| 摘要 |
1,242,719. Electrostatic printing; stencils. ELECTROPRINT Inc. 25 Sept., 1968 [6 Oct., 1967], No. 45571/68. Heading B6C. [Also in Division G2] An apparatus for electrostatic printing employs a two-layer composite screen on which an electrostatic charge image is formed so as to area-modulate a flow of charged toner particles. The composite screen comprises an apertured layer of insulative material in contact with an apertured layer of conductive material the apertures in the two layers coinciding. Preferably the insulative layer is photoconductive so that the charge image may be formed optically. A layer of induced charge is formed at the junction of the layers of the opposite polarity to an imagewise charge on the surface of the insulative material so that at a distance of more than a few screen thicknesses away from the screen, the resultant field is near zero allowing charged toner particles to pass through the screen in non-charged areas uninfluenced by the charged areas, while in the fully charged areas the particles fall on to the screen. The areas with reduced charge effectively limit the apertures of the screen, Fig. 9 (not shown). In a printing apparatus a continuous screen 121 comprising a photoconductive layer passes over rollers 122- 125. The screen is image-wise charged at station 130 then moves to a toner transfer station 140 where a toner agitating device 143 and an electric field produced by roller electrode 150 propel the toner particles towards the screen, those emerging falling on to a copy sheet 145 on which the image is fused by a heater 157.
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