Patent GB-1244765-A (GB)
Title: Improvements in or relating to reflex electrophotography
IPC: H01L31/08
Filed: 1968-08-30
Abstract: 1,244,765. Photoconductive element. INTERNATIONAL BUSINESS MACHINES CORP. 30 Aug., 1968 [18 Sept., 1967], No. 41417/68. Heading H1K. [Also in Division G2] A photoconductive element, suitable for use in electrophotographic reflex copying comprises a dichroic material having its axes of maximum absorption and transmission oriented in a unidirection, the element exhibiting dichroic photoconductivity and becoming conductive in those areas exposed to light having an electric vector parallel to the absorption axis. The photoconductive element has the advantage that it transmits all light polarized normal to its absorption axis and therefore does not become conductive and efficiently illuminates the document to be copied. The element may be composed of a dichroic photoconductor alone or in association with another material, or a photoconductor together with an oriented dichroic activator. In either case the dichroic material must be oriented so that it acts as a single dichroic unit.. This may be accomplished by (a) dispersing the dichroic material in a sheet of polyvinyl alcohol or polyvinyl formal and stretching it; (b) attaching the dichroic molecules chemically to a material that has a high degree of orientation; (c) coating the material on a sheet having a preferred orientation; or (d) coating them on a surface by unidirectional rubbing followed by stretching and extruding. Transparencies or translucencies which have been backed with depolarizing and reflecting elements can also be copied using this reflex technique. In the embodiments bis (dialkylaminoarylideneamino)benzo bisthiazoles are exemplified as dichroic photoconductors. In one embodiment, an aluminized cellulose triacetate sheet has a layer of bisthiazole formed thereon by rubbing on a dry powder in a unidirection and is overcoated with a layer of poly N-vinyl carbazole. In another embodiment, the layer of poly N-vinyl carbazole is adjacent the aluminized cellulose triacetate sheet and the bisthiazole is covered with cellulose acetate. In the embodiment exemplifying a dichroic activator, a polymer layer is stained with iodine to cause the polymer to exhibit dichroism and activate a photoconductive layer when applied thereto. In another embodiment a layer of an oriented polymeric photoconductor e.g. a terpolymer of N-pentenyl carbazole, N-hexenyl carbazole and pentene-1 is stained with 2,4,7- tinitrofluorenone. Polycarbonate or glass coated with tin oxide. A1 or Cu may be used as a support. The support may serve to polarize the light incident on the photoconductive layer so that its electric vector is in the proper direction for it to pass through the layer. A semi-transparent mirror which may be the metal layer on the support, may be used to reflect the depolarized light back into the layer. In one embodiment, an electrophotographic plate is built up by rubbing a bisthiazole in a unidirection on a film of poly-N-vinylcarbazole activated with tetrachlorophthalic anhydride and carried on a temporary polyethylene terephthalate support, coating the carbazole film with an aqueous solution of copoly(methylvinyl ether-maleic anhydride) and a quaternary ammonium salt, and then laminating the product with glass coated with polyvinylidene chloride. The terephthalate support is removed after lamination.