Butyl rubber applications, formulations

The materials selected for evaluation included three materials currently being used in these applications Biomer (Thoratec Laboratories Corporation, Emeryville, CA), representative of segmented ether-type polyurethanes Avcothane-51 (Avco Everett Research Laboratory, Inc., Everett, MA), a block copolymer of 10% silicone rubber and 90% polyurethane and Hexsyn (Goodyear Tire and Rubber Company, Akron, OH), a sulfur vulcanized hydrocarbon rubber that is essentially a polyhexene. Also selected, because of their easy availability, were Pellethane (Upjohn Company, North Haven, CT), an ether-type of polyurethane capable of being extruded in sheet form, and a butyl rubber formulation, compounded and molded at the National Bureau of Standards. The material thickness varied, but the sheets were generally about 1 mm thick. 

Several elastomers can be used in rubber-based adhesives. The elastomer provides the backbone of the adhesive, so the main performance of the adhesive is provided by the rubber properties. However, several specific properties for application are imparted by adding other ingredients in the formulations. The most common elastomers used in rubber-based adhesives are natural rubber (NR), butyl rubber (BR) and polyisobutylenes, styrene-butadiene rubber (SBR), nitrile rubber (NBR) and polychloroprene rubber Neoprene) (CR). 

Most butyl rubber is used in the tire industry. Isobutylene-based rubbers are used in underhood hose for the polymer s low permeability and temperature resistance, and high damping, resihent butyl rubbers are used for noise and vibration attenuation applications such as automotive mounts for the engine and vehicle. Chloro- and brominated butyl rubber formulations are used in automotive hose applications where contact with fuel or air conditioning fluids occurs. 

The Bayer Tear Analyser is described, and examples are presented of its use in predicting the cut growth performance of rubber compounds for high performance car tyre treads, car and truck tyre breakers, radial truck tyre treads and truck tyre inner liners. Good correlation between the test results and the service performance of various tyre components is demonstrated. The application of the machine in optimising tyre inner liner formulations based on bromobutyl robber and blends of bromobutyl and butyl rubber is also described. 6 refs. 

In terms of the butyl polymers the variable of greatest interest to the adhesives compounder is usually molecular weight. All grades of butyl rubber are of such low unsaturation that this characteristic does not affect most performance properties in uncured or partially cured formulations. However, in applications not requiring cure the lowest unsaturation grades are usually chosen for optimum aging. 

Butyl rubber is used in preformed, hot melt adhesive rods which can be fed through various types of automatic dispensing equipment. Butyl provides both strength and flexibility to the adhesive rope before application, flow control during application, and improves the properties of the adhesive bond. A formulation for a typical rope or coil form of hot melt adhesive is shown in Table 8. 

Table 26 Model formulation of butyl rubber (bladder) application ...

---