Figure 24. The top view of STL model file and the topography print cured using the PEGDA 700/water (80 %/20 %, wt) in the presence of IDGCM/Iod (0.5 %/2 %, wt) and 25 mM NaOH. (30 × 30 × 15 mm, L × W × H).[90]
In the process of photopolymerization 3D printing, the light transmitted through the solidified polymer layers is highly likely to trigger undesired lateral photopolymerization during the printing of subsequent layers and therefore leads to deteriorated print resolution.[91] Nonreactive light absorbers can improve print resolution by limiting light penetration, however, they also reduce printing speed.[92] It is a challenging to develop a 3D printing technique with both high print speed and resolution. Xie et al.[93] designed an efficient 3D printing method by using one ketocoumarin compound, i.e., 3,3′-carbonylbis(7-diethylaminocoumarin) (KCD), as the photosensitizer (also a reactive light absorber) because of its high photoinitiation efficiency, low bleaching capacity and high molar extinction coefficient of photolysis products (limiting light penetration and improving resolution). The processes of generating radicals through photooxidation or photoreduction are shown in Figure 25 a, it is difficult to limit the light penetration due to the obvious blue shift (61nm) of the product KCD ketyl radical in the photoreduction process, which resulting in low resolution and the printed feature could not be identifiable (Figure 25 c). In comparison, the photopolymerization 3D printing based on the photooxidation of KCD that functions as the photosensitizer can simultaneously deliver high print speed (5.1 cm h−1) and high print resolution (23 μ m). The method provides a viable solution towards efficient AM by controlling the photoreaction of photosensitizers during photopolymerization.