GB1088073A - Photo-charging of xerographic plates - Google Patents

Abstract

1,088,073. Electro-statically charging photo-conductors. RANK XEROX Ltd. Feb. 25, 1966 [March 1, 1965], No. 8541/66. Heading G2H. Photo-conductive insulating layers are electrostatically charged for the preparation of electrophotographic images by uniformly exposing the layer to electromagnetic radiation having a wavelength not longer than the threshold wavelength for the photo-emission of electrons from the layer and collecting the emitted electrons on a grid or transparent electrode which is maintained at a positive potential with respect to the layer. As shown in Fig. 2 a photo-conductive layer 22 on a conductive backing 21 in the form of a drum is charged by uniform exposure to short wave UV light from a broad spectrum source 27, the long wave UV and visible light being filtered out by a filter 31; the electrons emitted from the photoconductor are trapped by a transparent electrode 24 consisting of a quartz plate with a thin coating of tin oxide thereon, which is maintained at a positive potential and through which the exposure is made. The uniformly charged areas of the drum are then exposed; light from the source 27 is reflected off an original 32 held on a rotating drum 33 by a finger 36, through a slit 29 in the lamp housing 29 and focused on the drum by a glass lens 37, which as filters out the short wave UV radiation, and a mirror 38. The latent electrostatic image is then developed at station 41, the developed image transferred to a receiving sheet station 49 and the drum cleaned at station 57. In embodiments, the photo-conductive layer may be in the form of a plate on to which the short wave UV radiation is directed by a concave mirror Fig. 1 (not shown), the support for the photoconductor may be transparent so that the exposure may be effected therethrough and the photoconductive layer may be overcoated with a holetrapping material, e. g. thallium doped selenium, cadmium sulphide or cadmium sulphoselenide.