Patent GB-1434719-A (GB)
Title: Heat recoverable products
IPC: B29C70/68
Filed: 1972-09-01
Abstract: 1434719 Laminates RAYCHEM Ltd 31 Aug 1973 [1 Sept 1972 25 April 1973] 40751/72 and 19710/73 Headings B5N and B5A [Also in Division H2] A heat-recoverable article suitable for use with a high voltage electrical component comprises a laminate of an elastomeric polymeric portion which is deformed from its equilibrium configuration and a cross-linked non-elastomeric thermoplastic polymeric portion which has sufficient strength at ambient temperature to retain the elastomeric portion in a deformed configuration but which on heating becomes insufficiently strong to retain the elastomeric portion in a deformed configuration. The article may be in the form of a stress core or hollow, tubular, cable splice. The hollow article may comprise an outer elastomeric lamina containing an anti-tracking filler bonded to an inner lamina of crystalline non-elastomeric material which may be of insulating, conducting or semi-conducting material or non-linear electrical resistance material. Alternatively the outer lamina may be of crystalline non-elastomeric material having insulating and/or track resisting properties and the inner layer of elastomeric material having conducting, semi-conducting, insulating or non-linear resistance characteristics. A cable splice may comprise an outer crosslinked non-elastomeric thermoplastic electrically conductive layer, an inner insulating elastomeric layer and an elastomeric electrically conductive insert within the inner layer. The elastomer may be an ethylene-propylene, silicone, fluorosilicone, chlorosulphonated polyethylene, polyacrylate, polyester-polyether, natural, polyurethane or methyl methacrylate grafted rubber, oil extended ethylene/propylene/dienemonomer terpolymer polybutadiene, styrene/ butadiene, chlorinated polyethylene or nitrile rubber, which may contain alumina hydrate optionally in admixture with a transition metal oxide, silicon carbide, clay or carbon black. The non-elastomer may be produced from polyethylene, polyvinyl chloride, polyvinylidene fluoride, polybutadiene, polyisoprene, ethylene/ propylene diene polymer, ethylene-methyl or ethyl acrylate copolymer, ethylene-vinyl acetate copolymer or silicone block copolymer. The layers may be bonded together with an adhesive, e.g. a mixture containing ethylene/vinyl acetate/carboxylic acid terpolymer, ethylene/ ethyl acrylate copolymer and carbon black, which may contain an organic peroxide and a polymerizable unsaturated monomer. Alternatively the elastomeric portion may be formed on a mould and the non-elastomer applied thereto in molten condition and if necessary cross-linked by chemical means, e.g. using an organic peroxide or radiation, bonding optionally being improved by surface treatment with a primer, e.g. peroxy silanes or vinyl or methacrylate substituted silanes, or by mechanical, abrasion, corona discharge or chemical etching. The article may be rendered heatrecoverable by heating it to soften the non- elastomer, expanding it, e.g. over a mandrel, and cooling while keeping it in the expanded state. Further layers may be incorporated into the article, e.g. a layer of a fluoropolymer, nitrile polymer, acrylate polymer, PVC or chlorinated polyethylene to impart solvent resistance or a layer of polyvinylidene chloride or ethylene/monochlorotrifluoroethylene copolymer to impart resistance to water vapour.