Polyamide powder coating of copper substrates: Impact of process parameters on the surface properties, the adhesion strength and the interface microstructure

Abstract

The aim of this work was to assess the impact of coating process parameters on the quality of biopolyamide coating on copper substrates obtained by conventional hot dipping fluidized bed coating process (CHDFB). The experiments carried out in this study allowed to understand the decohesion mechanism of virgin biopolyamide 11 before having assessed coating properties by chemical, mechanical and microstructural characterizations. The investigations showed that a higher thickness and better surface finishing were obtained for high preheating temperatures and intermediate immersion times mainly thanks to a higher heat energy stored by the metal support whereas long immersion times compromised the aspect. A laboratory-developed mechanical test was also carried out to determine the adhesion strength. This allowed to overcome the variability linked to the analyzed surface preparation or the local radius of curvature of pull-off and peel conventional adhesion tests respectively that could influence the adhesion strength data. It was concluded that, even if more severe metal preheating conditions improved the coating physical properties, they led to a worse adherence. Surface morphology and spectrometry analyses of the coating side facing the interface correlated to the mechanical test results allowed to highlight the growing formation of copper oxide and copper hydroxide compromising the coating adhesion. From all the results, the optimal process parameters were determined.