Numerical Study of Metal Ink Behavior on the Wettability Pattern for Conductive Line Inkjet-Printing with Lattice Boltzmann Approach

In order to obtain a thin conductive wiring using inkjet printing, it is necessary to create a wetting pattern on the target surface to adjust the spread of the ink. MOD Ink is intended to be used as a conductive wiring material. Since MOD Ink reacts weakly to wettability, it is necessary to optimize the wettability pattern and this was performed through numerical analysis. The wetting pattern is a form in which a oleophilic line is drawn in the center of the oleophobic surface. The contact angle of each oleophobic region and the oleophilic region of the wetting pattern was a variable. The movement and shape change of the ink droplets on this wetting pattern were analyzed. In addition, it was also simulated that the surface treatment of the oleophilic line was uneven. And all simulations consider evaporation of solvents by natural convection. The simulation was carried out through the lattice Boltzmann method, which is optimized for micro-multiphase hydrodynamics. When the contact angle of the oil-repellent portion becomes too high, evaporation of the solvent is excessively displayed, and when the contact angle is low, the spread of the ink droplet is severe in the simulation, so that the gap between the wiring cannot be narrowed. Therefore, the contact angle of the oil-repellent portion needs an optimized value. Next, the optimized wettability pattern was applied to the experiment using the simulation, and MOD Ink was able to form a conductive wiring of $5\ \mu\mathrm{m}$ line width.