GB767797A - Improved organopolysiloxane adhesive compositions - Google Patents

Abstract

An adhesive composition is composed essentially of a mixture of (1) from 40 to 75 per cent by weight of a benzene-soluble resin copolymer of SiO2 and R3SiO0.5 units, where each R is a methyl, ethyl, propyl, vinyl or phenyl radical, at least 90 per cent of the total R radicals are aliphatic and in which copolymer the ratio of R3SiO0.5 units to SiO2 units is from 0.6 : 1 to 0.9 : 1 inclusive, and (2) from 25 to 60 per cent of a liquid hydroxyl-terminated di-organo polysiloxane of from 5000 to less than 1,000,000 cs. viscosity at 25 DEG C., in which liquid the organic radicals are methyl, ethyl, vinyl or phenyl, at least 75 per cent of the total number of organic radicals being aliphatic. The siloxanes used may be made by known processes, but preferably the copolymers (1) are made by the process of Specification 706,719 and the siloxanes (2) are made by the process of Specification 762,819. For an adhesive which will give a permanent bond, there are included in the siloxane mixture a curing catalyst and a cross-linking agent which is an alkyl polysilicate in which the alkoxy group contains 1 to 5 carbon atoms and/or a siloxane of the general formula <FORM:0767797/IV(a)/1> in which each R1 is a methyl, ethyl, propyl, vinyl or phenyl radical, n has an average value from 1 to 2.3, m has an average value from 0.2 to 1 and the total of n+m is from 1.9 to 2.5. The cross-linking agent and catalyst are used respectively in amounts of 0.5 to 6 per cent and preferably less than 5 per cent by weight of the siloxane mixture. Catalysts specified are alkali metal hydroxides, ferric chloride, aluminium chloride, butyl borates, quarternary ammonium compounds and metal carboxylates, preferably carboxylates, having less than 16 carbon atoms, of metals ranging from lead to manganese in the electromotive series, e.g. lead, cobalt and zinc naphthenates, iron and lead 2-ethylhexoates, chromium octoate, dibutyl tin dibenzoate, dibutyl tin adipate, lead sebacate, dibutyl tin dilactate and dibutyl tin dilaurate. Permanent bonding adhesives are made by mixing the components together, preferably with the aid of a hydrocarbon solvent. Both the pressure-sensitive and permanent bonding types of adhesive will adhere to any known solid surface, are effective at temperatures from -70 DEG to 300 DEG C. and are used for making cable insulation, transformers and laminates. Examples are given. Specification 740,573 also is referred to.