A multilayer composite wave-absorbing material with electromagnetic shielding function and a preparation method thereof

Abstract

This invention discloses a multilayer composite microwave absorbing material with electromagnetic shielding function and its preparation method. The preparation steps of the composite microwave absorbing material are as follows: 1) A GO solution is prepared using the Hummers method; 2) A C-GO film is prepared using an epichlorohydrin crosslinking agent and a coating process; 3) A silver coating is deposited on the upper and lower surfaces of the C-GO film to obtain a C-GO / Ag layer; 4) Polyaniline (PAni) is polymerized on the GO surface using in-situ free radical polymerization to obtain GO-PAni with high dispersibility; 5) GO-PAni is dispersed in a mixed solution of diisocyanate, diol, and diacid, and a prepolymer solution is obtained under the control of a catalyst, viscosity modifier, and chain extender; 6) The above polyurethane prepolymer solution is cast between and on both sides of the fixed two C-GO / Ag film, and after curing, a multilayer composite microwave absorbing material with electromagnetic shielding function is obtained. This material has high flexibility, conductivity, mechanical tensile properties, and electromagnetic shielding performance, and can be used in the field of electromagnetic shielding.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding, specifically to a multilayer composite absorbing material with electromagnetic shielding function and its preparation method. Background Technology

[0002] With the advancement and development of modern technology, various electronic and communication devices are becoming increasingly widespread, leading to increasingly complex electromagnetic pollution and interference. Electromagnetic pollution and interference can negatively impact the normal operation of electronic and communication equipment, equipment safety, information security, and even human health. Therefore, there is a demand for electromagnetic shielding in many fields, including military, aerospace, medical, and precision instrumentation, making the development of electromagnetic shielding materials an urgent necessity.

[0003] Electromagnetic shielding utilizes the guiding, absorbing, and reflecting effects of shielding materials to block or attenuate the transmission of electromagnetic energy on both sides of the shielding material. With a certain shielding material, it is possible to prevent the leakage of internal electromagnetic information and interference from external electromagnetic radiation. Its principle can be divided into three categories: (1) absorption loss that enters the shielding body without being reflected; (2) reflection loss at the incident surface; and (3) multiple reflection loss inside the shielding body.

[0004] Currently, electromagnetic shielding materials have been extensively studied and are mainly divided into three categories: 1) Metallic materials: metal materials are directly selected; 2) Filler materials: a certain proportion of conductive fillers are added to a non-conductive substrate to make the material conductive. The substrate can be silicone, plastic, etc., and the conductive fillers can be metal powder, conductive polymers, etc.; 3) Surface coating and conductive paint materials: coatings or conductive paints are introduced on the surface of the substrate.

[0005] However, the various electromagnetic shielding materials currently being prepared often suffer from problems such as low efficiency, high density, lack of flexibility, impermeability, complex manufacturing processes, and high costs. Therefore, the preparation of a new type of high-efficiency electromagnetic shielding material is of great significance to the field of electromagnetic shielding. Summary of the Invention

[0006] The purpose of this invention is to address the problems of low efficiency, high density, non-flexibility, impermeability, complex manufacturing process, and high cost of electromagnetic shielding materials, and to provide a multilayer composite absorbing material with electromagnetic shielding function and its preparation method.

[0007] This invention is achieved using the following technical solution:

[0008] A multilayer composite absorbing material with electromagnetic shielding function comprises five layers in sequence: a PU layer, a C-GO / Ag composite layer, a PU layer, a C-GO / Ag composite layer, and a PU layer, wherein the PU layer contains conductive filler.

[0009] The specific preparation steps of the multilayer composite absorbing material with electromagnetic shielding function are as follows:

[0010] 1) Preparation of GO solution using the Hummers method: Graphite with a diameter of 400-600 μm, concentrated sulfuric acid, and fuming nitric acid were mixed uniformly in a specific ratio and reacted for 2-6 hours. After washing and drying at 60°C, the product was placed in a muffle furnace at 1000°C for thermal expansion for 2-10 minutes to obtain high expansion rate graphite. The high expansion rate graphite was mixed uniformly with concentrated sulfuric acid, potassium persulfate, and phosphorus pentoxide in a specific ratio and reacted in an oil bath at 80°C for 2-8 hours. After washing with deionized water until neutral, it was dried to obtain strongly oxidized graphite. Concentrated sulfuric acid was added to the strongly oxidized graphite. Sulfuric acid was added slowly to potassium permanganate in an ice-water bath at 0°C with magnetic stirring. After the addition was complete, the system temperature was raised to 35°C and the reaction was allowed to proceed for 2-4 hours. After the solution cooled to room temperature, it was diluted with deionized water, and then 30% hydrogen peroxide solution was added dropwise until the solution turned bright yellow. The product was washed three times with 1 mol / L hydrochloric acid solution, and finally washed with deionized water until neutral. The product was collected by centrifugation at 12,000-15,000 rpm to obtain a concentrated GO solution with a mass fraction of 0.8-1.2 wt%.

[0011] 2) Take the concentrated GO solution from step 1), add epichlorohydrin crosslinking agent, and after ultrasonic dispersion, further transfer the solution to a magnetic stirrer and stir until uniform. Then, use a spraying device to circulate and spray the above-mentioned concentrated GO solution containing epichlorohydrin into a mold with a roughness of less than 0.5 micrometers, and then transfer it to a sealed crosslinking reaction at 70-80℃ for a certain period of time; then open the mold, dry it at 40-50℃, and demold to obtain the desired C-GO film layer;

[0012] 3) Using silver as the target material, a 1-3 micrometer thick silver coating was deposited on both the upper and lower surfaces of the C-GO film using physical vapor deposition technology.

[0013] 4) Prepare a dilute solution of GO prepared in step 1), then add aniline monomer and dopant phytic acid in sequence, disperse the raw materials under high-speed stirring at 1000-1500 rpm, and add initiator solution dropwise to achieve in-situ free radical polymerization of aniline on the GO surface to obtain GO-PAni with high dispersibility.

[0014] 5) GO-PAni was dispersed in a mixed solution of diisocyanate, diol and diacid, and a prepolymer emulsion was obtained under the control of catalyst, viscosity modifier and chain extender.

[0015] 6) Fix two layers of C-GO / Ag film in parallel within the mold, with the direction of fixing the two layers of C-GO / Ag film perpendicular to the ground. Use the fixed-mold casting method to cast the prepolymerized polyurethane solution after centrifugal degassing between and on both sides of the two layers of C-GO / Ag film. After curing, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

[0016] Further, in step 1), the ratio of the amount of graphite, concentrated sulfuric acid, and fuming nitric acid is 8-12g: 250-350ml: 80-125ml; the ratio of the amount of high expansion rate graphite, concentrated sulfuric acid, potassium persulfate, and phosphorus pentoxide is 2-10g: 250-350ml: 3.5-4.5g: 5.5-7g; and the ratio of the amount of strong oxidized graphite, concentrated sulfuric acid, and potassium permanganate is 1-2g: 18-250ml: 1-2g.

[0017] Further, in step 2), the amount of epichlorohydrin used is 5-10 wt%; the ultrasonic power is 100 watts, the ultrasonic time is 15-30 minutes; the magnetic stirring speed is 400-600 rpm, the stirring time is 2-4 hours; the spraying process parameters are: spraying distance is 50-80 mm, spraying pressure is 2-3 MPa, spray gun moving speed is 2-4 cm / s, and spraying temperature is 25℃; the mold is a square mold with an internal space of 20cm*10cm*1mm for pouring the solution, and the mold has a sealing cap for sealing; the crosslinking reaction time is 2-4 hours.

[0018] Further, in step 3), the silver target material is a silver block with a purity greater than 97%; the physical vapor deposition conditions are: a vacuum degree of less than 0.025 Pa in the vapor deposition chamber, an argon flow rate of 150-300 mL / min, a needle-tip clamp to reduce the area of ​​the clamp obstructing the sample, a clamp rotation speed of 2-3 rpm, a bias voltage of 80-100 V, a duty cycle of 65-75%, and a deposition time of 5-7 minutes. This process cleverly combines the characteristics of physical vapor deposition to successfully introduce a silver coating onto the surface of the C-GO film, avoiding the problems of C-GO damage and uneven coating that can occur with hydrothermal methods, and the flexible C-GO film also imparts flexibility to the C-GO / Ag coating.

[0019] Further, in step 4), the GO concentration is 0.01-0.05 wt%, the aniline monomer concentration is 0.5-0.6 wt%, the phytic acid concentration is 5-7 wt%, and the initiator concentration is 0.15-0.35 wt%, and the initiator is one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. The in-situ free radical polymerization temperature is 25℃, and the time is 4-6 hours. Dialysis with deionized water is performed until neutral, and the GO-PAni precipitate is obtained by centrifugation at 10000-12000 rpm for later use. This process utilizes GO, which has good dispersibility in water, as a core to successfully synthesize GO-PAni particles with good dispersibility, solving the dispersion problem of PAni. The GO-PAni solution does not precipitate after standing for 24 hours.

[0020] Further, in step 5), the formulation of the prepolymer solution is as follows: the mass ratio of each component is GO-PAni: diisocyanate: diol: dicarboxylic acid: catalyst: viscosity modifier: chain extender: water = 2-6 parts: 45-65 parts: 67-89 parts: 5-15 parts: 0.5-1.2 parts: 1-10 parts: 0.1-0.8 parts: 1-10 parts. The diisocyanate can be one or more of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, 2,4-toluene diisocyanate, etc.; the diol can be one or more of polytetrahydrofuran ether diol, polyethylene glycol, polybutylene glycol, phenylphosphonodichloro-p-polyethylene glycol, polybutylene adipate diol, polypropylene glycol, 1,4-butanediol, etc.; the diacid can be one or more of azelaic acid, succinic acid, glutaric acid, adipic acid, etc.; the catalyst is dibutyltin dilaurate; the viscosity modifier is one or more of D230, D400, acetone, etc.; and the chain extender is one or more of di(1-hydroxyethyl)diselenoether, 3,3'-dichloro-4,4'-diaminodiphenylmethane, isophorone diamine, etc.

[0021] Furthermore, in step 6), the centrifugation rate is 5000-7000 rpm, the time is 5-10 minutes, and the curing time is 12-24 hours.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1) The multilayer composite microwave absorbing material in this invention uses GO, silver, aniline, diisocyanate, diol and dicarboxylic acid as raw materials, and is prepared by a combination of processes such as Hummers method, physical vapor deposition, in-situ free radical polymerization, fixed-mold casting method and in-situ curing. Its structure consists of five layers in sequence: PU layer, C-GO / Ag composite layer, PU layer, C-GO / Ag composite layer and PU layer. The selection of raw materials and combination process as well as the design of the structure are all original to this invention.

[0024] 2) The multilayer composite microwave absorbing material in this invention consists of five layers from top to bottom: a PU layer, a C-GO / Ag composite layer, a PU layer, a C-GO / Ag composite layer, and a PU layer. When the microwave absorbing material functions, electromagnetic waves first enter the PU layer. Some of the electromagnetic waves are reflected on the material surface, while others are reflected and consumed between the GO-PAni particles after entering the material. The rest further penetrates into the material. When encountering the C-GO / Ag composite layer, most of the electromagnetic waves are reflected, while a small portion penetrates the C-GO / Ag composite layer and enters the middle PU layer. After penetrating the C-GO / Ag composite layer, the electromagnetic waves are reflected back and forth between the two C-GO / Ag composite layers and consumed in conjunction with the effect of the middle PU layer. Finally, a very small number of electromagnetic waves penetrate the second C-GO / Ag composite layer and enter the third PU layer, where they are reflected and consumed by the GO-PAni particles inside the third PU layer, thus achieving electromagnetic shielding.

[0025] 3) This invention designs a method for preparing a flexible C-GO thin film template using both chemical crosslinking and spraying methods. A silver coating is then introduced onto the template surface using physical vapor deposition (PVD) to obtain a C-GO / Ag composite layer. Subsequently, a fixed-mold casting method is used to introduce three PU layers between and on both sides of the two C-GO / Ag composite layers. This process cleverly combines the above techniques organically. Using C-GO as a soft template, to prevent damage and dissolution of C-GO by processes such as hydrothermal methods, a silver coating is uniformly and non-destructively introduced onto the C-GO surface using PVD, ensuring the flexibility of the C-GO / Ag layer. Simultaneously, the fixed-mold casting method achieves the fixation of the C-GO / Ag layer and the determination of the distance between the two C-GO / Ag layers, ultimately resulting in a multi-layered composite microwave absorbing material with stable material processing and structural parameters. It is precisely this combination of processes that ensures the excellent structure and performance of the microwave absorbing material. Although these processes are conventional in their respective fields, their combination and application in this invention represents a novel application of existing technologies, demonstrating significant innovation.

[0026] 4) The composite absorbing material of this invention possesses large-area processability, excellent flexibility, low density, and high-efficiency electromagnetic shielding capabilities. Large-area processability ensures mass production and reduced costs; excellent flexibility allows the absorbing material to be used in various fields, overcoming the shape-invariable problem of traditional metal absorbing materials; the low density further expands its application range, such as replacing lead aprons in the medical field; and high-efficiency electromagnetic shielding performance is fundamental to the application of this absorbing material. The organic synergy of these functions ensures the broad application prospects of this absorbing material. Attached Figure Description

[0027] Figure 1A schematic diagram of a multilayer composite absorbing material with electromagnetic shielding function;

[0028] Figure 2 This is a photograph of a C-GO film.

[0029] Figure 3 This is a picture of the actual GO-PAni nanofunctional filler. Detailed Implementation

[0030] The invention will be further illustrated below with specific examples.

[0031] Example 1:

[0032] 1) Preparation of GO solution using the Hummers method: 10g of graphite with a diameter of approximately 500μm, 250ml of concentrated sulfuric acid, and 100ml of fuming nitric acid were mixed thoroughly and reacted for 2h. After washing and drying at 60℃, the product was placed in a muffle furnace at 1000℃ for thermal expansion for 5min to obtain graphite with high expansion rate. 6g of graphite with high expansion rate was weighed and mixed thoroughly with 280ml of concentrated sulfuric acid, 3.5g of potassium persulfate, and 6g of phosphorus pentoxide. The mixture was reacted in an oil bath at 80℃ for 4h. After washing with a large amount of deionized water until neutral, it was dried to obtain strong oxidized graphite. 200ml of concentrated sulfuric acid was added to 10g of strong oxidized graphite. Under the conditions of an ice-water bath at 0℃ and magnetic stirring, 12g of potassium permanganate was slowly added. After the addition was complete, the system temperature was raised to 35℃ and reacted for 3h. After the solution temperature cooled to room temperature, it was diluted with deionized water, and then 10ml of deionized water was added dropwise. The product was washed three times with 30% hydrogen peroxide solution until it turned bright yellow; then washed with 1M hydrochloric acid solution until neutral with deionized water; and collected by centrifugation at 12,000 rpm to obtain a 1 wt% GO concentrated solution.

[0033] 2) Take the concentrated GO solution from step 1), add 5 wt% of epichlorohydrin crosslinking agent, and then ultrasonically disperse it at 100 W for 15 minutes. Next, transfer the solution to a magnetic stirrer and stir at 400 rpm for 2 hours until homogeneous. Then, use a spraying device to circulate and spray the above-mentioned epichlorohydrin-containing concentrated GO solution into a mold with a roughness of less than 0.5 micrometers (spraying distance 50 mm, spraying pressure 3 MPa, spray gun movement speed 2 cm / s, spraying temperature 25°C). Then, transfer it to a 70°C sealed crosslinking reaction environment for 2 hours. Finally, open the mold, dry it at 40°C, and demold to obtain the desired C-GO film layer with a thickness of approximately 250 micrometers.

[0034] 3) Using silver as the target material, combined with physical vapor deposition (vacuum degree in the vapor deposition chamber less than 0.025 Pa, argon flow rate of 200 ml / min, needle-tip clamp to reduce the area of ​​the clamp covering the sample, clamp rotation speed of 2 rpm, bias voltage of 80 V, duty cycle of 65%, deposition time of 5 minutes), a 1.2 μm thick silver coating was deposited on both the upper and lower surfaces of the C-GO film.

[0035] 4) Prepare a 0.05wt% dilute solution of GO prepared in step 1), then add 0.5wt% aniline monomer and 5wt% phytic acid in sequence, disperse the raw materials under high-speed stirring at 1000 rpm, add 0.15wt% ammonium persulfate initiator solution dropwise to achieve in-situ free radical polymerization of aniline on the GO surface, and after reacting for 4 hours, a GO-PAni solution with high dispersibility is obtained. Dialyze the product to neutral using deionized water, and centrifuge at 10000 rpm to obtain GO-PAni precipitate.

[0036] 5) Disperse 5 parts of GO-PAni in a mixed solution of 50 parts of diphenylmethane diisocyanate, 70 parts of polyethylene glycol, 10 parts of succinic acid, and 5 parts of water. Under the control of 0.5 parts of dibutyltin dilaurate catalyst, 5 parts of acetone viscosity modifier, and 0.5 parts of isophorone diamine chain extender, a prepolymer solution is obtained.

[0037] 6) Fix two layers of C-GO / Ag film parallel to each other in the mold. The direction in which the two layers of C-GO / Ag film are fixed is perpendicular to the ground. Using the fixed-mold casting method, pour the polyurethane prepolymer solution after centrifugation at 5000 rpm for 5 minutes into the space between and on both sides of the two layers of C-GO / Ag film. After curing for 12 hours, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

[0038] The resulting multilayer composite absorbing material has a total thickness of 2.4 mm, exhibits excellent flexibility, and can be freely bent and folded. At the same time, its electromagnetic shielding effectiveness is 32 dB.

[0039] Example 2:

[0040] 1) Preparation of GO solution using the Hummers method: 10g of graphite with a diameter of approximately 500μm, 250ml of concentrated sulfuric acid, and 100ml of fuming nitric acid were mixed thoroughly and reacted for 2h. After washing and drying at 60℃, the product was placed in a muffle furnace at 1000℃ for thermal expansion for 5min to obtain graphite with high expansion rate. 6g of graphite with high expansion rate was weighed and mixed thoroughly with 280ml of concentrated sulfuric acid, 3.5g of potassium persulfate, and 6g of phosphorus pentoxide. The mixture was reacted in an oil bath at 80℃ for 4h. After washing with a large amount of deionized water until neutral, it was dried to obtain strong oxidized graphite. 200ml of concentrated sulfuric acid was added to 10g of strong oxidized graphite. Under the conditions of an ice-water bath at 0℃ and magnetic stirring, 12g of potassium permanganate was slowly added. After the addition was complete, the system temperature was raised to 35℃ and reacted for 3h. After the solution temperature cooled to room temperature, it was diluted with deionized water, and then 10ml of deionized water was added dropwise. The product was washed three times with 30% hydrogen peroxide solution until it turned bright yellow; then washed with 1M hydrochloric acid solution until neutral with deionized water; and collected by centrifugation at 12,000 rpm to obtain a 1 wt% GO concentrated solution.

[0041] 2) Take the concentrated GO solution from step 1), add 5 wt% of epichlorohydrin crosslinking agent, and then ultrasonically disperse it at 100 W for 15 minutes. Next, transfer the solution to a magnetic stirrer and stir at 400 rpm for 2 hours until homogeneous. Then, use a spraying device to circulate and spray the above-mentioned epichlorohydrin-containing concentrated GO solution into a mold with a roughness of less than 0.5 micrometers (spraying distance 50 mm, spraying pressure 3 MPa, spray gun movement speed 2 cm / s, spraying temperature 25°C). Then, transfer it to a 70°C sealed crosslinking reaction environment for 2 hours. Finally, open the mold, dry it at 40°C, and demold to obtain the desired C-GO film layer with a thickness of approximately 250 micrometers.

[0042] 3) Using silver as the target material, combined with physical vapor deposition (vacuum degree in the vapor deposition chamber less than 0.025 Pa, argon flow rate of 200 ml / min, needle-tip clamp to reduce the area of ​​the clamp covering the sample, clamp rotation speed of 2 rpm, bias voltage of 80 V, duty cycle of 65%, deposition time of 7 minutes), a 1.8 μm thick silver coating was deposited on both the upper and lower surfaces of the C-GO film.

[0043] 4) Prepare a 0.05 wt% dilute solution of GO prepared in step 1), then add 0.5 wt% aniline monomer and 5 wt% phytic acid in sequence, and disperse the raw materials under high-speed stirring at 1000 rpm. Add 0.15 wt% ammonium persulfate initiator solution dropwise to achieve in-situ free radical polymerization of aniline on the GO surface. After 4 hours, a GO-PAni solution with high dispersibility is obtained. Dialyze the product to neutral using deionized water, and centrifuge at 10000 rpm to obtain GO-PAni precipitate.

[0044] 5) Disperse 5 parts of GO-PAni in a mixed solution of 50 parts of diphenylmethane diisocyanate, 70 parts of polyethylene glycol, 10 parts of succinic acid, and 5 parts of water. Under the control of 0.5 parts of dibutyltin dilaurate catalyst, 5 parts of acetone viscosity modifier, and 0.5 parts of isophorone diamine chain extender, a prepolymer solution is obtained.

[0045] 6) Fix two layers of C-GO / Ag film parallel to each other in the mold. The direction in which the two layers of C-GO / Ag film are fixed is perpendicular to the ground. Using the fixed-mold casting method, pour the polyurethane prepolymer solution after centrifugation at 5000 rpm for 5 minutes into the space between and on both sides of the two layers of C-GO / Ag film. After curing for 12 hours, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

[0046] Compared to Example 1, the physical vapor deposition time for silver was extended, and the thickness of the silver coating on the upper surface of C-GO increased from about 1.2 micrometers to about 1.8 micrometers. The total thickness of the resulting multilayer composite absorbing material was 2.4 mm, which has excellent flexibility and can be freely bent and folded. At the same time, due to the thicker silver coating, the reflection of electromagnetic waves and the reflection between the two C-GO layers with silver coatings were enhanced, which improved the electromagnetic shielding effectiveness to 37 dB.

[0047] Example 3:

[0048] 1) Preparation of GO solution using the Hummers method: 10g of graphite with a diameter of approximately 500μm, 250ml of concentrated sulfuric acid, and 100ml of fuming nitric acid were mixed thoroughly and reacted for 2h. After washing and drying at 60℃, the product was placed in a muffle furnace at 1000℃ for thermal expansion for 5min to obtain graphite with high expansion rate. 6g of graphite with high expansion rate was weighed and mixed thoroughly with 280ml of concentrated sulfuric acid, 3.5g of potassium persulfate, and 6g of phosphorus pentoxide. The mixture was reacted in an oil bath at 80℃ for 4h. After washing with a large amount of deionized water until neutral, it was dried to obtain strong oxidized graphite. 200ml of concentrated sulfuric acid was added to 10g of strong oxidized graphite. Under the conditions of an ice-water bath at 0℃ and magnetic stirring, 12g of potassium permanganate was slowly added. After the addition was complete, the system temperature was raised to 35℃ and reacted for 3h. After the solution temperature cooled to room temperature, it was diluted with deionized water, and then 10ml of deionized water was added dropwise. The product was washed three times with 30% hydrogen peroxide solution until it turned bright yellow; then washed with 1M hydrochloric acid solution until neutral with deionized water; and collected by centrifugation at 12,000 rpm to obtain a 1 wt% GO concentrated solution.

[0049] 2) Take the concentrated GO solution from step 1), add 5 wt% of epichlorohydrin crosslinking agent, and then ultrasonically disperse it at 100 W for 15 minutes. Next, transfer the solution to a magnetic stirrer and stir at 400 rpm for 2 hours until homogeneous. Then, use a spraying device to circulate and spray the above-mentioned epichlorohydrin-containing concentrated GO solution into a mold with a roughness of less than 0.5 micrometers (spraying distance 50 mm, spraying pressure 3 MPa, spray gun movement speed 2 cm / s, spraying temperature 25°C). Then, transfer it to a 70°C sealed crosslinking reaction environment for 2 hours. Finally, open the mold, dry it at 40°C, and demold to obtain the desired C-GO film layer with a thickness of approximately 250 micrometers.

[0050] 3) Using silver as the target material, combined with physical vapor deposition (vacuum degree in the vapor deposition chamber less than 0.025 Pa, argon flow rate of 200 ml / min, needle-tip clamp to reduce the area of ​​the clamp covering the sample, clamp rotation speed of 2 rpm, bias voltage of 80 V, duty cycle of 65%, deposition time of 5 minutes), a 1.2 μm thick silver coating was deposited on both the upper and lower surfaces of the C-GO film.

[0051] 4) Prepare a 0.05wt% dilute solution of GO prepared in step 1), then add 0.6wt% aniline monomer and 7wt% phytic acid in sequence, and disperse the raw materials under high-speed stirring at 1000 rpm. Add 0.15wt% ammonium persulfate initiator solution dropwise to achieve in-situ free radical polymerization of aniline on the GO surface. After 4 hours, a GO-PAni solution with high dispersibility is obtained. Dialyze the product to neutral using deionized water, and centrifuge at 10000 rpm to obtain GO-PAni precipitate.

[0052] 5) Disperse 6 parts of GO-PAni in a mixed solution of 50 parts of diphenylmethane diisocyanate, 70 parts of polyethylene glycol, 10 parts of succinic acid, and 5 parts of water. Under the control of 0.5 parts of dibutyltin dilaurate catalyst, 5 parts of acetone viscosity modifier, and 0.5 parts of isophorone diamine chain extender, a prepolymer solution is obtained.

[0053] 6) Fix two layers of C-GO / Ag film parallel to each other in the mold. The direction in which the two layers of C-GO / Ag film are fixed is perpendicular to the ground. Using the fixed-mold casting method, pour the polyurethane prepolymer solution after centrifugation at 5000 rpm for 5 minutes into the space between and on both sides of the two layers of C-GO / Ag film. After curing for 12 hours, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

[0054] Compared to Example 1, the amount of aniline monomer and phytic acid dopant used in GO-PAni polymerization is increased, and the amount of GO-PAni added in the polyurethane layer is also increased. This is equivalent to an increase in the conductivity of the polyurethane layer of the resulting multilayer composite microwave absorbing material. The total thickness of the material is about 2.5 mm, which has excellent flexibility and can be freely bent and folded. At the same time, the electromagnetic shielding effectiveness is 34 dB.

[0055] Example 4:

[0056] 1) Preparation of GO solution using the Hummers method: 10g of graphite with a diameter of approximately 500μm, 250ml of concentrated sulfuric acid, and 100ml of fuming nitric acid were mixed thoroughly and reacted for 2h. After washing and drying at 60℃, the product was placed in a muffle furnace at 1000℃ for thermal expansion for 5min to obtain graphite with high expansion rate. 6g of graphite with high expansion rate was weighed and mixed thoroughly with 280ml of concentrated sulfuric acid, 3.5g of potassium persulfate, and 6g of phosphorus pentoxide. The mixture was reacted in an oil bath at 80℃ for 4h. After washing with a large amount of deionized water until neutral, it was dried to obtain strong oxidized graphite. 200ml of concentrated sulfuric acid was added to 10g of strong oxidized graphite. Under the conditions of an ice-water bath at 0℃ and magnetic stirring, 12g of potassium permanganate was slowly added. After the addition was complete, the system temperature was raised to 35℃ and reacted for 3h. After the solution temperature cooled to room temperature, it was diluted with deionized water, and then 10ml of deionized water was added dropwise. The product was washed three times with 30% hydrogen peroxide solution until it turned bright yellow; then washed with 1M hydrochloric acid solution until neutral with deionized water; and collected by centrifugation at 12,000 rpm to obtain a 1 wt% GO concentrated solution.

[0057] 2) Take the concentrated GO solution from step 1), add 5 wt% of epichlorohydrin crosslinking agent, and then ultrasonically disperse it at 100 W for 15 minutes. Next, transfer the solution to a magnetic stirrer and stir at 400 rpm for 2 hours until homogeneous. Then, use a spraying device to circulate and spray the above-mentioned epichlorohydrin-containing concentrated GO solution into a mold with a roughness of less than 0.5 micrometers (spraying distance 50 mm, spraying pressure 3 MPa, spray gun movement speed 2 cm / s, spraying temperature 25°C). Then, transfer it to a 70°C sealed crosslinking reaction environment for 2 hours. Finally, open the mold, dry it at 40°C, and demold to obtain the desired C-GO film layer with a thickness of approximately 250 micrometers.

[0058] 3) Using silver as the target material, combined with physical vapor deposition (vacuum degree in the vapor deposition chamber less than 0.025 Pa, argon flow rate of 200 ml / min, needle-tip clamp to reduce the area of ​​the clamp covering the sample, clamp rotation speed of 2 rpm, bias voltage of 80 V, duty cycle of 65%, deposition time of 5 minutes), a 1.2 μm thick silver coating was deposited on both the upper and lower surfaces of the C-GO film.

[0059] 4) Prepare a 0.05 wt% dilute solution of GO prepared in step 1), then add 0.5 wt% aniline monomer and 5 wt% phytic acid in sequence, and disperse the raw materials under high-speed stirring at 1000 rpm. Add 0.15 wt% ammonium persulfate initiator solution dropwise to achieve in-situ free radical polymerization of aniline on the GO surface. After 4 hours, a GO-PAni solution with high dispersibility is obtained. Dialyze the product to neutral using deionized water, and centrifuge at 10000 rpm to obtain GO-PAni precipitate.

[0060] 5) Disperse 5 parts of GO-PAni in a mixed solution of 65 parts of diphenylmethane diisocyanate, 89 parts of polyethylene glycol, 15 parts of succinic acid, and 5 parts of water. Under the control of 0.5 parts of dibutyltin dilaurate catalyst, 5 parts of acetone viscosity modifier, and 0.8 parts of isophorone diamine chain extender, a prepolymer solution is obtained.

[0061] 6) Fix two layers of C-GO / Ag film parallel to each other in the mold. The direction in which the two layers of C-GO / Ag film are fixed is perpendicular to the ground. Using the fixed-mold casting method, pour the polyurethane prepolymer solution after centrifugation at 5000 rpm for 5 minutes into the space between and on both sides of the two layers of C-GO / Ag film. After curing for 12 hours, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

[0062] Compared to Example 1, the proportion of polyurethane molecules in the polyurethane preparation process is increased, resulting in a decrease in the conductivity of the resulting multilayer composite microwave absorbing material. The total thickness is 2.5 mm, exhibiting excellent flexibility and allowing for free bending and folding. Simultaneously, the electromagnetic shielding effectiveness is 29 dB.

Claims

1. A method for preparing a multilayer composite wave-absorbing material with electromagnetic shielding function, characterized in that, The multilayer composite absorbing material with electromagnetic shielding function comprises five layers in sequence: a PU layer, a C-GO / Ag composite layer, a PU layer, a C-GO / Ag composite layer, and a PU layer. The PU layer contains conductive filler. The preparation method is as follows: 1) Preparation of GO solution using the Hummers method: Graphite with a diameter of 400-600 μm, concentrated sulfuric acid, and fuming nitric acid were mixed uniformly and reacted for 2-6 h. After washing and drying at 60 °C, the product was placed in a muffle furnace at 1000 °C for thermal expansion for 2-10 min to obtain high expansion rate graphite. The high expansion rate graphite was mixed uniformly with concentrated sulfuric acid, potassium persulfate, and phosphorus pentoxide, and reacted in an oil bath at 80 °C for 2-8 h. After washing with deionized water until neutral, it was dried to obtain strong oxide graphite. Concentrated sulfuric acid was added to the strong oxide graphite, and potassium permanganate was slowly added under 0 °C ice-water bath and magnetic stirring conditions. After the addition was complete, the system temperature was raised to 35 °C and reacted for 2-4 h. After the solution temperature cooled to room temperature, it was diluted with deionized water, and then 30% hydrogen peroxide solution was added dropwise until the solution turned bright yellow. The product was washed three times with mol / L hydrochloric acid solution, and then washed with deionized water until neutral. The product was collected by centrifugation at 12,000-15,000 rpm to obtain a concentrated GO solution with a mass fraction of 0.8-1.2 wt%. 2) Take the concentrated GO solution from step 1), add epichlorohydrin crosslinking agent, and after ultrasonic dispersion, transfer the solution to a magnetic stirrer and stir until uniform; then spray the concentrated GO solution containing epichlorohydrin into a mold with a roughness of less than 0.5 micrometers, and then transfer it to a sealed crosslinking reaction at 70-80℃ for a certain period of time; then open the mold, dry it at 40-50℃, and demold to obtain the desired C-GO film layer; 3) Using silver as the target material, a 1-3 micrometer thick silver coating is deposited on both the upper and lower surfaces of the C-GO film using physical vapor deposition technology to obtain the C-GO / Ag layer; 4) Prepare a dilute solution of GO prepared in step 1), then add aniline monomer and dopant phytic acid in sequence, disperse the raw materials under high-speed stirring at 1000-1500 rpm, and add initiator solution dropwise to achieve in-situ free radical polymerization of aniline monomer on GO surface to obtain GO-PAni with high dispersibility. 5) GO-PAni was dispersed in a mixed solution of diisocyanate, diol, diacid and water, and a polyurethane prepolymer solution was obtained under the control of catalyst, viscosity modifier and chain extender. 6) Fix two layers of C-GO / Ag film in parallel in the mold, with the direction of fixing the two layers of C-GO / Ag film perpendicular to the ground. Use the fixed-mold casting method to cast the prepolymerized polyurethane solution after centrifugation and degassing into the space between and on both sides of the two layers of C-GO / Ag film. After curing, a multi-layer composite microwave absorbing material with electromagnetic shielding function is obtained.

2. The method for preparing the multi-layer composite wave-absorbing material with electromagnetic shielding function according to claim 1, characterized in that: In step 1), the ratio of graphite, concentrated sulfuric acid, and fuming nitric acid is 8-12g: 250-350ml: 80-125ml; the ratio of high expansion rate graphite, concentrated sulfuric acid, potassium persulfate, and phosphorus pentoxide is 2-10g: 250-350ml: 3.5-4.5g: 5.5-7g; and the ratio of strong oxidized graphite, concentrated sulfuric acid, and potassium permanganate is 1-2g: 18-25ml: 1-2g.

3. The method for preparing the multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: In step 2), the amount of epichlorohydrin used is 5-10 wt%; the ultrasonic power is 100 watts, and the ultrasonic time is 15-30 minutes; the magnetic stirring speed is 400-600 rpm, and the stirring time is 2-4 hours; the spraying process parameters are: spraying distance is 50-80 mm, spraying pressure is 2-3 MPa, spray gun moving speed is 2-4 cm / s, and spraying temperature is 25℃; the mold is a square mold with an internal space of 20cm*10cm*1mm for pouring the solution, and the mold has a sealing cap for sealing; the crosslinking reaction time is 2-4 hours.

4. The method for preparing a multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: Step 3) The silver target material is a silver block with a purity greater than 97%; the physical vapor deposition conditions are as follows: the vacuum degree in the vapor deposition chamber is less than 0.025 Pa, the argon flow rate is 150-300 ml / min, the clamping fixture is a needle-tip fixture, the fixture rotation speed is 2-3 rpm, the bias voltage is 80-100 V, the duty cycle is 65-75%, and the deposition time is 5-7 minutes.

5. The method for preparing a multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: In step 4), the GO concentration is 0.01-0.05 wt%, the aniline monomer concentration is 0.5-0.6 wt%, the phytic acid concentration is 5-7 wt%, and the initiator concentration is 0.15-0.35 wt%. The initiator is one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. The in-situ free radical polymerization temperature is 25°C, and the time is 4-6 hours. After the in-situ free radical polymerization reaction is completed, the product is dialyzed to neutral using deionized water, and the GO-PAni precipitate is obtained by centrifugation at 10,000-12,000 rpm.

6. The method for preparing a multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: In step 5), the polyurethane prepolymer solution is formulated as follows: the mass ratio of each component is GO-PAni: diisocyanate: diol: dicarboxylic acid: catalyst. Viscosity modifier: chain extender: water = 2-6 parts: 45-65 parts: 67-89 parts: 5-15 parts: 0.5-1.2 parts: 1-10 parts: 0.1-0.8 parts: 1-10 parts; The diisocyanate is one or more of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and 2,4-toluene diisocyanate; the diol is one or more of polytetrahydrofuran ether diol, polyethylene glycol, polybutylene glycol, phenylphosphonodichloro-p-polyethylene glycol, polybutylene adipate diol, polypropylene glycol, and 1,4-butanediol; the diacid is one or more of azelaic acid, succinic acid, glutaric acid, and adipic acid; the catalyst is dibutyltin dilaurate; the viscosity modifier is one or more of D230, D400, and acetone; and the chain extender is one or more of di(1-hydroxyethyl)diselenoether, 3,3'-dichloro-4,4'-diaminodiphenylmethane, and isophorone diamine.

7. The method for preparing a multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: In step 6), the centrifugation rate is 5000-7000 rpm, the time is 5-10 minutes, and the curing time is 12-24 hours.

8. The method for preparing a multilayer composite absorbing material with electromagnetic shielding function according to claim 1, characterized in that: The composite absorbing material has multiple absorbing functions, achieving electromagnetic shielding by absorbing and reflecting electromagnetic waves, and can be used in the field of electromagnetic shielding.

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