Modeling of the effect of heat flux on replication accuracy using roll-to-roll micro hot embossing

Abstract

R2R large area fabrication of functional panels gained popularity in recent years and micro 3D profiles for optical films and biomedical applications have gained momentum with improving replication accuracies in hot embossing systems. However, studies on the effect of heat flux on the replication accuracy have been lacking. In this study, a twin belt based roll-to-roll embossing system was designed and built to study the effects of various in-situ heat transfer at the hot embossing nip. Seamless embossing was then demonstrated on PVC film. The effects of different heat transfer schemes have been modeled using Solidworks simulation applying experimentally obtained mechanical properties of the polymer film. The simulation results are compared quantitatively to the experimental results to analyze the effect of heat transfer schemes on the replication accuracies. We achieved 92% replication accuracies on the PVC film replicated by application of heat on the side of the film not in contact with the mold. It is significantly higher than the features replicated using an isothermal condition at Tg and also heat transfer from the mold. Thermal simulation shows a steep thermal gradient between the polymer under nip and the immediate surrounding for the isothermal conditions and a gentle thermal gradient for the other two schemes. Displacement of the polymer shows a highest flow of material from the surrounding of the feature for the underside heating method. This results in a more accurate replication onto the PVC film.