A novel ink jet printing technology using ink mist jet has been developed. It enables multilevel printing within a single dot because a density controllable cluster of fine ink droplets is formed by focused ultrasonic waves. The ultrasonic wave radiated into an ink chamber is reflected by the parabolic chamber wall and focused on a nozzle hole. Under the suitable driving condition of the ultrasonic transducer, a traveling surface wave is generated at the ink meniscus and it separates many fine ink droplets at the peak point of the wave. Changing the number of ultrasonic waves within the interval to achieve one dot printing can control the density of the cluster. We have obtained a print sample with reduced graininess using a prototype print head employing a 10 MHz transducer that produces ink droplets with an average diameter of 2.5 μm. We also confirmed a basic performance having a maximum optical density of 2.3, 32 controllable gray levels and a resolution of 300 dpi using glossy paper with a dot frequency of 2 kHz.
Hiroshi Fukumoto, Jyunichi Aizawa, Hiroyuki Nakagawa, Hiromu Narumiya, Yasuhiko Ozaki, "Printing with Ink Mist Ejected by Ultrasonic Waves" in Journal of Imaging Science and Technology, 2000, pp 398 - 405, https://doi.org/10.2352/J.ImagingSci.Technol.2000.44.5.art00004