Halobutyl inner liner

The most important characteristics of butyl rubber are its low permeability to air and its thermal stability. These properties account for its major uses in inner tubes, tire inner liners, and tire curing bladders. Because of the poor compatibility of butyl with other rubbers (with respect to both solubility and cure), the halobutyls are preferred. The brominated p-methylstyrene-containing butyl rubbers are used in a number of grafting reactions for tire applications and adhesives. Other uses for butyl rubber are automotive mechanical parts (due to the high damping characteristics of butyl), mastics, and sealants.55... 

Critical to a tire s hfe cycle performance is the ability to maintain air pressure. Tire inner liners composed of halobutyl-based compounds exhibit very low air and moisture permeability. Therefore, tires built with the proper selection of compounds can reduce the rate of premature failure, again delaying entry into the scrap tire and solid waste streams. 

It can be seen that isobutylene-based products are the most important they range from viscous oils to high molecular weight elastomers, such as butyl and halobutyl rubbers (see Butyl Rubber). The latter exemplify most strikingly the practical importance of carbocationic polymerization. Butyl and halobutyl rubbers are used as inner tubes or inner liners in vehicle tires, because of their exceptional impermeability toward gases and moisture (3,4). Had butyl and halobutyl... 

Halogenation of the isoprene enchainments in butyl elastomers yields halobutyl elastomers. Reaction of the isoprene units with elementary bromine or chlorine leads to the formation of allylic halide units along the chain—a substitution as opposed to addition across the double bonds. This leads to much faster curing, which permitted the development of tubeless tires, as adhesion of halobutyl to the rest of the tire could be achieved. Halobutyls are primarily used by the tire industry to form the inner liner of the tubeless tire. Other applications are similar to that of butyl. Chlorobutyl is also used in pharmaceutical stoppers. 

Sandstrom and co-workers utilized the cyclized polyisoprene polymers incorporated into tyre tread compounds to improve traction, tread wear and tear resistance. Cyclized polyisoprene is further based upon the discovery that blends of cyclized polyisoprene polymers with halobutyl rubber and/or NR can be employed as tyre inner liner formulations. 

The tire industry is probably the most important consumer of halobutyl rubbers for inner liners, tubes, tire sidewall compounds, and tire curing members. Other applications include heat resistant conveyor belts, steam hoses, gaskets, pharmaceutical stoppers, chemically resistant tank linings, adhesives, and sealants. 

Halobutyl rubbers possessing an extremely low air permeability and compatibility with general-purpose rubbers are suited to inner liner formulations, minimizing air and moisture diffusion, allowing better retention of the proper inflation pressure inside the tire, and minimizing intracarcass pressure and degradation [101]. 

An example of an inner liner compound based on BUR and NR is presented in Table 20. In practice, blends of halobutyl rubbers with NR or BUR + CIIR are used. A medium reinforcing carbon black such as GPF (providing adequate green strength and flow properties)... 

Table 5. Physical properties of halobutyl based inner liner vulcanizates.

The most important characteristic of butyl rubber is its low permeability to air. This property accounts for its major use in inner tubes and tire inner liners. Because of the poor compatibility of butyl with other rubbers (with respect to both solubility and cure), the halobutyls are preferred. 

Halobutyl rubbers are used in inner liners and sidewalls for tyres, heat resistant inner tubes, tank linings, pharmaceuticals, automobile mounts, and an increasing number of other applications. Annual world consumption doubled between 1974 and 1979, and is expected to exceed 100 X lOH in 1980. 

Halobutyl rubbers are used in applications requiring butyl rubber behaviour but in which either standard butyl rubber cannot be used, or the halobutyl rubbers offer sufficient technical advantages over regular butyl to compensate for their higher cost. Thus, halobutyl rubbers are used in tubeless tyre inner liners, white sidewall and cover strip stocks, and blends... 

Table 29 Model formulations for halobutyl rubber (inner liners) ...

The above compound (Perkalink 900) was shown to be an effective antireversion agent for sulphur-cured diene elastomers. The performance advantages of using Perkalink 900 in butyl rubber (inner tubes, bladders), halobutyl rubber (iimer liners) and nitrile rubber were demonstrated, the aim being to improve the heat resistance of the compounds. A mechanistic interpretation of the chemistry underlying the crosslinking in butyl rubber and halobutyl rubber was provided. 15 refs. 

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