Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1994-10-31
1996-04-16
Lipman, Bernard
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525282, C08F27500
Patent
active
055083544
DESCRIPTION:
BRIEF SUMMARY
This invention relates to novel metal salts of (poly)citraconimide and (poly)itaconimide carboxylic acids, and a vulcanizable rubber composition comprising these novel metal salts and which, upon vulcanization, exhibits improved dynamic properties. More particularly, the invention also relates to a sulfur-vulcanized rubber composition which is vulcanized in the presence of particular anti-fatigue coagents, as well as to a sulfur-vulcanization process carried out in the presence of said coagents and the use of these coagents in the sulfur-vulcanization of rubber.
In the tire and belt industries, among others, better mechanical and dynamic properties are being demanded. It has long been known that the physiomechanical and mechanical-dynamic properties of rubber can be improved by using a large amount of sulfur as a cross-linking agent. However, under service conditions or prolonged vulcanization, excess sulfur produces reversion which results in the shortening of crosslinks and a marked decrease in heat resistance and resistance to flex cracking, among other properties in the final product.
One of these problems, the resistance to flex cracking, also known as fatigue resistance, is solved by the addition of a coagent in accordance with the present invention.
In order to eliminate the foregoing disadvantage, it has been proposed to add saturated carboxylic acids and their metal salts to sulfur-vulcanization systems. One example of a publication relating to this subject is U.S. Pat. No. 4,191,671. In comparative Example 8 and Examples 11-23 improvements in fatigue resistance are shown which are said to result from the addition of stearic acid and salts of stearic acid with zinc, calcium, magnesium, aluminum, sodium and cobalt, to a sulfur-vulcanization system. This patent also mentions the addition of unsaturated carboxylic acid salts to a combination peroxide/sulfur vulcanization system in order to improve the abrasion resistance of the rubber.
European patent application 0 191 931 suggests that the use of a bismaleimide compound in combination with a sulfenamide and a dithiophosphoric acid leads to further improvements in the mechanical and anti-reversion properties of sulfur-vulcanized rubbers. The patent specification claims that these rubbers exhibit improved resistance to reversion, resistance to heat ageing and resistance to flex cracking. However, this system is limited to vulcanization carried out in the presence of a sulfenamide accelerator in combination with a dithiophosphoric acid accelerator and is thus of limited utility in actual practice.
In the article, "Change in the Structure and Properties of Vulcanizates Based on Natural Rubber Under Prolonged Vulcanization in the Presence of Vulcanizing Systems Containing Sulfur and Bismaleimides," Chavchich, T. A., et al., Kauchuk i Rezina, vol. 4, pp. 20-3, 1981, there is disclosed that vulcanization of natural rubber tread stocks with sulfur in the presence of m-phenylenebismaleimide at 143.degree. C. over a 600-minute period gave vulcanizates with enhanced physical properties.
However, despite the fact that some of the above patents claim to reduce fatigue by addition of coagents, in actual practice, these systems fall short of the desired properties. For example, although stearic acid is widely used in the rubber industry, there remains a need for further improvements in the resistance to flex cracking for rubber articles which are subject to fatigue.
Accordingly, the present invention provides novel compounds which, when employed in sulfur-vulcanization of rubber, lead to a significant, unexpected improvement in the fatigue properties of the vulcanized rubber composition. The novel compounds of the present invention are represented by the formulas I and II: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from hydrogen, C.sub.1 -C.sub.18 alkyl groups, C.sub.3 -C.sub.18 cycloalkyl groups, C.sub.6 -C.sub.18 aryl groups, C.sub.7 -C.sub.30 aralkyl groups and C.sub.7 -C.sub.30 alkaryl groups and R.sub.2 and R.sub.3 may combine to
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"Change in the structure and properties of vulcanizates based on natural rubber under prolonged vulcanization in the presence of vulcanizing systems containing sulfur and bismaleimides", Chavchich, T. A. et al. Kauchuk i Rezina, vol. 4, pp. 20-23, 1981. Abstract Only.
"The Synthesis of Biscitraconimides and Polybiscitraconimides", Galanti. A. and Scola, D. A. Journal of Pol. Sci.,: Polymer Chemistry Edition, vol. 19 pp. 451-475. 1981.
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W. Hoffman, Rubber Technology Handbook, Chapter 4, "Rubber Chemicals and Additives" pp. 217-353, Hanser Publishers, Munich (1989).
Datta Rabindra N.
Talma Auke G.
Akzo Nobel N.V.
Lipman Bernard
Mancini Ralph J.
Morris Louis A.
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