GB1373208A - Method of making a transparency of a coloured image in a magneto- electric printing system - Google Patents

Abstract

1373208 Electro-photographic colour transparency R C A CORPORATION 17 May 1973 [17 May 1972] 23632/73 Heading G2H A copy transparency is made electrophotographically by exposure to a projected colour image of a photo-sensitive member comprising a mosaic three-colour filter 14, a panchromatic transparent photo-conductive layer 22 and a layer of magnetic and electrically attractable particles 34. An original transparency 38 is illuminated with white light, and its projected image is passed through light-transmitting substrate 12 and mosaic filter 14 to fall on the photoconductive layer, in the presence of a magnetic field insufficient to remove electrostatically bound particles 34 from the layer surface 28. Where blue light is projected through a blue portion of the mosaic filter, or red through a red portion, the underlying portion of the photo-conductive layer becomes conductive, and its surface charge drains away through transparent conductive layer 18. The particles 34 on that portion of the photoconductive layer are removed by the magnetic field, and the relevant parts of the mosaic filter become visible. After exposure, remaining parts of the layer of particles are fixed to the surface 28 by spraying with an adhesive, or by heat acting on a thermoplastic component. Passage of white light through the developed photo-sensitive member shows an image similar to that of the original transparency 38. During exposure, a guide to progress may be obtained by viewing the photo-sensitive member through aperture 48 in electromagnet 40, or by projecting the image on to a screen as it is formed. If required, the developed but unfixed image may be erased by increasing the magnetic field, and the photo-conductive member may be coated with a further layer of particles in preparation for reuse. A white light may be used to assist erasure.