The Surface Coating of Polyurethane Substrates, Part 1: A Review of Processing Practices from Theoretical Concepts

Abstract

Polyurethane (PU) foam products are now manufactured to meet demanding end property requirements and to compete with other polymers. For external uses, common PUs, i.e. those based on aromatic isocyanates, are prone to environmental attack, promoted by ultra violet and oxidative degradation. Increased resistance can be produced by the incorporation of anti-degradants but these have limitations. Equally the use of non-aromatic isocyanate based foams is commercially uneconomic. Therefore there is increased use of surface coatings to act as weather proofing barriers to PU foams. Four examples of the manufacture of coated PU products are given. Within each there has to be strict controls to ensure the finished article has good appearance and the desired properties. This means that the PU substrate has to be prepared and the surface coating carefully selected to maximise the properties of the resulting PU/PU composite. Generally techniques have been developed on a trial and error basis but fortunately, the currently used systems appear to follow reasonably sound surface science principles, as the second paper in this series will discuss. It is argued that painting of a PU moulding is a relatively expensive, labour intensive operation and the so-called in-mould technique has many advantages. However, there are limitations within all the coating processes involving PUs and it is hoped that the colour fastness of cheaper foam systems will be improved in the near future.