Flexible non-adhesive PDMS/PET release film for reducing separation force in bottom-up vat photopolymerization 3D-printing

Bottom-up vat photopolymerization is widely used for high-resolution additive manufacturing. However, excessive separation forces between the cured layer and the release film often lead to part distortion, delamination, and print failure, which is particularly pronounced when printing large cross-sections or with soft resins. To address this process bottleneck, a non-adhesive composite release film was developed by laminating a soft polydimethylsiloxane (PDMS) layer, grafted with a fluorinated liquid-repellent coating, onto a microporous polyethylene terephthalate (PET) substrate. The fluorinated surface reduces intrinsic resin–film adhesion, whereas the microporous PET allows air to penetrate and establish a pressure balance at the PDMS/PET interface, thereby enabling a large, controlled elastic deformation of the PDMS and transforming the separation step from rigid pull-off to a perimeter-dominated flexible peel. Compared with adhesively bonded unmodified PDMS/PET films and commercial FEP films, the non-adhesive PDMS/PET release film reduces the maximum separation force by up to 73.4% and 60.6%, respectively. Finite element simulations with a cohesive-zone model clarify the role of interface flexibility in lowering peak stresses. Demonstrations of tall (>190 mm) and geometrically complex parts printed with various resins confirm that this release-film design significantly enlarges the stable process window and improves the reliability of bottom-up vat photopolymerization.