Modified polyimide-based electromagnetic wave shielding material, preparation method thereof and application of modified polyimide-based electromagnetic wave shielding material to aviation cable

Abstract

The invention belongs to the technical field of electromagnetic shielding polymer materials, and particularly relates to a modified polyimide-based electromagnetic wave shielding material, a preparation method thereof and application of the modified polyimide-based electromagnetic wave shielding material to aviation cables. The material comprises polyimide resin, a mesoporous material, reduced graphene, a metal compound, a first filler, a second filler, an auxiliary agent and optional conductive carbon black, and the mass ratio of all the components is controlled within a reasonable interval range. The preparation method sequentially comprises the steps of dispersion, ball milling, spray drying, melt mixing and calendaring molding. The prepared material is suitable for an outer sheath of an aviation cable. By optimizing a filler system and constructing a multi-channel composite structure, multi-phase matching among a polyimide-based material, a conductive filler and a ceramic filler is achieved, and the material has good processing forming performance and structural continuity and is suitable for structural integration in a high-frequency complex electromagnetic environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic shielding polymer materials, and in particular relates to a modified polyimide-based electromagnetic wave shielding material, a preparation method thereof, and application in aviation cables. Background Art

[0002] With the rapid development of modern electronics, communications, and aerospace technologies, the application of various high-frequency and high-speed electronic devices in the aerospace field is becoming increasingly widespread, and the resulting electromagnetic interference (EMI) problem is becoming increasingly serious. Aviation cable systems, operating in complex electromagnetic environments, are particularly susceptible to external interference sources if they lack effective electromagnetic wave shielding. This can lead to signal distortion, data errors, and even equipment failure, seriously compromising aircraft safety and stability.

[0003] Currently, the materials commonly used for shielding aviation cables include metal braids, conductive coatings, and metal foils. However, these traditional shielding materials generally suffer from issues such as heavy weight, poor flexibility, limited heat resistance, and complex processing. These factors make them difficult to meet the performance requirements of aviation cables in extreme application environments, such as high temperature, high-frequency vibration, and lightweight design. Therefore, the development of lightweight non-metallic materials with excellent electromagnetic shielding, mechanical, and heat resistance properties has become a key area of development for aviation cable shielding technology.

[0004] Polyimide (PI) is widely used in high-tech fields such as aerospace and electronic packaging due to its excellent high-temperature resistance, thermal stability, electrical insulation, and mechanical strength. However, unmodified PI materials themselves lack good electromagnetic shielding capabilities. Therefore, how to achieve electromagnetic shielding through structural modification or filler introduction has become a hot topic of research.

[0005] In recent years, researchers have attempted to improve conductivity and shielding performance by introducing conductive fillers (such as carbon nanotubes, graphene, and metal particles) into polyimide matrices or by functionalizing the backbone or side chains through molecular structure design. However, existing technologies still suffer from issues such as poor filler dispersion, insufficient interfacial compatibility, and complex processing. These issues lead to unstable overall shielding effectiveness and a short service life, making it difficult to develop a reliable engineering application system.

[0006] Therefore, there is an urgent need to provide a modified polyimide-based electromagnetic wave shielding material with optimized structure, controllable process, and suitable for complex aviation electromagnetic environments, as well as corresponding preparation methods and practical application technologies in aviation cables, so as to enhance the anti-interference capability and reliability of avionics systems. Summary of the Invention

[0007] In response to the above problems, the purpose of the present invention is to propose: a modified polyimide-based electromagnetic wave shielding material, comprising the following components in parts by mass: 45-50 parts of polyimide resin; 5-10 parts of mesoporous material; 10-15 parts of reduced graphene; 5-15 parts of metal compound; 10-30 parts of first filler; 0.5-5 parts of second filler; and 1-5 parts of additive.

[0008] Furthermore, the mesoporous material includes one or more of mesoporous silica, mesoporous silicon nitride, mesoporous alumina, and mesoporous aluminum nitride.

[0009] Furthermore, the pore size of the mesoporous material is 1.2-2 nm, and the porosity is 60-70%.

[0010] Furthermore, the number of layers of the reduced graphene is 1-5.

[0011] Furthermore, the metal compound is molybdenum sulfide; the first filler is manganese tetraoxide and silicon carbide; and the second filler is titanium oxide.

[0012] Furthermore, the auxiliary agent is zinc thioglycolate.

[0013] The present invention also provides a method for preparing a modified polyimide-based electromagnetic wave shielding material, which is used to prepare the modified polyimide-based electromagnetic wave shielding material, comprising the following steps: S1. Add reduced graphene to a dispersion kettle, add deionized water thereto, stir for 0.5-1 hour, add a metal compound, and continue stirring for 2-3 hours to obtain a dispersion; wherein the mass ratio of reduced graphene to metal compound is 4:1-10:1; S2. Add the mesoporous material to the dispersion obtained in step S1, stir evenly, then add the auxiliary agent, and continue stirring for 3-5 hours to obtain a mixed dispersion; the amount of the auxiliary agent added is 0.5-1% of the total mass of the silica and metal compound in the dispersion; S3. Add the first filler and the second filler to the mixed dispersion obtained in step S2, and add deionized water at the same time, and fully disperse the mixed materials by ball milling to obtain a slurry; wherein the mass ratio of the first filler to the second filler is 5:1-60:1; S4, sending the slurry into a spray drying device for drying to obtain a solid mixture; wherein the drying temperature is 80-100° C. and the drying time is 10-20 minutes; S5, weighing and mixing the solid mixture and the polyimide resin in a mass ratio of 0.5:1-1.5:1, mixing evenly and then performing a hot melt treatment to obtain a molten composite material; S6. The molten composite material is subjected to a milling and calendering process to form a motherboard.

[0014] Furthermore, the heat-melting treatment temperature in step S5 is 250-280°C.

[0015] Furthermore, in step S6, the calendering temperature is 50-80° C., the calendering line speed is 1 m / min-5 m / min, and the calendered sheet thickness is 100 μm-250 μm.

[0016] The present invention also provides a modified polyimide-based electromagnetic wave shielding material. The material is constructed by introducing a variety of inorganic fillers and conductive fillers, combined with a specific proportion of polyimide resin to construct a composite system, and is suitable for use in covering layer processing in occasions such as aviation cables.

[0017] The modified polyimide-based electromagnetic wave shielding material includes the following components in parts by mass: polyimide resin: 45-55 parts; mesoporous material: 3-10 parts; reduced graphene: 8-15 parts; metal compound: 3-10 parts; first filler: 10-25 parts; second filler: 0.5-5 parts; supplementary conductive filler: 1-5 parts; and additive: 0.5-3 parts.

[0018] Among them, the polyimide resin is a thermosetting prepolymer with a particle size range of 20-60 μm; the mesoporous material includes one or more of mesoporous silica, mesoporous alumina, mesoporous aluminum nitride or mesoporous silicon nitride, the pore size range of the mesoporous material is 1.2-2.0 nm, and the porosity is 60%-70%; the number of layers of the reduced graphene is 1-5 layers, and the flake diameter is 1-5 μm; the metal compound is molybdenum sulfide powder with a particle size of less than 300 nm; the first filler includes manganese tetraoxide and silicon carbide in a mass ratio range of 1:1-2:1, and the particle sizes are controlled between 100-300 nm and 0.5-1.2 μm, respectively; the second filler is nano-titanium oxide with a particle size of 60-100 nm; the supplementary conductive filler is conductive carbon black with a specific surface area of not less than 800 m² / g; the auxiliary agent is zinc thioglycolate, which is a white or off-white powder with a purity of not less than 98%.

[0019] The present invention also provides a method for preparing the modified polyimide-based electromagnetic wave shielding material, comprising the following steps: S1. Dry-mix 8-15 parts of reduced graphene with 1-5 parts of conductive carbon black and add them to the dispersion system. Add deionized water to make the solid content 3%-6%, and mix at a stirring rate of 200-500 rpm for 0.5-1.5 hours. S2. Add 3-10 parts of the metal compound to the system in step S1, continue stirring for 1-3 hours, and adjust the viscosity of the system to 500-900 mPa·s; S3, add 3-10 parts of mesoporous material and 0.5-3 parts of auxiliary agent, stir for 2-5 hours, and keep the system temperature between 25-35 ° C; S4. Add 10-25 parts of the first filler and 0.5-5 parts of the second filler to the system obtained in step S3, add water in an appropriate amount, and then perform wet ball milling at a ball milling speed of 1200-1600 rpm for 5-8 hours to obtain a slurry; S5. The slurry is fed into a spray drying device with a spray temperature of 85-100°C, an atomization pressure of 0.4-0.7 MPa, and a spray time of 8-15 minutes to obtain a dry composite powder; S6, mixing the dry powder with 45-55 parts of polyimide resin in a mass ratio of 0.8:1-1.2:1, and performing a hot melt treatment at a temperature of 250-270° C. and stirring for 30-60 minutes; S7. The molten composite material is fed into a double-roll calendering device for forming. The calendering temperature is 50-80°C, the line speed is 1-5 m / min, and the roller distance is adjusted to a sheet thickness of 100-250 μm. After cooling and forming, a motherboard is obtained.

[0020] The present invention also provides application of the modified polyimide-based electromagnetic wave shielding material in aviation cables.

[0021] Furthermore, the modified polyimide-based electromagnetic wave shielding material is applied to the outer sheath of aviation cables.

[0022] Beneficial effects: The present invention provides a modified polyimide-based electromagnetic wave shielding material, which has been structured in terms of component selection, ratio setting and dispersion control. By introducing mesoporous materials with specific pore size and porosity parameters, combined with reduced graphene with controllable number of layers and metal compounds with uniform particle size, the proportion of various inorganic phase components and spatial uniform distribution are achieved, which is convenient for subsequent solid-state molding processing. The metal compound is compounded with graphene in a mass ratio-controlled manner and then introduced into a high pore volume mesoporous system, so that the compatibility between particles is easier to maintain and stable than the traditional doping route. The filler system adopts a double filler structure. By setting the mass ratio range of the first filler and the second filler, it is beneficial to achieve an optimized combination of particle size and packing density.

[0023] In terms of preparation methods, this invention achieves a closed-loop process from slurry preparation to solid-state motherboard construction by sequentially introducing the dispersion routes of each component, combined with a multi-stage wet mixing, ball milling pretreatment, spray drying, and hot-melt calendaring process. This process offers high controllability in terms of temperature control range, mixing sequence, and ratio adjustment, facilitating industrial replication and mass production.

[0024] In terms of application, the composite system constructed by the present invention can form a stable bonding layer with the polyimide resin, which is suitable for continuous extrusion or molding coating processes in aviation cable sheathing scenarios, and has strong process adaptability and material stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of comparative experimental test results (SE value) of the present invention; Figure 2 Schematic diagram of the comparative experimental test results (TGA) of the present invention. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0027] Example 1 This embodiment provides a modified polyimide-based electromagnetic wave shielding material, which is prepared according to the following steps and provides the specific mass ratio and technical parameters of each component.

[0028] Polyimide resin: 48 parts, BPDA-PDA system thermosetting polyimide prepolymer, particle diameter 20-50 μm; Mesoporous material: 8 parts, including 5 parts of mesoporous silica (average pore size 1.8 nm, porosity approximately 68%) and 3 parts of mesoporous silicon nitride (average pore size 1.4 nm, porosity approximately 63%), with a specific surface area greater than 500 m² / g; Reduced graphene: 12 parts, with the number of layers controlled within 3, an average sheet diameter of 2-5 μm, and a specific surface area of 600 m² / g; Metal compound: 8 parts, high-purity molybdenum sulfide powder, particle size about 300 nm; First filler: 22 parts, including 12 parts of manganese tetraoxide (average particle size of about 150 nm) and 10 parts of silicon carbide (particle size of about 0.8 μm); Second filler: 2 parts, anatase nano-titanium oxide, with particle size controlled within 80 nm; Additive: 2 parts, zinc thioglycolate powder, melting point of about 190 ° C, purity not less than 99%.

[0029] The preparation steps are as follows: S1. Add 12 parts of reduced graphene into a stainless steel dispersion kettle, add deionized water until the slurry solid content is 4%, and stir at 300 rpm for 40 minutes; S2. While stirring, slowly add 8 parts of molybdenum sulfide and continue stirring for 2 hours, maintaining the temperature at 25±2°C to form a uniform dispersion; S3, adding 8 parts of mesoporous silica and mesoporous silicon nitride to the dispersion, and adding 2 parts of zinc thioglycolate, and continuing stirring for 4 hours; S4, adding 22 parts of the first filler (Mn3O4+SiC) and 2 parts of the second filler (TiO2), continuing to add deionized water, adjusting the viscosity, and ball milling with zirconia balls at a ball-to-material ratio of 5:1, a ball milling speed of 1500 rpm, and a time of 6 hours to obtain a slurry; S5. Inject the obtained slurry into a spray drying device, set the air inlet temperature to 95°C, the air outlet temperature to 70°C, the atomization pressure to 0.6 MPa, and the spraying time to 15 minutes to obtain a dry solid mixed powder; S6. Weigh 48 parts of the solid mixture and mix it with 48 parts of polyimide resin (mass ratio 1:1). Place the mixture in an electric melting machine and melt and stir at 265°C for 45 minutes. S7. The molten composite material is conveyed to a double-roll calendering device. The calendering temperature is set to 60°C, the line speed is set to 3 m / min, and the roller distance is adjusted to obtain a sheet with a thickness of 200 μm. After cooling, the sheet is cut into standard motherboards.

[0030] Example 2 This embodiment provides another modified polyimide-based electromagnetic wave shielding material. The mass fractions of each component and the processing conditions are as follows: Polyimide resin: 46 parts, using ODPA-ODA system thermosetting polyimide powder, with a particle size of 30 μm; Mesoporous material: 6 parts, all made of mesoporous alumina (average pore size 1.5 nm, porosity 66%, specific surface area 520 m² / g); Reduced graphene: 15 parts, no more than 5 layers, 1.5 μm sheet diameter, 1.0 nm thickness, and less than 5 wt% oxygen content; Metal compound: 10 parts, ultrafine molybdenum sulfide powder, average particle size of 250 nm, gray-black powder; The first filler is 18 parts, including 8 parts of manganese tetraoxide and 10 parts of silicon carbide. The particle size of manganese tetraoxide is about 200 nm, and the silicon carbide is micron-sized particles. Second filler: 1 part, rutile nano-titanium oxide, particle size 90 nm; Additive: 3 parts, use industrial grade zinc thioglycolate, and sieve through 200 mesh before dispersion.

[0031] The specific steps are as follows: S1. Add 15 parts of reduced graphene into a high shear emulsification kettle, add deionized water to make the slurry solid content reach 5%, and pre-disperse at a stirring speed of 500 rpm for 30 minutes; S2. Slowly add 10 parts of molybdenum sulfide to the above system and continue stirring for 2 hours. During the whole process, control the system temperature not to exceed 30°C. S3, adding 6 parts of mesoporous alumina and 3 parts of zinc thioglycolate, switching to mechanical stirring mode, and stirring for 4 hours; S4, adding 18 parts of the first filler and 1 part of the second filler, adding water and then wet ball milling, with a ball-to-material ratio of 6:1, a rotation speed of 1400 rpm, and a grinding time of 8 hours to obtain a uniform slurry; S5. Drying is performed using a spray drying system with the air inlet temperature set at 90°C, the air outlet temperature set at 65°C, and the drying time set at 12 minutes to obtain a dry powder. S6. Weigh 44 parts of the dried powder and 46 parts of the polyimide resin at a mass ratio of 0.96:1, put them into a melt mixer, and mix them at a temperature of 255° C. for 40 minutes to obtain a molten composite material; S7. The composite material is fed into a calendering device, the roller temperature is set to 75°C, the calendering speed is 2 m / min, and the roller distance is adjusted so that the final sheet thickness is 120 μm. After cooling, the composite material is rolled up for use.

[0032] Example 3 This embodiment provides a modified polyimide-based electromagnetic wave shielding material containing carbon black as a supplementary conductive filler. The specific ratio and process are as follows: Polyimide resin: 50 parts, in the form of BPDA-ODA prepolymer powder with a particle size of 25-40 μm; Mesoporous material: 5 parts, mesoporous aluminum nitride, with an average pore diameter of 1.6 nm, a porosity of 62%, and a light gray powder appearance; Reduced graphene: 10 parts, with the number of layers controlled within 3, an average sheet diameter of 3 μm, and an oxygen content of less than 6%; Metal compound: 5 parts, in the form of spherical ultrafine molybdenum sulfide particles with a particle size controlled below 200 nm; First filler: 12 parts, including: 6 parts of manganese tetraoxide (spherical particles, particle size 180 nm), 6 parts of silicon carbide (black powder, particle size 0.9 μm); Second filler: 2 parts, anatase nano-titanium oxide, particle size 85 nm; Supplementary conductive filler: 3 parts, conductive carbon black (acetylene black), with a specific surface area of 1000 m² / g and an oil absorption value of 260 mL / 100 g; Additive: 1 part, use high-purity zinc thioglycolate, industrial grade dry powder.

[0033] The preparation process is as follows: S1. Dry-mix 10 parts of reduced graphene with 3 parts of carbon black and add them to a dispersion tank. Add appropriate amount of deionized water to make the solid content 4%, and pre-stir at 250 rpm for 1 hour. S2. Add 5 parts of molybdenum sulfide and continue stirring for 2 hours to adjust the system viscosity to 600-800 mPa·s; S3, add 5 parts of mesoporous aluminum nitride and 1 part of auxiliary agent, stir at low speed for 3 hours, and maintain the temperature not exceeding 28 ° C; S4, adding 12 parts of the first filler and 2 parts of the second filler, and adding deionized water at the same time, and wet ball milling using alumina balls for 7 hours at a speed of 1450 rpm; S5. Take out the slurry and use an experimental spray drying equipment to treat it with an inlet air temperature of 95°C, an atomization pressure of 0.5 MPa, and a spraying time of 10 minutes to obtain a gray-black composite dry powder; S6. Add 46 parts of the obtained dry powder and 50 parts of polyimide resin in a mass ratio of 0.92:1 into a melt mixing system, and melt-stir at 260° C. for 50 minutes; S7. Use a constant temperature double-roll calendering device with the roller temperature set to 55°C and the calendering speed set to 4 m / min. Adjust the roller gap to produce a sheet with a thickness of 250 μm. After natural cooling, rewind to form a motherboard.

[0034] Comparative experiment Comparative Example A The selected raw materials and their mass parts are: polyimide resin: 48 parts; reduced graphene: 12 parts; metal compound (molybdenum sulfide): 8 parts; first filler: manganese tetraoxide 12 parts, silicon carbide 10 parts; second filler: titanium oxide 2 parts; auxiliary agent: zinc thioglycolate 2 parts.

[0035] The preparation method is as follows: S1. Add 12 parts of reduced graphene to a dispersion kettle, add deionized water until the solid content is about 4%, and stir for 40 minutes; S2, add 8 parts of molybdenum sulfide and continue stirring for 2 hours to obtain a preliminary dispersion; S3, add 2 parts of zinc thioglycolate and continue stirring for 3 hours to obtain a uniform mixing system; S4, add 22 parts of manganese tetraoxide and silicon carbide, and 2 parts of titanium oxide, add water and then ball mill and disperse for 6 hours; S5. Drying is performed using a spray drying device with an inlet air temperature of 95°C for 15 minutes; S6. Mix the obtained dry powder with 48 parts of polyimide resin in a mass ratio of 1:1, with a melt mixing temperature of 265° C. for 45 minutes; S7. Roll the molten material into a sheet with the temperature set at 60°C, the line speed at 3 m / min, and the thickness controlled at 200 μm.

[0036] Comparative Example B The selected raw materials and their mass parts are: polyimide resin: 48 parts; mesoporous material: mesoporous silica 5 parts; reduced graphene: 12 parts; first filler: manganese tetraoxide 12 parts, silicon carbide 10 parts; second filler: titanium oxide 2 parts; auxiliary agent: zinc thioglycolate 2 parts.

[0037] The preparation method is as follows: S1. Add 12 parts of reduced graphene into a dispersion kettle, add appropriate amount of deionized water, and stir for 40 minutes; S2, adding 5 parts of mesoporous silica and 2 parts of zinc thioglycolate, and continuing stirring for 4 hours to form a dispersion; S3, adding 24 parts of the first filler and the second filler, adding water and then ball milling for 6 hours; S4, spray drying conditions are set at 95 °C for 15 minutes to obtain dry powder; S5, melt-mix the dry powder and polyimide resin in a mass ratio of 1:1 at a temperature of 265°C and a stirring time of 45 minutes; S6. The molten material is processed at a calendering temperature of 60°C, a line speed of 3 m / min, and a sheet thickness of 200 μm.

[0038] Comparative Example C The selected raw materials and their mass parts are: polyimide resin: 48 parts; mesoporous material: mesoporous silica 5 parts; metal compound (molybdenum sulfide): 8 parts; first filler: manganese tetraoxide 12 parts, silicon carbide 10 parts; second filler: titanium oxide 2 parts; auxiliary agent: zinc thioglycolate 2 parts.

[0039] The preparation method is as follows: S1, add 8 parts of molybdenum sulfide into a dispersion kettle, add deionized water and stir for 1 hour; S2, adding 5 parts of mesoporous silica and 2 parts of zinc thioglycolate, and continuing stirring for 3 hours to form a dispersion; S3, adding 24 parts of the first filler and the second filler, adding water and ball milling for 6 hours to obtain a uniform slurry; S4, preparing dry powder by spray drying (95 °C, 15 min); S5, dry powder and polyimide resin were mixed in a mass ratio of 1:1, and melt-kneaded at 265°C for 45 minutes; S6. Calender the material at a temperature of 60°C, a speed of 3 m / min, and a thickness of 200 μm.

[0040] Comparative Example D The selected raw materials and their mass parts are: polyimide resin: 50 parts; mesoporous material: mesoporous aluminum nitride: 5 parts (average pore diameter 1.6 nm, porosity 62%); reduced graphene: 10 parts (number of layers not exceeding 3, sheet diameter approximately 3 μm); metal compound: molybdenum sulfide: 5 parts (particle size less than 300 nm); first filler: manganese tetraoxide: 6 parts, silicon carbide: 6 parts (total 12 parts); second filler: titanium oxide: 2 parts (particle size approximately 85 nm); additive: zinc thioglycolate: 1 part; conductive carbon black: not added.

[0041] The preparation method is as follows: S1. Add 10 parts of reduced graphene into a dispersion kettle, add deionized water until the solid content is about 4%, and stir for 40 minutes; S2. Add 5 parts of molybdenum sulfide and continue stirring for 2 hours, maintaining the system temperature no higher than 30°C; S3, adding 5 parts of mesoporous aluminum nitride and 1 part of zinc thioglycolate, stirring for 3 hours to form a stable dispersion; S4, adding 14 parts of the first filler and the second filler to the dispersion, adding deionized water, and ball milling with zirconium oxide balls for 6 hours at a speed of 1450 rpm; S5, treating with a spray dryer, setting the air inlet temperature to 95°C and the spraying time to 15 minutes, and collecting the resulting dry powder; S6. Mix the dry powder with 50 parts of polyimide resin in a mass ratio of 1:1, and melt-stir the mixture at 260° C. for 50 minutes to obtain a molten composite. S7. Use a calendering device to calender the sheet into a sheet at a temperature of 60°C and a line speed of 3 m / min, with a controlled thickness of 200 μm. After cooling and rewinding, a sample motherboard is obtained.

[0042] In order to evaluate the comprehensive performance of the materials prepared in the examples and comparative examples of the present invention, the following test methods were used to test the performance of the samples: Electromagnetic shielding effectiveness test (SE value) The shielding material samples were tested according to ASTM D4935-10. The test frequency range was 30 MHz to 1500 MHz, and the test apparatus was a coaxial circular waveguide structure shielding effectiveness test system. The samples were pressed into discs with a diameter of 100 mm and a thickness of 200 μm and placed in the center of the test cavity. A network analyzer was used to record the transmission parameters and calculate the shielding effectiveness (SE). Each group of samples was tested three times, and the average value was taken as the final test result, and the maximum SE value was recorded.

[0043] Thermal stability test (TGA) Thermogravimetric analysis (TGA) was performed using a TA Instruments Q50 thermogravimetric analyzer under a nitrogen atmosphere at a flow rate of 60 mL / min. The test temperature range was from room temperature to 800°C, with a heating rate of 10°C / min. The temperature at which the sample lost 5% of its mass during heating (T5%) was recorded, and the carbon residue at 800°C was measured.

[0044] Forming performance evaluation Composite materials were calendered using a thermostatic twin-roll calendering machine, with the calendering temperature set at 60°C, the line speed at 3 m / min, and a target calendering thickness of 200 μm. The sheet was observed for continuity, edge warping, cracking, blistering, and surface finish during the forming process. Any defects such as poor calendering and breakage were noted. Each sample was calendered at least twice to verify forming stability.

[0045] Microstructure observation (SEM) The samples were cryosectioned and then analyzed by scanning electron microscopy (SEM) using a JEOL JSM-7600F instrument. The cross-sections were metallized to observe filler distribution, interfacial bonding, and conductive phase continuity. Details such as filler agglomeration, pores, and lamellar structural integrity were emphasized, with analysis performed at high magnification (1000×–5000×).

[0046] Test results: The test results of the embodiment and the comparative example are shown in Table 1:

[0047] Based on Table 1, Figure 1 and Figure 2 .

[0048] Result Analysis From the comparative test results of Examples 1 to 3 and Comparative Examples A to D, it can be seen that the modified polyimide-based electromagnetic wave shielding material has a significant influence on the molding performance and shielding performance in terms of component ratio and structural construction.

[0049] In terms of material forming performance, Examples 1 to 3 all produced stable sheets at the set calendering temperature and speed. The resulting sheets had a smooth surface and uniform thickness, without defects such as cracks or bubbles. However, Comparative Examples A (lacking the mesoporous material) and C (lacking the reduced graphene) exhibited edge warping, fracture, and surface discontinuity during the calendering process, respectively. This indicates that the missing key components lacked sufficient dispersion stability or bonding continuity during thermal processing.

[0050] In terms of electromagnetic shielding effectiveness (SE), Example 3 had the highest average SE value, reaching 36.8 dB, with a maximum value of 45.9 dB, followed by Example 2 and Example 1, with average SE values of 33.5 dB and 31.2 dB, respectively. In comparison, the average SE values of Comparative Examples A, B, C, and D were 19.5 dB, 21.0 dB, 17.8 dB, and 29.2 dB, respectively, all significantly lower than the Examples. Comparative Example C, in particular, had the lowest shielding effectiveness due to the lack of reduced graphene, preventing the conductive path from being established.

[0051] In terms of microstructural observation, cross-sectional images of the examples show uniform filler distribution, with no agglomeration or segregation between the conductive phase and the ceramic filler. In contrast, Comparative Examples A and B show distinct areas of filler aggregation or fractured lamellar structures, demonstrating the compatibility of the mesoporous material and the metal compound in constructing the multiphase structure. Comparative Example D, while retaining graphene and the metal compound, lacks the addition of conductive carbon black, resulting in insufficient continuity in the shielding network structure and a lower SE value than Example 3.

[0052] The comprehensive comparison results show that: 1. The introduction of mesoporous materials helps to disperse the filler and stabilize the interface; 2. The participation of metal compounds enhances the establishment of electromagnetic wave reflection and conduction paths within the material; 3. Reduced graphene is the core of the conductive network construction; 4. The introduction of auxiliary conductive fillers such as carbon black has a synergistic regulatory effect on the low-frequency response capability of the compensation layer network.

[0053] The technical solution of the present invention achieves higher shielding performance and good processing adaptability through the regulation of the proportion of each component and the design of a composite path without relying on excessive metal components.

[0054] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A modified polyimide-based electromagnetic wave shielding material, characterized in that: The invention comprises the following components in parts by mass: 45-50 parts of polyimide resin; 5-10 parts of mesoporous material; 10-15 parts of reduced graphene; 5-15 parts of metal compound; 10-30 parts of first filler; 0.5-5 parts of second filler; and 1-5 parts of auxiliary agent.

2. The modified polyimide-based electromagnetic wave shielding material according to claim 1, characterized in that: The mesoporous material includes one or more of mesoporous silica, mesoporous silicon nitride, mesoporous alumina, and mesoporous aluminum nitride.

3. The modified polyimide-based electromagnetic wave shielding material according to claim 2, characterized in that: The pore size of the mesoporous material is 1.2-2 nm, and the porosity is 60-70%.

4. The modified polyimide-based electromagnetic wave shielding material according to claim 1, characterized in that: The number of layers of the reduced graphene is 1-5.

5. The modified polyimide-based electromagnetic wave shielding material according to claim 1, characterized in that: The metal compound is molybdenum sulfide; the first filler is manganese tetraoxide and silicon carbide; and the second filler is titanium oxide.

6. The modified polyimide-based electromagnetic wave shielding material according to claim 1, characterized in that: The auxiliary agent is zinc thioglycolate.

7. The method for preparing a modified polyimide-based electromagnetic wave shielding material according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Add reduced graphene to a dispersion kettle, add deionized water thereto, stir for 0.5-1 hour, add a metal compound, and continue stirring for 2-3 hours to obtain a dispersion; wherein the mass ratio of reduced graphene to metal compound is 4:1-10:1; S2. Add the mesoporous material to the dispersion obtained in step S1, stir evenly, then add the auxiliary agent, and continue stirring for 3-5 hours to obtain a mixed dispersion; the amount of the auxiliary agent added is 0.5-1% of the total mass of the silica and metal compound in the dispersion; S3. Add the first filler and the second filler to the mixed dispersion obtained in step S2, and add deionized water at the same time, and fully disperse the mixed materials by ball milling to obtain a slurry; wherein the mass ratio of the first filler to the second filler is 5:1-60:1; S4, sending the slurry into a spray drying device for drying to obtain a solid mixture; wherein the drying temperature is 80-100° C. and the drying time is 10-20 minutes; S5, weighing and mixing the solid mixture and the polyimide resin in a mass ratio of 0.5:1-1.5:1, mixing evenly and then performing a hot melt treatment to obtain a molten composite material; S6. The molten composite material is subjected to a milling and calendering process to form a motherboard.

8. The method for preparing a modified polyimide-based electromagnetic wave shielding material according to claim 7, wherein: The heat-melting treatment temperature in step S5 is 250-280°C.

9. The method for preparing a modified polyimide-based electromagnetic wave shielding material according to claim 7, wherein: The calendering temperature in step S6 is 50-80° C., the calendering line speed is 1 m / min-5 m / min, and the calendered sheet thickness is 100 μm-250 μm.

10. Use of the modified polyimide-based electromagnetic wave shielding material according to any one of claims 1 to 6 in aviation cables, characterized in that: The modified polyimide-based electromagnetic wave shielding material is applied to the outer sheath of aviation cables.

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