A cross-resolution on-demand inkjet printing device and method

Abstract

The present invention discloses a cross-resolution on-demand inkjet printing device and method, belonging to the field of inkjet printing technology. The device comprises a nozzle structure, a driving system, and a high-voltage power supply unit; the nozzle structure comprises an ink storage tube and a limit ring, a spring, a guide screw, an insulating sleeve, and a tubular electrode sleeved on the outer wall of the ink storage tube; the driving system comprises a piezoelectric ceramic and a signal generating unit, which are used to drive the ink storage tube to reciprocate along an axis; the positive electrode of the high-voltage power supply unit is connected to the tubular electrode through a control switch, and the negative electrode thereof is grounded to a substrate, so as to form an induced electric field between the ink and the substrate; the present invention can realize two working modes of piezoelectric inkjet printing and electrohydrodynamic printing in an on-demand manner, and the volume of the ink droplets generated ranges from femtoliters to picoliters, and a printing resolution of submicron to submillimeter can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of inkjet printing, and in particular relates to a cross-resolution on-demand inkjet printing device and method. Background Art

[0002] As a non-contact manufacturing process without a mask, inkjet printing technology allows different types of inks to be arranged with high precision in a very economical way, and the required pattern can be easily realized by digital printing, which is especially suitable for prototyping and small batch manufacturing. So far, it has developed into a powerful manufacturing tool that supports customized design in the fields of display devices, flexible circuits, biopharmaceuticals, etc.

[0003] Although there is still great potential for creative applications of piezoelectric or thermal bubble inkjet printing technology in the scientific field, its printing characteristics have been fully demonstrated. How to make this traditional and mature technology effectively improve the compatibility with ink viscosity and printing resolution is a hot issue in the inkjet field, and it is also a difficult problem to solve. However, when different printing manufacturing technologies are used in coordination, it will have a very beneficial effect on improving the compatibility of printing technology, simplifying production processes and increasing manufacturing efficiency. Therefore, combined inkjet printing technology based on inkjet printing combined with other printing technologies has received widespread attention recently, providing a very advantageous solution for the manufacture of functional devices, such as the reported combinations of inkjet printing and 3D printing, inkjet printing and laser direct writing, inkjet printing and photolithography.

[0004] As the two most mature droplet generation technologies in the field of inkjet printing, inkjet printing is based on the superposition principle of one-dimensional pressure waves in the pipeline to drive the liquid surface at the nozzle to spray, allowing low-viscosity inks (1-20mPa·s) to be arranged with a precision of 20-200um; electrohydrodynamic printing technology is based on the Taylor cone effect, that is, by applying a high-intensity electric field between the nozzle and the substrate opposite to it, the ink at the nozzle is gradually "pulled" out of the nozzle under the action of electrical stress, so it has a wider viscosity compatibility (1-10000mPa·s) and can achieve sub-micron deposition accuracy. Since both inkjet printing and electrohydrodynamic printing can be used for displays, microlenses, microelectrode arrays, and interdigitated electrodes with different resolution requirements, the nozzle size and printing method need to be changed according to different resolution requirements during the printing process of the device, which will inevitably repeat the process of nozzle focusing and positioning, increasing the number of steps and time required for manufacturing. When inkjet printing and electrofluidic printing technologies are integrated into the same nozzle, cross-precision printing (from sub-micron to sub-millimeter) of devices with different line width requirements can be flexibly achieved, which can greatly simplify the printing process and improve manufacturing efficiency. Therefore, it is urgent to develop a printing technology that can integrate inkjet printing and electrofluidic printing into the same piezoelectric nozzle.

[0005] The electrofluidic printing technology based on liquid surface oscillation proposed in CN116100956B proves that the oscillating curved liquid surface in the electric field can form a fine electrofluidic jet, which solves the disadvantage of low efficiency of traditional EHD printing. However, the printing device designed in this patent needs to determine the resonant frequency by frequency sweeping method when in use. Based on the working principle of water hammer, the present invention proposes a droplet on-demand generation device that can realize inkjet printing and electrofluidic printing. No frequency sweeping is required. Inkjet printing can be realized when sufficient excitation voltage is applied to tubular / columnar piezoelectric ceramics; the excitation voltage is reduced so that the curved liquid surface only oscillates without spraying, and a suitable electric field is applied between the nozzle and the substrate to generate a fine electrofluidic jet with the same frequency as the liquid surface oscillation. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention proposes a cross-resolution on-demand inkjet printing device and method, which has a reasonable design, solves the shortcomings of the prior art, and has good effects.

[0007] In order to achieve the above-mentioned invention objective 1, the present invention adopts the following technical solution:

[0008] A cross-resolution on-demand inkjet printing device, comprising a nozzle structure, a drive system, and a high-voltage power supply unit;

[0009] The nozzle structure includes an ink storage tube and a limit ring, a spring, a guide screw, an insulating sleeve and a tubular electrode sleeved on the outer wall of the ink storage tube. The driving system includes piezoelectric ceramics and a signal generating unit, which are used to drive the ink storage tube to reciprocate along the axis. The positive electrode of the high-voltage power supply unit is connected to the tubular electrode through a control switch, and the negative electrode thereof is grounded to the substrate, so as to form an induced electric field between the ink and the substrate. The liquid supply system is used to provide ink to the ink storage tube.

[0010] Furthermore, the device also includes a metal shell, and a lower through hole is provided at the bottom of the shell;

[0011] The piezoelectric ceramic, the limiting ring and the spring are coaxially arranged inside the housing from top to bottom, and the limiting ring is fixedly bonded to the outer wall of the ink storage tube;

[0012] The piezoelectric ceramic is in a tubular or columnar shape, and its top is glued to the shell. The shape of the piezoelectric ceramic is selected according to the ink consumption. If the ink in the ink storage tube can complete the printing work, the columnar piezoelectric ceramic is selected. If the ink in the ink storage tube is not enough to complete the printing work, the tubular piezoelectric ceramic and the liquid supply system are selected.

[0013] The piezoelectric ceramic comprises two metal electrodes, the positive electrode is connected to the signal generating unit, and the negative electrode is grounded.

[0014] Furthermore, when the piezoelectric ceramic is tubular, the tubular piezoelectric ceramic is sleeved on the outer wall of the liquid storage tube, an upper through hole is provided on the top of the shell, and the top of the ink storage tube passes through the piezoelectric ceramic and the upper through hole and extends out of the shell.

[0015] Furthermore, the liquid supply system includes an ink supply hose, a liquid storage bottle, a ventilation hose and an air pressure regulating unit which are connected in sequence, the inlet end at the top of the ink storage tube is connected to one end of the ink supply hose, the other end of the ink supply hose is inserted into the ink in the sealed liquid storage bottle, and the liquid storage bottle is connected to the air pressure regulating unit through the ventilation hose.

[0016] Furthermore, when the piezoelectric ceramic is columnar, the top end of the ink storage tube abuts against the bottom surface of the columnar piezoelectric ceramic.

[0017] Furthermore, the guide screw is a 4-layer annular step structure with increasing diameters from top to bottom and is arranged coaxially with the spring. The first-layer step structure on the top of the guide screw extends into the interior of the spring, one end of the spring rests against the limit plate, and the other end rests against the horizontal surface of the second-layer step structure, and the spring is in a compressed pre-tightened state; the third-layer step structure is threadedly connected to the lower through hole, and the fourth-layer step structure is located outside the shell.

[0018] Furthermore, the guide screw and the insulating sleeve, and the insulating sleeve and the tubular electrode are adhesively coupled, the guide screw, the insulating sleeve and the tubular electrode are coaxially arranged, and the diameter of the axial through holes of the guide screw, the insulating sleeve and the tubular electrode is larger than the outer diameter of the ink storage tube by 0.1 mm to ensure undamped sliding of the ink storage tube, and the nozzle at the bottom of the ink storage tube extends out of the tubular electrode.

[0019] Furthermore, the high-voltage power supply unit selects different high-voltage generating devices according to actual needs. The high-voltage generating devices include but are not limited to high-voltage DC power supplies, voltage amplifiers or high-voltage pulse power supplies. The tubular electrodes apply high-voltage DC power, pulsed DC with voltage bias, or AC power in the form of positive and negative pulses according to needs.

[0020] Furthermore, the signal generating unit is a signal generator, a single chip microcomputer or any other device capable of generating a low voltage pulse, which is used to generate a custom editable low level signal, and the low level signal includes but is not limited to a square wave and a pulse wave.

[0021] In order to achieve the above-mentioned invention objective 2, the present invention adopts the following technical solution:

[0022] A cross-resolution on-demand inkjet printing method, using a cross-resolution on-demand inkjet printing device as described above, when working in the on-demand inkjet printing mode, the control switch is disconnected, there is no electric field between the nozzle and the substrate, and the signal generating unit applies an excitation signal to the piezoelectric ceramic. At this time, the excitation voltage amplitude is large enough so that the kinetic energy obtained by the curved liquid surface at the nozzle during the convex process is sufficient to overcome the energy required for the liquid bridge to break, thereby realizing droplet ejection, the ejection frequency is the same as the excitation signal, and the volume of the droplet is picoliter;

[0023] When working in the on-demand electrohydrodynamic printing mode, the amplitude of the excitation signal is reduced to be insufficient to drive the curved liquid surface to produce a jet, and only the curved liquid surface oscillation is produced; the control switch is closed to form an electric field between the nozzle and the substrate, and electrohydrodynamic jetting is achieved under the action of electric stress, and the volume of a single jet is femtoliter;

[0024] According to the actual demand for the volume of ejected liquid during the printing process, switching between the two printing modes is carried out to achieve cross-resolution printing.

[0025] Beneficial technical effects brought by the present invention:

[0026] 1. It can realize two working modes of piezoelectric inkjet printing and electrofluidic printing in an on-demand manner. The volume of the ink droplets generated ranges from femtoliters to picoliters, and the printing resolution can be from submicron to submillimeter. The present invention utilizes the inverse piezoelectric effect of piezoelectric ceramics to control the axial deformation of piezoelectric ceramics by controlling the waveform of the excitation electrical signal. The piezoelectric ceramics and the spring jointly drive the axial movement of the ink storage tube. According to the principle of laminar shear, it can be known that the axial reciprocating motion of the ink storage tube will generate positive and negative pressure waves in the tube, thereby driving the oscillation of the curved liquid surface at the nozzle. When the excitation signal is large enough, the liquid bridge of the curved liquid surface breaks during the convex process, and ink droplets of the picoliter (pL) level can be formed; when the excitation signal is reduced to a state where the curved liquid surface only oscillates but does not spray, the control switch is closed to apply an induced electric field between the nozzle and the substrate, which can generate a fine electrofluid jet of the femtoliter (fL) level with the same frequency as the excitation, solving the shortcoming that traditional inkjet printing technology is difficult to achieve cross-resolution on-demand printing.

[0027] 2. The ink storage tube can be replaced quickly. Ink storage tubes with different ink types and nozzle sizes can be replaced according to actual needs, which simplifies the printing process and has good economy. The structural design of the piezoelectric unit and the ink storage tube in the traditional piezoelectric inkjet printing device makes the two non-detachable, and there are disadvantages that it is difficult to replace the nozzle after it is damaged and the nozzle size is fixed, which makes it difficult to adjust the printing resolution. In the printing device proposed by the present invention, the ink storage tube is installed in a plug-in manner and fixed by a spring pre-tightening manner. Since the guide screw and the housing are threadedly connected, when the nozzle needs to be replaced due to blockage or damage, it is only necessary to remove the guide screw and replace the ink storage tube, and then tighten the guide screw to the housing to complete the replacement. It effectively ensures the working efficiency of the printing device and reduces the cost of use.

[0028] 3. The printing device is small in size and can be optionally equipped with an ink supply system, which can realize high-frequency on-demand injection in a flexible and economical way. The laminar shear of the liquid caused by the rapid movement of the piezoelectric ceramic-driven tube wall cooperates with the inertial force of the liquid itself to generate positive and negative pressure waves propagating along the axis. The pressure wave amplitude generated by this method is significantly higher than that of traditional piezoelectric inkjet devices. Only millimeter-sized piezoelectric ceramics and a smaller driving voltage are required to drive the liquid surface, so it has the advantage of a small printing device. In traditional inkjet printing devices, the ink supply system is not removable. Since a large amount of functional inks (Ag nano inks, quantum dot inks, organic light-emitting inks, etc.) are expensive and consume very little in the electrofluidic printing mode, a large amount of ink is wasted in the pipeline of the ink supply system. The present invention supports the realization of inkjet and electrofluidic cross-resolution on-demand printing in a flexible and economical manner without an ink supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of a cross-resolution on-demand inkjet printing device equipped with a liquid supply system in the present invention;

[0030] Figure 2 A curve diagram showing the change of the ink storage tube displacement and the pressure in the nozzle hole with time under the square wave excitation condition in the present invention;

[0031] Among them, (a) is the waveform of the applied square wave excitation signal; (b) is the curve diagram of the displacement of the ink storage tube changing with time; (c) is the curve diagram of the pressure at the nozzle changing with time;

[0032] Figure 3 It is a schematic diagram of the liquid level change in a single oscillation period under the condition of no induced electric field in the present invention;

[0033] Figure 4 A schematic diagram of droplet generation in a single jet cycle of electrofluidic power in the present invention;

[0034] Figure 5A schematic diagram of droplet generation in a single cycle during the inkjet printing process of the present invention;

[0035] Figure 6 It is a schematic diagram of a cross-resolution on-demand inkjet printing device without a liquid supply system in the present invention;

[0036] Among them, 1-ink storage tube; 2-ink; 3-limiting ring; 4-guide screw; 5-spring; 6-insulating sleeve; 7-tubular electrode; 8-high voltage power supply unit; 9-substrate; 10-piezoelectric ceramic; 11-signal generating unit; 12-positive electrode; 13-negative electrode; 14-ink drop; 15-housing; 16-control switch; 17-ink supply hose; 18-liquid storage bottle; 19-vent hose; 20-air pressure regulating unit; DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is further described below in conjunction with specific embodiments:

[0038] A cross-resolution on-demand inkjet printing device, comprising a nozzle structure, a drive system, and a high-voltage power supply unit 8;

[0039] The nozzle structure includes an ink storage tube 1 and a limit ring 3, a spring 5, a guide screw 4, an insulating sleeve 6 and a tubular electrode 7 which are sleeved on the outer wall of the ink storage tube 1. A substrate 9 is provided under the nozzle structure; the driving system includes a piezoelectric ceramic 10 and a signal generating unit 11, which are used to drive the ink storage tube 1 to reciprocate along the axis. The positive pole of the high-voltage power supply unit 8 is connected to the tubular electrode 7 through a control switch 16, and its negative pole is grounded to the substrate 9, which is used to form an induced electric field between the ink 2 and the substrate; by controlling the amplitude of the high-voltage power supply unit 8 and the control switch 16, ink droplets 14 can be generated on the substrate by inkjet printing and electrohydrodynamic printing respectively.

[0040] The device also includes a metal shell 15, and the bottom of the shell 15 is respectively provided with lower through holes; the piezoelectric ceramic 10, the limit ring 3, and the spring 5 are coaxially arranged inside the shell 15 from top to bottom, and the limit ring 3 is fixedly bonded to the outer wall of the ink storage tube 1;

[0041] The piezoelectric ceramic 10 is tubular or columnar, and its top is glued to the shell. The shape of the piezoelectric ceramic 10 is selected according to the consumption of the ink 2. If the ink 2 in the ink storage tube 1 can complete the printing work, the columnar piezoelectric ceramic is selected. If the ink 2 in the ink storage tube 1 is not enough to complete the printing work, the tubular piezoelectric ceramic and the liquid supply system are selected.

[0042] The piezoelectric ceramic 10 includes two metal electrodes, the positive electrode 12 is connected to the signal generating unit 11, and the negative electrode 13 is grounded; the signal generating unit 11 causes the piezoelectric ceramic 10 to extend and contract along its axial direction, thereby driving the ink storage tube 1 to reciprocate along the axis.

[0043] When the piezoelectric ceramic 10 is tubular, the tubular piezoelectric ceramic is sleeved on the outer wall of the liquid storage tube, and an upper through hole coaxial with the lower through hole is provided on the top of the shell 15. The top of the ink storage tube 1 passes through the piezoelectric ceramic and the upper through hole and extends out of the shell 15.

[0044] The liquid supply system includes an ink supply hose 17, a liquid storage bottle 18, a ventilation hose 19 and an air pressure regulating unit 20 which are connected in sequence. The inlet end at the top of the ink storage tube 1 is connected to one end of the ink supply hose 17, and the other end of the ink supply hose 17 is inserted into the ink in the sealed liquid storage bottle 18. The liquid storage bottle 18 is connected to the air pressure regulating unit 20 through the ventilation hose 19.

[0045] When the piezoelectric ceramic 10 is in a columnar shape, the top end of the ink storage tube 1 abuts against the bottom surface of the columnar piezoelectric ceramic.

[0046] The guide screw 4 is a 4-layer annular step structure with increasing diameters from top to bottom and is coaxially arranged with the spring 5. The first layer of the step structure at the top of the guide screw 4 extends into the spring 5. One end of the spring 5 abuts against the limit plate, and the other end abuts against the horizontal surface of the second layer of the step structure. The distance between the limit plate and the horizontal surface should be smaller than the free length of the spring to ensure that the spring 5 is in a compressed pre-tightened state after assembly, providing pre-tightening pressure for the ink storage tube 1 and the bottom surface of the piezoelectric ceramic 10; the third layer of the step structure is threadedly connected to the lower through hole, and the fourth layer of the step structure is located outside the housing 15;

[0047] The guide screw 4 and the insulating sleeve 6, as well as the insulating sleeve 6 and the tubular electrode 7 are adhesively coupled. The guide screw 4, the insulating sleeve 6 and the tubular electrode 7 are coaxially arranged, and the diameter of the axial through hole of the guide screw 4, the insulating sleeve 6 and the tubular electrode 7 is larger than the outer diameter of the ink storage tube 1 by 0.1 mm to ensure the undamped sliding of the ink storage tube 1. The nozzle at the bottom of the ink storage tube 1 extends out of the tubular electrode 7, and a nozzle hole is provided on the nozzle.

[0048] The high-voltage power supply unit 8 selects different high-voltage generating devices according to actual needs. The high-voltage generating devices include but are not limited to high-voltage DC power supplies, voltage amplifiers or high-voltage pulse power supplies. The tubular electrode 7 applies high-voltage DC power, pulsed DC with voltage bias, or AC power in the form of positive and negative pulses according to needs.

[0049] The signal generating unit 11 is a signal generator, a single chip microcomputer or any other device capable of generating a low voltage pulse, and is used to generate a custom editable low level signal, wherein the low level signal includes but is not limited to a square wave and a pulse wave.

[0050] As mentioned above Figure 1 The nozzle is in the initial position under the constraint of the spring preload and the tube piezoelectric ceramic. When the piezoelectric ceramic 10 is subjected to the following Figure 2When the square wave excitation signal shown in a is used, the rising edge signal will cause the tubular piezoelectric ceramic to stretch rapidly, driving the ink storage tube 1 to move downward to the lowest position, and the spring 5 will be further compressed. In this process, the ink in the ink storage tube 1 that adheres to the tube wall meets the conditions of no slip and continuous speed under the action of adhesion force. The ink at the axis of the ink storage tube 1 remains relatively static under the action of inertia force. Therefore, at the moment when the ink storage tube moves downward, the liquid surface at the top of the ink storage tube tends to bend toward the air side. Although this displacement is only at the nanometer level, according to the incompressibility condition of the liquid and the flow conservation condition, it can be known that the nanometer-level change of the liquid surface at the top of the ink storage tube will cause the curved liquid surface at the nozzle to produce a micron-level concave amplitude. At this time, the pressure at the nozzle is negative, and the curved liquid surface at the nozzle begins to be sucked back; then the negative pressure at the nozzle gradually decreases, and the curved liquid surface is concave to the maximum value. Under the action of laminar shear force The liquid column in the ink storage tube is accelerated, and tends to move along the axis toward the outside of the nozzle. Then, the falling edge of the excitation signal acts on the tubular piezoelectric ceramic, causing the tubular piezoelectric ceramic to shorten instantly, and the preload pressure of the spring pushes the ink storage tube upward to the highest position. At this moment, the movement direction of the ink storage tube is opposite to that of the ink at the nozzle. Since the nozzle is a gradually converging cone tube, a positive pressure peak is generated at the nozzle. The amplitude of this positive pressure is greater than the negative pressure generated previously, causing the liquid surface to accelerate outward. Then, the rising edge of the excitation signal is applied to the tubular piezoelectric ceramic again, causing it to stretch in the length direction and return to its initial position. The positive pressure at the nozzle gradually decreases to negative pressure, and the curved liquid surface completes a forced oscillation. During this process, the displacement of the ink storage tube and the pressure distribution at the nozzle are respectively as shown in the following figure: Figure 2 b and Figure 2 As shown in c.

[0051] When the excitation voltage is small, the deformation of the tubular piezoelectric ceramic is not enough to drive the curved liquid surface to produce a jet, and only the following Figure 3 The curved liquid surface oscillates as shown; after applying an electric field of a specific amplitude between the nozzle and the substrate, the liquid surface is stretched to a convex spherical shape under the action of electrical stress. Figure 2 When the excitation signal is shown in a, the elongation of the piezoelectric ceramic will cause negative pressure to be generated at the nozzle, and the liquid surface will sharpen to a pointed cone liquid surface during the back suction process. The pointed cone liquid surface will eventually break away from the top of the liquid surface during the outward convexity of the liquid surface, generating a beam of fine electrofluid jet. A single complete electrofluid dynamic printing process is shown in Figure 1. Figure 4 shown.

[0052] When no induced electric field is applied between the curved liquid surface and the substrate 9, the voltage of the excitation signal is increased, and the amplitude of the pulsating pressure at the nozzle hole is greatly increased, driving the curved liquid surface to obtain sufficient kinetic energy during the convex process. Therefore, at the end of the convex process, the liquid bridge is refined and a hanging drop-like liquid surface is formed at the nozzle hole. After that, the hanging drop-like liquid surface continues to move out of the nozzle hole, and finally the liquid bridge breaks to generate ink droplets 14. A single complete inkjet printing process is shown in FIG. Figure 5 shown.

[0053] In addition, cylindrical piezoelectric ceramics can also be used as excitation units, printing devices such as Figure 6 The printing device is suitable for the case where the ink consumption is small, and can effectively avoid the waste of precious ink in the ink supply system pipeline. Different from the bottom surface of the tubular piezoelectric ceramic being in contact with the limit ring 3, the bottom surface of the columnar piezoelectric ceramic used here is in surface contact with the top of the ink storage tube 1. The specific printing method and the printing effect that can be achieved are the same as those mentioned above. Figure 1 The printing devices are exactly the same.

[0054] A cross-resolution on-demand inkjet printing method, when working in the on-demand inkjet printing mode, the control switch 16 is disconnected, there is no electric field between the nozzle and the substrate 9, and the signal generating unit 11 applies an excitation signal to the piezoelectric ceramic. At this time, the excitation voltage amplitude is large enough so that the kinetic energy obtained by the curved liquid surface at the nozzle during the convex process is sufficient to overcome the energy required for the liquid bridge to break, so as to realize droplet ejection. The ejection frequency is the same as the excitation signal, and the volume of the droplet is picoliter.

[0055] When working in the on-demand electrohydrodynamic printing mode, the amplitude of the excitation signal is reduced to be insufficient to drive the meniscus to produce a jet, and only the meniscus oscillates; the control switch 16 is closed, so that an electric field is formed between the nozzle and the substrate 9, and electrohydrodynamic jetting is achieved under the action of electric stress, and the volume of a single jet is femtoliter;

[0056] According to the actual demand for the volume of ejected liquid during the printing process, switching between the two printing modes is carried out to achieve cross-resolution printing.

[0057] Example 1: Drop-on-demand inkjet printing mode

[0058] Use Figure 1 In the printing system shown, the control switch is disconnected, there is no electric field between the nozzle and the substrate, the signal generating unit uses a signal generator, the excitation signal applied to the columnar piezoelectric ceramic is a square wave with a peak-to-peak value of 18V and a frequency of 1kHz, the length of the tubular piezoelectric ceramic is 9mm, and the outer diameter / inner diameter is 2.5mm\1.6mm respectively. The ink storage tube is a drawn capillary glass tube with an outer diameter / inner diameter of 1.5mm / 0.87mm, a length of 70mm, and an inner diameter of the nozzle of 17μm. The ink used is an aqueous solution with a volume fraction of 20% propylene glycol and a viscosity of 1.76mPas.

[0059] Under the action of the excitation signal, the liquid surface at the nozzle first sucks back and then bulges outward. At this time, the excitation voltage amplitude is large enough to make the kinetic energy obtained by the curved liquid surface during the bulging process sufficient to overcome the energy required for the liquid bridge to break, and the ink droplet is generated. The obtained jet has the same frequency as the excitation of the piezoelectric ceramic, and the generated ink droplet diameter is 34.7μm, and the single jet volume is 21.8pL.

[0060] Example 2: On-demand electrohydrodynamic printing mode

[0061] In order to form a comparison with Example 1 in terms of printing accuracy and prove that the printing mode can be quickly switched from the inkjet printing mode to the electrohydrodynamic printing mode to achieve cross-precision printing, based on the experiment of Example 1, the printing device can be switched to the electrohydrodynamic printing mode by simply closing the control switch and reducing the amplitude of the excitation signal. In this embodiment, the high-voltage power supply unit uses a high-voltage DC power supply, and a 460V DC electric field is applied between the nozzle and the substrate. The distance between the nozzle and the base plate is 100μm. At this time, the liquid surface is stretched to a convex curved liquid surface under the action of electrical stress. The excitation signal applied to the columnar piezoelectric ceramic is a square wave with a peak-to-peak value of 7.4V and a frequency of 1kHz. The other parameters of this embodiment are consistent with those of Example 1.

[0062] The rising edge of the excitation signal will cause the tubular piezoelectric ceramic to elongate, thereby sucking back the liquid surface at the nozzle. The interaction between the flow field and the electrical stress causes the curved liquid surface to sharpen to a slender pointed cone-shaped liquid surface at the end of the sucking process. After that, the lower rising edge of the excitation signal causes the liquid surface to fill up quickly and bulge outward. With the decrease of the curvature of the cone top and the release of the induced charge, the surface tension regains the dominant position, and finally the jet ends in the initial stage of the bulging process. The single jet volume is only 5.1FL, and the jet frequency is the same as the excitation signal. The single jet volume of the electrohydrodynamic force in this embodiment is 1 / 823 of the inkjet printing volume in Example 1, so as to achieve cross-precision printing.

[0063] Example 3: Cross-resolution printing mode

[0064] Use Figure 6 In the printing system shown, the signal generating unit adopts a signal generator, and the length, width and height of the columnar piezoelectric ceramic are 5mm\2mm\2mm respectively. The ink storage tube is a drawn capillary glass tube, with an outer diameter / inner diameter of 1.5mm / 0.87mm, a length of 52mm, and an inner diameter of the nozzle of 12μm. A nanosilver ink with a solid content of 50% and a viscosity of 16mPas is used, the ink level in the ink storage tube is 30mm, and the distance between the nozzle and the substrate is 120um.

[0065] When the control switch is disconnected, the amplitude of the pulse signal applied to the columnar piezoelectric ceramics is 22V, the pulse width is 25us, and the frequency is 2kHz. The obtained jetting has the same frequency as the excitation of the piezoelectric ceramics. The diameter of the generated ink droplet is 21.6μm, the jet volume of a single jet is 5.2pL, and the printing line width is 32μm; when the control switch is closed, a DC electric field of 510V is applied between the nozzle and the substrate, and the amplitude of the pulse signal applied to the columnar piezoelectric ceramics is 17V, the pulse width is 25us, and the frequency is 2kHz. The obtained jetting has the same frequency as the excitation of the piezoelectric ceramics, the jet volume of a single jet is 3.1FL, and the printing line width is 3μm.

[0066] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A cross-resolution on-demand inkjet printing device, characterized in that: It includes nozzle structure, driving system and high voltage power supply unit; The nozzle structure includes an ink storage tube and a limit ring, a spring, a guide screw, an insulating sleeve and a tubular electrode sleeved on the outer wall of the ink storage tube. The driving system includes a piezoelectric ceramic and a signal generating unit, which are used to drive the ink storage tube to reciprocate along the axis. The positive electrode of the high-voltage power supply unit is connected to the tubular electrode through a control switch, and the negative electrode thereof is grounded to the substrate, so as to form an induced electric field between the ink and the substrate. The device also includes a metal shell, and a lower through hole is provided at the bottom of the shell; The piezoelectric ceramic, the limiting ring and the spring are coaxially arranged inside the housing from top to bottom, and the limiting ring is fixedly bonded to the outer wall of the ink storage tube; The piezoelectric ceramic is in a tubular or columnar shape, and its top is glued to the shell. The shape of the piezoelectric ceramic is selected according to the ink consumption. If the ink in the ink storage tube can complete the printing work, the columnar piezoelectric ceramic is selected. If the ink in the ink storage tube is not enough to complete the printing work, the tubular piezoelectric ceramic and the liquid supply system are selected. The piezoelectric ceramic comprises two metal electrodes, the positive electrode is connected to the signal generating unit, and the negative electrode is grounded.

2. The cross-resolution on-demand inkjet printing device according to claim 1, characterized in that: When the piezoelectric ceramic is tubular, the tubular piezoelectric ceramic is sleeved on the outer wall of the liquid storage tube, an upper through hole is provided on the top of the shell, and the top of the ink storage tube passes through the piezoelectric ceramic and the upper through hole and extends out of the shell.

3. The cross-resolution on-demand inkjet printing device according to claim 2, characterized in that: The liquid supply system includes an ink supply hose, a liquid storage bottle, a ventilation hose and an air pressure regulating unit which are connected in sequence. The inlet end at the top of the ink storage tube is connected to one end of the ink supply hose, and the other end of the ink supply hose is inserted into the ink in the sealed liquid storage bottle. The liquid storage bottle is connected to the air pressure regulating unit through the ventilation hose.

4. The cross-resolution on-demand inkjet printing device according to claim 1, characterized in that: When the piezoelectric ceramic is in a columnar shape, the top end of the ink storage tube abuts against the bottom surface of the columnar piezoelectric ceramic.

5. The cross-resolution on-demand inkjet printing device according to claim 4, characterized in that: The guide screw is a 4-layer annular step structure with increasing diameters from top to bottom and is coaxially arranged with the spring. The first-layer step structure on the top of the guide screw extends into the spring, one end of the spring rests against the limit plate, and the other end rests against the horizontal surface of the second-layer step structure, and the spring is in a compressed pre-tightened state; the third-layer step structure is threadedly connected to the lower through hole, and the fourth-layer step structure is located outside the shell.

6. The cross-resolution on-demand inkjet printing device according to claim 5, characterized in that: The guide screw and the insulating sleeve are adhesively coupled, and the insulating sleeve and the tubular electrode are coaxially arranged. The diameter of the axial through hole of the guide screw, the insulating sleeve and the tubular electrode is larger than the outer diameter of the ink storage tube by 0.1 mm to ensure the undamped sliding of the ink storage tube. The nozzle at the bottom of the ink storage tube extends out of the tubular electrode.

7. The cross-resolution on-demand inkjet printing device according to claim 6, characterized in that: The high-voltage power supply unit selects different high-voltage generating devices according to actual needs. The high-voltage generating devices include but are not limited to high-voltage DC power supplies, voltage amplifiers or high-voltage pulse power supplies. The tubular electrodes apply high-voltage DC power, pulsed DC with voltage bias, or AC power in the form of positive and negative pulses according to needs.

8. The cross-resolution on-demand inkjet printing device according to claim 7, characterized in that: The signal generating unit is a signal generator, a single chip microcomputer or any other device capable of generating a low voltage pulse, and is used to generate a custom editable low level signal, and the low level signal includes but is not limited to a square wave and a pulse wave.

9. A cross-resolution on-demand inkjet printing method, using a cross-resolution on-demand inkjet printing device as claimed in any one of claims 1 to 8, characterized in that: When working in the drop-on-demand inkjet printing mode, the control switch is disconnected, there is no electric field between the nozzle and the substrate, and the signal generating unit applies an excitation signal to the piezoelectric ceramic. At this time, the excitation voltage amplitude is large enough so that the kinetic energy obtained by the curved liquid surface at the nozzle during the convex process is sufficient to overcome the energy required for the liquid bridge to break, thereby realizing droplet ejection. The ejection frequency is the same as the excitation signal, and the volume of the droplet is picoliter. When working in the on-demand electrohydrodynamic printing mode, the amplitude of the excitation signal is reduced to be insufficient to drive the curved liquid surface to produce a jet, and only the curved liquid surface oscillation is produced; the control switch is closed to form an electric field between the nozzle and the substrate, and electrohydrodynamic jetting is achieved under the action of electric stress, and the volume of a single jet is femtoliter; According to the actual demand for the volume of ejected liquid during the printing process, switching between the two printing modes is carried out to achieve cross-resolution printing.

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