JPH02115860A - Electrophotographic planographic printing plate - Google Patents

Abstract

PURPOSE:To prevent the damage of an electrophotographic sensitive layer by friction, etc., by dispersing hard particles of specific sizes consisting of a specific material into the electrophotographic sensitive layer to form many projecting parts on this surface. CONSTITUTION:The electrophotographic sensitive layer 2 is formed on the surface of a water resistant base 1 and many fine particles 4 of photoconductive zinc oxide are bound into a binder essentially consisting of a styrene/butadiene copolymer and are dispersed in this layer 2. The particles 3 form the many projecting parts 6 on the surface of the layer 2. The projecting parts prevent the mechanical friction of the layer 2 itself by countering against the mechanical friction. The generation of scumming on printed matter is prevented in this way.

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 or has less occurrence of egg stain due to friction (rubbing).

[Conventional technology]

Printing plate materials for direct plate making using electrophotography are
For example, Special Publication No. 47-47610, Special Publication No. 48-40
No. 002, Special Publication No. 4B-18325, Special Publication No. 51-1
No. 5766, Japanese Patent Publication No. 51-257 (i1), etc. These printing plate materials have an electrophotographic photosensitive layer containing a photoconductive zinc oxide-resin binder dispersion mixture as a main component. Such printing plate materials have the advantages of being inexpensive, relatively sensitive, and having a simple plate-making process.

For electrophotographic lithographic printing plates, the printing plate material is usually subjected to a plate-making machine that processes corona charging, exposure, and photolithography in a desired pattern.
It is manufactured by subjecting it to developing and fixing operations, thereby forming a desired pattern of toner images on the photoconductive layer.

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, the resulting printing plate has advantages such as good reproducibility of halftone images, excellent resolution, and short time required for plate making. For this reason, electrophotographic lithographic printing plates manufactured by a wet development method are widely used.

Electrophotographic lithographic printing materials need to have various properties required as lithographic printing materials in addition to the image properties generally required as electrophotographic materials.

For example, when used as an offset printing plate material,
The printing plate material must be able to make non-image areas hydrophilic by treating the surface of the electrophotographic photosensitive layer with an etchant, and also to be able to withstand large amounts of dampening water used during printing. It is necessary to have excellent water resistance.

An electrophotographic photosensitive layer is generally made 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 it. It is formed by

Insulating resin binders generally include highly hydrophilic acrylic ester copolymers, methacrylic ester copolymers, vinyl acetate copolymers, silicone resins, butyral resins, etc. to prevent background smudges during printing. is used. At this time, in order to improve the image quality, physical properties of the paint, and mechanical strength of the coating film, the binder resin is copolymerized with a polymeric component having a functional group such as acrylic acid, methacrylic acid, or maleic acid. It's normal.

The electrophotographic photosensitive layer formed using such a resin binder has insufficient surface strength and is therefore easily abraded, and may be damaged during the manufacturing process of the electrophotographic printing plate material, during transportation, or During feeding in a plate-making machine, the electrophotographic photosensitive layer is damaged by pressure and friction (rubbing), and toner tends to adhere to the damaged areas. When such a plate material is used as a printing plate, it causes printing background stains on printed matter.

Attempts have also been made to increase the pressure resistance of electrophotographic photosensitive layers by using polystyrene resins and polymethyl methacrylate resins, which generally have high glass transition temperatures, as insulating resin binders. However, the above-mentioned resin binders have insufficient softness and flexibility, and when used for printing plates, the resulting printing plates tend to crack during use, which reduces printing durability. It was causing this.

In addition, increasing the blending ratio of the insulating resin binder may be considered as a method of increasing the coating strength of the electrophotographic photosensitive layer, but as the blending ratio of the resin binder increases, the photoconductivity of zinc oxide decreases. As a result, printing plates with such a photosensitive layer do not provide good image quality, the etching effect is insufficient, and the resulting prints are generally smeared and unsatisfactory.

In addition, JP-A No. 59-40654 discloses a zinc oxide photoreceptor for offset printing in which zinc oxide particles coated with an acrylic-butadiene copolymer having a particle size of 20 to 50 are included in an electrophotographic photosensitive layer. It is described that a large number of protrusions are formed on the surface of the photosensitive layer by dispersing the photosensitive layer, thereby preventing the occurrence of printing stains caused by mechanical abrasion. However, the resin of these acrylic-butadiene copolymer-coated zinc oxide particles has excessively high flexibility, which makes it difficult to crush. In addition, printing plates using acrylic-butadiene copolymer-coated zinc oxide particles have the drawbacks of poor electrophotographic properties, prone to fogging during platemaking, and often causing scumming on printed matter.

[Problem to be solved by the invention]

The present invention aims to solve the various problems of conventional lithographic printing materials using electrophotographic methods, and to provide an electrophotographic printing plate material that does not or has less occurrence of printing surface stains due to friction (rubbing). be.

Furthermore, the present invention also provides an electrophotographic lithographic printing plate material having a spectral sensitivity recordable using light sources of various wavelengths such as He--Ne laser light or semiconductor laser light.

[Means to solve the problem]

In order to solve the above problem, the present inventors conducted intensive research and found that hard particles of a specific size were dispersed and contained in the surface of the electrophotographic photosensitive layer, and a large number of protrusions were formed on this surface. They discovered that damage to the electrophotographic photosensitive layer could be prevented by selectively applying frictional force to the protruding portions, and completed the present invention.

The electrophotographic lithographic printing plate material of the present invention contains as a main component a mixture of an electrically conductive and water-resistant support, a resin binder, and zinc oxide particles, and is formed on at least one surface of the support. an electrophotographic photosensitive layer, the electrophotographic photosensitive layer comprises a plurality of zinc oxide particles bound together by a binder containing a styrene-butadiene copolymer resin as a main component; A large number of zinc oxide aggregate particles having an average particle size of ~60 - are dispersed, and a large number of protrusions are formed on the surface of the electrophotographic photosensitive layer by the zinc oxide aggregate particles. This is a characteristic feature.

The printing plate material of the present invention will be explained 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 having a thickness of approximately 20 mm is formed on one side of the support 1, and in this electrophotographic photosensitive layer, a large number of photoconductive zinc oxide fine particles 4 are contained in a resin binder 5. are dispersed, and further zinc oxide aggregate particles 3
are dispersed, and these aggregate particles 3 form a large number of protrusions 6 on the surface of the photosensitive layer 2.

As mentioned above, the zinc oxide photosensitive layer for lithographic printing plates generally uses a soft resin as a binder, so its surface is soft and easily susceptible to wear and damage.

Therefore, when this surface is mechanically rubbed, the electrophotographic sensitivity of the rubbed portion decreases, and its potential does not attenuate even when exposed to light. Therefore, in the developing process, toner adheres to the frictionally damaged portions, which causes printing stains on the printed matter and deteriorates the image quality.

On the other hand, in the electrophotographic photosensitive layer of the printing plate material of the present invention, hard particles of a specific size are scattered on the layer surface to form a large number of protrusions, which resist mechanical friction. As a result, mechanical abrasion of the electrophotographic photosensitive layer itself can be prevented, thereby preventing the occurrence of scumming on printed matter.

The zinc oxide aggregate particles of the present invention are formed by binding a plurality of zinc oxide fine particles with a styrene-butadiene copolymer resin. Specifically, zinc oxide aggregate particles are produced by dispersing zinc oxide fine particles with a particle size of about 0.2 to 0.5 tnn in an aqueous emulsion of a binder whose main component is styrene-butadiene copolymer resin. It is produced by drying and solidifying the dispersion and pulverizing this solidified material into particles with an average particle size of 20 to 60*. It is preferable to classify the obtained pulverized product into a desired average particle size.

As mentioned above, the average particle size of the zinc oxide aggregate particles is 20~
60 voices, preferably 20-30n. This average particle size is 60J! m (if this is the case, the surface of the resulting printing plate will become excessively rough and the image of the resulting printed matter will be rough; if it is less than 20 knots, the surface of the resulting photosensitive layer will resist the above friction). The resistance becomes insufficient, and the surface of the photosensitive layer is easily damaged, and therefore, printed matter is more likely to be smudged.

The dry weight ratio of the styrene-butadiene copolymer resin binder and zinc oxide in the zinc oxide aggregate particles is ZO
, S to l: preferably within the range of 15, l:l
It is more preferable that the ratio is in the range of 1:5 to 1:5.

The styrene-butadiene copolymer binder is preferably one that does not dissolve in the solvent of the coating liquid used to form the electrophotographic photosensitive layer (usually an aromatic hydrocarbon solvent such as toluene). It is preferable to increase the blending ratio of the styrene component (for example, 70 to 90 mol%).

The zinc oxide aggregate particles used in the present invention may contain additives such as a dispersant and/or a dye sensitizer, if necessary.

The electrophotographic photosensitive layer of the present invention is obtained by dispersing the zinc oxide aggregate particles having an average particle size of 20 to 60 μm in a typical photoconductive zinc oxide-insulating resin binder coating solution for electrophotographic photosensitive layers. ,
Dry film thickness of 20 mm on conductive and water resistant support
It is formed by coating and drying to a thickness of ~30 ml. A large number of zinc oxide aggregate particles are dispersed in the formed electrophotographic photosensitive layer, and a large number of protrusions are formed on the surface of the photosensitive layer. The height of the protrusion is preferably 5 to 25 cm. Further, the blending amount of the zinc oxide aggregate particles is 0.05 to 2.0% by weight of the solid content of the electrophotographic photosensitive layer.
It is preferably 0.1-1.0% by weight, and more preferably 0.1-1.0% by weight.

The insulating binder resin used in the electrophotographic photosensitive layer may be made of a single type of polymer, or may be a mixture of two or more types of polymer resins. Examples of such binder resin include polyester resin, acrylic resin, epoxy resin, polycarbonate resin, melamine resin, butyral resin, silicon resin, polyurethane resin, polyamide resin, alkyd resin, polystyrene resin, xylene resin, phenoxy resin, etc. is used.

In addition to the binder and zinc oxide, the electrophotographic photosensitive layer of the printing plate material of the present invention contains conventionally used dyes and electron-accepting substances, mainly for the purpose of improving electrophotographic properties such as sensitivity. Various aggravating agents and additives may be included as appropriate. In addition, in order to make the semiconductor laser sensitive to wavelength light, compounds of Noshiro (1) and (I[) below, which have maximum sensitivity to light in the range of 700 to 11000 nm, are contained as sensitizers. Good too.

and [However, in the above formula, R, , R, and R1 each independently represent -C)13, -CZII5, and -C
Represents one member selected from Il□-CIl=CH2 group, preferably -CIIZ-CH=C112 group, and X is B
r, Cj! represents a selected member of and, preferably C
1O,] The conductive and water-resistant support for the electrophotographic lithographic printing plate material of the present invention may be a known support, such as a metal sheet, metal foil, paper laminated with metal foil, a plastic film, or a vapor-deposited metal. It can be selected from paper or plastic film having a layer, and conductive treated or plastic film.

To make a printing plate from the lithographic printing plate material of the present invention, first, according to the usual electrophotographic method, the material is uniformly charged in a dark place using a corona charger, etc., and then a tungsten lamp, halogen Electrophotography is performed by reflection image exposure using a light source such as a lamp, xenon lamp, or fluorescent lamp, contact exposure through a transparent positive film, or scanning exposure with laser light such as a He-Ne laser, argon laser, or semiconductor laser. An electrostatic latent image is formed on the photosensitive layer, and this electrostatic latent image is developed with a toner and fixed by light to form a toner image on the plate.

Next, the non-printing areas of the obtained printing plate are desensitized using a normal fat-free treatment liquid, and then this printing piece is mounted on an offset printing machine and used for printing.

[Examples] Next, the present invention will be specifically explained with reference to Examples, but these are not intended to limit the scope of the present invention. In addition, "part" and "%" in the examples are unless otherwise indicated.
Represents parts by weight and % by weight, respectively.

Composition below for 1 serving: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZEX 112000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-188) 25
A mixture of 1 part rose bengal, 0.02 parts toluene and 120 parts was dispersed with a sand grinder to prepare a photosensitive liquid. On the other hand, the following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZEX 112000)
48% aqueous emulsion of 40 parts styrene-butadiene copolymer (manufactured by Nippon Zeon Co., Ltd., N1pol LX-416) 41.
7 parts water
After dispersing the mixed solution consisting of 18.3 parts for 20 minutes in a homomixer, it was dried and solidified at 100°C for 24 hours, ground in a mortar, and the resulting particles were then classified with a sieve to give 20 to 30 parts. Zinc oxide aggregate particles having a particle size of 40- were prepared.

Next, the zinc oxide aggregate particles were added to the photosensitive liquid in an amount of 1% by weight based on the solid content of the photosensitive liquid, and the mixture was stirred and dispersed using a stirrer to obtain a coating liquid for forming an electrophotographic S light layer.

As a support, a base paper of 180 g/rd with a thickness of 10
A composite sheet manufactured by laminating μ 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 thickness of this photosensitive layer was 22 mm. A large number of protrusions are formed on the surface of the photosensitive layer, and their height is up to 251! It was about m.

In order to evaluate the scratch resistance of the photosensitive layer of the obtained electrophotographic printing plate, the test plate was conditioned for 24 hours in a dark place at 25 ° C and 250% R11 atmosphere.
Lay another plate on the surface of this electrophotographic photosensitive layer so that its back side is in contact with the surface of the photosensitive layer, and place a 3 kg weight (
7 cm in diameter) and pulled the upper plate once for about 20 cm to damage the surface of the photosensitive layer. Thereafter, plate making and printing were performed using this plate, and the degree of printing stain in damaged areas (particularly non-image areas) was observed and sensory evaluated.

Plate making and printing for the test plate were performed as follows. That is, after making a plate with an Itek 235 type plate making machine and desensitizing it with an etchant (product of I Lek),
Printing was carried out using an offset printing machine (Ryobi 2800CD, Synflo type), and the image quality was examined, especially background smudges caused by friction.

The results are shown in Table 1.

Tintinitis 1 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZEX #2000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-188) 2
5 parts Sensitizer Compound of the above-mentioned Noshiro (II) [wherein R1 represents a -C■2CH=C)lx group and X represents a ■ atom] 0.02 parts Toluene
A photosensitive liquid was prepared by dispersing 120 parts of the mixed liquid using a sand grinder.

Next, the same zinc oxide aggregate particles as in Example 1 were added to the photosensitive liquid in an amount of 1% by weight based on the solid content of the photosensitive liquid to prepare a coating liquid for forming an electrophotographic photosensitive layer. An electrophotographic printing plate was prepared in the same manner as above.

The obtained electrophotographic printing plate was heated at 25°C, 150%RH.
After conditioning for 24 hours in a dark place in an atmosphere of 780nO1) was irradiated and scanned. Next, the electrophotographic photosensitive layer irradiated with laser light was developed using a positively charged toner (manufactured by ITek). After development, it was desensitized with Etch 1a (Itek product), and then printed using an offset printing machine (Ryobi 2800CD, Synflo type) to improve the image quality of the printed matter, especially the background stains caused by rubbing on one part. I looked into it.

The results are shown in Table 1.

Comparison ■Soil The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZII!X 12000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., LR-188) 25 parts Rose Bengal 0.1 part toluene A mixed solution of 120 parts was dispersed with a sand grinder to obtain a photosensitive liquid, and the zinc oxide aggregate particles were mixed therein. An electrophotographic lithographic printing plate was prepared by the same procedure as in Example 1, using an electrophotographic photosensitive layer coating solution without any process. Using the obtained electrophotographic printing plate,
Printing was carried out in the same manner as in Example 1, and the scumming of the printed matter was evaluated.

The results are shown in Table 1.

Comparison I A photosensitive liquid containing the same zinc oxide-insulating resin binder as in Example 1 was used.

Separately, the following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZEX 112000)
40 parts 50% aqueous emulsion of acrylic-butadiene copolymer (Nippon Zeon Co., Ltd., N1pol 1551) 20
Partial dispersant (condensate of naphthalene sulfonic acid and formaldehyde, Demol N manufactured by Kao Corporation) 1 part 28% ammonia water 1 part water
After dispersing 40 parts of the mixed solution in a homomixer for 20 minutes, it was heated at 100'C for 24 hours.
The powder was dried and solidified over time, ground in a mortar, and the resulting particles were classified using a sieve to prepare zinc oxide aggregate particles having a particle size of 40 to 60 pm.

The zinc oxide aggregate particles were added to the photosensitive liquid in an amount of 1% by weight based on the solid content thereof to prepare a coating liquid for forming an electrophotographic photosensitive layer. Using this coating liquid, an electrophotographic lithographic printing plate was prepared and printed in the same manner as in Example 1, and the scumming of the printed matter was evaluated.

The results are shown in Table 1.

A photosensitive solution containing zinc oxide and an insulating resin binder similar to that in Example 1 was prepared.

Separately, the following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., 5AZEX 12000)
20 parts PVA (manufactured by Kuraray Co., Ltd., 420) 1
0 parts water
After dispersing 90 parts of the mixed solution for 20 minutes in a homomixer, it was dried and solidified at 100"C for 24 hours, the solidified product was ground in a mortar, and the resulting particles were classified with a sieve. Zinc oxide aggregate particles with a particle size of ˜40 μm were prepared.

The obtained zinc oxide aggregate particles were added to the photosensitive liquid in an amount of 1% by weight based on the solid content thereof to prepare a coating liquid for forming an electrophotographic photosensitive layer. Using this coating liquid, an electrophotographic lithographic printing plate was prepared in the same manner as in Example 1. The obtained electrophotographic printing plate was printed in the same manner as in Example 1, and the scumming of the printed matter was evaluated.

The results are shown in Table 1.

The same operation as in Comparative Example 1 of Tokyo Charcoal Soil was performed. However, as an aggravating agent for the electrophotographic photosensitive layer coating liquid, the above-mentioned -Noshiro (n) [wherein R3 represents CHz C1l = Cll 2 groups, and
represents an I atom] was used. Table 1 shows the evaluation results of the scumming of the obtained printed matter.

The same operation as in Comparative Example 2 was performed. However, as an aggravating agent for the electrophotographic photosensitive layer coating solution, the above-mentioned compound of Noshiro (II) [wherein R3 represents a CL CH=C112 group and X represents one atom] was used. Table 1 shows the evaluation results of the scumming of the obtained printed matter.

Comparison 1 ILfc The same operation as in Comparative Example 3 was performed. However, as an aggravating agent for the electrophotographic photosensitive layer coating solution, the compound of -Noshiro (n) [wherein R3 represents a -CIl□-CI=CH group and X represents one atom] is used. there was. Table 1 shows the evaluation results for scumming of the obtained printed matter.

In Comparative Examples 2.3 and 5.6 of Table 1, the resin binding the zinc oxide fine particles is an acrylic-butadiene copolymer or polyvinyl alcohol (PVA), so the electrophotograph of the photosensitive layer is It is thought that the characteristics deteriorated, and the anti-greaseability also deteriorated, which caused plate-making fog and printing background stains.

Note) = 1) Plate-made and printed without applying mechanical friction.

2) Evaluation of resolution and image reproducibility.

O: Good △: Slightly poor ×: Poor As Table 1 clearly shows, the electrophotographic photosensitive layer of Example 1.2 according to the present invention has resistance to forced friction, and therefore It was possible to obtain printed matter without background smear during printing.

In Comparative Example 1.4, since no protrusions were formed on the surface of the photosensitive layer, the surface of the photosensitive layer was damaged by friction, resulting in scumming on the printed matter.

〔Effect of the invention〕

In the present invention, by dispersing and containing aggregate particles consisting of a plurality of zinc oxide particles bound together by a binder containing a styrene-butadiene copolymer as a main component in the electrophotographic photosensitive layer, It is possible to obtain an electrophotographic lithographic printing plate material with less damage to the electrophotographic photosensitive layer due to friction and the like, no or little staining on the printing background, and excellent image quality.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing the structure of the electrophotographic planographic printing plate material of the present invention. 1...Support, 2...Electrophotographic photosensitive layer,
3... Zinc oxide aggregate particles, 4... Zinc oxide fine particles, 5... Resin binder, 6...
·protrusion

Claims (1)

[Scope of Claims] 1. An electrophotographic photosensitive material comprising, as a main component, a conductive/water-resistant support and a mixture of a resin binder and zinc oxide fine particles, and formed on at least one surface of the support. layer, the electrophotographic photosensitive layer comprises a plurality of zinc oxide fine particles bound together by a binder containing a styrene-butadiene copolymer resin as a main component, and has a particle diameter of 20 to 60 μm. A large number of zinc oxide aggregate particles having an average particle size are dispersed, and a large number of protrusions are formed on the surface of the electrophotographic photosensitive layer by the zinc oxide aggregate particles. Photolithography printing plate material.