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
2002-07-29
2004-02-10
Harlan, Robert Deshon (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...
C525S329900, C525S330300, C525S330500, C525S370000, C525S374000
Reexamination Certificate
active
06689843
ABSTRACT:
TECHNICAL FIELD
This invention relates to an acrylic rubber composition that is a material for giving a crosslinked article having excellent heat resistance; a crosslinkable acrylic rubber composition; and a crosslinked article made by crosslinking the crosslinkable acrylic rubber composition. More specifically, it relates to in acrylic rubber composition and a crosslinkable acrylic rubber composition that is a material for giving a crosslinked article exhibiting a reduced variation in elongation upon the imposition of heat load; and a crosslinked article made by crosslinking these rubber compositions.
BACKGROUND ART
Acrylic rubbers have good heat resistance, and therefore, are widely used in an automobile field and related fields.
However, there has been an increasing demand for producing an acrylic rubber having more enhanced heat resistance. To meet this demand, an attempt of increasing the amount of an antioxidant incorporated in the rubber was proposed in the early stage. This proposal invited a problem such that, when a large amount of an antioxidant was incorporated, bloom occurred on crosslinked articles. Thus, it was impossible to enhance the heat resistance to a desired level by increasing the amount of an antioxidant.
As another attempt, it was proposed to incorporate a specific kind of an antioxidant. For example, an acrylic rubber composition having nickel dialkyldithiocarbamate incorporated therein as an antioxidant has been proposed in Japanese Unexamined Patent Publication No. S56-135539. The acrylic rubber composition in this publication caused bloom only to a negligible extent after it was crosslinked, even in the case when the amount of nickel dialkyldithiocarbamate was increased, but, the heat resistance of a crosslinked object could not be enhanced to a sufficiently high level. Especially the obtained crosslinked article tends to exhibit a large variation in elongation upon the imposition of heat load.
As still another attempt, it was proposed to two kinds of aromatic secondary amine antioxidants in an acrylic rubber to enhance the heat resistance (Japanese Unexamined Patent Publication No. H11-21411). However, the heat resistance of resulting crosslinked articles still could not be enhanced to a desired high level in some fields and especially, the crosslinked articles exhibited undesirably large variation in elongation depending upon the heat load applied. If the amount of the two kinds of secondary amine antioxidants is increased to enhance the heat resistance more, bloom is liable to occur.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide an crosslinked acrylic rubber article having excellent heat resistance and especially exhibiting a reduced variation in elongation upon the imposition of heat load, as compared with the conventional acrylic rubber articles.
The present inventors have found that an acrylic rubber composition comprising an acrylic rubber containing units of an ethylenically unsaturated monomer having a carboxyl group, an aromatic secondary amine compound and nickel dialkyldithiocarbamate gives a crosslinked article having excellent heat resistance and exhibiting a reduced variation especially in elongation upon the imposition of heat load. The present invention has been completed on the basis of this finding.
Thus, in accordance with the present invention, there are provided:
an acrylic rubber composition comprising 100 parts by weight of (a) an acrylic rubber having carboxyl groups, 0.3 to 8 parts by weight of (b) an aromatic secondary amine compound, and 0.3 to 8 parts by weight of (c) nickel dialkyldithiocarbamate.
a crosslinkable acrylic rubber composition comprising 100 parts by weight of (a) an acrylic rubber having carboxyl groups, 0.3 to 8 parts by weight of (b) an aromatic secondary amine compound, 0.3 to 8 parts by weight of (c) nickel dialkyldithiocarbamate, and 0.1 to 10 parts by weight of a crosslinking agent; and
a crosslinked article made by crosslinking the crosslinkable acrylic rubber composition.
BEST MODE FOR CARRYING OUT THE INVENTION
The acrylic rubber composition of the present invention comprises 100 parts by weight of (a) an acrylic rubber having carboxyl groups, 0.3 to 8 parts by weight of (b) an aromatic secondary amine compound, and 0.3 to 8 parts by weight of (c) nickel dialkyldithiocarbamate.
The acrylic rubber (a) having carboxyl groups used in the present invention (which acrylic rubber (a) is hereinafter called “acrylic rubber (a)” for brevity when appropriate) contains a carboxyl group preferably in an amount of 5×10
−4
to 4×10
−1
ephr, more preferably 2.5×10
−3
to 2×10
−1
ephr, and especially preferably 5×10
−3
to 1×10
−1
ephr. If the content of carboxyl groups in the acrylic rubber (a) having carboxyl groups is too small, the acrylic rubber composition cannot be crosslinked to a desirably sufficient extent and a crosslinked article made therefrom sometimes becomes difficult to retain its shape. In contrast, if the content of carboxyl groups is too large, a crosslinked article made therefrom sometimes becomes rigid and loses its rubber elasticity.
The acrylic rubber (a) may be a copolymer made by copolymerization of an acrylic acid ester monomer as the principal constituent with an ethylenically unsaturated monomer having a carboxyl group or carboxyl groups, and an optional other copolymerizable monomer. Alternatively, the acrylic rubber (a) may be a modified copolymer made by modifying a conventional acrylic rubber prepared by copolymerization, to introduce carboxyl groups therein. The acrylic rubber (a) will be more specifically described by the copolymer made by copolymerization of an acrylic acid ester monomer with an ethylenically unsaturated monomer having a carboxyl group or carboxyl groups.
As the acrylic acid ester monomer, an acrylic acid alkyl ester monomer, the alkyl group of which has 1 to 8 carbon atoms, can be used alone, or, preferably in combination with acrylic acid alkoxyalkyl ester, the alkoxyalkyl group of which has 2 to 16 carbon atoms.
As specific examples of the acrylic acid alkyl ester monomer having an alkyl group of 1 to 8 carbon atoms, there can be mentioned methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isopropyl acrylate, isobutyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate and cyclohexyl acrylate. Of these, acrylic acid alkyl ester monomers having an alkyl group of 2 to 4 carbon atoms are preferable. Ethyl acrylate and n-butyl acrylate are especially preferable.
As the acrylic acid alkoxyalkyl ester monomer having an alkoxyalkyl group of 2 to 16 carbon atoms, acrylic acid alkoxyalkyl ester monomers having an alkoxyalkyl group of 2 to 8 carbon atoms are preferable. As specific examples of the preferable acrylic acid alkoxyalkyl ester monomers having an alkoxyalkyl group of 2 to 8 carbon atoms, there can be mentioned methoxymethyl acrylate, ethoxymethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, 2-methoxyethyl acrylate, 2-propoxyethyl acrylate, 3-methoxypropyl and 4-methoxybutyl acrylate. Of these, 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are especially preferable.
The ethylenically unsaturated monomer having a carboxyl group or carboxyl groups is a monomer having an ethylenically unsaturated bond and containing a carboxyl group or carboxyl groups, or a carboxylic anhydride group.
As specific examples of the ethylenically unsaturated monomer having a carboxyl group or carboxyl groups, there can be mentioned carboxylic acid monomers such as acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, maleic acid, fumaric acid and citraconic acid; butenedioic acid monoalkyl ester monomers such as monomethyl maleate, monoethyl maleate, mono-n-butyl maleate, monomethyl fumarate, monoethyl fumarate and mono-n-butyl fumarate; and carboxylic acid anhydride monomers such as maleic anhydride and citraconic anhydride. Of these, butenedioic acid monoalkyl ester monomers are preferable. Monoethyl maleate, mono-n-butyl
Kubota Isao
Nishimura Koichi
Tsugawa Daisuke
Armstrong Kratz Quintos Hanson & Brooks, LLP
Harlan Robert Deshon
Zeon Corporation
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