JPH07110607A - Electrophotographic planographic printing plate material - Google Patents

Abstract

PURPOSE:To prevent the generation of printing surface staining occurring in friction by dispersing and incorporating spherical particles of a specific size into an electrophotographic sensitive layer, thereby forming many projecting parts on the surface of this photosensitive layer. CONSTITUTION:The electrophotographic sensitive layer 2 contg. a mixture composed of zinc oxide particles 5 (shown by many dots) and an insulating resin binder 6 as an essential component is formed on a conductive and water resistant substrate 1. Further, the spherical particles 3 essentially consisting of crosslinked polymethyl methacrylate having the average grain size of 5 to 50mum are incorporated into such electrophotographic sensitive layer 2. Many projections 4 are formed on the surface of the photosensitive layer. The images of a printing plate and printed matter rough increasingly if the average grain size of the spherical particulates essentially consisting of the crosslinked polymethyl methacrylate is larger than 50mum. There is no more effect of preventing friction and the surface staining arises in the printed matter if the average grain size of the particles is smaller than 5mum.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrophotographic lithographic printing plate material. More specifically, the present invention relates to an electrophotographic lithographic printing plate material which has little or no generation of printing background stains due to friction.

[0002]

2. Description of the Related Art Printing plate materials for direct plate making using electrophotography include, for example, Japanese Patent Publication Nos. 47-47610 and 48-4.
0002, Japanese Patent Publication No. 48-18325, Japanese Patent Publication No. 51-15766, Japanese Patent Publication No.
No. 51-25761, which have an electrophotographic photosensitive layer of a photoconductive zinc oxide-resin dispersion system. Such a printing plate has the advantages that it is inexpensive, has relatively high sensitivity, and has a simple plate-making process, and is widely used.

To produce an electrophotographic lithographic printing plate, the printing plate material is subjected to a plate making machine which is subjected to a corona charging, exposure, development and fixing process in the desired pattern, whereby the photoconductive layer thereof. A method of forming a toner image having a desired pattern on the surface is generally performed.

The above development process is classified into a dry development method using a mixture of toner and a carrier such as iron powder.
There is a wet development method using a developer in which toner is dispersed in an organic solvent such as Isopar. When the plate is made using the wet development method, the halftone reproducibility of the obtained printed matter is good, the resolution is excellent, and the platemaking time is short. The electrophotographic lithographic printing plate by is widely used.

The electrophotographic lithographic printing plate material is required to have various characteristics required as a lithographic printing material in addition to the image characteristics generally required as an electrophotographic material. The electrophotographic photosensitive layer is formed by applying a coating material comprising a photoconductive pigment such as zinc oxide or titanium oxide, an insulating resin binder, a sensitizing dye and a solvent onto a support and drying the coating.

As the insulating resin binder, generally, an acrylic acid ester copolymer, a methacrylic acid ester copolymer, which has high hydrophilicity, is used in order to prevent the occurrence of scumming during printing.
Vinyl acetate copolymer, silicone resin, butyral resin, etc. are used. In addition, acrylic acid, in order to improve image quality, paint properties, and mechanical strength of the coating film,
It is common practice to copolymerize a functional group such as methacrylic acid or maleic acid with the above resin.

However, the electrophotographic photosensitive layer using the above resin binder has insufficient surface strength,
It has a problem that it is easily worn. Therefore, the electrophotographic photosensitive layer is easily damaged by pressure and friction during the manufacturing process of the electrophotographic lithographic printing plate material, during transportation or during transportation in the plate making machine. Toner easily adheres to the scratched portion, and therefore, when a printing plate manufactured from such a plate material is used, printing spots often occur.

In order to solve such problems, it has been attempted to increase the pressure resistance of the electrophotographic photosensitive layer by using polystyrene resin or polymethylmethacrylate resin having a high glass transition temperature as an insulating resin binder. However, when such a resin binder is used, the flexibility and flexibility of the resulting photosensitive layer are low, and therefore cracks easily occur when used as a printing plate, which causes a reduction in printing durability. It causes problems such as.

Further, as a method of increasing the coating film strength, it is possible to increase the compounding ratio of the insulating resin binder in the photosensitive layer forming material, but the compounding ratio of zinc oxide is lowered and good image quality is obtained. Is not obtained, and the etching effect is insufficient, and the obtained printed matter is entirely dirty and insufficient.

Further, JP-A-59-40654 discloses a zinc oxide light-sensitive material for offset printing, in which an electrophotographic light-sensitive layer is coated with an acrylic-butadiene copolymer having a particle size of 20 to 50 μm. It is described that particles are dispersed and contained to form a large number of protrusions on the surface of the photosensitive layer, thereby reducing generation of print background stains due to friction.
However, the acryl-butadiene copolymer-coated zinc oxide particles have a problem that the flexibility of the resin is too high and the pulverization is difficult. Further, a printing plate using the zinc oxide particles coated with an acrylic-butadiene copolymer has a reduced electrophotographic property and is apt to cause fog during plate making, and also has a background stain on the printed matter. Further, the projections formed by the acryl-butadiene copolymer-coated zinc oxide particles have drawbacks such as not having sufficient hardness against mechanical wear. Further, there is a problem that many steps such as mixing and dispersing the resin and zinc oxide, drying, pulverizing and classifying are required.

Besides, it is said that undispersed zinc oxide particles are contained in the electrophotographic photosensitive layer to form a large number of protrusions on the surface of the photosensitive layer, thereby reducing the occurrence of print background stains due to friction. There is also technology. However, since the undispersed zinc oxide particles do not have a uniform shape, there is a problem in that the paint tends to be clogged with the filter during the coating operation or the dispersing operation, that is, the so-called paint permeability is poor.

[0012]

The problem to be solved by the present invention is to solve the above-mentioned problems of a lithographic printing plate material using a conventional electrophotographic method and to prevent the occurrence of printing background stains due to friction. Or to provide less electrophotographic printing plate material. Still another problem to be solved by the present invention is to provide an electrophotographic printing plate material having a spectral sensitivity capable of being recorded by light beams of various wavelengths such as He-Ne laser light or semiconductor laser light.

[0013]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted earnest research to achieve the above object, and as a result, a hard pigment having a specific size is dispersedly contained in an electrophotographic photosensitive layer, whereby The inventors have found that when a large number of protrusions are formed on the surface of the photosensitive layer, frictional force is selectively applied to the protrusions and damage to the electrophotographic photosensitive layer is prevented, and the present invention has been completed.

That is, the electrophotographic lithographic printing plate material according to the present invention comprises a conductive / water resistant support, zinc oxide particles and a resin binder formed on one surface of the conductive / water resistant support. An electrophotographic photosensitive layer containing as a main component a mixture of the above, wherein the electrophotographic photosensitive layer contains crosslinked polymethylmethacrylate as a main component and contains spherical fine particles having an average particle diameter of 5 to 50 μm dispersed therein. , Is characterized in that a large number of protrusions are formed on the surface.

FIG. 1 is a schematic sectional view showing the basic structure of the lithographic printing plate of the present invention. An electrophotographic photosensitive layer 2 containing a mixture of zinc oxide particles 5 (indicated by a large number of dots) and an insulating resin binder 6 as a main component is formed on a support 1. In the electrophotographic photosensitive layer 2, , And an average particle size of 5
It contains 50 μm of true spherical fine particles 3 containing cross-linked poly (methyl methacrylate) as a main component, and thereby a large number of protrusions 4 are formed on the surface of the photosensitive layer. The thickness of the electrophotographic photosensitive layer is generally 20 to 30 μm.

As described above, the zinc oxide light-sensitive material for lithographic printing generally contains a soft resin as a binder, so that its surface is soft and is therefore susceptible to abrasion and damage. When such a soft surface is mechanically rubbed, the electrophotographic sensitivity of the rubbed portion is lowered and the potential is not attenuated even after exposure, and the toner is attached to the rubbed portion in the developing process. However, it often causes print stains on the printed matter and deteriorates the image.

However, in the electrophotographic photosensitive layer of the present invention, since hard particles of a specific size are scattered on the surface to form protrusions, mechanical abrasion of the electrophotographic photosensitive layer itself is prevented, This makes it possible to prevent the occurrence of background stains on the printed matter.

In the present invention, the true spherical fine particles containing crosslinked poly (methyl methacrylate) as a main component have an average particle size of 5 to
50 μm is preferable, and 15 to 30 μm is preferable. When the average particle size of the fine particles is larger than 50 μm, the images of the printing plate and the printed matter become rough. Also, the average particle size of the fine particles is 5 μm.
When it becomes smaller, the effect of preventing abrasion is lost, and the printed matter is stained.

The particles containing cross-linked poly (methyl methacrylate) as a main component do not dissolve in the solvent (generally, an aromatic solvent such as toluene) of the coating solution for the electrophotographic photosensitive layer, which adversely affects the electrophotographic characteristics of the electrophotographic photosensitive layer. Never give. Further, since the particles have a spherical shape, they do not affect the paint permeability.

In the electrophotosensitive layer of the present invention, other organic pigments such as urea resin, high density polyethylene powder, starch, and polyester resin particles are used instead of the true spherical particles containing crosslinked polymethylmethacrylate as a main component. And inorganic pigments such as aluminum hydroxide, alumina,
When spherical silica balloons, spherical aluminosilicate particles, calcium metasilicate, and titanium oxide are used, regardless of the occurrence of print background stains due to friction, deterioration of electrophotographic characteristics and desensitization are caused. It causes possible plate-making fog and printing background stain, which makes it impossible to obtain a practical electrophotographic printing plate material.

In the electrophotographic photosensitive layer of the present invention, the spherical particles having a mean particle size of 5 to 50 μm and containing crosslinked poly (methyl methacrylate) as a main component are prepared by using a conventional photoconductive zinc oxide-insulating resin binder system. It is mixed and dispersed in a coating material for electrophotographic photosensitive layer, and this coating material is coated on a support having conductivity and water resistance to give a film thickness of 20.
It is formed by coating so as to have a thickness of 30 μm (after drying) and drying. In this electrophotographic photosensitive layer, the fine particles form a large number of protrusions on the surface of the photosensitive layer. Further, the addition amount of the fine particles is preferably 0.01 to 2.0% by weight of the solid content of the electrophotographic photosensitive layer coating material, 0.04
More preferably, it is ˜1.0 wt%.

The insulating resin binder used in the electrophotographic photosensitive layer may be composed of a single type of resin, or may be a mixture of two or more types of resin binders. As such a resin binder, for example, polyester resin, acrylic resin, epoxy resin, polycarbonate resin, melamine resin, butyral resin, silicon resin, polyurethane resin, alkyd resin, polystyrene resin, xylene resin, and phenoxy resin are used. .

In addition to zinc oxide, the electrophotographic photosensitive layer used in the present invention mainly contains a photosensitive coating material, an electron-accepting substance, and a photosensitive coating material conventionally used for the purpose of improving electrophotographic characteristics such as sensitivity. Various sensitizers and additives such as compounds having a maximum sensitivity to the light in the wavelength range of 700 to 1000 nm may be appropriately contained in order to make the light in the wavelength of the semiconductor laser sensitive.

As the conductive support of the electrophotographic lithographic printing plate material of the present invention, a known support can be used, for example, a metal sheet, a metal foil, a paper laminated with a metal foil, a plastic film, a vapor-deposited metal. It can be selected from papers and plastic films with layers, papers and plastic films that have been subjected to a conductive treatment, and the like.

To make a lithographic printing plate from the printing plate material of the present invention, the material is uniformly charged in a dark place by a corona charger or the like according to a usual electrophotographic method, and then a tungsten lamp or halogen is used. A reflective image exposure using a light source such as a lamp or a fluorescent lamp, a contact exposure through a transparent positive film, or a scanning exposure with a laser beam such as a He-Ne laser, an argon laser or a semiconductor laser, and an electrophotographic photosensitive layer. An electrostatic latent image is formed on the electrostatic latent image, and the electrostatic latent image is developed with toner and heat-fixed to form a toner image on the plate. The non-image area of the printing plate thus obtained is subjected to a desensitizing treatment using a normal desensitizing treatment liquid, and then this printing plate is mounted on an offset printing machine and used for printing.

[0026]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In the following, “parts” and “%” refer to parts by weight and% by weight, unless otherwise specified. EXAMPLE 1 Paint 1 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of toluene 100 parts of the paint 1 The mixture was dispersed with a sand grinder to prepare a photosensitive solution, and then the photosensitive solution was mixed with O. A coating material for forming an electrophotographic photosensitive layer was prepared by adding 1 part of crosslinked polymethylmethacrylate true spherical particles (trade name: MBX-20, manufactured by Sekisui Plastics Co., Ltd., average particle size: 17.8 μm).

As the support, a composite sheet produced by laminating a 10 μm thick aluminum foil on a base paper having a basis weight of 80 g / m ² was used. The above-mentioned coating material was applied onto the aluminum foil surface of the above support and dried to form an electrophotographic photosensitive layer. The thickness of this photosensitive layer is 25 μm
(After drying). A large number of protrusions having a height of 15 μm or less were formed on the surface of the photosensitive layer.

In order to evaluate the scratch resistance of the photosensitive layer of the obtained electrophotographic planographic printing plate material, 25 test printing plate materials were used.
The plate is placed in a dark place of an atmosphere of 50 ° C. and 50% RH for conditioning for 24 hours, and then another printing plate material is superposed on the surface of the electrophotographic photosensitive layer of this printing plate material so that the back surface thereof is in contact, A weight of 3 kg (diameter 7 cm) was placed on it, the upper printing plate material was pulled by about 20 cm, and the photosensitive layer surface of the lower printing plate material was damaged. After that, plate making and printing were carried out using this printing plate material, and in the obtained printed matter, the degree of print background stain on the damaged part (particularly for the non-image part) was sensorially evaluated.

Plate making and printing were performed as follows. That is, the plate was made using a 235 type plate making machine manufactured by Itek, desensitized with an etchant (product of Itek), and then printed using an offset printing machine (2800CD made by Ryobi, Shinflo type). The results are shown in Table 1.

[0030] Comparative Example 1 Paint 2 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of 100 parts of toluene The mixture was dispersed with a sand grinder to prepare a photosensitive solution. In this photosensitive liquid, without mixing resin particles,
This was used as a coating material for forming an electrophotographic photosensitive layer, and this was coated on a support in the same manner as in Examples to produce an electrophotographic lithographic printing plate material. Using the obtained printing plate material, plate making and printing were carried out in the same manner as in Examples to evaluate the printing background stain. The results are shown in Table 1.

[0031] Comparative Example 2 Paint 3 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of 100 parts of toluene The mixture was dispersed with a sand grinder to prepare a photosensitive solution, and 0.5 part of high-density polystyrene resin fine particles (made by Iron and Steel Chemical Co., Flow beads HE-5023, average particle size 18.7) were added.
μm) was added to prepare a coating material for forming an electrophotographic photosensitive layer. This was coated on a support in the same manner as in Example to produce an electrophotographic lithographic printing plate material. Using the obtained printing plate material, plate making and printing were carried out in the same manner as in Examples to evaluate the printing background stain. The results are shown in Table 1.

[0032] Comparative Example 3 Paint 4 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of 100 parts of toluene The mixture was dispersed with a sand grinder to prepare a photosensitive liquid, and 1.0 part of polymethylmethacrylate resin particles (Nippon Pure Chemical Co., Ltd., Julimer, MB-20, average particle size 19.1) were prepared.
μm) was added to prepare a coating material for forming an electrophotographic photosensitive layer. This was coated on a support in the same manner as in Example to produce an electrophotographic lithographic printing plate material. Using the obtained printing plate material, plate making and printing were carried out in the same manner as in Examples to evaluate the printing background stain. The results are shown in Table 1.

[0033] Comparative Example 4 Paint 5 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of 100 parts of toluene The mixture was dispersed with a sand grinder to prepare a photosensitive solution, and 1.0 part of starch was added thereto to prepare a coating material for forming an electrophotographic photosensitive layer. This was coated on a support in the same manner as in Example to produce an electrophotographic lithographic printing plate material. Using the obtained printing plate material, plate making and printing were carried out in the same manner as in Examples to evaluate the printing background stain. The results are shown in Table 1.

[0034] Comparative Example 5 Paint 6 Ingredient wt of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., SAZEX # 2000) 90 parts Polyacrylic resin (Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.02 parts of 100 parts of toluene The mixture was dispersed with a sand grinder to prepare a photosensitive solution, and 1.0 part of alumina (manufactured by Taiheiyo Random Co., Ltd.,
Nisso random, LA-400, average particle size 27.4 μm) was added to prepare a coating material for forming an electrophotographic photosensitive layer. This was coated on a support in the same manner as in Example to produce an electrophotographic lithographic printing plate material. Using the obtained printing plate material, plate making and printing were carried out in the same manner as in Examples to evaluate the printing background stain. The results are shown in Table 1.

[0035]

[Table 1]

As is clear from Table 1, the electrophotographic photosensitive layers of the examples according to the present invention were resistant to the forced friction and were able to obtain printed matters free of background stain during printing. In Comparative Example 1, since the projections were not formed on the surface of the photosensitive layer, the surface of the electrophotographic photosensitive layer was easily damaged by friction, and a large number of print background stains were generated. In Comparative Examples 2 to 5, pigment particles other than the crosslinked polymethylmethacrylate true spherical particles were added to the coating material for forming the photosensitive layer, and when these pigment particles were used, the occurrence of print background stains due to friction occurred. Regardless of the presence or absence of the above, the print background stain was considered to be due to the deterioration of the electrophotographic characteristics and the deterioration of the desensitizing property.

[0037]

According to the present invention, it is possible to obtain a printed matter excellent in image quality, with no or little damage to the electrophotographic photosensitive layer due to friction or the like, no generation of print background stains.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a configuration of a lithographic printing plate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Support, 2 ... Electrophotographic photosensitive layer, 3 ... Crosslinked polymethylmethacrylate true spherical fine particles, 4 ... Protrusions, 5 ... Zinc oxide particles, 6 ... Resin binder.

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Claims (1)

[Claims] 1. A conductive / water resistant support and the conductive / water resistant support.
An electrophotographic photosensitive layer formed on one surface of a water-resistant support and containing a mixture of zinc oxide particles and a resin binder as a main component, wherein the electrophotographic photosensitive layer is mainly composed of crosslinked polymethyl methacrylate. An electrophotographic lithographic printing plate material characterized in that spherical fine particles having a mean particle size of 5 to 50 μm are dispersed and contained as a component, and a large number of projections are formed on the surface.