Kim, Dong (2019-11). Investigation of an Optically Created Dead Zone by Low-One Photon Polymerization for Silicone Stereolithography. Doctoral Dissertation.
Thesis
Silicones have a variety of applications in many fields because of their unique properties such as bio-applicable, corrosion resistive, mechanically elastic and tough, and stable under a high temperature condition. 3D printing techniques have been actively studied freedom to fabricate complex geometries. Vat photopolymerization (VP) provides a high printing resolution, better mechanical isotropy, minimal structure defects, and fine surface finish. This study evaluated the printability of the silicone photopolymer with digital light processing. The results showed a good dimensional accuracy and better mechanical isotropy. However, it was found that the strong adhesion between the cured polymer and the bottom surface of a vat. The separation force to overcome the adhesion caused a slow printing speed and printing failures. To eliminate the separation force, an optical method to create a gap between the interface was investigated. Using a low one-photon polymerization (LOPP), a limited curing at the focal spot was successfully demonstrated. Three different wavelengths with different absorbance rates were selected and tested under the stationary and moving exposure conditions. the ultra-low absorbance wavelength showed a higher printing resolution and lower geometrical variation. With a small error, the data from the stationary exposure condition converted to the parameter for the moving exposure condition. However, it also found that the ultra-low absorbance wavelength required extremely high irradiance to compensate the time loss from its ultra-low absorbance. The time could not be linearly scaled by power due to the non-steady state polymerization kinetics.
