GB985663A - Charging of xerographic plates - Google Patents

Abstract

985,663. Electro-photographic apparatus. RANK-XEROX Ltd. March 15,1961 [March 17, 1960],No. 9530/61. Heading G2H. [Also in Division H1] A xerographic plate which includes a photoconductive insulating rectifying layer, allowing current flow in one direction only and being sufficiently insulating in the reverse direction to retain charge on its free surface, is charged by applying across the plate a field having a direction to cause current flow in said one direction so that a charge of opposite polarity to that of the charging member is retained on said surface when the applied field is removed. As shown in Fig. 1, the plate comprising layer 10 of photoconductive rectifying insulating material on a conductive backing 11 is charged by passing a spring loaded roller 20 comprising an inner electrode 21 surrounded by a layer 22 of material having a resistivity between 10<SP>5</SP> and 10<SP>11</SP> ohm-cms, across it twice, the roller drive automatically reversing due to the double helical screw 16. Other modifications show the plate charged by passing it between two rollers having opposite polarities, Fig. 2 (not shown), or by closing a pressure plate on to it, the pressure plate being at high potential, Fig. 3 (not shown). This last device can also be used to transfer a latent image on the surface of an insu-- lating plate to a second plate which has a ratifying insulating layer;the pressure plate being earthed in this application. The rectifying insulating layer 10 of the plate may comprise vitreous selenium doped to render it highly p-type or n-type or alternatively a rectifying barrier layer such as cuprons oxide may be inserted between the vitreous selenium and the conductive backing. In the automatic machine shown in Fig. 5, a drum 67, comprising a photoconductive insulating rectifying lazer 68 on an aluminium backing 70, is rotated through a charging station 71, an exposure station 72 and image induction stations 73 where the latent image is transferred to tape 78, which also comprises an insulating rectifying lazer, e.g. zinc oxide in an insulating binder, on a conductive backing e.g. foil. This image is printed by known means, e.g. using a magnetic brush. The drum may be erased at 75 and recycled, or alternatively, the charging, exposure and erase stations may be rendered inoperative and the machine used as a copier duplicator.