Synthesis And Performance Study On UV-curable Polyurethane Acrylate

Polyurethane acrylate (PUA) integrates the excellent performances of polyurethane (PU) and polyacrylate (PA). Prepolymer of different performances can be synthezed by adjusting the molecular structure and functionality to meet the different requirements. In this paper, PUA resin was synthesized via bulk polymerization and its UV curing process was also investigated.PUA prepolymer was synthesized by two-step method with isophorone diisocyanate (IPDI), pentaerythritol triacrylate (PETA), polypropylene glycol (PPG). Fruther the effect of reaction condition on the synthetic process was explored and finally the optimumized technological conditions were obtained: adding 0.1 wt% catalyst, 0.05 wt% inhibitor, remaining the temperature of 55℃during the first step reaction for 3 hours, the temperature of 65℃during the second step reaction for 6 hours with the -NCO content of no more than 0.5 wt% at the end of the reaction. FTIR and GPC were used to characterize the structure and the molecular weight of the prepolymer. The results showed that the product met the expected performances. The thermal performance test showed that the glass transition temperature of the PUA resin was -36℃,and the thermal degradation temperature of PUA resin remained at 180℃.The influential factors on the viscosity of PUA resin were discussed from their perspectives of molecular structure and process conditions. The route of synthesis and addition manner of raw materials would influence the structure of the PUA resin, resulting in different viscosity. The experimental results illustrated that the viscosity of the PUA resin reached a relative lower level by using the synthesis route 2 and by dripping manner. The molecular weight of PPG and the mixture ratio of raw materials can also bring impact on the viscosity of PUA resin. Both the higher molecular weight and degree of polymerization can increase the viscosity of the resin.The investigation of the UV curing process displayed that 1173/184 composite system brought higher efficiency in initiation and shorter curing time. The reactive diluent with little shrinkage was favourable to improve the adhesion of the cured film. The application of tertiary amine initiator and dithioglycol modified PUA resion could shorten the curing time and improve the curing efficiency.The optimized formulation of PUA coating was obtained by above analysis of main performance parameters of cured films, listing as PUA resin 60 wt%, BA reactive diluente 5 wt%, HDDA reactive diluente 10 wt%, TMPTA reactive diluente 15 wt%, 1173 photoinitiator 2 wt%, 184 photoinitiator 3 wt%, EDAB promoter 3 wt%, dithioglycol antioxidizer 2 wt%. It was shown by the UV curing experiments that the prepared coating can be cured with 27 second with the adhensive attraction of grade I, pencile hardness of 6 H, tensile strength of 4.43MPa, and endowed with excellent chemical resistance.