UV-curable self-healing, high hardness and transparent polyurethane acrylate coating based on dynamic bonds and modified nano-silica

Abstract

UV-curable coatings have been widely used because of their environmental friendliness and low emission of volatile organic compounds (VOCs). However, the fast curing-speed of UV-curable coatings will lead to internal structural defects, which greatly restricts its application and development. In this paper, we designed and prepared a UV-curable self-healing transparent polyurethane acrylate coating based on disulfide bonds and hardened the coating by modified nano-silica. The coating shows 93 % scratch repair efficiency under UV light at 50 °C, and the coating has high hardness (4H). In addition, the coating exhibits good transparency (85 % transmittance in the visible region), which means that the coating can meet the requirements of the applications of transparency protective coating. The defect that blending inorganic particles will hinder the movement of molecular chain was overcome owing to the modified nano-silica (SiO2-KH570) is not simply mixed with the other components but grafted onto the chain. Therefore, the addition of SiO2-KH570 not only harden the coating, but also can reduce the glass transition temperature (Tg) of the coating that is helpful for self-healing of the coating. What's more, it is proved that the introduction of disulfide reversible bonds is helpful to eliminate internal stress of UV-curing materials by preheating process, in which the mechanical properties of the coating with disulfide bonds significantly improved (increased by at most 209 %). The present study broadens the application of UV-curable coatings, and is expected to address the problem of internal stress defects in UV-curable materials.