Novel Waterborne UV-Curable Hyperbranched Polyurethane Acrylate/Silica with Good Printability and Rheological Properties Applicable to Flexographic Ink

Novel waterborne UV-curable hyperbranched polyurethane acrylate/silica (HBWPUA/SiO2) nanocomposites were prepared by a three-step procedure and sol–gel method. 1H NMR and 13C NMR results indicate that HBWPU is successfully synthesized. Surface tension and contact angle tests both demonstrate the good wettability of the nanocomposites. Besides, the kinetics of photopolymerization of HBWPUA/SiO2 films were analyzed by attenuated total reflection-Fourier transform infrared spectroscopy, which reveals that the modified SiO2 could accelerate the curing speed of HBWPUA coatings. Thermal gravity analysis indicates that the HBWPUA/SiO2 hybrid films have a better thermal stability than the pure HBWPUA cured films. Furthermore, the hybrid films show enhanced pencil hardness, abrasion resistance, and adhesion. On the basis of the above, HBWPUA/SiO2 nanocomposites were finally applied to waterborne UV-curing flexographic printing ink, which is printed on poly(ethylene terephthalate) and glass. The nanocomposite presents good rheological behavior because the ink has a lower Z0, a higher Z∞, and the viscosity rebuild time is 375 s. Three colors (red, yellow, and blue) of ink were used to test its printing quality, the curing time was below 30 s, and the adhesion was excellent without being stripped. All of the inks show good water resistance and abrasion resistance. Moreover, the red and blue inks possess better solid densities than the value of 1.07 of yellow ink, and are 1.83 and 1.84, respectively. The current study suggests that the process has promise in applications of food packages.