Surface Hardness of UV-Solidified Coatings Containing In-situ Synthesized, Self-dispersed Nano-gel Domains as a Function of Surface Roughness and Viscoelastic Characteristics

UV-curable coatings have attracted the interest of researchers in industry and academia because of their outstanding features. In this paper, the effect of monomer functionality and monomer concentration on the photo-induced nano-gelation of UV-curable coatings has been investigated. The coatings were prepared by incorporating an aliphatic urethane acrylate oligomer with a mono-functional monomer (phenoxy ethyl acrylate (PEA)) or multifunctional acrylate monomers (1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA)) to form different nano-gel domains. The viscoelastic properties of the coatings, including crosslinking density, glass transition temperature, and elastic modulus, were evaluated using dynamic mechanical thermal analysis (DMTA). The surface hardness of the applied coatings was measured by two different methods: the pendulum hardness test and Knoop micro-indentation. Surface roughness and dimensions of nano-gels were evaluated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed the effect of nano-gel dimensions on the mechanical properties of coatings. The surface hardness of the coatings obtained by different methods showed the same results. The findings of this study provide important insights into the design and optimization of UV-solidified coatings for applications in the field of automotive coatings.