G - Physics – 03 – G
Patent
G - Physics
03
G
314/17
G03G 15/045 (2006.01)
Patent
CA 1129481
Title of the Invention IMPROVED METHOD OF ELECTROPHOTOGRAPHY AND APPARATUS FOR PRACTICING THE SAME Abstract of the Disclosure My invention comprises an improved method of electrophotography which enables me to increase the effective speed of a photoconductor. The distinguishing feature of xerography is the creation of an electrostatic image at some point in the process. Most conveniently, a photoconductor is charged in the dark and then exposed to a light and shade image of the original to produce a latent electrostatic image of the original. In order to make a satisfactory copy, the exposure time must be such that sufficient contrast is achieved to enable the latent image to be made visible by the application of a developer formed of inherently colored or pigmented minute charged particles. The speed at which copies may be made is the function of the quantum of light falling on the photoconductive surface and the conductivity of the photoconductor under illumination. Since the rate at which a given photoconductor discharges applied surface potential through the action of light is limited, speed can be increased only by increasing the illumination. This requires energy and produces heat. My process deliberately underexposes a charged photoconductor to a light and shade image of the original to produce a -1- weak latent image of low contrast which is insufficient to make a satisfactory copy. The latent image, however, is sufficient in contrast to enable me to provide an optical mask or shield over the image by toning it. I then discharge the background or non-image areas of the photo- conductor by a blanket illumination of low intensity. The optical mask prevents the image areas from discharging while enhancing the contrast of the weak latent image. The enhanced image is easily developed by any known de- veloping method for making latent electrostatic images visible at a development station. The apparatus can be any of the electrophoto- graphic machines known to the art, which I provide with means for producing an optical shield over the weak latent electrostatic image and a background discharging floodlight lamp interposed between the shield-forming station and the image-development station of the electrophotographic machine. The means for producing the optical shield or mask is development station using usual or special development toners, which may be liquid-carried or be in dry powdered form. A salient feature of the apparatus is the means for applying developer to the weak latent image. This must be biased to a voltage above that of the background areas and below the potential of the image areas. This ensures that the background areas are unmasked or unshielded while the image areas are masked. -2-
324587
Macrae & Co.
Savin Corporation
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