Separation Process Comparison of Hydrogel Film and PTFE Film in Vat Photopolymerization

In constrained surface vat photopolymerization, the separation process between a newly printed layer and the vat film has long been a limiting factor for printing speed and feature size. This paper aims to compare the performance of a hydrogel film and a conventionally used polytetrafluoroethylene (PTFE) in terms of separation forces, vertical separation distances, and dimensional accuracies of the printed parts. PTFE is commonly adopted because of its low surface energy and thus low separation force, while the hydrogel film is hypothetically effective because of its repelling nature to the non-polar characteristic in most photopolymers. A custom-designed building platform with an integrated sensor is used to continuously sample the force at 1,000Hz with 0.1N resolution. The separation distance is calculated based on the ascending and descending force profiles. The results show a 26% reduction in separation forces and a 60% reduction in vertical separation distances, with 95% statistical significance when comparing the hydrogel film to the PTFE film. The dimensional accuracies of produced parts in both films are similar.