Adhesion to brass

One of the first published investigations into practical adhesion phenomena in which surface analysis techniques were used was that into the adhesion of rubber to brass by van Ooij in the mid-1970s. Subsequently this particular research was extended and refined, and publications by the same author on the topic now-cover more than two decades. The adhesion of vulcanized rubber to brass is of critical importance in the tire industry since the steel wires used for tire reinforcement are brass-plated to ensure good bonding to the rubber of the tire. The need to brass-plate the wires had been known for many years but it was not until van Ooij s benchmark publications of 1977 that the chemistry involved in this particular adhesion process became fully understood. 

In sub.sequent work [20-22] van Ooij developed the use of model compounds (in the case of natural rubber,. squalene) to simulate the physical and chemical interactions at the interface of the brass/natural rubber. system. Cuts in a tire carcass may lead to exposure of the steel/brass interface and the galvanic effects that give rise to dezincification may then become important [23]. The use of duplex Zn-Ni on Zn-Co alloys as replacements for brass has been propo.sed in order to 

It is perhaps worthwhile at this point reviewing briefly the electrochemical processes that are associated with metallic corrosion. The reaction responsible for the degradation of the metal (Me) occurs at the anode, and for this rea.son the proces,s is often described as anodic dissolution  

The reaction has led to the production of an Me ion and. v electrons each with a single negative charge. As electrical neutrality must be maintained the electrons are consumed in the cathodic reaction that occurs on an adjacent portion of the electrode termed the cathode. In aqueous electrochemistry the reaction involves water and oxygen as well as the electrons  

This reaction is referred to as the cathodic reduction of water (and oxygen) and leads to an increase in pH (alkalinity) in the environs of the cathode. In the 

---

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. 

Wire coats good adhesion to brass coated steel wire and to adjoining rubber compounds, tear, fatigue, and age resistance... 

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. 

Rubber tyre cord adhesion W J VAN OOlJ Adhesion to brass-coated steel Rubber-based adhesives J M MARTfN MARTInEZ General introduction Rubber-based adhesives compounding J M MARTIN MARTfNEZ Formulations, etc. 

Tyre cord adhesion W J VAN OOIJ Adhesion to brass-coated steel... 

Let us now examine changes in mineral adhesion that are related to the choice of drum material [137]. For the separation of powders such as quartz, magnetite, hematite, pyrite, barite, asbestos, and j3-spodumene, the yield of the retained fraction on brass and aluminum surfaces was found to vary from 26 to 50%, and on tin plate and steel from 46 to 66%. The adhesion of these powders to tin plate and steel was greater than the adhesion to brass or aluminum. 

The role of silica-only systems on adhesion has been studied using model compounds with squalene [59]. It was shown that the mechanism for increased adhesion to brass-coated wire-to-rubber was not just a simple improvement of the physical properties of the rubber, but that silica moderated the thickness and composition of the interfacial layer by a chemical interaction. SEM-EDX (scanning electron microscopy with energy dispersive analysis of X-rays), XPS, AES and PIXE (proton induced X-ray emission spectroscopy) revealed that silica affected the relative concentrations of compounds present in the interfacial layer, promoting zinc oxide formation in particular. 

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. 

RUBBER ADHESION TO BRASS-COATED STEEL WIRE... 

Rubber Compound Effects. Buchan " reviewed natural as well as synthetic rubber compounds and their adhesion to brass. However, compound studies are to some extent largely empirical because of the complexity of the different compound systems used in the rubber industry today. One can, however, draw several conclusions from the many adhesion studies made to date. 

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. 

HRH Systems. A review of currently available bonding agents such as HRH and modifications thereof, is given by Weaver." HRH designates the use of hexamethylenetetramine (hexa), resorcinol, and a hydrated silica as additives to rubber in order to improve adhesion to brass coated wire. Normally about 1.5 phr hexa, 2.5 phr resorcinol, and 15 parts of silica are added to a wire skim stock. Pre-... 

---