Printability of inkjet according to supply pressure

Abstract

To obtain uniform and high-resolution jetting, the drop-on-demand inkjet can be operated with various physical properties of inks. To determine how supply pressure control affects the stability of the jetting, an experimental study was conducted on eight model inks in a range of Z number (1 < Z < 17). The velocity and volume of drop were measured by a visualization method to analyze the performance of piezoelectric inkjet head. Increasing negative supply pressure reduced both velocity and volume. The decline of volume was uniform regardless of driving voltage, whereas the decline of velocity increased with decreasing driving voltage. The printability diagram of Z–We was derived to analyze the jetting behavior according to the ink properties, such as viscosity and surface tension, and operating conditions, such as driving voltage and supply pressure. For dimensionless numbers, Z and We, the surface tension term can be compensated by the supplementary Laplace pressure force generated by the supply pressure. In the printability diagram of the modified Z* and We*, the suppression of the satellite drop formation by negative supply pressure can be identified as a shift from the outer to the inner stable region. The critical aspect ratio at the pinch-off was estimated from the Taylor–Culick analysis of the liquid filament breakup. The damping time of residual vibration was measured according to the supply pressure within the printable range. We conclude that control of the supply pressure with slight droplet velocity and volume reduction can improve the printing stability and frequency.