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
2003-05-12
2004-12-28
Cheung, William K. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S942000, C525S295000, C525S329100
Reexamination Certificate
active
06835780
ABSTRACT:
TECHNICAL FIELD
This invention relates to a nitrile rubber composition having an enhanced heat aging resistance, and a vulcanized rubber article made by vulcanization thereof.
BACKGROUND ART
A nitrile rubber represented by an acrylonitrile-butadiene copolymer rubber (NBR) has hitherto been widely used as an oil-resistant rubber material for the production of rubber articles such as a seal, a hose and a belt. Hydrogenated NBR was developed for satisfying a demand of placing on the market a vulcanized rubber article having enhanced heat-aging resistance and high tensile strength, and thus, the use of nitrile rubbers has been more widened.
Hydrogenated NBR has a structure such that butadiene units in the molecular chain have been hydrogenated and thus the content of unsaturated bonds, i.e., double bonds, has been reduced to zero or an extremely small value. Therefore hydrogenated NBR has a remarkably enhanced resistance to oxidative degradation and is highly evaluated as a heat aging-resistant rubber.
However, as hydrogenated NBR still has unsaturated bonds even only in a minor amount, the heat aging resistance in a hot-air atmosphere is liable to be poor. Therefore, additives to be incorporated in NBR are being developed.
For example, Japanese Unexamined Patent Publication No. H11-293039 proposed the incorporation of a strong base, a salt of a strong base with a weak acid, or a salt of a weak acid in hydrogenated NBR to enhance the hot-air aging resistance, namely, heat aging resistance when the hydrog nated NBR is kept in a hot-air atmosphere.
The incorporation of the proposed ingredients can reduce the deterioration of elongation at break, i.e., ultimate elongation, as measured after the rubber is kept in a hot-air atmosphere, but, the deterioration of tensile strength cannot be reduced to a desired level.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a nitrile rubber composition which is a rubber material giving a vulcanized rubber article exhibiting a reduced deterioration in tensile strength and elongation to the desired extent when kept in a hot air atmosphere.
The inventors conducted researches to achieve the above-mentioned object, and found that the incorporation an organic sulfonic acid salt in a nitrile rubber gives the desired results. Based on this finding, the present invention has been completed.
Thus, in accordance with the present invention, there are provided a rubber composition comprising a nitrile rubber and an organic sulfonic acid salt, wherein the amount of the organic sulfonic acid salt is in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the nitrile rubber; and further a vulcanized rubber article made by vulcanizing this rubber composition.
BEST MODE FOR CARRYING OUT THE INVENTION
The nitrile rubber used in the present invention is a copolymer rubber made by copolymerization of an &agr;,&bgr;-ethylenically unsaturated nitrile monomer (a) with other monomer (b).
As specific examples of the monomer (a), there can be mentioned acrylonitrile, methacrylonitrile and &agr;-chloroacrylonitrile. Of these, acrylonitrile is preferable. These nitrile monomers (a) may be used either alone or in combination. The content of units of monomer (a) in the nitrile rubber is preferably in the range of 10 to 60% by weight, more preferably 12 to 55% by weight and especially preferably 15 to 50% by weight.
The monomer (b) to be copolymerized with the monomer (a) includes, for example, conjugated diene monomers, non-conjugated diene monomers, and &agr;-olefin monomers. In the case when the monomer (a) is copolymerized with a conjugated diene monomer, a copolymer rubber having a large iodine value tends to be produced. However, according to the need, the iodine value can be lowered further by hydrogenating the carbon-carbon unsaturated bonds in the copolymer rubber by a conventional procedure to produce a hydrogenated product.
As specific examples of the conjugated diene monomer, there can be mentioned 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene. Of these, 1,3-butadiene is preferable. In the case where the monomer (a), a conjugated diene monomer and an optional other copolymerizable monomer are copolymerized and optionally the copolymer rubber is further hydrogenated, the total amount of the units of non-hydrogenated conjugated diene monomer and the units of hydrogenated conjugated diene monomer in the copolymer rubber is preferably in the range of 40 to 90% by weight, more preferably 45 to 88% by weight and especially preferably 50 to 85% by weight.
The non-conjugated diene monomer preferably includes those which have 5 to 12 carbon atoms, and, as specific examples thereof, there can be mentioned 1,4-pentadiene, 1,4-hexadiene, vinylnorbornene and cyclopentadiene.
The &agr;-olefin monomer preferably includes those which have 2 to 12 carbon atoms, and, as specific examples thereof, there can be mentioned ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.
As other examples of the monomer (b), there can be mentioned &agr;,&bgr;-ethylenically unsaturated carboxylic acid ester monomers, aromatic vinyl monomers, fluorine-containing vinyl monomers, &agr;,&bgr;-ethylenically unsaturated monocarboxylic acid monomers, &agr;,&bgr;-ethylenically unsaturated dicarboxylic anhydride monomers, and copolymerizable antioxidants.
As specific examples of the &agr;,&bgr;-ethylenically unsaturated carboxylic acid ester monomers, there can be mentioned alkyl acrylates and alkyl methacrylates, each alkyl group of which has 1 to 18 carbon atoms, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, n-dodecyl acrylate, methyl methacrylate and ethyl methacrylate; alkoxyalkyl acrylates and alkoxyalkyl methacrylates, each alkoxyalkyl group of which has 2 to 12 carbon atoms, such as methoxymethyl acrylate, methoxymethyl methacrylate and methoxyethyl methacrylate; cyanoalkyl acrylates and cyanoalkyl methacrylates, each cyanoalkyl group of which has 2 to 12 carbon atoms, such as &agr;-cyanoethyl acrylate, &bgr;-cyanoethyl acrylate and cyanobutyl methaorylate; hydroxyalkyl acrylates and hydroxyalkyl methacrylates, each hydroxyalkyl group has 1 to 12 carbon atoms, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and hydroxypropyl acryalte; &agr;,&bgr;-ethylenically unsaturated dicarboxylic acid alkyl esters such as monoethyl maleate, dimethyl maleate, dimethyl fumarate, dimethyl itaconate, diethyl itaconate and di-n-butyl itaconate; amino group-containing &agr;,&bgr;-ethylenically unsaturated carboxylic acid esters such as dimethylaminoethyl acrylate and diethylaminoethyl acrylate; fluoroalkyl group-containing acrylates and fluoroalkyl group-containing methacrylates, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate; and fluorine-substituted benzyl acrylates and fluorine-substituted benzyl methacrylates, such as fluorobenzyl acrylate and fluorobenzyl methacrylate.
As specific examples of the aromatic vinyl monomer, there can be mentioned styrene, &agr;-methylstyrene and vinylpyridine. As specific examples of the fluorine-containing vinyl monomer, there can be mentioned fluoroethyl vinyl ether, fluoropropyl vinyl ther, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene and tetrafluoroethylene. As specific examples of the &agr;,&bgr;-ethylenically unsaturated carboxylic acid monomer, there can be mentioned acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and maleic anhydride. As specific examples of the copolymerizable antioxidant, there can be mentioned N-(4-anilinophenyl)-acrylamide, N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)cinnamamide, N-(4-anilinophenyl)crotonamide, N-phenyl-4-(3-vinylbenzyloxy)aniline and N-phenyl-4-(4-vinylbenzyloxy)aniline.
The above-recited copolymerizable monomers can be used either alone or as a combination of at least two thereof.
The Mooney viscosity (ML
1+4
, 100° C.), as measured according to JIS K6300, of the nitrile rubber used in the present invention is not particularly limit
Aimura Yoshiaki
Ito Suguru
Armstrong Kratz Quintos Hanson & Brooks, LLP
Cheung William K.
Zeon Corporation
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