JPH0222095A - Desensitizing treatment of planographic printing plate - Google Patents

Abstract

PURPOSE:To densensitize a planographic printing plate while removing the contaminate on said printing plate by treating the planographic printing plate with a plate surface protective agent containing water-soluble carboxyalkylated starch whose carboxyalkyl group introducing rate is 0.03-0.5. CONSTITUTION:A plate surface protective agent containing water-soluble carboxyalkylated starch whose carboxyalkyl group introducing rate is 0.03-0.5 is prepared. A planographic printing plate, wherein an image part is composed of the toner image formed on the photoconductor layer provided on a conductive substrate by an electrophotographic process and a non-image part is the conductive substrate is treated with the aforementioned prepared plate surface protective agent to perform the desensitizing treatment of the planographic printing plate. By this treatment, the removal of the contaminate causing substance from the planographic printing plate and the protection of the surface of said printing plate are performed simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for desensitizing a lithographic printing plate formed by an electrophotographic process.

[Conventional technology]

Today, as lithographic offset printing plates, PS plates that use positive-working photosensitizers whose main components are diazo compounds and phenolic resins, and negative-working photosensitizers whose main components are acrylic monomers and polymers are in practical use. Since these all have low sensitivity, plate making is performed by contact exposure of a silver halide photographic film master plate on which an image has been recorded in advance. On the other hand, advances in computer image processing, large-capacity data storage, and data communication technology have enabled manuscript input, correction, and
Electronic editing systems have been put into practical use, in which everything from editing and layout to page assembly is controlled by a computer, and can be immediately output to a terminal plotter in a remote location using high-speed communications networks or satellite communications. In particular, electronic editing systems are in high demand in the field of newspaper printing, which requires immediacy. Furthermore, even in fields where originals are preserved in the form of original film, and printing plates are reproduced as needed based on this, with the development of ultra-high capacity recording media such as optical discs, the originals are being stored on these recording media. It is thought that it will be stored as digital data.

However, direct printing plates that create printing plates directly from the output of terminal plotters have hardly been put into practical use.
Even in places where electronic editing systems are in operation, the current situation is that output is performed on silver halide photographic film, and based on this, printing plates are indirectly created by contact exposure to PS plates. This is the light source of the output block (e.g. He-N
This is because it is difficult to develop a direct printing plate with a sensitivity high enough to make a printing plate within a practical time using e-lasers, semiconductor lasers, etc.).

Electrophotographic photoreceptors are considered as photoreceptors with high photosensitivity that can provide direct printing plates.

Conventionally, as printing plate materials (printing original plates) using electrophotography, for example, Japanese Patent Publication No. 47-47610, Japanese Patent Publication No. 48
-40002, Special Publication No. 18325, Special Publication No. 18325, Special Publication No. 18325
Zinc oxide-resin dispersion offset printing plate materials described in Japanese Patent Publication No. 1-15766 and Japanese Patent Publication No. 51-25761 are known, and after forming a toner image by electrophotography, the non-image area is rendered non-greasy. For this purpose, it is used after wetting with a desensitizing solution (for example, a ferrocyanate or an acidic aqueous solution with a ferricyanate). Offset printing plates treated in this way have a stiffness resistance of approximately 5,000 to 10,000 sheets, making them unsuitable for printing beyond this 1. Also, if the composition is made suitable for desensitization, the electrostatic properties deteriorate. However, there are also drawbacks such as deterioration of image quality. It also has the disadvantage of using harmful cyanide as a fat-freeing solution.

Special Publication No. 37-17162, Special Publication No. 38-7758,
In the organic photoconductor-resin printing plate materials described in Japanese Patent Publication No. 46-39405 and Japanese Patent Publication No. 52-2437, for example, oxazole or oxadiazole compounds are combined with a styrene-maleic anhydride copolymer. An electrophotographic photoreceptor is used in which a photoconductive insulating layer is formed on a grained aluminum plate, and after a toner image is formed on this photoreceptor by electrophotography, the non-image area is dissolved with an alkaline organic solvent. It is removed (etched) to form a printing plate.

Further, JP-A-57-147656 discloses an electrophotographic photoreceptor containing a hydrazone compound and barbylic acid or thiobarbylic acid.

In addition, JP-A-59-147335, JP-A-59-
Dye-sensitized electrophotographic photoreceptors are known, such as those described in Japanese Patent Application Laid-open No. 152456, Japanese Patent Application Laid-open No. 168462, Japanese Patent Application Laid-Open No. 145495-1987, and the like. However, substances in the electrophotographic photosensitive layer are adsorbed to the non-image areas of printing plates made using the above electrophotographic photoreceptor and contaminate the non-image areas, resulting in ink adhering to the non-image areas of printed matter. There was a problem in that it became unusable as a printing plate due to the occurrence of "stains".

On the other hand, when making a lithographic printing plate, a plate surface protective agent (so-called gum liquid) is applied in the final step (ie, after etching).

The purpose of applying gum liquid is not only to protect the hydrophilicity of non-image areas, but also to modify images such as adding or erasing image areas, to preserve the image after making the plate until it is printed, or to preserve it until it is reused, and to install it in the printing machine. This is to prevent stains caused by the adhesion of fingerprints, oil, fat, dust, etc. during handling and handling, and to protect against scratches, etc., and also to suppress the generation of oxidation stains. Conventionally, gum arabic, cellulose gum, or an aqueous solution of a water-soluble polymeric substance having a carboxyl group in the molecule has been used as a gum solution for lithographic printing plates. However, when a large amount of organic staining substances adhere to these gum liquids, their desensitizing ability is poor and they become stained.

When stains occur due to the above causes, a step is required to remove organic stains, and stain removal liquids used for this purpose are also commercially available (for example, Plate Cleaner CU-3 manufactured by Fuji Photo Film ■).

However, the addition of such a step is not preferred due to the problem of reduced workability.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide a method for desensitizing a lithographic printing plate, which is useful for removing stain-causing substances from a lithographic printing plate formed by an electrophotographic process and at the same time protecting the plate surface. .

A further object of the present invention is to provide a desensitization treatment method for lithographic printing plates formed by an electrophotographic process by using a plate surface protective agent having particularly excellent desensitization ability.

[Means for solving problems]

One of the above objects is to use a water-soluble lithographic printing plate in which the image area consists of a toner image formed by an electrophotographic process on a photoconductor layer provided on a conductive substrate, and the non-image area is a conductive substrate. A desensitizing treatment for a lithographic printing plate, characterized in that it is treated with a plate surface protective agent containing a carboxyalkylated starch and having an introduction rate of carboxyalkyl groups in the carboxyalkylated starch from 0.03 to 0.5. It has been found that this can be achieved by a method.

This carboxyalkylated starch accounts for 90% by weight of the starch skeleton.
It is preferable that the above is an amylopectin type.

Specific examples of carboxyalkylated starch, which is the main component of the plate surface protectant used in the present invention, include carboxymethylated starch, carboxyethylated starch, carboxypropylated starch, and the like. Preferred is carboxymethylated starch. These carboxyalkylated starches are generally synthesized by reacting an alkaline suspension of starch with a monochlorocarboxylic acid such as monochloroacetic acid, monochloropropionic acid, or monochlorobutyric acid.

The introduction rate of carboxyalkyl groups (the number of carboxyalkyl groups introduced per glucose unit of starch) is determined by the charging ratio of starch and monochlorocarboxylic acid, reaction conditions, etc., but theoretically, Three hydroxyl groups of glucose residues in starch are substituted, that is, an introduction rate of up to 3 is possible. The introduction rate can be determined by preparing the carboxylic acid in advance and subjecting it to neutralization titration.

The present inventors tested aqueous solutions of carboxymethylated starch with various introduction rates as plate surface protectants, and found that the introduction rate was 0.
It has been found that suitable results can be obtained in the range of 0.03 to 0.5. More preferably, it is in the range of 0.05 to 0.3.

If the introduction rate is less than 0.03, its fat-unfavorable ability is comparable to that of general soluble starch or dextrin, and the object of the present invention cannot be achieved. On the other hand, if the introduction rate exceeds 0.5, it has the disadvantage that printing stains are likely to occur when the printing plate is stored under harsh conditions such as high temperatures.

On the other hand, starch has two types: amylose, which has a linear structure in which glucose residues are linked only through 1,4-glucosidic bonds, and amylopectin, which has a branched structure with mainly 1,4-glucosidic bonds and 1,6-glucosidic bonds. is known, and the composition of general starch is said to be 20 weight percent amylose type and 80 weight percent amylopectin type.

The present inventors conducted tests using various ratios of amylose type and amylopectin type carboxyalkylated starch as a plate surface protective agent, and found that a plate surface protective agent obtained from carboxymethylated starch containing 90% by weight or more of amylopectin type It has been found that excellent hydrophilicity can be obtained by using it in lithographic printing formed by an electrophotographic process. More preferably, the carboxymethylated starch is entirely of the amylopectin type.

In the present invention, "water soluble" includes not only cold water soluble but also hot water soluble.

The content of carboxyalkylated starch in the plate surface protective agent used in the present invention is preferably about 0.1 to 40% by weight, more preferably 0.5 to 25% by weight.

The carboxyl group of carboxyalkylated starch is usually a sodium salt or potassium salt, and such metal salts are preferably used in the present invention.

In the present invention, other water-soluble organic polymer compounds can be used in combination. Examples of such polymer compounds include cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, starch derivatives such as roasted starch, pregelatinized starch, dextrin, and dialdehyde starch, alginates, locust bean gum, and strafukun. Examples include natural or semi-synthetic polymeric compounds such as sterabic, pullulan and the like. Furthermore, synthetic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyvinyl methyl ether, polyethylene oxide, copolymers of vinyl methyl ether and maleic anhydride, and copolymers of vinyl acetate and maleic anhydride are also used. can. Furthermore, when gum arabic is used in combination, the object of the present invention can be achieved with a significantly smaller amount of gum arabic than conventionally used amounts. Plate protective agents are generally used in the acidic region, i.e. pH 2.
, 5 to 6 is more advantageous.

In order to adjust the pH value to 2.5 to 6, mineral acids, organic acids, or inorganic salts are generally added to the plate surface protectant.

The amount added is usually 0.01 to 2% by weight.

The above organic acids include citric acid, acetic acid, oxalic acid, malonic acid, p
-Toluenesulfonic acid, tartaric acid, malic acid, lactic acid, levulinic acid, organic phosphonic acid, etc. are used, and as mineral acids, nitric acid, sulfuric acid, phosphoric acid, etc. are useful.

Mineral acids, organic acids, inorganic salts, etc.
You may use more than one species together. Furthermore, by adding a surfactant to the plate surface protective agent of the present invention, the surface condition of the coating film, etc. can be improved. Surfactants that can be used include anionic surfactants and nonionic surfactants.

Examples of anionic surfactants include aliphatic alcohol sulfate ester salts, aliphatic alcohol phosphate ester salts, dibasic fatty acid ester sulfonate salts, fatty acid amide sulfonate salts, alkylaryl sulfonate salts, formaldehyde condensed naphthalene sulfonate salts, etc. used.

As the nonionic surfactant, polyethylene glycol alkyl ether, polyethylene glycol alkyl ester, sorbitan alkyl ester, polyoxypropylene polyoxyethylene ether, etc. are used.

Two or more kinds of these surfactants can be used in combination. The amount used is not particularly limited, but the preferred range is 0.01 to 10% by weight of the plate surface protectant.

In addition to the above components, lower polyhydric alcohols such as glycerin, ethylene glycol, and triethylene glycol can also be used as lubricants if necessary. The content of these lubricants in the composition is suitably 0.1 to 5.0% by weight, more preferably 0.5 to 3.0% by weight. In addition to the above, preservatives and the like can be added to the plate surface protectant in the present invention.

For example, benzoic acid and its derivatives, phenol, formalin, sodium dehydroacetate, etc. can be added in an amount of 5 to 2.0% by weight of O, OO.

Furthermore, the method of using the plate surface protective agent used in the present invention will be explained.

An appropriate amount of the plate surface protective agent used in the present invention is poured onto the etched lithographic printing plate prepared by the electrophotographic process described below, and rubbed with a sponge so as to coat the entire surface of the plate, followed by drying. A similar purpose can also be achieved by a commercially available gum coater that automates this process. As a result, stain-causing substances on the printing plate are removed, non-image areas are rendered fat-free, and the printing plate can be further protected.

When starting printing, the gum on the printing plate is generally washed with water to remove the so-called gum.) After that, printing may be carried out according to the usual procedure, or the non-fatting liquid used in the present invention may be washed with so-called gum remover. You can also start printing immediately without dropping the printer. Furthermore, during printing, it is possible to obtain satisfactorily clear printed matter immediately after printing, without producing many defective printed matter as in the conventional case.

The present invention will be explained in more detail below.

Conductive substrates used in electrophotographic photoreceptors include plastic sheets with conductive surfaces or papers made particularly solvent-impermeable and conductive, aluminum plates, zinc plates,
Or bimetal plates such as copper-aluminum plate, copper-stainless steel plate, chrome-copper plate, etc., or hydrophilic surfaces such as tri-metal plates such as chrome-copper-aluminum plate, chrome-lead plate, chrome-copper-stainless steel plate, etc. The thickness of the conductive substrate is preferably 0.1 to 3 mm, particularly preferably 0.1 to 0.5 mm. Among these substrates, aluminum plates are preferably used. The aluminum plate used in the present invention is a plate-shaped body such as pure aluminum whose main component is aluminum or an aluminum alloy containing a small amount of foreign atoms, and its composition is not specified, and publicly known and publicly used materials are used as appropriate. You can.

This aluminum plate can be used after being grained and anodized using a known method. Prior to the graining treatment, in order to remove rolling fat from the surface of the aluminum plate, degreasing treatment with a surfactant or an alkaline aqueous solution is performed, if desired, and then graining treatment is performed. Graining treatment methods include a method of mechanically roughening the surface, a method of electrochemically dissolving the surface, and a method of selectively dissolving the surface chemically. As a method for mechanically roughening the surface, a known method called a ball polishing method, a brush polishing method, a blast polishing method, a Huff polishing method, etc. can be used. Further, as an electrochemical surface roughening method, there is a method in which alternating current or direct current is used in a hydrochloric acid or nitric acid electrolyte. Furthermore, a method combining both methods can also be used, as disclosed in Japanese Patent Application Laid-Open No. 54-63902.

The aluminum plate thus roughened is subjected to alkali etching treatment and neutralization treatment as required.

The aluminum plate thus treated is anodized. As the electrolyte used in the anodizing treatment, sulfuric acid, phosphoric acid, oxalic acid, chromic acid, or a mixed acid thereof is used, and the electrolyte and its concentration are determined as appropriate depending on the type of electrolyte. Since the treatment conditions for anodizing vary depending on the electrolyte used, it cannot be generally specified, but for boat fishing, the electrolyte concentration is 1 to 80% by weight, and the liquid temperature is 5 to 70%.
°C1 current density 5-60A/d, voltage 1-100V,
It is preferable that the electrolysis time is in the range of 10 seconds to 50 minutes. The amount of anodic oxide film is preferably 0.1 to 10 g/rd,
More preferably, it is in the range of 1 to 6 g/rd.

A known electrophotographic photosensitive layer (photoconductive layer) is provided on the conductive substrate thus obtained to obtain an electrophotographic photoreceptor.

As the photoconductive material used in the photoconductive layer, many conventionally known organic or inorganic compounds can be used. For example, known dispersible photoconductive materials include inorganic photoconductive materials such as selenium, selenium-tellurium, cadmium sulfide, zinc oxide, and the like. In addition, as organic photoconductive compounds, 1) triazole derivatives described in US Pat. No. 3,112,197, etc., 2) oxadiazole derivatives, described in US Pat. No. 3,189,447, etc., 3) Imidazole derivatives described in Japanese Patent Publication No. 37-16096, etc., 4) U.S. Pat.
-10983, JP-A-51-93224, JP-A-55-
No. 108667, No. 55156953, No. 56-36
Polyarylalkane derivatives described in 656 specification, publications, etc. 5) U.S. Pat. No. 3,180,729, U.S. Pat. No. 4,278,746
No. 55-88064, 55-88065, 49-105537, 55-51086, 56-80051, 56-88141, 57-
No. 45545, No. 54-112637, No. 55-74
Virapurin derivatives and pyrazolone derivatives described in No. 546 specification, gazette, etc. 6) U.S. Patent No. 3,615,404, Japanese Patent Publication No. 51-10
105, 46-3712, 47-28336, JP-A-54-83435, JP-A-54-110836, JP-A-54-119925 specifications, publications, etc.; 7) U.S. Patent Nos. 3,567,450, 3,180,703, 3,240,597, 3,658,520, and 423
No. 2103, No. 4175961, No. 4012376, West German Patent (DSA) No. 1110518, Special Publication No. 1977
No.-35702, No. 39-27577, JP-A-55-
No. 144250, No. 56-119132, No. 56-2
8) Amino-substituted chalcone derivatives as described in US Pat. No. 3,526,501; 9) N as described in US Pat. No. 3,542,546.

N-virapurine derivatives, 10) Oxazole derivatives described in US Pat. No. 3,257,203, etc., 11) Styryl anthracene derivatives described in JP-A-56-46234, etc., 12) JP-A-54-110837, etc. Fluorenone derivatives described in 13) U.S. Pat. No. 3,717,462, JP-A-54-59
No. 143 (corresponding to U.S. Pat. No. 4,150,987), No. 5
No. 5-52063, No. 55-52064, No. 55-4
No. 6760, No. 55-85495, No. 57-1135
0, US Pat. No. 57-148749, US Pat. No. 57104144, publications, etc.; 14) US Pat.
No. 4265990, No. 4273846, No. 42
Benzidine derivatives described in JP-A-58-190953 and JP-A-59-9554, etc.
No. 0, No. 5997148, No. 59-195658,
Examples include stilhen derivatives described in JP-A No. 62-36674 and the like.

Further, in addition to the above-mentioned low-molecular photoconductive compounds, the following high-molecular compounds can also be used.

16) Polyvinylcarbazole and derivatives thereof described in Japanese Patent Publication No. 34-10966, 17) Japanese Patent Publication No. 43-18674 and Japanese Patent Publication No. 43-19192
18) Vinyl polymers such as polyvinylpyrene, polyvinylanthracene, poly-2-vinyl-4-(4'-dimethylaminophenyl)-5-phenyloxazole, and poly3-vinyl-N-ethylcarbazole described in the publication No. 18) Polymers such as polyacenaphthylene, polyindene, and copolymers of acenaphthylene and styrene described in Japanese Patent Publication No. 19193-1970, 19) Pyrene formaldehyde resins, frompyrene-formaldehyde resins, and ethyl resins described in Japanese Patent Publication No. 13940-1983. Condensation resins such as carbazole-formaldehyde resins, 20) JP-A-56-90883, JP-A-56-16155
In addition to the various triphenylmethane polymers described in Publication No. 0, various pigments, dyes, etc. can be used for purposes such as improving the sensitivity of the photoconductor and giving it a desired photosensitive wavelength range. I can do it. Examples of these include: 1) U.S. Pat. No. 4,436,800, U.S. Pat.
No. 59-78356, No. 60179746, No. 61
-148453, No. 61-238063, Special Publication No. 6
Monoazo, bisazo, and trisazo pigments described in No. 0-5941, No. 60-45664, etc. 2) U.S. Patent No. 3
Phthalocyanine pigments such as metal phthalocyanine or metal-free phthalocyanine described in No. 397086 and No. 4666802, etc. 3) Perylene pigments described in U.S. Pat. No. 3,371,884, etc. 4) Indigo and thioindigo derivatives described in British Patent No. 2,237,680, etc. ) Quinacridone pigments described in British Patent No. 2237679, etc. 6) British Patent No. 2237678, Japanese Patent Application Laid-open No. 59-18
7) Bisbenzimidazole pigments described in JP-A No. 47-30331, etc. 8) U.S. Pat. Nos. 4,396,610 and 4,644,082.
Squarium base pigments described in JP-A No. 59-53850 and JP-A No. 61-21254.
The azulenium salt pigment described in No. 2, etc. Also, as a sensitizing dye, see "Sensitizer" p. 125 (Kodansha 81987) r Electrophotography J 12 9 (197
3) “Organic Synthetic Chemistry J 24 No. 111010
(1966) and the like can be used. For example, 10) U.S. Pat. No. 3,141,770;
Pyrylium dyes described in Japanese Patent Publication No. 4283475, Japanese Patent Publication No. 48-25658, Japanese Patent Application Laid-Open No. 62-71965, etc. 11) pplied 0ptics 5up
ple+nent 3 50 (1969), JP-A-50-39548, etc. 12) Cyanine-based dyes, described in U.S. Pat. No. 3,597,196, etc. 13) JP-A-60-163,047, JP-A-59- 1645
Styryl dyes described in No. 88, No. 60252517, etc. These organic photoconductive materials may be used alone or in combination of two or more.

In the photoconductive layer of the present invention, for purposes such as improving sensitivity,
For example, electron-withdrawing compounds such as trinitrofluorenone, chloranil, and tetracyanoethylene, JP-A-58-6
No. 5439, No. 58-102239, No. 5B-129
Examples include compounds described in No. 439 and No. 62-71965.

In a photoreceptor for electrophotographic engraving, the photoconductive compound itself may have film properties, but if the photoconductive compound does not have film properties, a binding resin can be used. As the binding resin, resins known in the field of electrophotography can be used. In order to create a printing plate using a photoreceptor for electrophotographic engraving, it is necessary to finally remove the photoconductive layer in the non-image area, but this process is difficult due to the solubility of the photoconductive layer in the etching solution or the It is difficult to generalize because it depends on the relative relationship of the image to the etching solution, such as its resistivity. The binding resin is preferably a polymer compound that is soluble or dispersible in the etching solution described below.

Specifically, for example, a copolymer of styrene and maleic anhydride, a copolymer of styrene and monoalkyl maleic anhydride, a methacrylic acid/methacrylic ester copolymer, a styrene/methacrylic acid/methacrylic ester copolymer Acrylic acid esters such as acrylic acid/methacrylic acid ester copolymer, styrene/acrylic acid/methacrylic acid ester copolymer, vinyl acetate/crotonic acid copolymer, vinyl acetate/crotonic acid/methacrylic acid ester copolymer, etc. Copolymers of , methacrylic acid esters, styrene, vinyl acetate, etc. and carboxylic acid-containing monomers or acid anhydride group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic anhydride, fumaric acid, etc. and methacrylic acid amide, vinylpyrrolidone, copolymers containing monomers with phenolic hydroxyl groups, sulfonic acid groups, sulfonamide groups, and sulfonimide groups, phenolic resins, partially saponified vinyl acetate resins, xylene resins, polyvinyl butyral Examples include vinyl acecool resins such as

A copolymer containing a monomer having an acid anhydride group or a carboxylic acid group as a copolymerization component, and a phenol resin have a high charge retention ability of the photoconductive layer when used as a photoreceptor for electrophotographic engraving, resulting in good results. It can be used with.

As the copolymer containing a monomer having an acid anhydride group as a copolymerization component, a copolymer of styrene and maleic anhydride is preferable. Half esters of this copolymer can also be used.

Copolymers containing a monomer having a carboxylic acid group as a copolymerization component include two or more copolymers of acrylic acid or methacrylic acid and an alkyl ester, aryl ester module, or aralkyl ester of acrylic acid or methacrylic acid. Combination is preferred. Further, preferable examples include a copolymer of vinyl acetate and crotonic acid, and a terpolymer of vinyl acetate, a vinyl ester of a carboxylic acid having 2 to 18 carbon atoms, and crotonic acid. Among the phenolic resins, phenol, 0-cresol, m-
Examples include novolac resins obtained by condensing cresol or p-cresol with formaldehyde or acetaldehyde under acidic conditions. The binding resin may be used alone or in combination of two or more.

When using a photoconductive compound and a binding resin, the sensitivity decreases if the content of the photoconductive compound is small, so the amount of the photoconductive compound should be 0.05 part by weight or more per 1 part by weight of the binding resin. Preferably, it can be used in an amount of 0.1 part by weight or more. Furthermore, if the photoconductive layer is too thin, it will not be able to charge the charge necessary for development, and if it is too thick, etching in the plane direction called side etching will occur, making it impossible to obtain a good image. It can be used in a range of 1 to 30μ, more preferably 0.5 to 10μ.

The electrophotographic printing plate of the present invention can be obtained by coating a photoconductive layer on a conductive substrate according to a conventional method. When creating a photoconductive layer, the components constituting the photoconductive layer can be contained in the same layer, or they can be contained separately in two or more layers, for example, by using different charge carrier generating substances and charge carrier transporting substances. There are known methods for separating the layer into layers, and it can be produced by any of these methods. The coating solution is prepared by dissolving each component constituting the photoconductive layer in an appropriate solvent, but when using components that are insoluble in solvents such as pigments, a dispersing machine such as a ball mill, paint shaker, Dyno Mill, or Attritor is used. It is used after being dispersed to a particle size of 5 μm to 0.1 μm. The binding resin and other additives used in the photoconductive layer can be added during or after dispersing the pigment. The coating liquid prepared in this way can be applied by spin coating, blade coating, knife coating, reverse roll coating,
A printing plate for electrophotolithography can be obtained by coating and drying on a substrate by a known method such as tip coating, rod bar coating, or spray coating. As a solvent for creating a coating solution,
Halogenated hydrocarbons such as dichloromethane, dichloroethane, and chloroform, alcohols such as methanol and ethanol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, glycol ethers such as ethylene glycol monomethyl ether and 2-methoxyethyl acetate, tetrahydrofuran, and dioxane. and esters such as ethyl acetate and butyl acetate.

In addition to the photoconductive compound and the binding resin, the photoconductive layer may contain plasticizers, surfactants, and other additives as necessary to improve the film properties such as flexibility and coating surface condition of the photoconductive layer. agent can be added. Examples of the plasticizer include biphenyl, chlorinated biphenyl, 0-terphenyl, p-terphenyl, dibutyl phthalate, dimethyl glycol phthalate, dioctyl phthalate, triphenyl phosphoric acid, and the like.

The electrophotographic printing plate used in the present invention can be produced by a known process using the above-mentioned electrophotographic photoreceptor. That is, it is charged substantially uniformly in a dark place, and an electrostatic latent image is formed by imagewise exposure. As for the exposure method,
Examples include scanning exposure using a semiconductor laser, HeNe laser, etc., reflection image exposure using a xenon lamp, tungsten lamp, fluorescent lamp, etc. as a light source, and contact exposure using a transparent positive film. Next, the electrostatic latent image is developed with toner. As the developing method, various conventionally known methods such as cascade development, magnetic brush development, powder cloud development, and liquid development can be used. Among these, liquid development is capable of forming fine images and is suitable for creating printing plates. The formed toner image can be fixed by a known fixing method, such as heat fixing, pressure fixing, solvent fixing, or the like.

A printing plate can be prepared by allowing the toner image thus formed to act as a resist and removing the photoconductive layer in non-image areas with an etching solution.

As the etching solution for removing the photoconductive insulating layer in the non-image area after toner image formation, any solvent can be used as long as it can remove the photoconductive insulating layer, and is not particularly limited. Preferably, alkaline solvents are used. The alkaline solvent referred to here is an aqueous solution containing an alkaline compound, an organic solvent containing an alkaline compound, or a mixture of an aqueous solution containing an alkaline compound and an organic solvent. Alkaline compounds include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, potassium silicate, sodium metasilicate, potassium mekusilicate, sodium phosphate, potassium phosphate, ammonia, and monoethanolamine and jetanolamine. , amino alcohols such as triethanolamine, and any organic and inorganic alkaline compounds. As mentioned above, water or many organic solvents can be used as the solvent for the etching solution, but from the viewpoint of odor and pollution, an etching solution mainly composed of water is preferably used.

If necessary, various organic solvents can be added to the etching solution mainly composed of water. Preferred organic solvents include lower alcohols and aromatic alcohols such as methanol, ethanol, propatool, butanol, hensyl alcohol, and phenethyl alcohol, as well as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, cellosolves, and monoethanolamine. Amino alcohols such as jetanolamine and triethanolamine can be mentioned. Further, the etching solution used contains a surfactant, an antifoaming agent, and various other additives as necessary.

It is preferable that the toner forming the image area contains a resin component having resist properties to the etching solution. Examples of resin components include acrylic resins using methacrylic acid, methacrylic acid esters, etc., vinyl acetate resins, copolymers of vinyl acetate and ethylene or vinyl chloride, vinyl chloride resins, vinylidene chloride resins, and vinyls such as polyvinyl butyral. Acecool resin, polystyrene, copolymers of styrene and butadiene, methacrylic acid esters, etc., polyethylene, polypropylene and its chlorinated products, polyester resins (e.g., polyethylene terephthalate, polyethylene isophthalate, polycarbonate of bisphenol A 1-), polyamide Resins (e.g., polycapramide, polyhexamethyleneaziboamide, polyhexamethylene sehakamide), phenolic resins, xylene resins, alkyd resins, vinyl-modified alkyd resins,
Examples include gelatin, cellulose ester derivatives such as carboxymethyl cellulose, wax, polyolefin, and wax.

In the electrophotographic photoreceptor used in the present invention, if necessary, casein, polyvinyl alcohol, ethyl cellulose, phenol resin, styrene-maleic anhydride copolymer, polyacrylic acid, Monoaminomonocarboxylic acids such as monoethanolamine, jetanolamine, trimethanolamine, tripropaturamine, triethanolamine and their hydrochlorides, oxalates, phosphates, aminoacetic acid, alanine; for example, serine, threonine, oxyamino acids such as dihydroxyethylglycine; sulfur-containing amino acids such as cysteine and cystine; monoaminodicarboxylic acids such as aspartic acid and glutamic acid; diaminomonocarboxylic acids such as ricin; e.g. p-hydroxyphenylglycine, phenylalanine, Amino acids with an aromatic nucleus such as anthranilic acid; Amino acids with a heterocyclic ring such as tryptophan and proline; Aliphatic aminosulfonic acids such as sulfamic acid and cyclohexylsulfamic acid; For example, ethylenediaminetetraacetic acid, nitrilotriacetic acid,
(Poly)aminopolyacetic acids such as iminodiacetic acid, hydroxyethyliminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, ethylenediaminediacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, glycol etherdiaminetetraacetic acid; and one of the acid groups of these compounds An intermediate layer partially or entirely composed of a sodium salt, potassium salt, ammonium salt, etc. is provided for the purpose of improving the adhesion between the substrate and the photoconductive layer, the electrostatic properties, dissolution properties, and/or printing properties of the photoconductive layer. be able to.

Further, an overcoat layer that can be dissolved when the photoconductive layer is removed can be provided on the photoconductive layer, if necessary, for the purpose of improving the electrostatic properties of the photoconductive layer, the development properties during toner development, or the image properties. This overcoat layer may be mechanically matted or a resin layer containing a matting agent. As matting agents, silicon dioxide, zinc oxide, titanium oxide, zirconium oxide, glass particles,
Included are alumina, starch, polymer particles (eg particles of polymethyl methacrylate, polystyrene, phenolic resins, etc.) and matting agents as described in US Pat. No. 2,710,245 and US Pat. No. 2,992,101. Two or more of these can be used in combination. The resin used in the resin layer containing the matting agent is appropriately selected depending on the combination with the etching solution used.

Specifically, for example, gum arabic, glue, gelatin, casein, celluloses (e.g., viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc.), starches (e.g., soluble starch,
modified starch, etc.), polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyacrylamide, polyvinyl methyl ether, epoxy resin, phenolic resin (
Particularly preferred are novolac type phenolic resins), polyamides, polyvinyl butyral, and the like. Two or more of these can be used in combination.

The present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, in the examples, all parts or % indicate parts by weight or % by weight unless otherwise specified.

Examples 1 to 12 and Comparative Examples 1 to 3 100 parts by weight of carboxymethylated starches having various structures and compositions shown in Table 1 were dissolved in 740 parts by weight of pure water.

As a comparative example, 100 parts by weight each of gum arabic, roasted dextrin (trade name: Cream Dextrin #5, manufactured by Matsutani Kagaku ■), and enzymatically decomposed dextrin (trade name: Amicol 6H, manufactured by Hikaku Kagaku ■) were separately dissolved in 740 parts by weight of pure water. did.

Each of these aqueous solutions contained 35% of the anionic surfactant sodium isoprobylnafucrene sulfonate.
% aqueous solution and 0.3 parts by weight of sodium dehydroacetate, and further adjusted the pH to 3.5 using phosphoric acid (85%).
This was used as a plate protection agent sample.

Next, the surface of the JIS 1050 aluminum sheet was grained using a rotating nylon brush using a pumice water suspension as an abrasive. At this time, the surface roughness (center line average roughness) is 0
．． It was 5μ. After washing with water, it was immersed in a 10% caustic soda aqueous solution at 70°C, and the amount of dissolved aluminum was 6 g/n? I etched it to make it look like this. After washing with water, it was neutralized by immersing it in a 30% nitric acid aqueous solution for 1 minute, and was thoroughly washed with water. Then, in a 0.7% nitric acid aqueous solution, the voltage at the anode was 13 pols 1 to 1.
Electrolytic surface treatment was carried out for 20 seconds using a rectangular alternating waveform with a cathode voltage of 6 volts (described in Japanese Patent Publication No. 55-1.9191), and the surface was immersed in a 50°C solution of 20% nitric acid. After washing, it was washed with water. Furthermore, after anodizing in a 20% sulfuric acid aqueous solution so that the weight of the anodic oxide film was 3.0 g/rn, washing with water and drying, β-alanine was further added to 2.
A substrate was prepared by coating and drying at a concentration of 8 mg/rrT.

The following photoconductive layer coating solution was applied onto this substrate using a Percoater and dried at 120° C. for 110 minutes to prepare a photoreceptor for electrophotographic engraving.

(Coating liquid for photoconductive layer) Hydrazone compound shown below 25 parts Copolymer of benzyl methacrylate and methacrylic acid (methacrylic acid 3.0 mol%) 75 parts Thiopyrylium salt compound shown below 1.18 parts Methylene chloride
510 parts Methyl cell solve acetate 150
The dry film thickness of the electrophotographic photoreceptor thus prepared was 4 μm.

Next, this sample was charged with a surface potential of ++ using a corona charger in a dark place.
After being charged to 400 cm, it was exposed to tungsten light and developed with a liquid developer Ricoh MRP (IJ Co.), making it possible to obtain a clear positive image. Furthermore, the created image was heated at 120° C. for 2 minutes to fix the toner image.

This non-image area was removed with an etching solution prepared by diluting 40 parts of potassium silicate, 10 parts of potassium hydroxide, and 100 parts of ethanol in 800 parts of water, and the film was thoroughly washed with water.

Each of the above-mentioned plate surface protective agent samples was applied to the surface of the lithographic printing plate thus prepared using a sponge, and the excess was wiped off with a cloth to prepare a printing sample.

In order to evaluate the desensitizing power of these printing samples, the samples were left for 3 days at 35° C. and 85%. Attach the samples to the Huff Duster 900CD-X offset printer according to the normal method, after printing 1000 sheets, stop supplying dampening water and printing paper, and apply ink to the entire surface of the printing plate sample. Printing was performed again under normal printing conditions. According to this evaluation method, for printing plate samples using a plate surface protectant with strong desensitizing power such as gum arabic, the ink on the non-image areas was immediately wiped off (that is, removed) and good prints were obtained. . However, in Comparative Examples 2 and 3, the ink on the non-image areas was difficult to brush off, and it took 25 prints to obtain a good printed product. As shown in Table 1, among the plate surface protectants using carboxymethylated starch,
It was found that a carboxymethyl group introduction rate in the range of 0.03 to 0.5 was good, and that the amylopectin type had desensitizing power equivalent to that of gum arabic at 90% or more.

(Margin below) Very good.

Inferior.

○Excellent.

×Very poor.

Example 13 150 parts by weight of carboxymethylated starch (carboxymethyl group introduction rate of about 0.3 is of the vioo% amylopectin type and the viscosity of a 5% aqueous solution is 15 cps (25°C)),
5.0 parts by weight of a 40% aqueous solution of sodium alkyl diphenyl ether disulfonate, 0.2 parts by weight of p-oxybenzoic acid ether, 2.0 parts by weight of citric acid, 2.0 parts by weight of dibasic ammonium phosphate, and 790.8 parts by weight of pure water. On the other hand, the following photoconductive layer dispersion was applied to the substrate of Example 1 using a bar coater to prepare a photoreceptor for electrophotographic engraving.

Dispersion liquid for photoconductive layer Trisazo compound 1.0 parts Copolymer of vinyl acetate and crotonic acid (RESYN No. 28-1310 manufactured by Kanebo Nisniscy Co., Ltd.) 10 parts Tetrahydrofuran 100 parts to 500 parts
ml glass container with glass peas, disperse for 60 minutes with a paint shaker (Toyo Seiki Seisakusho ■),
A dispersion liquid for a photoconductive layer was prepared.

The thickness of this photoconductive layer was about 4 microns. Example 1
Toner development and etching were performed in the same manner as above.

The above printing plate was divided into two parts, and one side was coated with the above plate surface protection agent sample, and the other side was coated with the plate surface protection agent sample made of gum arabic of Comparative Example-1.

The two samples were stored in a constant temperature and humidity chamber at a temperature of 45° C. and a humidity of 85% for 7 days, and then printed using a Heidelberg KOR-D printing machine according to the usual method.

As a result, both samples produced 100,000 prints without any staining, and it was found that the sample using the plate protectant according to the present invention had desensitizing power equivalent to that of the plate protectant made of gum arabic.

Example 14 Carboxymethylated starch (amylopectin type, carboxymethyl group introduction rate 0.25.5% aqueous solution viscosity 300
cps (at 25°C)) and 15 parts by weight of enzymatically decomposed dextrin (trade name: Amicol IB manufactured by Nippon Depot Chemical Co., Ltd.)
0 parts by weight, 5.0 parts by weight of a 40% aqueous solution of sodium alkyl diphenyl ether disulfonate, 0.2 parts by weight of p-oxybenzoic acid ether, 2.0 parts by weight of citric acid, and 2.0 parts by weight of diammonium phosphate. A plate surface protectant sample was prepared by dissolving it in 790.8 parts by weight of water.

Next, carboxymethylated starch was removed from the above sample, and a plate protectant sample was prepared using only 200 parts by weight of enzymatically decomposed dextrin (Amicol IB) as a water-soluble resin.

The above sample was coated on a printing plate prepared in the same manner as in Example 1 using Gum Coater G-800 (manufactured by Fuji Photo Film ■) and dried to obtain a printing sample.

After storing these samples in a constant temperature and humidity chamber at a temperature of 45° C. and a humidity of 85% for 3 days, an ink removal test was performed using a Heidelberg KOR-D printing machine in the same manner as in Example 1.

As a result, the sample using a plate protectant containing carboxymethylated starch was able to remove the ink and produce good prints after 12 sheets, whereas the sample using only enzymatically decomposed dextrin did not produce good prints. It took 25 pages to print.

〔Effect of the invention〕

When the plate surface protective agent of the present invention is applied to a lithographic printing plate produced by an electrophotographic process, an excellent anti-greasing power equivalent to that of gum arabic can be obtained.

Claims (1)

[Claims] A lithographic printing plate in which the image area consists of a toner image formed by an electrophotographic process on a photoconductor layer provided on a conductive substrate and the non-image area is a conductive substrate is coated with water-soluble carboxyalkylated starch. and the carboxyalkylated starch has a carboxyalkyl group introduction rate of 0.03 to 0.
．． 5. A method for desensitizing a lithographic printing plate, comprising treating it with a plate surface protectant according to item 5.