JPH0251750B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved electrophotographic lithographic printing plate. Generally, an original plate for electrophotographic planographic printing is constructed by providing a layer containing an inorganic or organic optical semiconductor on a base material having characteristics such as water resistance and conductivity. Sheet materials such as paper, metal foil, and film are used as the base material, but when paper is used, it must be treated with water resistance.
Furthermore, in order to improve electrophotographic images, a coating layer containing an inorganic electrolyte such as sodium chloride, potassium chloride, calcium chloride, or an organic polymer electrolyte such as a quaternary ammonium salt, which is usually called a conductive agent, is provided. ing. However, when a lithographic printing original plate is prepared using paper that has been subjected to such treatment as a base material, plate elongation is unavoidable due to the application of dampening water during printing, even after water-resistant treatment. This causes problems such as wrinkles on the plate during printing, misregistration of printed matter, and irregularly sized ruled lines. If you use paper laminated with metal foil such as aluminum, zinc, or copper instead of paper, and have the metal foil layer between the photosensitive layer and the paper, water resistance can be satisfied and the dimensions A printing original plate with good stability can be obtained. (For example, Japanese Patent Publications Nos. 38-17249, 41-2426, and 41-12432) However, it is not possible to provide an electrophotographic photosensitive layer on metal foil laminated paper either directly on the metal foil or through an intermediate layer. Unlike electrophotographic printing plates that use this as a substrate, it currently has various drawbacks and is not suitable for practical use. One of the drawbacks is that there is a metal layer with extremely low electrical resistance in contact with the photosensitive layer or through an intermediate layer, so when corona charging is performed in the plate making machine, excessive conduction occurs in the form of pinholes. This is a phenomenon in which the photosensitive layer is destroyed and the metal foil is partially exposed. Even if this phenomenon is mild and does not lead to exposure of the metal foil surface, there are disadvantages such as white spots occurring in the image area or partial omission of halftone dots in the halftone dot image. This pinhole-like conduction should be avoided if the intermediate layer is used, but in reality, it is difficult to prevent pinhole-like coating defects due to the inclusion of fine bubbles or the inclusion of fine foreign matter when coating the intermediate layer. Since these cannot be prevented and cause pinhole-like conduction, it has been difficult to obtain industrially completed products. A technique has also been proposed in which an intermediate layer provided on a support having metal foil has a volume resistivity of 10 ¹¹ Ω・cm or more and a thickness of 3 μ or less (Japanese Patent Publication No. 1973-
As a result of thorough research into this technology, it was found that providing such a high-resistance layer between the metal layer and the zinc oxide photosensitive layer inhibits light attenuation and tends to result in images with a lot of fog. did. Furthermore, since the thickness of the intermediate layer is small, it is practically difficult to completely cover the metal foil, and it is not possible to prevent pinhole-like destruction of the photosensitive layer. It may be possible to increase the thickness of the intermediate layer to prevent partial conduction to the metal foil, but this would be economically disadvantageous, and there is a practical limit to the thickness that can be obtained with one coating. Furthermore, it is difficult to completely eliminate pinholes. The present invention was made as a result of intensive research to solve the above-mentioned problems, and its gist is that the intermediate layer has a two-layer structure, and each layer has a predetermined volume resistivity value. We have succeeded in industrially and stably producing an improved electrophotographic printing original plate that does not cause white spots on the screen or pinhole-like destruction of the photosensitive layer during plate making and has an extremely excellent plate image. By forming the intermediate layer into a two-layer structure, coating defects in each layer are compensated for each other, and conduction during corona charging due to pinholes is prevented. Further metal layer - first
The inventors have discovered that it is effective to prevent electrical conduction by arranging the intermediate layer, second intermediate layer, and photosensitive layer in the direction of increasing volume resistivity, and that a plate-made image with extremely good contrast can be obtained in this arrangement. has been reached. In the arrangement of metal layer - first intermediate layer - second intermediate layer - photosensitive layer, the volume resistivity values of the metal layer and photosensitive layer are almost constant, but the resistance values of the first intermediate layer and the second intermediate layer depend on their materials. It is variable within a certain range by selecting . Setting the first intermediate layer and the second intermediate layer to predetermined thicknesses is also effective in preventing pinhole-like destruction of the photosensitive layer. As a result of experiments conducted by the present inventors by changing the thickness and resistance value of the first intermediate layer and the second intermediate layer as a model, it was found that the arrangement of these characteristic values has a deep relationship with image quality. That is, the metal layer-
Only the configuration in which the volume resistivity was increased in the order of first intermediate layer - second intermediate layer - photosensitive layer was able to obtain an excellent plate-made image with clearly better contrast than the other configurations. Further, it is preferable that the difference in resistance value between each layer is not excessively large or small. The present invention, which was made based on such knowledge, provides an original plate for electrophotographic lithographic printing in which a paper laminated with metal foil is used as a base, and an intermediate layer and a photosensitive layer are sequentially provided on the metal foil. 1st
It consists of an intermediate layer and a second intermediate layer, and the volume resistivity of the first intermediate layer is 1×10 ⁶ to 9×10 ⁹ Ω·cm, and the volume resistivity of the second intermediate layer is 1×10 ^{10 to 9} ×10 This is an original plate for electrophotographic planographic printing characterized by a resistance of ¹³ Ω・cm. Furthermore, it is more effective to achieve the object of the present invention if the thickness of the first intermediate layer is 2 μ or more and the thickness of the second intermediate layer is 3 μ or more. The volume resistivity value in the present invention is measured as follows. The paint to be tested was applied onto 15μ aluminum foil to obtain a uniform thickness and dried at 100°C for 1 minute. After exposing this sample piece to an atmosphere of 25° C. and 50% RH for 24 hours, the volume resistivity value was measured in the same atmosphere using a resistivity cell model 16008A manufactured by Hüret-Paccard. In this case, the volume resistivity of the aluminum foil is sufficiently low (on the order of 10 ^-3 Ωcm) compared to the resistance of the paint components, so it can be ignored. FIG. 1 is a drawing showing an embodiment of the present invention. In the intermediate layer having a two-layer structure, the layer in contact with the metal foil is the first intermediate layer 5, and the layer on the first intermediate layer and in contact with the photosensitive layer is the second intermediate layer 6. In the figure, numeral 7 indicates a photosensitive layer, which is an image formed by electrophotography, and contains a photosemiconductor as its basic component. Generally, inorganic photoconductor powders such as zinc oxide, titanium dioxide, and cadmium sulfide are dispersed in an insulating binder resin, or organic photoconductors such as polyvinyl carbazole are used as electrophotographic photosensitive layers. .
The metal foil layer 3 is made by laminating a metal foil of aluminum, zinc, copper, etc. onto paper. The first intermediate layer must be applied to the metal foil surface without defects such as pinholes, and for this purpose, the coating thickness (displayed when dry, the same applies hereinafter)
2.0μ or more is required. Further, the volume resistivity value of the first intermediate layer needs to be in the range of 1×10 ⁶ to 9×10 ⁹ Ω·cm. If the resistance value is lower than this, it will approach the resistance value of the metal foil layer, so the significance of providing the first intermediate layer will be diminished, and even if the second intermediate layer is provided, conduction will easily occur during corona charging, and vice versa. If the value is higher than this, light attenuation will be inhibited in the plate making machine, resulting in more fog on the image. The second intermediate layer has a coating thickness of 3.0μ or more, and a volume resistivity of 1×10 ¹⁰ to 9×
It is in the range of 10 ¹³ Ω・cm. When the coating thickness is less than 3.0 μm, the effect of providing the second intermediate layer is reduced. That is, since the first intermediate layer has a lower resistance than the second intermediate layer, conduction occurs more easily during corona charging. This is because the second intermediate layer itself becomes too thin.
This is due to the lack of shielding effect on the first intermediate layer. Also, when the volume resistance value is less than 1×10 ¹⁰ Ω·cm, conduction during corona charging tends to occur. On the other hand, if it exceeds 9×10 ¹³ Ω·cm, there will be a lot of fog in the plate-made image. The upper limit of the thickness of the first and second intermediate layers is not particularly limited, but is naturally limited by the performance and economic efficiency of the coating machine. In addition, the thickness of each of the first and second intermediate layers may be adjusted depending on the printing durability required of this lithographic printing original plate, and the thickness of each intermediate layer may be adjusted.
A range of 5μ to 20μ is most desirable. The volume resistivity of each of the first and second intermediate layers is determined by conductive powder such as carbon black, or inorganic salt,
It can be adjusted by blending a water-soluble conductive substance such as a quaternary ammonium type conductive agent. In addition, if the first and second intermediate layers are made of a material having a volume resistivity within the range specified above,
It is also possible to use the substance alone without blending with a conductive substance. Furthermore, it is of course possible to incorporate known water-resisting agents into the intermediate layer for lithographic printing plates, or to incorporate powder substances such as clay, calcium carbonate, and titanium dioxide, as long as they do not deviate from the above-mentioned range. be. The first intermediate layer and the second intermediate layer are usually obtained by coating each layer once. However, each layer may be applied twice or more as long as the resistance value and thickness are within a predetermined range. In addition, although the back layer 8 is provided in FIG. 1, if problems such as blistering occur due to the back surface being shielded when thermally fixing the developer during plate making, for example, this layer may be used. The back layer can also be omitted, and this does not impede the meaning of the present invention in any way. Next, the present invention will be explained by examples, but the present invention is not limited thereto. Note that "parts" in Examples and Comparative Examples all represent solid content weight ratios. Example 1 Acrylic acid ester copolymer emulsion (Hoechst Synthesis, Movinyl 987) was applied as a laminating adhesive to a commercially available high-quality paper (100 g/m ² ) to give a dry weight of 2.0 g/m ² , and a 15 μm thick paper was coated. Laminated with aluminum foil. Using this aluminum laminated paper as a base material, a composition paint was first applied as a first intermediate layer onto the aluminum surface to a dry thickness of 5.0 μm. The volume resistivity of this layer was 5.0×10 ⁵ Ω·cm. (Composition) Clay 30 parts Acrylic resin emulsion (Hoechst Synthesis, Movinyl DM772) 55 parts Quaternary ammonium type conductive agent (Dow Chemical,
ECR-77) 10 parts Waterproofing agent (Sumitomo Chemical, Sumiretsu 613) 5 parts
The dry thickness of the paint composition as an intermediate layer is 5.0μ
It was applied so that The volume resistance value of this layer is 2.0
×10 ¹² Ω・cm. (Composition) Clay 20 parts Acrylic resin emulsion (Nippon Acrylic, Primal AC-34) 65 parts Polyvinyl alcohol (Kuraray, PVA-105)
10 parts Glyoxal 5 parts Next, the back side of the base material (paper side opposite to the aluminum foil)
A coating liquid having the following composition was applied as a back layer at 5.0 g/m ² . Polyvinyl alcohol (Kuraray, PVA-105)
30 parts acrylic resin emulsion (Hoechst Synthesis, Movinyl DM772) 50 parts quaternary ammonium type conductive agent (Dow Chemical,
ECR-77) 20 parts Next, a photosensitive layer with the following composition was coated on the second intermediate layer at a weight of 22.0 g/m ² . Zinc oxide (Sakai Chemical Co., Ltd., Sazetx #2000) 80 parts Acrylic resin (Nippon Reichhold Co., Ltd., 7-1021)
20 parts Rose Bengal 0.1 part The sheet thus obtained was heated to 65% at 20℃.
An original plate for electrophotographic lithographic printing was obtained by dark adaptation in an RH atmosphere for 24 hours or more. Example 2 Using the same aluminum laminated paper as in Example 1,
As a layer corresponding to the first intermediate layer, a paint of the composition is used.
It was applied in two coats of 10μ each (total 20μ). Subsequently, the steps after the second intermediate layer were carried out in exactly the same manner as in Example 1 to obtain an electrophotographic printing original plate. Comparative Examples 1 to 7 Using the same aluminum laminated paper as in Example 1 as a base material, original plates serving as various comparative examples were created by changing the intermediate layer conditions. The contents and results are shown in Example 1.
It is shown in Table 1 together with the results of ~2. (Method for evaluating original plates) The original plates obtained in the above Examples and Comparative Examples were plate-made using an ITEC 175 plate-making machine using a predetermined original drawing. Next, thoroughly wet the plate surface with absorbent cotton impregnated with etching solution (manufactured by ITETSUKU Co., Ltd.)
Printing was done on an 800-inch printing machine. when printing

[Table] The dampening solution used was a mixture of the above etching solution and water in a ratio of 1:5. Guns (Black 5500) was used as the printing ink. Peeling of the photosensitive surface was determined as the end point of printing durability. As is clear from the above description, according to the present invention, the image quality is extremely excellent and the printing durability is also significantly improved, so the advantages obtained by the present invention are great.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention. The names of each layer are as follows. 1...Base paper, 2...Lamination adhesive layer, 3...
...Metal foil, 4...Base material, 5...First intermediate layer, 6...
...Second intermediate layer, 7...Photosensitive layer, 8...Back layer.

Claims (1)

[Claims] 1. An original plate for electrophotographic planographic printing in which an intermediate layer and a photosensitive layer are sequentially provided on a metal foil of metal foil laminated paper, wherein the intermediate layer has a resistance of 1×10 ⁶ to 9×10 ⁹ Ω・
a first intermediate layer with a volume resistivity of cm and a volume resistivity of 1×10 ¹⁰ ~
An original plate for electrophotographic lithographic printing, comprising a second intermediate layer having a volume resistivity of 9×10 ¹³ Ω·cm. 2. The first intermediate layer has a thickness of 2.0μ or more.
The original plate for electrophotographic lithographic printing according to claim 1, comprising an intermediate layer and a second intermediate layer having a thickness of 3.0 μm or more.