Patent ID: 8389650

Claim:
A curable polyorganosiloxane composition comprising: a component (A) which is an alkenyl group-containing polyorganosiloxane which comprises: a component (A1) which is a branched polyorganosiloxane comprising an SiO 4/2 unit and an R 3 SiO 1/2 unit with a molar ratio of the R 3 SiO 1/2 unit to the SiO 4/2 unit in the range of 1:0.8 to 1:3, and optionally an R 2 SiO unit and/or an RSiO 3/2 unit, wherein at least three R per molecule are alkenyl groups, and 100 mol % of R, excluding the alkenyl groups, are methyl groups and optionally a component (A2) which is a linear polyorganosiloxane having R bonded to a silicon atom, wherein at least two R per molecule are alkenyl groups, and 100 mol % of the R, excluding the alkenyl groups, are methyl groups; a component (B) which is a polyalkylhydrogensiloxane comprising an SiO 4/2 unit and an R 3 (CH 3 ) 2 SiO 1/2 unit with a molar ratio of the R 3 (CH 3 ) 2 SiO 1/2 unit to the SiO 4/2 unit is in the range of 1.5:1 to 2.2:1, the polyalkylhydrogensiloxane being represented by the formula [R 3 (CH 3 ) 2 SiO 1/2 ] 8 [SiO 4/2 ] 4 or the formula [R 3 (CH 3 ) 2 SiO 1/2 ] 10 [SiO 4/2 ] 5 , wherein each R 3 represents a hydrogen atom; and a component (C) which is a platinum-vinylsiloxane complex having a platinum group metal atom, wherein the component (B) is contained in an amount such that the number of the R 3 as a hydrogen atom is 0.5 to 2.0, relative to one alkenyl group present in the component (A), wherein the component (C) is contained in an amount of 0.1 to 1,000 ppm by weight in terms of the platinum group metal atom, relative to the weight of the component (A), wherein the amount of the component (A1) is 50 to 100% by weight and the amount of the component (A2) is 50 to 0% by weight, relative to 100% by weight of the component (A), and wherein the R as an alkenyl group is a vinyl group.