GB818068A - Methods for producing a base for electrostatic printing - Google Patents

Abstract

818,068. Semi-conductor devices. RADIO CORPORATION OF AMERICA. Dec. 2, 1955 [Dec. 15, 1954], No. 34637/55. Class 37. [Also in Group XX] A base for electrostatic printing is formed by applying a dispersion in water of a finelydivided photo-conductor and an electricallyinsulating film-forming vehicle, to a backing plate to form a coating and then drying the coating. The dispersion may be made by mixing a dispersion of the photo-conductor with a dispersion of the vehicle or by mixing the photo-conductor and vehicle and dispersing the mixture. The backing plate may be of mica, paper, cellulose acetate, copper, brass, aluminium or glass. The photo-conductor may be an oxide, sulphide, selenide, telluride, or iodide of Cd, Hg, Sb, Bi, Mo, T1, A1, Pb, or Zn, arsenic trisulphide, cadmium arsenide, lead chromate, or selenium or mixtures thereof chosen to provide a suitable spectral response. The filmforming vehicle may be a polyvinyl acetate resin, a natural or synthetic resin, wax, or silicone resin of high dielectric constant and dielectric, strength, a cellulose ester, polystyrene or shellac, or a resin monomer which is polymerized after dispersion. In one example a dispersion of 100 grams of photo-conductive ZnO and 2 grams of a dispersing agent, e.g. a mix of sodium salts of polymerized alkyl naphthalene sulphonic acids in 100 grams of water is mixed with a dispersion of 77 grams of polyvinyl acetate resin in 63 grams of water which has been agitated for half an hour with 8 grams of the plasticizer tricresyl phosphate and the mixture applied to a base plate which is then heated at 105‹ C. for 5 minutes to dry it. An electrostatic print is formed on such a base by first placing it on an earthed base in a dark enclosure and electrostatically charging its surface uniformly, and then projecting an image of the subject to be printed formed by infra-red ultra-violet or visible light or by electrons on to the surface. A developer such as a charged ink mist or a charged powder is then applied to the surface and adheres to the parts of it which have retained some charge. The image may be fixed where a powder developer is used by applying a coating of a solvent for the powder or the vehicle to the surface to cause the powder to adhere to the surface and then evaporating the solvent, by pressing the powder image into the surface or, if the powder or vehicle has a low-melting point by heating to fuse the powder to the coating.