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
2000-02-28
2002-05-14
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S193000, C525S223000, C525S230000
Reexamination Certificate
active
06388015
ABSTRACT:
TECHNICAL FIELD
This invention relates to a rubber composition exhibiting, when crosslinked, good heat resistance and cold resistance, and having an especially improved extrusion-processability. It further relates to an electric wire having a protective covering or coating layer formed by crosslinking the rubber composition in the state of surrounding the electric wire.
BACKGROUND ART
Electric wire coating materials are exposed to a severe temperature environment for a long term due to heat generated by application of electricity. Therefore they are subject to crack-formation due to heat deterioration and sometimes insulation failure or dielectric breakdown is caused. Further, electric wire covering materials are subject to external heating depending upon the particular surrounding environment.
The electric wire covering materials are comprised of rubber. The rubber used includes natural rubber, a styrene-butadiene rubber and other synthetic rubbers. When a high heat resistance is required for an electric wire protecting covering, covering materials made of rubbers such as a fluororubber, an ethylene-propylene-diene copolymer rubber and a silicone rubber are used. However, these rubbers have problems in that a fluororubber is expensive, an ethylene-propylene-diene copolymer rubber has a relatively low heat resistance, and a silicone rubber has a poor mechanical strength.
It is known that a blend of a nitrile group-containing highly saturated copolymer rubber with an acrylic rubber has a good heat resistance. As a specific example of the rubber blend, a rubber composition comprising a blend of a hydrogenated, unsaturated nitrile-conjugated diene copolymer rubber, which is a nitrile group-containing highly saturated copolymer rubber, with an acrylic rubber, having incorporated therein an organic peroxide and a bismaleimide compound, is described in Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) No. H2-3438. This rubber composition is referred to as having good heat resistance, abrasion resistance, flexural resistance and oil resistance. The acrylic rubber contained in this rubber composition contains crosslinkable monomer units having a carbon-carbon unsaturated bond as a crosslinkable ingredient, and therefore, when a crosslinked product of this rubber composition is exposed to a high temperature environment having a temperature of, for example, about 150° C. for long hours, it is hardened and deteriorated. Therefore, this rubber composition is not suitable for an electric wire protective coating for which good heat resistance is required.
In conventional electric wire protective covering materials containing a rubber ingredient, a resinous ingredient such as polyethylene or an ethylene-vinyl acetate copolymer is often incorporated to impart a good extrusion processability thereto. For example, when polyethylene is incorporated in an electric wire protective covering material a protective covering made by crosslinking the protective covering material has good cold resistance, but poor heat resistance. Furthermore, when an ethylene-vinyl acetate copolymer is blended, for example, with an elastomer having a nitrile group, 25 to 140 nitrile nitrogen atoms per 1000 carbon atoms, and not more than 35 unsaturated bonds, as taught in JP-A S60-112839, a cable sheath having good heat resistance is obtained by radically crosslinking the blend of an ethylene-vinyl acetate copolymer with an elastomer. However, an electric wire protective covering made from the ethylene-vinyl acetate copolymer with an elastomer exhibits poor cold resistance although the protective covering has good heat resistance.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a rubber composition which can give an electric wire protective covering having good and balanced heat resistance and cold resistance and, even when it is exposed to a high temperature environment, the protective coating being not hardened nor deteriorated, and thus, keeping good rubber characteristics, and which rubber composition possesses good extrusion processability.
Another object of the present invention is to provide an electric wire protective covering material comprising the above-mentioned rubber composition.
A further object of the present invention is to provide an electric wire having a protective covering layer having good properties, which is made by crosslinking the above-mentioned electric wire covering material.
In one aspect of the present invention, there is provided a rubber composition comprising (A) a rubber ingredient comprised of (a) a nitrile group-containing highly saturated copolymer rubber having an iodine value of not larger than 120 and (b) an acrylic ester polymer rubber containing at least 80% by mole of at least one kind of monomer units selected from alkyl acrylates and alkoxyalkyl acrylate, and which is free from a carbon-carbon unsaturated bond except for the carbon-carbon double bonds of a benzene ring, at an (a)/(b) ratio of 40/60 to 90/10 by weight, and (B) an ethylene-&agr;-olefin copolymer, the (A)/(B) ratio being in the range of 30/70 to 70/30 by weight; said rubber composition further comprising an organic peroxide and being free from an auxiliary capable of covulcanizing the rubber ingredient (a) and the rubber ingredient (b) with the organic peroxide.
In another aspect of the present invention, there is provided an electric wire covering material comprising the above-mentioned rubber composition.
In still another aspect of the present invention, there is provided an electric wire having a protective covering layer which is formed by extruding the above-mentioned electric wire covering material around an electric wire and crosslinking the extruded covering
BEST MODE FOR CARRYING OUT THE INVENTION
Nitrile Group-Containing Highly Saturated Copolymer Rubber
The nitrile group-containing highly saturated copolymer rubber, i.e., ingredient (a) in the rubber ingredient (A) used in the invention, has an iodine value of not larger than 120. The iodine value is preferably not larger than 80, and more preferably not larger than 15. If the iodine value is too large, a crosslinked product of the rubber composition has poor heat resistance.
The Mooney viscosity of the nitrile group-containing highly saturated copolymer rubber is not particularly limited, but, in view of mechanical strength of a crosslinked product of the rubber composition and extrusion processability of the rubber composition, the Mooney viscosity is usually at least 15 and not larger than 200, and preferably at least 30 and not larger than 100.
The nitrile group-containing highly saturated copolymer rubber can be prepared by (i) a first process of copolymerizing an unsaturated nitrile monomer, an &agr;-olefin monomer and an optional copolymerizable monomer, or (ii) a second process of copolymerizing an unsaturated nitrile monomer, a conjugated diene monomer and an optional copolymerizable monomer, and then, hydrogenating the thus-obtained copolymer or terpolymer rubber whereby at least part of the unsaturated bonds in the conjugated diene monomer units of the copolymer or terpolymer rubber is saturated. The &agr;-olefin monomer used in the first process preferably has 2 to 12 carbon atoms and includes, for example, ethylene, propylene, butene-1,4-methylpentene-1, hexene-1 and octene-1. Of the above-mentioned two processes, the second process is preferable.
As specific examples of the unsaturated nitrile monomer, there can be mentioned acrylonitrile, methacrylonitrile and &agr;-chloroacrylonitrile. These unsaturated nitrile monomers may be used either alone or in combination. Of these, acrylonitrile is preferable.
The content of nitrile group-containing monomer units in the nitrile group-containing highly saturated copolymer rubber is preferably at least 10% by weight and not larger than 50% by weight, and more preferably at least 15% by weight and not larger than 40% by weight.
As specific examples of the conjugated diene monomer to be copolymerized with the unsaturated nitrile monomer, there
Aimura Yoshiaki
Asai Manabu
Armstrong Westerman & Hattori, LLP
Buttner David J.
Nippon Zeon Co. Ltd.
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