Influence of cure conditions on the adhesion of rubber compound to brass-plated steel cord. Part I. Cure temperature

The effect of the cure temperature of rubber compound on the adhesion with brass-plated steel cord was investigated in conjunction with the formation, growth and degradation of the adhesion interphase formed between the rubbe r compound and brass-plated steel cord. With increasing cure temperature fr om 130 degreesC to 190 degreesC, the pull-out force after cure decreased li nearly. This decrease in adhesion force at higher temperature may be explai ned by the limitation of the mass transfer of vulcanizing agents into the a dhesion interphase and/or rubber compound near the adhesion interphase, res ulting in a deficiency of sulfur due to the fast cure of the rubber compoun d which significantly retards the diffusion of vulcanizing chemicals. Also, at a high temperature, an adhesion interphase with a ZnS-rich layer, which may act as a barrier to copper diffusion for the formation of the adhesion interphase of copper sulfide, was formed. After thermal aging of the adhes ion samples, the pull-out force decreased in comparison with that of the un aged. The decrease of pull-out force after thermal aging stemmed mainly fro m the decline of the tensile properties after thermal aging. The adhesion p roperty after humidity aging was completely different from that after therm al aging. With increase in the cure temperature to 160 degreesC, the pull-o ut force increased. But further increase in the cure temperature caused a d ecline in pull-out force. This phenomenon can be explained by the degradati on of the adhesion interphase. At lower cure temperatures, a severe growth of copper sulfide and a large extent of dezincification were observed in th e adhesion interphase. At higher cure temperatures, a significant growth of copper sulfide in the adhesion interphase appeared. The proper formation o f the adhesion interphase and good physical properties of the rubber compou nd at a moderate cure temperature can result in high retention of adhesion properties.