HIGH CONTRAST PHOTORECEPTOR FOR REFLEX COPIER
Original Publication Date: 1983-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
In a reflex imaging system such as that illustrated in Figure 1, light must pass through a photoreceptor 10 to a document 12 to be copied and then reflect off the white background areas 14 of the document 12 back to the photoreceptor 10. Although the light falling on the image areas 16 is absorbed, the amount of light reflected back from the white background areas 14 is quite small compared to the light initially passing through the photoreceptor 10. This results in an undesirably low voltage contrast. To overcome this low voltage contrast, a multilayer photoreceptor is proposed having a "S" shaped photoinduced discharge curve characteristic as illustrated in Figure 2, as opposed to the usual linear discharge indicated by the dashed line. This "S" shaped discharge will achieve a high voltage contrast for small exposure differences in reflex imaging. The photoreceptor that will provide the above discharge characteristic is shown in Figure 3. The photoreceptor is comprised of a transparent substrate 20 which may be a drum or belt of any suitable material such as a polymer or glass. The substrate 20 is coated with a semi-transparent conductive layer 22 such as metal, indium oxide, conduc-tive ceramic coating and the like. Overlying the semi-transparent conductive layer 22 is a transparent charge transport layer 24 comprised of semi-conductive particles, such as zinc oxide particles, in a suitable transparent insulating binder. The semi-conductive particles should be smaller than about 0.1 micrometer or larger than about 1 micrometer to permit transmission of visible light without undue scattering and matched as closely as possible in the index of refraction to the binder material. The loading of the particles relative to the binder is in the range of 5% to 60% by volume. The loading is optimized to achieve randomly connected conducting paths. The latter property provides the photoreceptor with the "S" shaped discharge characteristic.