A 3D printing preparation method for a high-absorption electromagnetic shielding composite material with a gradient structure

Abstract

The present invention relates to a 3D printing preparation method for a high-absorption electromagnetic shielding composite material with a gradient structure, comprising: adding Fe3O4 and CNT to a dimethyl sulfoxide solution, thoroughly shaking and ultrasonically dispersing the mixture, continuously adding TPU particles, continuously mechanically stirring at room temperature, and adding different CNT contents as needed to prepare a variety of Fe3O4 / CNT / PU composite inks; sequentially inputting the various Fe3O4 / CNT / PU composite inks into a 3D printer for extrusion printing in a coagulation bath to obtain a composite frame, which is then soaked and rinsed in deionized water and then dried at a constant temperature to obtain a composite frame with a porous structure; and bonding and curing the composite frame with a highly conductive flexible MXene film using a polyurethane solution to obtain the composite material. This solves the problem of serious secondary electromagnetic radiation pollution caused by the electromagnetic wave (EMW) reflection characteristics of existing conductive electromagnetic interference shielding composite materials.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of electromagnetic shielding composite materials, and in particular to a 3D printing preparation method of a high-absorption electromagnetic shielding composite material with a gradient structure. Background Art

[0002] With the rapid development of human society and the widespread application of modern electronic communication technology, in order to ensure the normal operation of precision electronic devices and human health, it is necessary to develop lightweight, flexibly customizable, and ultra-efficient electromagnetic interference (EMI) shielding materials. Compared with traditional metal-based electromagnetic shielding materials with poor processing performance, high density, and easy corrosion, polymer-based magneto-electric composites have been rapidly developed in multiple application fields due to their corrosion resistance, easy processing, and flexible magneto-electric network design. Generally speaking, various conductive fillers, such as two-dimensional (2D) transition metal carbides / nitrides (MXene), carbon nanotubes (CNTs), graphene, and metal nanowires, have been incorporated into polymers to manufacture high-performance EMI shielding polymer composites.

[0003] However, these conductive EMI shielding composite materials have obvious electromagnetic wave (EMW) reflection characteristics, which leads to serious secondary electromagnetic radiation pollution. Therefore, in order to minimize the secondary electromagnetic radiation pollution, it is urgent to develop high electromagnetic shielding polymer-based composite materials based on electro-magnetic networks with absorption as the main feature for the next generation of electronic devices. Summary of the Invention

[0004] In order to solve the problem of how to reduce the serious secondary electromagnetic radiation pollution caused by the electromagnetic wave (EMW) reflection characteristics of existing conductive electromagnetic interference shielding composite materials, the present invention provides a 3D printing preparation method of a high-absorption electromagnetic shielding composite material with a gradient structure.

[0005] In a first aspect, the present invention provides a 3D printing method for preparing a high-absorption electromagnetic shielding composite material having a gradient structure, the preparation method comprising:

[0006] Step 1: Preparation and collection of Fe3O4 / CNT / PU composite ink: Fe3O4 and CNT were added to dimethyl sulfoxide solution, shaken thoroughly and ultrasonically dispersed for 25-35 minutes, and TPU particles were added. The mixture was mechanically stirred continuously at room temperature for 11-13 hours to obtain Fe3O4 / CNT / PU composite ink. Different CNT contents were added as needed to prepare various Fe3O4 / CNT / PU composite inks.

[0007] Step 2: Preparation of a composite framework with a porous structure: The various Fe3O4 / CNT / PU composite inks prepared above are sequentially input into a 3D printer for extrusion printing in a coagulation bath to obtain a composite framework with a three-dimensional gradient structure. The composite framework is then soaked and rinsed in deionized water, and then dried at a constant temperature to obtain a composite framework with a porous structure.

[0008] Step 3: Preparation of a high-absorption electromagnetic shielding composite material with a gradient structure: The composite frame with a porous structure prepared above is bonded and cured using a polyurethane solution and a highly conductive flexible MXene film obtained by vacuum filtration to obtain a high-absorption electromagnetic shielding composite material with a gradient structure.

[0009] In some embodiments, the composite frame is formed by stacking multiple structural frames with different lattice scales from bottom to top, and the lattice scales of the multiple structural frames show an increasing trend in sequence. Each of the structural frames is made of the Fe3O4 / CNT / PU composite ink with one CNT content by immersion precipitation 3D printing, and the CNT content of each Fe3O4 / CNT / PU composite ink shows a decreasing trend in sequence. The highly conductive and flexible MXene film is bonded to the bottom of the composite frame and is located on the surface of the side of the structural frame with the smallest lattice scale.

[0010] In some embodiments, the composite frame is soaked and rinsed with ionized water at least 2 to 3 times.

[0011] In some embodiments, the composite frame is dried at a constant temperature for at least 10 hours, and the constant temperature range is 32° C. to 45° C.

[0012] In some embodiments, the lattice scale difference between two adjacent structural frames ranges from 0.05 mm to 1 mm.

[0013] In some embodiments, the method for preparing the highly conductive and flexible MXene film comprises the following steps:

[0014] (1) LiF and hydrochloric acid were mixed and placed in a water bath with a temperature of ≤42°C with magnetic stirring;

[0015] (2) Add Ti3AlC2 powder and heat to ≥45°C, and continue stirring for 48 to 72 hours;

[0016] (3) The reaction solution was centrifuged at 4500-5500 rpm for ≥2 min and the supernatant was removed;

[0017] (4) Add hydrochloric acid, ultrasonically treat for ≥5 min, and centrifuge twice at 4500-5500 rpm. Wash with water and centrifuge for ≥5 times until the solution is neutral, i.e., pH ≥5. After the reaction is complete, place in an ice-water bath and ultrasonically disperse for ≥2 h.

[0018] (5) high-speed centrifuging the MXene solution obtained in step (4) to obtain a dispersion of few-layer MXene nanosheets;

[0019] (6) The few-layer MXene nanosheet dispersion obtained in step (5) is subjected to vacuum-assisted filtration to prepare the highly conductive flexible MXene film.

[0020] In some embodiments, the flexible MXene film has an average thickness of 12 μm and an electrical conductivity of 3.1×10 5 S / m.

[0021] In some embodiments, the mass ratio of the Fe3O4, CNT and TPU particles is 1:0 to 1:8.5 to 9.5.

[0022] In some embodiments, the CNT content in the Fe3O4 / CNT / PU composite ink is 0 wt% to 8.9 wt%.

[0023] In some embodiments, the conductivity variation range between two adjacent structural frames is 1×10 -8 ~3.1×10 5 S / m.

[0024] In order to solve the problem of how to reduce the serious secondary electromagnetic radiation pollution caused by the electromagnetic wave (EMW) reflection characteristics of existing conductive electromagnetic interference shielding composite materials, the present invention has the following advantages:

[0025] Through the technical solution of the present invention, a high-performance electromagnetic interference (EMI) shielding flexible composite material with excellent mechanical properties and absorption-based properties is provided. Immersion deposition 3D printing technology is used to continuously and precisely control the printing wire spacing, i.e., the lattice scale, from bottom to top in a coagulation bath. At the same time, the content of the conductive filler CNT in the Fe3O4 / CNT / PU composite ink is adjusted to obtain a layered and porous composite framework, which is further bonded and assembled with a highly conductive flexible MXene film to obtain a high-absorption electromagnetic shielding composite material with a gradient structure, achieving high EMI shielding and excellent mechanical properties with asymmetric adjustable absorption coefficients (A) on the front and back sides of the composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic flow chart showing a method for preparing a high-absorption electromagnetic shielding composite material with a gradient structure is shown;

[0027] Figure 2 (a) shows an SEM micrograph of multilayer Ti3C2Tx;

[0028] Figure 2 (b) shows the SEM micrograph of the exfoliated Ti3C2Tx nanosheets;

[0029] Figure 2 (c) shows the TEM image of the exfoliated Ti3C2Tx nanosheets;

[0030] Figure 2 (d) shows a digital image of a flexible Ti3C2Tx film with a thickness of approximately 12 μm and bending flexibility properties;

[0031] Figure 2 (e) shows a schematic diagram of the top layer of DGFCP&M-10 lightweight composite material;

[0032] Figure 2 (f) shows a schematic diagram of the cross section of layers 5-10 of the DGFCP&M-10 lightweight composite material;

[0033] Figure 2 (g) shows SEM micrographs of layers 1-4 with MXene films.

[0034] Figure 2 (h) shows a schematic diagram of the cross section of a DGFCP&M-10 lightweight composite monofilament;

[0035] Figure 2 (i) shows Figure 2 (h) SEM micrograph of the middle part;

[0036] Figure 2 (j) shows the EDS image of a partial cross section of the DGFCP&M-10 lightweight composite material;

[0037] Figure 3 (a) shows the schematic structural diagram of the grid-filled dual-gradient DGFCP&M-10 lightweight composite material;

[0038] Figure 3 (b) shows a schematic diagram Figure 3 (a) Schematic diagram of the lightweight composite X-band EMISET shown;

[0039] Figure 3 (c) shows a schematic diagram Figure 3 (a) The average SE of the lightweight composite material T 、SE A 、SE R value;

[0040] Figure 3 (d) shows a schematic diagram Figure 3 (a) The values ​​of A, R, and T coefficients of the lightweight composite material shown;

[0041] Figure 3 (e) shows the schematic structural diagram of the single gradient SGFCP&M-10 composite material;

[0042] Figure 3 (f) shows a schematic diagram Figure 3 (e) Schematic diagram of the composite X-band EMISET;

[0043] Figure 3 (g) shows a schematic diagram Figure 3 (e) The average SE of the composite material shown T 、SE A 、SE R value;

[0044] Figure 3 (h) shows a schematic diagram Figure 3 (e) A, R, and T coefficient values ​​of the composite materials shown;

[0045] Figure 3 (i) Schematic diagram showing the structure of the non-gradient FCP&M-10 composite material;

[0046] Figure 3 (j) shows a schematic diagram Figure 3 (i) Schematic diagram of the composite X-band EMISET shown;

[0047] Figure 3 (k) shows a schematic diagram Figure 3 (i) Average SE of the composite materials shown T 、SE A 、SE R value;

[0048] Figure 3 (l) shows a schematic diagram Figure 3 (i) A, R, and T coefficient values ​​of the composite materials shown. DETAILED DESCRIPTION

[0049] The present disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the present disclosure, rather than to imply any limitation on the scope of the present disclosure.

[0050] As used herein, the term "including" and its variations are to be interpreted as open-ended terms meaning "including, but not limited to." The term "based on" is to be interpreted as "based, at least in part, on." The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment." The term "another embodiment" is to be interpreted as "at least one other embodiment." Terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "vertical," "horizontal," "transverse," and "longitudinal" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. These terms are primarily intended to better describe the present application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed and operated in a specific orientation. Furthermore, some of the above terms may be used to indicate other meanings besides orientation or positional relationships. For example, the term "on" may, in certain circumstances, be used to indicate a dependency or connection relationship. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances. Furthermore, the terms "installed," "disposed," "provided with," "connected," and "connected" are to be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be an internal connection between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0051] According to research, the rational distribution of magneto-electric synergistic networks can improve the absorption and dissipation of electromagnetic waves in polymer-based materials. At the same time, the incorporation of structural designs (such as isolation structures, foam structures, and gradient structures) into electro-magnetic synergistic polymer-based composites has been widely adopted and has become a popular strategy for enhancing absorption and EMI shielding performance. Therefore, a flexible and simple strategy for combining filler functions and structural design in polymer-based EMI shielding materials has important practical significance for the development of lightweight materials with excellent mechanical properties, high absorption, and high EMI shielding properties.

[0052] 3D printing technology has significant advantages such as controllable design, easy construction of complex structures and precise integration of multiple components. It has had a significant impact on the optimized design and controlled manufacturing processes in the fields of aerospace, electronics and biomedicine. In recent years, DIW3D printing technology has been successfully applied in many fields such as biomedicine, microelectronic devices and electrochemical energy storage due to its advantages such as flexible structural customization and simple operation. Among them, a DIW3D printing method based on a polymer-solvent-nonsolvent (PS-NS) ternary system (called immersion precipitation 3D printing, ip3DP) provides the ability to use inks with a wide range of viscosities to manufacture 3D porous models, and serves as a useful toolkit in the 3D printing of hierarchical structures and functional scaffolds. It is expected to become a new strategy for the integrated customized preparation of highly absorbent and highly electromagnetic interference shielding polymer-based materials.

[0053] Therefore, the present application discloses a 3D printing method for preparing a high-absorption electromagnetic shielding composite material with a gradient structure, such as Figures 1 to 3 As shown in (1), the preparation method comprises:

[0054] Step 1: Preparation and collection of Fe3O4 / CNT / PU composite ink: Fe3O4 and CNT were added to dimethyl sulfoxide solution, shaken thoroughly and ultrasonically dispersed for 25-35 minutes, and TPU particles were added. The mixture was mechanically stirred continuously at room temperature for 11-13 hours to obtain Fe3O4 / CNT / PU composite ink. Different CNT contents were added as needed to prepare various Fe3O4 / CNT / PU composite inks.

[0055] Step 2: Preparation of a composite framework with a porous structure: The various Fe3O4 / CNT / PU composite inks prepared above are sequentially input into a 3D printer for extrusion printing in a coagulation bath to obtain a composite framework with a three-dimensional gradient structure. The composite framework is then soaked and rinsed in deionized water, and then dried at a constant temperature to obtain a composite framework with a porous structure.

[0056] Step 3: Preparation of a High-Absorption Electromagnetic Shielding Composite Material with a Gradient Structure: The porous composite frame prepared above is bonded and cured using a polyurethane solution and a highly conductive, flexible MXene film obtained by vacuum filtration to obtain a high-absorption electromagnetic shielding composite material with a gradient structure. In this application, the high-absorption electromagnetic shielding composite material with a gradient structure also exhibits excellent mechanical properties.

[0057] Furthermore, the composite frame is formed by stacking multiple structural frames with different lattice scales from bottom to top, and the lattice scales of the multiple structural frames show an increasing trend in sequence. Each of the structural frames is made of the Fe3O4 / CNT / PU composite ink with one CNT content by immersion precipitation 3D printing. The CNT content of each Fe3O4 / CNT / PU composite ink shows a decreasing trend in sequence, so that the electrical conductivity of each Fe3O4 / CNT / PU composite ink shows a decreasing trend from bottom to top. The highly conductive flexible MXene film is bonded to the bottom of the composite frame and is located on the surface of the side of the structural frame with the smallest lattice scale.

[0058] Furthermore, the composite frame is soaked and rinsed with ionized water at least 2 to 3 times.

[0059] Furthermore, the composite frame is dried at a constant temperature for at least 10 hours, and the constant temperature range is 32° C. to 45° C.

[0060] Furthermore, the lattice scale difference between two adjacent structural frames ranges from 0.05 mm to 1 mm.

[0061] Furthermore, the method for preparing the highly conductive and flexible MXene film comprises the following steps:

[0062] (1) LiF and hydrochloric acid were mixed and placed in a water bath with a temperature of ≤42°C with magnetic stirring;

[0063] (2) Add Ti3AlC2 powder and heat to ≥45°C, and continue stirring for 48 to 72 hours;

[0064] (3) The reaction solution was centrifuged at 4500-5500 rpm for ≥2 min and the supernatant was removed;

[0065] (4) Add hydrochloric acid, ultrasonically treat for ≥5 min, and centrifuge twice at 4500-5500 rpm. Wash with water and centrifuge for ≥5 times until the solution is neutral, i.e., pH ≥5. After the reaction is complete, place in an ice-water bath and ultrasonically disperse for ≥2 h.

[0066] (5) high-speed centrifuging the MXene solution obtained in step (4) to obtain a dispersion of few-layer MXene nanosheets;

[0067] (6) The few-layer MXene nanosheet dispersion obtained in step (5) is subjected to vacuum-assisted filtration to prepare the highly conductive flexible MXene film.

[0068] Furthermore, the average thickness of the flexible MXene film is 12 μm, and the electrical conductivity is 3.1×105 S / m.

[0069] Furthermore, the mass ratio of the Fe3O4, CNT and TPU particles is 1:0 to 1:8.5 to 9.5.

[0070] Furthermore, the CNT content in the Fe3O4 / CNT / PU composite ink is 0wt% to 8.9wt%.

[0071] Furthermore, the conductivity variation range between two adjacent structural frames is 1×10 -8 ~3.1×10 5 S / m.

[0072] The present application provides a method for preparing a high-absorption electromagnetic shielding composite material with a gradient structure by using a flexible and simple vacuum filtration process-assisted immersion precipitation 3D printing technology (ip3DP). First, by using a 3D printing technology with an integrated multi-nozzle extrusion control system, the printing wire spacing is continuously and accurately controlled from bottom to top in a coagulation bath, and the content of CNT in the Fe3O4 / CNT / PU ink is adjusted to obtain a lightweight and porous composite frame. Furthermore, the porous composite frame is bonded and assembled with a highly conductive flexible MXene film obtained by a vacuum filtration process to form a high-absorption electromagnetic shielding composite material with a dual gradient structure design. Among them, a lightweight and porous structural frame with a large-scale lattice printed with a magnetic low-conductivity ink is used as the electromagnetic absorption layer, i.e., the impedance matching layer, at the top of the composite frame, and a lightweight and porous structural frame with a small-scale lattice printed with a magnetic high-conductivity ink is used as the bottom structure of the composite frame and bonded and assembled with an ultra-high-conductivity MXene film as an electromagnetic reflection layer, forming a "weak reflection-absorption-strong reflection-reabsorption" interface. In addition, the microscopic porous structure within the composite frame further restricts the incident wave from penetrating the material in a specific direction and dissipates the electromagnetic wave through multiple reflections at the rich interface, effectively expanding the dissipation path of the electromagnetic wave. As expected, thanks to the synergistic effect of the excellent mechanical properties of the polymer PU and the filler, the DGFCP&M lightweight composite frame has a high EMISE of 72.7dB and a high absorption coefficient A of 0.62, while also having an excellent elongation at break of up to 128% and a tensile strength of 2.2MPa.

[0073] The present invention provides a new approach for developing lightweight materials with excellent mechanical properties, low reflection and high electromagnetic interference shielding performance, and has broad application prospects in multiple high-end electromagnetic shielding fields such as biological health protection, ultra-precision electronic components and aerospace.

[0074] Preparation of highly conductive flexible MXene films;

[0075] Among them, layered MXene was obtained by etching the Ti3AlC2 phase in LiF / HCl solution, followed by ultrasonic exfoliation, and highly conductive and flexible MXene films were prepared by combining vacuum-assisted filtration.

[0076] The specific preparation process is as follows: first, lithium fluoride (2 g) is added to hydrochloric acid (40 mL, 9 mol·L -1 ) and stirred magnetically in a 42°C water bath for 30 min at a speed of 600 r·min -1 .

[0077] Subsequently, 2 g Ti3AlC2 powder was gradually added to the above solution, and the mixed solution was continuously stirred in a 45 °C water bath for 48 h for etching; the etched solution was centrifuged at 5000 rpm for 5 min to remove the supernatant, and a certain amount of hydrochloric acid (1 mol·L -1 ), shaken and then ultrasonicated, wherein the ultrasonic power is 350 W and the ultrasonic time is 10 min; and then centrifuged twice at 5000 rpm for 5 min.

[0078] Then, water washing centrifugal expansion treatment was adopted, that is, the multilayer MXene was repeatedly washed 8-10 times with deionized water by the expansion principle of high-speed centrifugation (i.e., three centrifugations at a speed of 5000 rpm for 1 min) until the solution pH was ≥5.

[0079] Subsequently, the precipitate was ultrasonically dispersed in deionized water in an ice-water bath for 2 hours, and the MXene solution was collected and centrifuged at 3500 rpm for 30 minutes to obtain a black-brown supernatant, which was the dispersion of few-layer MXene nanosheets.

[0080] Finally, 5 ml of the few-layer MXene dispersion (12 mg mL -1 ), a high-conductive flexible MXene film of a certain thickness was prepared by vacuum-assisted filtration. In this application, the average thickness of the high-conductive flexible MXene film is preferably 12 μm, and its conductivity is 3.1×10 5 S / m.

[0081] Preparation of Fe3O4 / CNT / PU composite ink;

[0082] First, 0.4 g of Fe3O4 with a solid content of 8.9 wt% and 0.2 g of CNTs (carbon nanotubes) with a solid content of 4.5 wt% were added to 20 ml of dimethyl sulfoxide solution, shaken thoroughly and ultrasonically dispersed for 30 minutes. Then, 3.88 g of TPU particles with a solid content of 86.6 wt% were added and mechanically stirred continuously at room temperature for 12 hours to obtain Fe3O4 / CNT / PU-4.5 composite ink (named FCP-4.5).

[0083] By varying the CNT content, inks with varying CNT contents were obtained. The composite inks were named FCP-x, where x was 0, 2.3, 4.5, 6.7, and 8.9 wt%, respectively.

[0084] ip3DP process and manufacturing process of high-absorption electromagnetic shielding composite materials with gradient structure;

[0085] The prepared FCP-x composite ink was respectively loaded into independent syringes, and a self-built 3D printer with integrated multi-nozzle extrusion control was used to perform customized structure printing in combination with air pressure drive control extrusion. The needle specification selected for printing is 23G, i.e., a diameter of 0.3mm. The needle is immersed in a coagulation bath, i.e., an aqueous solution of DMSO with a solid content of 50wt%, wherein the coagulation bath is placed in a plastic culture dish made of polystyrene, effectively ensuring the reliable adsorption of the bottom extruded filaments to the surface of the culture dish. In this application, the structural framework ".gcode" files of different lattice scales can be generated in advance through MATLAB software programming, and then they are sequentially imported into the 3D printer control software RepetierHost to execute the motion control program. The molding accuracy of the extruded filaments is controlled by adjusting the pressure value of the air pressure drive, and the free switching of the printing inks is achieved through the multi-nozzle extrusion control system. In this embodiment, four dual-gradient (i.e., lattice size and conductive filler content) structural frameworks were constructed, named "dual-gradient Fe3O4 / CNT / PU&MXene-y (DGFCP&M-y)", where y refers to the number of printed layers of the composite frame, with preferred values ​​of 4, 6, 8, and 10, but this application is not limited to this.

[0086] In this embodiment, a typical dual-gradient lightweight composite material frame preparation process is selected for introduction.

[0087] First, we use FCP-8.9 composite ink to print the first and second layers of lattice structure with a lattice scale of 0.3mm, that is, by adjusting the spacing and arrangement of the printed wire strips, the printed structure of the structural frame is obtained. The adjacent wire strips of the first layer are arranged at intervals of 0.3mm, and the second layer is arranged perpendicular to the first layer, with the adjacent wire strips also arranged at intervals of 0.3mm; then switch to FCP-6.7 ink to print the third and fourth layers of lattice structure with a lattice scale of 0.4mm, that is, the third layer of wire strips is arranged parallel to the first layer, and the spacing between adjacent wire strips of the third layer is 0.4mm. The fourth layer is arranged in the same way as the third layer, but the arrangement direction is perpendicular to the third layer; then switch to FCP-4.5 ink to print the fifth and sixth layers of lattice structure with a lattice scale of 0.5mm, that is, the fifth The arrangement of the first and second lattice structures is parallel to the third layer, the spacing between adjacent filaments in the fifth layer is 0.5mm, and the arrangement of the sixth layer is the same as the fifth layer, but the arrangement direction is perpendicular to the fifth layer; switching to FCP-2.3 ink to print the seventh and eighth lattice structures, the lattice scale is 0.6mm, that is, the seventh layer filaments are arranged parallel to the fifth layer, the spacing between adjacent filaments in the seventh layer is 0.6mm, the arrangement of the eighth layer is the same as the seventh layer, but the arrangement direction is perpendicular to the seventh layer; switching to FCP-0 ink to print the ninth and tenth lattice structures, the lattice scale is 0.7mm, that is, the ninth layer filaments are arranged parallel to the seventh layer, the spacing between adjacent filaments in the ninth layer is 0.7mm, and the arrangement of the tenth layer is the same as the ninth layer, but the arrangement direction is perpendicular to the ninth layer, obtaining a composite framework with a three-dimensional gradient structure. In this application, the coagulation bath used for printing is a dimethyl sulfoxide (DMSO) aqueous solution with a concentration range of 30%-60%.

[0088] Secondly, the printed composite frame was repeatedly soaked and rinsed with deionized water 4 to 5 times to ensure the complete non-solvent-induced phase separation process and remove the residual DMSO solvent.

[0089] Subsequently, the structural support was placed in a vacuum drying oven at 38°C for continuous drying for 12 hours to obtain a composite frame with multiple layers of different porous structures.

[0090] Finally, the highly conductive flexible MXene film coated with polyurethane solution was bonded and cured to the surface of the first layer printed in the dried composite frame to obtain a high-absorption electromagnetic shielding composite material with a gradient structure.

[0091] By using ip3DP technology, Fe3O4 / CNT / PU inks with different carbon nanotube contents are precisely and continuously extruded and printed in a coagulation bath to obtain a lightweight composite frame with excellent consistency and stability of the surface lattice size. Figure 2(f) It can be seen that as the gradient of the printed lattice size is controlled, the macroscopic spacing of the printed wires of the DGFCP&M-y composite material gradually increases from 0.3mm to 0.7mm. At the same time, as the carbon nanotube content changes gradually during the printing process, the color of the DGFCP&M-y composite material gradually changes from dark black to light gray, which also makes the composite frame of the three-dimensional gradient structure also form a multi-layer porous structure, that is, each layer of the wire of each structural frame also has a large number of porous structures. By changing the concentration of the carbon nanotube content during the printing process, the wire of each structural frame has a porous structure with different pores, so that the composite frame with a three-dimensional gradient structure forms a composite frame with a multi-porous structure. In addition, the existing conductive electromagnetic interference shielding composite material has a large amount of electromagnetic waves reflected due to its electromagnetic wave (EMW) reflection characteristics. Enter the composite frame with a multi-porous structure for multi-interface electromagnetic wave reflection dissipation.

[0092] In addition, the strong hydrogen bonding effect of polymer PU in FCP-x composite ink effectively ensures the good connection between the two adjacent layers of printed wires. Figure 2 (g) to Figure 2 (h) shows the phase separation of 3D-printed extruded filaments in a coagulation bath, with segregation and enrichment of different components, ultimately forming a rich porous structure at the filament interface. The PU polymer phase separates to form a continuous matrix phase, while CNT and Fe₃O₄ fillers accumulate in the pores. This results in the porous structure of the DGFCP&M-y lightweight composite material consisting of a gradient macroscopic lattice pore structure and a continuous microscopic porous structure. Furthermore, the lightweight composite framework is bonded to a flexible MXene film obtained by vacuum filtration using a polyurethane adhesive, resulting in a porous structure with dual gradients in lattice size and conductive filler, the DGFCP&M-y lightweight composite material.

[0093] The electromagnetic shielding performance of the DGFCP&M-y lightweight composite material is demonstrated by utilizing ip3DP technology integrated with a multi-nozzle extrusion control system to construct a DGFCP&M-y lightweight composite with dual gradients in lattice size and filler. The composite framework of this DGFCP&M-y lightweight composite utilizes a lattice size gradient while maintaining a constant Fe₃O₄ magnetic filler content in the ink. Controlling the content of the conductive filler carbon nanotubes (CNTs) adjusts the conductivity of each layer of the printed scaffold. Combined with an ultra-highly conductive, flexible MXene film (conductivity: 3.1×10⁵ S·m⁻¹) at the bottom, this achieves a gradient conductivity from the top to the bottom layer of the composite. When the CNT content of the FCP-x (x = 0, 2.3, 4.5, 6.7, 8.9, representing the mass fraction of CNTs) ink used for multi-material 3D printing increases from 2.3wt% to 8.9wt%, the conductivity increases from 0.16 to 18.1 S·m⁻¹, a roughly 113-fold improvement in conductivity. The top two layers were printed with FCP-0 ink at a 0.7mm lattice size as the impedance matching layer. The bottom two layers were printed with FCP-8.9 ink at a 0.3mm lattice size and bonded to the flexible MXene film to form the impedance mismatch layer. The middle layers were printed with FCP-2.3, FCP-4.5, and FCP-6.7 inks at lattice sizes of 0.4mm, 0.5mm, and 0.6mm, respectively, as transition layers.

[0094] For comparison, this application also discloses single lattice gradient Fe3O4 / CNT / PU&MXene-y (SGFCP&M-y) and uniform non-gradient Fe3O4 / CNT / PU&MXene-y (FCP&M-y) composites. Both FCP&M and SGFCP&M composites are derived from FCP-4.5 composite ink to ensure that the content of carbon nanotubes and Fe3O4 in each layer is the same. As the number of printed layers increases, the average thickness of the FCP&M composite increases from 0.9mm to 2.1mm, while the lattice size of each layer is set to a constant 0.5mm. Similarly, the SGFCP&M composite also shows an increase in average thickness (1.0-2.1mm) with the increase in the number of printed layers and the gradient lattice size from bottom to top (0.4-0.7mm).

[0095] In order to highlight the DGFCP&M's "lattice-filler" grid-filled dual-gradient architecture composite material (i.e. Figure 3 (a) shows) in terms of enhancing the EMI shielding performance, the present application also discloses a single grid lattice gradient SGFCP & M-y (ie Figure 3 (c)) and uniform FCP&M-y (and Figure 3(i) Composite material. Due to the excellent electrical conductivity of carbon nanotubes and MXene and the magnetic permeability of Fe3O4, the EMISET of FCP&M and SGFCP&M composite materials are both higher than 50.0dB, which fully meets the main demand of commercial EMI shielding of 20dB. In addition, the EMISET of FCP&M and SGFCP&M composite materials in the x-band continues to increase with the increase of the number of printed layers. The maximum EMISET of FCP&M-4 can reach 57.1dB. As the number of layers increases, the maximum EMISET of FCP&M-10 increases moderately to 70.4dB, as shown in Figure 2. Figure 3 In addition, the EMISET of SGFCP&M-10 is slightly better than that of FCP&M-10 with the same number of layers, with a maximum value of 72.5dB, which fluctuates slightly with frequency in the x-band, as shown in Figure 3 f. Similarly, the average SE of SGFCP&M and FCP&M composites T 、SE R and SE A And the power coefficients A and R are as follows Figure 3 (h) Figure 3 (k) and Figure 3 (l) As shown in Figure 1, it is obvious that the average SET and SEA of SGFCP&M and FCP&M composite materials gradually increase with the increase of the number of printed layers. In particular, at the 10th layer, the average SET of SGFCP&M-10 and FCP&M-10 is greatly improved to 67.7dB and 65.1dB, respectively. Figure 3 (g) and Figure 3 (k) shows that at the same number of layers, the average SET of SGFCP&M is slightly higher than that of FCP&M, indicating that the single gradient structure is superior to the uniform structure in improving EMISE. However, the SER of FCP&M and SGFCP&M composites decreases slightly with the increase of the number of layers, but does not exceed 7.0 dB, which is due to the improvement of impedance matching between adjacent layers and the thickening of the porous structure. Therefore, SE T The enhancement is mainly due to SE A Rise instead of SE R This is attributed to the increase of mobile carriers and electromagnetic synergy.

[0096] In addition, the A of FCP&M and SGFCP&M frameworks visually shows an increasing trend with the increase of the number of layers, while the R of the composite framework shows the opposite trend, e.g. Figure 3(h) As shown. It is worth noting that the A (<0.5) of all FCP&M frames is significantly smaller than R (>0.5), indicating that the shielding principle of the homogeneous FCP&M composite is mainly reflection. It is worth noting that the A of SGFCP&M-8 and SGFCP&M-10 are 0.52 and 0.55, respectively, which are slightly larger than their respective R, indicating the obvious advantage of EMW absorption. However, at the same number of layers, the SET-12 and A-12 of the DGFCP&M frame are greater than the SET-12 and A-12 of the SGFCP&M and FCP&M composite frames, which shows that the "lattice-filler" lattice filling dual gradient design strategy has great advantages for manufacturing excellent light-absorbing EMI shielding composites with absorption as the main feature.

[0097] according to Figure 3 (b)- Figure 3 (d) SE of DGFCP&,My composite material with double gradient structure in X-band T The maximum value can reach 76.9dB, and the average absorption coefficient A can reach up to 0.62. Compared with the single lattice gradient SGFCP&M-y composite framework, SE T The average absorption coefficient (A) significantly improved by approximately 14%, and the average absorption coefficient (A) significantly increased by approximately 13%. This is due to the continuous optimization of the impedance matching layer on the dual-gradient structure surface, which further reduced electromagnetic wave reflection at the incident interface. Furthermore, the dual-gradient structure composite material was rationally designed to achieve optimal interface matching of absorption, reflection, and reabsorption between the top, middle, and bottom layers. The carbon nanotube content in each layer was customized to maximize EMI shielding and improve absorption efficiency. It is noteworthy that the average absorption coefficient (A) of the DGFCP&M-y lightweight composite material shows a pattern of increasing with the number of layers, first increasing sharply from 0.28 to 0.62, and then slowly decreasing to 0.56. When the number of layers (y) is ≥ 6 (average thickness ≥ 1.25 mm), the electromagnetic shielding of the composite frame shifts to an absorption-dominated loss mechanism, significantly outperforming single-lattice-sized single-gradient and non-gradient uniform structure composites. This is likely due to the fact that as the number of printed layers increases, the thickness and density of the material improve the magnetic and conductive networks, promoting a rapid increase in electromagnetic wave absorption efficiency. However, when the number of printing layers increases further, the porosity and internal cavities of the dual-gradient structure reduce the density of the material, which may weaken the ability to absorb electromagnetic waves and cause the absorption coefficient A to slowly decrease.

[0098] In summary, the present application provides a high-performance electromagnetic interference (EMI) shielding flexible composite material with excellent mechanical properties and absorption-based properties. It adopts immersion deposition multi-nozzle 3D printing technology to continuously and accurately control the printing wire spacing, i.e., the lattice scale, from bottom to top in the coagulation bath. At the same time, the CNT content in the Fe3O4 / CNT / PU composite ink is adjusted to obtain a porous composite frame, which is further bonded and assembled with a highly conductive flexible MXene film to obtain a high-absorption electromagnetic shielding composite material with a gradient structure, achieving high EMI shielding and excellent mechanical properties with asymmetric adjustable absorption coefficient.

[0099] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0100] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A 3D printing method for preparing a high-absorption electromagnetic shielding composite material with a gradient structure, characterized in that: The preparation method comprises: Step 1: Preparation and collection of Fe3O4 / CNT / PU composite ink: Fe3O4 and CNT were added to dimethyl sulfoxide solution, shaken thoroughly and ultrasonically dispersed for 25-35 minutes, and TPU particles were added. The mixture was mechanically stirred continuously at room temperature for 11-13 hours to obtain Fe3O4 / CNT / PU composite ink. Different CNT contents were added as needed to prepare various Fe3O4 / CNT / PU composite inks. Step 2: Preparation of a composite framework with a porous structure: The various Fe3O4 / CNT / PU composite inks prepared above are sequentially input into a 3D printer for extrusion printing in a coagulation bath to obtain a composite framework with a three-dimensional gradient structure. The composite framework is then soaked and rinsed in deionized water, and then dried at a constant temperature to obtain a composite framework with a porous structure. Step 3: Preparation of a high-absorption electromagnetic shielding composite material with a gradient structure: The composite frame with a porous structure prepared above is bonded and cured with a polyurethane solution and a highly conductive flexible MXene film obtained by vacuum filtration to obtain a high-absorption electromagnetic shielding composite material with a gradient structure; The composite frame is formed by stacking multiple structural frames with different lattice scales from bottom to top, and the lattice scales of the multiple structural frames show an increasing trend in sequence. Each of the structural frames is made of the Fe3O4 / CNT / PU composite ink with one CNT content through immersion precipitation 3D printing. The CNT content of each Fe3O4 / CNT / PU composite ink shows a decreasing trend in sequence. The highly conductive and flexible MXene film is bonded to the bottom of the composite frame and is located on the surface of the side where the structural frame with the smallest lattice scale is located.

2. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The composite frame is soaked and rinsed with deionized water at least 2 to 3 times.

3. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The composite frame is dried at a constant temperature for at least 10 hours, and the constant temperature range is 32° C. to 45° C.

4. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The lattice scale difference between two adjacent structural frames ranges from 0.05 mm to 1 mm.

5. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The method for preparing the highly conductive flexible MXene film comprises the following steps: (1) LiF and hydrochloric acid were mixed and placed in a water bath with a temperature of ≤42°C with magnetic stirring; (2) Add Ti3AlC2 powder and heat to ≥45°C, and continue stirring for 48~72h; (3) Centrifuge the reaction solution at 4500-5500 rpm for ≥2 min and remove the supernatant; (4) Add hydrochloric acid, ultrasonically treat for ≥5 min and centrifuge for a second time at 4500-5500 rpm, wash with water and centrifuge for ≥5 times, and make the solution neutral, i.e., pH ≥5. After the reaction is completed, place in an ice water bath and ultrasonically disperse for ≥2 h; (5) high-speed centrifuging the MXene solution obtained in step (4) to obtain a dispersion of few-layer MXene nanosheets; (6) The few-layer MXene nanosheet dispersion obtained in step (5) is subjected to vacuum-assisted filtration to prepare the highly conductive flexible MXene film.

6. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1 or 5, characterized in that: The average thickness of the highly conductive flexible MXene film is 12 μm, and the electrical conductivity is 3.1×10 5 S / m.

7. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The mass ratio of the Fe3O4, CNT and TPU particles is 1:0~1:8.5~9.

5.

8. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1 or 7, characterized in that: The CNT content in the Fe3O4 / CNT / PU composite ink is 0 wt% to 8.9 wt%.

9. The 3D printing preparation method of the high-absorption electromagnetic shielding composite material with a gradient structure according to claim 1, characterized in that: The conductivity variation range between two adjacent structural frames is 1×10 -8 ~3.1×10 5 S / m.

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