Enhanced adhesion of aramid tire cords via argon plasma etching and acetylene plasma polymerization

Abstract

Aramid tire cords were subjected to argon plasma etching and plasma polymerization of acetylene in order to enhance their adhesion to rubber compounds. Two different reactors were utilized for plasma treatments for comparison purpose of the adhesion results and film characteristics from each reactor. Plasma polymerizations were performed as a function of treatment time and pulse rate, while argon plasma etching conditions were kept constant. Adhesion of aramid tire cords to rubber was evaluated via a standard industrial pull-out force adhesion test. The failure surfaces of the tested tire cords were analyzed by SEM to evaluate rubber coverage. Plasma polymerized coatings on metal plates, instead of on tire cords themselves due to the difficulty in analyzing plasma polymer coatings on the cords, were characterized by ellipsometry, FT-IR and TOF-SIMS. Among the treatment conditions, the combination of argon plasma etching and 10 min of acetylene plasma polymerization using an RF source provided greatly improved pull-out force of 91 N compared to 34 N with as-received aramid tire cord. The FT-IR spectrum of this plasma polymer coating showed some functional moieties such as C=C or C≡C, which could attribute to the enhanced adhesion of aramid cords. Moreover, the adhesion of plasma-polymer-coated cords was dependent on the degree of unsaturation (cross-link density) of the plasma polymerized films, as was concluded from characterization data by SIMS.