Synthesis Of Polyurethane-modified Epoxy Emulsion And Study Of Its Curing

With the stricter environmental laws and regulations and people’s more attention to environment protection, the use of solvent-based coatings is limited due to its high VOC, while the exploration of environmental counterparts especially waterborne coating becomes more and more important, and the production of emulsion with excellent combined properties is the key to obtain high performance waterborne coating. On this occasion, terminal isocyanate polyurethane prepolymer has been prepared by the way of toluene diisocyanate(TDI) reaction with polyether diols(Diol-1000) and dihydroxymethylpropionic acid (DMPA). Using this prepolymer reaction with epoxy resin, the hydrophilic components will be introduced to the backbone of the epoxy resin which make the modified epoxy resin hydrophilic and can be dispersed. Through the FTIR analysis, it has been found that terminal isocyanate group of the prepolymer reacts with hydroxyl group of epoxy resin and epoxy groups remain basically unchanged, which ensure the character of the epoxy resin undestroyed.Technological and formulation factors of the synthesis of polyurethane-modified epoxy emulsion have been inspected. Factors such as materials addition sequence, addition mode, reaction temperature, stirring intensity, OH/NCO value, polyether Diol-1000 content, -COOH group content and the neutralization degree have significant impact on emulsion and coating properties. In order to get a good emulsion and coating, the addition sequence should be former Diol latter DMPA; The DMPA and solid epoxy resin should be dissolved or molten in the form of liquid to add; the reaction temperature between Diol and TDI is controlled at 70°C, and DMPA reaction temperature should be controlled between 75°C and 80°C, epoxy resin as well; OH/NCO ratio between epoxy resin and prepolymers should be 1.3:1; weight ratio of Diol and epoxy CYD-012 should be 4:15; -COOH content should be 1.3%; neutralization degree should be 90% -100%.The curing agent which matches with polyurethane-modified epoxy emulsion has been synthesized, and curing degree of the film has been studied in differential scanning calorimetry. By comparing to the glass transition temperature, it is suggested that particle size, curing temperature, reactivity of curing agent and matching degree between epoxy emulsion and curing agent have great impacts on the curing degree. In the experimental range, the smaller the particle size of epoxy latex, the more favorable the curing system, the better mechanical properties of the film; the maximum curing extent exists in the case of the proper curing temperature; The film has better mechanical properties and water resistance with primary amine than secondary amine as curing agent; After modification, curing agent enhances matching with epoxy emulsion, which lead to improvement of the film’s curing extent and mechanical properties.After testing, the excellent properties of the coating made by the polyurethane modified epoxy emulsion are following: 60°gloss≥90, 48h water absorption≤20%, pencil hardness 1H, excellent water resistance, flexibility 1mm, the adhesion level l, to have a good market for application and popularization.