Brass adhesion cobalt-naphthenate

Another market appHcation for naphthenic acid is the tire industry, where cobalt naphthenate is used as an adhesion promoter (see Adhesives Tire cords). Cobalt naphthenate improves the bonding of brass-plated steel cords to mbber, presumably by suppressing the de-zincification of brass (50). Its first reported use was in 1970 and the first patent for its use was issued in 1975 (51). About 900 t of cobalt naphthenate is used worldwide as an adhesion promoter, half of it in North America. The unit value fluctuates between 8.75—13.25 /kg because of the volatility of cobalt prices. Although it is the industry standard, the use of cobalt naphthenate is declining with the advent of more economical high metal-containing substitutes. 

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. 

Cobalt Salts. Barker" studied the effects of cobalt stearate, cobalt naphthenate, and a proprietary boron-containing metal-organic complex on adhesion to brass. He concluded that, with properly optimized compounds, little or no benefit is obtained from the use of cobalt insofar as initial adhesion is concerned. All salts, however, improved steam-aged adhesion to some extent. Other studies tend to support these claims. 

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