CLEVELAND - TriMax LLC is handing out grades in thermoplastic elastomer overmolding, with some materials passing and others flunking.
The Boulder, Colo.-based marketing and design firm - a division of resin distributor Prime Alliance of Des Moines, Iowa - is releasing the results of its ``Thermoplastic/TPE Bonding Study,'' which analyzed how 29 different TPEs provided by 14 different materials makers performed when overmolded onto nine different plastic substrates.
TriMax partner Joe Muhs revealed some of the study's basic findings at Performance Elastomers & TPEs 2001, an industry conference hosted May 14-15 by Principia Partners in Cleveland.
All materials submitted to TriMax were tested at 90- and 180-degree adhesion to substrate plaques at three common processing temperatures, which varied for each TPE family.
The five common TPE families - thermoplastic vulcanizates, thermoplastic polyurethanes, styrenic block copolymers, copolyesters and thermoplastic olefins - were tested along with a sixth alloy category that consisted of combinations of the five common TPEs.
All testing for the study was conducted by Akron Rubber Development Lab, a private research facility in Akron, Ohio.
In the study, copolyesters showed the best adhesion qualities to ABS, polystyrene and polycarbonate. TPOs had excellent adhesion to polypropylene, while only one of the 29 TPEs tested - a styrenic block copolymer - adhered well to nylon.
Copolyesters, TPUs, styrenic block copolymers and TPE alloys showed ``respectable'' bonding to copolyesters. Copolyesters, TPUs and TPE alloys also showed good adhesion to cellulose acetate butyrate.
Muhs admitted that TriMax's motivation for doing the study - which was funded by the 14 TPE makers involved - was somewhat selfish.
``We had gotten into hot water a couple of times when our product development team recommended materials to processors that didn't work,'' Muhs said. ``There was a lot of information out there about overmolding TPEs, but it wasn't consistent. Different producers would give conflicting information about the same material. We decided we had to try to go to a level playing field.''
The study's finding also debunked a commonly held overmolding myth: A better bond can be achieved merely by increasing processing temperatures.
In 80 percent of cases, increasing the temperature failed to improve the bond or made it worse, Muhs said.
Muhs added that he hopes those purchasing the study - which TPE makers are allowing TriMax to market - will follow the compiled test results to achieve better results in their overmolding ventures.
``Now we can recommend the right family and right grade of TPEs and teach processors what questions to ask of their TPE suppliers,'' Muhs said.
Companies participating in the Trimax TPE study were Advanced Elastomer Systems LP, BASF Corp., Bayer Corp., BFGoodrich Co., Diamond Polymers Inc., Dow Chemical Co., DSM Engineering Plastics, DuPont Co., GLS Corp., PolyOne Corp., Kraiburg, J-Von NA LLC and Montell Polyolefins Inc.