Patent GB-917226-A (GB)
Title: Silicone rubber-forming compositions and vulcanisation products thereof
IPC: C08L83/04
Filed: 1960-02-03
Abstract: A self-adhering elastomer, obtained by known vulcanization of a mixture comprising, by weight, (1) 100 parts of a diorganosiloxane and (2) 0,5 to 50 parts of a siloxane resin prepared by heating a partially condensed siloxane resin with a boric acid complex (see Group IV(a)), is used as a bonding agent to bond boron-free silicone elastomers to metal, wood and other base materials. In Example 3 a self-adhering silicone elastomer is used for bonding a boron-free silicone elastomer to the surface of a steel cylinder which had been primed with hexaethoxydisiloxane.ALSO:A silicone rubber-forming composition comprises, by weight, a mixture of (1) 100 parts of a diorganopolysiloxane and (2) from 0,5 to 50 parts of an organosiloxane resin prepared by (a) mixing a resinous, partially condensed organopolysiloxane in which at least 50% of the organic radicals are alkyl, and at least 0,5% per gram mol. of the Si atoms therein have alkoxy radicals attached thereto, with a complex of boric acid with water, a liquid mono- or poly-hydric alcohol or a liquid phenol, and (b) heating the mixture in the range of 50 DEG to 250 DEG C. to yield a resinous, fusible product that is tack-free in the solvent-free state. Siloxane (1) consists essentially of R2SiO units and may contain minor amounts of RSiO 3/2 and SiO2 units, in which each R is an alkyl, alkenyl, aryl, cycloalkyl, alkaryl, aralkyl, or halohydrocarbon radical, and terminal Si-bonded OH or OR radicals or H atoms. Siloxanes (2) are described in U.S.A. Specification 2,842,521.  The compositions may also contain fillers, e.g. TiO2, ZnO, SiO2 (fume, aerogels and xerogels), diatomaceous earth, ground quartz, argillaceous earth, C blacks, glass fibres, glass powder, clay, iron oxide, cork, polytetrafluoroethylene, polychlorotrifluoroethylene, other organic resins and copper phthalocyanine, compression additives and pigments.  The reinforcing fillers may be surface modified with organosilyl groups. Vulcanization may be effected (i) by heating with organic peroxides, (ii) by high energy ionizing radiation, or (iii) by means of a cross-linking agent selected from alkyl ortho- and poly-silicates and a methyl hydrogen siloxane and, as catalyst, a metal carboxylate, as disclosed in Specification 841,825.  In typical examples, (1) a partially condensed siloxane resin containing Si-bonded ethoxy radicals (using a boric acid-methanol complex as in U.S.A. Specification 2,842,521) was milled with fume silica, 2:4-dichlorobenzoylperoxide and a dimethylsiloxane gum, and the resulting mix was calendered on to glass cloth and heated at 250 DEG C.; (2) a mixture of a siloxane resin (using a boric acid-glycerine complex), CaCO3 and a dimethylsiloxane polymer was milled and cured by means of a methyl hydrogen siloxane and dibutyl tin diacetate. Uses: As self-adherent tapes; as bonding agents to bond silicon elastomers to metal, wood, etc.; for making silicone rubber laminates; and for joining layers of silicone rubber and repairing cuts and slices in silicone rubber insulation.ALSO:In Example (2) the mixture obtained by milling a methylsiloxane resin (prepared by heating a partially condensed siloxane resin with a boric acid-glycerine complex), calcium carbonate, a rubber-forming dimethylsiloxane polymer and, as catalyst, methylhydrogensiloxane and dibutyl tin diacetate (see Group IV (a)) was applied to the underside of a dental plate made of polymethylmethacrylate and allowed to vulcanize under light pressure in the mouth of a patient.