'Soft-on-soft' is newest option in soft-touch molding. (Injection Molding).* It's hailed as a breakthrough for soft-touch injection molding injection molding n. A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold. : Collaborative efforts by three companies have resulted in the commercialization of an SEBS-based TPE TPE Thermoplastic Elastomer TPE Terminal de Paiement Electronique (French) TPE Total Power Exchange TPE Twisted Pair Ethernet TPE Tampines Expressway (Singapore) TPE Therapeutic Plasma Exchange vehicle handle in which a very soft (28 Shore A) surface layer is coinjected onto a substrate of a firmer--but still soft and rubbery--60 Shore A compound. This "soft-on-soft" molding opens the door to new design options that were thwarted thwart tr.v. thwart·ed, thwart·ing, thwarts 1. To prevent the occurrence, realization, or attainment of: They thwarted her plans. 2. by previous limitations in materials and molding techniques. The partners say that to their knowledge, all of the rapidly multiplying "soft-touch" applications in handles, grips, buttons, and knobs have been "soft-on-hard" structures. In these applications, a 60 Shore A thermoplastic elastomer Thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) which consist of materials with both thermoplastic and elastomeric properties. is typically coinjected onto a rigid polypropylene polypropylene (pŏl'ēprō`pəlēn), plastic noted for its light weight, being less dense than water; it is a polymer of propylene. It resists moisture, oils, and solvents. or ABS (Automatic Backup System) See backup program. substrate using twin-shot molding. The arrival of soft-on-soft capability means that designers of soft-touch parts can now differentiate products further by tapping a broader range of softness. The molder mold·er v. mold·ered, mold·er·ing, mold·ers v.intr. To crumble to dust; disintegrate. v.tr. To cause to crumble. See Synonyms at decay. of the breakthrough soft-on-soft TPE handle is Slate-bond in Corsham, Wiltshire, U.K., which used a pair of Evoprene G compounds from U.S.-based AlphaGary Corp. The compounds were based on Kraton G SEBS resins supplied by Kraton Polymers. A new-generation grade with enhanced flow properties was used for the super-soft surface layer. Slatebond says it can make parts as soft as 15 Shore A hardness. According to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. Slatebond's commercial manager, Adrian Mumford, its variable-softness handle puts endusers in the "best of all worlds." He says the surface softness prevents hand blisters, while the firmer substrate resists abuse and chemicals. Slatebond's design replaces an existing vehicle handle of a 60 Shore A SEBS that was slipped onto a rigid handle. Soft-on-soft challenge Previous barriers to soft-on-soft molding included a tendency for the pressures of injection molding to deform soft substrates. Strong adhesion adhesion /ad·he·sion/ (ad-he´zhun) 1. the property of remaining in close proximity. 2. the stable joining of parts to one another, which may occur abnormally. 3. between different soft TPE materials was also hard to achieve. Derek Fraser, AlphaGary's global business manager, compares the problem to attempting to stick a stamp onto an envelope that is lying on a soft pillow. The challenge is especially difficult when it involves a thin-wall part. Fraser says the handle made by Slatebond consists of a 1 mm-thick, softer surface layer over-molded on a 3-mm substrate. Fraser says one key to the solution was adapting the hot-runner and gating design in the tool previously used to make the single-hardness, 60 Shore A handle. Equally important was the special high-flow SEBS resin developed by Eraton for the 28 Shore A compound. That resin's easier flow helped prevent voids at the soft-soft interface. It also minimized knit line formation and ensured good adhesion of the soft layers, according to Fraser. Exploring new territory The partners are exploring potential for soft-soft design in additional applications. They argue that if the concept works for a vehicle handle, it can also be used for numerous other handles and grips for anything from knives to crates Crates (krā`tēz), fl. 449 B.C., Athenian comic dramatist. He is said to have introduced into comedy themes other than those of personal satire, and he was one of the first to show the comic possibilities of the drunkard. to wheelbarrows. Slatebond is already working on other applications. Kraton Polymers anticipates that soft-on-soft molding will catch on rapidly once initial applications prove themselves in the market. Roif Schrauwen, Kraton's compounding account manager, says target markets include appliances, packaging, sports gear, and auto interior parts. He sees soft-soft designs replacing some current soft-hard applications and fostering entirely new uses. Schrauwen compares the status of the soft-soft concept today to that of hard-soft products a decade ago. NEED TO KNOW MORE? AlphaGary Corp., Leominster Mass Tel: (800) 221-6599 www.alphagary.com Kraton Polymers Houson Tel: (713) 222-6492 www.kraton.com |
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