Characterizing and improving performance properties of thin solid films produced by weatherable water-borne colloidal suspensions on bronze substrates

While the development and application for transparent protective coatings for metals continues and broadens, the use of these coatings on high-value outdoor bronze objects, such as statues and architectural elements, requires extensive testing before use. Recent efforts in coatings technology have produced high-performance water-borne latex dispersions containing polyacrylics and poly(vinylidene fluoride) (PVDF) targeting extended coating lifetimes and improved UV resistance. Our studies show that a two-layer polymer film with a solvent based primer (Paraloid™ B-44) and a high performance water-borne topcoat (Kynar Aquatec™ RC-10206) exhibits high impedance as measured by electrochemical impedance spectroscopy. Upon annealing, those films further increased in impedance, suggesting improved corrosion protection compared to unannealed films. When soaking in water, films that contained high loading levels of coalescing agent (Dipropylene glycol monomethyl ether, DPM) in the topcoat formulation resulted in a visible whitening of the basecoat and a decrease in coating resistance. Characterization of the whitened layer by FT-IR indicated the presence of coalescent in the basecoat, suggesting that coalescent migrated from the topcoat into the primer basecoat. Annealing studies were performed to reduce uptake and reverse or inhibit water whitening.

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► We studied a water-borne coating with an acrylic/PVDF resin for use on bronze.
► Inter-layer electrodes were used to independently analyze multi-layer systems by EIS.
► We characterized coalescent migration by impedance changes and by FTIR.
► EEC models explain incomplete film formation and reversible water sensitivity.