GB797024A - Improvements in electrostatic printing - Google Patents

Abstract

797,024. Electrophotographic processes. GENERAL DYNAMICS CORPORATION. Jan. 16. 1956 [Jan. 26, 1955], No. 1420/56. Class 98(2) A visual reproduction of an object is made by contacting the surface of a photoconductive layer on a conductive backing with the surface of an electrically semiconductive layer on a conductive backing, projecting a light image corresponding to the object on to the photoconductive layer either immediately before, during or after its contact with the semiconductive layer, applying a potential difference between the conductive backing layers, and then developing the latent image formed, either on the photoconductive layer or on an insulating layer to which it has been transferred from the photoconductive layer. The method is distinguished from that of Specification 755,486 in that the electrostatic latent image is formed initially on the photoconductive layer itself. The photoconductive element and the semiconductive element may be in the form of cylinders or plain surfaces. Fig. 1 shows a cylinder 6 comprising a transparent cylinder 8, a transparent conducting layer 9 and a photoconductive layer 10 in rolling -contact with a cylinder 7 comprising a metal core 11 coated with, semiconductor material 12 such as a semiconducting rubber. A battery 15 maintains a potential difference between, the conductors 9 and 11. A transparent original 14 is placed inside the cylinder 8 and illuminated by a lamp 13. A shield 26, which remains stationary when the drum rotates, is positioned to restrict the illumination to a narrow strip of layer 10 at the time of contact between he cylinders. The layer 10 also may be exposed before or after the line of contact with the semiconductive surface, and in either case the image may be projected on the layer 10 from a position external to the drum. In any case, an electrostatic latent image is formed on photoconductive layer 10 as the cylinders rotate, and is developed thereon at 22, for example with carbon black. The carbon is preferably suspended in an insulating liquid and applied by means of a roller. At 16 the powder image is transferred to paper strip 17 and the surface 10 cleaned at 18. In a modification, the drum 7 comprises a central metal core, a resilient rubber layer, then a conducting layer (which is connected to the battery) and finally the semi-conductive layer 12. In a further modification, the latent image is not developed on photoconductive layer 10, but is transferred to another cylinder comprising a metal core and insulating coating and situated on the opposite side of cylinder 6 to cylinder 7. This insulating cylinder is provided with developer means and means to transfer the powder image to a paper strip as described above. In further modifications, firstly the cylinder 6, and secondly both cylinders 6 and 7 are replaced by similarly constructed flat plates. Specifications 672,767, 679,533 and U.S.A. Specifications 2,221,776, 2,277,013 and 2,551,582 are referred to.