Novel inductive hot embossing for increasing micromolding efficiency

摘要

Hot embossing is one of the most common methods used for replicating microstructures on a polymeric substrate and has been widely used to fabricate precise optical products. Hot embossing is simple and provides a uniform forming pressure and high replication rate. However, periodic heating and cooling of the mold is required. Consequently, hot embossing requires a long molding cycle time and high production cost, thus reducing its applicability for mass production. To increase the molding efficiency of hot embossing, this study developed a novel hot embossing technique of rapidly heating the stamper surface by using induction coils, instead of volumetrical-ly heating the entire mold by using conventional approaches. Consequently, heating and cooling times are reduced. Furthermore, a new magnetic shielding method associated with ferrite materials was used for designing induction coils to solve the problem of uneven heating caused by the proximity effect. In this study, a novel inductive hot embossing method was used with pressurized gas for replicating microstructures on a polymeric substrate. Moreover, the crucial process parameters influencing heating uniformity, molding cycle time, and replication rate were systematically investigated. The experimental results revealed that applying ferrite magnetic shielding on a single-layer spiral coil reduced the deviation of surface temperature only from 20.3 to 11.5 ℃. In particular, when replication quality was constant, the molding cycle time was markedly reduced by over 50% (the cycle time was approximately 45 s) compared with conventional hot embossing.