Synthesis Of UV Curable Resins And Studies On Their Films

Epoxy acrylate(EA)and polyurethane acrylate(PUA) are two most important prepolymers in UV curing system. However they also have disadvantages. The major disadvantages of EA are its high viscosity and poor film flexibility. The drawbacks of PUA are its high price and the use of organo-tin catalyst in its synthesis process, a substance that has been limited by the new environmental law. Furthermore, the traditional UV curable coatings need to add quite more reactive diluents (monomers) to adjust their viscosity. Thus, the cost of coatings improved and the abilities of the cured films got worse. So it is important to study resins with low viscosity, with no using organo-tin catalyst and UV curable waterborne resins, etc.EA resin with low viscosity was prepaered at the presence of hybrid assistant system composed of catalyst and inhibitor, and the best synthesis method was obtained by studing the influences of hybrid assistant system and the reaction temperature. It is revealed that the hybrid assistant system can reduce the reactive energy of the reaction easier and the inhibitor has better inhibitable effect because it can combine with peroxide free radical even more easier. The viscosity of EA resin obtained by this method is 3000-4000 mPa.s/60℃, only 1/3 of the product on sale now.UV curable PUA was synthesized without catalyst, and the catalysis mechanism was discussed. The experimental results showed that the reaction followed second-order kinetics with the lower reactive energy of 22.86 kJ·mol-1·K-1. This ensured that the reaction could happen with no any catalyst. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the micro phase separation of PUA films were investigated by differential scanning calorimetry (DSC) method. And the results revealed that with soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segment decreased, and micro phase separation of PUA got better. Soft segment crystallization appeared with molecular weight was over 2000, and when its value got up to 4000, an obvious melting apex in DSC curve appeared. Symmetry and regularity of isocyanate, led to hard segment domains'collecting, and phase separation improved,while rigid benzene ring was good for crystallization. Increasing the function degree of diluent, the crosslinking density with hard segment got up, and this was good for phase separation, on the contrary, increasing the level of reactive dluent led to the opposite because of phase reversion. Micro phase separation got worse both quenching and annealing due to post-curing of HDDA at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.The modified EA resin with lower viscosity and excellent film flexibility was preparared. TDI/80 was chosen as modifier and its content was determined by studying the influences of isocyanate type and content on resins and their films. The effects of photoinitiator, reactive monomers and the light intensity on the UV-curing kinetics of the resins were also discussed. The results showed that Irgacure 1000 has the best efficiency because of its wider absorbing range of UV light at 245nm,280nm and 331nm and the possible synergistic work of Darocur1173 and Irgacure184. The monomers and the light intensity had the same influences on the kinetics. Increasing their contents, the reaction rate and the conversion rate of C=C bound got up too. Furthermore, it was also found that the reaction rate was low at the beginning of the reaction in the induction period, after that the reaction rate became fast because of high content of C=C bound and photoinitiator, and then the reaction rate decreased because of the formation of cross-link networks. Finally, the molecular chain was frozen because of vitrifaction, and the reaction finished.The UV curable waterborne PUA/EA hybrid emulsion was prepared from waterborne PUA which was used as emulsor and EA resin by the method of phase inversion. And the effects of–COOH content, neutralization degree and EA content were studied. The test results by transmission electron microscopy (TEM) showed that the particles of emulsion had an anomalous core-shell shape structure because there is no chemical bound between PUA and EA molecular, and EA has similar polarity with PUA hard segment. The films of the emulsion exhibit excellent abilities for the two resins'connection by C=C bounds after UV curing.