Effect of ZnO contents at the surface of brass-plated steel cord on the adhesion property to rubber compound

An effect of ZnO concentration at the surface of brass-plated steel cord on the adhesion property between a rubber compound and a brass-plated steel cord was investigated. Cord composition was determined by an Auger microscope with Ar ion sputtering. Two different steel cords were prepared; one (cord A) had higher ZnO concentration at the cord surface compared to the other (cord B). Pull-out force of unaged adhesion sample of cord A was lower than that of cord B. But the adhesion durability of the humidity-aged adhesion sample of cord A was better than the latter. Rubber coverage of the pull out cord for the unaged adhesion samples of cord A was poor, indicating insufficient formation of an adhesion layer. Pull-out force of the thermal-aged adhesion samples decreased with increasing aging time and that of cord A was lower than that of cord B. The enhancement of rubber coverage during initial aging period could be explained by an additional formation of copper sulfide at the adhesion interphase and an increase of modulus of rubber compound adjacent to the adhesion layer. With further increases of aging time, adhesion interphase grew excessively and the physical property of rubber compound deteriorated significantly, such that rubber coverage of adhesion samples decreased markedly with increasing aging time.