Effect of acrylic acid on the physical properties of UV-cured poly(urethane acrylate-co-acrylic acid) films for metal coating

UV-cured poly(urethane acrylate-co-acrylic acid) (PU-co-AA) films with five different compositions were prepared by reacting isophorone diisocyanate (IPDI), polycaprolactone triol (PCLT), 2-hydroxyethyl acrylate (HEA), and different weight ratios of trimethylolpropane triacrylate (TMPTA) and acrylic acid (AA) as diluents. Their synthesis and physical properties including gel content, adhesion properties, morphological structure, thermal properties, and mechanical hardness were investigated as a function of the AA content. It was found that the physical properties of the PU-co-AA films are strongly dependent upon the AA content. Crosscut tests showed that PU-co-AA films with lower AA content showed 0% adhesion (0B), and the adhesion of films increased dramatically as the AA content increased to 40–50%. The pull-off measurements showed that the adhesion force of the PU-co-AA films to stainless steel substrates varied from 6 to 31 kgf/cm2 and increased linearly with increasing AA content. PU-co-AA films with higher AA content can be good candidates for UV-curable coating of metal substrates such as stainless steel. However, the thermal stabilities and mechanical hardness decreased with increasing AA content, which results from the relatively linear and flexible structure of AA.