Automotive coatings are multicomponent mixtures with complex rheological profiles that are typically applied via spray atomization processes. For any given automotive coatings system there are multiple processes including: evaporation of atomized droplets during spray, ambient drying of the applied film, heated drying of the applied film, and heated reaction of the applied film. Understanding the relative evaporative rates of various solvents throughout this process can provide insight leading to optimized flow and leveling of a coating, which ultimately results in a layer smoother in surface structure with better mechanical and aesthetic properties. For traditional solventborne automotive coatings, relative evaporation rates as well as mathematical models have been well documented. Waterborne coatings, by contrast, present a more complex system for determining evaporative rates. The high polarity and hydrogen bonding of water itself is not estimated accurately in parameters of most historical models, and in waterborne coatings different evaporative regions are present in aqueous zones versus zones with relatively hydrophobic co-solvents. Relative evaporation rates of co-solvents were determined experimentally by gas chromatograph and are reported on films of waterborne coatings at ambient conditions. Co-solvents of various chemical families were investigated including: alcohols, glycol ethers, and others.
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