Tire-reinforcing materials

Fibers spun had been demonstrated to be useful as tire-reinforcing materials of good fatigue characteristics. 

In the 1940s rayon was used almost exclusively in tires. It was difficult to adhere rayon to rubber mechanically because of the smooth surface of the rayon filaments. Fortunately, two Dupont Co. chemists, W. H. Charch and D. B. Maney found that incorporating a resorcinol-formaldehyde thermosetting resin into a rubber latex made a cord adhesive which gave excellent adhesion of rayon to rubber carcass compounds. The same RFL cord adhesive was also used when nylon was introduced as a tire reinforcing material in 1947 and when glass fiber was introduced as belt material in belted bias and radial tires. 

Reinforcing Resins. Reinforcement and stiffness of a compound can also be achieved with the use of reactive resins. Resins consisting of two-component systems of resorcinol or resorcinol condensation products and a methylene donor such as hexamethoxymethylmel amine (HMMM) or hexamethyltetramine (HMT) are the most popular in tires. These materials can be prereacted and added to the formula, or for more effective results they can react in situ ie, they can be added separately into the formula and react when the tire is vulcanized. 

Textiles are among the most ubiquitous materials ia society. They provide shelter and protection from the environment ia the form of apparel, as weU as comfort and decoration ia the form of household textiles such as sheets, upholstery, carpeting, drapery, and wall coveting, and they serve a variety of iadustrial functions, eg, as tire reinforcement, tenting, filter media, conveyor belts, iasulation, and reinforcement media ia various composite materials. 

Thermal and Chemical Stability. In addition to load-bearing properties, tire reinforcement must be able to resist degradation by chemicals in cured mbber and heat generation. The most critical degradant depends on the material in use. Most thermoplastic reinforcements are either modified directiy or stabiH2ed with additives to offset some, mostiy thermal, degradation (32,33). 

In reinforcing materials double-dipped polyesters for improved tire durability, plasma-treated yams for improved bonding in tire, and increased usage of aramid fabric as belt and application of PEN are the areas where manufacturers are showing interest. Introduction of new styles of steel wire geometry for improved mbber to metal adhesion and new steel wire coating formulations for improved mbber to metal bonding are other focused areas of development. 

Other Reinforcement Materials. Other materials that have been used in tire compounds for reinforcement are chopped wire (brass-coated), cotton and nylon flock, chopped nylon strands, polyethylene, zinc oxide, and chopped Kevlar. Most of these materials have very limited application and some are obsolete. Others are used more extensively in solid mbber industrial tires than in pneumatics. 

For a variety of technical reasons the development of aromatic polyamides was much slower in comparison. Commercially introduced in 1961, the aromatic polyamides have expanded the maximum temperature well above 200°C. High-tenacity, high-modulus polyamide fibers (aramid fibers) have provided new levels of properties ideally suited for tire reinforcement. More recently there has been considerable interest in some new aromatic glassy polymers, in thermoplastic polyamide elastomers, and in a variety of other novel materials. 

Plies Textile or steel cords extending from bead to bead and thereby serving as the primary reinforcing material in the tire casing. 

Table VIII illustrates the evolution of the range of reinforcement materials which have been used in tires.

Several other common thermoplastics emerged about the same time as LDPE in 1930s. Polystyrene, for instance, was first produced in 1930 and by 1934 plants were in operation producing the commercial resin in both Germany and Ihe United States. Poly(methyhnethacrylate) (PMMA) was developed by ICI about the same period. Carothers s discovery of nylons (introduced in 1939 at the World s Fair in New York) yielded a material that particularly served the allied war effort. Nylon was used extensively in tire reinforcement, parachute fabric, as well as in everyday products such as toothbrushes and women s stockings. Engineering thermoplastics such as polycarbonate by comparison are a more recent development, with commercialization by General Electric Company around 1958. 

Tire cord n. A textile material used to impart the flex resistance necessary for tire reinforcement. Tire yarns of polyester, rayon, nylon, aramid, glass, or steel are twisted to 5-12 turns/in. Two or more of these twisted yarns are twisted together in the opposite direction to obtain a cabled tire cord. The twist level required depends on the material, the yarn linear density, and the particular application of the cord. Normally, tire cords are twisted to about the same degree in the S and Z directions, which mean that the net effect is almost zero twist in the finished cord. 

Radiation processing is being applied all over the world in various fields such as polymer crosslinking (tapes, plates, tubes, cables, tires, reinforcement fibers, optical fibers, commodities), vulcanization, production of new materials by grafting, sterilization of medical wear and food package, art objects conservation and many other practical processes. 

Disordered carbon-black-polymer composites have many common uses in modem technology. These uses include inks, automobile tires, reinforced plastics, wire and cable sheaths, antistatic shielding, resettable fuses, and self-regulating heaters. As an immediate example, the inked letters on this page consist of a disordered carbon-black-polymer composite bound to the surface of the paper. Despite these widespread applications, many of the important physical properties of these composites are not well understood. There is a long history of experimental and theoretical work on disordered carbon-black-polymer composites [7]. One of the most exciting recent advances in the field has been the application of the scaling theory of percolation [2] to these composites. This is based on the many similarities between the percolative transition in a disordered conductor-insulator composite and the thermodynamic phase transition common in many materials. 

Vulcanization converts the material from a high viscosity liquid to an amorphous solid, suppressing creep and flow, and enhancing long-range rubber elasticity. Because cis-polyisoprenes crystallize on extension, they form extremely tough, self-reinforcing materials. Before the advent of synthetic rubber such as SBR, natural rubber was the only material for automobile tires. Nowadays, it remains the material of preference for heavy-duty tires such as are used by airplanes and trucks. 

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. 

Of all the tire cord reinforcement materials, glass has one of the highest modulus properties (about 200 g denier) but is somewhat limited in relative durability. Also, its ultimate elongation (before it breaks) is about 4.8%. 

There has been a tremendous number of changes and improvements in the design and composition of tires over the years. These improvements have been made to improve tire performance, especially rolling resistance, to achieve better fuel economy. Therefore, new reinforcing materials are continually being tried and evaluated. These improvements have been slow but steady, and this experience will likely continue into the foreseeable future. 

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