Patent GB-895723-A (GB)
Title: Electrophotographic elements
IPC: G03G5/09
Filed: 1958-04-16
Abstract: 895,723. Coated fabrics. KODAK Ltd. April 16, 1958 [April 17, 1957], No. 12107/58. Class 140. [Also in Group XXXVI] An electrophotographic device comprises a coating of zinc oxide in an insulating material, the surface of the coating containing minute areas having a sensitivity or spectral range, different from that of the background material. The areas may cover 2 to 98% of the surface area and number between 100 and 90,000 per square inch. Control of the relative areas, and sensitivities enables different exposure curves to be selected. In operation, the layer is electrically charged, exposed to a light image to form a charge pattern and exposed to powder which adheres to a low-melting solid forming part of the insulating binder, to form a final print. The sensitivity of zinc oxide may be extended by treatment with carbon dioxide or ammonia or sensitizing dye. In one example, a 100 parts of zinc oxide are mixed with 20 parts of a styrene-butadiene resin, toluene and 0.02 parts of Rose Bengal dye to provide a green sensitive layer on a baryta covered paper. A second similar dispersion but using 0.01 parts of 3,3<SP>1</SP>-di(#-hydroxyethyl) thiadicarbocyanine bromide in place of Rose Bengal is sprayed on the first coating to provide red sensitive minute areas. Curve 1 of Fig. 5 shows the density/log exposure curve for this arrangement in ultraviolet light, curve 3 the curve for exposure to green and red light, and curve 2 the curve for the material without the surface areas, exposed to green and red light. Curve 3 indicates the lengthening. of the exposure scale produced by the minute areas. In a modification, a zinc oxide toluene dope containing styrene-butadiene resin and Rose Bengal is sprayed on a layer of a similar zinc oxide toluene dope without the Rose Bengal. In a further example a similar zinc oxide layer containing 0.08 parts of Rose Bengal dye is sprayed on a layer containing 0.02 parts of Rose Bengal to provide areas with a different sensitivity, but sensitive to the same spectral region, as that of the first layer ; in this case the exposure scale may be varied by varying ultra-violet content of the light. Differences in ultra-violet sensitivity may be obtained by using an ultra-violet absorbing dye. In a further example, the coating comprises an unsensitized zinc oxide dispersion mixed with a green sensitive zinc oxide dispersion, to provide areas of differing sensitivity; the results are improved if a dye having non-wandering properties is used such as 5-[(3-ethyl-2-dihydro- α - naphthothiazolyidene) ethylidene] - 3 - nheptyl - 1 - phenyl - 2 - thiohydantoin or others containing a long chain alkyl group. The dark decay time may be reduced by adding a metallic drier to the resinous binder composition such as one or more of the naphthenates of lanthanum, cerium, zirconium, cobalt and lead, lanthanum 2-ethylhexoate and cerium 2-ethylhexoate. Examples of dyes for conferring green sensitivity are given including merocyanine, cyanine, dicarbocyanine, carbocyanine and complex merocyanine dyes. Specifications 532,098, 748,190, 770,494, 885,716, 885,717 and 887,812 are referred to.