TECHNICAL FIELD

The present technology relates to a pneumatic tire with a tread portion comprising a rubber composition for a tread including silica.

BACKGROUND ART

Examples of required performances of a pneumatic tire include excellent dry performance and wet performance, low rolling resistance, and excellent wear resistance at high speeds. In particular, high performance tires require these performances to be obtained in a compatible manner to a high degree. Blending a large amount of silica with a rubber composition for a tread used in tread portions of pneumatic tires is a known technique for providing dry performance and wet performance in a compatible manner to a high degree (see Japan Unexamined Patent Publication No. 2010-077257 for example). However, simply blending silica affects rolling resistance and wear resistance at high speeds, resulting in all of the performances being unable to be obtained in a well-balanced manner to a high degree. Thus, there is a demand for a way to improve rolling resistance and wear resistance at high speeds and also for maintaining excellent dry performance and wet performance obtained by blending a large amount of silica.

SUMMARY

The present technology provides a pneumatic tire with a tread portion comprising a rubber composition for a tread including silica, the pneumatic tire having improved rolling resistance and wear resistance at high speeds while maintaining excellent dry performance and wet performance.

A pneumatic tire according to an embodiment of the present technology comprises:

a designated mounting direction with respect to a vehicle; and

a tread portion with an annular shape extending in a tire circumferential direction, the tread portion comprising

longitudinal grooves extending in the tire circumferential direction and/or lateral grooves extending in a tire lateral direction, and being made of a rubber composition for a tread; wherein

a groove area ratio Sin of a vehicle inner side region corresponding to a vehicle inner side of a tire equator of the tread portion ranges from 30% to 39%;

a difference ΔS between the groove area ratio Sin and a groove area ratio Sout of a vehicle outer side region corresponding to a vehicle outer side of a position the tire equator of the tread portion ranges from 6% to 14%; and

the rubber composition for a tread comprises

a diene rubber comprising from 10 parts by mass to 30 parts by mass of natural rubber and from 70 parts by mass to 90 parts by mass of a solution polymerized styrene-butadiene rubber and/or an emulsion polymerized styrene-butadiene rubber per 100 parts by mass of the diene rubber,

from 80 parts by mass to 150 parts by mass of silica,

from 0.5 parts by mass to 10 parts by mass of a cyclic polysulfide expressed by Formula 1 below, and

from 3 mass % to 10 mass % of an alkyltriethoxysilane having an alkyl group having from 3 to 20 carbons relative to an amount of the silica



(in Formula 1, R is a substituted or unsubstituted alkylene group having from 4 to 8 carbons, or a substituted or unsubstituted oxyalkylene group having from 4 to 8 carbons; x is a number averaging from 3 to 5; and n is an integer from 1 to 5).

The pneumatic tire according to an embodiment of the present technology is made of the rubber composition for a tread with the composition described above. Thus, it can provide excellent dry performance and wet performance, reduced rolling resistance, and enhanced wear resistance at high speeds. Dry performance and wet performance are relatively difficult to enhance via only modifying the physical properties of the rubber composition for a tread. However, by setting the groove area ratio Sin and the difference ΔS in the appropriate ranges described above, these performances can be obtained in a well-balanced manner to a high degree. In addition to the relationship described above, by setting the groove area ratio Sout to from 20% to 30%, dry performance and wet performance can be further effectively enhanced.

In an embodiment of the present technology, preferably the silica has a CTAB (cetrimonium bromide) adsorption specific surface area ranging from 180 m2/g to 250 m2/g. This improves the physical properties of the rubber composition for a tread and is advantageous in obtaining good dry performance, wet performance, rolling resistance, and wear resistance at high speeds in a compatible manner.

In an embodiment of the present technology, preferably from 1 part by mass to 25 parts by mass of an aromatic terpene resin is blended per 100 parts by mass of the diene rubber. This improves the physical properties of the rubber composition for a tread and is advantageous in obtaining good dry performance, wet performance, rolling resistance, and wear resistance at high speeds in a compatible manner.

Note that in the present technology, the groove area ratio Sin of the vehicle inner side region and the groove area ratio Sout of the vehicle outer side region are groove area ratios for within the ground contact region of the tread portion and are ratios (%) of the total area of groove portions in the region to the total area of the region including land portions and groove portions. “Ground contact region” is the region between end portions (ground contact edges) in the tire axial direction of the surface (ground contact surface) that comes into contact with the surface the tire is placed on when the tire is mounted on a regular rim and inflated to a regular internal pressure, and placed vertically upon a flat surface with a regular load applied thereto. “Regular rim” is a rim defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a “standard rim” in the case of JATMA, refers to a “design rim” in the case of TRA, and refers to a “measuring rim” in the case of ETRTO. “Regular internal pressure” is an air pressure defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to a “maximum air pressure” in the case of JATMA (Japan Automobile Tyre Manufacturers Association, Inc.), refers to a maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA (The Tire and Rim Association, Inc.), and refers to the “INFLATION PRESSURE” in the case of ETRTO (European Tire and Rim Technical Organization). “Regular internal pressure” is 180 kPa for a tire on a passenger vehicle. “Regular load” is a load defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a “maximum load capacity” in the case of JATMA, refers to a maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, and refers to “LOAD CAPACITY” in the case of ETRTO. If the tire is for use with a passenger vehicle, a load corresponding to 88% of the loads described above is used.

