Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-02-10
2003-11-18
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C525S232000, C525S241000, C525S191000, C524S836000
Reexamination Certificate
active
06649724
ABSTRACT:
TECHNICAL FIELD
This invention relates to a novel conjugated diene rubber gel, a rubber composition comprising the conjugated diene rubber gel, and a process for producing a conjugated diene rubber. More specifically it relates to a conjugated diene rubber gel capable of giving a rubber composition suitable for a tire having a high abrasion resistance and a low heat-build up, and the rubber composition comprising the conjugated diene rubber gel, and a process for producing a conjugated diene rubber with enhanced productivity.
BACKGROUND ART
In recent years, improvement of various properties is required for a rubber composition used for an automobile tire. Especially, improvement of mechanical properties, abrasion resistance and appropriately reduced rolling resistance (i.e., low heat-build up) is required for a rubber composition used for sidewall and bead of an automobile tire.
Natural rubber is consumed in a large amount for an automobile tire. In many cases, other rubbers are blended with natural rubber for improving various properties or natural rubber. In one example, a polybutadiene rubber is blended for improving the abrasion resistance, and, in another example, a styrene-butadiene copolymer rubber is blended for improving the mechanical properties. However, there is a basic contradiction between properties required for a tire rubber, and thus, all of the properties required for an automobile tire are difficult to satisfy concurrently. For example, enhancement of abrasion resistance is accompanied by mechanical properties, and enhancement of mechanical properties is accomplished by increase of heat-build up.
In view of miscibility of a rubber raw material with a reinforcing agent or other additives, it is usually desired that a rubber raw material does not have a gel structure. However, a rubber gel having a gel structure has been proposed for giving a rubber having low heat-build up and high abrasion resistance. For example, a rubber composition comprising a polychloroprene gel was proposed in Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) No. H3-37246. This rubber composition gives a rubber exhibiting satisfactory low heat-build up and high abrasion resistance, but, as the polychloroprene gel contains chlorine, it causes a problem of damaging the environment when scrap tires are incinerated, which makes it's practical use difficult.
Further, as for a conjugated diene rubber, a rubber composition comprising a polybutadiene gel, and a rubber composition comprising a styrene-butadiene copolymer rubber gel were proposed in JP-A H6-57038 and JP-A H10-204217, respectively. These rubber compositions give rubbers having satisfactory low heat-build up, but the resulting rubbers occasionally exhibit poor abrasion resistance, reduced breaking elongation and poor mechanical properties.
An emulsion polymerization procedure is widely employed for the production of a conjugated diene rubber. In the production process by an emulsion polymerization procedure, a latex prepared by emulsion polymerization in a manner such that a desired polymer composition is obtained is coagulated with an inorganic salt as a coagulant to form crumbs having a size of about 1 to 10 mm, water is separated therefrom, and the crumbs are washed and then dried to give an object rubber. However, for example, in the case where a butadiene-styrene copolymer rubber having a high, e.g. about 35 to 50% by weight of, bound styrene content is produced by an emulsion polymerization procedure, a latex as obtained by emulsion polymerization exhibits a poor coagulability, and therefore, there is a tendency such that the latex is partly non-coagulated and the thus-formed sticky crumbs are bonded together to form unusually large crumbs. Such large crumbs have a problem such that water tends to remain inside of each crumb and thus, a substantially long period is required for drying and partial drying failure occurs to form a wet spot. Further, the sticky crumbs are liable to be deposited on an inner wall of a coagulating vessel or on stirrer vanes.
To solve the above-mentioned problems caused by the sticky crumbs, procedures for appropriately adjusting the concentration of an inorganic salt coagulant, the solid content in the latex, the coagulation temperature and the stirring conditions, or for using a polymeric flocculant or a heat-sensitive coagulant in addition to the inorganic salt coagulant. However, the above-mentioned problems are difficult or even impossible to completely solve by these procedures.
DISCLOSURE OF THE INVENTION
In view of the foregoing, a first object of the present invention is to provide a conjugated diene rubber gel capable of giving a rubber composition exhibiting improved abrasion resistance and reduced heat-build up without deterioration of mechanical properties.
A second object of the present invention is to provide a rubber composition exhibiting improved abrasion resistance and reduced heat-build up without deterioration of mechanical properties.
A third object of the present invention is to provide a process for producing a conjugated diene rubber gel with enhanced productivity.
A fourth object of the present invention is to provide a process for producing a conjugated diene-aromatic vinyl copolymer rubber having a high bound aromatic vinyl content, which is characterized as forming non-sticky crumbs and exhibiting enhanced coagulability.
Thus, in a first aspect of the present invention, there is provided a conjugated diene rubber gel comprising 80% to 99% by weight of conjugated diene monomer units and 20% to 1% by weight of aromatic vinyl monomer units and having a swelling index in the range of 16 to 70 as mentioned in toluene.
In a second aspect of the present invention, there is provided a rubber composition comprising a conjugated diene rubber gel comprising 80% to 99% by weight of conjugated diene monomer units and 20% to 1% by weight of aromatic vinyl monomer units and having a swelling index in the range of 16 to 17 as measured in toluene, and a rubber capable of being crosslinked with sulfur.
In a third aspect of the present invention, there is provided a process for producing a conjugated diene rubber gel having a swelling index of not larger than 70 as measured in toluene, characterized in that a monomer mixture comprising 50% to 99.9% by weight of a conjugated diene monomer, 0% to 30% by weight of an aromatic vinyl monomer, 0% to 20% by weight of other ethylenically unsaturated monomer and 0.1% to 20% by weight of a crosslinking monomer is copolymerized by an emulsion polymerization procedure.
In a fourth aspect of the present invention, there is provided a process for producing a conjugated diene-aromatic vinyl copolymer rubber, characterized in that a monomer mixture comprising 15% to 69.8% by weight of a conjugated diene monomer, 30.1% to 65% by weight of an aromatic vinyl monomer, 0% to 20% by weight of other ethylenically unsaturated monomer and 0.1% to 20% by weight of a crosslinking monomer is copolymerized by an emulsion polymerization procedure.
BEST MODE FOR CARRYING OUT THE INVENTION
Conjugated Diene Rubber Gel
The conjugated diene rubber gel of the present invention is characterized as comprising 80% to 99% by weight, preferably 83% to 95% by weight and more preferably 86% to 90% by weight, of conjugated diene monomer units and 20% to 1% by weight, preferably 17% to 5% by weight and more preferably 14% to 10% by weight, of aromatic vinyl monomer units. This conjugated diene rubber gel may be produced either by using or without use of a crosslinking monomer, but is preferably produced by copolymerization using a crosslinking monomer. If desired, other copolymerizable ethylenically unsaturated monomer may be copolymerized for the production of the copolymer rubber gel.
Thus, the conjugated diene rubber gel of the present invention usually comprises 80 to 99% by weight of conjugated diene monomer units, 1% to 20% by weight of aromatic vinyl monomer units, 0% to 19% by weight of other ethylenically unsaturated monomer units and 0% to 1.5
Endo Koichi
Nakamura Masao
Birch & Stewart Kolasch & Birch, LLP
Lu Caixia
Zeon Corporation
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