JPS60191274A - Electrophotographic offset master - Google Patents

Abstract

PURPOSE:To provide high print resistance and high image characteristic to an offset master by providing a layer consisting of a conductive pigment and solvent type high polymer material between an electrophotographic sensitive layer and a base at 0.5-20g/m<2> weight after drying and adjusting the surface resistance value of the layer at the specified range. CONSTITUTION:A pigment having electrical conductivity is diluted into a solvent consisting of a solvent type high polymer material and thereafter the soln. is coated on base paper having solvent resistance, water resistance and electrical conductivity so as to be coated at 0.5-20g/m<2> weight after drying thereon and is then dried. The surface resistance value of the coated layer is adjusted to a 10<7>-10<14>OMEGA range. A photosensitive liquid for electrophotography is then coated thereon to make the coating layer adaptive to darkness and thereafter the plate is photoengraved. The high print resistance and high image characteristic are thus provided to the offset master.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic paper obtained by dispersing a photoconductive substance such as acclimatized 1F lead in a resin and coating it on a base paper, and more specifically relates to an electrophotographic paper obtained by coating with a solvent. The present invention relates to an electrophotographic offset master having an intermediate layer formed by the above method.

As is well known, the structure of electrophotographic paper is to provide an undercoat layer and a backing layer on both sides of the base paper in order to impart conductivity, solvent resistance, water resistance, curling properties, adhesion to the base paper, etc. Furthermore, a photosensitive layer is provided on the undercoat layer. The photoconductive materials used in this photosensitive layer include oxidized lead, titanium oxide,
Inorganic materials such as zinc sulfide have been used, and recently organic materials such as polyvinylcarbazole have also been used. When this electrophotographic paper is used as an offset master plate, properties such as adhesion and water resistance are required between the photosensitive layer and the undercoat layer in order to improve printing durability and the accuracy of printed images. becomes.

As a method for this purpose, it has been devised to provide an intermediate layer between the photosensitive layer and the undercoat layer. For example, the special public service in 1977-35
700, which is coated with a small amount of solvent-soluble resin (polymer material) with an intermediate layer 1@, has been proposed.

However, with these types of products, there is a large fluctuation in printing durability due to the small amount of resin applied, or the image quality is easily fogged, and is easily affected by humidity, and when the relative humidity IW decreases, the image 1 @ decreases. It had significant drawbacks such as: Furthermore, in order to obtain higher printing durability with such an intermediate layer, the amount of coating must be increased, but in this case, the electrical conductivity between the photosensitive layer and the undercoat layer is almost completely lost, resulting in poor image quality. This was not desirable because it caused the photosensitive layer to overcoat, and the coating film was prone to cracking due to drying shrinkage when the photosensitive layer was applied. Another drawback was that the resins to be used for the intermediate layer were very limited.

The purpose of the present invention is to improve these drawbacks,
Even if the coating amount of the intermediate layer is large, there are no drawbacks such as deterioration of image quality. Our goal is to provide an offset master plate.

Considering the characteristics of the master plate used in offset printing, when the printing ink is transferred to the blanket, the master plate is repeatedly subjected to upward force perpendicular to the plate image. For this reason, an adhesive strength of Kana 9 or above is required between the base and the base.

Furthermore, since water is used in offset printing, the water that permeates from the plate surface reaches the adhesive interface and tends to cause peeling between the base and the photosensitive layer, so water resistance is also required.

Electrophotography also requires a certain range of electrical conductivity between the photosensitive layer and the base. This is necessary to allow electrons on the photosensitive layer supplied by corona discharge to escape during exposure. In order to obtain this conductivity, inorganic electrolytes such as sodium chloride, calcium chloride, and magnesium chloride, and organic electrolytes such as quaternary ammonium salts, sulfonates, and carboxylates are added to the undercoat layer. added. However, such an electrolytic substance absorbs moisture in the air and imparts conductivity, and when used in electrophotography, it becomes susceptible to the influence of the humidity atmosphere in the air.

The inventors of the present invention have intensively studied an offset master plate that does not have these drawbacks and provides high printing durability and high image quality, and as a result, they have devised the following method and have completed the present invention.

That is, in the present invention, a conductive pigment dispersed in a solvent-soluble resin is coated as an intermediate layer on a base, and the coated amount after drying is 0.5 to 20F! -~, and the surface resistance value of the film layer after drying is 107Ω~1014
Ω range, and a photosensitive layer is further coated on top of this. Here, the conductive pigments include carbon black, zinc oxide, titanium oxide, stannic oxide, indium oxide, metal powder, and the like. Among these conductive pigments, carbon black is more preferably used.

Carbon black can be classified into acetylene black, Ketjen black, furnace black, and channel black based on raw materials and manufacturing methods, but acetylene black and Ketjen black are particularly preferred as the carbon black that imparts conductivity to be used in the present invention.

Generally, the resin to be used with these conductive pigments may be one that is soluble in a solvent, but from the viewpoint of adhesion between the base and photosensitive layer, water resistance, dispersion stability of the pigment, etc.
Preferred are vinyl chloride, vinyl acetate, polyester, alkyd, or copolymers thereof. Among these, copolymers of vinyl chloride and vinyl acetate are particularly preferred.

Further, the solvent to be used may be any solvent as long as it can dissolve the resin used, and aromatic compounds, ketones, esters, etc. are suitable for use. After these are mixed and dispersed, they are coated on a base, but this base needs to be solvent resistant so that the above mixture can be coated. Specifically, it is necessary to coat the base paper with a solvent resistant coating. It may be a coated layer, a paper laminated with aluminum foil, or even a film.The film layer of these mixtures must have a conductivity within a certain resistance value range after coating and drying, which is preferable. The range of conductivity is from 107Ω to 1014Ω.If the resistance value is less than 107Ω, the image quality will deteriorate significantly, which is undesirable.If the resistance value is more than 1014Ω, the image quality will be affected by background fogging. The coating amount of the intermediate layer is from 0-5 t/n? to 20 y-y by weight after drying.
If the coating amount is small, the adhesion between the photosensitive layer and the base and water resistance will be insufficient, resulting in a decrease in printing durability during printing. On the other hand, if the amount of coating is too large, the printing durability will be good, but the curl balance of the plate will be disturbed and handling will be inconvenient.

The present invention will be explained below using specific examples.

Example 1 After diluting a paint in which the following conductive pigment was dispersed in a solvent, a solvent-resistant, water-resistant, and conductive base (
5 in weight after drying on top of base paper) / I applied it with a Meyer bar so that it looks like this. The surface resistance value at this time is 1012
It was Ω.

Conductive carbon black paint 10 parts by weight toluene 6
0 〃 Methyl ethyl ketone 40 〃 The following electrophotographic photosensitive liquid was prepared on this coated material, and applied with a Meyer bar so that the coating amount after drying was 25 P/rrl.

Zinc oxide for electrophotography ioo Parts by weight Acrylic resin 20 P Loose Bengal 0.2 Toluene 150 After dark-adapting this coated material for a day and night, it was processed using Faxmaster plate making machine HP-11 (manufactured by Mitsubishi Paper Mills). When the plate was made, it had good image quality.

Furthermore, when this plate was etched with an etchant (LOM-OH manufactured by Mitsubishi Paper Industries) and then printed using a small offset printing machine (Toko Model 810 manufactured by Tokyo Aircraft Instruments), it was found that even after printing 5,000 sheets of high-quality paper, there were no gaps or stains on the plate. Good printed matter was obtained without causing any problems.

On the other hand, as a comparative example, the electrophotographic photosensitive liquid of the example was applied with a Mayer bar onto the solvent-resistant, water-resistant and conductive base paper used in the example. When this coated material was dark-adapted in the same manner as in the examples and then plate-made, the image quality was slightly inferior to that in the examples.

In addition, when this plate-made product was printed on a small offset printing machine in the same manner as in the example, the photosensitive layer in the image area was separated (separated) on 1000 sheets of high-quality paper, and the printed matter had defects such as chipping and staining of the image, as well as stretching of the printed image. Occurrence of defects was observed.

Furthermore, when the coated products of Examples and Comparative Examples were left in an atmosphere of 10°C and 20% RH for 5 hours and immediately passed through a plate making machine, the coated products of Comparative Examples showed fogging in non-image areas and a decrease in density in image areas. It was seen. On the other hand, the coating material of the example has good image quality with almost no fogging or decrease in density.

Example 2 After thoroughly mixing and dispersing the following substances, the mixture was coated on a solvent-resistant base paper using a Meyer bar so that the weight after drying was 10 P/ryl. The surface resistance value at this time was 1010Ω.

Ketjen black 10 parts by weight Kanevirac L-CM16 // (Vinyl chloride and vinyl acetate copolymer manufactured by Kanebuchi Chemical Co., Ltd.) Toluene 60 parts by weight Methyl ethyl ketone 40 Furthermore, on top of this coating material, an electrophotographic coating similar to Example 1 was applied. The weight of the photosensitive liquid after drying is 251i'/W? I applied it with a Meyer bar so that it looked like this. After dark-adapting this coated material for a day and night, it was plate-made using a Faxmaster plate-making machine QP-5 (manufactured by Iwasaki Tsushinki Co., Ltd.), and the image quality was good. Further, when this plate-made product was printed on a small offset printing machine after etching treatment, it was possible to obtain good printed matter without causing plate blanking or staining even on 5,000 sheets of high-quality paper.

Claims (1)

[Claims] 1. Between the electrophotographic photosensitive layer and the base, a layer consisting of a conductive pigment and a solvent-based polymer compound 'σ is added between 0.5 and 2 after drying.
■The surface resistance value of this layer is 107~1014Ω.
An electronic photo offset master featuring a range of features.