Powder coating films with latent adhesive function for metal-plastic hybrids

In the presence of specific catalysts the reaction between uretdione crosslinkers and Ohpolyester resins results in a two-step curing mechanism. A polyallophanate network is formed at crosslinking temperatures up to 150 °C. At temperatures higher than 170° C the polyallophanate network is transferred into polyurethane structures completely. It was already proved earlier that the second reaction can be used as a reactive adhesive layer in a subsequent injection moulding process. The goal of this study was to investigate the influence of the OH number of the resin on powder coating properties, the formability of aluminiumpowder coating systems and resulting adhesive strength after injection moulding of thermoplastic polyurethane to the precoated aluminium substrate. Very flexible powder coating films were developed which are able to post-form by e.g. deep drawing. It was shown that the adhesive strength between the powder coating layer and the following injection moulded thermoplastic is relatively independent on the OH group content.