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...
Patent
1998-06-19
1999-12-07
Cain, Edward J.
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...
524496, C08K 300
Patent
active
059985313
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to vulcanizable rubber compositions for use as hot-water seals.
BACKGROUND ART
It is known that compositions comprising a mixture of a nitrile-containing highly saturated copolymer rubber obtained by hydrogenating the unsaturated bonds of the butadiene portions of an acrylonitrile-butadiene copolymer rubber, and an ethylene-propylene copolymer rubber can yield vulcanized products having excellent weather resistance and processability, having good heat resistance and oil resistance, and hence suitable for use as seals (for example, Japanese Patent Laid-Open Nos. 283639/'86 and 124951/'90).
Although the vulcanized products of these rubber compositions are rubber materials suitable for applications requiring excellent weather resistance and processability in combination with high strength and oil resistance, especially for automobile parts and the like, much has been unknown as to whether they can be used for applications other than automobile parts and the like. For example, it has been believed that they do not have satisfactory performance when used for applications in which they come into long-term contact with hot water containing bleaching powder capable of generating hypochlorous acid, such as hot-water seals used in hot-water generators for home or business use.
In such hot-water generators, ethylene-propylene copolymer rubber and acrylonitrile-butadiene copolymer rubber (NBR) have conventionally been used as rubber materials for hot-water seals. However, in the case of ethylene-propylene copolymer rubber, its long-term use tends to cause the release of carbon black used as the reinforcing agent. Moreover, NBR has the disadvantage that the rubber progressively hardens to produce a large number of cracks in the rubber surface. Consequently, it has been desired to develop an improved technique.
The present inventors have now discovered that, when a mixture of a nitrile-containing highly saturated copolymer rubber and ethylene-propylene copolymer rubber is vulcanized and then immersed in hot water containing bleaching powder for a long period of time, its change in volume is unexpectedly slight. The present invention has been completed on the basis of this discovery.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a vulcanizable rubber composition for use as hot-water seals comprising 100 parts by weight of a rubber mixture composed of 90 to 50% by weight of a nitrile-containing highly saturated copolymer rubber obtained by hydrogenating the conjugated diene portions of an unsaturated nitrile-conjugated diene copolymer rubber or unsaturated nitrile-conjugated diene-ethylenically unsaturated monomer terpolymer rubber, and 10 to 50% by weight of an ethylene-.alpha.-olefin copolymer rubber (in which the sum of these components is 100% by weight); and 0.1 to 30 parts by weight of an organic peroxide vulcanizing agent.
The nitrile-containing highly saturated copolymer rubber used in the present invention is obtained by hydrogenating the conjugated diene portions of an unsaturated nitrile-conjugated diene copolymer rubber or unsaturated nitrile-conjugated diene-ethylenically unsaturated monomer terpolymer rubber. This nitrile-containing highly saturated copolymer rubber has a bound acrylonitrile content of 10 to 50% by weight and preferably 15 to 40% by weight, an iodine value of not greater than 80, preferably not greater than 60, and more preferably not greater than 30, and a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 30 to 300, preferably 50 to 200, and more preferably 60 to 150. The bound acrylonitrile content is chosen so as to be most suitable for performance requirements. If the iodine value is greater than 80, the thermal resistance and strength of the resulting seals will be reduced. No particular limitation is placed on the lower limit of the iodine value. However, the iodine value should generally be at least 1 because unduly low iodine values may make it difficult to vulcanize the rubber. If the Mooney viscosity i
REFERENCES:
patent: 5807948 (1998-09-01), Sagane et al.
Aimura Yoshiaki
Ohnishi Hiroko
Cain Edward J.
Nippon Zeon Co Ltd
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