Nonaxisymmetric Effects in Drop-On-Demand Piezoacoustic Inkjet Printing

Drop-on-demand (DOD) inkjet printing is well characterized and a well-studied problem, but nonaxisymmetric effects are typically ignored, while these effects can severely reduce the print-head performance and its stability. In this paper we first review nonaxisymmetric droplet formation originating from geometrical effects. We then focus on the possibility that observed nonaxisymmetry arises from surface instabilities of the meniscus by a Rayleigh-Taylor-like (RT) mechanism. It is shown theoretically that the meniscus can become RT unstable beyond a critical acceleration. A comparison with data extracted from high-speed recordings of the meniscus oscillations show that the critical accelerations are exceeded. Using the time duration that the critical acceleration is exceeded and the maximal growth rate, the extent of growth of the unstable wave is estimated.