TECHNICAL FIELD

The present technology relates to a rubber composition for a tire tread and a pneumatic tire.

BACKGROUND ART

In the related art, rubber compositions for tires that are used in tire treads of studless tires have been known. For example, claim 1 of Japan Unexamined Patent Publication No. 2015-067636 describes “a rubber composition for a tire comprising: 100 parts by mass of a diene rubber (A); from 30 to 100 parts by mass of a carbon black and/or a white filler (B); and from 0.3 to 30 parts by mass of a cured product (C) obtained by curing a crosslinkable oligomer or polymer (c1) that is not compatible with the diene rubber (A); JIS A hardness of the cured product (C) being from 3 to 45”.

When the present inventors studied the rubber composition for a tire described in Japan Unexamined Patent Publication No. 2015-067636, it was found that at least one of performance on ice (frictional force on ice), wet grip performance, a low heat build-up, or wear resistance may be insufficient.

SUMMARY

The present technology provides a rubber composition for a tire tread that exhibits excellent performance on ice, wet grip performance, low heat build-up, and wear resistance when formed into a tire; and a pneumatic tire which uses this rubber composition for a tire tread in a tread.

Specifically, the present technology provides the following [1] to [7].

[1] A rubber composition for a tire tread containing: 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 (Japanese Industrial Standard) A hardness of the cured product being from 3 to 45.

[2] The rubber composition for a tire tread according to [1] above, where the polyorganosiloxane group is a group bonded to a terminal of a butadiene chain through a linking group formed from a divalent hydrocarbon group from 1 to 20 carbons which may have a substituent or through an ether group.

However, a part of —CH2— of the divalent hydrocarbon group from 1 to 20 carbons which may have a substituent may be replaced by —O—.

Furthermore, a silicon-containing linking group represented by General Formula (Si) described below may be 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.

[3] The rubber composition for a tire tread according to [1] or [2] above, where the cured product has particles having an average particle diameter of from 5 to 250 μm.

[4] The rubber composition for a tire tread according to any one of [1] to [3] above, where the crosslinkable oligomer or polymer is a polyether-based or siloxane-based polymer or copolymer and has a silane functional group.

[5] The rubber composition for a tire tread according to any one of [1] to [4] above, further containing an aromatic modified terpene resin having a softening point of from 60 to 150° C., where 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.

[6] The rubber composition for a tire tread according to any one of [1] to [5] above, further containing thermally expanding microcapsules, where 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.

[7] A pneumatic tire including the rubber composition for a tire tread described in any one of [1] to [6] above in a tread.

The present technology can provide a rubber composition for a tire tread that exhibits excellent performance on ice, wet grip performance, low heat build-up, and wear resistance when formed into a tire; and a pneumatic tire which uses this rubber composition for a tire tread in a tread.

