Bond Strength of Tread and Breaker Stocks under Repeated Deformations

Abstract

Abstract As the tire industry changed over to production from synthetic rubber a new form of service failure was encountered—stripping of the tread from the breaker. This phenomenon is most noticeable where SBR rubbers are used, and also at the boundary layer of pliedup rubbers differing in composition, having different moduli and different degree of cure in the zone of contact with each other. In recent times there have been carried out a considerable number of investigations of the dynamic strength of a system of pliedup rubbers. The results show that an important influence is exerted upon the bond strength of pliedup rubbers by their flow, which governs the increase in contact area in the boundary layers, by the diffusion of the separate links of the chain molecules of one pliedup layer into the other by the degree of the pliedup rubbers, and the bonding layers between the layers of rubber. The compounding ingredients also affect the bond strength. As a result a number of technological measures were taken to increase bond strength between the components of tires on the adoption of SBR in the industry. These were directed towards increasing the surface contact between the layers, and towards improving the surface of the semifinished products before plyingup. An important effect upon the improvement of the surface properties of tires was evidenced by increased pressure in the building process, roughening of the tread and breaker, pressing of the uncured casings after building, and introducing into tire formulas accelerator groups which ensure increase in the time spent by the stocks in the viscous flow state in the initial period of vulcanization. One method of attaining higher dynamic strength in the tread-breaker system was some increase in the modulus of the breaker rubber by increaisng the amount of channel black. A recently developed formula for tread rubber with increased elasticity and for a stiff breaker noticeably reduced the failures of tires from stripping of the tread from the breaker. Nevertheless this problem still occupies the center of attention in the industry.