A perspective on resins for aqueous coatings

Aqueous binder resins are becoming increasingly diversified and encompass classical latexes, latex-like polyurethane dispersions, and various aqueous dispersion polymers. Unlike classical and urethane latexes, the dispersion polymers are synthesized in non-aqueous media, have low molecular weights and are dispersed into water by mechanical means. The preparation of classical latexes from unsaturated monomers is scientifically well understood. Modem classical latex technology provides precise particle size control and the means to impart core-shell morphology to the particles. Core-shell morphology is beneficial for improved film formation, rheology and crosslink acceptance. Polyurethane dispersions are made by extending the molecular weight of isocyanate-terminated prepolymers with aqueous diamines. Though more expensive, polyurethane dispersion binders complement classical latexes by yielding tougher and generally more solvent resistant films. The low molecular weight acrylic, alkyd, polyester and epoxy dispersion polymers have advantages in good atomization, high gloss and flow-out in film formation. Current progress includes improved scientific understanding of urethane latexes and of dispersion polymers. This is paralleled by the development of novel crosslinking systems.