Study Of Droplet Impact On Substrate In Ink-jet Printing

The ink-jet printing technology has been widely used in electronic technology and additive manufacturing,especially in flexible electronic manufacturing.In ink-jet printing technology,a key technical problem is the deposition of ink-jet droplets on the substrate following by the formation of patterns.This process could be affected by many factors such as fluid properties,ink-jet parameters(e.g.,driving voltage and frequency),substrate properties,etc.To date,researchers have mainly focused on the horizontal substrate.However,the shape of the substrate is usually non-horizontal in industrial manufacturing.For example,the substrate is usually bent in flexible electronic manufacturing.Therefore,understanding the mechanism and controlling the impact process are crucial to improving the manufacturing accuracy and product quality.The evolution of the morphology of a droplet impacting the substrate has received much attention in hydrodynamics.The local deformation characteristics are strongly nonlinear coupling with the complex flow in this process.Hence,the assumption and simplification of ideal fluid are invalid for getting an analytical solution through theoretical analysis.In our study,the high-speed camera is used to build the experimental observation system of droplets impacting the substrate.Besides,a numerical model focusing on the deformation process of droplets impacting the substrate is established based on the Level-Set method.The horizontal,inclined,and spherical substrates have been studied,respectively.From our study with the dimensionless parameter analysis and empirical relationship fitting,the main conclusions are listed as follows:Firstly,for the horizontal substrate,the maximum spreading radius increases as the enhance of the initial velocity and density.Besides,larger surface tension or a larger viscosity leads to a smaller spreading radius.The wettability of the substrate can promote the maximum spreading radius.An empirical relation of the maximum spreading radius(βmax)is fitted with the Reynold(Re)and Weber(We)numbers,as βmax=0.5Re0.16We0.12,where 40<Re<3300,2<We<73,which has been verified in predicting the maximum spreading factor of droplets.Then,for the inclined substrate,the inclined angle(a)and Weber number(We)significantly affect the maximum spreading radius,which increases as the increase of a or We.A fitting curve between the maximum spreading radius and the Weber number and inclined angles can be described as βmax=0.003We1.5·tan2α+0.95We0.25,where 5<We<40,5<a<40,which has been verified by our experiments.Finally,for the spherical substrate,the maximum spreading radius decreases with the rising of curvatures.The viscosity and surface tension can restrain the spreading and retracting process.With a high viscosity or a high surface tension,the maximum spreading radius is small and the minimum height factor is large,which is caused by the slow spreading and retracting processes.In this thesis,the numerical analysis and experimental methods of the morphology evolution dynamics of a droplet impacting the substrate have been systematically studied.The evolution of the droplet morphology is revealed and the empirical formula of spreading factor is obtained,which provides theoretical guidance and optimization direction for improving the deposition and pattern formation quality in the ink-jet printing.