Pneumatic Conveying Printing Based on Super Hydrophobic Surface

Abstract

tree of printing technologies which also comprise the contact printing techniques, such as roll-to-roll printing, [6] microcontact printing, [7] nanoimprint [8] technique, and so on. Traditional IJP techniques, such as piezoelectric IJP and thermal-bubble IJP, are typical drop-on-demand (DOD) printing techniques. The principle of IJP is based on the utilization of the transient high pressure, generated either by the rapid transform of the micropiezoelectric crystal attached to the ink chamber (piezoelectric IJP) or by the rapid expansion of a microbubble within the chamber (thermal-bubble IJP), to eject ink drops out of a small orifice. For both traditional IJP techniques, the viscosity of the inks should not excess several tens mPa s to ensure printability. [9] Currently, three strategies are normally adopted by IJP for printing viscous inks. The first strategy reduces the viscosity of the ink to a value accepted by the traditional IJP techniques (normally by heating the ink during printing). Now, inkjet nozzles integrated with heating component are commercially available. This strategy is limited since many inks cannot be heated, for instance, inks containing temperature sensitive materials which might be destroyed irreversibly by high temperature or the viscosity cannot be further reduced below the acceptable value even after heating. The second strategy is based on an increase of the transient pressure within the chamber in order to fiercely eject the viscous ink and give the ink sufficient momentum for the detachment of a drop and its subsequent flying. A typical method is the valve-based printing technique, [10] in which a piston, driven by piezostack, [11][12][13] electromagnetic coil [14] or pressure [15] is used to generate the extremely high pressure in the chamber. More often, viscosity reducing and pressure increasing are adopted at the same time [10b,16] for handling inks with extremely high viscosity, for instance, silica gel, adhesive, sealant and so on. [17,18] The third strategy is utilizing external forces generated by other mechanisms and devices outside the ink chamber/pipeline, to print/dispense the viscous inks without reducing the viscosity or increasing the pressure within the chamber/pipeline. This strategy is represented by the well-known electro-hydrodynamic printing (also known as e-jet printing), [19] and the recently developed acoustophoretic printing technique. [20] For the e-jet printing, high voltage is applied between the conductive nozzle and the opposite conductive printed surface (or a conductive substrate beneath the insulating printed surface).In today's era, the inkjet printing (IJP) technique plays important roles in the fabrication of mechanical, electronical, and even biological devices. However, the current IJP techniques are incapable of handling viscous inks, which greatly hinder the extensive industrial application. Here, it is found that utilizing the superhydrophobic materials on the end surface of a nozzle combined with the dragging and shearing effects of an a...