Two-component polyurethane molding is an innovative solution which raises the operational characteristics of footwear, improves the design and combines various materials and their properties (for example, PU / nitrile rubber).
Two-layer molding technology uses the foamed PU for the weight reduction of footwear, and one of three other materials as the outer layer:/p>
- the outer layer is made of a densified PU with the high abrasion resistance;
- the outer layer is made of TPU;
- the outer layer is made of nitrile rubber.
The process of forming the sole outer layer consists of several stages.
1. In case of employing PU/PU technology, the more dense and firm polyurethane painted in the other color is injected into the lower part of the pressing mold. While using the PU/PTU technology, the granulates of thermoplastic polyurethanes (TPU) while melting in the extruder fill the lower part of the pressing mold accurately repeating the tread pattern.
In case of employing the PU/Nitrile technology, the preliminary treated and vulcanized cover plate made of nitrile rubber is inserted into the pressing mold.
2. The upper shoe layer, drawn tight over the last, is lowered into the pressing mold without tightly adjoining the formed lower outer layer. Further, PU is injected into the pressing mold. The foamed PU is a thermoreactive liquid polymer that is initially in the liquid state. The polymer changes into the solid state under the high temperature conditions and, by expanding, fills the space between the shoe upper and the outer layer which is inside the pressing mold (PU or nitrile, or TPU).
3. At the final stage, the sole rises to the foortwear top in the injection unit under the established temperature modes and the sole is finally formed, whose properties considerably exceed the properties of a thermoelastoplastic (TEP) and polyvinylchloride (PVC) sole.