Electromagnetic shielding agent, method for preparing the same, and polyester composite film

Abstract

The electromagnetic shielding agent, a preparation method thereof and a polyester composite film, the electromagnetic shielding agent is of a core-shell structure and comprises: a core material prepared by calcining a composite of carbon nanotubes and ZIFs; a shell material containing molybdenum disulfide; the shell material covers the core material, and the mass ratio of the core material to the shell material is (20-45):(20-55); in the composite, the carbon nanotubes load the ZIFs, and the mass ratio of the carbon nanotubes to the ZIFs is (1-5):(20-40). The composite of the carbon nanotubes and the ZIFs is effectively enhanced in conductivity after high-temperature calcination, the ZIFs retain high specific surface area, are loose inside and rich in dense pores, metal ions play an important absorption role in electromagnetic shielding, the carbon nanotubes themselves also have a porous structure, and these dense pores and layered molybdenum disulfide structures can effectively reflect and absorb electromagnetic waves, so that the purpose of shielding electromagnetic signals is achieved.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials, and particularly relates to an electromagnetic shielding agent, its preparation method, and a polyester composite film. Background Technology

[0002] In recent years, the rapid development of the electronics and information industry has led to the widespread application of wireless communication equipment and high-frequency electronic devices in various fields. While enjoying the convenience of technology, the increasingly serious electromagnetic interference and pollution cannot be ignored. These not only interfere with and even damage electronic components, but also pose potential health hazards to human beings. After water, air, and noise pollution, electromagnetic radiation has become the fourth major form of pollution. Long-term exposure to electromagnetic radiation can cause irreversible damage to the human nervous system, organs, and systems. Therefore, developing electromagnetic shielding materials with high absorption loss, wide absorption bandwidth, and light weight is an effective way to solve the problem of electromagnetic radiation pollution.

[0003] Electromagnetic shielding utilizes shielding materials to block external electromagnetic energy from reaching the shielded area or to attenuate the propagation of electromagnetic energy between the shielded area and the outside world. To mitigate the impact of electromagnetic interference on equipment, most electronic devices currently use metals such as aluminum, steel, and iron for their components to achieve electromagnetic interference resistance. However, these materials are relatively expensive and require significant quantities.

[0004] Invention CN114775330B discloses a carbon fiber electromagnetic shielding paper, its preparation method, and its application. The raw materials include carbon fibers and a microwave absorbing agent loaded onto the carbon fibers. The microwave absorbing agent is molybdenum disulfide (MoS2) and iron (Fe). The microwave absorbing agent fills the pores after the carbon fibers are formed into paper. The mass fraction of molybdenum disulfide in the electromagnetic shielding paper is 3%-25%, and the mass fraction of iron is 2-8%. The preparation method involves first pressing a preliminary carbon paper, then ultrasonically impregnating it with a microwave absorbing agent selected from molybdenum disulfide and iron powder, followed by pressing, hot pressing, and drying. However, this electromagnetic shielding paper uses carbon fiber paper as a carrier and blends molybdenum disulfide and iron as microwave absorbing agents in a certain proportion for ultrasonic impregnation. This results in a large amount of carbon fiber used and significant losses, leading to high material costs and a relatively simple structure, thus limiting its application.

[0005] Invention CN104853577A discloses an ultrathin electromagnetic shielding film and its preparation method. The method involves setting an adhesive layer into a mesh structure and filling the mesh pores with conductive metal to form a mesh-like electromagnetic shielding layer, thus achieving electromagnetic shielding. However, this invention achieves electromagnetic shielding by filling with conductive metal, which is a complex process, unsuitable for large-scale production. Furthermore, the edges and corners of the mesh cannot fully contact the metal, leading to an increase in the conductivity of the electromagnetic shielding film and negatively impacting its electromagnetic shielding performance.

[0006] Therefore, how to select the material composition and structure of electromagnetic shielding agents in order to reduce their proportion and cost and simplify the production process while ensuring their excellent electromagnetic shielding effect, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides an electromagnetic shielding agent and its preparation method, including a polyester composite film containing the aforementioned electromagnetic shielding agent and its preparation method. This electromagnetic shielding agent exhibits high shielding effectiveness and stability, and can be formulated into an electromagnetic shielding coating and coated onto a polyester base film to obtain a polyester composite film with excellent electromagnetic shielding performance. The process is simple, effectively reducing the cost and processing difficulty of electromagnetic shielding materials in application.

[0008] In a first aspect, the present invention provides an electromagnetic shielding agent, wherein the electromagnetic shielding agent has a core-shell structure and comprises:

[0009] The core material is prepared by calcination of a composite of carbon nanotubes and ZIFs; in the composite, carbon nanotubes are loaded with ZIFs, and the mass ratio of carbon nanotubes to ZIFs is (1-5):(20-40).

[0010] Shell material, containing molybdenum disulfide;

[0011] The shell material covers the core material, and the mass ratio of the core material to the shell material is (20-45):(20-55).

[0012] The electromagnetic shielding agent of this invention comprises ZIFs, carbon nanotubes, and molybdenum disulfide (MoS2). The core material is a composite calcined material of carbon nanotubes and ZIF-67, with molybdenum disulfide coated on the outer layer to form the shell. On the one hand, the electromagnetic shielding effect is effectively achieved by the synergistic absorption and reflection loss of electromagnetic waves by the various components; on the other hand, the protective effect of the core-shell structure can provide a long-lasting and stable electromagnetic shielding effect.

[0013] Preferably, the ZIFs include ZIF-67, the ZIF-67 having a size of 200-600 nm, preferably 300-500 nm, and a BET area of ​​1200-1800 m². 2 / g, preferably 1400-1600m 2 / g, with a pore size of 1-40nm;

[0014] The carbon nanotubes are multi-walled carbon nanotubes and / or single-walled carbon nanotubes, with a tube length of 0.1-20 μm, preferably 0.1-10 μm, more preferably 0.5-5 μm, and a tube diameter of 1-50 nm, preferably 10-50 nm, more preferably 20-30 nm.

[0015] Carbon nanotubes possess high electrical conductivity, effectively guiding current and reducing electromagnetic wave propagation, making them excellent electromagnetic shielding materials. The porous structure of ZIF-67 can act as a scattering center for electromagnetic waves. Scattering dissipates the energy of electromagnetic waves, reducing their propagation distance and further enhancing the electromagnetic shielding effect. The synergistic effect of these two materials results in superior electromagnetic shielding. Introducing carbon nanotubes as a matrix into a composite metal-organic framework not only compensates for the low mechanical strength of metal-organic frameworks but also creates a beaded structure with a large specific surface area, high porosity, diverse structures, and modifiable pore structures. Furthermore, coating the outer layer with molybdenum disulfide, whose layered structure forms a good interface with the carbon nanotube and ZIF-67 composite, improves the overall stability and electromagnetic shielding effect of the material. This combination may further enhance the material's absorption and scattering of electromagnetic waves.

[0016] Secondly, the present invention provides a method for preparing the aforementioned electromagnetic shielding agent, comprising the following steps:

[0017] Step 1: Acidify the carbon nanotubes with nitric acid solution;

[0018] Step 2: Place the acidified carbon nanotubes into a methanol hydrothermal reactor, add soluble metal salts and organic ligands, then place in an oven, and centrifuge and dry after reaction to obtain a carbon nanotube-loaded ZIFs composite.

[0019] Step 3: Calcine the composite under argon protection, cool and collect to obtain the core material;

[0020] Step 4: Add the core material, sodium molybdate, thioacetamide and silicotungstic acid to a hydrothermal reactor for reaction, centrifuge, wash and dry to obtain the electromagnetic shielding agent.

[0021] Specifically, carboxyl carbon nanotubes are first obtained through acidification. These carboxyl carbon nanotubes are then used as a matrix to prepare ZIFs (zinc-insoluble iron-containing fiber structures) through the corresponding reactions of soluble metal salts and organic ligands. Simultaneously, a beaded composite is formed around the carbon nanotube framework. After calcination, the composite yields a core material. This core material is then mixed with molybdenum disulfide raw material, and a molybdenum disulfide shell encapsulating the core material is prepared via a hydrothermal reaction. This invention sequentially forms the core and shell material through in-situ reactions, resulting in a uniform and stable core-shell structure electromagnetic shielding agent.

[0022] Preferably, the soluble metal salt is selected from at least one of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc chloride, ferric nitrate nonahydrate, nickel nitrate hexahydrate, and cobalt nitrate hexahydrate;

[0023] The organic ligand is selected from at least one of 2-methylimidazole, benzimidazole, and 2-nitroimidazole;

[0024] The weight ratio of soluble metal salt to organic ligand is (0.5-1):1.

[0025] Preferably, the soluble metal salt includes cobalt nitrate hexahydrate, and the organic ligand includes 2-methylimidazole;

[0026] In step 2, the oven temperature is 120-140℃, and the reaction time is 3-6 hours.

[0027] The calcination temperature in step 3 is 600-800℃, the heating rate is 1-10℃ / min, and the calcination time is 2-4h.

[0028] The reaction temperature in step 4 is 160-180℃, and the reaction time is 20-30h.

[0029] By controlling the parameters of the above methods, the preparation process of electromagnetic shielding agents can be reasonably regulated to obtain products with good uniformity and reliable performance.

[0030] Thirdly, the present invention provides a polyester composite film comprising the electromagnetic shielding agent, including:

[0031] Polyester-based film, with a thickness of 15-150μm;

[0032] Electromagnetic shielding layer, 20-50μm;

[0033] An electromagnetic shielding agent and a curing agent are dispersed in a solution containing a film-forming agent and a solvent to obtain an electromagnetic shielding coating. The coating is applied to at least one surface of a polyester base film and dried to form an electromagnetic shielding layer, thereby obtaining the polyester composite film.

[0034] In the 8.2-12.4 GHz band, the total shielding effectiveness (SE) of the polyester composite film is... T ≥25dB, and absorption loss SE A With reflection loss SE R The ratio is ≥4.

[0035] Preferably, the electromagnetic shielding coating comprises, by weight, the following components:

[0036]

[0037] The film-forming agent comprises polyvinyl alcohol and modified polyvinyl alcohol in a weight ratio of (5-20):(1-5);

[0038] In the solvent, the volume ratio of deionized water, anhydrous ethanol, and acetone is 100:(1-3):(1-3).

[0039] Preferably, the curing agent is selected from epoxy curing agents, isocyanate curing agents, amine curing agents, and organosilicon curing agents, with organosilicon curing agents being more preferred. Water-based organosilicon curing agents can improve the dispersibility of materials and the water resistance of coatings in water-based polyvinyl alcohol (PVA) systems.

[0040] Preferably, the method for preparing the modified polyvinyl alcohol includes the following steps:

[0041] Step 1: Add glycidyl methacrylate monomer (GMA) to a DMSO solution of polyvinyl alcohol at a temperature of 50-65℃ and stir thoroughly;

[0042] Step 2: Add tetramethylethylenediamine to the solution from Step 1 and allow it to react completely;

[0043] Step 3: Add excess distilled water to the solution in Step 2 to obtain a gel-like modified polyvinyl alcohol precipitate, filter and dry.

[0044] Furthermore, after step 3, a purification process can be added. If a purification process is used, the precipitate in step 3 can be temporarily left unfiltered and dried, and the following operations can be performed instead:

[0045] Step 4: Dissolve the above-mentioned gel-like modified polyvinyl alcohol precipitate in acetone / ethanol solvent at 60-70℃;

[0046] Step 5: Add excess distilled water to the solution in Step 4, and precipitate to obtain modified polyvinyl alcohol.

[0047] By modifying polyvinyl alcohol (PVA) through transesterification using GMA under TEMED catalysis, unsaturated double bonds can be introduced, enhancing the reactivity and crosslinking density of PVA. This modification is based on the transesterification reaction between the acrylate groups in GMA and the hydroxyl groups (-OH) on the PVA molecular chain, resulting in the replacement of the PVA hydroxyl groups with acrylate groups from GMA. The introduced unsaturated double bonds can play a role in subsequent chemical reactions, such as forming crosslinked structures through free radical polymerization. This crosslinked structure is beneficial for improving the material's mechanical properties, thermal stability, and chemical resistance.

[0048] Furthermore, the addition of modified polyvinyl alcohol (PVA) is beneficial to improving the overall electromagnetic shielding performance of the product. Firstly, it effectively enhances the interfacial compatibility with electromagnetic shielding agents, helping to improve dispersibility and thus more effectively utilizing the conductivity and electromagnetic shielding effectiveness of CNTs, ZIFs, and MoS2. Secondly, when modified PVA is combined with electromagnetic shielding agents, its improved compatibility and plasticity allow for the formation of a more continuous and uniform conductive network, improving the overall conductivity and electromagnetic shielding efficiency of the material. Thirdly, modified PVA can form a denser network structure through cross-linking reactions, which is beneficial to improving overall durability and enhancing the electromagnetic shielding effect.

[0049] Preferably, the polyester composite film further comprises a polyaniline layer outside the electromagnetic shielding layer, and is prepared by the following steps:

[0050] (1) Add aniline monomer to hydrochloric acid solution and disperse it fully. Coat the solution onto the surface of the electromagnetic shielding layer and cool the composite film to 0-5℃.

[0051] (2) Prepare a hydrochloric acid solution of ammonium persulfate and apply it to the surface of the composite membrane containing aniline monomers to allow for full reaction;

[0052] (3) Wash with distilled water and methanol respectively, and then vacuum dry.

[0053] Fourthly, the present invention provides a method for manufacturing the aforementioned polyester composite film, comprising the following steps:

[0054] S1. Preparation of electromagnetic shielding agent;

[0055] S2. Extruding polyester resin into a film to obtain a polyester-based film, wherein the polyester-based film may be subjected to unidirectional or bidirectional stretching;

[0056] S3. Disperse the electromagnetic shielding agent and curing agent in a solution containing a film-forming agent and a solvent to obtain an electromagnetic shielding coating. Apply the coating to at least one surface of a polyester base film and dry it to form an electromagnetic shielding layer.

[0057] Optionally, S4 involves reacting outside the electromagnetic shielding layer to form a polyaniline layer.

[0058] The present invention has at least the following beneficial effects:

[0059] (1) The electromagnetic shielding agent of the present invention is simple to manufacture and easy to use. The core material of this high-performance electromagnetic shielding agent is a beaded ZIFs / carbon nanotube composite core material. Carbon nanotubes have a porous structure, and ZIFs, especially ZIF-67, retain a high specific surface area with a loose interior containing dense pores. Metal ions play an important absorption role in electromagnetic shielding. Based on the characteristics of each material and the overall configuration, the ZIFs / carbon nanotube composite core material exhibits a higher specific surface area and a stable structure. In addition to the core material with dense pores, the layered molybdenum disulfide shell material can effectively reflect and absorb electromagnetic waves, thereby further improving the shielding effect of electromagnetic signals.

[0060] (2) This invention utilizes polyvinyl alcohol as the base of the coating, which has a good interfacial adhesion effect with PET. Furthermore, the polyvinyl alcohol polymer chains and the core-shell structured electromagnetic shielding agent can effectively bond together through physical entanglement during stirring, which is beneficial for improving the service life of the material. In particular, the use of a small amount of PVA for modification introduces unsaturated double bonds through transesterification, which enhances the compatibility with the core-shell structured electromagnetic shielding agent. Good interfacial compatibility helps improve the dispersibility of the electromagnetic shielding agent, thereby more effectively utilizing the conductive properties of CNTs, ZIF-67, and MoS2, and enhancing conductivity and electromagnetic shielding effectiveness.

[0061] (3) The polyaniline layer set outside the electromagnetic shielding layer can not only further improve the electromagnetic shielding performance, but also provide a certain degree of protection for the electromagnetic shielding layer containing the electromagnetic shielding agent, which is conducive to providing long-lasting and stable electromagnetic shielding performance. Detailed Implementation

[0062] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0063] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0064] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0065] Firstly, the electromagnetic shielding agent has a core-shell structure, comprising a core and a shell, wherein the mass ratio of the core to the shell is (20-45):(20-55).

[0066] (1) Core material: It is prepared by calcination of a composite of carbon nanotubes and ZIFs, with the mass ratio of carbon nanotubes to ZIFs being (1-5):(20-40).

[0067] (2) Shell material: contains molybdenum disulfide.

[0068] Core-shell electromagnetic shielding agents are prepared through the following steps:

[0069] 1.1 Acidify 0.5-2g of carbon nanotubes with 100±2ml of concentrated nitric acid solution at 80-90℃;

[0070] 1.2 The carbon nanotubes obtained in step 1.1 are placed in a hydrothermal reactor containing methanol solution. A soluble metal salt and an organic ligand are added, and the reactor is then placed in an oven at 120-140°C for 3-6 hours. After the reaction, the reactor is centrifuged and dried to obtain a carbon nanotube-loaded ZIFs complex. Preferably, the weight ratio of the soluble metal salt to the organic ligand is (0.5-1):1. The soluble metal salt is selected from at least one of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc chloride, ferric nitrate nonahydrate, nickel nitrate hexahydrate, and cobalt nitrate hexahydrate, preferably including cobalt nitrate hexahydrate. The organic ligand is selected from at least one of 2-methylimidazole, benzimidazole, and 2-nitroimidazole, preferably including 2-methylimidazole.

[0071] 1.3 The composite obtained in step 1.2 was placed in a muffle furnace and calcined under the protection of argon gas at a temperature of 600-800℃, a heating rate of 1-10℃ / min, and a calcination time of 2-4h. After cooling, the core material was collected.

[0072] 1.4 Add the core material, sodium molybdate, thioacetamide and silicotungstic acid obtained in step 1.3 to a hydrothermal reactor and react fully at 160-180℃ for 20-30 hours. Then centrifuge, wash and dry to obtain the electromagnetic shielding agent.

[0073] The ZIFs include ZIF-67, which has a size of 200-600 nm, preferably 300-500 nm, and a BET area of ​​1200-1800 m². 2 / g, preferably 1400-1600m 2 / g, with a pore size of 1-40nm;

[0074] The carbon nanotubes are multi-walled carbon nanotubes and / or single-walled carbon nanotubes, with a tube length of 0.1-20 μm, preferably 0.1-10 μm, more preferably 0.5-5 μm, and a tube diameter of 1-50 nm, preferably 10-50 nm, more preferably 20-30 nm.

[0075] Secondly, the electromagnetic shielding coating, comprising the electromagnetic shielding agent, includes, by weight percentage:

[0076]

[0077] The film-forming agent comprises polyvinyl alcohol, preferably comprising polyvinyl alcohol and modified polyvinyl alcohol in a weight ratio of (5-20):(1-5);

[0078] The solvent includes deionized water, and preferably includes deionized water, anhydrous ethanol and acetone in a volume ratio of 100:(1-3):(1-3) after the use of modified polyvinyl alcohol.

[0079] The curing agent is selected from epoxy curing agents, isocyanate curing agents, amine curing agents, and silicone curing agents, with silicone curing agents being preferred (e.g., XR-501).

[0080] The method for preparing the modified polyvinyl alcohol includes the following steps:

[0081] Step 1: Add glycidyl methacrylate monomer to a polyvinyl alcohol DMSO solution at a temperature of 50-65℃ and stir thoroughly; the concentration of the polyvinyl alcohol DMSO solution is 5-15 w / v, and the mass ratio of glycidyl methacrylate monomer GMA to polyvinyl alcohol PVA is (0.5-1):1;

[0082] Step 2: Add tetramethylethylenediamine to the solution from Step 1 and allow it to react completely; the volume ratio of tetramethylethylenediamine (TEMED) to glycidyl methacrylate monomer (GMA) is (0.02-0.12):1.

[0083] Step 3: Add excess distilled water to the solution in Step 2 to obtain a gel-like modified polyvinyl alcohol precipitate. Optionally, the precipitate can be filtered and dried.

[0084] Preferably, the process also includes a purification step: Step 4, dissolving the above-mentioned gel-like modified polyvinyl alcohol precipitate in an acetone / ethanol solvent at 60-70°C; wherein the volume ratio of acetone to ethanol in the solvent is 1:(1-3);

[0085] Step 5: Add excess distilled water to the solution in Step 4, and precipitate to obtain modified polyvinyl alcohol.

[0086] The electromagnetic shielding coating is prepared through the following steps:

[0087] 2.1 By mass percentage, the film-forming agent and solvent are thoroughly mixed at 50-100℃ for 2-4 hours to obtain a solution;

[0088] 2.2 Add the aforementioned electromagnetic shielding agent and curing agent to the above solution, mechanically stir at 500-600 r / min for 15-30 min, and then stir with a homogenizer at 20000-40000 r / min for 2-5 min to obtain the electromagnetic shielding coating.

[0089] Thirdly, the polyester composite film containing the electromagnetic shielding agent includes:

[0090] (1) Polyester-based film with a thickness of 15-150μm;

[0091] (2) Electromagnetic shielding layer with a thickness of 20-50 μm; the electromagnetic shielding coating is applied to at least one surface of the polyester base film and dried to form an electromagnetic shielding layer.

[0092] The polyester composite film is prepared as follows:

[0093] S1. Preparation of electromagnetic shielding agent;

[0094] S2. Extruding polyester resin into a film to obtain a polyester-based film, wherein the polyester-based film may be subjected to unidirectional or bidirectional stretching;

[0095] S3. The electromagnetic shielding coating is applied to at least one surface of the polyester base film and dried to form an electromagnetic shielding layer. The coating thickness of the coating liquid is about 100-250 μm, and after drying, an electromagnetic shielding layer with a thickness of 20-50 μm, preferably 30-40 μm, is formed.

[0096] Option S4 involves reacting a polyaniline layer outside the electromagnetic shielding layer, prepared through the following steps:

[0097] (1) Add aniline monomer to a 0.5-1.2 mol / L hydrochloric acid solution and disperse it fully. The aniline concentration is 0.1-0.3 mol / L. Coat the solution onto the surface of the electromagnetic shielding layer and cool the composite film to 0-5℃.

[0098] (2) Prepare an ammonium persulfate hydrochloric acid solution using a 0.5-1.2 mol / L hydrochloric acid solution and coat it onto the surface of a composite membrane containing aniline monomers, allowing it to react fully; the mass ratio of ammonium persulfate to aniline is (1.2-2):1;

[0099] (3) Wash with distilled water and methanol respectively;

[0100] (4) Vacuum dry at 45-52℃ to constant weight to obtain a polyaniline layer with a mass of 1-10% of the electromagnetic shielding layer.

[0101] In the 8.2-12.4 GHz band, the thickness of the polyester composite film is 70-170 μm, preferably 100-150 μm, and the total shielding effectiveness SE T ≥25dB, SE preferred T ≥40dB, preferably SE T ≥50dB, and absorption loss SE A With reflection loss SE R The ratio is ≥4, preferably ≥5, and more preferably ≥6.

[0102] Example 1

[0103] The polyester composite film in this embodiment includes:

[0104] (1) Polyester-based film, approximately 100 μm;

[0105] (2) An electromagnetic shielding layer, approximately 30 μm thick; formed by coating an electromagnetic shielding coating onto one surface of a polyester base film and drying it. The electromagnetic shielding coating, by mass percentage, comprises:

[0106]

[0107] The electromagnetic shielding agent has a core-shell structure, comprising:

[0108] (1) Core material: It is prepared by calcination of a composite of carbon nanotubes and ZIF-67, with a mass ratio of carbon nanotubes to ZIF-67 of approximately 1:20.

[0109] (2) Shell material: contains molybdenum disulfide, and the mass ratio of core material to shell material is approximately 21:20.

[0110] The ZIF-67 has a size of approximately 450-550 nm and a BET area of ​​approximately 1500 m². 2 / g, with a pore size of 30±3nm;

[0111] The carbon nanotubes are single-walled carbon nanotubes with a length of 1-3 μm and a diameter of 20-30 nm.

[0112] Polyester composite films were prepared according to the following method:

[0113] S1: Preparation of electromagnetic shielding agent

[0114] 1.1 Acidify 1g of the aforementioned carbon nanotubes with 100ml of concentrated nitric acid solution at 80℃.

[0115] 1.2 The carbon nanotubes obtained in step 1.1 were placed in a hydrothermal reactor containing methanol solution. Cobalt nitrate hexahydrate and 2-methylimidazole were added, and the reactor was placed in an oven at 120°C for 4 hours. The mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole was 0.8:1. After the reaction was complete, the reactor was centrifuged and dried to obtain the carbon nanotube-loaded ZIF-67 composite.

[0116] 1.3 The composite obtained in step 1.2 was placed in a muffle furnace and calcined under the protection of argon gas. The calcination temperature was 600℃, the heating rate was 5℃ / min, and the calcination time was 4h. After cooling, the core material was collected.

[0117] 1.4 The core material obtained in step 1.3, sodium molybdate, thioacetamide and silicotungstic acid were added to a hydrothermal reactor and reacted at 160°C for 24 hours. After that, the mixture was centrifuged, washed and dried to obtain an electromagnetic shielding agent. The ratio of ZIF-67, molybdenum disulfide and carbon nanotubes was approximately 20:20:1.

[0118] S2: Preparation of coating solution:

[0119] 2.1 By mass percentage, 7 parts polyvinyl alcohol and 61 parts deionized water are thoroughly mixed at 80°C for 4 hours;

[0120] 2.2 Add 30 parts of electromagnetic shielding agent and 2 parts of curing agent to the above polyvinyl alcohol solution, mechanically stir at 600 r / min for 20 min, and then stir at 30000 r / min for 3 min with a homogenizer to obtain electromagnetic shielding coating liquid;

[0121] S3: Preparation of polyester composite film:

[0122] 3.1 Polyester resin was extruded into a film and biaxially stretched to obtain a polyester-based film with a thickness of approximately 100 μm that had undergone biaxial stretching;

[0123] 3.2 The electromagnetic shielding coating is applied to one surface of a polyester base film using a coating machine and dried to form a polyester composite film with an electromagnetic shielding layer, the thickness of which is approximately 30 μm.

[0124] Example 2

[0125] The difference between this embodiment and Embodiment 1 is that, by adjusting the amount of raw materials, the ratio of ZIF-67, molybdenum disulfide and carbon nanotubes in the electromagnetic shielding agent is approximately 20:20:1.5.

[0126] Example 3

[0127] The difference between this embodiment and Embodiment 1 is that, by adjusting the amount of raw materials, the ratio of ZIF-67, molybdenum disulfide and carbon nanotubes in the electromagnetic shielding agent is 20:20:2.

[0128] Example 4

[0129] The difference between this embodiment and Embodiment 1 is that, by adjusting the amount of raw materials, the ratio of ZIF-67, molybdenum disulfide and carbon nanotubes in the electromagnetic shielding agent is 20:20:2.5.

[0130] Example 5

[0131] The difference between this embodiment and embodiment 4 is that the coating thickness of the electromagnetic shielding coating is increased. On one surface of a 100μm thick polyester base film, an electromagnetic shielding layer with a thickness of 40μm is dried to obtain a polyester composite film sample.

[0132] Example 6

[0133] The difference between this embodiment and embodiment 4 is that, by adjusting the amount of raw materials, the ratio of ZIF-67, molybdenum disulfide and carbon nanotubes in the electromagnetic shielding agent is 30:20:2.5.

[0134] Example 7

[0135] The difference between this embodiment and embodiment 4 is that, by adjusting the amount of raw materials, the ratio of ZIF-67, molybdenum disulfide and carbon nanotubes in the electromagnetic shielding agent is 20:25:2.5.

[0136] Example 8

[0137] The difference between this embodiment and Embodiment 4 lies in the composition of the electromagnetic shielding coating material. A small amount of modified polyvinyl alcohol is used in the film-forming agent, comprising, by mass percentage:

[0138]

[0139] The film-forming agent contains polyvinyl alcohol and modified polyvinyl alcohol in a weight ratio of 19:1;

[0140] The solvent contains deionized water, anhydrous ethanol, and acetone in a volume ratio of 100:2:2.

[0141] The modified polyethylene is prepared by the following steps:

[0142] Step 1: Add glycidyl methacrylate monomer to a 10 w / v % polyvinyl alcohol DMSO solution at 60°C and stir thoroughly; the mass ratio of glycidyl methacrylate monomer to PVA is 0.75:1.

[0143] Step 2: Add tetramethylethylenediamine (TEMED) to the solution from Step 1 and allow it to react completely; the volume ratio of TEMED to glycidyl methacrylate monomer (GMA) is 0.035:1.

[0144] Step 3: Add excess distilled water to the solution in Step 2 to obtain a gel-like modified polyvinyl alcohol precipitate;

[0145] Step 4: Dissolve the above-mentioned gel-like modified polyvinyl alcohol precipitate in a 1:1 volume ratio of acetone and ethanol at 68°C.

[0146] Step 5: Add excess distilled water to the solution in Step 4, and precipitate to obtain modified polyvinyl alcohol.

[0147] The electromagnetic shielding coating is applied to one surface of a 100μm thick polyester base film using a coating machine, and then dried to form a polyester composite film with an electromagnetic shielding layer, the thickness of which is approximately 30μm.

[0148] Example 9

[0149] The difference between this embodiment and Embodiment 8 is that the composition ratio of the film-forming agent in the electromagnetic shielding layer is different. The film-forming agent contains polyvinyl alcohol and modified polyvinyl alcohol in a weight ratio of 3:1. The modified polyvinyl alcohol is prepared in the same way as in Embodiment 8.

[0150] Example 10

[0151] The difference between this embodiment and Embodiment 8 is that a polyaniline layer is also provided outside the electromagnetic shielding layer, and the polyaniline layer is prepared in the following manner:

[0152] (1) Add aniline monomer to a 1 mol / L hydrochloric acid solution and disperse it fully to obtain an aniline hydrochloric acid solution with a concentration of 0.15 mol / L. Coat the solution onto the surface of the electromagnetic shielding layer and cool the composite film to 3°C.

[0153] (2) Apply the hydrochloric acid solution of ammonium persulfate to the surface of the composite membrane containing aniline monomer and allow it to react fully; the mass ratio of ammonium persulfate to aniline is 1.5:1;

[0154] (3) Wash with distilled water and methanol respectively;

[0155] (4) The polyaniline layer was vacuum dried at 50°C to constant weight, and a mass of about 3% of the electromagnetic shielding layer mass was obtained.

[0156] Example 11

[0157] The difference between this embodiment and Embodiment 10 is that the mass percentage of the polyaniline layer outside the electromagnetic shielding layer is different. The polyaniline layer is prepared in the following manner:

[0158] (1) Add aniline monomer to a 1 mol / L hydrochloric acid solution and disperse it fully to obtain an aniline hydrochloric acid solution with a concentration of 0.30 mol / L. Coat the solution onto the surface of the electromagnetic shielding layer and cool the composite film to 3°C.

[0159] (2) Apply the hydrochloric acid solution of ammonium persulfate to the surface of the composite membrane containing aniline monomer and allow it to react fully; the mass ratio of ammonium persulfate to aniline is 1.5:1;

[0160] (3) Wash with distilled water and methanol respectively;

[0161] (4) The polyaniline layer was vacuum dried at 50°C to constant weight, and the mass of the polyaniline layer was approximately 5% of that of the electromagnetic shielding layer.

[0162] Comparative Example 1

[0163] The difference between this comparative example and Example 1 is that carbon nanotubes are not added to the electromagnetic shielding agent; that is, ZIF-67 is prepared directly and then coated with molybdenum disulfide. The specific preparation process includes the following:

[0164] Dissolve 3-5g of cobalt nitrate hexahydrate in 200ml of anhydrous methanol, add 2-methylimidazole, stir at 500r / min for 2h, and then centrifuge and dry to obtain ZIF-67; the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 0.8:1;

[0165] ZIF-67, sodium molybdate, thioacetamide and silicotungstic acid were added to a hydrothermal reactor and reacted at 160°C for 24 hours. After centrifugation, washing and drying, an electromagnetic shielding agent was obtained. The mass ratio of ZIF-67 to molybdenum disulfide was approximately 1:1.

[0166] Comparative Example 2

[0167] The difference between this comparative example and Example 1 is that ZIFs are not added to the electromagnetic shielding agent. Instead, carbon nanotubes are treated and then coated with molybdenum disulfide. The specific preparation process includes the following steps:

[0168] 1g of the aforementioned carbon nanotubes was acidified with 100ml of concentrated nitric acid solution at 80℃;

[0169] Acidified carbon nanotubes, sodium molybdate, thioacetamide and silicotungstic acid were added to a hydrothermal reactor and reacted at 160°C for 24 hours. After centrifugation, washing and drying, an electromagnetic shielding agent was obtained, wherein the ratio of molybdenum disulfide to carbon nanotubes was approximately 5:2.

[0170] Comparative Example 3

[0171] The difference between this comparative example and Example 1 is that molybdenum disulfide is not added to the electromagnetic shielding agent, meaning that the electromagnetic shielding agent does not have a core-shell structure. The specific preparation process includes the following:

[0172] Carbon nanotubes were acidified with 100 ml of concentrated nitric acid solution at 80 °C.

[0173] Acidified carbon nanotubes were placed in a hydrothermal reactor containing methanol solution. Cobalt nitrate hexahydrate and 2-methylimidazole were added, and the reactor was placed in an oven at 120°C for 4 hours. The mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole was 0.8:1. After the reaction was complete, the reactor was centrifuged and dried to obtain a carbon nanotube-supported ZIF-67 composite.

[0174] The composite was placed in a muffle furnace and calcined under argon protection at a temperature of 600℃, a heating rate of 5℃ / min, and a calcination time of 4h. After cooling, the electromagnetic shielding agent was collected, in which the ratio of ZIF-67 to carbon nanotubes was approximately 20:1.

[0175] Performance testing

[0176] The measurements of Examples 1-11 and Comparative Examples 1-3 were performed using a vector network analyzer (AV3672C) based on the waveguide method, with a measurement range of 8.2-12.4 GHz. T Represents overall shielding effectiveness, SE A Represents absorption efficiency, SE R This represents the reflection efficiency. The test results are shown in Table 1:

[0177] Table 1

[0178]

[0179]

[0180] The test results show that all groups in the examples have good electromagnetic shielding capabilities. In the 8.2-12.4 GHz band, the total shielding effectiveness (SE) of the polyester composite film is [missing information]. T ≥25dB, SE preferred T ≥40dB, preferably SE T ≥50dB, and absorption loss SE A With reflection loss SE R The ratio is ≥4, preferably ≥5, and more preferably ≥6.

[0181] From Examples 1 to 4, the shielding ability of the composite material is significantly improved with the increase of carbon nanotube content. This is because carbon nanotubes themselves have good electromagnetic shielding performance, and they also provide a better framework system and better uniform loading of ZIF-67, resulting in a sample with more stable electromagnetic shielding performance, which fully meets the needs of normal applications. Under similar conditions to Example 4, Example 6 increases the proportion of ZIF-67, which helps to increase the amount of ZIF-67 loaded on the carbon nanotubes and increase the density of the beaded structure, thus improving electromagnetic shielding performance. Furthermore, Example 5 increases the thickness of the electromagnetic shielding layer compared to Example 4, which significantly improves the electromagnetic shielding effect of the polyester composite film. In Examples 8 and 9, partially replacing polyvinyl alcohol with modified polyvinyl alcohol helps to improve the electromagnetic shielding effectiveness of the product. Further, Examples 10 and 11 add a polyaniline layer, which can significantly improve the electromagnetic shielding effectiveness. The product of this invention has multiple shielding effectiveness designability. In addition, the shielding ability of the polyester composite film of this invention is mainly absorption-based, with reflection as a secondary factor, SE A Much larger than SE R It meets the requirements of the current mainstream pursuit of green EMI materials.

[0182] In contrast, Comparative Examples 1-3 omitted some components of the electromagnetic shielding agent, resulting in a significant reduction in electromagnetic shielding performance.

[0183] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the invention includes the preferred embodiments as well as all related changes and modifications. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. If such modifications and modifications based on the invention fall within the scope of the invention and its equivalents, the invention also intends to include these modifications and modifications.

Claims

1. A polyester composite film containing an electromagnetic shielding agent, characterized in that, include: Polyester-based film, with a thickness of 15-150μm; Electromagnetic shielding layer, 20-50μm; An electromagnetic shielding agent and a curing agent are dispersed in a solution containing a film-forming agent and a mixed solvent to obtain an electromagnetic shielding coating. The coating is applied to at least one surface of a polyester base film and dried to form an electromagnetic shielding layer, thereby obtaining the polyester composite film. The electromagnetic shielding agent has a core-shell structure and includes: The core material is prepared by calcination of a composite of carbon nanotubes and ZIF-67; in the composite, the carbon nanotubes are loaded with ZIF-67, and the mass ratio of carbon nanotubes to ZIF-67 is (1-5):(20-40); Shell material, containing molybdenum disulfide; The shell material covers the core material, and the mass ratio of the core material to the shell material is (20-45):(20-55). In the 8.2-12.4 GHz band, the total shielding effectiveness (SE) of the polyester composite film is... T ≥25dB, and absorption loss SE A With reflection loss SE R The ratio is ≥4.

2. The polyester composite film as described in claim 1, characterized in that, The ZIF-67 has a size of 200-600 nm and a BET area of ​​1200-1800 m². 2 / g, with a pore size of 1-40 nm.

3. The polyester composite film as described in claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes and / or single-walled carbon nanotubes, with a tube length of 0.1-20 μm and a tube diameter of 1-50 nm.

4. The polyester composite film as described in claim 1, characterized in that, The electromagnetic shielding coating comprises, by weight, the following components: 30-50 parts of electromagnetic shielding agent; 5-15 parts of film-forming agent; 45-75 parts of mixed solvent; 2-10 parts of curing agent The film-forming agent comprises polyvinyl alcohol and modified polyvinyl alcohol in a weight ratio of (5-20):(1-5); In the mixed solvent, the volume ratio of deionized water, anhydrous ethanol, and acetone is 100:(1-3):(1-3).

5. The polyester composite film as described in claim 4, characterized in that, The method for preparing the modified polyvinyl alcohol includes the following steps: Step 1: Add glycidyl methacrylate monomer to a DMSO solution of polyvinyl alcohol at a temperature of 50-65 °C and stir thoroughly; Step 2: Add tetramethylethylenediamine to the solution from Step 1 and allow it to react completely; Step 3: Add excess distilled water to the solution in Step 2 to obtain a gel-like modified polyvinyl alcohol precipitate, filter and dry.

6. The polyester composite film according to any one of claims 1-5, characterized in that, The polyester composite film, in addition to the electromagnetic shielding layer, also has a polyaniline layer, and is prepared by the following steps: (1) Add aniline monomer to hydrochloric acid solution and disperse it fully. Coat the solution onto the surface of the electromagnetic shielding layer and cool the composite film to 0-5 °C. (2) Prepare a hydrochloric acid solution of ammonium persulfate and apply it to the surface of the composite membrane containing aniline monomers to allow for full reaction; (3) Wash with distilled water and methanol respectively, and then vacuum dry.

7. A method for manufacturing a polyester composite film as described in claims 1-6, characterized in that, Includes the following steps: S1. Preparation of electromagnetic shielding agent; S2. Extruding polyester resin into a film to obtain a polyester-based film, wherein the polyester-based film may be subjected to unidirectional or bidirectional stretching; S3. Disperse the electromagnetic shielding agent and curing agent in a solution containing a film-forming agent and a mixed solvent to obtain an electromagnetic shielding coating. Apply the coating to at least one surface of a polyester base film and dry it to form an electromagnetic shielding layer. Optionally, S4 involves reacting outside the electromagnetic shielding layer to form a polyaniline layer.

8. The manufacturing method as described in claim 7, characterized in that, Step S1 includes the following steps: Step 1: Acidify the carbon nanotubes with nitric acid solution; Step 2: The acidified carbon nanotubes were placed in a hydrothermal reactor with methanol, and soluble metal salts and organic ligands were added. The reactor was then placed in an oven and centrifuged and dried after the reaction to obtain a carbon nanotube-loaded ZIFs complex. The soluble metal salts included cobalt nitrate hexahydrate, the organic ligands included 2-methylimidazole, and the ZIFs included ZIF-67. Step 3: Calcine the composite under argon protection, cool and collect to obtain the core material; Step 4: Add the core material, sodium molybdate, thioacetamide and silicotungstic acid to a hydrothermal reactor for reaction, centrifuge, wash and dry to obtain the electromagnetic shielding agent.

9. The manufacturing method as described in claim 8, characterized in that, The weight ratio of soluble metal salt to organic ligand is (0.5-1):

1.

10. The manufacturing method as described in claim 8 or 9, characterized in that, In step 2, the oven temperature is 120-140℃, and the reaction time is 3-6 hours. The calcination temperature in step 3 is 600-800℃, the heating rate is 1-10℃ / min, and the calcination time is 2-4h. The reaction temperature in step 4 is 160-180℃, and the reaction time is 20-30h.

Images