Study On Inkjet Printing Technology By A Multiphase Lattice Boltzmann Method

Inkjet printing technology has been used in all kinds of emerging industrial applications,such as cell printing,3D printing,electronic packaging,production of DNA materials and so on.Because of the popularity applications of inkjet printing technology,now more and more people study on this technology.The inkjet printing quality is closely related to the jetting speed of the droplet.Therefore,how to control the jetting speed of droplets is the most basic and important problem that we need to study.However,the study of jetting speed involves very complex knowledge of hydrodynamics.So in order to carry out in-depth study and analysis of the evolution of droplets to guide the actual production needs,many researchers have paid a lot of time and effort,the methods they used are mainly scientific experiments,through the scientific experiment,we can understand the specific behavior of the long tail and the droplet ejection,and also provide the indispensable basic data for the numerical simulation.However,due to the limitations of the experimental method itself and the complexity of the inkjet itself,the repeatability of the experiment is not easy to achieve,these limitations also limit the use of experimental methods.With the development of technology,some scholars have used numerical simulation method to simulate the formation of droplets,but these methods lack accuracy,and those traditional method based on the traditional continuity theory requires to solve the complex Navier-Stokes equations,which requires a lot of calculation and expensive simulation costs.Especially,the Navier-Stokes equations based on the traditional method may encounter some topological deformation during breakage and coalescence of interfaces,and in these situation,numerical simulation method is very difficult to realise.Therefore,in order to study the inkjet printing technology in depth,a more simpler and efficient way to avoid to solve the Navier-Stokes equations directly and track the complex interface will be very necessary.Currently,a multiphase lattice Boltzmann model based on large density ratio is proposed,and we use this model to simulate the jetting behavior of the ink drop.The algorithm of lattice Boltzmann method has a clear physical background,efficient calculation method and natural parallelism.This method has been widely used in Poisson flow,square cavity flow,chemical flow and so on.In this paper,the multiphase lattice Boltzmann model with large density ration is used to study the formation of the ink drop and analysis its influencing factors.The main contents of the study are:First,in the inkjet printing,the wettability of the inner wall of the nozzle and the surface tension of the ink droplet can control the flying speed of the droplet and determine the quality of inkjet printing.In order to analyze the effect of these two factors on the inkjet printing,we establish a multiphase lattice Boltzmann model which based on large density ratio.The final simulation results are in good agreement with the experimental results obtained by high-speed and high-resolution cameras,so we can verify that lattice Boltzmann method has the ability to study the formation of droplets in the inkjet printing.Because the attribute of the silicone oil and ink is very similar,so in here,the fluid we used is silicone oil,the multiphase lattice Boltzmann method is used to simulate the formation of ink droplets in inkjet printing.The shape,velocity and the breakup time of the ink drop in the initial stage,necking stage,fracture stage and shrinkage stage was mainly analyzed.Second,in the existing simulation experiment,the driving force in the piezoelectric inkjet printing is generated by the pressure difference reduced by pressure oscillation.In the simulation experiment in this paper,in order to simulate the driving force of the inner wall of the nozzle,we use a time-varying driving force to push the ink drop ejection.We can adjust the driving force by changing the positive pulse duration,negative pulse duration and idle duration to achieve the desired driving effect.After lots of trial and error,a full time period is set to a positive pulse of 5?s duration,a negative pulse of 3?s duration and an idle duration of 8?s duration.Third,we mainly simulate the influence of the inner wall of the nozzle and the surface tension of the ink droop on the formation of droplets.Before studying the effect on the droplet formation process,we first simulate the quantitative relationship between the contact angle 9 and the wetting potential ?.The conclusion is that the wetting potential decreases with the increase of the contact angle,at the same time,the hydrophilicity of the solid wall gradually weakened.This provides theoretical guidance for the study on the wettability of the inner wall of the nozzle.Then,the effects of the wettability of the inner wall of the nozzle and the surface tension of the droplets on the formation and flight of the droplets in inkjet printing are simulated by us.We find that as the contact angle of the nozzle inner wall decreases,the breakup time of droplet is shortened and the flight speed increase.As the surface tension coefficient increases,the breakup time of droplet is shortened and the flight speed increase.So the hydrophilic and higher surface tension coefficient are optimized for design.From the results of the simulation study,we can conclude that the multiphase lattice Boltzmann method based on has a good practicability for simulating the formation of droplets.The analysis of the droplet formation process can make us have a more profound understanding of the principle of droplet formation,and give us instructions to improve the quality of inkjet printing.