Mechanism of forming defects in roll-to-roll hot embossing of micro-pyramid arrays I: experiments

Abstract

Roll-to-roll (R2R) hot embossing is a promising process for the continuous fabrication of micro-structures on polymers with high accuracy and high throughput. This paper presents an experimental investigation into forming defects for micro-pyramid arrays during the R2R hot embossing process, aiming at a comprehensive understanding of the mechanism of forming defects as well as providing effective guidance for large-area fabrication of micro-structures on polymers. Four defect modes, the platform-like defect, the collapse-like defect, the high-low defect, and the bubble-like defect, have been discovered so far and the corresponding assessment methods have also been preliminarily established using Polypropylene (PP) as an example. The influence of two key process parameters including mold temperature and feeding speed on forming defects have been systematically investigated as well. It is demonstrated that the forming defects change from a platform-like defect to a collapse-like defect, then to a high-low defect, and finally disappear as the mold temperature increases. In the meantime, a bubble-like defect may occur if the feeding speed exceeds 1.2 m min−1. Besides, the forming defects are also observed in the R2R hot embossing of other polymer materials, such as poly(vinyl chloride), polymethyl-methacrylate and polycarbonate. Analysis of the mechanism of forming defects is beneficial to the understanding of the flow behavior in the R2R hot embossing process and to the realization of process control for high-accuracy replication of large-area polymer films with micro-structures.