A laminated electromagnetic shielding composite

Abstract

The application relates to the technical field of shielding materials, and discloses a layered electromagnetic shielding composite material and a preparation method thereof. The composite material comprises a reflection layer, a loss layer and a reflection layer which are sequentially stacked; the reflection layer is a reflection layer with gradient distribution of metal particles obtained through electric field induction; and the loss layer is a loss layer with uniform distribution of ferrite obtained through electric field induction. The film material prepared in the application presents a multilayer structure of loss-reflection-loss, reduces the percolation threshold, and effectively improves the electromagnetic shielding performance of the material.

Description

Technical Field

[0001] This invention relates to the field of shielding materials technology, and more specifically, to a layered electromagnetic shielding composite material and its preparation method. Background Technology

[0002] With the rapid development of wireless communication and electronic science and technology, electromagnetic waves, as carriers, have permeated all aspects of people's lives in various communication, heating, and medical devices. For example, radio waves are used for signal transmission in radios and televisions; microwaves are used in mobile phone communication, radar detection, and satellite navigation. With the dramatic increase in the number of aerospace vehicles, military probes, and civilian smart communication devices, electromagnetic pollution is becoming increasingly serious. Electromagnetic radiation can interfere with the operation of some precision electronic devices, and severe electromagnetic radiation can even affect the health of biological organisms. The main protective measure against electromagnetic pollution is to use electromagnetic shielding materials to enclose and protect the objects that need protection. Furthermore, the rapid development of the electronics industry, the development of digital electronic products such as smartphones and tablets, and technological advancements and social demands have led to further miniaturization, lightweighting, and high-density assembly of electronic products. Electromagnetic shielding materials are being used extensively in electronic communication product circuits. In the field of shielding materials, traditional metallic electromagnetic shielding materials are being replaced by lighter and more portable polymer film electromagnetic shielding materials.

[0003] Chinese patent CN110769666A discloses an electromagnetic shielding film and its preparation method, comprising a first shielding layer, a first insulating layer, a second shielding layer and an adhesive film layer stacked sequentially. The first shielding layer has a first through hole penetrating its upper and lower surfaces, and the second shielding layer has a second through hole penetrating its upper and lower surfaces. Different layers are bonded together by the adhesive film layer, and there are convex conductor particles between the layers.

[0004] Chinese patent CN111132533A discloses an electromagnetic shielding film, which is a composite electromagnetic shielding film made of MXene, silver nanowires, and a binder. The mass ratio of MXene to silver nanowires is 0.05–20, and the mass amount of binder is 0.001–10% of the total mass of MXene and silver nanowires. The preparation method includes: thoroughly mixing a silver nanowire solution with a binder to obtain a mixture 1; then thoroughly mixing mixture 1 with an MXene solution to obtain a mixture 2; and finally filtering mixture 2 to form a film, thus obtaining the MXene / silver nanowire composite electromagnetic shielding film. Summary of the Invention

[0005] The technical problem solved by this invention:

[0006] (1) For electromagnetic shielding polymer materials to have good electromagnetic shielding performance, they must first have a certain electrical conductivity. For conductive particles in polymer materials to exhibit a sudden change in dielectric properties, their addition amount must reach the percolation threshold of the material. This will also lead to an increase in the cost of material preparation. It is necessary to optimize the state of particles in the structure, reduce their percolation threshold, and control the preparation cost.

[0007] (2) Simply increasing conductivity can improve the shielding performance of electromagnetic shielding materials, but there are limitations. This is because electromagnetic waves are formed by alternating electric and magnetic waves. Therefore, to significantly improve the shielding performance of materials, it is necessary to effectively combine the materials.

[0008] The technical solution adopted in this invention is as follows:

[0009] To address the aforementioned technical problems, the present invention aims to provide a layered electromagnetic shielding composite material and its preparation method.

[0010] First, the present invention provides a layered electromagnetic shielding composite material, comprising a reflective layer, a loss layer, and a reflective layer stacked sequentially.

[0011] The reflective layer is a reflective layer with a gradient distribution of metal particles induced by an electric field;

[0012] The loss layer is a loss layer in which ferrite is uniformly distributed and induced by an electric field.

[0013] Second, the present invention provides a method for preparing the aforementioned layered electromagnetic shielding composite material.

[0014] S1 Prepares the reflective layer

[0015] The suspension 1 or film 1 is dried under a DC electric field to obtain a reflective layer; the suspension 1 or film 1 is obtained by dispersing inorganic particles or metal particles in a polymer system;

[0016] DC electric field: intensity of 2000~5000V / cm;

[0017] S2 Preparation of Loss Layer

[0018] The suspension 2 or film 2 is dried under an alternating electric field to obtain a loss layer; the suspension 2 or film 2 is obtained by dispersing porous carbon, ferrite, and carbon nanotubes (CNT) in a polymer system; the alternating electric field has a frequency of 50-200 Hz and an intensity of 5000 V / cm.

[0019] S3 Preparation of Reflective Layer

[0020] The process is the same as S1.

[0021] In this invention, the inorganic particles include at least one of graphene, carbon nanotubes, and porous carbon, with a length of 100–50 nm and a diameter of 5–10 nm; or the inorganic particles include at least one of nano-silica and nano-titanium dioxide, with a particle size of 5–100 nm; or both.

[0022] In this invention, the metal particles include at least one of nano-silver and nano-silver coated copper, and the particle size of the metal particles is 5 to 100 nm; or the metal particles include nano-metal fibers (i.e., at least one of nano-silver fibers, nano-copper fibers, and nano-nickel fibers), and the length of the metal particles is 100 to 50 nm and the diameter is 5 to 10 nm; or both.

[0023] In this invention, the mass ratio of inorganic particles to metal particles is 0.5-1.5:1-1.5.

[0024] In this invention, the porous carbon has a pore size of 20-50 nm; the ferrite has a diameter of 15 nm; the carbon nanotube has a diameter of <15 nm and a length of 1-15 μm; and the mass ratio of porous carbon, ferrite, and carbon nanotube is 1-2:0.5-1:0.5-1.

[0025] In this invention, the reflective layer and the lossy layer are each independently selected as either a suspension or a thin film:

[0026] The polymer system in the suspension is a polymer solution; the polymer includes at least one of polyvinylidene fluoride (PVDF) and polylactic acid (PLA);

[0027] The polymer system in the film is a molten polymer, and the polymer includes at least one of polypropylene (PP), polyethylene (PE), and polymethyl methacrylate (PMMA).

[0028] In this invention, the polymer solution is obtained by dissolving the polymer, sodium dodecylbenzenesulfonate (SDBS), or sodium dodecyl sulfate (SDS) in an organic solvent; the organic solvent is at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). The mass ratio of sodium dodecylbenzenesulfonate or sodium dodecyl sulfate to carbon nanotubes is 2-3:1. 。 The mass ratio of organic solvent to polymer is 10–15:1.

[0029] In this invention, when the condition is suspension 1, drying is performed under an infrared lamp for 4-5 minutes; when the condition is suspension 2, drying is performed under an infrared lamp for 2-3 minutes; when the condition is film 1, drying is performed by natural cooling; when the condition is film 2, drying is performed by natural cooling.

[0030] The preparation methods of suspension 1 (polymer system: polymer solution) and film 1 (polymer system: molten polymer) are described in detail below:

[0031] The preparation method of suspension 1 is as follows: sodium dodecylbenzenesulfonate is dissolved in an organic solvent, a polymer is added and then dissolved again, and then inorganic particles and metal particles are added and dispersed to obtain suspension 1.

[0032] The preparation method of film 1 is as follows: polymer, inorganic particles and metal particles are mixed in an internal mixer, then placed in a mold frame, placed under a flat vulcanizing machine, and pressed to obtain film 1.

[0033] The technical effects achieved by this invention are as follows:

[0034] (1) Reflective Layer: This invention utilizes the fact that the electric forces experienced by metal particles and inorganic particles in an electric field are in different directions. By alternating between DC and AC electric fields of different intensities, particles are induced to move in a liquid polymer material to form a layered structure. In a DC electric field, due to their different properties, metal particles move towards the negative electrode, while inorganic particles move towards the positive electrode. Therefore, in a material filled with both metal and inorganic particles, under the induction of the DC electric field, they accumulate in their respective directions of motion to form a layered structure.

[0035] (2) Dissipative layer: After mixing ferrite, porous carbon, and carbon nanotubes to form a suspension, although the ferrite does not respond strongly to the electric field, after the ferrite is wrapped by the porous carbon, under the action of the electric field, the porous carbon is ordered to arrange itself in the suspension by dielectric electrophoresis. After solidification, the ferrite is distributed in the material along with the porous carbon. Specifically, since carbon materials respond more strongly to the electric field at low frequencies, the porous carbon is first oriented at low frequencies, and the carbon nanotubes are also oriented accordingly, forming a point-line and line-plane conductive and thermally conductive network with the porous carbon and ferrite, which can significantly reduce the conductivity threshold of the material. In the dissipation layer, the main electromagnetic loss performance is provided by ferrite. Porous carbon does not have a significant effect on electromagnetic loss, but due to its porous structure and the good reflection effect of carbon materials on electromagnetic waves, electromagnetic waves are continuously reflected inside the material. Since the porous carbon is wrapped with ferrite, the reflected electromagnetic waves are dissipated by the ferrite in the form of heat energy. At the same time, the oriented carbon nanotubes can effectively conduct the heat energy generated by electromagnetic wave loss and conduct it to the material surface in combination with the ordered structure in the reflective layer.

[0036] Overall, the membrane material prepared in this application exhibits a multilayer structure of loss-reflection-loss, which effectively improves the electromagnetic shielding performance of the material while reducing the percolation threshold. Summary of the Invention

[0038] Figure 1 SEM image of the material prepared in Example 1;

[0039] Figure 2 This is a graph showing the electromagnetic shielding data of the material prepared in Example 1. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0041] Example

[0042] Example 1:

[0043] This embodiment utilizes a layered electromagnetic shielding composite material, comprising the following steps:

[0044] Step 1: Take 0.06g of SDBS and add it to 30ml of DMF and stir to dissolve. Then add 2g of PVDF and stir in a 55℃ water bath until completely dissolved. Then evaporate the solution to 10ml in an oven.

[0045] Step 2: Add 0.02g CNT and 0.02g nano copper-coated silver metal particles, seal and stir in a 40℃ water bath for 2 hours, and then sonicate for 0.5 hours to obtain a uniformly dispersed suspension 1.

[0046] Step 3: Add 0.09g of SDBS to 30ml of DMF and stir to dissolve. Then add 2g of PVDF and stir in a 55℃ water bath until completely dissolved. Then evaporate the solution to 10ml in an oven.

[0047] Step 4: Add 0.02g porous carbon, 0.01g ferrite particles and 0.01g CNT, seal and stir in a 40℃ water bath for 2 hours, and then sonicate for 0.5 hours to obtain a uniformly dispersed suspension 2.

[0048] Step 5: Use a dropper to draw 1-2 ml of suspension into the mold, apply a DC electric field with an electric field strength of 3000 V to 5000 V under an electric field device, and dry it under an infrared lamp. After about 4-5 minutes, the material is dried and solidified, and a reflective layer with a gradient distribution of conductive particles is obtained.

[0049] Step 6: Use a dropper to draw 1-2 ml of suspension into the mold. Apply an alternating electric field with a frequency of 50 Hz to 200 Hz and an electric field strength of 5000 V / cm under an electric field device, and dry it under an infrared lamp. After about 2-3 minutes, the material is dried and solidified, and the first layer of electromagnetic wave dissipation layer with uniformly distributed conductive particles is obtained.

[0050] Step 7: Using a dropper, add 1-2 ml of suspension to the mold. Apply a DC electric field of 3000 V to 5000 V under an electric field device and dry under an infrared lamp. After about 4-5 minutes, the material will dry and solidify, resulting in a reflective layer with a gradient distribution of conductive particles. The same mold is used throughout the preparation process, with each subsequent suspension added sequentially on top of the previous substrate layer.

[0051] Example 2

[0052] Compared with Example 1, in this embodiment, the nano-copper-coated silver particles in the second step are replaced with nano-silver, the CNTs in the fourth step are replaced with nano-titanium dioxide, and the electric field strength in the fifth and seventh steps is reduced to 2000-3000V, while the other steps remain unchanged.

[0053] Example 3:

[0054] This embodiment provides a layered electromagnetic shielding composite material, including the following steps:

[0055] Step 1: Take 40g of PP, 0.2g of CNT, and 0.2g of nano copper-coated silver metal particles and mix them in a mixer at 180℃, 30r / min, and for 20min.

[0056] Step 2: Place the sample in a 0.2mm mold frame, place it under a flat vulcanizing machine, and press it into a film at 180℃ to obtain film 1;

[0057] The third step is to place the thin film 1 in the heating device of the electric field alignment equipment, melt it, apply a DC electric field with an electric field strength of 3000V-5000V, turn off the heating after 10 minutes, and gradually cool it under the electric field to obtain the reflective layer.

[0058] Step 4: Take 40g PP, 0.02g porous carbon, 0.01g ferrite particles and 0.01g CNT, mix them in an internal mixer at 180℃, 30r / min and 20min.

[0059] Step 5: Place the sample in a 0.2mm mold frame, place it under a flat vulcanizing machine, and press it into a film at 180℃ to obtain film 2;

[0060] Step 6: Place the thin film 2 in the heating device of the electric field alignment equipment, melt it, and then apply an AC electric field with a frequency of 50Hz to 200Hz and an electric field strength of 5000V / cm. After 10 minutes, turn off the heating and cool it under the electric field to obtain the dissipative layer.

[0061] Step 7: The film is cold-pressed together with adhesive in the order of reflective layer-dissipative layer-reflective layer.

[0062] Comparative Example

[0063] Comparative Example 1:

[0064] The difference between this comparative example and Example 1 is that it does not contain a dissipation layer.

[0065] Comparative Example 2:

[0066] The difference between this comparative example and Example 1 is that no DC electric field was applied in step 5, no AC electric field was applied in step 6, and no DC electric field was applied in step 7.

[0067] Test case

[0068] Using the material prepared in Example 1 as a sample, the cross-sectional morphology (SEM) of the material was measured, and the results are as follows: Figure 1 As shown.

[0069] The tests were conducted using Examples 1-3 and Comparative Examples 1-2 as samples. Film thickness was measured with a micrometer, and electromagnetic shielding was tested using an electrochemical analyzer. Shielding effectiveness is shown in Table 1. Figure 2 Where SET is the total shielding effectiveness, SER is the reflection loss effectiveness, and SEA is the absorption loss effectiveness.

[0070] Table 1

[0071] Example 1 0.24 81.6 Example 2 0.24 72.7 Example 3 0.45 84.2 Comparative Example 1 0.19 42.3 Comparative Example 2 0.24 56.7

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A layered electromagnetic shielding composite material, characterized in that, It includes a reflective layer, a lossy layer, and a reflective layer stacked in sequence; The reflective layer is a reflective layer with a gradient distribution of metal particles induced by an electric field; The loss layer is a loss layer with a uniform distribution of ferrite induced by an electric field. The preparation method of layered electromagnetic shielding composite material includes the following steps: S1 Fabrication of the reflective layer The suspension 1 or film 1 is dried under a DC electric field to obtain a reflective layer; the suspension 1 or film 1 is obtained by dispersing inorganic particles or metal particles in a polymer system; S2 Preparation of Loss Layer The suspension 2 or the thin film 2 is dried under an alternating electric field to obtain a loss layer; Suspension 2 or film 2 is obtained by dispersing porous carbon, ferrite, or carbon nanotubes in a polymer system; S3 Preparation of the reflective layer The process is the same as S1; When using suspension as raw material, the layered structure obtained from the previous suspension is used as the matrix, and the next suspension is added dropwise. When using thin film as raw material, the two reflective layers and loss layer prepared are laminated to obtain a composite material.

2. The layered electromagnetic shielding composite material according to claim 1, characterized in that, The raw material for suspension 1 or film 1 includes at least one of features (1-1) to (1-5): (1-1) Inorganic particles include at least one of graphene, carbon nanotubes, and porous carbon, with a length of 100-50 nm and a diameter of 5-10 nm. (1-2) The inorganic particles include at least one of nano-silica and nano-titanium dioxide, and the particle size of the inorganic particles is 5~100nm; (1-3) The metal particles include at least one of nano-silver and nano-silver coated copper, and the particle size of the metal particles is 5~100nm; (1-4) The metal particles include at least one of silver nanofibers, copper nanofibers, and nickel nanofibers, and the length of the metal particles is 100-50 nm and the diameter is 5-10 nm. (1-5) The mass ratio of inorganic particles to metal particles is 0.5~1.5:1~1.

5.

3. The layered electromagnetic shielding composite material according to claim 1, characterized in that, The raw material for suspension 2 or film 2 includes at least one of features (2-1) to (2-4): (2-1) The pore size of porous carbon is 20~50 nm; (2-2) The diameter of the ferrite is 15 nm; (2-3) The diameter of carbon nanotubes is <15nm and the length is 1~15μm; (2-4) The mass ratio of porous carbon, ferrite and carbon nanotubes is 1~2:0.5~1:0.5~1.

4. The layered electromagnetic shielding composite material according to claim 1, characterized in that, The reflective layer and the lossy layer can each be selected independently as either a suspension or a thin film: The polymer system in the suspension is a polymer solution; the polymer includes at least one of polyvinylidene fluoride and polylactic acid. The polymer system in the film is a molten polymer, and the polymer includes at least one of polypropylene, polyethylene, and polymethyl methacrylate.

5. The layered electromagnetic shielding composite material according to claim 4, characterized in that, The polymer solution is obtained by dissolving the polymer and sodium dodecylbenzenesulfonate or sodium dodecyl sulfate in an organic solvent.

6. The layered electromagnetic shielding composite material according to claim 5, characterized in that, The mass ratio of organic solvent to polymer is 10~15:1; the organic solvent includes at least one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The layered electromagnetic shielding composite material according to any one of claims 1 to 6, characterized in that, Includes at least one of features (3-1) to (3-2): (3-1) DC electric field: intensity is 2000~5000V / cm; (3-2) Alternating current electric field: frequency 50~200Hz, intensity 5000V / cm.

8. The layered electromagnetic shielding composite material according to any one of claims 1 to 6, characterized in that, Including features (4-1) to (4-2), or (4-3) to (4-4): (4-1) When the condition is suspension 1, drying: dry under infrared lamp for 4~5 minutes; (4-2) When the condition is suspension 2, drying: dry under infrared lamp for 2~3 minutes; (4-3) For film type 1, drying: natural cooling; (4-4) When the condition is film 2, drying: natural cooling.

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