Structural design and preparation of LED/moisture dual-cured polyurethane acrylate coatings with comprehensive properties

LED curing technology makes up for some drawbacks of UV mercury lamps with its merits of no ozone emission and low energy consumption, and gradually replaces traditional UV mercury lamps in numerous fields. Nevertheless, a solitary LED curing coating struggles to fulfill the requirements in terms of curing depth, curing chroma, and comprehensive performance. Based on these, four types of polyurethane acrylate (PUA) coatings were fabricated through two-step synthesis and LED/moisture dual curing technology using cycloaliphatic isocyanate (IPDI), aliphatic isocyanate (HDI), monofunctional acrylate (HEMA), and trifunctional acrylate (PETA) as the primary raw materials. The dual curing system integrates the advantages of LED curing and moisture curing, and mitigates the shortcomings of incomplete curing and poor comprehensive performance of single LED. The experimental results show that these four dual-curing coatings show a certain degree of optimization in comprehensive properties such as curing properties, thermal properties, mechanical properties, and coating properties. In particular, the dual-curing coating prepared with HDI as the hard segment and PETA as the end-capping agent has a surface drying time of only 5 s. After dual curing, the gel content, water contact angle, tensile strength, shear strength, hardness, and adhesive force of the sample can respectively reach 97.8 %, 112.4°, 17.26 MPa, 3.7 MPa, 58.5 Shore D, and 5 B. Additionally, the coating also exhibited outstanding solvent resistance, with the absorption rates of 0.35 %, 8.42 %, 1.35 %, and 1.16 % respectively after 48 h immersion in water, ethanol, 10 wt% NaOH, and 10 wt% HCl solutions. It is also notable that the curing depth of the dual-cured coating can reach 8.96 mm, which is significantly higher than the 3.76 mm of the single light curing, and the colored curing is complete. Four kinds of coatings can be selected and customized in accordance with diverse application requirements, which is of great significance for the further development of environmental protection coatings and holds substantial practical value in industrial production.