On characterizing microscopically the adhesion interphase for the adhesion between metal and rubber compound. Part IV. Effects of Co salt of adhesion between rubber compound and brass-plated steel cord with low Cu content

This study aims to investigate the effect of cobalt salt incorporation into rubber compounds on improving the adhesion durability between steel cords coated with low-copper brass and rubber compounds. Specifically, it examines how cobalt salt adhesion promoters facilitate the formation of the adhesion interphase immediately after vulcanization and enhance durability by restricting copper migration during humidity aging, thereby inhibiting the growth and transformation of the adhesion interphase. Experimental results demonstrated enhanced adhesion at cobalt salt loadings of 0.43–0.86 phr; however, the adhesion performance slightly deteriorated at the loading level of 0.86 phr, especially under extended humidity aging (15 days). For the Co-salt-free compound, the unaged pullout force was very low, but it increased significantly after five days of humidity aging. Depth profile analysis via Auger electron spectroscopy (AES) was used to evaluate the effect of Co salt incorporation on the adhesion interphase. The results show that the cobalt salt loadings of 0.43–0.86 phr promoted the formation of the interphase during vulcanization but did not promote the growth of the interphase during hostile aging. In the adhesion between rubber compounds and steel cords coated with low-Cu brass, cobalt salts are considered to promote the formation of the adhesion interphase immediately after vulcanization while inhibiting excessive growth of the adhesion interphase during hostile aging. This behavior may result from the enhanced robustness of the adhesion interphase due to cobalt salt incorporation during hostile aging.