Patent GB-1494883-A (GB)
Title: Non-stick coatings
IPC: C08K3/00
Filed: 1976-03-04
Abstract: 1494883 Organopolysiloxane compositions WACKER-CHEMIE GmbH 4 March 1976 [5 March 1975] 08688/76 Heading C3T [Also in Division B2] A composition for the manufacture of a non-stick coating comprises (i) a vinylsiloxyterminated diorganopolysiloxane in which from 3 to 30 mole per cent of the non-terminal siloxane units are diphenylsiloxane units, and in which at least 50 mole per cent of the organic radicals in the siloxane units other than the diphenylsiloxane units are methyl radicals, and which has a plasticity of from 300 to 800 mkp measured on a Brabender plastograph at 25 C. and 60 rev./min., (ii) an organohydrogenopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (iii) a catalyst to promote the addition of a Si-bonded hydrogen atom to a vinyl group, and (iv) an organic solvent. The diorganopolysiloxane suitably has the general formula where R is an optionally substituted monovalent hydrocarbon radical, at least 50 mole per cent of which are methyl radicals. Preferred organohydrogenopolysiloxanes have the general formula where R<SP>1</SP> is a methyl, ethyl or phenyl radical and R<SP>2</SP> is a hydrogen atom or a methyl, ethyl or phenyl radical such that the siloxane contains from 0À1 to 1À66% wt. of Si-bonded hydrogen atoms, and p is 20-500. The organohydrogenopolysiloxane preferably has a viscosity of 30-80 cP at 25 C. and a molar ratio of organohydrogenosiloxane units to diorganosiloxane units of from 10 : 1 to 1 : 10 and is preferably present in the composition in an amount of from 1-20% wt. based on the diorganopolysiloxane. Suitable catalysts are Pt, Ru, Rh, Pd and Ir and compounds and complexes of these elements, e.g. platinum (IV) chloride, chloroplatinic acid, Pt-olefin complexes, Pt-ketone complexes, Pt-vinyl siloxane complexes, and carbonyls of Fe, Ni or- Co. The organic solvent is preferably anhydrous and may be an alkane mixture having a boiling range of 80-110 C. at 760 torr, benzene, toluene, xylene, a haloalkane, an ether, ester or ketone and is generally used in an amount of from 200-5000% wt., based on the diorganopolysiloxane. The composition may also contain an agent to prevent or retard crosslinking at room temperature such as benztriazole, an alkylthiourea, a dialkylformamide, methyl ethyl ketoxime or pyrogenic SiO 2 . The compositions can be applied to the surface of absorbent or non-absorbent substrates and cured by heating at 80-250 C. Suitable substrates are paper, cardboard, asbestos board, wood, cork, plastics films, e.g. polyethylene films, fabrics of natural or synthetic fibres, metal, glass and ceramics. In the examples compositions prepared from (a) a toluene solution of a vinyldimethyl siloxy-terminated diorganopolysiloxane (plasticity 360-730 mkp), containing (CH 3 )SiO and (C 6 H 5 ) 2 SiO units; (b) an organohydrogenosiloxane (40-60 cP) consisting of (CH 3 ) 3 SiO, H(CH 3 )SiO and either (CH 3 ) 2 SiO or (C 6 H 5 ) 2 SiO units; (c) a catalyst prepared by reacting chloroplatinic acid and cyclohexanone; (d) a solvent which is an alkane mixture (B.Pt. 80-110 C. at 760 torr) are coated on to glassine paper and cured by heating.