GB833141A - Organosiloxane compositions - Google Patents

Abstract

A composition useful as a fuel tank sealing coating comprises by weight (1) 100 parts of a dimethyl- and/or phenylmethyl-siloxane which can contain up to 20 mol. per cent of diphenyl-siloxane units and up to 1 mol. per cent of other siloxane units of the formula RnSiO 4-n/2 , where each R is a monovalent hydrocarbon or halogenated hydrocarbon radical and n is 0, 1, 2 or 3, (2) 10 to 100 parts of a benzene-soluble copolymer consisting essentially of SiO2 and R13SiO 1/2 units with up to 0.2 R12SiO units per SiO2 unit, in which R1 is methyl, ethyl, propyl or phenyl, at least 90% of the total R1 radicals are alkyl radicals and the ratio R1/Si has an average value from 1 : 1 to 1.7 : 1, and (3) 80 to 250 parts of a filler of which at least 80 parts are selected from metal zirconates and titanates, zirconium and titanium silicates and metal fluoro-zirconates and -titanate (see Group IV (a)). Many essential fillers are specified. Additional fillers specified are diatomaceous earth, silica aerogels and xerogels, fume silica, CaCO3, MgCO3, TiO2, iron oxide, Al powder, and silica fillers treated with silanes, siloxanes or silazanes. Pigments, dyes and stabilizers may also be added. The compositions may be cured by heating in air or in the presence of organic peroxides. The addition of a compatible neutral organic compound boiling above 260 DEG C., e.g. a polybutadiene, a chlorinated polyphenyl or a glycol-dicarboxylic acid polyester, reduces the time of curing. The composition may be dispersed in a solvent, e.g. toluene, petroleum ether or perchloroethylene. The examples disclose the coating of stainless steel panels.ALSO:A siloxane composition comprises by weight a mixture of (1) 100 parts of a dimethyl- and/or phenylmethyl-siloxane which can contain up to 20 mol. per cent of diphenylsiloxane units and up to 1 mol. per cent of other siloxane units of the formula <FORM:0833141/IV (a)/1> where each R is a monovalent hydrocarbon or halogenated hydrocarbon radical and n is 0, 1, 2 or 3; (2) 10 to 100 parts of a benzene soluble copolymer consisting essentially of SiO2 and R13SiO 1/2 units with up to 0.2 R12SiO units per SiO2 unit, in which each R1 is a methyl, ethyl, propyl or phenyl radical, at least 90% of the total R1 radicals are alkyl and the ratio R1/Si has an average value from 1 : 1 to 1.7 : 1 ; and (3) 80 to 250 parts of a filler of which at least 80 parts are selected from metal zirconates and titanates, zirconium and titanium silicates and metal fluoro-zirconates and -titanates. Siloxane (1) may contain as R radicals alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, alkaryl or aralkyl radicals per se or halogenated. Many essential fillers are specified. Additional fillers specified are diatomaceous earth, silica aerogels and xerogels, fume silica, CaCO3, MgCO3, TiO2, iron oxide, aluminium powder and silica fillers treated with silares, siloxanes or silazanes. Pigments, dyes and stabilizers may also be added. The compositions may be cured by heating in air or by using a peroxide, e.g. benzoyl-, dicumyl- or 2 : 4-dichlorobenzoyl-peroxide or t-butylperbenzoate. The addition of a compatible neutral organic compound boiling above 260 DEG C., e.g. a polybutadiene, a chlorinated polyphenyl or a glycoldicarboxylic acid polyester, reduces the time of curing. The compositions may be dispersed, e.g. in toluene, petroleum ether or perchloroethylene. Examples are given. Uses.-As fuel tank sealing coatings and coatings for glass cloth, where high heat stability and resistance to aliphatic hydrocarbons are required. Specifications 706,719, 755,198, 798,667 and U.S.A. Specification 2,489,138 are referred to.