Curable organopolysiloxane composition and optical semiconductor device

A curable organopolysiloxane composition comprising at least the following components:

• (A) an alkenyl-containing organopolysiloxane that comprises 15 to 35 wt. % of constituent (A-1) and 65 to 85 wt. % of constituent (A-2), wherein
• constituent (A-1) comprises an organopolysiloxane of the following average compositional formula:
• (R13SiO1/2)a(R12SiO2/2)b(R1SiO3/2)c(SiO4/2)d
• where R1 designates phenyl groups, methyl groups, or alkenyl groups having 2 to 10 carbon atoms;
• 0.4 to 50 mole % of all R1 groups are alkenyl groups having 2 to 10 carbon atoms;
• methyl groups constitute 90 mole % or more of the sum of methyl and phenyl groups contained in R1;
• “a”, “b”, “c”, and “d” are numbers that satisfy the following conditions:
• 0≦a≦0.05;
• 0.9≦b≦1;
• 0≦c≦0.03;
• 0≦d≦0.03;
• and a+b+c+d=1;
• constituent (A-2) comprises an organopolysiloxane of the following average compositional formula:
• (R23SiO1/2)e(R22SiO2/2)f(R2SiO3/2)g(SiO4/2)h(HO1/2)i
• where R2 designates phenyl groups, methyl groups, or alkenyl groups having 2 to 10 carbon atoms;
• 5 to 10 mole % of all R2 groups are alkenyl groups having 2 to 10 carbon atoms;
• methyl groups constitute 90 mole % or more of the sum of methyl and phenyl groups contained in R2;
• “e”, “f”, “g”, “h” and “i” are numbers that satisfy the following conditions:
• 0.4≦e≦0.6;
• 0≦f≦0.05;
• 0≦g≦0.05;
• 0.4≦h≦0.6;
• 0.01≦i≦0.05;
• and e+f+g+h=1;
• (B) an organopolysiloxane that contains silicon-bonded hydrogen atom and comprises 10 to 50 wt. % of constituent (B-1), 50 to 90 wt. % of constituent (B-2), and 0 to 30 wt. % of constituent (B-3);
• in an amount that the silicon-bonded hydrogen atoms in component (B) are in the range of 0.5 to 2.0 moles per 1 mole of the total content of alkenyl groups in component (A), wherein
• constituent (B-1) comprises an organopolysiloxane that contains at least 0.5 wt. % of silicon-bonded hydrogen atoms and that is represented by the following average molecular formula:
• R33SiO(R32SiO)j(R3HSiO)kSiR33
• where R3 designates phenyl groups or methyl groups;
• methyl groups constitute 90 mole % or more of all groups contained in R3;
• “j” is a number in the range of 0 to 35;
• and “k” is a number in the range of 5 to 100;
• constituent (B-2) comprises an organopolysiloxane that contains at least 0.5 wt. % of silicon-bonded hydrogen atoms and that is represented by the following average compositional formula:
• (HR42SiO1/2)l(R43SiO1/2)m(R42SiO2/2)n(R4SiO3/2)o(SiO4/2)p(R5O1/2)q
• where R4 designates phenyl groups or methyl groups;
• methyl groups constitute 90 mole % or more of all groups contained in R4;
• R5 designates hydrogen atoms or alkyl groups having 1 to 10 carbon atoms;
• and “l”, “m”, “n”, “o”, “p” and “q” are numbers that satisfy the following conditions:
• 0.4≦l≦0.7;
• 0≦m≦0.2;
• 0≦n≦0.05;
• 0≦o≦0.5;
• 0.3≦p≦0.6;
• 0≦q≦0.05;
• and l+m+n+o+p=1;
• constituent (B-3) is an organopolysiloxane represented by the following average molecular formula:
• HR62SiO(R62SiO)rSiR62H
• where R6 represents phenyl or methyl groups;
• methyl groups constitute at least 90% of all groups contained in R6;
• and “r” is a number in the range of 10 to 100;
• and
• (C) a hydrosilylation-reaction catalyst, in an amount sufficient for curing the composition.