EP0526208A1

EP0526208A1 - Photosensitive member and electrophotographic apparatus using same

Info

Publication number: EP0526208A1
Application number: EP92306962A
Authority: EP
Inventors: Toshiyuki C/O Canon Kabushiki Kaisha Yoshihara; Masahiro C/O Canon Kabushiki Kaisha Goto; Nobuyuki c/o Canon Kabushiki Kaisha Hanami; Hideki C/O Canon Kabushiki Kaisha Anayama; Junichi c/o Canon Kabushiki Kaisha Kishi; Hiroaki C/O Canon Kabushiki Kaisha Miyake; Hideyuki C/O Canon Kabushiki Kaisha Ainoya; Manabu C/O Canon Kabushiki Kaisha Takano; Yuzi c/o Canon Kabushiki Kaisha Ishihara; Kenji C/O Canon Kabushiki Kaisha Matsuda; Hiroshi c/o Canon Kabushiki Kaisha Koyama; Hidetoshi C/O Canon Kabushiki Kaisha Hirano
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1991-07-31
Filing date: 1992-07-30
Publication date: 1993-02-03

Abstract

An electrophotographic photosensitive member (101) for being charged by a charging member (102) which is contacted thereto and which is supplied with an oscillating voltage (103) includes a photosensitive layer (101b); a base member (101a) for supporting the photosensitive layer (101b); a portion for receiving driving force; and total weight divided by total volume of the photosensitive member (101) is not less than 0.65 g/cm². This structure avoids vibrations of the photodrum (101) when an AC-fed contact charger (102) is used.

Description

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an electrophotographic apparatus such as a copying machine or a printer, an electrophotographic photosensitive member usable therewith and a process cartridge detachably mountable to said apparatus. More particularly, the electrophotographic photosensitive member is electrically charged or discharged by a contact type charging member supplied with a voltage.
In an image forming apparatus such a laser beam printer or a copying machine using an electrophotographic process, an electrostatic recording process or the like, the charging or discharging of the electrophotographic photosensitive member has generally been carried out by a non-contact type corona discharger.
However, a contact type charging device using a charging roller or charging member (electrically conductive) supplied with a voltage becomes more widely used for the advantageous that the voltage of the voltage source may be reduced and that the amount of ozone production is small.
Referring to Figure 5, an example thereof is shown. A photosensitive member (photosensitive drum) is in the form of a rotatable drum or cylinder. The photosensitive drum 101 comprises an aluminum base member 101a and an organic photoconductive layer 101b on the outer periphery thereof. It is rotated in the indicated clockwise direction at a predetermined peripheral speed (process speed).
A roller type charging member 102 is contacted to the photosensitive drum 101 and is driven by the rotation of the photosensitive drum 101. The charging roller 102 comprises an electrically conductive core metal 102a made of iron or stainless steel or the like and an electrically conductive elastic layer 102b made of carbon containing urethane rubber or the like. The charging roller 102 is press-contacted to the photosensitive drum 101 by unshown spring members at longitudinally opposite ends of the conductive core 102a.
The conductive core 102a of the charging roller 102 is supplied with a voltage of a predetermined level and polarity from a high voltage source 103, by which the peripheral surface of the rotating photosensitive drum 101 is electrically charged or discharged by the contacting charging roller 102.
Around the outer periphery of the photosensitive drum 101, there are disposed, in addition to the charging roller 102, exposure means, developing means, transfer means, cleaning means, image fixing means and sheet feeding means or other image forming process means, so that the image forming apparatus is constituted. However, they are omitted for simplicity of explanation.
For the purpose of uniform charging, the voltage applied to the charging roller 102 is preferably an oscillating voltage in the form of a DC biased AC voltage. Further preferably, the peak-to-peak voltage of the oscillating voltage is not less than twice a charge starting voltage which is the voltage at which the charging occurs when only a DC voltage is applied between the photosensitive member and the charging member. Then, the uniform charging is further improved, as disclosed in Japanese Laid-Open Patent Application No. 149669/1988.
However, where the photosensitive drum 101 is charged or discharged by the application of the oscillating voltage to the charging roller 102, the cyclic non-uniformity becomes more significant with the increase of the peripheral speed of the photosensitive drum 101. Therefore, the frequency of the oscillating voltage applied to the charging roller 102 is required to be increased. However, if the frequency exceeds 200 Hz, the charging noise becomes significant due to the vibration between the photosensitive drum 101 and the charging roller 102.
The mechanism of the production of the noise has been found. When the oscillating electric field is formed by the application of the oecillating voltage to the charging roller 102, the photosensitive member 101 and the charging member 102 are attracted electrostatically to each other. At the maximum and minimum peaks of the oscillating voltage, the attraction force is large, so that the charging roller 102 is pressed and deformed to the photosensitive member 101. At the center of the oscillation, the attraction force is small, and therefore, the charging member 102 tends to be away from the photosensitive member 101 due to the restoration of the charging member 102. Therefore, the vibration is produced at the frequency which is twice the frequency of the oscillating voltage.
The charging member 102 and the photosensitive member 101 are rubbed with each other. When the attracting electrostatic force is large at the maximum and minimum peaks of the oscillating voltage, the charging member 102 is attracted strongly to the photosensitive member 101 with the result of the relative movement being retarded. On the contrary, at the center of the oscillating voltage, the attracting force is small so that the relative movement is not retarded. Therefore, the vibration is also caused by stick and slip, as when a wet glass is rubbed with a finger. This vibration also has a frequency which is twice the frequency of the applied oscillating voltage.
When the oscillating voltage is applied between the charging member and the photosensitive member, the charging noise is generated by vibration. The basic frequency of the noise is twice the frequency of the applied oscillating voltage. If the oscillating voltage includes 300 Hz AC voltage, the produced noise has the component of 600 Hz. The noise may include a higher frequency which is an integer multiple of that frequency. In some cases, the noise includes the frequency component which is an integer multiple of the frequency of the applied oscillating voltage.
The noise includes a noise component produced directly from the contact area between the charging member and the photosensitive member and a noise component which is caused by the vibration of the photosensitive member transmitted to the process cartridge and/or to the main assembly of the image forming apparatus and then being caused to the noise, wherein the process cartridge includes the photosensitive member and is detachably mountable to the image forming apparatus.
The problem of the charging noise equally applied to the roller type charging member, the blade type charging member, the pad type charging member, the block type charging member, the rod type charging member, and the wire type charging-member or the like.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to provide a photosensitive member, a process cartridge and an electrophotographic apparatus in which the charging noise is suppressed by suppressing the vibration of the photosensitive member which is the main cause of the charging noise.
It is another object of the present invention to provide a process cartridge and an electrophotographic apparatus in which the cyclic unevenness of the charging is prevented.
It is a further object of the present invention to provide a process cartridge and an electrophotographic apparatus capable of high speed operation.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional view of an electrophotographic apparatus according to an embodiment of the present invention.
Figure 2 is a perspective view illustrating mounting and dismounting of the process cartridge relative to the electrophotographic apparatus.
Figure 3 is a perspective view and sectional view of a photosensitive drum according to an embodiment of the present invention.
Figure 4 is a sectional view of a photosensitive drum and a charging roller.
Figure 5 is a sectional view of a conventional charging device.
Figure 6 is a perspective view and sectional view of a photosensitive drum according to another embodiment of the present invention.
Figure 7 is a perspective view of a material in the photosensitive drum.
Figure 8 is a perspective view and a sectional view of a photosensitive drum according to a further embodiment of the present invention.
Figure 9 is a perspective view of a material in the photosensitive drum.
Figure 10 is a longitudinal sectional view of a further embodiment of the present invention.
Figure 11 is a sectional view of a photosensitive drum according to a further embodiment of the present invention.
Figure 12 is a longitudinal sectional view of a photosensitive drum according to a further embodiment of the present invention.
Figure 13 is a graph of a relation between weight of the photosensitive member per unit volume and a noise pressure level.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figures 1 and 2, there are shown an image forming apparatus and a process cartridge according to an embodiment of the present invention. In Figure 2, the mounting and demounting of the process cartridge are illustrated.
The image forming apparatus according to this embodiment is in the form of a laser beam printer using an image transfer type electrophotographic process, wherein a process cartridge is detachably mountable thereto.
As shown in Figure 1, an electrophotographic photosensitive member in the form of a rotatable drum 3 is rotated at a predetermined peripheral speed (process speed) in the indicated clockwise direction through a drive transmission from a driving source.
A charging member 4 is press-contacted to the photosensitive drum 3 with a predetermined pressure, and is in the form of a charging roller in this embodiment. The charging roller 4 comprises an electrically conductive core metal 4a of stainless steel and an electrically conductive elastic layer 4b of carbon containing urethane rubber. The outer diameter is 12 mm. It is press-contacted to the surface of the photosensitive drum 3 by unshown spring members at the longitudinally opposite ends of the conductive core 4a. The charging roller is rotated by rotation of the photosensitive drum 3. The conductive core metal 4a is supplied with a predetermined voltage from a voltage source, by which the peripheral surface of the rotating photosensitive drum 3 is directly and uniformly charged or discharged to a predetermined potential of a predetermined polarity. As shown in Figure, the charging member is in the form of a roller or a blade or other form.
The thus charged surface of the rotating photosensitive drum 3 is raster high scanned by way of mirror 2 with a laser beam which is modulated and emitted in accordance with time series electric digital picture element signal representative of the intended image information from the laser scanner unit, so that an electrostatic latent image is formed on the peripheral surface of the rotating photosensitive drum 3 in accordance with the image information.
The electrostatic latent image is visualized into a toner image through a reverse development with toner 6 in the developing device 5. The toner image is sequentially transferred onto the surface of the transfer material 14 fed to between the transfer roller 6 and the photosensitive drum 3 at the position of the transfer roller 7. The transfer roller 7 is supplied with a transfer bias voltage of a plurality opposite to that of the toner from an unshown power source. By the application of the opposite polarity charge to the backside of the transfer material, the toner image is transferred from the rotating photosensitive drum 3 onto the transfer material.
A sheet feeding cassette 12 is detachably mountable to the main assembly of the image forming apparatus, and the transfer material 14 in the cassette is separated and fed out one by one by a sheet feeding roller 13 operates sheet feeding signal and a separation pad (not shown) faced to the roller 13. The sheet is fed to registration rollers 15 constituting a pair along upper and lower guide. The registration roller 15 is not rotated until the transfer material comes to it, so that the oblique transportation of the transfer material 14 is corrected by the leading edge of the transfer material 14 abutting them. The registration roller 15 feed the transfer material to the transfer position between the photosensitive drum 3 and the transfer roller 7 at a timed relation with the leading edge of the image formed on the photosensitive drum 3. The transfer material now having the toner image is separated from the photosensitive drum 3, and is conveyed to the fixing device 17 by conveying rollers along conveying guide 16. The fixing device 17 functions to fuse and fix the toner image on the transfer material 14 by heat and pressure into a recorded image. The transfer material 14 after image fixing is discharged to a tray 18 or tray 13 along a passage selected by an unshown flapper.
The surface of the rotating photosensitive drum 3 after the toner image transfer, is cleaned by a cleaner 8 so that the contaminations such as the residual toner or the like are removed, and therefore, is used repeatedly for image formation. As shown in Figure 1, means L for erasing the residual charge after the image transfer, may be used.
In the printer of this embodiment, the photosensitive drum 3, the charging roller 4, the developing device 5 and the cleaner 8 are contained in a common cartridge cover 9 to constitute a process cartridge 10 which is detachably mountable to the main assembly of the printer. When the process cartridge 10 is mounted or dismounted relative to the main assembly of the printer, a front door 30 of the main assembly of the printer is opened, as shown in Figure 2, and the process cartridge 10 is engaged with a guide 11 (Figure 1) of the main assembly of the printer. Then, the process cartridge 10 is inserted into the main assembly or retracted therefrom. When the process cartridge 10 is sufficiently inserted into the main assembly, the process cartridge 10 is mechanically and electrically coupled with the main assembly of the printer.
The process cartridge may contain at least a photosensitive drum 3 and a charging member (charging roller 4).
Figure 3 is a perspective view of a photosensitive member and a sectional view of a central portion of the photosensitive member usable with the electrophotographic apparatus of Figure 1 and a process cartridge of Figure 2.
As shown in Figure 3A, the photosensitive member comprises an electrically conductive base member 21 in the form of a cylinder or a column, a photoconductive layer 22 formed thereon, a drive transmission gear 23 mounted to one of the longitudinal ends of the base member 23 and for receiving driving force by way of driving gear from a driving source of the main assembly of the image forming apparatus, and a flange 24 mounted to the other end. It is possible that electric connection member for establishing electric connection between the base member and the main assembly of the electrophotographic apparatus may be provided in the inside of the base member, although not shown.
Figure 4 is a side view of the photosensitive drum and the charging roller (contact type charging member). The voltage applied to the core metal 4a of the charging roller 4 from the voltage source 24, is preferably an oscillating voltage in the form of a DC biased AC voltage. The oscillating voltage is a voltage in which the voltage level thereof periodically changes with time. It is preferable that the peak-to-peak voltage of the oscillating voltage is not less than twice the charge starting voltage which is the voltage when the charge occurs to the photosensitive member when only DC voltage is applied. This is so, in order to prevent the spot-like unevenness of the charging. The waveform is not limited to the sine wave, but it may be a rectangular, triangular or pulse wave. From the standpoint of reducing the charging noise, the sine wave is preferable since it does not contain a high frequency component. The base member 21 is electrically grounded.
In this embodiment of the present invention, in order to suppress the charging noise produced between the charging member and the photosensitive member due to the application of the vibration voltage, the weight per unit volume of the photosensitive member is made larger than a predetermined level. The noise producing mechanisms such that the photosensitive member makes elastic vibration due to the oscillating voltage to the charging member. It would be considered that by adding weight to the photosensitive member, the vibration absorbing effect will be provided. According to the investigation of the inventors, it has been confirmed that the noise reducing effect is proportional to the squared weight of the photosensitive member.
In view of the above phenomenon and the actual acoustic effects, it has been found that the weight of the photosensitive member including the drive transmission or bearing portion, relative to the volume, is preferably not less than 0.65 g/cm³.
For the purpose of further stabilized noise controlling effect, 0.80 g/cm³ or larger is preferable. Since the noise reducing effect is proportional to the squared weight, and therefore, the noise reducing effect curve has a inflection point. Figure 13 is a graph showing a relation between the weight per unit volume of the photosensitive member and the noise pressure level during the printing operation of the printer using the photosensitive member. The pressure level was measured by a noise meter "NL-02" (available from Rion Kabushiki Kaisha). In Figure 13, a curve A is for the photosensitive drum having a base member having an outer diameter of 30 mm, a length of 246 mm to which an AC voltage having a frequency of 470 Hz and a peak-to-peak voltage of 1800 V is applied. A curve B is for a photosensitive member having a base member having a outer diameter of 30 mm, a length of 346 mm to which an AC voltage having a frequency of 350 Hz and a peak-to-peak voltage of 1800 V is applied.
The weight of 0.6 g/cm³ of the photosensitive drum per unit volume corresponds to immediately above the inflection point, and therefore, it is the point where the noise reduction effect becomes remarkable when the weight is increased. Where the weight is 0.80 g/cm³, the inclination of the curve becomes less steep, so that the noise reducing effect is stabilized. From the standpoint of the stabilization, 0.80 g/cm³ or larger is preferable. Where the weight is not less than 10 g/cm³, the noise level hardly reduces.
The noise preventing or suppressing effect is slightly different depending on the size of the base member. When the length of the photosensitive member is shorter than 300 mm, 0.8 g/cm³ or more is preferable, and when it is larger than 300 mm, 0.65 g/cm³ or larger is preferable. If the weight of the photosensitive drum per unit volume is too large, the drum rotation is influenced due to the increase of the required torque, with the result of the increased load to the driving mechanism or the bearings, and therefore, it is preferably not more than 3.0 g/cm³.
As for the means for adding the weight, the thickness of the cylindrical base member for the photosensitive member may be increased, or the base member may be in the form of a solid column. By increasing the thickness, the rigidity of the photosensitive member is increased. When the base member is made of aluminum, the thickness is not less than 2.5 mm in order to satisfy the above desirable condition. In place of increasing the thickness of the base member, a material may be inserted in the base member.
Specific examples of the photosensitive member according to the embodiment of the present invention will be described. For the purpose of providing the electrophotographic photosensitive member with a certain weight per unit volume, a base member having a certain level of weight is used. The material may be metal, resin or compound material using the resin as a base member. It may be cylindrical or columnar. From the standpoint of easy machining, better productivity, the weight increasing effect, cost or the like, the aluminum is preferable among them. As regards the photosensitive layer on the base member, there is no particular limit. Therefore, the photosensitive layer-may be made of known photoconductive material through photoconductive means. From the standpoint of the direct contact between the photosensitive layer and the charging member, the photosensitive member may be provided with a surface organic photoconductive layer comprising resin as a base material. In the case of the photoconductive layer comprising the organic material as the main material, a plurality of layers are laminated.
To the longitudinal ends of the base member having the photosensitive layer, a drive transmission gear or supporting flange are mounted, as shown in Figure 3A. These members are contributable to increasing the weight of the photosensitive member. As for the material for these members, aluminum, polycarbonate resin are used from the standpoint of formability, machinability, sliding nature, durability or the like.
The description will be made as to the embodiment of the photosensitive member.

Embodiment 1

The base member had an outer diameter of 30 mm, a length of 260 mm and a thickness of 2.5 mm, and was aluminum cylinder. The photosensitive member had the following layers:

(1) Conductive coating layer mainly comprising phenol resin in which tin oxide and titanium oxide powder is dispersed, having a film thickness of 18 microns;
(2) Lower layer mainly comprising modified nylon and copolymer nylon, having a thickness of 1.0 micron;
(3) Charge generating layer mainly comprising acrylic resin in which diazo pigment having the light absorbing nature in the non-visible long wave length region is dispersed, having a thickness of 0.2 micron; and
(4) Charge transporting layer mainly comprising hydrazone compound having a charge carrying nature solved in polycarbonate resin, having a thickness of 25 microns.

To the longitudinal ends of the base member, a gear and a flange made of polycarbonate resin is mounted by bonding agent, as shown in Figure 3A. Thus, the electrophotographic photosensitive member is prepared. The weight per unit volume of the photosensitive member including the gear and the flange was 0.81 g/cm³. The photosensitive member is incorporated in a process cartridge shown in Figure 2, and the process cartridge is incorporated in a laser beam printer of Figure 1 having a process speed of 16 sheets (A4, lateral feeding) per minute. Then, the noise produced by the charging is measured. The operating conditions of the electrophotographic apparatus were the process speed of 94 mm/sec, the applied DC voltage of 700 V and a frequency of the applied AC voltage of 500 Hz, the peak-to-peak voltage of 2000 V. The picture element density supplied to the printer was 300 dpi.
As for the measurement of the noise, the printer was placed in an anechoic having a background noise level of 30 dB(A), and the noise meter "NL-2", available from Rion Kabushiki Kaisha was set at a position 50 cm away from the front face of the photosensitive member (the front side in the direction perpendicular to the axis of the photosensitive member). The unit of the noise level dB(A) is the one corrected by A-characteristics frequency (the frequency component outside the audible range was filtered out). Printer was modified so that only the photosensitive member can be rotated without the other operating noise produced. The measurements were effected to the noise pressure level X dB(A) when only the photosensitive member is rotated and to that when the photosensitive member is rotated with the charging roller applied with the voltage, Y dB(A). The difference Δ = 5Y-X dB(A) is deemed as the charging noise level.

Comparison Example 1

The base member of the photosensitive member was an aluminum cylinder having an outer diameter of 30 mm, a length of 260 mm and a thickness of 0.7 mm. In the other respects, it was the same as that of Embodiment 1.

Comparison Example 2

The base member of the photosensitive member was an aluminum cylinder having an outer diameter of 30 mm, a length of 260 mm and a thickness of 1.8 mm. In the other respects, it was the same as of Embodiment 1.
With respect to the photosensitive members of the Comparison Examples, the noise pressure level was measured when it is incorporated in the same cartridge and in the same printer.
The results of experiments are shown in Table 1 which will be given hereinafter. As a result of investigations by the inventors, the noise level has been confirmed practically and acoustically of no problem if the difference Δ is not more than 4 dB(A). THerefore, from Table 1, the sufficient advantageous effects of the embodiment has been confirmed.

Embodiment 2

The base member of the photosensitive member was an aluminum cylinder having an outer diameter of 30 mm, a length of 260 mm and a thickness of 2.2 mm. In the other respects, it was the same as in Embodiment 1. The photosensitive member was incorporated in the same process cartridge, and the process cartridge was incorporated in the same printer, and the noise level was measured. The results of of experiments are shown in Table 1.

Embodiment 3

The base member of the photosensitive member was an aluminum cylinder having an outer diameter of 30 mm, a length of 240 mm and a thickness of 5.0 mm. In the other respects, it was the same as the photosensitive member in Embodiment 1. The photosensitive member was incorporated in the same cartridge, and the cartridge was incorporated in the same printer, and the noise pressure was measured. The results are shown in Table 1.

Embodiment 4

The base member of the photosensitive member was carbon containing conductive ABS resin material having an outer diameter of 30 mm, a length of 260 mm. In the other respects, it was the same as in Example 1. The photosensitive member of this embodiment was incorporated in the same cartridge, and the cartridge was incorporated in the same printer, and the noise level was measured. The results of experiments are shown in Table 1.

Embodiment 5

The electrophotographic laser beam printer was modified to receive 600 dpi input image, and the AC voltage frequency was set to 650 Hz. In the other respect, the experiment conditions are-the same as in Embodiment 1.

Comparison Example 3

The base member of the photosensitive member of this Example was an aluminum cylinder having an outer diameter of 30 mm, a length of 260 mm and a thickness of 0.7 mm. In the other respects, it was the same as the photosensitive member of Embodiment 5. The photosensitive member was incorporated in the same process cartridge, which was in turn set in the same printer, and the noise level was measured.
The results of experiment are shown in Table 1. As will be understood from Table 1, in the comparison example, the noise pressure increases due to the increase of the frequency required from the increased picture element density. In the embodiment of the present invention, however, the noise suppressing effect is sufficiently provided.

Embodiments 6 and 7

The base members for the photosensitive members having a diameter of 30 mm and a length of 302 mm were prepared. As for the thickness, they had 2.2 mm and 2.7 mm, respectively. They were made of aluminum. The photosensitive layers were formed in the same manner as in Embodiment 1. To the photosensitive member, a gear and a flange were bonded, so that an electrophotographic photosensitive member was prepared.
Each of them was loaded in a laser beam printer having a printing speed of 8 sheet/min. (A4), and the charging noise were measured. In the electrophotographic apparatus, the process speed was 47 mm/sec., the applied AC voltage was 650 V, and the frequency of the applied voltage was 470 Hz, and the peak-to-peak voltage thereof was 1800 V. In the printer, the input picture element density was 600 dpi.
Similarly to the foregoing embodiment, the noise level was measured. The results of experiments are shown in Table 1.
The base members for the photosensitive members were prepared to have an outer diameter of 30 mm, a length of 346 mm. They were made of aluminum, and had thickness of 2.2 mm and 2.7 mm, respectively. The photosensitive layer was prepared by the following laminated layer:

(1) Conductive coating mainly comprising tin oxide and titanium oxide powder dispersed in phenol resin, and having a film thickness of 18 microns;
(2) Lower layer mainly comprising modified nylon and copolymer nylon, and having a film thickness of and copolymer nylon, and having a film thickness of 0.5 micron.

As for the charging conditions, the process speed was 120 mm/sec, the DC voltage applied was 730 V, the frequency of the applied AC voltage was 800 Hz, and a peak-to-peak voltage thereof was 2200 V.
Using such a photosensitive member and apparatus, the noise level was measured in the same manner as in Embodiment 1. The results of experiments are shown Table 1 below.
Referring to Figures 6A and 6B, another embodiment will be described in which a material 26 is inserted into the base member 21 of the photosensitive material. Figure 6A is a perspective view of the photosensitive drum 3 of this embodiment, and Figure 6B is a sectional view of the longitudinally central portion of the photosensitive drum of this embodiment. The same reference numerals as in the foregoing embodiment are assigned to the element having the corresponding functions, and the detailed description thereof are omitted for simplicity.
Figures 7A and 7B shows the configuration of the rigid filling material in this embodiment. In Figure 7A it is cylindrical and, in Figure 7B it is columnar. The outer peripheral surface thereof is required to be substantially in contact with the inside surface of the base member 21 to effectively absorb the vibration caused by the charging action to the photosensitive member. The material is not limited if the weight per unit volume of the photosensitive member (g/cm³) satisfy the above-described conditions. Particularly, it is preferable that the density of the material is not less than 2.0 g/cm³. This is because the vibration absorbing effect is higher if the density is higher, because the size is smaller to provide the same weight, and therefore, the insertion is easy, and because the productivity is increased. The examples of the material having the density not less than 2.0 g/cm³ include metal such as aluminum, copper, iron, brass or lead, ceramic material such as alumina, quartz, plaster, silica carbide, borone nitride, kaolinite, monmorilonite or the like. Among them, proper material can be selected by one skilled in the art in consideration of various factors such as machinability, productivity, cost or the like. From the standpoint of easy recycling use of the photosensitive drum, it is preferable that the base member and the filling material is the same, for example, the both are made of aluminum.
The material 26 may be fixed by press-fitting , or a bonding agent is usable as auxiliary means depending on the gap between the inside surface of the base member and the filling material.
The length of the filling material 26 may be any if the above-described requirement of the weight of the photosensitive drum per unit volume is satisfied, when it is inserted in the photosensitive member 3.
Generally speaking, however, it is preferably shorter than the length of the base member. If the length of the material 26 is smaller than the length of the photosensitive drum, it is easy to manufacture, and the inserting stroke into the photosensitive member is shorter, so that the concentricity with the photosensitive member is easily established, and therefore, the productivity is better.
When it is shorter than the base member 21, the position of the material 26 is preferably in the middle of the base member 21 in the longitudinal direction. In other words, the center of the material 26 in the axial direction is substantially the same as the center of the base member 21 of the photosensitive member 3 in the axial direction. Then, the center of gravity of the base member is substantially coincident with the center of the gravity of the material 26, and it has empirically been found that the arrangement is most effective in reducing the charging noise. The number of the inserting materials 26 is not limiting. When it is plural, the members are symmetrically disposed in the direction of the length of the base member.
As for the material of the photosensitive member, it is not limited if it is proper to form into a cylinder. In consideration of the formability, machinability and strength at the time when the material is inserted, a metal, particularly aluminum, is preferable.
The more specific examples in which the materials are inserted in the base member, will be described.

Embodiment 10

The base member was an aluminum cylinder having an outer diameter of 30 mm, a length of 260 mm and a thickness of 0.75 mm. On the outer peripheral surface thereof, the layers as in Embodiment 1 were laminated into a photosensitive layer.
Into the photosensitive member, the material as stated in Table 2 was inserted into the photosensitive member and was bonded to the inside surface thereof with cyanoacylate bonding material. To the longitudinal ends of the photosensitive member, a gear and a flange made of polycarbonate resin, as shown in Figure 6, are mounted, so that an electrophotographic photosensitive member was produced. The weight per unit volume of this photosensitive member was 0.85 g/cm³.
Then, the photosensitive member was placed in a process cartridge having a structure shown in Figure 2, and the charging noise Δ = (Y-X) dB(A) was measured under the same condition as in Embodiment 1.

Comparison Example 4

The photosensitive member of this Example was the same as in Embodiment 10 except that the filling material is not inserted in the photosensitive member.

Comparison Example 5

The photosensitive member of this Example was the same as of Embodiment 10 except that it was as stated in Table 2. The photosensitive member was set in the same process cartridge, and the process cartridge was set in the same printer, and the noise was measured.
The results of experiments are shown in Table 2.

Embodiments

11, 12 and 13

The inserted materials are as stated in Table 2. The photosensitive members were the same as in Embodiment 10 in the other respects. They were set in the same process cartridge, which was in turn set in the same printer. In Embodiment 11, the thickness of the base member was 1.2 mm, and the material was inserted with the force of 50 kg.
It will be understood that the effects of the present invention are sufficiently provided.

Embodiment 14

The electrophotographic laser beam printer was modified to accept 600 dpi input picture element signal, and the frequency of the applied AC voltage was set to 650 Hz. In the other respects, this embodiment is the same as the Embodiment 10.

Comparison Example 6

The filing material is not inserted. In the other respects, it was the same as in Embodiment 14. The photosensitive member was set in the same process cartridge, which was set in the same printer.
The results of experiments are shown in Table 2. As will be understood from this Table, in the comparison example, the increase of the frequency due to the increase in the picture element-density results in the charging noise increase, whereas in the embodiment of the present invention, the noise controlling effect is sufficient.

Embodiments 15 and 16

The base member for the photosensitive member was an aluminum cylinder having an outer diameter of 30 mm, a length of 302 mm and a thickness of 0.75 mm. On the outer peripheral surface thereof, the layers as in Embodiment 10 were laminated into a photosensitive layer. Into the photosensitive member, the material stated in Table 2 was inserted, and the gear and the flange were bonded to the longitudinal ends, respectively.
Then, the photosensitive member was mounted in a laser beam printer having a printing speed of 8 sheets (A4) per minute, and the charging noise was measured. The operating conditions of the electrostatic printer was such that the process speed was 47 mm/sec.; the DC voltage applied was 650 V; the AC voltage applied had a frequency of 470 Hz and a peak-to-peak voltage of 100 V. The input image density was 600 dpi.
The charging noise was measured in the same manner as in the foregoing embodiment.

Embodiments 17 and 18

As for the base member for the photosensitive member, an aluminum cylinder having an-outer diameter of 30 mm, a length of 346 mm and a thickness of 0.75 mm was prepared. The photosensitive layer was formed thereon by applying sequentially the layers as in Embodiments 8 and 9.
Into the photosensitive member, the material stated in Table 2 was inserted. Then, to the longitudinal ends of the base member, a gear and a flange of polycarbonate resin material, as shown in Figure 6, were bonded by a bonding agent. Thus, the electrophotographic photosensitive member was prepared. In Example 18, two materials were prepared and were inserted symmetrical positions. As for the electrophotographic apparatus, a plain paper copying machine NP-2020, available from Canon Kabushiki Kaisha, Japan was modified to be used with a direct charging device as shown in Figure 1. The copy speed of this copying machine was 20 sheets (A4) per minutes. As for the charging conditions, the process speed of 120 mm/sec; a DC applied voltage was 730 V, a frequency of applied AC voltage was 800 Hz; and a peak-to-peak voltage thereof was 2200 V.
Using the photosensitive member and the apparatus, the noise level was measured in the same manner as in Embodiment 10. The results are shown in Table 2.
The description will be made as to the two layer structure comprising a rigid material and an elastic material, in place of the rigid material as the filling material for the photosensitive drum.
Referring to Figures 8A and 8B, there is shown such a photosensitive drum provided therein with the filling material of two layer structure, in perspective view and sectional view adjacent the longitudinally central portion. The same reference numerals are assigned to the elements having the corresponding functions, and the detailed description thereof are omitted for simplicity.
Figure 9 is a sectional view of the filling material used in the embodiment of Figures 8A and 8B. Designated by a reference numeral 27 is a rigid material, and designated by a reference numeral 28 is the elastic material thereon. The rigid material 27 is effective to add the rigidity and the weight to the filling material. Therefore, the material may be a metal such as aluminum or brass, or a ceramic material such as cement, plaster or earthenware material. Among them, the proper material may be selected by one skilled in the art in consideration of the productivity, the machinability, the weight providing effect and cost. The configuration is preferably columnar or cylindrical.
The elastic material 28 is effective to the vibration controlling function. For this purpose, the material is required to be in close contact with the inside surface of the base member of the photosensitive member when it is inserted. For this reason, the filling material is columnar or cylindrical having a diameter slightly larger than the inside diameter of the base member. By doing so, the filling material is properly retained inside the base member if it is simply press-fitted thereinto. As auxiliary means, the bonding agent is usable.
The thickness of the elastic layer 28 may be properly selected in accordance with the side of the photosensitive member, but if it is two thick, the weight adding effect becomes small, and if it is too thin, the vibration suppressing effect is reduced, and in addition, the press-fitting into the base member 21 utilizing the elasticity, becomes difficult. Therefore, it is generally preferably 1 - 5 mm.
Usable materials include urethane rubber, chloroprene rubber or another usual elastic material.
The length of the filling material may be any, if it satisfies the above-described weight per unit volume of the photosensitive drum (g/cm³) when it is inserted in the photosensitive member. However, generally, it is preferably shorter than the length of the base member. If it is shorter than the length of the base member, the filling material is preferably in the longitudinally central portion of the base member. The number of filling material may be plural. In that case, the filling materials may be disposed symmetrically in the longitudinal direction of the base member.
The more specific examples of this embodiment having the two layer structure, will be described.

Embodiment 19

The base member was an aluminum cylinder having an outer diameter of 300 mm, a length of 260 mm and a thickness of 0.75 mm. The photosensitive layer was formed on the outer peripheral surface thereof as in Embodiment 1.
Into this photosensitive member, the filling material as stated in Table 3, was press-fitted by the force of approx. 80 kg. To the longitudinal ends of the photosensitive member, the gear and flange made of polycarbonate resin, as shown in Figure 8, are mounted by the bonding agent, respectively. In this manner, the electrophotographic photosensitive member was prepared. The weight per unit volume of the photosensitive member was 0.85 g/cm³.
The photosensitive member was incorporated in the process cartridge having the structure shown in Figure 2, and the noise level difference Δ = (Y-X) dB(A) was determined as the charging noise, in the same manner as in Embodiment 1.

Comparison Example 7

The photosensitive member was prepared in the same manner as in Embodiment 19, except that the filling material is not inserted in the photosensitive member.

Comparison Example 8

The photosensitive member was prepared in the same manner as in Embodiment 19, except that the filling material was as stated in Table 3.
The photosensitive members of these comparison examples were incorporated in the same cartridge which was in turn incorporated in the same printer, and the charging noise was measured.
The results of experiments were shown in Table 3.

Embodiments

20, 21 and 22

The filling material was as stated in Table 3. In the other respects, the photosensitive member was prepared in the same manner as with Embodiment 19. It was mounted in the same process cartridge, and the process cartridge was mounted in the same printer, and the noise difference was measured. The results of experiments are shown in Table 3.

Embodiment 23

The electrophotographic apparatus in the form of a laser beam printer was modified so that it is operable in 600 dpi density. The frequency of the applied AC voltage was 650 Hz. In the other respects, the experiment conditions were the same as in Embodiment 19.

Comparison Example 9

The photosensitive member was prepared in the same manner as in Embodiment 23, except that no filling material was inserted. It was mounted in the same process cartridge, which was loaded in the same printer, and the charging noise was measured.
The results of the tests were also in Table 3. As will be understood from this Table, the charging noise increases in comparison example by the increase of the frequency required by the increase of the picture element density, but in the embodiment of this invention, the noise controlling effect is sufficient.

Embodiments 24 and 25

An aluminum cylinder having an outer diameter of 30 mm, a length of 302 mm and a thickness of 0.75 mm was prepared for the base member of the photosensitive member. The same photosensitive layer as in Embodiment 19 was formed thereon. The filling material stated in Table 3 was inserted, and the gear and the flange were mounted by bonding agent to provide the electrophotographic photosensitive member. This was mounted in a laser beam printer having a printing speed of 8 sheets (A4) per minute, and the charging noise was measured. As for the operating conditions of the electrophotographic apparatus, the process speed is 47 mm/sec; the applied DC voltage is 650 V; the applied AC voltage has a frequency of 470 Hz and a peak-to-peak voltage of 1800 V. The input image picture element density of 600 dpi.
The noise level was measured in the same manner as in the foregoing embodiment. The results are shown in Table 3.

Embodiments 26 and 27

An aluminum cylinder having an outer diameter of 30 mm, a length of 346 mm and a thickness of 0.75 mm was prepared as a base member of the photosensitive member. The photosensitive layer was formed thereon in the same manner as in Embodiments 8 and 9. To the longitudinal ends of the base member, the gear and the flange made of polycarbonate resin illustrated in Figure 8, were mounted by bonding agent, so that an electrophotographic photosensitive member was prepared. In Embodiment 27, the filling material was divided into two parts, and they were placed at symmetrical positions.
As for an electrophotographic apparatus, a plain paper copying machine "NP-2020", available from Canon Kabushiki Kaisha, Japan, was modified so as to be usable with a direct charging member shown in Figure 1. The copy speed of this machine is 20 sheets (A4) per minute. As for the charging conditions, the process speed was 120 mm/sec; the applied AC voltage was 730 V; and the applied AC voltage had a frequency of 800 Hz and the peak-to-peak voltage of 2200 V. Using the photosensitive member and the apparatus, the noise was measured in the same method as in Embodiment 19. The results are shown in Table 3.
The description will be made as to the embodiment in which the filling material is in the photosensitive drum, and it is bonded to the inside surface of the base member.
When the filling material made of rigid and/or elastic material is inserted in the photosensitive member, the gap between the inside surface of the base member and the outer surface of the filling material is preferably not more than 100 microns, and it is'preferable that the filling material is bonded to the inside surface of the base member. This will be described in detail.
Referring to Figures 10 and 11, the photosensitive drum 3 is shown in a longitudinal sectional view (Figure 10), and an enlarged sectional view taken along a line N-N is shown in Figure 11. The photosensitive drum 3 comprises a base member 21 of aluminum having a thickness of 1 mm and an organic photosensitive layer 22 formed on the outer surface of the base member. The outer diameter is 30 mm.
Designated by a reference numeral 31 is a rigid material or elastic material as the filling material. The material thereof may be a metal such as aluminum or brass, ceramic material such as cement or plaster, or a rubber material such as natural rubber. Among them, the proper material may be selected by one skilled in the art in consideration of the productivity, the machinability, the weight adding performance and cost or the like. As for the configuration of the filling material 31, it is preferably columnar or cylindrical. When the inside diameter of the base member 21 of the photosensitive drum 3 is 28.5 H8, for example, the outer diameter of the filling material 31 is determined so as to be smaller than that by 100 microns. That is, the gap between the base member 21 and the filling material 31 is made not more than 100 mm, and the gap is filled by a bonding agent (for example, cyanoacrylate material, or epoxy resin material), thus fixing the filling material 31 in the photosensitive drum. By doing so, the weight and the rigidity of the photosensitive drum 3 is increased. As the means for the bonding, the bonding material 32 may be applied to the inside surface of the base member 21, beforehand, or otherwise, the bonding material may be applied to the outer surface of the material 31. Flanges 33 and 33 are mounted to the longitudinal ends of the photosensitive drum 3, respectively. It is preferable that the filling material is concentric with the base member 21. As compared with the case in which the material 31 is press-fitted into the base member 21, the case in which the gap is provided between the base member and the filling material is preferable in that the drum manufacturing is easier. In addition, the range of the usable material increases, and therefore, the cost can be reduced.
Table 4 shows a relation between the noise pressure level and a gap between the photosensitive drum 3 and the filling material 31. The noise pressure level is expressed as Δ = (X-X) dB(A), that is, the increase of the noise level due to the charging noise. The peripheral speed of the photosensitive drum was 50 mm/sec, and the other conditions are the same as in Embodiment 1.
As will be understood from Table 4, if the gap D between the base member 21 and the material 31 is not more than 100 microns, the noise level is practically no problem if the filling material 31 is fixed to the base member 21 by the bonding material 32. However, it should be noted that the weight per unit volume of the photosensitive drum satisfies the above-described condition. If the bonding material 32 is not applied in the entirety of the gap D, the charging noise suppression effect is sufficient. As for the manufacturing method of the photosensitive drum, similarly to the conventional method, the organic photosensitive layer 22 is formed on the outer peripheral surface of the drum base 21, and dried. Thereafter, the filling material 31 is inserted, and is bonded by the bonding agent 32. Therefore, the productivity is not extremely worsened by longer time period is required for the organic photosensitive member 22 formation and the drying process because of the increase of the thermal capacity of the base member 21.
As for the configuration of the filling material 31, a step 33 may be formed in the cylindrical material, at which in Figure 12, for the purpose of uniformly applying the bonding agent 32, or a knurled shape may be formed for the same purpose.
In this case, too, the above-described condition for the weight per unit volume of the photosensitive drum should be satisfied. The gap D between the photosensitive drum and the material 31 is not less than 100 microns in the basic dimensions.
In the foregoing embodiments, the charging member is in the form of a roller, but it may be in the form of a blade, a pad, a block, a rod or a wire or the like, and the above-described noise suppressing effect of the present invention is effective in those forms of the charging members.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
The content of our other two European patent applications (agent's ref. 2219230 and 2219330) having the same priority and filing dates as the present application, are incorporated herein by reference.

Claims

An electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a portion for receiving driving force; and
total weight divided by total volume of said photosensitive member is not less than 0.65 g/cm².
A member according to Claim 1, wherein the total weight divided by the total volume is not less than 0.8 g/cm³.
A member according to Claim 1, wherein said photosensitive member is longer than 300 mm.
A member according to Claim 2, wherein said photosensitive member is not longer than 300 mm.
A member according to Claim 1, wherein said base member is cylindrical.
A member according to Claim 1 or 2, wherein said photosensitive member includes a material within said base member.
A member according to Claim 6, wherein the material is rigid.
A member according to Claim 7, wherein the rigid material has a density, not less than 2.0 g/cm³.
A member according to Claim 6, wherein the material comprises a rigid material and an elastic material thereon.
A member according to Claim 9, wherein the elastic material has a thickness of 1.5 mm.
A member according to Claim 9, wherein the elastic member is of rubber material.
A member according to Claim 6, wherein said base member is cylindrical, and the material is cylindrical or columnar.
A member according to Claim 6, wherein a clearance between an inside surface of said base member and an outer surface of the material is not more than 100 microns, and they are bonded by a bonding material.
A member according to Claim 13, wherein the material comprises a first portion bonded to the inside surface of said base member and a second portion spaced from the inside surface of said base member.
A member according to Claim 6, wherein the filling material is provided for a part of an entire length of said photosensitive member.
A member according to Claim 15, wherein the material is adjacent a longitudinally central portion of said photosensitive member.
A member according to Claim 16, wherein a longitudinal center of the material is substantially aligned with a longitudinal center of said photosensitive member.
A process cartridge detachably mountable to an electrophotographic apparatus, comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, said photosensitive member comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a portion for receiving driving force; and
total weight divided by total volume of said photosensitive member is not less than 0.65 g/cm².
A cartridge according to Claim 18, wherein the total weight divided by the total volume is not less than 0.8 g/cm³.
An electrophotographic apparatus, comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, said photosensitive member comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a portion for receiving driving force; and
total weight divided by total volume of said photosensitive member is not less than 0.65 g/cm².
A cartridge according to Claim 20, wherein the total weight divided by the total volume is not less than 0.8 g/cm³.
An apparatus according to Claim 20, wherein the oscillating voltage has a peak-to-peak voltage which is not less than a charge starting voltage for said photosensitive member.
An apparatus according to Claim 22, wherein the oscillating voltage is a DC biased AC voltage.
An electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein said material is for a part of said photosensitive member in a direction of a length of said photosensitive member.
A member according to Claim 24, wherein the material is rigid.
A member according to Claim 25, wherein the rigid material has a density, not less than 2.0 g/cm³.
A member according to Claim 24, wherein said base member is cylindrical, and the material is cylindrical or Columnar.
A member according to Claim 24, wherein a clearance between an inside surface of said base member and an outer surface of the material is not more than 100 microns, and they are bonded by a bonding material.
A member according to Claim 28, wherein the material comprises a first portion bonded to the inside surface of said base member and a second portion spaced from the inside surface of said base member.
A member according to Claim 24, wherein the material is adjacent a longitudinally central portion of said photosensitive member.
A member according to Claim 30, wherein said material is concentric with said photosensitive member.
A process cartridge detachably mountable to an electrophotographic apparatus, comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein said material is for a part of said photosensitive member in a direction of a length of said photosensitive member.
An electrophotographic apparatus, comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein said material is for a part of said photosensitive member in a direction of a length of said photosensitive member.
An apparatus according to Claim 33, wherein the oscillating voltage has a peak-to-peak voltage which is not less than a charge starting voltage for said photosensitive member.
An apparatus according to Claim 34, wherein the oscillating voltage is a DC biased AC voltage.
An electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein a gap between said base member and said material is not more than 100 microns, and they are bonded by a bonding material.
A member according to Claim 36, wherein said base member Is cylindrical, and the material is cylindrical or columnar.
A member according to Claim 37, wherein the material comprises a first portion bonded to the inside surface of said base member and a second portion spaced from the inside surface of said base member.
A process cartridge detachably mountable to an image forming apparatus, comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, said photosensitive member comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein a gap between said base member and said material is not more than 100 microns, and they are bonded by a bonding material.
An electrophotographic apparatus comprising:
an electrophotographic photosensitive member for being charged by a charging member which is contacted thereto and which is supplied with an oscillating voltage, comprising:
a photosensitive layer;
a base member for supporting said photosensitive layer;
a material inserted in said base member;
wherein a gap between said base member and said material is not more than 100 microns, and they are bonded by a bonding material.
An apparatus according to Claim 40, wherein the oscillating voltage has a peak-to-peak voltage which is not less than a charge starting voltage for said photosensitive member.
An apparatus according to claim 41, wherein the oscillating voltage is a DC biased AC voltage.
A charging or discharging apparatus for use with a photosensitive drum comprising a charging member and means for applying an electric field between the charging member and the drum, said electric field having an alternating component, characterised by means for reducing the magnitude of noise caused by the cyclical attraction between the charging member and the drum (e.g. at twice the frequency of the alternating component).
A method of charging or discharging an image bearing drum comprising applying thereto an electric field at a predetermined frequency, and suppressing vibrations of the drum at twice or higher multiples of said frequency.
A reproducing apparatus which comprises a charging member and an image receiving drum, the charging member generating an electric field between the charging member and the drum having a component alternating at a predetermined frequency, characterised in that the drum is filled with a material which is sufficiently rigid to substantially suppress vibrations at twice or higher multiples of the field frequency.