Pole-type ground electrode in nozzle for electrostatic field induced drop-on-demand inkjet head

This paper presents a novel mechanism for an electrostatic field induced drop-on-demand ink-jetting device that features a nozzle with a conductive pole located inside the nozzle, referred to here as a pole-type nozzle. The effects of the pole-type nozzle on the efficiency of the jetting are numerically and experimentally investigated. The electric voltage signal applied allows for a strong electric field to be concentrated in the vicinity of the apex of the liquid meniscus and thus micro-dripping ejection of droplet takes place. That is, a tiny droplet is removed from the peak of the dome-shaped liquid meniscus. Electrostatic jetting of liquids is a physical process caused by an electric force applied to the surface of a liquid. The electrical shear stress elongates the liquid meniscus formed at the opening of the nozzle and generates a tiny droplet as a result of the balance between electrical and surface tension forces. This paper presents optimal conditions for applied voltage, electric conductivity, and flow rate for generating a stable drop-on-demand droplet using the micro-dripping mode. It is also verified experimentally that the use of the pole-type nozzle allows a stable and sustainable micro-dripping mode of droplet ejection for a wide range of applied voltages, demonstrating the feasibility of an electrostatic field induced drop-on-demand ink-jetting device as an alternative to conventional inkjet print heads. (c) 2007 Elsevier B.V. All rights reserved.