Rubber composition for tire treads

1. A rubber composition for tire treads obtained by blending, per 100 parts by mass of a diene rubber, 5 to 150 parts by mass of silica and 0.5 to 20 parts by mass of a silicone oligomer represented by the following siloxane average formula (1):

(X) a (Y) b (R 1 ) c (R 2 ) d SiO (4-a-b-c-d)/2   (1)

(wherein X is a mercapto group-containing organic group, Y is a hydrolyzable group, R 1 is a monovalent hydrocarbon group having from 4 to 10 carbon atoms, R 2 is a monovalent hydrocarbon group having from 1 to 3 carbon atoms), wherein in the siloxane average formula (1), a, b, c, and d each satisfy 0<a<0.5, 1.2<b<1.6, 0.5<c<1, and 0≦d≦0.1 and 0<a+b+c+d<4);

the diene rubber containing an aromatic vinyl-conjugated diene copolymer in an amount of at least 50 parts by mass per 100 parts by mass of the diene rubber, the aromatic vinyl-conjugated diene copolymer having an aromatic vinyl content of 20 to 45 mass % and a vinyl bond content in the conjugated diene of 10 to 50%.

2. The rubber composition for tire treads according to claim 1 , wherein at least a portion of the silica is silica with an N 2 SA of 100 to 300 m 2 /g.

3. The rubber composition for tire treads according to claim 1 , wherein in the siloxane average formula (1), R 1 is the following organic group (2), and X is the following organic group (3):

—C 8 H 17   (2); and

—C 3 H 6 SH  (3).

4. The rubber composition for tire treads according to claim 1 , wherein the weight average molecular weight of the silicone oligomer is from 500 to 2000.

5. The rubber composition for tire treads according to claim 1 , wherein at least a portion of the silica is silica with an N 2 SA from 150 to 300 m 2 /g.

6. A pneumatic tire having tire treads formed using the rubber composition for tire treads described in claim 1 .

7. A rubber composition for tire treads obtained by blending, per 100 parts by mass of a diene rubber, 5 to 150 parts by mass of silica and 0.5 to 20 parts by mass of a silicone oligomer represented by the following siloxane average formula (1):

(X) a (Y) b (R 1 ) c (R 2 ) d SiO (4-a-b-c-d)/2   (1)

wherein X is a mercapto group-containing organic group, Y is a hydrolyzable group, R 1 is a monovalent hydrocarbon group having from 4 to 10 carbon atoms, R 2 is a monovalent hydrocarbon group having from 1 to 3 carbon atoms, wherein in the siloxane average formula (1), a, b, c, and d each satisfy 0<a<1, 0<b<2, 0<c<1, and 0≦d<1, and 0<a+b+c+d<4);

the diene rubber containing an aromatic vinyl-conjugated diene copolymer in an amount of at least 50 parts by mass per 100 parts by mass of the diene rubber, the aromatic vinyl-conjugated diene copolymer having an aromatic vinyl content of 20 to 45 mass % and a vinyl bond content in the conjugated diene of 10 to 50%, and

further containing a silane having a polysulfide structure and a hydrolyzable group.

8. The rubber composition for tire treads according to claim 7 , wherein at least a portion of the silica is silica with an N 2 SA of 100 to 300 m 2 /g.

9. The rubber composition for tire treads according to claim 7 , wherein in the siloxane average formula (1), R 1 is the following organic group (2), and X is the following organic group (3):

—C 8 H 17   (2); and

—C 3 H 6 SH  (3).

10. The rubber composition for tire treads according to claim 7 , wherein in the siloxane average formula (1), a, b, c, and d each satisfy 0<a<0.5, 1.2<b<1.6, 0.5<c<1, and 0≦d≦0.1.

11. The rubber composition for tire treads according to claim 7 , wherein the weight average molecular weight of the silicone oligomer is from 500 to 2000.

12. A pneumatic tire having tire treads formed using the rubber composition for tire treads described in claim 7 .

13. A rubber composition for tire treads obtained by blending, per 100 parts by mass of a diene rubber, 5 to 150 parts by mass of silica and 0.5 to 20 parts by mass of a silicone oligomer represented by the following siloxane average formula (1):

(X) a (Y) b (R 1 ) c (R 2 ) d SiO (4-a-b-c-d)/2   (1)

wherein X is a mercapto group-containing organic group, Y is a hydrolyzable group, R 1 is a monovalent hydrocarbon group having from 4 to 10 carbon atoms, R 2 is a monovalent hydrocarbon group having from 1 to 3 carbon atoms, wherein in the siloxane average formula (1), a, b, c, and d each satisfy 0<a<1, 0<b<3, 0<c<2, and 0≦d<2, and 0<a+b+c+d<4);

the diene rubber containing an aromatic vinyl-conjugated diene copolymer in an amount of at least 50 parts by mass per 100 parts by mass of the diene rubber, the aromatic vinyl-conjugated diene copolymer having an aromatic vinyl content of 20 to 45 mass % and a vinyl bond content in the conjugated diene of 10 to 50%, and

further containing a silane having a polysulfide structure and a hydrolyzable group.

14. The rubber composition for tire treads according to claim 13 , wherein in the siloxane average formula (1), R 1 is the following organic group (2), and X is the following organic group (3):

—C 8 H 17   (2); and

—C 3 H 6 SH  (3).

15. The rubber composition for tire treads according to claim 13 , wherein the weight average molecular weight of the silicone oligomer is from 500 to 2000.

16. A pneumatic tire having tire treads formed using the rubber composition for tire treads described in claim 13 .

17. The rubber composition for tire treads according to claim 13 , wherein at least a portion of the silica is silica with an N 2 SA of 100 to 300 m 2 /g.