Improved Adhesion of NR to Brass Plated Steel Cord.

Using commercially available bonding promotors, best overall performance in terms of adhesion and ultimate physical properties is obtained with cobalt soaps and in particular with cobalt-boron compounds. Best results are obtained in natural rubber compounded with 0. 5 phr of stearic acid, 5-10 phr of silica and with a curing system based on 0. 7 phr MBS and 4. 0 phr of sulphur. Now, new rubber chemicals based on hexamethylene bis thiosulfate have been found to be good adhesion promotor. In particular, they give improved overall adhesion characteristics with excellent retention of bond strength in saline environment especially with the nickel salt. With these new products, silica is not necessary to improve the retention of adhesion during ageing and the stearic acid level can be maintained at 2 phr.