Minoru Sawai

Super Low Density Polyurethane Systems for Sports Shoes

This paper describes in detail a new concept of producing super light weight (0.24-0.26 g/cm3) polyurethane (PU) midsoles to compete with EVA for sports shoes. Materials for the midsole of the dual density sport shoes are composed of PU or EVA. Though PU midsole has good cushioning (resilience), adhesive and processing properties compared with conventional EVA systems, it is difficult to reduce the molding foam density drastically. Recently, developments for high performance PU systems have focused on reducing the density while maintaining high physical properties. To solve this problem, we have developed several new progressive technologies. The first uses a polyesterpolyol with functional cohesive units in the main polymer chains. Using this polyesterpolyol, the hard segments of PU become tougher. The second is distributing the cell diameter gradient toward the center of the foam cross section. The split tear, which is one of the most important physical properties for a midsole, has been improved drastically. These new technologies are the best way to spread super light weight PU to new applications and markets.