By David Reed, UT EditorLeverkusen , Germany-Bayer MaterialScience AG has developed a thermoplastic polyurethane compound which, it claims, has “unusually high water vapour permeability.” The firm has also just helped to develop a scratch-resistant TPU suitable for use in flexible windows.The first material, tradenamed Desmopan DP 6580A MVT (Moisture Vapour Transmission) is used to make films for coating fabrics. The water vapour permeability of a 15-micrometer thick film is 5400 grams per square metre per day at 38°C and 90-percent relative humidity, when tested according to DIN Standard 53122.”This high breathability opens up completely new possibilities for coating sports and leisurewear, particularly when using membrane technology,” says Jens Ufermann, head of the coatings and films segment in the TPU business unit of Bayer MaterialScience.The polyether-based TPU can be extruded to produce blown and flat films which are compatible with the adhesives commonly used to bond textiles to films, and are also suitable for lamination. They additionally display very good mechanical strength for films of this type, Bayer adds.The TPU for windows, designated Texin DP 3041, is a further development of a TPU that has already been used in the rear window of BMW AG’s Z8 Roadster. The particular strength of this plastic is its scratch-resistance, which ensures that the panels have long-lasting transparency. “I set about finding a flexible material that would remain transparent over an extended period of use,” recalls Dieter Gnegeler, a water sports enthusiast and yacht owner, explaining that “it really used to annoy me when I had to replace the window panels of my sprayhood extension after only one season because they were scratched and I couldn’t see through them properly.” The ‘sprayhood extension’ is a tent that covers the open cockpit of a yacht to create additional interior space, for example, somewhere to sit out of the rain or in the shade. Its windows are usually made of plastic and are subject to great stress as a result of the harsh conditions at sea.Gnegeler is, in fact, the owner of GEBA Kunststoffcompounds GmbH in Ennigerloh, Westphalia, Germany-a company with a Europe-wide reputation for compounding and upgrading plastics, “so he knew exactly what he was doing,” explained a BMS statement.”We have optimised the material so that it is softened somewhat when heated by the sun, enabling any unevenness to be levelled out. This means that small scratches caused, for example, by abrasive sea salt crystals when cleaning the panels, practically repair themselves,” says Jürgen Winkler, sailing enthusiast and TPU specialist at Bayer, who was involved in the development of the material.The TPU material is also free of plasticisers, Bayer emphasises, so the panels retain their flexibility for a long time. Panels made of PVC (polyvinyl chloride) become brittle over time because the plasticiser gradually escapes from the plastic. A further advantage that TPU has over PVC is its high flexural fatigue strength and buckling resistance. This ensures that there are no annoying cracks or clouding at the folds of the panels.The company that produced the actual panels was IMS Kunststoff AG, based in Ittigen, Switzerland. It helped create the outstanding optical quality of the panels, using a special process it has developed. “We use a polishing technique developed in-house that uses double-belt presses and produces outstanding high-gloss surfaces,” explained Claus Gruner, IMS expert, in the Bayer statement.”
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