Rubber composition for tire, and pneumatic tire

1. A rubber composition for tires, comprising:

epoxidized natural rubber;

polybutadiene rubber;

silica; and

a silane coupling agent represented by formula (1) below,

the epoxidized natural rubber and the polybutadiene rubber being present in amounts of 20% by mass or more and 20% by mass or more, respectively, based on 100% by mass of a rubber component in the rubber composition,

the silica being present in an amount of 50 parts by mass or more per 100 parts by mass of the rubber component,

[Y 1 R 1 S x —] m [G 1 (R 2 SiX 1 X 2 X 3 ) a ] n [G 2 ] o [R 3 Y 2 ] p   (1)

wherein each G 1 independently represents a C1-C30 polyvalent hydrocarbon group containing a polysulfide group, represented by [(CH 2 ) b -] c R 4 [—(CH 2 ) d S x -] e ;

each G 2 independently represents a C1-C30 polyvalent hydrocarbon group containing a polysulfide group, represented by [(CH 2 ) b -] c R 5 [—(CH 2 ) d S x —] e ;

each of Y 1 and Y 2 independently represents a silyl group represented by —SiX 1 X 2 X 3 , a hydrogen atom, a carboxyl group, or an ester group represented by —C(═O)OR 6 ;

each X 1 independently represents —Cl, —Br, —OH, —OR 6 , or R 6 C(═O)O—;

each of X 2 and X 3 independently represents a hydrogen atom, R 6 , X 1 , or a —OSi— containing group formed by silanol condensation;

each of R 1 and R 3 independently represents a C1-C20 divalent hydrocarbon group;

each R 2 independently represents a linear hydrocarbon group represented by —(CH 2 ) f —;

each R 4 independently represents a C1-C28 polyvalent hydrocarbon group or a heteroatom-containing C1-C27 polyvalent hydrocarbon group;

each R 5 independently represents a C1-C28 polyvalent hydrocarbon group;

R 6 represents a C1-C20 monovalent hydrocarbon group; and

a, b, c, d, e, f, m, n, o, p, and x are independent from one another, each of a, c, and e represents a number of 1 to 3, each of b and d represents a number of 1 to 5, f represents a number of 0 to 5, each of m and p represents a number of 1 to 100, n represents a number of 1 to 15, o represents a number of 0 to 10, and x represents a number of 1 to 10.

2. The rubber composition for tires according to claim 1 ,

wherein the silane coupling agent of formula (1) is a compound represented by the following formula:

wherein each of Y 1 and Y 2 independently represents a silyl group represented by —SiX 1 X 2 X 3 , a hydrogen atom, a carboxyl group, or an ester group represented by —C(═O)OR 6 ;

each X 1 independently represents —Cl, —Br, —OH, —OR 6 , or R 6 C(═O)O—;

each of X 2 and X 3 independently represents a hydrogen atom, R 6 , X 1 , or a —OSi— containing group formed by silanol condensation;

each of R 1 and R 3 independently represents a C1-C20 divalent hydrocarbon group;

each R 2 independently represents a linear hydrocarbon group represented by —(CH 2 ) f —;

each R 4 independently represents a cyclic alkyl, alkenyl, alkynyl, aryl, or aralkyl group in which a+c+e−1 hydrogen atoms have been replaced;

R 6 represents a C1-C20 monovalent hydrocarbon group; and

a, b, c, d, e, f, m, n, p, and x are independent from one another, each of a, c, and e represents a number of 1 to 3, each of b and d represents a number of 1 to 5, f represents a number of 0 to 5, each of m and p represents a number of 1 to 100, n represents a number of 1 to 15, and x represents a number of 1 to 10.

3. The rubber composition for tires according to claim 1 , wherein the polybutadiene rubber contains a functional group reactive with silica.

4. The rubber composition for tires according to claim 1 , further comprising at least one selected from the group consisting of sulfide silane coupling agents, liquid coumarone-indene resins, and aluminum hydroxide.

5. A pneumatic tire, formed from the rubber composition according to claim 1 .

6. A studless winter tire, formed from the rubber composition according to claim 1 .

7. The rubber composition for tires according to claim 3 ,

wherein

the epoxidized natural rubber amount is 30% by mass or more and 70% by mass or less,

the polybutadiene rubber amount is 40% by mass or more and 70% by mass or less, and

the combined amount of the epoxidized natural rubber and polybutadiene rubber is 75% by mass to 100% by mass, and

wherein all amounts are based on 100% by mass of the rubber component.

8. The rubber composition for tires according to claim 3 ,

wherein

the epoxidized natural rubber amount is 35% by mass or more and 65% by mass or less,

the polybutadiene rubber amount is 50% by mass or more and 65% by mass or less, and

the combined amount of the epoxidized natural rubber and polybutadiene rubber is 90% by mass to 100% by mass, and

wherein all amounts are based on 100% by mass of the rubber component.

9. A pneumatic tire, formed from the rubber composition according to claim 7 .

10. A pneumatic tire, formed from the rubber composition according to claim 8 .