Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-02-28
1998-09-15
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
524436, 524556, 524557, 524571, 524572, 525189, 526 85, 526222, 526335, 526338, 526342, C08F23612, C08F 238
Patent
active
058079416
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an unsaturated nitrile-conjugated diene copolymer, a process for producing the same, and a vulcanizable rubber composition comprising the copolymer and a vulcanizer. More particularly, it relates to a nitrile-conjugated diene copolymer having good mechanical strength and processability, a process for producing this copolymer wherein a specific thiol compound as a molecular weight modifier is added in lots in the course of polymerization, and a vulcanizable rubber composition comprising the copolymer and a sulfur-containing vulcanizer.
BACKGROUND ART
In recent years, injection molding has been widely employed for molding an acrylonitrile-butadiene rubber (hereinafter abbreviated to "NBR") in view of productivity and rationality, that is used in applications for which good oil resistance and thermal resistance are required. Recently the range of its use is increasing, which includes vibration insulating rubbers, electrical parts, automobile parts, industrial moldings and footwear.
For injection molding of NBR, a high fluidity and a high crosslinking efficiency, i.e., a high-rate vulcanizability, at a high-temperature and short-time vulcanization are generally required. However, in general, the higher the vulcanization temperature of rubber, the lower the degree of the crosslinking efficiency. Therefore injection molded articles have poor tensile stress and impact resilience as compared with compression molded articles (for example, see Journal of Society of Rubber Industry, Japan, vol. 59, No. 4, p 214-215, 1986).
To impart a high-rate vulcanizability to NBR, many proposals have been made, which include for example a method of introducing a functional group such as a carboxyl group or an amino group, a method of incorporating a suitable vulcanization promotor, and a method of conducting an emulsion polymerization using minimum amounts of an emulsifier and a coagulant and thus minimizing residual catalyst in NBR. However, the high-rate vulcanizability attained by these proposals is not on a high level and in some cases physical properties such as cold resistance and permanent set are impaired.
Further, contamination of a mold is conspicuous in the injection molding of NBR wherein vulcanization is carried out at a high temperature. That is, where the molding is repeated, staining materials are gradually deposited on the mold with the result of contamination of moldings and spoiling of the surface appearance. Therefore the mold must be cleaned at regular intervals, but the cleaning is time-consuming and costly and leads to reduction in productivity.
To avoid the contamination of a mold, proposals have been made wherein talc, sodium thiosulfate, carbon wax or silicone oil is incorporated in rubber. However, these proposals are generally not effective for commercially available general purpose NBR. Especially where the vulcanization is effected at a high temperature and a high rate as in injection molding, it is difficult to avoid the mold contamination.
Further, NBR is not satisfactory in processability although good processability is recently required. Therefore there is an increasing demand for improving the processability. As methods of improving the processability, there can be mentioned a method of incorporating a liquid polymer or a plasticizer and a method of conducting polymerization under conditions such that production of a high-molecular-weight fraction is suppressed. For example, a method is proposed in Japanese Unexamined Patent Publication No. 53-23390 wherein copolymerization of an unsaturated nitrile with a conjugated diene is carried out by using a combination of an alkyl mercaptan with a dialkyl-xanthogen disulfide as a molecular weight modifier, and by adding 20 to 70% of the unsaturated nitrile in the course of polymerization.
The method of incorporating a liquid polymer or a plasticizer and the method of suppressing the production of a high-molecular-weight fraction are effective for improving processability, but have a problem such that the vulc
REFERENCES:
patent: 4421884 (1983-12-01), Oyama
patent: 4965326 (1990-10-01), Horpel et al.
patent: 5556919 (1996-09-01), Oyama
patent: 5627250 (1997-05-01), Tsuji
Tsuji Suguru
Uchizono Yuichi
Nippon Zeon Co. Ltd.
Zitomer Fred
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