Novel inductive hot embossing for increasing micromolding efficiency

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 volumetrically 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 °C. 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.