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
1998-05-26
2001-12-25
Mulcahy, Peter D. (Department: 1713)
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...
C524S398000, C524S399000, C524S400000
Reexamination Certificate
active
06333375
ABSTRACT:
TECHNICAL FIELD
This invention relates to rubber compositions which yield vulcanized rubbers showing improvements in heat build-up, tensile strength, abrasion resistance and processability.
BACKGROUND ART
In recent years, as growing importance is attached to resource saving and environmental protection, the demand for a reduction in the fuel consumption of automobiles has become increasingly stronger. Also for automobile tires, it is desired to reduce their rolling resistance and thereby contribute to a reduction in fuel consumption. In order to reduce the rolling resistance of tires, it is common practice to use, as the rubber material for tires, a rubber material which can yield a vulcanized rubber showing a low degree of heat build-up.
Conventionally, it has been proposed to reduce heat build-up by using, as the rubber material for tires, a rubber composition comprising a diene rubber into which, in place of carbon black, silica is incorporated as a reinforcing agent. However, as compared with carbon black-filled rubber compositions, such silica-filled rubber compositions have the disadvantage that they fail to achieve sufficient abrasion resistance and tensile strength. One of the causes therefor is believed to be that silica has a lower affinity for diene rubbers than carbon black and hence fails to exhibit a sufficient reinforcing effect.
Conventionally, a method for enhancing the affinity of silica for diene rubbers by using a silane coupling agent has been proposed (Japanese Patent Laid-Open No. 252431/'91. Japanese Patent Laid-Open No. 252433/'91, etc.). However, in order to achieve a satisfactory effect, this method requires the use of a large amount of an expensive silane coupling agent.
As another improvement, the use of a diene rubber into which a substituent group having an affinity for silica has been introduced is being investigated. For example, diene rubbers having a tertiary amino group introduced thereinto (Japanese Patent Laid-Open No. 101344/'89) have been proposed for diene rubbers formed by emulsion polymerization; and diene rubbers having introduced thereinto an alkylsilyl group (Japanese Patent Laid-Open No. 188501/'89), a halogenated silyl group (Japanese Patent Laid-Open No. 230286/'93) or a substituted amino group (Japanese Patent Laid-Open No. 22940/'89) have been proposed for diene rubbers formed by anionic polymerization.
However, most of the diene rubbers having the aforesaid substituent groups introduced thereinto show poor processability because, when they are mixed with silica, they cohere strongly with silica and cannot be dispersed satisfactorily. Moreover, they also have the disadvantage that their properties such as heat build-up, tensile strength and abrasion resistance are not fully improved.
An object of the present invention is to provide a rubber composition containing a diene rubber component and a reinforcing agent, and capable of yielding a vulcanized rubber which shows a low degree of heat build-up, exhibits excellent tensile strength and abrasion resistance, and has good processability.
DISCLOSURE OF INVENTION
The present inventors have made intensive investigations with a view to overcoming the above-describe problems of the prior art. As a result, it has now been discovered that a composition obtained by incorporating a fatty acid salt (e.g., calcium stearate) into a mixture of a diene rubber and a reinforcing agent can yield a vulcanized rubber showing improvements in heat build-up, tensile strength, abrasion resistance and processability. The present invention has been completed on the basis of this discovery.
Thus, the present invention provides a rubber composition comprising 100 parts by weight of a diene rubber component, 10 to 200 parts by weight of a reinforcing agent, and 0.1 to 15 parts by weight of a fatty acid salt.
Diene Rubber Component
No particular limitation is placed on the type of the diene rubber component used in the present invention, provided that it is a rubber-like polymer formed chiefly from a conjugated diene. Specific examples thereof include natural rubber (NR), polyisoprene rubber (IR), emulsion-polymerized styrene-butadiene copolymer rubber (SBR), solution-polymerized random SBR (containing 5 to 50% by weight of bound styrene and having a 1,2-linkage content of 10 to 80% in the portions consisting of combined butadiene units), high-trans SBR (having a trans-form content of 70 to 95% in the portions consisting of combined butadiene units), low-cis polybutadiene rubber (BR), high-cis BR, high-trans BR (having a trans-form content of 70 to 95% in the portions consisting of combined butadiene units), styrene-isoprene copolymer rubber (SIR), butadiene-isoprene copolymer rubber, solution-polymerized random styrene-butadiene-isoprene copolymer rubber (SIBR), emulsion-polymerized SIBR, high-vinyl SBR/low-vinyl SBR block copolymer rubber, and block copolymers such as polystyrene-polybutadiene-polystyrene block copolymers. Among them, NR, BR, IR, SBR and SIBR are preferred. From the viewpoint of processability, NR and IR are particularly preferred.
Diene Rubbers Having a Heteroatom-containing Polar Group
In the present invention, it is preferable to use, as the diene rubber component, a diene rubber having a heteroatom-containing polar group or a combination of a diene rubber having a heteroatom-containing polar group and another diene rubber, because they can give a highly balanced combination of properties such as heat build-up, tensile strength, abrasion resistance and processability.
The term “heteroatom” as used herein means an atom of an element belonging to the second to fourth periods of the period table and to group VB or VIB thereof. Specific examples thereof include nitrogen, oxygen, sulfur and phosphorus atoms. Among them, nitrogen and oxygen atoms are preferred.
Polar groups containing such a heteroatom include, for example, hydroxyl, oxy, epoxy, carboxyl, carbonyl, oxycarbonyl, sulfide, disulfide, sulfonyl, sulfinyl, thiocarbonyl, imino, amino, nitrile, ammonium, imido, amido, hydrazo, azo and diazo groups. Among them, hydroxyl, oxy, epoxy, sulfide, disulfide, imino and amino groups are preferred; hydroxyl, amino and oxy groups are more preferred; and hydroxyl and amino groups are most preferred.
No particular limitation is placed on the type of the diene rubber having a heteroatom-containing polar group, provided that it is a diene rubber having, in the molecule, at least one polar group as described above. Specifically, the diene rubber having a heteroatom-containing polar group may comprise, for example, (1) a polar group-containing diene rubber such as a copolymer formed from a vinyl monomer having a heteroatom-containing polar group and a conjugated diene, or a copolymer formed from a vinyl monomer having a heteroatom-containing polar group, a conjugated diene and an aromatic vinyl, or (2) a polar group-containing diene rubber obtained by providing a polymer of a conjugated diene which has a combined active metal in the molecule or a copolymer of a conjugated diene and an aromatic vinyl which has a combined active metal in the molecule, and reacting the (co)polymer with a modifying agent to introduce a heteroatom-containing polar group into the (co)polymer.
In the above-described diene rubber (1) having a heteroatom-containing polar group which is formed by copolymerization, the contents of various monomers may be suitably chosen according to the intended purpose. In the case of a copolymer formed from a vinyl monomer having a heteroatom-containing polar group and a conjugated diene, the content of combined vinyl monomer units having a heteroatom-containing polar group is usually in the range of 0.01 to 20% by weight, preferably 0.05 to 15% by weight, and more preferably 0.1 to 10% by weight; and the content of combined conjugated diene units is usually in the range of 80 to 99.99% by weight, preferably 85 to 99.95% by weight, and more preferably 90 to 99.9% by weight. In order to achieve a highly balanced combination of heat build-up and wet skid resistan
Nakamura Masao
Takagishi Yukio
Mulcahy Peter D.
Zeon Corporation
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