Patent GB-1179016-A (GB)
Title: Photoconductive Imaging Member
IPC: G03G5/04
Filed: 1967-02-06
Abstract: 1,179,016. Electrophotographic materials. HARRIS-INTERTYPE CORP. 6 Feb., 1967 [7 Feb., 1966], No. 5639/67. Heading H1K. [Also in Division D2] The photo-conductive layer of an electrophotographic material consists of a particulate photo-conductor dispersed in and chemically associated with an intertwined matted fibrous material. The fibres may be cellulosic materials obtained from wood pulp or cotton. In the purification of wood pulp, lignin is removed to leave cellulose and polyglucuronic acid, the carboxyl groups of which are thought responsible for the association between the fibres and the photo-conductor (zinc oxide, titanium dioxide, or zinc sulphide). Treated wood pulp contains residues of many processing agents; these should be washed from the pulp before making it into copy paper. The carboxyl content of the fibres may be increased by one or more of several methods: (A) bleaching the pure pulp increases the carboxyl content by oxidation-bleach residue &c. should be washed out. (B) One component (ferrous ions, for example) of a polymerization catalyst system may be absorbed on the fibres by ion exchange involving the existing carboxyl groups, and a carboxylated ethylenically unsaturated monomer added to the fibre slurry together with the second component (hydrogen peroxide) of the catalyst system. The monomer then polymerizes and, though it may only be closely associated with the fibre, probably forms a graft polymer with the fibre using reactive groups near the carboxyl groups bearing the catalyst component. Suitable monomers are acrylic acid, α- and #-methacrylic acids, itaconic acid, and maleic acid. They may be incorporated as homopolymers or as copolymers with non- acidic vinyl monomers. (C) The fibrous furnish may be mixed with a latex of a carboxylated polymer-with a latex of small particle size the particles become associated with the fibres by secondary valence effects. Suitable polymers are copolymers of crotonic acid and vinyl acetate; carboxylated styrene-butadiene copolymers; and terpolymers of styrene and butadiene with acrylic, fumaric or crotonic acid. The fibres, treated or untreated, are dispersed with the photo-conductor and may be fed to a vertical paper-making machine. Alternatively non-woven fabric techniques may be used and supplementary adhesives incorporated, or high temperatures may be us d to melt flow the fibre-polymer adduct to form a sheet. Additives which may be incorporated in the photo-conductive layer include ammonium lignin sulphonate (with or without wood sugars), inorganic titanium gels, optical sensitizers, and pigments to change the colour of the layers. The photo-conductive layer may be used alone or may be attached to relatively conductive backing. Such a backing may have photo-conductive layers on both surfaces. The layers may be separately exposed and developed. To attach the backing the photo-conductive layer may be wet-laminated to a partially dewatered paper base stock containing one or more of chrysotile asbestos, alkyl ketene dimers or non-photo-conductive conductive pigments (e.g. certain forms of zinc oxide) to increase its conductivity. Paper processing additives are preferably removed from the backing to prevent their diffusion into the photo-conductive layer.