In water-reducible waterborne epoxies, acidic or basic functionalities are introduced into an epoxy polymer, which upon respective
Figure 2.57: Important routes for water-reducible epoxy resin |
neutralization with a fugitive base or acid, generates an ionic group that renders it water reducible (Figure 2.57).
Acid functionalized epoxy resins are generally prepared by esterification of epoxy resin with an excess of acid equivalents, or by grafting of acrylic copolymers containing methacrylic acid or acrylic acid onto the epoxy backbone. They are generally cured by an aminoplast at elevated temperature.
Base-rich epoxy resins are prepared by reaction of epoxy resins with an amine (preferably a secondary amine). These types of epoxies are commonly employed in cathodic electrodeposition coating, often cured by a blocked isocyanate and termed thermal curing.