Research On The Synthesis And Application Of Polyester Dispersions For Two-component Water-borne Polyurethane Coatings

Two-component waterborne polyurethane systems combine the good film properties ofsolvent-borne polyurethane with low VOC values of waterborne system. At present, researchand development on waterborne polyester which will be used on two-component waterbornepolyurethane have attracted more and more interest. However, applications are limitedbecause it is easilyhydrolyzable. Thus, in this paper a kind of waterborne polyester dispersionwith high stability was prepared, and the influence of various factors on its synthesis processwas discussed, and then prepares film with mixed hydroxyl component isocyanate, lookingfor appropriate curing conditions.In this paper, EG, NPG and TMPwere chose as alcohol component, THPAand CHDAasacid component, at the same time high stability waterborne polyester dispersoid wassynthesized through esterification process with the sulfonic hydrophilic monomer. It is foundthat the performance of waterborne polyurethane was influenced by varying degree ofpreparation process, materials, content of hydrophilic monomer, catalyst and so on. Whencombination of melting reaction and reflux process was adopted, great loss of material wasavoided and resin of low acid value was obtained; with the addition of TMP to regulate theamount of hydroxyl value of polyester resin, when the dosage of TMP was 8%~10%,hydroxyl value of the resin was 120~140 mgKOH/g; when the molar ratio of THPA and 1,4-CHDA was 3:1, overall performance of the waterborne polyester resin was the best;hydrophilic monomer has different level impact on the water dispersion, viscosity, stabilityand water resistance of aqueous polyester dispersion, and the proper hydrophilic monomercontent was 5.3%(w/w); chose organic tin compounds as catalyst and the dosage of catalystwas 0.1%; when the dosage of mixed cosolvents(DGME:solvent oil=7:3) was 10%, it couldform a stable emulsion, and the film looked flat, good leveling and had no bubbles; chosingDMEA as a neutralizer it could increase the dissolution parameters, reducing the amount ofhydrophilic monomer, the color of paint, improving the gloss and water resistance of thecoating; when neutralization degree was about 90%, the water-based polyester had suitableviscosityand the coating film had good fullness degree.The self-made water-based polyester, Bayer waterborne acrylic (Bayhydrol A 145) and Bayer waterborne polyester (Bayhydrol D270) were used as the hydroxyl group torespectively compound with Bayer solidifying agent (Bayhydur ? XP 2487/1) at thecondition of -NCO/-OH molar ratio 1.5, curing temperature 25~80℃, curing time 7 days.Results showed that two-component waterborne polyurethane coating varnish mixed fromself-made polyester resin dispersion has high hardness, good gloss, strong adhesion, excellentwater resistance and so on. Its overall performance of coating varnish is better than that mixedfrom the Bayer water-based acrylic and polyester resin.