A double-ring induced focusing electrojet printing method

Abstract

The present invention belongs to the field of advanced manufacturing technology, and proposes an electrojet printing method with double-ring induced focusing. The method uses double conductive rings as induction electrodes to generate an electrostatic focusing electric field, thereby inducing the ink at the tip of the metal microneedle to print a pattern with a resolution of micro-nanoscale. First, a printing device is prepared and installed, and then the ink is covered on the surface of the tip of the metal microneedle in a manner similar to a dip pen. Then the double conductive rings are grounded, and the metal microneedle is connected to a power supply, and an electrostatic focusing electric field is formed between the double conductive rings and the metal microneedle. Under the action of electrostatic focusing, the ink forms a Taylor cone and is further sharpened, and finally emitted to a receiving substrate. The method places the metal microneedle in the double conductive rings, which can realize electrojet printing on an insulating substrate, and at the same time can increase the printing distance to the millimeter level. It is easy to operate, has a high printing resolution, and has strong ink adaptability.

Description

Technical Field

[0001] The invention relates to the field of advanced manufacturing technology, and in particular to an electro-jet printing method with double-ring induced focusing. Background Art

[0002] Electrojet printing (E-Jet printing), based on the principles of electrohydrodynamics (EHD), utilizes electrostatic forces to draw a fluid from a nozzle into a large, scaled-down microjet. Combined with the planar motion of a work platform, this technology can directly form micro-nanostructured devices on a receiving substrate. The operating principle is as follows: An external electric field of a certain strength is applied between the nozzle and the receiving plate, generating polarized charges within the liquid. These charges, combined with free charges in the liquid, move toward the liquid's outer surface under the influence of the electric field. The charges accumulated on the liquid surface generate an electric force under the influence of the electric field, driving the liquid toward the top of the liquid film and drawing it into a sharp cone (a Taylor cone). Ultimately, a stable conical jet forms at the end of the cone, which is deposited onto the receiving substrate. During this process, the electric force, surface tension, gravity, and viscous forces acting on the liquid cone achieve a dynamic equilibrium, maintaining the stability of the E-Jet jet. Current E-Jet printing technology offers significant advantages over traditional piezoelectric, thermal, or bubble-driven inkjet technologies. For example, electrojet printing does not require a complex nozzle manufacturing process, only a metal tube, which reduces the difficulty of nozzle production; at the same time, the most obvious advantage of electrojet over inkjet printing is that it can use a simple method to obtain a jet with a jet diameter that is much smaller than the nozzle diameter by 1 to 2 orders of magnitude.

[0003] Controlling the electric field of an electrohydrodynamic jet is a key step in electrojet printing. During electrojet printing, the electric field force is easily affected by the distance between the receiving substrate and the nozzle, as well as the properties of the substrate material, causing it to become discrete. This not only makes it difficult to achieve a precisely focused, stable jet, but also significantly reduces the quality of the printed pattern.

[0004] Existing research shows that in order to improve the stability of the jet, the printing distance is usually set to the micron level. However, when the electric field is regulated on this basis, not only is voltage breakdown easily generated, but the printed pattern also affects the distribution of the electric field lines, reducing the uniformity of the printing. The literature "N.Martinez-Prieto, M.Abecassis, J.Xu, P.Guo, J.Cao, and K.F.Ehmann, Feasibility of Fiber-Deposition Control by Secondary ElectricFields in Near-Field Electrospinning, J.Micro Nano-Manufacturing, 2015, 3(4), 1–6." By adding an auxiliary electrode ring between the nozzle and the substrate to induce the jet flow, the printing distance can be effectively increased. However, edge effects will occur, which will cause the jet to move to the auxiliary electrode, so the position of the auxiliary electrode needs to be adjusted in time, otherwise the continuity of the jet will be seriously affected. In addition, electrojet printing on insulating substrates also faces huge challenges. On the one hand, a stable electrostatic field cannot be formed between the insulating substrate and the nozzle, and even the generation of the jet is inhibited. On the other hand, the polarization of the insulating substrate repels the charged jet, severely impacting printing accuracy. The paper "C. Wei, H. Qin, C. P. Chiu, Y. S. Lee, and J. Dong, Drop-on-demand E-jet printing of continuous interconnects with AC-pulse modulation on highly insulating substrates, J. Manuf. Syst., 2015, 37, 505–510" uses AC pulse voltage for printing to offset charge accumulation on the insulating substrate. However, substrate polarization cannot be avoided, thus affecting electrojet printing quality. Therefore, none of the aforementioned methods can simultaneously address both the insulating substrate and printing distance issues, severely hindering the development and application of electrojet printing technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and invent a double-ring induced focusing electrojet printing method. In this method, double rings are used as induction electrodes to generate an electrostatic focusing electric field, thereby inducing the focus of ink at the tip of the metal microneedle and ejecting droplets with micro-nanoscale resolution. This breaks through the near-field distance limitation of electrojet printing and its dependence on the receiving substrate. Not only can patterned printing at the micro-nanoscale be achieved under millimeter-level printing distance conditions, but it is also independent of the material properties of the receiving substrate. In other words, micro-nanoprinting can also be achieved on insulating substrates. It has the characteristics of high printing resolution, low cost, and wide material adaptability.

[0006] The technical solution adopted by the present invention is as follows: a double-ring induced focusing electrojet printing method, in which the double rings are set as induction electrodes to generate an electrostatic focusing electric field, which is used to induce the ink at the tip of the metal microneedle 1 to eject tiny droplets onto the receiving substrate 5, thereby realizing the manufacture of micro-nano devices. The specific steps are as follows:

[0007] The first step is to prepare and install the printing device;

[0008] The metal microneedle 1 is corroded to provide a roughened surface structure 3, thereby changing its surface energy and allowing ink to penetrate the surface to provide a sufficient amount of ink. The bottom end of the corroded metal microneedle 1 is fixed to a base 8, with the tip located between the upper conductive ring 4 and the lower conductive ring 2. A pulse power supply 6 is connected to a high-voltage amplifier 7, and the amplified voltage is applied to the metal microneedle 1. The lower conductive ring 2 and the upper conductive ring 4 are grounded as ground electrodes, forming an electrostatic focusing electric field between them and the metal microneedle 1.

[0009] The second step is to print micro-nano droplets;

[0010] A printing ink is configured, and a trace amount of ink is attached to the tip of the metal microneedle 1 in a manner similar to a dipping pen, so that the tip is completely immersed in the ink; the ink improves its own wettability under the action of the roughened surface structure 3 and remains on the surface of the tip of the microneedle 1; a DC voltage or a pulse voltage is applied to the metal microneedle 1 through a pulse power supply 6 and a high-voltage amplifier 7, and the pulse amplitude, pulse duty cycle and pulse frequency are adjusted, so that the trace amount of ink at the tip of the metal microneedle 3 overcomes the surface tension and viscosity of the liquid film under the action of the electrostatic focusing electric field, further deforms, focuses and sharpens, forms micro-nano droplets, and is emitted onto the insulating substrate 5 0.01 to 5 mm away from the tip of the metal microneedle 1, and then the ink soaked on the surface of the tip roughened structure 3 enters the next droplet emission cycle.

[0011] The upper conductive ring 4 and the lower conductive ring 2 are fixed on the mobile platform respectively, and their central axes are coaxial; the metal microneedle 1 is located on the central axes of the two conductive rings.

[0012] The tip curvature radius of the metal microneedle 1 is 0.01 to 10 μm.

[0013] The voltage value of the DC voltage is 50-2000V; the pulse amplitude of the pulse voltage is 50-1000V, and the pulse frequency is 10-5000Hz, which controls the printing rate; the pulse duty ratio is 10-40%, which controls the droplet volume.

[0014] In the first step, the metal microneedles 1 are corroded using a ferric chloride solution.

[0015] The beneficial effects of the present invention are as follows: it is possible to realize micro-nanoscale electrojet printing at a printing distance of millimeters. In addition, the printing process may not depend on the material properties of the receiving substrate, and high-resolution pattern printing can be achieved even on an insulating substrate. By changing the parameters of the applied pulse voltage (pulse amplitude, pulse frequency, and pulse duty cycle), the ink focusing state can be adjusted, and the droplet printing speed and droplet volume can be further controlled. The use of a double-ring electrostatic focusing electric field for electrojet printing can effectively expand the adaptability of the receiving substrate material and ink type, and at the same time can achieve micro-nano pattern printing at a printing distance of millimeters. This method has broad application prospects in the fields of flexible thin film transistors and microlenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1( a ) is a schematic diagram of an electrofluidic printing device with double-ring induced focusing;

[0017] Figure 1(b) is a partial enlarged view of the tip of the metal microneedle in Figure 1(a);

[0018] Figure 2 Schematic diagram of the metal microneedle tip infiltrating ink in a double-ring induced focusing electrojet printing device.

[0019] Figure 3 This is a high-resolution photograph of the metal microneedle tip prepared by the etching process in the present invention.

[0020] Figure 4a)-Figure 4d) The following are simulation diagrams of different droplet shapes after applying pulse voltage, where: Figure 4a ) is the initial state of the liquid level, Figure 4b ) is the Taylor cone focused by the liquid surface, Figure 4c ) is a further sharpening of the Taylor cone, Figure 4d ) is the emission droplet.

[0021] Figure 5 This is a photo of micro-nano droplets printed using the method proposed by the present invention.

[0022] Among them: 1-metal microneedle, 2-lower conductive ring, 3-roughened structure, 4-upper conductive ring, 5-receiving substrate, 6-pulse power supply, 7-high voltage amplifier, 8-base. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0024] FIG1 is a schematic diagram of a double-ring induced focusing electrojet printing device of the present invention. As shown in FIG1 , in the double-ring induced focusing electrojet printing method, a printing device is first prepared and installed. The specific steps of the method are as follows:

[0025] The first step is to prepare and install the printing device;

[0026] First, the tip of a metal microneedle 1 with a curvature radius of 0.01 to 10 μm is placed in a 1 to 2 mol / L ferric chloride solution for 2 to 5 minutes to cause the surface to present a roughened structure 3, thereby changing its surface energy and enabling the ink to infiltrate its surface to provide a sufficient amount of ink, such as Figure 2 As shown; the corroded metal microneedle 1 is fixed on the base 8 by PDMS thermal curing to achieve the effect of isolation from the outside world; next, the upper conductive ring 4 and the lower conductive ring 2 are fixed on the micro-motion platform at the same time to facilitate the adjustment of the ring position; then the metal microneedle 1 is vertically placed in the approximate central axis position of the two conductive rings, and ensure that the tip of the metal microneedle 1 is between the two conductive rings, as shown Figure 3 As shown; the pulse voltage generated by the pulse power supply 6 and the high-voltage amplifier 7 is applied to the metal microneedle 1; finally, the lower conductive ring 2 and the upper conductive ring 4 are grounded, and an electrostatic focusing electric field is formed between them and the metal microneedle 1.

[0027] The second step is to print micro-nano droplets;

[0028] Configure the printing ink, and attach a small amount of ink to the tip of the metal microneedle 1 in a manner similar to a dip pen, so that the tip is completely immersed in the ink; the ink improves its own wettability under the action of the roughened structure 3, and can stay on the surface of the tip of the metal microneedle 1 for a long time; then apply a pulse voltage to the metal microneedle 1 through the pulse power supply 6 and the high-voltage amplifier 7, and adjust the pulse amplitude (50-1000V), pulse duty cycle (10-40%) and pulse frequency (10-5000Hz), so that the small amount of ink at the tip of the metal microneedle 1 overcomes the surface tension and viscosity of the liquid film under the action of the electrostatic focusing electric field induced by the double conductive rings, further deforms, focuses and sharpens, forming micro-nano droplets, which are finally emitted onto the insulating receiving substrate 5, and then the ink soaked on the surface of the tip roughened structure 3 enters the next droplet emission cycle. The printed droplets are as follows Figure 5 shown.

[0029] Figure 4a)-Figure 4d)This is a simulation diagram of the morphology of micro-nano droplets at different stages after applying a pulse voltage. It can be seen from the figure that after applying the pulse voltage, the focused liquid cone on the tip of the metal microneedle continues to sharpen under the action of the tangential electric field force, and eventually breaks through the constraints of the liquid viscosity, surface tension and inertia force, and is pulled and broken to form micro-nano droplets that are ejected onto the receiving substrate 5.

[0030] The proposed dual-ring induced focusing electrojet printing method overcomes the near-field distance limitations and substrate dependency of electrojet printing. By utilizing the electrostatic focusing field generated by the dual-ring induction technique, electrojet printing effectively expands the adaptability of substrate materials and ink types, while enabling the printing of micro-nano patterns at millimeter-scale printing distances. This method has broad application prospects in areas such as flexible thin-film transistors and microlenses.

Claims

1. A double-ring induced focusing electrojet printing method, characterized in that: A double ring is set as an induction electrode to generate an electrostatic focusing electric field to induce the ink at the tip of the metal microneedle (1) to eject tiny droplets to the receiving substrate (5); the specific steps are as follows: The first step is to prepare and install the printing device; The metal microneedle (1) is corroded to have a roughened structure (3) on its surface, thereby changing its surface energy and enabling ink to infiltrate its surface to provide a sufficient amount of ink; the bottom end of the corroded metal microneedle (1) is fixed on a base (8), with the tip located between the upper conductive ring (4) and the lower conductive ring (2); a pulse power supply (6) is connected to a high-voltage amplifier (7), and the amplified voltage is applied to the metal microneedle (1); the lower conductive ring (2) and the upper conductive ring (4) are grounded as grounding electrodes, forming an electrostatic focusing electric field between the metal microneedle (1); The second step is to print micro-nano droplets; The printing ink is configured and attached to the tip of the metal microneedle (1) by dipping the pen so that the tip is completely immersed in the ink; the ink improves its own wettability under the action of the roughened surface structure (3) and remains on the tip surface of the metal microneedle (1); A pulse voltage is applied to the metal microneedle (1) through a pulse power supply (6) and a high-voltage amplifier (7), and the pulse amplitude, pulse duty cycle and pulse frequency are adjusted, so that the trace ink at the tip of the metal microneedle (3) overcomes the surface tension and viscosity of the liquid film under the action of the electrostatic focusing electric field, further deforms, focuses and sharpens, forms micro-nano droplets, and is emitted to an insulating substrate (5) 0.01~5mm away from the tip of the metal microneedle (1). The ink then infiltrates the surface of the roughened structure (3) at the tip and enters the next droplet emission cycle.

2. The double-ring induced focusing electrojet printing method according to claim 1, characterized in that: The upper conductive ring (4) and the lower conductive ring (2) are respectively fixed on the mobile platform, and their central axes are coaxial; the metal microneedle (1) is located on the central axes of the two conductive rings.

3. The double-ring induced focusing electrojet printing method according to claim 1 or 2, characterized in that: The tip curvature radius of the metal microneedle (1) is 0.01-10 μm.

4. The double-ring induced focusing electrojet printing method according to claim 3, characterized in that: The pulse amplitude of the pulse voltage is 50-1000V, the pulse frequency is 10-5000Hz, and the pulse duty cycle is 10-40%.

5. The double-ring induced focusing electrojet printing method according to claim 1 or 2, characterized in that: The corroded metal microneedles (1) in step 1 are corroded using a ferric chloride solution.

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