| Powder coatings are a type of environmentally-friendly coatings that emit no VOCs and are increasingly being used in the coating industry.However,the high curing temperature of traditional powder coatings(180-200 °C)limits the choice of substrate.Imidazole is a kind of powder coating curing agent with high reactivity,but its high activity also results in poor storage stability at room temperature.Therefore,in this study,the active sites on the imidazole molecule were modified to have a certain degree of thermal retardation,and investigation in powder coatings with modified imidazole curing agents was studied,especially on thermal sensitive substrates.This study investigated the curing performance of modified imidazoles with different structures.Triphenol methane triglycidyl ether(TMGE)was synthesized and its structure was characterized,one triglycidyl ether and two other diglycidyl ethers,diglycidyl ether of bisphenol A(DGEBA)and polypropylene glycol diglycidyl ether(PPGDGE),were selected for local reactions with commonly used imidazoles such as2-methylimidazole,nine modified imidazole curing agents with different structures were synthesized.FTIR and NMR characterization showed that the characteristic peaks of the epoxy group in glycidyl ether and the secondary amine group in imidazole disappeared,indicating that ring opening substitution of the epoxy group occurred.The optimal curing temperature of the nine modified imidazole curing agents is around 140 °C,and the gelation time at the optimal curing temperature is about 300 seconds.The curing process meets the requirements for low-temperature curing.Based on the above research,epoxy resin powder coatings using this type of curing agent were further prepared.The commonly used E-12 bisphenol A diglycidyl ether epoxy resin was selected as the main resin to prepare pilot scale samples of powder coatings.The corresponding coatings were obtained by heating and curing after electrostatic spraying,and their performance was evaluated and compared using corresponding coating test standards.The results showed that the coating cured with TMGE modified 2-ethyl-4-methylimidazole had the best comprehensive properties in terms of hardness,solvent resistance,and coating appearance.The powder coating prepared based on the TMGE modified curing agent formulation system was selected for spraying on heat sensitive substrates such as medium density fiberboard,solid wood board,PET plastic board,and the coating effect was excellent.The relevant research results provide a possible solution for the low temperature and green application of the powder coatings,and potentially achieve large-scale application. |
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