Photoluminescent ZnO nanoparticles photoinitiators for the photo-curing depths of pigment coatings

UV light has poor penetration in the photo-curable thick pigment coatings, and their small photo-curing depths were often measured. In order to increase the photo-curing depths, the photoluminescent ZnO nanoparticles (NPs) photoinitiators were synthesized and added into the photo-curable thick pigment coatings. With the sol-gel method, the ZnO NPs synthesis conditions (stirring speed and peristaltic pump speed for dropping NaOH) were optimized by the data of X-ray diffraction, photoluminescence spectra, particle sizes, and zeta potentials etc. The results showed that the best stirring speed was 2200 r/min and the best peristaltic pump speed was 15 rpm. Then, the ZnO NPs photoinitiators were added into the photo-curable thick coatings with SiO2 and TiO2, and their photo-curing depths were increased, which were compared with those of without ZnO NPs. The maximum photocuring depths were 11 mm of SiO2 and 7.8 mm of TiO2, respectively, with 0.4 wt% ZnO NPs. Furtherly, the ZnO NPs photoinitiators were chemically bonded onto the pigments' surface using a silane coupling agent, 3-aminopropyl triethoxysilane. The results of infrared spectra, energy dispersion analysis, scanning electron microscopy, and thermogravimetric data demonstrated that this modification was successful. Their maximum photo-curing depths of the modified SiO2 and TiO2 systems were increased to be 14 mm and 11 mm, respectively. This investigation confirmed that the using of the photoluminescent ZnO NPs photoinitiators was an effective strategy for the deep photo-curing of the thick photo-curable pigment coatings.