Numerical And Experimental Study Of Ink Droplet Impact Process On Fabric For Inkjet Printing

Digital inkjet printing compared with traditional printing eliminates the cumbersome processes of plate making or color matching.Printing can be achieved by controlling the movement of the print head through a computer,which has the advantages of low energy consumption,low pollution,few pattern restrictions and a wide color gamut.In the era of personalization and customization,inkjet printing is more suitable for multicolor design and small-scale production,so it is gradually popularized in production and life.The working principle of digital direct inkjet printing is that after the ink droplets impact the fabric,they spread on the surface of the fabric and penetrate and diffuse inside the fabric,eventually adhering to the surface of the fabric to form a pattern.Therefore,revealing the laws and mechanisms of a single ink droplet impacting and penetrating the fabric spreading has important guiding significance for improving the quality of printed patterns.This paper first uses the VOF method to simulate the dynamic process of ink droplets impacting plain weave polyester cotton fabric.To characterize the influence of porous medium resistance and capillary force of ink flow in yarns,source terms are added to the momentum equation through UDF.By comparing the simulation and experiment of ink droplets impacting the fabric surface under the same conditions,the validity of the model is verified.By analyzing the morphological changes of ink droplets after impacting the fabric surface,it is found that ink droplets spread and retract on the fabric surface accompanied by partial penetration.The influence laws of ink droplet velocity,diameter,viscosity and other factors on the spreading and penetration process are studied.The results show that increasing the impact velocity of ink droplets promotes the spreading of ink droplets,but changes in velocity have little effect on penetration.As the ink droplet diameter increases,the maximum spreading coefficient increases and the time to reach the maximum spreading coefficient lengthens.In contrast,an increase in ink droplet diameter will reduce the penetration coefficient.An increase in ink droplet viscosity does not significantly affect spreading,but an increase in ink droplet viscosity reduces the fluidity of the ink,inhibiting the penetration of ink droplets into the fabric.Secondly,high-speed photography is used to carry out experimental research on the dynamic process of ink droplets impacting the fabric surface.The influence of ink droplet velocity,ink droplet diameter,fabric thickness and fabric pretreatment on ink droplet spreading is analyzed from the warp and weft directions.The results show that the influence laws of ink droplet velocity and diameter on ink droplet spreading are basically consistent with the results of numerical simulation.Increased ink droplet velocity will increase the difference in spreading between the warp and weft directions.Changes in fabric thickness or pretreatment of the fabric,although leading to different yarn density,porosity and microstructure in yarns,due to the short duration of the impact process dominated by ink droplet inertia,the spreading coefficient mainly depends on the kinetic energy of the ink droplets.Therefore,changes in fabric thickness and pretreatment have little effect on the spreading process.Finally,the diffusion behavior of ink droplets on the fabric surface is further studied.By overhead recording of the long diffusion process of ink droplets and measuring the final color depth of the fabric,the influence of ink droplet velocity,ink droplet diameter,fabric thickness and pretreatment on ink droplet diffusion behavior and color rendering performance is studied.The results show that ink droplets are more likely to diffuse along the yarn direction,making the final diffusion shape elliptical.Changes in ink droplet velocity have little effect on its diffusion behavior,but increased velocity will enhance the final color depth of the fabric.Increasing the diameter of ink droplets or the thickness of fabrics,the maximum diffusion coefficient and the difference in diffusion between the warp and weft directions decrease,the coloring effect is improved,the time for ink droplets to reach the maximum diffusion coefficient increases with the increase of ink droplet diameter,but decreases with the increase of fabric thickness.After fabric pretreatment,some gaps between fibers are blocked,the diffusion distance and diffusion time of ink droplets decrease,and the diffusion shape is closer to a perfect circle,so the final color rendering effect of the fabric can be improved.