The Drop Generation Mechanism And Regulation Of Drop-on-Demand Electrohydrodynamic Jet Printing

Inkjet printing has the characteristics of non-contact printing,digitized manufacturing and is adaptable to flexible substrates.It has a good application prospect.Electrohydrodynamic jet(e-jet)printing ejects droplets by electric force.It can adopt nozzles with diameters much smaller than those used in traditional inkjet printing,so it can print high resolution patterns.In e-jet printing,the jet diameter,pulsation frequency and the flight behavior of the satellite droplets change with the process parameters.The mechanism of controllable drop generation is complex.This thesis investigated the influence of process parameters on the ejection volume and pulsation frequency under constant voltage,the stable and high-resolution printing under pulsed voltage,the charged satellite droplet flight behavior in dripping printing mode.The innovation points of the investigation are shown below:1)The influence of the conductivity of the liquid,the viscosity of the liquid,the applied voltage and the nozzle-to-substrate distance on the ejection volume and the pulsation frequency under constant voltage was investigated.The applied voltage and nozzle-to-substrate distance have significant influence on the ejection volume which was neglected in the previous investigations.A model on the relationship between the ejection volume and four above-mentioned parameters was fitted from the results of well-designed experiments.The model can be implemented in the selection of process parameters.2)Various printing states under pulsed voltage for different voltage pulse durations were experimentally discovered.The continuous and intemittent second jet ejection mechanisms were experimentally explained,and the critical voltage pulse frequency distinguishing the two different mechanisms was determined.The phase diagram of the influence of voltage pulse frequency and duration on printing stability was experimentally found.The process parameter window for stable and high-resolution printing was given in the phase diagram.Furthermore,the influence of voltage parameters on the uniformity of printed droplets at the beginning of printing was investigated.The uniformity of printed droplets at the beginning of printing can be improved by optimizing the process parameters.3)Distributions of the electric potential,surface charge density and electric stress along the surface for fluids with different charge relaxation times during drop breakup were obtained by simulation.The mechanism of the influence of charge relaxation phenomenon on the drop breakup process and satellite droplet flight behavior was explained for the first time.The influence of the supplied flow rate and dielectric constant of the liquid on the critical charge relaxation time discriminating the different satellite droplet flight behaviors was investigated.By choosing appropriate process parameters,the satellite droplets can merge with the meniscus,so the contamination of the printed patterns can be prevented.4)Micro lens arrays for improving the light extraction efficiency in OLED display,conductive tracks and encapsulation films of flexible OLED display were fabricated by e-jet printing.A model on the relationship between the printed micro lens volume and pulsed voltage parameters was proposed.Appropriate parameters were chosen to get micro lenses with diameter of 20 ?m based on the fitted model.By choosing appropriate voltage pulse duration,the printing process remained stable and smooth conductive tracks with width of 20 ?m were printed.By choosing appropriate printed drop space,the breakup of printed encapsulation films was prevented and the film with specified thickness was obtained.The printed functional structures exhibited good performance through tests.