GB1449871A - Heat-curable organopolysiloxanes - Google Patents

Abstract

1449871 Organopolysiloxanes DOW CORNING CORP 11 March 1975 [13 Jan 1975] 10042/75 Heading C3T A heat-curable composition comprises a mixture of (A) an organopolysiloxane resin having from 1-1À7 monovalent hydrocarbon substituents per silicon atom selected from C 1 -C 3 alkyl radicals and phenyl, and a Si-OH content of at least 0À25 wt. per cent, and (B) a catalytic amount of dicyandiamide, preferably in an amount of from 0À5-7À5 wt. per cent based on (A), and optionally a catalyst accelerator which is preferably a carboxylic acid, alcohol amide, polyamide, amine, amine salt, phosphonium salt or sulphonamide. The composition may also include a filler generally in an amount of 5-90 wt. per cent based on the weight of the composition, e.g. glass fibres, diatomaceous earth, crushed quartz, clays, asbestos, fume silica, treated fume silica, precipitated silica, zirconium silicate, lithium silicate, iron oxide, MgO, TiO 2 and CaCO 3 ; and conventional additives. The composition is cured by heating generally above 100‹ C. In the examples a phenylmethylsiloxane resin of R/Si ratio 1À1-1À2 and Si-OH content 5-6 wt. per cent is catalysed by stirring into the resin melt dicyandiamide alone or together with any one of the following accelerators: guanidine stearate, tetramethylammonium hydroxide, triethylbenzylammonium chloride, triethylene diamine, 2,4,6-(tris-dimethylaminomethyl(phenol or the stearate salt thereof, or and then cured by heating. In Example 2 a moulding composition prepared from the siloxane resin of Example 1, a siloxane block copolymer of R/Si ratio 1 : 4, C 5 H 5 /Si ratio 0À4 and Si-OH content 1 wt. per cent, glass fibres, amorphous silica, carbon black pigment, calcium stearate and any one of the dicyandiamide/ accelerator mixtures of Example 1 or dicyandiamide plus the benzoate salt of 2,4,6-(trisdimethylaminomethyl)phenol by roll-milling is granulated and then transfer moulded. Uses.-Moulding compounds for encapsulating electronic devices; or dissolved in a solvent as an impregnating resin in the manufacture of laminates.