Improved molding of micro structures using PVD-coated mold inserts

摘要

Micro structured optical plastics components are intensively used, i.e. in consumer electronics, for optical sensors in metrology, innovative LED-lighting, or laser technology. Injection molding has been proven successful for the large-scale production of these parts. However, the production of these parts still causes difficulties due to challenges in the molding and demolding of plastics parts created with laser-structured mold inserts. A complete molding of the structures often leads to increased demolding forces, which then cause a breaking of the structures and a clogging of the mold. An innovative approach is to combine physical vapor deposition (PVD)-coated, laser-structured inserts and a variothermal molding process to create functional micro structures in a one-step process. Therefore, a PVD coating is applied after the laser-structuring process in order to improve the wear resistance and the anti-adhesive properties against the plastics melt. In a series of molding trials with polycarbonate (PC) and polymethyl methacrylate (PMMA) using different coated molds, the mold temperature during injection was varied in the range of the glass transition and the melt temperature of the polymers. Subsequently, the surface topography of the molded parts was evaluated by digital three-dimensional laser-scanning microscopy. The influence of the molding parameters and the coating of the mold insert on the molding accuracy and the demolding behavior were analyzed. It was shown that micro structures created by ultra-short pulse laser ablation can be successfully replicated in a variothermal molding process. Due to the mold coating, significant improvements could be achieved in producing micro structured optical plastics components.