Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-08-24
2002-04-16
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S096000, C521S139000, C521S153000
Reexamination Certificate
active
06372809
ABSTRACT:
TECHNICAL FIELD
This invention relates to a foamable rubber composition and a foamed rubber. More particularly, it relates to a foamable rubber composition having enhanced processability and giving a foamed and shaped rubber article having enhanced hardness, and good shrink-resistance tear-resistance and abrasion-resistance; and the foamed and shaped rubber article.
BACKGROUND ART
A foamed rubber article has a reduced specific gravity and thus is light-weight, and exhibits good impact absorption and heat-insulation, and therefore, is used in many fields. As rubber materials for foamed rubber articles, there can be mentioned natural rubber, and synthetic rubbers such as a polyisoprene rubber, an acrylonitrile-butadiene copolymer rubber, a styrene-butadiene copolymer rubber, an ethylene-propylene copolymer rubber and an ethylene-vinyl acetate copolymer rubber.
Recently, there was proposed a foamed rubber article made from a foamable rubber composition comprising a hydrogenated acrylonitrile-butadiene copolymer rubber having incorporated therein a zinc salt of an ethylenically unsaturated carboxylic acid, a metal salt of a higher fatty acid, a foaming agent and an organic peroxide (for example, Japanese Unexamined Patent Publication No. H6-107740). This foamable rubber composition was proved to give a foamed and shaped rubber product exhibiting a large shrinkage after crosslinked or after heat-treated in the course of making the foamed and shaped rubber article, namely, the rubber composition is difficult to shape into a foamed and shaped rubber article.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a foamable rubber composition giving a foamed and shaped rubber article exhibiting no shrinkage after crosslinked or after heat-treated in the course of making the foamed and shaped rubber article, the conditions for making the foamed and shaped rubber article from which composition are easy to control at the step of making the foamed and shaped rubber article, and which composition exhibits good foamability.
Another object of the present invention is to provide a foamed and shaped rubber article exhibiting improved tear-resistance, abrasion-resistance and other properties, and having large elongation and high hardness.
The present inventors made extensive researches to achieve the above-mentioned objects and found that a foamable rubber composition comprising a nitrile group-containing highly saturated copolymer rubber and polyethylene exhibited enhanced processability and foamability, and gave a foamed and shaped article exhibiting good shrink- resistance, tear-resistance and abrasion resistance and having large elongation and high hardness. Based on this finding, the present invention has been completed.
In accordance with the present invention, there is provided a foamable rubber composition comprising a nitrile group-containing highly saturated copolymer rubber, polyethylene, a metal salt of an ethylenically unsaturated carboxylic acid, an organic peroxide and a foaming agent.
In accordance with the present invention, there is further provided a foamed and shaped rubber article made by foaming and shaping the above-mentioned foamable rubber composition,
BEST MODE FOR CARRYING OUT THE INVENTION
Nitrile Group-Containing Highly Saturated Copolymer Rubber
The nitrile group-containing highly saturated copolymer rubber is a rubber having an iodine value not larger than 120 obtained by copolymerization of an &agr;, &bgr;-ethylenically unsaturated nitrile monomer with other monomer or monomers. Iodine value is an indication demonstrating the degree of unsaturation of carbon-carbon bond, and expressed in terms of amount in gram of iodine capable of being added to 100 g of a rubber.
The monomer to be copolymerized with an &agr;, &bgr;-ethylenically unsaturated nitrile monomer includes, for example, conjugated diene monomers, non-conjugated diene monomers and &agr;-olefin monomers. In the case where an &agr;, &bgr;-ethylenically unsaturated nitrile monomer is copolymerized with a conjugated dione monomer, a copolymer rubber having too large iodine value tends to be produced. When a copolymer rubber having too large iodine value is produced, the copolymer rubber may be subjected to hydrogenation addition whereby the carbon-carbon unsaturated bonds in the copolymer rubber are hydrogenated and the iodine value of copolymer rubber is lowered.
The &agr;, &bgr;-ethylenically unsaturated nitrile monomer includes, for example, acrylonitrile, methaorylonitrile and &agr;-chloroacrylonitrile. Of these, acrylonitrile is, preferable. These monomers may be used either alone or in combination.
The lower limit of the content of &agr;, &bgr;-ethylenically unsaturated nitrile monomer units in the nitrile group-containing highly saturated copolymer rubber is preferably 10% by weight, and the upper limit thereof is preferably 60% by weight, more preferably 55% by weight and especially preferably 50% by weight.
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 nitrile group-containing highly saturated copolymer rubber is a copolymer of an &agr;, &bgr;-ethylenically unsaturated nitrile monomer, a conjugated diene monomer and an optional copolymerizable monomer or monomers, or its hydrogenation product, the lower limit of the content of conjugated dione monomer units in the copolymer rubber is preferably 30% by weight, more preferably 40% by weight and especially preferably 30% by weight, and the upper limit thereof is preferably 90% by weight.
The non-conjugated dione monomer preferably includes those which have 5 to 12 carbon atoms, such as, for example, 1,4-pentadiene and 1,4-hexadiene.
The &agr;-olefin monomer preferably includes those which have 2 to 12 carbon atoms, such as, for example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.
The optional monomer copolymerizable with an &agr;, &bgr;-ethylenically unsaturated nitrile monomer includes, for example, unsaturated carboxylic acid esters, aromatic vinyl monomers, fluorine-containing vinyl monomers, unsaturated monocarboxylic acids, unsaturated dicarboxylic acids and anhydrides thereof, and copolymerizable antioxidants.
As specific examples of the unsaturated carboxylic acid esters, there can be mentioned alkyl acrylates and alkyl methacrylates, which have 1 to 18 carbon atoms in the alkyl group, such as methyl acrylate, ethyl acrylate, n-dodecyl acrylate, methyl methacrylate and ethyl methacrylate; alkoxyalkyl acrylates and alkoxyalkyl methacrylates, which have 2 to 12 carbon atoms in the alkoxyalkyl group, such as methoxymethyl acrylate and methoxyethyl methacrylate; cyanoalkyl acrylates and cyanoalkyl methacrylates, which have 2 to 12 carbon atoms in the cyanoalkyl group, such as &agr;-cyanoethyl acrylate, &bgr;-cyanoethyl acrylate and cyanobutyl methacrylate; hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and hydroxypropyl acrylate; monoalkyl or dialkyl esters of unsaturated dicarboxylic acids such as monoethyl maleate, dimethyl maleate, dimethyl fumarate, dimethyl itaconate, n-butyl itaconate and diethyl itaconate; amino group-containing unsaturated carboxylic acid esters such as dimethylaminomethyl acrylate and diethylaminoethyl acrylate; fluoroalkyl group-containing acrylates and fluoroalkyl group-containing methacrylates, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate; and fluoro-substituted benzyl acrylates and fluoro-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 ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene and tetrafluoroethylene. As specific examples of the unsaturated monocar
Aimura Yoshiaki
Asai Manabu
Foelak Morton
Zeon Corporation
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