GB943215A - Electrostatic printing - Google Patents

Abstract

943,215. Electrophotographic multicolour processes. RADIO CORPORATION OF AMERICA. March 16,1960 [April 13, 1959], No. 9350/60. Heading G2H. A method of producing a visible image in a plurality of colours on a recording element comprising a particulate photoconductor dispersed in a resinous binder coated on a paper backing comprises the steps of producing on the coated surface of said recording element a pattern consisting of electrostatically charged areas and of substantially reduced charge areas in substantial configuration with one colour of said visible image; applying to said pattern a mixture comprising electroscopic particles of said one colour dispersed in an insulating liquid to develop on said coated surface an image of said particles of said one colour; mechanically removing excess insulating liquid from said surface leaving thereon only a thin film of said liquid; and, with said thin film on said surface, repeating the aforesaid steps at least once to produce an image of electroscopic particles of another of said plurality of colours on said coated surface. The particulate photoconductor may comprise zinc oxide, and the process may comprise for example the steps of exposing a precharged photo-conductive sheet to light from a colour transparency with the yellow light removed, developing the resultant electrostatic image with a developer comprising a dispersion of a yellow pigment in, for example, dimethyl polysiloxane fluid, removing excess developer by means of draining, squeegeeing, or with mangle rollers, and repeating the charging, exposure and developing processes for magenta and cyan or other colours. The sheet may be heated finally to help fix the images. As an alternative to the pigment dispersions mentioned above, the developer may also comprise dispersions of coloured resins - preferably thermoplastic resins of styrene or terpenehaving suitable dyes or pigments incorporated therein. U. S. A. Specification 2, 486, 351 is referred to.