Embedded 3D printing bubble defect inhibition method based on micro-droplet spraying

Abstract

The invention provides an embedded 3D printing bubble defect inhibition method based on micro-droplet jetting. According to the method, a new thought that an electric field induction effect is adopted to restrain the bubble defect in the embedded 3D printed part based on microdroplet jetting is provided, and when the charge level of charged microdroplets reaches a critical value, the bottoms of the charged microdroplets are stretched outwards through electric stress and make contact with a flexible substrate in a Taylor cone mode firstly; the air entrapment behavior in the micro-droplet embedding process is fundamentally inhibited, the bubble defect in the embedded printed part is effectively inhibited, the technical bottleneck of the structure forming defect of the embedded 3D printing technology based on micro-droplet spraying is expected to be broken through, and a feasible technical scheme is provided for preparing high-performance functional devices with complex structures and compounded by various materials.

Description

Technical Field

[0001] The present invention relates to the technical field of embedded 3D printing, and in particular to a method for suppressing bubble defects in embedded 3D printing based on droplet injection. Background Art

[0002] Functional devices are guided by functional requirements. Through the integrated design and manufacturing of "material-structure-function", advanced design, manufacturing and evaluation technologies are integrated to obtain devices with highly integrated structure, performance and function. They play an important role in aerospace, military defense, communication sensing, biomedicine and other fields. Additive manufacturing (3D printing), as a revolutionary manufacturing technology, has multi-scale, multi-material and multi-dimensional manufacturing capabilities, which has greatly promoted the development and application of functional devices. Among them, the collaborative design relationship between materials and structures is the basis for realizing the functionality of the structure of the parts. Functional materials need to be compounded and assembled in a strict, precise and scientific manner. To this end, the development of design and manufacturing technologies for complex three-dimensional functional structures is a prerequisite for realizing the integration of "material-structure-function" of functional devices.

[0003] Embedded 3D printing technology based on droplet jetting is an innovative additive manufacturing method. This technology introduces a flexible substrate based on inkjet printing technology. By controlling parameters such as pulse pressure and vibration waveform, the printing ink is jetted to form uniform droplets of micrometer to sub-millimeter scale, and then the droplets are precisely controlled to deposit on the surface of the flexible substrate. The rheological properties of the flexible substrate are used to inhibit the diffusion and rebound of the droplets, so that the droplets can sink into the flexible substrate and form an embedded structure. Finally, after post-processing processes such as curing and sintering, an integrated functional device with a stable structure is obtained. Embedded 3D printing technology based on droplet jetting eliminates the cumbersome support removal or secondary packaging process in traditional processes, greatly simplifies the manufacturing process, and does not require special raw materials and special expensive equipment. It has unique advantages in the rapid manufacturing of functional devices and is a feasible solution for realizing the integrated design and manufacturing of "material-structure-function".

[0004] However, the embedded 3D printing technology based on droplet jetting uses discrete droplets as manufacturing units. The deposition and embedding process of droplets on the surface of flexible substrates is usually accompanied by collision and entrainment behavior. This part of the gas is entrained into the interior of the part and forms bubble defects. Figure 1 When the droplet impacts the flexible substrate, the gas pressure at the bottom of the droplet gradually increases. Under the action of the high-pressure gas, the flexible substrate is slightly deformed, and the bottom gas is gradually compressed to form a high-pressure gas film. The bottom of the droplet is concave to a certain extent and contacts the flexible substrate in a ring shape. The method for suppressing bubble defects in embedded 3D printing based on droplet injection-1-

[0005] A disc-shaped air film is formed. With the embedding of the droplet, the disc-shaped air film further shrinks under the action of surface tension to form single / multiple bubble defects, which are attached to the liquid-liquid interface between the droplet and the flexible substrate. The generation of such bubble defects is an inherent characteristic of droplet collision dynamics, and bubbles at the liquid-liquid interface are difficult to be driven out by buoyancy under the joint constraints of surface tension and capillary action. During the droplet embedding process, bubbles will aggregate and distribute secondary at the liquid-liquid interface with the movement of the droplet, inducing structural morphology distortion. Secondly, during the post-processing process, the bubbles inside the workpiece will expand, deform, or even burst due to heat, further affecting the functionality of the workpiece structure. Internal bubble defects will not only reduce the forming accuracy of the printed structure, but also have a significant impact on the performance and stability of the functional device. The air entrainment behavior of the embedded 3D printing process based on droplet injection seriously restricts the practical application of this technology.

[0006] Therefore, it is of great significance to develop a method to suppress bubble defects in embedded 3D printing based on droplet jetting. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for suppressing embedded 3D printing bubble defects based on droplet injection, by charging the droplets and using the electric field to change the physical process of the droplets impacting a flexible deformable substrate, thereby suppressing the air entrainment at the liquid-liquid interface and achieving stable deposition and embedding of the droplets, thereby improving the stability of the printing process and the structural fidelity.

[0008] To achieve the above object, the present invention is achieved through the following technical solutions:

[0009] The embedded 3D printing device based on charged droplet injection includes an industrial computer, an on-demand droplet generator, a charging electrode, a flexible substrate, a deposition substrate, a heating plate, an insulating plate, a three-dimensional workbench, a function generator and a high-voltage power supply arranged in a clean environment.

[0010] The upper surface of the three-dimensional workbench is covered with an insulating plate, a heating plate and a deposition substrate in order from bottom to top. The three-dimensional workbench has an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis to realize movement in three directions of XYZ. The three-dimensional workbench is grounded. The upper surface of the deposition substrate is coated with a flexible substrate. The deposition substrate is connected to a high voltage power supply.

[0011] The on-demand droplet generator is arranged above the flexible substrate. A nozzle is arranged at the bottom of the on-demand droplet generator. The on-demand droplet generator is connected to a function generator. The on-demand droplet generator is grounded.

[0012] The charging electrode is arranged between the nozzle and the flexible substrate. The charging electrode is an annular sheet structure. A hole is provided in the center of the charging electrode for the charging droplets to pass through. Method for suppressing bubble defects in embedded 3D printing based on droplet jetting -2-

[0013] The charging electrode is connected to a high voltage power source.

[0014] The function generator, high voltage power supply and three-dimensional workbench are all connected to the industrial computer.

[0015] The method for suppressing bubble defects in embedded 3D printing based on droplet jetting includes the following steps:

[0016] 1) Prepare printing ink. By adjusting the mass ratio of solute, solvent and dopant, a printing ink with uniform and stable dispersion suitable for droplet jetting is obtained.

[0017] 2) The processed printing ink is supplied to a droplet-on-demand generator.

[0018] 3) Pre-treating the deposition substrate, and coating the flexible substrate on the pre-treated deposition substrate.

[0019] 4) Printing is initialized, the three-dimensional workbench is moved to the printing position, and the flexible substrate is adjusted to a set distance from the nozzle.

[0020] 5) Start the on-demand droplet generator, and the function generator outputs an excitation signal to drive the printing ink to be squeezed out at the nozzle to form a jet.

[0021] 6) Under the induction of the charging electrode, the charges gather on the jet, and when the jet length reaches a certain threshold, it breaks to form charged droplets.

[0022] 7) The charged droplets fly through the central hole of the charging electrode toward the flexible substrate. An electrostatic field is formed between the charged droplets and the flexible substrate. Under the induction of the electrostatic field, the surface charge of the charged droplets is polarized. As the distance between the charged droplets and the flexible substrate decreases, the charge density on the surface of the charged droplets and the flexible substrate increases sharply, and the electric field strength increases. When the electric field strength reaches a certain level, the charged droplets and the flexible substrate are deformed under the action of electric stress to overcome the surface tension and the pressure of the surrounding gas. The bottom of the charged droplets is stretched downward by the electric stress, and the upper surface of the flexible substrate is stretched upward by the electric stress.

[0023] 8) The charged droplets are deposited onto the flexible substrate. Under the action of strong electric stress, the bottom of the charged droplets and the flexible substrate form a Taylor cone and make single-point contact. In the subsequent flow embedding process, they continue to wetting outward, and the ambient gas in the droplet deposition microdomain is discharged.

[0024] 9) The industrial computer generates a printing program according to the target structure, repeatedly controls the function generator and the high-voltage power supply to generate charged droplets on demand, and controls the coordination between the printing deposition of the charged droplets and the movement of the three-dimensional workbench to achieve point-by-point, line-by-line, and layer-by-layer printing, and finally forms the target three-dimensional structure.

[0025] 10) Post-process the printed parts to improve the stability of the printed structure.

[0026] Furthermore, the printing ink material is a mixture of one or more of polymer, ceramic, metal, glass, biomaterial or composite material. The material of the flexible substrate is a yield stress fluid or a Newtonian fluid.

[0027] Furthermore, in step 3), the deposited substrate is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropanol for 10 minutes, then rinsed with deionized water, and then blown dry with nitrogen. Finally, a plasma treatment machine is used to perform plasma bombardment treatment on the surface of the deposited substrate to modify the surface of the deposited substrate and improve the adhesion of the surface of the deposited substrate.

[0028] Further, in step 3), the flexible substrate is coated by spin coating, blade coating or roller coating.

[0029] Furthermore, the heating plate preheats the flexible substrate according to the structural forming requirements before printing to change the rheological properties of the material of the flexible substrate. After printing, the heating plate heats and cures the formed structure as a whole to improve the stability of the structure.

[0030] Furthermore, the high voltage power supply is a periodic high voltage power supply, and the voltage is continuously adjustable in the range of -5000 to 5000V.

[0031] Furthermore, the inner diameter of the nozzle is 20 μm to 3 mm. The thickness of the flexible substrate is 100 μm to 3 mm.

[0032] The present invention also discloses an application of the suppression method described in any one of the above items in printing continuous structures through an AC signal modulation strategy, which realizes continuous variable polarity printing of charged droplets through a pulse AC signal modulation strategy, so that the charges carried by adjacent charged droplets are of opposite polarity, and the continuous deposition and embedding behavior of multiple charged droplets is regulated. While the charges carried by the charged droplets are effectively neutralized, the overlapping process between continuous droplets is promoted, thereby improving the contour quality of the target three-dimensional structure.

[0033] The present invention also discloses an application of the suppression method described in any one of the above items in printing an embedded microchannel structure inside a flexible substrate using sacrificial ink. After printing is completed, the overall structure is first cured, and then local heating, cooling, solvent flushing or vacuum extraction is used to liquefy the sacrificial ink and remove it from the cured flexible substrate, leaving a hollow structure, and finally obtaining an embedded microchannel structure.

[0034] The present invention also discloses an application of the suppression method described in any one of the above items in printing a high aspect ratio structure through a sacrificial flexible substrate, wherein the printing ink is printed inside the sacrificial flexible substrate under the restrictive wrapping effect of the sacrificial flexible substrate to obtain a high aspect ratio structure, the flexible substrate is removed by high temperature or solvent washing, and the high aspect ratio structure is sintered to further fuse the materials to obtain a stable high aspect ratio structure.

[0035] The technical effect of the present invention is unquestionable: it proposes a new idea of ​​using electric field induction to suppress uniform droplet jetting to embed bubble defects inside printed parts. When the charge level of the charged droplet reaches a critical value, the electric stress stretches the bottom of the charged droplet outward and first contacts the flexible substrate in the form of a Taylor cone, fundamentally suppressing the air entrainment behavior during the droplet collision process, thereby effectively suppressing bubble defects inside the printed parts. It is expected to break through the technical bottleneck of structural forming defects of embedded 3D printing technology based on droplet jetting, and provide a feasible technical solution for the preparation of high-performance functional devices with complex configurations and multiple materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of embedded 3D printing bubble defects based on droplet jetting;

[0037] Figure 2 It is a schematic diagram of the structure of an embedded 3D printing device based on charged droplet jetting;

[0038] Figure 3 Schematic diagram of the morphology evolution of the charged droplet impacting the flexible substrate surface and the embedding process;

[0039] Figure 4 The embedded microcircuit structure based on embedded 3D printing of droplet jetting in Example 6;

[0040] Figure 5 The AC signal modulation strategy for embedded 3D printing continuous structure based on droplet jetting in Example 7;

[0041] Figure 6 The microchannel structure of embedded 3D printing based on droplet jetting of sacrificial ink in Example 8;

[0042] Figure 7 This is the high aspect ratio structure of droplet jetting embedded 3D printing based on a sacrificial flexible substrate in Example 9.

[0043] In the figure: on-demand droplet generator 1, nozzle 2, jet 3, charging electrode 4, charged droplet 5, target three-dimensional structure 6, flexible substrate 7, deposition substrate 8, heating plate 9, insulating plate 10, three-dimensional workbench 11, function generator 12, high-voltage power supply 13, clean environment 14, industrial computer 15, electrostatic field 16, Taylor cone 17. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0045] Embodiment 1:

[0046] This embodiment provides a method for suppressing bubble defects in embedded 3D printing based on droplet jetting, see Figure 2 The embedded 3D printing device based on charged droplet injection includes an industrial computer 15, and an on-demand droplet generator 1, a charging electrode 4, a flexible substrate 7, a deposition substrate 8, a heating plate 9, an insulating plate 10, a three-dimensional workbench 11, and a method for suppressing bubble defects in embedded 3D printing based on droplet injection-5-

[0047] A number generator 12 and a high voltage power supply 13.

[0048] The upper surface of the three-dimensional workbench 11 is laid with an insulating plate 10, a heating plate 9 and a deposition substrate 8 in order from bottom to top. The three-dimensional workbench 11 has an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis to realize movement in three directions of XYZ. The three-dimensional workbench 11 is grounded. The upper surface of the deposition substrate 8 is coated with a flexible substrate 7. The deposition substrate 8 is connected to a high voltage power supply 13.

[0049] The on-demand droplet generator 1 is arranged above a flexible substrate 7. A nozzle 2 is provided at the bottom of the on-demand droplet generator 1. The on-demand droplet generator 1 is connected to a function generator 12. The on-demand droplet generator 1 is grounded.

[0050] The charging electrode 4 is arranged between the nozzle 2 and the flexible substrate 7. The charging electrode 4 is an annular sheet structure. A hole is provided in the center of the charging electrode 4 for the charged droplets 5 to pass through. The charging electrode 4 is connected to a high voltage power supply 13. The charging electrode 4 and the deposition substrate 8 are both connected to high voltage of the same polarity to form an equipotential, so as to avoid the formation of an electric field between the charging electrode and the deposition substrate, which affects the movement of the charged droplets 5.

[0051] The function generator 12 , the high voltage power supply 13 and the three-dimensional workbench 11 are all connected to the industrial computer 15 .

[0052] The method for suppressing bubble defects in embedded 3D printing based on droplet jetting includes the following steps:

[0053] 1) Prepare printing ink. By adjusting the mass ratio of solute, solvent and dopant, a printing ink with uniform and stable dispersion suitable for droplet jetting is obtained.

[0054] 2) The processed printing ink is supplied to the on-demand droplet generator 1 .

[0055] 3) Pre-treating the deposition substrate 8 and coating the flexible substrate 7 on the pre-treated deposition substrate 8 .

[0056] 4) Printing is initialized, the three-dimensional workbench 6 is moved to the printing position, and the flexible substrate 7 is adjusted to a set distance from the nozzle 2.

[0057] 5) Start the on-demand droplet generator 1, and the function generator 12 outputs an excitation signal to drive the printing ink to be squeezed out at the nozzle 2 to form a jet 3.

[0058] 6) Under the induction of the charging electrode 4, the charges are gathered on the jet 3, and when the length of the jet 3 reaches a certain threshold, it breaks to form charged droplets 5.

[0059] 7) The charged droplet 5 flies through the central hole of the charging electrode 4 toward the flexible substrate 7. An electrostatic field 16 is formed between the charged droplet 5 and the flexible substrate 7. Under the induction of the electrostatic field 16, the surface charge of the charged droplet 5 is polarized. As the charged droplet 5 and the flexible substrate 7 move toward each other, the charged droplet 5 moves toward the flexible substrate 7.

[0060] As the distance between the charged droplets 5 and the flexible substrate 7 decreases, the charge density on the surface of the charged droplet 5 and the flexible substrate 7 increases sharply, and the electric field strength increases. When the electric field strength reaches a certain level, the charged droplet 5 and the flexible substrate 7 overcome the surface tension and the pressure of the surrounding gas under the action of the electric stress and deform. The bottom of the charged droplet 5 is stretched downward by the electric stress, and the upper surface of the flexible substrate 7 is stretched upward by the electric stress.

[0061] 8) See Figure 3The charged droplet 5 is deposited on the flexible substrate 7. Under the action of strong electrical stress, the bottom of the charged droplet 5 forms a Taylor cone 17 with the flexible substrate 7 and makes single-point contact. In the subsequent flow embedding process, it continuously wetting outwards, and the ambient gas in the droplet deposition area is discharged.

[0062] 9) The industrial computer 15 generates a printing program according to the target structure, repeatedly controls the function generator 12 and the high-voltage power supply 13 to generate charged droplets 5 on demand, and controls the coordinated matching between the printing deposition of the charged droplets 5 and the movement of the three-dimensional workbench 11, so as to realize point-by-point, line-by-line, and layer-by-layer printing, and finally forms the target three-dimensional structure 6.

[0063] 10) Post-process the printed parts to improve the stability of the printed structure.

[0064] Embodiment 2:

[0065] The main contents of this embodiment are the same as those of embodiment 1, wherein the printing ink material is a mixture of one or more of polymer, ceramic, metal, glass, biomaterial or composite material. The material of the flexible substrate 7 is a yield stress fluid or a Newtonian fluid.

[0066] Embodiment 3:

[0067] The main contents of this embodiment are the same as those of embodiment 1 or 2, wherein, in step 3), the deposition substrate 8 is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropyl alcohol for 10 minutes, then rinsed with deionized water, and then blown dry with nitrogen. Finally, a plasma treatment machine is used to perform plasma bombardment treatment on the surface of the deposition substrate to modify the surface of the deposition substrate 8 and improve the adhesion of the printing material. In step 3), the flexible substrate 7 is coated by spin coating, scraper coating or roller coating.

[0068] Embodiment 4:

[0069] The main content of this embodiment is the same as any one of embodiments 1 to 3, wherein the heating plate 9 preheats the flexible substrate 7 according to the structural forming requirements before printing, and can change the rheological properties of the material of the flexible substrate 7 within a certain range. After printing, the heating plate 9 performs overall heating and curing on the formed structure to improve the stability of the structure.

[0070] Embodiment 5:

[0071] The main contents of this embodiment are the same as any one of embodiments 1 to 4, wherein the high-voltage power supply 13 is a periodic high-voltage power supply, and the voltage is continuously adjustable within the range of -5000 to 5000 V. The voltage of the high-voltage power supply 13 is determined according to the droplet size and actual needs. The deposition substrate 8 and the charging electrode 4 form an electrostatic shield together to avoid the formation of an interfering electric field that affects the deposition and embedding of the charged droplets 5.

[0072] The electrical properties of the charged droplet 5 are determined by the charging electrode. When the charging electrode 4 is connected to a positive high voltage, the droplet is negatively charged; when the charging electrode 4 is connected to a negative high voltage, the droplet is positively charged. The Rayleigh limit q of the charge of the charged droplet 5 is R for:

[0073]

[0074] Where ε is the dielectric constant of the gas in the deposition environment. δ is the surface tension of the charged droplet. R is the radius of the charged droplet.

[0075] Embodiment 6:

[0076] This embodiment provides an application of the method described in any one of embodiments 1 to 5 to directly manufacture highly integrated embedded microcircuits inside a flexible material. Figure 4 , this embodiment includes the following steps:

[0077] 1) preparing printing ink, selecting uniform nanosilver particles with a particle size range of 50 to 100 nm as conductive functional materials, using polyvinyl pyrrolidone (PVP) as a stabilizing dispersant, using water and ethylene glycol as solvents, and the concentration range of the nanosilver particles is 1 to 10 wt.%, and then ultrasonically treating the mixed solution to obtain uniformly and stably dispersed nanosilver ink suitable for droplet injection.

[0078] 2) The nanosilver ink is supplied to the on-demand droplet generator 1, and the inner diameter of the nozzle 2 is selected to be 200 μm.

[0079] 3) Pre-treating the deposition substrate 8, which is a single crystal silicon wafer, firstly ultrasonically treating the silicon wafer with deionized water for 10 minutes, then drying it with nitrogen, and finally using a plasma processor to perform plasma bombardment treatment on the surface of the silicon wafer to improve the adhesion between the printing material and the silicon wafer.

[0080] The material of the flexible substrate 7 is liquid PDMS. A layer of liquid PDMS polymer is spread on the surface of the deposition substrate 8. An appropriate amount of Dow Corning 184 canned glue is selected. The PDMS monomer and its corresponding curing agent are evenly mixed in a ratio of 10:1, and then placed in a centrifuge for centrifugal treatment to remove bubbles; the treated liquid PDMS is poured on a silicon wafer, and a layer of PDMS flexible substrate with a thickness of about 100 μm is spin-coated on the surface of the silicon wafer by using a glue spreader.

[0081] 4) Printing initialization. Move the three-dimensional workbench 11 to the printing position, and adjust the PDMS flexible substrate to a set distance from the nozzle 2. The deposition substrate 8 is connected to the high-voltage power supply 13 through a wire. Turn on the heating plate 9 to pre-cure the PDMS flexible substrate at 60°C for 10 minutes to improve the support force of the PDMS flexible substrate for the nanosilver ink.

[0082] 5) Start the on-demand droplet generator 1, and the function generator 12 outputs an excitation signal to drive the printing ink to be squeezed out at the nozzle 2 to form a jet 3.

[0083] 6) Under the induction of the charging electrode 4, the charges are gathered on the jet 3, and when the length of the jet 3 reaches a certain threshold, it breaks to form charged droplets 5.

[0084] 7) The charged droplet 5 flies toward the flexible substrate 7 through the charging electrode 4. An electrostatic field 16 is formed between the charged droplet 5 and the upper surface of the PDMS flexible substrate. Under the induction of the electrostatic field 16, the surface charge of the charged droplet 5 is polarized. The charged droplet 5 and the flexible substrate 7 are deformed under the action of electrical stress to overcome the surface tension and the pressure of the surrounding gas. The bottom of the charged droplet 5 is stretched downward by the electrical stress, and the upper surface of the flexible substrate 7 is stretched upward by the electrical stress.

[0085] 8) The charged droplet 5 is deposited on the PDMS flexible substrate. Under the action of strong electrical stress, the bottom of the charged droplet 5 forms a Taylor cone 17 with the PDMS flexible substrate and makes single-point contact. In the subsequent flow spreading process, it continuously wets outwards, and the ambient gas in the droplet deposition area is discharged.

[0086] 9) The embedded microcircuit of this embodiment is designed as a wire grid structure. The industrial computer 15 writes the print head motion path program, sets the printing starting point, repeatedly controls the function generator 12 and the high voltage power supply 13 to generate charged droplets 5 on demand, and controls the coordination between the printing deposition of the charged droplets 5 and the movement of the three-dimensional workbench 11, and finally forms the target wire grid structure. The main process parameters are: the printing frequency is set to 5-50Hz, the function generator 12 and the high voltage power supply 13 use pulse waveforms, the voltage is set to 500-1000V, the voltage duty cycle is set to 1-5%, and the speed of the three-dimensional workbench 11 is set to 50mm / s.

[0087] 10) The printed parts are post-processed and cured at 150° C. for 2 h to completely cure the PDMS flexible substrate, sinter the nanosilver particles, and decompose the protective agent to obtain a stable embedded microcircuit structure.

[0088] This embodiment uses the characteristics of charged droplets 5 being deformed by force under the action of electric field induction to regulate the deposition and embedding behavior of charged droplets 5, so that the bottom of the charged droplet 5 generates a Taylor cone 17 and single-point contact occurs when it approaches the flexible substrate 7, thereby changing the form and movement trajectory of the liquid-liquid-gas three-phase contact line, and discharging the ambient gas in the droplet deposition microdomain, fundamentally suppressing the bubble defects inside the embedded microcircuit structure.

[0089] Embodiment 7:

[0090] This embodiment provides an application of the method described in any one of embodiments 1 to 5 to realize the continuous polarity-varying printing of charged droplets 5 through a pulse AC signal modulation strategy. Figure 5 , this embodiment includes the following steps:

[0091] 1) Prepare printing ink, and obtain printing ink that is uniformly and stably dispersed and suitable for droplet injection by adjusting the mass ratio of solute, solvent and dopant.

[0092] 2) The processed printing ink is supplied to the on-demand droplet generator 1 .

[0093] 3) Pre-treating the deposition substrate 8, and coating a layer of flexible base material 3 on the pre-treated deposition substrate 4 by spin coating, scraper coating, roller coating, etc.

[0094] 4) Printing is initialized, the three-dimensional workbench 6 is moved to the printing position, and the flexible substrate 3 is adjusted to a set distance from the nozzle 2. The deposition substrate 8 is connected to the high-voltage power supply 13 through a wire.

[0095] 5) Start the on-demand droplet generator 1, and the function generator 12 outputs an excitation signal to drive the printing ink to be squeezed out at the nozzle 2 to form a jet 3.

[0096] 6) A pulse AC signal modulation strategy is set. Under the induction of the charging electrode 4, the charges are gathered on the jet 3. When the length of the jet 3 reaches a certain threshold, it breaks to form charged droplets 5. The waveform of the high-voltage power supply 7 is set to a square wave, the high level is set to +500~1000V, the low level is set to -500~1000V, the pulse frequency is set to be greater than 100Hz, the duty cycle is set to 10~50%, the printing speed is set to 1~50mm / s, and adjacent charged droplets 5 carry equal amounts of heterogeneous charges.

[0097] 7) The charged droplet 5 flies toward the flexible substrate 7 through the charging electrode 4. An electrostatic field 16 is formed between the charged droplet 5 and the flexible substrate 7. Under the induction of the electrostatic field 16, the surface charge of the charged droplet 5 is polarized. As the distance between the charged droplet 5 and the flexible substrate 7 decreases, the charge density on the surface of the charged droplet 5 and the surface of the flexible substrate 7 increases sharply, and the electric field strength increases. When the electric field strength reaches a certain level, the charged droplet 5 and the flexible substrate 7 are deformed under the action of electrical stress to overcome the surface tension and the pressure of the surrounding gas.

[0098] 8) The charged droplet 5 is deposited on the flexible substrate 7. The bottom of the charged droplet 5 forms a Taylor cone 17 with the flexible substrate 7 under the action of strong electrical stress and a single point contact occurs. In the subsequent flow spreading process, the charged droplet 5 continuously wets outwards, and the ambient gas in the droplet deposition area is discharged. The newly deposited charged droplet 5 wets and combines with the embedded droplet under the guidance and attraction of the heterogeneous charge. The residual charge inside the flexible substrate 7 is neutralized, and the contour quality of the continuous feature structure is improved.

[0099] 9) The industrial computer 15 generates a printing program according to the target structure, repeatedly controls the function generator -10-12 and the high-voltage power supply 13 to generate charged droplets 5 on demand, and controls the coordination between the printing deposition of the charged droplets 5 and the movement of the three-dimensional workbench 11 to achieve point-by-point, line-by-line, and layer-by-layer printing, and finally forms the target three-dimensional structure 6.

[0100] 10) Post-process the printed parts to improve the stability of the printed structure.

[0101] This embodiment makes use of the characteristic of droplet induction charging under the action of electric field induction, and realizes continuous variable polarity printing of charged droplets 5 through pulse AC signal modulation strategy, so that the charges carried by adjacent charged droplets 5 are of opposite polarity, and the continuous deposition and embedding behavior of multiple charged droplets is regulated. While the charges carried by the charged droplets 5 are effectively neutralized, the overlapping process of continuous droplets is promoted, thereby improving the contour quality of the target three-dimensional structure 6.

[0102] Embodiment 8:

[0103] This embodiment provides an application of the method described in any one of embodiments 1 to 5 to print an embedded microchannel structure inside a flexible substrate using sacrificial ink. Figure 6 , this embodiment includes the following steps:

[0104] 1) Printing ink was prepared by dissolving 23 wt.% of Pluronic F127 (Sigma-Aldrich) in deionized water at 4°C, stirring for 3 hours to fully dissolve the ink, and then vacuuming and defoaming the ink to obtain sacrificial ink.

[0105] 2) The sacrificial ink is supplied to the on-demand droplet generator 1, the bottom of the on-demand droplet generator 1 is provided with a nozzle 2, and the inner diameter of the nozzle 2 is selected to be 300 μm.

[0106] 3) Pre-treating the deposition substrate 8, which is organic glass. First, the organic glass is ultrasonically treated with deionized water for 10 minutes, then blown dry with nitrogen, and finally the surface of the organic glass is plasma bombarded with a plasma treatment machine to improve the surface adhesion of the organic glass.

[0107] The flexible substrate 7 is made of F127-DA. 100 g of Pluronic F127 is dissolved in 400 mL of dry toluene at 60° C., triethylamine is added, and acryloyl chloride is added dropwise, and stirred overnight to generate F127-DA. F127-DA is poured on the surface of organic glass, and a layer of F127-DA flexible substrate with a thickness of about 1000 μm is spin-coated on the surface of organic glass using a coating machine.

[0108] 4) Printing is initialized, the three-dimensional workbench 6 is moved to the printing position, and the F127-DA flexible substrate is adjusted to a set distance from the nozzle 2. The deposition substrate 8 is connected to the high-voltage power supply 13 through a wire.

[0109] 5) Start the on-demand droplet generator 1, and the function generator 12 outputs an excitation signal to drive the sacrificial ink to be squeezed out at the nozzle 2 to form a jet 3.

[0110] 6) Under the induction of the charging electrode 4, the charges are gathered on the jet 3, and when the length of the jet 3 reaches a certain threshold, it breaks to form charged droplets 5. The charging electrode 4 is arranged between the nozzle 2 and the F127-DA flexible substrate, and is connected to the high voltage power supply 13 through a wire.

[0111] 7) The charged droplet 5 flies toward the F127-DA flexible substrate through the charging electrode 4. An electrostatic field 16 is formed between the charged droplet 5 and the F127-DA flexible substrate. Under the induction of the electrostatic field 16, the surface charge of the charged droplet 5 is polarized. The charged droplet 5 and the F127-DA flexible substrate are deformed under the action of electrical stress to overcome the surface tension and the pressure of the surrounding gas. The bottom of the charged droplet 5 is stretched downward by the electrical stress, and the upper surface of the F127-DA flexible substrate is stretched upward by the electrical stress.

[0112] 8) The charged droplet 5 is deposited on the F127-DA flexible substrate. Under the action of strong electrical stress, the bottom of the charged droplet 5 forms a Taylor cone 17 and a single-point contact occurs with the F127-DA flexible substrate. In the subsequent flow spreading process, it continuously wetting outwards, and the ambient gas in the droplet deposition area is discharged.

[0113] 9) The industrial computer 15 generates a nozzle motion path program for the embedded microchannel structure of this embodiment, sets the printing starting point, repeatedly controls the function generator 12 and the high-voltage power supply 13 to generate charged droplets 5, and controls the coordination between the printing deposition of the charged droplets 5 and the movement of the three-dimensional workbench 11, and finally forms the target three-dimensional microchannel structure.

[0114] 10) The printed part was post-processed by curing the F127-DA flexible substrate with 365nm UV light for 5 minutes to chemically cross-link the F127-DA gel matrix to form a mechanically stable structure. The sacrificial ink undergoes a phase change and liquefies at low temperatures (4°C). After the entire structure is cooled, a slight vacuum is applied to liquefy the sacrificial ink and remove it from the cured F127-DA flexible substrate, leaving a hollow structure, and finally obtaining an embedded microchannel structure.

[0115] This embodiment is based on the embedded 3D printing technology of droplet injection, which uses sacrificial ink to print the embedded microchannel structure. By charging the deposited droplets, the collision and entrainment behavior of the droplets is suppressed, the bubble defects that may be introduced in the printing process are avoided, and the inner surface quality of the microchannel structure is further optimized.

[0116] Embodiment 9:

[0117] This embodiment provides an application of the method described in any one of embodiments 1 to 6 to print a high aspect ratio structure through a sacrificial flexible substrate. Figure 7 , this embodiment includes the following steps:

[0118] 1) Prepare printing ink, select high-temperature sintered silver paste as functional material, use water and ethylene glycol as solvents, and the concentration range of nanosilver particles is 1-10wt.%. Ultrasonic treatment is performed on the mixed solution to obtain uniform and stable dispersion of nanosilver ink suitable for droplet injection. Method for suppressing bubble defects in embedded 3D printing based on droplet injection-12-

[0119] 2) The nanosilver ink is supplied to the on-demand droplet generator 1 , the bottom of which is provided with a nozzle 2 , and the inner diameter of the nozzle 2 is selected to be 200 μm.

[0120] 3) Pre-treating the deposition substrate 8, which is a single crystal silicon wafer, firstly ultrasonically treating the silicon wafer with deionized water for 10 minutes, then drying it with nitrogen, and finally using a plasma processor to perform plasma bombardment treatment on the surface of the silicon wafer to improve the adhesion between the printing material and the silicon wafer.

[0121] The flexible substrate 7 material is liquid PDMS. A layer of liquid PDMS polymer is spread on the surface of the deposition substrate. An appropriate amount of Dow Corning 184 canned glue is selected. The PDMS monomer and its corresponding curing agent are evenly mixed in a ratio of 10:1, and then placed in a centrifuge for centrifugal treatment to remove bubbles. The treated liquid PDMS is poured on a silicon wafer, and a layer of PDMS flexible substrate with a thickness of about 1000 μm is spin-coated on the surface of the silicon wafer by using a glue spreader.

[0122] 4) Printing is initialized, the three-dimensional workbench 6 is moved to the printing position, and the PDMS flexible substrate is adjusted to a set distance from the nozzle 2. The deposition substrate 8 is connected to the high-voltage power supply 13 via a wire.

[0123] 5) The on-demand droplet generator 1 is started, and the function generator 12 outputs an excitation signal to drive the nanosilver ink to be extruded at the nozzle 2 to form a jet 3.

[0124] 6) Under the induction of the charging electrode 4, the charges are gathered on the jet 3, and when the length of the jet 3 reaches a certain threshold, it breaks to form charged droplets 5. The charging electrode 4 is arranged between the nozzle 2 and the PDMS flexible substrate, and is connected to the high voltage power supply 13 through a wire.

[0125] 7) The charged droplet 5 flies toward the PDMS flexible substrate through the charging electrode 4. An electrostatic field 16 is formed between the charged droplet 5 and the PDMS flexible substrate. Under the induction of the electrostatic field 16, the surface charge of the charged droplet 5 is polarized, and the charged droplet 5 and the PDMS flexible substrate are deformed under the action of electrical stress to overcome the surface tension and the pressure of the surrounding gas.

[0126] 8) The charged droplet 5 is deposited on the PDMS flexible substrate. Under the action of strong electrical stress, the bottom of the charged droplet 5 forms a Taylor cone 17 with the PDMS flexible substrate and makes single-point contact. In the subsequent flow spreading process, it continuously wets outwards, and the ambient gas in the droplet deposition area is discharged.

[0127] 9) The industrial computer 15 generates a printing program according to the embedded high aspect ratio structure of this embodiment, repeatedly controls the function generator 12 and the high voltage power supply 13 to generate charged droplets 5 on demand, and controls the coordinated matching between the printing deposition of the charged droplets 5 and the movement of the three-dimensional workbench 11, so as to realize point-by-point, line-by-line, and layer-by-layer printing, and the aspect ratio of the final formed structure is greater than 10:1.

[0128] 10) The printed product was post-processed by sintering at 400°C for 10 min to remove the PDMS flexible substrate. Subsequently, the high aspect ratio silver mesh was placed in a sintering furnace at 630°C for further treatment for 3 min to further fuse the nanosilver particles and obtain a stable high aspect ratio structure.

[0129] This embodiment is based on the embedded 3D printing technology of droplet injection, and uses a sacrificial flexible substrate to print high aspect ratio structures. By charging the deposited droplets, the collision and entrainment behavior of the droplets is suppressed, and the potential disturbance factor of bubbles at the interface to the local formed structure is avoided, thereby improving the stability of the printed structure.

Claims

1. A method for suppressing bubble defects in embedded 3D printing based on droplet jetting, characterized in that: The embedded 3D printing device based on charged droplet jetting comprises an industrial computer (15), and an on-demand droplet generator (1), a charging electrode (4), a flexible substrate (7), a deposition substrate (8), a heating plate (9), an insulating plate (10), a three-dimensional workbench (11), a function generator (12) and a high-voltage power supply (13) arranged in a clean environment (14); The upper surface of the three-dimensional workbench (11) is covered with an insulating plate (10), a heating plate (9) and a deposition substrate (8) in sequence from bottom to top; the three-dimensional workbench (11) has an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis to achieve movement in three directions of X, Y and Z; the three-dimensional workbench (11) is grounded; the upper surface of the deposition substrate (8) is coated with a flexible base (7); the deposition substrate (8) is connected to a high-voltage power supply (13); The on-demand microdroplet generator (1) is arranged above a flexible substrate (7); a nozzle (2) is provided at the bottom of the on-demand microdroplet generator (1); the on-demand microdroplet generator (1) is connected to a function generator (12); the on-demand microdroplet generator (1) is grounded; The charging electrode (4) is arranged between the nozzle (2) and the flexible substrate (7); the charging electrode (4) is an annular sheet structure; a hole is provided at the center of the charging electrode (4) for the charged droplets (5) to pass through; the charging electrode (4) is connected to a high voltage power supply (13); The function generator (12), the high voltage power supply (13) and the three-dimensional workbench (11) are all connected to an industrial computer (15); The method for suppressing bubble defects in embedded 3D printing based on droplet jetting includes the following steps: 1) preparing printing ink; obtaining printing ink that is uniformly and stably dispersed and suitable for droplet ejection by adjusting the mass ratio of solute, solvent and dopant; 2) supplying the processed printing ink to an on-demand droplet generator (1); 3) pre-treating the deposition substrate (8), and coating the flexible substrate (7) on the pre-treated deposition substrate (8); 4) Printing initialization, moving the three-dimensional workbench (6) to the printing position, and adjusting the flexible substrate (7) to a set distance from the nozzle (2); 5) starting the on-demand droplet generator (1), and the function generator (12) outputs an excitation signal to drive the printing ink to be extruded at the nozzle (2) to form a jet (3); 6) Under the induction of the charging electrode (4), the charges are gathered on the jet (3), and when the length of the jet (3) reaches a certain threshold, it breaks to form charged droplets (5); 7) the charged droplet (5) passes through the central hole of the charging electrode (4) and flies toward the flexible substrate (7); an electrostatic field (16) is formed between the charged droplet (5) and the flexible substrate (7); under the induction of the electrostatic field (16), the surface charge of the charged droplet (5) is polarized; as the distance between the charged droplet (5) and the flexible substrate (7) decreases, the charge density on the surface of the charged droplet (5) and the surface of the flexible substrate (7) increases sharply, and the electric field strength increases; when the electric field strength reaches a certain level, the charged droplet (5) and the flexible substrate (7) are deformed under the action of electric stress to overcome the surface tension and the pressure of the surrounding environment gas, and the bottom of the charged droplet (5) is stretched downward by the electric stress, and the upper surface of the flexible substrate (7) is stretched upward by the electric stress; 8) The charged microdroplet (5) is deposited on the flexible substrate (7). Under the action of strong electrical stress, the bottom of the charged microdroplet (5) and the flexible substrate (7) form a Taylor cone (17) and a single-point contact occurs. In the subsequent flow embedding process, the charged microdroplet (5) continuously wetting outwards, and the ambient gas in the microdomain of the microdroplet deposition is discharged. 9) The industrial computer (15) generates a printing program according to the target structure, repeatedly controls the function generator (12) and the high voltage power supply (13) to generate charged droplets (5) as needed, and controls the coordination between the printing deposition of the charged droplets (5) and the movement of the three-dimensional workbench (11), so as to realize point-by-point, line-by-line, and layer-by-layer printing, and finally forms the target three-dimensional structure (6); 10) Post-process the printed parts to improve the stability of the printed structure.

2. The method for suppressing bubble defects in embedded 3D printing based on droplet injection according to claim 1, characterized in that: The printing ink material is a mixture of one or more of polymers, ceramics, metals, glass, biomaterials or composite materials; the material of the flexible substrate (7) is a yield stress fluid or a Newtonian fluid.

3. The method for suppressing bubble defects in embedded 3D printing based on droplet injection according to claim 1, characterized in that: In step 3), the deposited substrate (8) is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropanol for 10 minutes, then rinsed with deionized water, and then blown dry with nitrogen. Finally, a plasma treatment machine is used to perform plasma bombardment treatment on the surface of the deposited substrate (8) to modify the surface of the deposited substrate (8) and improve the adhesion of the surface of the deposited substrate (8).

4. The method for suppressing bubble defects in embedded 3D printing based on droplet injection according to claim 1, characterized in that: In step 3), the flexible substrate (7) is coated by spin coating, doctor blade coating or roller coating.

5. The method for suppressing bubble defects in embedded 3D printing based on droplet jetting according to claim 1, characterized in that: The heating plate (9) can pre-treat the flexible substrate (7) according to the structural forming requirements before printing, thereby changing the rheological properties of the flexible substrate (7) material; and the heating plate (9) can perform overall heating and curing treatment on the formed structure after printing is completed, thereby improving the stability of the structure.

6. The method for suppressing bubble defects in embedded 3D printing based on droplet jetting according to claim 1, characterized in that: The high-voltage power supply (13) is a periodic high-voltage power supply, and the voltage is continuously adjustable within the range of -5000 to 5000V.

7. The method for suppressing bubble defects in embedded 3D printing based on droplet jetting according to claim 1, characterized in that: The inner diameter of the nozzle (2) is 20 μm to 3 mm; the thickness of the flexible substrate (7) is 100 μm to 3 mm.

8. An application of the suppression method according to any one of claims 1 to 7 in printing continuous structures by an AC signal modulation strategy, characterized in that: The continuous variable polarity printing of the charged microdroplets (5) is achieved through a pulse AC signal modulation strategy, so that the charges carried by adjacent charged microdroplets (5) have opposite polarities, and the continuous deposition and embedding behavior of multiple charged microdroplets (5) is regulated. The charges carried by the charged microdroplets (5) are effectively neutralized, and the overlapping process between continuous microdroplets is promoted, thereby improving the contour quality of the target three-dimensional structure (6).

9. An application of the suppression method according to any one of claims 1 to 7 to printing an embedded microchannel structure inside a flexible substrate by using sacrificial ink, characterized in that: After printing is completed, the overall structure is first cured, and then the sacrificial ink is liquefied and removed from the cured flexible substrate (7) by local heating, cooling, solvent washing or vacuum extraction, leaving a hollow structure, and finally obtaining an embedded microchannel structure.

10. An application of the suppression method according to any one of claims 1 to 7 in printing a high aspect ratio structure through a sacrificial flexible substrate, characterized in that: Under the restrictive wrapping effect of the sacrificial flexible substrate, the printing ink is printed inside the sacrificial flexible substrate to obtain a high aspect ratio structure. The sacrificial flexible substrate is removed by high temperature or solvent washing, and the high aspect ratio structure is sintered to further fuse the materials to obtain a stable high aspect ratio structure.

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