TPEs | Innovation
sion properties than alternative styrenic-based nylon bondable TPE materials.”
Teknor Apex has an interesting position on styrenics versus EPDM-based TPEs. Almost four years ago, this compounding company took over the Sarlink range of TPVs from DSM. Now it is extending the brand, but this time with grades based on styrenic (TPE-S) chemistry. Teknor Apex, which claims to be the most diversifi ed manufacturer of TPEs, says this will expand the range of economic and performance alternatives available to manufacturers of sealing systems and other automotive components by providing similar, and in some cases improved, performance.
Figure 1: Compression set performance of Thermolast V (TV6VNZ grade) Source: Kraiburg TPE
cable bushings, timing belt covers and radiator covers. In addition to good mechanical properties, temperature resistance up to 140°, and very low compression set (Figure 1), the compounds also feature good adhesion to non-polar polypropylene and polar polyamides. Thermolast V compounds are partially cross-linked
TPVs. But rather than containing EPDM rubber, Thermolast V grades use styrene-ethylene/butylene- styrene (SEBS)—which is where the compatibility with polyamide comes from. With an ideal confi guration of processing parameters in the two-component injection moulding process, Thermolast V and polyamide can achieve good adhesion of more than 5 N/mm, claims the company. Chemical cross-linking during the production
Right:
ExxonMobil’s Santoprene – the longest established
TPV - has found widespread application in automotive ducting
process increases the continuous use temperature to as high as 140°C. The company says this means the materials are comparable to TPV-(EPDM+PP) and conventional rubber compounds based on EPDM, CR, NBR and HNBR. Kraiburg is not alone in emphasizing the importance of being able to co-mould TPEs with polyamides. Last year, another major compounder, US-headquartered RTP Company, licensed manufacturing rights from ExxonMo- bil Chemical for types of Santoprene (the original TPV) that bond to polyamides. At the time, RTP said it would provide current users a seamless supply transition and would also develop new markets and applications. The materials are marketed as the RTP 6091 Series. They are available globally with hardness of 55 to 85 Shore A, in various colours. RTP says the compounds “offer superior thermal resistance (up to 135°C), excellent chemical resistance, and better compres-
18 INJECTION WORLD | April 2014
The new compounds are physical blends of styrene block copolymers (SBCs) with narrow molecular weight distribution, and other, unspecifi ed, ingredients. Properties can be varied easily and widely by modifying the compound formulation, the supplier says. And there are some cost advantages.
“Unlike the widely used TPV automotive compounds with which the Sarlink brand has been identifi ed, the Sarlink TPE-S compounds are not affected by variations in the price of EPDM rubber, a key ingredient in TPV manufacture,” says Ger Vroomen, senior marketing manager for automotive. “In the past, interest in TPE-S compounds intensifi ed as a result of sharply increasing costs for EPDM, but, although TPE-S compounds still retain an economic advantage, they have also emerged as practical alternatives to TPVs because of their properties.”
According to Teknor Apex, TPE-S compounds
generally exhibit strength and elasticity comparable to TPVs (Figure 2). They provide smoother part surfaces and equivalent or better long-term UV stability than TPVs and exhibit a broader processing window in injection moulding. TPE-S compounds are available in a
www.injectionworld.com
PHOTO: EXXONMOBIL
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