Entrapped air bubbles in piezo-driven inkjet printing: Their effect on the droplet velocity

Air bubbles entrapped in the ink channel are a major problem in piezo-driven inkjet printing. They grow by rectified diffusion and eventually counteract the pressure buildup at the nozzle, leading to a breakdown of the jetting process. Experimental results on the droplet velocity u(drop) as a function of the equilibrium radius R-0 of the entrained bubble are presented. Surprisingly, u(drop)(R-0) shows a pronounced maximum around R-0=17 mu m before it sharply drops to zero around R-0=19 mu m. A simple one-dimensional model is introduced to describe this counterintuitive behavior which turns out to be a resonance effect of the entrained bubble. (c) 2006 American Institute of Physics.