GB1017593A - Electrostatic printing, reproducing or copying process - Google Patents

Abstract

1,017,593. Printing processes. L. F. W. LAWES, and N. G. SHREEVE. March 11, 1963 [Dec. 13, 1961], No. 44681/61. Heading B6C. [Also in Division G2] An electrostatic printing, reproducing or copying process comprises applying a high voltage charge to a surface of a layer of material of high dielectric strength and of sufficiently high resistivity to prevent migration of the charge, applying a conductivity pattern formed by a printed or embossed sheet of paper or other material, a specially formed template, a coin or a dial face, against said charged surface to effect differential discharge and form an electrostatic image, and developing said image. Alternatively the conductivity pattern may be applied against the surface before the high voltage charge so that it subsequently controls the distribution of the charge to form the electrostatic image. The layer may be of silicone resin, polythene terephthalate, polystyrene, polythene, polypropylene, polytetrafluoroethylene, polytetrachloroethylene or polycarbonate. In one embodiment a rotatable drum is provided with a layer of one of the said materials and a backing of conductive material. At a charging station a fine wire parallel to the drum axis and spaced from the surface thereof is connected to an electrical supply and gives a corona discharge which imposes an electrostatic charge on the surface of the layer. At a conductivity patternapplying station a belt or roller presses a printed sheet to be copied against the drum surface and the charge leaks from those areas where the paper contacts the layer, leaving an electrostatic image. Powder is applied to the image by blowing, dusting or brushing or from a liquid suspension at a developing station. At the next station a sheet of paper &c. is fed between the drum and a pressure member such as a roller and a charging head applies an appropriate charge to the paper to effect transfer of the image. The image is subsequently fixed by heat &c. and the charge and any excess powder are removed from the drum. The backing sheet of the layer is earthed and a corona discharge device is provided between the pattern applying station and the developing station to give the layer a small reverse charge to prevent background cluttering. The apparatus may be non- rotary with the layer in the form of a plate. It is stated that the conductivity pattern may be applied by the selective use of conductive and non-conductive dyes or inks on a sheet of conductive or non-conductive material.