| The UV curable waterborne coating has both the advantages of waterborne coating and UV curable coating, such as environmental, fast curable speed, saving energy sources, excellent performance of film, etc. It has been an important direction of coating. The polyurethane-acrylate (PUA) coating has the best performance.PUA prepolymer was firstly synthesized , emulsificated and added to photoinitiator, so UV curable waterborne coating was obtained. The emulsification of PUA prepolymer can be realized through extra-emulsifying, but the disadvantage of emulsifying agent migrating can affect the performance of film and bring sanitation safety hidden trouble. In many research works, PEG and DMPA were used to react with TD1 ( which is called one-step way) , so PUA prepolymer can be obtained and self-emulsified. But the solid content is low, which is between 20% and 30%. The low solid content also limits the performance of the latter, such as gloss, curing speed, etc. Why the solid content is low? How to improve the solid content? It need to be solved as fast as soon.The reason of low solid content is possibly that the reaction activity of PEG, DMPA and HEMA whit TD1 were different. The hydrophilic group can not be distributed in PUA prepolymer macromolecular on average. In this paper, a UV curable waterborne PUA prepolymer was prepared from TDI, PEG, DMPA and HEMA by stepwise way. The PUA prepolymer could be easily dispersed in water in the fonn of self-emulsified latex after carboxvl group was neutralized with tertiary amine (TEA) and UV curable waterborne coating with high solid content was prepared. The relation between structure and performance of UV-curing PUA film were discussed, and the reaction kinetics of TDI and PEG, TDI and DMPA, TDI and HEMA were studied.(1) The UV curable coating was prepared with stepwise way. The solid content was 36%, stability was high and the whole performance of the film was good.(2) The best mol ratio of PEG, TDI, DMPA and HEMA is 2: 6: 2.5: 3.5, the dosage of TEA and photoinitiator is 100% and 1%, respectively.( 3 ) The point of phase transition is lagged with the increase of dosage of TEA and of molecular weight of PEG.( 4 ) The resistance to water of film can be improved when the dosage of silicone; While the curing speed of film can be improved by chain-extened PUA.( 5 ) The results of the reaction kinetics studied by di-n-butylamine methodshowed that the reaction between TDI and PEG, TDI and DMPA, TDI and HEMA are all second-order reaction; The reaction rate constant and reaction activation energy of TDI and PEG, TDI and DMPA, and TDI and HEMA were obtained, which were 1.874xl0-3L-mor1-s"1,5.199xl0-2L-mor1-s"1. 1.4819xl0"2L-morI-s"1and29.55kJ-mol, 88.24kJ-mor', 55.97kJ-mor', respectively.(6) The reaction rate constant of TDI and PEG, TDI and DMPA of which themo! are all equal at 75°C were obtained, which were 5.63xlO~3L-mor'-s"1. 2.88x10"L-mor'-s"1, respectively. The latter was four times of the former, so the previousconclusion that stepwise way was superior to one-step was proved from the point ofview of reaction kinetics. |
PDF Full Text Request