GB770803A - Improvements in rubber treatment - Google Patents

Abstract

A vulcanizate of low-torsional hysteresis and high electrical resistivity is prepared by mixing synthetic rubber with a large amount of carbon black and a small amount of a solely aliphatic azo compound having bonded to each nitrogen of the azo group an aliphatic carbon atom having bonded to it a cyano group, an alkyl group with 1 to 5 carbon atoms, and a hydrogen atom or a methyl or ethyl radical, heating the mixture at a temperature of at least 275 DEG F., but below that at which the rupber would be harmed by thermal decomposition, masticating the mixture either during, subsequent to, or alternately with the heat treatment, incorporating vulcanizing and other ingredients, shaping and vulcanizing. To avoid premature decomposition of the azo compound or premature reaction thereof with the synthetic rubber, the azo compound is mixed with the carbon black and the rubber at a relatively low temperature, e.g. below 250 DEG F. The azo compound may comprise a ,a 1-azo bis-isobutyronitrile, a ,a 1-azo bis - (2 - methyl - butyronitrile), a ,a 1-azo bis - (2 - methylheptanonitrile), a ,a 1-azo bis - (a ,g ,g - tri - methylvaleronitrile), a 1,a 1 - azo bis - (a - ethy - butyronitrile), or a ,a 1-azo bis-(propionitrile). The synthetic rubber may comprise a polymer of a conjugated diolefin, e.g. butadiene or isoprene, or copolymers thereof with styrene, a -methylstyrene, acrylonitrile, a monovinylpyridine, ethyl or methyl acrylate, methyl vinyl ketone, methyl isopropenyl ketone, or methyl methacrylate. Preferably 1 to 5 parts by weight of azo compound and 40 to 100 parts of carbon black are mixed with 100 parts of rubber. U.S.A. Specification 2,118,601 is referred to.ALSO:A vulcanizate of low torsional hysteresis and high electrical resistivity is prepared by mixing natural or synthetic rubber with a large amount of carbon black and a small amount of a solely aliphatic azo compound having bonded to each nitrogen of the azo group an aliphatic carbon atoms having bonded to it a cyano group, an alkyl group with 1 to 5 carbon atoms, and a hydrogen atom or a methyl or ethyl radical, heating the mixture at a temperature of at least 275 DEG F. but below that at which the rubber would be harmed by thermal decomposition, masticating the mixture either during, subsequent to, or alternately with the heat treatment, incorporating vulcanizing and other ingredients, shaping and vulcanizing. To avoid premature decomposition of the azo compound or premature reaction thereof with the natural or synthetic rubber the azo compound is mixed with the carbon black and the rubber at a relatively low temperature, e.g. below 250 DEG F. The azo compound may comprise a , a 1-azobis-isobutyronitrile, a , a 1-azo bis-(2-methyl-butyronitrile), a , a 1-bis bis (2-methylheptanonitrile), a , a 1-azo bis (a , g , g , trimethylvaleronitrile), a , a 1-azo bis (a -ethylbutyronitrile), or a , a 1-azo bis-(propionitrile). The synthetic rubber may comprise a polymer of a conjugated diolefin, e.g. butadiene or polyisoprene, or copolymers thereof with styrene, a -methylstyrene, acrylonitrile, a monovinylpyridine, ethyl or methyl acrylate, methyl vinyl ketone, methyl isopropenyl ketone, or methyl methacrylate. Preferably 1 to 5 parts by weight of azo compound and 40 to 100 parts of carbon black are mixed with 100 parts of rubber. In examples vulcanizates are prepared using (1) 100 parts natural rubber, 50 parts carbon black, 1,5 parts a , a 1 azobix-isobutyronitrile, (2) 100 parts butadiene-styrene, 52 parts carbon black, 6 parts hydrocarbon oil, 1 part stearic acid, 2,5 parts a , a 1-azobis-isobutyronitrile, (3) 100 parts butadiene-acrylonitrile, 50 parts carbon black, 6 parts hydrocarbon oil, 1 part stearic acid, and 2,5 parts a , a 1-azobis-isobutyronitrile, (4) 100 parts butadiene-styrene, 37,5 parts hydrocarbon oil, 72 parts carbon black, 3 parts a , a 1-azobis-isobutyronitrile, vulcanizing and other ingredients being added after the heat treatment. U.S.A. Specification 2,118,601 is referred to.