Preparation and characterization of low gloss UV-curable coatings based on silica surface modification using an acrylate monomer

UV-curable coatings are attractive for a wide range of applications due to several advantages, including rapid polymerization rates, increased production rate, and low environmental impact (from limited use of volatile organic compounds). In the present work, UV-curable formulations were prepared from various acrylate oligomers and monomers and modified silica as a matting agent. To improve compatibility between the acrylate-based coating and silica, the surface of the silica particles was modified in two steps. First, to introduce amino-reactive groups to the surface, (3-aminopropyl) triethoxysilane (APTES) was grafted onto the silica. Subsequently, the second step consisted of grafting an acrylate monomer, dipropylene glycol diacrylate (DPGDA), via the aza-Michael reaction. The functionalization with acrylate chains promotes compatibility with the acrylate-based coating formulation and results in a very low gloss surface. The modified silica was characterized through a variety of techniques, including thermogravimetric analysis (TGA), 29Si and 13C NMR and laser diffraction particle size analysis. The matte UV-curable coatings were characterized using viscometry, photo-DSC (kinetic analysis) and real-time FTIR (conversion rate determination), gloss measurements, profilometry (surface roughness analysis), as well as scratch testing (abrasion resistance). This silica modification allows the formation of coatings with low gloss levels at loadings as low as 10% wt modified silica.