Drops-on-drops micro-film formation by stable electrostatic jets

Applying micro spray state of electrostatic inkjet to precision film coating was examined experimentally. High quality coating could be expected by drops-on-drops of super fine and mono-diameter droplets. At first, the most preferable jetting condition was determined through experiments for two types of coating liquid, one of which was dilute dispersion and the other was viscous solution. Then, with those parameters examined, the surface quality of the coated films was evaluated through several coating tests. Along increasing applied voltage, jetting mode was varied from Mode I, dripping mode, to Mode 2, jetting mode. The basics of jetting mode variation was equivalent for both types of coating liquid, although a larger nozzle had to be used for the viscous solution to avoid clogging. The most favorable condition for coating was the stable cone-jet mode in Mode 2, where a well-oriented thread was jetted from the stable Taylor cone at the nozzle tip and broken up into mist during flight. Both types of quality coating, a submicron film with the dilute dispersion and a thick film, over 10 micrometers, with the viscous liquid could be demonstrated by piling up the single-digit-micron-size droplets.