Patent GB-737371-A (GB)
Title: Electroconductive articles
Inventor: LINDER CYRIL SVEN
IPC: C03C17/23
Filed: 1951-01-29
Abstract: 737,371. Electric heating resistances. PITTSBURGH PLATE GLASS CO. Jan. 29, 1951, No. 2225/51. Class 39 (3). An electrically conductive article comprises at least one pair of bus-bars each in linear contact along its whole length with a conductive film on a refractory base, said film having one or more areas of conductivity different from other areas in order to obtain even or other desired current distribution in the film. The base may be of glass and the film is also transparent and may be laminated with a plastic such as polyvinyl butyral and glass to form a laminated windscreen, which may be heated for de-icing on vehicles. The bus-bars 14 are placed on opposite sides of a rectangular, circular or other-shaped windsheld coated with a conductive film, which is divided into areas of preferably equal resistance by channels 19 which are poorly conductive or are non-conductive. The channels extend wholly or some partly across the film and are closer together where the bus-bars are closer together, to obtain more even heating. The channels may be straight and may have perpendicular spurs or branches or may be curved, e.g. concave or convex towards the centre of the windshield. The edges parts 12 of the windshield may be unheated, or may have non-conducting channels extending inwardly therefrom. The number of short perpendicular branches may increase as the distance between the bus-bars decreases. The lengths of channels 19a which extend only partly across the film increase as the distance between the bus-bars increases. In Fig. 7, juxtaposed areas of higher conductivity occur where the bus-bars are wider apart to obtain more even heating. The conductivity of the film is increased gradually or in zones either by increasing its thickness or using coating materials of greater conductivity. The coating may be deposited on lime soda glass, borosilicate glass, phosphate glass, china, mica, silicon carbide, tungsten carbide, porcelain, stone or other refractory melting above 1105‹ F. The bus-bars comprise a metal powder, e.g. gold or silver, and a vitrifying binder and may include silica and the oxides of lead and boron with French fat oil and turpentine or water and alcohol and 'may be painted on. The glass is then heated to 400-800‹ F. and the conductive coating is sprayed on, e.g. a tin salt such as tin tetrachloride in aqueous solution or vapour with a reducing agent such as methanol or phenyl hydrazine hydrochloride. The coating comprises largely tin oxide, but a conductive oxide of cadmium, antimony, cobalt, zinc, indium, silicon, titanium, silver, thallium, chromium, platinum or other metal may be used prepared from a bromide, chloride or acetate of the metal. Areas of glass not to be covered are covered with a paste comprising silica, alumina, alkalies and a boron compound in a liquid medium of methanol, glycerol, dioctyl sodium sulfosuccinate and a sulphonated bicarboxylic acid in water, this paste being finally removed: or the plate may be wholly coated and parts of the coating may be removed by depositing thereon a powdered metal more electronegative than the coating and a dispersing agent such as zinc and a water-dispersible binder, the zinc coated base being then sprayed with acid. A final washing with water then removes the acid and the covered part of the coating from the glass. Parts of the coating not to be removed may be previously covered with an easily removable plastic film such as regenerated cellulose tape. Parts of the coating may be removed by a knife. Specification 724,086 and U.S.A. Specification 2,614,944 are referred to.