3.2. 3D Printing
Different from traditional manufacturing methods, the three-dimensional (3D) printing techniques were introduced during the 1980s with the aim to fabricate customized/complex objects without the need for molds or machining, also known as additive manufacturing (AM) technology.[80-82] 3D printing method based on the photopolymerization techniques has been a hot topic in recent years due to many advantages such as highest accuracy, high production efficiency, material utilization rate of nearly 100 % and mild facilities.[83-84] Therefore, photopolymerization 3D printing have received revitalized attentions in a variety of 3D printing such as stereolithography (SLA),[85]direct laser writing (DLW),[86] digital light processing (DLP),[87] ink jetting,[88] and real-time curing of DIW.[63, 89]
Several commercial UV-light-sensitive PIS such as TPO, BAPO, Irgacure 184, and Irgacure 369 were used for the 3D printing processes of photopolymerization under irradiation at UV light.[35] Whereas, as explained in section 2.2, visible light source has obvious advantages over traditional UV light source, hence the development for novel PIs or PISs for photopolymerization 3D printing induced by visible light is essential. Xiao et al.[35] investigated a series of disubstituted aminoanthraquinone derivatives which are capable of initiating the radical photopolymerization under irradiation at blue to red LEDs. The chemical structures of the studied disubstituted aminoanthraquinone derivatives (AHAQ, 14-DAAQ, and 15-DAAQ) and additives (Iod, NVK, TEAOH, and R-Br) are shown in Figure 21.15-DAAQ/TEAOH/R-Br PISs was used for the 3D printing due to the highest capacity to initiate the radical polymerization of acrylates and the 3D resin. It took less than 8 min to print the keyring when using15-DAAQ/TEAOH/R-Br system under irradiation at polychromatic visible light (400–730) nm with light intensity 3.6 mW cm-2, as a contrast, TPO took 35 min. Markedly, the printing speed was significantly enhanced when using the 15-DAAQ/TEAOH/R-Br as the PISs, which indicates that 15-DAAQ/TEAOH/R-Br system can be used as a promising PIS for fast 3D printing. The experimental 3D printing product using 15-DAAQ/TEAOH/R-Br PISs is shown in the Figure 22.
Figure 21 Chemical structures of the studied disubstituted aminoanthraquinone derivatives and additives.[35]