Plating on plastics, the electroless deposition of a metallic coating on a plastic substrate, requires a certain surface-pretreatment process. This includes etching, which is probably the most critical step of the process. During this step, the plastic substrate is immersed in a “chemically aggressive solution” (e.g., an acidic or alkaline and oxidizing solution) to modify the chemical structure and the morphology of its surface. Etching leads to the partial cleavage of the polymeric bonds and the formation of a complex interconnected network of hydrophilic microcavities. These act as anchoring points and enhance the stable interlocking between the chemically deposited metallic coating and the plastic substrate.
Currently, the dominant oxidizing agent used in most industrial processes is an acidic CrVIO3 water solution, operating at a temperature between 50 oC and 80 oC. However, hexavalent chromium solutions are toxic and carcinogenic identified and therefore have been included in the REACH authorization list. Therefore, it is critical to replace Cr(VI)-based etching systems with less hazardous chemicals.
In the framework of the FreeMe project, Creative Nano has developed a new process for the successful etching of ABS (Acrylonitrile Butadiene Styrene), PC-ABS (Polycarbonate-ABS) and Nylon-12 or PA12 (Polyamide 12) plastic substrates using H2SO4/H2O2 mixtures (piranha solutions) instead of hexavalent chromium. The optimization of the etching step led to the electroless deposition of a uniform Ni-P alloy coating with high adhesion and good mechanical properties.