| 摘要 |
1466427 Metal carbonate blowing agents FISONS Ltd 2 April 1975 [3 April 1974] 14763/74 Heading C3C Blowing agents, which are used to expand thermoplastic polymers, comprise as primary blowing agent (i.e. provides at least 50% by volume of the gas evolved on heating) a carbonate of zinc, lead, cadmium and/or lithium, with the proviso that where lead carbonate is used there is less than 2% by wt. of strong acid present in the composition and where lithium carbonate is used the polymer is not a polyamide, polymethyl methacrylate, polyvinyl chloride or an acrylonitrile/butadiene/styrene copolymer. Polymers are expanded by heating a composition containing the above blowing agent, e.g. to a temperature between 200‹ C. and the degradation temperature of the polymer and above the in situ decomposition temperature of the blowing agent and above the softening point of the polymer; the composition may be free from strong acid and contain a nucleating agent, e.g. a pigment, filler, magnesium or aluminium silicate, a clay, fumed oxide, silica or magnesium oxide. The polymer may be a polycarbonate, polyphenylene sulphide, polysulphone, polyamide, polyester or a styrene polymer. In the examples blowing agents consisting of basic zinc carbonate talc, and optionally palmitic, lauric, stearic or trimesic acids; zinc carbonate and optionally talc and lauric acid; basic cadmium carbonate (CdCO 3 .2CdO.3H 2 O) and talc; or zinc and potassium carbonate were used to expand a polycarbonate, acrylonitrile/butadiene/styrene copolymer, asbestos or glass fibre reinforced polypropylene, nylon 6, polystyrene, polypropylene, polyethylene, modified polyphenylene oxide or polyethersulphone, by feeding the mixtures into injection moulding machines. In an Example (11) the blowing agent was mixed with polyethylene and formed into pellets which were then used as the blowing agent. |
