Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-05-20
2002-12-03
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S092000, C524S243000, C524S257000, C524S565000, C524S566000
Reexamination Certificate
active
06489385
ABSTRACT:
TECHNICAL FIELD
This invention relates to a highly saturated nitrile group-containing copolymer rubber with an enhanced processability having a Mooney viscosity lowered by imparting thereto a high shearing stress; a process for producing the same; a composition comprising the nitrile group-containing copolymer rubber with a lowered Mooney viscosity and a heat-resistant rubber; and a composite of the highly saturated nitrile group-containing copolymer rubber with a fiber.
BACKGROUND ART
A highly saturated nitrile group-containing copolymer rubber, i.e., a hydrogenation product of an unsaturated nitrile-conjugated diene copolymer rubber, is known as having excellent heat resistance, oil resistance and weather resistance. A vulcanizate having reinforcing fibers integrated therewith by imparting high tenacity characteristics thereto also is known. The rubber used for the fiber-reinforced rubber vulcanizate must have good fluidity or processability so that the rubber penetrates into and thoroughly filled in voids among the reinforcing fibers to give a vulcanizate having sufficiently high tenacities.
To impart a good processability to a highly saturated nitrile copolymer rubber, a process has been proposed wherein its Mooney viscosity is lowered by applying a high shearing force to the rubber (Japanese Unexamined Patent Publication No. H3-122103). The proposed process comprises imparting a high shearing stress to a hydrogenated nitrile rubber with a Mooney viscosity of from 55 to 100 in the presence of an oxygen donor such as oxygen or a peroxide compound and a radical transferring agent whereby the rubber is subject to thermal-oxidative degradation so that the Mooney viscosity is reduced to a value of from 30 to 50.
In the proposed process, free radicals generated upon the thermal-oxidative degradation are stabilized by an oxygen donor. It has been found that the rubber gels due to peroxides, a carboxyl group and carbonyl group, remaining after the high-shearing-force applying treatment. Even if a conventional aging inhibitor is added to the rubber after the high-shearing-force applying treatment, the Mooney viscosity increases during storage of the rubber.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a highly saturated nitrile group-containing rubber, which has a Mooney viscosity reduced by applying a high shearing force thereto and exhibits an enhanced processability, and, which has a good stability and exhibits a reduced increase in viscosity during storage after the high-shearing-force applying treatment; a process for producing the rubber having such good processability; a heat-resistant rubber composition having a good processability; and a composite of the rubber having a good processability with a fiber.
In one aspect of the present invention, there is provided a highly saturated nitrile group-containing copolymer rubber having a Mooney viscosity lowered by 15 points or more by applying a high shearing force thereto in the presence of an aging inhibitor, which has a Mooney viscosity of from 5 to 135 and a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 3 to 5, and exhibits an increase in Mooney viscosity of 10 points or fewer while the rubber is allowed to stand in the air at room temperature for 30 days after the above-lowering of Mooney viscosity.
In another aspect of the present invention, there is provided a process for producing a highly saturated nitrile group-containing copolymer rubber having a low Mooney viscosity, wherein a high shearing force is applied to a highly saturated nitrile group-containing copolymer rubber to lower the Mooney viscosity thereof, characterized in that the application of high shearing force is carried out in the presence of an aging inhibitor.
In still another aspect of the present invention, there is provided a heat-resistant rubber composition comprising the above-mentioned highly saturated nitrile group-containing copolymer rubber with a reduced Mooney viscosity, and a heat-resistant rubber, characterized in that the amount of the highly saturated nitrile group-containing copolymer rubber is at least 5% by weight.
In a further aspect of the present invention, there is provided a composite of the above-mentioned highly saturated nitrile group-containing copolymer rubber with a reduced Mooney viscosity, and a fiber.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention will be in detail described in the following.
Highly Saturated Nitrile Group-Containing Nitrile Rubber
The highly saturated nitrile group-containing copolymer rubber of the present invention, to be subjected to a high-shearing-force-applying treatment according to the invention, is a rubber made by hydrogenating carbon-to-carbon double bonds in an unsaturated nitrile group-containing copolymer rubber, which is a copolymer of an ethylenically unsaturated nitrile such as acrylonitrile, methacrylonitile or á-chloroacrylontrile with a conjugated diene such as 1,3-butadiene, isoprene, 1,3-pentadiene or 2,3-dimethyl-1,3-butadiene, or a copolymer of such ethylenically unsaturated nitrile and conjugated diene with at least one other copolymerizable monomer such as, for example, a vinylaromatic compound such as styrene, acrylic acid, methacrylic acid, an alkyl acrylate, an alkyl methacrylate, an alkoxyalkyl acrylate, an alkoxyalkyl methacrylate, a cyanoalkyl acrylate or a cyanoalkyl methacrylate.
More specifically the highly saturated nitrile group-containing copolymer rubber is made by hydrogenating at least 70%, preferably at least 90% of the carbon-to-carbon double bonds of an unsaturated nitrile group-containing copolymer comprising.usually 10 to 60% by weight, preferably 30 to 50% by weight of ethylenically unsaturated nitrile monomer units, usually 40 to 90% by weight of conjugated diene monomer units, and 0 to 50% by weight of optional copolymerizable monomer units. If the content of ethylenically unsaturated nitrile monomer units in the unsaturated nitrile group-containing copolymer is smaller than 10% by weight, the resulting rubber has a poor oil resistance. In contrast, if the content of ethylenically unsaturated nitrile monomer units is larger than 60% by weight, the resulting rubber has a poor elasticity. If the content of unhydrogenated carbon-to-carbon double bonds in the hydrogenated copolymer exceeds 30% by weight, the resulting rubber has poor tenacity characteristics. The highly saturated nitrile group-containing copolymer generally has good oil resistance, heat resistance and weather resistance.
As specific examples of the highly saturated nitrile group-containing copolymer rubber, there can be mentioned a hydrogenated acrylonitrile-butadiene copolymer rubber, a hydrogenated acrylonitrile-isoprene copolymer rubber, a hydrogenated acrylonitrile-butadiene-acrylate copolymer rubber and a hydrogenated acrylonitrile-butadiene-acrylate-methacrylic acid copolymer rubber.
The highly saturated nitrile group-containing copolymer rubber usually has a Mooney viscosity ML
1+4
(100° C.) of from 60 to 150, preferably from 80 to 100, as measured before the application of a high shearing force (which is hereinafter referred to as “high Mooney-viscosity highly saturated nitrile group-containing copolymer rubber”, when appropriate), and further has an iodine value of not larger than 120, preferably not larger than 60 and more preferably not larger than 30.
Aging Inhibitor
A low Mooney highly saturated nitrile group-containing copolymer rubber with a lowered Mooney viscosity of the invention having a good processability is prepared by applying a high shearing force to the high-Mooney-viscosity highly saturated nitrile group-containing copolymer rubber in the presence of an aging inhibitor to thereby reduce its Mooney viscosity ML
4
.
The aging inhibitor used in the invention is an organic compound exhibiting a function of changing a rubber radical or rubber hydroperoxy radical, which is produced by oxidation of rubber, to a type incapable of being subject to an oxidative chain transfer reaction, or changing
Fujii Yoshinori
Ikeda Atsumi
Armstrong Westerman & Hattori, LLP
Mulcahy Peter D.
Nippon Zeon Co. Ltd.
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