Optimization of acrylic polyols for low VOC two-component water reducible polyurethane coatings using tertiary isocyanate crosslinkers

Polyol development is critical in order to develop a two-component waterborne polyurethane coating that can attain a 250 g/l VOC while maintaining performance requirements. This paper discusses a statistical study to develop a 250 g/l, two-component water reducible polyurethane coating using a tertiary isocyanate crosslinker with dry times and reactivity equivalent to a two-component solventborne system. The effects of acrylic molecular weight, glass transition temperature (T_g), and hydroxyl concentration on viscosity and dry time have been analyzed and statistical models identified that describe the relationships between these experimental factors and responses. Contour plots show tradeoffs between obtaining a low viscosity resin and maintaining fast dry time of the applied formulation. The data from the statistical study suggests that it is difficult to achieve the overall performance desired for an automotive refinish system with the simple four-component acrylic system investigated. The addition of either a longer chain hydroxyl functional monomer or styrene in the acrylic polyol improved the overall performance of the system. Faster cure was also demonstrated with an alternate catalyst.