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...
Reexamination Certificate
2000-12-18
2002-12-17
Wu, David W. (Department: 1713)
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...
C524S439000, C524S435000, C524S551000, C524S552000, C524S847000, C525S331900, C525S333100
Reexamination Certificate
active
06495625
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a chloroprene type rubber composition. More particularly, it relates to a chloroprene type rubber composition which provides a vulcanizate having a significantly improved heat resistance.
BACKGROUND ART
Heretofore, several methods have been proposed to improve the heat resistance of a vulcanizate of a chloroprene rubber composition. For example, JP-A-50-87437 discloses a method to improve the heat resistance by adding a zinc powder and water to a chloroprene rubber, JP-A-2-34645 discloses a method to improve the heat resistance by adding a zinc powder and thermal black, and JP-A-3-81350 discloses a method to improve the heat resistance by adding a zinc powder and 4,4′-(&agr;,&agr;-dimethylbenzyl)diphenylamine to a chloroprene rubber. However, the requirement for the heat resistance becomes strict with applications for e.g. rubber components for automobiles. Accordingly, the heat resistance is not always satisfactory with such known methods, and it has been desired to improve the heat resistance.
DISCLOSURE OF THE INVENTION
The present invention resides in a composition comprising a chloroprene type rubber and a specific carbon black and zinc powder incorporated in said rubber, and it is an object of the present invention to improve the heat resistance of a vulcanizate thereof.
Namely, the present inventors have conducted extensive studies to improve the heat resistance of a vulcanizate of a chloroprene type rubber composition and as a result, have found it possible to achieve the object by a combination of a chloroprene type rubber, a carbon black having an average stacking height Lc of at least 2 nm in a C axis direction of the layer planes in the crystallites, and a zinc powder. The present invention has been accomplished on the basis of this discovery.
Now, the present invention will be described in detail.
The chloroprene type rubber in the chloroprene type rubber composition of the present invention contains a chloroprene rubber as the main component, but may contain in addition to the chloroprene rubber, e.g. natural rubber, SBR, butyl rubber, BR, NBR or EPDM, as the case requires.
The chloroprene type rubber of the present invention may be a homopolymer of chloroprene or a copolymer (hereinafter often referred to as a chloroprene type rubber) obtained by polymerizing a mixture (hereinafter referred to as a chloroprene type monomer) comprising chloroprene and at least one other monomer copolymerizable with chloroprene.
Monomers copolymerizable with chloroprene include, for example, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, sulfur, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene as well as acrylic acid, methacrylic acid and esters thereof, and they can be used within a range to satisfy the purpose of the present invention.
With respect to the polymerization method to obtain the chloroprene rubber to be used in the present invention, there is no particular limitation, and a conventional polymerization method may be employed. Namely, the chloroprene type monomer may be emulsion-polymerized by a conventional method in the presence of a polymerization initiator which is commonly used for polymerization of chloroprene, to obtain the chloroprene rubber.
The emulsifier to be used for this emulsion polymerization is not particularly limited, and an emulsifier which is commonly used for the emulsion polymerization of chloroprene, such as an alkali metal salt of a C
6-22
saturated or unsaturated fatty acid, an alkali metal salt of rosin acid or disproportionated rosin acid, or an alkali metal salt of a formalin condensate of &bgr;-naphthalene sulfonic acid, may, for example, be used.
Chloroprene rubbers are classified into a sulfur-modified type, a mercaptan-modified type and a xanthogen-modified type, depending upon the type of the molecular weight modifier. The sulfur-modified type is one obtained by copolymerizing sulfur and chloroprene to obtain a polymer and plasticizing the polymer with thiuram disulfide to have a predetermined Mooney viscosity. The mercaptan-modified type is one obtained by using as a molecular weight modifier an alkyl mercaptan such as n-dodecyl mercaptan, tert-dodecyl mercaptan or octyl mercaptan. Likewise, the xanthogen-modified type is one prepared by using as a molecular weight modifier an alkylxanthogen compound.
As the chloroprene type rubber of the present invention, any modified type may be used. Further, a chloroprene type rubber modified by a combination of sulfur, mercaptan and xanthogen may also be used. However, the sulfur-modified type has a poor heat resistance of the polymer itself as compared with the mercaptan-modified or xanthogen-modified type, and accordingly, it is preferred to use the mercaptan-modified or xanthogen-modified type in the case where a higher heat resistance is required.
Specific examples of the alkylxanthogen compound to be used for the xanthogen-modified type include dimethylxanthogen disulfide, diethylxanthogen disulfide, diisopropylxanthogen disulfide and diisobutylxanthogen disulfide.
The amount of the alkylxanthogen compound is selected so that the molecular weight of the chloroprene type polymer (or the Mooney viscosity of a chloroprene type rubber obtainable by isolating the polymer) will be proper. It is used usually in an amount within a range of from 0.05 to 5.0 parts by weight, preferably from 0.3 to 1.0 part by weight, based on 100 parts by weight of the chloroprene type monomer, although the amount may vary depending upon the structure of the alkyl group or the desired molecular weight.
As the polymerization initiator, known potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide or an organic peroxide such as t-butyl hydroperoxide, may be used, which is commonly used for emulsion polymerization of chloroprene.
In the present invention, the polymerization temperature and the final conversion of the monomer are not particularly limited. However, the polymerization temperature is preferably from 0 to 50° C., more preferably from 20 to 50° C. Further, the polymerization is preferably carried out so that the final conversion of the monomer will be within a range of from 50 to 90%, and when this conversion has been reached, a small amount of a polymerization inhibitor may be added to terminate the polymerization.
As the polymerization inhibitor, a commonly employed inhibitor such as thiodiphenylamine, 4-tert-butylcatechol or 2,2-methylenebis-4-methyl-6-tert-butylphenol, may, for example, be used.
An unreacted monomer may be removed, for example, by steam stripping, and then the pH of the latex is adjusted, followed by e.g. conventional freeze solidification, washing with water and hot air drying to isolate the polymer.
The carbon black to be incorporated to the chloroprene type rubber composition of the present invention may be any one of thermal black and acetylene black prepared by a thermal decomposition method and furnace black and channel black prepared by an incomplete combustion method. However, such carbon blacks are required to have an average stacking height Lc of at least 2 nm in a C axis direction of the layer planes in the crystallites, and particularly preferred is one having an average stacking height Lc of at least 2.5 nm in a C axis direction of the layer planes.
Further, a preferred carbon black is one having an average particle size of at most 60 nm, and having a DBP oil absorption of preferably from 100 to 350 ml/100 g, more preferably from 120 to 300 ml/100 g, particularly preferably from 140 to 300 ml/100 g.
If the average stacking height Lc is less than 2 nm in a C axis direction of the layer planes in the crystallites, the heat resistance of a vulcanizate obtained by vulcanizing the chloroprene type rubber composition will be inadequate.
Further, acetylene black is a carbon black obtained by thermally decomposing acetylene gas, and the chloroprene type rubber composition using acetylene black is most preferred as the effect to improve the heat resistance of its vulcanizate is signific
Abe Yasushi
Aoki Kazuomi
Nakada Mitsuyuki
Yamagishi Isao
Denki Kagaku Kogyo Kabushiki Kaisha
Hu Henry
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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