A versatile approach to numerically investigate the trapped air bubble in piezoelectric inkjet printing process

Abstract

The piezoelectric inkjet (PIJ) printing technique, as a typical drop-on-demand (DOD) inkjet process, employs the electric potential for activating the mechanical vibration of a lead zirconium titanate (PZT) membrane. As a result, the constant flow of the fluidic ink within the solid channel is attained, resulting in the formation of a droplet in the nozzle. This droplet will be subsequently deposited on a substrate, which renders the PIJ method one of the most indispensable tools for various applications in MEMS, cell printing, LCD fabrication, etc. However, by considering a specific driving waveform, an air bubble will be generated and trapped within the solid channel after the ink droplet is ejected from the nozzle, which would inevitably affect the subsequent printing process. Additionally, there are scarce reports in the literature that have dealt with this issue in depth. Along these lines, in this work, a conservative level set method in conjunction with the inverse piezoelectric effect and the fluid–structure interaction is proposed for analyzing the PIJ printing process. On top of that, benchmark effectiveness against the experimental tests is introduced, in which an air bubble can be observed to be generated and further be trapped within the nozzle channel. The evolution of air bubble formation and trapping process was then visually analyzed in depth by considering the ink–solid–air interaction in the form of numerical investigation, which has never been reported in the literature according to our best knowledge. In addition, a variety of both numerical and experimental results have been provided to illustrate the coalescence of the trapped air bubbles from smaller bubbles to a large bubble and to demonstrate how exactly the trapped air bubbles affect the print quality. Furthermore, the influence of the driving waveform on the evolution of the trapped air bubble was explored, which could be of great advantage for the better control of the printing process for various PIJ printheads.