The inkjet printhead, originally developed for use in office printer, has recently been used in a variety of applications including semiconductor, display, medical, and biotechnology. In particular, as the textile industry becomes digitized, DTP(digital textile printing) systems using inkjet printhe...
The inkjet printhead, originally developed for use in office printer, has recently been used in a variety of applications including semiconductor, display, medical, and biotechnology. In particular, as the textile industry becomes digitized, DTP(digital textile printing) systems using inkjet printhead have been developed, and the Single Pass DTP system is very productive. However, the performance of the DTP system mainly depends on the speed and the size of the droplet because the ink is ejected onto the substrate which is transported at high speed.
In this study, the performance improvement method of Single-Pass has been proposed. One nozzle region among the inkjet printhead system was extracted and CFD simulation was performed to predict the performance of inkjet printhead. For this, the characteristics of the droplet behavior from the nozzle and the flow fields between the nozzle and the substrate were analyzed. Since the ink ejected from the nozzle generates an interface with the air, a volume of fluid(VOF) method is applied to analyze the two-phase flow, which is defined as the volume ratio of the ink. The object function for predicting the performance of inkjet printhead were selected based on the speed and size of the droplet. The design variables affected the performance were selected as the shape of the nozzle(shape of the nozzle wall, shape of the nozzle inlet/outlet) and ink properties(density, viscosity, surface tension) in the present work.
In the inkjet printhead driving method, a piezolelctirc inkjet method is employed in which ink is ejected at a displacement generated by applying an electrode to a piezoelectric element in a chamber. Since it is difficult to simulate the computation, a velocity function defined by a Dirichlet boundary condition is applied to the nozzle inlet section. As the frequency increases, the droplet speed increases. At 20 frequency, the droplet speed at the nozzle outlet is very fast and the droplet is ejected incompletely. In this study, a frequency of 10 in the available frequency rage of 5, 10, 15, and 20 was judged to be appropriate for the DTP system.
For the curved shape nozzle shape, the cross sectional area of the wall surface is increased compared with that of the straight nozzle, so that the friction between the ink and the nozzle wall surface is increased. As the friction increases, the droplet speed decreases by 0.5 and the droplet size increases by 0.1 compared with the linear type because the ejection speed at the curved nozzle exit decreases by 0.09 . The shape of the inlet/outlet of the nozzle was selected as a circle nozzle and a square nozzle. In this case, the hydraulic diameter and the volume of the nozzle were set to the same conditions. The droplet velocity for the square nozzle was decreased by 0.64 compared with that of circle nozzle, the size of the droplet was decreased by 66%, and the breakup time and breakup distance were shorter and the stabilization of the meniscus occurred rapidly. Therefore, the square nozzle is suitable for the DTP system for continuous inkjet ejection.
The density, viscosity, and surface tension of the ink were selected as one of the design parameters. As the density increases, the deflection of the droplet due to the gravity effect increases and thus both droplet velocity and size are increased. The larger the viscosity and the surface tension, the better the stability of the meniscus, which is advantageous for continuous ejection. However, since the velocity of the droplet decreases, it is important to select an appropriate viscosity and surface tension. As the result of computational simulation, the ink properties of 1,082 , 5.5~6 , 30 were selected, respectively, as the most suitable properties for the DTP system.
In the DTP system, as the substrate is moved with high speed, a Couette flow between the nozzle and substrate is occurred, which may affect the behavior of the droplet. The result shows that the Couette flow was observed and its formation was depend on the moving speed. It was also found that a the effect of substrate speed is negligibly small (i.e. the maximum misleading is calculated as 1 or less). However, due to the collision between the downward flow of the ejected droplet and the Couette flow, a vortex was generated. This phenomenon caused the adsorption position of the droplet to be shifted up to 4.4 , but it had a small effect on the diameter of the droplet.
The inkjet printhead, originally developed for use in office printer, has recently been used in a variety of applications including semiconductor, display, medical, and biotechnology. In particular, as the textile industry becomes digitized, DTP(digital textile printing) systems using inkjet printhead have been developed, and the Single Pass DTP system is very productive. However, the performance of the DTP system mainly depends on the speed and the size of the droplet because the ink is ejected onto the substrate which is transported at high speed.
In this study, the performance improvement method of Single-Pass has been proposed. One nozzle region among the inkjet printhead system was extracted and CFD simulation was performed to predict the performance of inkjet printhead. For this, the characteristics of the droplet behavior from the nozzle and the flow fields between the nozzle and the substrate were analyzed. Since the ink ejected from the nozzle generates an interface with the air, a volume of fluid(VOF) method is applied to analyze the two-phase flow, which is defined as the volume ratio of the ink. The object function for predicting the performance of inkjet printhead were selected based on the speed and size of the droplet. The design variables affected the performance were selected as the shape of the nozzle(shape of the nozzle wall, shape of the nozzle inlet/outlet) and ink properties(density, viscosity, surface tension) in the present work.
In the inkjet printhead driving method, a piezolelctirc inkjet method is employed in which ink is ejected at a displacement generated by applying an electrode to a piezoelectric element in a chamber. Since it is difficult to simulate the computation, a velocity function defined by a Dirichlet boundary condition is applied to the nozzle inlet section. As the frequency increases, the droplet speed increases. At 20 frequency, the droplet speed at the nozzle outlet is very fast and the droplet is ejected incompletely. In this study, a frequency of 10 in the available frequency rage of 5, 10, 15, and 20 was judged to be appropriate for the DTP system.
For the curved shape nozzle shape, the cross sectional area of the wall surface is increased compared with that of the straight nozzle, so that the friction between the ink and the nozzle wall surface is increased. As the friction increases, the droplet speed decreases by 0.5 and the droplet size increases by 0.1 compared with the linear type because the ejection speed at the curved nozzle exit decreases by 0.09 . The shape of the inlet/outlet of the nozzle was selected as a circle nozzle and a square nozzle. In this case, the hydraulic diameter and the volume of the nozzle were set to the same conditions. The droplet velocity for the square nozzle was decreased by 0.64 compared with that of circle nozzle, the size of the droplet was decreased by 66%, and the breakup time and breakup distance were shorter and the stabilization of the meniscus occurred rapidly. Therefore, the square nozzle is suitable for the DTP system for continuous inkjet ejection.
The density, viscosity, and surface tension of the ink were selected as one of the design parameters. As the density increases, the deflection of the droplet due to the gravity effect increases and thus both droplet velocity and size are increased. The larger the viscosity and the surface tension, the better the stability of the meniscus, which is advantageous for continuous ejection. However, since the velocity of the droplet decreases, it is important to select an appropriate viscosity and surface tension. As the result of computational simulation, the ink properties of 1,082 , 5.5~6 , 30 were selected, respectively, as the most suitable properties for the DTP system.
In the DTP system, as the substrate is moved with high speed, a Couette flow between the nozzle and substrate is occurred, which may affect the behavior of the droplet. The result shows that the Couette flow was observed and its formation was depend on the moving speed. It was also found that a the effect of substrate speed is negligibly small (i.e. the maximum misleading is calculated as 1 or less). However, due to the collision between the downward flow of the ejected droplet and the Couette flow, a vortex was generated. This phenomenon caused the adsorption position of the droplet to be shifted up to 4.4 , but it had a small effect on the diameter of the droplet.
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#Numerical analysis DTP Inkjet Wood-grain defect Injection Condition
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