Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-04
2003-12-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S492000, C524S493000, C524S494000, C524S495000, C524S496000
Reexamination Certificate
active
06656992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition providing a tire which exhibits improved abrasion resistance while the excellent performance on wet roads and the low fuel consumption exhibited by a tire using a conventional rubber composition containing aluminum hydroxide are maintained.
2. Description of the Related Arts
Carbon black is generally used as the reinforcing filler for rubber compositions because carbon black can provide higher reinforcing ability and more excellent abrasion resistance than other fillers to rubber compositions.
Energy saving is a recent social requirement and smaller heat buildup in a rubber composition for a tire, which means smaller rolling resistance of a tire, is required to achieve reduction of fuel consumption of automobiles. For this purpose, the amount of carbon black used in the rubber compositions may be decreased or carbon black having greater particle diameters may be used. However, it is known that the reinforcing property, abrasion resistance and the gripping property on wet roads are inevitably deteriorated in both cases.
As the filler which can satisfy the requirement for the low heat buildup while the reinforcing property, abrasion resistance and the gripping property on wet roads are maintained, precipitated silica is known, and many patent applications have been made on them. Examples of such applications include Japanese Patent Application Laid-Open Nos. Heisei 3(1991)-252431, Heisei 6(1994)-248116, Heisei 7(1995)-70369, Heisei 7(1995)-188466, Heisei 7(1995)-196850, Heisei 8(1996)-225684, Heisei 8(1996)-245838 and Heisei 8(1996)-337687.
However, precipitated silica has a drawback in that a rubber composition containing precipitated silica has a smaller storage modulus than a rubber composition containing carbon black having approximately the same specific surface area, and provides a tire showing inferior driving performance on dry roads.
It is known that the gripping property on wet roads can be improved by raising the glass transition temperature (Tg) of rubber, i.e., by increasing tan &dgr; at 0° C. However, raising Tg of rubber causes problems in that properties at low temperatures become inferior, and in that rolling resistance increases, i.e., the low fuel consumption deteriorates.
Various technologies have been disclosed to overcome the above problems. Examples of such technologies include: (1) a rubber composition for a tire tread which provides an improved gripping property on wet roads by the use of a specific silica and of an improved mixing method (European Patent No. 501227); (2) a rubber composition for a tire tread which provides improved wet skid resistance while maintaining low heat buildup property without adverse effect on workability and abrasion resistance (Japanese Patent Application Laid-Open No. Heisei 7(1995)-149950); (3) a rubber composition for a tire tread which provides an improved gripping property on wet roads and semi-wet roads in low and high temperature ranges and improved workability (Japanese Patent Application Laid-Open No. Heisei 8(1996)-59893); and (4) a rubber composition for a tire tread which provides an improved gripping property on wet roads and semi-wet roads in low and high temperature ranges without adverse effect on abrasion resistance (Japanese Patent Application Laid-Open No. Heisei 8(1996)-59894).
However, the above technologies have drawbacks. In the technology described in (1), the rubber composition shows inferior workability (processability). In the technology described in (2), the rubber composition does not provide sufficient abrasion resistance. In the technologies described in (3) and (4), the reinforcing filler must be used in an excessively great amount.
On the other hand, it is known that aluminum hydroxide can be used as a reinforcing filler for rubber. A tire in which a rubber composition containing aluminum hydroxide is used for its tire tread shows excellent performance, such as the gripping property on wet roads, and provides the low fuel consumption. However, this tire has a drawback in that abrasion resistance is inferior.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a rubber composition for a tire tread which, when the rubber composition is used for a tire tread for automobiles, provides improved abrasion resistance while the excellent performance on wet roads and the low fuel consumption exhibited by a tire using a conventional rubber composition containing aluminum hydroxide are maintained.
As the result of intensive studies by the present inventors to develop a rubber composition having the above advantageous properties, it was found that the above object can be achieved by mixing a specific amount of specific aluminum hydroxide particles with a rubber component selected from the group consisting of natural rubber and synthetic diene-based rubbers and using a specific amount of carbon black and/or silica powder in combination. The present invention has been completed on the basis of this knowledge.
The present invention provides a rubber composition for a tire tread which comprises (A) a rubber component selected from the group consisting of natural rubber and synthetic diene-based rubbers, (B) 5 to 50 parts by weight per 100 parts by weight of the rubber component of (b1) aluminum hydroxide particles which are treated with a surface treating agent on a surface and have an average diameter of secondary D
2
of 10 &mgr;m or smaller or (b2) aluminum hydroxide particles which have an average diameter of secondary particles D
2
of 0.8 &mgr;m or smaller and a ratio (D
2
/D
1
) of the average diameter of secondary particles D
2
to an average diameter of primary particles D
1
of 1.7 or smaller and (C) 5 to 80 parts by weight per 100 parts by weight of the rubber component of at least one filler selected from carbon black and silica.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the rubber composition of the present invention, natural rubber and/or synthetic diene-based rubbers are used as component (A). Examples of the synthetic diene-based rubber include synthetic polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR) and butyl rubber (IIR).
A single type or a combination of two or more types of natural rubber and/or synthetic diene-based rubbers may be used as component (A).
As the aluminum hydroxide particles D
2
of component (b
1
) used in the rubber composition of the present invention, aluminum hydroxide particles which are treated with a surface treating agent on the surface and have an average diameter of secondary particles D
2
of 10 &mgr;m or smaller are used. The surface of the aluminum hydroxide particles (aluminum hydroxide powder) is treated with a surface treating agent so that particles having particularly large diameters in the used particles do not work as nuclei of failure and formation of aggregates of aluminum hydroxide particles which may work as nuclei of failure is prevented.
When the average diameter of secondary particles D
2
in the aluminum hydroxide particles which are treated with a surface treating agent on the surface exceeds 10 &mgr;m, the reinforcing effect is not sufficiently exhibited to cause inferior abrasion resistance and, moreover, the gripping property on wet roads (the performance on wet roads) becomes inferior. Moreover, as the average diameter of secondary particles D
2
becomes smaller, the particles agregates more readily. As a result, the properties of the rubber compostion may be detriorated due to the insufficient dispersion of the particles into rubber. From the standpoint of the balance between abrasion resistance, the performance on wet roads and the low fuel consumption, the average diameter of secondary particles D
2
in the aluminum hydroxide particles is preferably in the range of 0.2 to 10.0 &mgr;m and more preferably in the range of 0.4 to 0.8 &mgr;m.
The surfa
Ezawa Naofumi
Fukushima Yasuo
Shibusawa Susumu
Bridgestone Corporation
Rajguru U. K
Seidleck James J.
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