Role of Solvents in E-Coating

Q. What role do solvents play in an e-coat system? C.A.

A. The solvents used in current electrocoat systems primarily play three roles.

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First, they serve as rheological agents as they affect the viscosity, shear resistance and liquid flow of the electrocoat paint in the bath. Basically, they modify the Reynolds’s number and enable the electrocoat paint in the bath to behave more in a “laminar” flow instead of in a “turbulent” flow. Electrocoat paint is heavily pumped and filtered during use, so this property is important.

Engineers can accurately calculate liquid properties and models only if liquids behave in “laminar” flow. If the liquid, due to high velocity, low viscosity, low density and other physical characteristics, behaves in “turbulent” flow patterns like in eddies, rapids and such, then the accurate calculations turn into estimated predictions.

Second, the solvents act as coalescing agents, helping maintain the solids in suspension to avoid settling.

Third, they act as flow agents during curing, enabling the film to lose the water and solvent at controlled rates, while enabling the electrocoat paint to flow and polymerize and close completely without pinholes or voids. In older technologies, solvents also played the role of antibacterial agents, providing a toxic environment for them. Hexyl cellosolve was one of those solvents used in formulations in the past that controlled bacteria in electrocoat systems. Newer formulations use other antibacterial mechanisms.