GB658640A - Improvements in and relating to methods of preparing compositions containing methyl-substituted polysiloxanes - Google Patents

Abstract

Adhesive and coating compositions are made (1) by heating a mixture comprising a liquid polymeric dimethyl siloxane containing up to 2 mol. per cent co-polymerized monomethyl-siloxane and in which the methyl to silicon ratio is for example 1.98 to 2 and an iron halide until the thickening-mass reaches a stage wherein a sample drop removed from the mass, when immediately touched with rod, fails to give a string upon withdrawal of the rod but instead snaps back, and (2) adding to the molten mass obtained in (1) a finely divided, water-insoluble, wholly inorganic pigment selected from metallic oxides and salts. Iron halides specified are anhydrous ferric chloride and ferric chloride hexahydrate. Pigments specified are: lithopone, titanium dioxide, zirconium oxide, lead carbonate, calcium sulphate, ferric oxide, zinc chromate, calcium carbonate, zinc oxide, chromic oxide and alumina, and they may be used in amount, e.g. of 0.25 to 3 parts by weight per part of the condensed polysiloxane. Lubricants such as stearic acid may be added, in amount, e.g. of 0.05 to 0.5 per cent by weight of the reaction mass, with the pigment. Curing or vulcanizing agents such as benzoyl peroxide and tertiary butyl perbenzoate may also be added either after cooling of the reaction mass or immediately before use; the amount added may be up to 15 per cent by weight of the polysiloxane. In examples: (1) the liquid polysiloxane and anhydrous ferric chloride are heated with stirring to 120 DEG C. and titania and stearic acid are added when the mass has become "stringy"; heating at 120 DEG C. is continued for 3-4 hours followed by cooling and mixing with lead oxide (as stabilizer) and benzoyl peroxide; (3) to the paste of example (1) is added benzoyl peroxide in amount to give a content of 12 per cent by weight of the liquid polysiloxane. The paste may be thinned with volatile liquids, e.g. toluene. The paste may be used as a coating composition for backing materials such as glass cloth or metal surfaces, or it may be used for bonding metal to p sheet elastic polymeric methylsiloxane, metal to metal, silicone rubber to laminated glass cloth, and glass or ceramics which may first be coated with methylhalogenopolysiloxanes. The composition may also be used as a potting composition, e.g. for high temperature electronic tubes and as a sealer for lap joints in metals. Specifications 586,188, 586,189, 592,018, 594,481, 597,178, 629,642 and 650,247 are referred to.