Novel Polyurethane Systems for Footwear as Replacement for EVA and Rubber

Abstract

Polyester based microcellular polyurethanes are usually dimensionally unstable at low densities and show shrinkage.

Polyether based polyurethane soling materials however are usually dimensionally stable at these lower densities but exhibit unacceptably low mechanical properties. The density of these soles is therefore limited by the required properties.

Shrinkage occurs, at lower densities, because there is insufficient strength to support the foam and because of inherently high closed cell content. Problems of shrinkage have been overcome by the development of a new ICI prepolymer. This product acts as a reactive surfactant thereby controlling reactant compatibilities, cell size and open/closed cell ratios. Stable foams down to the free rise density are now possible.

The nature of the product is such that the derived products maintain satisfactory properties even at densities down to ca. 200 – 250 kg/m³. This constitutes a major weight saving per sole. Conventional midsoles have densities of ca. 400 – 500 kg/m³, so achieving, with the new prepolymer, a weight saving of ca. 50 %.

The low density midsole system can be used in conjunction with almost any outsole material. But of special interest is the use of the recently developed, high slip resistant outsole. The construction of this combi-sole allows direct replacement of EVA/Rubber soles - but with the usual all-PU processing/handling advantages. The high slip resistant PU outsole system is a soft formulation, which employs novel hydrophobic soft blocks and retains excellent mechanical properties.