Self-emulsifying Hydroxy Acrylic Polymer Dispersions for Two Component Waterborne Polyurethane Coatings

Novel self-emulsifying acrylic polymer aqueous dispersions (NPAD) for two component waterborne polyurethane coatings (2K-WPU) were prepared by the emulsification of self-emulsifying polymer blends in water, which the polymer blends typically consist of two acrylic polymers, one is a salt group containing polymer (P1), the other is a polymer without salt groups (P2). The dynamic light scattering (DLS) analysis showed that the NPAD have a bimodal particle size distribution and the particle diameters can be controlled by the amount of salt group containing polymer and the concentration of salt groups in this polymer. Transmission electron microscopy (TEM) images also testified that the NPADs possess small particles consisted of P1 and core-shell structure large particles which are composed of the P1 in the shell parts and the P2 in the core parts. The property comparisons of the NPAD, conventional polyacrylic dispersion (CPAD) and poylacrylic emulsion (PAE) for 2K-WPU disclosed that the NPADs possess higher solid contents up to 45 wt% and much lower carboxy salt contents than those of the CPAD, and the NPAD-based 2K-WPU films display much better performance including 90% of the gloss, 0.81 of the pendulum hardness, much better solvent- and water-resistance than those of the CPAD and PAE. The TGA curves indicated the NPAD-based 2K-WPU films display good thermal stability.