Enhanced adhesion of steel filaments to rubber via plasma etching and plasma-polymerized coatings

Zinc-plated steel filaments were coated with RF plasma polymers of acetylene or butadiene in order to enhance adhesion to rubber compounds. Plasma polymerization was carried out as a function of the plasma power, deposition time, and gas pressure. In order to maximize adhesion, argon plasma etching was performed and carrier gases such as argon, nitrogen, and oxygen were used. Plasma polymer coatings were characterized by FT-IR, Alpha-Step, and a dynamic contact angle analyzer. The adhesion of steel filaments was evaluated via a tire cord adhesion test (TCAT). The best results were obtained from a combined process involving argon etching (90 W, 10 min, 30 mTorr) and acetylene plasma polymer coating (10 W, 30 s, 30 mTorr) with argon carrier gas (25/5, acetylene/argon). These samples exhibited a pull-out force of 285 N, which is comparable to that from the brass-plated steel filament (290 N).