Flame retardant silicone compositions

1. A flame retardant silicone composition comprising

(A) 100 parts by weight of an organopolysiloxane having at least one alkenyl group having 2 to 6 carbon atoms, in a molecule of the organopolysiloxane, represented by the following general formula (1):

R a R 1 b SiO (4−a−b)/2   (1)

wherein R is an alkenyl group having 2 to 6 carbon atoms, R 1 is a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, “a” is a positive number of 0.0001 to 0.2, “b” is a positive number of 1.7 to 2.2, and the sum of a+b is 1.9 to 2.4,

(B) an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicon atoms in a molecule, in an amount to give 0.1 to 5 silicon atom-bonded hydrogen atoms per alkenyl group in component (A),

(C) a platinum catalyst in an amount to give 0.1 to 1,000 ppm of platinum element based on the weight of component (A), and

(D) 0.0001 to 1 part by weight of at least one compound selected from the group consisting of indoline, benzoxazole, 2-hydroxybenzoxazole, 5-benzyloxyindole, 1,2-benzisoxazole, 2,1 -benzisoxazole, and 1,3-benzodioxole.

2. The composition of claim 1 wherein components (A) and (B) contain low-molecular-weight cyclic siloxane fractions D 3 to D 10 in a total amount of up to 1,000 ppm.

3. The composition of claim 1 , comprising indoline.

4. The composition of claim 1 , comprising benzoxazole.

5. The composition of claim 1 , comprising 2-hydroxybenzoxazole.

6. The composition of claim 1 , comprising 5-benzyloxyindole.

7. The composition of claim 1 , comprising 1,2-benzisoxazole.

8. The composition of claim 1 , comprising 2,1-benzisoxazole.

9. The composition of claim 1 , comprising 1,3-benzodioxole.

10. The composition of claim 1 , wherein the organopolysiloxane having the at least one alkenyl group in a molecule is capped at both ends of its molecular chain with triorganosiloxy groups.

11. The composition of claim 10 , wherein the organopolysiloxane is a straight-chain organopolysiloxane.

12. The composition of claim 1 , wherein the organopolysiloxane is a branched organopolysiloxane.

13. The composition of claim 1 , comprising:

dimethylpolysiloxane capped with dimethylvinylsiloxy groups at both ends of its molecular chain;

a methylhydrogenpolysiloxane of the following formula (3)

a chioroplatinic acid/vinyl siloxane complex; and

benzoxazole.

14. A cured transparent and flame retardant composition obtained by curing the composition of claim 1 .

15. An integrated circuit covered with a flame retardant composition obtained by curing the composition of claim 1 .

16. The integrated circuit of claim 15 , wherein the cured composition is in the form of a transparent gel or transparent rubbery product.

17. A flame retardant silicone composition comprising

(A) 100 parts by weight of an organopolysiloxane having at least one alkenyl group having 2 to 6 carbon atoms, in a molecule of the organopolysiloxane, represented by the following general formula (1):

R a R 1 b SiO (4−a−b)/2   (1)

wherein R is an alkenyl group having 2 to 6 carbon atoms, R 1 is a substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, “a” is a positive number of 0.0001 to 0.2, “b” is a positive number of 1.7 to 2.2, and the sum of a+b is 1.9 to 2.4,

(B) an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicon atoms in a molecule, in an amount to give 0.1 to 5 silicon atom-bonded hydrogen atoms per alkenyl group in component (A),

(C) a platinum catalyst in an amount to give 0.1 to 1,000 ppm of platinum element based on the weight of component (A), and

(D) 0.0001 to 1 part by weight of at least one compound other than said platinum catalyst (C) selected from the group consisting of indoline, indazole, benzoxazole, 2-hydroxybenzoxazole, 5-benzyloxyindole, 1,2-benzisoxazole, 2,1-benzisoxazole, and 1,3-benzodioxole,

wherein components (A) and (B) contain low-molecular-weight cyclic siloxane fractions D 3 to D 10 in a total amount of up to 1,000 ppm.