GB854613A - Improvements in and relating to rubber compositions - Google Patents

Abstract

In the preparation of a vulcanizable composition, carbon black, formaldehyde or a compound which releases formaldehyde on heating and a condensation catalyst are dispersed in natural or synthetic rubber, in the absence of extraneous formaldehyde-reactive materials, and the mixture is subjected to a heat treatment without vulcanizing it. The synthetic rubber may consist of a polymer of a conjugated diene, e.g. polybutadiene, or a copolymer such as butadiene - acrylonitrile, butadienestyrene, or isobutylene - butadiene copolymers, or a polymer of a substituted conjugated diene containing the group CH2 : C.Cl, e.g. polychloroprene. Vulcanizable reclaims of such rubbers and compositions of such rubbers containing extender oils may also be used. The heat treatment may be effected at 100 DEG to 200 DEG C. for a period of 2,5 to 40 minutes, preferably at 140 DEG to 160 DEG C. for 10 to 25 minutes. The mixture may comprise, in parts by weight, rubber 100, formaldehyde 0,1 to 10, preferably 1 to 2, carbon black 5 to 150, preferably 5 to 75, and condensation catalyst 0,1 to 0,5. The compound which liberates formaldehyde on heating may comprise formaldehyde, metaformaldehyde, or hexamethylene tetramine. A separate condensation catalyst is not required when hexamethylene tetramine is used since the ammonia liberated by that compound on heating functions as a condensation catalyst. When hexamethylene tetramine is not used the condensation catalyst may consist of aluminium chloride. Examples are described illustrating that vulcanizates having high values of hardness and resilience are obtained by the vulcanization of compositions prepared by the process according to the invention from mixtures comprising natural rubber or butadiene styrene copolymer.