Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1985-12-17
1988-04-12
Lilling, Herbert J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524285, 524311, 524313, 524314, 525237, 5253329, C08K 510, C08K 304
Patent
active
047375353
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a tire tread rubber composition improved in grip characteristics, steering stability and low temperature characteristics.
2. Background Art
In recent years, tires have been increasingly demanded to have a strong gripping force and a steering stability with development of automobiles having high performances. For instance, in order to increase an area contacting the ground, tires having an aspect ratio as high as 60% or 50% are developed and put on the market. With respect to such tires, from the viewpoint of the structure, the responsibility is improved by making the surface of tread flat to increase the effective ground-contacting area and increasing the width of a steel belt to increase the rigidity of the tread portion, and improvements in cornering characteristics and handle responsiblity are contemplated by reinforcing the bead portion with fibers or steel cords. Also, from the viewpoint of the formulation for tread rubber which directly contacts the surface of road, a high styrene SBR which has a high styrene content is mainly employed as a polymer for the purpose of improving the grip characteristic, and also, in recent years, it is proposed to use a solution-polymerized SBR, the styrene content and vinyl content of which are somewhat higher than those of a conventional emulsion-polymerized SBR, in tread rubber for such high performance tires.
Further, as carbon black, those called N 339, N 200, N 110, etc. in ASTM which have a relatively small particle size are used in a large amount to make the hardness somewhat higher than that of general tires, whereby improvements in responsibility and steering characteristics are contemplated.
Since in such high performance tires the grip characteristic is improved by using a high styrene SBR or solution-polymerized SBR having a high glass transition temperature (Tg), the tires have the drawback that under a low temperature condition like the winter season, the rubber becomes hard, so the tread surface cannot meet small roughness of the road, thus the effective ground-contacting area is decreased and consequently the grip is lowered. When the hardness at a low temperature is lowered, for instance, by using a softening agent such as an oil, etc. in order to eliminate this drawback, the hardness at ordinary temperature is also lowered simultaneously, thus resulting in lowering of the handle responsibility. This has hitherto been a problem.
DISCLOSURE OF THE INVENTION
The present invention relates to an improvement in the drawback that a conventional high performance tire tread rubber wholly loses the grip characteristic at a low temperature because of becoming hard, when such a hardness as exhibiting steering characteristics at a temperature in running is imparted to the rubber.
That is to say, the present invention relates to an entirely new tread rubber composition that the grip characteristic and steering stability characteristic are maintained by using an improved solution-polymerized SBR and the low temperature characteristics are improved by using a low-temperature resisting plasticizer.
In accordance with the present invention, there is provided a rubber composition for tire tread comprising 15 to 50 parts by weight of a solution-polymerized styrene-butadiene rubber which has an intrinsic viscosity of from not less than 1.7 to less than 3.0 in toluene at 30.degree. C., a bonded styrene content of from not less than 27% by weight to less than 40% by weight and a vinyl content in butadiene portion of from not less than 37% by weight to less than 45% by weight, and in which the proportion of the polymer chains modified with a trifunctional or tetrafunctional coupling agent if from 40 to 65% by weight, 50 to 85 parts by weight of at least one rubber selected from the group consisting of an emulsion-polymerized styrene-butadiene rubber, natural rubber, a synthetic polyisoprene rubber and a butadiene rubber, at least one plasticizer selected from the group consisting of a sebacic acid ester, an
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Furukawa Hiroshi
Imai Akio
Saito Yuichi
Yoshida Nobuyuki
Lilling Herbert J.
Sumitomo Chemical Company Limited
Sumitomo Rubber Industries Ltd.
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