| Waterborne UV-curing systems have advantages of non-contamination, nontoxicity, non-skin irritation and safety of production, and become an attractive research and application areas. It has become one of the main development direction of UV-curing systems and the green environmental product for 21 st century.In this article, three series of waterborne UV-curing polyurethane acrylate (PUA) resins, which include polyether PUA, polyester PUA and PUA with photoinitial radical, were prepared from different materials.As for polyether PUA, a new hydrophilic diol (T-M) was synthesized from trimethylol propane and maleic anhydride. UV-curable waterborne polyether PUA resin was then prepared from 2-hydroxyethyl acrylate(HEA), toluene diisocyanate(TDI), polypropylene glycol(PPG) and T-M.As for polyester PUA, UV-curable waterborne polyester PUA resin was prepared from TDI, polybutylene adipate glycol (PBA), dimethylol propionic acid (DMPA) and HEA.The synthesis, hydrophilicity, the effects of hydrophilic group content and neutralization degree on emulsions were studied for above-mentioned two kinds of PUA resins. The effect of neutralization degree, drying condition, the type and concentration of photoinitiator, neutralization agent type and structure of prepolymers on curing rate were discussed in detail. The properties of UV-cured films were also determined.The results show that with the increase of content of hydrophilic group and neutralization degree, hydrophilicity of molecular chains increases and particle sizes decrease whereas emulsion dispersability and stability both increase. As for polyether PUA, Darcocur 4265 is preferred, and curing rate is fastest when neutralization degree is 80%.As for polyester PUA, Irgacure 1000 is preferred, and curing rate decreases with the increase of neutralization degree. Curing rate is fastest when the amount of photoinitiator is 3%. Drying condition has considerable impact on curing rate and curing rate is fastest without drying. Curing rate accelerates with the increase of ratio of PBA/DMPA or PPG/T-M. The higher the ratio of HEA/DMPA or HEA/T-M, the faster the curing rate. When NaOH is used as neutralization agent, curing rate is faster than that of triethylamine. UV-cured films of the said two kinds of PUA resins have good water resistance, solvent resistance and acid resistance, but strong base resistance thereof is on general level.A new UV-curable PUA resin with photoinitial radical, which is dispersed in water in the form of self-emulsification, was prepared from toluene-2, 4-diisocyanante (TDI), polyoxytetramethylene glycol (PTMG), dimethylol propionic acid (DMPA), HEA and Irgacure 2959(2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropionphenone) as photoinitiator. The disadvantage of poor compatibility between oil soluble photoinitiator and waterborne resin is solved by incorporating photoinitiator into resin structure, which has advantages of fast curing rate, high conversion, non-volatility and non-migration. The structure of reaction products is controlled by adjusting the amount of Irgacure 2959, namely the ratio of Irgacure 2959/HEA. The resins containing high content of Irgacure 2959 can be used as photoinitiator for other waterborne resins. Their curing rate is considerably faster than systems containing additional Irgacure 2959. |
