DE1797524A1 - Electrophotographic material convertible to a lithographic printing plate - Google Patents

Description

Electrophotographic convertible to a lithographic printing plate Material The invention relates to an electrophotographic material which is incorporated into a lithographic printing plate is convertible.

The wide field of lithography, in which an image is fixed on a lithographic Kattenberg which is coated with C> a photosensitive material, wherein the plate is exposed through a mask or a transparency, is known as photolithography. Photolithography is related to photography in that both use light to define an image (often latent) in a photoresponsive material which is then treated with various chemical and / or physical agents to create, in the case of photography, an image to produce a visible image and, in the case of photolithography, to produce a printable image (where on a lithographic press some surfaces take on color and others do not).

The various requirements for creating a printable image as opposed to a visible image have resulted in both areas In general, very different development programs were pursued. The tight ones and very different surface requirements for a photolithographic Must be met have caused the photolithography behind the plate Photography lagged behind by a few years in terms of the apparently analogue development. So to this day the preparations for the printing of commercially available ones are in progress Photolithographic plates are relatively time consuming and, typically, require several Minutes to Complete Work-Electrophotographic Method of Processing of the exposed electrophotographic material are known Electrophotographic development processes can include that of the present invention electrophotographic material converted into a lithographic printing plate be, with the image areas the pressure plate can be set, without the transferred image lier se or any modification thereof as color-receiving lithographic image to be used.

It became an electrophotographic convertible into a lithographic printing plate Material with a backing and a hydrophilic layer found that this is characterized in that the base is a conductive metal with a reduction promoter Serving oleophilic photoconductive surface layer on which a perfect liquid-permeable hydrophilic layer of colloidal silicon dioxide arranged is.

As has been found, after exposure and development of the The electrophotographic material of the present invention bleached the metal image obtained are so that the hydrophilic layer is removed and the underlying oleophilic surface is exposed, creating one for the press finished lithographic plate is obtained.

The invention will now be explained with reference to the drawing. Fig. 1 shows an embodiment of the invention in edge sectional views of the various states or stages of the electrophotographic material according to the invention and the lithographic printing plate that can be produced therefrom. As step A shows, the electrophotographic material consists of a sheet 20 with a conductive metal surface 201 which is coated with a firmly bonded oleophilic layer 21 which is photoconductive, ie contains light-sensitive material. A layer of liquid-permeable hydrophilic material 22 lies above and firmly connected to it. The photoconductive material contained in layer 21 serves as a metal ion reduction promoter. In stage B, the structure of stage A is shown after it has been exposed to an image. The areas 21a of the oleophilic layer in the interface between this layer and the overlying hydrophilic layer (and everywhere else in the entire thickness) were made electrically conductive by the exposure. In stage 0 , the structure of stage B is shown after the plate has been connected to an electrical potential (with the metal surface 20 and the electrically conductive area 21a serving as a cathode) in the presence of an electrolyte that contains reducible metal ions (e.g. Contains silver ions. After some time, due to the electroconductive forces, the silver ions come into contact with the cathode surface of the regions 21a and are deposited thereon, and they are reduced to their metallic state, giving a black image 23 which is negative with respect to the original The stage D shows the structure of stage C after the further B. # treatment to remove the deposited silver of the image 23 as well as the overlying hydrophilic layer 22a, so that the underlying oleophilic surface is exposed in the areas 21a and a color absorbing Print image is determined. The remaining areas 22b of the hydrophilic layer 22 remain firmly connected to define the hydrophilic background areas of the plate.

In the figure, the letter Ilb! T becomes the drawing of areas are used, which correspond to the dark areas of the original, and the letter "all is corresponding to the identification of the light areas of the original Areas used. It can be seen that the embodiment according to FIG contains b areas as background areas and the a areas as pressure areas, i.e. that this is a negative acting plate.

All dimensions in the drawing are greatly exaggerated for the sake of clarity and are not intended to represent the relative thicknesses of the individual layers. However, it can be observed in connection with the figure of the drawing that an interface area which contains a metal ion reduction promoter is defined in the interface areas of the hydrophilic, liquid-permeable layer and the underlying oleophilic layer.

The invention is illustrated in more detail in the following example.

Example A base sheet of paper was coated with an 8 Miron thick aluminum foil, which in turn g with about 0925 per dm 2 (dry weight) an oleophilic photoconductive layer having the following formulation coated serviceable Constituent quantity in- £ Polystyrene butadiene resin (Goodyear) 1992 Polystyrene 1298 TiO 2 pigment 1996 ZnO pigment 13490 Toluene Solvent 20694 Methanol solvent 890 Phosphine R - dye 0p044 The oleophilic layer was then coated with 0.05 g per dm 2 (dry weight) of a hydrophilic layer with the following recipe Component amount in g Colloidal silica 60 Water 33 Methanol 7 The plate was exposed for 30 seconds by projection through negative Llicrofilm at a distance of 1.2 m using a projector with a 400 W / 65 V lamp. The plate was then developed by electroplating a silver image in the areas struck by the light. The anode consisted of a sieve made of silver wire and the electrolyte consisted of a solution of 0.1N silver nitrate. The aluminum coating and exposed, conductive zincogide image areas acted as the cathode and a sponge layer held the anode and cathode about 6 mm apart. A direct current having a potential of 4 V was 5 sec created long, and a visible black image was obtained The silver image was bleached by the plate Were you about 5 seconds at about 24 00 immersed in a Bleichlösuhg having the following composition Constituent parts by weight Water 6 Potassium bromide 1 Potassium ferric yanide 1 As a result of the bleaching, the silver metal was removed from the hydro-. The philic layer was leached and the remaining bleach solution was removed by rinsing the plate with water. The plate was then gently wiped with a cotton pad as it washed, which cleanly removed the silica from the image areas to reveal the underlying, color-receptive oleophilic surface. The remaining silica layer in the non-image areas remained firmly bonded to the oleophilic surface to form the ink repellent ettering areas of the plate. The record was then ready for the press. Several hundred exact prints were made in a test run.

Claims (2)

Claims , 112 Electrophotographic material convertible into a lithographic printing plate with a base and a hydrophilic layer, characterized in that the base has a conductive metal with an oleophilic photoconductive surface layer serving as a reduction promoter, on which a completely liquid-permeable hydrophilic layer of colloidal silicon dioxide is arranged. 2, a process for the production of a lithographic printing plate using the electrophotographic material according to claim 1 with image-wise exposure of the electrophotographic material, characterized in that after developing by an electrophotographic process a metal image formed on the electrophotographic material by exposure is made from the hydrophilic layer by means of a bleach solution and by removing the hydrophilic layer in the image areas, the ciaophilic ink-receiving layer is exposed in these areas.