A low-reflection magnetic electromagnetic shielding polyimide nonwoven fabric and its preparation and application

Abstract

The present invention discloses a low-reflection magnetic electromagnetic shielding polyimide non-woven fabric and its preparation and application, belonging to the technical field of electromagnetic shielding materials. The present invention adopts green and environmentally friendly water-alcohol electrospinning and thermal imidization process to prepare polyimide fiber non-woven fabric, and uses a roughening liquid to roughen the fiber surface; at the same time, a specific metal salt is used as an activator of the chemical plating solution to achieve surface metallization of the polyimide fiber, and then a specific surfactant is used to perform surface treatment on it, and a "needle-shaped" magnetic material outer layer loading is achieved through a hydrothermal method and high-temperature annealing treatment. The preparation process of the present invention is simple and easy to operate, and is expected to be applied to fields that require electromagnetic shielding, such as aerospace, military equipment, microelectronic equipment, and civilian electrical appliances.

Description

Technical Field

[0001] The invention relates to a low-reflection magnetic electromagnetic shielding polyimide non-woven fabric and its preparation and application, belonging to the technical field of electromagnetic shielding materials. Background Art

[0002] With the rapid development of the electronic information industry, especially the miniaturization and high integration of electronic components, electromagnetic leakage and interference in electrical equipment have become increasingly prominent. Electromagnetic shielding materials, as functional protective materials that effectively isolate incident electromagnetic waves, have been widely used in the field of electromagnetic protection.

[0003] Although the introduction of highly conductive functional components can improve electromagnetic shielding effectiveness, it often causes a large amount of electromagnetic waves to be reflected on the material surface, which can easily cause secondary electromagnetic pollution. Therefore, the design and preparation of new electromagnetic shielding materials with low reflection and high absorption efficiency has become one of the most urgent needs in the field of electromagnetic pollution control.

[0004] Currently, the most commonly used method for preparing electromagnetic shielding materials is through chemical plating; however, chemical plating is difficult, especially chemical plating without palladium activation, and its plating efficiency is significantly reduced; and for chemical silver plating, the solution reacts too violently after the addition of a reducing agent, resulting in the precipitation of silver oxide particles, making it impossible for silver nanoparticles to be deposited on the fiber surface and inside in large quantities; in addition, the fiber surface is inert after silver metallization, making it difficult to effectively re-modify the magnetic material, which seriously affects the electromagnetic dissipation performance of the composite material.

[0005] Therefore, how to achieve a polymer fiber material with a strongly bonded roughened surface, efficient and stable metallization, and an effective load of magnetic particles to obtain a magnetic electromagnetic shielding material with good stability and low reflection has become a key issue and challenge that needs to be solved urgently. Summary of the Invention

[0006] [Technical Issues]

[0007] (1) Conventional chemical silver plating makes the silver load on the surface of the material uneven, making it difficult to modify the magnetic material.

[0008] (2) Conventional electromagnetic shielding materials do not have low reflectivity.

[0009] [Technical solution]

[0010] In order to solve the above problems, the present invention adopts green and environmentally friendly water-alcohol electrospinning and thermal imidization processes to prepare polyimide fiber non-woven fabrics, and uses a roughening liquid to roughen the fiber surface; at the same time, a specific metal salt is used as an activator in the chemical plating solution to achieve surface metallization of the polyimide fiber, and then a specific surfactant is used to perform surface treatment on it, and a hydrothermal method and high-temperature annealing treatment are used to achieve the outer layer loading of "needle-shaped" magnetic material.

[0011] Specifically:

[0012] (1) The polyimide fiber nonwoven fabric was prepared by water-alcohol electrospinning and thermal imidization, which has a three-dimensional network structure inside, which can lay the foundation for the subsequent multiple scattering / reflection of electromagnetic waves;

[0013] (2) The solute polymer in the specific roughening solution can form a polymer coating with very strong adhesion on the surface of the polyimide fiber non-woven fabric through polymerization reaction in the aqueous solution. At the same time, the solute polymer contains a large number of functional groups, which have a strong reducing ability for metal ions and can in situ reduce specific non-palladium noble metal ions to metal elements. It can use this as a catalytic center to efficiently promote the reduction of metal ions such as copper / silver in the chemical plating solution, thereby depositing metal copper / silver on the surface, providing a "chemical" anchoring point for subsequent chemical plating, thereby improving the bonding strength between the subsequent metal plating layer and the polyimide fiber non-woven fabric, and extending the stability and service life of the material;

[0014] (3) The present invention adopts a palladium-free and fluorine-free activation process, which provides a new path for the efficient and green preparation of polyimide fiber non-woven fabric surface metallization;

[0015] (4) The rational construction of the multi-level microstructure inside the metallized polyimide fiber will provide new possibilities for enhancing its electromagnetic shielding effectiveness and broadening the bandwidth;

[0016] (5) The load of the outer layer of "needle-shaped" three-dimensional structure magnetic material will provide the material with magnetic loss and more scattering sites for the incident electromagnetic waves, thereby enhancing its electromagnetic dissipation performance and helping to avoid secondary contamination of electromagnetic waves.

[0017] The first object of the present invention is to provide a method for preparing a low-reflection magnetic and electromagnetic shielding polyimide fiber non-woven fabric, comprising the following steps:

[0018] (1) Preparation of metallized polyimide fiber nonwoven fabric:

[0019] The polyimide fiber nonwoven fabric is placed in a roughening liquid for roughening treatment, and after the roughening treatment is completed, the nonwoven fabric is taken out, washed, and dried to obtain a roughened polyimide fiber nonwoven fabric;

[0020] The roughened polyimide fiber nonwoven fabric is then placed in an activation solution for treatment. After treatment, the nonwoven fabric is taken out, washed, and dried to obtain an activated polyimide fiber nonwoven fabric; wherein the solute in the activation solution is a silver salt or a copper salt with a concentration of 0.5 to 25 g / L;

[0021] The activated polyimide fiber nonwoven fabric is then placed in a metal plating solution for metallization treatment. After completion, the nonwoven fabric is taken out, washed, and dried to obtain a metallized polyimide fiber nonwoven fabric. The metallization treatment time is 10 to 90 minutes and the temperature is 10 to 20°C.

[0022] (2) Preparation of modified metallized polyimide fiber nonwoven fabric:

[0023] The metallized polyimide fiber nonwoven fabric is placed in a surfactant solution for modification, and after modification, the nonwoven fabric is taken out, washed, and dried to obtain a modified metallized polyimide fiber nonwoven fabric; wherein the surfactant is one or both of sodium dodecylbenzene sulfonate and sodium stearate, and the concentration is 5 to 8 g / L;

[0024] (3) Preparation of magnetic electromagnetic shielding polyimide fiber nonwoven fabric:

[0025] The modified metallized polyimide fiber nonwoven fabric is immersed in a cobalt-nickel solution, and then subjected to a hydrothermal reaction at 100-160° C. for 6-12 hours. After the reaction is completed, it is taken out; then it is placed in an inert gas atmosphere for annealing treatment, taken out, washed, and dried to obtain a magnetic electromagnetic shielding polyimide fiber nonwoven fabric.

[0026] In one embodiment of the present invention, the method for preparing the polyimide fiber nonwoven fabric described in step (1) comprises the following steps:

[0027] The dibasic anhydride and the diamine are mixed in an organic solvent, and the monomer polymerization is carried out at 0-10°C for 2-8 hours; then an organic base is added, and after stirring for 1.5-4.5 hours, another organic solvent is used for sufficient solvent exchange for 1-3 hours, and after static precipitation, the precipitate is placed in a vacuum oven at 40-80°C for drying to obtain a polyamic acid salt; then the polyamic acid salt is fully dissolved in a water-alcohol mixed solution to obtain a polyamic acid salt spinning solution with a solid content of 5-10wt%; wherein the dibasic anhydride monomer is pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride ( The diamine monomer is one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), and 4,4"-diamino-p-terphenyl (DAT); the organic solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), and N-methylpyrrolidone (NMP); the organic base is one or more of triethylamine (TEA), quinoline (QL), and N,N-dimethylethanolamine (DMEA); the mass ratio of alcohol in the water-alcohol mixed solution is 40-90wt%, and the alcohol solvent is any one of ethanol, methanol, and propanol;

[0028] The polyamic acid salt spinning solution is subjected to electrostatic spinning, with the positive electrode voltage set to 18-30 kV, the negative electrode voltage to 0-2 kV, the propulsion speed to 0.2-0.4 mL / min, and the distance between the needle and the receiver to 15-35 cm. After the spinning, the polyamic acid fiber non-woven fabric is placed in an inert gas atmosphere and subjected to thermal imidization treatment at 300-400° C. for 1-3 hours to obtain a polyimide fiber non-woven fabric material. The inert protective gas is one or more of nitrogen, argon, and helium. The thermal imidization treatment process also includes using a porcelain boat and a quartz sheet to press the polyamic acid salt fiber non-woven fabric for thermal imidization treatment.

[0029] In one embodiment of the present invention, the polyimide fiber nonwoven fabric in step (1) has a porous structure, and the pore size formed by the intersection of fibers is 10 to 50 μm.

[0030] In one embodiment of the present invention, the solute of the roughening solution in step (1) is one or more of dopamine, citric acid, polyphenolamine, and tannic acid; the concentration is 2 to 10 g / L, and the solvent is a buffer solution, specifically a HCl-tris solution with a pH of 8.5.

[0031] In one embodiment of the present invention, the roughening treatment in step (1) is performed at room temperature (20-30° C.) and 400-700 rpm for 6-24 hours; a rotation speed that is too fast can easily cause the non-woven fabric to become entangled in the solution, and a rotation speed that is too low can make it difficult for the solute to be evenly distributed in the solution.

[0032] In one embodiment of the present invention, the roughening treatment in step (1) is performed by first soaking the polyimide fiber nonwoven fabric in a buffer solution, and then adding a solute of the roughening solution and stirring.

[0033] In one embodiment of the present invention, after the roughening treatment in step (1), washing is performed using water or ethanol, and drying is performed at 40-80° C. for 1-2 hours.

[0034] In one embodiment of the present invention, the silver salt of the activation solution in step (1) includes one or more of silver chloride, silver nitrate, and silver sulfate; the copper salt includes one or more of copper chloride, copper nitrate, and copper sulfate.

[0035] In one embodiment of the present invention, the solvent of the activation solution in step (1) is ultrapure water.

[0036] In one embodiment of the present invention, the activation treatment in step (1) is carried out at room temperature (20-30° C.) for 10 min to 200 min.

[0037] In one embodiment of the present invention, after the activation treatment in step (1), washing is performed using water or anhydrous ethanol, and drying is performed at 40-80° C. for 1-2 hours.

[0038] In one embodiment of the present invention, the metal plating solution in the metallization treatment in step (1) includes a metal salt, a chelating agent, a reducing agent, and ultrapure water; wherein the metal salt is one or more of silver sulfate, silver chloride, silver nitrate, and copper chloride, and the concentration is 20-60 g / L; the chelating agent is one or more of lactic acid, sodium citrate, acetic acid, sodium acetate, malic acid, thiourea, ammonium chloride, ammonia water, and disodium edetate, and the concentration is 20-400 g / L; the reducing agent is one or more of glucose, dimethylaminoborane, potassium sodium tartrate, anhydrous ethanol, and boric acid, the concentration of dimethylaminoborane is 1-5 g / L, the concentration of boric acid is 2-6 g / L, the concentration of glucose and anhydrous ethanol is 1-100 g / L, and the concentration of potassium sodium tartrate is 1-5 g / L.

[0039] In one embodiment of the present invention, after the metallization treatment in step (1), washing is performed using ultrapure water or anhydrous ethanol, and drying is performed at 40-80° C. for 1-2 hours.

[0040] In one embodiment of the present invention, the solvent of the surfactant solution in step (2) is water.

[0041] In one embodiment of the present invention, the modification treatment in step (2) is performed by soaking at room temperature (20-30° C.) for 1-3 hours.

[0042] In one embodiment of the present invention, after the modification treatment in step (2), washing is performed with water, and drying is performed at 40-80° C. under vacuum conditions for 1-2 hours.

[0043] In one embodiment of the present invention, the drying temperature in step (2) is too high, which may cause the surfactant to fall off the non-woven fabric, and the vacuum environment is to prevent the silver layer from being oxidized at high temperature.

[0044] In one embodiment of the present invention, the cobalt-nickel solution in step (3) comprises a cobalt salt, a nickel salt, and a pH regulator; wherein the cobalt salt is cobalt nitrate with a concentration of 15 to 40 g / L; the nickel salt is nickel nitrate with a concentration of 15 to 40 g / L; the pH regulator is one or more of ammonia water, sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, and urea with a concentration of 1.5 to 3 g / L, and the pH is adjusted to 5 to 10; and the solvent is ultrapure water.

[0045] In one embodiment of the present invention, the washing in step (3) is performed with water, and the drying is performed at 40-80° C. under vacuum conditions for 1-2 hours.

[0046] In one embodiment, the annealing temperature in step (3) is 200-400° C., and the time is 6-12 hours; and the inert protective gas is one or more of nitrogen, argon, and helium.

[0047] The second object of the present invention is a low-reflection magnetic and electromagnetic shielding polyimide fiber non-woven fabric prepared by the method of the present invention.

[0048] In one embodiment of the present invention, the low-reflection magnetic electromagnetic shielding polyimide fiber non-woven fabric is a multi-level magnetic polyimide fiber non-woven fabric with a "needle-type" structure.

[0049] The third object of the present invention is to use the low-reflection magnetic electromagnetic shielding polyimide fiber non-woven fabric of the present invention in the field of electromagnetic protection of aerospace devices, military equipment or precision electronic instruments.

[0050] [Beneficial Effects]

[0051] (1) The present invention synthesizes aqueous polyamic acid salt and dissolves the polyamic acid salt in a water-alcohol solution, and uses electrospinning technology to prepare polyimide fiber non-woven fabrics. Then, through roughening, activation, chemical plating and hydrothermal loading, a multi-level magnetic polyimide-based fiber non-woven fabric with a "needle-shaped" structure is obtained. The preparation method is simple to operate and is green and environmentally friendly.

[0052] (2) The present invention effectively endows the composite material with excellent low-reflection and high-efficiency electromagnetic shielding performance based on the multi-level impedance gradient structure and the multiple scattering and high-efficiency dielectric loss, conductivity loss and magnetic loss of the incident electromagnetic wave inside the material.

[0053] (3) The preparation process of the present invention is simple and easy to operate, and is expected to be applied to fields that require electromagnetic shielding, such as aerospace, military equipment, microelectronic equipment, and civilian electrical appliances.

[0054] (4) The magnetic electromagnetic shielding polyimide fiber nonwoven fabric prepared by the present invention has both excellent electromagnetic shielding and low reflection performance, with a shielding performance of up to 50dB and an absorption coefficient A of up to 0.86; and has very excellent low-temperature resistance and high-temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Scanning electron microscope images of the polyimide fiber non-woven fabric PI (a), the metallized polyimide fiber non-woven fabric PI@Ag (b) and the magnetic electromagnetic shielding polyimide fiber non-woven fabric PI@Ag@NiCo2O4 (c) in Example 1.

[0056] Figure 2 Shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber non-woven fabric PI@Ag@NiCo2O4 in Example 1.

[0057] Figure 3 The shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber non-woven fabric PI@Ag@NiCo2O4 in Example 1 after being immersed in liquid nitrogen environment for 24 hours.

[0058] Figure 4 The shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber non-woven fabric PI@Ag@NiCo2O4 in Example 1 after being treated in a 200°C environment for 24 hours.

[0059] Figure 53. The electromagnetic shielding effectiveness and power coefficient comparison diagram of the metallized polyimide non-woven fabric formed at different plating times in Example 2; (a), (c), and (e) are shielding performance diagrams for plating times of 30 min, 60 min, and 90 min, respectively; (b), (d), and (f) are power coefficient diagrams for plating times of 30 min, 60 min, and 90 min, respectively. DETAILED DESCRIPTION

[0060] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0061] Test method:

[0062] 1. Determination method of scanning electron microscope image:

[0063] The images were taken using a JSM 6490LV field emission electron microscope from JEOL, Japan.

[0064] 2. Electromagnetic shielding effectiveness determination method:

[0065] The S parameters (S 11 、S 22 、S 21 、S 12 ), and then calculate the corresponding shielding performance SE T and the absorption coefficient A.

[0066] The specific calculation of the absorption coefficient A is as follows:

[0067] R = |S 11 ∣ 2 =|S 22 ∣ 2 (1)

[0068] T = |S 21 ∣ 2 =|S 12 ∣ 2 (2)

[0069] A = 1 – R – T (3)

[0070] Shielding performance SE T The specific calculation is as follows:

[0071] SE R =–10log(1 – R) (4)

[0072] SEA = – 10log(T / (1 – R)) (5)

[0073] SE T = SE R + SE A = –10logT = –20log∣S 21 ∣ (6)

[0074] 3. Conductivity determination method:

[0075] The electrical conductivity of the composite fiber material was measured using a Suzhou Jingge Electronics ST2263 dual-electric digital four-probe tester using the standard four-point contact method.

[0076] The raw materials used in the embodiment are:

[0077] The preparation method of polyimide fiber nonwoven fabric comprises the following steps:

[0078] (1) Preparation of polyamic acid salt powder:

[0079] 96.6 g of N,N-dimethylformamide (DMF), 8 g of 4,4'-diaminodiphenyl ether (ODA), and 8.9 g of pyromellitic dianhydride (PMDA) were sequentially added to a three-necked flask, and mechanical stirring was continued in a water bath at 0-10°C for 2.5 hours. Subsequently, 100 g of DMF was added, and stirring was continued for 1.5 hours. Then, 5.2 mL of N,N-dimethylethanolamine (DMEA) was slowly added, and stirring was continued for 3 hours to carry out a polymerization reaction. Finally, the reacted polymer was transferred to acetone, stirred for a period of time, and then allowed to stand. After complete sedimentation, the supernatant was poured out. After repeating the above steps three times, the precipitate was placed in a vacuum oven and vacuum-dried at 50°C for 8 hours to obtain a polyamic acid salt powder.

[0080] (2) Preparation of polyamic acid salt spinning solution:

[0081] 5 g of the polyamic acid salt powder prepared above was weighed and added to 45 g of a 50% water 50% ethanol mixture, and stirred continuously for 24 h to fully dissolve the mixture to obtain a polyamic acid salt spinning solution (solid content of 10 wt%);

[0082] (3) Preparation of polyimide fiber nonwoven fabric:

[0083] Take 100 mL of polyamic acid salt spinning solution and perform electrospinning at a propulsion speed of 0.2 mL / min, a positive voltage of 30 kV, a negative voltage of 0 kV, and a receiving distance of 20 cm. After the end, the non-woven fabric is peeled off from the receiving roller to obtain a polyamic acid salt fiber non-woven fabric; then place it in a tubular furnace (argon atmosphere) at 350°C for 1 hour, cool it to room temperature and take it out to obtain a polyimide fiber non-woven fabric; named PI.

[0084] The solutions involved in the embodiments do not specifically mention the solvent, all of which are ultrapure water; the various treatments mentioned (roughening, activation, metallization, modification, hydrothermal reaction loading, etc.) are all non-woven fabrics treated according to the specified bath ratio (fabric to solution weight ratio of 1:200 to 1:500), and the specific bath ratios are: roughening (1:500), activation (1:385), metallization (1:385), modification (1:500), hydrothermal reaction (1:266); the % mentioned without specific meaning refers to mass percentage.

[0085] Example 1

[0086] A method for preparing a low-reflection magnetic and electromagnetic shielding polyimide fiber nonwoven fabric comprises the following steps:

[0087] (1) Preparation of metallized polyimide fiber nonwoven fabric:

[0088] 0.25 g of polyimide fiber nonwoven fabric was placed in 125 mL of tris solution with a pH of 8.5, and ultrasonicated for 2 minutes to completely soak the polyimide fiber nonwoven fabric. Then, 0.375 g of dopamine was added and stirred continuously for 24 hours under magnetic stirring (500 rpm). After completion, the fabric was washed with ultrapure water 2 to 3 times, ultrasonically cleaned for 1 minute, and then washed once with anhydrous ethanol. Finally, the fabric was placed in a vacuum oven at 50° C. and vacuum dried for 2 hours to obtain a roughened polyimide fiber nonwoven fabric.

[0089] Then, 0.26 g of the roughened polyimide fiber nonwoven fabric was immersed in 100 mL of 5 g / L silver nitrate solution at room temperature for 2 hours. After the end, it was taken out, thoroughly washed with ultrapure water and anhydrous ethanol, and placed in a vacuum oven at 50°C for 2 hours to obtain an activated polyimide fiber nonwoven fabric;

[0090] Then, 0.26 g of the activated polyimide fiber nonwoven fabric was placed in 100 mL of metal plating solution and plated at 15°C for 60 min. After the plating, the fabric was taken out and thoroughly washed with ultrapure water and anhydrous ethanol. Finally, it was placed in a vacuum oven at 50°C for 2 h to obtain a metallized polyimide fiber nonwoven fabric, named PI@Ag. The metal plating solution contained 40 g / L silver nitrate, 300 g / L ammonia, 80 g / L glucose, and 100 g / L anhydrous ethanol, with the remainder being ultrapure water.

[0091] (2) Preparation of modified metallized polyimide fiber nonwoven fabric:

[0092] 0.3 g of metallized polyimide fiber nonwoven fabric was placed in 150 mL of 5 g / L sodium dodecylbenzene sulfonate solution and soaked at room temperature for 2 h for modification. After the modification, the fabric was taken out, washed with ultrapure water, and finally dried in a vacuum oven at 50 ° C for 2 h to obtain a modified metallized polyimide fiber nonwoven fabric;

[0093] (3) Preparation of magnetic electromagnetic shielding polyimide fiber nonwoven fabric:

[0094] 0.3 g of modified metallized polyimide fiber nonwoven fabric was immersed in 80 mL of cobalt-nickel solution at room temperature for 2 hours, followed by hydrothermal reaction at 120°C for 8 hours. After the reaction, it was taken out; then it was placed in an argon atmosphere and annealed at 400°C for 6 hours, taken out, washed with ultrapure water, and finally placed in a vacuum oven at 50°C for 2 hours to obtain a magnetic electromagnetic shielding polyimide fiber nonwoven fabric, named PI@Ag@NiCo2O4; wherein the concentration of nickel nitrate in the cobalt-nickel solution is 20 g / L, the concentration of cobalt nitrate is 35 g / L, the concentration of urea is 2 g / L, the pH is about 9, and the rest is water.

[0095] The obtained polyimide fiber nonwoven fabric PI, metallized polyimide fiber nonwoven fabric PI@Ag and magnetic electromagnetic shielding polyimide fiber nonwoven fabric PI@Ag@NiCo2O4 were subjected to performance tests, and the test results are as follows:

[0096] Figure 1 Scanning electron microscope images of polyimide fiber nonwoven fabric PI (a), metallized polyimide fiber nonwoven fabric PI@Ag (b) and magnetic electromagnetic shielding polyimide fiber nonwoven fabric PI@Ag@NiCo2O4 (c); Figure 1It can be seen that the structure of the polyimide fiber non-woven fabric is porous, the diameter of the PI fiber is 1.5-2μm, and the pore size formed by the intersection of the fibers is 10-50μm; after chemical silver plating, the surface morphology of the PI@Ag fiber changes significantly, the metal coating is successfully coated on the PI fiber, and shows good uniformity, while the diameter increases; after being loaded with nickel cobalt oxide magnetic material, the morphology of the PI@Ag@NiCo2O4 fiber changes significantly, and the overall structure presents a needle-like three-dimensional structure. At the same time, it is successfully loaded on the PI@Ag fiber and shows good uniformity.

[0097] Figure 2 The shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber non-woven fabric PI@Ag@NiCo2O4. Figure 2 As can be seen from (a), the shielding performance of PI@Ag@NiCo2O4 non-woven fabric is as high as 50dB, which has high shielding performance; Figure 2 As can be seen in (b), the absorption coefficient A of PI@Ag@NiCo2O4 reaches 0.86, proving that the material has both excellent electromagnetic shielding and low reflection properties.

[0098] Figure 3 The shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber nonwoven fabric PI@Ag@NiCo2O4 after being immersed in liquid nitrogen for 24 hours. Figure 2 and Figure 3 From the comparison, it can be seen that the electromagnetic properties and power coefficient of PI@Ag@NiCo2O4 after 24 hours of liquid nitrogen low-temperature treatment are not much different from those before treatment. This is mainly due to the strong bonding force of the coating. This also fully demonstrates that the magnetic material-loaded metallized polyimide fiber non-woven fabric prepared by the method of the present invention has very excellent low-temperature resistance.

[0099] Figure 4 The shielding performance diagram (a) and power coefficient diagram (b) of the magnetic electromagnetic shielding polyimide fiber nonwoven fabric PI@Ag@NiCo2O4 after being treated in a 200℃ environment for 24 hours. Figure 2 and Figure 4 From the comparison, it can be seen that the electromagnetic properties and power coefficient of PI@Ag@NiCo2O4 after high-temperature treatment at 200°C for 24 hours are not much different from those before treatment. This is mainly because the outer layer NiCo2O4 and the base PI have good high-temperature resistance. At the same time, the tight and uniform loading of the outer layer NiCo2O4 can well prevent the oxidation of the intermediate metal silver layer. This also fully demonstrates that the magnetic material loaded metallized polyimide fiber non-woven fabric prepared by the method of the present invention has excellent high-temperature resistance.

[0100] Example 2

[0101] The plating time of the metallization treatment in step (1) of Example 1 was adjusted to 30 min and 90 min, and the other steps were kept consistent with Example 1 to obtain a metallized polyimide fiber nonwoven fabric.

[0102] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing, and the test results were as follows: Figure 5 ;

[0103] Figure 5 The following is a comparison chart of the electromagnetic shielding effectiveness and power coefficient of metallized polyimide nonwoven fabrics formed at different plating times. Figure 5 It can be seen from (a), (c) and (e) that as the plating time increases from 30 min to 90 min, the conductivity increases from 10 S / cm to 83 S / cm, and the shielding effectiveness increases from 18 dB to 69 dB, and the increase gradually decreases; Figure 5 As can be seen in Figures (b), (d), and (f), the power coefficients (R, A, T) indicate a reflection coefficient (R) as high as 0.9, indicating that the composite's electromagnetic shielding performance is primarily reflection-based. Furthermore, the power coefficients (R, A, T) do not change significantly with increasing plating time. Furthermore, higher conductivity of the nonwoven fabric increases the difficulty in constructing the subsequent impedance gradient, so a plating time of 60 minutes is optimal here.

[0104] Example 3

[0105] The concentration of the silver nitrate solution in the metallization treatment of step (1) of Example 1 was adjusted to 20 g / L, the plating time was 90 min, and the other conditions were kept consistent with Example 1 to obtain a metallized polyimide fiber nonwoven fabric.

[0106] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0107] The results showed that the reaction rate was relatively slow due to the reduction in the concentration of the silver nitrate solution. After extending the plating time, the metallized polyimide fiber non-woven fabric was obtained. However, after testing, its shielding performance was only 30dB, which was a significant decline in performance.

[0108] Example 4

[0109] The concentration of the silver nitrate solution in the metallization treatment of step (1) of Example 1 was adjusted to 60 g / L, the plating time was 30 min, and the other conditions were kept consistent with Example 1 to obtain a metallized polyimide fiber nonwoven fabric.

[0110] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0111] The results showed that increasing the silver nitrate concentration increased the reaction rate, allowing the metallized polyimide fiber nonwoven fabric to be produced in a short period of time. Testing demonstrated a shielding performance of approximately 50dB. However, during the plating process, the high concentration caused instability in the entire plating solution and uneven distribution of the metallic silver layer, resulting in significant fluctuations in shielding performance.

[0112] Example 5

[0113] The silver nitrate in the activation step (1) of Example 1 was adjusted to copper nitrate, and the plating solution in the metallization was adjusted to have a copper chloride concentration of 10 g / L, a disodium ethylenediaminetetraacetic acid concentration of 20 g / L, a boric acid concentration of 5 g / L, and the rest being water to prepare a copper plating layer; the rest was consistent with Example 1 to obtain a magnetic and electromagnetic shielding polyimide fiber non-woven fabric.

[0114] The obtained magnetic electromagnetic shielding polyimide fiber nonwoven fabric was subjected to performance testing;

[0115] The results showed that the shielding performance was around 40dB and the absorption coefficient A was 0.6, but the absorption coefficient fluctuated greatly. From the final morphology, the subsequent nickel cobalt oxide was unevenly distributed and difficult to load. At the same time, the presence of nitric acid in the subsequent hydrothermal reaction might damage the metal copper layer to a certain extent.

[0116] Example 6

[0117] The temperature of the hydrothermal reaction in step (3) of Example 1 was adjusted to 80° C., 160° C., and 200° C., and the other conditions remained the same as in Example 1 to obtain a magnetic and electromagnetic shielding polyimide fiber nonwoven fabric.

[0118] The obtained magnetic electromagnetic shielding polyimide fiber nonwoven fabric was subjected to performance testing, and the test results are as follows:

[0119] For the sample heated at 80°C, the color of the final material remained essentially unchanged, and no precipitation was generated in the hydrothermal reactor. The reaction solution was pink and clear, and the sample was non-magnetic, indicating that the material ultimately contained no nickel cobalt oxide.

[0120] For the sample at 160℃, the whole has certain magnetism, but the overall shielding performance is reduced to about 40dB, and the absorption coefficient (A) is only about 0.5, and the overall performance has been attenuated to a certain extent;

[0121] For the sample at 200°C, its final performance is far below 20dB, and the material is not magnetic. On the one hand, the high temperature causes the silver layer to melt and fall off in the alkaline environment of high temperature and high pressure. On the other hand, the shedding of the silver layer with surfactant causes the pure PI to be exposed, making it difficult for subsequent cobalt and nickel metal ions to adsorb on the material.

[0122] Comparative Example 1

[0123] The sodium dodecylbenzenesulfonate in step (2) of Example 1 was adjusted to octadecyl mercaptan, polyacrylamide, and sodium α-olefin sulfonate, and the other ingredients were kept consistent with Example 1 to prepare a magnetic and electromagnetic shielding polyimide fiber non-woven fabric.

[0124] The obtained magnetic electromagnetic shielding polyimide fiber nonwoven fabric was subjected to performance testing;

[0125] The results showed that: judging from the surface morphology of the prepared samples, the apparent color distribution was uneven, and there was basically no obvious color change. At the same time, basic magnetic testing of the material using a strong magnet revealed that the material had basically no magnetism, indicating that there was no nickel cobalt oxide loading on the surface of the material after subsequent hydrothermal and annealing treatments.

[0126] Comparative Example 2

[0127] The concentration of the sodium dodecylbenzenesulfonate solution in step (2) of Example 1 was adjusted to 2.5 g / L and 10 g / L, and the other parameters were kept consistent with Example 1 to obtain a magnetic and electromagnetic shielding polyimide fiber nonwoven fabric.

[0128] The obtained magnetic electromagnetic shielding polyimide fiber nonwoven fabric was subjected to performance testing, and the test results are as follows:

[0129] For the comparison sample with a concentration of 2.5g / L, its apparent color changed from silver to black, and its shielding performance was around 50dB, but its absorption coefficient A value was only 0.4. From the results, it is believed that the surfactant concentration is too low, resulting in too low a loading amount of metal ions on the material surface, resulting in an absorption coefficient A value of only 0.4, and the material is still mainly reflective;

[0130] For samples with a concentration of 10 g / L, since the concentration of surfactant was too high, agglomeration occurred in the solution, and a very small part was adsorbed on the surface of the material, resulting in basically no nickel cobalt oxide loading on the surface of the final product and basically no change in the apparent color.

[0131] Comparative Example 3

[0132] The concentration of the urea solution in step (3) of Example 1 was adjusted to 0.5 g / L, 1 g / L, 4 g / L, and 8 g / L, and the other concentrations were kept consistent with Example 1 to obtain a magnetic and electromagnetic shielding polyimide fiber nonwoven fabric.

[0133] The obtained magnetic electromagnetic shielding polyimide fiber nonwoven fabric was subjected to performance testing, and the test results are as follows:

[0134] For samples with concentrations of 0.5 g / L and 1 g / L, the urea concentration was too low and the solution pH was imbalanced, making it difficult for the nickel cobalt oxide to maintain its needle-like three-dimensional structure after hydrothermal and annealing treatments, resulting in a collapse phenomenon. This, in turn, caused the material's absorption coefficient (A) to be lower than 0.5, resulting in an overall reflection-dominated performance that did not meet the experimental requirements.

[0135] For samples with concentrations of 4g / L and 8g / L, due to the high urea concentration and the high overall pH of the solution, the metallic silver layer ablated and fell off under the high temperature and high pressure environment of the hydrothermal reaction, resulting in the final shielding performance of the material being far below the minimum standard of 20dB, which did not meet the experimental requirements.

[0136] Comparative Example 4: Plating temperature is too high

[0137] The plating temperature in the metallization treatment in step (1) of Example 1 was adjusted to 25° C.; other conditions remained the same as in Example 1, and a metallized polyimide fiber nonwoven fabric was obtained.

[0138] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0139] The results showed that the plating solution quickly became turbid and the entire plating process was unstable, which made it difficult to obtain a uniform and dense metallic silver layer on the metallized polyimide fiber non-woven fabric, and the metallic silver was unevenly distributed on the polyimide non-woven fabric.

[0140] Comparative Example 5: Plating temperature is too high

[0141] The plating temperature in the metallization treatment of step (1) of Example 1 was adjusted to 25° C., and the concentrations of silver nitrate, ammonia water, and glucose in the plating solution were adjusted to 50 g / L, 300 g / L, and 60 g / L, respectively, and anhydrous ethanol was omitted; the rest of the steps were kept consistent with those of Example 1 to obtain a metallized polyimide fiber nonwoven fabric.

[0142] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0143] The results showed that the plating solution quickly became turbid and the entire plating process was unstable, which made it difficult to obtain a uniform and dense metallic silver layer on the metallized polyimide fiber non-woven fabric, and the metallic silver was unevenly distributed on the polyimide non-woven fabric.

[0144] Comparative Example 6: Plating temperature is too low

[0145] The plating temperature in the metallization treatment in step (1) of Example 1 was adjusted to 0° C.; other conditions remained the same as in Example 1, and a metallized polyimide fiber nonwoven fabric was obtained.

[0146] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0147] The results showed that due to the decrease in plating temperature, the reaction rate decreased, and the obtained metallized polyimide fiber non-woven fabric had poor uniformity and low electrical conductivity of only 18S / cm.

[0148] Comparative Example 7: Plating temperature is too high

[0149] The plating temperature in the metallization treatment of step (1) of Example 1 was adjusted to 40° C.; the other conditions were kept consistent with Example 1, and a metallized polyimide fiber nonwoven fabric was obtained.

[0150] The obtained metallized polyimide fiber nonwoven fabric was subjected to performance testing;

[0151] The results showed that: due to the high overall temperature of the plating solution, the reaction rate was too fast, causing the plating solution to lose stability in a short period of time. At the same time, the silver plating effect on the polyimide non-woven fabric was uneven, and the conductivity was too low, only 16S / cm.

[0152] Comparative Example 8

[0153] The activation step in step (1) of Example 1 was omitted, and the rest remained the same as in Example 1.

[0154] The results showed that due to the absence of active sites, no metal was deposited on the fiber surface during the plating process and the chemical plating process could not proceed.

[0155] Comparative Example 9

[0156] The sodium dodecylbenzenesulfonate treatment in step (2) of Example 1 was omitted, and other conditions were consistent with those of Example 1.

[0157] The results showed that: since the metallized polyimide non-woven fabric was not surface modified, during the hydrothermal reaction, the material was hydrophobic as a whole, and there were no sites on the surface of the metallized non-woven fabric fibers for the adsorption of cobalt and nickel metal ions. As a result, the final material did not successfully load nickel cobaltate, and the material itself did not have magnetic properties.

[0158] Comparative Example 10

[0159] The addition of urea in step (3) of Example 1 was omitted, and other conditions were consistent with those of Example 1.

[0160] The results showed that due to the lack of urea addition, only a small amount of nickel cobalt oxide precursor was generated in the hydrothermal reaction, which failed to be evenly loaded on the material. At the same time, its overall morphology collapsed, making it difficult to meet the experimental requirements.

[0161] Comparative Example 11

[0162] The cobalt-nickel solution was adjusted such that cobalt nitrate was changed to cobalt sulfate or cobalt chloride, and nickel nitrate was changed to nickel sulfate or nickel chloride. Other changes were the same as in Example 1.

[0163] The results showed that the previously prepared metallic silver layer had fallen off and melted into the solution, making it impossible to obtain magnetic electromagnetic shielding polyimide fiber non-woven fabric.

[0164] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a low-reflection magnetic and electromagnetic shielding polyimide fiber nonwoven fabric, characterized in that: The method includes the following steps: (1) Preparation of metallized polyimide fiber nonwoven fabric: The polyimide fiber nonwoven fabric is placed in a roughening liquid for roughening treatment, and after the roughening treatment is completed, the nonwoven fabric is taken out, washed, and dried to obtain a roughened polyimide fiber nonwoven fabric; The roughened polyimide fiber nonwoven fabric is then placed in an activation solution for treatment. After treatment, the nonwoven fabric is taken out, washed, and dried to obtain an activated polyimide fiber nonwoven fabric; wherein the solute in the activation solution is a silver salt or a copper salt with a concentration of 0.5 to 25 g / L; The activated polyimide fiber nonwoven fabric is then placed in a metal plating solution for metallization treatment. After completion, the nonwoven fabric is taken out, washed, and dried to obtain a metallized polyimide fiber nonwoven fabric. The metallization treatment time is 10 to 90 minutes and the temperature is 10 to 20° C. The metal plating solution comprises a metal salt, a complexing agent, a reducing agent, and ultrapure water. The metal salt is silver nitrate, the complexing agent is one or more of lactic acid, sodium citrate, acetic acid, sodium acetate, malic acid, thiourea, ammonium chloride, ammonia water, and disodium ethylenediaminetetraacetate, and the reducing agent is one or more of glucose, dimethylaminoborane, potassium sodium tartrate, anhydrous ethanol, and boric acid. (2) Preparation of modified metallized polyimide fiber nonwoven fabric: The metallized polyimide fiber nonwoven fabric is placed in a surfactant solution for modification, and after modification, the nonwoven fabric is taken out, washed, and dried to obtain a modified metallized polyimide fiber nonwoven fabric; wherein the surfactant is one or both of sodium dodecylbenzene sulfonate and sodium stearate, and the concentration is 5 to 8 g / L; (3) Preparation of magnetic electromagnetic shielding polyimide fiber nonwoven fabric: The modified metallized polyimide fiber nonwoven fabric is immersed in a cobalt-nickel solution, followed by a hydrothermal reaction at 100-160° C. for 6-12 hours. After the reaction is completed, the nonwoven fabric is taken out; the nonwoven fabric is then placed in an inert gas atmosphere for annealing, taken out, washed, and dried to obtain a magnetic and electromagnetic shielding polyimide fiber nonwoven fabric; the cobalt-nickel solution comprises a cobalt salt, a nickel salt, and a pH regulator; wherein the cobalt salt is cobalt nitrate and the nickel salt is nickel nitrate; and the pH regulator is urea with a concentration of 1.5-3 g / L.

2. The method according to claim 1, characterized in that In the metallization treatment of step (1), the metal plating solution comprises a metal salt, a chelating agent, a reducing agent, and ultrapure water; wherein the metal salt is silver nitrate, and the concentration is 20 to 60 g / L; the chelating agent is one or more of lactic acid, sodium citrate, acetic acid, sodium acetate, malic acid, thiourea, ammonium chloride, ammonia water, and disodium ethylenediaminetetraacetate, and the concentration is 20 to 400 g / L; the reducing agent is one or more of glucose, dimethylaminoborane, potassium sodium tartrate, anhydrous ethanol, and boric acid, the concentration of dimethylaminoborane is 1 to 5 g / L, the concentration of boric acid is 2 to 6 g / L, the concentration of glucose and anhydrous ethanol is 1 to 100 g / L, and the concentration of potassium sodium tartrate is 1 to 5 g / L.

3. The method according to claim 1, characterized in that The cobalt-nickel solution in step (3) comprises a cobalt salt, a nickel salt, and a pH regulator; wherein the cobalt salt is cobalt nitrate with a concentration of 15 to 40 g / L; the nickel salt is nickel nitrate with a concentration of 15 to 40 g / L; the pH regulator is urea with a concentration of 1.5 to 3 g / L, and the pH is adjusted to 5 to 10; and the solvent is ultrapure water.

4. The method according to claim 1, wherein The polyimide fiber nonwoven fabric described in step (1) has a porous structure, and the pore size formed by the intersection of fibers is between 10 and 50 μm.

5. The method according to claim 1, wherein The solute of the roughening solution in step (1) is one or more of dopamine, citric acid, polyphenolamine, and tannic acid; the concentration is 2-10 g / L, and the solvent is a buffer solution.

6. The method according to claim 1, characterized in that The roughening treatment in step (1) is carried out at room temperature and 400-700 rpm for 6-24 hours.

7. The method according to claim 1, characterized in that The silver salt of the activation solution in step (1) is silver nitrate; the copper salt includes one or more of copper chloride, copper nitrate, and copper sulfate; and the activation treatment is performed at room temperature for 10 to 200 minutes.

8. The method according to claim 1, characterized in that The modification treatment in step (2) is performed by soaking at room temperature for 1 to 3 hours.

9. A low-reflection magnetic and electromagnetic shielding polyimide fiber nonwoven fabric prepared by the method according to any one of claims 1 to 8.

10. Use of the low-reflection magnetic electromagnetic shielding polyimide fiber nonwoven fabric according to claim 9 in the field of electromagnetic protection of aerospace devices, military equipment or precision electronic instruments.

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