A lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, its preparation method and application.

Abstract

This invention discloses a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, its preparation method, and its applications, belonging to the field of electromagnetic shielding materials technology. The fiber composite material of this invention is prepared by electrospinning to create a porous polyurethane fiber membrane. Then, a roughening solution is used to roughen the surface of the polymer material. A specific metal salt is used as an activator in the wet-chemical plating solution, and a formaldehyde-free plating solution is employed for efficient and controllable construction of the metallized polymer material. Repeated cyclic stretching of the metallized fiber membrane disrupts the conductive pathways to enhance its impedance matching. Finally, liquid metal is sprayed onto the surface to enhance its electromagnetic shielding and infrared stealth performance. This material possesses high absorption and efficient electromagnetic shielding effectiveness and excellent infrared stealth performance, and is expected to be applied in aerospace, military equipment, microelectronic devices, and consumer electronics.

Description

Technical Field

[0001] This invention relates to a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, its preparation method and application, belonging to the field of electromagnetic shielding material technology. Background Technology

[0002] Electromagnetic shielding materials, as functional protective materials that effectively isolate incident electromagnetic waves through reflection loss on the material's exterior and absorption loss inside, have been widely used in the field of electromagnetic protection. In recent years, with the rapid development of 5G communication technology, the miniaturization and high integration of electronic components have made electromagnetic leakage and interference problems in electrical equipment increasingly prominent, especially in the field of military protection, where they can easily lead to information leakage and infrared exposure.

[0003] Therefore, higher performance requirements have been put forward for high-performance electromagnetic shielding materials, requiring them to not only be thin, light, wide, and strong, but also have high electromagnetic wave absorption and infrared stealth effects.

[0004] Polyurethane fiber materials have attracted widespread attention due to their excellent mechanical properties. However, because polyurethane fibers are non-conductive and non-magnetic, they do not provide significant shielding against incident electromagnetic waves. To obtain high-performance electromagnetic shielding materials, it is usually necessary to endow polyurethane fibers with excellent electrical and magnetic properties. Generally, surface metallization of the polymer matrix is ​​a common method to achieve excellent conductivity and magnetism.

[0005] However, high conductivity often generates a large number of reflected waves, leading to impedance mismatch between the air and the electromagnetic shielding material, resulting in secondary electromagnetic (EM) radiation pollution. According to Schelkunoffs' transmission theory, the shielding effectiveness (EMI SE) of a shielding material is positively correlated with its conductivity; once the incident wave reaches the surface of the shielding material, reflection occurs. Therefore, the primary strategy for reducing reflection is to reduce conductivity. However, under these circumstances, it is difficult to maintain high shielding effectiveness of the shielding material.

[0006] In recent years, researchers have focused on improving magnetic permeability while simultaneously adjusting electrical conductivity to achieve high EMISE and high electromagnetic wave absorption coefficient (A) in shielding materials. Based on this, it has been found that constructing a suitable electromagnetic gradient layer is a feasible method to effectively improve EMISE and electromagnetic wave absorption coefficient. In this method, the outer layer exhibits extremely low electrical conductivity and high magnetic permeability, while subsequent layers provide increased conductivity. This allows for the design of an absorption-reflection-reabsorption EM wave dissipation process. This process reduces reflection and lengthens the dissipation path, ultimately effectively increasing the absorption effect of electromagnetic waves.

[0007] Furthermore, in order to obtain high-performance infrared stealth materials, the Stefan-Boltzmann infrared radiation law must be satisfied: E = εσT 4 In the formula, E represents the infrared radiation intensity of the material, ε represents the infrared emissivity of the material, σ is the Stefan-Boltzmann constant, and T is the absolute temperature of the material. Infrared stealth is achieved by reducing the infrared emissivity or surface temperature of the material to suppress the increase in infrared radiation intensity from high-temperature heat sources, making it close to the infrared radiation intensity of the background environment. Currently, most methods reduce the surface resistivity of materials by introducing highly conductive metals, conductive polymers, carbon materials, or semiconductor doping, electrochromism, or thermal phase transitions, thereby enhancing the reflection of mid- and far-infrared light. However, ultra-low surface resistivity leads to impedance mismatch on the material surface, causing most electromagnetic waves to be reflected back to the original medium, resulting in serious secondary electromagnetic pollution. On the other hand, reducing the surface temperature of materials can be achieved by introducing heat-insulating materials to block the heat diffusion of high-temperature heat sources; porous heat-insulating materials are the best choice, as they can easily achieve infrared stealth functionality against high-temperature heat sources once they reach a sufficient thickness (>1 cm). However, due to the presence of a large amount of free space, porous thermal insulation materials have low dielectric constant and magnetic permeability, making it difficult to effectively dissipate incident electromagnetic waves. Summary of the Invention

[0008] [Technical Issues]

[0009] Due to the metal autocatalytic acceleration effect, it is difficult to control the formation of the metal coating, making it difficult to achieve impedance matching and thus impossible to achieve high absorption of electromagnetic waves. For infrared stealth, the material thickness is relatively large, making it difficult to achieve the integrated construction of efficient electromagnetic shielding and infrared stealth functions of a single material.

[0010] Therefore, how to construct a gradient structure of impedance and thermal insulation of a single material to obtain a lightweight, flexible electromagnetic protection material with high electromagnetic shielding absorption and infrared stealth has become a key problem and challenge that urgently needs to be solved.

[0011] [Technical Solution]

[0012] To address the aforementioned problems, this invention provides a method for preparing a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material. The aim is to overcome the bottlenecks of traditional electromagnetic shielding materials, such as low shielding effectiveness, high reflectivity, and the inability to simultaneously achieve infrared stealth. This invention uses electrospinning technology to electrospin polyurethane fiber membranes to construct a porous fiber skeleton. Then, a specific roughening solution is used to roughen the surface of the polymer material. A specific metal salt is used as an activator in the wet-chemical plating solution, employing a formaldehyde-free plating solution for efficient and controllable construction of the metallized polymer material. Repeated stretching cycles disrupt the conductive pathways of the metal layer to construct an impedance gradient. Finally, liquid metal is used for surface modification treatment to enhance its infrared stealth performance.

[0013] Specifically: (1) This invention uses electrospinning technology to prepare polyurethane fiber membranes and constructs a porous fiber membrane skeleton, enabling the fibers to contact each other and laying the foundation for the conductive pathway of metallized fibers; (2) A specific roughening solution can form a polymer coating with very strong adhesion on the surface of polymer materials through polymerization reaction in aqueous solution. At the same time, the polymer has a strong complexing and reducing ability for metal ions, reducing specific non-palladium noble metal ions to metal elements in situ, and using this as a catalytic center to efficiently promote the reduction of metal ions such as copper / nickel / silver in chemical plating solution, thereby improving the bonding force between the subsequent metal coating and polymer materials, and extending the stability and service life of the materials; (3) This invention uses a palladium-free and fluorine-free activation process and a formaldehyde-free plating solution system, providing a new path for the efficient, green and environmentally friendly preparation of metallized material surfaces; (4) Nickel, as a high magnetic permeability conductive metal, metallizes polyurethane. The rational construction of the multi-level microstructure inside the fiber will provide new possibilities for enhancing its electromagnetic interference shielding effectiveness and widening the bandwidth. Stretching the metal layer and destroying its conductive path will increase the effectiveness of improving the impedance matching of the composite material. (5) Liquid metal, as a low emissivity material, is used as an infrared surface modification layer in conjunction with a porous heat insulation structure to construct a heat insulation gradient structure through a layered composite method to achieve high-temperature infrared stealth function. At the same time, liquid metal can also be used as an electromagnetic reflection layer, in conjunction with an electromagnetic dissipation layer to construct an impedance gradient structure, so as to realize the "introduction and absorption" of incident electromagnetic waves in the electromagnetic dissipation layer from high impedance to low impedance, "reflection" in the electromagnetic reflection layer with the lowest impedance, and then return to the electromagnetic dissipation layer for "re-absorption", extending the electromagnetic wave dissipation path and providing new possibilities for obtaining high absorption and high efficiency electromagnetic shielding materials and further reducing the thickness of composite materials.

[0014] The purpose of this invention is to provide a method for preparing a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, the method comprising the following steps:

[0015] (1) Preparation of polyurethane fiber membrane

[0016] Thermoplastic polyurethane particles are dissolved in an organic solvent and subjected to hydrothermal stirring reaction. After thorough stirring, a polyurethane spinning solution is obtained. The obtained spinning solution is processed by electrospinning to obtain polyurethane fiber membrane material.

[0017] (2) Preparation of metallized polyurethane fiber membranes

[0018] The polyurethane fiber membrane obtained in step (1) is first roughened in a roughening solution; then the roughened polyurethane fiber membrane is immersed in an activation solution; finally, the activated polyurethane fiber membrane is immersed in a plating solution for plating, cleaned, and dried to obtain a metallized polyurethane fiber membrane material; the solute in the activation solution is chloroplatinic acid, the concentration is 0.1-20 g / L, and the activation treatment time is 30 min-120 min; the plating treatment time is 10-60 min, and the temperature is 10-30℃.

[0019] (3) Surface spraying treatment

[0020] The metallized polyurethane fiber membrane material prepared in step (2) is subjected to 1000 to 2000 stretching cycles; then a liquid metal mesh is sprayed onto one side of the surface to obtain a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material; the degree of damage from the stretching cycles is 50% to 200%; the content of the sprayed liquid metal is 0.1 to 0.5 ml; and the side length of the metal mesh is 1 to 5 mm.

[0021] In one embodiment, the polyurethane particles in step (1) are TPU BASF 1185A from Germany.

[0022] In one embodiment, the organic solvent in step (1) is one or both of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).

[0023] In one embodiment, the temperature of the hydrothermal stirring reaction in step (1) is 50-100°C and the time is 2-5 hours.

[0024] In one embodiment, the solid content of the polyurethane spinning solution in step (1) is 10-30%.

[0025] In one embodiment, the electrospinning process parameters in step (1) are: positive electrode voltage of 10-20kV; negative electrode voltage of 1-5kV; feed speed of 0.1-0.2mL / min; and distance between the needle tip and the receiver of 10-30cm.

[0026] In one embodiment, the solute in the roughening solution in step (2) is one or more of dopamine, citric acid, polyphenol amine, and tannic acid; the concentration is 2 to 6 g / L, and the treatment time is 1 to 24 hours.

[0027] In one embodiment, the roughened polyurethane fiber membrane described in step (2) needs to be vacuum dried before being immersed in the activation solution for 1 to 2 hours at a temperature of 40 to 60°C.

[0028] In one embodiment, the activated metallized polyurethane fiber membrane described in step (2) needs to be vacuum dried for 1 to 2 hours before being immersed in the plating solution, and the drying temperature is 40 to 60°C.

[0029] In one embodiment, the plating solution in step (2) includes a metal salt, a complexing agent, a reducing agent, and a pH adjuster.

[0030] In one embodiment, the metal salt is one or more of nickel sulfate, nickel chloride, and nickel nitrate, with a concentration of 8-80 g / L.

[0031] In one embodiment, the complexing agent is one or more of lactic acid, sodium citrate, tartaric acid, acetic acid, sodium acetate, malic acid, thiourea, and ammonium chloride, with a concentration of 5–20 g / L.

[0032] In one embodiment, the reducing agent is one or more of dimethylamine borane and sodium hypophosphite, with a concentration of 1 to 10 g / L.

[0033] In one embodiment, the pH adjuster is one or more of ammonia, sodium hydroxide, potassium hydroxide, hydrochloric acid, and sulfuric acid, adjusting the pH to 4.8-10.

[0034] In one embodiment, the plating process in step (2) takes 10 to 60 minutes and the temperature is 10 to 30°C.

[0035] In one embodiment, the vacuum drying time after the polyurethane fiber membrane is coated in step (2) is 1 to 2 hours, and the drying temperature is 40 to 60°C.

[0036] In one embodiment, the liquid metal spraying content in step (3) is 0.1 to 0.5 ml, and the side length of the liquid metal mesh is 1 to 2 mm.

[0037] In one embodiment, the liquid metal in step (3) is a gallium-indium alloy or a gallium-indium-tin alloy.

[0038] In one embodiment, the gallium-indium alloy has a gallium content of 75% and an indium content of 25%.

[0039] In one embodiment, the elongation rate at the time of tensile cycle failure in step (3) is 100%; the side length of the metal mesh is 1.25 mm, and the spraying amount is 0.4 ml.

[0040] The second objective of this invention is to provide a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material prepared by the method described above.

[0041] In one embodiment, the thickness of the lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material is 0.5 mm to 1.2 mm; preferably 1 mm.

[0042] A third objective of this invention is to provide an application of the aforementioned lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material in the fields of electromagnetic protection for aerospace devices, electronic instruments, or military defense.

[0043] The beneficial effects of this invention are:

[0044] (1) The preparation method of the present invention is simple to operate. Polyurethane microfibers are prepared by dissolving polyurethane particles in an organic solution and using electrospinning technology. Then, lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite materials are obtained by roughening, activating, plating, stretching and surface spraying of polyurethane fibers.

[0045] Electrospinning yields a porous fiber membrane material, allowing for multiple scattering / reflection of electromagnetic waves within the material, significantly improving electromagnetic shielding effectiveness. Through roughening, active functional groups such as amino, carboxyl, and phenolic hydroxyl groups are successfully loaded onto the polyurethane fiber surface. Based on the adsorption and reduction properties of these functional groups for metal ions, metal ions are reduced in situ and successfully loaded onto the polyurethane fiber surface during activation. These catalytically active metal particles can serve as active centers during plating, achieving palladium-free and fluorine-free activation, making it environmentally friendly and significantly increasing plating uniformity and efficiency. Repeated stretching of the cyclic metal layer improves its impedance matching, giving the fiber membrane material obtained in this invention broad application prospects.

[0046] (2) Based on the principle of multiple scattering and reflection loss attenuation of incident electromagnetic waves inside the material, this invention obtains a lightweight and porous polyurethane fiber membrane material through electrospinning technology, successfully loads metallic nickel on the polyurethane fiber through chemical plating process, and then breaks the metallic nickel layer by stretching the fiber membrane, thereby breaking the conductive network and achieving impedance matching effect, so that electromagnetic waves can enter the interior of the material as much as possible, and effectively lose electromagnetic waves based on the conductivity and magnetic permeability of nickel; in addition, the porous structure inside the material allows electromagnetic waves to undergo multiple scattering / reflection inside the material, and the electromagnetic shielding effectiveness (>20dB) can cover the entire waveband.

[0047] (3) Based on the principle of multiple scattering and reflection loss attenuation of incident electromagnetic waves inside the material and the infrared radiation law of infrared stealth materials, the present invention sprays liquid metal mesh on the surface of metallized polyurethane fiber membrane. By utilizing the low infrared emissivity and high conductivity of liquid metal, the integrated construction of thermal insulation gradient structure and electromagnetic impedance gradient structure is realized, thereby enabling the film to exhibit higher electromagnetic shielding efficiency and infrared stealth effect in a thinner case.

[0048] (4) This invention utilizes the resonant structure of liquid metal mesh to effectively achieve high absorption of electromagnetic waves, and effectively achieves its SE from ~24 to ~14dB by stretching the polyurethane fiber membrane, realizing rapid switching from EM wave shielding (i.e., open state) to EM wave transmission (i.e., closed state).

[0049] (5) The preparation process of this invention is simple and easy to operate, and it is expected to be applied to fields such as aerospace, military equipment, microelectronic devices, and civilian appliances that require electromagnetic shielding. Attached Figure Description

[0050] Figure 1 The images show the physical images of polyurethane fiber membrane material (TPU), metallized polyurethane fiber membrane material (Ni@TPU), and lightweight flexible high-absorption electromagnetic shielding and infrared stealth fiber composite material (LM / Ni@TPU) in Embodiment 1 of the present invention; (a) polyurethane fiber membrane; (b) metallized polyurethane fiber membrane; (c) lightweight flexible high-absorption electromagnetic shielding and infrared stealth fiber composite material.

[0051] Figure 2 Scanning electron microscope images of the polyurethane fiber membrane material and the metallized polyurethane fiber membrane material before and after stretching in Embodiment 1 of the present invention; (a) polyurethane fiber membrane material; (b) metallized polyurethane fiber membrane material before stretching; (c) metallized polyurethane fiber membrane material after stretching.

[0052] Figure 3 The following are data graphs showing the electromagnetic shielding effectiveness and power coefficient of materials with different thicknesses in Embodiment 2 of the present invention: (a) Electromagnetic shielding effectiveness; (b) Power coefficient;

[0053] Figure 4 The following are data graphs showing the electromagnetic shielding effectiveness and power coefficient of the materials formed after different tensile cycles in Embodiment 3 of the present invention: (a) Electromagnetic shielding effectiveness; (b) Power coefficient;

[0054] Figure 5 Electromagnetic shielding effectiveness and power coefficient data of LM / Ni@TPU prepared with liquid metal meshes of different sizes in Example 4 of the present invention; (a) Electromagnetic shielding effectiveness; (b) Power coefficient;

[0055] Figure 6 The following are data graphs showing the electromagnetic shielding effectiveness and power factor of LM / Ni@TPU and LM@TPU in Example 1 and Comparative Example 1: (a) Electromagnetic shielding effectiveness; (b) Power factor.

[0056] Figure 7 The following are graphs showing the electromagnetic shielding effectiveness and power factor of LM / Ni@TPU and Ni@TPU for Example 1 and Comparative Example 2: (a) Electromagnetic shielding effectiveness; (b) Power factor.

[0057] Figure 8 The following are data graphs showing the electromagnetic shielding effectiveness and power coefficient of LM / Ni@TPU with different stretching degrees in Embodiment 1 and Comparative Example 3 of the present invention; (a) Electromagnetic shielding effectiveness; (b) Electromagnetic switch;

[0058] Figure 9 Infrared imaging effects of four fiber membrane materials, TPU, LM@TPU, Ni@TPU, and LM / Ni@TPU, on a hot stage at different temperatures: (a) 50℃; (b) 100℃; (c) 150℃. Detailed Implementation

[0059] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0060] Characterization and performance testing:

[0061] 1. Method for determining scanning electron microscopy images: Scanning electron microscopy images of composite fiber membrane materials were taken using a JSM 6490LV field emission electron microscope.

[0062] 2. Electromagnetic shielding effectiveness measurement method: The S-parameters of the composite thin film were measured by waveguide method in the frequency range of 8.2 to 40 GHz using an Agilent E5063A vector network analyzer.

[0063] 3. Methods for determining mechanical properties: The mechanical properties of the composite fiber membrane were determined using a universal UTM2203 tensile testing machine (Sun Technology Co., Ltd.).

[0064] 4. Infrared thermal imaging test: Use an infrared thermal imager (FLUKE Ti400+) to observe the infrared imaging of the composite fiber membrane.

[0065] Example 1

[0066] A method for preparing a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, the method comprising the following steps:

[0067] (1) Preparation of polyurethane fiber membrane

[0068] Preparation of polyurethane spinning solution: Weigh 40g of polyurethane particles and add them to a mixture of 80g of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). Heat and stir at 80℃ in a water bath for 2 hours to fully dissolve the polyurethane spinning solution (solid content 20.0%).

[0069] Preparation of polyurethane fiber membrane: Take 80 mL of the polyurethane spinning solution prepared above and perform electrospinning at a feed speed of 0.1 mL / min, a positive electrode voltage of 16 kV, a negative electrode voltage of 2 kV, and a receiving distance of 60 cm. After the electrospinning is completed, peel the fiber membrane off the receiving roller to obtain the polyurethane fiber membrane TPU.

[0070] (2) Preparation of metallized polyurethane fiber membranes

[0071] Roughening: The polyurethane fiber membrane prepared in step (1) was placed in a Tris solution with pH = 8.5 and sonicated for 2 min to completely wet the polyurethane fiber membrane. Then, 1 g of dopamine was added and stirred continuously under magnetic stirring for 24 h. After the end, the polyurethane fiber membrane was washed with ultrapure water 2 to 3 times, sonicated for 1 min, washed once with anhydrous ethanol, and finally placed in a vacuum oven at 50 ℃ for vacuum drying for 2 h to obtain the roughened polyurethane fiber membrane.

[0072] Activation: The roughened polyurethane fiber membrane was placed in 150 mL of 0.5 g / L chloroplatinic acid solution and continuously stirred magnetically for 0.5 h. After washing thoroughly with ultrapure water and anhydrous ethanol, it was placed in a vacuum oven at 50 °C and vacuum dried for 2 h to obtain the activated polyurethane fiber membrane.

[0073] Plating: The activated polyurethane fiber membrane was placed in 150 mL of plating solution and plated at 25 °C for 30 min. After plating, it was taken out and thoroughly washed with ultrapure water and anhydrous ethanol. Finally, it was placed in a vacuum oven at 50 °C and vacuum dried for 2 h to obtain the metallized polyurethane fiber membrane, named Ni@TPU.

[0074] The plating solution contains nickel sulfate hexahydrate at a concentration of 80 g / L, sodium citrate dihydrate at a concentration of 40 g / L, lactic acid at a concentration of 20 g / L, and dimethylamine borane at a concentration of 10 g / L.

[0075] (3) Preparation of lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite materials

[0076] The polyurethane fiber membrane after metallization in step (2) was stretched for 2000 cycles at 100% elongation. Then, a liquid metal (gallium indium alloy) mesh with a side length of 1.25 mm was sprayed onto one side of the membrane with an airbrush and the amount of spraying was 0.4 mL. This yielded a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, named LM / Ni@TPU.

[0077] Example 2

[0078] The polyurethane spinning solution in step (1) of Example 1 was adjusted to 50 ml and 110 ml respectively; other parameters and conditions were the same as in Example 1.

[0079] Example 3

[0080] The elongation at tensile failure in step (3) of Example 1 was adjusted to 50% and 150% respectively; other parameters and conditions were the same as in Example 1.

[0081] Example 4

[0082] In step (3) of Example 1, the side lengths of the liquid metal mesh were adjusted to 1 mm and 1.5 mm respectively, while other parameters and conditions were the same as in Example 1.

[0083] Comparative Example 1

[0084] A method for preparing a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, the method comprising the following steps:

[0085] (1) Preparation of polyurethane fiber membrane

[0086] Preparation of polyurethane spinning solution: Weigh 40g of polyurethane particles and add them to a mixture of 80g of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). Heat and stir in a water bath for 2 hours to fully dissolve the polyurethane spinning solution (solid content of 20.0%).

[0087] Preparation of polyurethane fiber membrane: Take 80 mL of polyurethane spinning solution and electrospin at a feed rate of 0.1 mL / min, a positive electrode voltage of 16 kV, a negative electrode voltage of 2 kV, and a receiving distance of 80 cm. After the electrospinning is completed, peel the fiber membrane off the receiving roller to obtain the polyurethane fiber membrane TPU.

[0088] (2) Preparation of polyurethane / liquid metal mesh composite fiber membrane

[0089] A liquid metal mesh with a side length of 1.25 mm was sprayed onto one side of the polyurethane fiber membrane prepared in step (1) using an airbrush, with a spraying amount of 0.4 mL; thus, a polyurethane / liquid metal mesh composite fiber material was obtained, named LM@TPU.

[0090] Comparative Example 2

[0091] The only difference from Example 1 is that the polyurethane fiber membrane after metallization in step (3) is not stretched, but liquid metal mesh is directly sprayed on the same side. All other parameters and conditions are the same as in Example 1.

[0092] Test Analysis

[0093] 1. Morphology determination of polyurethane composite fiber membrane material

[0094] Figure 1 These are physical images of the polyurethane fiber membrane material (TPU), the metallized polyurethane fiber membrane material (Ni@TPU), and the lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material (LM / Ni@TPU) used in Example 1. Figure 1 (a) is a photograph of a real TPU product. Figure 1 (b) For Ni@TPU, Figure 1 (c) is a photograph of the actual LM / Ni@TPU.

[0095] from Figure 1 As can be seen, the polyurethane fiber membrane obtained by electrospinning has a very smooth surface and good macroscopic uniformity. The polyurethane fiber membrane after chemical nickel plating shows excellent uniformity on a macroscopic scale. The polyurethane fiber membrane after being coated with liquid metal mesh has a clear metallic mesh luster as shown in the figure.

[0096] 2. Structural Characterization of Polyurethane Composite Fiber Membrane Materials

[0097] Figure 2 Scanning electron microscope images of polyurethane fiber membrane materials and metallized polyurethane fiber membrane materials before and after tensile failure. Figure 2 (a) and Figure 2 (b, c) are scanning electron microscope images of TPU fibers and Ni@TPU fibers in Example 1, respectively.

[0098] from Figure 2 As can be seen, the TPU fiber diameter is 1.5-2μm; after electroless nickel plating, the Ni@TPU fiber shows obvious changes, with an increase in diameter. At the same time, the metal coating is successfully coated on the TPU fiber and exhibits good uniformity; after 2000 stretching cycles, the metal coating successfully breaks.

[0099] 3. The effect of different polyurethane fiber membrane thicknesses on electromagnetic shielding effectiveness and power coefficient

[0100] The effects of different thicknesses on electromagnetic shielding effectiveness and power coefficient in Example 2 are shown in the following results. Figure 3As shown in the figure: the data shows that as the thickness of the fiber membrane increases, the electromagnetic shielding effectiveness (SE) decreases. T As the thickness of the LM / Ni@TPU film gradually decreases from 0.5 mm to 1.2 mm (TPU spinning solution content from 50 ml to 110 ml), the electromagnetic interference (EMI) shielding effectiveness decreases from 32.2 dB to 28.5 dB. This indicates that the thicker the film, the more interaction there is between the electromagnetic wave (EMW) and the inner wall of the film, the longer the EMW loss path, and the stronger the film's absorption capacity for electromagnetic waves.

[0101] 4. The effect of different tensile failure degrees on electromagnetic shielding effectiveness and power coefficient

[0102] The effects of different tensile failure degrees on electromagnetic shielding effectiveness and power coefficient in Example 3 are shown in the following results. Figure 4 As shown in the figure, the EMI shielding effectiveness of LM / Ni@TPU decreases from 34.6dB to 24.9dB as the tensile strength increases from 50% to 150%. The greater the stretching of the Ni@TPU, the more the conductive network formed by the nickel layer breaks down, leading to increased SE (Self-Shielding) performance. T The impedance is reduced, allowing more electromagnetic waves to pass through the Ni@TPU dissipation layer and achieve impedance matching.

[0103] 5. The effect of different liquid metal mesh sizes on electromagnetic shielding effectiveness and power coefficient

[0104] The effects of different liquid metal mesh sizes on electromagnetic shielding effectiveness and power coefficient in Example 4 are shown in the following results. Figure 5 As shown in the figure, the electromagnetic shielding effectiveness gradually decreases while the absorption coefficient gradually increases with the increase of the liquid metal mesh size. The 1.5mm mesh film exhibits good absorption in the 5G high-frequency band, but its shielding effectiveness is poor, failing to reach 20dB. The 1mm mesh film has good shielding effectiveness, but its absorption of electromagnetic waves in the 5G band is poor, with electromagnetic wave dissipation mainly occurring through surface reflection. The 1.25mm mesh LM / Ni@TPU film achieves a shielding effect of over 25dB in the 5G band and a high absorption rate of over 60%.

[0105] 6. Determination of the electromagnetic shielding effectiveness of polyurethane / liquid metal mesh composite fiber membrane

[0106] Figure 6 The figures (a) and (b) show the electromagnetic shielding effectiveness and power coefficient of the composite fiber membranes without metallization treatment in Example 1 and Comparative Example 1.

[0107] Figure 7 The electromagnetic shielding effectiveness (a) and power coefficient (b) of the composite fiber membranes without tensile damage treatment in Example 1 and Comparative Example 2 are shown.

[0108] In terms of electromagnetic shielding effectiveness, the LM / Ni@TPU-1 fiber membrane prepared in Example 1 exhibits excellent impedance matching in the Ni@TPU dissipation layer obtained after stretching and breaking. This significantly reduces the attenuation of electromagnetic waves reflected at the air-film interface, allowing most electromagnetic waves to penetrate the membrane. Furthermore, the liquid metal mesh on the surface forms a continuous conductive network, with electrons primarily transported within this mesh. The extremely high conductivity of the liquid metal causes a large number of incident electromagnetic waves to be reflected back into the Ni@TPU for further electromagnetic dissipation, achieving a "introduction-absorption-reflection-reabsorption" effect. Ultimately, this results in an excellent electromagnetic absorption coefficient (>0.5) for the LM / Ni@TPU composite fiber, thus achieving a high-absorption electromagnetic shielding effect. In contrast, the LM@TPU fiber membrane without metallization treatment lacks an electromagnetic dissipation layer, resulting in poor shielding performance for electromagnetic waves (SE). T <20dB), unable to achieve a shielding effect. Ni@TPU fiber membranes obtained without tensile stress treatment, with liquid metal mesh sprayed on the same side, suffer from high impedance and poor matching, causing electromagnetic waves to be reflected before entering the shielding material, resulting in a low electromagnetic wave absorption coefficient (A). Figure 7 As shown in Figure b, the metallized film in Comparative Example 2 was not subjected to stretching and breaking treatment. The conductivity of the nickel layer was too high, and the absorption coefficient of the resulting LM / Ni@TPU-2 was not higher than 0.1. 90% of its electromagnetic waves were basically reflected.

[0109] 7. Performance testing of electromagnetic switches using lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite materials.

[0110] The electromagnetic shielding effectiveness of the composite fiber membrane LM / Ni@TPU prepared in Example 1 was tested by stretching it to different degrees (0%, 20%, 40%, 60%), and the changes in its electromagnetic shielding effectiveness were observed. The results are as follows... Figure 8 As shown, electromagnetic shielding effectiveness data diagram (a) and electromagnetic switch data diagram (b) are presented;

[0111] from Figure 8 Data shows that, with stretching from 0% to 60%, the fiber membrane exhibits high EMI shielding effectiveness (SE) in the initial unstretched stage at the 5G frequency point (40GHz). T =24.6dB), putting the EMI shielding switch in the "ON" state; as the elongation increases, the metal mesh gradually becomes larger, the film gradually becomes thinner, SE T Gradually decrease; when the elongation reaches 60% SE TThe EMI shielding level is reduced to 14dB, which is considered "OFF" according to the application standards for commercial EMI shielding materials. Furthermore, even with tensile deformation from 0% to 60%, the LM / Ni@TPU film maintains high absorption of electromagnetic waves, with absorption coefficients consistently exceeding 0.5.

[0112] 8. Determination of the infrared stealth performance of lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite materials

[0113] The LM / Ni@TPU prepared in Example 1 was placed on a high-temperature hot stage at 50°C, 100°C, and 150°C for infrared stealth performance testing; the results are as follows. Figure 9 As shown in the figure, the infrared imaging temperature of the LM / Ni@TPU surface is much lower than that of the hot stage, and the infrared imaging color is similar to the background color (blue), demonstrating excellent high-temperature infrared stealth performance.

[0114] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material, characterized in that, The method includes the following steps: (1) Preparation of polyurethane fiber membrane Thermoplastic polyurethane particles are dissolved in an organic solvent and subjected to hydrothermal stirring reaction. After thorough stirring, a polyurethane spinning solution is obtained. The obtained spinning solution is processed by electrospinning to obtain polyurethane fiber membrane material. (2) Preparation of metallized polyurethane fiber membranes The polyurethane fiber membrane obtained in step (1) is first roughened in a roughening solution; then the roughened polyurethane fiber membrane is immersed in an activation solution; finally, the activated polyurethane fiber membrane is immersed in a plating solution for plating, cleaned, and dried to obtain a metallized polyurethane fiber membrane material; the solute in the activation solution is chloroplatinic acid, the concentration is 0.1-20 g / L, and the activation treatment time is 30 min-120 min; the plating treatment time is 10-60 min, and the temperature is 10-30℃. (3) Surface spraying treatment The metallized polyurethane fiber membrane material prepared in step (2) is subjected to 1000 to 2000 stretching cycles; then a liquid metal mesh is sprayed onto one side of the surface to obtain a lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material; the degree of damage from the stretching cycles is 50% to 200%; the content of the sprayed liquid metal is 0.1 to 0.5 ml; and the side length of the metal mesh is 1 to 5 mm.

2. The method according to claim 1, characterized in that, The organic solvent in step (1) is one or both of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).

3. The method according to claim 1, characterized in that, The solid content of the polyurethane spinning solution in step (1) is 10-30%.

4. The method according to claim 1, characterized in that, The electrospinning process parameters in step (1) are as follows: positive electrode voltage is 10-20kV; negative electrode voltage is 1-5kV; feed speed is 0.1-0.2mL / min; and the distance between the needle and the receiver is 10-30cm.

5. The method according to claim 1, characterized in that, The plating solution in step (2) includes metal salts, complexing agents, reducing agents, and pH adjusters.

6. The method according to claim 1, characterized in that, The liquid metal spraying content in step (3) is 0.1-0.5 ml, and the side length of the liquid metal mesh is 1-2 mm.

7. The method according to claim 1, characterized in that, The degree of damage from the tensile cycle in step (3) is 100%; the side length of the metal mesh is 1.25 mm.

8. The lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material prepared by the method according to any one of claims 1 to 7.

9. The lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material according to claim 8, characterized in that, The thickness of the lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material is 0.5 mm to 1.2 mm.

10. The application of the lightweight, flexible, high-absorption electromagnetic shielding and infrared stealth fiber composite material as described in claim 8 or 9 in the fields of electromagnetic protection for aerospace devices, electronic instruments, or military defense.

Images