Publication release date: November 30, 2023
For more than 40 years, BASF is a leading supplier of tailor-made high-performance footwear materials for all types of shoes and soles. With our portfolio of polyurethane systems (PU), thermoplastic polyurethanes (TPU) and engineering plastics, we offer leading companies in the footwear industry an integrated toolbox of solutions which is unique. Next to our deep material expertise, we also have an intimate understanding of the value chain; from raw materials supply and production to how to attach the shoe sole.
In general, shoes comprise an upper and a sole made from several components, for example a midsole and an outsole. Depending on the specific type of shoe, different properties are needed. From protective needs to cushioning or high grip, different materials are used to manufacture shoe soles. For example, ethylene-vinyl acetate (EVA) allows for good cushioning properties, while thermoplastic polyurethane (TPU) is known for providing strong abrasion resistance.
Infinergy® is the world's first expanded thermoplastic polyurethane (E-TPU) used in midsoles making the shoe comfortable to wear and delivering excellent running properties. E-TPU midsoles are conventionally produced on steam chest molding machines with pressures of about 0.6 to 2.2 bar and steam temperatures in the range of 110 to 130°C.
BASF recently introduced storable thermoplastic particle foams, having a polymeric surface functionalization (see news below). This functionalization offers a wide range of novel properties and enables the efficient production of parts like midsoles in conventional compression molding machines, i.e., under heat and pressure without the need of steam. The loading of the mold with these novel surface-tuned foam particles can be done manually but preferably automatized with at least one feeding line and the aid of e.g., compression air.
The molding conditions depend on the surface functionalization and/or the expanded thermoplastic material. With E-TPU, molding temperatures in the range of 100 to 150°C and molding time between one and 30 minutes are usually applied. The characteristics (like density) and the properties of the molded parts can be influenced by varying the compactaction of the beads, the heat, the molding time and the cooling time, before demolding of the desired part. With the heat treatment and the adequate mold surface, it is also possible to texturize the surface of the molded part without significantly changing the overall properties. Thus, endless designs of the surface of midsoles can be realized, for example also grid-shaped design.
Shoe soles components such as midsole, outsole and other functional elements are usually manufactured separately and then subsequently glued or sewed together. With BASF’s surface-treated thermoplastic particle foams, it is now possible to combine different kind of materials (EVA, rubber, thermoplastic materials) and/or different thermoplastic particle foams (different mixture of E-TPU, E-TPS, E-PS, E-PP, E-TPA, E-TPC, E-TPO) and/or embed inserts in one processing step.
This new technology from BASF is not only limited to compression molding, but also well suited for other molding processes like RF and steam chest molding. This innovation facilitates tailor-made design of shoe soles in short cycle times with a lower environmental footprint.
