Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-07-11
2001-03-06
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C152S209100, C525S349000
Reexamination Certificate
active
06197890
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition for a tire tread and a pneumatic tire using the rubber composition, and more particularly, to a rubber composition for a tire tread which provides both an excellent controllability (herein after referred to as controllability) and an excellent vibration quality in a car ride (hereinafter referred to as ride quality) throughout its life, and a pneumatic tire using the rubber composition.
2. Description of the Related Art
Due to the recent higher power, the greater functionality, and the longer life among automobiles, it is required to provide tires achieving high levels in controllability and in ride quality simultaneously and maintain the performances on the road throughout its life. Particularly, as tires for passenger cars change from bias tires to radial tires and the aspect ratio of radial tires changes from 82 to 70, and further to 65, ride quality is not always improved even though controllability is remarkably improved. Therefore, it is strongly desired that both properties simultaneously exhibit high levels.
In order to satisfy the above-mentioned requirements, various rubber additives for a tire tread have been discussed. For example, regarding a vulcanization accelerator, Japanese Patent Application Laid-Open (JP-A) No. 58-87138 discloses that the resistant to thermoset and appearance of a tire in the final period of its use can be improved by using a rubber composition comprising a combination of a specific antioxidant and a specific vulcanization accelerator, yet nothing is mentioned about the improvement of tire performance, e.g., controllability and ride quality. In JP-A No. 56-139542, a specific vulcanization accelerator is disclosed, and it is therein described that the workability of a rubber composition, especially the scorching property upon kneading, can be improved by using this vulcanization accelerator, yet nothing is mentioned about tire performance using the vulcanization accelerator.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a rubber composition for a tire tread which exhibits both excellent controllability and excellent ride quality throughout the tire life and a pneumatic tire using the rubber composition.
The present inventors focused on polymers and various ingredients mixed into a tread rubber composition, and it was discovered that the above object can be achieved by the following means.
Accordingly, the present invention provides:
(1) a rubber composition for a tire tread which comprises 100 parts by weight of a rubber component comprising 50 parts by weight or more of styrene-butadiene rubber (SBR) and a remaining amount of a synthetic rubber and/or natural rubber; as well as 25 parts by weight or more of a softener and 0.5 to 5.0 parts by weight of a vulcanization accelerator represented by the following general formula (I):
wherein R
1
and R
2
each independently represents an atom or a group selected from a group consisting of a hydrogen atom, alkyl groups, and aryl groups, excluding a case in which each of R
1
and R
2
simultaneously represents a hydrogen atom;
(2) a rubber composition according to (1), wherein the alkyl group represented by R
1
or R
2
is selected from alkyl groups having 1 to 6 carbon atoms;
(3) a rubber composition according to (2), wherein the alkyl group is a methyl group or an ethyl group;
(4) a rubber composition according to (1), wherein the aryl group represented by R
1
or R
2
is selected from aryl groups having 6 to 10 carbon atoms;
(5) a rubber composition according to (4), wherein the aryl group is a phenyl group;
(6) a rubber composition according to (1), wherein the vulcanizing accelerator is at least one type selected from a group consisting of bis(monoalkylbenzothiazolyl-2)-disulfides and 2-mercapto-monoalkylbenzothiazoles;
(7) a rubber composition according to (6), wherein the bis(monoalkylbenzothiazolyl-2)-disulfide is at least one type selected from a group consisting of bis(4-methyl-benzothiazolyl-2)-disulfide and bis(5-methylbenzo-thiazolyl-2)-disulfide;
(8) a rubber composition according to (6), wherein the 2-mercapto-monoalkylbenzothiazole is at least one type selected from a group consisting of 2-mercapto-4-methylbenzothiazole and 2-mercapto-5-methylbenzothiazole;
(9) a rubber composition according to (1), wherein the amount of SBR comprised in the rubber component is adjusted so that the styrene unit in SBR is 20% by weight or more of the total rubber component;
(10) a rubber composition according to (1), wherein SBR containing 30% to 70% by weight of styrene is comprised;
(11) a rubber composition according to (9), wherein SBR containing 30% to 70% by weight of styrene is comprised;
(12) a rubber composition according to (1), wherein the softener is an aromatic oil;
(13) a rubber composition according to (9), wherein the softener is an aromatic oil;
(14) a rubber composition according to (10), wherein the softener is an aromatic oil; and
(15) a pneumatic tire comprising a tread composed of a multilayerora single layer, wherein the rubber composition of at least one of the layers comprises 100 parts by weight of a rubber component comprising 50 parts by weight or more of SBR and a remaining amount of a synthetic rubber and/or natural rubber; as well as 25 parts by weight or more of a softener and 0.5 to 5.0 parts by weight of a vulcanization accelerator represented by the following general formula (I):
wherein R
1
and R
2
each independently represents an atom or a group selected from a group consisting of a hydrogen atom, alkyl groups, and aryl groups, excluding a case in which each of R
1
and R
2
simultaneously represents a hydrogen atom.
Moreover, in the pneumatic tire of the present invention, the rubber composition in the tread composed of a multilayer or a single layer satisfies the conditions described in any one of (1) to (14).
An excellent effect is exhibited by each of the above mentioned rubber composition for a tire tread, such that the tire using the rubber composition in its tread can maintain high levels of controllability and ride quality throughout its life.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is necessary that the rubber composition comprises 50 parts by weight or more, preferably 70 parts by weight or more, of SBR per 100 parts by weight of the rubber component. When the amount of SBR is less than 50 parts by weight, controllability and ride quality are inferior, and such an amount is not preferable. It is also preferable that the content of SBR in the rubber component is adjusted so that the styrene unit in SBR is 20% by weight or more, preferably from 20% to 70% by weight, of the total rubber component. This means, 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, the content of the styrene unit in SBR should be 40% by weight or more.
In another embodiment, it is preferable that SBR containing 30% to 70% by weight of styrene is comprised in the rubber component. 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 are mixed together as the rubber composition, the obtained composition is also included in the present invention although the content of the styrene unit in total 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 emulsion 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, natural rubber, and synthetic rubbers, such as isoprene rubber, butadiene rubber, butyl rubber (including halogenated butyl rubber), and ethylene-propylene rubber, can be used in combination with SBR.
The rubber composition of the present invention comprises a softener in an amount of
Nakamura Eiji
Okamura Nobuyuki
Bridgestone Corporation
Henderson Christopher
Sughrue Mion Zinn Macpeak & Seas, PLLC
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