Brass-coated steel tire cord

Cobalt is important to the rubber industry to promote rubber-to-metal adhesion. The use of cobalt salts, such as cobalt stearate or cobalt naphthenate as compounding additives, will promote better adhesion between cured rubber and brass-coated steel tire cord. 

Resorcinol formaldehyde resin is a vital ingredient in the HRH rubber adhesion compounds (such as wire coat stock or breaker stock) in order to achieve good rubber-to-brass-coated steel tire cord adhesion. 

While it is possible to get some adhesion using HRH without the hydrated silica, many times insufficient adhesion is imparted. Thus hydrated precipitated silica is a very important component of the HRH system if it is used to achieve adequate rubber-to-metal adhesion. This is particularly true with rubber-to-brass-coated steel tire cord adhesion where there are very few practical alternatives. 

Zinc metal is also used to alloy with copper to form brass. Brass-coated steel tire cord is used to achieve good rubber-to-metal adhesion. 

Zinc oxide is essential in rubber technology because it is the most commonly used activator for sulfur cure systems. Just about every rubber compound that uses sulfur as the vulcanizing agent will most likely contain a small amount of zinc oxide to activate the cure. Also zinc is alloyed with copper to form brass. Special brass-plated steel tire cord is a primary reinforcing material for producing steel-belted radial tires. The brass coating of the steel tire cord enables very good rubber-to-metal adhesion. Therefore, zinc metal and zinc oxide are very important to the rubber industry. 

Tire Cord. Melamine resins are also used to improve the adhesion of mbber to reinforcing cord in tires. Textile cord is normally coated with a latex dip solution composed of a vinylpyridine—styrene—butadiene latex mbber containing resorcinol—formaldehyde resin.. The dip coat is cured prior to use. The dip coat improves the adhesion of the textile cord to mbber. Further improvement in adhesion is provided by adding resorcinol and hexa(methoxymethyl) melamine [3089-11 -0] (HMMM) to the mbber compound which is in contact with the textile cord. The HMMM resin and resorcinol cross-link during mbber vulcanization and cure to form an interpenetrating polymer within the mbber matrix which strengthens or reinforces the mbber and increases adhesion to the textile cord. Brass-coated steel cord is also widely used in tires for reinforcement. Steel belts and bead wire are common apphcations. Again, HMMM resins and resorcinol [108-46-3] are used in the mbber compound which is in contact with the steel cord to reinforce the mbber and increase the adhesion of the mbber to the steel cord. This use of melamine resins is described in the patent Hterature (49). 

Recently, van Ooij et al. have reviewed adhesion of steel tire cord to rubber (van Ooij et al., 2009). The authors reviewed the literature extensively and provided an updated model for adhesion to brass-plated tire cord, which incorporated observations made by many techniques. They discussed the effects of different compounding ingredients and the possible alternatives to the current brass coatings. They note that the use of cobalt compounds improves the adhesion between rubber and brass-coated cords, but new adhesion promoters have been developed as replacements for Co, or for combined use with Co. They also discussed the use of phenolic-resin adhesion promoters. They describe the various techniques that have been developed to study the rubber-brass interface and its aging mechanism. 

Insoluble Sulfur. In natural mbber compounds, insoluble sulfur is used for adhesion to brass-coated wire, a necessary component in steel-belted radial tires. The adhesion of mbber to the brass-plated steel cord during vulcanization improves with high sulfur levels ( 3.5%). Ordinary rhombic sulfur blooms at this dose level. Crystals of sulfur on the surface to be bonded destroy building tack and lead to premature failure of the tire. Rubber mixtures containing insoluble sulfur must be kept cool (<100°C) or the amorphous polymeric form converts to rhombic crystals. 

Adhesives in the Tire Industry. Cobalt salts are used to improve the adhesion of mbber to steel. The steel cord must be coated with a layer of brass. During the vulcanization of the mbber, sulfur species react with the copper and zinc in the brass and the process of copper sulfide formation helps to bond the steel to the mbber. This adhesion may be further improved by the incorporation of cobalt soaps into the mbber prior to vulcanization (53,54) (see Tire cords). 

The thin coating of brass on the steel cord is the primary adhesive used in steel-to-rubber bonding. The quality of this bonding system built up during vulcanization of, for example, a radial tire will influence the performance of the steel ply or steel belt in the tire and, ultimately, the durability of the product. Though the mechanism of bond formation in rubber-steel cord adhesion is very complex, a brief review of the current understanding of wire to rubber adhesion is presented. 

---