Electrophotographic process and apparatus

Abstract

A process and apparatus for forming an electrostatic image on a photosensitive plate having a conductive base, a photoconductive layer overlying the base and exhibiting p-type or n-type semiconductivity, and an insulative layer overlying the photoconductive layer. The photosensitive plate is characterized in having carrier charge of a polarity corresponding to the conductivity type of the photoconductive layer injectable from the conductive base into the photoconductive layer and bound in the region of the interface between the insulative and photoconductive layers. The conductive base is transparent to activating light and the insulative layer is opaque to the activating light. A first charge of a polarity opposite to the conductivity type of the photoconductive layer is applied onto the insulative layer to inject and bind carrier charge in the region of the interface between the insulative and photoconductive layers. Then, the photoconductive layer is exposed to a pattern of activating image light by projecting the image light through the transparent conductive base while a corona discharge is applied onto the insulative layer. Thereafter, the photoconductive layer is exposed to activating light through the transparent conductive base to discharge bound carrier charge remaining in the region of the interface and form a high constrast electrostatic image.