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TPUs bring versatility to footwear makers
Updated: 2004-08-16:00:00 Source: Modern Plastics Editorial Staff share:

Huntsman Polyurethanes' smartLite injection moldable microcellular thermoplastic polyurethane technology is intended to help shoemakers respond to consumer demands for performance and address new environmental and consumer legislation requirements.

The company says smartLite "is the first footwear technology to combine lightweight properties, strong aesthetic possibilities, and high-quality performance." Soles made from the material are 40% lighter than rubber, can be used in combination with other soling materials like leather, and are recyclable.

The smartLite brand comprises a complete material line and Moldflow analysis and quality auditing services. Huntsman has patent coverage related to the foaming technology, which uses chemical and physical blowing agents.

The company is currently targeting premium brands now using vulcanized rubber soles. But as the technology develops, it hopes to take on more commodity materials such as EVA (ethylene vinyl acetate), since the new TPU scores in terms of bondability and paintability—smartLite requires no mechanical or chemical surface pretreatment.

Commercial grades currently include: smartLite 303, which offers performance equivalent to traditional rubber, but at a density upwards of 700 kg/cu m; smartLite 304 (minimum 600 kg/cu m) general-purpose grade; and high-performance grade 344 for complex moldings and midsoles of dual density units with densities from 550 to 700 kg/cu m. Global marketing manager Craig Roberts says the intent is to reach densities as low as 200 kg/cu m. He says this will be achieved through a combination of new technologies in polymer and blowing agents.

The materials' high flexibility gives a low risk of flex cracking. Huntsman says that during development of smartLite, more than a million pairs of shoes were introduced into the market and at press time no returns had been reported. Materials can be colored, insert molding is straightforward, and soles can be molded directly onto uppers.

The microcellular materials complement existing solid TPUs already in Huntsman's portfolio. "We have always had an eye on the thermoplastic market," says Roberts, "but we only had solid TPUs, and we couldn't get [far] into the market because they are quite hard and heavy. Now we can access a much wider market."

Huntsman conducted an industrial validation period with three pilot customers: Next (Italy), Noel (France) and Jercol (Spain). This "smartLite alliance" has since extended to include companies serving Ecco, Clarks, Camper, and Tod's. The technology is also being rolled out in Asia. Over the past two seasons, Yeon Jen, a Taiwanese sole manufacturer, has started smartLite production for the La New brand, and in China, Evais is completing validation. Huntsman has dedicated smartLite production in Osnabruck, Germany, its main European TPU facility. Huntsman Polyurethanes, Everberg, Belgium; +32 2 758 9874;


Polyolefin processing aid

Kynar Flex PPA 5300, a fluorinated polymer, helps enhance film and blowmolding applications' appearance by eliminating surface defects. The substance quickly coats barrels and screw surfaces to reduce shear forces. It eliminates orange peel, improves transparency, and can increase output as much as 10% by boosting extrusion speed, says Pierre Elmerich, market manager, Atofina. It also inhibits the formation of knots and drool at extrusion die surfaces. Processors can obtain this material either as a masterbatch or neat so it can be dosed directly during processing.

Elmerich says the aid is also particularly good in eliminating melt fracture in metallocene grades of linear-low-density polyethylene. Atofina, Paris, France; +33 1 49007030;


PC provides high glazing durability for automotive

Polycarbonate glazing systems for automotive applications require resins with good scratch resistance and long life. Exatec 900 is an improved version of the existing 500 grade. It has enhanced abrasion resistance and weathering performance.

A predictive weathering model shows that parts should withstand more than 10 years of outdoor exposure to high-UV light without reduction in properties. Key to this technology is a proprietary weathering coating, Exatec SHX, developed as an interlayer. Also the weathering layer's water-based primer, Exatec SHP 9X, is less aggressive on molded parts than the previous grade and is said to be more environmentally friendly. Using this new system provides a 50% weight reduction in windows over conventional glass. Exatec, LLC, Wixom, MI, USA; +1 248-926-4200;

EVA with broad spectrum

Part of the Levamelt range of ethylene vinyl acetate (EVA) copolymer is designed for processing protective films for glass windows and screens, protective coatings for machinery, or for sealing layers on re-sealable food package closures. The vinyl acetate content is from 40% to 90%. Content above 50% is best for films for use in low temperatures. It requires no phthalate modifiers for flexibility. Used as a tie layer, the material's adhesion can be adjusted to account for the various substrates, enabling processors to use just one tie layer material for a broad range of materials. Bayer, Leverkusen, Germany, +49 214 301;


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