JPH0250465B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electrophotographic lithographic printing plate material. More specifically, the present invention relates to an improved electrophotographic lithographic printing plate material that has good printing durability and low plate elongation. [Prior Art] In recent years, with the development of small offset printing presses and automatic printing presses, the mainstream of light printing is shifting to offset printing. Much research and development has been carried out on such offset printing plate materials, and various materials have been put into practical use. Among these materials, electrophotographic lithographic printing original plates having a photoconductive layer mainly composed of zinc oxide are the mainstream of light printing plate materials because they are inexpensive and have a simple plate-making process. ing. Electrophotographic lithographic printing plates are usually produced by subjecting the printing plate material to corona charging, exposure, development and fixing processes in a desired pattern using a plate-making machine, thereby creating a desired pattern in the photoconductive layer. Manufactured by forming an image. The above-mentioned developing process includes a dry developing method using a mixture of toner and a carrier such as iron powder, and a wet developing method using a developer in which toner is dispersed in an organic solvent such as Isopar. When plate making is performed using the above-mentioned wet development method, there are advantages such as good halftone reproducibility, excellent resolution, short plate making time, and no correction required. A method for manufacturing electrophotographic lithographic printing plates using a wet development method is widely used. In addition to the image properties typically required for electrophotographic copying materials, electrophotographic lithographic printing plate materials
It is also necessary that it possesses various properties generally required for lithographic printing materials. For example, a printing plate that has undergone a development process must be able to be desensitized in its non-image areas. In addition, as a plate material for offset printing, it is possible to make non-image areas hydrophilic by treating the surface of the photoconductive layer with an etchant, and it is also possible to make the non-image area hydrophilic by treating the surface of the photoconductive layer with an etchant. However, it is necessary to have excellent water resistance. It is known to form various intermediate layers between the support and the photoconductive layer in order to improve the water resistance as described above. The photoconductive layer is formed by applying a paint consisting of a photoconductive pigment such as zinc oxide or titanium oxide, an insulating binder, a sensitizer, and a solvent onto the intermediate layer and drying it. Ru. Insulating binders for photoconductive layers are generally acrylic ester copolymers, methacrylic ester copolymers, and vinyl acetate copolymers, which have good hydrophilic properties and are effective in preventing scumming during printing. , silicone resin, butyral resin, etc. are used. These resins contain acrylic acid,
Usually, functional groups such as methacrylic acid and maleic acid are copolymerized. The intermediate layer formed between the support and the photoconductive layer is for firmly bonding the support base and the photoconductive layer, and is required to have the following properties. 1. Excellent water resistance and ability to prevent peeling of the photoconductive layer due to application of water. 2. It should be located between the supporting substrate and the photoconductive layer, so that they can be firmly adhered to each other to prevent the photoconductive layer from peeling off due to external physical forces such as straining or bending. 3. When coating a photoconductive layer, it must be possible to prevent the solvent such as water or organic solvent or adhesive component from penetrating into the support. 4 Especially when using as an original plate for electrophotographic planography,
When creating an image, it should not cause contrast deterioration such as a decrease in image density or an increase in fog. Conventionally, binders for intermediate layers that satisfy these characteristics are generally water-soluble polymers such as polyvinyl alcohol, casein, and starch, and water-resistant agents such as amino resin condensates of these water-soluble polymers. crosslinking reaction products with are widely used. It is also known to mix synthetic resin emulsions and the like with these binders. However, when using the above-mentioned crosslinking reaction product, if the crosslinking reaction is carried out in the paint before being applied to the support, the paint will thicken and gel, making it practically impossible to coat. In addition, in order to cause a crosslinking reaction during or after coating, it is necessary to heat the coating at a temperature of at least 150° C. for 5 minutes or more.
Such heating conditions cannot be adopted in terms of productivity and profitability on an industrial scale. In addition, if the support is exposed to such high temperatures for a long time, the support becomes brittle, making it impossible to obtain a lithographic printing original plate having the necessary physical strength. Therefore, the temperature and time expected from the commonly used coating conditions are completely insufficient to complete the crosslinking reaction, and the desired desired water resistance cannot be obtained. The printing plate precursor has extremely low printing durability. Furthermore, when a hydrophilic substance is used as an intermediate layer of an electrophotographic original plate, the adhesion between the intermediate layer and the lipophilic adhesive in the photoconductive layer becomes insufficient. In addition, it is conventionally known to use a paint consisting of a vinyl resin and an amino resin containing a functional monomer (hydroxyethyl acrylate) in the intermediate layer (Japanese Patent Publication No. 47-47610); The reaction between the group and the amino resin is slow, the resulting printing plate precursor has low water resistance, and light attenuation during image formation is poor, resulting in images with a lot of fog and poor contrast. It is also known to coat a synthetic polymer resin infiltrated or swollen with a photoconductive coating solvent between the hydrophilic polymer coating layer and the photoconductive coating applied to the surface of the support (particularly Publication No. 40-7332), but in this method, one more step is added in order to add one more lipophilic layer between the hydrophilic polymer layer and the photoconductive layer, which also causes high costs. In addition, this oleophilic layer has the disadvantage of having a negative effect on the light attenuation of the photoconductive layer. [Problems to be Solved by the Invention] The present invention solves problems caused by providing an intermediate layer between the support and the photoconductive layer in electrophotographic lithographic printing plate materials, namely, deterioration of image quality and insufficient image quality. The objective is to eliminate or reduce printing durability and plate elongation. [Means and effects for solving the problems] The electrophotographic lithographic printing plate material of the present invention includes a support, a photoconductive pigment, and an electrically insulating bond formed on one surface of the support. and a photoconductive layer containing an adhesive, and has an average particle diameter of 5 to 50 μm between the support and the photoconductive layer. It is characterized in that an intermediate layer containing wet-pulverized muscovite powder and a binder is formed. The average particle diameter of the muscovite powder used in the present invention was measured using a light transmission particle size analyzer model SKN-1000 manufactured by Seishin Enterprise Co., Ltd. In the printing plate material of the present invention, the intermediate layer formed between the support and the photoconductive layer is prepared by a wet grinding method, and has a thickness of 5 to 50 μm, preferably 5 to 40 μm,
More preferably, it contains muscovite powder having an average particle diameter of 10 to 40 μm and a binder. This intermediate layer is effective in enhancing the image quality of the resulting printing plate material, improving printing durability, and reducing plate elongation. The chemical composition of the muscovite powder used in the present invention is represented by the general formula: K _{2 O.3Al 2} O _3.6SiO 2.2H ₂ O. A pigment similar to the muscovite of the present invention is sericite clay. Sericite is called sericite because it has a silky luster when wet with water. The chemical compositions of muscovite and sericite clay are as follows.

【table】

〔Example〕

The present invention will be further explained below with reference to Examples. Example 1 An electrophotographic printing plate material was prepared by steps (1) to (5) described below, and then a printing plate was made, and step (b)
The characteristics were measured and evaluated. (1) A barrier layer of the following composition is applied on one side of base paper with a basis weight of 100 g/m ² by size and press treatment.
m ² (dry coating weight). Polyvinyl alcohol 80 parts (solid weight) Sodium polyacrylate 20 parts (〃 〃 ) (2) Press-treated base paper of the above size (thickness)
An intermediate layer paint having the following composition was applied to the surface of the barrier layer (110 μm) and dried to form an intermediate layer with a dry coating weight of 10 g/m ² . Muscovite A-21 (*) ₁ 40 parts (by weight) Polyurethane aqueous dispersion (*) ₂ 40 parts ( ) Casein aqueous solution 10 parts ( ) Silane coupling (*) ₃ 10 parts ( ) Notes (*) ₁ ...Manufactured by Yamaguchi Mica Co., Ltd. Average particle diameter = 20μm (*) ₂ ...Trademark: Azerax S-1071, manufactured by Hodogaya Chemical (*) ₃ ...Trademark: SH6040, manufactured by Toray Silicone (3) On the surface of the intermediate layer A photoconductive layer paint having the following composition was applied and dried to form a photoconductive layer with a dry coating weight of 25 g/m ² . Photoconductive zinc oxide (*) ₄ 100 parts (by weight) Silicone resin (*) ₅ 30 parts (〃) Rose Bengal 0.1 part (〃) Toluene 150 parts (〃) Notes (*) ₄ …Trademark: SAZEX2000, Sakai Chemical Manufactured by (*) ₅ ...Trademark: KR-211, Shin-Etsu Chemical (4) A conductive layer paint with the following composition was applied and dried on the back side of the photoconductive layer to form a conductive layer with a dry coating weight of 8 g/ ^m2 . did. Polyvinyl alcohol (*) ₆ 30 parts (by weight) Vinyl acetate resin (*) ₇ 50 parts (〃) Quaternary ammonium type polymer conductive agent (*) ₈
20 copies (〃) Notes (*) ₆ ...Trademark: T-330, manufactured by Nippon Gosei (*) ₇ ...Trademark: Sepian A-522, manufactured by Daicel (*) ₈ ...Trademark: Chemistat 5500, manufactured by Sanyo Chemical (5) ) The obtained printing plate material was subjected to acclimatization treatment for 24 hours in a dark room atmosphere at 50% RH and 25℃, and then
A printing plate having a predetermined pattern was created using a 175-type electronic plate making machine. (6) The printing test of the obtained printing plate was carried out by first desensitizing the printing plate with an etching liquid (manufactured by ITETICS Co., Ltd.), using an offset printing machine (Hamada Star 500), and using New Champion F as the ink. A printing durability test (picking evaluation) and plate elongation test were conducted using gloss (black). The results are shown in Table 1. Comparative Example 1 The same operation as in Example 1 was performed. However, the intermediate layer paint had the following composition. Zeeklite (*) ₉ 40 parts by weight polyurethane aqueous dispersion 40 parts by weight casein aqueous solution 10 parts by weight Silane coupling agent 10 parts by weight Note (*) ₉ ...Manufactured by Zeeklite Kogyo Co., Ltd., plate elongation containing 35% sericite and the printing durability test results are shown in Table 1. Comparative Example 2 The same operation as in Example 1 was performed. However, the composition of the intermediate layer paint was as follows. Sericite clay (sericite) (*) ₁₀ parts by weight Aqueous polyurethane dispersion 40 parts by weight Aqueous casein solution 10 parts by weight Silane coupling agent 10 parts by weight The results of the plate elongation and printing durability tests are shown in Table 1. Note (*) ₁₀ …Micro Clean (manufactured by Dowa Mining Co., Ltd.) Average particle size 0.57μm

〔Effect of the invention〕

In the present invention, the average particle size of the intermediate layer is 5 to 50μ.
By containing muscovite, the water resistance of the intermediate layer can be improved, the printing durability of the resulting printing plate can be improved, and plate elongation can be significantly reduced.

Claims (1)

[Scope of Claims] 1. A support, formed on one surface of the support,
and a photoconductive layer comprising a photoconductive pigment and an electrically insulating binder, and having an average particle size of 5 to 50 μm between the support and the photoconductive layer. An electrophotographic lithographic printing plate material in which an intermediate layer containing wet-milled muscovite powder and a binder is formed. 2. The printing plate material according to claim 1, wherein the intermediate layer binder is formed from a mixture containing a synthetic resin aqueous emulsion, a water-soluble polymer compound, and a water-resistant agent. 3. The printing plate material according to claim 1, wherein the muscovite powder content in the intermediate layer is in the range of 30 to 70% by weight. 4. The printing plate material according to claim 1, wherein the dry weight of the intermediate layer is within the range of 5 to 15 g/ ^m2 .