JPH047555A - Original plate for planographic printing - Google Patents

Abstract

PURPOSE:To obtain the original plate for planographic printing which has an excellent water retaining property and good durability while maintaining good electrophotographic characteristics and physical strength by incorporating silica into a photosensitive layer. CONSTITUTION:The silica is incorporated into the photosensitive layer of the original plate for planographic printing formed by providing the photosensitive layer contg. zinc oxide as a photoconducting agent on a base. The silica to be used is porous body essentially consisting of silicon dioxide and has the effect of improving the water retaining property of the photosensitive layer for its porosity when the silica is added into the photosensitive layer. Particularly the silica which is not subjected to a hydrophobing treatment on the surface among various kinds of the silica has a silanol group on the surface of porous particles and has consequently a high hydrophilic property; therefore, this silica is more adequately used. The good electrophotographic characteristics and the excellent physical strength are maintained in this way and the water retaining property is improved. The plate staining is suppressed and the durability is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a lithographic printing original plate made by an electrophotographic method, and more specifically, to printing of a lithographic printing original plate using zinc oxide as a photoconductive agent. It relates to the improvement of suitability, specifically water retention.

<Prior art> In general, lithographic printing original plates using zinc oxide as a photoconductive agent, which are made by electrophotography, contain zinc oxide powder in the binder, sensitizing dyes as necessary, various additives, etc. A photosensitive layer formed by dispersing is provided on a support. Such a lithographic printing original plate must have excellent printing properties as a printing original plate, as well as other properties such as electrophotographic properties and physical strength.

In recent years, there has been a strong demand for durability of original plates for printing, but conventional lithographic printing original plates using zinc oxide did not have sufficient durability, especially water retention. When a printing plate has excellent water retention, so-called "plate smudge" is less likely to occur, and as a result, clear printed matter can be obtained. It is interpreted that this is caused by the ink being transferred even to non-image areas because the ink has not been made fat (hydrophilic). Therefore, conventionally, in order to improve the water retention of a zinc oxide photosensitive layer, desensitization was strengthened by increasing the blending ratio of zinc oxide and binder in the photosensitive layer. methods have been proposed. It has also been proposed to add a surfactant to the photosensitive layer to improve the hydrophilicity of the photosensitive layer itself.

However, although these methods improve water retention, they have problems in that they result in a significant decrease in physical strength, typified by plate removal of the photosensitive layer, and a decrease in electrophotographic properties. As described above, in the prior art, it has not been possible to obtain a printing original plate that has excellent water retention without impairing other properties, that is, has sufficient durability.

<Problems to be Solved by the Invention> In view of the above circumstances, the present invention provides a planographic printing original plate provided with a photosensitive layer using zinc oxide as a photoconductive agent, which maintains good electrophotographic properties and physical strength. However, the present invention provides a lithographic printing original plate having excellent water retention and good durability.

<Means for Solving the Problems> The present invention provides a lithographic printing original plate comprising a photosensitive layer containing zinc oxide as a photoconductive agent on a support, characterized in that the photosensitive layer contains silica. This is an original plate for lithographic printing.

The silica used in the present invention has an average particle size of 5 nm to 20 nm.
It is a porous powder whose main component is silicon dioxide of about μm size, and due to its porosity, it has the effect of improving the water retention of the photosensitive layer when added to the photosensitive layer. In the present invention, in addition to silica without surface treatment, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrichlorosilane, T-glycidylpropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, T-anilinopropyltrimethoxysilane, T-
Various silane compounds such as chloropropyltrimethoxysilane and aminosilane, as well as dimethyl silicone oil,
Examples include various types of silica, including those that have been hydrophobized with silicone oils such as methyl hydrogen silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, and carboxy-modified silicone oil to improve solvent miscibility, but are not particularly limited. isn't it. Also, -
Not only the powdered silica used by boat, but also various silica sols dispersed in organic solvents such as methanol can be used. In the present invention, among the above-mentioned silicas, silica that has not been subjected to surface hydrophobization treatment is particularly preferably used because it has high hydrophilicity due to the presence of silanol groups on the surface of the porous particles.

The blending ratio of silica in the photosensitive layer as described above is preferably 0.5 to 50%, particularly preferably 1 to 10% by weight relative to zinc oxide. Here, if the amount added is less than 0.5%, the expected effect will not be obtained much, and if it is more than 50%, there is a risk of deterioration of electrophotographic characteristics.

The photosensitive layer in the present invention has a composition in which zinc oxide as a photoconductive substance, the above-mentioned silica, and various other additives such as sensitizing dyes and sensitizers are dispersed in a binder as necessary. be. Examples of binders used in the photosensitive layer include acrylic resins, other vinyl resins, silicone resins, polyester resins, polyurethane resins, cellulose resins, polybutyral resins, styrene-butadiene copolymer resins, and epoxy resins. , alkyd resin, fluororesin, etc. can be used, and are not particularly limited.

The blending ratio of zinc oxide and binder in the photosensitive layer is preferably zinc oxide/binder = 172 to 4/1.

Additives that may be used in the photosensitive layer as needed include triphenylmethane, xanthine, cyanine,
Examples include sensitizing dyes such as fluoran-based sensitizing dyes, sensitizers such as phthalic anhydride, maleic anhydride, and the like.

Supports in the present invention include paper, synthetic paper, various resin films, nonwoven fabrics, metal foils, metal plates, and composites thereof, and those to which water resistance is imparted by coating or laminating. These materials can be used as appropriate, such as those subjected to conductive treatment, and are not particularly limited.

The lithographic printing original plate of the present invention has a photosensitive layer as described above provided on a support. To form a photosensitive layer, a coating material containing the binder, zinc oxide, silica, and other additives dispersed in a suitable solvent is coated with an air knife coater or a roll coater.
, a wire percoat was installed.

It is done by drying. In providing the photosensitive layer, it is preferable to provide an under layer on the support in advance in order to prevent the photosensitive layer paint from permeating into the support and to improve water resistance.

It is also suitable to provide a back layer to improve water resistance and prevent curling. The under layer and back layer can be made of the same resin as the binder for the photosensitive layer, and can be provided on the support by a known coating method.

<Example> Next, the present invention will be explained in detail with reference to Examples.

Note that all parts indicating formulations represent parts by weight.

Example 1 A 100 g/m2 high-quality paper was used as a support, and a paint having the following composition was coated on both sides of the support and dried to form an under layer and a back layer (coating amount of each 10 g/m"). A photosensitive layer coating material having the following composition was coated on the layer and dried to provide a photosensitive layer having a thickness of 15 μm, thereby preparing a lithographic printing original plate of the present invention.

Example 2 Except for using the following composition as the coating for the photosensitive layer:
A lithographic printing original plate of the present invention was prepared in exactly the same manner as in Example 1.

Except for this, a lithographic printing original plate of the present invention was produced in the same manner as in Example 1.

Example 3 Except for using the following composition as the coating for the photosensitive layer:
A lithographic printing original plate of the present invention was prepared in exactly the same manner as in Example 1.

Comparative Example Except for using the following composition as the paint for the photosensitive layer:
A comparative lithographic printing original plate was prepared in exactly the same manner as in Example 1.

Example 4 The lithographic printing original plates prepared in Examples 1 to 4 and Comparative Examples above using the compositions below as coatings for the photosensitive layer were subjected to plate making, etching, and a continuous printing test of 5,000 sheets in the following manner. The condition of the plate stain and the stain of the printed matter were evaluated by visual observation. As a result, the lithographic printing original plates of Examples 1 to 4 according to the present invention were found to have a
No plate staining was observed during the printing process of 00 sheets, confirming excellent water retention. On the other hand, in the lithographic printing original plate of the comparative example, plate staining was clearly observed, and the printed matter was also problematic in practical use. In addition, the printed matter obtained from the lithographic printing original plates of Examples 1 to 4 according to the present invention not only provides good images and has good plate-making or electrophotographic properties, but also shows no plate dropping during continuous printing and the surface of the photosensitive layer is good. It was confirmed that the material had sufficient physical strength.

<Effects of the Invention> The lithographic printing original plate of the present invention has the above-mentioned structure, so it maintains good electrophotographic properties and excellent physical strength, and has excellent water retention, so it is difficult to cause plate staining. This has the effect of good durability.

Patent applicant: Tomoekawa Paper Mills Co., Ltd.

Claims (2)

[Claims] (1) A lithographic printing original plate comprising a photosensitive layer containing zinc oxide as a photoconductive agent on a support, wherein the photosensitive layer contains silica. (2) The lithographic printing original plate according to claim 1, wherein the silica is silica that has not been subjected to a hydrophobic treatment.