Rubber composition for a tire tread and pneumatic tire using the same

1. A rubber composition for a tire tread comprising: a diene rubber, silica, and a cured product;

a content of the silica being from 20 to 100 parts by mass per 100 parts by mass of the diene rubber, a content of the cured product being from 0.3 to 30 parts by mass per 100 parts by mass of the diene rubber;

the diene rubber containing a natural rubber and a modified butadiene rubber having a polyorganosiloxane group at a terminal, a content of the natural rubber in the diene rubber being from 30 to 90 mass %, a content of the modified butadiene rubber in the diene rubber being from 10 to 70 mass %; and

the cured product being a cured product obtained by curing a crosslinkable oligomer or polymer that is incompatible with the diene rubber, JIS A hardness of the cured product being from 3 to 45,

wherein the polyorganosiloxane group is a group bonded to a terminal of a butadiene chain as a main chain of the modified butadiene rubber through a linking group formed from a divalent hydrocarbon group from 1 to 20 carbons which may have a substituent;

the butadiene chain contains from 85 to 100 mass % of butadiene units;

a part of —CH 2 — of the linking group formed from a divalent hydrocarbon group from 1 to 20 carbons which may have a substituent may be replaced by —O—;

a silicon-containing linking group represented by General Formula (Si) below is present in between the linking group formed from a divalent hydrocarbon group from 1 to 20 carbons which may have a substituent; and the terminal of the butadiene chain;

*1-Q 1 -Si(R L1 ) 2 -A 1 -Si(R L2 ) 2 -Q 2 -*2  (Si)

wherein,

Q 1 and Q 2 are each independently a chemical single bond or —O—;

R L1 and R L2 are each independently a substituent, and a plurality of R L1 and R L2 may be the same or different;

A 1 is a chemical single bond, a polymethylene group having from 1 to 20 carbons represented by (CH 2 ) k wherein k is an integer from 1 to 20, an arylene group having from 6 to 20 carbons, or a cycloalkylene group having from 5 to 20 carbons;

*1 is a linkage position with *2 in another silicon-containing linking group or with the linking group formed from a divalent hydrocarbon group from 1 to 20 carbons which may have a substituent; and

*2 is a linkage position with *1 in another silicon-containing linking group or with the terminal of the butadiene chain.

2. The rubber composition for a tire tread according to claim 1 , wherein the cured product contains particles having an average particle diameter of from 5 to 250 μm.

3. The rubber composition for a tire tread according to claim 2 , wherein the crosslinkable oligomer or polymer is a polyether-based or siloxane-based polymer or copolymer and has a silane functional group.

4. The rubber composition for a tire tread according to claim 2 , further comprising an aromatic modified terpene resin having a softening point of from 60 to 150° C., wherein a content of the aromatic modified terpene resin is from 2 to 20 parts by mass per 100 parts by mass of the diene rubber.

5. The rubber composition for a tire tread according to claim 1 , wherein the crosslinkable oligomer or polymer is a polyether-based or siloxane-based polymer or copolymer and has a silane functional group.

6. The rubber composition for a tire tread according to claim 5 , further comprising an aromatic modified terpene resin having a softening point of from 60 to 150° C., wherein a content of the aromatic modified terpene resin is from 2 to 20 parts by mass per 100 parts by mass of the diene rubber.

7. The rubber composition for a tire tread according to claim 1 , further comprising an aromatic modified terpene resin having a softening point of from 60 to 150° C., wherein a content of the aromatic modified terpene resin is from 2 to 20 parts by mass per 100 parts by mass of the diene rubber.

8. The rubber composition for a tire tread according to claim 1 , further comprising thermally expanding microcapsules, wherein a content of the thermally expanding microcapsules is from 0.5 to 20 parts by mass per 100 parts by mass of the diene rubber.

9. The rubber composition for a tire tread according to claim 1 , wherein the butadiene chain contains from 70 to 100 mass % of conjugated diene monomer units.

10. The rubber composition for a tire tread according to claim 9 , wherein the cured product contains particles having an average particle diameter of from 5 to 250 μm.

11. The rubber composition for a tire tread according to claim 9 , wherein the crosslinkable oligomer or polymer is a polyether-based or siloxane-based polymer or copolymer and has a silane functional group.

12. The rubber composition for a tire tread according to claim 9 , further comprising an aromatic modified terpene resin having a softening point of from 60 to 150° C., wherein a content of the aromatic modified terpene resin is from 2 to 20 parts by mass per 100 parts by mass of the diene rubber.

13. The rubber composition for a tire tread according to claim 1 , wherein the butadiene chain is a homopolymer chain of conjugated diene monomers.

14. The rubber composition for a tire tread according to claim 13 , wherein the cured product contains particles having an average particle diameter of from 5 to 250 μm.

15. The rubber composition for a tire tread according to claim 13 , wherein the crosslinkable oligomer or polymer is a polyether-based or siloxane-based polymer or copolymer and has a silane functional group.

16. A pneumatic tire comprising the rubber composition for a tire tread described in claim 1 in a tread.