Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-11-13
2000-04-04
Henderson, Christopher
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
5253326, 525370, C08C 1920
Patent
active
060462809
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a sulfur-vulcanized rubber composition having improved physical and mechanical properties. More particularly, it relates to a sulfur-vulcanized rubber composition which is vulcanized in the presence of an anti-reversion coagent and an effective amount of zinc, complexed with carboxylic acid. The invention also relates to a sulfur-vulcanization process which is carried out in the presence of an anti-reversion coagent and the complexed zinc and the use of an anti-reversion coagent in combination with the complexed zinc in the sulfur-vulcanization of rubber. Finally, the invention also relates to rubber products comprising rubber vulcanized with sulfur in the presence of an anti-reversion coagent and the complexed zinc.
In the tire and belt industries, among others, a better resistance to reversion is being demanded. This curing characteristic results in improved mechanical and heat resistance properties.
It has been observed that the sulfur-vulcanization of a composition comprising a rubber and an anti-reversion coagent comprising at least two groups selected from citraconimide and/or itaconimide groups results in a substantial reduction in the reversion of sulfur-vulcanized rubber compositions. This concept is generally disclosed in PCT patent applications WO 92/07904 and WO 92/07828.
However, these sulfur-vulcanized rubber products still exhibit an initial fall in torque after vulcanization is complete and subsequently a marching cure which results in a gradual increase in torque during overcure causing a "dip" in the cure curve. This leads to rubber products whose basic characteristics do not remain constant over time.
It is therefore the primary object of the present invention to improve upon the compositions disclosed by WO 92/07904 and 92/07828 by providing an effective amount of zinc, complexed with carboxylic acid, which will solve the problems associated with these compositions. It has been found that the presence of the complexed zinc during sulfur vulcanization of rubber with an anti-reversion coagent can avoid the initial fall in torque and the subsequent marching effect, shown by a substantially constant modulus after vulcanization over time, resulting in constant or even improved physical and mechanical properties.
For example, the heat resistance is improved by the use of the anti-reversion coagent in combination with the zinc complex. No detrimental effects on the properties have been observed as a result of the use of an effective amount of complexed zinc in the compositions disclosed by the above-mentioned international patent applications.
Accordingly, the present invention relates to a sulfur-vulcanized rubber composition which comprises the vulcanization reaction product of a composition containing at least: sulfur donor to provide the equivalent of 0.1 to 25 parts by weight of sulfur; comprising at least two groups selected from citraconimide and/or itaconimide groups; and carboxylic acid of the formula R--COOH (I), wherein R is selected from the group of C.sub.5-24 alkyl, C.sub.5-24 alkenyl, C.sub.5-24 cycloalkyl, C.sub.6-24 aryl, C.sub.7-24 alkylaryl, and C.sub.7-24 arylalkyl, optionally containing oxygen and/or nitrogen, optionally substituted with one or more electron donating or withdrawing groups.
Examples of electron donating or withdrawing groups include oxygen, nitrogen, silicon, SiO.sub.2, sulfoxy, boron, sulfur, phosphorus, amido, imino, azo, diazo, hydrazo, azoxy, alkoxy, hydroxy, halogen, carbonyl, carboxy, ester, ether, carboxylate, SO.sub.2, SO.sub.3, sulphonamido, SiO.sub.3, nitro, imido, thiocarbonyl, cyano, and epoxy groups. Prefered electron donating or withdrawing groups are halogen, hydroxy, ester, and ether groups.
Examples of carboxylic acids according to formula I include C.sub.8-10 coconut acid, stearic acid, lauric acid, oleic acid, octanoic acid, benzoic acid, chlorobenzoic acid, methylbenzoic acid, and naphthyl carboxylic acid.
Zinc is complexed by mixing zinc oxide, zinc hydroxide, or zinc carbonate with at least one carboxylic acid
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B. G. Crowther, High efficiency by rubber additives, paper presented at Rubbercon 1992, Jun. 15-19th 1992, Brighton, UK, organized by The Plastic & Rubber Institute, London.
B. G. Crowther, Zinc Soaps--The New Generation, paper presented at Tyretech 1990, Nov. 5-6th 1990, 65-75, Strewsubry UK, organized by European Rubber Journal and Rapra Technology Ltd.
W. Hoffmann, Rubber Technology Handbook, Chapter 4, Rubber Chemicals and Additives, pp. 217-353, Hanser Publishers, Munich 1989.
Synthesis of N-Substituted Bisitaconimide Monomers for Use as Thermosetting Polyimide Resins, S. L. Hartford, et al. Journal of Polymer Science: Polymer Chemistry Edition, vol. 16, 137-153 (1978).
Datta Rabindra Nath
de Hoog Arie Jacob
Wilbrink Johannes Hermanus
Akzo Nobel nv
Henderson Christopher
Mancini Ralph J.
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