Rubber Composition for Tire Treads

A rubber composition for use in tire treads, the composition comprising, per 100 parts by weight of a diene rubber containing from 35% to 89% by weight of a modified conjugated diene polymer rubber and from 11% to 40% by weight of butadiene rubber,

• from 3 to 60 parts by weight of aromatic modified terpene resin;
• and
• from 100 to 150 parts by weight of a filler;
• the filler containing not less than 70% by weight of silica;
• a ratio Wte/Wbr of the compounded amount of aromatic modified terpene resin Wte to the compounded amount of butadiene rubber Wbr being from 0.5 to 1.3;
• the modified conjugated diene polymer rubber having a terminal modified group, obtained by reacting at least one type of compound comprising a functional group that is reactable with an active terminal of an active conjugated diene polymer chain, with the active conjugated diene polymer chain obtained by copolymerizing a conjugated diene monomer and an aromatic vinyl monomer in a hydrocarbon solvent using an organic active metal compound as an initiator;
• the terminal modified group comprising a functional group that interacts with silica;
• an aromatic vinyl unit content being from 38% to 48% by weight of the modified conjugated diene polymer rubber, vinyl unit content being from 20% to 35% by weight of the modified conjugated diene polymer rubber, and weight-average molecular weight of the modified conjugated diene polymer rubber being from 600,000 to 1,000,000;
• and
• a softening point of the aromatic modified terpene resin being from 100° C. to 150° C.;
• and
• the compound comprising the functional group that is reactable with the active terminal of the active conjugated diene polymer chain comprises at least one type of polyorganosiloxane compound selected from general formulae (I) to (III) below:
• In formula (I), R1 to R8 are identical or different and are alkyl groups having from 1 to 6 carbons or aryl groups having from 6 to 12 carbons;
• X1 and X4 are identical or different and are groups having functional groups that react with the active terminal of the active conjugated diene polymer chain, alkyl groups having from 1 to 6 carbons, or aryl groups having from 6 to 12 carbons;
• X2 is a group having a functional group that reacts with the active terminal of the active conjugated diene polymer chain;
• X3 is a group including from 2 to 20 repeating alkylene glycol units, a portion of the X3 moieties optionally being groups derived from groups including from 2 to 20 repeating alkylene glycol units;
• and m is an integer from 3 to 200, n is an integer from 0 to 200, and k is an integer from 0 to 200.
• In formula (II), R9 to R16 are identical or different and are alkyl groups having from 1 to 6 carbons or aryl groups having from 6 to 12 carbons;
• and X5 to X8 are groups having functional groups that react with the active terminal of the active conjugated diene polymer chain.
• In formula (III), R17 to R19 are identical or different and are alkyl groups having from 1 to 6 carbons or aryl groups having from 6 to 12 carbons;
• and X9 to X11 are groups having functional groups that react with the active terminal of the active conjugated diene polymer chain;
• and s is an integer from 1 to 18.