Water-borne UV-Curable Polyurethane Acrylate

With polyurethane acrylate as model systems, we investigated some special issues of UV-curable water solution and emulsion. According to its special molecular structure, a UV-curable polyurethane acrylate was applied to an emulsion polymerization of microgels.In order to study the UV-curable water solution with low viscosity and high concentration, four types of polyurethane acrylates with different molecular structures were synthesized and characterized. The solubility in water was investigated. Two kinds of polyurethane, i.e., TDG and IDG, were found to be soluble in water. It was demonstrated that a high carboxylic amount is not sufficient for obtaining the solubility of polyurethane in water. A study on the rheological behavior showed that the solutions are Newtonian fluids with a rather low viscosity even at a high solid fraction of 0.55.The effects of the solvent's ratio on the emulsification of self-emulsified polyurethane acrylates and the ultimate properties of emulsion was investigated. The changes of viscosity and conductivity was monitored during the emulsification. With a proper amount solvent, the viscosity was greatly reduced during the process of emulsification and a stable emulsion was successfully produced. However, the stable emulsion could not be obtained when the solvent's level was higher than a critical value. A ternary phase diagram and a formulation-composition diagram were used to explain the phenomenon. The effects of the carboxylic content on the emulsification and the properties of emulsion were also studied. The lowest carboxylic content for stability was found. Since the phase inversion was determined by thermodynamic and dynamic factors, the effect of agitaion on the stability was also investigated. Stable UV curable emulsions with narrow drop size distributions were produced, with small drop sizes from 20nm to 130nm.The polyurethane acrylate microgels were obtained by the emulsionpolymerization of the self-emulsified polyurethane acrylate without additional emulsifier and crosslinker. The polyurethane acrylate microgel was also used as a stabilizer and crosslinker to synthesize poly(methyl methacrylate) - polyurethane composite microgels. The kinetics of microgel synthesis was studied by a GPC. The dynamic rheological behaviors indicated that a cross-linked structure was formed. The frequency dependence of the loss tangent and complex viscosities were investigated and showed a strong relationship with the microgel structure. The swelling of all the microgels in tetrahydrofuran exhibit high viscosities and strong shear thinning behavior. Their swelling behaviors were controlled not only by the crosslink density but also by the solubility properties of the constituent polymer. As a type of flexible microgels, the polyurethane microgels exhibit distinct properties from those hard microgels. They could form coherent films at a room temperature.The drying and UV curing of water-borne polyurethane acrylate coatings, including water solution, emulsion and the composite emulsion, were also studied by a weighing method and a Sohxlet extraction method. The influences of molecular structure, experimental conditions and blending on the drying and curing were discussed. It was found that the drying of emulsion was quicker than the water solution, which was ascribed to the different drying mechanism between them. The longer diffusion stage of water solution was considered a bottleneck of the drying.Furthermore, the effects of molecular structure, curing extent, thickness, photoinitiator content and blending on the coating properties were investigated. It was found that the UV curable self-emulsified polyurethane acrylate coating had excellent mechanical properties and decorative effect and it was also a healthy product with lowvoc.