Robust UV-curable polyurethane acrylate coating

In a new study, a UV-curable, self-healing, transparent polyurethane-acrylate coating based on disulfide bonds was developed
and hardened by modified nano-silica.

UV curable coatings are widely used because of their environmental friendliness and low emissions of volatile organic compounds (VOC).
However, the fast curing speed of UV curable coatings often leads to internal structural defects, which severely limits their application and development. The coating produced in the new study shows 50% repair efficiency under UV light at 93°C
from scratches and the coating has a high hardness (4H). In addition, the coating has good transparency (85% visible transmittance), which means the coating can meet the requirements of transparent protective layers.

The deficiency that the admixture of inorganic particles hinders the movement of the molecular chain was overcome by using the modified nano-silica (SiO₂-KH570) is not simply mixed with the other components, but grafted onto the chain. Therefore, the addition of SiO hardens₂-KH570 not only the coating, but also can lower the glass transition temperature of the coating, which is helpful for the self-healing of the coating. Furthermore, it was demonstrated that the introduction of reversible disulfide bonds helps to eliminate internal stresses in UV-curing materials by preheating, with the mechanical properties of the coating with disulfide bonds improving significantly (by at most 209%).
As the developers point out, their study expands the application range of UV-curable coatings and aims to address the problem of internal stress defects in UV-curable materials.

Source: Farb + Lack / Lit.: Progress in Organic Coatings, Volume 172, 11-2022