ExxonMobil's Santoprene Division has been offering TPEs that bond to various engineering thermoplastics for years. But there's always room for more TPEs that can chemically bond to their substrates, according to Seth Barron, consumer products manager for Santoprene. "We've seen tremendous growth in this area," he says. So much growth that the company has just extended its portfolio of materials that targets thermoplastics used often in the consumer electronics industry. These include ABS, polycarbonate, polystyrene and related blends. The company's new B 150 bonding grades, thermoplastic vulcanizates containing EPDM and an undisclosed polymer, are available in 60 and 75 Shore A hardnesses. The company's earlier B 100 EPDM-polypropylene bonding grade for engineering thermoplastics came only in a 55 Shore A hardness. The two new grades are not only harder but also improve on two key technical attributes. They do a significantly better job sticking to ABS substrates, Barron reports. Whereas the B 100 material offered a bond strength of about 21 pli on ABS, the new grades offer a bond that's stronger than the elastomer itself, which has a 800 psi tear strength. "The bond just does not fail. The TPE fails cohesively," says Barron. The new grades also offer better adhesion when overmolding TPE over a previously-molded "cold" insert — as opposed to overmolding over a "hot" first shot in a two-shot tool. B 100 has also under-gone an important change of its own. It recently received FDA approval for some food contact applications, including resealable containers and closures.
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