Patent GB-1017204-A (GB)
Title: Improvements in or relating to developing electrostatic latent images
IPC: G03G9/12
Filed: 1962-06-07
Abstract: 1,017,204. Liquid developers for electrostatic images; electrophotography. HARRIS-INTERTYPE CORPORATION. June 7, 1962 [June 8, 1961], No. 22138/62. Heading G2H. A liquid developer for developing an electrostatic latent image comprises a non-conducting liquid suspension medium having dispersed in it finely divided marking elements capable of attraction to and deposition imagewise on the charge image bearing surface, each marking element comprising a marking agent and a liquid fixing agent preferentially associated with it, the fixing agent being present in the developer in excess of the marking agent. Preferably each marking element also includes a separate charge control agent preferentially associated with the marking agent and the suspension medium is a non-polar liquid. As described the developer is a modification of that of Specification 940,242 in which the resin droplet surrounding the pigment marking agent serves also as a fixing agent on removal of the suspension medium and is intended for development of charge images on polar polymeric binder layers of electrophotographic image-receiving surfaces as in Specification 888,371. Suitable liquid suspension media are liquid mainly aliphatic hydrocarbons such as kerosene or mineral spirits in which are dispersed organic or mineral pigments, e.g. azo yellow, carbon black, iron oxide black, cadmium red and yellow, or commercial black printing ink, while the resin may be boiled linseed oil, an alkyd resin, or an oleo resin varnish comprising rosin-modified phenolic resin and mixed linseed and tung oil. Surfactants may also be included in the developer e.g. long chain organic acids such as oleic, tiglic, linoleic, linolenic or naphthenic acids or their copper, zinc, lead, chromium, manganese, nickel or cobalt salts, octoates, tall oil, phosphoric acid, lecithin, malic acid and its metallic salts, mono-, di-, and tri-ethyl-or ethanol-amines or quaternary nitrogen compounds. Typically the developer is formed by melting the selected resin and diluting it with tung oil varnish and mineral spirits, placing the resulting liquid with carbon black in a ball mill and adding more of the liquid at intervals until a constant shading strength is obtained, then further diluting the ballmilled product with more of the resin-varnish liquid, adding metal driers such as cobalt, manganese, and lead phthalates, and mixing 0. 4 to 1 part of this concentrate with 99. 6 to 99 parts of a turpentine, naphtha or benzene dispersion of manganese linoleate containing 0. 5% of the salt. Reference is made to development by charge repulsion and deposition in the uncharged areas but as described the marking agent deposite on the charge image. As shown, the apparatus employed may be as described in Specification 940,242 with the differences only that the exposing light source may be an intermittently energized high speed flash lamp, so that the photoconductive web may be in continuous movement, and the development electrode may be omitted. Preferably however the developing unit comprises a web-guiding roller 156, a developer applicator roller 155, and a squeegee roller 170 having a coating of polar properties similar to the suspension medium, e.g. of vulcanized linseed oil or synthetic rubber, together with a doctor blade 169. For multicolour work, the web passes continuously or intermittently through a corona charging device 65, a first exposure station at which a colour separation record and a registration mark is projected on to it by a flash lamp and then through a developing unit 75 as just described to produce a visible record and a visible registration mark. Succeeding colour separation records are similarly formed at stations 95, 105, 115, 125 under control of photo-electric sensing of the registration mark to produce registered images, which are then cut off at 140 and delivered into a hopper 149. An exhaust hood 149 extracts volatile developer components.