Polyurethane in Shoes and Shoe Machinery

The use of solid polyurethane rubber for ladies’s shoe heel top pieces has been known for several year. Cast grades of medium to high hardness have generally been employed for this purpose, but more recently the thermoplastic polyurethane have been graining ground. The material cost of polyurethane are high compared with more conventional heeling materials and to be competitive the processing cost must be as low as possible. The high cost has so far prevented the use of solid polyurethanes for the soles of shoes but the development of the cellular varieties of the solid materials has reawakened interest in this outlet. By using cellular grades with a specific gravity of 0.4, material cost are reduce to a third of those of the solid. Provided the process can be refined sufficiently to keep the costs low, soles for hard-wearing applications are a distinct possibility. In this case closed cell matreial is necessary to prevent excessive uptake of water.

The process for shoe manufacture is becoming highly automated. The high hardness, toughness and flexibility of the solid polyurethanes make them excellent materials for many items in this application. Replacement of a natural rubber diaphragm by polyurethane increased the diaphragm life from two months to a yeas.