Dynamics of Jetted Liquid Filaments

Abstract

The formation of liquid filaments is a topic of great interest because of its frequent occurrence in a wide variety of engineering applications such as coating, spraying and ink-jet printing technologies. Given the rapid evolution of the latter technology and the everincreasing demand for enhanced resolution, good to excellent printer performances under different operating conditions are deemed necessary. The required performances could be in terms of drop sizes, optical density, color gamut and uniformity and so on. It is well known that critical issues in print quality are imperfections related to the manufacturing of print heads, the uneven spreading of ink on the print media and certainly above all the ability of the inks to be ejected from the print-heads and the evolution in time of the jetted liquid filaments. This last topic is the one which is considered in detail in this paper.More and more markets are opening towards drop on demand ink-jet printing, ranging from the packaging industry to printing on electronic components. At the same time, there is need to cut down drastically the costs related to numerous and time consuming experiments. For this purpose, we have developed an automated print quality optimization apparatus, which allows us to follow the drop from the exit of the nozzle to drop impact. This device will be briefly discussed and used to follow the full ejection process and to detail the drop formation from pinch-off to the recoiling with eventual secondary breakup.In this paper, we also focus on the design of the electronic control of jetting by means of a specific wave form generator for ink-jet print-heads. This computer controlled device has a versatile architecture and can be used to drive different print-heads. It proved to be invaluable notably in generating different forms of satellite drops with a given print-head.Finally, the different measurements which have been performed using the above two devices allow to better quantify the various non-linear hydrodynamic phenomena for the free surface flow under consideration. We show that the framework of dynamic singularities which has been largely used elsewhere to construct similarity solutions for hydrodynamic problems can prove to be helpful in the analysis of the pinch-off phenomenon in DOD ink-jet printing.