Impact of Interface Flexibility on Separation Force in Liquid Crystal Display Vat Photopolymerization: A Comprehensive Analysis

Liquid crystal display (LCD) vat photopolymerization (VPP) is becoming popular in additive manufacturing for its precision and affordability. However, the bottom-up approach generates a significant separation force when detaching the cured part from the interface. In the LCD VPP, the interface is edge-fixed and placed directly on the LCD panel, mentioned as a flexible interface. While most research focuses on separation force analysis based on rigid interfaces (interface fixed on a substrate) using the digital light processing VPP, the understanding of flexible interface behavior remains limited. This study comprehensively analyzes the interface flexibility’s impact on separation force using polydimethylsiloxane (PDMS) in both flexible and rigid configurations. Interface thickness emerges as a critical parameter, showing contrasting effects between flexible and rigid interfaces. Although the separation force increases with print object size, it has a lesser effect on flexible interfaces compared to that on rigid ones. Notably, the rigid PDMS interface exhibits up to a 100-fold higher separation force than the flexible interface under identical printing conditions. Additionally, commercially used Teflon as a flexible interface demonstrates a 10-fold higher separation force than flexible PDMS due to its higher elastic modulus. The proposed analytical model based on Kendall adhesion theory predicts maximum separation forces with error margins of 15% for flexible PDMS and 10% for Teflon. The study also highlights the importance of interface flexibility for achieving complex structures and high-resolution printing in an LCD VPP.