EP0456268A2

EP0456268A2 - Electrophotographic printing plate precursor

Info

Publication number: EP0456268A2
Application number: EP91107653A
Authority: EP
Inventors: Eiichi C/O Fuji Photo Film Co. Ltd. Kato; Sadao C/O Fuji Photo Film Co. Ltd. Osawa
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1990-05-11
Filing date: 1991-05-10
Publication date: 1991-11-13
Also published as: JPH0418565A; EP0456268A3; JP2618518B2

Abstract

The present invention provides an electrophotographic printing plate precursor wherein the binder resin contained in the photoconductive layer is formed of a copolymer containing at least one monomeric component component represented by the following formula (I) and at least one monomeric component having an acidic functional group copolymerizable with said first monomeric component, said copolymer having an acidic functional group bonded to one terminal of its main chain and having a weight-average molecular weight lying in the range of 1 x 10³ to 1 x 10⁴, whereby its response speed and sensitivity to etching can be improved with elimination of fogging problems.

wherein R stands for an aliphatic or aryl group.

Description

The present invention relates to an electrophotographic printing plate precursor, which includes a photoconductive layer containing an organic photoconductive compound, and which is formed into a printing plate by forming a toner image by an electrophotographic process and then removing the photoconductive layer from the non-image region other than the toner image region. More specifically, this invention concerns an electrophotographic printing plate precursor, which makes it possible to reduce the plate-making time by shortening the time from the completion of exposure to light to the initiation of toner development, and which has an improved response to light.
Nowadays, PS plates, etc., which make use of a positive type of photosensitizers containing diazo compounds and phenolic resins as main ingredients or a negative type of photosensitizers containing prepolymers as an essential component, have been practically used as lithographic offset printing plates. Due to their low sensitivity, however, they are all made by contact exposure through pre-imaged film negatives.
In recent years, because of advances in computer-aided image processing, mass-storage equipment for data and data communications techniques, electronic editing systems have been practiced, in which everything from original input, correction, editing, layout to paging is computerized, and which are connectable on a real time basis with terminal plotters located on remote places through high-speed communications networks or satellite communications. In particular, they would be highly desirable in newspaper printing fields in need of an immediate response.
In some fields where printing plates are optionally reproduced on the basis of originals stored in the form of negative films, the originals will sooner or later be stored in very large mass-storage media, like optical discs, in consideration of advances in them.
However, a direct type of printing plate designed to be made in direct association with outputs from terminal plotters is now in embryo. In order to make printing plates even where the electronic editing systems are in operation, their outputs must still be transferred onto silver salt photographic films. Then, such films are subjected to contact exposure through SP plates, etc.
For one thing, this would be attributable to the fact that light sources used with output plotters - for instance, He-Ne lasers and semiconductor lasers - make it difficult to develop the direct type of printing plate having such a high sensitivity as to enable it to be made within practical periods of time.
Electrophotographic photosensitive materials, on the other hand, have been envisioned as photosensitive materials having such a high sensitivity so as to provide the direct type of printing plates, and many types of electrophotographic printing plate precursors are already known, in which, after toner image formation, the photoconductive layers are removed from the non-image regions. Such electrophotographic printing plate precursors, for instance, are described in Japanese Patent Publications Nos. Sho. 37-17162, 38-6961, 38-7758, 41-2426 and 46-39405 and Japanese Provisional Patent Publications Nos. Sho. 50-19509, 50-19510, 52-2437, 54-145538, 54-134632, 55-105254, 55-153948, 55-161250, 57-147656 and 57-161863.
In order to use electrophotographic photosensitive materials as printing plates, the non-image regions should be etched out to expose the hydrophilic planes to open view. For this reason, the binder resins used should often be dissolved or swollen in alkaline solvents for dissociation. Usually, these highly hydrophilic resins cannot give uniform dispersions and hence photosensitive materials, because they interact even more strongly with inorganic photoconductive compounds than do polycarbonate or other resins widely used as the binder resins for electrophotographic photosensitive materials.
Reducing the hydrophilic nature of such resins renders it impossible to remove non-imagewise regions by etching, giving rise to another problem that no practical printing negatives are obtainable, because the imagewise regions are indistinguishable from the non-imagewise regions (i.e. the hydrophillic regions).
Resins dissolvable or dispersible in alkaline solvents, on the other hand, are so ill-compatible with organic photoconductive compounds that their introduction into electrophotographic sensitive layers formed by the organic photoconductive compounds is limited. If the photoconductive layers have a low content of the organic photoconductive compounds even when enough carriers to counter surface charges are generated in them, then the moving speed of carriers through the photoconductive layers drops, resulting in a reduction in the decay or response speed of the surface charges. After the completion of exposure, there is thus no time available to enable the surface charges to decay to a level sufficient to start toner development with no fogging. Reducing the process time as much as possible may be achieved by increasing the intensity of exposure, thereby shortening the exposure time. However, the shorter the exposure time, the longer the response time. Thus, it is this lingering response speed which offers a serious obstacle to shortening the entire process time.
A still another problem arises when scanning exposure is carried out with high-intensity light sources such as laser devices. In other words, slow response speeds make a difference in the rate of decay of surface charges between the regions where writing has been initiated and ceased. As a result, no fogging takes place where writing has been started, but much fogging occurs where writing has been ceased, causing much trouble to making printing plates.
As well known from Japanese Patent Publications Nos. Sho. 41-2426, 37-17162 and 38-6961 and Japanese Provisional Patent Publications Nos. Sho. 52-2437, 54-19803, 54-134632, 55-105254, 50-19509 and 50-19510, conventional binder resins used with electrophotographic printing plate precursors, in which organic photoconductive compounds are used, include styrene-maleic anhydride copolymers, vinyl acetate-crotonic acid copolymers, vinyl acetate-maleic anhydride copolymers and phenolic resins.
As already known in the art, these resins pose numerous problems when used with electrophotographic printing plate precursors.
That is, the use of styrene-maleic anhydride copolymers as binder resins make films so hard that the resulting printing plates can crack upon bending or curving. Nor can they stand up to making a number of prints.
The use of phenolic resins as binders give films so fragile that the resulting printing plates become poor in resistance to printing. Vinyl acetate-crotonic acid and vinyl acetate-maleic anhydride copolymers again offer a problem in connection with resistance to printing.
Japanese Provisional Patent Publications Nos. Sho. 57-161863 and 58-76843 disclose that the above-mentioned various problems stemming primarily from a serious shortage of resistance to printing could be solved by using copolymers of acrylic or methacrylic ester monomers with carboxylic acid-containing monomers. It might be true that these binder resins are usable to prepare electrophotographic printing plate precursors.
However, it has now been found that the resulting printing plate precursor is still insufficient in terms of how well the non-image region is etched out. In other words, when the non-image region is made fully hydrophilic after the complete removal of the photoconductive layer and etched to such an extent that the non-image regions of prints will not be stained, etching proceeds unavoidably from the peripheral side of the toner image region, so that the image region is rid of fine lines and characters or becomes limited in available space, leading to a drop of image reproducibility.
It is a first object of this invention to provide an electrophotographic printing plate precursor, which is of high sensitivity and has a rapid response speed.
It is a second object of this invention to provide an electrophotographic printing plate precursor, in which the non-image regions and image regions are well etched out and improved in terms of resistance to printing, respectively.
It is a third object of this invention to provide an electrophotographic printing plate recursor, which lends itself well-fit for image formation by scanning exposure with laser, etc.
It is a fourth object of this invention to provide a process for preparing electrophotographic printing plate precursor, which excels in electrostatic properties and resistance to printing and is well etched.
In general, the present invention provides an electrophotographic printing plate precursor, in which an electrically conductive support includes thereon a photoconductive layer containing at least a photoconductive compound and a binder resin and which is formed into a printing plate by exposing an image to light to form a toner image and, thereafter, removing part of the photoconductive layer from a non-image region other than the toner image region, characterized in that:
the binder resin of said photoconductive layer is a copolymer containing at least one monomeric component having the following general formula (I) and at least one monomeric component having an acidic functional group copolymerizable with the first monomeric component,
said copolymer having an acidic functional group bonded to one terminal of its main chain and having a weight-average molecular weight of 1 x 10³ to 1 x 10⁴.

where R stands for an aliphatic or aryl group.
More specifically, the binder resin comprising the copolymer specified in this invention is characterized in that it is constructed from a copolymeric component having a specific recurring unit and a copolymeric component containing an acidic group (which is understood as embracing a cyclic acid anhydride, unless otherwise stated in the present disclosure), has an acidic functional group bonded to one terminal of its main chain, and has a weight-average molecular weight of 1 x 10³ to 1 x 10⁴.
When the conventional known photosensitive materials comprising known binder resins and organic photoconductive compounds are used in combination with a process for making printing plates by etching following electrophotographic image formation, many problems should be cleared up so as to satisfy etching suitability lending itself well-fit for rlrvyto-photography and high resistance to printing (i.e. a property that ensures to retain toner image regions faithful to the originals and achieve high resistance to printing).
More exactly, uniform dispersion of photoconductive compounds and binder resins depends upon hydrophilic group-containing components contained in the latter. Increasing the content of the hydrophilic group-containing component to improve etching suitability does so much damage to dispersibility that the resulting photosensitive material fails to meet such electrophotographic characteristics as initial potential, sensitivity to light and dark decay.
Decreasing the content of the hydrophilic group-containing component, on the contrary, may allow the photosensitive material to satisfy the electrophotographic characteristics, but the removal of the non-image region by etching, if achievable, becomes insufficient because of the binder resin being poor in water solubility, thus befogging the non-image regions of prints.
On the other hand, binder resins well-fit for alkali etching, like maleic anhydride copolymers and aliphatic vinyl carboxylates-crotonic acid copolymers by way of example, are less than satisfactory in terms of electrophotographic characteristics. In particular, these resins provide nothing more than a low-quality reproduction of images in a scanning exposure fashion using laser light sources.
With the binder resin of this invention, such incompatible problems can be well overcome.
It is believed that the present binder, because of being a copolymer containing a polymeric component represented by Formula (I) and a polymeric component including an acidic functional group, having an acidic functional group bonded to one terminal of its main chain and having a specific molecular weight, makes uniform dispersion of a photoconductive layer-forming dispersed material possible, enables the interaction of that material with the photoconductive compound to occur properly, and improves electrophotographic characteristics significantly.
Moreover, the non-image region is much more alkali-etched out at higher speeds, limiting the penetration of the etchant into the toner image region from its side and thereby eliminating fine line and character deficiencies or giving the image region a sufficient space. Thus, it is possible to achieve a faithful reproduction of the original image.
In addition, high resistance to printing is attainable, although there is a fear that the resistance to printing may drop due to a decrease in the film strength of the image region, which is inevitably caused by a decreased content of resin. This reason appears to be that the binder resin of this invention is regulated to a specific molecular weight, thereby maintaining the desired film strength through the synergistic effect that uniform dispersion of material and a specific location of the acidic functional group produce together.
Thus, the electrophotographic printing plate precursor according to this invention is so excellent in response speed and sensitivity to etching that a number of copies true to the original can be reproduced.
With the electrophotographic printing plate precursor according to this invention, it is possible to solve fogging problems that arise by an increase in the residual potential of the region where writing has been ceased, which is attributable to a slow response speed of the direct type of printing plate prepared in a scanning exposure fashion using laser, etc.
The first copolymeric component of the binder resin according to this invention includes a methacrylate component represented by the aforesaid Formula (I) wherein R stands for an aliphatic or aryl group.
Preferable as R are an alkyl group having 1 to 6 carbon atoms - for example, methyl, ethyl, propyl, butyl, pentyl and hexyl groups; a C₇₋₁₃ aralkyl group which may be substituted - for instance, benzyl, phenetyl, 3-phenylpropyl, naphthylmethyl, 2-naphthylethyl, 2-methylbenzyl, 2,6-dimethylbenzyl, 2-chlorobenzyl, 2,6-dichlorobenzyl, 2-bromobenzyl, 2,6-dibromobenzyl and 2-chloro-6-methylbenzyl groups; and an aryl group which may be substituted - for instance, phenyl, naphthyl, 2-methylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 2-propylphenyl, 2-butylphenyl, 2-chlorophenyl, 2-bromophenyl, 2,6-dichlorophenyl, 2,6-dibromophenyl, 2-iodophenyl, 2-bromo-6-chlorophenyl, 2-chloro-6-methylphenyl, o-biphenyl, 2-acetylphenyl, 2-propionylphenyl, 2-benzoylphenyl, 2-methoxycarbonylphenyl-2-ethoxycarbonylphenyl, 2-benzoyloxycarbonylphenyl and 2-cyanophenyl groups. More preferably, R is a substituent containing a benzene or naphthalene ring which may be substituted.
The second copolymeric component of the binder resin according to this invention may be a copolymeric component containing an acidic functional group.
The acidic functional group, for instance, may be -PO₃H₂, -SO₃H, -COOH, -P(R)O₂H, phenolic OH or a cyclic acid anhydride-containing group. Particular preference is given to -PO₃H₂, -SO₃H, -COOH or a cyclic acid anhydride-containing group.
In the above-mentioned -P(R)O₂H group, R stands for a hydrocarbon group or an OR' group wherein R' is a hydrocarbon group. Preferably, each of R and R' represents an aliphatic group having 1 to 7 carbon atoms - for instance, methyl, ethyl, propyl, butyl, hexyl, 2-chloroethyl, 2-methoxyethyl, 3-ethoxypropyl, allyl, crotonyl, butenyl, benzyl, chlorobenzyl, fluorobenzyl and methoxybenzyl groups; and an aryl group which may be substituted - for instance, phenyl, tolyl, ethylphenyl, propylphenyl, chlorophenyl, fluorophenyl, bromophenyl, chloromethylphenyl, dichlorophenyl, methoxyphenyl, cyanophenyl, acetoamidophenyl, acetylphenyl and butoxyphenyl groups.
By the "cyclic acid anhydride-containing group" is meant a group containing at least one cyclic acid anhydride which, by way of example, may be an aliphatic or aromatic dicarboxylic anhydride.
Examples of the aliphatic dicarboxylic acid include succinic, glutaconic, maleic, cyclopentane-1,2-dicarboxylic, cyclohexane-1,2-dicarboxylic, cyclohexene-1,2-dicarboxylic, 2,3-bicyclo[2,2,2]octane-dicarboxylic anhydride rings, which may be substituted by such halogen atoms as chlorine and bromine atoms and such alkyl groups as methyl, ethyl, butyl and hexyl groups.
Examples of the aromatic dicarboxylic anhydride include phthalic, naphthalene-dicarboxylic, pyridine-dicarboxylic and thiophene-dicarboxylic anhydride rings which may be substituted by such halogen atoms as chlorine and bromine atoms; such alkyl groups as methyl, ethyl, propyl and butyl groups; hydroxyl groups; cyano groups; nitro groups; and alkoxy-carbonyl groups with the alkoxy moieties being a methoxy or ethoxy group by way of example.
The polymeric component containing an acidic functional group may be any one of acidic functional group-containing vinylic compounds copolymerizable with a monomer corresponding to the polymeric component represented by Formula (I). For instance, they are referred to in "Polymer Handbook - Basics" edited by Kobunshi Gakkai, Baifu-Kan (1986) or other literature.
More specifically, mention is made of compounds containing said acidic functional groups in the substituents of half esters of vinyl or allyl groups of acrylic acid; α and β-substituted acrylic acids - for instance, α-acetoxy, α-acetoxymethyl, α-(2-amino)methyl, α-chloro, α-bromo, α-fluoro, α-tributyl-silyl, α-cyano, β-chloro, β-bromo, α-chloro-β-methoxy and α,β-dichloro products; methacrylic acid; itaconic acid, or its half esters or amides; crotonic acid; 2-alkenylcarboxylic acids - for instance, 2-pentenoic, 2-methyl-2-hexenoic, 2-octenoic, 4-methyl-2-hexenoic and 4-ethyl-2-octenoic acids; maleic acid, or its half esters or amides; vinylbenzenecarboxylic acid; vinylbenzenesulfonic acid; vinylsulfonic acid, vinylphosphonic acid; and dicarboxylic acids; and ester or amide derivatives of these carboxylic or sulfonic acids.
Specifically but not exclusively, typical examples of the acidic functional group-containing polymeric component will be given on the following pages.
It is noted that throughout the following compounds b₁ = H or CH₃ and b₂ = H, CH₃ or -CH₂COOCH₃.
In addition to the above-mentioned, essentially required polymeric components, the binder resin of this invention may contain other polymeric components - for instance, acrylonitrile, methacrylonitrile, acrolein, vinylidene chloride, vinyl chloride, α-olefins, acrylates such as methyl acrylate, ethyl methacrylate, propyl methacrylate, 2-hydroxyethyl acrylate and butyl acrylate, styrene derivatives such as styrene, vinyltoluene, α-methylstyrene, chlorostyrene and acetylstyrene, vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone and butyl vinyl ketone, vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and propyl vinyl ether, vinyl esters of aliphatic carboxylic acids such as acetic, propionic, butyric and valeric acids, vinyl or allyl esters of aromatic carboxylic acids such as benzoic, methylbenzoic and naphthalenecarboxylic acids, carboxylic acid amide derivatives containing double bond groups such as acrylic, methacrylic and crotonic acid amide derivatives, and heterocyclic compounds whose double bond groups are substituted, such as vinylpyridine, vinylimidazole, vinylthiophene and vinylpyrrolidone.
The copolymer according to this invention is further characterized by having an acidic functional group bonded to only one terminal of its main chain. This acidic functional group may be the same as those referred to in connection with the above-mentioned acidic functional group-containing polymeric component.
The aforesaid acidic functional group bonded to only one terminal of the polymer's main chain is of a chemical structure where it is bonded directly or through any connecting roup to one terminal thereof. The connecting groups, for instance, is provided by any desired combination of atomic groups having a (single or double) carbon/carbon bond, a carbon/hetero-atom bond wherein the hetero-atom may typically be an oxygen, sulfur, nitrogen or silicon atom or a hetero-atom/hetero-atom bond.
For instance, mention is made of

wherein R₂₁ and R₂₂ each represent a hydrogen atom, a halogen atom such as fluorine, chlorine or bromine, a cyano group, a hydroxyl group or an alkyl group such as methyl, ethyl or propyl,

wherein R₂₃ and R₂₄ each represent a hydrogen atom or a C₁₋₈ hydrocarbon group such as methyl, ethyl, propyl, butyl, benzyl, phenetyl, phenyl or tolyl, or - OR₂₅ wherein R₂₅ has the same meaning as referred to in connection with R₂₃.
The resin according to this invention, which has an acidic functional group bonded to only one terminal of its main chain, may be prepared by various synthesis processes, e.g. (1) the ionic polymerization process wherein various reagents are allowed to react with the terminals of living polymers obtained by conventional known anionic or cationic polymerization, (2) the radical polymerization process using a polymerization initiator and/or a chain transfer agent having an acidic functional group therein and (3) the process wherein the polymer obtained by the ionic or radical polymerization process and having a reactive group at its terminal is converted to the specific acidic functional group of this invention through polymeric reactions.
More specifically, the instant resin may be prepared by such processes as set forth in P. Dreyfuss and R.P. Quirk, "Encycl. Polym. Sci. Eng.", 7:551 (1987); Yoshiki Nakajo and Masaya Yamashita, "Dyes and Pharmaceuticals", 30, 232 (1985); and Akira Ueda and Susumu Nagai, "Chemistry and Industry", 60, 57 (1986), and literature referred to therein.
More illustratively, the copolymer according to this invention may be prepared by the following four processes wherein:

(1) the monomer corresponding to the recurring unit represented by Formula (I), the polyfunctional monomer for forming the aforesaid crosslinked structure, any other desired monomer(s) and the chain transfer agent having the acidic functional group to be bonded to one terminal of the resulting polymer are mixed together and polymerized with the use of such a polymerization initiator as azobis compounds and peroxides;
(2) the polymerization is effected with the use of an acidic functional group-containing polymerization initiator in the absence of any chain transfer agent;
(3) the polymerization is effected with the use of a chain transfer agent and a polymerization initiator, both containing an acidic functional group; and
the polymerization (2), (2) or (3) is carried out using a compound containing an amino group, a halogen atom, an epoxy group, an acid halide group or like other group as the substituent of the chain transfer agent or polymerization initiator, and the polymer is then allowed to react with these functional groups through high-molecular reactions to introduce the acidic functional group into it.

The chain transfer agent used, for instance, includes mercapto compounds containing an acidic functional group or a substituent from which the acidic functional group can be derived - for instance, thioglycolic acid, thiomalic acid, thiosalicylic acid, 2-mercaptopropinonic acid, 3-mercaptopropionic acid, 3-mercaptobutyric, N-(2-mercaptopropionyl) glycine, 2-mercaptonicotinic acid, 3-[N-(2-mercaptoethyl)carbamoyl]propionic acid, 3-[N-(2-mercaptoethyl) amino]propionic acid, N-(3-mercaptopropionyl)alanine, 2-mercaptoethanesulfonic acid, 3-mercaptopropanesulfonic acid, 4-mercaptobutanesulfonic acid, 2-mercaptoethanol, 3-mercapto-1,2-propanediol, 1-mercapto-2-propanol, 3-mercapto-2-butanol, mercaptophenol, 2-mercaptoethylamine, 2-mercaptoimidazole and 2-mercapto-3-pyridinol; or iodized alkyl compounds having the aforesaid acidic functional group or a substituent - for instance, iodopropionic acid, 2-iodoethanol, 2-iodoethanesulfonic acid and 3-iodopropanesulfonic acid. Preference is given to the mercapto compounds.
These chain transfer agents or polymerization initiators are each used in an amount lying in the range of 0.5 to 15 parts by weight, preferably 1 to 10 parts by weight per 100 parts by weight of the entire monomers.
Specifically but not exclusively, the binder resins of this invention will not be exemplified on the following pages.
In the description that follows, it is noted that R has the same meaning as referred to in connection with R in Formula (I) and a stands for - H, - CH₃ or -CH₂COOH.
In the binder resin of this invention, the monomer represented by Formula (I) accounts for 40 to 90 % by weight, preferably 50 to 80 % by weight of 100 parts by weight of said polymer. Also, the acidic functional group-containing monomer accounts for 10 to 60 parts by weight, preferably 20 to 50 parts by weight of 100 parts by weight of said polymer.
The acidic functional group bonded to one terminal of the polymer's main chain is in an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the copolymer.
The weight-average molecular weight of the binder resin lies in the range of 1 X 10³ to 1 x 10⁴, preferably 5 X 10³ to 9 x 10³.
When the content of the monomer having Formula (I) falls short of 40 % by weight or the content of the acidic functional group-containing monomer exceeds 60 % by weight, there are drops of electrophotographic characteristics - high sensitivity, high dark charge retention and response speed.
When the content of the monomer having Formula (I) exceeds 90 % by weight or the content of the acidic functional group-containing monomer falls short of 10 % by weight, the resulting printing plate precursor is so ill-etched that the quality of prints deteriorates - for instance, the occurrence of fogging and discrete fine lines or characters. There is a drop of the film strength of the image region as well, which poses problems in connection with resistance to printing.
The amount of the acidic functional group allowed to exist at one terminal of the polymer's main chain governs the weight-average molecular weight of the binder resin. At below 0.5 % by weight, the weight-average molecular weight exceeds 1 x 10⁴, making etching than satisfactory.
At higher than 15 % by weight, on the other hand, the weight-average molecular weight falls short of 1 x 10³ with deteriorations of the resistance to printing of the printing plate precursor as a result.
The binder resin of this invention may be easily prepared by the conventional known processes wherein the monomers selected from the group of monomers having Formula (I) and the group of monomers having an acidic functional group are copolymerized at any desired ratio with the use of a compound selected from chain transfer agents and/or polymerization initiators. For that polymerization, conventional known solution, suspension, precipitation, emulsion and like polymerization techniques may be used.
Preference is given to the solution polymerization process wherein the monomers are polymerized with a given compound in a solvent or solvents which, for instance, may be benzene, toluene, xylene, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, isopropanol and methoxypropyl acetate to obtain a copolymer solution, and the solution is then dried or added to a poor solvent for precipitation, thereby obtaining the desired copolymer.
In the present invention, two or more binder resins may be mixed together for use. When two or more binders resins are used, at least one of them should be the specific binder resin according to this invention, and may be mixed with other resin or resins so far known in the art. However, said other resin(s) should preferably account for up to 30 parts by weight of the entire binder resins.
A group of organic compounds should preferably be used as the photoconductive compound suitable for this invention. Usable to this end is any one of the compounds so far known in the art. More illustratively, the following two types of electrophotographic printing plate precursors have heretofore been known in the art.
The first type of printing plate precursor includes a photoconductive layer composed mainly of an organic photoconductive compound, a sensitizer dye and a binder resin, as disclosed in Japanese Patent Publications Nos. Sho. 37-17162 and 62-51462 and Japanese Provisional Patent Publications Nos. Sho. 52-2437, 54-19803, 56-107246 and 57-161863, and the second type of printing plate precursor has a photoconductive layer composed mainly of a charge generator, a charge carrier and a binder resin, as set forth in Japanese Provisional Patent Publications Nos. Sho. 56-146145, 60-17751, 60-17752, 60-17760, 60-254142 and 62-54266.
As a special example of the second type of printing plate precursor, a double-layer photoconductive structure has been known, which contains in separate layers a charge generator and a charge carrier, as set forth in Japanese Provisional Patent Publications Nos. Sho. 60-230147, 60-230148 and 60-238853.
The electrophotographic printing plate precursor may assume either one of the above-mentioned two forms. In the second form, the organic photoconductive compound referred to in the present disclosure plays a charge carrier role.
As the organic photoconductive compounds suitable for this invention, use may be made of:

(a) such triazole derivatives as set forth in U.S. Patent No. 3,112,197 specification;
(b) such oxadiazole derivatives as disclosed in U.S. Patent No. 3,189,447;
(c) such imidazole derivatives as described in Japanese Patent Publication No. Sho. 37-16,096;
(d) such poly(aryl)alkanes as set forth in U.S. Patent Nos. 3,615,402, 3,820,989 and 3,542,544 specifications as well as Japanese Patent Publications Nos. Sho. 45-555 and 51-10,983 and Japanese Provisional Patent Publications Nos. Sho. 51-93,224, 55-108,667, 55-156953 and 56-36,656;
(e) such pyrazoline and pyrazolone derivatives as disclosed in U.S. Patent Nos. 3,180,729 and 4,278,746 as well as Japanese Patent Publications Nos. 55-88,064, 55-88,065, 49-105,537, 55-51,086, 56-80,051, 56-88,141, 57-45,545, 54-112,637 and 55-74,546;
(f) such phenylenediamine derivatives as described in U.S. Patent No. 3,615,404 specification as well as Japanese Patent Publications Nos. Sho. 51-10,105, 46-3,712 and 47-28,336 and Japanese Provisional Patent Publications Nos. Sho. 54-83,435, 54-110,836 and 54-119,925;
(g) such arylamine derivatives as set forth in U.S. Patent Nos. 3,567,450, 3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961 and 4,012,376 specifications; DAS 1,110,518; Japanese Patent Publications Nos. Sho. 49-35,702 and 39-27,577; and Japanese Provisional Patent Publications Nos. Sho. 55-144,250, 56-119,132 and 56-22,437;
(h) such amino-substituted calcon derivatives as set forth in U.S. Patent No. 3,526,501 specification;
(i) such N,N-bicarbazyl derivatives as described in U.S. Patent No. 3,542,546 specification;
(j) such oxazole derivatives as disclosed in U.S. Patent No. 3,257,203;
(k) such styrylanthracene derivatives as set forth in Japanese Provisional Patent Publication No. Sho. 56-46,234;
(l) such fluorenone derivatives as set forth Japanese Provisional Patent Publication No. Sho. 54-110,837;
(m) such hydrazone derivatives as set forth in U.S. Patent No. 3,717,462, Japanese Provisional Patent Publications Nos. Sho. 54-59,143 (corresponding to U.S. Patent No. 4,150,987), 55-52,063, 55-52,064, 55-46,760, 55-85,495, 57-11,350, 57-148,749 and 57-104,144;
(n) such bendidine derivatives as set forth in U.S. Patent Nos. 4,047,948, 4,047,949, 4,265,990, 4,273,846, 4,299,897 and 4,306,008 specifications.
(o) such stilbene derivatives as set forth in Japanese Provisional Patent Publications Nos. Sho. 58-190,953, 59-95,540, 59-97,148, 59-195,658 and 62-36,674;
(p) polyvinylcarbazole and its derivatives such as those described in Japanese Patent Publication No. 34-10,966;
(q) such vinyl polymers as set forth Japanese Patent Publication Nos. 43-18,674 and 43-19,192 - for instance, polyvinyl pyrene, polyvinyl anthracene, poly-2-vinyl-4-(4'-dimethylaminophenyl)-5-phenyl-oxazole and poly-3-vinyl-N-ethylcarbazole;
(s) such polymers as disclosed in Japanese Patent Publication No. Sho. 43-19,193 - for instance, polyacenaphthylene, polyindene and acenapthylene/styrene copolymers;
(t) such condensation resins as set forth in Japanese Patent Publication No. 56-13,940 - for instance, pyrene/formaldehyde resin, bromopyrene/formaldehyde resin and ethylcarbazole/formaldehyde resin; and
(u) various triphenylmethane polymers such as those set forth in Japanese Patent Publication Nos. 56-90,883 and 56-161,550.

It is noted that the organic photoconductive compounds used in this invention are not limited to the compounds (a) to (u); all organic photoconductive compounds so far known in the art may be used. In some cases, these organic photoconductive compounds may be used in combination of two or more.
For the sensitizer dye contained in the first type of photoconductive layer, all sensitizer dyes heretofore known in the art and used for electrophotographic photosensitive materials may be used. These are set forth in "Electrophotography", 12, 9 (1973), "Organic Synthesis Chemistry", 24 (11), 1010 (1966) and other literature. For instance, preference is given to such pyrylium dyes as set forth in U.S. Patent Nos. 3,141,770 and 4,283,475, Japanese Patent Publication No. 48-25658 and Japanese Provisional Patent Publication No. 62-71965; such triallylmethane dyes as set forth in "Applied Optics Supplement", 3, 50 (1969) and Japanese Provisional Patent Publication No. 50-39548; such cyanine dyes as set forth in U.S. Patent No. 3,597,196; and such styryl dyes as set forth in Japanese Provisional Patent Publications Nos. Sho. 60-163047, 59-164588 and 60-252517.
For the charge generator contained in the second type of photoconductive layer, various organic and inorganic charge generators so far known in the electrophotographic photosensitive material art may be used. For instance, use may be made of selenium, selenium/tellurium, cadmium sulfide, zinc oxide and the following organic pigments (1) to (9).

(1) Such azo pigments as set forth in U.S. Patent Nos. 4,436,800 and 4,439,506; Japanese Provisional Patent Publications Nos. Sho. 47-37,543, 58-123,541, 58-192,042, 58-219,263, 59-78,356, 60-179,746, 61-148,453 and 61-238,063; and Japanese Patent Publications Nos. Sho. 60-5941 and 45,664 - for instance, monoazo, bisazo and trisazo pigments.
(2) Such phthalocyanine pigments as set forth U.S. Patent Nos. 3,397,086 and 4,666,802 and Japanese Provisional Patent Publications Nos. Sho. 51-90,827 and 52,55,643 - for instance, non-metal or metal phthalocyanine pigments.
(3) Such perylene pigments as set forth in U.S. Patent No. 3,371,884 and Japanese Provisional Patent Publication No. Sho. 47-30330.
(4) Such indigo and thioindigo derivatives as set forth British Patent No. 2,237,680 and Japanese Provisional Patent Publication No. Sho. 47-30331.
(5) Such quinacridone pigments as set forth in British Patent No. 2,237,679 and Japanese Provisional Patent Publication No. Sho. 49-30332.
(6) Such polycyclic quinone pigments as set forth in British Patent No. 2,237,678 and Japanese Provisional Patent Publications Nos. Sho. 59-184,348, 62-28,738 and 47-18544.
(7) Such bisbenzimidazole pigments as set forth in Japanese Provisional Patent Publications Nos. Sho. 47-30,331 and 47-18543.
(8) Such squalium salt pigments as set forth in U.S. Patent No. 4,396,610 and 4,644,082.
(9) Such azulenium salt pigments as set forth in Japanese Provisional Patent Publications Nos. 59-53,850 and 61-212,542. These may be used alone or in combination of two or more.

Referring to the mixing ratio of the organic photoconductive compound(s) with the binder resin(s), the upper limit of the content of the organic photoconductive compound(s) is determined by their compatibility. The organic photoconductive compound(s), when used in an amount above that upper limit, shows an unpreferable crystallization tendency.
The less the content of the organic photoconductive compound(s), the lower the electrophotographic sensitivity. Thus, it should preferably be used in as much an amount as possible, but within the range in which its crystallization is unlikely to occur. The content of the organic photoconductive compound(s) lies in the rnage of 5 to 120 parts by weight, preferably 10 to 100 parts by weight based on 100 parts by weight of the binder resin(s). The organic photoconductive compounds may be used alone or in admixture of two or more.
The photoconductive layer of the electrophotographic printing plate precursor according to this invention may contain various additives so far used with electrophotographic photosensitive materials. These additives include chemical sensitizers for improving electrophotographic sensitivity and various plasticizers and surfactants for improving film characteristics. The chemical sensitizers used, for instance, include such electron attractive compounds as p-benzoquinone, chloranil, fluoranil, bromanil, dinitrobenzene, anthraquinone, 2,5-dichlorobenzoquinone, nitrophenol, tetrachlorophthalic anhydride, 2,3-dichloro-5,6-dicyanobenzoquinone, dinitrofluorenone, trinitrofluorenone and tetracyanoethylene; and such compounds as set forth in Japanese Provisional Patent Publications Nos. Sho. 58-65439, 58-102239, 58-129439 and 62-71965.
The plasticizers used to improve the flexibility of the photoconductive layer, for instance, include dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, triphenyl phosphate, diisobutyl adipate, dimethyl sebacate, dibutyl sebacate, butyl laurate, methyl phthalyl ethyl glycolate and dimethyl glycol phthalate. These plasticizers may be incorporated in the photoconductive layer in such an amount so as not to cause degradation of its electrostatic characteristics and its sensitivity to etching.
More additionally, the photoconductive layer may contain a photosensitizer in order to promote the decomposition by exposure to light of the binder resin of this invention. This photosensitizer may be used in an amount lying in the range of 0.1 to 20 parts by weight per 100 parts by weight of the binder resin of this invention. For the photosensitizer, all compounds so far known for photosensitive polymersmay be used. For instance, mention is made of such compounds as described in Takahiro Tsunoda, "Photosensitive Resins", Insatsu Gakkai Shuppan-Bu (1972) and Gentaro Nagamatsu and Hideo Inui, "Photosensitive Polymers", Kodan-Sha, (1977) and referred to therein. More illustratively and by way of example alone, preference is given to benzophenone, Michler's ketone, bipheyl, anthraquinone, methyl-β-naphthyl ketone, butyl benzoate and thiobenzoate;
The photoconductive layer of this invention fails to carry thereon the surface potential needed for development at too small a film thickness and tends to suffer planar etching, generally referred to as the "side etching", during its removal at too large a film thickness. In neither case is any satisfactory printing plate obtained. Thus, it is desired that the photoconductive layer be 0.1 µm to 30 µm, preferably 0.5 µm to 10 µm in film thickness.
The electrically conductive support used in this invention may be formed of materials with the surfaces being made hydrophilic - for instance, plastic sheets having their surfaces made electrically conductive, paper made impermeable to solvents and electrically conductive, aluminium sheets, zinc sheets, bimetal sheets such as copper/aluminium and copper/stainless sheets, and trimetal sheets such as chromium/copper/aluminium, chromium/lead/iron and chromium/copper/stainless sheets, and is 0.1 mm to 3 mm, preferably 0:1 mm to 0.5 mm in thickness. Of these sheets, the most preference is given to the aluminium sheets. The aluminium sheets used in this invention may be made of pure aluminium or aluminium alloys containing traces of different atoms, and are not critical in composition. All materials so far known and used in the art may thus be employed.
For use, the aluminium sheet may be sandblasted in conventional manners and anodized. Before sandblasting, it may be degreased with surfactants or alkaline aqueous solutions, as desired, so as to clear its surface of rolling grease. Sandblasting may be achieved by mechanical surface roughening, electrochemically surface fusion and chemically selective surface fusion. The mechanical surface roughening may be achieved by known processes including ball, brush, blast and buff polishing - to name some examples. The electrochemical surface roughening may be achieved by passing a.c. or d.c. currents through hydrochloric or nitric acid electrolytes. As taught in Japanese Provisional Patent Publication No. Sho. 54-63902, both the surface roughening techniques may be used in combination.
The thus surface-roughened aluminium sheet may be alkali etched and neutralized, if required, and then anodized. The electrolytes used for anodization may be sulfuric, phosphoric, oxalic and chromic acids which may be used alone or in admixture, with their concentration being determined depending upon their type. The conditions for anodization are not generally determined, since they vary with the type of electrolyte used. Usually, however, it is desired that the electrolyte be used at a concentration of 1 % by weight to 80 % by weight, a temperature of 5°C to 70°C, a current density of 5 A/cm² to 60 A/cm², a voltage of 1 V to 100 V and an electrolysis time of 10 seconds to 50 minutes. Suitably, the amount of the film to be anodized should lie in the range of 0.1 g/m² to 10 g/m², preferably 1 g/m² to 6 g/m².
After anodization, the aluminium sheet may further or preferably be dipped in an aqueous solution of an alkali metal silicate. Silicate electrodeposition may also be effective to this end, as desclosed in U.S. Patent No. 3,658,662 specification. This is true of such polyvinylsulfonic acid treatments as set forth in DAS 1,621,478.
According to this invention, an alkali-soluble intermediate layer formed of such material as casein, polyvinyl alcohol, ethylcellulose, phenolic resin, styrene/maleic anhydride copolymer and polyacrylic acid may additionally be interleaved between the electrically conductive and photoconductive layers so as to increase adhesion and improve the electrostatic characteristics of the electrophotographic printing plate precursor or for other purposes.
According to this invention, if required, an overcoat may added onto the photoconductive layer so as to improve development characteristics at the time of toner development or image and printing characteristics or other purposes, said overcoat being designed to be removed simultaneously with the photoconductive layer. The overcoat used may be mechanically matted or formed of a matting agent-containing resinous layer. The matting agents used may include silicon dioxide, glass particles, alumina, starch, titanium oxide, zinc oxide, polymer particles such as polymethyl methacrylate, polystyrene and phenolic resin particles, and those set forth in U.S. Patent Nos. 2,701,245 and 2,992,101 specifications. These agents may be used in combination of two or more.
The resin used for the overcoat may optionally be chosen in consideration of its combination with the etchant for removing the photoconductive layer. More illustratively and by way of example alone, mention is made of gum arabic, glue, celluloses, starches, polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyacrylamide, polyvinyl methyl ether, epoxy resin, phenolic resin, polyamide and polyvinyl butyral, which may be used alone or in combination of two or more.
The toners used in this invention are colored to make a discrimination between the non-image and image regions exposed to light. For this invention, all toners so far used as such electrophotographic toners as dry and liquid types of developers, if they are resistant to non-image region-removing etchants and function to prevent the photoconductive layer part of the toner image region from being etched off by this etchant. However, it is preferable to use the liquid type of developer so as to obtain images of high resolution. More preferably, use is made of toners that are hydrophobic and ink-receptive in nature.
For the toner particle component, use may be made of such polymeric materials as polystyrene resins, polyester resins, acrylic ester homopolymers and copolymers, methacrylic ester homopolymers and copolymers, ethylene copolymers, cyclized rubber, vinyl acetate homopolymers and copolymers and vinyl chloride. The toner may also contain colorants - for instance, carbon black, nigrosine pigments and such pigments and dyes as Phthalocyanine Blue, Phthalocyanine Green, Benzidine Yellow, Alkali Blue and Carmine 6B - in such an amount so as not to have an adverse influence on toner's fixation, dispersibility and resistance to etching, and may include various charge regulators and other additives as well.
As the etchants for removing the photoconductive insulating layer of the toner non-image region after toner image formation, use may be made of any desired solvent that can remove that layer. Although not critical, preference is given to alkaline solvents. The "alkaline solvents" referred to in the present disclosure are understood to include an aqueous solution containing alkaline compounds, an organic solvent containing alkaline compounds or a mixture of aqueous solutions with organic solvents, both containing alkaline compounds.
Usable as the alkaline compounds are any desired ones, whether inorganic or organic, for instance, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, sodium phosphate, potassium phosphate, ammonia and amino-alcohols such as monoethanolamine, diethanolamine and triethanolamine.
As already mentioned, water or many organic solvents may be used as etchant solvents. In view of smell or pollution, however, preference is given to etchants that comprise water substantially and may contain various organic solvents, if required.
Preferable organic solvents, for instance, are such lower and aromatic alcohols as methanol, ethanol, propanol, butanol, benzyl alcohol and phenethyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, Cellosolves, and such amino-alcohols as monoethanolamine, diethanolamine and triethanolamine.
The etchants used may contain surfactants, defoamers and other various additives, if required.
Reference will now be made to how to prepare printing plates from the electrophotographic printing plate precursor according to this invention. With the electrophotographic printing plate precursor according to this invention, images are formed by conventional, known electrophotographic processes wherein it is unformly electrified in the dark to form an electrostatic latent image by image exposure. Usable to this end are reflection image exposure using a xenon, tungsten or fluorescent lamp as the light source, contact exposure through a transparent positive film or scanning exposure with laser light, light emitting diodes or the like.
For scanning exposure, use may be made of such laser light sources as helium-neon laser, helium-cadmium laser, argon ion laser, krypton ion laser, YAG laser, ruby laser, nitrogen laser, semiconductor laser like GaAa/GaAlAs and InGaAsP, alexandrite laser, copper vapor laser and erbium laser, or light emitting diodes or liquid crystal shutters (inclusive of a line printer type of light source using a light emitting diode or liquid crystal shutter array).
Then, the above-mentioned electrostatic latent image is developed by suitable development processes, e.g. dry development processes (cascade, magnetic brush and powder cloud processes) or liquid development processes. Among others, the liquid development processes, because of being able to form fine images, are best-suited for making printing plates.
Moreover, positive-positive development or negative-positive development by reverse development with the application of a suitable bias voltage is possible. The formed toner image is then fixed by heat, pressure, light irradiation, solvent or the like. While using this toner image as a resist, the photoconductive layer part of the non-image region is etched off to prepare a printing plate.
In the description that follows, some examples of synthesis of the binder resins according to this invention will be explained specifically but not exclusively.

Synthesis Example 1 ... Synthesis of Binder Resin P-1

A mixed solution consisting of 75 g of benzyl methacrylate, 25 g of methacrylic acid, 2 g of thioglycolic acid and 200 g of methoxypropyl acetate was heated to a temperature of 75°C in a nitrogen stream.
Added to this solution were 1.5 g of azobisisobutyronitrile (A.I.B.N.) for a 4-hour reaction, and an additional 0.8 g of A.I.B.N. was added for a further 3-hour reaction. After cooling, the reaction product was re-precipitated in 1 liter of hexane, followed by filtration and precipitate drying.
The polymer, obtained in powdery forms with a yield of 80 g, was found to have a weight-average molecular weight or Mw of 8 x 10³.

Synthesis Examples 2-13 ... Synthesis of Binder Resins P-2 to P-13

In order to prepare various polymers, the procedures of Ex. 1 were followed with the exception that the mercapto compounds, tabulated on the next page, were used in place of the benzyl methacrylate and thioglycolic acid. These polymers were found to have Mws in the range of 6 x 10³ to 9 X 10³.

Synthesis Example 14 ... Synthesis of Binder Resin P-14

A mixed solution consisting of 50 g of benzyl methacrylate, 30 g of ethyl methacrylate, 20 g of acrylic acid and 200 g of methoxypropyl acetate was heated to a temperature of 85°C in a nitrogen stream. Added to this solution were 8 g of 4,4'-azobis(4-cyanovaleric acid) (A.B.C.V.) for a 4-hour reaction, and an additional 1 g of A.I.B.N. was added for a further 3-hour reaction.
After cooling, the reaction product was reprecipitated in 1 liter of hexane, followed by filtration and precipitate drying. The polymer, obtained in powdery forms with a yield of 83 g, was found to have a weight-average molecular weight or Mw of 7.8 X 10³.

Synthesis Example 15 ... Synthesis of Binder Resin P-15

A mixed solution consisting of 80 g of 2-chlorophenyl methacrylate, 20 g of 2-carboxyethyl acrylate, 3 g of thiosalicylate and 200 g of methoxypropyl acetate was heated to 75°C in a nitrogen stream. Added to this solution was 1 g of A.B.C.V. used in Ex. 14 for a 5-hour reaction, and an additional 0.6 g of A.B.C.V. was added for a further 3-hour reaction. The obtained polymer had an Mw of 7.5 X 10³.
In what follows, the present invention will now be explained in greater detail with reference to the following example. However, this invention is understood to be not limited to such examples, unless it departs from the purport of the invention. In the examples, the "parts" are all given by weight.

Example 1

One (1) part of the following trisaszo compound as a charge generator,

2.0 parts of the following hydrazone compound as an organic photoconductive compound,

10.0 parts of Copolymer P-1 and 100 parts of tetrahydrofuran were put together with glass beads in a 500-ml glass vessel, and then dispersed with a paint shaker (made by Toyo Seiki Seisakusho K.K.) for 60 minutes. After that, the glass beads were removed by filtration to prepare a photoconductive layer-forming dispersion.
Then, this dispersion was coated on a sandblasted, 0.25-mm thick aluminium sheet and dried thereon to prepare an electrophotographic printing plate precursor, which includes a photoconductive layer having a thickness of 5.1 µm on dry basis.

Comparative Examples A-C

The procedures of Ex. 1 were followed with the exception that the following resins were used in lieu of the copolymer P-1, thereby preparing electrophotographic photosensitive materials.

Comp. Ex. A

Copolymer A
Styrene/maleic anhydride copolymer (having a maleic anhydride content of 33 mol %)

Comp. Ex. B

Copolymer B
Vinyl acetate/crotonic acid copolymer (made by Kanebo NSC Co., Ltd; RESYN-28-1310)

Comp. Ex. C

Copolymer C
Benzyl methacrylate/methacrylic acid (at a weight ratio of 75/25; Mw = 4.0 x 10⁴
The printing plates prepared in this manner were each used in conventional manners with an offset printing machine "Hamada Star 600CD" to estimate their printabilities (resistance to printing, etc.).
The results are reported in Table 1.
The characteristics set out in Table 1 were estimated in the following manners.

Note 1. Electrostatic Characteristics

The photosensitive material samples were each charged by corona discharge to a voltage of + 7 kV for 20 seconds in a dark room at 20°C and 65% RH and 30°C and 80% RH using a paper analyzer ("Paper Analyzer SP-428" manufactured by Kawaguchi Denki K.K.). Ten (10) seconds later, its surface potential V₁₀ were measured. The sample was subsequently kept stationary in the dark for 180 seconds to measure its potential V₁₉₀, whereby a potential retention or a dark decay retention - DRR in % - after 180-second decay was found by:

$(V₁₉₀/V₁₀) x 100 (%).$

After electrified on the surface to + 400 V by corona discharge, the photoconductive layer was irradiated with visible light at an illumination of 2.0 luxes to measure the time taken for the surface potential V₁₀ to decay to 1/2, from which the amount of exposure E₁/₂ in lux·second was in turn calculated.
Likewise, the time taken for V₁₀ to decay to 1/10 was measured to find the amount of exposure E_1/10 in lux·second.

Note 2. Image Quality

The photosensitive material samples were each allowed to stand for a whole day and night under ambient conditions at 20°C and 65% RH and 30°C and 80% RH.
After electrified to a surface potential of + 450 V in the dark, the sample was exposed to 633-nm light with an He-Ne laser at an exposure amount of 30 erg/cm², as measured on its surface. This was then developed with a liquid developer at a bias voltage of 30 V applied to opposite electrodes to obtain a toner image, said liquid developer being prepared by dispersing 5 g of toner polymethyl methacrylate particles (with a particle size of 0.3 µm) in 1 liter of "Isoper H" manufactured by Esso Standard Co., Ltd. and adding 0.01 g of a charge regulator soybean oil lecithin to the dispersion.
The toner image was then fixed by 1-minute heating at 100°C. A visual estimation was made of how faithfully the original image was reproduced on the printing negative obtained after plate-making (i.e., fogging and image quality).

Note 3. Etching Processability

The printing negatives after plate-making, obtained according to Note 2., were each treated by dipping it in an etchant prepared by diluting 40 parts, of potassium silicate, 10 parts of potassium hydroxide and 100 parts of ethanol with 800 parts of water, washed with water for 30 seconds and dried with a dryer.
With the use of a loupe of 60 magnifications manufactured by PEAK Co., Ltd., visual estimations were made of to what degree the film remained in the non-image region of each printing negative and whether or not fine lines and characters were found in the image region.

Note 4. Resistance to Printing

The photosensitive material samples were each formed into a plate under the same conditions as mentioned in Note 1., provided thereon with a toner image, etched under the same conditions as stated in Note 3., and rubberized to prepare an offset printing negative.
The printing negative was used with an offset printing machine - "Oliver 52 Model" manufactured by Sakurai Seisakusho K.K. to make an estimation of how much prints were obtained until their non-image regions were stained and their image regions degraded in image quality. It is noted that the more the number of prints, the better the resistance to printing.
The negative of Comparative Example C was satisfactory in terms of electrostatic characteristics, but was much inferior to the present negatives in terms of photosensitivity - E_1/10 and E_1/100. The negatives of Comparison Examples A and B were less than satisfactory in terms of D.R.R. and photosensitivity - E, which were found to suffer a further degradation when placed under varied ambient conditions.
A close examination of the quality of the images obtained with these photosensitive materials indicated that it was the present ones that could reproduce excellent images even under varied ambient conditions.
Then, these samples were etched into printing plates. As a result, it was found that the non-image regions according to this invention and Comparative Examples A and B could be completely etched out within a time as short as 5 seconds, but that according to Comparative Example C was not, leaving a substantial part of the film non-etched.
Further, the printing plates were used as offset master negatives for printing. As a result, it was only the negatives according to this invention that could provide stain-free, clear-cut prints of as much as 100,000. The negative according to Comparative Example C, because of being poor in sensitivity to etching, provided prints with their non-image regions being seriously stained, already in an early stage of printing.
Referring to Comparative Examples A and B, the non-image regions were well-etched without stain at all, but the reproduced images were far from satisfactory, providing prints with image deficiencies already in an early stage of printing.
As described above, it was only the printing plate precursor according to this invention that could satisfy electrophotographic characteristics and printing properties.

Examples 2 - 10

The procedures of Example 1 were repeated with the exception that the copolymers enumerated in Table 2, given later, were used in place of Copolymer P-1, thereby preparing printing negatives for making electrophotographic plates.
In similar manners as used in Example 1, estimations were made of electrostatic characteristics, image quality and printability. Table 2 sets out the electrostatic characteristics measured under severe conditions - at 30°C and 80% RH.
The photosensitive materials were all of improved performance, as with Example 1, and equivalent to that of Example 1 in terms of image quality and printability - such resistance to printing so as to enable at least 100,000 copies to be printed.

Example 11

The procedures of Example 1 were repeated with the exception that as the organic photoconductive compound the following oxadiazole compound was used for the hydrazone compound, thereby preparing an electrophotographic printing plate precursor.
The same measurement as in Ex. 1 was carried out. As a result, it was found that all the properties were identical with those of Ex. 1.

Example 12

Twenty five (25) parts of the following organic photoconductive hydrazone compound, 75 parts of Copolymer P-9 as a binder resin and 1.18 parts of the following thiopyrylium compound as a sensitizing dye were dissolved in a mixed solvent consisting of 510 parts of methylene chloride and 150 parts of methyl Cellosolve acetate.
The resulting solution was coated on a sandblasted, 0.25-mm thick aluminium sheet and dried thereon to prepare an electrophotographic printing plate precursor, which included a photoconductive layer having a thickness of 5.3 µm on dry basis.
Then, this sample was exposed to 632-nm light with an He-Ne laser after electrification to a surface potential of + 450 V in the dark, and was then developed with a liquid developer prepared by dispersing 10 g of toner polymethyl methacrylate particles - of 0.3 µm in particle size - in 1 liter of "Isoper H" manufactured by Esso Standard Co., Ltd. and adding 0.01 g of a charge regulator soybean lecithin. As a result, a clear-cut, positive toner image could be obtained, wherein the regions, in which writing had been initiated and ceased, were both fog-free.
Further, the toner image was fixed by heating at 100°C. The obtained electrophotographic printing plate precursor was immersed for about 5 seconds in an etchant obtained by dissolving 70 g of sodium metasilicate hydrate in 140 ml of glycerin, 550 ml of ethylene glycol and 150 ml of ethanol, and lightly brushed with a water stream, whereby the toner-free, non-image region could be completely cleared of the photoconductive layer.
The thus prepared printing plate was used with a printing machine "Hamada Star 600CD" for printing in conventional manners. In consequence, 100,000 clear-cut copies without stain on the non-image regions could be printed.

Example 13 and Comparative Examples D to F

One point nine (1.9) parts of an X type of non-metal phthalocyanine - made by Dainippon Ink & Chemicals, Inc. - as an organic photoconductive compound, 0.15 parts of the following additive thiobarbituric acid compound,

17 parts of Copolymer P-1 and 100 parts of a mixed solution consisting of tetrahydrofuran and cyclohexane at a 8:2 weight ratio were placed along with glass beads in a 500-ml glass vessel, and dispersed for 60 minutes by means of a paint shaker. After that, the glass beads were filtered out to obtain a photoconductive layer-forming dispersion.
Then, this dispersion was coated on a sandblasted, 0.25-mm thick aluminium sheet and dried thereon to prepare an electrophotographic printing plate precursor, which included a photoconductive layer having a thickness of 6.0 µm on dry basis. Comparative Examples D to F
The procedures of Ex. 13 were followed with the exception that the following resins were used for Copolymer P-1, thereby preparing electrophotographic photosensitive materials.
Comp. Ex.
D ... Copolymer B
E ... Copolymer C
F ... Copolymer D
Benzyl methacrylate/methacrylic acid at a 75/25 weight ratio and with Mw = 4 x 10⁴.
The electrostatic characteristics and image quality of these photosensitive materials, as measured, are reported in Table 3.
The characteristics set out in Table 2 were estimated in the following manners.

5. Electrostatic Characteristics

The photosensitive material samples were each charged by corona discharge to a voltage of + 6 kV for 20 seconds in a dark room at 20°C and 65% RH and 30°C and 80% RH using a paper analyzer ("Paper Analyzer SP-428" manufactured by Kawaguchi Denki K.K.). Ten (10) seconds later, its surface potential V₁₀ were measured.
The sample was subsequently kept stationary in the dark for 180 seconds to measure its potential V₁₉₀, whereby a potential retention or a dark decay retention - DRR in % - after 180-second decay was found by:

$(V₁₉₀/V₁₀) x 100 (%).$
After electrified on the surface to + 400 V by corona discharge, the photoconductive layer was irradiated with monochromatic light of 780 nm in wavelength to measure the time taken for the surface potential V₁₀ to decay to 1/2, from which the amount of exposure E_1/2 in erg/cm² was in turn calculated.
Likewise, after electrification to + 400 V by corona discharge, the photoconductive layer was irradiated with monochromatic light of 780 nm in wavelength. The time taken for V₁₀ to decay to 1/10 was the measured to find the amount of exposure E_1/10 in erg/cm².

Note 6. Image Quality

The photosensitive material samples were each allowed to stand for a whole day and night under ambient conditions of 20°C 65 % RH and 30°C 80 % RH.
After electrified to a surface potential of + 5 kV, the sample was exposed to laser light emanating from a 2.8-mW output Ga/Al/As semiconductor laser (having an oscillation wavelength of 780 nm) at a dose of 60 erg/cm², as measured on its surface, a pitch of 25 µm and a scanning speed of 300 m/sec., then developed with the same liquid developer as used in Ex. 1 and fixed, and finally irradiated with light to obtain a reproduced image. The image was visually estimated on whether or not it suffered fogging and its quality.
Image-taking was carried out at 20°C 65 % RH and 30°C 80 % RH.
Referring to the electrostatic characteristics of the respective photosensitive materials, Comparative Example D was inferior to the rest. Comparative Example E, on the other hand, was better than D in terms of V₁₀, D.R.R. E_1/2 and E_1/10. However, their changes, if not large, were insufficient under severer conditions - at 30°C and 80 % RH.
By contrast, the photosensitive materials according to this invention and Comparative Example F were much more improved in terms of every electrostatic property and showed very small changes even under ambient conditions. However, Comparative Example F was inferior to this invention in terms of sensitivity of light.
Actual image representations obtained on the photosensitive materials by semiconductor laser light scanning were in keeping with the above-mentioned electrostatic characteristics; this means that the present invention was better than the comparative examples.
Further, printing was done with the offset printing negatives obtained from the photosensitive materials in similar manners as mentioned in Ex. 1. As a result, it was only the present negative that could provide 100,000 prints. Examples 14 to 24
The procedures of Ex. 13 were repeated with the exception that the copolymers expressed by the formula, given below, and set out on the following page were used for Copolymer P-1, thereby preparing electrophotographic printing plate precursor.
The properties of the obtained negatives were measured in similar manners as mentioned in Ex. 13. The photosensitive material all showed satisfactory electrostatic characteristics and image quality. Even under severer conditions - at 30°C and 80 % RH, good performance was achieved, as with Example 13.
The materials were etched into offset master negatives. As a result, the non-image regions could be rapidly etched out. Actual printing could provide prints with fog-free, clear-cut images even after printing of 50,000 copies.

Claims

An electrophotographic printing plate precursor in which an electrically conductive support includes thereon a photoconductive layer containing at least a photoconductive compound and a binder resin and which is formed into a printing plate by exposing it to an image to form a toner image and, thereafter, clearing a non-image region other than the toner image region of the photoconductive layer, wherein:
the binder resin of said photoconductive layer is a copolymer containing at least one monomeric component represented by the following formula (I) and at least one monomeric component having an acidic functional group copolymerizable with said first monomeric component,
said copolymer having an acidic functional group bonded to one terminal of its main chain and having a weight-average molecular weight lying in the range of 1 x 10³ to 1 x 10⁴.
wherein R stands for an aliphatic or aryl group.