Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1997-09-05
2002-01-01
Lipman, Bernard (Department: 1713)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S548000, C152S564000, C525S332600, C525S332800, C525S332900, C525S333100, C525S333200, C525S341000
Reexamination Certificate
active
06334476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire showing excellent controllability at high speed (hereinafter, referred to as high speed controllability).
2. Description of Related Art
In recent years, it has become important that automobiles show higher speed performance due to the growing network of expressways. Therefore, excellent high speed controllability is required not only in sports car tires but also in tires of family cars.
As one of the methods to satisfy the requirement, tires having a radial structure, particularly low profile radial tires are used. The size of a low profile radial tire is different from the size of a conventional tire. Replacing a tire with another tire having a different size is restricted by the size of the tire house of the vehicle to which the tires are attached, in other words, by the design of the vehicle. Moreover, when an owner of a vehicle equipped with conventional tires replaces the conventional tires with low profile radial tires to obtain enhanced high speed controllability, the radius of the wheels is usually increased, and new wheels have to be bought. Therefore, a means of increasing high speed controllability with tires of the same size has been desired.
To solve the above problem, improvement in a rubber composition for tire tread has been attempted, and specific combinations of polymer, carbon black, and softener have been examined. However, satisfactory improvement in high speed controllability of tires has not been achieved. As for the case in which a vulcanizing agent and a vulcanization accelerator are particularly examined among components of rubber composition, a rubber composition is proposed in Japanese Patent Application Laid-Open No. (JPA) 52-40549, in which natural rubber or synthetic isoprene rubber is used as a rubber component, and a zinc dithiophosphate is used as a reversion inhibitor. However, this rubber composition is used for preventing reversion, and no description or suggest ion is found about tire performance. In JPA 54-85243, it is proposed that vulcanization in which no sulfur is used can be conducted by a rubber composition comprising (1) a derivative of benzothiazole and (2) a compound selected from a group consisting of zinc dithiophosphates, metal xanthates, and amine salts of dithiocarbamic acid in specific amounts relative to the amount of a diene rubber. However, this technology is not related to improvement in tire performance.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above facts, and the object of the present invention is to provide a pneumatic tire having excellent high speed controllability.
The present inventors conducted extensive studies on polymers and various types of ingredients which are compounded into tread rubber, and found that by the following means the above object can be achieved and the present invention can be completed.
Accordingly, the present invention provides a pneumatic tire comprising a tread,
wherein the rubber composition of the tread layer comprises 50 parts by weight or more of SBR in 100 parts by weight of the rubber component and, in an amount of 0.2 to 5.0 parts by weight to 100 parts by weight of the rubber component, a vulcanization accelerator represented by the following general formula (I):
wherein R
1
and R
2
each independently represents an alkyl group having 1 to 10 carbon atoms which may be linear, branched, or cyclic or an aryl group having 6 to 10 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is necessary that the rubber composition of the tread layer comprises 50 parts by weight or more, preferably 70 parts by weight or more, of SBR in 100 parts by weight of the rubber component. When the amount of SBR is less than 50 parts by weight, the property of gripping road surfaces which contributes to controllability is inferior, and such an amount is not preferable.
It is also preferable that the rubber composition comprises SBR in an amount such that the amount of the styrene units in the SBR contained in 100% by weight of the rubber component is 20% by weight or more. When the amount of the styrene units in the SBR contained in the rubber component is 20% by weight or more, hysteresis loss generated by the cohesive energy of styrene is increased, and the property of gripping road surfaces can be improved. For example, when 50 parts by weight of SBR is mixed with 50 parts by weight of natural rubber used as the other component of the rubber component, this means that the content of the styrene units in the SBR is 40% by weight or more.
In another embodiment, it is preferable that the rubber composition comprises SBR containing 30% by weight or more of styrene in 100 parts by weight of the rubber component. When SBR containing 30% by weight or more of styrene is comprised, the property of gripping road surfaces can be improved even when the content of the styrene unit in 100% by weight of the total rubber component is less than 20% by weight because SBR containing a large amount of styrene forms microscopic domains, and the hysteresis loss generated by the cohesive energy of styrene is increased. For example, when 10 parts by weight of SBR containing 35% by weight of styrene, 40 parts by weight of SBR containing 23.5% by weight of styrene, and 50 parts by weight of natural rubber used as the other component of the rubber component are mixed together, the obtained composition is also included in the preferred embodiment of the present invention although the content of the styrene units in 100% by weight of the obtained rubber component is less than 20% by weight.
An example of SBR used in the present invention may be, but is not limited to, commercially available emulsified polymerized SBR, solution polymerized SBR, and the like, so long as the SBR is satisfactory with regard to the above-mentioned requirements.
In the present invention, other types of SBR, natural rubber, and synthetic rubbers, such as isoprene rubber, butadiene rubber, butyl rubber (including halogenatedbutyl rubber) , and ethylene-propylene rubber, can be used in the rubber component in combination with SBR specified in the present invention.
In the present invention, the rubber composition preferably comprises a softener in an amount of 20 parts by weight or more, more preferably 25 to 60 parts by weight for desired effects, to 100 parts by weight of the rubber component. When the amount of the softener is less than 20 parts by weight, the surface of the prepared rubber is too hard and cannot absorb the roughness of the road, and the property of gripping road surfaces is decreased. Therefore, such an amount is not preferable. An aromatic oil is preferably used as the softener. The aromatic oil is not particularly limited and can be selected from the many types of commercially available aromatic oils.
It is necessary that the rubber composition of at least one of the rubber cap layer and the rubber base layer in the tread layer composed of two layers, or the rubber composition of the tread layer composed of a single layer comprise 0.2 to 5.0 parts by weight, preferably 0.2 to 2.0 parts by weight, of the vulcanization accelerator represented by the above general formula (I) per 100 parts by weight of the rubber component. When the amount is less than 0.2 parts by weight, the effect of increasing high speed controllability is low. When the amount exceeds 5.0 parts by weight, no further increase in the effect is seen. Thus, any addition above 5.0 parts by weight is uneconomical.
In the following general formula (I) representing the vulcanization accelerator used in the present invention, i.e., a zinc dithiophosphate, R
1
and R
2
each independently represents an alkyl group having 1 to 10 carbon atoms which may be linear, branched, or cyclic or an aryl group having 6 to 10 carbon atoms.
R
1
and R
2
each is preferably an alkyl group having 3 to 4 carbon atoms, such as the alkyl groups in the compounds expressed by the
Hojo Masahiro
Okamura Nobuyuki
Bridgestone Corporation
Lipman Bernard
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