Dependence of Ink Jet Dynamics on Fluid Characteristics

Measurements of jet velocity, separation length, and stream stability (freedom from random fluctuations in drop position) were made for several fluids, including two inks. The data were then compared with modified fluid flow and jet stability equations. In one case velocity is related to applied pressure drop through a flow equation that depends primarily on the shape and size of the nozzle and on fluid viscosity. In the other case Weber's equation is modified to include forced oscillation, so that separation length is related to the voltage applied to a piezoelectric crystal, to disturbance growth rate, and to velocity. These two equations were applicable to “normal” liquids (those having good stream stability) having viscosities between 0.9 and 4.3 grams/(second · meter) and dynamic surface tensions between 20 and 60 grams/s2, but not to dilute solutions of a high molecular weight polymer, owing to their viscoelastic character. Furthermore, the stream stability of the polymer solutions was poor and depended inversely on concentration and molecular weight.