A process for sensitising electrophotographic layers

摘要

1,020,831. Electro-photographic processes. AGFA A.G. May 22, 1963 [June 16,1962], No. 20476/63. Heading G2H. [Also in Division H1] An electrophotographic material is sensitized by forming an electrostatic charge image on the photo-conductive layer and treating the layer with a sensitizing dyestuff in such an amount that the sensitizing dyestuff is deposited in a practically invisible pattern corresponding to the image. The process is utilized in several ways. In the first, an unsensitized material is given a uniform negative charge, exposed to a picture image, and developed with a positively charged aerosol containing the sensitizing dyestuff. The material is allowed to stand in the dark for some hours and is then recharged negatively and exposed uniformly to a diffuse light source. When developed a reversed image of the original is formed. In the second use, an unsensitized material is negatively charged, exposed to a screen image, developed with a positively charged aerosol of the sensitizing dyestuff, allowed to stand in the dark, exposed to a picture image using light to which both sensitized and unsensitized regions of the plate are sensitive (perhaps to different extents), and developed to obtain a non-reversed half-tone image. In another screen process a multiple screen may be produced by using dyes which are sensitizers for different wavelengths, the differently sensitized regions being formed so that they do not, or at the most only partly, overlap. Materials of this type are used for the subsequent development of multicoloured images. In the particularly described embodiments development at all stages is carried out using electrostatically atomised positively charged aerosols but in general the dyestuff sensitizer may be applied to the photo-conductive layer by known processes using either solutions of the dyestuff or the solid dyestuff. Cascade and dust cloud processes are possible using the powdered dyestuff to form a dry powder image which is fixed by aftertreatment with a solvent, and processes may be used which depend on the different wetting capacities of charged and uncharged regions of the material.