Control of Droplet Formation in Inkjet Printing Using Ohnesorge Number Category: Materials and Processes

The dimensionless Ohnesorge number (Oh) describes the relative importance of viscous to surface tension effects, which is commonly used to characterize jet breakup. In this study, the experimental results have proven that single droplets can be jetted for 0.02 < Oh < 1.5, for viscosity > 50 mPas, using different mixture compositions of glycerol in water (0 - 80 wt%) as the ink. This is contrary to previous published literature [1, 2]. However, the findings are in good agreement with Reis and Derby [2] that the velocity of the ejected droplet exhibits a maximum (i.e. inverted 'U' curve) and is a function of pulse width. This velocity curve is apparently governed by the Ohnesorge numbers. From a practical standpoint, with the large variety of inkjet printing inks having different properties, these results can be useful for waveform tailoring to achieve optimal performance for droplet formation control.