Adhesion Accelerators

With the advancement of tire technology, radial tires have captured 90-95% of the tire market in most of the advanced countries and steel cord has been established as the best carcass and belt material for radial tires. It has a number of advantages like higher tenacity that leads to higher load carrying capacity, higher modulus, higher fatigue life, low extension and highest durability, etc., over all kinds of presently available commercial tire cords. But due to wide variation of physical as well as chemical properties, a good marriage between rubber and steel cord is not so easy. A number of adhesion accelerators and silane adhesion promoters are available in the market to enhance the bonding, but most of them have failed to retain the bonding substantially after different aging conditions especially at elevated temperatures. This problem is more aggravated e.g., in a country like India due to to overloading, rough road conditions, high humidity and temperature, or in advanced countries where the tires are abused due to higher speeds which leads to higher heat development and gradual separation of steel cord from rubber. The problem is even more severe when cuts develop in the tire through which engress of moisture, water, dirt, etc., takes place and ultimately affects the adhesion between rubber and steel cords. Although cobalt boron acylate alone can take care of good adhesion in normal conditions as well as under salt aging or steam aging conditions even at elevated temperature, to maintain the physicals as well as adhesion properties in anaerobic aging condition, it is essential to have a suitable network structure which can be achieved by using specialty chemicals like post vulcanization stabilizer (PVS) such as hexamethylene-l,6-bisthio sulfate disodium salt dihydrate (HTSNa) and bis-(3-triethoxy silylpropyl) tetrasulfide (TESPT).