A visible light-curable yet visible wavelength-transparent resin for stereolithography 3D printing

Herein, a new polymeric resin for stereolithography (SLA) three-dimensional printing (SLA-3DP) is reported. An ultraviolet (UV) or visible (VIS) light source is critical for SLA printing technology. UV light can be used to manufacture 3D objects in SLA-3DP, but there are significant occupational safety and health issues (particularly for eyes). These issues prevent the widespread use of SLA-3DP at home or in the office. Through the use of VIS light, the safety and health issues can largely be solved, but only non-transparent 3D objects can be manufactured, which prevents the application of 3DP to the production of various common transparent consumer products. For these reasons, we developed a VIS light-curable yet visibly transparent resin for SLA-3DP, which also retains UV curability. The key was to identify the photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (DPTBP). DPTBP was originally designed as a UV photoinitiator, but we found that VIS light irradiation is sufficient to split DPTBP and generate radicals due to its slight VIS light absorption up to 420 nm. The cured resin displays high transparency and beautiful transparent colors by incorporating various dyes; additionally, its mechanical properties are superior to those of commercial resins (Arario 410) and photoinitiators (Irgacure 2959). A custom-designed polymer resin makes it possible to safely print transparent 3D objects in machines designed for homes or offices. Stereolithography printers use ultraviolet lasers to initiate free-radical photopolymerization inside liquid resins, enabling layer-by-layer assembly into solid shapes. Haeshin Lee from the Korea Advanced Institute of Science and Technology, Daejeon, and colleagues now report a polymer mix containing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (DPTBP) that can be printed using visible light, a shift that lessens the risks of eye damage from accidental exposures. The DPTBP/polymer mixture at an optimized ratio has the additional advantage of being colorless, a property absent from most stereolithography resins. The team showed that a blend of the transparent photo-initiator with acrylic polymers allowed 3D printing of complex items such as chess pieces with desirable optical transparency and mechanical properties superior to commercial resins. In this study, the transparent polymer resin in visible wavelength ranges yet ironically be curable by visible light is introduced for stereolithography three-dimensional printings. The key is to use the photoinitiator, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (DPTBP), which generates radicals at the edge wavelength of visible light ranges (~420 nm). The developed resin has high transparency, commercial dyes incorporations, and superior mechanical strength to the existing resins.