GB978606A - An electrically conductive plastic mass containing a metallic filler and process for preparing said filler - Google Patents

Abstract

An electrically conductive plastic mass comprises a plastic matrix holding in electrical particle to particle contact a metal filler comprising a finely divided conductive metal powder having a solid core of copper or iron coated with copper, and a continuous film of silver thereon. The metal powder is preferably 3.5-350 microns in size and at least 20% by volume of the metal powder is incorporated in the plastic matrix which may be thermosetting or thermoplastic resins and elastomers such as asphalts, polyvinyl chlorides, polyurethanes, epoxies, polyamides, acrylate and natural rubber. Other fillers such as asbestos, bentonite, pigments, silica, alumina, titania and zinc oxide may also be incorporated in the plastic matrix. Examples of the following compositions are given: (a) 11 parts by weight of diglycidyl ether of bisphenol A and 89 parts silver coated copper powder mixed with 11 parts of a polyamide and 89 parts of silver coated copper powder. (b) 89 parts of silver coated copper powder and 11 parts of polyvinyl chloride plastisol with a curing temperature of 330 DEG F. (c) 80 parts of copper coated iron powder coated with silver and 20 parts of polyvinyl chloride plastisol.ALSO:A powder metal filler for incorporation in a plastic matrix is produced by a replacement plating process in which copper particles are continuously agitated in a silver plating solution containing 2-10 ozs./gallon silver ions and 8-22 ozs./gallons cyanide ions. Alternatively iron powder may be replacement plated with copper from a copper sulphate solution followed by replacement plating with silver from a solution containing 3-8 ozs./gallon silver ions and 6-20 ozs./gallon cyanide ions, the gm. moles of copper deposited. A film of gold may be formed on the silver coating and the coated particles may be ball milled or fluxed and fused to consolidate the silver film. The preferred size of the metal powder is 3.5-350 microns and an electrically conducting plastic mass is made by incorporating at least 20% by volume of the metal filler in a plastic matrix such as thermosetting or thermoplastic resins and elastomers. Examples of the matrix materials are asphalts, polyvinyl chlorides, polyurethanes, epoxies, polyesters, polyamides, acrylates and natural rubber.ALSO:A conductive plastic composition comprising 89 parts by weight of a powder having a core of copper or copper coated iron and an outer coating of silver (see Division C7) and 11 parts by weight of polyvinyl chloride plastisol is spread on to a 30 mesh 10 mil aluminium wire screen and cured. The reinforced sheet is then rolled to form electrically conductive gaskets for sealing microwave flanges.