Electrostatic Generation of Fine Paint Droplets

Small vibrating capillaries have been used with good success to generate uniform liquid droplets as small as 20 ¿m in diameter. However, this technique has not been successful for viscous highly pigmented fluids such as paints. Since paint tends to clog fine capillaries, the smallest droplet that can be reproducibly obtained with conventional methods is about 400 ¿m. A method is described for electrostatically generating paint droplets down to 30 ¿m. A 250 ¿m diameter paint jet is vibrated by an electromechanical transducer at a frequency of 2200 Hz in the presence of an electric field. Fine ligaments are formed between the large drops. Under the action of the electric field the ligaments break up into small highly charged droplets which can be spatially segregated according to size. Calculations of droplet charge based on the equations of motion for the system indicate that the charge on the finer droplets approaches the Rayleigh limit.