Study on organic coating to improve the adhesion properties of Cu/Sn-plated bead wire and rubber

The bead is the key part of the radial tire, which plays the role of supporting the cord layer and fixing the tire on the rim. The good adhesion of the bead wire and rubber is the key factor to ensure the performance of the bead. In this work, for the purpose of improving the adhesion properties of Cu/Sn-plated bead wire and rubber, chlorinated natural rubber (CNR), epoxidized natural rubber (ENR), two kinds of modified alkyl phenolic resin (KPA、HY-2006) were used to coat the surface of the wire, and the effects of type and content of organic coating on the adhesion between bead wire and rubber after vulcanization were studied. The pull-out force (POF) and rubber coverage were used to evaluate the adhesion effects. The microstructure and the element analysis of the vulcanized interface between bead wire and rubber were observed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. Raman spectrometer, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to determine the chemical composition of the vulcanized interface, and the interfacial thickness was studied by XPS depth profiling. The results showed that the POF of the blank coated bead wire-rubber composite is 579.1 N, and the rubber coverage is 63 %. 0.41%CNR60 solution has the best effect on promoting the adhesion between bead wire and rubber (816.3 N, 93 %). The 1.23%KPA solution (703 N, 69 %) and 0.83%ENR solution (657.2 N, 80 %) also play a good role. The interfaces between vulcanized rubber and wires coated with blank, 0.41%CNR60, 0.41%KPA, 0.41%ENR and 0.41%HY-2006 solutions are composed of CuS, Cu _1·8S, Cu ₂S, SnS ₂ and SnO ₂ etc., and the proportion of Cu _xS is different. The Cu _x S layer of the interface coated with 0.41%CNR60 solution is the thickest, followed by ENR, blank, KPA and HY-2006 solutions. This work not only obtains an organic coating formula that could effectively improve the adhesion properties of Cu/Sn-plated bead wire and rubber, but also explored the composition of the interface layer, which provided the necessary information for elucidated the adhesion mechanism between Cu/Sn-plated bead wire and rubber.