Drop-on-demand jetting and velocity control of droplet by using the hybrid jetting system

Abstract

Direct write techniques have been widely studied because it is a low-cost, high-speed, and environmentally-friendly manufacturing process. The technique is based on ink-jet or EHD. The ink-jet printing method can make droplets with high jetting-frequency(10-100 kHz), while the droplet size is limited to become larger than the nozzle size. On the contrary to this, the EHD printing method can makes droplets ten-times smaller than the nozzle size, but the jetting-frequency is limited due to time delay for Taylor-Cone formation. In order to generate ultra fine droplets with high-throughput, a technical convergence of ink-jet and EHD methods is required. And also, to realize multi-nozzle jetting systems, a control technique of drop-velocity from each nozzle is required. In this paper, we developed two types of hybrid printing system which are ring extractors integrated hybrid jetting system and thermal bubble hybrid jetting system.Ring extractors integrated hybrid jetting system (HJS) that solves the problems of pin electrode of previous HJS. By using this system, ultra fine droplets (1.33pl) were generated with short jetting cycle at relatively low DC voltage (2.3kV), in comparison with previous HJS (~5kV). In addition, in order to control the droplet velocity, we tested jetting performance for various DC voltages of ring extractors at fixed driving waveform. As a result, the drop velocity could be controlled by tuning the applied DC voltage to the HPS. It can contribute to reduce velocity deviation of droplets in multi-nozzle jetting systems without changing volume of droplets. For multi nozzle HJS, we made thermal inkjet head. By using PCB nozzle, we improved the electrical insulating properties of nozzle surface and reduced fabrication cost. Using these multi nozzle hybrid jetting head, we could control the meniscus and eject droplets with frequency of 500Hz.