| Currently, the low-glossed waterborne polyurethane coating is becoming more and more popular.To get a better effect of matte, it is prepared by adding matting agent in WPU dispersion to get a variety of water-based polyurethane matting coating composite.But adding matting agent brings defect such as coating brittleness increases, flatting agent precipitation,weak water resistance, low solid content due to the incompatibility between the matting agent and polyurethane. To solve the problems as mentioned above, the water borne polyurethane was modified by epoxy resin, latex particles size was controlled to make a lot of uniform spherical structure of latex particles and different raw material ratios was analyzed, The waterborne polyurethane coatings with excellent low-glossed、water resistance performance and more than solid content of 40% were prepared.In this paper, the WPU coating was prepared by polytetrahydrofuran glycol (PTMG,1000), isophorone diisocyanate (IPDI), xylylene diisocynate(XDI), epoxy resin(E-44) as main reaction monomers, dihydroxy methyl propionic acid (DMPA),2-[(2-aminoethyl) amino] ethyl sulfonic acid sodium and ethanediamine as chain extender,540# flow ping agent, 686# defoaming agent,547# curing agent,534# thickener. The structure and morphology of the WPU films were characterized by FTIR、SEM、UV-vis、TG、AFM、Gloss meter、 Nanometer particle sizer、Universal testing machine. Factors influencing the coating properties are discussed.(1)Preparation of waterborne polyurethane emulsion was modified by epoxy resin reaction condition as follows:prereaction in 50℃(1h),70℃(1h),75℃(1h),80℃(1h); Neutralization reaction in 40℃ for 30 min, emulsification under 35℃ for 30 min. neutralization process is adopted and emulsifying speed should be controlled by 3000-3500r/min. The successful synthesis of the WPU was proved by the FT-IR spectra.(2)The surface contact Angle test and the absorption test in distilled water,10% NaOH solution water studied the effect of E-44 on the properties of WPU water resistance, alkali resistance; The effect of E-44 on the property of WPU film heat resistance was studied by thermogravimetric analysis; By scanning electron microscope and particle size test, the gloss and the influence of latex particle size of WPU was discussed.(3) The waterborne polyurethane emulsion viscosity and solid content of the relationship was analysised; the latex particles inside between the friction force and shear viscosity increased when the solid content was increased, The WPU with varying of solid content was studied by means of controlling neutralization degree. Secondary extender chain was moderate and particle size distribution was wide, latex solid content was relatively high when R value was controlled. The viscosity of emulsion reduced and the solid content increased with the relative content of A-95 increased, but emulsion particle size became significantly smaller leading to high gloss, this did not conform to the requirement of the low gloss coating. The WPU coating with solid content of 40% could be prepared by controlling the relative content of 30% of A-95,the glossiness was less than 5.(4) Using epoxy resin modified waterborne polyurethane emulsion and flow ping agent, defoaming agent, curing agent were mixed together into WPU extinction coating. Analyze the influence factors of film gloss which included DMPA, R value and nEDA/nA-95 by SEM, UV-vis, nanometer particle sizer and gloss meter test. AFM tests verified WPU generating rough surface microstructure, it was conformed to the principle of extinction. The effect of epoxy resin(E-44) on the water resistance was studied by water absorption test. The main mechanical properties of WPU film were analysised by stretching, rubbing fastness, folding resistance and adhesion test. |
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