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Processing Guidelines
TPUs can be processed with the conventional extrusion and injection molding equipment, recycled and colored.
Extrusion
Pearlthane® and Pearlcoat® grades are particularly suited for the extrusion process, and standard extrusion equipment works in most cases. Due to the shear sensitivity of TPU, a gradual transition from feed to metering zone is recommended.
A compression ratio of 3:1 will suffice for proper melting of the material. Hence, standard single screws used for polyethylene or PVC are suitable, whilst the typical nylon (short compression) screws will certainly not work. Barrier-type screws have also proven to be suitable for Pearlthane® TPUs.
Injection
The standard injection molding equipment will normally be suitable for Pearlthane® TPU. Generally, short and wide sprues and gates are most suitable in order to improve the flowability and demolding operations. Cooling of the mould or polishing the mould surface can enhance demolding in the case of sticky and thick walled moldings.
The average shrinkage values are between 1-3%, depending on the material hardness and other factors.
Balanced venting is highly recommended in order to facilitate trapped air and gas to escape from the mould. Processing temperatures normally ranges from 160°C to 220°C as indicated in the Figure below.
