Application of electrostatic inkjet phenomena to micro-film formation by spraying viscous liquid from multi-nozzles

Micro spray mode of electrostatic inkjet has been examined experimentally for the application of precision film coating. Critical issues of this technology lie in productivity and jetting viscous liquid. The former is that the amount of liquid jetted from a single nozzle is too small to obtain sufficiently high coating speed. The latter is that the stable jetting window of viscous liquid is narrow and the distribution of the droplet is not uniform. To overcome the situation, a possibility of jetting viscous solution from multi-nozzles was investigated in this report. As results, jetting from seven nozzles made of stainless steel was fanned out toward the opposite plate electrode. By intentionally clogging the both end-nozzles and making them as electrodes, the direction was remedied and parallel jets were obtained. According to the increment of applied voltage, jetting mode was varied from dripping mode to stable cone-jet mode. Although the variation of jetting mode was qualitatively the same as that of a single nozzle, for the multi-nozzle the higher voltage was required to obtain the stable jetting mode. Calculated results suggested that the electric field at the tips of the multi-nozzles were lower than that of a single nozzle so that the much higher voltage was required to obtain the same family of jetting mode. From coating experiments on a drum it was demonstrated that the multi-nozzles with dummy electrodes at high applied voltage could jet well-oriented fine droplets to acquire thick and flat film, although the droplets were not uniform. It was confirmed that the coating speed was improved according to the number of the nozzles but the more fiowrate was indispensable to obtain thick film.