The Research Of Drop-On-Demand Piezeoelectrric Inkjet Droplets Formation And Deposition

Inkejet printing technology is a non-contact and highly efficient approach for depositing mircon-sized droplets from a small orifice onto a designated position on a substrate. It is compatible with various materials so it has been successfully applied in a lot of scientific and engineering fields, s uch as electronic manufacturing, life science and additive manufacturing. Accompanying with the progress of inkjet printing, Drop-onDemand(DOD) piezoelectric inkjet printing, one of the major technology, has raised a lot of attention because of its great compatibility for inks.The objective of the research is to develop fundamental understanding of the process of DOD inkjer printing. The inter-relationship between inkjet printability and printing parameters has been investigated. The final state of the material left on the substrate after solvent ecaporation is significantly influenceed by two important processes involved DOD inkjet printing: drop formation and impaction on the substrates. The simplified mathematical model has been built to analyze the wave propagation.Firstly, the dynamic of droplet formation has been studied experimentally using an imaging system. Both the operating parameters of the piezoelectric printing head and the rheological properties of inks have important effects on droplet formation. The operating parameters are the voltage, dwell time and frequency of a single waveform. The dimensionless parameter Oh-1 is chosen to represent the physical properties of inks. The volume and velocity of droplets under different experimental conditions have been measured. As satellite droplets are undesirable for applcations of inkjet pringting, the avoidance of satellite droplets has been also studied. In addition, the defect of inkjet such as droplet retraction and misleading jetting are simulated.Secondly, the impaction of micron-droplets impaction on substrates is discussed and presented by computational fluid mechanic software FLUENT. The theoretical formula for spreading coefficient is derivated. The problem of mixing air during impaction has been alse also analyzed. Besides, the effects of contact angle and droplet velocity on the spreading of droplets have been investigated by numerical simulation.Finally, nano silver conductive ink had been prepared by a new green and chemistry method. Then the ink was printed on the substrate, which made a thin conductive film. The film was measured and proved to be of great conductivity.