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A selective catalyst for two-component waterborne polyurethane coatings

Abstract

The potential for formulating low VOC, high performance, two-component waterborne isocyanate crosslinked coatings has generated a great deal of interest. The difficulties in formulating these coatings, however, are significant. A major problem associated with such systems is the isocyanate-water side reaction, which can lead to gassing/foaming, loss of isocyanate functionality, low gloss, and a reduced pot life. To compensate for this side reaction, these formulations usually contain a large excess of isocyanate. One novel approach to control the water side reaction is the use of catalysts which selectively catalyze the isocyanate-polyol reaction and not the isocyanate-water reaction. The selectivity of a variety of metal catalysts to catalyze the preferred reaction was measured using an FTIR method. A zirconium complex has shown unusually high selectivity for the isocyanate-polyol reaction in comparison to the standard dibutyltin dilaurate catalyst. This zirconium complex catalyst has been evaluated in several waterborne polyurethane formulations and has demonstrated less gassing/foaming, longer pot life, and higher gloss than dibutyltin dilaurate at equal cure time. The mechanism of catalysis and formulating techniques of this novel zirconium catalyst will be discussed.

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He, Z.A., Blank, W.J. & Picci, M.E. A selective catalyst for two-component waterborne polyurethane coatings. Journal of Coatings Technology 74, 31–36 (2002). https://doi.org/10.1007/BF02697963

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  • DOI: https://doi.org/10.1007/BF02697963

Keywords

  • Isocyanate
  • Waterborne Polyurethane
  • Metal Carboxylate
  • Dibutyltin Dilaurate
  • Acrylic Emulsion