GB1306821A - - Google Patents

Abstract

1306821 Electrographic processes ELECTROPRINT INC 18 Feb 1970 [18 Feb 1969] 7842/70 Heading G2H An electrostatic latent image comprising two layers of opposite charge is formed on a screen and developer particles are projected through the apertures of the screen to deposit on a receiver in imagewise configuration, the process being repeated to produce amulti-colouredcopy. As shown, an endless photo-conductive screen 600 having a conductive backing is imagewise exposed through successive colour filters 623 and subjected to a field Ec, to produce latent colour separation images. Optionally the screen is precharged at 609. A conductive conveyor 630 held at a potential E p feeds copy sheets 631 past toner sources 640-643 and, as each latent image passes, the appropriate source is energized with a potential E T so that toner is propelled by a rotating brush through the screen and onto the paper. E T is adjustable to control toner deposition. Vacuum cleaners 651-653 clean the screen. The whole process is controlled by a timer 663. In Fig.36, belt 675 may be insulating and drum 674 photoconductive. In another modification, a latent image is formed on an insulating plate Figs.8-10; (not shown) or on a photoconductive plate Figs. 14- 16, 31,32; (not shown) and transferred to an insulating screen, which is optionally precharged Figs. 11-13; (not shown). In Fig.33 (not shown) a photoconductive screen (511) is charged in a vertical position by a reciprocating corona discharge device (519) exposed and then pivoted up into a horizontal position for toner projection. In Fig. 37 (not shown) dichroic filters (707,709) produce colour separation images on screens (710-712). In Figs. 38-44 (not shown), a multi-colour filter (750) is placed over a screen (755), and the screen is subjected to a field of one polarity while being uniformly exposed to light, and then to a field of the opposite polarity while being imagewise exposed to a full colour image. Developing is carried out by registering an apertured mask (770) in a different position with respect to the screen for each differently coloured toner. Ink droplets or aerosols may be used instead of toner powder.