ABSTRACT
UV-curable polyurethane dispersions (UV-PUDs) have applications in coatings for a variety of materials. Historically, the neutralization and dispersion steps of the UV-PUD production process have been performed in batch. However, continuous processing might reduce capital and operating costs, improve the dispersion characteristics, and facilitate scale-up. Static mixers and inline high-shear mixers are able to provide the necessary shear forces to obtain miniemulsions. The production of a UV-PUD is therefore studied in a continuous setup, whereby the neutralization step is performed in static mixers and the dispersion step is performed either in static mixers or in a high-shear mixer. The influence of the prepolymer temperature, mixing energy, and feed flow rate on the particle size and stability of the UV-PUD particles in water is explored. The results show that the neutralization step is mixing-sensitive, and the temperature of the neutralized prepolymer influences the particle size in the dispersion process. The amount of shear force applied during the dispersion step has a limited effect on the particle size. UV-PU dispersions with an average particle size below 80 nm and PDI below 0.1 are obtained with static mixers or in an inline rotor-stator mixer, at flow rates of 5.2 and 7.2 L/h, respectively. This research demonstrates that continuous processing using static mixers and high-shear mixing is a viable option for the neutralization and dispersion of UV-PUDs.
