JP3014481B2 - Electrophotographic lithographic printing plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic lithographic printing plate, and more particularly to a photosensitive member obtained by dispersing zinc oxide as a photoreceptor in a resin as a binder and applying the dispersion to a conductive support. It relates to a zinc oxide lithographic printing plate.

[0002]

2. Description of the Related Art An electrophotographic copying method is a so-called electrofax method in which an electrophotographic photosensitive layer is coated on a conductive support.
In this method, a copy is obtained through a process of development and fixing.
An electrophotographic lithographic printing plate applies such a method to an offset printing plate. This electrophotographic lithographic printing plate can be developed and fixed, and then hydrophilized in the non-image area with a desensitizing solution (etching solution), so that printed matter can be obtained by using an offset printing machine. It is necessary that there is no.

[0003] In addition to the insufficiency of the desensitization of the photosensitive layer itself, the stains on the printed matter may be caused by localized scratches on the surface of the photosensitive layer of the lithographic printing plate. Insufficient printing may result in stains on printed matter. Such scratches in the photosensitive layer are so-called fog,
In particular, conventional electrophotographic lithographic printing plates are more likely to cause fogging than other printing plates, and have not been described as lithographic materials that can be used safely.

[0004] The fog of the electrophotographic lithographic printing plate is of various types, but the fogging that is more conspicuous than other printing plates is fogging due to so-called mechanical stress called rubbing fogging or pressure fogging. Such fogging can cause strong fogging if the printing plate operator mistakenly strikes the printing plate against another object or drops it on the floor, but the printing plate manufacturing process, that is, the application of an electrophotographic photosensitive liquid -Various mechanical stresses are applied in each of the processes such as drying, winding, cutting, and finishing, which may leave rubbing marks and pressure marks and cause fogging. In particular, fogging may occur during the summer months when the temperature rises, and sometimes products having such fogging are mixed in products. In the manufacturing process, measures are taken to prevent such fogging from the mounting surface or working surface, but it is difficult to completely eliminate fogging.

In order to eliminate such fogging, the production efficiency may be reduced, and the yield may be reduced.

[0006] As a method of solving these problems,
JP-A-57-185 discloses a method for improving the surface of zinc oxide.
No. 441, JP-A-57-186756, JP-A-60-1985.
Although JP-A-250362 has been proposed, it was not always satisfactory to completely prevent the occurrence of fogging.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic lithographic printing plate which causes less fogging on the surface of a zinc oxide photosensitive layer. That is, an object of the present invention is to reduce stains during printing.
To provide an electrophotographic lithographic printing plate. Another object of the present invention is to provide an electrophotographic lithographic printing plate having good plate making properties and printing durability.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has found the following method and has completed the present invention. That is, in the present invention, in an electrophotographic lithographic printing plate comprising a conductive support provided with a zinc oxide photosensitive layer, two or more resins are mixed (blended) and used as a binder for the photosensitive layer. The glass transition point (Tg) of all resins is 23 ° C. or higher, and preferably the calculated average glass transition point (Tg) of the mixed resins is 40 ° C. or higher. The calculated average glass transition point is a value obtained by multiplying the glass transition point of each resin by the used weight of each resin and dividing the total by the total resin weight.

[0009] The resin as a binder for use in the present invention, known resins der luer click <br/> Lil resin used in the zinc oxide photosensitive layer, Mirikon resins, polyester resins, alkyd resins, Examples thereof include a vinyl chloride resin and a vinyl acetate resin. Among these resins, an acrylic resin is preferable from the viewpoint of plate making properties, printing durability, cost, and the like. The acrylic resin may be a homopolymer such as an acrylate or a methacrylate, or a copolymer of an acrylate or a methacrylate, or a copolymer of styrene or vinyl acetate. It may be modified with an acid, methacrylic acid, maleic acid, phthalic acid, crotonic acid, phthalic anhydride, itaconic acid, citraconic acid, acrylic malonic acid, or the like.

In order to use the above-mentioned resin as a binder for a zinc oxide photosensitive layer in practice, it is difficult to satisfy good properties such as plate making and printing durability with only one kind. There are, be used as a mixture of several kinds of resins is common. The present invention stipulates the conditions of the resin when a mixture of several kinds of such resins is used.

The resin used must have a glass transition point of at least 23 ° C. for each single resin, and the calculated average glass transition point of the resin when two or more resins are mixed and used is 40 ° C. It is preferable to be above. When a resin having a glass transition point of a single resin of less than 20 ° C. is used at all,
Even under normal manufacturing conditions, the resistance to fogging of the entire photosensitive layer is reduced, which may cause fogging. For this reason, the glass transition points of the resins used must all be 23 ° C. or higher. Also, considering production in summer and use by end users,
The calculated average glass transition point of the entire photosensitive layer is 40 ° C.
It is necessary to be above. For lower ones,
It is conceivable that a mechanical stress is locally applied to each process at the time of manufacturing or a state where the temperature is considerably high at the time of use by a user, which may cause fogging.

The weight-average molecular weight of the resin used is preferably in the range of 20,000 to 120,000. If the weight average molecular weight is less than 20,000, printing durability and plate making quality deteriorate. On the other hand, if the weight average molecular weight is more than 120,000, the coating properties of the photosensitive solution deteriorate, which is not preferable. The amount of these resins used is from 10% by weight to 30% by weight of zinc oxide.
If it is out of these ranges, characteristics such as plate making image quality and printing durability deteriorate.

As a support on which the zinc oxide photoreceptor is coated, paper having conductivity, solvent resistance and water resistance on the surface,
Aluminum-laminated paper, plastic-laminated paper, plastic sheets, aluminum plates, etc. are good, and are used depending on the application.

A method for forming a photosensitive layer using a zinc oxide photoreceptor is to prepare a photoreceptor such as zinc oxide, a sensitizing dye, and additives in a solution of the above resin in an organic solvent such as toluene, xylene, acetone or methyl ethyl ketone. well mixed, after dispersion, wire bar, Ribasuro Lumpur, coating air knife or the like
What is necessary is just to apply | coat to the said support body by a cloth system, and to dry.

[0015]

The present invention will be described below with reference to specific examples.

Example 1 Photoconductive zinc oxide (Sasex # 2000 manufactured by Sakai Chemical) 1
00 parts by weight, acrylic resin A (Tg 23 ° C., solidification ratio 50
%) 20 parts by weight, acrylic resin B (Tg 65 ° C., solidification ratio 50%) 20 parts by weight (the calculated average Tg is 4
4 ° C.) and 150 parts by weight of toluene and 0.1 part by weight of Rose Bengal were mixed and stirred well to prepare a zinc oxide photosensitive solution. The photosensitive solution was applied to a base paper having conductivity, solvent resistance, and water resistance using a wire bar so that the coating amount of the dryer was about 25 g / m ^2, and dried with hot air.

Two such zinc oxide photoconductors are superposed so that one photoconductive surface is in contact with the other back surface, and are rubbed with each other while applying a constant load at room temperature of 35 ° C., or pressed with a pressing machine, and then contacted with the back surface. Electrophotographic plate making machine Diafax EP-31V (Mitsubishi Paper)
The plate was made in, and subjected to desensitization treatment with an etch liquid for diamond electrophotography, DIAFAX LOM-OH (manufactured by Mitsubishi Paper Mills), and printed with a printing machine Ryobi 3200 (manufactured by Ryobi). Fog was hardly seen. In addition, plate making quality and printing durability were good.

Example 2 As a resin used for the photosensitive layer, resin A (acrylic resin, T
g 23 ° C, solidification ratio 50%) 10 parts by weight, resin C (acrylic resin, Tg 43 ° C, solidification ratio 50%) 20 parts by weight, resin D (acrylic, styrene copolymer resin, Tg60 ° C, solidification ratio 50%) ) 10 parts by weight (the calculated average Tg is 4
(2.3 ° C.), an electrophotographic lithographic printing plate was prepared in the same manner as in Example 1. After applying the same stress as in Example 1, plate-making printing was performed, and almost no fog was observed. In addition, plate making quality and printing durability were good.

Example 3 Resins E (acrylic resin, T
g 27 ° C. , solidification rate 50%) 10 parts by weight, resin C (acrylic resin, Tg 43 ° C., solidification rate 50%) 10 parts by weight, resin F (acrylic resin, Tg 55 ° C., solidification rate 50%) 10 parts by weight , Resin G (acrylic, styrene copolymer resin, Tg6
5 ° C., 50% solid ratio) 10 parts by weight (on these calculations Rights
A lithographic printing plate was prepared and tested in the same manner except that a paper laminated with aluminum foil was used as the base paper of Example 1 with an average Tg of 47 ° C.). In addition, plate making image quality and printing durability were good.

Comparative Example 1 Resins H (acrylic resin, T
g15 ° C., solidification ratio 50%) 20 parts by weight, Resin I (acrylic resin, Tg 30 ° C., solidification ratio 50%) 20 parts by weight ( the average Tg in these calculations is 22.5 ° C.) An electrophotographic lithographic printing plate was prepared in the same manner as in Example 1, and after applying the same stress as in Example 1, plate printing was performed. As a result, strong fogging occurred at the rubbed and pressed portions.

Comparative Example 2 Resin J (acrylic resin, T
g 18 ° C., solidification ratio 50%) 10 parts by weight, resin K (acrylic resin, Tg 30 ° C., solidification ratio 50%) 20 parts by weight, resin D (acrylic, styrene resin, Tg 60 ° C., solidification ratio 50)
%) 10 parts by weight (the calculated average Tg is 34.5)
C)), except that lithographic printing plates were prepared in the same manner as in Example 1 and a similar test was conducted. As a result, fogging was observed.

[0022]

EFFECT OF THE INVENTION In the electrophotographic lithographic printing plate, the use of the resin as described in the present invention makes it difficult to cause fogging on the surface of the photosensitive layer and provides an electrophotographic lithographic printing plate with less stain during printing. I can do it.

Claims (1)

(57) [Claims] 1. An electrophotographic lithographic printing plate comprising a conductive support on which a zinc oxide photosensitive layer is provided, wherein two or more resins are used as a binder for the photosensitive layer, and the glass transition points of all resins used. Is 20 ° C. or higher , and the mixed resin
An electrophotographic lithographic printing plate characterized in that the calculated average glass transition point is 40 ° C. or higher .