Water-borne coatings that share the mechanism of action of oil-based coatings

Abstract

Because oil- or solvent-based coatings (e.g. paints, varnishes, sealants) emit volatile organic compounds (VOCs), replacement with aqueous coating formulations is desirable. However, water-based (latex) coatings which are dispersions of polymer particles, are out-performed by solvent-based coatings in hardness, durability, gloss and cold-weather application. The challenge with latexes is that discrete polymer particles must coalesce to form a complete film, a complex process that often leads to imperfections in the coating. Proof-of-concept results show that CO₂-responsive copolymers can form the basis of a water-borne coating in which the polymer is fully dissolved before application and yet water-resistant after application to a surface. These polymers are insoluble in neutral water, but dissolve fully in carbonated water. When a carbonated solution of polymer is cast onto a substrate, the subsequent loss of CO₂ and water by evaporation results in a clear, continuous water-resistant coating. With further development, these new coatings may retain the VOC-free advantage of water-based coatings while eliminating the need for coalescence of particles.