Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1995-03-29
1997-05-06
Teskin, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526224, 5262928, 526342, 526917, 5253326, 2643282, 26433113, 428 368, C08F23604, C08F 238
Patent
active
056272502
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an unsaturated nitrile-conjugated diene copolymer, a process for producing the same, and a rubber composition comprising the same and a vulcanizer. More particularly, it relates to an unsaturated nitrile-conjugated diene copolymer suitable for injection molding, a process for producing the unsaturated nitrile-conjugated diene copolymer by using a specific thiol compound as a molecular weight modifier, and a rubber composition comprising the unsaturated nitrile-conjugated diene copolymer and a sulfur-containing vulcanizer.
BACKGROUND ART
In recent years, injection molding has been widely employed for molding an acrylonitrile-butadiene rubber (hereinafter referred to as "NBR") into articles in view of productivity and rationality, for which good oil resistance and heat resistance are required. Recently such articles broadly include, for example, rubber vibration insulators, electrical parts, automobile parts, industrial parts and footwear.
It is required for the injection molding of NBR that NBR has a good flowability and, when NBR is vulcanized at a high temperature for a short time, the vulcanization is effected at a high efficiency. Namely, a high-rate vulcanizability is required. In general, the higher the vulcanization temperature, the lower the degree of vulcanization of rubber. Thus injection molded articles have poorer tensile stress and impact resilience than those of compression molded articles (for example, Journal of the Society of Rubber Industry, Japan, vol. 59, No. 4, p 214-215, 1986).
To obtain a high rate of vulcanization in the injection molding of NBR, many methods have been proposed which include, for example, a method of introducing a functional group such as a carboxyl group or an amino group into the molecule of NBR, a method of incorporating a special vulcanization promotor, and a method of, when an emulsion polymerization is conducted for the production of NBR, using minimum amounts of an emulsifier and a coagulant so that minimum amounts of the emulsifier and the coagulant remain in the resulting NBR. These proposed methods have problems such that the enhancement of the rate of vulcanization is not sufficient and some other characteristics such as cold resistance and compression set are deteriorated.
Further, the contamination of a mold is conspicuous in the injection molding of NBR wherein vulcanization is carried out at a high temperature. Namely, when the molding of NBR is repeated, staining materials are gradually deposited on the mold with the result of contamination of NBR moldings and spoiling of the surface appearance. Therefore the mold must be cleaned at regular intervals. The cleaning is time-consuming and costly and leads to reduction in productivity.
To avoid the contamination of a mold, an attempt has been made wherein talc, sodium thiosulfate, carbon wax or silicone oil is incorporated in NBR. However, even when this attempt is made for injection molding of commercially available general-purpose NBR wherein vulcanization is carried out at a high temperature and a high rate, the contamination can be avoided only to a limited extent.
DISCLOSURE OF INVENTION
An object of the present invention is to provide an unsaturated nitrile-conjugated diene copolymer which can be vulcanized at a high rate and is suitable for injection molding.
Another object of the present invention is to provide a process for producing the unsaturated nitrile-conjugated diene copolymer at a high efficiency in productivity.
Still another object of the present invention is to provide a vulcanizable rubber composition comprising the unsaturated nitrile-conjugated diene copolymer and a vulcanizer, which is suitable for a high rate of vulcanization.
In accordance with the present invention, there are provided: mole, per 100 moles of the monomeric units constituting the molecule, of an alkylthio group having 12 to 16 carbon atoms, which include at least three tertiary carbon atoms, and having a sulfur atom which is directly bound to at least one of the ter
REFERENCES:
patent: 4060680 (1977-11-01), Hendy
patent: 4082818 (1978-04-01), Coffey et al.
Asada Misako
Tsuji Suguru
Uchizono Yuichi
Nippon Zion Co., Ltd.
Teskin Fred
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