JPH0551910B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a photosensitive material for electrophotographic printing plates using a novel conductive waterproof paper as a support.

[Prior Art] Electrophotographic printing plates are currently widely used as direct offset printing plates for light printing because they are highly sensitive, allow quick platemaking work, and are inexpensive. Among these, the most commonly used is one in which a conductive and water-resistant paper is used as a support, and a photoconductive layer in which zinc oxide is dispersed in a binder resin is provided on the support. This photosensitive material for printing plates is charged,
After image exposure, a toner image is formed by toner development, and after the toner is fixed, the non-image area is made hydrophilic with a desensitizing liquid containing a yellow blood salt, and the printing machine is installed and ink and a wet liquid containing a yellow blood salt are applied. Printing is performed using the offset method using water.

This type of photosensitive material for electrophotographic printing plates has the features of rapid processing and low cost, but because it uses paper as a support, it has insufficient water resistance and cannot be used when subjected to the desensitization treatment described above. , the disadvantage is that when it comes into contact with dampening water during printing, water soaks into the paper support and stretches the printing plate, and if you continue printing further, the printing plate may break, and usually the printing plate will be damaged by several thousand at most. The reality is that only one sheet can be printed.

Several attempts have been made to improve this drawback. For example, there is a method in which aluminum foil is attached to conductive and water-resistant paper, and a photoconductive layer is provided on top of the aluminum foil. There is also a support in which a photoconductive layer is provided on a support made by melt-laminating polyethylene containing conductive carbon black on both sides of conductive treated paper. These materials have a significantly improved waterproof effect and less plate spreading during printing, resulting in greatly improved printing durability and the ability to print more than 10,000 sheets.

[Problems to be Solved by the Invention] However, although such highly durable printing plates have excellent performance, they require a process of laminating aluminum foil onto the paper support and a process of laminating the paper support with electrically conductive materials. This requires a process of melting and laminating polyethylene containing carbon black, making it more expensive than conventional photosensitive materials for printing plates.

Therefore, an object of the present invention is to provide a photosensitive material for electrophotographic printing plates that has high printing durability and is inexpensive to manufacture.

As a result of various studies, the present inventors found that the above purpose was to provide a thermoplastic synthetic resin pulp layer containing carbon fibers on both sides of a conductive paper support and then melt the synthetic resin pulp by heat treatment. We have therefore found that this can be achieved by using a support provided with an electrically conductive waterproof layer.

That is, the present invention provides a photosensitive material for an electrophotographic printing plate having a conductive waterproof layer on both sides of a conductive paper support and an intermediate layer and a photoconductive layer on one side thereof.
The conductive waterproof layer is formed by providing a thermoplastic synthetic resin pulp layer containing carbon fibers on a conductive paper support and then melting the thermoplastic synthetic resin pulp by heat treatment. This is a photosensitive material for electrophotographic printing plates.

The present invention will be explained in detail below.

The support used in the present invention (having a conductive waterproof layer) is produced by the following procedure.

First, a thermoplastic synthetic resin pulp containing 1 to 20% by weight of carbon fibers is made using, for example, a cylinder paper machine, and then ordinary paper pulp containing a conductive agent is made on top of that. A thermoplastic synthetic resin pulp containing 1 to 20% by weight of carbon fiber is made and then dried.
Next, when heated to a temperature higher than the melting point of the thermoplastic synthetic resin pulp, the thermoplastic synthetic resin pulp melts and becomes a film. If the material is finished by applying pressure during or after heating using a super calender, etc., an electrically conductive, water-resistant support with a good surface can be obtained.

An intermediate layer is then applied to one side, followed by a photoconductive layer. The carbon fibers used in the present invention may be pitch-based, rayon-based, or polyacrylonitrile-based carbon fibers, but fibers with a length of 1 mm or more are particularly suitable. length is 1
Materials smaller than mm tend to fall off during paper making and are difficult to make. Fibers with a diameter of 30μ or less are particularly suitable. When the thickness exceeds 30μ, the surface flatness deteriorates. The amount of carbon fiber added is preferably 1 to 20% by weight based on the thermoplastic synthetic resin pulp. If it is less than 1%, the conductivity may become insufficient, and if it is more than 20%,
Since the conductivity hardly increases any further, there is no need to add any more.

Thermoplastic resin pulps used in the present invention include polyethylene, polypropylene, ethylene-propylene copolymers, copolymers of ethylene or propylene with other monomers having ethylenically unsaturated groups, polyether, polyacrylonitrile, polychlorinated Pulp consisting of thermoplastic polymers such as vinyl, copolymers of vinyl chloride and other monomers with ethylenically unsaturated groups, styrene-butadiene copolymers, etc. may be used, or two or more of these may be mixed. good. Further, ordinary paper pulp may be further mixed. There is no particular limit to the thickness of the completed conductive waterproof layer, but it is usually about 10μ to 50μ, and the thickness on both sides may be changed to balance the curl.

The paper pulp used for the paper support of the present invention may be any of the commonly used chemical pulps, semi-chemical pulps, kraft pulps, ground pulps, etc., or a mixture thereof may be used.
Further, synthetic resin pulp may be further mixed. When synthetic resin pulp is mixed, the adhesive strength with the conductive waterproof layer is improved. The conductive agents added to this pulp include calcium chloride, sodium chloride,
Organic conductive substances such as inorganic electrolyte compounds, amine compounds, and sulfone compounds, polymeric conductive substances, conductive carbon, carbon fibers, or mixtures thereof can be used. Further, as a sizing agent, a sizing agent commonly used for paper can be added. These additives are preferably added to the pulp slurry during paper making.

In the intermediate layer used in the present invention, it is preferable that the surface electrical resistance of the layer directly in contact with the conductive substance is 10 ⁹ or less. If a photoconductive layer is provided directly on a conductive waterproof layer without an intermediate layer and a toner image is formed using an electrophotographic method, uneven density in the image area and uneven density due to fog in the non-image area may occur. be. This is presumed to be because the carbon fibers added and dispersed in the conductive waterproof layer are mixed unevenly, resulting in uneven conductivity on the surface of the conductive waterproof layer. Ru. and the surface resistance of the intermediate layer.
When the resistance is set to 10 ⁹ Ω or less, the above-mentioned influence can be eliminated, and a good image without unevenness can be obtained. When two or more intermediate layers are provided, the surface resistance of the intermediate layer in direct contact with the conductive waterproof layer may be 10 ⁹ Ω or less.

Another function of the intermediate layer is to strengthen the adhesion between the conductive waterproof layer and the photoconductive layer, and if the surface of the conductive waterproof layer is subjected to surface treatment such as corona discharge treatment before forming the intermediate layer. The effect is further improved.

There are no particular restrictions on the material used for the intermediate layer, and any known intermediate layer material may be used, and methods for controlling the surface resistance of the intermediate layer may include known inorganic metal salts, organic amine compounds, conductive pigments, etc. may be selected and added as necessary.

A preferable photoconductive layer used in the photosensitive material for electrophotographic printing plates of the present invention is one containing zinc oxide as a main component. Zinc oxide powder is mixed with an acrylic polymer, a silicone polymer, etc. in a solution state, and if necessary, a photoconductive layer is used. A sensitizer is added, coated on the intermediate layer and dried.

To perform plate making using the photosensitive material for electrophotographic printing of the present invention, charging, image exposure, toner development, and fixing are performed using an electrophotographic plate making machine to apply toner to the photoconductive layer. An image is formed and then the non-image areas of the photoconductive layer are etched with an etching solution (desensitizing solution).
The photoconductive layer to which no toner is attached is made hydrophilic by treatment, and a printing plate is prepared.

If the printing plate thus produced is run on an osset printing machine and printed using ink and dampening water, more than 10,000 pieces of high-quality printed matter can be obtained.

Example 1 Thermoplastic synthetic resin pulp, SWP UL400 (Mitsui Petrochemical Co., Ltd., polyethine resin, melting point 122°C)
and carbon fibers (polyacrylonitrile type, fiber length: about 3 mm, single fiber diameter: about 12 μm) were mixed and dispersed in water at a weight ratio of 9:1 to prepare a dispersion ().

On the other hand, LBKP was dispersed in water, and 1% sodium stearate, 1.5% carboxyl-modified pyrivinyl alcohol, and 5% aluminum chloride were added to the LBKP to prepare a dispersion ().

First, the dispersion liquid () was made with a basis weight of 40 using a cylinder paper machine.
g/m ² , then on top of that, the dispersion () is made to have a basis weight of 120 g/m ² , and on top of that, the dispersion () is again made to have a basis weight of 40 g/m ² . Combined excerpts. Water is squeezed out using a press roll, and a cylinder dryer is used to dry the surface at a temperature of 100 to 110.
Dry at °C. Next, it is passed through a machine calender with a surface temperature of 120 to 130°C at a linear pressure of about 70 kg/cm ² to melt the thermoplastic resin pulp layer containing carbon fibers on the front and back sides, and at the same time smooth the surface to make it conductive. A waterproof paper support was obtained.

The surface electrical resistance of the conductive waterproof paper support thus obtained was 10 ⁵ Ω or less.

One side of this conductive waterproof paper support is 5KVA.
corona discharge treatment under the conditions of sec/m ² , and then a composition for the intermediate layer as shown below at a dry weight of 2 g/m ²
It was applied and dried at 100°C for 2 minutes.

Alcohol-soluble nylon 10 parts by weight Conductive carbon (acetylene black)
2 parts by weight Methanol 88 parts by weight The surface electrical resistance of the intermediate layer was 1×10 ⁸ Ω.

Next, a photoconductive composition as shown below was coated on top of this at a dry weight of 25 g/m ² and heated at 90°C.
and dried for 5 minutes.

Copolymer of n-butyl methacrylate and methyl methacrylate (molar ratio 1:1) 12 parts by weight Zinc oxide 60 parts by weight 10% methanol solution of rose bengal
2 parts by weight Toluene 55 parts by weight The photosensitive material for electrophotographic printing plates thus produced was processed as toner ELP-T (manufactured by Fuji Photo Film Co., Ltd.) using an electrophotographic plate making machine ELP404V (manufactured by Fuji Photo Film Co., Ltd.).
A good image was obtained when the plate was made using the following. Next, after processing with etching liquid ELP-E (manufactured by the same company), printing was performed using an offset printing machine, and 20,000 good prints were obtained.

Example 2 Thermoplastic synthetic resin pulp, ES-chop (Chitsuso Co., Ltd.)
A dispersion liquid () was prepared by mixing and dispersing carbon fiber (polyacrylonitrile type, fiber length approximately 3 mm, single fiber diameter approximately 12 μm) in water at a weight ratio of 10:1.

On the other hand, LBKP was dispersed in water and a dispersion liquid (2) was prepared using the same recipe and method as in Example 1.

Using a cylinder paper machine in the same manner as in Example (1), first make the dispersion liquid () to a basis weight of 40 g/m ² or more, and then add the dispersion liquid ( ) to a basis weight of 120 g/m ² on top of it. Then, add the dispersion liquid () on top of it again to
The paper was combined to give a weight of 40 g/m ² . This was squeezed with a press roll and dried using a cylinder dryer at a dryer surface temperature of 120 to 130°C.
Next, it is passed through a machine calender with a surface temperature of 170 to 180°C at a linear pressure of about 70 kg/m ² to melt the thermoplastic resin pulp layer containing carbon fibers on the front and back sides, and at the same time smooth the surface to make it conductive waterproof. A paper support was obtained.

The surface electrical resistance of the conductive waterproof paper support thus obtained was 10 ⁵ Ω or less.

One side of this conductive waterproof paper support is 5KVA.
corona discharge treatment under the conditions of sec/m ² , and then the following first intermediate layer composition was applied on the dry weight of 1.5
g/m ² and dried at 100°C for 5 minutes.

Ionomer solids content 50% emulsion
20 parts by weight (90 mol% ethylene, 10 mol% methacrylic acid, degree of neutralization 90%, metal K ⁺ ) Snowtex C (colloidal silica manufactured by Nissan Chemical) 5 parts by weight Conductive carbon (acetylene black)
5 parts by weight Water 70 parts by weight The surface electrical resistance of the first intermediate layer was 1×10 ⁷ Ω.

Next, a second intermediate layer composition as shown below was applied on top of this to give a dry weight of 1.5 g/ ^m2 .
Dry for 2 minutes at °C.

Alcohol-soluble nylon 10 parts by weight Methanol silica (colloidal silica manufactured by Nissan Chemical) 3 parts by weight Methanol 80 parts by weight The surface electrical resistance of the second intermediate layer was 1×10 ¹³ Ω.

Subsequently, the same photoconductive composition as used in Example 1 was applied thereon at a dry weight of 25 g/m ² and dried at 90° C. for 5 minutes.

The photosensitive material for electrophotographic printing plates produced in this way was used in an electrophotographic plate making machine ELP404V (Fuji Photo Film).
When a plate was made using ELP-T (manufactured by the same company) as a toner, a good image was obtained. Next, after processing with etching liquid ELP-E (manufactured by the same company), printing was performed using an offset printing machine, and 20,000 good prints were obtained.

[Effects of the Invention] As described above, the photosensitive material for electrophotographic printing plates of the present invention can be obtained by a relatively simple process using inexpensive materials, and can provide a printing plate with greatly improved printing durability. I can do it.

Claims (1)

[Scope of Claims] 1. A photosensitive material for an electrophotographic printing plate having a conductive waterproof layer on both sides of a conductive paper support and an intermediate layer and a photoconductive layer on one side, wherein the conductive waterproof layer is conductive. An electrophotographic printing plate characterized in that it is formed by providing a thermoplastic synthetic resin pulp layer containing carbon fibers on a paper support and then melting the thermoplastic synthetic resin pulp by heat treatment. photosensitive material. 2. Claim 1, wherein the thermoplastic synthetic resin pulp is a polyolefin-based synthetic pulp, and the carbon fiber content is 1 to 20% by weight of the synthetic pulp.
The photosensitive material for electrophotographic printing plates described in . 3 The intermediate layer consists of one layer or two or more layers, and the surface resistivity of the intermediate layer in direct contact with the conductive waterproof layer is 10 ⁹ Ω.
A photosensitive material for an electrophotographic printing plate according to claim 1 or 2 below. 4. The photosensitive material for an electrophotographic printing plate according to any one of claims 1 to 3, wherein the photoconductive layer contains zinc oxide.