Patent GB-543708-A (GB)
Title: Method of producing a conductive metal coating upon a non-conductive object and to objects formed thereby
IPC: H01B1/00
Filed: 1940-08-28
Abstract: 543,708. Coating non-metallic surfaces with metals; electrolysis, electric cables, condensers and resistances; coated fabrics; deaf vibratory diaphragms. RUBEN, S. Aug. 28, 1940, No. 13576. [Class 82 (ii)] [Also in Groups IV, VIII and XXXVI] To provide a conductive coating on a non- conductive object, a coating of copper base particles, normally having a high resistance superficial oxide layer, and a binder, are applied to the object and the coating is subjected to the action of a reducing acid which reacts chemically with the particles and removes the oxide, thus converting the high resistance surface to a conductive state. Copper base particles may comprise copper, copper alloys or a mixture of copper and other metals such as zinc, cadmium, magnesium beryllium or aluminium. The acid may be used in vapour form or when copperzinc bronze particles are used the object may be dipped in or pressed through a zinc-dissolving acid such as hydrochloric acid. Instead of hydrochloric acid, hydrofluoric, phosphoric, lactic or sulphuric acids may be used, while hydrochloric, hydrofluoric, hydrobromic or hydroiodic acids may be used in vapour form. The coated object may be electro-plated with copper, silver, gold, chromium, cadmium, nickel, zinc or tin. The objects to be coated may be made of " Cellophane " (Registered Trade Mark), regenerated cellulose, paper treated with urea formaldehyde resin or impregnated with plasticized styrene, dialysed regenerated cellulose, or non-fibrous sheet material such as ethyl cellulose or cellulose acetate. As binders may be used, urea formaldehyde resin, styrene, cellulose lacquer, solution of nitro-cellulose in amyl acetate, shellac or a 3 per cent. solution of styrene plasticized with a dimer of dehydronaphthalene, preferably in xylol in the order of 25 per cent. of the styrene content. Plasticizerface "Cellophane" 1 passes from a roll between spray guns 2, 3 which spray the sheets with a coating of urea formaldehyde resin and zincbronze powder, and then through a heater 4 maintained at 140‹C. which dehydrates the "Cellophane" and bakes the coating, the resin waterproofing the sheet. The coated sheet then passes via a pulley 5 and under rollers 8, 9 in a chamber 6 containing concentrated hydrochloric acid, the vapours of which react with the coating and thence through a heater 10 over a pulley 11 and then between rollers 12 and around rollers 17 in a copper plating bath 13 provided with electrodes 14. The plated sheet then passes over a roller 18 through a washing tank 19 and a heater 21 and is wound on a roll 22. The sheet may be coated, before electroplating, on one side only. Instead of spraying a mixture of resin and bronze particles, the sheet may be first coated with the resin and then with the bronze powder by brushing and rubbing on with rotary brushes. Insulated wire forming co-axial conductors may be coated with copper bronze powder using a quick drying binder such as a solution of nitro-cellulose in amyl-acetate, and the coating may be electro-plated. In carrying out this process, the enamel or rubber covered wire is passed through the bronze suspended in the binder, then through a heater, a tank containing hydrochloric acid and a washing tank before being passed through the plating bath. In the production of di-electric sheets for condensers, a film 216, Fig. 6, of plasticized styrene is coated with electrodes 217, 218 and in Fig. 7 is shown regenerated cellulose films 221, 227 provided with bronze coatings 222, 223 and 228, 229, as well as uncoated margins 224, 225 and 230, 231 and copper foil terminal 226 making contact with the coating 222 and terminal 232 with coatings 223, 228. The process may be applied to the production of electro-static speaker diaphragms coating of end terminals on electric resistance units, coating and plating of shingles, electrotypes, oddshaped bodies of insulating materials, electrostatic shields for glass radio tubes, coated moulded plastics, e.g. for door knobs and handles, and conductive metal coated paper for facsimile transmission systems.