CA1262073A - Process for preparing printing forms - Google Patents
Process for preparing printing formsInfo
- Publication number
- CA1262073A CA1262073A CA000517864A CA517864A CA1262073A CA 1262073 A CA1262073 A CA 1262073A CA 000517864 A CA000517864 A CA 000517864A CA 517864 A CA517864 A CA 517864A CA 1262073 A CA1262073 A CA 1262073A
- Authority
- CA
- Canada
- Prior art keywords
- weight
- decoater
- decoating
- layer
- base material
- 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
- G03G13/00—Electrographic processes using a charge pattern
- G03G13/26—Electrographic processes using a charge pattern for the production of printing plates for non-xerographic printing processes
- G03G13/28—Planographic printing plates
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
- G03G5/02—Charge-receiving layers
- G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
- G03G5/05—Organic bonding materials; Methods for coating a substrate with a photoconductive layer; Inert supplements for use in photoconductive layers
- G03G5/0503—Inert supplements
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
- G03G5/02—Charge-receiving layers
- G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
- G03G5/06—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being organic
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
- H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
- H05K3/061—Etching masks
- H05K3/065—Etching masks applied by electrographic, electrophotographic or magnetographic methods
Abstract
ABSTRACT OF THE DISCLOSURE
Printing forms or metallized images can be pre-pared electrophotographically by a process comprising the electrostatic chargeup, imagewise exposure and tonering of a photoconductor layer applied to an electroconductive base material, followed by fixing of the tonered image areas, removal of the photoconductive layer in the non-image areas by decoating and, where appropriate, etching of the bared base material surface. A recording material is used that comprises a photoconductive layer containing at least one organic n-conducting pigment in a concentra-tion between 10 and 50 percent by weight and an organic p-conducting photoconductor in a concentration of 0 to 20 percent by weight, based on the layer weight, together with a binder which is soluble or dispersible in aqueous-alkaline solution. The decoating is carried out with an aqueous-alkaline decoater solution, which preferably con-tains alkali metal hydroxides and/or phosphates. The decoating is preferably carried out at an elevated tem-perature, for example, between about 30° to 60°C.
Printing forms or metallized images can be pre-pared electrophotographically by a process comprising the electrostatic chargeup, imagewise exposure and tonering of a photoconductor layer applied to an electroconductive base material, followed by fixing of the tonered image areas, removal of the photoconductive layer in the non-image areas by decoating and, where appropriate, etching of the bared base material surface. A recording material is used that comprises a photoconductive layer containing at least one organic n-conducting pigment in a concentra-tion between 10 and 50 percent by weight and an organic p-conducting photoconductor in a concentration of 0 to 20 percent by weight, based on the layer weight, together with a binder which is soluble or dispersible in aqueous-alkaline solution. The decoating is carried out with an aqueous-alkaline decoater solution, which preferably con-tains alkali metal hydroxides and/or phosphates. The decoating is preferably carried out at an elevated tem-perature, for example, between about 30° to 60°C.
Description
~ '7~
PROCESS FOR PREPARING PRINTING ~ORMS
. _ . .
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing printing forms or metallized images by electro-photographic means through electrostatic chargeup, image-wise exposure and tonering of a photoconductor layer applied to an electroconductive base material; fixing the tonered image areas; removing the photoconductor layer in the nonimage areas by decoating and, where appropriate, etching the bared base material surface.
Processes for preparing printing forms, such as offset printing plates, and printed circuits by electro-photographic means are known. For instance, offset printing plates with a photoconductor layer which con-tains zinc oxide can be prepared by subjecting the plate, which is imagewise covered with toner after development, to controlled hydrophilization with a hydrophilizing agent, for example, by treatment with ferricyanide solu-tion, in the nonimage areas. As a result, differentia-tion is obtained between ink-accepting, hydrophobic, tonered image areas and the hydrophilized layer surEace.
The disadvantage of such a process is the necessity of having to repeat the hydrophilizing step more than once, and the relatively short print run.
To overcome the disadvantages described, there ~,-'.1 has been a trend, in the field vf electrophotographically presensitized o~set printing plates, toward systems where the hydrophilizing step is replaced by a decoating step. It is thus possible, according to German Auslegeschrift No. 1,117,391 (co~responding to British Patent No~ 94~,126), to obtain image differentiation by using as the binder of the photoconductive layer a high molecular weight compound that contains alkali-solubilizing groups. ~onering and fixing the tonered image areas yields a mask which restricts decoating with an alkaline decoater to the nonimage areas of the photo-conductor layer. By using a hydrophilic base material, such as an electrochemically or mechanically roughened and anodized aluminum base, it is thus possible to obtain differentiation between hydrophobic toner image or hydro-phobic photoconductor layer, on the one hand, and the bared hydrophilic base material surface, on the other hand.
For decoating, solutions of inorganic and/or organic alkaline substances in water and/or organic solvents are used. Sparingly volatile amines or amino alcohols, which are used in concentrations between about 1 and 5% as solution in polyhydric alcohols and/or water, are considered particularly suitable. Application can be effected not only by simply wiping, for example, with an impregnated pad of absorbent cotton, or by dipping into a decoating bath, but also by means of appropriate mecha-nized apparatus in which the alkaline liquid is applied.
It is known (German Auslegeschrift No. 1,117,391 and German Patent No. 2,322,046, corresponding to British Patent No. 1,~65,926) that good decoating action is obtained in particular when the decoater contains sol-vents, especially alcohols. Such solvents are capable of dissolving the organic photoconductor which is dissolved in the binder matrix of the m~ntioned layers, thereby speeding up the decoating step. This is of particular importance for mechanized processing, where the required decoating rate and service life of decoater are high.
Solvent-containing decoaters also offer advantages with regard to machine soiling, since, by virtue of their dis-solving power vis-a-vis the photoconductor, they prevent undesirable photoconductor deposits in the apparatus.
Solvent-free decoater compositions cannot be used for this purpose.
On the other hand, solvent-containing decoaters have a number of disadvantages. For instance, when amines are used it is generally not possible to avoid a certain odor nuisance. For safety reasons, furthermore, the choice of solvents which can be used is restricted with respect to flash point or, alternatively, it is necessary to take expensive safety precautions. Finally, the toner of the de~eloper - in general, polymers without alkali-solubilizing groups - frequently exhibits a cer-tain solubility or swellability in the solvents used.
This is true in particular of liquid developers of the dispersimer type as known, fox example, from German Auslegeschrift ~o. 2,114,773, corresponding to U.S.
Patent No. 3,753,760. Solubility or swellability of the fixed toner during the decoating step results in consid-erable losses, particularly in the case of fine image elements. The decoater, passing through the toner mask, also attacks the photoconductor layer underneath; this can give rise to etching underneath the mask and to the subsequent float-off of the toner mask. This is also true o toner masks from dry developers, although - owing to the different manufacturing process - to a reduced degree.
The switch in preparing printing forms to photo-conductive layers that contain small amounts of photocon-ductor dissolved in the binder and, in addition, very high amounts of photoconductive organic pigments, as described in German Offenlegungsschrift 34 17 951 leads (in the case of using solvent-containing photoconductor layers) to undesirable~ significantly slower decoating speeds which are no longer suficient for practical use~
Complete decoating cannot be guaranteed in these cases.
SUMMA.RY OF THE INVENTION
It is therefore an object of the present inven-tion to provide for the processing of printing forms and metallized images using recording materials that have photoconductive layers containing a high proportion of organic pigment and a low amount of organic photoconduc-tors dissolved in a binder.
It is also an object of the present invention to provide an electrophotographic imaging process that per-mits efficient differentiation between tonered and non-tonered areas, regardless of whether a liquid or dry developer is used, and that accommodates, with respect to service life and decoating speed, implementation in a mechanized processing system.
In accomplishing the foregoing objects, there has been provided, in accordance with one aspect of the present invention, an electrophotographic process for preparing printing forms or metallized images using recording material comprised of an electroconductive base material and a photoconductor layer provided cn the base material, comprising the steps of (A) subjecting the recording material to electrostatic chargeup;
(B) imagewise exposing and tonering of - the photoconductive layer ko produce tonered image areas thereon;
(C) fixing the toner image areas on the photoconductive layer; and there-aEter (D) treating the photoconductive layer with an aqueous-alkaline decoater solution such tha~ nonimage areas of the photoconductive layer are removed and portions of the base material are exposed, wherein the photoconductor layer contains (i) at least one organic, n-conducting pigment in a concentration be-tween about 10 and 50 percent by weight, based on total weight of the photoconductor layer; (ii) an organic, p-conducting photoconductor in a concentration of rom 0 to 20 percent by weight, based on total weight of the photo-conductor layer; and (iii) an amount of a binder that is soluble or dispersible in aqueous-alkaline solution, the amount being sufficient to stabilize the photoconductor layer structurally. In one preferred embodiment, the decoater solution contains an alkali metal hydroxide and/
or phosphate, preferably in a concentration between of about 0.01 and 10 percent by weight. In another pre-ferred embodiment, the decoating solution is substan-tially free of organic solvents. In further preferred embodiment, step tD) is carried out at an elevated tempe-rature--.
With the present invention, electrophotographic recording materials comprising a photoconductor layer as descrlbed above are rendered usable for producing printiny forms and metallized images which conform to industrially high standards. The decoating solutions of the present invention possess a higb decoating speed and a satisfactory service life. Surprisingly, decoating solutions used accordiny to the present invention repro-duce particularly fine image elements, and sub-mask etching is avoided.
, . .
,;, ;
DETAILED DESCRIPTION OF THE PRE~ERRED EMBODIMENTS
. _ _ Recording materials which can be used according to the present invention have a relatively high content of photoconductive organic pigments, which are embedded in binders that are soluble or dispersible in aqueous alkaline solution. To increase electrophotographic sen-sitivity, such photoconductor layers can also contain small amounts oE an organic p-conductor. For instance, the materials described in German Of~enlegungsschrift 34 17 951 as comprising photoconductive organic pigment and a carbonyl-containing binder can be used when the binder is rendered soluble or dispersible in aqueous alkaline solution by incorporation of carboxylic acid or carboxylic acid anhydride groups. Preferred binders in this regard are copolymers of methacrylic acid esters, methacrylic acid and, where appropriate, with other mono-mers t such as styxene. In addition to the known binders with carbonyl functional groups, the process of the pre-sent invention can be used to process even those layers that comprise binders having, for example, sulfonic acid, phosphonic acid, carbonic acid and similar, alkalisolubi-lizing varieties.
Aqueous alkaline decoater solutions that are used in accordance with the present invention are aqueous solutions of inorganic substances. Suitable inorganic alkaline substances are ammonia, alkali metal and alka-line earth metal hydroxides, alkali metal and alkaline earth metal phosphates, hydrogenphosphates, carbonates, silicates, borates and the like. It is preferable to use alkali metal hydroxides and phosphates. These inorganic substances are used in aqueous solution in concentrations between about 0.01 and 10 percent by weight, preferably between 1 and 5 percent by weight. The decoater solution can include organic solvents in small amounts without '7`~
changing the desirable properties of the developer. In a preferred embodiment, organic solvents are dispensed with entirelyO
To increase the rate of decoating and to mini-mize soiling of the decoating apparatus, it has been found to be advantageous, in the context of the present invention, to add suitable dispersants to the decoater solution. Suitable for use as dispersants in this regard are all anionic, cationic and nonionic surfactants gener-ally suitable for aqueous systems. Exemplary dispersants of this sort are alkylsulfonates, alkyl phosphonates, al-kali metal salts oE fatty alcohol hemiesters of sulfuric acid, fatty amine deri~-atives, oligomers of ethylene oxide with suitable end groups, such as nonylphenol, and siloxanes. Surfactants that are particularly suitable for increasing the decoating rate, and for stabilizing the pigment thus removed in the resulting decoater dis-persion, are the alkali metal alkylsulfates, such as sodium octylsulfate. The dispersants are added to the decoater solution in concentrations between about 0.1 a~d percent by weight. Particularly good results are obtained with concentrations between about 0.5 and 3 per-cent by weight.
In the preparation of offset printing plates on anodized base material, it has been found to be advan-tageous to add substances that protect the anodiæed aluminum/aluminum oxide surface Erom attack by the decoater solution. Illustrative of such substances are silicate compounds.
To increase the service life of the decoater and the constancy oE decoating conditions, particularly in the case of mechanized decoating, it has been discovered that it is advantageous to keep the pH of the decoater solution substant:ially constant either by adding a buf-fer, such as a phosphate buffer or one of the other 37~
buffer systems described in the literature, or by topping up with a co~centrate of higher pH.
The decoating can be carried out at room tem-perature, but it can also be carried out at elevated tem perature. The decoating is preferably carried out within the range from 30C to 60C.
The development at elevated temperature of light-sensitive planographic printing plates which func-tion on a non-electrophotographic basis is well-known.
For instance, German Offenlegungsschrift No. 2,~0~,130, corresponding to Japanese Kokai No. 50-108,005, discloses that, with positive- as well as negative-working systems that distinguish chemically~ by photoreaction, between image and nonimage areas, increasing the temperature at which the development is carried out makes possible the processing even of printing plates that have been stored for a prolonged period. The developer solutions used have ~omponents that have a boiling point of above 80C, at atmospheric pressure. The solutions axe high in solvent content~ Industrial utilization of this process, however, has not been disclosed.
Electrophotographic recording materials, by contrast, generally have considerably higher layer thicknesses for the photoconductor layer than the layers of the above-described light-sensitive systems. Unlike the latter, electrophotographic systems distinguish phy-sically between image and nonimage areas, in that the former are covered up by a toner mask. The photoconduc-tor layer underneath this toner mask is not changed in its chemical composition and, hence, in its behavior toward a decoater solution.
Solvent-containing decoaters cause swelling of the toner as well as of the photoconductor layer nonimage areas that are not protected by a toner mask. The result is also swelling or dissolving of the photoconductor layer image areas underneath the toner mask. ~'his leads ,~
to image losses on the printing form or to weak areas in the hydrophobic layer which, in the course of printing, result in ima~e losses on the information carrier.
It has now been found that the attac~ remains limited to the nonimage areas oE the photoconductor layer, and the above-mentioned decoating faults are not observed, when a solvent-free decoater is used, a result that was not readily foreseeable. Surprisi~gly, this decoating behavior is not even affected by an increase in the temperature. On the contrary, increasing the tem-perature leads to excellent differentiation between image and nonimage areas, even in the case of liquid toner masks which are more sensitive to decoating. It is gener-ally assumed that due to carbon dioxide absorption from the air with subsequent neutralization, the service life of alkaline decoating solutions is drastically reduced when these are applied at higher temperatures. In con trast to the above even an increase in service life is found in practicing the present invention as long as purely aqueous-alkaline decoaters are used. ~ check of the respective state of the decoating solution of the present invention can be effected via a relatively simple pH measurement, and topping up is no problem.
A particularly suitable temperature range for decoating the pigment layers, following the present invention, has been found to be in the range between about 30 and 60C. The lower limit of this range makes it possible to reduce the requisite control outlay for the temperature, compared with mechanized decoating at room temperature. The upper limit is less clearly defined, and is essentially determined by the vapor pressure of the water and any safety measures required for handling the particular hot decoater solutions.
Development of the latent electrostatic image can be eEfected not only with a dry developer but also in a liquid developer. Developing by tonering with a liquid _9_ ., .
developer is preferred in the process of the present in-vention.
To prepare metallized etch images, metallized plastic supports in the form of sheets or plates are used, and the metal layer can be applied by vapor deposi-tion, by laminating and by chemical or galvanic deposi-tion. Decoating is then followed by etching o$ the bared surface of the base material.
A further advantage of using the process accord-ing to the invention is, finally, the relatively simple disposal of the spent decoater solution. By simply neu-tralizing with acids customary in chemistry, such as hy-drochloric acid, or by breaking the dispersion by adding substances that complex with ox precipitate the disper-sant or that affect its dissociation behavior. For example, by adding milk of lime or sodium chloride in the case of sodium octylsulfate, a large portion of the ori-ginal layer constituents is precipitated and can be removed by a ~iltration step. The filter cake obtained can, if desired,-be subjected to further processing to isolate the layer components for use again in preparing presensitized offset printing plates.
The present invention is illustrated in more detail by means of the following illustrative examples and comparative examples.
E _ ple 1 An electrochemically pretreated and anodised aluminum plate had applied to it the following disper-sion in such a way that a dry layer weight o~ 6 g/m2 resulted:
15 g of N,N'-(3-methoxyphenyl)perylenetetracar-boxylic acid 3,4,9,10-diimide (Paliogen~
black, B~SF R~), 3 g of 4-methoxybenzaldehydediphenylhydrazone, and 42 g of a terpolymer of styrene, hexyl methacry-late and methacrylic acid in a molar ratio of 10~60:30 in 540 g of tetrahydrofuranO
Following an electrostatic chargeup (negative) by means of a corona, the layer was imagewise exposed and was treated with a commercially available dry developer having positively charged toner particles. The toner image was fixed at 150C for 5 minutes. Decoating was effected in a commercially available decoating apparatus using the following decoater solutions:
(a) 50 parts by weight of isopropanol, parts by weight of benzyl alcohol, 4 parts by weight of potassium hydraxide~
36 parts by weight of water;
(b) 5.6 parts by weight of potassium hydroxide, 994.4 parts by weight of water;
(c) 5.6 parts by wei.ght of potassium hydroxide, parts by weight of sodium octylsulfate, 974.4 parts by weight of water;
(d) 7.1 parts by weight of disodium phosphate,
PROCESS FOR PREPARING PRINTING ~ORMS
. _ . .
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing printing forms or metallized images by electro-photographic means through electrostatic chargeup, image-wise exposure and tonering of a photoconductor layer applied to an electroconductive base material; fixing the tonered image areas; removing the photoconductor layer in the nonimage areas by decoating and, where appropriate, etching the bared base material surface.
Processes for preparing printing forms, such as offset printing plates, and printed circuits by electro-photographic means are known. For instance, offset printing plates with a photoconductor layer which con-tains zinc oxide can be prepared by subjecting the plate, which is imagewise covered with toner after development, to controlled hydrophilization with a hydrophilizing agent, for example, by treatment with ferricyanide solu-tion, in the nonimage areas. As a result, differentia-tion is obtained between ink-accepting, hydrophobic, tonered image areas and the hydrophilized layer surEace.
The disadvantage of such a process is the necessity of having to repeat the hydrophilizing step more than once, and the relatively short print run.
To overcome the disadvantages described, there ~,-'.1 has been a trend, in the field vf electrophotographically presensitized o~set printing plates, toward systems where the hydrophilizing step is replaced by a decoating step. It is thus possible, according to German Auslegeschrift No. 1,117,391 (co~responding to British Patent No~ 94~,126), to obtain image differentiation by using as the binder of the photoconductive layer a high molecular weight compound that contains alkali-solubilizing groups. ~onering and fixing the tonered image areas yields a mask which restricts decoating with an alkaline decoater to the nonimage areas of the photo-conductor layer. By using a hydrophilic base material, such as an electrochemically or mechanically roughened and anodized aluminum base, it is thus possible to obtain differentiation between hydrophobic toner image or hydro-phobic photoconductor layer, on the one hand, and the bared hydrophilic base material surface, on the other hand.
For decoating, solutions of inorganic and/or organic alkaline substances in water and/or organic solvents are used. Sparingly volatile amines or amino alcohols, which are used in concentrations between about 1 and 5% as solution in polyhydric alcohols and/or water, are considered particularly suitable. Application can be effected not only by simply wiping, for example, with an impregnated pad of absorbent cotton, or by dipping into a decoating bath, but also by means of appropriate mecha-nized apparatus in which the alkaline liquid is applied.
It is known (German Auslegeschrift No. 1,117,391 and German Patent No. 2,322,046, corresponding to British Patent No. 1,~65,926) that good decoating action is obtained in particular when the decoater contains sol-vents, especially alcohols. Such solvents are capable of dissolving the organic photoconductor which is dissolved in the binder matrix of the m~ntioned layers, thereby speeding up the decoating step. This is of particular importance for mechanized processing, where the required decoating rate and service life of decoater are high.
Solvent-containing decoaters also offer advantages with regard to machine soiling, since, by virtue of their dis-solving power vis-a-vis the photoconductor, they prevent undesirable photoconductor deposits in the apparatus.
Solvent-free decoater compositions cannot be used for this purpose.
On the other hand, solvent-containing decoaters have a number of disadvantages. For instance, when amines are used it is generally not possible to avoid a certain odor nuisance. For safety reasons, furthermore, the choice of solvents which can be used is restricted with respect to flash point or, alternatively, it is necessary to take expensive safety precautions. Finally, the toner of the de~eloper - in general, polymers without alkali-solubilizing groups - frequently exhibits a cer-tain solubility or swellability in the solvents used.
This is true in particular of liquid developers of the dispersimer type as known, fox example, from German Auslegeschrift ~o. 2,114,773, corresponding to U.S.
Patent No. 3,753,760. Solubility or swellability of the fixed toner during the decoating step results in consid-erable losses, particularly in the case of fine image elements. The decoater, passing through the toner mask, also attacks the photoconductor layer underneath; this can give rise to etching underneath the mask and to the subsequent float-off of the toner mask. This is also true o toner masks from dry developers, although - owing to the different manufacturing process - to a reduced degree.
The switch in preparing printing forms to photo-conductive layers that contain small amounts of photocon-ductor dissolved in the binder and, in addition, very high amounts of photoconductive organic pigments, as described in German Offenlegungsschrift 34 17 951 leads (in the case of using solvent-containing photoconductor layers) to undesirable~ significantly slower decoating speeds which are no longer suficient for practical use~
Complete decoating cannot be guaranteed in these cases.
SUMMA.RY OF THE INVENTION
It is therefore an object of the present inven-tion to provide for the processing of printing forms and metallized images using recording materials that have photoconductive layers containing a high proportion of organic pigment and a low amount of organic photoconduc-tors dissolved in a binder.
It is also an object of the present invention to provide an electrophotographic imaging process that per-mits efficient differentiation between tonered and non-tonered areas, regardless of whether a liquid or dry developer is used, and that accommodates, with respect to service life and decoating speed, implementation in a mechanized processing system.
In accomplishing the foregoing objects, there has been provided, in accordance with one aspect of the present invention, an electrophotographic process for preparing printing forms or metallized images using recording material comprised of an electroconductive base material and a photoconductor layer provided cn the base material, comprising the steps of (A) subjecting the recording material to electrostatic chargeup;
(B) imagewise exposing and tonering of - the photoconductive layer ko produce tonered image areas thereon;
(C) fixing the toner image areas on the photoconductive layer; and there-aEter (D) treating the photoconductive layer with an aqueous-alkaline decoater solution such tha~ nonimage areas of the photoconductive layer are removed and portions of the base material are exposed, wherein the photoconductor layer contains (i) at least one organic, n-conducting pigment in a concentration be-tween about 10 and 50 percent by weight, based on total weight of the photoconductor layer; (ii) an organic, p-conducting photoconductor in a concentration of rom 0 to 20 percent by weight, based on total weight of the photo-conductor layer; and (iii) an amount of a binder that is soluble or dispersible in aqueous-alkaline solution, the amount being sufficient to stabilize the photoconductor layer structurally. In one preferred embodiment, the decoater solution contains an alkali metal hydroxide and/
or phosphate, preferably in a concentration between of about 0.01 and 10 percent by weight. In another pre-ferred embodiment, the decoating solution is substan-tially free of organic solvents. In further preferred embodiment, step tD) is carried out at an elevated tempe-rature--.
With the present invention, electrophotographic recording materials comprising a photoconductor layer as descrlbed above are rendered usable for producing printiny forms and metallized images which conform to industrially high standards. The decoating solutions of the present invention possess a higb decoating speed and a satisfactory service life. Surprisingly, decoating solutions used accordiny to the present invention repro-duce particularly fine image elements, and sub-mask etching is avoided.
, . .
,;, ;
DETAILED DESCRIPTION OF THE PRE~ERRED EMBODIMENTS
. _ _ Recording materials which can be used according to the present invention have a relatively high content of photoconductive organic pigments, which are embedded in binders that are soluble or dispersible in aqueous alkaline solution. To increase electrophotographic sen-sitivity, such photoconductor layers can also contain small amounts oE an organic p-conductor. For instance, the materials described in German Of~enlegungsschrift 34 17 951 as comprising photoconductive organic pigment and a carbonyl-containing binder can be used when the binder is rendered soluble or dispersible in aqueous alkaline solution by incorporation of carboxylic acid or carboxylic acid anhydride groups. Preferred binders in this regard are copolymers of methacrylic acid esters, methacrylic acid and, where appropriate, with other mono-mers t such as styxene. In addition to the known binders with carbonyl functional groups, the process of the pre-sent invention can be used to process even those layers that comprise binders having, for example, sulfonic acid, phosphonic acid, carbonic acid and similar, alkalisolubi-lizing varieties.
Aqueous alkaline decoater solutions that are used in accordance with the present invention are aqueous solutions of inorganic substances. Suitable inorganic alkaline substances are ammonia, alkali metal and alka-line earth metal hydroxides, alkali metal and alkaline earth metal phosphates, hydrogenphosphates, carbonates, silicates, borates and the like. It is preferable to use alkali metal hydroxides and phosphates. These inorganic substances are used in aqueous solution in concentrations between about 0.01 and 10 percent by weight, preferably between 1 and 5 percent by weight. The decoater solution can include organic solvents in small amounts without '7`~
changing the desirable properties of the developer. In a preferred embodiment, organic solvents are dispensed with entirelyO
To increase the rate of decoating and to mini-mize soiling of the decoating apparatus, it has been found to be advantageous, in the context of the present invention, to add suitable dispersants to the decoater solution. Suitable for use as dispersants in this regard are all anionic, cationic and nonionic surfactants gener-ally suitable for aqueous systems. Exemplary dispersants of this sort are alkylsulfonates, alkyl phosphonates, al-kali metal salts oE fatty alcohol hemiesters of sulfuric acid, fatty amine deri~-atives, oligomers of ethylene oxide with suitable end groups, such as nonylphenol, and siloxanes. Surfactants that are particularly suitable for increasing the decoating rate, and for stabilizing the pigment thus removed in the resulting decoater dis-persion, are the alkali metal alkylsulfates, such as sodium octylsulfate. The dispersants are added to the decoater solution in concentrations between about 0.1 a~d percent by weight. Particularly good results are obtained with concentrations between about 0.5 and 3 per-cent by weight.
In the preparation of offset printing plates on anodized base material, it has been found to be advan-tageous to add substances that protect the anodiæed aluminum/aluminum oxide surface Erom attack by the decoater solution. Illustrative of such substances are silicate compounds.
To increase the service life of the decoater and the constancy oE decoating conditions, particularly in the case of mechanized decoating, it has been discovered that it is advantageous to keep the pH of the decoater solution substant:ially constant either by adding a buf-fer, such as a phosphate buffer or one of the other 37~
buffer systems described in the literature, or by topping up with a co~centrate of higher pH.
The decoating can be carried out at room tem-perature, but it can also be carried out at elevated tem perature. The decoating is preferably carried out within the range from 30C to 60C.
The development at elevated temperature of light-sensitive planographic printing plates which func-tion on a non-electrophotographic basis is well-known.
For instance, German Offenlegungsschrift No. 2,~0~,130, corresponding to Japanese Kokai No. 50-108,005, discloses that, with positive- as well as negative-working systems that distinguish chemically~ by photoreaction, between image and nonimage areas, increasing the temperature at which the development is carried out makes possible the processing even of printing plates that have been stored for a prolonged period. The developer solutions used have ~omponents that have a boiling point of above 80C, at atmospheric pressure. The solutions axe high in solvent content~ Industrial utilization of this process, however, has not been disclosed.
Electrophotographic recording materials, by contrast, generally have considerably higher layer thicknesses for the photoconductor layer than the layers of the above-described light-sensitive systems. Unlike the latter, electrophotographic systems distinguish phy-sically between image and nonimage areas, in that the former are covered up by a toner mask. The photoconduc-tor layer underneath this toner mask is not changed in its chemical composition and, hence, in its behavior toward a decoater solution.
Solvent-containing decoaters cause swelling of the toner as well as of the photoconductor layer nonimage areas that are not protected by a toner mask. The result is also swelling or dissolving of the photoconductor layer image areas underneath the toner mask. ~'his leads ,~
to image losses on the printing form or to weak areas in the hydrophobic layer which, in the course of printing, result in ima~e losses on the information carrier.
It has now been found that the attac~ remains limited to the nonimage areas oE the photoconductor layer, and the above-mentioned decoating faults are not observed, when a solvent-free decoater is used, a result that was not readily foreseeable. Surprisi~gly, this decoating behavior is not even affected by an increase in the temperature. On the contrary, increasing the tem-perature leads to excellent differentiation between image and nonimage areas, even in the case of liquid toner masks which are more sensitive to decoating. It is gener-ally assumed that due to carbon dioxide absorption from the air with subsequent neutralization, the service life of alkaline decoating solutions is drastically reduced when these are applied at higher temperatures. In con trast to the above even an increase in service life is found in practicing the present invention as long as purely aqueous-alkaline decoaters are used. ~ check of the respective state of the decoating solution of the present invention can be effected via a relatively simple pH measurement, and topping up is no problem.
A particularly suitable temperature range for decoating the pigment layers, following the present invention, has been found to be in the range between about 30 and 60C. The lower limit of this range makes it possible to reduce the requisite control outlay for the temperature, compared with mechanized decoating at room temperature. The upper limit is less clearly defined, and is essentially determined by the vapor pressure of the water and any safety measures required for handling the particular hot decoater solutions.
Development of the latent electrostatic image can be eEfected not only with a dry developer but also in a liquid developer. Developing by tonering with a liquid _9_ ., .
developer is preferred in the process of the present in-vention.
To prepare metallized etch images, metallized plastic supports in the form of sheets or plates are used, and the metal layer can be applied by vapor deposi-tion, by laminating and by chemical or galvanic deposi-tion. Decoating is then followed by etching o$ the bared surface of the base material.
A further advantage of using the process accord-ing to the invention is, finally, the relatively simple disposal of the spent decoater solution. By simply neu-tralizing with acids customary in chemistry, such as hy-drochloric acid, or by breaking the dispersion by adding substances that complex with ox precipitate the disper-sant or that affect its dissociation behavior. For example, by adding milk of lime or sodium chloride in the case of sodium octylsulfate, a large portion of the ori-ginal layer constituents is precipitated and can be removed by a ~iltration step. The filter cake obtained can, if desired,-be subjected to further processing to isolate the layer components for use again in preparing presensitized offset printing plates.
The present invention is illustrated in more detail by means of the following illustrative examples and comparative examples.
E _ ple 1 An electrochemically pretreated and anodised aluminum plate had applied to it the following disper-sion in such a way that a dry layer weight o~ 6 g/m2 resulted:
15 g of N,N'-(3-methoxyphenyl)perylenetetracar-boxylic acid 3,4,9,10-diimide (Paliogen~
black, B~SF R~), 3 g of 4-methoxybenzaldehydediphenylhydrazone, and 42 g of a terpolymer of styrene, hexyl methacry-late and methacrylic acid in a molar ratio of 10~60:30 in 540 g of tetrahydrofuranO
Following an electrostatic chargeup (negative) by means of a corona, the layer was imagewise exposed and was treated with a commercially available dry developer having positively charged toner particles. The toner image was fixed at 150C for 5 minutes. Decoating was effected in a commercially available decoating apparatus using the following decoater solutions:
(a) 50 parts by weight of isopropanol, parts by weight of benzyl alcohol, 4 parts by weight of potassium hydraxide~
36 parts by weight of water;
(b) 5.6 parts by weight of potassium hydroxide, 994.4 parts by weight of water;
(c) 5.6 parts by wei.ght of potassium hydroxide, parts by weight of sodium octylsulfate, 974.4 parts by weight of water;
(d) 7.1 parts by weight of disodium phosphate,
2.2 parts by weight of sodium hydroxide, 1529 parts by weight of water; and ~e) 2.75 parts by weight of sodium hydxoxide, 4 parts by weight of sodium silicate nona-- hydrate,
3.75 parts by weight of n-butylglycol and 389.5 parts by weight of water.
The rates of decoating listed in the table below were obtained. ~s a result oE the added dispersant in solution (c), a distinctly more stable dispersion of the colored pigment of the decoater solution was obtained; no layer constituent settled out in the decoater stock reservoir vessel. A service life trial ~ithout pH read-justment gave for example (c) the most favorable consump-tion value of 125 ml/m2, the temperature being raised from an initial 33C to 39C at the end of the experimen-tal series in small temperature steps oE 1C and the rate of decoating being kept constant.
Table LayerDecoater Tempe- Rate of Repro~uction Removal of solution rature decoat-of background (decoat- inghighlight shadow staining ing C) m/min ... _ _ E~le 1 a 26 1.4 _ _ b 33 1.7 + +
c 33 1.7 ++ ~+ ++
c 55 4.8 ++ ~ ++
d 33 1.7 + +
e 26 1.7 + +
_ _ . ___ __ . _ Compara- a 26 1.9 + +
tive b 50 0.4 + ~ +
E~ple 1 c 50 0.9 .. _ _ +
. _ - weak -~ good -~+ very good .
Comparative Example 1 Example 1 was repeated, except that the pigment plate was replaced by a plate which, on an appropriately pretreated aluminum base material, carried a 6 g/m2-thick layer consisting of 50 parts by weight of 2 copolymer of maleic acid hemiester and styrene (Scripset~) 540, Monsanto), 50 parts by weight of a photoconductor bis(N,N-diethylaminophenyl)-1,3,4-oxadiazoler and 0.5 part by weight of Rhodamin B.
Although decoating with decoater variants (b) and (c) proved possible at distinctly increased tem-peratures, compared wi-th Example 1, redeposition of layer constituents on the transport rolls of the decoating apparatus did occur.
Example 2 Example 1 was repeated, except that the dry developer was replaced by a dispersimer-based liquid developer as described in German Auslegeschrit No.
2,114,773. ':~
~ nder decoating conditions unchanged compared with Example 1, use of solvent-containing decoater solu-tion (a) gave distinct losses at the highlights of half-tone fields. Although increasing the rate of decoating resulted in an improvement in this regard, it was not enough to give complete decoating in nonimage areas and shadows. The decoater variants (b) and (c), by contrast, gave image reproductions free from background staining, with excellent reproduction not only of the shadows but also of the highlights.
Com~rative Exam~le 2 Example 1 was repeated, except that the decoater solution used comprised -.~3 180 parts of 2-propanol, parts by weight of benzyl alcohol, 2.5 parts by weight of monoethanolamine and 3 parts by weight of sodium octylsulfate.
This decoater solution corresponded in com-position to the decoater solution listed in Example 1 of German Offenlegungsschrift No. 2,504,130 for chemically differentiating diazo layers, and led to good results in that context. But when it was used as a decoater solu-tion for highly pigmented electrophotographic layers, the toner image, prepared by dry as well as by liquid deve-loper, was massively attacked. Fine image elements were lost during the decoating process.
The rates of decoating listed in the table below were obtained. ~s a result oE the added dispersant in solution (c), a distinctly more stable dispersion of the colored pigment of the decoater solution was obtained; no layer constituent settled out in the decoater stock reservoir vessel. A service life trial ~ithout pH read-justment gave for example (c) the most favorable consump-tion value of 125 ml/m2, the temperature being raised from an initial 33C to 39C at the end of the experimen-tal series in small temperature steps oE 1C and the rate of decoating being kept constant.
Table LayerDecoater Tempe- Rate of Repro~uction Removal of solution rature decoat-of background (decoat- inghighlight shadow staining ing C) m/min ... _ _ E~le 1 a 26 1.4 _ _ b 33 1.7 + +
c 33 1.7 ++ ~+ ++
c 55 4.8 ++ ~ ++
d 33 1.7 + +
e 26 1.7 + +
_ _ . ___ __ . _ Compara- a 26 1.9 + +
tive b 50 0.4 + ~ +
E~ple 1 c 50 0.9 .. _ _ +
. _ - weak -~ good -~+ very good .
Comparative Example 1 Example 1 was repeated, except that the pigment plate was replaced by a plate which, on an appropriately pretreated aluminum base material, carried a 6 g/m2-thick layer consisting of 50 parts by weight of 2 copolymer of maleic acid hemiester and styrene (Scripset~) 540, Monsanto), 50 parts by weight of a photoconductor bis(N,N-diethylaminophenyl)-1,3,4-oxadiazoler and 0.5 part by weight of Rhodamin B.
Although decoating with decoater variants (b) and (c) proved possible at distinctly increased tem-peratures, compared wi-th Example 1, redeposition of layer constituents on the transport rolls of the decoating apparatus did occur.
Example 2 Example 1 was repeated, except that the dry developer was replaced by a dispersimer-based liquid developer as described in German Auslegeschrit No.
2,114,773. ':~
~ nder decoating conditions unchanged compared with Example 1, use of solvent-containing decoater solu-tion (a) gave distinct losses at the highlights of half-tone fields. Although increasing the rate of decoating resulted in an improvement in this regard, it was not enough to give complete decoating in nonimage areas and shadows. The decoater variants (b) and (c), by contrast, gave image reproductions free from background staining, with excellent reproduction not only of the shadows but also of the highlights.
Com~rative Exam~le 2 Example 1 was repeated, except that the decoater solution used comprised -.~3 180 parts of 2-propanol, parts by weight of benzyl alcohol, 2.5 parts by weight of monoethanolamine and 3 parts by weight of sodium octylsulfate.
This decoater solution corresponded in com-position to the decoater solution listed in Example 1 of German Offenlegungsschrift No. 2,504,130 for chemically differentiating diazo layers, and led to good results in that context. But when it was used as a decoater solu-tion for highly pigmented electrophotographic layers, the toner image, prepared by dry as well as by liquid deve-loper, was massively attacked. Fine image elements were lost during the decoating process.
Claims (13)
1. An electrophotographic process for pre-paring printing forms or metallized images using recording material comprised of an electroconductivy base material and a photoconductor layer provided on said base material, comprising the steps of (A) subjecting said recording material to electrostatic chargeup;
(B) imagewise exposing and tonering of said photoconductive layer to produce tonered image areas thereon;
(C) fixing said toner image areas on said photoconductive layer; and there-after (D) treating said photoconductive layer with an aqueous-alkaline decoater solution such that nonimage areas of said photoconductive layer are removed and portions of said base material are exposed, wherein said photoconductor layer contains (i) at least one organic, n-conducting pigment in a concentration bet-ween about 10 and 50 percent by weight, based on total weight of said photoconductor layer; (ii) an organic, p-conductor in a concentration of from 0 to 20 percent by weight, based on total weight of said photoconductor layer; and (iii) an amount of a binder that is soluble or dispersible in aqueous-alkaline solution, said amount being sufficient to stabilize said photoconductor layer structurally.
(B) imagewise exposing and tonering of said photoconductive layer to produce tonered image areas thereon;
(C) fixing said toner image areas on said photoconductive layer; and there-after (D) treating said photoconductive layer with an aqueous-alkaline decoater solution such that nonimage areas of said photoconductive layer are removed and portions of said base material are exposed, wherein said photoconductor layer contains (i) at least one organic, n-conducting pigment in a concentration bet-ween about 10 and 50 percent by weight, based on total weight of said photoconductor layer; (ii) an organic, p-conductor in a concentration of from 0 to 20 percent by weight, based on total weight of said photoconductor layer; and (iii) an amount of a binder that is soluble or dispersible in aqueous-alkaline solution, said amount being sufficient to stabilize said photoconductor layer structurally.
2. An electrophotographic process as claimed in Claim 1, further comprising after step (D) the step of etching said portions of said base material.
3. A process as claimed in Claim 1, wherein said decoater solution contains at least one compound from the group consisting of an alkali metal hydroxide and an alkali metal phosphate.
4. A process as claimed in Claim 3, wherein said decoater solution contains said compound in a con-centration of about 0.01 to 10 percent by weight.
5. A process as claimed in Claim 1, wherein said decoater solution contains a dispersant.
6. A process as claimed in Claim 1, wherein said decoater solution is buffered.
7. A process as claimed in Claim 1, wherein step (D) is carried out at an elevated temperature.
8. A process as claimed in Claim 7, wherein step (D) is carried out at a temperature within the range from about 30°C to 60°C.
9. A process as claimed in Claim 1, wherein said decoater solution contains a silicate.
10. A process as claimed in Claim 1, wherein said binder in said photoconductive layer comprises a copolymer comprised of a methacrylic acid ester and methacrylic acid.
11. A process as claimed in Claim 10, wherein said copolymer further comprises styrene.
12. A process as claimed in Claim 1, wherein said tonering of said photoconductive layer is effected with a liquid developer.
13. A process as claimed in Claim 1, wherein said decoater solution is substantially free of organic solvents.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19853532346 DE3532346A1 (en) | 1985-09-11 | 1985-09-11 | METHOD FOR PRODUCING PRINTING FORMS |
| DEP3532346.9 | 1985-09-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1262073A true CA1262073A (en) | 1989-10-03 |
Family
ID=6280628
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000517864A Expired CA1262073A (en) | 1985-09-11 | 1986-09-10 | Process for preparing printing forms |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4684594A (en) |
| EP (1) | EP0214596A3 (en) |
| JP (1) | JPS6261077A (en) |
| CA (1) | CA1262073A (en) |
| DE (1) | DE3532346A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5069992A (en) * | 1989-11-17 | 1991-12-03 | Fuji Photo Film Co., Ltd. | Electrophotographic printing plate precursor containing alkali-soluble polyurethane resin as binder resin |
| DE19510526A1 (en) * | 1995-03-23 | 1996-09-26 | Hoechst Ag | Electrophotographic recording material for the production of printing plates |
| US6624272B2 (en) | 1999-12-20 | 2003-09-23 | Jsr Corporation | Hollow crosslinked cationic polymer particles, method of producing said particles, and paint composition, cationic electrodeposition paint composition, resin composition, filled paper, paper coating composition, and coated paper |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1117391B (en) * | 1959-03-18 | 1961-11-16 | Kalle Ag | Electrophotographic process for the production of printing forms |
| US3753760A (en) * | 1970-01-30 | 1973-08-21 | Hunt P | Liquid electrostatic development using an amphipathic molecule |
| DE2322046C3 (en) * | 1973-05-02 | 1979-11-22 | Hoechst Ag, 6000 Frankfurt | Process for the production of printing forms |
| JPS50108005A (en) * | 1974-01-31 | 1975-08-26 | ||
| DE3024772A1 (en) * | 1980-06-30 | 1982-01-28 | Hoechst Ag, 6000 Frankfurt | ELASTIC, LAMINATE LIGHT SENSITIVE LAYER |
| JPS5876844A (en) * | 1981-10-31 | 1983-05-10 | Mitsubishi Paper Mills Ltd | Production of printing plate |
| JPS6017759A (en) * | 1983-07-12 | 1985-01-29 | Ricoh Co Ltd | Printing plate for electrophotographic plate making |
| DE3417951A1 (en) * | 1984-05-15 | 1985-11-21 | Hoechst Ag, 6230 Frankfurt | ELECTROPHOTOGRAPHIC RECORDING MATERIAL |
-
1985
- 1985-09-11 DE DE19853532346 patent/DE3532346A1/en not_active Withdrawn
-
1986
- 1986-09-02 EP EP86112110A patent/EP0214596A3/en not_active Withdrawn
- 1986-09-09 US US06/905,236 patent/US4684594A/en not_active Expired - Fee Related
- 1986-09-10 CA CA000517864A patent/CA1262073A/en not_active Expired
- 1986-09-11 JP JP61212872A patent/JPS6261077A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| US4684594A (en) | 1987-08-04 |
| EP0214596A3 (en) | 1990-02-07 |
| EP0214596A2 (en) | 1987-03-18 |
| DE3532346A1 (en) | 1987-03-12 |
| JPS6261077A (en) | 1987-03-17 |
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