Patent GB-1087431-A (GB)
Title: Electrowetting reproduction process
IPC: G03G15/10
Filed: 1964-01-04
Abstract: 1,087,431. Electro-photographic copying processes. MINNESOTA MINING & MANUFACTURING CO. Jan.4, 1965 [Jan. 3, 1964; March 23, 1964], No. 335/65. Heading G2H. In an electro-photographic copying process, an ionically conductive liquid developer is applied to a liquid repellent receptor surface in the presence of an electric field pattern corresponding to the original and an electric potential between said surface and the developer, whereby said surface is differentially wetted by the developer according to the pattern. The angle of contact between the liquid developer surface and the repellent surface is reduced by the electric field. The receptor surface comprises an insulating sheet, as of paper or plastics, coated with photoconductive material and has a field electrode which is integral with the sheet or which is a separate sheet or surface. The electrode may be paper, cotton cloth, metallic plates and foils, glass, or plastics sheets, and is coated with a photo-conductor in the integral case. A potential, or corona discharge, source is connected to the conductivity pattern produced on the photo-conductive surface by exposure to a visible light image after dark resting, and a field pattern is produced on the field electrode. The photo-conductor may be vapour deposited or carried in an insulating binder such as a copolymer of butadiene and styrene. Inorganic photo-conductors are: zinc oxide, cadmium sulphide, cadmium selenide, cadmium telluride, lead iodide, and indium oxide. Alternatively, conductivity patterns may be produced by differentially heating plastics films such as cellulose acetate, polystyrene, polyvinyl chloride and polyvinylidene chloride. Organic photo-conductors may be used such as anthracene, 1, 2, 4-triazenes and oxalones. Liquid developer may be organic, an aqueous liquid or a powder suspension and must be ionically conductive, the receptor being treated by fluorocarbon compounds or silicones to provide a hydro- or o].eophobic surface for water- or oil-based liquids. The developer is applied by a roller, plate, or brush. A roller may be covered with a porous nylon or polyethylene mesh which absorbs the developer, or porous or etched metal rollers may be used. Hollow rollers are also used. The polarity of the applied potential during development determines whether a positive or negative copy is obtained. Developers are used such as follows:- an aqueous suspension of graphite, aqueous solution of Rose Bengal, black dye-stuffs in aqueous solution, a binder being used in each case. Powder developer such as toner particles are cascaded on to the tacky image produced by development with a polyethylene glycol, in another embodiment. The image is heat fixed if resin particles are included. A positive lithographic off-set master is made developing an aqueous dispersion of a styrene butadiene latex plus an electrolyte, the zinc oxide of the background surface then being etched with chrome alum to make it hydrophilic. A developed image is transferred to a separate receptor by using a developer of an aqueous solution of colloidal graphite with catechol. A receptor sheet surfaced with ferric stearate is placed in contact with the image and exposed to infrared radiation to heat the graphite whereby catechol is transferred to the receptor where it reacts with the soap to give a blue image. A pulsed charging system used before exposure is disclosed. Reference has been directed by the Comptroller to Specification 987, 766.