Formentrennmittel

摘要

A release material suitable for coating the interior of ovens consists of a mixture of three different organopolysiloxanes: (A) from 2 to 55% by wt. of a diorganopolysiloxane of average formula in which each R is an alkyl, alkenyl or aryl radical, n has an average value 1.98 to 2.0145 and m an average value of not more than 2.0145 and n+m is not > 2.0145. At least 90% of the units are dimethylsiloxane and not greater than 2 mol per cent are units with alkenyl radicals; the polymer has a viscosity of at least 350 cs. at 25 DEG C.; (B) a phenylmethylpolysiloxane: in which x has an average value from 0.08 to 1.1, y an average value 0.9 to 1.92 and x+y=2. The polymer is chain-stopped with hydroxyl radicals or trioganosiloxy units having Si-CH3 or Si-C6H5 bonds and has a viscosity of at least 50 cs. at 25 DEG C. (C) A block copolymer consisting essentially of (i) polymer blocks: [(CH3)2SiO]s[R12SiO]t[R1 SiO1. 5]u in which R1 is a methyl, ethyl, vinyl or phenyl radical, s+t+u has an average value from 6 to 100 inclusive and t and u each have a value up to 10% of the sum of s+t+u, and (ii) polymer blocks: in which q has an average value from 1 to 1.25, w has an average value up to 0.25 and q+w is not > 1.25. The siloxane units (1) comprise 10 to 75 mol. per cent of the block copolymer and the units (2) from 25 to 90 mol per cent. In preferred examples polymer (A) is either a hydroxyl or trimethylsiloxy chain-stopped dimethylpolysiloxane and the units (1) of the block copolymer are dimethylsiloxane units. The mixture may have a viscosity of at least 1000 cs. at 25 DEG C. It may be used as a solution in an organic solvent, as an aqueous dispersion or from an aerosol package.