Optimization of liquid electrostatic coating

Soybean oil with emulsifiers was atomized by electrohydrodynamic spraying. The relationships between voltage (20–40 kV), flow rate (28–88 g/s), emulsifier content (10–15%), apparent viscosity (45–53 mPa-s), conductivity (0.1–0.2 μS/m) and surface tension (43.1–46.0 mN/m) and both coating reproducibility and efficiency were mapped utilizing Response Surface Methodology. Voltage had the most significant effect on reproducibility, followed closely by conductivity, and then flow rate. Viscosity had the least significant effect on coating reproducibility and was only significant through interaction with other factors. Surface tension was not a significant effect. Reproducibility was increased by increasing charge concentration, which decreased droplet size. This was achieved at intermediate voltage, low conductivity, high viscosity and low flow rate. Flow rate had the most significant effect on efficiency followed by voltage and emulsifier content. Efficiency increased at low flow rate and voltage. Optimum conditions produce an optimum charge concentration, resulting in the most reproducible and efficient coating.