Steel cords brass plated

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. 

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. 

Silica. The main uses of siUca are in the treads of off-the-road tines for improved chunking and tear resistance and as a component of the bonding system for brass and 2inc-plated steel cord. These are commonly used in radial passenger and tmck tire belt skim stock. In addition the body pHes of steel radial tmck tires, hoses and belts, and footwear use significant volumes of siUca as a reinforcing filler. 

Other types of coupling agents include 1,2-diketones for steel,27 nitrogen heterocyclic compounds such as benzotriazole for copper,28,29 and some cobalt compounds for the adhesion of brass-plated tire cords to rubber.30... 

The adhesion between rubber and brass-plated steel (e.g., steel tire cords for belted radial tires) has been the subject of much study and speculation. Brass plating is the major method of obtaining adhesion between natural rubber and the steel of tire cords. Over the years there has been much speculation about its mechanism, but there is agreement on one aspect of the adhesion of natural rubber to brass-plated steel the actual adhesion between the natural rubber and the brass-plated cord, formed in situ during the vulcanization process, is an interfacial layer of sulfides and oxides of copper (Buchan, 1959 van Ooij, 1979, 1984). 

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. 

Wire and fiberglass, being high-modulus inorganic belt cords, are not processed like textile cords. Steel cord is brass plated at the foundry and, thus, can be used directly at the calendars. Glass yarn is treated with adhesive dip and then used directly in the weaving operation. 

The adhesion between rubber and brass-plated steel (e.g., steel tire cords for belted radial tires) has been the subject of much study and speculation. 

Reviews on the subject of brass-plated steel cord-natural rubber adhesion have been written by van Ooij who has done much of the work in the field. Van Ooij [46] has given a model for rubber-brass adhesion, in which a copper sulfide layer forms on the brass before the onset of crosslink formation. The thin film of copper sulfide has good adhesion and cohesion. In addition, the film is so porous that rubber molecules can become entangled with it. It is not required that the film forms simultaneously with the formation of crosslinks during vulcanization but, rather, it is required that the copper sulfide film be completely formed before crosshnking starts. Indeed, adhesion between brass-plated steel and natural rubber can frequently be improved by the use of the retarder, CTP [4] or by using a more delayed action accelerator such as N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) [47]. 

The bond is not unduly sensitive to influences such as humidity, low mix viscosity and low vulcanizing pressures. The main drawbacks are connected with the plating process, which requires considerable investment and expertise. Brass plating has now been largely superseded by the use of proprietaiy bonding agents, except in the tyre industry, where bonding to brass-coated steel cords is still undertaken. ... 

Phenolic novolak resins and high styrene SBR resins are used for reinforcing and increasing the hardness and modulus of rubber compounds. Resorcinol novolak resins are used as a part of the adhesion system between rubber and brass plated steel cord or organic fibers. Both phenolic novolak and resorcinol novolak resins require the addition of a methylene donor such as hexamethoxymethylmelamine (HMMM) or hexamethylenetetramine (HMTA) to fully crosslink and become a thermoset. Phenol, alkyl phenols, and resorcinol can be reacted in bulk or in a polymeric formulation with methylene donors. Typical donors are 2-nitro-2methylpropanol (NMP), HMTA, and HMMM, used to produce a thermoset resin network in the... 

However, the brass plating process has proven quite successful for certain applications such as steel cords for automotive tyres. 

Only very few recent papers have been published in which new development of substrate treatments were reported. Krone reported on the optimum brass copper content and plating weight for rubber adhesion [44] and confirmed data that were known previously. A more detailed study was published by Goryaev [45]. Several steel cords were prepared and their overall thickness, homogeneity and surface composition altered. The adhesion to a standard NR compound was determined. Among the findings were that ... 

Despite this success of silanes, which are easy to use and apply, their use as metal pre-treatments for bonding metals to rubber has been lacking. The only rubber-related use is as a treatment of rubber-grade silica [32, 33]. This process improves the adhesion of the silica to the rubber and therefore the mechanical rubber properties. There is only one patent that describes the use of a silane to bond bare steel cord (in other words not plated with brass) to sulphur-vulcanised tyre cord skim stocks, published by Sharma in 1982 [54]. Good adhesion was reported but only if the compound contained a certain resin. Apparently, the silane reacted more with the resin than with the rubber compound. 

Overall this new process is very attractive and has several environmental advantages, if it could replace brass on steel tyre cords. Tests with silane-treated tyre cords are in progress. The authors proposed use of a new tyre cord without brass coating but with a zinc coating instead, as tyre cords without brass coating are difficult to manufacture (the brass lubricates the die in the final wire drawing process). The final zinc-plated cord is then passed through a silane bath and dried. Quite remarkable in this system is that the silane-based film does not impair the adhesion of brass to sulphur-cured compound. If the adhesion of a brass plated cord is mediocre, the silane process actually improves its performance, as shown in Table 6.1 [58]. 

Brass plated steel cord that contains low levels of copper is not so sensitive to decohesion caused by moisture. Initial adhesion may be lower because of fewer copper inclusions, but a more coherent ZnO is formed which reduces the amount of Zn ions diffusing through the Cu S layer and so less ZnO/Zn(OH)2 is formed at the interface. Compounding with high levels of ZnO also helps to inhibit the dezincification process by reducing the diffusion rate of Zn ions to the cord surface. 

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. 

Steel tire cord is usually brass plated in order to achieve good rubber-to-metal adhesion. Also, tire bead wire is commonly plated with bronze to achieve rubber-to-metal adhesion. The steel cable used in rubber mining belts may also be brass or bronze plated. 

Resorcinol formaldehyde resin is an extremely important component of the HRH system for achieving good rubber-to-brass-plated steel tire cord adhesion. This RF resin functions as a resorcinol donor in the rubber compound that reacts with the... 

DCBS is a commonly used sulfenamide accelerator that is selected when good scorch safety is needed combined with a relatively slow cure rate. The selection of DCBS is particularly useful when a slow cure rate is needed to optimize rubber adhesion to brass-plated steel tire cord. 

---