Study on Press Formability and Properties of UV-Curable Polyurethane Acrylate Coatings with Different Reactive Diluents

UV-curable coatings have numerous advantages, including environmental sustainability due to 100% solid content, economic feasibility attributable to relatively fast curing time, decent appearance, mechanical properties, chemical resistance, and abrasion resistance. However, UV-curable polyurethane acrylate coatings on metals apparently restrict their engineering applications owing to low mechanical properties and poor thermal stability, giving UV-curable coatings less flexibility and formability. In this study, we evaluated the property change of films according to the type of reactive diluents that lowers the viscosity of UV-curing coatings for pre-coated metal and has a substantial effect on the curing rate, viscoelastic properties, adhesive properties, and flexibility of the film. Moreover, there are many changes in the properties of coatings according to varied curing conditions in order to evaluate the oxygen inhibition phenomenon during the curing process in the atmosphere. In particular, to evaluate the effect of reactive diluents on forming formability, which is the most crucial property for the pre-coated metal, this study used conventional formability tests, such as t-bending or the Erichsen test. Moreover, a cross-die cup drawing mold with a similar form as failure and Safety Zone was utilized in order to obtain clearer information on its actual formability. The analysis on the effect of failure and safety zone on the material used in press forming was conducted by assessing limit punch height and forming a limit diagram of the manufactured film according to varied reactive diluents.