A method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting

Abstract

This invention provides a method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting. The method proposes a novel approach using electric field induction to suppress internal bubble defects in embedded 3D printed parts. When the charge level of the charged microdroplets reaches a critical value, the electrical stress stretches the bottom of the charged microdroplets outwards, causing them to contact the flexible substrate first in the form of a Taylor cone. This fundamentally suppresses air entrapment during the microdroplet embedding process, effectively suppressing internal bubble defects in embedded printed parts. This method is expected to overcome the technical bottleneck of structural forming defects in embedded 3D printing based on microdroplet jetting, providing a feasible technical solution for fabricating high-performance functional devices with complex configurations and multiple material composites.

Description

Technical Field

[0001] This invention relates to the field of embedded 3D printing technology, and in particular to a method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting. Background Technology

[0002] Functional devices are devices designed and manufactured with a focus on functional requirements, integrating materials, structure, and function through integrated design and manufacturing. They combine advanced design, manufacturing, and evaluation technologies to achieve a high degree of integration of structure, performance, and function, playing a crucial role in aerospace, military defense, communications sensing, and biomedicine. Additive manufacturing (3D printing), as a revolutionary manufacturing technology, possesses multi-scale, multi-material, and multi-dimensional manufacturing capabilities, greatly promoting the development and application of functional devices. The collaborative design relationship between materials and structure is fundamental to achieving the functionality of the component structure. Functional materials require rigorous, precise, and scientific composite and assembly. Therefore, developing design and manufacturing technologies for complex three-dimensional functional structures is a prerequisite for realizing the integration of materials, structure, and function in functional devices.

[0003] Microdroplet jetting-based embedded 3D printing is an innovative additive manufacturing method. Building upon inkjet printing, it introduces a flexible substrate. By controlling parameters such as pulse pressure and vibration waveform, printing ink is jetted into uniform microdroplets ranging from micrometers to sub-millimeters. These droplets are then precisely deposited onto the flexible substrate surface. The rheological properties of the flexible substrate suppress droplet diffusion and rebound, allowing the droplets to sink into the substrate and form an embedded structure. Finally, post-processing steps such as curing and sintering yield an integrated functional device with a stable structure. Microdroplet jetting-based embedded 3D printing eliminates the cumbersome support removal or secondary encapsulation processes of traditional methods, significantly simplifying the manufacturing process. Furthermore, it eliminates the need for specialized raw materials and expensive equipment, offering unique advantages in the rapid manufacturing of functional devices. It represents a feasible solution for achieving integrated design and manufacturing of materials, structure, and function.

[0004] However, embedded 3D printing technology based on microdroplet jetting uses discrete droplets as manufacturing units. During the deposition and embedding of droplets on the flexible substrate surface, collisional gas entrainment often occurs, and some of this gas is trapped inside the part, forming bubble defects. See also Figure 1 When a droplet impacts a flexible substrate, the gas pressure at the bottom of the droplet gradually increases. Under the action of high-pressure gas, the flexible substrate undergoes slight deformation, and the gas at the bottom is gradually compressed to form a high-pressure gas film. The bottom of the droplet experiences a certain degree of indentation and makes circumferential contact with the flexible substrate. This is the first step in a method to suppress bubble defects in embedded 3D printing based on microdroplet jetting.

[0005] A disc-shaped gas film is formed, and with the embedding of droplets, the disc-shaped gas film further contracts under the action of surface tension, forming single or multiple bubble defects that adhere to the liquid-liquid interface between the droplet and the flexible substrate. The generation of these bubble defects is an inherent characteristic of droplet collision dynamics, and bubbles located at the liquid-liquid interface are difficult to expel by buoyancy due to the combined constraints of surface tension and capillary action. During droplet embedding, bubbles aggregate and redistribute at the liquid-liquid interface with the movement of the droplet, inducing structural morphology distortion. Furthermore, during post-processing, internal bubbles may expand, deform, or even burst due to heat, further affecting the functionality of the part structure. Internal bubble defects not only reduce the forming accuracy of the printed structure but also significantly impact the performance and stability of functional devices. The air entrapment behavior in the microdroplet jet-based embedded 3D printing process severely restricts the practical application of this technology.

[0006] Therefore, it is of great significance to develop a method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting. By charging the microdroplets and using an electric field to change the physical process of the microdroplets impacting the flexible deformable substrate, the method suppresses air entrapment at the liquid-liquid interface while achieving stable deposition and embedding of the microdroplets, thereby improving the stability and structural fidelity of the printing process.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] An embedded 3D printing device based on charged droplet jetting includes an industrial computer, as well as an on-demand droplet generator, charging electrodes, a flexible substrate, a deposition substrate, a heating plate, an insulating plate, a 3D stage, a function generator, and a high-voltage power supply arranged in a clean environment.

[0010] The upper surface of the three-dimensional worktable is sequentially covered with an insulating plate, a heating plate, and a deposition substrate from bottom to top. The three-dimensional worktable has X-axis, Y-axis, and Z-axis movement axes, enabling movement in all three directions. The three-dimensional worktable 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 positioned above a flexible substrate. A nozzle is located 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 positioned between the nozzle and the flexible substrate. The charging electrode has a ring-shaped sheet structure. A hole is provided at the center of the charging electrode to allow charging microdroplets to pass through. Method 2 for suppressing bubble defects in embedded 3D printing based on microdroplet jetting.

[0013] The charging electrode is connected to the high-voltage power supply.

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

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

[0016] 1) Prepare printing ink. By adjusting the mass ratio of solute, solvent and dopant, a uniformly and stably dispersed printing ink suitable for microdroplet ejection is obtained.

[0017] 2) Supply the processed printing ink to the on-demand droplet generator.

[0018] 3) Pre-treat the deposition substrate and coat it with a flexible substrate.

[0019] 4) Printing initialization: Move the 3D worktable to the printing position and adjust the distance between the flexible substrate and the nozzle to the set distance.

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

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

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

[0023] 8) Charged microdroplets are deposited onto a flexible substrate. Under strong electrical stress, the bottom of the charged microdroplets and the flexible substrate form a Taylor cone and make single-point contact. During the subsequent flow embedding process, the microdroplets are continuously wetted outward, and the ambient gas in the microdroplet deposition microdomain is discharged accordingly.

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

[0025] 10) Perform post-processing on the printed parts to improve the stability of the printed structure.

[0026] Furthermore, the printing ink material is one or more of polymers, ceramics, metals, glass, biomaterials, or composite materials. The flexible substrate is made of a yield stress fluid or a Newtonian fluid.

[0027] Further, in step 3), the deposition substrate is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropanol for 10 minutes, then rinsed with deionized water, then dried with nitrogen, and finally the deposition substrate surface is subjected to plasma bombardment treatment using a plasma treatment machine to modify the deposition substrate surface and improve the adhesion of the deposition substrate surface.

[0028] Furthermore, 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, thereby altering the rheological properties of the flexible substrate material. After printing, the heating plate performs overall heating and curing treatment on the formed structure to improve the stability of the structure.

[0030] Furthermore, the high-voltage power supply is a periodic high-voltage power supply with a voltage that is continuously adjustable within 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] This invention also discloses an application of the suppression method according to any one of the above in printing continuous structures using an AC signal modulation strategy. The continuous variable polarity printing of charged microdroplets is achieved by using a pulsed AC signal modulation strategy, so that the charge polarity carried by adjacent charged microdroplets is opposite. This regulates the continuous deposition and embedding behavior of multiple charged microdroplets. The charge carried by the charged microdroplets is effectively neutralized, while promoting the overlapping process between continuous microdroplets, thereby improving the contour quality of the target three-dimensional structure.

[0033] The present invention also discloses an application of the suppression method according to any one of the above in printing an embedded microchannel structure inside a flexible substrate using sacrificial ink. After printing, the overall structure is first cured, and then the sacrificial ink is liquefied and removed from the cured flexible substrate by means of local heating, cooling, solvent washing or vacuum extraction, leaving a hollow structure, and finally obtaining an embedded microchannel structure.

[0034] This invention also discloses an application of the suppression method according to any one of the above in printing high aspect ratio structures through a sacrificial flexible substrate. The printing ink is bound by the sacrificial flexible substrate to print a high aspect ratio structure inside the sacrificial flexible substrate. The flexible substrate is removed by high temperature or solvent washing, and the high aspect ratio structure is sintered to further fuse the materials and obtain a stable high aspect ratio structure.

[0035] The technical effects of this invention are undeniable: it proposes a novel approach to suppress bubble defects inside uniformly jetted embedded 3D printed parts by using electric field induction. When the charge level of the charged microdroplets reaches a critical value, the electric stress stretches the bottom of the charged microdroplets outward and makes them contact the flexible substrate first in the form of a Taylor cone. This fundamentally suppresses the air entrapment behavior during the microdroplet collision process, effectively suppressing bubble defects inside the printed parts. It is expected to break through the technical bottleneck of structural forming defects in embedded 3D printing technology based on microdroplet jetting, and provide a feasible technical solution for the preparation of high-performance functional devices with complex configurations and multiple material composites. Attached Figure Description

[0036] Figure 1 A schematic diagram of bubble defects in embedded 3D printing based on microdroplet jetting;

[0037] Figure 2 This is a schematic diagram of an embedded 3D printing device based on charged droplet jetting.

[0038] Figure 3 A schematic diagram illustrating the morphological evolution of charged microdroplets impacting the surface of a flexible substrate and the embedding process.

[0039] Figure 4 This refers to the embedded microcircuit structure based on microdroplet jetting embedded 3D printing in Example 6;

[0040] Figure 5 This refers to the AC signal modulation strategy for the embedded 3D printed continuous structure based on microdroplet jetting in Example 7;

[0041] Figure 6 This refers to the microchannel structure based on sacrificial ink droplet jetting embedded 3D printing in Example 8;

[0042] Figure 7 This refers to the high aspect ratio structure of microdroplet jet embedded 3D printing based on a sacrificial flexible substrate in Example 9.

[0043] In the figure: 1. On-demand droplet generator, 2. Nozzle, 3. Jet, 4. Charging electrode, 5. Charged droplet, 6. Target 3D structure, 7. Flexible substrate, 8. Deposition substrate, 9. Heating plate, 10. Insulating plate, 11. 3D worktable, 12. Function generator, 13. High voltage power supply, 14. Clean environment, 15. Industrial control computer, 16. Electrostatic field, 17. Taylor cone. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0045] Example 1:

[0046] This embodiment provides a method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting. See [link to relevant documentation]. Figure 2 An embedded 3D printing device based on charged droplet jetting 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 worktable 11, and a method for suppressing bubble defects in embedded 3D printing based on droplet jetting -5-

[0047] Number generator 12 and high voltage power supply 13.

[0048] The upper surface of the three-dimensional worktable 11 is sequentially covered from bottom to top with an insulating plate 10, a heating plate 9, and a deposition substrate 8. The three-dimensional worktable 11 has X-axis, Y-axis, and Z-axis movement axes, enabling movement in the X, Y, and Z directions. The three-dimensional worktable 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 the 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 the function generator 12. The on-demand droplet generator 1 is grounded.

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

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

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

[0053] 1) Prepare printing ink. By adjusting the mass ratio of solute, solvent and dopant, a uniformly and stably dispersed printing ink suitable for microdroplet ejection is obtained.

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

[0055] 3) Pre-treat the deposition substrate 8 and coat the pre-treated deposition substrate 8 with a flexible substrate 7.

[0056] 4) Printing initialization: Move the 3D worktable 6 to the printing position and adjust the distance between the flexible substrate 7 and the nozzle 2 to the set distance.

[0057] 5) Start the on-demand microdroplet generator 1. The function generator 12 outputs an excitation signal to drive the printing ink to be extruded at the nozzle 2, forming a jet 3.

[0058] 6) Under the induction of the charging electrode 4, the charge accumulates on the jet 3. When the length of the jet 3 reaches a certain threshold, it breaks to form charged microdroplets 5.

[0059] 7) Charged microdroplets 5 pass through the central hole of the charging electrode 4 and fly towards the flexible substrate 7. An electrostatic field 16 is formed between the charged microdroplets 5 and the flexible substrate 7. Under the induction of the electrostatic field 16, the surface charge of the charged microdroplets 5 is polarized. As the charged microdroplets 5 and the flexible substrate 7 move together, the surface charge of the charged microdroplets 5 becomes polarized. (This is followed by a seemingly unrelated sentence: "Method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting - 6 -")

[0060] As the distance between them decreases, the charge density on the surfaces of the charged droplets 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 droplets 5 and the flexible substrate 7 deform under the action of electric stress, overcoming the surface tension and the surrounding gas pressure. The bottom of the charged droplets 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 3Charged microdroplets 5 are deposited onto a flexible substrate 7. Under strong electrical stress, the bottom of the charged microdroplets 5 and the flexible substrate 7 form a Taylor cone 17 and make single-point contact. During the subsequent flow embedding process, the microdroplets continuously wet outward, and the ambient gas in the deposition area is discharged accordingly.

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

[0063] 10) Perform post-processing on the printed parts to improve the stability of the printed structure.

[0064] Example 2:

[0065] This embodiment is largely the same as Embodiment 1, except that the printing ink material is one or a mixture of polymers, ceramics, metals, glass, biomaterials, or composite materials. The flexible substrate 7 is made of a yield stress fluid or a Newtonian fluid.

[0066] Example 3:

[0067] The main content of this embodiment is the same as that of Embodiment 1 or 2. However, in step 3), the deposition substrate 8 is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropanol for 10 minutes, rinsed with deionized water, dried with nitrogen, and finally subjected to plasma bombardment treatment 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, blade coating, or roller coating.

[0068] Example 4:

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

[0070] Example 5:

[0071] The main content of this embodiment is the same as any one of embodiments 1 to 4, wherein the high-voltage power supply 13 is a periodic high-voltage power supply with a voltage that is continuously adjustable within the range of -5000 to 5000V. 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 together form an electrostatic shield to avoid the formation of an interfering electric field that affects the deposition and embedding of charged droplets 5.

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

[0073]

[0074] In the formula, 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] Example 6:

[0076] This embodiment provides an application of the method described in any one of Embodiments 1 to 5 to directly fabricate highly integrated embedded microcircuits within flexible materials. See also Figure 4 This embodiment includes the following steps:

[0077] 1) Prepare printing ink by selecting uniform silver nanoparticles with a particle size range of 50-100nm as conductive functional materials, using polyvinylpyrrolidone (PVP) as a stabilizing dispersant, and water and ethylene glycol as solvents. The concentration range of the silver nanoparticles is 1-10wt.%. Then, the mixed solution is ultrasonically treated to obtain uniformly and stably dispersed silver nanoparticle ink suitable for microdroplet jetting.

[0078] 2) Supply the nano-silver ink to the on-demand microdroplet generator 1, and select nozzle 2 with an inner diameter of 200μm.

[0079] 3) Pre-treatment of the deposition substrate 8, which is a single-crystal silicon wafer, is carried out. First, the silicon wafer is ultrasonically treated with deionized water for 10 minutes, then dried with nitrogen, and finally the silicon wafer surface is subjected to plasma bombardment treatment using a plasma treatment machine to improve the adhesion between the printing material and the silicon wafer.

[0080] The flexible substrate 7 is made of liquid PDMS. A layer of liquid PDMS polymer is coated on the surface of the deposition substrate 8. An appropriate amount of Dow Corning 184 canned adhesive is selected. The PDMS monomer and its corresponding curing agent are mixed evenly in a ratio of 10:1 and then centrifuged in a centrifuge to remove air bubbles. The treated liquid PDMS is poured onto the silicon wafer, and a layer of PDMS flexible substrate with a thickness of about 100μm is spin-coated on the surface of the silicon wafer using a spin coater.

[0081] 4) Printing Initialization. Move the 3D stage 11 to the printing position and adjust the distance between the PDMS flexible substrate and the nozzle 2 to the set distance. The deposition substrate 8 is connected to the high-voltage power supply 13 via wires. Turn on the heating plate 9 to pre-cur the PDMS flexible substrate at 60°C for 10 minutes to improve the support of the PDMS flexible substrate for the nano-silver ink.

[0082] 5) Start the on-demand microdroplet generator 1. The function generator 12 outputs an excitation signal to drive the printing ink to be extruded at the nozzle 2, forming a jet 3.

[0083] 6) Under the induction of the charging electrode 4, the charge accumulates on the jet 3. When the length of the jet 3 reaches a certain threshold, it breaks to form charged microdroplets 5.

[0084] 7) The charged droplet 5 passes through the charging electrode 4 and flies toward the flexible substrate 7. 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 electric stress, overcoming the surface tension and the surrounding gas pressure. The bottom of the charged droplet 5 is stretched downward by electric stress, and the upper surface of the flexible substrate 7 is stretched upward by electric stress.

[0085] 8) Charged microdroplets 5 are deposited onto the PDMS flexible substrate. The bottom of the charged microdroplets 5 and the PDMS flexible substrate form a Taylor cone 17 under strong electrical stress and make single-point contact. During the subsequent flow and spreading process, they are continuously wetted outward, and the ambient gas in the microdroplet deposition area is discharged accordingly.

[0086] 9) In this embodiment, the embedded microcircuit is designed as a wire grid structure. The industrial control computer 15 programs the printhead movement path, sets the printing start point, and repeatedly controls the function generator 12 and the high-voltage power supply 13 to generate charged droplets 5 as needed. It also controls the coordination and matching between the printing deposition of charged droplets 5 and the movement of the three-dimensional stage 11, ultimately forming 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 stage 11 is set to 50mm / s.

[0087] 10) Post-process the printed parts by curing them at 150°C for 2 hours to fully cure the PDMS flexible substrate, sinter the nano-silver particles, and decompose the protective agent to obtain a stable embedded microcircuit structure.

[0088] This embodiment utilizes the characteristic of charged microdroplets 5 deforming under the influence of an electric field to regulate the deposition and embedding behavior of charged microdroplets 5. This causes the bottom of the charged microdroplets 5 to form a Taylor cone 17 and make single-point contact as it approaches the flexible substrate 7. This changes the form and trajectory of the liquid-liquid-gas three-phase contact line, expelling the ambient gas within the microdroplet deposition microdomain and fundamentally suppressing bubble defects inside the embedded microcircuit structure.

[0089] Example 7:

[0090] This embodiment provides an application of the method described in any one of Embodiments 1 to 5 to achieve continuous variable polarity printing of charged microdroplets 5 using a pulsed AC signal modulation strategy. See also Figure 5 This embodiment includes the following steps:

[0091] 1) Prepare printing ink by adjusting the mass ratio of solute, solvent and dopant to obtain a uniformly and stably dispersed printing ink suitable for micro-droplet jetting.

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

[0093] 3) The deposition substrate 8 is pretreated by coating a flexible substrate material 3 onto the pretreated deposition substrate 4 through spin coating, scraping coating, roller coating or other methods.

[0094] 4) Printing initialization: Move the 3D stage 6 to the printing position and adjust the distance between the flexible substrate 3 and the nozzle 2 to the set distance. The deposition substrate 8 is connected to the high-voltage power supply 13 via wires.

[0095] 5) Start the on-demand microdroplet generator 1. The function generator 12 outputs an excitation signal to drive the printing ink to be extruded at the nozzle 2, forming a jet 3.

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

[0097] 7) The charged droplet 5 passes through the charging electrode 4 and flies towards 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 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 deform under the action of electric stress, overcoming the surface tension and the surrounding gas pressure.

[0098] 8) Charged microdroplets 5 are deposited onto the flexible substrate 7. Under strong electrical stress, the bottom of the charged microdroplets 5 forms a Taylor cone 17 with the flexible substrate 7 and makes single-point contact. During the subsequent flow and spreading process, the microdroplets continuously wet outward, and the ambient gas in the deposition area is expelled. The newly deposited charged microdroplets 5 are wetted and combined with the embedded microdroplets under the guiding attraction of opposite charges. 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 control computer 15 generates a printing program based on the target structure, repeatedly controls the function generator based on the micro-droplet jet embedded 3D printing bubble defect suppression method-10-12 and the high voltage power supply 13 to generate charged micro-droplets 5 as needed, and controls the coordination and matching between the printing deposition of charged micro-droplets 5 and the movement of the three-dimensional worktable 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) Perform post-processing on the printed parts to improve the stability of the printed structure.

[0101] This embodiment utilizes the characteristic of microdroplets being induced to charge under the influence of an electric field. By employing a pulsed AC signal modulation strategy, it achieves continuous variable polarity printing of charged microdroplets 5, making the charge polarities of adjacent charged microdroplets 5 opposite. This regulates the continuous deposition and embedding behavior of multiple charged microdroplets, effectively neutralizing the charge carried by the charged microdroplets 5 while promoting the overlapping process of continuous microdroplets, thereby improving the contour quality of the target three-dimensional structure 6.

[0102] Example 8:

[0103] This embodiment provides an application of the method described in any one of Embodiments 1 to 5 to print embedded microchannel structures within a flexible substrate using sacrificial ink. See also Figure 6 This embodiment includes the following steps:

[0104] 1) To prepare the printing ink, dissolve 23 wt.% of Pluronic F127 (Sigma-Aldrich) in deionized water at 4°C, stir for 3 hours until fully dissolved, and then perform vacuum defoaming treatment to obtain sacrificial ink.

[0105] 2) Sacrificial ink is supplied to the on-demand microdroplet generator 1, the bottom of which is provided with a nozzle 2, and the nozzle 2 is selected with an inner diameter of 300μm.

[0106] 3) Pre-treat the deposition substrate 8, which is an organic glass. First, the organic glass is ultrasonically treated with deionized water for 10 minutes, then dried with nitrogen, and finally the surface of the organic glass is subjected to plasma bombardment treatment using a plasma treatment machine to improve the adhesion of the organic glass surface.

[0107] The flexible substrate 7 material is F127-DA. 100g of Pluronic F127 was dissolved in 400mL of dry toluene at 60°C, triethylamine was added, and acryloyl chloride was added dropwise. The mixture was stirred overnight to generate F127-DA. F127-DA was then cast onto an acrylic glass surface, and a flexible substrate of approximately 1000μm thickness was spin-coated onto the acrylic glass surface using a spin coater.

[0108] 4) Printing initialization: Move the 3D stage 6 to the printing position and adjust the distance between the F127-DA flexible substrate and the nozzle 2 to the set distance. The deposition substrate 8 is connected to the high-voltage power supply 13 via wires.

[0109] 5) Start the on-demand microdroplet generator 1. The function generator 12 outputs an excitation signal to drive the sacrificial ink to be extruded at the nozzle 2 to form a jet 3.

[0110] 6) Under the induction of the charging electrode 4, charge accumulates on the jet 3. When the length of the jet 3 reaches a certain threshold, it breaks to form charged microdroplets 5. The charging electrode 4 is disposed 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 passes through the charging electrode 4 and flies towards the F127-DA flexible substrate. 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 electric stress, overcoming the surface tension and the surrounding gas pressure. The bottom of the charged droplet 5 is stretched downward by electric stress, and the upper surface of the F127-DA flexible substrate is stretched upward by electric stress.

[0112] 8) Charged microdroplets 5 are deposited onto the F127-DA flexible substrate. The bottom of the charged microdroplets 5 and the F127-DA flexible substrate form a Taylor cone 17 and make single-point contact under strong electrical stress. During the subsequent flow and spreading process, the microdroplets continuously wet outward, and the ambient gas in the deposition area is discharged accordingly.

[0113] 9) The industrial control computer 15 in this embodiment is embedded in the microchannel structure generation nozzle motion path program, sets the printing start point, repeatedly controls the function generator 12 and the high voltage power supply 13 to generate charged microdroplets 5, and controls the coordination and matching between the printing deposition of charged microdroplets 5 and the movement of the three-dimensional worktable 11, and finally forms the target three-dimensional microchannel structure.

[0114] 10) Post-process the printed part by curing the F127-DA flexible substrate with 365nm UV light for 5 minutes to chemically cross-link the F127-DA gel matrix into a mechanically stable structure. The sacrificial ink undergoes a phase transition and liquefies at low temperature (4℃). After cooling the entire structure, a slight vacuum is applied to liquefy the sacrificial ink and remove it from the cured F127-DA flexible substrate, leaving a hollow structure, ultimately obtaining an embedded microchannel structure.

[0115] This embodiment is based on microdroplet jet embedded 3D printing technology. By using sacrificial ink to print embedded microchannel structures, the collision and air entrapment behavior of the deposited microdroplets is suppressed by charging the deposited microdroplets, avoiding air bubble defects that may be introduced during the printing process, and further optimizing the internal surface quality of the microchannel structure.

[0116] Example 9:

[0117] This embodiment provides an application of the method described in any one of Embodiments 1 to 6 for printing high aspect ratio structures on a sacrificial flexible substrate. See also Figure 7 This embodiment includes the following steps:

[0118] 1) Prepare the printing ink by selecting high-temperature sintered silver paste as the functional material and water and ethylene glycol as solvents. The concentration range of the nano-silver particles is 1–10 wt.%. The mixed solution is ultrasonically treated to obtain a uniformly and stably dispersed nano-silver ink suitable for microdroplet jetting. Method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting - 12 -

[0119] 2) The nano-silver ink is supplied to the on-demand microdroplet generator 1, and the bottom of the on-demand microdroplet generator 1 is provided with a nozzle 2, and the nozzle 2 is selected with an inner diameter of 200μm.

[0120] 3) Pre-treatment of the deposition substrate 8, which is a single-crystal silicon wafer, is carried out. First, the silicon wafer is ultrasonically treated with deionized water for 10 minutes, then dried with nitrogen, and finally the silicon wafer surface is subjected to plasma bombardment treatment using a plasma treatment machine to improve the adhesion between the printing material and the silicon wafer.

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

[0122] 4) Printing initialization: Move the 3D stage 6 to the printing position and adjust the distance between the PDMS flexible substrate and the nozzle 2 to the set distance. The deposition substrate 8 is connected to the high-voltage power supply 13 via wires.

[0123] 5) Start the on-demand microdroplet generator 1. The function generator 12 outputs an excitation signal to drive the nano-silver ink to be extruded at the nozzle 2, forming a jet 3.

[0124] 6) Under the induction of the charging electrode 4, charge accumulates on the jet 3. When the length of the jet 3 reaches a certain threshold, it breaks to form charged microdroplets 5. The charging electrode 4 is disposed 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 passes through the charging electrode 4 and flies toward the PDMS flexible substrate. 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. Under the action of electric stress, the charged droplet 5 and the PDMS flexible substrate overcome the surface tension and the surrounding gas pressure and deform.

[0126] 8) Charged microdroplets 5 are deposited onto the PDMS flexible substrate. The bottom of the charged microdroplets 5 and the PDMS flexible substrate form a Taylor cone 17 under strong electrical stress and make single-point contact. During the subsequent flow and spreading process, they are continuously wetted outward, and the ambient gas in the microdroplet deposition area is discharged accordingly.

[0127] 9) The industrial control computer 15 generates a printing program based on 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 microdroplets 5 as needed, and controls the coordination and matching between the printing deposition of charged microdroplets 5 and the movement of the three-dimensional worktable 11 to achieve 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) Post-process the printed parts by sintering at 400℃ for 10 min to remove the PDMS flexible substrate. Then, place the high aspect ratio silver mesh into a sintering furnace at 630℃ for further processing for 3 min to further fuse the nano-silver particles and obtain a stable high aspect ratio structure.

[0129] This embodiment is based on microdroplet jet embedded 3D printing technology. It uses a sacrificial flexible substrate to print high aspect ratio structures. By charging the deposited microdroplets, the collision and air entrapment behavior of the droplets is suppressed, avoiding the potential disturbance factors of bubbles at the interface to the local area of ​​the formed structure, thus improving the stability of the printed structure.

Claims

1. A method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting, characterized in that: The embedded 3D printing device based on charged droplet jetting 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 worktable (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 worktable (11) is covered with an insulating plate (10), a heating plate (9), and a deposition substrate (8) from bottom to top; the three-dimensional worktable (11) has an X-axis, a Y-axis, and a Z-axis, realizing movement in the XYZ directions; the three-dimensional worktable (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); The on-demand droplet generator (1) is arranged above the 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 the function generator (12); the on-demand droplet generator (1) is grounded; The charging electrode (4) is arranged between the nozzle (2) and the flexible substrate (7); the charging electrode (4) has an annular sheet structure; the charging electrode (4) has a hole in the center for charged microdroplets (5) to pass through; the charging electrode (4) is connected to a high-voltage power supply (13); The function generator (12), high-voltage power supply (13) and three-dimensional worktable (11) are all connected to the industrial control computer (15); The method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting includes the following steps: 1) Prepare printing ink; by adjusting the mass ratio of solute, solvent and dopant, obtain a uniformly and stably dispersed printing ink suitable for microdroplet jetting; 2) The processed printing ink is supplied to the on-demand microdroplet generator (1); 3) Pre-treat the deposition substrate (8) and coat the pre-treated deposition substrate (8) with a flexible substrate (7); 4) Printing initialization: Move the 3D worktable (11) to the printing position and adjust the distance between the flexible substrate (7) and the nozzle (2) to the set distance; 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); 6) Under the induction of the charging electrode (4), the charge accumulates on the jet (3). 基于微滴喷射的嵌入式3D打印气泡缺陷的抑制方法 -1- When the length of the jet (3) reaches a certain threshold, it breaks to form charged microdroplets (5); 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 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, overcoming the surface tension and the surrounding gas pressure. The bottom of the charged droplet (5) is stretched downward by electric stress, and the upper surface of the flexible substrate (7) is stretched upward by electric stress. 8) Charged microdroplets (5) are deposited onto the flexible substrate (7). The bottom of the charged microdroplets (5) and the flexible substrate (7) form a Taylor cone (17) under strong electrical stress and make single-point contact. During the subsequent flow embedding process, they are continuously wetted outward, and the ambient gas in the microdroplet deposition microdomain is discharged accordingly. 9) The industrial control 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 microdroplets (5) as needed, and controls the coordination and matching between the printing deposition of charged microdroplets (5) and the movement of the three-dimensional worktable (11) to achieve point-by-point, line-by-line, and layer-by-layer printing, and finally forms the target three-dimensional structure (6). 10) Perform post-processing on the printed parts to improve the stability of the printed structure.

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

3. The method for suppressing bubble defects in embedded 3D printing based on microdroplet jetting according to claim 1, characterized in that: In step 3), the deposition substrate (8) is first ultrasonically cleaned with acetone for 10 minutes, then ultrasonically cleaned with isopropanol for 10 minutes, then rinsed with deionized water, then dried with nitrogen, and finally plasma bombardment treatment is performed on the surface of the deposition substrate (8) to modify the surface of the deposition substrate (8) and improve the adhesion of the surface of the deposition substrate (8).

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

5. The method for suppressing bubble defects in embedded 3D printing based on microdroplet 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; after printing, the heating plate (9) performs overall heating and curing treatment on the formed structure to improve the stability of the structure.

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

7. The method for suppressing bubble defects in embedded 3D printing based on microdroplet 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 using an AC signal modulation strategy, characterized in that: By using a pulsed AC signal modulation strategy to achieve continuous polarity printing of charged microdroplets (5), the polarity of the charges carried by adjacent charged microdroplets (5) is opposite. This controls the continuous deposition and embedding behavior of multiple charged microdroplets (5). The charges carried by the charged microdroplets (5) are effectively neutralized, while promoting the overlapping process between continuous microdroplets, 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 in printing embedded microchannel structures within a flexible substrate using sacrificial ink, characterized in that: After printing, 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 the embedded microchannel structure is obtained.

10. An application of the suppression method according to any one of claims 1 to 7 in printing high aspect ratio structures using a sacrificial flexible substrate, characterized in that: The printing ink, under the restrictive encapsulation of the sacrificial flexible substrate, prints a high aspect ratio structure inside the sacrificial flexible substrate. 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 together, resulting in a stable high aspect ratio structure.

Images