Effects of resin/curing agent stoichiometry and coalescence of emulsion particles on the properties of waterborne epoxy coatings upon accelerated weathering

The properties of waterborne epoxy coatings applied to 1020 carbon-steel plates were evaluated based on two factors: stoichiometry and the amount of coalescing aid used. The effects of the interactions between these two factors on coating properties were evaluated at three levels using a 32 factorial design and the Statistica 13.3-Trial software. The coatings were subjected to accelerated weathering and salt-spray tests and evaluated based on gloss, yellowing, Fourier-transform infrared spectroscopy, atomic force microscopy, and differential scanning calorimetry. The evaluation of gloss showed that stoichiometry (F = 334.45) was a more important factor than the amount of coalescent (F = 62.81). An excess amount of curing agent produced glossier coatings. Yellowing was strongly influenced by both factors, with lower amounts of curing agent and higher amounts of coalescent resulting in coatings with higher resistance to yellowing. A salt-spray test was conducted to evaluate the corrosion resistance of the coatings. The coatings produced with an excessive amount of coalescent and curing agents exhibited the lowest corrosion resistance. The best results were obtained with 7% coalescent agent and reduced amounts of curing agent.