An Alternative Pre-Treatment for Metallization of Polymeric Materials and Its Applications

Abstract

Metallization of polymers is a challenging process due to the intrinsic difference in the chemical nature of Polymeric and metallic materials. This leads, in the best scenario, to metallic deposits having poor adhesion to the polymeric substrate1. Neglecting wet processes2, that are based on hazardous chemicals (as chromic acid) and limited to specific polymers, plasma activation has been considered a promising option for more than thirty years. In the past, pioneering studies demonstrated that low pressure plasma is a valid alternative pre-treatment to chemical etching. This is due to the ability of plasma to graft nitrogen-containing functionalities that bind to palladium in the activation bath3–5. Technological advancement in the field of plasmas allowed developing open air systems, thus reducing operational costs and dimensional limitations. Since, in principle, plasma parameters can be tuned to be effective on different classes of polymers6,7, this pre-treatment allows electrochemical metallization of polymers that couldn’t be plated due to the ineffectiveness of wet chemical etching. In this study open-air roll-to-roll dielectric barrier discharge (DBD) equipment was used to pretreat different polymers including Polyetheretherketone (PEEK), Ethylene ChloroTriFluoroEthylene (ECTFE) and Poly Vinyldene fluoride (PVDF) films with nitrogen-based plasma. The plasma modified surface of the films was therefore coated with metal by means of a commercial electroless copper or nickel lines or homemade silver baths. Different thickness values have been considered for the metallic coating. While thin deposits (up to about 250nm) were obtained by electroless only, thicker coatings were obtained performing electrodeposition on top on the metallic layer previously obtained. Specific characterization of the metallic-coated polymers was performed depending on their final application: this spans from barrier layer to fluids to flexible concentrator mirror for solar thermodynamic. Further studies were performed to understand the nature of the modification induced by plasma to the polymer surface, both from a chemical and morphological point of view, in the first case by means of XPS and in the second by AFM. Nucleation and growth of the metallic layer was studied by SEM. Adhesion between polymer and metal was studied by cross cut test (ASTM D3359), which confirmed excellent adhesion levels.