JPS5953854A - Electrophotographic offset printing plate material - Google Patents

Abstract

PURPOSE:To obtain a stable and sharp image superior in resistance to water and org. solvents, by using a pigment contg. sericite for the component of a precoat layer. CONSTITUTION:The precoat layer formed between a substrate and a photoconductive layer is prepared by coating the substrate with a mixture of sericite, or an inorg. pigment contg. sericite, a synthetic resin emulsion, a water-soluble polymer, an agent for insolubilizing said polymer, and a conductivity giving agent, and drying the coat material. A desirable content of sericite is >=30%, especially preferably >=50%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an original plate for electrophotographic offset printing.

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 this 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 original plate for electrophotographic offset printing is required to have properties not only as a general electrophotographic copying material but also as an original plate for offset printing. This means that the photoconductive surface must be wetted with a special aqueous surface treatment solution, a so-called etch solution, so that its non-imaged surface is oil-free after imaging, and large amounts of dampening water are used during offset printing. Because of this, the original plate for offset printing is required to have excellent water resistance, and it is also required that the photoconductive layer does not peel off during printing. There have been many proposals in the past to provide a precoat layer on the support before forming the layer, 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. It is also required to have excellent resistance to organic solvents since images are formed by a liquid development method in which toner is dispersed in a hydrocarbon-based organic solvent.

It is desirable for both water resistance and organic solvent resistance to be at a high level, but in general, surface 1 water resistance and organic solvent resistance are mutually contradictory properties. There is still no precoat layer that completely satisfies these requirements, and due to the insufficient level of their properties and the poor tolerance of their properties, only blanks for electrophotographic offset printing can be obtained that have various drawbacks. This is one of the most difficult techniques for those skilled in the art.

Japanese Patent Publication No. 40-1.8708 discloses that the water resistance and organic solvent resistance of the precoat layer can be improved by using film-forming resins having reactive hydroxyl or carboxyl groups, such as copolymers of styrene, hexyl acrylate, acrylonitrile, and methacrylic acid; Polyvinyl alcohol, copolymers of carboxylated styrene and maleic anhydride, copolymers of carboxylated ethylene and maleic anhydride, hydroxyethyl cellulose, copolymers of crotonate and vinyl acetate, etc., and dimethylolmelamine. It has been proposed that this problem be solved by crosslinking with an initial condensation product of aminoplastics such as dimethyltrimethylolmelamine or urea formaldehyde to make it water-insoluble, and several crosslinking methods have since been reported.

However, the present inventors have confirmed that even though the precoat layer obtained in this manner has water resistance in the sense that it is not soluble in water, it cannot be completely prevented from penetrating with water.

Good water resistance is also required for the backcoat layer, usually the conductive layer. Since a relatively large amount of conductive agent is used in the conductive backcoat layer, it is more difficult to prevent penetration of etch, solution, and dampening solution. Therefore, in order to reduce the amount of the conductive agent in the conductive layer as much as possible, it is possible to impregnate the paper support with inorganic salts or to include the conductive agent in the precoat layer in view of the electrophotographic properties. If it is contained, the water resistance will be poor.

An object of the present invention is to provide an original plate for electrophotographic offset printing having a precoat layer that has good electrophotographic properties and does not suffer from drawbacks due to water resistance and organic solvent resistance.

The above object of the present invention is to provide an original plate for electrophotographic offset printing in which a photoconductive layer is formed on the surface of a conductive support via a precoat layer, in which the precoat layer is made of sericite, an inorganic pigment containing sericite, a synthetic resin emulsion, or a water-soluble It has been found that this can be achieved by applying and drying a coating liquid consisting of a water-soluble polymer compound, an insolubilizing agent for the water-soluble polymer compound, and a conductive agent.

The reason why the precoat layer containing the sericite component has excellent water resistance and organic solvent resistance, and yet consistently provides stable and clear images, is not clear, but it is thought to be due to the crystal form unique to sericite.

The sericite used in the present invention is also called sericite, and its chemical composition is close to that of white mica fB, but it is a very fine sericite that shows slight changes compared to the ideal chemical composition of muscovite. The composition varies depending on the symptoms. The ideal chemical composition of muscovite is K2O.3A620.・(3Si
o2 2H20, but sericite has a larger S 102 /Al2O ratio than muscovite, and K
It is characterized by low 2O and high H2O (water released at temperatures above 105°C).

In the chemical composition of sericite, potassium is loosely contained between the crystal layers (
Because they are sandwiched, the crystal particles easily peel off at that part (,
That is, it is easy to open and exhibits "lubricity" physically. The external shape of sericite is a hexagonal plate-like crystal, and the height of the unit crystal is IO
It is A.

In the present invention, it is preferable to use pure sericite, but from the viewpoint of cost and liquid properties, it may be mixed with other pigments such as kaolin, calcium carbonate, aluminum hydroxide, etc., or an inorganic pigment containing a sericite component may be used. You may do so. In this case, the content of the sericite component is preferably 30% or more, particularly preferably 50% or more.

The synthetic resin emulsion used as the precoat liquid component of the present invention includes acrylic acid or its ester,
Examples include water-dispersible emulsions obtained by emulsion polymerization or emulsion copolymerization of vinyl group-containing monomers such as methacrylic acid or its esters, vinyl chloride, vinylidene chloride, vinyl acetate, acrylonitrile, phthadiene, and styrene.

The water-soluble polymer compound used as the precoat liquid component of the present invention is particularly a polymer compound having a carboxyl group, a hydroxyl group, an amine group, or an imino group, such as starch or its derivatives, cellulose derivatives, casein, polyvinyl alcohol, styrene-maleic anhydride copolymer,
Vinyl acetate-maleic anhydride copolymer or the like can be used.

Examples of insolubilizing agents for water-soluble polymer compounds include known compounds such as aminogellast initial condensates, aldehyde compounds such as glyoxal and dimethylurea, dialdehyde starch, polyamides, epoxidized polyamides, and epoxy compounds.

Known conductive agents can be used in the present invention. For example, polyvinyltrimethylammonium chloride, polyvinylbenzyltrimethylammonium chloride, poly-4-vinylpyridine, poly-2-vinylpyridine polymethacrylate diethylaminoethyl hydrochloride, di-2-ethylhexyl sulfosuccinate, sodium cetyl phosphate, polystyrene sulfone Mention may be made of inorganic salts such as acid sodium or ammonium salts, polyacrylates, methyl vinyl ether anhydrous polymeric acid copolymer sodium salts, or chlorides.

By adding a conductive agent, it is possible to obtain a good image free from fog, especially at low humidity, but on the contrary, printing durability may be reduced.

In the precoat layer of the present invention, even if a certain amount of conductive agent is used, the printing durability does not decrease at all and a good image can be obtained due to the sericite component in the inorganic pigment.

The offset printing original plate of the present invention has its characteristics in the precoat layer, and any conventionally known materials can be used as the photosensitive layer and support.

For example, the photosensitive layer is made of a photoconductive material such as zinc oxide, a resin, a sensitizing material, etc., and the weight ratio of zinc oxide to resin is usually about 3:1 to 61. Further, as the resin, acrylic copolymer, silicone resin, vinyl acetate resin, styrene-butadiene copolymer, polyester such as nylon, etc. are used.

In addition, as a support, for example, a back coat layer is provided on the back side of a substrate such as paper (the opposite side to where the precoat layer and photosensitive layer are laminated) to provide conductivity and prevent curling. Alternatively, a substrate with an adhesive layer made of polyvinyl alcohol or the like further provided on the surface of the substrate may be used.

In order to impart electrical conductivity, the above-mentioned electrically conductive agent can be used as a component of the back coat layer. Note that by using a conductive agent in the backcoat layer and, if necessary, using a conductive paper support impregnated with inorganic salts, the amount of conductive agent used in the conductive backcoat layer can be relatively reduced. Therefore, it has the advantage of being able to alleviate the drawbacks due to the water resistance of the back coat layer.

The precoat layer in the method of the invention does not exclude the use of other ingredients, such as dispersants, antifoaming agents, etc.

3 The precoat layer according to the present invention has a dry coating weight of 3 to 30
9/rrj, preferably 5-20! ! /m' by a conventional method and dried.

The present invention will be explained below using examples.

Example 1 A coating solution for forming a back coat layer having the following composition is applied to the back side of a wet reinforced paper having a basis weight of 1201/rrl as a support so that the dry coating amount becomes 1311/rrl and dried.

[Coating liquid for forming back coat layer]

Kaolin (50% aqueous dispersion, trade name Hydrasperse,
Heater-1ug) 6 oz 4B oxidized starch (10 parts aqueous solution) 2 ootrSBR latex (solid content 48 parts) 450 Boristyrene/ammonium sulfonate 200 # (solid content 30%) Melamine-formaldehyde initial condensate 15 (solid content 80 parts, (Product name: Sumishisotsu Resin - 613 manufactured by Sumitomo Chemical ■) On the other hand, on the front side of the paper, apply a coating solution for forming a precoat layer with the following composition to a dry coating amount of 15 g/ni'', dry, and coat the precoat layer surface (surface specific Resistance 7'X 10
A 10Ω pan, 20° C., 60% RH) was supercalendered, and a photoconductive layer was formed on the surface.

[Coating liquid for pre-coat layer formation]

Sericite content 95% inorganic face 600 parts by weight (
50 aqueous dispersion, trade name: Sericron Murakami Clay (manufactured by 1 (1)) Oxidized starch (10% aqueous solution) 20Q t+S
BR latex (solid content 48%) 450 tt
Ammonium polystyrene sulfonate 20 (
Solid content: 30%) Melamine-formaldehyde initial condensate 15 (Solid content: 80%, product name: Violet Resin-613, manufactured by Sumitomo Chemical) It was applied at a concentration of 20 g/rrl and dried.

[Coating liquid for forming photoconductive layer]

, Zinc oxide for electrophotography 200 parts by weight Acrylic resin (50% liquid) 80 Rose Bengal (2% methanol solution) 15/7 xylene 250 Photoconductive layer coated surface is uniform with no cracks or pinholes It had quality.

This electrophotographic offset printing original plate was heated to 60% R at 20°C.
Seasoned under H and 20% RH conditions, and plate-made using an electrophotographic engraving machine Diafax GP-11 (manufactured by Mitsubishi Paper Industries, Ltd., liquid development plate making machine). (
The paper was desensitized using Mitsubishi Paper Corporation (manufactured by ■) and printed using an offset printing machine Toko Model 1810 (manufactured by Tokyo Aircraft Instruments ■).

Under the conditions of 60% RH and 20% RI, there was no occurrence of capri, etc., and a clear image with high density was obtained. Even after processing with the etch solution, there was no occurrence of curl, etc., and the process was smooth and easy to operate. It can be attached to a printing machine, and even when printing with dampening water or printing more than 5,000 sheets, there is no occurrence of plate wrinkles or peeling of the photosensitive layer (the printing plate obtained by the present invention is extremely It was confirmed that it was excellent.

Furthermore, after putting this original plate for electrophotographic offset printing in a black polyethylene bag and storing it at a temperature of 20°C and 60% RH for one year, it was made into a plate in the same manner as above, and offset printing was performed. After printing 5000 sheets. However, there was no occurrence of plate wrinkles or peeling of the photosensitive layer, and no deterioration due to storage was observed. A precoat layer was prepared in the same manner except that the amount was changed to 0%) and tested in the same manner.

After printing up to 3,000 sheets, scumming due to plate wrinkles and the like occurred, confirming the superiority of the printing plate of Example 1.

Example 2 A printing plate was prepared in exactly the same manner as in Example 1, except that the same amount of sericite (sericite content: 35%, manufactured by Zikrite Chemical Co., Ltd.) was used.
Almost the same results were obtained.

Comparative Example 2 A printing plate was prepared in exactly the same manner as in Example 1 except that sericite was replaced with the same amount of talc. However, capri was observed during plate making and an image with insufficient density was obtained. Incidentally, even in offset printing, when printing up to 2,000 sheets, wrinkles and other background stains occurred, confirming the superiority of the printing plate of Example 1.

Example 3 The sericite of Example 1 was replaced with sericite (50% aqueous dispersion)
A printing plate was prepared in the same manner as in Example 1, except that 350 parts by weight and 250 parts by weight of kaolin (50% aqueous dispersion, trade name Hydrasperse) were used.The same results as in Example 1 were obtained.

The results are summarized below and shown in Table 1.

Claims (1)

[Claims] Source (1) An original plate for electrophotographic offset printing comprising at least a precoat layer and a photosensitive layer on a support, characterized in that a pigment containing a serizite component is used in the precoat layer. An original plate for electrophotographic offset printing. (2) The original plate for electrophotographic offset printing according to claim 1, wherein the pigment contains 30% or more of sericite. (3) The original plate for electrophotographic offset printing according to claim 1, wherein the pigment contains 50 or more sericite.