JPH0228146B2 - DENSHISHASHINHEIBANINSATSUHANNOSEIZOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an electrophotographic lithographic printing material. Generally, an electrophotographic light-sensitive material has a photoconductive layer made of a photoconductive substance and a binder provided on the surface of a support that has been subjected to conductive treatment. Forming an image on the photoconductive layer through the process and using it as a plate for offset printing is widely used in the field of light printing because the plate-making operation is simple, quick, and inexpensive. . An electrophotographic lithographic printing material is required to have properties as a lithographic printing material in addition to properties as a general electrophotographic copying material. That is, after image formation, the non-image area becomes oil-insensitive.
Because the photoconductive surface must be wetted with a special aqueous surface treatment solution, the so-called etch solution, and because large amounts of dampening water are used during lithographic printing, lithographic printing materials must have excellent water resistance. It is also required that the photoconductive layer does not peel off during printing. In view of these demands, many proposals have been made to date to provide a precoat layer on a conductive support before forming a photoconductive layer on the support, and to form a photoconductive layer on this precoat layer. . In addition to the requirements for the above-mentioned properties such as water resistance, this precoat layer is made of an aromatic hydrocarbon solvent so that the coating liquid for forming the photoconductive layer has a photoconductive substance dispersed in a binder resin. or using
Furthermore, since images are formed using a liquid development method in which toner is dispersed in a hydrocarbon-based organic solvent, it is also required to have excellent resistance to organic solvents. It is desirable for both water resistance and organic solvent resistance to be at a high level, but in general, water resistance and organic solvent resistance are mutually contradictory properties, so the precoating methods proposed so far As yet, there is no layer that completely satisfies these requirements, and due to the insufficient level of their properties and the imbalance of their properties, only electrophotographic lithographic materials with various drawbacks can be obtained. This has become one of the most difficult techniques for those skilled in the art. Japanese Patent Publication No. 40-18708 describes how to improve the water resistance and organic solvent resistance of the precoat layer by using resins with reactive hydroxyl or carboxyl groups, such as styrene, hexyl acrylate, acrylonitrile, methacrylic acid copolymers, polyvinyl alcohol, and carboxylated resins. Copolymers of styrene and maleic anhydride, copolymers of carboxylated ethylene and maleic anhydride, hydroxyethylcellulose, copolymers of crotonic acid and vinyl acetate, etc. are used to produce dimethylolmelamine, dimethyltrimethylolmelamine, etc. It has been proposed to solve this problem by crosslinking with an aminoplastic initial condensate such as urea formaldehyde to make it water-insoluble, and several crosslinking methods have since been reported. However, even though the precoat layer obtained in this way has water resistance in the sense that it does not dissolve in water, it cannot completely prevent water penetration and swelling; resin to prevent,
That is, an aqueous dispersion of a lipophilic (hydrophobic) resin, preferably a vinyl synthetic resin, such as acrylic acid or its ester, methacrylic acid or its ester, vinyl chloride, vinylidene chloride, vinyl acetate, acrylonitrile, butadiene, styrene, etc. It is also necessary to use a water-dispersible emulsion or the like obtained by emulsion polymerization or emulsion copolymerization of a monomer having a vinyl group. However, if the ratio of lipophilic resin is increased in order to increase water resistance, organic solvent resistance will be relatively reduced. Inferior water resistance causes serious drawbacks such as the penetration of desensitizing liquid and dampening solution into the paper layer of the support, resulting in plate wrinkling and peeling of the photoconductive layer during printing. However, the poor organic solvent resistance causes defects such as surface cracking and pinholes on the plate surface during the coating formation of the light guide layer, making it no longer possible to use the plate as a lithographic printing plate. Therefore, there is a need for a precoat layer technology that does not suffer from drawbacks due to low levels of water resistance or organic solvent resistance. An object of the present invention is to provide a method for producing an electrophotographic lithographic printing plate that does not suffer from drawbacks due to either the water resistance or organic solvent resistance of the precoat layer. Further objects and advantages of the invention will become apparent from the following description. The above-mentioned and below-mentioned objects of the present invention are as follows:
A method for producing an electrophotographic lithographic printing plate in which a photoconductive layer is formed on the surface of a conductive support via a precoat layer, which comprises at least an aqueous dispersion of a water-soluble resin and a vinyl-based synthetic resin, and the water-soluble resin is completely solid. Applying a pre-coat liquid consisting of a styrene copolymer or a combination of styrene copolymer and a styrene copolymer, the proportion of which is about 10% by weight or less, and the aqueous dispersion is about 30% by weight of the total solids, It has been found that this can be achieved by drying. In the method of the present invention, by forming the precoat layer with the above-mentioned composition,
Even without the special use of a crosslinking agent as described in
This has the advantage that it is possible to obtain an electrophotographic lithographic printing plate that has excellent water resistance and organic solvent resistance, and therefore has high printing durability. Water-soluble resins used in the present invention include polymeric compounds having carboxyl groups, hydroxyl groups, amino groups, imino groups, etc., such as starch or its derivatives, cellulose derivatives, gelatin, casein, polyvinyl alcohol, styrene-maleic anhydride. Examples include water-soluble resins such as copolymers, and as described above, these water-soluble resins can be made water-insoluble after being applied with a precoat by using a crosslinking agent together. The aqueous dispersion of a styrene copolymer used in the present invention usually contains a styrene monomer and a suitable vinyl monomer, such as an acrylic ester, an α-substituted acrylic ester (such as methyl methacrylate, butyl methacrylate, etc.), acrylamide,
It is produced by emulsion copolymerization of one or more of vinyl halide (eg, vinyl chloride), ethylene, propylene, butylene, butadiene, acrylonitrile, and the like. The styrene monomer is
Substituted styrene (e.g. α-methylstyrene, etc.),
The substituted styrenes (eg, hydroxystyrene, chlorostyrene, methylstyrene, etc.) can also be used. Particularly preferred styrene copolymers for use in the present invention are carboxylated modified styrene copolymers obtained by copolymerization of up to about 20 mole percent of unsaturated acids such as itaconic acid, acrylic acid, methacrylic acid, etc. This is an aqueous dispersion (latex) of a chemically modified styrene-butadiene copolymer. The proportion of the styrene component in the styrene copolymer can be arbitrary, but is preferably about 25
It ranges from mol % to about 50 mol %. The styrene polymer used in combination with the styrene copolymer may be obtained by emulsion polymerization of the styrene monomer to form a latex, or may be a pigment-like product obtained by finely dispersing polystyrene powder in water. In the method of the present invention, other vinyl synthetic resins may be used in combination without impairing the effects of the present invention. The general range of the component ratio of the precoat layer in the method of the present invention is from about 1 to about 1% of the solid content of the precoat liquid.
10% by weight, preferably from 2 to 8% by weight of water-soluble resin, from about 30 to about 80% by weight, preferably from 35 to 75% by weight
It can be obtained by blending a precoat layer coating solution to form an aqueous styrene resin dispersion. Other pigments to improve smoothness and prevent blocking, dispersants for them as necessary,
Antifoaming agents etc. are added. The precoat layer coating liquid has a dry solid content of approximately 3
It is coated and dried at a weight of ~30 g/m ² , preferably 5-20 g/m ² . By reducing the water-soluble resin content and increasing the styrene resin content in the precoat layer, an electrophotographic lithographic printing plate has been discovered that has excellent printing durability without any defects in water resistance or organic solvent resistance. However, depending on the conditions, this may give unsatisfactory results in terms of photographic properties, such as slight fogging at low humidity. In an improved aspect of the present invention, a small amount of a conductive agent is added to the precoat layer coating solution, that is, the surface resistivity of the precoat layer is 20°C and a relative humidity of 60%.
It has been found that an electrophotographic lithographic printing plate having good image characteristics can be obtained without impairing the object of the present invention by including the oxide in an amount of 10 ¹⁰ to ^{10 11} Ω·cm. As the conductive agent, polyvinylmethylammonium chloride, polyvinylbenzyltrimethylammonium chloride, poly-4-vinylpyridine, poly-2-vinylpyridine, polydiethylaminoethyl methacrylate hydrochloride, di-2-ethylhexylsulfosuccinate, sodium cetylphosph Known polymer electrolytes such as 8, sodium or ammonium salt of polystyrene sulfonic acid, sodium polyacrylate, sodium salt of methyl vinyl ether maleic anhydride copolymer, or inorganic electrolytes such as calcium chloride and sodium chloride can be used. The support used in the present invention is made of ordinary papermaking pulp or a pulp suspension containing a small amount of synthetic fiber, synthetic resin, etc., and a moisture strengthening agent such as a thermosetting condensation resin, polyamide resin, starch, or polyvinyl alcohol. , a sizing agent, a filler, etc., or a cype-pressed wet-strengthened paper can be used, and it can also be impregnated with a hygroscopic inorganic salt to impart conductivity. On the back side of these paper substrates, a conductive backcoat layer consisting primarily of resin and a conductive agent is provided. The present invention will be explained below using examples. Example 1 A coating liquid for forming conductivity having the following composition was applied to the back side of a paper base mainly made of N pulp at a dry coating amount of 13 g/m ²
Apply and dry. [Coating liquid for forming conductive layer] Kaolin clay (50% aqueous dispersion) 600 parts by weight polyvinyl alcohol (10% aqueous solution)
200 〃 Carboxyl-modified SBR latex (solid content 50%) 45 parts by weight polyvinylbenzyltrimethylammonium chloride (solid content 30%) 200 〃 Meanwhile, on the surface of the paper base, a coating liquid for forming a precoat layer with the following composition was dried and applied. After coating and drying in an amount of 9 g/m ² , the surface of the precoat layer was supercalendered, and a photoconductive layer was formed on the surface. [Coating liquid for pre-coat layer formation] Kaolin clay (50% aqueous dispersion) 300 parts by weight Finely divided polystyrene 150 (Average particle size 0.5μ, 48.5% aqueous dispersion) Polyvinyl alcohol (10% aqueous solution)
300 〃 Carboxyl-modified SBR latex 150 〃 (Solid content: 50%, commercially available) The coating solution for forming the photoconductive layer has the following formulation, and is applied at a dry coating amount of approximately 20 g/m ² at 110°C.
It was dried. [Coating liquid for forming photoconductive layer] Zinc oxide 200 parts by weight Acrylic resin (50% solution) 80 Rose Bengal (2% methanol solution)
15 〃 Toluene 250 〃 The obtained lithographic printing plate had good surface quality without surface cracks or pinholes. This plate was processed using an electrophotographic engraving machine Diafax EP-11 (Mitsubishi Paper Industries) under the conditions of 20℃ and 50% relative humidity.
Co., Ltd., a liquid development plate making machine), and an etch liquid diamond fax LOM for electrophotographic lithography master.
It was desensitized using OH (manufactured by Mitsubishi Paper Mills Co., Ltd.) and printed using a printing machine Toko Model 810 (manufactured by Tokyo Aircraft Instruments Co., Ltd.). A clear image without fogging was obtained on the photoconductive layer, and even after printing 4000 sheets, high-quality printed matter was obtained without any smudges due to printing wrinkles or the like. Comparative Examples 1 to 6 Carboxyl-modified styrene-butadiene copolymer (SBR) in the precoat layer coating solution of Example 1
A lithographic printing plate was prepared in the same manner except that the latex was replaced with the same amount of the following aqueous dispersion (all commercially available products).

[Coating liquid for forming pre-coat layer]

Parts by weight Kaolin clay (50% aqueous dispersion) 500 Carboxyl cellulose (10% aqueous solution) 250 SBR latex (50% solids, commercially available) 500 Melamine-formaldehyde initial condensate 20 (80% solids, violet resin) -613, manufactured by Sumitomo Chemical) Example 3 Example 1 was repeated except that a precoat layer coating solution having the following composition was used. The same results as in Example 1 were obtained, and no fogging occurred in a low-humidity atmosphere. Part by weight Polyvinyl alcohol (10% aqueous solution) 500 SBR latex 1000 (50% solids, manufactured by Daura Chemical) Kaolin clay (50% aqueous dispersion) 900 Ammonium polystyrene sulfonate (30% aqueous solution) 10 Solids coating amount 10g/ ^m2

Claims (1)

[Claims] 1. In a method for producing an electrophotographic printing plate in which a photoconductive layer is formed on the surface of a conductive support via a precoat layer, the method includes at least an aqueous dispersion of a water-soluble resin and a vinyl-based synthetic resin, and the water-soluble resin has a total solid content. A coating for forming a precoat layer consisting of a styrene copolymer or a combination of styrene copolymer and a styrene polymer, in which the proportion of the mold content is approximately 10% by weight or less, and the aqueous dispersion accounts for approximately 30% by weight or more of the total solid content. A method for producing an electrophotographic lithographic printing plate, characterized by applying a liquid and drying it.