GB1202647A - Improvements in or relating to method, devices and papers for electrophotographic copying - Google Patents

Abstract

1,202,647. Electro-photographic processes. ANICET ANSTALT. May 17, 1968 [May 24, 1967], No.23717/68. Heading G2H. In a method of electro-photographic copying, an electrostatic latent image formed upon a photoconductive surface 2b carried upon a conducting base 2a is transferred to a uniformly charged insulating surface 1b of a paper sheet 1 by bringing the two surfaces into contact or in the immediate vicinity of each other and applying an electric field between the two surfaces having a high frequency component and a continuous component. The distance between the surfaces is from 0 to 120 micromillimetres, the h.f. component has a frequency from 1À2 kilohertz to 3000 megahertz and the continuous component is of the order of a few tens of volts. As shown, the surfaces pass over conductive drums 3, 4 and form a region 14 within which ionisation of the air gap takes place under the action of the electric field. The latent image pattern on surface 26 is not destroyed during the interaction, and further copies can be made. The photo-conductive material may be on an endless band, either passing over drums Fig. 7 (not shown) or over a flat conductive grid to which it is applied by air suction, the copy material passing over a similar closely adjacent grid, Fig. 8 (not shown). In a further embodiment, Fig.4 (not shown) the continuous component of the electric field is produced by gradually covering with a previously charged electret as assembly consisting of two metal plates (42<SP>1</SP>), (43<SP>1</SP>) between which are maintained in contact a photo-conductive paper sheet 2<SP>1</SP> and a paper sheet having a insulating layer. The paper sheet consists of a dispersion of calcium stearate in a binder of methyl polymethacrylate. The photo-conductive material may be zinc oxide, cadmium sulphide, anthracene, triazoles, oxaziles thiazoles or triazines, and may contain a sensitizing agent selected from orange acridine, fluorescein, eosine, Bengal pink or methylene blue. The supporting structure may be a natural or synthetic rubber or a synthetic plastic e.g. butadiene-vinyl chloride, butadiene styrene or acrylonitrile-vinylidene chloride copolymers, polyvinyl-butyral polyesters, or pliolites 3 to 6. A corona discharge unit for the initial charging of the photo-conductive and insulating surfaces is of the scorotron type having a inner tungsten wire of 80 micromillimetres diameter surrounded by an incomplete cylinder of 20 cm. diameter, a meshed element of insulating material closing the cylinder.