Patent ID: 8217388

Claim:
A curable organopolysiloxane composition comprising at least the following components: (A) a component selected from the group consisting of the following items (i) through (iii): (i) a linear diorganopolysiloxane (A 1 ) with a mass average molecular weight of at least 3,000 represented by the general formula: R 1 2 R 2 SiO(R 1 2 SiO) m (R 1 R 2 SiO) n SiR 1 2 R 2 (where R 1 is a substituted or unsubstituted monovalent hydrocarbon group that does not have aliphatic unsaturated bonds, with at least one R 1 in one molecule being an aryl group, R 2 is an alkenyl group, “m” is a positive integer, and “n” is a positive integer), (ii) a mixture of the above-mentioned component (A 1 ) and a linear diorganopolysiloxane (A 2 ) with a mass average molecular weight of less than 3,000 represented by the general formula: R 1 2 R 2 SiO(R 1 2 SiO) m′ (R 1 R 2 SiO) n′ SiR 1 2 R 2 (where R 1 is the same as above, with at least one R 1 in one molecule being an aryl group, R 2 is the same as above, “m′” is a positive integer, and “n′” is a positive integer), and (iii) a mixture of the above-mentioned component (A 1 ) and a linear diorganopolysiloxane (A 3 ) represented by the general formula: R 1 2 R 2 SiO(R 1 2 SiO) m″ SiR 1 2 R 2 (where R 1 is the same as above, with at least one R 1 in one molecule being an aryl group, R 2 is the same as above, and “m″” is a positive integer); (B) a branched organopolysiloxane represented by the average unit formula: (R 3 SiO 3/2 ) a (R 3 2 SiO 2/2 ) b (R 3 3 SiO 1/2 ) c (SiO 4/2 ) d (XO 1/2 ) e (where R 3 is a substituted or unsubstituted monovalent hydrocarbon group, with at least one R 3 in one molecule being an alkenyl group and at least one R 3 being an aryl group, X is a hydrogen atom or an alkyl group, “a” is a positive number, “b” is 0 or a positive number, “c” is 0 or a positive number, “d” is 0 or a positive number, “e” is 0 or a positive number, “b/a” is a number between 0 and 10, “c/a” is a number between 0 and 5.0, “d/(a+b+c+d)” is a number between 0 and 0.3, and “e/(a+b+c+d)” is a number between 0 and 0.4) {in an amount such that the ratio of the mass of component (B) to component (A) is in the range of from 1/99 to 99/1}; (C) an organopolysiloxane having, on average, at least 2 silicon-bonded aryl groups and, on average, at least 2 silicon-bonded hydrogen atoms in one molecule {in an amount such that the amount of the silicon-bonded hydrogen atoms in the present component per 1 mol of the total of the alkenyl groups in component (A) and component (B) is in the range of from 0.1 to 10 mol}, and (D) a hydrosilylation reaction catalyst (in a catalytic amount).