AQUEOUS ACRYLIC-POLYURETHANE HYBRID DISPERSIONS AND THEIR USE IN INDUSTRIAL COATINGS

Acrylic and polyurethane aqueous dispersions have been used extensivel y in coating applications, both independently and as physical blends. The resulting coatings display a balance of properties from the inhere nt characteristics of acrylics and polyurethanes. Nonetheless, these p roperties often fail short of those predicted from the traditional ''r ule of mixtures.'' In contrast, a process has been developed whereby a crylic monomers and urethane prepolymers are intimately mixed and mutu ally polymerized in an aqueous dispersion, thereby resulting in ''hybr id'' polymer dispersions. This process causes an interpentrating netwo rk (IPN) of the polymers which subsequently display unique properties compared to standard acrylic, polyurethane, or macroscopically blended acrylic/urethane dispersions. These properties appear to be directly attributable to the acrylic-polyurethane hybrid morphology. Scanning e lectron microscopy (SEM) and atomic force microscopy (AFM) were used t o study film formation, coalescence, and coating surface topography. T hermal analysis was performed to characterize glass transition and the rmal degradation. The microscopy and thermal response data were used t o further understand the molecular mixing and polymer morphology resul ting from the hybrid polymerization and polymerization process. In add ition, clear and pigmented coatings were formulated using the hybrid d ispersions. Performance properties were compared and differences were explained relative to morphological effects. These morphological effec ts are responsible for performance advantages over traditional binder systems in waterborne coatings.