JPH0541983B2 - - 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 electrophotographic lithographic printing plate material that does not cause or has little occurrence of printing background staining caused by friction. [Prior art] Printing plate materials for direct plate making using electrophotography are disclosed, for example, in Japanese Patent Publication No. 47-47610,
No. 48-40002, Special Publication No. 18325, Special Publication No. 18325, Special Publication No. 1832-
These are disclosed in Japanese Patent Publication No. 15766, Japanese Patent Publication No. 51-25761, etc., and these have an electrophotographic photosensitive layer containing a photoconductive zinc oxide-resin dispersion system. Such printing plates have the advantages of being inexpensive, relatively sensitive, and simple in the plate-making process, and are widely used in practice. To produce an electrophotographic printing plate, the printing plate material is submitted to a plate making machine and subjected to a corona charging, exposure, development and fixing process in the desired pattern, thereby forming the desired pattern on the photoconductive layer. A method of forming a toner image with a pattern is generally used. The development process can be categorized into a dry development method using a mixture of toner and a carrier such as iron powder, and a wet development method using a developer in which toner is dispersed in an organic solvent such as Isopar. When plate making is carried out using the above-mentioned wet development method, the resulting printed matter has advantages such as good halftone reproducibility, excellent resolution, and short plate making time. Therefore, electrophotographic lithographic printing using this wet development method is widely used. An electrophotographic lithographic printing material needs to have various properties required as a lithographic printing material in addition to image characteristics generally required as an electrophotographic material. For example, as a plate material for offset printing, it is possible to make non-image areas hydrophilic by treating the surface of the electrophotographic photosensitive layer with an etchant;
Moreover, it is necessary to have excellent water resistance against the large amount of dampening water used during printing. The electrophotographic photosensitive layer is formed by coating a support with a paint consisting of a photoconductive pigment such as zinc oxide or titanium oxide, an insulating resin binder, a sensitizing dye, and a solvent, and drying the coating. Insulating resin binders generally include highly hydrophilic acrylic ester copolymers, methacrylic ester copolymers, vinyl acetate copolymers, silicone resins, and butyral to prevent scumming during printing. Resin etc. are used. Furthermore, for the purpose of improving image quality, physical properties of paints, and mechanical strength of coating films, it is common practice to copolymerize functional groups such as acrylic acid, methacrylic acid, and maleic acid to the above resins. However, the electrophotographic photosensitive layer using the resin binder as described above has a problem in that the surface strength is insufficient and it is easily abraded. For this reason, during the manufacturing process of electrophotographic printing plate materials,
The electrophotographic photosensitive layer is easily damaged by pressure and friction during transportation or feeding in a plate-making machine.
Toner tends to adhere to these scratched areas, so when a printing plate made from such a plate material is used, printing surface stains often occur. In order to solve these problems, attempts have been made to increase the pressure resistance of the electrophotographic photosensitive layer by using polystyrene resin or polymethyl methacrylate resin, which have a high glass transition temperature, as an insulating resin binder. However, when such a resin binder is used, the resulting photosensitive layer has low flexibility and flexibility, which tends to cause cracks when used as a printing plate, resulting in low printing durability. This causes problems. In addition, increasing the blending ratio of the insulating resin binder in the photosensitive layer forming material may be considered as a method of increasing the strength of the coating film, but increasing the resin binder ratio will reduce the blending ratio of zinc oxide. The photoconductivity of the resulting photosensitive layer is reduced, good image quality is not obtained, the etching effect is insufficient, and the resulting printed matter is smudged and unsatisfactory. Furthermore, JP-A-59-40654 discloses a zinc oxide photosensitive material for offset printing in which zinc oxide particles coated with an acrylic-butadiene copolymer having a particle size of 20 to 50 μm are dispersed in the electrophotographic photosensitive layer. It is described that the presence of such a compound in the photosensitive layer forms a large number of protrusions on the surface of the photosensitive layer, thereby reducing the occurrence of printing stains caused by mechanical friction. However, the acrylic-butadiene copolymer-coated zinc oxide particles have a problem in that the resin is too flexible and is difficult to crush. Furthermore, printing plates using acrylic-butadiene copolymer-coated zinc oxide particles have poor electrophotographic properties, tend to cause fogging during plate making, and are prone to background smear on printed matter. Furthermore, the protrusions formed by the acrylic-butadiene copolymer-coated zinc oxide particles have drawbacks such as not having sufficient hardness against mechanical wear. The present inventors dispersed and contained zinc oxide aggregate particles obtained by bonding a plurality of zinc oxide particles with a styrene-butadiene copolymer in an electrophotographic photosensitive layer, thereby coating the surface of the photosensitive layer. We considered forming a large number of protrusions. In this case, it was possible to almost eliminate the occurrence of printing stains caused by friction, but it was desirable to further improve the strength and hardness against mechanical wear. Furthermore, a method using the acrylic-butadiene copolymer-coated reinforced zinc particles and styrene-
Both methods using zinc oxide bound particles made of butadiene copolymer have a problem in that they require many steps such as mixing and dispersing the resin and zinc oxide, drying, pulverization, and classification. [Problems to be Solved by the Invention] The problems to be solved by the present invention are to solve the above-mentioned problems of lithographic printing materials using conventional electrophotographic methods, and to eliminate the occurrence of printing surface stains due to friction, or It is an object of the present invention to provide less electrophotographic printing plate materials. Furthermore, other problems to be solved by the present invention are:
An object of the present invention is to provide an electrophotographic lithographic printing plate material having a spectral sensitivity recordable with light beams of various wavelengths such as He--Ne laser light or semiconductor laser light. [Means/Actions for Solving the Problems] In order to achieve the above object, the present inventors conducted intensive research and found that hard pigments of a specific size are dispersed and contained in an electrophotographic photosensitive layer. They discovered that by forming a large number of protrusions on the surface of the photosensitive layer, frictional force is applied selectively to the protrusions, thereby preventing damage to the electrophotographic photosensitive layer, and completed the present invention. It is. The electrophotographic lithographic printing plate material of the present invention has electrical conductivity and
on a water-resistant support; and an electrophotographic photosensitive layer containing a mixture of zinc oxide particles and a resin binder as a main component and formed on at least one surface of the support, in the electrophotographic photosensitive layer, Resin particles containing a benzoguanamine-formaldehyde condensation reaction product as a main component and having an average particle size of 10 to 60 μm are dispersed therein, thereby forming a large number of protrusions on the surface of the electrophotographic photosensitive layer. The non-protruding flat portion of the electrophotographic photosensitive layer has a thickness of 20 to 30 μm. The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view showing the basic structure of the lithographic printing plate of the present invention. An electrophotographic photosensitive layer 2 containing as a main component a mixture of zinc oxide particles 5 (indicated by a large number of dots) and an insulating resin binder 6 is formed on a support 1. In this electrophotographic photosensitive layer 2, Furthermore, benzoguanamine-formaldehyde condensation resin particles 3 having an average particle diameter of 10 to 60 μm are dispersed therein, thereby forming a large number of protrusions 4 on the surface of the photosensitive layer. The thickness of the non-protruding flat portion of the electrophotographic photosensitive layer is generally 20 to 30 μm. If the thickness of this non-flat part is less than 20 μm, the retention force of the benzoguanamine-formaldehyde condensation resin particles may be insufficient and excessive protrusions may be formed; if it exceeds 30 μm, The height of the protrusion becomes insufficient, and the desired effect becomes insufficient. As mentioned above, zinc oxide photosensitive materials for lithographic printing generally contain a soft resin as a binder.
Its surface is soft and therefore susceptible to wear and tear. When such a soft surface is mechanically rubbed, the electrophotographic sensitivity of the rubbed area decreases and the potential does not attenuate even after exposure, and toner adheres to the rubbed area during the development process. This often causes smudges on printed matter, degrading the image. However, since the electrophotographic photosensitive layer of the present invention has hard particles of a specific size scattered on its surface to form protrusions, the electrophotographic photosensitive layer itself can be prevented from mechanical abrasion. Therefore, it is possible to prevent the occurrence of background stains on printed matter. The average particle diameter of the benzoguanamine-formaldehyde condensation resin particles in the present invention is 10 to 60 μm, and it is preferable to use particles classified into 20 to 30 μm. When the average particle size of the resin particles is larger than 60 μm, images on printing plates and printed matter become rough. Moreover, if it becomes smaller than 10 μm, the anti-wear effect is lost and scumming occurs on printed matter. Since benzoguanamine-formaldehyde condensation resin particles do not dissolve in the solvent of the electrophotographic photosensitive layer coating solution (generally an aromatic solvent such as toluene),
This does not adversely affect the electrophotographic properties of the electrophotographic photosensitive layer. In the electrophotographic photosensitive layer of the present invention, other organic pigments such as urea resin pigments, polymethyl methacrylate resin particles, high-density polyethylene fine powder, starch, and polyester resin particles are used instead of the benzoguanamine-formaldehyde condensation resin particles, and Inorganic pigments such as aluminum hydroxide, alumina, spherical silica balloons, spherical aluminosilicate particles, calcium metasilicate,
When using materials such as titanium oxide and titanium oxide, plate-making fog and printing stains occur, which are thought to be due to deterioration of electrophotographic properties and deterioration of desensitization properties, regardless of whether or not printing stains occur due to friction. Practical electrophotographic printing plate materials cannot be obtained. The electrophotographic photosensitive layer of the present invention has an average particle size of 10
~60 μm benzoguanamine-formaldehyde condensation resin particles are mixed and dispersed in a typical photoconductive zinc oxide-insulating resin binder coating solution for electrophotographic photosensitive layers, and this coating solution is coated with a conductive and water-resistant support. It is formed by applying it onto the body so that the thickness of the non-protruding flat part is 20 to 30 μm (after drying) and drying it. In this electrophotographic photosensitive layer, the resin particles form a large number of protrusions on the surface of the photosensitive layer. The height of this protrusion is preferably 5 to 25 μm. Further, the amount of the resin particles added is preferably 0.05 to 1.0% by weight, more preferably 0.1 to 0.5% by weight, based on the solid content of the electrophotographic photosensitive layer coating liquid. The insulating resin binder used in the electrophotographic photosensitive layer may be made of a single type of resin, or may be a mixture of two or more types of resin binders. Examples of such resin binders include polyester resins, acrylic resins, epoxy resins,
Polycarbonate resin, melamine resin, butyral resin, silicone resin, polyurethane resin, polyamide resin, alkyd resin, polystyrene resin,
Xylene resin, phenoxy resin, etc. are used. The electrophotographic photosensitive layer used in the present invention is
In addition to zinc oxide, various sensitizers and additives, such as photosensitive dyes and electron-accepting substances, which have been conventionally used, are mainly used to improve electrophotographic properties such as sensitivity. good. In addition, in order to have sensitivity to the light beam of the wavelength of the semiconductor laser, the photosensitive layer contains
Compounds of the following general formulas () and () having maximum sensitivity to light in the wavelength range of 700 to 1000 nm may be included as sensitizers. and [However, in the above formula, R ₁ , R ₂ and R ₃ each independently represent -CH ₃ , -C ₂ H ₅ and -CH ₂ -
Represents one member selected from CH=CH ₂ group, preferably -CH ₂ -CH=CH ₂ group, and X is Br, Cl and an atom, and ClO ₄ and

〔Example〕

Next, the present invention will be explained in more detail with reference to examples, but these are not intended to limit the content of the present invention. Note that "parts" and "%" in the examples represent parts by weight and % by weight, unless otherwise specified. Example 1 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) A photosensitive solution was prepared by dispersing a mixture of 25 parts Rose Bengal, 0.02 parts, and 120 parts of toluene using a sand grinder.Next, 0.1 part of benzoguanamine-formaldehyde condensation resin particles (manufactured by Nippon Shokubai Co., Ltd., trademark) was added to this photosensitive solution. : Epostor L, average particle size:
27.6 μm) and stirred and dispersed using a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer. As a support, base paper with a weight of 80 g/m ² and a thickness of
A composite sheet manufactured by laminating 10 μm aluminum foil was used. The coating solution was applied onto the aluminum foil surface of the support and dried to form an electrophotographic photosensitive layer. The non-protruding flat area of this photosensitive layer was 25 μm (dry). The height of many protrusions formed on the surface of the photosensitive layer was approximately 15 μm or less. In order to evaluate the scratch resistance of the photosensitive layer of the obtained electrophotographic printing plate, the printing plate material for testing was heated at 25°C.
Conditioning was performed for 24 hours in a dark place with an atmosphere of 50% RH, and then another printing plate material was placed on the surface of the electrophotographic photosensitive layer of this printing plate material so that the back surface was in contact with the other printing plate material. A 3 kg weight (7 cm in diameter) was placed on top of the plate and the upper plate was pulled once for about 20 cm to damage the surface of the photosensitive layer of the lower plate. After that, platemaking and printing were performed using this printing plate material, resulting in damaged areas (especially non-image areas).
The degree of staining on the printed surface was sensory evaluated. Plate making and printing were performed as follows. That is, the plate was made using an Itek 235 type plate making machine, desensitized with an etchant (Itek product), and then printed using an offset printing machine (Ryobi 2800CD, Synflo type).
The image quality of the resulting printed matter was evaluated by observing, especially the scumming caused by friction. The results are shown in Table 1. Example 2 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) 25 parts sensitizer: General formula () [however, formula R ₃ is CH ₂
A photosensitive solution was prepared by dispersing a mixed solution consisting of 0.02 parts of a compound of -CH= _CH2 group and X represents an atom and 120 parts of toluene using a sand grinder. Next, 0.1 of benzoguanamine-formaldehyde condensation resin particles similar to those in Example 1 were added to the photosensitive solution.
A coating solution for forming an electrophotographic photosensitive layer was prepared. Next, an electrophotographic lithographic printing plate material was prepared in the same manner as in Example 1. The obtained electrophotographic printing plate material was heated to 50% at 25°C.
After conditioning for 24 hours in a dark place in an RH atmosphere, the surface of the photosensitive layer was subjected to frictional damage in the same manner as in Example 1, and was then irradiated with semiconductor laser light (5 mW, Irradiation scanning was carried out at a wavelength of 780 nm. Next, the electrophotographic photosensitive layer irradiated with the laser beam was developed using a positively charged toner (manufactured by Itek). After development, apply etching solution (Itek
After desensitizing the prints using a commercially available product, the prints were printed using an offset printing machine (Ryobi 2800CD, Synflo type), and the image quality of the resulting prints was evaluated by observing, especially scumming caused by friction. The results are shown in Table 1. Comparative Example 1 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) A photosensitive solution was prepared by dispersing a mixture of 25 parts rose bengal, 0.1 part toluene and 120 parts using a sand grinder. This photosensitive solution was used as an electrophotographic photosensitive layer coating solution without mixing resin particles, and was coated on a support in the same manner as in Example 1 to produce an electrophotographic lithographic printing plate material. Using the obtained electrophotographic printing plate material, plate making and printing were carried out in the same manner as in Example 1, and printing background staining was evaluated. The results are shown in Table 1. Comparative Example 2 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) 25 parts Rose Bengal 0.02 parts Toluene Disperse 120 parts of the photosensitive liquid using a sand grinder, and add 0.5 parts of high-density polyethylene resin fine powder (manufactured by Tetsu Kagaku Co., Ltd., Flow Beads HE-5023, average particle size
18.7 μm) was added and stirred and dispersed using a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer. This coating liquid was applied onto a support in the same manner as in Example 1 to produce an electrophotographic lithographic printing plate. Using the obtained electrophotographic printing plate material, plate making and printing were performed in the same manner as in Example 1, and the printing background stain was evaluated. The results are shown in Table 1. Comparative Example 3 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) A photosensitive solution consisting of 25 parts rose bengal 0.02 parts toluene 120 parts was dispersed with a sand grinder. To this was added 1.0 part of polymethyl methacrylate resin particles (manufactured by Nippon Pure Chemical Industries, Ltd., Dulymer MB-20, average particle size 19.1 μm), and the mixture was stirred and dispersed with a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer. . This coating liquid was coated onto a support in the same manner as in Example 1 to produce an electrophotographic lithographic printing plate. Using the obtained electrophotographic printing plate, plate making and printing were carried out in the same manner as in Example 1, and printing background staining was evaluated. The results are shown in Table 1. Comparative Example 4 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) 25 parts Rose Bengal 0.02 parts Toluene 120 parts of a photosensitive solution was dispersed with a sand grinder. To this was added 1.0 part of starch, and the mixture was stirred and dispersed using a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer.
This coating liquid was coated onto a support in the same manner as in Example 1 to produce an electrophotographic lithographic printing plate. Using the obtained electrophotographic printing plate, plate making and printing were carried out in the same manner as in Example 1, and the printing background stain was evaluated. The results are shown in Table 1. Comparative Example 5 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., SAZEX#2000) 90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-
188) 25 parts Rose Bengal 0.02 parts Toluene 120 parts of a photosensitive solution was dispersed with a sand grinder. Next, add 1.0 part of alumina (manufactured by Pacific Random Co., Ltd., Nitso Random LA400, average particle size 27.4 μm) to this.
was added and dispersed by stirring with a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer. This coating liquid was coated onto a support in the same manner as in Example 1 to produce an electrophotographic lithographic printing plate. Using the obtained electrophotographic printing plate, plate making and printing were carried out in the same manner as in Example 1, and printing background staining was evaluated. The results are shown in Table 1. Comparative Example 6 An electrophotographic lithographic printing plate was produced in the same manner as in Comparative Example 1. However, as a sensitizer for the electrophotographic photosensitive layer coating solution, the general formula () [wherein R ₃ is CH ₂ −
A compound in which CH= _CH2 group and X represents an atom was used. Using the obtained electrophotographic printing plate, plate making and printing were carried out in the same manner as in Example 2, and printing background staining was evaluated. The results are shown in Table 1.

〔Effect of the invention〕

In the lithographic printing plate material of the present invention, by dispersing and containing benzoguanamine-formaldehyde condensation resin particles in the electrophotographic photosensitive layer, there is no or little damage to the electrophotographic photosensitive layer due to friction, etc., and therefore printing stains are also prevented. It is possible to obtain printed matter with excellent image quality without or with a small amount of image quality.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing the structure of the lithographic printing plate of the present invention. DESCRIPTION OF SYMBOLS 1... Support, 2... Electrophotographic photosensitive layer, 3... Benzoguanamine-formaldehyde condensation resin particles, 4
...protrusions, 5...zinc oxide particles (indicated by dots),
6...Resin binder, 7...Non-protruding flat portion.

Claims (1)

[Scope of Claims] 1. An electrophotographic photosensitive layer containing as a main component a mixture of a conductive and water-resistant support, zinc oxide particles, and a resin binder, and formed on at least one surface of the support. and, in the electrophotographic photosensitive layer, benzoguanamine-
Resin particles containing a formaldehyde condensation reaction product as a main component and having an average particle size of 10 to 60 μm are dispersed therein, thereby forming a large number of protrusions on the surface of the electrophotographic photosensitive layer. , the thickness of the non-protrusion flat part of the electrophotographic photosensitive layer is
An electrophotographic lithographic printing plate material characterized by having a diameter of 20 to 30 μm.