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
2002-02-28
2004-03-02
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C525S241000
Reexamination Certificate
active
06699935
ABSTRACT:
FIELD OF THE ART
The present invention relates to a rubber composition with a specific composition. Vulcanized rubber made of the rubber composition of the present invention shows low rolling resistance and excellent wet skid resistance, as well as satisfactory wear resistance, tensile strength and the like, and is particularly useful for tire treads.
BACKGROUND ART
Recent requirements for lower fuel consumption by automobiles have created a need for a composition such as conjugated diene-based rubber compositions whose rubbers have low rolling resistance, excellent wear resistance and fracture properties, and high wet skid resistance as a representative indicator of good driving stability.
The tire rolling resistance can be reduced by lowering hysteresis loss of the vulcanized rubber. This hysteresis loss can be evaluated based on various properties. For example, a composition having high impact resilience at 50 to 80° C., low tan &dgr; at 50 to 80° C. or low Goodrich heat release, is preferable. A raw rubber having low hysteresis loss include natural rubber, isoprene rubber, butadiene rubber and the like, but these are also associated with the problem of low wet skid resistance.
On the other hand, there have been proposed a method of using an inorganic filler such as silica and the like as a reinforcing agent, or a method of combining an inorganic filler and carbon black in recent years. Tire treads employing an inorganic filler or both an inorganic filler and carbon black show low rolling resistance and excellent driving stability represented by wet skid resistance. However, they exhibit a problem of poor wear resistance, tensile strength and the like for the vulcanized rubber. The cause is believed to be the fact that the affinity of the inorganic filler for the conjugated diene-based rubber is lower than that of the carbon black, such that a sufficient reinforcing effect cannot be achieved.
In order to increase the affinity between the inorganic filler and the conjugated diene-based rubber, it has been attempted to use a conjugated diene-based rubber introduced a functional group with affinity for an inorganic filler therein. For example, there have been proposed a conjugated diene-based rubber introduced a hydroxyl group therein (WO96/23027), a conjugated diene-based rubber introduced an alkoxysilyl group therein (JP-A-9-208623) and a conjugated diene-based rubber introduced an alkoxysilyl group and an amino and/or a hydroxyl group therein (JP-A-9-208633). However, most conjugated diene-based rubbers introduced such functional group exhibit strong interaction with the inorganic filler when the inorganic filler is combined therewith, and this creates such problems as impaired dispersion of the inorganic filler, greater heat release during processing, poor proccessability and the like.
It is an object of the invention to overcome the problems referred to above by providing a rubber composition which can give a vulcanized rubber having low rolling resistance and excellent wet skid resistance, as well as satisfactory wear resistance and tensile strength, which is useful for automobile tire treads and the like.
DISCLOSURE OF THE INVENTION
A rubber composition for formation of a tire tread and the like usually contains a reinforcing agent for the purpose of improving tensile strength and wear resistance, but an inorganic filler such as silica is not easily dispersed uniformly because of their tendency to aggregate. Using a rubber composition in which a reinforcing agent is not uniformly dispersed leads to a result that a desired effect of including the reinforcing agent cannot be achieved, as well as that the proccessability is also notably impaired. For this reason, it has generally been attempted to improve the dispersion properties by formulating a silane coupling agent when using a silica as an inorganic filler. However, it was found that inclusion of fine particles composed of crosslinked rubber having a specific composition in a rubber composition can adequately improve tensile strength even with a small amount of a silane coupling agent or even without including a silane coupling agent, and that the resulting rubber composition has excellent proccessability.
The present invention is based on the findings described above and can be described as follows.
A rubber composition of the first aspect of the invention is characterized in that it comprises [1A] a crosslinked rubber particle containing, as repeating units, (a1) 40 to 79.99% by weight of a conjugated diene monomer unit, (a2) 20 to 50% by weight of an aromatic vinyl monomer unit and (a3) 0.01 to 10% by weight of a monomer unit formed by a monomer having at least two polymerizable unsaturated groups with respect to 100% by weight of the total of (a1), (a2) and (a3), and [2A] a conjugated diene/aromatic vinyl copolymeric rubber wherein vinyl bond content of the conjugated diene unit is 10 to 30% by weight and 1,4-trans bond content is exceeding 55% by weight.
A rubber composition of the second aspect of the invention is characterized in that it comprises [1B] a crosslinked rubber particle containing, as repeating units, (b1) 40 to 99.89% by weight of a conjugated diene monomer unit, (b2) 0 to 50% by weight of an aromatic vinyl monomer unit, (b3) 0.01 to 10% by weight of a monomer unit formed by a monomer having at least two polymerizable unsaturated groups and (b4) 0.1 to 30% by weight of a monomer unit formed by a monomer having one polymerizable unsaturated group and at least one functional group selected from the group consisting of carboxylic group (CO
2
H and/or CO
2
−
), hydroxyl group and epoxy group with respect to 100% by weight of the total of (b1), (b2), (b3) and (b4), and [2B] a conjugated diene/aromatic vinyl copolymeric rubber wherein vinyl bond content of the conjugated diene unit is 10 to 30% by weight and 1,4-trans bond content is exceeding 55% by weight.
The crosslinked rubber particle according to the first aspect of the invention is prepared by polymerizing a conjugated diene monomer forming a conjugated diene monomer unit (a1), an aromatic vinyl monomer forming an aromatic vinyl monomer unit (a2), and a monomer having at least two polymerizable unsaturated groups.
And the crosslinked rubber particle according to the second aspect of the invention is prepared by polymerizing a conjugated diene monomer forming a conjugated diene monomer unit (b1), an aromatic vinyl monomer forming an aromatic vinyl monomer unit (b2) as necessary, a monomer having at least two polymerizable unsaturated groups, and a monomer having one polymerizable unsaturated group and at least one functional group selected from the group consisting of carboxylic group (CO
2
H and/or CO
2
−
), hydroxyl group and epoxy group.
In both first and second aspects of the invention, another polymerizable unsaturated monomer described hereunder may also be used.
As the conjugated diene monomer forming the conjugated diene monomer unit (a1) and (b1) described above, there may be used 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, chloroprene and the like. Any of these monomers may be used alone or in combination of two or more, respectively.
The content of the conjugated diene monomer unit (a1) according to the first aspect of the invention is 40 to 79.99% by weight and preferably 55 to 79.99% by weight. The content of the conjugated diene monomer unit (b1) according to the second aspect of the invention is 40 to 99.89% by weight and preferably 55 to 99.89% by weight. If the content of the conjugated diene monomer unit described above is under the respective lower limits, proccessability is not improved and tensile strength of the vulcanized rubber is lowered.
As the aromatic vinyl monomer forming the aromatic vinyl monomer unit (a2) and (b2) described above there may be used styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, &agr;-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, tert-butoxystyrenes and the like. These monomers may be used alon
Akema Hiroshi
Fueki Takafumi
Kondou Hajime
Konno Tomohisa
Tadaki Toshihiro
JSR Corporation
Nutter Nathan M.
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