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With recent changes in environmental law, the trend toward lower VOCs in coatings has increased. Water-borne coatings properties are approaching those of conventional solvent-borne technologies with the added benefit of lower VOC and greatly reduced or no flammability. New developments in water-borne epoxy technology has opened the field of applications, but this new technology requires significant new formulation knowledge.
Water-borne epoxies can be divided into two categories. The first, Type I, consists of a liquid epoxy resin of low molecular weight and epoxy equivalent weight of around 190. Two examples are EPON 828 and DER 331. The amine curing agents used are typically polyamines or polyamidoamines which are reacted with acid to form the quaternary ammonium salt which gives greater solubility in water and allows it to emulsify the liquid epoxy. Epoxies are typically packaged as Part A, the epoxy components and Part B, containing the amine.
Formulating resin ratios (epoxy:amine) depends upon the final properties desired of the coating. Epoxy to amine ratios can vary from stoichiometric by up to 20 percent in either direction. Below is a chart of property changes with variation in the epoxy to …