GB1095504A - - Google Patents

Abstract

1,095,504. Electro-photographic development processes. RESEARCH LABORATORIES OF AUSTRALIA PTY. Ltd. March 1, 1965 [March 6, 1964], No.8736/65. Heading G2H. A charge image of negative polarity is reversal developed to provide stain-free areas, where most of the initial charge is retained, by contact with a developer consisting of a dispersion, in an insulating carrier liquid, of charge inhibited toner particles depositable only in the presence of a soluble mineral oil or grease as development inducing agent. The oil or grease contains specified quantities of anti-oxidant and detergent-dispersant. The developer is stated to give a clean cut-off where a predeterminable fraction of the initial charge is retained and a uniform deposition over all other less charged or uncharged areas. When used in preparing positive copies of printed matter from low-density negatives, in which the background (i.e. non-image areas) is not completely opaque, a stain-free background is thus obtained. Chargeable toner particles may be made charge inhibited by coating them with an oleoresinous polarity control agent which takes a charge of the opposite polarity and may be further coated so that they do not adsorb the development inducing agent. Alternatively, oppositely chargeable toner particles may be mixed to form charge inhibited aggregates which are treated with a dispersant which also prevents the particles from adsorbing the development inducing agent. According to one example, carbon black pigment is coated by milling with a hydrogenated rosin, as polarity control agent, and further coated with boiled linseed oil to prevent adsorption of the development inducing agent. This charge inhibited toner is then dispersed in one of the following carrier liquids: paraffinic, iso-paraffinic or aliphatic liquid, mineral spirit, cyclo-hexane, perchlorethylene, carbon tetrachloride or trichlorotrifluoroethane. The development inducing agent may be paraffin oil containing zinc alkyl dithiophosphate or a substituted para cresol as anti-oxidant and sodium alkyl benzene sulphonate or sodium naphtha sulphonate as detergentdispersant. In another example, phthalocyanine toner particles are coated with a pentaerithritol resin as polarity control agent and a wheel base grease containing additives is used as development inducing agent.