A Waveform Design Practice Guided by Rheology for Achieving Satellite-Free Droplet Formation in 3D Inkjet Printing

In inkjet printing (IJ), achieving stable, satellite-free droplet formation is critical for good print quality. Traditional approaches rely on “printability windows” based on dimensionless numbers that relate material properties such as density, surface tension, and viscosity. However, these windows often fail to predict jetting behavior accurately, particularly for polymer-based inks, as they neglect non-Newtonian effects under the highly dynamic conditions of IJ, characterized by high shear rates, high frequency and short timescales. To address this issue, a systematic approach that correlates rheological characterisation of inks waveform design and droplet formation attributes was proposed. Three UV-curable acrylate inks with unknown formulation were systematically characterized in terms of complex viscosity, viscoelasticity, relaxation time, dynamic surface tension, oscillatory damping behavior, and density. Measurements were conducted across five temperatures using a highfrequency squeeze-flow rheometer, bubble tensiometer and densimeter. Cross, Hua & Rosen, Maxwell, Arrhenius, and Eötvös models were applied to extrapolate these properties to inkjet-relevant regimes and across several temperatures. Dropwatching studies were conducted with the inks and satellite formation was found to depend primarily on droplet velocity, with distinct regimes: