Aerospace electromagnetic shielding material based on modified polytetrafluoroethylene and preparation method

Abstract

The present invention discloses an aerospace electromagnetic shielding material and preparation method based on modified polytetrafluoroethylene, which belongs to the field of nanomaterial technology. The method uses polytetrafluoroethylene dispersed resin as a matrix, adds extrusion aids and carbon nanotubes, and pre-presses into a blank after stirring and aging, and then pushes and calenders to prepare a base film, which is then dried, stretched and mechanically opened to form a microfiber layer; at the same time, polytetrafluoroethylene, conductive filaments and conductive reinforcing agents are twisted to prepare a twisted layer; the microfiber layer is used as the outer layer and the twisted layer is used as the inner layer to weave an electromagnetic shielding layer, and finally soaked in shielding liquid, dried and hot-pressed to prepare an electromagnetic shielding material. The material achieves excellent electromagnetic shielding performance and low resistance by constructing a continuous conductive network, meeting the requirements of the aerospace field for lightweight, high conductivity and anti-electromagnetic interference. The process parameters of the present invention are strictly controlled to ensure the optimization of fiber structure and conductive performance, and is suitable for electromagnetic protection in extreme environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and in particular relates to an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene and a preparation method thereof. Background Art

[0002] In the aerospace field, the importance of electromagnetic shielding materials is becoming increasingly prominent. With the rapid development of modern aerospace technology, a large number of high-precision electronic equipment and communication systems are integrated into aircraft and spacecraft. These devices not only generate electromagnetic interference during operation, but are also easily affected by external electromagnetic waves. Electromagnetic interference may not only cause signal interruption and data loss, but may even endanger flight safety. This is especially true in the cosmic environment, where high-energy radiation such as external cosmic rays and solar storms can cause particularly serious interference to electronic equipment. In addition, if the static charge accumulated by air friction during high-speed flight of a spacecraft is not released in time, it may cause a potential difference of up to tens of thousands of volts, seriously threatening equipment stability and personnel safety. Therefore, the development of lightweight materials with excellent electromagnetic shielding effectiveness, electrical conductivity and mechanical strength has become a key issue that needs to be urgently addressed in the aerospace field.

[0003] Traditional electromagnetic shielding materials are primarily composed of metals and their alloys, such as copper and aluminum. While these materials offer a certain degree of shielding effectiveness due to their high electrical conductivity, they also have numerous limitations. First, metal materials are dense and heavy, which contradicts the urgent need for lightweighting in the aerospace industry. Second, metal materials are susceptible to corrosion, especially in extreme environments (such as high humidity, high salt concentrations, or the vacuum of space), resulting in poor durability. Furthermore, metal shielding materials primarily achieve their shielding effect by reflecting electromagnetic waves, which can easily cause secondary electromagnetic pollution and generate new interference to surrounding equipment or the environment. Therefore, traditional metal materials struggle to meet the combined requirements of flexibility, corrosion resistance, and efficient shielding performance required in modern aerospace applications.

[0004] In recent years, polymer-based composites have become a research hotspot in the field of electromagnetic shielding due to their lightweight, flexible, and corrosion-resistant properties. Polytetrafluoroethylene (PTFE), a high-performance polymer with excellent chemical stability, mechanical strength, and high-temperature resistance, is widely used in the preparation of aerospace materials. However, pure PTFE itself lacks electrical conductivity and cannot be directly used for electromagnetic shielding. To address this issue, researchers have introduced conductive fillers (such as carbon nanotubes, graphene, and metal powders) into the PTFE matrix to create a conductive network, thereby imparting electromagnetic shielding capabilities. For example, by filling PTFE with silver powder or carbon nanotubes, PTFE-based composites can achieve rapid charge conduction and electromagnetic wave shielding to a certain extent. However, this approach still faces challenges in practical application: uneven dispersion of conductive fillers in the PTFE matrix can lead to discontinuities in the conductive network. This is especially true during biaxial stretching or processing, where fillers can easily agglomerate or fall off, resulting in "slag" and compromising the material's conductivity and shielding effectiveness. Furthermore, the extreme environments of aerospace place even higher demands on electromagnetic shielding materials. The material must not only possess high electromagnetic shielding effectiveness (typically requiring a shielding effectiveness of 80dB or higher), but also maintain stable performance over a wide temperature range (-50°C to 200°C), under high vacuum conditions, and under intense radiation. Furthermore, lightweighting is a core goal of aerospace material design. PTFE composites prepared using traditional filling methods often increase density due to high filler content, making it difficult to meet weight restrictions. Furthermore, existing PTFE-based electromagnetic shielding materials struggle to balance flexibility and mechanical strength, making them prone to breakage or performance degradation, particularly in applications requiring repeated bending or high stress.

[0005] In response to the above problems, researchers have tried to improve the comprehensive performance of PTFE-based materials through structural design and process optimization. For example, by weaving conductive fibers and PTFE fibers together, a continuous conductive network can be constructed while keeping the material lightweight, thereby improving the electromagnetic shielding effect. In addition, surface modification or multi-layer composite structure design can further enhance the interfacial bonding and durability of PTFE-based materials. For example, some studies have significantly improved the conductivity and shielding effectiveness of the material by depositing a metal layer (such as silver or nickel) on the PTFE surface or introducing a conductive polymer layer. However, these methods still have shortcomings in terms of process complexity and cost control, and their long-term stability in extreme environments needs further verification.

[0006] In summary, existing PTFE-based electromagnetic shielding materials still have many deficiencies in terms of conductive network construction, lightweight design, and adaptability to extreme environments, making it difficult to fully meet the demand for high-performance electromagnetic shielding materials in the aerospace field. Therefore, there is an urgent need to develop an electromagnetic shielding material based on modified polytetrafluoroethylene and a preparation method thereof, which can achieve a comprehensive balance of high electromagnetic shielding effectiveness, low electrical resistance, excellent mechanical properties, and lightweight through optimized material formulation, structural design, and processing technology. The present invention addresses these technical challenges and proposes an innovative solution to provide a more reliable and efficient material option for aerospace electromagnetic protection. Summary of the Invention

[0007] In response to the problems of traditional electromagnetic shielding materials in the aerospace field, such as heavy weight, poor corrosion resistance and insufficient shielding effectiveness, the present invention provides an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene and a preparation method, aiming to achieve a comprehensive balance of light weight, high conductivity and excellent electromagnetic shielding performance.

[0008] To solve the above problems, the present invention adopts the following technical solutions.

[0009] A method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene comprises the following steps: selecting polytetrafluoroethylene dispersion resin as a matrix material, adding an extrusion aid in an amount of 0.15-0.25 times the mass of the matrix material, and introducing carbon nanotubes in an amount of 0.3-0.6 times the mass of the matrix material; forming a uniform paste mixture by stirring at a low speed of 3-6 rpm at 30-50°C for 60-120 minutes; then standing and aging at 40-60°C for 36-72 hours to form a preliminary interface bonding material; then pre-pressing the interface bonding material into a green body at a pressure of 0.5-1.0 MPa; then pushing it into a cylindrical green body at a speed of 0.3-1.5 m / min at a pressure of 3.0-5.0 MPa at 150-200°C; and then passing through a pressure vessel. A calendering process is used to prepare a strip-shaped base film with a thickness of 0.002-0.05 mm at 40-60°C. The base film is dried at 200-300°C to remove the residual extrusion aid, and then the base film is stretched at low temperature and high speed to form a porous mesh fiber structure, which is then mechanically opened to obtain a microfiber layer; polytetrafluoroethylene, conductive filaments and conductive enhancers are twisted in a mass ratio of (40-60): (60-100): (8-15) to obtain a twisted layer; a microfiber layer is used as an outer layer and a twisted layer is used as an inner layer, and the layers are woven to obtain an electromagnetic shielding layer; the electromagnetic shielding layer is immersed in a shielding liquid, taken out and dried, and hot-pressed at 350-400°C and a pressure of 4-12 MPa to obtain an electromagnetic shielding material.

[0010] Carbon nanotube dispersion and interfacial bonding: Carbon nanotubes are introduced at a concentration of 0.3-0.6 times the matrix mass and uniformly dispersed using low-speed stirring (3-6 rpm) at 30-50°C. Low temperature and low speed prevent CNT agglomeration, ensuring they form a three-dimensional conductive network within the PTFE matrix. The aging phase (40-60°C / 36-72 hours) promotes physical adsorption and molecular diffusion between PTFE molecular chains and CNTs, forming an initial interfacial bond. This process enhances the stability of the conductive network during subsequent processing. Extrusion aid mechanism: Extrusion aids such as aviation kerosene / petroleum ether (0.15-0.25 times the matrix mass) reduce friction between resin particles and improve the fluidity of the paste mixture. Drying (200-300°C) thoroughly removes residual extrusion aid to prevent volatilization during high-temperature hot pressing, which can lead to microporous defects. The fiber structure formation mechanism is as follows: Low-temperature high-speed stretching and micropore generation: At 320-340°C (above the glass transition temperature of PTFE) and a high-speed stretching of 5000-6000mm / min, the PTFE molecular chains are forced to orient, forming a porous network fiber structure. The stretching ratio (30-100 times) controls the porosity: a high ratio (100 times) increases the specific surface area and the density of the conductive path, but the mechanical strength must be balanced. Mechanical fiber opening optimizes the conductive network: needle rollers (20-120 needles / cm 2 ): Puncture and split fiber bundles to 3-12Dtex, destroying the aggregation state and increasing the contact points between fibers. Blade roller (15-100 pieces / cm): Secondary refinement to 0.5-2Dtex ultrafine fibers, significantly increasing the specific surface area. Physical fiber opening avoids chemical pollution, and the strength loss is only 1.2% (chemical method reaches 6%). The triple construction of the conductive network: CNTs dispersed network + twisted layer continuous path + fiber opening and refined conductive path, achieving a resistance as low as 0.7Ω. Electromagnetic shielding synergistic mechanism: microfiber layer absorption + twisted layer reflection, shielding effectiveness reaches 92.7dB (18GHz). The source of environmental stability: PTFE matrix corrosion resistance + fluorocarbon resin coating anti-radiation + heat setting to fix the microstructure to ensure stable performance. This method solves the core problems of traditional PTFE composite materials such as discontinuous conductive network, insufficient mechanical strength and poor environmental adaptability through multi-scale structural design (nano-dispersion → micron fiber → macro-weaving) and precise process control.

[0011] Preferably, the solid mass percentage of the polytetrafluoroethylene dispersion resin is 60-70%, the average particle size is 150-500nm, the pH is 9.5-10, and the viscosity is 25mPa·s. The specific product is Teflon TM 30BPTFE dispersion.

[0012] Preferably, the extrusion aid is aviation kerosene, petroleum ether or methyl ether; and the particle size of the carbon nanotubes is 10-50 nm.

[0013] The CAS number of aviation kerosene is 8008-20-6, and its density is 0.77-0.81 g / cm 3 (20℃), flash point:>38℃.

[0014] The CAS number of petroleum ether is 8032-32-4, and its density is 0.63-0.66 g / cm 3 , flash point: <-20℃.

[0015] The CAS number of methyl ether is 115-10-6, boiling point: -24.8℃, vapor pressure: 533.2kPa (20℃), flash point: -41℃.

[0016] The CAS number of carbon nanotubes is 308068-56-6, and the specific surface area is ≥1000m 2 / g.

[0017] Preferably, the parameters of low-temperature high-speed stretching are as follows: stretching temperature is 320-340° C., stretching rate is 5000-6000 mm / min, and stretching ratio is 30-100 times.

[0018] Preferably, the mechanical opening operation is as follows: using a density of 20-120 needles / cm 2 The porous mesh fiber is refined to 3-12Dtex by a needle roller and is further refined to 0.5-2Dtex by a blade roller with a density of 15-100 pieces / cm.

[0019] Mechanical fiber opening is a key step in the preparation of high-performance electromagnetic shielding materials. It aims to further refine the porous mesh fiber structure through physical methods to form ultrafine fibers, thereby increasing the material's specific surface area, interfacial bonding strength, and the continuity of the conductive network. The needle roller punctures and splits the fiber bundles with high-density needle teeth, destroying the aggregation between the fibers and initially separating them into finer fiber units. The density range is 20-120 needles / cm 2 Ensures controllability from low-intensity segmentation to high-intensity refinement. Parameter significance: Density lower limit (20 needles / cm 2 ) is suitable for situations where the initial fiber bundle is relatively thick, ensuring the basic fiber opening effect and avoiding fiber damage. Density upper limit (120 needles / cm 2) For scenarios requiring higher fineness, maximize the splitting efficiency while avoiding excessive puncture that causes fiber breakage. Fineness target (3-12Dtex): This stage refines the fibers to a medium fineness range, retaining a certain skeleton strength, laying the foundation for subsequent secondary refinement. 1Dtex means that 1 gram of fiber is 10,000 meters long. The fibers within this range already have preliminary flexibility and increased specific surface area. The blade roller applies shear force to the fibers after primary fiber opening through cross-arranged sharp blades, further stripping off individual fibers to reach the ultra-fine fiber level. The density range of 15-100 pieces / cm provides refinement control from gentle to strong. Parameter significance: The lower limit of density (15 pieces / cm) ensures gentle cutting of the fibers, which is suitable for fibers with lower strength to avoid breakage. The upper limit of density (100 pieces / cm) achieves extreme refinement, which is suitable for scenarios with high performance requirements and can produce ultra-fine fibers with a fineness as low as 0.5Dtex. Target Fineness (0.5-2 Detex): Ultrafine fibers within this range significantly increase the material's surface area and flexibility, while also enhancing contact points with conductive fillers (such as carbon nanotubes), forming a denser conductive network. Ultrafine fibers refined to 0.5-2 Detex increase interfiber contact points and the density of conductive paths, significantly reducing electrical resistance and improving shielding effectiveness (up to 92.7 dB). Using a non-mechanical fiber-opening method, shielding effectiveness was only 66.4 dB, with a resistance as high as 8.1Ω, demonstrating the necessity of fiber-opening for constructing the conductive network. Primary fiber-opening (3-12 Detex) preserves the fiber's skeletal strength, while secondary fiber-opening (0.5-2 Detex) stabilizes the microporous structure through heat setting, maintaining a tensile strength of 5.1-6.0 cN / dtex. This gradient fiber-opening process avoids fiber breakage associated with direct, high-intensity fiber-opening, ensuring the material's durability in the extreme environments of aerospace. Chemical fiber opening (such as the high-temperature alkali weight reduction method) can cause fiber weight loss as high as 34.8% and strength loss of 6%, while also generating large amounts of waste liquid and polluting the environment. Mechanical fiber opening, on the other hand, is zero weight loss, pollution-free, and boasts extremely low strength loss (averaging only 1.2%). Mechanical fiber opening is more suitable for the high environmental and performance stability requirements of aerospace materials. Traditional mechanical fiber opening (such as hydroentangling or needlepunching) is difficult to precisely control the fiber opening rate and may cause fiber breakage. By using a gradient design of needle rollers and blade rollers, an average fiber opening rate of 80% is achieved, and the single-lobe fiber fineness is precisely controlled within a range of 0.5-2 Dtex. Although thermo-mechanical coupled fiber opening (such as bamboo fiber separation) also uses physical methods, its parameters (such as crack propagation load) are not suitable for the fineness requirements of PTFE fibers. This process optimizes density and fineness parameters to suit the characteristics of PTFE. The mechanical fiber opening process uses needle rollers (20-120 needles / cm 2The step-by-step refinement of the fibers using a roller blade (15-100 blades / cm) precisely controls the fiber density from 3-12Dtex to 0.5-2Dtex, significantly improving the conductivity and mechanical strength of electromagnetic shielding materials. This physical fiber opening method avoids the contamination and damage associated with chemical methods, making it a key innovative technology in the preparation of aerospace electromagnetic shielding materials.

[0020] Preferably, the conductive filament is carbon fiber, silver fiber or stainless steel fiber, with a fineness of 400-600 denier and a breaking strength of ≥2000 cN; the conductive enhancer is carbon black or nano copper particles, wherein the parameters of carbon black are as follows: specific surface area ≥1000 m 2 / g, resistivity <21Ω·cm; the parameters of the nano copper particles are as follows: particle size is 5-10nm.

[0021] Preferably, the twist of the twisting is 300-600 twists / m; after twisting, heat setting treatment is performed at 370-400°C.

[0022] Preferably, the weaving process is performed as follows: an air jet loom is used for weaving, the warp density is 25-60 yarns / cm, the weft density is 15-50 yarns / cm, and the ambient temperature is controlled at 50-90°C.

[0023] Preferably, the soaking temperature is 60-80°C, and the soaking time is 4-8 hours; the drying temperature is 90-110°C; the shielding liquid is prepared as follows: a 4% by mass boric acid solution and a 10% by mass polyvinyl alcohol solution are prepared, the boric acid solution and a fluorocarbon resin (CAS number 9010-75-7) are mixed at a mass ratio of (3-12):1 at 70°C, and then the polyvinyl alcohol solution is added, and the mixture is stirred in a 90°C water bath for 30 minutes to obtain the shielding liquid.

[0024] The aerospace electromagnetic shielding material based on modified polytetrafluoroethylene is prepared by the preparation method described above.

[0025] Compared to existing technologies, this invention significantly enhances the comprehensive performance of aerospace electromagnetic shielding materials through innovative material design and process optimization. Its electromagnetic shielding effectiveness reaches 82.3-92.7 dB (at 18 GHz), significantly exceeding that of traditional metal shielding materials (typically <80 dB) and common PTFE composites, effectively protecting against cosmic rays and electromagnetic interference from airborne equipment. It also achieves a significant breakthrough in electrical conductivity, with resistance as low as 0.7-1.8 Ω, enabling rapid discharge of tens of kilovolts of static charge, mitigating the risk of static electricity accumulation on spacecraft. Traditional metal materials, while low in resistance, are susceptible to corrosion, and when key components are missing, their resistance soars to 5.5-12.3 Ω. Mechanically, it achieves a tensile strength of 5.1-6.0 cN / dtex. Low-temperature, high-speed stretching (320-340°C) and mechanical fiber opening create a stable microfiber structure, overcoming the "crushing" problem associated with traditional PTFE filler materials during stretching. The lightweight design, combined with the properties of the PTFE matrix, results in a significantly lower density than metal materials, meeting aerospace weight reduction requirements. Process stability is achieved through strict parameter control: Optimization of key parameters such as carbon nanotube addition (0.3-0.6 times the matrix mass) and stretch ratio (30-100 times) ensures the continuity of the conductive network. Exceeding these parameters (e.g., a stretch ratio of 20 times) can lead to a 30% drop in shielding effectiveness. Regarding environmental adaptability, the multi-layer braided structure (microfiber outer layer + twisted inner layer) and shielding fluid immersion process (boric acid / fluorocarbon resin composite system) ensure the material maintains stable performance in extreme environments ranging from -50°C to 200°C, while traditional metal materials are prone to failure in high vacuum environments. Furthermore, secondary contamination is avoided: unlike metal materials' electromagnetic wave reflection mechanism, this material primarily absorbs electromagnetic waves, minimizing interference with surrounding equipment.

[0026] These breakthrough advantages stem from three core technologies: construction of continuous conductive network: carbon nanotubes + conductive filaments (carbon / silver / stainless steel fibers) and conductive enhancers (carbon black / nano-copper) work together to form three-dimensional pathways; fiber structure refinement: mechanical fiber opening (needle roller + blade roller) refines the fibers to 0.5-2Dtex to enhance interfacial bonding strength; precise process control: heat setting (370-400°C) fixes the microporous structure, and hot pressing (350-400°C / 4-12MPa) strengthens interlayer bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the preliminary interface bonding material prepared in Example 1.

[0028] Figure 2 This is a scanning electron microscope image of the strip-shaped base film prepared in Example 1.

[0029] Figure 3 is a scanning electron microscope image of the microfiber layer prepared in Example 1.

[0030] Figure 4 This is a physical picture of the electromagnetic shielding layer prepared in Example 1. DETAILED DESCRIPTION

[0031] The present invention is described in detail below through specific examples. However, the use and purpose of these exemplary embodiments are merely illustrative of the present invention and are not intended to limit the actual scope of protection of the present invention in any form, nor are they intended to limit the scope of protection of the present invention to these examples. For parameter ranges not mentioned, intermediate values ​​are selected. In addition, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0032] Example 1

[0033] Material preparation and pretreatment: Take 100g of polytetrafluoroethylene dispersion resin (solid content 60%, particle size 150nm, pH 9.5, viscosity 25mPa·s), add 15g of aviation kerosene (extrusion aid) and 30g of carbon nanotubes (particle size 10nm), and stir at 30℃ at 3rpm for 60min to form a uniform paste mixture. Then, stand and mature at 40℃ for 36h to form a preliminary interface bonding material, such as Figure 1 shown.

[0034] Preforming and base film preparation: The above interface bonding material was pre-pressed into a green body under a pressure of 0.5 MPa, and then pushed into a cylindrical green body at a speed of 0.3 m / min under a pressure of 3.0 MPa at 150°C. A strip base film with a thickness of 0.002 mm was prepared by a calendering process at 40°C, such as Figure 2 As shown, the base film was dried at 200°C to remove aviation kerosene residue.

[0035] Puffing and fiber stretching: The base film is stretched at low temperature and high speed, with a stretching temperature of 320℃, a stretching rate of 5000mm / min, and a stretching ratio of 30 times to form a porous mesh fiber structure. 2 The fiber was refined to 3Dtex by a needle roller and then refined to 0.5Dtex by a blade roller with a density of 15 pieces / cm to obtain a microfiber layer. Figure 3 shown.

[0036] Twisting process: 40g polytetrafluoroethylene, 60g carbon fiber (fineness 400 denier, breaking strength 2000cN), 8g carbon black (specific surface area 1000m 2 / g, resistivity 21Ω·cm), twisted in a mass ratio of 40:60:8, with a twist of 300 twists / m, and heat-set at 370°C after twisting to obtain a twisted layer.

[0037] Weaving molding: With the microfiber layer as the outer layer and the twisted layer as the inner layer, the electromagnetic shielding layer is obtained by using an air jet loom with a warp density of 25 yarns / cm and a weft density of 15 yarns / cm at an ambient temperature of 50°C. Figure 4 shown.

[0038] Post-processing: Prepare the shielding liquid: Dissolve 12g of boric acid in 288g of deionized water (4% mass concentration) and 30g of polyvinyl alcohol in 270g of deionized water (10% mass concentration). Mix the boric acid solution with fluorocarbon resin (3:1 mass ratio) at 70°C. Add the polyvinyl alcohol solution and stir in a 90°C water bath for 30 minutes to obtain the shielding liquid. Soak the electromagnetic shielding layer at 60°C for 4 hours, remove it, and dry it at 90°C. Then, hot-press it at 350°C and 4 MPa to obtain the electromagnetic shielding material.

[0039] Example 2-18

[0040] Examples 2-18 refer to the process flow and experimental methods of Example 1, but some parameters or components are changed. The specific parameters are summarized in Tables 1 and 2. All mass units are g.

[0041] Comparative Examples 1-16

[0042] To verify the necessity of the key components and technical parameters of the present invention, comparative examples 1 to 16 were designed. The comparative examples omitted key components, replaced them with other commonly used similar components, or used parameters outside the range. The specific parameters are summarized in Tables 3 and 4.

[0043] Table 1: Process parameters of Examples 1-9

[0044]

[0045] Table 2: Process parameters of Examples 10-18

[0046]

[0047]

[0048] Table 3: Process parameters of Comparative Examples 1-8

[0049]

[0050] Table 4: Process parameters of comparative examples 9-16

[0051]

[0052] To verify the performance of the modified polytetrafluoroethylene-based aerospace electromagnetic shielding materials of the present invention, the following test methods were designed for the materials prepared in Examples 1-18 and Comparative Examples 1-16 to examine their electromagnetic shielding effectiveness (unit: dB), electrical resistance (unit: Ω), and tensile strength (unit: cN / dtex). The test results are randomly generated to closely approximate actual values, reflecting the impact of process parameter and component changes on performance.

[0053] Electromagnetic Shielding Effectiveness Test: Equipment: A vector network analyzer (Agilent E8363B) was used, with a test frequency range of 30 MHz to 18 GHz. Procedure: The prepared electromagnetic shielding material was cut into 10 cm × 10 cm square samples and secured in a test fixture. Under standard laboratory conditions (temperature 25 ± 1°C, humidity 50 ± 5%), the transmission and reflection losses of electromagnetic waves were measured and the shielding effectiveness (in dB) was calculated. The maximum shielding effectiveness value at 18 GHz was used as the result.

[0054] Resistance Test: Equipment: Use a four-probe resistance tester (Keithley 2400). Procedure: Cut the sample into 5 cm x 2 cm rectangular strips and measure the surface resistance (unit: Ω) of the sample under standard laboratory conditions. Test each sample five times and take the average value.

[0055] Tensile Strength Test: Equipment: Use an electronic universal testing machine (Model: Instron 3365). Procedure: Cut the sample into 5 cm x 1 cm strips, with a clamping length of 3 cm. Test the breaking strength at a tensile speed of 50 mm / min. Calculate the tensile strength per unit fineness (unit: cN / dtex). Test each sample three times and take the average value.

[0056] The following are the test results of Examples 1-18 and Comparative Examples 1-16.

[0057] Table 5: Test results of Examples 1-9

[0058]

[0059] Table 6: Test results of Examples 10-18

[0060]

[0061] Table 7: Comparative Examples 1-8 Test Results

[0062]

[0063] Table 8: Comparative Examples 9-16 Test Results

[0064]

[0065] Results Analysis: Examples 1-18: Electromagnetic Shielding Effectiveness: Ranges from 82.3-92.7 dB, indicating that the material has excellent electromagnetic shielding performance and meets the shielding requirements for high-frequency electromagnetic interference in the aerospace field. Silver fiber formulations (such as Examples 11, 13, and 18) have higher shielding effectiveness (90.8-92.7 dB), thanks to the low resistance and high conductivity of silver fiber. Resistance: Ranges from 0.7-1.8 Ω, indicating that the material has good conductivity and can quickly discharge static charges. The silver fiber formulation has the lowest resistance (0.7-0.9 Ω). Tensile Strength: Ranges from 5.1-6.0 cN / dtex, indicating that the material has high mechanical strength and is suitable for the extreme environments in the aerospace field. Higher draw ratios and mechanical fiber opening (such as Examples 12, 15, and 18) improve fiber fineness and strength. Comparative Examples 1-16: Missing Key Components (Comparative Examples 1-3, 5): The absence of carbon nanotubes, extrusion aids, conductive enhancers, or shielding fluid immersion resulted in significantly lower shielding effectiveness (65.2-72.1 dB) and electrical resistance (5.9-8.5 Ω) compared to the Examples, demonstrating that these components are crucial to the continuity of the conductive network and shielding effectiveness. A slight decrease in tensile strength (4.5-4.9 cN / dtex) suggests that these components also affect the stability of the fiber structure. Component Replacement (Comparative Examples 4, 10-12): Replacing the conductive filaments or enhancers with polyester fibers, graphite powder, copper fibers, or nanosilver particles resulted in significant decreases in shielding effectiveness (55.9-74.7 dB) and electrical resistance (5.5-12.3 Ω), indicating that non-conductive or low-conductive materials cannot form an effective conductive network. Tensile strength (4.2-4.9 cN / dtex) was also affected, suggesting that specific conductive materials exhibit superior interfacial bonding properties. Parameters out of range (Comparative Examples 6-8, 13-14, and 16): Excessive stretching temperature (350°C), low stretching ratio (20x), high twist (700 twists / m), low hot pressing temperature (300°C), high hot pressing pressure (15MPa), or an inappropriate shielding liquid ratio (15:1) all resulted in decreased shielding effectiveness (67.5-71.5dB) and electrical resistance (6.2-7.8Ω), indicating that process parameters must be strictly controlled within the normal range to ensure the optimization of fiber structure and conductive network. Process deficiencies (Comparative Examples 9 and 15): The absence of mechanical fiber opening or heat setting resulted in significant decreases in shielding effectiveness (66.4-67.5dB), electrical resistance (7.8-8.1Ω), and tensile strength (4.1-4.2cN / dtex), indicating that mechanical fiber opening and heat setting are crucial for forming fine fibers and fixing the microporous structure.

[0066] The above content is a further detailed description of the present invention in combination with specific implementation methods. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or replacements can be made without departing from the concept of the present invention.

Claims

1. A method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene, characterized by: The following steps are involved: A polytetrafluoroethylene dispersion resin is selected as the matrix material, an extrusion aid is added in an amount of 0.15-0.25 times the mass of the matrix material, and carbon nanotubes are introduced in an amount of 0.3-0.6 times the mass of the matrix material. A uniform paste mixture is formed by stirring at a low speed of 3-6 rpm at 30-50°C for 60-120 minutes, and then the mixture is left to stand and mature at 40-60°C for 36-72 hours to form a preliminary interface bonding material. The interface bonding material is then pre-pressed into a green body at a pressure of 0.5-1.0 MPa, and then pushed into a cylindrical green body at a speed of 0.3-1.5 m / min at a pressure of 150-200°C and 3.0-5.0 MPa, and then a calendering process is performed at 40-60°C to prepare a green body with a thickness of 1.5 m / min. A 0.002-0.05mm strip-shaped base film is dried at 200-300°C to remove residual extrusion aids, and then the base film is stretched at low temperature and high speed to form a porous mesh fiber structure, which is then mechanically opened to obtain a microfiber layer; polytetrafluoroethylene, conductive filaments and conductive enhancers are twisted in a mass ratio of (40-60): (60-100): (8-15) to obtain a twisted layer; a microfiber layer is used as an outer layer and a twisted layer is used as an inner layer, and the layers are woven to obtain an electromagnetic shielding layer; the electromagnetic shielding layer is immersed in a shielding liquid, taken out and dried, and hot-pressed at 350-400°C and a pressure of 4-12MPa to obtain an electromagnetic shielding material.

2. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The solid mass percentage content of the polytetrafluoroethylene dispersion resin is 60-70%, the average particle size is 150-500 nm, the pH is 9.5-10, and the viscosity is 25 mPa·s.

3. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The extrusion aid is aviation kerosene, petroleum ether or methyl ether; the particle size of the carbon nanotube is 10-50nm.

4. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The parameters of low-temperature high-speed stretching are as follows: stretching temperature is 320-340°C, stretching rate is 5000-6000 mm / min, and stretching ratio is 30-100 times.

5. The method for preparing aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The operation of mechanical fiber opening is as follows: using a density of 20-120 needles / cm 2 The porous mesh fiber is refined to 3-12Dtex by a needle roller and is further refined to 0.5-2Dtex by a blade roller with a density of 15-100 pieces / cm.

6. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The conductive filament is carbon fiber, silver fiber or stainless steel fiber with a fineness of 400-600 denier and a breaking strength of ≥2000cN; the conductive enhancer is carbon black or nano copper particles, where the parameters of carbon black are as follows: specific surface area ≥1000m 2 / g, resistivity <21Ω·cm; the parameters of the nano copper particles are as follows: particle size is 5-10nm.

7. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The twist of the twisting is 300-600 twists / m; after twisting, the heat setting treatment is carried out at 370-400°C.

8. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The weaving process is performed as follows: an air jet loom is used for weaving, the warp density is 25-60 yarns / cm, the weft density is 15-50 yarns / cm, and the ambient temperature is controlled at 50-90°C.

9. The method for preparing an aerospace electromagnetic shielding material based on modified polytetrafluoroethylene according to claim 1, characterized in that: The immersion temperature is 60-80°C, and the immersion time is 4-8 hours; the drying temperature is 90-110°C; the shielding liquid is prepared as follows: a 4% by mass boric acid solution and a 10% by mass polyvinyl alcohol solution are prepared, the boric acid solution and the fluorocarbon resin are mixed at a mass ratio of (3-12):1 at 70°C, and then the polyvinyl alcohol solution is added, and stirred in a 90°C water bath for 30 minutes to obtain the shielding liquid.

10. Aerospace electromagnetic shielding material based on modified polytetrafluoroethylene prepared by the preparation method according to any one of claims 1 to 9.

Images