Waterborne crosslinked polyurethane latex film formed from acrylic and blocked polyisocyanate particles

Waterborne latex films are an essential material in coating, print, and adhesive industries. There have been continuous researches on introduction of cross-linked structures to the latex films to improve their mechanical properties. In this study, we develop latex film fabricated from aqueous dispersion of hydroxy group-containing acrylic latex particles (AL particles) as a base film-forming material and blocked polyisocyanate nanoparticles (BPI nanoparticles) as a crosslinker. Electrophoretic light scattering, transmission electron microscopy and attenuated total reflection-infrared studies indicate that AL particles and BPI nanoparticles do not interact with each other and exist independently in aqueous media, and that removal of water from the dispersion via drying at 25 °C causes the particles to contact each other, generating a blend film. Furthermore, heating of the blend film at 90 °C, above the glass transition temperatures of the AL particles and BPI nanoparticles, leads to interdiffusion of the AL and BPI components. Formation of crosslinking is realized by heating at 140 °C via urethane bond formation between hydroxy groups in AL and isocyanate groups generated from BPI by release of blocking agents. Tensile tests, scratch hardness tests and surface hardness measurements confirm that mechanical property of the films is improved via urethane-based crosslinking.