Page 318 - Handbook of Plastics Technologies

ELASTOMERS

4.110 CHAPTER 4

FIGURE 4.40 Schematic of blow molding.

transition temperature, if there is no crystallinity), then pressure or vacuum is used to
stretch the softened sheet over or into a mold or form. Draw ratios up to 3:1 (thickness of
original sheet to final part thickness) can be attained with some TPEs. TPVs are particu-
larly suited for both this technique and blow molding.
Welding is a fast and simple method for bonding a TPE to itself or to another compati-
ble thermoplastic material. The surfaces to be joined must be heated above the melting
point and held together under slight pressure (preferably after some flow has occurred) un-
til the joint cools and solidifies. Surface heating can be by direct contact with hot air or a
hot surface, radiation heating, or other methods.
TPEs can readily be via foamed extrusion to lower their macroscopic hardness and
density. Closed-cell foamed tubing, sheeting, and profiles with a thin, solid skin are now
routinely fabricated by extruding TPEs with a chemical or physical blowing agent.

4.6.5 Uses for TPEs
TPEs find uses in many applications where thermoset rubbers are used, but not in pneu-
matic vehicle tires, which account for slightly more than one half of the worldwide rubber
consumption. There are, however, a number of TPEs that are used for solid, nonpneumatic
tires, and caster wheels for carts, lawn equipment, toys, and so on.
Nontire automotive uses where the service requirements are not too demanding (tem-
perature below 70°C and little or no fuel and oil resistance required) have provided numer-
ous markets for both the styrenic and TPO materials. These uses include weather
stripping, bumpers, fascia, dashboard trim, plugs, and grommets, to mention a few.
The higher-performance COPs, TPUs, and TPVs are used in those areas where the ser-
vice-temperature range, mechanical abuse, and fluid resistance demand a higher level of
performance. Such applications include seals and gaskets, convoluted grease-filled boots
for steering and front-wheel drive, and assemblies and covers for safety air bags.
The growth of TPE usage in nonautomotive applications has also been rapid. Specific
parts are as diverse as dishwasher sump boots, architectural window glazing, flashlight
housings, hand-tool gaskets, typewriter and printer rollers, and household plumbing seals.
Low dielectric constant, high electrical resistance, high dielectric strength, and low
power factor make hydrogenated styrenic block copolymers and EPDM/PP TPVs espe-

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