Improving Waterborne Alkyd Resins With Fatty Acids
The ever-increasing attention paid to environmental protection has produced a lot of legislation aimed at reducing emissions from industrial activities, particularly VOCs used as diluents in coatings. Besides the safety and protection regulations placed on plants, emissions from VOCs are also being substantially reduced through the development and use of new low-solvent and solvent-free coatings, such as high-solids paints, waterborne coatings and powder coatings.
The ever-increasing attention paid to environmental protection has produced a lot of legislation aimed at reducing emissions from industrial activities, particularly VOCs used as diluents in coatings1. Besides the safety and protection regulations placed on plants, emissions from VOCs are also being substantially reduced through the development and use of new low-solvent and solvent-free coatings, such as high-solids paints, waterborne coatings and powder coatings. Regarding waterborne coatings, many efforts have been made to produce alkyd resins able to provide dispersion paints with less organic solvent (less than 10 to 15%) for the finishing of metal surfaces.
Waterborne alkyd resins2 are polymeric derivatives with a high acid number (AN greater than 50) which provides the required water solubility upon neutralization and salt formation with aliphatic amines, usually trimethylamine for air-drying alkyd resins, or dimethylethanolamine for oven-drying alkyd resins3. This method is mainly applied with medium- (40 to 60% oil content) and short- (less than 40% oil content) oil resins, modified with drying and semidrying oils/fatty acids. Since the short-oil resins can be crosslinked by reaction with oligomeric aliphatic or aromatic isocyanates4, it is thus possible to produce two-pack systems to be mixed immediately before application that quickly give rise to crosslinking. Optimal paint films are generally formed when the NCO/OH ratio is equal to 1.