JPS588696A - Electrophotographic negative plate for lithographic printing - Google Patents

Abstract

PURPOSE:To obtain an excellent plate image having distinguished contrast, by providing differences in volume resistivity by steps among the metal layer provided on a metallic foil, 1st intermediate layer, 2nd intermediate layer and a light-sensitive layer. CONSTITUTION:In the intermediate layer consisting of double layers, 1st intermediate layer 5 is contacted with a metallic foil, whereas 2nd intermediate layer 6, being placed above said 1st intermediate layer, is in contact with a light-sensitive layer. Said light-sensitive layer 7 designates an image created by electrophotographic process and contains a photo semiconductor as a basic component. Said 1st layer and 2nd layer constituting said intermediate layer have the volume resistivity of 1X10<6>-9X10<9>OMEGA.cm and 1X10<10>-9X10<13>OMEGA.cm, respectively, each having thickness of preferably 5mu-20mu. Volume resistivity is specified in this way to obtain proper conduction when corona charging, thereby preventing the fog of a plate image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved electrophotographic lithographic printing plate. In general, electrophotographic planographic printing plates are 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 if paper is used, the rim should be treated with water resistance.
Furthermore, in order to improve electrophotographic images, coatings containing inorganic electrolytes such as sodium chloride, potassium chloride, calcium chloride, etc., and organic polymer electrolytes such as quaternary ammonium salts, which are usually called conductive agents, are used to improve electrophotographic images. There are layers.

However, when a lithographic printing plate is created using paper that has been treated in this way as a base material, the addition of dampening water during printing causes problems.
Even with water-resistant treatment, plate elongation is unavoidable. This causes problems such as wrinkles on the plate during printing, misregistration of printed matter, and irregularly sized ruled lines.

Water resistance can be satisfied by using paper laminated with metal foil such as aluminum, zinc, or copper as the paper substitute, and by placing the metal foil layer between the photosensitive layer and the paper. It is possible to obtain a printing original plate with good dimensional stability.
2426, Publication No. 41-12432) However, providing an electrophotographic photosensitive layer on metal foil laminated paper either directly on the metal foil or through an intermediate layer is an electrophotographic printing method using ordinary paper itself as a base. The current situation is that it is different from the original version and has various drawbacks, making it unusable 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 in that white spots occur in the image area and halftone dots are partially missing 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 10110·a or more and a thickness of 3 μ or less (Japanese Patent Publication No. 51-8334), but this technique has not been sufficiently discussed. As a result of research, 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 produce images with a large amount of capri.

Further, 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 is possible to increase the thickness of the intermediate layer to prevent partial conduction to the metal foil, but this is economically disadvantageous, and there is a practical limit to the thickness that can be obtained with one coating. However, 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 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. Furthermore, metal layer - first intermediate layer - second intermediate layer -
The present invention was achieved by discovering that arranging the photosensitive layer in a direction in which the volume resistivity increases successively is effective in preventing electrical conduction, and that in this arrangement, a plate-made image with extremely good contrast can be obtained. In the arrangement of metal layer - first intermediate layer - second intermediate layer - photosensitive layer, the volume resistivity of the metal layer and the photosensitive layer is almost fixed, but the resistance of the first intermediate layer and the second intermediate layer depends on the material. It is variable within a certain range depending on the selection. 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. The inventors have discovered that the first intermediate layer, the second intermediate layer,
As a result of conducting experiments by changing the thickness and resistance value of the intermediate layer as a model, it was found that the arrangement of these characteristic values is closely related to image quality. That is, the metal layer - the first intermediate layer -
Only the configuration in which the volume resistivity was increased in the order of the second intermediate layer and the 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. Consisting of a first intermediate layer and a second intermediate layer, the volume resistivity of the first intermediate layer is I x 10' to 9 x 10
'Ω・Vice resistance, the volume resistance value of the second intermediate layer is 1×101
This is an original plate for electrophotographic planographic printing characterized by having a resistance of 0 to 9 x 10"Ω・m.Furthermore, if the thickness of the first intermediate layer is 2μ or more and the thickness of the second intermediate layer is 3μ or more, This is more effective in achieving the purpose of the invention.

1 1 The volume resistivity value in the present invention was measured as follows. The paint to be tested was applied onto a 15μ aluminum foil to obtain a uniform thickness and dried at 100t:' for 1 minute. After exposing this sample piece to an atmosphere of 25C and 50% RH for 24 hours, the volume resistance value was measured in the same atmosphere using a 16008Ai resistivity cell manufactured by Hulett Paracard. In this case, the volume resistivity of the aluminum foil is sufficiently low (io"" Ω closed) 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 top of the first intermediate layer in contact with the photosensitive layer is the second intermediate layer (6). In the figure, numeral 7 indicates a photosensitive layer. The photosensitive layer is an image formed by an electrophotographic method, 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 in order to do so, the coating thickness (expressed when dry, hereinafter the same) must be 2.0μ or more. 1, and the volume resistivity of the first intermediate layer is 1×10
It is necessary that the resistance is in the range of 1'1 to 9×10°Ω·m. 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.
On the other hand, if it is higher than this, light attenuation will be inhibited in the plate-making machine, resulting in more capri in the image. The coating thickness of the tlS2 intermediate layer should be 3.0μ or more, and the volume resistivity should be I x 10”~
It is in the range of 9 x 10”Ω.The coating thickness is 3.0
If it is less than μ, the effect of providing the second intermediate layer will be reduced. In other words, since the first intermediate layer has a lower resistance than the second intermediate layer, conduction occurs more easily when the coil is charged. This is because the second intermediate layer itself is too thin and lacks a shielding effect on the first intermediate layer. Also, the volume resistance value is I
When the resistance is less than 9 x 10"Ω, conduction occurs more easily during cycorona charging.On the contrary, when the resistance is less than 9 x 10"Ω
When the image is exceeded, there will be many capris 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, depending on the printing durability required for this lithographic printing original plate,
It is only necessary to adjust the thickness of each of the first and second intermediate layers,
The thickness of each intermediate layer is most preferably in the range of 5μ to 20μ.

The volume resistivity of each of the first and second intermediate layers is a conductive powder such as carbon black, or an inorganic salt.

It can be adjusted by adding a water-soluble conductive substance such as a quaternary ammonium type conductive agent.

Further, as long as the first and second intermediate layers have a volume resistivity within the range defined above, it is possible to use the material alone without adding a conductive material. In addition, it is obvious that it is 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. first middle layer,
The second intermediate layer is usually obtained by coating each layer once. However, each layer may be coated in two or more times, as long as the resistance value and thickness are within a predetermined range. Good. In addition, although a back layer (8) is provided in FIG. 1, problems such as blisters may occur due to the back surface being shielded during plate making and heat fixing of developer. If present, this back layer may be omitted, and this does not impede the meaning of the present invention in any way.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto. In addition, in Examples and Comparative Examples, “
"Part" indicates the solid content weight ratio.

(Example 1) Acrylic ester copolymer emulsion (Hoechst Synthesis, Movinyl 987) was applied as a laminating adhesive to commercially available high-quality paper (1001/d) at a dry weight of 2.0 t/d.
lr? It was coated with aluminum foil having a thickness of 15μ and laminated with aluminum foil. Using this aluminum laminated paper as a base material, a paint having the following composition was first coated on the aluminum surface as a first intermediate layer so that the dry thickness was 5.0 μm. The volume resistance value of this layer is 5
．． It was a 0x10'Ω saw.

(Composition 1) 30 parts of clay; ゛A paint of composition (1) was applied as a second intermediate layer on the thus obtained first intermediate layer so that the dry thickness was 5.0 μm. The volume resistance value of this layer is 2.0×10120・
He was a deputy.

(Composition ■) Clay 20 parts Glyoxal 5 parts Next, apply a coating liquid with the following composition at 5.0f/+r? as a back layer on the back side of the base material (paper side opposite to the aluminum foil). Coated.

Next, a photosensitive layer with the following composition was formed on the second intermediate layer.
It was coated so that it became 0 f/-.

0.1 part of Rose Bengal The thus obtained sheet was dark adapted for 24 hours or more in an atmosphere of 20 tll' and 65% RH to obtain an original plate for electrophotographic planographic printing.

(Example 2) Using the same aluminum laminated paper as in Example 1, the coating material of composition I was applied in two coats of 10 μm each (20 μm in total) as a layer corresponding to the first intermediate layer.

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 Table 1 together with the results of Examples 1 and 2.

(Evaluation method of original plate) The original plates obtained in the above Examples and Comparative Examples were plate-made using an Itic 175 type plate-making machine using a predetermined original drawing. Next, the plate surface was thoroughly wetted with absorbent cotton impregnated with an etchant (manufactured by Itic Co., Ltd.), and printed using a Toko 800 type printing machine. 121 The dampening solution used during printing was a mixture of the above etchant and water in a ratio of 1:5. The printing ink is Guns (Black 5)
500) was used. Peeling in the photosensitive direction 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 rigidity of printing is also significantly improved, so the advantages obtained by the present invention are great.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention. The names of each layer are as follows. DESCRIPTION OF SYMBOLS 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, Patent applicant
Oji Paper Co., Ltd. Representative Patent Attorney Masaaki Kobayashi 161

Claims (2)

[Claims] (1) In an original plate for electrophotographic planographic printing in which an intermediate layer and a photosensitive layer are sequentially provided on the metal foil of metal foil laminated paper, the intermediate layer has a volume resistivity of I x 10' to 9 x 10'' Ω/image. a first intermediate layer having 1×1010~9×
1. An original plate for electrophotographic planographic printing, comprising a second intermediate layer having a volume resistivity of 10"Ω. (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.