UV Pre-Treatment for Polycarbonate for Bonding LSR in a Multi-Component Injection Molding Process

Abstract

AbstractIn this study, the influence of UVC radiation and the influence of ozone on the surface energy of specimens made of polycarbonate were investigated. In an additional step, the peeling resistance of silicone flaps, which were overmolded, onto pre-treated PC plates of multicomponent specimens were analyzed. For this purpose, the samples were exposed to UVC radiation for different lengths of time, ranging from 5 s to 3 600 s. To further evaluate the influence of the ozone created by the UVC in the presence of oxygen, treatments were also performed in pure oxygen and nitrogen atmospheres. Contact angle measurements as well as analyses of the surface roughness were carried out to evaluate the effect of the treatment. Two phenomena were identified during the investigations. In room air and oxygen atmospheres, a short-term effect of UVC radiation was observed, which led to an increase in the surface energy, and, therefore, also to an increase in the wettability after an exposure time of only 10 s. In addition, a long-term effect was also found when tests were performed in a nitrogen atmosphere. This effect became visible after at least 60 s, and increased over the course of the duration exposure. The surface roughness of the polycarbonate plates increased up to about 60 % after 10 s of UVC exposure time in an air atmosphere, after 300 s of exposure to UVC radiation the roughness values had more than doubled. A modular injection molding tool was designed for the production of multi-component specimens. In this tool, a thermoplastic plate is molded on the one side, and is then automatically transferred by a robot system to be overmolded with silicone on the other side. The employed injection molding technique makes an intermediate treatment, such as surface activation of the thermoplastic plate, possible before it is overmolded. Also, the short-term and long-term effects of UVC treatment were able to be verified again for the peeling resistance of the material. These tests were only carried out for specimens treated in air.