Piezo inkjet printing is a widely known technology to generate small droplets for accurate patterning of functional materials. The droplet generation is a complex interaction of the internal pump dimensions, the piezo electric driving characteristics and the liquid properties. For low viscosity inks standard drop formation is executed by employing the keynote mode of the waveguide type of print head. In such a print head the pump chambers are long, in order to allow for a close staking of the nozzles to end up with a large native drop per inch (DPI) number. This keynote mode produces droplets with a diameter that is of the order of the nozzle diameter. As there is a need for patterns with finer and finer features, especially for non-graphical applications, while still maintaining a robust printing process, i.e. without clogging of the nozzle, it is very interesting to generate smaller sized droplets while using a standard print head. In this paper it is shown experimentally and theoretically that such droplets can be made via higher order oscillatory meniscus modes. In such a mode the fluid motion is confined to the very close environment of the meniscus. When the print head and pulse are designed such that an overtone of the waveguide coincides with a symmetric resonance mode of the meniscus, it is possible to make stable droplets that are more than an order of magnitude smaller than the standard droplet.
Paul C. Duineveld, J. Frits Dijksman, "Ultra Small Droplet Generation in Inkjet Printing by Higher Order Meniscus Oscillations" in Proc. IS&T Printing for Fabrication: Int'l Conf. on Digital Printing Technologies (NIP34), 2018, pp 147 - 150, https://doi.org/10.2352/ISSN.2169-4451.2018.34.147