Integrated electrochemical approach for the investigation of silane pre-treatments for painting copper

Abstract

Copper surfaces are sometimes protected with an organic coating to improve the durability or the aesthetic properties. Examples of industrial applications are household appliances and heat exchanger components. In order to extend the service life of the organic coated copper a specific surface pre-treatment is often required. Nevertheless, probably because of the limited market of this application, no specific pre-treatments for copper are industrially developed, with the exception of cleaning procedures, but simply extensions of existing pre-treatments optimised for other metals (aluminium, zinc, magnesium alloys) are used. The application of silane pre-treatments as adhesion promoters for organic coated metals is remarkably increasing in the last decade, because silanes offer very good performance together with high environmental compatibility. The idea is therefore to try to develop a specific silane based pre-treatment for copper. The starting point is the existing silane products for aluminium, modifying the composition and the application conditions (concentration, pH of the bath, additives, etc.) in order to develop a high performance copper alloy pre-treatment increasing the protective properties and the adhesion of a successively applied organic coating. The deposits were analysed using FT-IR spectroscopy and optical and electron microscopic observations. A electrochemical characterization was carried out to highlight the silane properties and to evaluate the performance of the different deposits. A final powder coating was applied and the properties of the complete protecting cycle was evaluated. The electrochemical approach is based mainly on electrochemical impedance spectroscopy measurements.