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The lightweight that offers a heavyweight performance

Bayer MaterialScience AG : 27 April, 2004  (Company News)
The Bayflex
The superior material characteristics of polyurethanes mean that this material is not only a serious rival to EVA when it comes to density, Bayflex® lightweight also 'streamlines' the manufacturing process for particularly lightweight fashion and leisure footwear.

'Previously, lightweight footwear was associated with disadvantages in terms of abrasion and life span,' explains Wolfgang Grimm, a process developer at Bayer MaterialScience. 'This problem was only solved when we managed to combine robust outsoles, for example using Desmopan® thermoplastic polyurethane from Bayer MaterialScience AG, with a particularly light midsole material, which ensures that the shoe remains comfortable. But from time to time, the Bayer developers still fall back on EVA, a material that caused difficulties due to its problematic long-term set behavior and comparably complex processing.

'These challenges have now been easily overcome with Bayflex® lightweight,' says Grimm. The density of this polyester polyurethane is between 200 and 300 grams per liter, is therefore far lighter than the densities of comparable polyurethane soling materials and falls right in the middle of the former EVA range. Joint process development between Bayer MaterialScience and Desma meant that all the benefits of polyurethane processing technology could be transferred to this material.

'Unprocessed polyurethane displays exceptional levels of adhesion to other shoe materials, e.g. leather and other polyurethanes including lightweight, abrasion-resistant and transparent TPUs. As a result, lightweight Bayflex® midsoles can be directly cast onto the outsoles with ease,' points out Wolfgang Grimm. Unlike EVA, new and improved Bayflex® enables efficient direct soling. 'This is where we were able to make significant improvements to the material,' says the engineer. 'As far as direct soling is concerned, Bayflex® lightweight now also offers the possibility at the foaming stage of forming long-lasting bonds with other shoe materials without the need for adhesives. The exact design replication resulting from the 1:1 surface reproduction which is characteristic of polyurethane and step-by-step variable coloring means our new, lightweight midsole material meets the greater demands arising from increasingly flexible footwear production,' says Grimm. Anyone looking to find out more about direct soling should not miss the demonstrations at the Desma trade show booth at SIMAC.

'Bayflex® lightweight naturally also features dynamic properties typical of polyurethane, i.e. exceptional shock absorption and resilience,' says Grimm of the material's additional benefits. Despite its low density, Bayflex® lightweight displays lower dynamic set than EVA and provides constant energy loss over a longer deformation path. This means that it offers much softer shock absorption properties than EVA. Utilizing polyurethane in the manufacturing process also means it is possible to dispense with air cushions and wedges. As changes in the force and deformation behavior of Bayflex® are extremely low over the entire life span of the shoe, the wearer is guaranteed comfort over a longer period. The foam used by Bayer MaterialScience in the Bayflex active, fashion, and safety footwear-material product lines also has excellent mechanical properties, placing it way ahead of other midsole materials.
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