Curable silicone composition, and optical semiconductor device

1. A curable silicone composition comprising:

(A) 100 parts by mass of an organopolysiloxane having at least two alkenyl groups in a molecule;

(B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in a molecule, in an amount providing from 0.1 to 10.0 moles of silicon-bonded hydrogen atoms relative to 1 mole of total alkenyl groups contained in components (A) and (C);

(C) from 0.1 to 50 parts by mass of an adhesion promoter represented by the average unit formula:

(R 1 R 2 SiO 2/2 ) a (R 2 R 3 SiO 2/2 ) b (R 4 SiO 3/2 ) c

wherein, R 1 is an alkenyl group having from 2 to 12 carbons; R 2 are the same or different alkyl groups each having from 1 to 12 carbons, aryl groups each having from 6 to 20 carbons, or aralkyl groups each having from 7 to 20 carbons; R 3 is an epoxy group-containing organic group; R 4 is an aryl group having from 6 to 20 carbons or an aralkyl group having from 7 to 20 carbons; and a, b, and c are numbers satisfying: 0.1≤a≤0.6, 0.1≤b≤0.5, 0.3≤c<0.8, 0.15≤a/c≤1.5, 0.15≤b/c≤1.8, and a+b+c=1; and

(D) a hydrosilylation reaction catalyst in an amount effective in accelerating curing of the composition.

2. The curable silicone composition according to claim 1 , wherein component (A) contains an organopolysiloxane resin having at least two alkenyl groups in a molecule and represented by the average unit formula:

(R 1 R 5 2 SiO 1/2 ) d (R 5 2 SiO 2/2 ) e (R 4 SiO 3/2 ) f

wherein, R 1 and R 4 are the same groups as defined above; R 5 are the same or different alkyl groups each having from 1 to 12 carbons, alkenyl groups each having from 2 to 12 carbons, aryl groups each having from 6 to 20 carbons, or aralkyl groups each having from 7 to 20 carbons; and d, e, and f are numbers satisfying: 0.01≤d≤0.5, 0≤e≤0.7, 0.1≤f<0.9, and d+e+f=1.

3. The curable silicone composition according to claim 2 , wherein component (A) contains a straight-chain organopolysiloxane having at least two silicon-bonded alkenyl groups and at least one silicon-bonded aryl group in a molecule.

4. The curable silicone composition according to claim 1 , wherein component (A) contains a straight-chain organopolysiloxane having at least two silicon-bonded alkenyl groups and at least one silicon-bonded aryl group in a molecule.

5. The curable silicone composition according to claim 4 , wherein R 3 in component (C) is a glycidoxyalkyl group, an epoxycyclohexylalkyl group, or an epoxyalkyl group.

6. The curable silicone composition according to claim 1 , wherein R 3 in component (C) is a glycidoxyalkyl group, an epoxycyclohexylalkyl group, or an epoxyalkyl group.

7. The curable silicone composition according to claim 1 , further comprising (E) a hydrosilylation reaction inhibitor in an amount from 0.01 to 3 parts by mass per 100 parts by mass total of components (A) to (D).

8. An optical semiconductor device comprising an optical semiconductor element encapsulated by a cured product of the curable silicone composition according to claim 1 .