Curable silicone composition, cured product thereof, and optical semiconductor device

1. A curable silicone composition comprising:

(A) 100 parts by mass of a linear organopolysiloxane having at least two alkenyl groups and at least one aryl group in a molecule;

(B) 10 to 60 parts by mass of a branched organopolysiloxane represented by the following average unit formula:

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

wherein, R 1 are the same or different, and are alkyl groups having from 1 to 12 carbon atoms, or aryl groups having from 6 to 20 carbon atoms, with at least one R 1 in a molecule being an aryl group; R 2 are the same or different, and are alkyl groups having from 1 to 12 carbon atoms, alkenyl groups having from 2 to 12 carbon atoms, or aryl groups having from 6 to 20 carbon atoms; and subscripts a, b, and c are numbers that satisfy the following conditions: 0.1≤a≤0.6, 0≤b≤0.1, 0.4≤c≤0.9, and a+b+c=1;

(C) an organosiloxane having at least two silicon atom-bonded hydrogen atoms in a molecule, in an amount such that the number of silicon atom-bonded hydrogen atoms in this component is from 0.4 to 5 moles per 1 mole of total alkenyl groups in components (A) and (B), wherein the organosiloxane is:

(C1) an organosiloxane represented by the following general formula:

HR 5 2 SiO(R 5 2 SiO) n SiR 5 2 H

wherein, R 5 are the same or different, and are alkyl groups having from 1 to 12 carbon atoms, or aryl groups having from 6 to 12 carbon atoms, with at least one R 5 in a molecule being an aryl group; and subscript n is a number from 1 to 100;

(C2) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in a molecule and represented by the following average unit formula:

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

wherein, each R 5 is independently selected and defined above, with at least one R 5 in a molecule being an aryl group; and subscripts d, e, and f are numbers that satisfy the following conditions: 0.1<d≤0.7,0≤e≤0.5,0.1≤f<0.9, and d+e+f=1; or

a mixture of components (C1) and (C2); and

(D) an effective quantity of a hydrosilylation reaction catalyst.

2. The curable silicone composition according to claim 1 , wherein component (A) is represented by the following general formula:

R 3 2 R 4 SiO(R 3 2 SiO) m SiR 3 2 R 4

wherein, R 3 are the same or different, and are substituted or unsubstituted monovalent hydrocarbon groups free of aliphatic unsaturated bonds, with at least one R 3 in a molecule being an aryl group having from 6 to 12 carbon atoms; R 4 are the same or different, and are alkenyl groups having from 2 to 12 carbon atoms; and subscript m is a positive number.

3. The curable silicone composition according to claim 1 , wherein component (B) has a number average molecular weight (Mn) of at least 1500.

4. A method of preparing a cured product, said method comprising:

providing a curable silicone composition; and

curing the curable silicone composition to give the cured product;

wherein the curable silicone composition is the curable silicone composition according to claim 1 .

5. A cured product obtained by curing the curable silicone composition according to claim 1 .

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

7. An optical semiconductor device comprising:

an optical semiconductor element; and

a cured product sealing the optical semiconductor element, the cured product being the cured product of claim 5 .