In 2018, we studied droplet temperature as a function of ambient air temperature. The reason is that it is important to control all of the variables that we can in our process. If we control the temperature, and therefore the viscosity of our paint so that its viscosity is always constant, we can check that off the list when we are analyzing an issue. Moreover, we can adjust the viscosity by shifting the temperature of the paint to compensate for other issues. It changes viscosity from a variable, to a constant, and then to a tool we can use to control our process. But if it is just going to change when it hits the substrate, why bother? This temperature-based change in viscosity affects things like flow out, run and sag, orange peel, and gloss, just to name a few. Maintaining a stable and consistent paint temperature assures a stable and consistent viscosity - a major factor in paint process outcomes. It is also easier and more economical to control than substrate temperature. Next is paint temperature. The key point here is viscosity. Temperature inversely affects paint viscosity. As the temperature increases, the viscosity decreases. Conversely, as the temperature falls, the viscosity increases. The final point here is that substrate is the most difficult to control. The greater the mass of an object, the more energy is required to change its temperature. Since we all know that energy costs money, substrate temperature control costs the most to design, install and operate. If the substrate is too warm, it can cause the viscosity of the paint to decrease suddenly, causing it to flow in ways we don’t want it to, which can result in runs and sags, or pulling away from sharp corners leaving them unprotected. Or it can cause the paint to cure prematurely, by driving off solvent too quickly or accelerating the 2K curing rate, stopping the paint from flowing out properly, resulting in gloss and orange peel issues, for instance. By the same token, if the substrate is too cold, it can cause the viscosity of the paint to increase suddenly and also prevent it from flowing out the way we need it to. And that’s the rub - improper substrate temperature can produce the same defects whether it is too warm or too cold making its impact very difficult to analyze.
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