MOLDING COMPOSITIONS CONTAINING SILANOL-FREE RESINS

摘要

1416092 Silicone resin moulding compositions GENERAL ELECTRIC CO 23 Feb 1973 [2 March 1972] 9085/73 Heading C3T A thermosetting silicone resin composition comprises (a) a 'high-silanol' resin of average unit formula wherein R2 is a C 1-8 alkyl, C 5-7 cycloalkyl, C 2-8 alkenyl, or mononuclear aryl radical or anarylalkyl having a C 1-6 alkyl radical, or a halogenated derivative of one of these, OR21 is a C 1-8 alkoxy radical, q is up to 1À0, r is 0-1À0, s is 1À0-1À8, q+r is 0À01-1À0, and the OH plus alkoxy content is at least 4 wt. per cent with the OH content at least 3 wt. per cent; (b) a "lowsilanol" resin of units RSiO 1À5 and R 2 SiO in 1 : 0-8À5 molar ratio and silanol OH content less than 0À5 wt. per cent, wherein R is alkyl, cycloalkyl, alkenyl, or mononuclear aryl or aralkyl, optionally halogenated; (c) a catalyst; and (d) a filler. Preferably (a) contains 4-11 wt. per cent OH; (b) has an R : Si ratio of 1À7-1À9 : 1 and R is Me or Ph, at least 40% being Ph; (c) amounts to 0À01-6 wt. per cent of the composition and comprises 2PbCO 3 .Pb- (OH) 2 , PbO, Pb 2 O 3 , Pb 3 O 4 or PbO 2 and a carboxylic acid; (d) comprises a silica filler added first and glass fibres added later. There may also be present a process aid, e.g. a hydroxy- or alkoxy-silane or siloxane, and a release agent, e.g. stearyl alcohol or Ca stearate. In the examples (a) is obtained from MeSi(OEt) 3 , MeSiCl 3 , PhSiCl 3 and Me 2 SiCl 2 added to water in toluene/acetone, (b) is obtained from MeSiCl 3 PhSiCl 3 , Me 2 SiCl 2 and Ph 2 SiCl 2 , hydrolysed, and refluxed with KOH in toluene; the "low silanol" resin (b) is mixed with ground fused SiO 2 and silazane-treated fume silica, then there is mixed in (i) a dimethyl diphenyl polysiloxane diol process aid, a black pigment, stearyl alcohol, PbCO 3 and benzoic anhydride, (ii) the "high silanol" resin (a), and (iii) glass fibres; the mixture is formed into a sheet, granulated and moulded.