WATERBORNE EPOXY NOVOLAC'S FOR COATINGS

摘要

Both liquid and solid waterborne epoxy resins based on diglycidyl ether of bisphenol-A (DGEBPA) have been used successfully for industrial maintenance coatings for over 20 years. The higher molecular weight solid DGEBPA resins have the advantages of quick dry and improved corrosion resistance over their lower molecular weight counterparts. However, they are generally deficient in the area of severe chemical resistance. Low molecular weight liquid DGEBPA resins have the advantage of higher solids at lower viscosities but are generally slower curing and have poorer corrosion resistance. Multifunctional novolac epoxy resins represent a class of liquid-semisolid resins that are used to increase the crosslink density of cured films resulting in improved chemical resistance. Viscosity constraints have traditionally limited novolac epoxy resins to solventborne coatings. However, recent developments have resulted in two novel novolac waterborne dispersions capable of generating performance properties comparable to solventborne novolac systems. This paper will characterize the relative differences between waterborne and solventborne novolac resins in several model coatings formulations.