressure contact of the developer and mixed foreign substances are liable to occur between the two surfaces. Also, 113E~7Z3 1 maintaining such a fine clearance often involves difficulties in designing of the apparatus.
A second problem is that images obtained by the above-described toner transfer development usually lack tone reproducibility. In the toner transfer development, the toner does nct fly until the toner overcomes the binding power to the toner supporting member by the electric field of the electrostatic image.
This power which binds the toner to the toner supporting member is the resultant force of the Van der Waals force between the toner and the toner supporting member, the force of adherence among the toner particles, and the reflection force between the toner and the toner supporting member resulting from the toner being charged. Therefore, flight of the toner takes place only when the potential of the electrostatic image has become greater than a predetermined value (hereinafter referred to as the transition threshold value of the toner) and the electric field resulting therefrom has exceeded the aforementioned binding force of the toner, whereby adherence of the toner to the electrostatic image bearing surface takes .
place. But the binding power of the toner to the supporting member differs in value from particle to particle or by the particle diameter of the toner even if the toner has been manufactured or prepared in accord-,' ', ' '' ',' , ~ 113~17Z3 1 ance with a predetermined prescription, and therefore,it is considered to be distributed narrowly around a substantially constant value and correspondingly, the threshold value of the electrostatic image surface potential at which the flight of toner takes place also seems to be distributed narrowly around a certain constant value. Such presence of the threshold value during the flight of the toner from the supporting member causes adherence of the toner to that part of the image area which has a surface potential exceeding : such threshold value, but causes little or no toner to adhere to that part of the image area which has a surface potential lower than the threshold value, with a result that there are only provided images which lack the tone gradation having steep y (the gradient of the character-istic curve of the image density with respect to the electrostatic image potential).
In view of such problems, a developing device in which a pulse bias of very high frequency is introduced across an air gap to ensure movement of charged toner particles flying through the air gap, whereby the charged toner particles are made more readily available to the charged image is disclosed in U.S. Patents Nos.
3,866,574; 3,890,929 and 3,893,418.
Such high frequency pulse bias developing device 113~Z3 1 may be said to be a developing system suitable for the line copying in that a pulse bias of several KHz or higher is applied in the clearance between the toner donor member and the image retaining member to improve the vibratory characteristic of the toner and present the toner from reaching the non-image area in any pulse bias phase but cause the toner to transit only to the image area, thereby preventing fogging of the non-image area. However, the aforementioned U.S. Patent No.
3,893,418 states that a very high frequency (18 KHz -22 KHz) is used for the applied pulse voltage in order to make the device suitable for the reproduction of tone gradation of the image.
U.S. Patent No. 3,346,475 discloses a method which comprises immersing two electrodes in insulating liquid contained in a dielectrophoretic cell and applying thereto an AC voltage of very low frequency (lower than about 6 Hz) to thereby effect the develop-ment of a pattern corresponding to the conductivity variance.
Further, U.S. Patent No. 4,014,291 disclosesa transfer development which uses dry one-component magnetic toner, but this patent does not suggest that a bias is applied for the above-described purpose of preventing fog.
1131~23 SUMMARY OF THE INVENTION
- The present invention has been made to eliminate the above-noted problems peculiar to the various developing methods using one-component developer. The present invention relates to a developing method which enables obtainment of visible images which are free of fog and excellent in edge reproduction and tone gradation, and an apparatus therefor.
- The present invention also relates to a developing method based on the principle of development in which a low frequency alternate electric field having a phase of a particular polarity which causes the developer to one-sidedly reach both the image area and the non-image area of a latent image bearing member from a developer carrier and a phase of the opposite polarity to the particular polarity which lS applies a bias in a direction to cause the developer having reached at least the non-image area to return to the de-veloper carrier side is applied in the developing clearance to thereby ensure transition of the developer to the non-image area and back transition of the developer to the developer carrier to be alternately repeated even in the clearance between the developer carrier and the non-image area in the developing station and enable a develop-ment very excellent in tone reproduction to be accomplished by such reciprocal movement of the developer, and an appara-tus therefor.
The present invention further relates to a developing method which has a first process in which an extraneous vibratory electric field is imparted so that the low fre-quency electric field in the developing clearance may alternate in at least the non-image area of the latent image bearing member, whereby reciprocal movement of the developer particles may take place between the non-imaye area and the developer carrier, and a second process in which the in-tensity of the extraneous vibratory electric field is ; 35 adjusted to cause one-sided transition of the developer particles from the developer carrier to the image area and ,:
:
11315~7Z3 from the non-image area to the developer carrier, thereby obtaining a result of development which is free of fog and excellent in tone gradation, and an apparatus therefor.
.~
The present invention still further relates to a developing method in which the second process is imparted in a process in which the latent image bearing member and --the developer carrier are stationary and opposed to each other and the amplitude of the extraneously applied vibra-tory electric field is attenuated toward the termination of the development and converged into a predetermined value, and an apparatus therefor.
The present invention still further relates to a de-veloping method in which the extraneously applied vibratory :
alternate voltage is maintained constant and the latent image bearing member and the developer carrier are opposed to each other while being moved to increase the clearance there-between gradually, to thereby impart the second process, and an apparatus therefor.
The present invention still further relates to a developing method which comprises disposing a latent image bearing member and a developer carrier carrying a developer layer thereon in opposed relationship in a developing station with a clearance maintained therebetween, the clearance being greater than the thickness of the developer layer, and effec-ting development while applying an alternate electric fieldin a range satisfying.; , .
400 V _ Vp p ~ 2500 V
40 Hz _ f ~ 1.5 KHz : where Vp_p represents the amplitude of the alternate electric; 30 field (V : peak-to-peak value) and f represents the alter-: nating frequency of the alternate electric field to apply _g_ . J ~
113~'~ 23 an alternate electric field having a phase of a particular polarity which causes the developer to one-sidedly reach both the image area and the non-image area of the latent image bearing member from the developer carrier in the developing clearance and a phase of the opposite polarity - to the particular polarity for applying a bias in a direc-tion to cause the developer having reached at least the non-image area to return to the developer carrier side, and an apparatus therefor.
.
The present invention further relates to a developing method which comprises disposing a latent image bearing member and a developer carrier in opposed relationship in a developing station with a clearance maintained therebetween, and effecting development by applying to the clearance an alternate voltage of a frequency lower than 1.5 KHz, the frequéncy and amplitude value of the alternate voltage being selectively changed over in accordance with the kind of the image to be reproduced, and an apparatus therefor.
More particularly, the present invention relates to ~ method of applying dry developer to an image bearing member, comprising thé steps of: disposing an image bearing ,.. . .
member and a developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alter-nating electric field having a phase wherein the electric field formed in the clearance corresponding to an image area ~; of the image bearing member is in the direction of trans-ferring the developer from the developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the trans-ferred developer from the image area of the image bearing member to the developer carrier.
113~23 The present invention also relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a . developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is - greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
The present invention further relates to a method of applying dry developer to an image bearing member, comprising : 20 the step~ of: disposing an image bearing member and a developercarrier for carrying a layer of developer on the surface . thexeof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alter-nating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier and wherein the electric field formed in the clearance corres-ponding to the image area is in the direction of transferring : the developer from the developer carrier to the image bearing member.
~ I
~13F~723 The present invention still further relates to amethod of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and apply-ing an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric 10 field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance correspond- .
15 ing to a non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the : developer carrier, the alternating electric field having a fre~uency low enough to allow the developer to transfer and 20 transfer back repeatedly between the image bearing member and the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, com-prising the steps of: disposing an image bearing member and 25 a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relation-ship in a developing station with a clearance maintained there-: between which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating 30 means therewithint and applying an alternating electric fieldacross the clearance, the alternating electric field having a phase where.in the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring the developer from the 35 developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to -lla-.. , . . . _, . . .. .. ... . .
1~3t3723 an image area of the image bearing member is in the direc-tion of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alter-nating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, com-prising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of .
magnetic developer on the surface thereof in opposed re-lationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image ar~a of the image bearing member, and a phase wherein -llb-the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, and wherein the ele~tric field formed in the clearance corres-ponding to the non-image area is in the direction of trans-ferring the developer from thè developer carrier to the image bearing member.
The present invention.yet further relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance main-tained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric ield across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alter-nating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly be-tween the image bearing member and the developer carrier.
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of: forming a layer of one-component developer on the surface of a developing carrier disposed in opposed re-lationship with the image bearing member in a developer j -11 ~ 1 3t~Z3 station with a clearance maintained therebetween which is . greater than the thickness of the developer layer; apply-ing an alternating electric field across the developing clearance, the field having a frequency sufficient to cause reciprocating movement of the one-component developer particles between the electrostatic image bearing member and the de-veloper carrier in accordance with the alternating electric field; and changing the intensity of the alternative elec-~ tric field acting on the developing clearance to thereby ; 10 convert the reciprocating movement to one-sided movement of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member in the image area and to one-sided movement of the developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer : carrier in the non-image area.
, , .
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of: forming a layer of one-component developer on the surface of a developer carrier disposed in opposed re-lationship with the image bearing member in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; applying an alternating electric field across the developing clearance, the field having a frequency sufficient to cause the developer particles to transit from the developer layer through the clearance and contact the image area and the non-image area of the electrostatic image bearing member, and then to cause the developer particles having so contacted the image bearing member to return to the developer carrier and such reciprocating movement of the developer is repeated; and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the -lld-113~23 reciprocating movement to one-sided movement in which the developer particles one-sidedly transit from the developer carrier to the image area.of the electrostatic image bearing member and contact the image area and the developer particles : 5 present in the non-image area one-sidedly return to the developer carrier and such movement of the developer is repeated.
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member, comprising the steps of: disposing an electro-static image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed rela-tionship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; applying an alternating electric field across the developing clearance, the field having a suffi-cient frequency so that its direction in the developing clearance alternates in at least the non-image area of the electrostatic image bearing member, to thereby cause the developer to reach the non-image area as well, and then cause the developer to return to the developer carrier, such reciprocal movement of the developer particles taking place repeatedly in the developing clearance; and adjusting the intensity of the alternating electric field to cause the transition of the developer particles to take place in the image area one-sidedly in a direction from the developer carrier to the image area and to take place in the non-image area one-sidedly in a direction from the non-image area to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an electrostatic i.mage bearing member, comprising the steps of: disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed ~i -lle 7;~3 relationship in a developing station with a clearance main-tained therebetween which is greater than the thickness of the developer layer; applying an alternating electric .; field in the clearance, the field having a sufficient frequency so that the electric field in the developing clearance alternates both in the image area and the non-image area of the electrostatic image bearing member, thereby causing reciprocal movement of the developer particles be-' tween the electrostatic image bearing member and the de-; 10 veloping clearance; and adjusting the alternating electric field in the developing clearance to cause one-sided transition of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member and one-sided transition of developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing . member, comprising: a carrier for carrying developer;
means for defining a developing zone by disposing said de-veloper carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corres-ponding to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
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~13~'Z3 ... .
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier for carrying developer; means for defining a developing zone by dis-: 5 posing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alter-: 10 nating electric field across the clearance, the alternating electric field having a phase wherein the eleatric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image : area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is : in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
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The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined alearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transerred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direc-tion of transferring the developer from the developer carrier to the image bearing member.
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~131~7Z3 The present invention yet further relates to a device for applying dry developer to an image bearing ; member, comprising: a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a pre-determined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alter-nating electric field across the clearance, the alternatingelectric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corres-ponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred . developer from the non-image area of the image bearing member to said~developer carrier, the alternating electric field having a fre~uency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and said developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-magnetic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrier for forming a magnetic field to convey the developer to the developing station; and means for applying an alterna-ting electric field across the clearance, the alternating -llh-113~7Z3 .
.-.; .
electric field having a phase wherein the electric field formed in the clearance corresponding to an image area : of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the . image area, and a phase wherein the electric field formed -~ in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
i .
-llh(i)-11~3~23 The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-mag-netic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a develop-ing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carr~ing means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric -ela. formed in the clearance is in the direction of trans-ferring back the thus transferred developer from the image area area and the non-image area of the image bearing member to said developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprisiny: a carrier, which is made of non-magnetic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alter-nating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both of an image area and a non-image area of the image bearing member, and a - --1 li--~3~7;~:3 phase wherein the electric field formed in the clearance - corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-magnetic material, : for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by ~aid developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across said clearance, said alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase whereinthe electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and sai.d developer carrier.
The present invention yet further relates to a device for applying dry developer to an electrostatic image bearing drum, comprising: a conductive developer carrying cylinder -11 j- , 113~ 3 for carrying one-component developer; means for defining .
a developing zone by disposing said developer carrying cylinder in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness -~ of a developer layer carried by said developer carrying cylinder; means for supplying the developer to said developer carrying cylinder; means for limiting the thickness of the developer layer formed on said developer carrying cylinder; means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrying cylinder to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direc-tion of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to the developer carrying cylinder; and means for rotating the developer carrying cylinder and the electrostatic latent.
image bearing dr~n to change the clearance therebetween.
The present invention yet further relates to a device for applying dry developer to an electrostatic image bearing drum, comprising: a non-magnetic and conductive sleeve for carrying one-component magnetic developer; a magnetic roller, enclosed with the sleeve, having a transporting magnetic pole for transporting the magnetic developer; means for defining a developing zone by disposing said sleeve in opposed re-lationship to the image bearing drum in a developlng station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the sleeve; means for supplying the magnetic developer to the sleeve; a magnetic blade, made of magnetic material or a magnet, for limiting the thickness of the developer layer on the sleeve, the magnetic blade being opposed to a magnetic pole of said magnetic roller; means for applying an alternating electric field across the clearance, the alternating electric h . - llk-' ~131317Z3 field having a phase wherein the electric field formed in the clearance is in the dir~ction of transferring the developer from said sleeve to both an image area and a non-image area of the image bearing drum, and a phase wherein 5 the electric field formed in the clearance is in the direc- .
tion of transferring back the thus transferred developer : from the image area and the non-image area of the image bearing drum to said sleeve; and means for rotating the developer carrying sleeve and the electrostatic latent image 10 bearing drum to change the clearance therebetween.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: means for carrying a one-component developer;
means for defining a developing zone by disposing said de-15 veloper carrying means in opposed relationship to the imagebearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means; means for applying an alternating electric field 20 across the clearance; and means for selectively changing the voltage for providing the alternating electric field.
The present invention ~et further relates to a device for applying dry developer to an image bearing member, comprising: means for carrying a one-component developer;
25 means for defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
30 means for applying an alternating electric field across the clearance; and means for selectively changing the frequency of the alternating electric field, wherein the frequency is not more than 1.5 KHz.
The present invention yet further relates to a 35 device for applying dry developer to an image bearing member, 1~3~3~23 .
comprising: means for carrying a one-component developer;
means îor defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a pre-determined clearance therebetween, the clearance beinggreater than the thickness of a developer layer carried by the carrying means; means for applying an alternating elec-tric field across the clearancei and means for selectively changing the frequency and voltage for pro-~iding the alter-nating electric field.
The present invention yet further relates to a methodof aéveIoping an electrostatic latent image on an image bearing member, comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer; and causing transi-tion of developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
The present invention yet further relates to a method of developing an electrostatic latent image on an image bearing member comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer and creating in said gap an alternating electric field which, in a first stage, causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensity than in the first stage, to leave a developed image on said image bearing member.
The present invention yet further relates to an appara-tus for developing an electrostatic latent image on an imagebearing member, comprising a carrier for supporting a layer -llm-,. I
113~723 of charged dry developer at a developing zone with a gap between the image bearing member and the carrier, means for forming on said carrier a said layer of charged dry developer such that the thickness of the layer is less than the width of the gap, and means for causing transi-tion of the developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
The present invention yet further relates to an apparatus for developing an electrostatic latent image on an image bearing member comprising a carrier for supporting a layer of charged dry developer at a developing zone with a gap between the image bearing member and the carrier;
means for forming on said carrier a said layer of charged dry developer having a thickness which is less than the width of the gap; and means for creating in said gap , an alternating electric field which, in a first stage, : causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensitv than in the first stage, to leave a developed image on the image bearing member.
Other features of the present invention will become apparent from the following detailed description of some embodiments of the invention taken in conjunction with the accompanying drawings.
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113E~7Z3 BRIEF DESCRIPTION OF THE DRAWINGS
Figure l illustrates the amount of transition ; of the toner and the`characteristic of the degree of -toner back transition for the potential of a latent image, as well as an example of the voltage waveform applied.
Figures 2 A - F and Figures 3 A and B illustrate the developing process of the developing method accord-ing to the present invention.
Figure 4 illustrates the electric line of force produced from the electrostatic image in the developing method according to the prior art.
Figure 5 illustrates the electric line of force produced from the electrostatic image in the developing method according to the present invention.
Figures 6 A and B show the characteristic of the electrostatic image potential versus image density as the result of the experiment effected on the developing method according to the present invention, with the frequency of the applied alternate electric field varied.
Figures 7 A and B show the characteristic of .
the electrostatic image potential versus image density as the result of the experiment effected on the develop-ing method according to the present invention, with the amplitude o he applied alternate electric field ',.~.~
, ' ' .
1 varied.
Figure 8 shows the characteristic of the electro-static image potential versus image density as the result of the experiment effected on the developing 5 method according to the present invention, with the frequency and amplitude of the applied alternate voltage -~ varied.
Figure 9 is a graph illustrating the range of selection of the amplitude versus frequency of the applied alternate electric field as the result of the experiment effected on the developing method accord-ing to the present invention.
Figures 10 A, 10 B, 11, 12, 13 A and 14 A
illustrate the developing method according to the present invention and embodiments of the apparatus therefor.
Figure 13 B illustrates the voltage waveform applied to the apparatus shown in Figure 13 A.
Figure 14 B shows the output circuit of the alternate voltage applied to the embodiment shown in Figure 14 A, and Figure 14 C shows the output voltage waveform thereof. , Figures 15 A - D to Figures 18 A - D illustrate the process of movement and vibration of the developer to the image area and the non-image area in the process of development.
~ 113B7Z3 Reference in first had to Figure l to describe the principle of fog prevention and enhanced tone repro-duction of visualized image which may be expressed as the objects and effects of the present invention.
Figure l is a graph in which the abscissa represents the electrostatic image potential and the ordinate . represents the amount of transition of toner from a developer carrier (hereinafter also referred to as the toner carrier) to an electrostatic image bearing surface (positive direction) or the degree of back transition of toner which means that the toner having adhered to the electrostatic image bearing surface is stripped off therefrom (the degree of transition in the negative direction will hereinafter be described). The electro-static image potential is represented with the non-image area potential VL (which is usually the potential of the surface in a region corresponding to the light portion of an image and has a minimum value as the potential) and the image area potential (which is usually the potential of the surface in a region corresponding .
to the dark portion of the image and has a maximum value as the potential) as the potentials at the ends.
The surface potential of the half-tone region of the image including half-tone assumes a potential intermediate ~; 113~3'723 1 VD and VL due to the degree of that tone.
In the lower portion of Figure,l, the voltage waveform applied to the toner carrier is depected with the abscissa representing the potential and with the ordinate representing the time. A rectangular wave is exemplarily shown there, whereas waveform is not restricted to such waveform. The rectangular wave shown exemplarily is such a periodical alternating waveform that the minimum voltage Vmin of the toner carrier with the back electrode of the electrostatic image bearing member as the standard is applied in a ; time interval t, and the bias voltage of the maximum voltage Vmax is applied in a time interval t2.
The image area potential VD assumes a positive potential in some cases and assumes a negative potential in other cases, depending on the electrostatic image formation process used, and this also holds true with the non-image area potential VL. Herein, however, to make the invention more easily understood, description will be made with respect to the case where V~ is a positive potential. Of course, this is only for the purpose of illustration and the invention is not restricted thereto. When VD ~ O, the relation between VD and the non-image area potential VL becomes VD > VL. Now, if the relation between the maximum voltage Vmax and the 1131~723 1 minimum voltage Vmin applied to the toner carrier and VL is set the satisfy. i Vmax > VL > Vmin ...................... (l), S the bias voltage Vmin acts to cause toner particles to transit from the toner carrier toward the electrostatic image bearing member at the time interval tl and therefore, this s*age is called the toner transition stage. At the time interval t2, the bias voltage Vmax acts with a tendency to cause the toner which has transited to the electrostatic image bearing member in the time interval tl to be returned to the toner carrier and therefore this stage is called the toner back transition stage.
In the upper portion of Figure l, the amount of toner transition at tl and the degree of toner back transition at t2 are plotted with respect to the electro-static image potential. Here, the term "degree of toner back transition" is used to represent the probability of the toner back transition which takes place from the electrostatic image bearing member back to the toner carrier if the bias voltage Vmax is applied in a supposed , case that toner as a uniform layer adheres to both ; the image area and the non-image area of the electrostatic image bearing member.
Now, the amount of toner transition from the .
~3~387;~3 1 toner carrier to the electrosta~ic image bearing member in the toner transition stage is such as indicated by curve l shown by broken line in Figure l. The gradient of this curve is substantially equal to the gradient of the curve obtained when no bias alternate voltage is applied. This gradient is great and the amount of the toner transition tends to be saturated at a value intermediate VL and VD and accordingly, it is not suited for the reproduction of half-tone images and provides poor tone gradation. Curve 2 indicated by another broken line in Figure l represents the afore-mentioned probability of the toner back txansition in the toner back transition stage.
In the developing method according to the present invention, an alternating electric field is imparted 50 that such toner transition stage and toner back transition are alternately repeated and in the bias phase (t1) of the toner transition stage of the alternating electric field, toner is caused to once reach even the non-image area of the electrostatic image bearing member (of course, the toner is caused to reach the image area as well), and the toner is also caused to sufficiently adhere to the half-tone potential portion having a low potential approximate to the light region potential (VL) to thereby enhance the tone 1~3t~Z3 1 reproduction, whereafter in the bias phase (t2) of the toner back transition stage, the bias is caused to act in the direction opposite to the direction of toner transition to thereby cause the toner having reached the non-image area to be returned to the toner carrier. In this toner back transition stage, as will hereinafter the described, the toner having reached the non-image area as described tends to return to the toner carrier from the non-image area as soon as the bias field of the opposite polarity is applied, because the non-image area originally have no image potential.
On the other hand, since the toner having once adhered to the image area including the half-tone area is attracted to the image area charge, little amount of lS toner actually returns to the toner carrier from the image area even if the reverse bias is applied in the direction opposite to this attraction. By so causing the bias fields of the opposite polarities to alternate at a preferable amplitude and frequency, the toner transition and back transition may be repeated a number of times at the developing station. Thus, the amount : of the toner transiting to the latent image surface may be rendered, to an amount of transition faithful to . the potential of the electrostatic image. That i5, it is possible to provide a developing action which may 1 result in a variation in amount of toner transition having a small gradient and substantially uniform from : the potential VL to VD as shown by curve 3 in Figure 1.
Accordingly, practically no toner adheres to the non-image area while, on the other hand, the adherence of the toner to the half-tone image areas is so good that there is provided an excellent visible image having a very good tone reproduction corresponding to the surface potential thereof. This tendency may be made more pronounced by setting the clearance between the electro-static image bearing member and the toner carrier so that it is greater toward the end of the developing process and by decreasing and converging the intensity of the above-described field in the developing clearance.
As a method of adjusting the intensity of such electric field in the developing clearance, there is a first method of gradually converging the applied alternate voltage to a suitable predetermined DC value, and a second method of increasing the developing clearance itself with the developing time. These two methods will hereinafter be described respectively.
The developing process in the first method is shown in Figures 2 A - D.
Figure 2 A shows, in order of (l), ~2) and (3), the variation th time in an exemple of the ~aveform : 1 of the applied alternate voltage in the case of the above-mentioned first method. Of course, both of continuous variation and intermittent variation are possible, and in the case of continuous variation, (2) in the shown example shows the intermediate state of the variation.
Figures 2 B and C exemplarily show the manner of toner transition and toner back transition in the image area and the non-image area of the electrostatic image bearing member, with the variation in the develop-ing time. In these Figures, the direction of solid-line arrows shows the electric field in the toner transition direction, and the length of the arrows represents the intensity of the electric field. Broken line arrows show the electric field in the toner back transition direction and the length thereof represents the intensity of the electric field.
In Figures 2 A - C, the initial process (l) is called a first process, and the process t2) from an intermediate stage (which will later be described in greater detail) to the termination is called a second process. (3) designates the termination of the develop-; ment whereat the alternation of the applied voltage is terminated and the voltage is converged to an appropriate predetermined DC value (VO) intermediate 1138~Z3 1 VD and VL.
It is important that the action of the oppositepolarity to the toner transition in the image area and the non-image area in the first and the second process is varied. This status will be described phenomeno-logically. First, in the image area, as exemplarily shown in Figure 2 B, Vmax ~ VD Vmin process (l) and therefore, in the time period tl tapplied voltage is Vmin), a relatively strong toner transition field occurs from the toner carrier toward the image area of the electrostatic image bearing member and toner reaches and adheres to the image area. On the other hand, in the time period t2 (applied voltage is Vmax), a relatively weak toner back transition field occurs toward the electrostatic image bearing member and part of the toner is returned from the image area to the toner carrier. Each time the time periods tl and t2 are 80 repeated, the toner transition and back transition occur between the toner carrier and the non-image area.
Since the relation between the applied voltages Vmin and Vmax and the image area potential VD is set to .
¦Vmax ~ VDI < IVD Vminl ....... t2), ;
the amount of toner transition from the toner carrier to the image area is much greater than the amount of toner i~3~7~3 1 back transition in the first process and therefore, it practically offers no problem that the toner back transition reduces the toner transition, namely, the effect of development.
Subsequently, when the amplitude of the applied voltage is continuously or intermittently attenuated to a predetermined value of max VD + ¦Vth-r¦ ................ (3) .
as shown by (2) in Figure 2 A, the amount of back transition of the toner to the toner carrier from the electrostatic image bearing member to which the toner have once adhered in the time period t2 becomes substantially zero.
¦Vth-r¦ is the minimum absolute potential difference between the electrostatic image formation surface and the toner carrier surface at which the toner can be separated from the electrostatic image formation surface and can effect back transition to the toner carrier.
Further, when Vmax < VD + ¦Vth-r¦ .............. (4) is reached, the back transition occurs no longer and instead, there is produced an electric field which expedites the toner transition from the toner carrier to the electrostatic image bearing member, although this 113~723 1 toner transition is smaller in amount than the toner transition during the time period t1.
Accordingly, when the applied voltage is attenuated to satisfy the relation that max _ VD lvth.rl this process is called the second process in the image area. Such phenomenon in the image area progresses to termination while becoming smaller in amount until the alternating component of the applied voltage becomes null and is converged to a predetermined DC value, whereupon the phenomenon reaches the state of (3).
The process of toner movement in the non-image area (potential VL) of the electrostatic image bearing member will now be described by reference to Figure 2 C .
In the first process shown as ~l), VmaX ~ VL > Vmin and so, during the time period tl (applied voltage is Vmin), a relatively weak toner transition field occurs from the , toner carrier to the non-image area of the electrostatic image bearing member and the toner adheres to the non-, image area. On the other hand, during the time period .
t2 (applied voltage is Vmax), a relatively strong toner back transition field occurs from the non-image area toward the toner carrier and the toner is returned from the non-image area to the toner carrier. Each time . . .
113~723 1 the time periods tl and t2 are so repeated, the toner transition and back transition occurs between the non-image area and the toner carrier and the toner is considered to effect reciprocal movement therebetween. It is considered 5 that the amount of toner back transition becomes greater in probability than the amount of toner transition because the relation between the applied voltages Vmin and Vmax and the non-image area potential VL is set to ~ VLI ~ IVL Vminl .................. (6).
Of course, in this case, no more than the toner having adhered actually effects the back transition.
Next, when the amplitude of the applied bias voltage is continuously or intermittently attenuated to a predetermined value of Vmin = VL - ¦Vth-f¦ ...................... (7) as shown by (2) in Figure 2 A, the amount of toner ; transiting from the toner carrier to the electrostatic image bearing member during the time period t1 becomes substantially ., zero. ¦Vth-f¦ i8 the minimum absolute potential difference between the electrostatic image formation surface and the ; toner carrier at which the toner can be separated from the , toner carrier surface and can transit to the electrostatic image formation surface. This value is varied with the conditions of the developer and development.
Further, when l min VL ¦Vth f¦ ....................... (8) is reached, such transition occurs no longer and instead, there is produced an electric field which expedites the tendency of the toner to back-transit from the electrostatic image bearing member toward the toner carrier, although such back-transition is smaller in amount than the toner back transition during the time period t 2 Accordingly, when the applied voltage is attenuated (in this case, Vmin is greater) to satisfy the relation that i Vmin - VL ~ ¦Vth-fl this process is called the second process in the non-image area. Such phenomenon in the non-image area progresses to termination while becoming smaller in amount until the alternating component of the applied voltage becomes null and is converged to a predetermined DC value.
In other words, the fog or the phenomenon of contact of the toner with the non-image area takes place in the first process, but it is eliminated in the second process.
Figure 2 D shows a modification of the application of the bias voltage shown in Figure 2 A, and Figures 2 E
and F represent the mode of toner transition or ~131~23 1 toner back transition with respect to the image area and the non-image area in that case. The application of the bias voltage in the case of Figure 2 D satisfies Vmin < VL < Vmax and has added thereto the condition of Vmax < VD + ¦Vth r¦. In the case of such bias voltage application, as compared with the case of the bias voltage application shown in Figure 2 A, there is no phenomenon of toner back transition in the image area and the phenomenon in the non-image area does not ' 10 substantially greatly differs from the state shown in Figure 2 C. As shown in Figure 2 E, there is no back transition of the toner in the first process (1) and this holds true with the second process (2). In this case, the boundary between the first and the second process is the time when Vmin = VL - ¦Vth f¦ and it is considered that the second process is entered when Vmin becomes greater than that.
Description has hitherto been simply made of the extreme cases of the image area (dark area) and the non-image area (light area), but as regards the half-tone, the amount of final toner transition to the electrostatic image surface is determined by the magnitudes of the amounts of toner transition and toner back transition corresponding to the potential of the half-tone area. Therefore, the curve of the ~13E~-~23 1 amount of toner transition for the electrostatic image potential is smaller in gradient than the curve l as shown by curve 3 in Figure l and becomes substantially uniformly varied from the non-image area potential VL
to the image area potential VD. By this, there is obtained a visible image having a good tone reproduction from the light area to the dark area, including the half-tone of the image. In the first process in the above-described first method, it is essential to make such a design that the electric field alternates in the non-image area, whereby the tone once adheres to the non-image area as well, and this leads to the possibility of the toner positively adhering also to the half-tone image area having a density adjacent to the non-image area, which in turn leads to an advantage that a visible image having a good tone reproduction of such half-tone area may be obtained by effecting the strip-off (back transition) of the once deposited toner in accordance with the non-image area potential.
An example of the developing process in the second method is shown in Figures 3 A and B. As shown in , Figures 3 A and B, the electrostatic image bearing member 4 moves in the direction of arrow and passes through the developing areas (1) and (2) to the area (3).
Designated by S i~ the toner carrier. Figure 3 A shows ` ~ 1131~7~:3 ' ~
1 1 the toner transition and back transition fields from ; I the toner carrier 5 in the image area of the electro-i static image bearing member and Figure 3 B shows the toner transition and back transition fields from the carrier in the non-image area. In these figures, solid-line arrows indicate the toner transition field and broken-line arrows indicate the toner back transition field. The direction of the arrows indicates the directions of the electric fields and the length of the arrows indicates the intensity of the electric fields.
This second method, as will hereinafter be described, is directed chiefly to increasing the developing clearance and thus decreasing the intensity of the electric field I rather than attenuating the voltage itself.
1~ As shown in Figure 1, Vmax and Vmin as , voltage are repetitively applied at time intervals t~ and ¦ t2, and of course, the waveforms of the applied voltages ! are not restricted to those shown. As already described, the condition of Vmax > VL > Vmin is given as a premise and the conditions that ¦Vmax ~ VL¦ > ¦ VL Vminl a max VDI ~ IVD ~ Vminl are set.
By doing so, in the image area, both the toner transition and the toner back transition alternately occur in the developing area (1), as shown in Figure 3 A.
This developme t has been desaribed in detail by referenae ~, .
ll 113E~723 ' 1 to Figure 2 B. Accordingly, in this developing area (l) wherein the developing clearance is small, the first process of development occurs. Next, when the developing area (2) in which the developing clearance is larger is entered, the already described second process occurs.
In this developing area (2), the developing clearance is wider so that the electric field becomes weaker in inverse ; proportion to the widening of the clearance even if there is no variation in the value of the applied voltage, and the back transition field becomes lower than the threshold value ¦Vth-r¦ necessary for the back transition and thus, the toner transition is possible but the toner back transition cannot take place. Accordingly, the boundary between (l) and (2) correspond~ to the time when Vmax = VD + ¦Vth-r¦ if it is made to correspond to the case where the clearance is constant while the applied voltage is varied. When the developing area (3) is entered, the clearance becomes so wide that neither of the toner transition and the back transition takes place any longer and the development is terminated thereat.
In the case of the non-image area shown in Figure 3 B, the areas (l) and (2) correspond to the first and the second process, respectively. In the area (l), both the transition and the back transition of toner 113~37~ 3 1 occur as previously described with respect to Figure 2 C.
Thus, fog takes place in this area. When the area (2) is entered, the intensities of the electric fields resulting from the voltages of Vmax and Vmin both become weaker in inverse proportion to the widening of the developing clearance and the back transition of the toner is possible but no transition field which will cause the transition of the toner is produced. Accordingly, the fog is fully eliminated in this area (2).
Subsequently, when the developing area (3) is entered, neither the transition nor the back transition of the toner occurs any longer and the development is terminated.
Thus, again by this method, there is obtained an effect substantially equal to the effect of varying the applied bias voltage and not only the fog can be eliminated but also, as regards the half-tone, the final amount of toner tran~ition to the electrostatic image bearing member is determined by the magnitudes of the toner transition and back transition corresponding to the surface potential of the half-tone image, with a result that the curve of the electrostatic image potential versus toner transition amount becomes one having a good tone reproduction as shown by curve 3 in Figure 1.
The conditions that lVmaX ~ VLI ~ IVL Vminl and -` 113!~723 :~
1 lVmax VD¦ ~ ¦VD - Vmin¦ when the image area charge is positive become lVmin ~ VLI ' IVL maxl ; lVmin VD¦ < ¦VD - VmaXl when the image area charge is negative.
S As hitherto described, the application of an ; extraneous alternate voltage between the electrostatic image formation surface and the toner carrier remarkably improves the tone gradation of the resultant image, and it is possible to further improve the reproducibility of line images as well by selecting the amplitude and frequency of the extraneous alternate image to suitable magnitudes as will hereinafter be described.
Description will hereinafter be made with the electrostatic image formation charge as being positive.
In the toner transfer development, as shown in Figure 4, thc electric line of force emanating from the latent image edges goes around the back electrode of the latent image formation surface and cannot reach the tonexlayer, thus tending to result in thinned line or poor sharpness of the edges of the image during the development.
On the other hand, when the alternating wave as shown in Figure l is applied and when the minimum value Vmin of the applied voltage is lower than the latent image light area potential VL as shown in this figure, the electric line of force in the developing area at 1 the development expediting stage becomes such as shown in Figure 5. That is, the electric line of force goes less around the edges of the latent image and parallel ~- electric fieldsand fon~ in the developing area. Thus, even the edges are developed clearly.
To enhance the reproducibility of the edges of the image in this manner, it is preferable to select the development expediting bias (Vmin) to a sufficiently low value (in case of a positive electrostatic image), but too low a value for such bias would result in excessive developer adhering to the non-image area in the toner transition stage and even if the back transition bias is increased to strip off such excessive toner, the resultant image will be poor in contrast, after all.
On the other hand, in order that the toner may be separated from one of the toner carrier and the electro-static image formation surface and transit to the other, there must be a threshold of a certain finite potential difference between the two. As such threshold value, there is ¦Vth-r¦ when the toner transition occurs from the toner carrier to the latent image formation surface .
as previously described, and there is ¦Vth-r¦ when the toner back transition occurs from the latent image formation surface to the toner carrier. In order to increase the reproducibility of line image while avoiding :
~ - 32 -113~7Z3 1 the adherence of excessive developer to the non-image area in the toner transition stage, ¦Vth-f¦ may be selected to a sufficiently great value and the develop-ment expediting bias (Vmin) may be decreased.
The proper value thereof substantially lies in the range VL 2¦Vth fl ~ Vmin ~ VL ............... (10), and most preferably lies in Vmin ~ VL ¦Vth f¦ ..................... (11).
If Vmin is below VL - 2 ¦Vth-f¦, the fog in the non-image area will be unavoidable.
If, in a preferred embodiment of the developing method according to the present invention, magnetic toner is used as the developer and a non-magnetic sleeve enclosing a magnet therein i5 used as the toner carrier, it has become apparent that there may be obtained images which are clear at the edges of the images and excellent in half-tone reproduction.
An advantage of using the magnetic toner lies in that by suitably setting the magnetism of the toner and the magnetic force of the toner carrier, the binding force of the toner to the toner carrier is enhanced and accordingly, ¦Vth-f¦ becomes greater with a result that the Vmin of the extraneous alternate field can be ' .
~ 1:~38~23 1 selected to a sufficiently low value. Further, the proper valué of Vmax corresponding to the proper value L I l Vmin ~ VL is VD < Vmax ~ VD + 2lvth-rl (12) It has become clear that these values enhance the effect of improving the reproducibility to the greatest degree by a minimum alternate voltage value. To cause the toner : to fly through the developing clearance and temporally reach the non-image area as well to thereby improve the tone reproduction and then to cause the toner to be stripped off chiefly from the non-image area, it is necessary to properly select the amplitude and alternating frequency of the applied alternate bias voltage.
The results of the experiment in which the effect of the present invention has clearly appeared due to such selection will be shown below.
Figure~ 6 A and B show the plotted results of an experiment in which the image reflection density (~) for the electrostatic image potential ~V) is measured with the amplitude of the applied alternate voltage fixed and with the frequency thereof varied. These curves will hereinafter be referred to as the V - D , curves. This experiment was carried out under the following construction. A positive electrostatic charge latent image is formed on a cylindrical electrostatic image formation surface. The toner used is a magnetic 1~3B723 1 toner which will hereinafter be described (containing 30% magnetite). The toner is applied to a thickness of about 60 ~ on a non-magnetic sleeve enclosing a magnet therein, and negative charge is imparted to the toner by the friction between the toner and the sleeve surface.
The result when the minimum developing clearance between the electrostatic image formation surface and the magnetic sleeve was maintained at 100 ~ is shown in Figure 6 A, and the result when such clearance was maintained at 300 ~ is shown in Figure 6 B. The density of the magnetic flux in the developing station resulting from the magnet enclosed in the sleeve is about 700 gausses. The cylindrical electrostatic image formation surface and the sleeve are rotated substantially at the ~ame speed of about 110 mm/sec. in the same direction.
Accordingly, the electrostatic image formation surface passes through the minimum clearance in the developing station, and then gradually goes away from the toner carrier. The alternate electric field applied to this sleeve is a sine wave of amplitude Vp p = 800 V (peak-to-peak value) with a DC voltage of ~200 V superimposed thereon. Figures 6 A and B show the V - D curves when the alternating frequency of the applied voltage is 100 Hz, 400 Hz, 800 Hz, 1 KHz and 1.5 KHz (only in Figure 6 A), and the V - D rvAs when no bias field io applied but Il - 35 -1 the back electrode of the electrostatic image formation surface and the sleeve are made to conduct.
From these results, it is seen that when no bias field is applied, the gradient on the so-called ~ value of the V - D curves is very great but by an alternate electric field of low frequency being applied, the y . value becomes very small to greatly enhance the tone gradation. As the frequency of the extraneous electric field is increased from lO0 Hz, the ~ value gradually becomes greater and the effect of enhancing the tone gradation becomes poorer and in the case of a clearance of lO0 ~, the effect becomes very weak under the afore-mentioned amplitude (Vp p = 800 V) when the frequency exceeds 1 KHz; in the case of a clearance of 300 ~, if the amplitude is Vp p = 800 V as described above, the : effect is decreased when the frequency becomes 800 Hz or so, and the effect of tone reproduction becomes very weak when the frequency exceeds 1 KHz. This is considered attributable to the following reason. A finite time is necessary to ensure reciprocal movement of the toner . when the toner repeats its adherence and separation in , the clearance between the sleeve surface and the latent image formation surface during the developing process in which an alternate electric field is applied.
2S Particularly, when the toner transits by being subjected . .
113~3~23 to a weak electric field, it takes a long time for the . ~ toner to positively effect its transition. On the other hand, to reproduce the density of half-tone, it is necessary for the toner subjected to an electric field which is weak but greater than a certain threshold value to positively transit to the image area within one-half of the period of the alternate electric field.
For that purpose, a lower frequency is more advantageous if the amplitude of the alternate electric field is constant, and thus, especially good tone reproduction may be obtained for an alternate electric field of very low frequency as represented by the results of the experiment. This speculation is justified by the comparison between the results of the experiment shown in Figures 6 A and B. The results shown in Figure 6 B
have been obtained under the same conditions as those shown in Figure 6 A except that the clearance between the electrostatic image formation surface and the sleeve surface is as great as 300 ~. The wider clearance results in a lower intensity of the electric field to which the toner i9 subjected, and consequently a lower velocity of transition of the toner. The wider clearance further results in a longer distance of jump and after all, a longer time of transition. As i3 actually apparent from Figure 6 B, the y value becomes considerably ~3~1~723 great for the order of 800 Hz and, when l KHz is exceeded, the y value becomes almost equal to that when no alternate voltage is applied. Therefore, in order to obtain the same effect of enhanced tone reproduction as that when the clearance is narrow, it is preferable to reduce the frequency or to increase the intensity (amplitude) of the alternate voltage as will later be described.
On the other hand, too low a frequency would - 10 not result in sufficient repetition of the reciprocating movement of the toner during the time the latent image formation surface passes through the developing station, and tends to cause irregular development to be created in the image by the alternate voltage. As the result of the foregoing experiment, generally good images have been provided down to the frequency of 40 Hz, and when the frequency is below 40 Hz, irregularity has been created in the visible image. It has been found that the lower limit of the frequency for which no irregularity is created in the visible image depends on the developing conditions, above all, the developing speed (also referred to as the process speed, Vp mm/sec.). In the present experiment, the velocity of movement of the electro-static image formation ~urface has been llO mm/sec. and therefore, the lower limit of the frequency is 40/llO x Vp 113~723 1 ~ 0.3 x Vp ...... (13). As regards the waveform of the alternate voltage applied, it has been confirmed that any of sine wave, rectangular wave, saw-tooth wave or asymmetric wave of these is effective.
Such application of an alternate bias of low frequency brings about remarkable enhancement of the tone gradation, but the voltage value thereof must be properly set. That is, too great a value for the ¦Vmin¦ of the alternate bias may result in an excessive amount of toner contacting the non-image area during the toner transition stage and this may present sufficient removal of such toner in the second process of the development, which may in turn lead to fog or stain left in the image.
Also, too great a value for jVmaxl would cause a great amount of toner to be returned from the image area, thus reducing the density of the so-called solid black portion. To prevent these phenomena and to sufficiently enhance the tone gradation, VmaX and Vmin may preferably and reasonably be selected to the following degrees:
Vmax ~ VD + ¦Vth rl ..................... (14) Vmin ~ VL ~ IVth fl ..................... (15) Vth-f and Vth-r are the potential threshold values already described. If the voltage values of the alternate bias are so selected, the excess amount of toner adhering 113~23 1 to the non-image area in the toner transition stage and the excessive amount of toner returned from the image area in the back transition stage would be prevented to ensure obtainment of proper development result.
This will be shown by the results of an experiment.
: Figures 7 A and B show the V - D curves when the frequencyof the alternate electric field has been fixed (200 Hz) and the amplitude Vp p thereof has been varied.
Figure 7 A shows the result when the developing clearance has been set to lO0 ~, and Figure 7 B shows the result when the developing clearance has been set to 300 ~.
All the other conditions are the same as those of Figures 6 (A and B). When the developing clearance is relatively small, the result of enhanced tone gradation appears if the amplitude Vp p exceeds 400 V, as compared with the case where no electric field is applied. If the Vp p exceeds 1500 V, the tone reproduction is good but fog begins to appear in the non-image area, and if the Vp p exceeds 2000 V, much fog appears. In this case, prevention of the fog may be accomplished by making the alternating frequency higher than 200 Hz. , When the developing clearance is as wide as 300 ~, an effect of improved tone reproduction has begun to appear for Vp p - 400 V or higher, and formation of good images excellent in tone reproduction and almost , . .
113B~Z3 1 free of fog has become possible for the order of 800 V.
When the Vp p exceeds 2000 V, the tone reproduction is good but fog is created and in this last case, it is necessary to increase the alternating frequency.
When the developing clearance _ is thus relatively great, it is advisable that the Vp p of the voltage applied be greater and f be higher than when d is small.
In order to enhance the tone gradation of the image, it is necessary to set the alternating frequency and the amplitude value of the applied alternate voltage to suitable ranges, and it has been found that depending on the property of the image, it is possible to selectively change over and select the relation between the frequency and the amplitude value of the applied voltage within an appropriate range. That is, when the relation between the frequency and the voltage value of the alternate voltage is studied more strictly, it has become apparent that the developing characteristic (V - D curves) can be arbitrarily selected in accordance with the values of those. ~n example thereof is shown in Figure 8.
Figure 8 shows the developing characteristic ; when the clearance between a photosensitive drum which is the latent image bearing member and a sleeve which is the developer carrier is 300 ~, the thickness of the developer layer on the sleeve is about lO0 ~ and as ~ 113B~23 1 the toner, use is made of lO0 parts of styrene acryl resin, 60 parts of ferrite, 2 parts of carbon black and 2 parts of anriferous dye as the charge control agent mixed and ground and having 0.4% by weight of colloidal silical extraneously added thereto. The conditions of each of the shown curve are the bias conditions (alternating frequency f (Hz) and amplitude value (Vp p)) for visualizing the dark region potential (about 500 V) by the light region potential of about O V. The waveform of the applied voltage is a sine wave with a DC voltage superimposed thereon. (The slight difference of Figure 8 from the previously mentioned graph is attribut-able to the difference of the developer used).
As is apparent from the graphs of Figures 6 A and B and Figure 8, when the frequency f is low, there is usually obtained a developing characteristic having high tone gradation and when the frequency f is slightly high, there i9 obtained a developing characteristic having a great value for y. By varying the amplitude of the alternate voltage in addition to such variation in frequency, it i8 possible to obtain any desired developing characteristic corresponding to the kind of the image.
(The DC component is also varied slightly.) The curve ~a) shown in Figure 8 is the VD curve when the frequency f is 200 Hz, Vp p = 900 V and the .- ' , ' .
113?37Z3 1 superimposed DC component is 220 V, and it is seen therefrom that this bias condition has a good tone gradation. The curve (b) is the VD curve when the frequency and the amplitude value have been increased to f = 400 Hz and Vp p = 1600 V, respectively, with a DC
component of 220 V, and it is somewhat greater in r than the curve (a) but still has a relatively high tone gradation.
If, with respect to the curve (b), the frequency i3 increased to 700 Hz and 900 Hz with the amplitude Vp p maintained constant (the superimposed DC voltage is decreased), the r becomes greater and greater as indicated by the curves (c) and (d), thus resulting in poor tone gradation. On the other hand, however, as shown by the curve (d), it can be seen that even if the electrostatic image potential is low, good development at that potential is possible. Further, although the tone gradation is poor, the so-called edge effect becomes great to provide yood reproducibility of the line image and reduced fog.
By so varying the bias conditions, it is possible to ensure all-round quality of image corresponding to .
the original or to the li~ing of the user.
A preferable range of combination between the alternating bias conditions (frequency f (Hz) and amplitude value Vp p (V)) on the basis of each experiment 1131~723 is shown in Figure 9. Figure 9, with the ordinate representing the amplitude Vp p (V) of the applied :
voltage and the abscissa representing the alternating : frequency f (Hz) thereof, shows a preferable range of combination between the two selectable in accordance with the image.
In Figure 9, the solid-line curve P indicates the boundary of the range at which fog relatively tends . - to appear when the developing clearance is 300 ~, and the shaded area A indicates a range in which the fog tends to appear and which is not suited for the line :
copy. Also, the solid-line curve q indicates the boundary at which the quality of the tone gradation is judged when the developing clearance is 300 ~, and the .
shaded area C indicates a range in which the effect thereof i8 low. Thus, the range B surrounded by the two curves p and q is a range in which fog is reduced and the lmage is excellent in definition and tone gradation. .
Of course, the positions of these curves p and q may be more or leqs varied by a variation in size of the developing clearance d. When d ic relatively small, the curves p and q become displaced to dot-and-dash line positions p' and q', respectively.
Particularly, in the area encircled by a broken line S, the overall effect of the bi~s by the alternate ,, .
: - 44 -. .
' . ~ ' ': ~ ' . .
3-t 1 field of low frequency is pronounced. The lower limit value of the frequency in this area S is a value determined by the previously mentioned relation that f _ 0.3 x Vp, and the upper limit value thereof is determined with a view to well maintain the SN ratio. This SN ratio will now be described. When the frequency of the applied alternate field is increased as mentioned previously, it is necessary to make the amplitude Vp p of the applied voltage great in order to ensure the reciprocal movement of the developer (the movement of the developer which temporally reaches the non-image area, also) to take place between the developer carrier and the latent image bearing member. However, when such a voltage value becomes high, it i8 much higher than the potential difference (VD) of the image area to be visualized and the transition phenomenon of the developer to the image area can hardly sense the potential difference VD. If 50, the definition of the image becomes reduced so that the line reproducibility becomes poor and the fog becomes ready to appear.
In addition, the use of a high voltage (higher than about 2500 V) in particular tends to cause the discharging phenomenon with respect to neighboring members and this leads to a problem in constructing an apparatus.
Therefore, under the above-described standard i~ 25 set conditions, the amplitude may preferably be Vp p ~ 2500 V, 1~.3Q7~3 : 1 and particularly preferably be Vp p ~ 2000 V, and the frequency may particularly preferably be f ~ l KHz.
Depending on the combination with the amplitude, the frequency may practically be f ~ 1.5 KHz to thereby obtain the intended effect.
As has hitherto been described, the application of an extraneous alternate voltage between the latent image formation surface and the toner carrier leads to ;
remarkably enhanced tone gradation of the image and preventing of fog. Further, by using magnetic toner as the developer and a sleeve enclosing a permanent magnet as the developer carrier and by properly setting the extraneous alternate voltage value, as will hereinafter be described, it is possible to further enhance the reproducibility of line images at the same time.
Description will hereinafter be made with the electrostatic image formation charge as being positive, whereas the invention is not restricted thereto. In the so-called toner transfer developing method, the electric line of force produced from the end of the latent image ; goes around the back electrGde of the latent image formation surface as shown in Figure 4 and cannot reach the surface of the toner carrier, and accordingly the toner which has started from the toner carrier can 1:~3~7~3 1 hardly adhere to the end of the image. Thus, the resultant image tends to suffer from thinning of lines and poor sharpness of the end, which in turn offers a problem in line copying.
Therefore, in this system, if an alternating bias is applied and if the Vmin thereof is selected to a sufficiently low value, the electric line of force in the developing station during the toner transition stage goes so little around the end of the electrostatic image, as shown in Figure 5, that there are formed parallel electric fields. This enables the toner to positively adhere to the end of the electrostatic image. However, as already noted, too low a value for Vmin would usually cause fog or stain to be created in the non-image area.
In the present embodiment of the invention, the advantage resulting from the use of the magnetic toner as the developer and the sleeve enclosing the permanent magnet as the developer carrier lies chiefly in solving this problem. By properly setting the content ; 20 of the magnetic material in the developer and the intensity of the magnetic field of the permanent magnet, it is possible to uniformly enhance the restraining force of the toner onto the sleeve and accordingly select the value of ¦Vth-f¦ to a sufficiently great value. As the result, Vmin can be set to a low value with the amount 113~J23 1 of the toner adhering to the non-image area during the toner transition stage being minimized.
Thus, by applying an alternating bias in the toner transfer developing method using magnetic toner, it is possible to obtain images of good tone gradation which are clear at the end and free of fog and which are excellent also in line copying.
On the other hand, it is a very difficult problem to convey the developer to the developing station in the high resistance toner transfer development and to impart a charge. The method using magnetic toner as the developer and conveying the developer by means of a sleeve and imparting a charge by frictional charging between the sleeve surface or an applicator member and the toner is considered to be one of very advantageous , methods.
Also, application of the magnetic toner onto the sleeve may be effected by a method of urging a resilient member against the sleeve or a method of maintaining a magnetic member in opposed relationship with the magnetic pole of the permanent magnet within .
the sleeve and in non-contact with the sleeve surface and controlling the thickness of the magnetic toner by the magnetic force. In the conventional toner transfer development wherein development is effected ~,th the -- 113~3~23 1 sleeve opposed to the electrostatic image bearing member and with these members being rotated in the same : direction and at the same velocity, the state of the . toner applied onto the sleeve directly affects the quality of image and when the application of the toner is effected by the former method, the status of application is relatively delicate and ensures a good quality of image. In this method of application, however, the toner strongly rubs against the sleeve surface and therefore 10 the resin content of the toner adheres to the sleeve surface to remarkably prevent the toner from being charged.
On the other hand, if the latter method is used, the adherence of the toner to the sleeve surface is minimized but the status of the toner applied onto the sleeve surface presents scattered lumps of toner particles and is coarse and accordingly, the image after developed becomes coarse.
In contrast, by applying an alternating bias in the developing station according to the present invention, toner particles are caused to effect reciprocal movement between the latent image and the sleeve surface and are separated into individual particles in that process, so that the toner can finely adhere to the image 25 area of the electrostatic image surface.
i~ 1~723 Some specific examples will be shown below in detail.
Example l The example shown in Figure 10 A is of a construction in which the applied bias alternate voltage is attenuated, and shows a mode in which a source voltage comprising an AC voltage of low frequency with a DC
component superimposed thereon is attenuated by the use of a mechanical sliding electrode. Figure 10 B shows a modified portion for attenuating the voltage by the use of an electric circuit.
In Figure 10 A, reference numeral 10 designates ZnO photosensitive paper which has formed thereon an ,, electrostatic image at another station, not shown.
The paper 10 is conveyed to the shown developing station by a pair of rollers 13,13 and stopped there for develop-ment, and then again conveyed for fixation. Designated by 12 is a toner carrier comprising an electrically conductive rubber belt and driven by a pair of metal rollers 14,14. The ZnO photosen~itive paper 10 as the electrostatic image bearing member and the toner carrier , 12 are transported to the developing station by the rollers 13 and 14 being intermittently driven by motors 21 and 22, and become stationary during the developing process, and shift before the next developing cycle is ', ~'~
~131~7Z3 1 started. The toner carrier effect one-half of a full rotation andlis stopped again. Denoted by 15 is an insulating toner contained in a container 7 and it comprises styrene resin, 3% carbon black and 2% positive polarity charge control agent, all by weight. Also, to improve the fluidity, 0.2~ by weight of colloidal silica is extraneously added. The toner is conveyed by the toner carrier 12, and the thickness of the toner applied is controlled to 100 to 200 ~ by a me~ber 16 slidably contacting the carrier 12, and positive charge ,j is imparted to the toner by a corona charger 18 before development is started. The clearance between the electrostatic image bearing 10 and the toner carrier 12 is maintained at 500 ~. Designated by 14a is a slidable electrode which is in contact with the core of the rotary roller 12, and which applies an alternate voltage to the toner carrier 12 from a power source 9. Denoted by 20 is a fur fru~h for stirring the developer to supply it to the toner carrier 12.
The dark region potential of the electrostatic image formed on the electrostatic image bearing member 10 was -450 V and the light region potential of such image was -40 V. The voltage applied comprised an AC
voltage 1200 Vpp of frequency ranging from 10 - 1000 Hz, with a DC voltage of -200 V superimposed thereon, and ~ 113~Z3 1 only the AC voltage i9 attenuated to 0 at a time constant of about 0.5 in 0.2 second after the start of the development.
Description will now be made of the construction of the power source 9 for causing such attenuation.
Reference numeral 21 designates a motor for moving the sliding electrode 26 on the secondary winding side of an AC transformer 27. Reference numeral 24 designates an AC power source, and 25 a DC power source.
Designated by 23 is a power source for driving a timing signal generating circuit and motors 21, 22.
In 0.2 second after the start of the development, the sliding electrode 26 moves from its position A to its position B at a uniform velocity after 0.5 second.
- 15 Upon displacement of the sliding electrode 26 to its position B, the motor 22 is driven to cause the toner carrier 12 to effect one-half of a full rotation and during this time, the sliding electrode returns to its position A.
Figure 10 B shows a power source 9' using a well-known RLC attenuating circuit instead of using a .
sliding electrode. In 0.2 second after the start of the development, the switch is changed over from its position A' to its position B'. The time constant of this attenuating circuit is set to 0.5 sec. The change-- 1~L3!~23 1 over of the switch can be accomplished in a timing fashion by known means such as a relay or the like.
Thus, the development by the previously des-cribed first method can be applied and the resultant image is substantially free of fog and excellent in tone gradation particularly in an area wherein the alternating frequency f of the applied alternate voltage is low, and especially good images have been obtained for f < 1000 Hz.
Example 2 ; This example realizes the previously described second method which effects development by varying the developing clearance in accordance with the develop-ing process, and will be described by reference to Figure 11. Designated by 31 is an Se photosensitive belt having formed thereon an electrostatic image at another station, not shown, and developed at the shown station, and the image thereon is fixed or transferred at a further station, not shown. Reference character 32 is a toner carrier comprising an electrically conductive rubber belt, and driven by a metal roller 33.
Denoted by 35 is an insulating toner contained in a container 37 and comprising polyester resin, 2% by weight of carbon black and 2% by weight of negative polarity charge control agent. To improve the fluidity of the ., ~ toner, 0.1% by weight of colloidal silica is extraneously : added. The toner is conveyed by the toner carrier 32 and the thickness of the toner on the toner carrier is controlled to 50 - 150 ~ by a resilient member 36 urged ,~ 5 against the roller 33. Before the development is started, negative charge is imparted to the toner by a corona charger 38. The electrostatic image bearing member 31 is held in the developing station with a ~' minimum clearance of 300 ~ with respect to the toner carrier 32 by a metal roller 41. At a point spaced apart about 30 mm from that position, the distance between the members 31 and 32 is maintained at about 2 mm by a metal roller 42 (adjustable). Designated by 43 is a driving member for adjusting the position of the metal roller 41. The members 31 and 32 are so configured that they pas~ through the moct proximate position and then gradually widen the clearance therebetween. The members 31 and 32 move in the same direction at the same speed of 200 mm/sec. De-c~ignated by 39 is an alternate voltage application source.
The image area potential and the non-image area .
potential of the electrostatic image formed on the member 31 are 800 V and 200 V, respectively. The applied voltage is an alternating current 1000 Vp_p of frequency 200 Hz with a DC voltage of 400 V superimposed thereon.
1 Thus, there have been obtained fogless good images which ~; are of high tone gradation.
Example 3 Referring to Figure 12, reference numeral 51 designates a photosensitive drum having an Se film, and 52 denotes a toner carrier comprising an electrically conductive rubber sheet and driven by a metal roller 53.
The movement velocity of the toner carrier 52 is substantially equal to the peripheral velocity of the electrostatic image bearing member 51, and it is 200 mm/sec. Designated by 45 is a non-magnetic insulating toner contained in a container 47, and it is conveyed by the friction force between the toner and the toner carrier 52 and by Van der Waals force. The thickness of the toner on the toner carrier is controlled to about 60 ~ by a resilient applicator member 46, and negative charge is imparted to the toner by a corona charger 48 before the development is started. The clearance between the members 51 and 52 is maintained at a minimum of 400 ~, but this clearance becomes gradually larger with the rotation of the members 51 and 52, to thereby form a developing area having the .
previously described first and second processes. Denoted by 44 i8 a sliding electrode contacting the core of a rotatable member 53. The electrode 44 applies an alternate voltage to the members 52, 53 and 44 by a power 113B~23 1 source 49 with respect to the electrically conductive support member for the groundedimember 51. The frequency of the alternate electric field is 100 Hz, and the electro-static image potential is +700 V for the image area and +50 V for the non-image area, and the potential of the member 42 is Vmax = ~750V for the maximum value and Vmin= - 50 V for the minimum value.
Under the above-described construction, there have been obtained clear images of high tone reproduction.
Example 4 Referring to Figure 13 A, reference character 61 designates a photosensitive drum having a radius of 40 mm and having a CdS layer and an insulating layer.
Designated by 62 is a non-magnetic sleeve having a radius of 15 mm and enclosing a permanent magnet 63 therein. The members 61 and 62 are rotated at the same peripheral velocity of 100 mm/sec. in the same direction.
Denoted by 65 is an insulative magnetic toner which comprises 60% by weight of styrene resin, 35% by weight of magnetite, 3% by weight of carbon black and 2% by weight of negative charge control agent. To improve , the fluidity of the toner, 0.3% by weight of colloidal silica is extraneously added. The toner is conveyed by the sleeve 62, and the thickness of the toner applied onto the sleeve is controlled to about 70 ~ by a magnetic 1 blade 66 disposed in proximity to the sleeve. Also, the toner is imparted negative charge by the friction charging between the toner and the sleeve 62.
The clearance between the members 61 and 62 is maintained at a minimum of 200 ~, but the movement velocities of and the clearance between the two members are set so as to satisfy the conditions already described with respect to Figures 3 A and B, with the rotation of the members 61 and 62. The members 62 and 66 are kept electrically conductive, and an alternate voltage is applied to the electrically conductive support member of the member 61 by a power source 69. The alternate voltage is a sine wave having a frequency of 200 Hz and the relation between the voltage value and the electrostatic image potential is such as shown in Figure 13 B.
The electrostatic image potential is 500 V for the image area and O V for the non-image area, and is a sine wave of amplitude 400 V t800 Vpp) with a DC voltage of +200 V superimposed thereon. Under the above-described construction and by the low frequency based onthe developing action fully described with respect to Figures 3 A and B, there have been obtained images which are high in tone gradation and clear.
113f3~23 1 Example 5 In Figure 14 A, reference numeral 71 designates an electrostatic latent image bearing member having an insulating layer on a CdS layer. Reference numeral 72 denotes the back electrode of the member 71.
The members 71 and 72 together form a drum shape.
78 designates a non-magnetic stainless sleeve having a magnet 77 therewithin. The electrostatic image bearing member 71 and the sleeve 78 have the minimum clearance therebetween maintained at 300 ~ by a well-known clearance maintaining means. Designated by 74 is a one-component magnetic developer contained in a developer container 79 and comprising 70% by weight of styrene maleic acid resin, 25% by weight of ferrite, 3% by weight of carbon black and 2% by weight of negative charge control agent mixed and ground and having extraneously added thereto 0.2% by weight of colloidal silica to improve the fluidity of the developer. Denoted by 76 is an iron blade opposed to the magnetic pole 77a (850 G) of the magnet roll 77 enclosed in the sleeve 73.
The blade 76 controls the thickness of the magnetic developer 74 applied onto the sleeve 73 by the magnetic force. The clearance between the blade 76 and the sleeve 73 is maintained at about 240 ~, and the thickness of the developer layer applied onto the sleeve 73 by the blade 76 is about 100 ~. Designated by 75 is a variable altérnate voltage source which is applied between the ; back electrode 72 and the conductive portion of the : sleeve 73. Also, to prevent irregular application of the developer, the blade 76 is rendered to the same potential as the sleeve 73.
The average value of the electrostatic image potential is +500 V for the dark region potential and OV for the light region potential, and the extraneous alternate voltage is a sine wave of frequency 400 Hz and peak-to-peak 1500 V imparted a distortion so as to be rendered into a distorted sine wave having an amplitude ratio of 1.9 : 1 between the positive phase and the negative phase. Again by this embodiment, there have been obtained good visible images which are excellent in tone gradation and high in definition and free of fog.
An example of the circuit for providing such a distorted sine wave is shown in Figure 14 B.
The circuit of Figure 14 B generates such a distorted sine wave as shown in Figure 14 C by reducing only the negative (-) of the sine wave AC voltage by a diode 80 and resistors 81 and 82. I the resistor 81 of the output terminal O is slidden, it is possible to make the negative (-) side voltage variable. This circuit construction leads to the greater ease with . , 13~3~37Z3 1 which the circuit is constructed, as compared with the superimposed DC type.
Example 6 The power source 75 of Example 5 is modified into a plurality of voltage sources, each of which has change-over means 78 so that the frequencies and amplitude values of (a), (b) and (d) may be selected from among the four types shown in Figure 8, for example.
The change-over means 78 may be a known electrical change-over means. By operating the buttons ~ - ~
of the change-over means, the following bias conditions can be selected.
~ f = 200 Hz, Vp p = 900 V (DC superimposed 220 V). At this time, the user can obtain photographic lS images of delicate quality in a soft tone.
~ f z 400 Hz, Vp p = 1600 V (DC superimposed 220 V). This condition is used to obtain ordinary copies.
~ f = 900 Hz, Vp p = 1600 V (DC superimposed 120 V). At this time, the user can reproduce originals which are so low in den ity as to tend to create fog or originals of colored images or originals which consist , chiefly of lines, without fog and in good quality.
Of course, these selective combinations are illustrative examples and if within the aforementioned proper range, combinations of other frequencies and ~` 113~Z3 ; 1 voltage values may be adopted.
Figures 15 A - 15 D to Figures 18 A - 18 C
: illustrate the reciprocal movement of the developer in the developing clearance under the low frequency condition ~ 5 applied to the developing method according to the present .: invention and the vibratory movement of the developer when the frequency f of the bias voltage applied is a high frequency (higher than 2 KHz). In the result of the experiment shown in Figures 6 A and B, a preferable range of frequency for enhancing the tone gradation has been shown, and the reciprocal movement of the developer, for example, in each of the above-described Examples, ; is schematically illustrated in Figures lS A - D and Figures 17 A - D.
Figures lS A - D show the movement of the developer in the clearance between the image area of the latent image bearing member 4 to be visualized and the toner carrier S, and Figures 17 A - D show the movement of the developer in the clearance between the non-image area of the latent image bearing member 4 which is not to be visualized and the toner carrier S. A in each of these .
Figures shows the initial state in which the bias field is not applied yet. In the toner transition stage shown in B of each Figure, more developer transits from . 25 the toner carrier S to the image area 4a than to the :' 1 non-image area due to the electrostatic attraction.
It should be noted that the developer transits to and reach the non-image area 4b as well from the toner carrier 5. Arrows indicate the direction of movement of the developer. Next, as shown in C of each Figure, in the toner back transition stage in which the electric field applied assumes the reverse phase, a relatively small amount of developer returns from the image area to the toner carrier, but since, in the non-image area, there is no charge which attracts the toner, almost all of the toner which has transited in the toner transition stage returns to the toner carrier in accordance with the reverse bias. Next, when the phase of the bias changes again, there occurs the toner transition stage as shown in D of each Figure, and thereafter such reciprocal movement of the developer is repeated as noted above.
Thus, a number of reciprocal movements are effected and in the meantime, the developer is caused to once reach the non-image area as well, whereby from the half-tone image area approximate to the light region in which the potential is relatively low to the solid black image portion, there is obtained a visualizing action faithful to the potential held thereby.
On the other hand, when the alternating frequency is increased to a high frequency, for example, 2 KHz or 113~3723 1 higher, the tone gradation is reduced. This phenomenon will be described by reference to Figures 16 A - D and Figures 18 A - D. A in each of these Figures shows the states of the latent image bearing member 4 and the toner carrier 5 before the bias is applied. When the bias for toner transition is applied in the ima~e area, the toner is liberated from the toner carrier toward the image area 4a as shown in Figure 16 B, but the force acting on the individual toner particles causes more or less irregularity of the degree of transition and since the alternating frequency of the bias is high before such irregularity is converged, the reverse bias is applied to the toner which has reached the image area and the toner which is still suspended in the developing clearance, and it is believed that most of the suspended toner returns to the toner carrier side as shown in Figure 16 C. Since the bias phase is reversed before this return movement is terminated, the toner is again subjected to the bias force directed toward the image area. Thus, vibration of the toner rather than reciprocal movement of the toner occurs in the clearance between the image area and the toner carrier.
Such vibratory movement of the toner is pronounced in the clearance between the non-image area in which no latent image charge is present and the toner carrier.
' _ '1~3B~Z3 1 This state is shown in Figures 18 A - D. From the initial state shown in Figure 18 A, the bias phase for toner transition is applied. In this case, if a bias exceeding the transition threshold value is applied, the toner is liberated from the toner carrier but since the alternating frequency of the bias is high as shown in Figure 18 B, the phase of the bias is reversed before the toner reaches the non-image area 4b, and the toner returns to the toner carrier (Figure 18 C).
Next, when the toner transition bias is entered, the toner is again liberated from the toner carrier, but the reverse bias is again applied during the time these toner particles are suspended in the aforementioned clearance, so that the toner particles go toward the toner carrier.
Thus, the toner is vibrated in the clearance and does not substantially reach the non-image area 4a and therefore, even when the development has been terminated, the toner does not adhere the non-image area and no fog is created.
On the other hand, however, the adherence of the toner to the region having a half-tone image potential approximate to the light region (the non-image area) does not sufficiently take place, thus resulting in reduced toner gradation. It is theoretically considered that this phenomenon continues to take place until a certain degree of high frequency exceeding 2 KHz is reached, and it ~ 113!37Z3 1 brings about difficulties in the reproduction of tone gradation as in the present invention.
The foregoing description has been made with respect to a case where the image area potential VD is positive, whereas the invention is not restriated to such case but the invention is also applicable to a case where the image area potential is negative, and : in that case, equations (2) - (12) previously mentioned may be expressed as follows:
¦Vmin - VDI < IVD Vmaxl (2') : Vmin = VD - ¦Vth~r¦ (3~) Vmin > VD - ¦Vth-r¦ (4~) min _ VD - IVth-rl IVmin - VLI > IVL Vmaxl (6') : Vmax = VL + ¦Vth-f¦ (7') max VL ¦Vth f¦ (8') Vmax _ VL + ¦Vth-f¦ (g') VL Vmax < VL + 2lvth-fl (10') Vmax ~ VL + ¦Vth-f¦ (11') VD 2¦Vth rl < Vmin < VD (12') ,= .. ~, , ~ ' ''' ~'''' ' '.' ' , , .~ 1~387:~3 1 The present invention is not restricted to the above-described embodiments, but is applicable to the development of images formed by the electrophotographic method, the electrostatic recording method and other image formation methods.
Such high frequency pulse bias developing device 113~Z3 1 may be said to be a developing system suitable for the line copying in that a pulse bias of several KHz or higher is applied in the clearance between the toner donor member and the image retaining member to improve the vibratory characteristic of the toner and present the toner from reaching the non-image area in any pulse bias phase but cause the toner to transit only to the image area, thereby preventing fogging of the non-image area. However, the aforementioned U.S. Patent No.
3,893,418 states that a very high frequency (18 KHz -22 KHz) is used for the applied pulse voltage in order to make the device suitable for the reproduction of tone gradation of the image.
U.S. Patent No. 3,346,475 discloses a method which comprises immersing two electrodes in insulating liquid contained in a dielectrophoretic cell and applying thereto an AC voltage of very low frequency (lower than about 6 Hz) to thereby effect the develop-ment of a pattern corresponding to the conductivity variance.
Further, U.S. Patent No. 4,014,291 disclosesa transfer development which uses dry one-component magnetic toner, but this patent does not suggest that a bias is applied for the above-described purpose of preventing fog.
1131~23 SUMMARY OF THE INVENTION
- The present invention has been made to eliminate the above-noted problems peculiar to the various developing methods using one-component developer. The present invention relates to a developing method which enables obtainment of visible images which are free of fog and excellent in edge reproduction and tone gradation, and an apparatus therefor.
- The present invention also relates to a developing method based on the principle of development in which a low frequency alternate electric field having a phase of a particular polarity which causes the developer to one-sidedly reach both the image area and the non-image area of a latent image bearing member from a developer carrier and a phase of the opposite polarity to the particular polarity which lS applies a bias in a direction to cause the developer having reached at least the non-image area to return to the de-veloper carrier side is applied in the developing clearance to thereby ensure transition of the developer to the non-image area and back transition of the developer to the developer carrier to be alternately repeated even in the clearance between the developer carrier and the non-image area in the developing station and enable a develop-ment very excellent in tone reproduction to be accomplished by such reciprocal movement of the developer, and an appara-tus therefor.
The present invention further relates to a developing method which has a first process in which an extraneous vibratory electric field is imparted so that the low fre-quency electric field in the developing clearance may alternate in at least the non-image area of the latent image bearing member, whereby reciprocal movement of the developer particles may take place between the non-imaye area and the developer carrier, and a second process in which the in-tensity of the extraneous vibratory electric field is ; 35 adjusted to cause one-sided transition of the developer particles from the developer carrier to the image area and ,:
:
11315~7Z3 from the non-image area to the developer carrier, thereby obtaining a result of development which is free of fog and excellent in tone gradation, and an apparatus therefor.
.~
The present invention still further relates to a developing method in which the second process is imparted in a process in which the latent image bearing member and --the developer carrier are stationary and opposed to each other and the amplitude of the extraneously applied vibra-tory electric field is attenuated toward the termination of the development and converged into a predetermined value, and an apparatus therefor.
The present invention still further relates to a de-veloping method in which the extraneously applied vibratory :
alternate voltage is maintained constant and the latent image bearing member and the developer carrier are opposed to each other while being moved to increase the clearance there-between gradually, to thereby impart the second process, and an apparatus therefor.
The present invention still further relates to a developing method which comprises disposing a latent image bearing member and a developer carrier carrying a developer layer thereon in opposed relationship in a developing station with a clearance maintained therebetween, the clearance being greater than the thickness of the developer layer, and effec-ting development while applying an alternate electric fieldin a range satisfying.; , .
400 V _ Vp p ~ 2500 V
40 Hz _ f ~ 1.5 KHz : where Vp_p represents the amplitude of the alternate electric; 30 field (V : peak-to-peak value) and f represents the alter-: nating frequency of the alternate electric field to apply _g_ . J ~
113~'~ 23 an alternate electric field having a phase of a particular polarity which causes the developer to one-sidedly reach both the image area and the non-image area of the latent image bearing member from the developer carrier in the developing clearance and a phase of the opposite polarity - to the particular polarity for applying a bias in a direc-tion to cause the developer having reached at least the non-image area to return to the developer carrier side, and an apparatus therefor.
.
The present invention further relates to a developing method which comprises disposing a latent image bearing member and a developer carrier in opposed relationship in a developing station with a clearance maintained therebetween, and effecting development by applying to the clearance an alternate voltage of a frequency lower than 1.5 KHz, the frequéncy and amplitude value of the alternate voltage being selectively changed over in accordance with the kind of the image to be reproduced, and an apparatus therefor.
More particularly, the present invention relates to ~ method of applying dry developer to an image bearing member, comprising thé steps of: disposing an image bearing ,.. . .
member and a developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alter-nating electric field having a phase wherein the electric field formed in the clearance corresponding to an image area ~; of the image bearing member is in the direction of trans-ferring the developer from the developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the trans-ferred developer from the image area of the image bearing member to the developer carrier.
113~23 The present invention also relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a . developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is - greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
The present invention further relates to a method of applying dry developer to an image bearing member, comprising : 20 the step~ of: disposing an image bearing member and a developercarrier for carrying a layer of developer on the surface . thexeof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alter-nating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier and wherein the electric field formed in the clearance corres-ponding to the image area is in the direction of transferring : the developer from the developer carrier to the image bearing member.
~ I
~13F~723 The present invention still further relates to amethod of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a developer carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and apply-ing an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric 10 field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance correspond- .
15 ing to a non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the : developer carrier, the alternating electric field having a fre~uency low enough to allow the developer to transfer and 20 transfer back repeatedly between the image bearing member and the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, com-prising the steps of: disposing an image bearing member and 25 a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relation-ship in a developing station with a clearance maintained there-: between which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating 30 means therewithint and applying an alternating electric fieldacross the clearance, the alternating electric field having a phase where.in the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring the developer from the 35 developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to -lla-.. , . . . _, . . .. .. ... . .
1~3t3723 an image area of the image bearing member is in the direc-tion of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alter-nating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an image bearing member, com-prising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of .
magnetic developer on the surface thereof in opposed re-lationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image ar~a of the image bearing member, and a phase wherein -llb-the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, and wherein the ele~tric field formed in the clearance corres-ponding to the non-image area is in the direction of trans-ferring the developer from thè developer carrier to the image bearing member.
The present invention.yet further relates to a method of applying dry developer to an image bearing member, comprising the steps of: disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance main-tained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric ield across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alter-nating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly be-tween the image bearing member and the developer carrier.
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of: forming a layer of one-component developer on the surface of a developing carrier disposed in opposed re-lationship with the image bearing member in a developer j -11 ~ 1 3t~Z3 station with a clearance maintained therebetween which is . greater than the thickness of the developer layer; apply-ing an alternating electric field across the developing clearance, the field having a frequency sufficient to cause reciprocating movement of the one-component developer particles between the electrostatic image bearing member and the de-veloper carrier in accordance with the alternating electric field; and changing the intensity of the alternative elec-~ tric field acting on the developing clearance to thereby ; 10 convert the reciprocating movement to one-sided movement of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member in the image area and to one-sided movement of the developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer : carrier in the non-image area.
, , .
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of: forming a layer of one-component developer on the surface of a developer carrier disposed in opposed re-lationship with the image bearing member in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; applying an alternating electric field across the developing clearance, the field having a frequency sufficient to cause the developer particles to transit from the developer layer through the clearance and contact the image area and the non-image area of the electrostatic image bearing member, and then to cause the developer particles having so contacted the image bearing member to return to the developer carrier and such reciprocating movement of the developer is repeated; and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the -lld-113~23 reciprocating movement to one-sided movement in which the developer particles one-sidedly transit from the developer carrier to the image area.of the electrostatic image bearing member and contact the image area and the developer particles : 5 present in the non-image area one-sidedly return to the developer carrier and such movement of the developer is repeated.
The present invention yet further relates to a method of applying dry developer to an electrostatic image bearing member, comprising the steps of: disposing an electro-static image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed rela-tionship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; applying an alternating electric field across the developing clearance, the field having a suffi-cient frequency so that its direction in the developing clearance alternates in at least the non-image area of the electrostatic image bearing member, to thereby cause the developer to reach the non-image area as well, and then cause the developer to return to the developer carrier, such reciprocal movement of the developer particles taking place repeatedly in the developing clearance; and adjusting the intensity of the alternating electric field to cause the transition of the developer particles to take place in the image area one-sidedly in a direction from the developer carrier to the image area and to take place in the non-image area one-sidedly in a direction from the non-image area to the developer carrier.
The present invention yet further relates to a method of applying dry developer to an electrostatic i.mage bearing member, comprising the steps of: disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed ~i -lle 7;~3 relationship in a developing station with a clearance main-tained therebetween which is greater than the thickness of the developer layer; applying an alternating electric .; field in the clearance, the field having a sufficient frequency so that the electric field in the developing clearance alternates both in the image area and the non-image area of the electrostatic image bearing member, thereby causing reciprocal movement of the developer particles be-' tween the electrostatic image bearing member and the de-; 10 veloping clearance; and adjusting the alternating electric field in the developing clearance to cause one-sided transition of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member and one-sided transition of developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing . member, comprising: a carrier for carrying developer;
means for defining a developing zone by disposing said de-veloper carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corres-ponding to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
-llf-i;
~13~'Z3 ... .
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier for carrying developer; means for defining a developing zone by dis-: 5 posing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alter-: 10 nating electric field across the clearance, the alternating electric field having a phase wherein the eleatric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image : area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is : in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
. , .. I
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined alearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transerred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direc-tion of transferring the developer from the developer carrier to the image bearing member.
-llg-.
~131~7Z3 The present invention yet further relates to a device for applying dry developer to an image bearing ; member, comprising: a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a pre-determined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alter-nating electric field across the clearance, the alternatingelectric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corres-ponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred . developer from the non-image area of the image bearing member to said~developer carrier, the alternating electric field having a fre~uency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and said developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-magnetic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrier for forming a magnetic field to convey the developer to the developing station; and means for applying an alterna-ting electric field across the clearance, the alternating -llh-113~7Z3 .
.-.; .
electric field having a phase wherein the electric field formed in the clearance corresponding to an image area : of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the . image area, and a phase wherein the electric field formed -~ in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
i .
-llh(i)-11~3~23 The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-mag-netic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a develop-ing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carr~ing means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric -ela. formed in the clearance is in the direction of trans-ferring back the thus transferred developer from the image area area and the non-image area of the image bearing member to said developer carrier.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprisiny: a carrier, which is made of non-magnetic material, for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alter-nating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both of an image area and a non-image area of the image bearing member, and a - --1 li--~3~7;~:3 phase wherein the electric field formed in the clearance - corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: a carrier, which is made of non-magnetic material, : for carrying developer; means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by ~aid developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across said clearance, said alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of trans-ferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase whereinthe electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and sai.d developer carrier.
The present invention yet further relates to a device for applying dry developer to an electrostatic image bearing drum, comprising: a conductive developer carrying cylinder -11 j- , 113~ 3 for carrying one-component developer; means for defining .
a developing zone by disposing said developer carrying cylinder in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness -~ of a developer layer carried by said developer carrying cylinder; means for supplying the developer to said developer carrying cylinder; means for limiting the thickness of the developer layer formed on said developer carrying cylinder; means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrying cylinder to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direc-tion of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to the developer carrying cylinder; and means for rotating the developer carrying cylinder and the electrostatic latent.
image bearing dr~n to change the clearance therebetween.
The present invention yet further relates to a device for applying dry developer to an electrostatic image bearing drum, comprising: a non-magnetic and conductive sleeve for carrying one-component magnetic developer; a magnetic roller, enclosed with the sleeve, having a transporting magnetic pole for transporting the magnetic developer; means for defining a developing zone by disposing said sleeve in opposed re-lationship to the image bearing drum in a developlng station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the sleeve; means for supplying the magnetic developer to the sleeve; a magnetic blade, made of magnetic material or a magnet, for limiting the thickness of the developer layer on the sleeve, the magnetic blade being opposed to a magnetic pole of said magnetic roller; means for applying an alternating electric field across the clearance, the alternating electric h . - llk-' ~131317Z3 field having a phase wherein the electric field formed in the clearance is in the dir~ction of transferring the developer from said sleeve to both an image area and a non-image area of the image bearing drum, and a phase wherein 5 the electric field formed in the clearance is in the direc- .
tion of transferring back the thus transferred developer : from the image area and the non-image area of the image bearing drum to said sleeve; and means for rotating the developer carrying sleeve and the electrostatic latent image 10 bearing drum to change the clearance therebetween.
The present invention yet further relates to a device for applying dry developer to an image bearing member, comprising: means for carrying a one-component developer;
means for defining a developing zone by disposing said de-15 veloper carrying means in opposed relationship to the imagebearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means; means for applying an alternating electric field 20 across the clearance; and means for selectively changing the voltage for providing the alternating electric field.
The present invention ~et further relates to a device for applying dry developer to an image bearing member, comprising: means for carrying a one-component developer;
25 means for defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
30 means for applying an alternating electric field across the clearance; and means for selectively changing the frequency of the alternating electric field, wherein the frequency is not more than 1.5 KHz.
The present invention yet further relates to a 35 device for applying dry developer to an image bearing member, 1~3~3~23 .
comprising: means for carrying a one-component developer;
means îor defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a pre-determined clearance therebetween, the clearance beinggreater than the thickness of a developer layer carried by the carrying means; means for applying an alternating elec-tric field across the clearancei and means for selectively changing the frequency and voltage for pro-~iding the alter-nating electric field.
The present invention yet further relates to a methodof aéveIoping an electrostatic latent image on an image bearing member, comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer; and causing transi-tion of developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
The present invention yet further relates to a method of developing an electrostatic latent image on an image bearing member comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer and creating in said gap an alternating electric field which, in a first stage, causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensity than in the first stage, to leave a developed image on said image bearing member.
The present invention yet further relates to an appara-tus for developing an electrostatic latent image on an imagebearing member, comprising a carrier for supporting a layer -llm-,. I
113~723 of charged dry developer at a developing zone with a gap between the image bearing member and the carrier, means for forming on said carrier a said layer of charged dry developer such that the thickness of the layer is less than the width of the gap, and means for causing transi-tion of the developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
The present invention yet further relates to an apparatus for developing an electrostatic latent image on an image bearing member comprising a carrier for supporting a layer of charged dry developer at a developing zone with a gap between the image bearing member and the carrier;
means for forming on said carrier a said layer of charged dry developer having a thickness which is less than the width of the gap; and means for creating in said gap , an alternating electric field which, in a first stage, : causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensitv than in the first stage, to leave a developed image on the image bearing member.
Other features of the present invention will become apparent from the following detailed description of some embodiments of the invention taken in conjunction with the accompanying drawings.
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, ~
113E~7Z3 BRIEF DESCRIPTION OF THE DRAWINGS
Figure l illustrates the amount of transition ; of the toner and the`characteristic of the degree of -toner back transition for the potential of a latent image, as well as an example of the voltage waveform applied.
Figures 2 A - F and Figures 3 A and B illustrate the developing process of the developing method accord-ing to the present invention.
Figure 4 illustrates the electric line of force produced from the electrostatic image in the developing method according to the prior art.
Figure 5 illustrates the electric line of force produced from the electrostatic image in the developing method according to the present invention.
Figures 6 A and B show the characteristic of the electrostatic image potential versus image density as the result of the experiment effected on the developing method according to the present invention, with the frequency of the applied alternate electric field varied.
Figures 7 A and B show the characteristic of .
the electrostatic image potential versus image density as the result of the experiment effected on the develop-ing method according to the present invention, with the amplitude o he applied alternate electric field ',.~.~
, ' ' .
1 varied.
Figure 8 shows the characteristic of the electro-static image potential versus image density as the result of the experiment effected on the developing 5 method according to the present invention, with the frequency and amplitude of the applied alternate voltage -~ varied.
Figure 9 is a graph illustrating the range of selection of the amplitude versus frequency of the applied alternate electric field as the result of the experiment effected on the developing method accord-ing to the present invention.
Figures 10 A, 10 B, 11, 12, 13 A and 14 A
illustrate the developing method according to the present invention and embodiments of the apparatus therefor.
Figure 13 B illustrates the voltage waveform applied to the apparatus shown in Figure 13 A.
Figure 14 B shows the output circuit of the alternate voltage applied to the embodiment shown in Figure 14 A, and Figure 14 C shows the output voltage waveform thereof. , Figures 15 A - D to Figures 18 A - D illustrate the process of movement and vibration of the developer to the image area and the non-image area in the process of development.
~ 113B7Z3 Reference in first had to Figure l to describe the principle of fog prevention and enhanced tone repro-duction of visualized image which may be expressed as the objects and effects of the present invention.
Figure l is a graph in which the abscissa represents the electrostatic image potential and the ordinate . represents the amount of transition of toner from a developer carrier (hereinafter also referred to as the toner carrier) to an electrostatic image bearing surface (positive direction) or the degree of back transition of toner which means that the toner having adhered to the electrostatic image bearing surface is stripped off therefrom (the degree of transition in the negative direction will hereinafter be described). The electro-static image potential is represented with the non-image area potential VL (which is usually the potential of the surface in a region corresponding to the light portion of an image and has a minimum value as the potential) and the image area potential (which is usually the potential of the surface in a region corresponding .
to the dark portion of the image and has a maximum value as the potential) as the potentials at the ends.
The surface potential of the half-tone region of the image including half-tone assumes a potential intermediate ~; 113~3'723 1 VD and VL due to the degree of that tone.
In the lower portion of Figure,l, the voltage waveform applied to the toner carrier is depected with the abscissa representing the potential and with the ordinate representing the time. A rectangular wave is exemplarily shown there, whereas waveform is not restricted to such waveform. The rectangular wave shown exemplarily is such a periodical alternating waveform that the minimum voltage Vmin of the toner carrier with the back electrode of the electrostatic image bearing member as the standard is applied in a ; time interval t, and the bias voltage of the maximum voltage Vmax is applied in a time interval t2.
The image area potential VD assumes a positive potential in some cases and assumes a negative potential in other cases, depending on the electrostatic image formation process used, and this also holds true with the non-image area potential VL. Herein, however, to make the invention more easily understood, description will be made with respect to the case where V~ is a positive potential. Of course, this is only for the purpose of illustration and the invention is not restricted thereto. When VD ~ O, the relation between VD and the non-image area potential VL becomes VD > VL. Now, if the relation between the maximum voltage Vmax and the 1131~723 1 minimum voltage Vmin applied to the toner carrier and VL is set the satisfy. i Vmax > VL > Vmin ...................... (l), S the bias voltage Vmin acts to cause toner particles to transit from the toner carrier toward the electrostatic image bearing member at the time interval tl and therefore, this s*age is called the toner transition stage. At the time interval t2, the bias voltage Vmax acts with a tendency to cause the toner which has transited to the electrostatic image bearing member in the time interval tl to be returned to the toner carrier and therefore this stage is called the toner back transition stage.
In the upper portion of Figure l, the amount of toner transition at tl and the degree of toner back transition at t2 are plotted with respect to the electro-static image potential. Here, the term "degree of toner back transition" is used to represent the probability of the toner back transition which takes place from the electrostatic image bearing member back to the toner carrier if the bias voltage Vmax is applied in a supposed , case that toner as a uniform layer adheres to both ; the image area and the non-image area of the electrostatic image bearing member.
Now, the amount of toner transition from the .
~3~387;~3 1 toner carrier to the electrosta~ic image bearing member in the toner transition stage is such as indicated by curve l shown by broken line in Figure l. The gradient of this curve is substantially equal to the gradient of the curve obtained when no bias alternate voltage is applied. This gradient is great and the amount of the toner transition tends to be saturated at a value intermediate VL and VD and accordingly, it is not suited for the reproduction of half-tone images and provides poor tone gradation. Curve 2 indicated by another broken line in Figure l represents the afore-mentioned probability of the toner back txansition in the toner back transition stage.
In the developing method according to the present invention, an alternating electric field is imparted 50 that such toner transition stage and toner back transition are alternately repeated and in the bias phase (t1) of the toner transition stage of the alternating electric field, toner is caused to once reach even the non-image area of the electrostatic image bearing member (of course, the toner is caused to reach the image area as well), and the toner is also caused to sufficiently adhere to the half-tone potential portion having a low potential approximate to the light region potential (VL) to thereby enhance the tone 1~3t~Z3 1 reproduction, whereafter in the bias phase (t2) of the toner back transition stage, the bias is caused to act in the direction opposite to the direction of toner transition to thereby cause the toner having reached the non-image area to be returned to the toner carrier. In this toner back transition stage, as will hereinafter the described, the toner having reached the non-image area as described tends to return to the toner carrier from the non-image area as soon as the bias field of the opposite polarity is applied, because the non-image area originally have no image potential.
On the other hand, since the toner having once adhered to the image area including the half-tone area is attracted to the image area charge, little amount of lS toner actually returns to the toner carrier from the image area even if the reverse bias is applied in the direction opposite to this attraction. By so causing the bias fields of the opposite polarities to alternate at a preferable amplitude and frequency, the toner transition and back transition may be repeated a number of times at the developing station. Thus, the amount : of the toner transiting to the latent image surface may be rendered, to an amount of transition faithful to . the potential of the electrostatic image. That i5, it is possible to provide a developing action which may 1 result in a variation in amount of toner transition having a small gradient and substantially uniform from : the potential VL to VD as shown by curve 3 in Figure 1.
Accordingly, practically no toner adheres to the non-image area while, on the other hand, the adherence of the toner to the half-tone image areas is so good that there is provided an excellent visible image having a very good tone reproduction corresponding to the surface potential thereof. This tendency may be made more pronounced by setting the clearance between the electro-static image bearing member and the toner carrier so that it is greater toward the end of the developing process and by decreasing and converging the intensity of the above-described field in the developing clearance.
As a method of adjusting the intensity of such electric field in the developing clearance, there is a first method of gradually converging the applied alternate voltage to a suitable predetermined DC value, and a second method of increasing the developing clearance itself with the developing time. These two methods will hereinafter be described respectively.
The developing process in the first method is shown in Figures 2 A - D.
Figure 2 A shows, in order of (l), ~2) and (3), the variation th time in an exemple of the ~aveform : 1 of the applied alternate voltage in the case of the above-mentioned first method. Of course, both of continuous variation and intermittent variation are possible, and in the case of continuous variation, (2) in the shown example shows the intermediate state of the variation.
Figures 2 B and C exemplarily show the manner of toner transition and toner back transition in the image area and the non-image area of the electrostatic image bearing member, with the variation in the develop-ing time. In these Figures, the direction of solid-line arrows shows the electric field in the toner transition direction, and the length of the arrows represents the intensity of the electric field. Broken line arrows show the electric field in the toner back transition direction and the length thereof represents the intensity of the electric field.
In Figures 2 A - C, the initial process (l) is called a first process, and the process t2) from an intermediate stage (which will later be described in greater detail) to the termination is called a second process. (3) designates the termination of the develop-; ment whereat the alternation of the applied voltage is terminated and the voltage is converged to an appropriate predetermined DC value (VO) intermediate 1138~Z3 1 VD and VL.
It is important that the action of the oppositepolarity to the toner transition in the image area and the non-image area in the first and the second process is varied. This status will be described phenomeno-logically. First, in the image area, as exemplarily shown in Figure 2 B, Vmax ~ VD Vmin process (l) and therefore, in the time period tl tapplied voltage is Vmin), a relatively strong toner transition field occurs from the toner carrier toward the image area of the electrostatic image bearing member and toner reaches and adheres to the image area. On the other hand, in the time period t2 (applied voltage is Vmax), a relatively weak toner back transition field occurs toward the electrostatic image bearing member and part of the toner is returned from the image area to the toner carrier. Each time the time periods tl and t2 are 80 repeated, the toner transition and back transition occur between the toner carrier and the non-image area.
Since the relation between the applied voltages Vmin and Vmax and the image area potential VD is set to .
¦Vmax ~ VDI < IVD Vminl ....... t2), ;
the amount of toner transition from the toner carrier to the image area is much greater than the amount of toner i~3~7~3 1 back transition in the first process and therefore, it practically offers no problem that the toner back transition reduces the toner transition, namely, the effect of development.
Subsequently, when the amplitude of the applied voltage is continuously or intermittently attenuated to a predetermined value of max VD + ¦Vth-r¦ ................ (3) .
as shown by (2) in Figure 2 A, the amount of back transition of the toner to the toner carrier from the electrostatic image bearing member to which the toner have once adhered in the time period t2 becomes substantially zero.
¦Vth-r¦ is the minimum absolute potential difference between the electrostatic image formation surface and the toner carrier surface at which the toner can be separated from the electrostatic image formation surface and can effect back transition to the toner carrier.
Further, when Vmax < VD + ¦Vth-r¦ .............. (4) is reached, the back transition occurs no longer and instead, there is produced an electric field which expedites the toner transition from the toner carrier to the electrostatic image bearing member, although this 113~723 1 toner transition is smaller in amount than the toner transition during the time period t1.
Accordingly, when the applied voltage is attenuated to satisfy the relation that max _ VD lvth.rl this process is called the second process in the image area. Such phenomenon in the image area progresses to termination while becoming smaller in amount until the alternating component of the applied voltage becomes null and is converged to a predetermined DC value, whereupon the phenomenon reaches the state of (3).
The process of toner movement in the non-image area (potential VL) of the electrostatic image bearing member will now be described by reference to Figure 2 C .
In the first process shown as ~l), VmaX ~ VL > Vmin and so, during the time period tl (applied voltage is Vmin), a relatively weak toner transition field occurs from the , toner carrier to the non-image area of the electrostatic image bearing member and the toner adheres to the non-, image area. On the other hand, during the time period .
t2 (applied voltage is Vmax), a relatively strong toner back transition field occurs from the non-image area toward the toner carrier and the toner is returned from the non-image area to the toner carrier. Each time . . .
113~723 1 the time periods tl and t2 are so repeated, the toner transition and back transition occurs between the non-image area and the toner carrier and the toner is considered to effect reciprocal movement therebetween. It is considered 5 that the amount of toner back transition becomes greater in probability than the amount of toner transition because the relation between the applied voltages Vmin and Vmax and the non-image area potential VL is set to ~ VLI ~ IVL Vminl .................. (6).
Of course, in this case, no more than the toner having adhered actually effects the back transition.
Next, when the amplitude of the applied bias voltage is continuously or intermittently attenuated to a predetermined value of Vmin = VL - ¦Vth-f¦ ...................... (7) as shown by (2) in Figure 2 A, the amount of toner ; transiting from the toner carrier to the electrostatic image bearing member during the time period t1 becomes substantially ., zero. ¦Vth-f¦ i8 the minimum absolute potential difference between the electrostatic image formation surface and the ; toner carrier at which the toner can be separated from the , toner carrier surface and can transit to the electrostatic image formation surface. This value is varied with the conditions of the developer and development.
Further, when l min VL ¦Vth f¦ ....................... (8) is reached, such transition occurs no longer and instead, there is produced an electric field which expedites the tendency of the toner to back-transit from the electrostatic image bearing member toward the toner carrier, although such back-transition is smaller in amount than the toner back transition during the time period t 2 Accordingly, when the applied voltage is attenuated (in this case, Vmin is greater) to satisfy the relation that i Vmin - VL ~ ¦Vth-fl this process is called the second process in the non-image area. Such phenomenon in the non-image area progresses to termination while becoming smaller in amount until the alternating component of the applied voltage becomes null and is converged to a predetermined DC value.
In other words, the fog or the phenomenon of contact of the toner with the non-image area takes place in the first process, but it is eliminated in the second process.
Figure 2 D shows a modification of the application of the bias voltage shown in Figure 2 A, and Figures 2 E
and F represent the mode of toner transition or ~131~23 1 toner back transition with respect to the image area and the non-image area in that case. The application of the bias voltage in the case of Figure 2 D satisfies Vmin < VL < Vmax and has added thereto the condition of Vmax < VD + ¦Vth r¦. In the case of such bias voltage application, as compared with the case of the bias voltage application shown in Figure 2 A, there is no phenomenon of toner back transition in the image area and the phenomenon in the non-image area does not ' 10 substantially greatly differs from the state shown in Figure 2 C. As shown in Figure 2 E, there is no back transition of the toner in the first process (1) and this holds true with the second process (2). In this case, the boundary between the first and the second process is the time when Vmin = VL - ¦Vth f¦ and it is considered that the second process is entered when Vmin becomes greater than that.
Description has hitherto been simply made of the extreme cases of the image area (dark area) and the non-image area (light area), but as regards the half-tone, the amount of final toner transition to the electrostatic image surface is determined by the magnitudes of the amounts of toner transition and toner back transition corresponding to the potential of the half-tone area. Therefore, the curve of the ~13E~-~23 1 amount of toner transition for the electrostatic image potential is smaller in gradient than the curve l as shown by curve 3 in Figure l and becomes substantially uniformly varied from the non-image area potential VL
to the image area potential VD. By this, there is obtained a visible image having a good tone reproduction from the light area to the dark area, including the half-tone of the image. In the first process in the above-described first method, it is essential to make such a design that the electric field alternates in the non-image area, whereby the tone once adheres to the non-image area as well, and this leads to the possibility of the toner positively adhering also to the half-tone image area having a density adjacent to the non-image area, which in turn leads to an advantage that a visible image having a good tone reproduction of such half-tone area may be obtained by effecting the strip-off (back transition) of the once deposited toner in accordance with the non-image area potential.
An example of the developing process in the second method is shown in Figures 3 A and B. As shown in , Figures 3 A and B, the electrostatic image bearing member 4 moves in the direction of arrow and passes through the developing areas (1) and (2) to the area (3).
Designated by S i~ the toner carrier. Figure 3 A shows ` ~ 1131~7~:3 ' ~
1 1 the toner transition and back transition fields from ; I the toner carrier 5 in the image area of the electro-i static image bearing member and Figure 3 B shows the toner transition and back transition fields from the carrier in the non-image area. In these figures, solid-line arrows indicate the toner transition field and broken-line arrows indicate the toner back transition field. The direction of the arrows indicates the directions of the electric fields and the length of the arrows indicates the intensity of the electric fields.
This second method, as will hereinafter be described, is directed chiefly to increasing the developing clearance and thus decreasing the intensity of the electric field I rather than attenuating the voltage itself.
1~ As shown in Figure 1, Vmax and Vmin as , voltage are repetitively applied at time intervals t~ and ¦ t2, and of course, the waveforms of the applied voltages ! are not restricted to those shown. As already described, the condition of Vmax > VL > Vmin is given as a premise and the conditions that ¦Vmax ~ VL¦ > ¦ VL Vminl a max VDI ~ IVD ~ Vminl are set.
By doing so, in the image area, both the toner transition and the toner back transition alternately occur in the developing area (1), as shown in Figure 3 A.
This developme t has been desaribed in detail by referenae ~, .
ll 113E~723 ' 1 to Figure 2 B. Accordingly, in this developing area (l) wherein the developing clearance is small, the first process of development occurs. Next, when the developing area (2) in which the developing clearance is larger is entered, the already described second process occurs.
In this developing area (2), the developing clearance is wider so that the electric field becomes weaker in inverse ; proportion to the widening of the clearance even if there is no variation in the value of the applied voltage, and the back transition field becomes lower than the threshold value ¦Vth-r¦ necessary for the back transition and thus, the toner transition is possible but the toner back transition cannot take place. Accordingly, the boundary between (l) and (2) correspond~ to the time when Vmax = VD + ¦Vth-r¦ if it is made to correspond to the case where the clearance is constant while the applied voltage is varied. When the developing area (3) is entered, the clearance becomes so wide that neither of the toner transition and the back transition takes place any longer and the development is terminated thereat.
In the case of the non-image area shown in Figure 3 B, the areas (l) and (2) correspond to the first and the second process, respectively. In the area (l), both the transition and the back transition of toner 113~37~ 3 1 occur as previously described with respect to Figure 2 C.
Thus, fog takes place in this area. When the area (2) is entered, the intensities of the electric fields resulting from the voltages of Vmax and Vmin both become weaker in inverse proportion to the widening of the developing clearance and the back transition of the toner is possible but no transition field which will cause the transition of the toner is produced. Accordingly, the fog is fully eliminated in this area (2).
Subsequently, when the developing area (3) is entered, neither the transition nor the back transition of the toner occurs any longer and the development is terminated.
Thus, again by this method, there is obtained an effect substantially equal to the effect of varying the applied bias voltage and not only the fog can be eliminated but also, as regards the half-tone, the final amount of toner tran~ition to the electrostatic image bearing member is determined by the magnitudes of the toner transition and back transition corresponding to the surface potential of the half-tone image, with a result that the curve of the electrostatic image potential versus toner transition amount becomes one having a good tone reproduction as shown by curve 3 in Figure 1.
The conditions that lVmaX ~ VLI ~ IVL Vminl and -` 113!~723 :~
1 lVmax VD¦ ~ ¦VD - Vmin¦ when the image area charge is positive become lVmin ~ VLI ' IVL maxl ; lVmin VD¦ < ¦VD - VmaXl when the image area charge is negative.
S As hitherto described, the application of an ; extraneous alternate voltage between the electrostatic image formation surface and the toner carrier remarkably improves the tone gradation of the resultant image, and it is possible to further improve the reproducibility of line images as well by selecting the amplitude and frequency of the extraneous alternate image to suitable magnitudes as will hereinafter be described.
Description will hereinafter be made with the electrostatic image formation charge as being positive.
In the toner transfer development, as shown in Figure 4, thc electric line of force emanating from the latent image edges goes around the back electrode of the latent image formation surface and cannot reach the tonexlayer, thus tending to result in thinned line or poor sharpness of the edges of the image during the development.
On the other hand, when the alternating wave as shown in Figure l is applied and when the minimum value Vmin of the applied voltage is lower than the latent image light area potential VL as shown in this figure, the electric line of force in the developing area at 1 the development expediting stage becomes such as shown in Figure 5. That is, the electric line of force goes less around the edges of the latent image and parallel ~- electric fieldsand fon~ in the developing area. Thus, even the edges are developed clearly.
To enhance the reproducibility of the edges of the image in this manner, it is preferable to select the development expediting bias (Vmin) to a sufficiently low value (in case of a positive electrostatic image), but too low a value for such bias would result in excessive developer adhering to the non-image area in the toner transition stage and even if the back transition bias is increased to strip off such excessive toner, the resultant image will be poor in contrast, after all.
On the other hand, in order that the toner may be separated from one of the toner carrier and the electro-static image formation surface and transit to the other, there must be a threshold of a certain finite potential difference between the two. As such threshold value, there is ¦Vth-r¦ when the toner transition occurs from the toner carrier to the latent image formation surface .
as previously described, and there is ¦Vth-r¦ when the toner back transition occurs from the latent image formation surface to the toner carrier. In order to increase the reproducibility of line image while avoiding :
~ - 32 -113~7Z3 1 the adherence of excessive developer to the non-image area in the toner transition stage, ¦Vth-f¦ may be selected to a sufficiently great value and the develop-ment expediting bias (Vmin) may be decreased.
The proper value thereof substantially lies in the range VL 2¦Vth fl ~ Vmin ~ VL ............... (10), and most preferably lies in Vmin ~ VL ¦Vth f¦ ..................... (11).
If Vmin is below VL - 2 ¦Vth-f¦, the fog in the non-image area will be unavoidable.
If, in a preferred embodiment of the developing method according to the present invention, magnetic toner is used as the developer and a non-magnetic sleeve enclosing a magnet therein i5 used as the toner carrier, it has become apparent that there may be obtained images which are clear at the edges of the images and excellent in half-tone reproduction.
An advantage of using the magnetic toner lies in that by suitably setting the magnetism of the toner and the magnetic force of the toner carrier, the binding force of the toner to the toner carrier is enhanced and accordingly, ¦Vth-f¦ becomes greater with a result that the Vmin of the extraneous alternate field can be ' .
~ 1:~38~23 1 selected to a sufficiently low value. Further, the proper valué of Vmax corresponding to the proper value L I l Vmin ~ VL is VD < Vmax ~ VD + 2lvth-rl (12) It has become clear that these values enhance the effect of improving the reproducibility to the greatest degree by a minimum alternate voltage value. To cause the toner : to fly through the developing clearance and temporally reach the non-image area as well to thereby improve the tone reproduction and then to cause the toner to be stripped off chiefly from the non-image area, it is necessary to properly select the amplitude and alternating frequency of the applied alternate bias voltage.
The results of the experiment in which the effect of the present invention has clearly appeared due to such selection will be shown below.
Figure~ 6 A and B show the plotted results of an experiment in which the image reflection density (~) for the electrostatic image potential ~V) is measured with the amplitude of the applied alternate voltage fixed and with the frequency thereof varied. These curves will hereinafter be referred to as the V - D , curves. This experiment was carried out under the following construction. A positive electrostatic charge latent image is formed on a cylindrical electrostatic image formation surface. The toner used is a magnetic 1~3B723 1 toner which will hereinafter be described (containing 30% magnetite). The toner is applied to a thickness of about 60 ~ on a non-magnetic sleeve enclosing a magnet therein, and negative charge is imparted to the toner by the friction between the toner and the sleeve surface.
The result when the minimum developing clearance between the electrostatic image formation surface and the magnetic sleeve was maintained at 100 ~ is shown in Figure 6 A, and the result when such clearance was maintained at 300 ~ is shown in Figure 6 B. The density of the magnetic flux in the developing station resulting from the magnet enclosed in the sleeve is about 700 gausses. The cylindrical electrostatic image formation surface and the sleeve are rotated substantially at the ~ame speed of about 110 mm/sec. in the same direction.
Accordingly, the electrostatic image formation surface passes through the minimum clearance in the developing station, and then gradually goes away from the toner carrier. The alternate electric field applied to this sleeve is a sine wave of amplitude Vp p = 800 V (peak-to-peak value) with a DC voltage of ~200 V superimposed thereon. Figures 6 A and B show the V - D curves when the alternating frequency of the applied voltage is 100 Hz, 400 Hz, 800 Hz, 1 KHz and 1.5 KHz (only in Figure 6 A), and the V - D rvAs when no bias field io applied but Il - 35 -1 the back electrode of the electrostatic image formation surface and the sleeve are made to conduct.
From these results, it is seen that when no bias field is applied, the gradient on the so-called ~ value of the V - D curves is very great but by an alternate electric field of low frequency being applied, the y . value becomes very small to greatly enhance the tone gradation. As the frequency of the extraneous electric field is increased from lO0 Hz, the ~ value gradually becomes greater and the effect of enhancing the tone gradation becomes poorer and in the case of a clearance of lO0 ~, the effect becomes very weak under the afore-mentioned amplitude (Vp p = 800 V) when the frequency exceeds 1 KHz; in the case of a clearance of 300 ~, if the amplitude is Vp p = 800 V as described above, the : effect is decreased when the frequency becomes 800 Hz or so, and the effect of tone reproduction becomes very weak when the frequency exceeds 1 KHz. This is considered attributable to the following reason. A finite time is necessary to ensure reciprocal movement of the toner . when the toner repeats its adherence and separation in , the clearance between the sleeve surface and the latent image formation surface during the developing process in which an alternate electric field is applied.
2S Particularly, when the toner transits by being subjected . .
113~3~23 to a weak electric field, it takes a long time for the . ~ toner to positively effect its transition. On the other hand, to reproduce the density of half-tone, it is necessary for the toner subjected to an electric field which is weak but greater than a certain threshold value to positively transit to the image area within one-half of the period of the alternate electric field.
For that purpose, a lower frequency is more advantageous if the amplitude of the alternate electric field is constant, and thus, especially good tone reproduction may be obtained for an alternate electric field of very low frequency as represented by the results of the experiment. This speculation is justified by the comparison between the results of the experiment shown in Figures 6 A and B. The results shown in Figure 6 B
have been obtained under the same conditions as those shown in Figure 6 A except that the clearance between the electrostatic image formation surface and the sleeve surface is as great as 300 ~. The wider clearance results in a lower intensity of the electric field to which the toner i9 subjected, and consequently a lower velocity of transition of the toner. The wider clearance further results in a longer distance of jump and after all, a longer time of transition. As i3 actually apparent from Figure 6 B, the y value becomes considerably ~3~1~723 great for the order of 800 Hz and, when l KHz is exceeded, the y value becomes almost equal to that when no alternate voltage is applied. Therefore, in order to obtain the same effect of enhanced tone reproduction as that when the clearance is narrow, it is preferable to reduce the frequency or to increase the intensity (amplitude) of the alternate voltage as will later be described.
On the other hand, too low a frequency would - 10 not result in sufficient repetition of the reciprocating movement of the toner during the time the latent image formation surface passes through the developing station, and tends to cause irregular development to be created in the image by the alternate voltage. As the result of the foregoing experiment, generally good images have been provided down to the frequency of 40 Hz, and when the frequency is below 40 Hz, irregularity has been created in the visible image. It has been found that the lower limit of the frequency for which no irregularity is created in the visible image depends on the developing conditions, above all, the developing speed (also referred to as the process speed, Vp mm/sec.). In the present experiment, the velocity of movement of the electro-static image formation ~urface has been llO mm/sec. and therefore, the lower limit of the frequency is 40/llO x Vp 113~723 1 ~ 0.3 x Vp ...... (13). As regards the waveform of the alternate voltage applied, it has been confirmed that any of sine wave, rectangular wave, saw-tooth wave or asymmetric wave of these is effective.
Such application of an alternate bias of low frequency brings about remarkable enhancement of the tone gradation, but the voltage value thereof must be properly set. That is, too great a value for the ¦Vmin¦ of the alternate bias may result in an excessive amount of toner contacting the non-image area during the toner transition stage and this may present sufficient removal of such toner in the second process of the development, which may in turn lead to fog or stain left in the image.
Also, too great a value for jVmaxl would cause a great amount of toner to be returned from the image area, thus reducing the density of the so-called solid black portion. To prevent these phenomena and to sufficiently enhance the tone gradation, VmaX and Vmin may preferably and reasonably be selected to the following degrees:
Vmax ~ VD + ¦Vth rl ..................... (14) Vmin ~ VL ~ IVth fl ..................... (15) Vth-f and Vth-r are the potential threshold values already described. If the voltage values of the alternate bias are so selected, the excess amount of toner adhering 113~23 1 to the non-image area in the toner transition stage and the excessive amount of toner returned from the image area in the back transition stage would be prevented to ensure obtainment of proper development result.
This will be shown by the results of an experiment.
: Figures 7 A and B show the V - D curves when the frequencyof the alternate electric field has been fixed (200 Hz) and the amplitude Vp p thereof has been varied.
Figure 7 A shows the result when the developing clearance has been set to lO0 ~, and Figure 7 B shows the result when the developing clearance has been set to 300 ~.
All the other conditions are the same as those of Figures 6 (A and B). When the developing clearance is relatively small, the result of enhanced tone gradation appears if the amplitude Vp p exceeds 400 V, as compared with the case where no electric field is applied. If the Vp p exceeds 1500 V, the tone reproduction is good but fog begins to appear in the non-image area, and if the Vp p exceeds 2000 V, much fog appears. In this case, prevention of the fog may be accomplished by making the alternating frequency higher than 200 Hz. , When the developing clearance is as wide as 300 ~, an effect of improved tone reproduction has begun to appear for Vp p - 400 V or higher, and formation of good images excellent in tone reproduction and almost , . .
113B~Z3 1 free of fog has become possible for the order of 800 V.
When the Vp p exceeds 2000 V, the tone reproduction is good but fog is created and in this last case, it is necessary to increase the alternating frequency.
When the developing clearance _ is thus relatively great, it is advisable that the Vp p of the voltage applied be greater and f be higher than when d is small.
In order to enhance the tone gradation of the image, it is necessary to set the alternating frequency and the amplitude value of the applied alternate voltage to suitable ranges, and it has been found that depending on the property of the image, it is possible to selectively change over and select the relation between the frequency and the amplitude value of the applied voltage within an appropriate range. That is, when the relation between the frequency and the voltage value of the alternate voltage is studied more strictly, it has become apparent that the developing characteristic (V - D curves) can be arbitrarily selected in accordance with the values of those. ~n example thereof is shown in Figure 8.
Figure 8 shows the developing characteristic ; when the clearance between a photosensitive drum which is the latent image bearing member and a sleeve which is the developer carrier is 300 ~, the thickness of the developer layer on the sleeve is about lO0 ~ and as ~ 113B~23 1 the toner, use is made of lO0 parts of styrene acryl resin, 60 parts of ferrite, 2 parts of carbon black and 2 parts of anriferous dye as the charge control agent mixed and ground and having 0.4% by weight of colloidal silical extraneously added thereto. The conditions of each of the shown curve are the bias conditions (alternating frequency f (Hz) and amplitude value (Vp p)) for visualizing the dark region potential (about 500 V) by the light region potential of about O V. The waveform of the applied voltage is a sine wave with a DC voltage superimposed thereon. (The slight difference of Figure 8 from the previously mentioned graph is attribut-able to the difference of the developer used).
As is apparent from the graphs of Figures 6 A and B and Figure 8, when the frequency f is low, there is usually obtained a developing characteristic having high tone gradation and when the frequency f is slightly high, there i9 obtained a developing characteristic having a great value for y. By varying the amplitude of the alternate voltage in addition to such variation in frequency, it i8 possible to obtain any desired developing characteristic corresponding to the kind of the image.
(The DC component is also varied slightly.) The curve ~a) shown in Figure 8 is the VD curve when the frequency f is 200 Hz, Vp p = 900 V and the .- ' , ' .
113?37Z3 1 superimposed DC component is 220 V, and it is seen therefrom that this bias condition has a good tone gradation. The curve (b) is the VD curve when the frequency and the amplitude value have been increased to f = 400 Hz and Vp p = 1600 V, respectively, with a DC
component of 220 V, and it is somewhat greater in r than the curve (a) but still has a relatively high tone gradation.
If, with respect to the curve (b), the frequency i3 increased to 700 Hz and 900 Hz with the amplitude Vp p maintained constant (the superimposed DC voltage is decreased), the r becomes greater and greater as indicated by the curves (c) and (d), thus resulting in poor tone gradation. On the other hand, however, as shown by the curve (d), it can be seen that even if the electrostatic image potential is low, good development at that potential is possible. Further, although the tone gradation is poor, the so-called edge effect becomes great to provide yood reproducibility of the line image and reduced fog.
By so varying the bias conditions, it is possible to ensure all-round quality of image corresponding to .
the original or to the li~ing of the user.
A preferable range of combination between the alternating bias conditions (frequency f (Hz) and amplitude value Vp p (V)) on the basis of each experiment 1131~723 is shown in Figure 9. Figure 9, with the ordinate representing the amplitude Vp p (V) of the applied :
voltage and the abscissa representing the alternating : frequency f (Hz) thereof, shows a preferable range of combination between the two selectable in accordance with the image.
In Figure 9, the solid-line curve P indicates the boundary of the range at which fog relatively tends . - to appear when the developing clearance is 300 ~, and the shaded area A indicates a range in which the fog tends to appear and which is not suited for the line :
copy. Also, the solid-line curve q indicates the boundary at which the quality of the tone gradation is judged when the developing clearance is 300 ~, and the .
shaded area C indicates a range in which the effect thereof i8 low. Thus, the range B surrounded by the two curves p and q is a range in which fog is reduced and the lmage is excellent in definition and tone gradation. .
Of course, the positions of these curves p and q may be more or leqs varied by a variation in size of the developing clearance d. When d ic relatively small, the curves p and q become displaced to dot-and-dash line positions p' and q', respectively.
Particularly, in the area encircled by a broken line S, the overall effect of the bi~s by the alternate ,, .
: - 44 -. .
' . ~ ' ': ~ ' . .
3-t 1 field of low frequency is pronounced. The lower limit value of the frequency in this area S is a value determined by the previously mentioned relation that f _ 0.3 x Vp, and the upper limit value thereof is determined with a view to well maintain the SN ratio. This SN ratio will now be described. When the frequency of the applied alternate field is increased as mentioned previously, it is necessary to make the amplitude Vp p of the applied voltage great in order to ensure the reciprocal movement of the developer (the movement of the developer which temporally reaches the non-image area, also) to take place between the developer carrier and the latent image bearing member. However, when such a voltage value becomes high, it i8 much higher than the potential difference (VD) of the image area to be visualized and the transition phenomenon of the developer to the image area can hardly sense the potential difference VD. If 50, the definition of the image becomes reduced so that the line reproducibility becomes poor and the fog becomes ready to appear.
In addition, the use of a high voltage (higher than about 2500 V) in particular tends to cause the discharging phenomenon with respect to neighboring members and this leads to a problem in constructing an apparatus.
Therefore, under the above-described standard i~ 25 set conditions, the amplitude may preferably be Vp p ~ 2500 V, 1~.3Q7~3 : 1 and particularly preferably be Vp p ~ 2000 V, and the frequency may particularly preferably be f ~ l KHz.
Depending on the combination with the amplitude, the frequency may practically be f ~ 1.5 KHz to thereby obtain the intended effect.
As has hitherto been described, the application of an extraneous alternate voltage between the latent image formation surface and the toner carrier leads to ;
remarkably enhanced tone gradation of the image and preventing of fog. Further, by using magnetic toner as the developer and a sleeve enclosing a permanent magnet as the developer carrier and by properly setting the extraneous alternate voltage value, as will hereinafter be described, it is possible to further enhance the reproducibility of line images at the same time.
Description will hereinafter be made with the electrostatic image formation charge as being positive, whereas the invention is not restricted thereto. In the so-called toner transfer developing method, the electric line of force produced from the end of the latent image ; goes around the back electrGde of the latent image formation surface as shown in Figure 4 and cannot reach the surface of the toner carrier, and accordingly the toner which has started from the toner carrier can 1:~3~7~3 1 hardly adhere to the end of the image. Thus, the resultant image tends to suffer from thinning of lines and poor sharpness of the end, which in turn offers a problem in line copying.
Therefore, in this system, if an alternating bias is applied and if the Vmin thereof is selected to a sufficiently low value, the electric line of force in the developing station during the toner transition stage goes so little around the end of the electrostatic image, as shown in Figure 5, that there are formed parallel electric fields. This enables the toner to positively adhere to the end of the electrostatic image. However, as already noted, too low a value for Vmin would usually cause fog or stain to be created in the non-image area.
In the present embodiment of the invention, the advantage resulting from the use of the magnetic toner as the developer and the sleeve enclosing the permanent magnet as the developer carrier lies chiefly in solving this problem. By properly setting the content ; 20 of the magnetic material in the developer and the intensity of the magnetic field of the permanent magnet, it is possible to uniformly enhance the restraining force of the toner onto the sleeve and accordingly select the value of ¦Vth-f¦ to a sufficiently great value. As the result, Vmin can be set to a low value with the amount 113~J23 1 of the toner adhering to the non-image area during the toner transition stage being minimized.
Thus, by applying an alternating bias in the toner transfer developing method using magnetic toner, it is possible to obtain images of good tone gradation which are clear at the end and free of fog and which are excellent also in line copying.
On the other hand, it is a very difficult problem to convey the developer to the developing station in the high resistance toner transfer development and to impart a charge. The method using magnetic toner as the developer and conveying the developer by means of a sleeve and imparting a charge by frictional charging between the sleeve surface or an applicator member and the toner is considered to be one of very advantageous , methods.
Also, application of the magnetic toner onto the sleeve may be effected by a method of urging a resilient member against the sleeve or a method of maintaining a magnetic member in opposed relationship with the magnetic pole of the permanent magnet within .
the sleeve and in non-contact with the sleeve surface and controlling the thickness of the magnetic toner by the magnetic force. In the conventional toner transfer development wherein development is effected ~,th the -- 113~3~23 1 sleeve opposed to the electrostatic image bearing member and with these members being rotated in the same : direction and at the same velocity, the state of the . toner applied onto the sleeve directly affects the quality of image and when the application of the toner is effected by the former method, the status of application is relatively delicate and ensures a good quality of image. In this method of application, however, the toner strongly rubs against the sleeve surface and therefore 10 the resin content of the toner adheres to the sleeve surface to remarkably prevent the toner from being charged.
On the other hand, if the latter method is used, the adherence of the toner to the sleeve surface is minimized but the status of the toner applied onto the sleeve surface presents scattered lumps of toner particles and is coarse and accordingly, the image after developed becomes coarse.
In contrast, by applying an alternating bias in the developing station according to the present invention, toner particles are caused to effect reciprocal movement between the latent image and the sleeve surface and are separated into individual particles in that process, so that the toner can finely adhere to the image 25 area of the electrostatic image surface.
i~ 1~723 Some specific examples will be shown below in detail.
Example l The example shown in Figure 10 A is of a construction in which the applied bias alternate voltage is attenuated, and shows a mode in which a source voltage comprising an AC voltage of low frequency with a DC
component superimposed thereon is attenuated by the use of a mechanical sliding electrode. Figure 10 B shows a modified portion for attenuating the voltage by the use of an electric circuit.
In Figure 10 A, reference numeral 10 designates ZnO photosensitive paper which has formed thereon an ,, electrostatic image at another station, not shown.
The paper 10 is conveyed to the shown developing station by a pair of rollers 13,13 and stopped there for develop-ment, and then again conveyed for fixation. Designated by 12 is a toner carrier comprising an electrically conductive rubber belt and driven by a pair of metal rollers 14,14. The ZnO photosen~itive paper 10 as the electrostatic image bearing member and the toner carrier , 12 are transported to the developing station by the rollers 13 and 14 being intermittently driven by motors 21 and 22, and become stationary during the developing process, and shift before the next developing cycle is ', ~'~
~131~7Z3 1 started. The toner carrier effect one-half of a full rotation andlis stopped again. Denoted by 15 is an insulating toner contained in a container 7 and it comprises styrene resin, 3% carbon black and 2% positive polarity charge control agent, all by weight. Also, to improve the fluidity, 0.2~ by weight of colloidal silica is extraneously added. The toner is conveyed by the toner carrier 12, and the thickness of the toner applied is controlled to 100 to 200 ~ by a me~ber 16 slidably contacting the carrier 12, and positive charge ,j is imparted to the toner by a corona charger 18 before development is started. The clearance between the electrostatic image bearing 10 and the toner carrier 12 is maintained at 500 ~. Designated by 14a is a slidable electrode which is in contact with the core of the rotary roller 12, and which applies an alternate voltage to the toner carrier 12 from a power source 9. Denoted by 20 is a fur fru~h for stirring the developer to supply it to the toner carrier 12.
The dark region potential of the electrostatic image formed on the electrostatic image bearing member 10 was -450 V and the light region potential of such image was -40 V. The voltage applied comprised an AC
voltage 1200 Vpp of frequency ranging from 10 - 1000 Hz, with a DC voltage of -200 V superimposed thereon, and ~ 113~Z3 1 only the AC voltage i9 attenuated to 0 at a time constant of about 0.5 in 0.2 second after the start of the development.
Description will now be made of the construction of the power source 9 for causing such attenuation.
Reference numeral 21 designates a motor for moving the sliding electrode 26 on the secondary winding side of an AC transformer 27. Reference numeral 24 designates an AC power source, and 25 a DC power source.
Designated by 23 is a power source for driving a timing signal generating circuit and motors 21, 22.
In 0.2 second after the start of the development, the sliding electrode 26 moves from its position A to its position B at a uniform velocity after 0.5 second.
- 15 Upon displacement of the sliding electrode 26 to its position B, the motor 22 is driven to cause the toner carrier 12 to effect one-half of a full rotation and during this time, the sliding electrode returns to its position A.
Figure 10 B shows a power source 9' using a well-known RLC attenuating circuit instead of using a .
sliding electrode. In 0.2 second after the start of the development, the switch is changed over from its position A' to its position B'. The time constant of this attenuating circuit is set to 0.5 sec. The change-- 1~L3!~23 1 over of the switch can be accomplished in a timing fashion by known means such as a relay or the like.
Thus, the development by the previously des-cribed first method can be applied and the resultant image is substantially free of fog and excellent in tone gradation particularly in an area wherein the alternating frequency f of the applied alternate voltage is low, and especially good images have been obtained for f < 1000 Hz.
Example 2 ; This example realizes the previously described second method which effects development by varying the developing clearance in accordance with the develop-ing process, and will be described by reference to Figure 11. Designated by 31 is an Se photosensitive belt having formed thereon an electrostatic image at another station, not shown, and developed at the shown station, and the image thereon is fixed or transferred at a further station, not shown. Reference character 32 is a toner carrier comprising an electrically conductive rubber belt, and driven by a metal roller 33.
Denoted by 35 is an insulating toner contained in a container 37 and comprising polyester resin, 2% by weight of carbon black and 2% by weight of negative polarity charge control agent. To improve the fluidity of the ., ~ toner, 0.1% by weight of colloidal silica is extraneously : added. The toner is conveyed by the toner carrier 32 and the thickness of the toner on the toner carrier is controlled to 50 - 150 ~ by a resilient member 36 urged ,~ 5 against the roller 33. Before the development is started, negative charge is imparted to the toner by a corona charger 38. The electrostatic image bearing member 31 is held in the developing station with a ~' minimum clearance of 300 ~ with respect to the toner carrier 32 by a metal roller 41. At a point spaced apart about 30 mm from that position, the distance between the members 31 and 32 is maintained at about 2 mm by a metal roller 42 (adjustable). Designated by 43 is a driving member for adjusting the position of the metal roller 41. The members 31 and 32 are so configured that they pas~ through the moct proximate position and then gradually widen the clearance therebetween. The members 31 and 32 move in the same direction at the same speed of 200 mm/sec. De-c~ignated by 39 is an alternate voltage application source.
The image area potential and the non-image area .
potential of the electrostatic image formed on the member 31 are 800 V and 200 V, respectively. The applied voltage is an alternating current 1000 Vp_p of frequency 200 Hz with a DC voltage of 400 V superimposed thereon.
1 Thus, there have been obtained fogless good images which ~; are of high tone gradation.
Example 3 Referring to Figure 12, reference numeral 51 designates a photosensitive drum having an Se film, and 52 denotes a toner carrier comprising an electrically conductive rubber sheet and driven by a metal roller 53.
The movement velocity of the toner carrier 52 is substantially equal to the peripheral velocity of the electrostatic image bearing member 51, and it is 200 mm/sec. Designated by 45 is a non-magnetic insulating toner contained in a container 47, and it is conveyed by the friction force between the toner and the toner carrier 52 and by Van der Waals force. The thickness of the toner on the toner carrier is controlled to about 60 ~ by a resilient applicator member 46, and negative charge is imparted to the toner by a corona charger 48 before the development is started. The clearance between the members 51 and 52 is maintained at a minimum of 400 ~, but this clearance becomes gradually larger with the rotation of the members 51 and 52, to thereby form a developing area having the .
previously described first and second processes. Denoted by 44 i8 a sliding electrode contacting the core of a rotatable member 53. The electrode 44 applies an alternate voltage to the members 52, 53 and 44 by a power 113B~23 1 source 49 with respect to the electrically conductive support member for the groundedimember 51. The frequency of the alternate electric field is 100 Hz, and the electro-static image potential is +700 V for the image area and +50 V for the non-image area, and the potential of the member 42 is Vmax = ~750V for the maximum value and Vmin= - 50 V for the minimum value.
Under the above-described construction, there have been obtained clear images of high tone reproduction.
Example 4 Referring to Figure 13 A, reference character 61 designates a photosensitive drum having a radius of 40 mm and having a CdS layer and an insulating layer.
Designated by 62 is a non-magnetic sleeve having a radius of 15 mm and enclosing a permanent magnet 63 therein. The members 61 and 62 are rotated at the same peripheral velocity of 100 mm/sec. in the same direction.
Denoted by 65 is an insulative magnetic toner which comprises 60% by weight of styrene resin, 35% by weight of magnetite, 3% by weight of carbon black and 2% by weight of negative charge control agent. To improve , the fluidity of the toner, 0.3% by weight of colloidal silica is extraneously added. The toner is conveyed by the sleeve 62, and the thickness of the toner applied onto the sleeve is controlled to about 70 ~ by a magnetic 1 blade 66 disposed in proximity to the sleeve. Also, the toner is imparted negative charge by the friction charging between the toner and the sleeve 62.
The clearance between the members 61 and 62 is maintained at a minimum of 200 ~, but the movement velocities of and the clearance between the two members are set so as to satisfy the conditions already described with respect to Figures 3 A and B, with the rotation of the members 61 and 62. The members 62 and 66 are kept electrically conductive, and an alternate voltage is applied to the electrically conductive support member of the member 61 by a power source 69. The alternate voltage is a sine wave having a frequency of 200 Hz and the relation between the voltage value and the electrostatic image potential is such as shown in Figure 13 B.
The electrostatic image potential is 500 V for the image area and O V for the non-image area, and is a sine wave of amplitude 400 V t800 Vpp) with a DC voltage of +200 V superimposed thereon. Under the above-described construction and by the low frequency based onthe developing action fully described with respect to Figures 3 A and B, there have been obtained images which are high in tone gradation and clear.
113f3~23 1 Example 5 In Figure 14 A, reference numeral 71 designates an electrostatic latent image bearing member having an insulating layer on a CdS layer. Reference numeral 72 denotes the back electrode of the member 71.
The members 71 and 72 together form a drum shape.
78 designates a non-magnetic stainless sleeve having a magnet 77 therewithin. The electrostatic image bearing member 71 and the sleeve 78 have the minimum clearance therebetween maintained at 300 ~ by a well-known clearance maintaining means. Designated by 74 is a one-component magnetic developer contained in a developer container 79 and comprising 70% by weight of styrene maleic acid resin, 25% by weight of ferrite, 3% by weight of carbon black and 2% by weight of negative charge control agent mixed and ground and having extraneously added thereto 0.2% by weight of colloidal silica to improve the fluidity of the developer. Denoted by 76 is an iron blade opposed to the magnetic pole 77a (850 G) of the magnet roll 77 enclosed in the sleeve 73.
The blade 76 controls the thickness of the magnetic developer 74 applied onto the sleeve 73 by the magnetic force. The clearance between the blade 76 and the sleeve 73 is maintained at about 240 ~, and the thickness of the developer layer applied onto the sleeve 73 by the blade 76 is about 100 ~. Designated by 75 is a variable altérnate voltage source which is applied between the ; back electrode 72 and the conductive portion of the : sleeve 73. Also, to prevent irregular application of the developer, the blade 76 is rendered to the same potential as the sleeve 73.
The average value of the electrostatic image potential is +500 V for the dark region potential and OV for the light region potential, and the extraneous alternate voltage is a sine wave of frequency 400 Hz and peak-to-peak 1500 V imparted a distortion so as to be rendered into a distorted sine wave having an amplitude ratio of 1.9 : 1 between the positive phase and the negative phase. Again by this embodiment, there have been obtained good visible images which are excellent in tone gradation and high in definition and free of fog.
An example of the circuit for providing such a distorted sine wave is shown in Figure 14 B.
The circuit of Figure 14 B generates such a distorted sine wave as shown in Figure 14 C by reducing only the negative (-) of the sine wave AC voltage by a diode 80 and resistors 81 and 82. I the resistor 81 of the output terminal O is slidden, it is possible to make the negative (-) side voltage variable. This circuit construction leads to the greater ease with . , 13~3~37Z3 1 which the circuit is constructed, as compared with the superimposed DC type.
Example 6 The power source 75 of Example 5 is modified into a plurality of voltage sources, each of which has change-over means 78 so that the frequencies and amplitude values of (a), (b) and (d) may be selected from among the four types shown in Figure 8, for example.
The change-over means 78 may be a known electrical change-over means. By operating the buttons ~ - ~
of the change-over means, the following bias conditions can be selected.
~ f = 200 Hz, Vp p = 900 V (DC superimposed 220 V). At this time, the user can obtain photographic lS images of delicate quality in a soft tone.
~ f z 400 Hz, Vp p = 1600 V (DC superimposed 220 V). This condition is used to obtain ordinary copies.
~ f = 900 Hz, Vp p = 1600 V (DC superimposed 120 V). At this time, the user can reproduce originals which are so low in den ity as to tend to create fog or originals of colored images or originals which consist , chiefly of lines, without fog and in good quality.
Of course, these selective combinations are illustrative examples and if within the aforementioned proper range, combinations of other frequencies and ~` 113~Z3 ; 1 voltage values may be adopted.
Figures 15 A - 15 D to Figures 18 A - 18 C
: illustrate the reciprocal movement of the developer in the developing clearance under the low frequency condition ~ 5 applied to the developing method according to the present .: invention and the vibratory movement of the developer when the frequency f of the bias voltage applied is a high frequency (higher than 2 KHz). In the result of the experiment shown in Figures 6 A and B, a preferable range of frequency for enhancing the tone gradation has been shown, and the reciprocal movement of the developer, for example, in each of the above-described Examples, ; is schematically illustrated in Figures lS A - D and Figures 17 A - D.
Figures lS A - D show the movement of the developer in the clearance between the image area of the latent image bearing member 4 to be visualized and the toner carrier S, and Figures 17 A - D show the movement of the developer in the clearance between the non-image area of the latent image bearing member 4 which is not to be visualized and the toner carrier S. A in each of these .
Figures shows the initial state in which the bias field is not applied yet. In the toner transition stage shown in B of each Figure, more developer transits from . 25 the toner carrier S to the image area 4a than to the :' 1 non-image area due to the electrostatic attraction.
It should be noted that the developer transits to and reach the non-image area 4b as well from the toner carrier 5. Arrows indicate the direction of movement of the developer. Next, as shown in C of each Figure, in the toner back transition stage in which the electric field applied assumes the reverse phase, a relatively small amount of developer returns from the image area to the toner carrier, but since, in the non-image area, there is no charge which attracts the toner, almost all of the toner which has transited in the toner transition stage returns to the toner carrier in accordance with the reverse bias. Next, when the phase of the bias changes again, there occurs the toner transition stage as shown in D of each Figure, and thereafter such reciprocal movement of the developer is repeated as noted above.
Thus, a number of reciprocal movements are effected and in the meantime, the developer is caused to once reach the non-image area as well, whereby from the half-tone image area approximate to the light region in which the potential is relatively low to the solid black image portion, there is obtained a visualizing action faithful to the potential held thereby.
On the other hand, when the alternating frequency is increased to a high frequency, for example, 2 KHz or 113~3723 1 higher, the tone gradation is reduced. This phenomenon will be described by reference to Figures 16 A - D and Figures 18 A - D. A in each of these Figures shows the states of the latent image bearing member 4 and the toner carrier 5 before the bias is applied. When the bias for toner transition is applied in the ima~e area, the toner is liberated from the toner carrier toward the image area 4a as shown in Figure 16 B, but the force acting on the individual toner particles causes more or less irregularity of the degree of transition and since the alternating frequency of the bias is high before such irregularity is converged, the reverse bias is applied to the toner which has reached the image area and the toner which is still suspended in the developing clearance, and it is believed that most of the suspended toner returns to the toner carrier side as shown in Figure 16 C. Since the bias phase is reversed before this return movement is terminated, the toner is again subjected to the bias force directed toward the image area. Thus, vibration of the toner rather than reciprocal movement of the toner occurs in the clearance between the image area and the toner carrier.
Such vibratory movement of the toner is pronounced in the clearance between the non-image area in which no latent image charge is present and the toner carrier.
' _ '1~3B~Z3 1 This state is shown in Figures 18 A - D. From the initial state shown in Figure 18 A, the bias phase for toner transition is applied. In this case, if a bias exceeding the transition threshold value is applied, the toner is liberated from the toner carrier but since the alternating frequency of the bias is high as shown in Figure 18 B, the phase of the bias is reversed before the toner reaches the non-image area 4b, and the toner returns to the toner carrier (Figure 18 C).
Next, when the toner transition bias is entered, the toner is again liberated from the toner carrier, but the reverse bias is again applied during the time these toner particles are suspended in the aforementioned clearance, so that the toner particles go toward the toner carrier.
Thus, the toner is vibrated in the clearance and does not substantially reach the non-image area 4a and therefore, even when the development has been terminated, the toner does not adhere the non-image area and no fog is created.
On the other hand, however, the adherence of the toner to the region having a half-tone image potential approximate to the light region (the non-image area) does not sufficiently take place, thus resulting in reduced toner gradation. It is theoretically considered that this phenomenon continues to take place until a certain degree of high frequency exceeding 2 KHz is reached, and it ~ 113!37Z3 1 brings about difficulties in the reproduction of tone gradation as in the present invention.
The foregoing description has been made with respect to a case where the image area potential VD is positive, whereas the invention is not restriated to such case but the invention is also applicable to a case where the image area potential is negative, and : in that case, equations (2) - (12) previously mentioned may be expressed as follows:
¦Vmin - VDI < IVD Vmaxl (2') : Vmin = VD - ¦Vth~r¦ (3~) Vmin > VD - ¦Vth-r¦ (4~) min _ VD - IVth-rl IVmin - VLI > IVL Vmaxl (6') : Vmax = VL + ¦Vth-f¦ (7') max VL ¦Vth f¦ (8') Vmax _ VL + ¦Vth-f¦ (g') VL Vmax < VL + 2lvth-fl (10') Vmax ~ VL + ¦Vth-f¦ (11') VD 2¦Vth rl < Vmin < VD (12') ,= .. ~, , ~ ' ''' ~'''' ' '.' ' , , .~ 1~387:~3 1 The present invention is not restricted to the above-described embodiments, but is applicable to the development of images formed by the electrophotographic method, the electrostatic recording method and other image formation methods.
Claims (99)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to an image area of the image bearing member is in the direction of transferring the developer from the de-veloper carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to an image area of the image bearing member is in the direction of transferring the developer from the de-veloper carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
2. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
3. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
4. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alternat-ing electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
disposing an image bearing member and a de-veloper carrier for carrying a layer of developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alternat-ing electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
5. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to an image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to an image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to the developer carrier.
6. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to the developer carrier.
7. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, and wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, and wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
8. A method of applying dry developer to an image bearing member, comprising the steps of:
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alternat-ing electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
disposing an image bearing member and a non-magnetic developer carrier for carrying a layer of magnetic developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer, the developer carrier having magnetic field generating means therewithin; and applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corre-sponding to a non-image area of the image bearing member is in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to the developer carrier, the alternat-ing electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
9. A method according to Claim 1 or 2, wherein the electric field in the direction of transferring the developer from the developer carrier to the image area of the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier.
10. A method according to Claim 5 or 6, wherein the electric field in the direction of transferring the developer from the developer carrier to the image area of the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier.
11. A method according to Claim 2 or 6, wherein the electric field in the direction of transferring the developer from the developer carrier to the image area of the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier, and wherein the electric field in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member has a strength lower than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier.
12. A method according to Claim 2, 3 or 4, wherein the electric field in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member has a strength lower than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier.
13. A method according to Claim 6, 7 or 8, wherein the electric field in the direction of transferring the developer from the developer carrier to the non-image area of the image bearing member has a strength lower than that of the elec-tric field in the direction of transferring back the de-veloper, which has been transferred to the image area, from the image area to the developer carrier.
14. A method according to Claim 1 or 2, further comprising the step of applying an alternating electric field, across the clearance, having a phase wherein the developer is transferred from the developer carrier to the image area of the image bearing member, and a phase wherein the developer is not transferred back from the image area of the image bearing member to the developer carrier.
15. A method according to Claim 5 or 6, further comprising the step of applying an alternating electric field, across the clearance, having a phase wherein the developer is trans-ferred from the developer carrier to the image area of the image bearing member, and a phase wherein the developer is not transferred back from the image area of the image bearing member to the developer carrier.
16. A method according to Claim 2 or 6, further comprising the step of applying an alternating electric field, across the clearance, having a phase wherein the developer is trans-ferred from the developer carrier to the image area of the image bearing member, and the developer is not transferred from the developer carrier to the non-image area of the image bearing member, and a phase wherein the developer is not transferred back from the image area of the image bear-ing member to the developer carrier, and the developer is transferred back from the non-image area of the image bearing member to the developer carrier.
17. A method according to Claim 2, 3 or 4, further comprising the step of applying an alternating electric field, across the clearance, having a phase wherein the de-veloper is transferred back from the non-image area of the image bearing member to the developer carrier, and a phase wherein the developer is not transferred from the developer carrier to the non-image area of the image bearing member.
18. A method according to Claim 6, 7 or 8, further comprising the step of applying an alternating electric field, across the clearance, having a phase wherein the developer is trans-ferred back from the non-image area of the image bearing member to the developer carrier, and a phase wherein the developer is not transferred from the developer carrier to the non-image area of the image bearing member.
19. A method according to Claim 1, 2 or 3, wherein the alternating electric field has a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
20. A method according to Claim 5, 6 or 7, wherein the alternating electric field has a frequency low enough to allow the developer to transfer and transfer back repeatedly be-tween the image bearing member and the developer carrier.
21. A method according to Claim 1, 2 or 3, wherein the frequency of the alternating electric field is 1.5 KHz or lower.
22. A method according to Claim 4, 5 or 6, wherein the frequency of the alternating electric field is 1.5 KHz or lower.
23. A method according to Claim 7 or 8, wherein the frequency of the alternating electric field is 1.5 KHz or lower.
24. A method according to Claim 1, 2 or 3, wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
25. A method according to Claim 4, 5 or 6, wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
26. A method according to Claim 7 or 8 wherein the alternating electric field satisfies the relations:
400 V ?Vp-p - 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
400 V ?Vp-p - 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
27. A method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of:
forming a layer of one-component developer on the surface of a developing carrier disposed in opposed relation-ship with the image bearing member in a developer station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the developing clearance, the field having a frequency suffi-cient to cause reciprocating movement of the one-component developer particles between the electrostatic image bearing member and the developer carrier in accordance with the alternating electric field; and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the reciprocating movement to one-sided movement of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member in the image area and to one-sided movement of the developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier in the non-image area.
forming a layer of one-component developer on the surface of a developing carrier disposed in opposed relation-ship with the image bearing member in a developer station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the developing clearance, the field having a frequency suffi-cient to cause reciprocating movement of the one-component developer particles between the electrostatic image bearing member and the developer carrier in accordance with the alternating electric field; and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the reciprocating movement to one-sided movement of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member in the image area and to one-sided movement of the developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier in the non-image area.
28. A method of applying dry developer to an electrostatic image bearing member bearing an electrostatic image thereon, comprising the steps of:
forming a layer of one-component developer on the surface of a developer carrier disposed in opposed relation-ship with the image bearing member in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the de-veloping clearance, the field having a frequency sufficient to cause the developer particles to transit from the developer.
layer through the clearance and contact the image area and the non-image area of the electrostatic image bearing member, and then to cause the developer particles having so contacted the image bearing member to return to the developer carrier and such reciprocating movement of the developer is repeated;
and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the reciprocating movement to one-sided movement in which the developer particles one-sidedly transit from the developer carrier to the image area of the electrostatic image bearing member and contact the image area and the developer particles present in the non-image area one-sidedly return to the developer carrier and such movement of the developer is repeated.
forming a layer of one-component developer on the surface of a developer carrier disposed in opposed relation-ship with the image bearing member in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the de-veloping clearance, the field having a frequency sufficient to cause the developer particles to transit from the developer.
layer through the clearance and contact the image area and the non-image area of the electrostatic image bearing member, and then to cause the developer particles having so contacted the image bearing member to return to the developer carrier and such reciprocating movement of the developer is repeated;
and changing the intensity of the alternative electric field acting on the developing clearance to thereby convert the reciprocating movement to one-sided movement in which the developer particles one-sidedly transit from the developer carrier to the image area of the electrostatic image bearing member and contact the image area and the developer particles present in the non-image area one-sidedly return to the developer carrier and such movement of the developer is repeated.
29. A method of applying dry developer to an electro-static image bearing member, comprising the steps of:
disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the developing clearance, the field having a sufficient fre-quency so that its direction in the developing clearance alternates in at least the non-image area of the electro-static image bearing member, to thereby cause the developer to reach the non-image area as well, and then cause the developer to return to the developer carrier, such recipro-cal movement of the developer particles taking place re-peatedly in the developing clearance; and adjusting the intensity of the alternating electric field to cause the transition of the developer particles to take place in the image area one-sidedly in a direction from the developer carrier to the image area and to take place in the non-image area one-sidedly in a direction from the non-image area to the developer carrier.
disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carrying a layer of one-component developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field across the developing clearance, the field having a sufficient fre-quency so that its direction in the developing clearance alternates in at least the non-image area of the electro-static image bearing member, to thereby cause the developer to reach the non-image area as well, and then cause the developer to return to the developer carrier, such recipro-cal movement of the developer particles taking place re-peatedly in the developing clearance; and adjusting the intensity of the alternating electric field to cause the transition of the developer particles to take place in the image area one-sidedly in a direction from the developer carrier to the image area and to take place in the non-image area one-sidedly in a direction from the non-image area to the developer carrier.
30. A method according to Claim 29, wherein the adjusting step is carried out in a manner that the electrostatic image bearing member and the developer carrier are stationary and opposed to each other and the amplitude of the alter-nating electric field is attenuated toward the termination of the development and converged into a predetermined value.
31. A method according to Claim 29, wherein an applied voltage of the alternating field is maintained constant, and the electrostatic image bearing member and the developer carrier are opposed to each other while being moved to gradually increase the clearance therebetween to thereby impart the adjusting step.
32. A method according to Claim 29, wherein the frequency of the alternating electric field is 1.5 KHz or lower.
33. A method according to Claim 31, satisfying the relations:
0.3 x Vp < f < 1000 (Hz) where Vp (mm/sec.) represents the velocity of movement of the electrostatic image bearing member and f (Hz) represents the frequency of the applied alternating electric field.
0.3 x Vp < f < 1000 (Hz) where Vp (mm/sec.) represents the velocity of movement of the electrostatic image bearing member and f (Hz) represents the frequency of the applied alternating electric field.
34. A method of applying dry developer to an electrostatic image bearing member, comprising the steps of:
disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carry-ing a layer of one-component developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field in the clearance, the field having a sufficient frequency so that the electric field in the developing clearance alternates both in the image area and the non-image area of the electrostatic image bearing member, thereby causing reciprocal movement of the developer particles between the electrostatic image bearing member and the developing clearance; and adjusting the alternating electric field in the develop-ing clearance to cause one-sided transition of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member and one-sided transition of developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier.
disposing an electrostatic image bearing member bearing an electrostatic image thereon and a developer carrier carry-ing a layer of one-component developer on the surface thereof in opposed relationship in a developing station with a clearance maintained therebetween which is greater than the thickness of the developer layer;
applying an alternating electric field in the clearance, the field having a sufficient frequency so that the electric field in the developing clearance alternates both in the image area and the non-image area of the electrostatic image bearing member, thereby causing reciprocal movement of the developer particles between the electrostatic image bearing member and the developing clearance; and adjusting the alternating electric field in the develop-ing clearance to cause one-sided transition of the developer particles in a direction from the developer carrier to the image area of the electrostatic image bearing member and one-sided transition of developer particles in a direction from the non-image area of the electrostatic image bearing member to the developer carrier.
35. A method according to Claim 34, satisfying the relations:
when VD> VL
¦Vmax - VL¦ > ¦VL - Vmin¦
¦Vmax - VD¦ > ¦VD - Vmin¦
or when VL > VD
¦Vmin - VL¦ > ¦VL - Vmax¦
¦Vmin - VD¦ > ¦VD - Vmax¦
where Vmax and Vmin respectively represent the maximum value and minimum value of the alternating voltage of the developer carrier with a back electrode of the electrostatic image bearing member as the standard, VD represents the image area potential and VL represents the non-image area potential.
when VD> VL
¦Vmax - VL¦ > ¦VL - Vmin¦
¦Vmax - VD¦ > ¦VD - Vmin¦
or when VL > VD
¦Vmin - VL¦ > ¦VL - Vmax¦
¦Vmin - VD¦ > ¦VD - Vmax¦
where Vmax and Vmin respectively represent the maximum value and minimum value of the alternating voltage of the developer carrier with a back electrode of the electrostatic image bearing member as the standard, VD represents the image area potential and VL represents the non-image area potential.
36. A method according to Claim 34 satisfying the relations:
when VD >VL
VL - 2¦Vth-f¦<Vmin<VL
or when VL >Vd VL < Vmax < VL + 2¦Vth?f¦
where Vmax and Vmin respectively represent the maximum value and minimum value of the alternating voltage of the developer carrier with a back electrode of the electrostatic image bearing member as the standard, VD represents the image area potential, VL represents the non-image area potential, and ¦Vth?f¦ represents the minimum absolute potential between the electrostatic image formation surface and the developer carrier surface whereat the developer is separated from the developer carrier surface and can effect transition to the electrostatic image formation surface.
when VD >VL
VL - 2¦Vth-f¦<Vmin<VL
or when VL >Vd VL < Vmax < VL + 2¦Vth?f¦
where Vmax and Vmin respectively represent the maximum value and minimum value of the alternating voltage of the developer carrier with a back electrode of the electrostatic image bearing member as the standard, VD represents the image area potential, VL represents the non-image area potential, and ¦Vth?f¦ represents the minimum absolute potential between the electrostatic image formation surface and the developer carrier surface whereat the developer is separated from the developer carrier surface and can effect transition to the electrostatic image formation surface.
37. A method according to Claim 35,satisfying the relations:
when VD >VL
VD > Vmax >VD + 2¦Vth?r¦
or when VL > VD
VD - 2¦vth?r¦ <Vmin <VD
where ¦Vth?r¦ represents the minimum absolute potential difference between the electrostatic image formation surface and the developer carrier surface whereat the developer is separated from the electrostatic image formation surface and can effect back transition to the developer carrier.
when VD >VL
VD > Vmax >VD + 2¦Vth?r¦
or when VL > VD
VD - 2¦vth?r¦ <Vmin <VD
where ¦Vth?r¦ represents the minimum absolute potential difference between the electrostatic image formation surface and the developer carrier surface whereat the developer is separated from the electrostatic image formation surface and can effect back transition to the developer carrier.
38. A method according to Claim 36, wherein the ¦Vth?f¦ is imparted by using a magnetic toner as the developer and using a developer carrier having a magnetic binding force.
39. A method according to Claim 27, 28 or 29, wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
40 Hz ? f ? 1.5 KHz where Vp p represents the amplitude of the alternating electric field and f represents the alternating frequency of the alternating electric field.
400 V ? Vp-p ? 2500 V
40 Hz ? f ? 1.5 KHz where Vp p represents the amplitude of the alternating electric field and f represents the alternating frequency of the alternating electric field.
40. A method according to Claim 34, wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
40 Hz ? f ? 1.5 KHz where Vp-p represents the amplitude of the alternating elec-tric field and f represents the alternating frequency of the alternating electric field.
400 V ? Vp-p ? 2500 V
40 Hz ? f ? 1.5 KHz where Vp-p represents the amplitude of the alternating elec-tric field and f represents the alternating frequency of the alternating electric field.
41. A device for applying dry developer to an image bearing member, comprising:
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bear-ing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance correspond-ing to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of trans-ferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bear-ing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance correspond-ing to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of trans-ferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
42. A device for applying dry developer to an image bearing member, comprising:
a. carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
a. carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
43. A device for applying dry developer to an image bearing member, comprising:
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus trans-ferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from the developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area is in the direction of transferring back the thus trans-ferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
44. A device for applying dry developer to an image bearing member, comprising:
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back re-peatedly between the image bearing member and said developer carrier.
a carrier for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back re-peatedly between the image bearing member and said developer carrier.
45. A device for applying dry developer to an image bearing member, comprising:
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrier for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrier for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the image area, and a phase wherein the electric field formed in the clearance corresponding to an image area of the image bearing member is in the direction of transferring back the thus transferred developer from the image area of the image bearing member to said developer carrier.
46. A device for applying dry developer to an image bearing member, comprising;
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing member to said developer carrier.
47. A device for applying dry developer to an image bearing member, comprising:
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corre-sponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station; and means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrier to both of an image area and a non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corre-sponding to the non-image area is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, and wherein the electric field formed in the clearance corresponding to the image area is in the direction of transferring the developer from the developer carrier to the image bearing member.
48. A device for applying dry developer to an image bearing member, comprising:
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station, and means for applying an alternating electric field across said clearance, said alternating electric field having a phase wherein the' electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and said developer carrier.
a carrier, which is made of non-magnetic material, for carrying developer;
means for defining a developing zone by disposing said developer carrier in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrier; and means, enclosed with the developer carrying means, for forming a magnetic field to convey the developer to the developing station, and means for applying an alternating electric field across said clearance, said alternating electric field having a phase wherein the' electric field formed in the clearance corresponding to a non-image area of the image bearing member is in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member, and a phase wherein the electric field formed in the clearance corresponding to the non-image area of the image bearing member is in the direction of transferring back the thus transferred developer from the non-image area of the image bearing member to said developer carrier, the alternating electric field having a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and said developer carrier.
49. A device according to Claim 41 or 42, wherein the electric field in the direction of transferring the de-veloper from said developer carrier to the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to said developer carrier.
50. A device according to Claim 45 or 46, wherein the electric field in the direction of transferring the developer from said developer carrier to the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to said developer carrier.
51. A device according to Claim 42 or 46, wherein the electric field in the direction of transferring the developer from said developer carrier to the image area of the image bearing member has a strength higher than that of the electric field in the direction of transferring back the developer, which has been transferred to the image area, from the image area to the developer carrier, and wherein the electric field in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member has a strength lower than that of the electric field in the direction of transferring back the developer, which has been transferred to the non-image area, from the non-image area to said developer carrier.
52. A device according to Claim 42, 43 or 44, wherein the electric field in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member has a strength lower than that of the electric field in the direction of transferring back the developer, which has been transferred to the non-image area, from the non-image area to said developer carrier.
53. A device according to Claims 46, 47 or 48, wherein the electric field in the direction of transferring the developer from said developer carrier to the non-image area of the image bearing member has a strength lower than that of the electric field in the direction of transferring back the developer, which has been transferred to the non-image area, from the non-image area to said developer carrier.
54. A device according to Claims 41, 42 or 46, wherein the alternating electric field is produced by an alternating voltage, and the device further comprises means for changing the alternating voltage.
55. A device according to Claim 42, further comprising means for changing the clearance.
56. A device according to Claim 55, wherein the image bearing member is drum shaped.
57. A device according to Claim 55, wherein the developer carrier is sleeve shaped.
58. A device according to Claim 55, wherein the developer carrier is an endless belt.
59. A device according to Claims 41, 42 or 46, wherein the image bearing member carries an electrostatic latent image thereon.
60. A device according to Claims 41, 42 or 46, wherein the developer carrier is conductive.
61. A device according to Claim 42, wherein the developer is one-component insulating developer.
62. A device according to Claim 42, further comprising means for supplying developer to the developer carrier, and means for limiting the thickness of a layer of the developer formed by the thus supplied developer.
63. A device according to Claim 62, wherein the limiting member is maintained at the same potential as the developer carrier.
64. A device according to Claims 41, 42 or 46, wherein the alternating electric field has a frequency low enough to allow the developer to transfer and transfer back repeatedly between the image bearing member and the developer carrier.
65. A device according to Claims 41, 42 or 46, wherein the frequency in the alternating electric field is 1.5 KHz or lower.
66. A device according to Claims 41, 42 or 46, wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
67. A device according to Claims 41, 42 or 46, wherein the magnetic field forming means includes a fixed magnetic pole.
68. A device according to Claim 62, wherein the thickness limiting member includes a magnetic blade of magnetic material or a magnet.
69. A device according to Claim 62, wherein the magnetic field forming means has a magnetic pole at a position opposing said thickness limiting means.
70. A device according to Claim 42, wherein the alterna-ting electric field is produced by an alternating voltage, and the device further comprises means for selectively changing the alternating voltage.
71. A device according to Claim 70, wherein the ampli-tude of the voltage is changed.
72. A device according to Claim 70, wherein a D.C.
voltage is superposed on the alternating voltage, and the D.C. voltage is changed.
voltage is superposed on the alternating voltage, and the D.C. voltage is changed.
73. A device according to Claim 70, wherein the maximum value of the voltage is changed.
74. A device according to Claim 70, wherein the minimum value of the voltage is changed.
75. A device according to Claim 41, 42 or 46, wherein the frequency of the electric field is selectively changed.
76. A device according to Claim 41, 42 or 46, wherein the alternating electric field is produced by an alternating voltage, and the device further comprises means for selectively changing the voltage value and the frequency of the alternating voltage.
77. A device for applying dry developer to an electrostatic image bearing drum, comprising:
a conductive developer carrying cylinder for carrying one-component developer;
means for defining a developing zone by disposing said developer carrying cylinder in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrying cylinder;
means for supplying the developer to said developer carrying cylinder;
means for limiting the thickness of the developer layer formed on said developer carrying cylinder;
means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrying cylinder to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to the developer carrying cylinder; and means for rotating the developer carrying cylinder and the electrostatic latent image bearing drum to change the clearance therebetween.
a conductive developer carrying cylinder for carrying one-component developer;
means for defining a developing zone by disposing said developer carrying cylinder in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by said developer carrying cylinder;
means for supplying the developer to said developer carrying cylinder;
means for limiting the thickness of the developer layer formed on said developer carrying cylinder;
means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said developer carrying cylinder to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to the developer carrying cylinder; and means for rotating the developer carrying cylinder and the electrostatic latent image bearing drum to change the clearance therebetween.
78. A device for applying dry developer to an electrostatic image bearing drum, comprising:
a non-magnetic and conductive sleeve for carrying one-component magnetic developer;
a magnetic roller, enclosed with the sleeve, having a transporting magnetic pole for transporting the magnetic developer;
means for defining a developing zone by disposing said sleeve in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the sleeve;
means for supplying the magnetic developer to the sleeve;
a magnetic blade, made of magnetic material or a magnet, for limiting the thickness of the developer layer on the sleeve, the magnetic blade being opposed to a magnetic pole of said magnetic roller;
means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said sleeve to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to said sleeve; and means for rotating the developer carrying sleeve and the electrostatic latent image bearing drug to change the clearance therebetween.
a non-magnetic and conductive sleeve for carrying one-component magnetic developer;
a magnetic roller, enclosed with the sleeve, having a transporting magnetic pole for transporting the magnetic developer;
means for defining a developing zone by disposing said sleeve in opposed relationship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the sleeve;
means for supplying the magnetic developer to the sleeve;
a magnetic blade, made of magnetic material or a magnet, for limiting the thickness of the developer layer on the sleeve, the magnetic blade being opposed to a magnetic pole of said magnetic roller;
means for applying an alternating electric field across the clearance, the alternating electric field having a phase wherein the electric field formed in the clearance is in the direction of transferring the developer from said sleeve to both an image area and a non-image area of the image bearing drum, and a phase wherein the electric field formed in the clearance is in the direction of transferring back the thus transferred developer from the image area and the non-image area of the image bearing drum to said sleeve; and means for rotating the developer carrying sleeve and the electrostatic latent image bearing drug to change the clearance therebetween.
79. A device according to Claim 77 or 78, wherein the one-component developer is insulating.
80. A device according to Claim 77 or 78, wherein the limiting member is maintained at the same potential as the developer sleeve.
81. A device according to Claim 77 or 78, wherein the frequency in the alternating electric field is 1.5 KHz or lower.
82. A device according to Claim 77 or 78,wherein the alternating electric field satisfies the relations:
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
400 V ? Vp-p ? 2500 V
wherein Vp-p represents the amplitude of the alternating electric field.
83. A device according to Claim 77 or 78, wherein the alternating electric field is produced by an alternating voltage, and the device further comprises means for selectively changing the alternating voltage.
84. A device according to Claim 77 or 78, wherein the frequency of the electric field is selectively changed.
85. A device according to Claim 77 or 78, wherein the alternating electric field is produced by an alternating voltage, and the device further comprises means for selectively changing the voltage value and the frequency of the alternating voltage.
86. A device for applying dry developer to an image bearing member, comprising:
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relation-ship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the voltage for providing the alternating electric field.
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relation-ship to the image bearing drum in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the voltage for providing the alternating electric field.
87. A device according to Claim 86, wherein the changing means changes the amplitude of the voltage.
88. A device according to Claim 86, wherein the changing means changes a D.C. voltage which is superposed on the alternating voltage.
89. A device according to Claim 86, wherein the changing means changes the maximum value of the voltage.
90. A device according to Claim 86, wherein the changing means changes the minimum value of the voltage.
91. A device for applying dry developer to an image bearing member, comprising:
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the frequency of the alternating electric field, wherein the frequency is not more than 1.5 KHz.
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relationship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the frequency of the alternating electric field, wherein the frequency is not more than 1.5 KHz.
92. A device for applying dry developer to an image bearing member, comprising:
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relation-ship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the frequency and voltage for providing the alternating electric field.
means for carrying a one-component developer;
means for defining a developing zone by disposing said developer carrying means in opposed relation-ship to the image bearing member in a developing station with a predetermined clearance therebetween, the clearance being greater than the thickness of a developer layer carried by the carrying means;
means for applying an alternating electric field across the clearance; and means for selectively changing the frequency and voltage for providing the alternating electric field.
93. A method according to any one of Claims 1, 2 or 6, wherein the developer carrier means is moved, at the position where the development is effected, in the same direction and at the same surface speed as the surface of the image bearing member.
94. A device according to any one of Claims 41, 42 or 46, wherein the developer carrier means a sleeve is moved, at the position where the development is effected, in the same direction and at the same surface speed as the surface-of the image bearing member or drum.
95. A device according to Claim 61, wherein the one-component insulating developer includes fine particles to improve fluidity.
96. A method of developing an electrostatic latent image on an image bearing member, comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer; and causing transition of developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
97. A method of developing an electrostatic latent image on an image bearing member comprising bringing a layer of charged dry developer on a carrier to a developing zone in which the gap between the image bearing member and the carrier is greater than the thickness of the layer and creating in said gap an alternating electric field which, in a first stage, causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensity than in the first stage, to leave a developed image on said image bearing member.
98. Apparatus for developing an electrostatic latent image on an image bearing member, comprising a carrier for supporting a layer of charged dry developer at a developing zone with a gap between the image bearing member and the carrier, means for forming on said carrier a said layer of charged dry developer such that the thickness of the layer is less than the width of the gap, and means for causing transition of the developer from the carrier to the image bearing member and back transition of developer from said member to said carrier to leave a developed image on said member.
99. Apparatus for developing an electrostatic latent image on an image bearing member comprising a carrier for supporting a layer of charged dry developer at a developing zone with a gap between the image bearing member and the carrier; means for forming on said carrier a said layer of charged dry developer having a thickness which is less than the width of the gap; and means for creating in said gap an alternating electric field which, in a first stage, causes transition of developer from the carrier to the image bearing member and back transition of developer from the member to the carrier and which, in a second stage, is of lower intensity than in the first stage, to leave a developed image on the image bearing member.
Applications Claiming Priority (10)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP92107/1978 | 1978-07-28 | ||
| JP9210678A JPS5518657A (en) | 1978-07-28 | 1978-07-28 | Electrophotographic developing method |
| JP9210778A JPS5518658A (en) | 1978-07-28 | 1978-07-28 | Electrophotographic developing method |
| JP92106/1978 | 1978-07-28 | ||
| JP92105/1978 | 1978-07-28 | ||
| JP53092105A JPS5832375B2 (en) | 1978-07-28 | 1978-07-28 | Development method |
| JP5264179A JPS55144255A (en) | 1979-04-28 | 1979-04-28 | Developing method and its apparatus |
| JP52641/1979 | 1979-04-28 | ||
| JP68564/1979 | 1979-06-01 | ||
| JP6856479A JPS55161252A (en) | 1979-06-01 | 1979-06-01 | Method and device for development |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1138723A true CA1138723A (en) | 1983-01-04 |
Family
ID=27523020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000332015A Expired CA1138723A (en) | 1978-07-28 | 1979-07-18 | Developing method for developer transfer under electrical bias and apparatus therefor |
Country Status (8)
| Country | Link |
|---|---|
| US (3) | US4395476A (en) |
| AU (1) | AU531301B2 (en) |
| CA (1) | CA1138723A (en) |
| DE (1) | DE2930619A1 (en) |
| FR (1) | FR2433780B1 (en) |
| GB (1) | GB2028176B (en) |
| HK (1) | HK35784A (en) |
| SG (1) | SG24383G (en) |
Families Citing this family (79)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5194359A (en) * | 1978-07-28 | 1993-03-16 | Canon Kabushiki Kaisha | Developing method for one component developer |
| JPS56101169A (en) * | 1980-01-14 | 1981-08-13 | Canon Inc | Electrophotographic developing method |
| JPS55118048A (en) * | 1979-03-05 | 1980-09-10 | Canon Inc | Method and apparatus for developing |
| US4363861A (en) * | 1979-03-06 | 1982-12-14 | Canon Kabushiki Kaisha | Toner transfer development using alternating electric field |
| DE3008913A1 (en) * | 1979-03-08 | 1980-09-18 | Canon Kk | High resolution toner developer unit for photocopier - uses toner bristles of limited thickness and HF field to transfer toner |
| GB2073057B (en) * | 1980-03-04 | 1984-08-08 | Canon Kk | Developing electrostatic images |
| JPS58108566A (en) * | 1981-12-22 | 1983-06-28 | Konishiroku Photo Ind Co Ltd | Developing method |
| US4565764A (en) * | 1982-09-10 | 1986-01-21 | Canon Kabushiki Kaisha | Microcapsule toner and process of making same |
| DE3243705C1 (en) * | 1982-11-25 | 1984-04-12 | Elfotec AG, 8126 Zumikon | Method and device for electrophotographic imaging |
| GB2141643B (en) * | 1983-03-31 | 1986-10-22 | Konishiroku Photo Ind | Developing electrostatic latent images |
| JPS59220771A (en) * | 1983-05-31 | 1984-12-12 | Canon Inc | Combination copying machine and printer |
| DE3427813A1 (en) * | 1983-07-29 | 1985-02-07 | Canon K.K., Tokio/Tokyo | Development process |
| GB2145942B (en) * | 1983-08-05 | 1987-03-18 | Konishiroku Photo Ind | Developing latent eletrostatic images |
| US4610531A (en) * | 1983-09-05 | 1986-09-09 | Canon Kabushiki Kaisha | Developing method and apparatus |
| USRE36304E (en) * | 1983-10-03 | 1999-09-14 | Konica Corporation | Multiplex image reproducing method |
| EP0280337B1 (en) * | 1983-10-03 | 1994-04-06 | Konica Corporation | Multiplex image reproducing method |
| DE3483877D1 (en) * | 1983-10-03 | 1991-02-07 | Konishiroku Photo Ind | MI-MULTIPLE IMAGE REPRODUCTION PROCESS. |
| JPS6087347A (en) * | 1983-10-19 | 1985-05-17 | Canon Inc | Developing method |
| JPH0642087B2 (en) * | 1984-05-31 | 1994-06-01 | 富士ゼロックス株式会社 | Development method |
| US4666804A (en) * | 1984-07-06 | 1987-05-19 | Konishiroku Photo Industry Co., Ltd. | Method of and apparatus for image forming |
| JPS6159361A (en) * | 1984-08-31 | 1986-03-26 | Mita Ind Co Ltd | Formation of negative and positive image by electrophotography |
| CA1250779A (en) * | 1984-09-06 | 1989-03-07 | Satoshi Haneda | Method and apparatus for reproducing multi-color image and photoreceptor thereof |
| JPS61190361A (en) * | 1985-02-20 | 1986-08-25 | Toshiba Corp | Developing device |
| US4660059A (en) * | 1985-11-25 | 1987-04-21 | Xerox Corporation | Color printing machine |
| US4844008A (en) * | 1986-07-03 | 1989-07-04 | Canon Kabushiki Kaisha | Non-contact developing apparatus utilizing a tangential magnetic field |
| US4937630A (en) * | 1986-12-10 | 1990-06-26 | Canon Kabushiki Kaisha | Image forming apparatus employing non-magnetic and magnetic toner |
| JPH0250182A (en) * | 1988-05-30 | 1990-02-20 | Canon Inc | Developing device |
| US5027157A (en) * | 1988-12-02 | 1991-06-25 | Minolta Camera Kabushiki Kaisha | Developing device provided with electrodes for inducing a traveling wave on the developing material |
| US5110705A (en) * | 1989-03-31 | 1992-05-05 | Kabushiki Kaisha Toshiba | Contact type developing method and developing unit |
| US5177536A (en) * | 1989-03-31 | 1993-01-05 | Canon Kabushiki Kaisha | Developing apparatus having a magnetic seal |
| US5227849A (en) * | 1989-07-03 | 1993-07-13 | Canon Kabushiki Kaisha | Developing apparatus and developer carrying member usable therewith |
| JP2892456B2 (en) * | 1989-08-04 | 1999-05-17 | キヤノン株式会社 | Developing device |
| JP2974334B2 (en) * | 1989-08-31 | 1999-11-10 | キヤノン株式会社 | Developing device |
| DE69004896T2 (en) * | 1989-08-31 | 1994-06-30 | Canon Kk | Imaging device. |
| US5202731A (en) * | 1989-09-27 | 1993-04-13 | Canon Kabushiki Kaisha | Image forming apparatus having an alternating bias electric field |
| DE69006997T2 (en) * | 1989-09-27 | 1994-06-23 | Canon Kk | Imaging process and device. |
| JPH03200989A (en) * | 1989-10-04 | 1991-09-02 | Canon Inc | Image forming device |
| US5185496A (en) * | 1990-03-02 | 1993-02-09 | Canon Kabushiki Kaisha | Electrostatic latent image device having a coating layer provided on a developer carrying member |
| CA2039290C (en) * | 1990-03-29 | 1994-10-11 | Masaaki Taya | Magnetic toner |
| US5677099A (en) * | 1990-04-19 | 1997-10-14 | Canon Kabushiki Kaisha | Method of developing electrostatic latent image using oscillating bias voltage |
| JP2899079B2 (en) * | 1990-07-10 | 1999-06-02 | キヤノン株式会社 | Developing device |
| US5442421A (en) * | 1990-10-01 | 1995-08-15 | Canon Kabushiki Kaisha | Process cartridge and image forming apparatus using the same |
| JPH04166850A (en) * | 1990-10-30 | 1992-06-12 | Canon Inc | Micr printer |
| US5239344A (en) * | 1991-01-16 | 1993-08-24 | Ricoh Company, Ltd. | Developing roller having insulating and conductive areas |
| JP3245680B2 (en) * | 1991-01-25 | 2002-01-15 | 株式会社リコー | Developer carrier and image forming method using the same |
| JPH0511582A (en) * | 1991-02-05 | 1993-01-22 | Fuji Xerox Co Ltd | Electrophotographic copying machine |
| JPH04276778A (en) * | 1991-03-05 | 1992-10-01 | Canon Inc | Image forming device |
| JP3057299B2 (en) * | 1991-03-22 | 2000-06-26 | 株式会社リコー | Image forming method |
| DE69213992T2 (en) * | 1991-04-16 | 1997-05-15 | Matsushita Electric Ind Co Ltd | Electrophotographic process and device |
| JP2974452B2 (en) * | 1991-06-19 | 1999-11-10 | キヤノン株式会社 | Magnetic toner |
| DE69218689T2 (en) * | 1991-07-26 | 1997-07-24 | Matsushita Electric Ind Co Ltd | Electrophotographic process and apparatus therefor |
| US5424810A (en) * | 1991-09-13 | 1995-06-13 | Canon Kabushiki Kaisha | Magnetic toner, magnetic developer, apparatus unit, image forming apparatus and facsimile apparatus |
| US5262828A (en) * | 1991-12-13 | 1993-11-16 | Minolta Camera Kabushiki Kaisha | Developing bias power unit for use in an image forming apparatus |
| CA2290700C (en) | 1992-07-24 | 2004-08-31 | Canon Kabushiki Kaisha | Ink container, ink and ink jet recording apparatus using ink container |
| US6332675B1 (en) | 1992-07-24 | 2001-12-25 | Canon Kabushiki Kaisha | Ink container, ink and ink jet recording apparatus using ink container |
| US5985506A (en) * | 1992-07-29 | 1999-11-16 | Matsushita Electric Industrial Co., Ltd. | Reversal electrophotographic developing method employing recyclable magnetic toner |
| US5434651A (en) * | 1992-09-28 | 1995-07-18 | Matsushita Electric Industrial Co., Ltd. | Image forming apparatus and a charging device |
| US5521683A (en) * | 1992-12-21 | 1996-05-28 | Canon Kabushiki Kaisha | Image forming apparatus using constant voltage or constant current AC signal applied to developer bearing member, and control function in accordance with detected voltage or current of developer bearing member |
| JP3423348B2 (en) * | 1993-03-19 | 2003-07-07 | キヤノン株式会社 | Image forming device |
| TW290661B (en) * | 1993-08-30 | 1996-11-11 | Canon Kk | |
| ATE178722T1 (en) * | 1993-10-08 | 1999-04-15 | Canon Kk | MAGNETIC DEVELOPER, PROCESS CARTRIDGE AND IMAGE MAKING METHOD |
| US5941775A (en) * | 1994-10-14 | 1999-08-24 | Sega Of America, Inc. | Data processing system, method thereof and memory cassette |
| US5991587A (en) | 1995-10-31 | 1999-11-23 | Kyocera Corporation | Developing apparatus having developing roller which is loaded via an intermediate roller |
| DE19546248A1 (en) * | 1995-12-12 | 1997-06-19 | Heidelberger Druckmasch Ag | Electrostatic latent image development on movable intermediate carrier |
| DE19547546A1 (en) * | 1995-12-20 | 1997-07-03 | Heidelberger Druckmasch Ag | Device for acting on sheets in a sheet delivery |
| JP2001147570A (en) | 1999-11-19 | 2001-05-29 | Fujitsu Ltd | Color image forming method |
| CA2337087C (en) | 2000-03-08 | 2006-06-06 | Canon Kabushiki Kaisha | Magnetic toner, process for production thereof, and image forming method, apparatus and process cartridge using the toner |
| US6537715B2 (en) | 2000-07-28 | 2003-03-25 | Canon Kabushiki Kaisha | Toner, image-forming method and process cartridge |
| JP2002156774A (en) * | 2000-11-16 | 2002-05-31 | Canon Inc | Image forming device and process cartridge |
| JP4018495B2 (en) * | 2002-09-27 | 2007-12-05 | キヤノン株式会社 | Dry toner |
| JP2005173484A (en) | 2003-12-15 | 2005-06-30 | Canon Inc | Image forming apparatus and process cartridge |
| JP2005173485A (en) * | 2003-12-15 | 2005-06-30 | Canon Inc | Developing device, process cartridge and image forming apparatus |
| JP4510493B2 (en) | 2004-03-29 | 2010-07-21 | キヤノン株式会社 | Image forming apparatus |
| JP4649217B2 (en) * | 2005-01-28 | 2011-03-09 | キヤノン株式会社 | Developing device, process cartridge, and image forming apparatus |
| JP4785408B2 (en) * | 2005-04-18 | 2011-10-05 | キヤノン株式会社 | Developing device, process cartridge, and image forming apparatus |
| JP4785407B2 (en) * | 2005-04-18 | 2011-10-05 | キヤノン株式会社 | Developing device, process cartridge, and image forming apparatus |
| JP2008309964A (en) * | 2007-06-13 | 2008-12-25 | Konica Minolta Business Technologies Inc | Image forming apparatus |
| JP2009300482A (en) * | 2008-06-10 | 2009-12-24 | Konica Minolta Business Technologies Inc | Image forming apparatus |
| JP2010066531A (en) * | 2008-09-11 | 2010-03-25 | Seiko Epson Corp | Image forming apparatus and image forming method |
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| JPS51126836A (en) * | 1975-04-26 | 1976-11-05 | Shigekazu Enoki | Magnetic toner |
| JPS5217417A (en) * | 1975-07-31 | 1977-02-09 | Sanyo Chem Ind Ltd | Process for removal of compound to cause abnormal polymerization |
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| US4473627A (en) * | 1978-07-28 | 1984-09-25 | Canon Kabushiki Kaisha | Developing method for developer transfer under electrical bias and apparatus therefor |
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-
1979
- 1979-07-18 CA CA000332015A patent/CA1138723A/en not_active Expired
- 1979-07-20 AU AU49116/79A patent/AU531301B2/en not_active Expired
- 1979-07-24 GB GB7925725A patent/GB2028176B/en not_active Expired
- 1979-07-27 FR FR7919482A patent/FR2433780B1/en not_active Expired
- 1979-07-27 DE DE19792930619 patent/DE2930619A1/en active Granted
-
1981
- 1981-05-18 US US06/264,516 patent/US4395476A/en not_active Expired - Lifetime
-
1983
- 1983-05-11 SG SG243/83A patent/SG24383G/en unknown
-
1984
- 1984-04-26 HK HK357/84A patent/HK35784A/en not_active IP Right Cessation
-
1987
- 1987-03-04 US US07/022,598 patent/US4913088A/en not_active Expired - Fee Related
-
1991
- 1991-03-18 US US07/671,019 patent/US5096798A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE2930619A1 (en) | 1980-02-07 |
| US5096798A (en) | 1992-03-17 |
| SG24383G (en) | 1985-01-11 |
| US4913088A (en) | 1990-04-03 |
| AU531301B2 (en) | 1983-08-18 |
| FR2433780B1 (en) | 1986-03-21 |
| DE2930619C2 (en) | 1989-11-16 |
| FR2433780A1 (en) | 1980-03-14 |
| AU4911679A (en) | 1980-01-31 |
| HK35784A (en) | 1984-05-04 |
| US4395476A (en) | 1983-07-26 |
| GB2028176A (en) | 1980-03-05 |
| GB2028176B (en) | 1983-03-09 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |