Patent ID: 8299186

Claim:
A curable organopolysiloxane composition comprising: (A) an organopolysiloxane of the following average structural formula: R 1 a SiO (4-a)/2 (wherein R 1 designates unsubstituted or halogen-substituted monovalent hydrocarbon groups; however, in one molecule at least two groups designated by R 1 are alkenyl groups and at least 30 mole % of all groups designated by R 1 are aryl groups; and “a” is a number ranging from 0.6 to 2.1); (B) an organopolysiloxane that contains in one molecule at least two silicon-bonded hydrogen atoms and at least 15 mole % of all silicon-bonded organic groups in the form of aryl groups; (C) a branched-chain organopolysiloxane of the following average unit formula: (R 2 SiO 3/2 ) b (R 2 2 SiO 2/2 ) c (R 2 3 SiO 1/2 ) d (SiO 4/2 ) e (XO 1/2 ) f {wherein each R 2 independently designates an alkyl group, alkenyl group, aryl group, or an epoxy-containing organic group; however, in one molecule at least 5 mole % of all groups designated by R 2 are alkenyl groups, at least 15 mole % of all groups designated by R 2 are aryl groups, and at least 10 mole % of all groups designated by R 2 are epoxy-containing organic groups; X designates a hydrogen atom or an alkyl group; and “b” is a positive number, “c” is 0 or a positive number,“d” is 0 or a positive number, “e” is 0 or a positive number, “f” is 0 or a positive number, “c/b” is a number ranging from 0 to 10, “d/b” is a number ranging from 0 to 5, “e/(b+c+d+e)” is a number ranging from 0 to 0.3, and “f/(b+c+d+e)” is a number ranging from 0 to 0.02}; and (D) a hydrosilylation catalyst; wherein component (B) is used in such an amount that the mole ratio of the silicon-bonded hydrogen atoms contained in component (B) to the alkenyl groups contained in components (A) and (C) is in the range of 0.1 to 5; component (C) is contained in an amount of 0.1 to 20 parts by mass per 100 parts by mass of the sum of components (A) and (B); and component (D) is contained in an amount sufficient to accelerate curing of the composition.