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.