JPH08166693A - Material for electrophotographic planographic printing plate - Google Patents

Abstract

PURPOSE: To obtain an electrophotographic planographic printing plate material showing little image fog but excellent dimensional stability even when the plate making process is done at low temp. by incorporating synthetic hectorite into a back layer. CONSTITUTION: The plate material is produced by forming an intermediate layer and a photoconductive layer successively on a water-resistant supporting body and forming a back layer containing synthetic hectorite on the opposite side of the supporting body. Hectorite is one kind of montmorillonite, and natural hectorite shows a color because it contains a lot of impurities. A synthetic hectrite has higher whiteness than natural hectorite. The synthetic hectorite is conductive and insoluble with water so that the electric resistance of the plate material can be decreased without decreasing water resistance. Further, the back layer consists of not only the synthetic hectorite but a pigment, binder resin and auxiliary additives which may be added if necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic lithographic printing plate material, and more specifically, an electrophotographic lithographic printing plate excellent in dimensional stability with less image fog even in a plate-making product at low humidity. It is about materials.

[0002]

2. Description of the Related Art In recent years, with the development of small offset printing machines and the development of automatic printing machines, the mainstream of light printing is shifting to offset printing. Many researches and developments have been made on such offset printing plate materials, and various materials have been put to practical use. Among these materials, the electrophotographic lithographic printing plate material having a photoconductive layer containing zinc oxide as a main component occupies the mainstream of light printing plate materials because it is inexpensive and the plate making process is simple. .

An electrophotographic lithographic printing plate material is usually subjected to corona charging, exposure, development and fixing processes in a desired pattern using a plate making machine to form a visible image of the desired pattern on the photoconductive layer. Obtained by In the developing step, there are a dry developing method using a mixture of toner and a carrier such as iron powder, and a wet developing method using a developing solution in which the toner is dispersed in an organic solvent such as Isopar. When the plate is produced using the wet development method, there are advantages that the halftone reproducibility is good, the resolution is excellent, the time required for plate making is short, and no correction is required. For this reason, electrophotographic lithographic printing plate materials by the wet development method are widely used in Japan.

In recent years, computers have been remarkably used in the printing industry, and the digital system is being replaced with the analog system. Electrophotographic lithographic printing plate material costs 7
By blending a cyanine dye that sensitizes in the vicinity of 80 nm, a so-called computer-to-plate system, in which computer data is directly exposed to a plate material by a semiconductor laser beam, has been used.

The electrophotographic lithographic printing plate material is used in addition to the image characteristics generally required as an electrophotographic copying material (for example, image density, fog, sharpness, image uniformity, printing background stain, etc.). It is necessary to have various characteristics required as the above (for example, the non-image portion of the printing plate that has undergone the development process can be desensitized). Further, recently, colorization has spread in the field of light printing, and high dimensional stability (plate elongation) has been required. The causes of plate elongation include permeation of dampening water into the water-resistant support from the surface during printing and permeation of the etchant from the back surface into the water-resistant support due to etching (desensitization).

In order to improve the above-mentioned image characteristics and dimensional stability, it has been proposed to form a back layer on the back surface of the electrophotographic lithographic printing plate material. Japanese Patent Publication 62-46
No. 854, JP-A-59-170860, and JP-A-4-319662 propose improvement of fog caused by mechanical stress. However, the above method has a problem that fog is generated in an image in plate making under a condition of low humidity.

Japanese Unexamined Patent Publication (Kokai) No. 58-124695 proposes to use a water-dispersible hydrophobic resin as a binder resin for a back layer and to form an intermediate layer containing carbon black for improving fog. . However, the dispersion of hydrophobic carbon black requires the use of a large amount of surfactant, and as a result, the surfactant absorbs the etchant, resulting in poor water resistance and good dimensional stability. It was hard to get.

[0008]

SUMMARY OF THE INVENTION The present invention solves the drawbacks of the prior art and provides an electrophotographic lithographic printing plate material having less image fog and excellent dimensional stability even in plate making under low humidity. It is in.

[0009]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventors have found that an intermediate layer and a photoconductive layer are sequentially provided on a water-resistant support and The inventors of the present invention have found that this can be achieved by incorporating synthetic hectorite in the back layer on the opposite side, and have reached the present invention.

When the back layer in the present invention is formed of only the binder resin and the pigment, the water resistance is good and the plate elongation can be reduced. However, under low humidity conditions, the electric resistance of the back layer is high and the light attenuation is poor, so that the image is fogged and a good image cannot be obtained. In order to obtain a good image with less image fog, the surface electric resistance value of the back layer is 1.0 × 10 ⁷ Ω / □ to 1.0 × 10 ¹¹ Ω.
/ □ is appropriate. Therefore, when the synthetic hectorite was contained in the back layer, the electric resistance could be made a target value without impairing the water resistance.

Hectorite is one of the montmorillonite group minerals and is naturally produced in California, USA, but it is colored because it contains many impurities. On the other hand, synthetic hectorite has higher whiteness than natural hectorite.
Synthetic hectorite

[Si ₈ (Mg _5.34 Li _0.66 ) O ₂₀ (OH _X F _(X-1) ) ₄ ] M ⁺ _0.66 or

[Si ₈ (Mg _5.34 Li _0.66 ) O ₂₀ (OH) ₄ ] It is represented by a chemical composition such as M ⁺ _0.66 . Synthetic hectorite itself is a conductive substance,
Moreover, since it is not a water-soluble substance, it is considered possible to reduce the electric resistance without impairing the water resistance.

The compounding ratio of the synthetic hectorite is preferably within the range of 1 to 15% by weight based on the weight of the coating solid content of the back layer. It is more preferably 2 to 12% by weight. 1% by weight
If it is less, it does not contribute to the reduction of electric resistance. On the other hand, if it is more than 15% by weight, the viscosity of the paint becomes high and the coatability becomes poor.

The back layer of the present invention comprises a pigment, a binder resin, and an auxiliary additive component which can be added if necessary, in addition to synthetic hectorite. As the pigment that can be used in the back layer of the present invention, for example, calcium carbonate, magnesium carbonate, kaolin, talc, calcined clay, silica,
Inorganic pigments such as diatomaceous earth, mica, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, and barium sulfate, and organic resin fine particles such as urea-formalin resin, styrene-methacrylic acid copolymer, and polystyrene resin. A powder etc. can be mentioned. The blending ratio of the pigment is 10% by weight to 80% by weight based on the solid content of the paint in the back layer
It is preferable to use in the range of.

The binder resin used in the back layer of the present invention may be a water-dispersible hydrophobic resin and / or a water-soluble resin. The blending ratio of the water-dispersed hydrophobic resin is preferably in the range of 10% by weight to 80% by weight based on the weight of the solid coating material in the back layer. Examples of the water-dispersible hydrophobic resin include styrene-butadiene latex, acrylic emulsion, emulsion of vinyl acetate-acrylic acid ester copolymer, polyurethane emulsion, polyvinyl chloride emulsion, polyvinylidene chloride emulsion, methacrylic acid ester copolymer. And emulsion of acrylic acid ester copolymer. Further, when the water-soluble resin is mixed in a large amount, the water resistance is deteriorated, and therefore the water-soluble resin needs to be used in an amount of 10% by weight or less based on the solid weight of the coating material in the back layer. Examples of the water-soluble resin include polyvinyl alcohol, oxidized starch, modified starch, gum arabic, gelatin, casein, chitosan, methyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid salt, polyacrylic amide, and styrene-maleic anhydride. Acid copolymer salt, methyl vinyl ether-maleic anhydride copolymer salt, methyl vinyl ether-
Maleic anhydride copolymers, isopropylene-maleic anhydride copolymer salts and the like can be used. Of course, it is not limited to these.

Further, in order to improve water resistance, these binder resins may be provided with a reactive group that participates in a crosslinking reaction. For example, hydroxy ester of α / β-unsaturated carboxylic acid, α / β-unsaturated amide or glycidyl (meth) acrylate, N-methylol acrylamide, monomer having two or more double bonds (diallyl phthalate, allyl glycidyl). Ether), 3-chloro-2-hydroxypropyl methacrylate, and the like, which are copolymerized with a small amount of widely known reactive monomers, can be used.

As the auxiliary additive component, for example, a dispersant,
There are water-proofing agents and the like to make the water resistance stronger. As the water resistance agent, for example, expensive aldehyde compounds such as glyoxal, glutaraldehyde, dialdehyde starch, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, diglycidyl compounds such as glycerin diglycidyl ether, dimethylol urea Compounds, as well as ammonium persulfate and ferric chloride,
Inorganic compounds such as magnesium chloride, boric acid, and borax can be used. Of course, it is not limited to these.

To form the back layer in the present invention,
A water-based paint containing the above-mentioned materials is applied to the back surface of the water-resistant support (the surface opposite to the side where the photoconductive layer is provided), and the applied layer is dried and solidified to form a film. At this time, preferably 80 to 15
When dried at a temperature of 0 ° C., a water resistant back layer can be formed. The weight of the back layer is 5 to 30 g / m ^2.
It is preferably within the range. As a method of applying the back layer coating material, a Meyer bar method, an air knife method, a blade method, a reverse roll method, a slit die method, or the like can be used. Of course, it is not limited to these.

The water-resistant support used to form the electrophotographic lithographic printing plate material of the present invention is a paper that has been subjected to a size press treatment, a laminated paper in which aluminum or polyethylene is attached to the paper, or a synthetic paper. Etc., and generally has a thickness of 70 to 150 μm.

In the present invention, an intermediate layer is formed between the water resistant support and the photoconductive layer for the purpose of preventing penetration of dampening water into the water resistant support during printing. The components of the intermediate layer are pigments, binder resins and the like. In addition, an auxiliary additive component such as a dispersant, a conductive agent, and a water resistant agent for strengthening water resistance may be added to the intermediate layer, if necessary. A pigment used for the intermediate layer of the present invention, a binder resin,
As the dispersant and the water-proofing agent, for example, those similar to the back layer can be used.

As the conductive agent used in the intermediate layer of the present invention, for example, a cationic conductive resin such as polyvinylbenzyl trimethyl ammonium chloride, polydimethyl diallyl ammonium chloride, styrene acrylic acid trimethylaminoethyl chloride copolymer, or polystyrene sulfone is used. Examples thereof include anionic conductive resins such as acid salts, polyacrylic acid salts, and polyvinyl sulfonates, carbon black, and conductive whiskers.

The weight of the intermediate layer after drying is 3 to 30 g / m.
It is preferably within the range of ² . More preferably 5
It is preferably 20 g / m ² . If it is less than 3 g / m ² , penetration of dampening water cannot be sufficiently prevented, and if it is more than 30 g / m ² , curling to the photoconductive layer side becomes too large. As the method for applying the intermediate layer paint, for example, the same method as for the back layer can be used.

The photoconductive layer of the present invention comprises zinc oxide, titanium oxide or the like as a photoconductive pigment, a binder resin, a sensitizing dye,
And a solvent are applied on the intermediate layer, and the coating is dried. The weight of the photoconductive layer after drying is 20 to 30 g /
It is preferably in the range of m ² . When the amount is less than 20 g / m ² , the image density is low, and when the amount is more than 30 g / m ² , the charging potential reaches saturation, which is meaningless because the image density is not improved and the cost is increased. As the method for applying the photoconductive layer coating material, the same method as for the back layer can be used.

As the binder resin used in the photoconductive layer of the present invention, an acrylic ester copolymer, a methacrylic ester copolymer, a vinyl acetate copolymer, a silicone resin, a butyral resin, etc., which are generally hydrophilic, are used. Can be mentioned. For the purpose of improving the image quality and the like of these binder resins, there is no problem with copolymerizing a monomer having a functional period such as acrylic acid, methacrylic acid or maleic acid. The binder resin contained in the photoconductive layer is preferably 10 to 30% by weight, more preferably 15 to 20% by weight based on the photoconductive pigment.

As the sensitizing dye used in the photoconductive layer of the present invention, for example, rose bengal, uranine, BPB (bromphenol blue), nigrosine, etc., which are conventionally used photosensitive paints, electron accepting substances, and Wavelength of 700-
Various sensitizers such as compounds having maximum sensitivity to light rays in the range of 1000 nm are used. If necessary, an auxiliary additive component such as a sensitization aid may be added to the photoconductive layer of the present invention. Examples of the sensitization aid include maleic anhydride, phthalic anhydride, cobalt salt, manganese salt and the like.

The electrophotographic lithographic printing plate material of the present invention obtained as described above is a low-humidity plate-making product with less image fog and excellent dimensional stability, and provides a very excellent printing plate material. I was able to.

[0026]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these. In each example, "part" represents "dry weight%".

Example 1 An electrophotographic lithographic printing plate material was prepared in the following manner and its characteristics were evaluated. (1) A barrier layer having the following composition was formed on the surface of a base paper having a basis weight of 100 g / m ² by a size press treatment with a dry coating amount of ² g / m ² . Size / press composition Polyvinyl alcohol 80 parts Sodium polyacrylate 20 parts (2) Next, one side of the size / press-treated base paper (water-resistant support) was coated with the following intermediate layer coating solution to a dry weight of 10 g / m ^2. Was applied to. Intermediate layer coating solution Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 30 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 35 parts Urethane emulsion (trademark: Vylok RL-3, manufactured by Kanebo NSC) 35 parts (3) 10 g of the following back layer coating liquid on the opposite surface of the water resistant support (on the water resistant support opposite to the intermediate layer).
It was applied so that the dry weight was m ² . The viscosity of the back layer coating material (solid content: 30% by weight) at a liquid temperature of 20 ° C. was measured by a B-type viscometer at 60 rpm. Back layer liquid Synthetic hectorite (trademark: Laponite B, manufactured by Laporte Industries) 1 part Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 54 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR ( Trademark: L-1537A, manufactured by Asahi Kasei) 25 parts (4) Further, the following photoconductive layer coating solution was applied onto the intermediate layer so as to have a dry weight of 25 g / m ² . Photoconductive layer coating liquid Photoconductive zinc oxide (trademark: Sazex 2000, manufactured by Sakai Chemical) 100 parts Silicon resin (trademark: KR-211, manufactured by Shin-Etsu Chemical) 17 parts Rose Bengal 0.1 part Obtained as described above. Printing plate at 20 ℃, 30% RH
After acclimatization was carried out for 24 hours in a dark place having an atmosphere of (low humidity), plate making was carried out by an ITEC 275 type electronic plate making machine, and image fog was examined. In addition, a printing plate with a length of exactly 200 mm entered is etched (etcher [made by Ricoh] once, etching solution: made by Aitec Co., Ltd.), and after 10 minutes, the length is measured to prevent plate elongation due to etching. I investigated the effect. The results are shown in Table 1.

Example 2 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Synthetic hectorite (trademark: Laponite S, manufactured by Laporte Industries) 5 parts Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 50 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (Trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

Example 3 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Synthetic hectorite (trademark: Mizukanite SH1, manufactured by Mizusawa Chemical) 15 parts Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 40 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (Trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

Example 4 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Synthetic hectorite (trademark: Laponite B, manufactured by Laporte Industries) 20 parts Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 35 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (Trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

Comparative Example 1 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 55 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

Comparative Example 2 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Carbon black aqueous dispersion (trademark: LKB-100, manufactured by Hoechst Synthetic) 5 parts Kaolinite clay (trademark: Hydrogloss 90, manufactured by Huber) 50 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

Comparative Example 3 An electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1 except that the back layer coating liquid was changed to the following composition, and its characteristics were evaluated. The results are shown in Table 1. Back layer coating liquid Firing clay (trademark: Ansilex 95, manufactured by Engelhard) 55 parts Acrylic emulsion (trademark: A-104, manufactured by Toagosei) 20 parts SBR (trademark: L-1537A, manufactured by Asahi Kasei) 25 parts

[0034]

[Table 1]

[0035]

Industrial Applicability According to the present invention, it is possible to produce an electrophotographic lithographic printing plate material which is free from image fog and has good dimensional stability even in plate making under low humidity and has excellent image quality. , Very useful.

Claims (1)

[Claims] 1. A water resistant support, an intermediate layer formed on one surface of the water resistant support, a photoconductive layer formed on the intermediate layer, and an opposite surface of the water resistant support. An electrophotographic lithographic printing plate material having a formed back layer, wherein the back layer contains a synthetic hectorite.