Sandwich-structure efficient electromagnetic shielding film and preparation method thereof

Abstract

The invention relates to a sandwich-structured efficient electromagnetic shielding film and a preparation method thereof. The preparation method comprises the following steps: providing a single-walled carbon nanotube dispersion and a silver nanowire dispersion; alternately pouring the single-walled carbon nanotube dispersion and the silver nanowire dispersion into a funnel with filter paper of a suction filtration device for suction filtration to obtain a composite film; the composite film is taken out and dried, the filter paper is stripped, and the efficient electromagnetic shielding film of the sandwich structure is obtained. The distance between the composite film layers is regulated and controlled by controlling the suction filtration quality of the single-layer dispersoid, electromagnetic waves can be reflected and absorbed for multiple times due to the large distance between the layers, so that the electromagnetic shielding performance of the material is enhanced, secondary pollution of the electromagnetic waves can be prevented due to multiple electromagnetic absorption, and a good green shielding effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic shielding materials, and in particular to a sandwich structure high-efficiency electromagnetic shielding film and a preparation method thereof. Background Art

[0002] With the advent of the 5G era and the integration of electronic devices, electromagnetic interference has intensified, causing information leakage, affecting the normal operation of equipment, and even threatening human health. Therefore, it is crucial to develop high-performance electromagnetic shielding materials to reduce the adverse effects of electromagnetic radiation.

[0003] An excellent EMI shielding material can effectively control harmful electromagnetic radiation. Therefore, all types of materials are under development, including printing inks, metal meshes, independent films, and lightweight aerogels. Among these materials, film is one of the most widely used materials because it can meet the requirements of complex applications such as broadband, lightweight, and ultra-thin. Due to these characteristics, many shielding films, including carbon and MXene films, have been created. Carbon-based shielding materials (such as graphite, graphene, carbon fiber, and carbon nanotubes (CNTs)) are more attractive due to their common characteristics such as lightweight and satisfactory stability.

[0004] Carbon nanotubes (CNTs) have high potential for incorporation into lightweight EMI shielding materials due to their electrical conductivity, high aspect ratio, and ease of forming thin films and inducing polarization losses to reduce electromagnetic waves. The electromagnetic interference shielding effectiveness (EMI SE) of the CNT / epoxy composite is 8 dB at a thickness of 4.25 mm, and SE / t (thickness) is 1.9 dB mm -1 . Due to the limited conductivity of pure CNTs, the shielding material must be relatively thick to achieve satisfactory performance. Silver nanowires (AgNWs) are considered as a potential metal-based material for EMI shielding applications due to its ultra-thin properties and excellent conductivity of high-concentration carriers, and it causes considerable ohmic losses to attenuate electromagnetic waves. The EMI SE of AgNWs / MWCNT / cellulose composite paper is 24.8dB and SE / t is 3757dB mm -1 , the EMI SE of AgNWs / MWCNT / PVDF fabric is 34dB, and SE / t is 87dB mm -1 , which indicates that the combination of CNTs and AgNWs is valuable. When two shielding fillers are introduced, controllable structural design is particularly important in order to give full play to the performance of each component.

[0005] Fang et al. developed AgNWs / PANI composite films and proved that the conductivity of the layered composite films in the x-band is better than that of the directly mixed composite films. Pradip et al. synthesized a three-layer reduced graphene oxide (rGO) / AgNWs / rGO flexible composite film (8mm) with an x-band EMI SE of 38 dB. It has been proven that a better EMI SE can be obtained by adopting a layered structure design. However, most of the composite films in the prior art are compact multilayer structures, which cannot scatter and reflect multiple times, cannot effectively produce the synergistic effect of dielectric loss and magnetic loss, and do not improve the loss capacity of electromagnetic waves. Summary of the invention

[0006] Based on this, the purpose of the present invention is to provide a sandwich structured high-efficiency electromagnetic shielding film and a preparation method thereof. The spacing between the composite film layers is regulated by controlling the filtration quality of the single-layer dispersion. A larger interlayer spacing can allow electromagnetic waves to be reflected and absorbed multiple times, thereby enhancing the electromagnetic shielding performance of the material. Multiple electromagnetic absorption can also prevent secondary pollution of electromagnetic waves, thereby achieving a good green shielding effect.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for preparing a sandwich structure high-efficiency electromagnetic shielding film, which comprises the following steps: S1. providing a single-walled carbon nanotube dispersion and a silver nanowire dispersion; S2. The single-walled carbon nanotube dispersion and the silver nanowire dispersion are alternately poured into a funnel with filter paper in a filtration device for filtration to obtain a composite film; S3. Take out the composite film and dry it, peel off the filter paper, and obtain a sandwich structure high-efficiency electromagnetic shielding film.

[0008] The present invention regulates the spacing between composite membrane layers by controlling the filtration quality of a single-layer dispersion. A larger interlayer spacing can allow electromagnetic waves to be reflected and absorbed multiple times, thereby enhancing the electromagnetic shielding performance of the material. Multiple electromagnetic absorptions can also prevent secondary contamination of electromagnetic waves, thereby achieving a good green shielding effect.

[0009] As a further improvement of the above scheme of the present invention, the single filtration volume of the single-walled carbon nanotube dispersion remains consistent; and / or the single filtration volume of the silver nanowire dispersion is 1.5-2.5 times the single filtration volume of the single-walled carbon nanotube dispersion.

[0010] As a further improvement of the above solution of the present invention, the single-walled carbon nanotube dispersion is obtained by dispersing the single-walled carbon nanotubes in ethanol.

[0011] As a further improvement of the above solution of the present invention, the concentration of the single-walled carbon nanotube dispersion is 0.5-1 mg / mL.

[0012] As a further improvement of the above solution of the present invention, the silver nanowire dispersion is obtained by dispersing the silver nanowire dispersion in deionized water.

[0013] As a further improvement of the above solution of the present invention, the concentration of the silver nanowire dispersion is 0.5-1 mg / mL.

[0014] As a further improvement of the above scheme of the present invention, the preparation method of the silver nanowires is: polyvinyl pyrrolidone, potassium bromide, and ethylene glycol are mixed and heated, silver chloride is added, and after continuous stirring, a silver nitrate solution is added dropwise for reaction; after the reaction is completed, the reaction is filtered to obtain silver nanowires.

[0015] As a further improvement of the above scheme of the present invention, the dosage ratio of polyvinyl pyrrolidone, potassium bromide, ethylene glycol, silver chloride and silver nitrate solution is 1.336-2.672g:20-200mg:40-80mL:0.1-0.2g:4-8mL; and / or, the concentration of the silver nitrate solution is 100-1100mg / mL, and the dropping speed of the silver nitrate solution is 0.006-0.06mL / s; the heating is heated to 160-180°C, and the reaction is reacted at 160-180°C for 90-120min.

[0016] As a further improvement of the above solution of the present invention, in step S4, the drying is performed at 50-70° C. for 4-6 hours.

[0017] The present invention also provides a sandwich structure high-efficiency electromagnetic shielding film, which is prepared by the preparation method as described above.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a filtration technology to obtain a composite film with a sandwich structure by using a single-walled carbon nanotube dispersion and a silver nanowire dispersion. The spacing between composite film layers is regulated by controlling the filtration mass of a single-layer dispersion. The reduction of the filtration mass of the single-layer dispersion is controlled, and the interlayer spacing between film layers gradually increases. This is because the filtration mass of the single-layer dispersion is small, and the fibrous single-walled carbon nanotubes in a microscopic structure can rely on the fibers to support the entire single layer. Therefore, the lighter the filtration mass of the single-layer dispersion, the more the fibers can support the single layer, thereby regulating the interlayer spacing, thereby achieving the effect of increasing the effective area. A larger interlayer spacing can allow electromagnetic waves to be reflected and absorbed multiple times, thereby enhancing the electromagnetic shielding performance of the material, and multiple electromagnetic absorption can also prevent secondary pollution of electromagnetic waves, thereby achieving a good green shielding effect and improving the electromagnetic shielding performance of the composite film.

[0019] The silver nanowires of the present invention introduce a three-dimensional conductive network, and with the help of the effective electromagnetic absorption ability of single-walled carbon nanotubes, efficient green electromagnetic shielding can be performed. Both materials have excellent mechanical properties and can still ensure efficient electromagnetic shielding effects after 1,000 bends.

[0020] The sandwich structure high-efficiency electromagnetic shielding composite film prepared by the preparation method with adjustable interlayer spacing of the present invention has excellent electromagnetic shielding performance and green shielding efficiency, is environmentally friendly and safe, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 1; Figure 2 This is a graph showing the electromagnetic interference shielding effectiveness of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 1; Figure 3 This is a SEM image of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 2; Figure 4 This is a graph showing the electromagnetic interference shielding effectiveness of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 2; Figure 5 This is a SEM image of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 3; Figure 6 This is a graph showing the electromagnetic interference shielding effectiveness of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 3; Figure 7 This is a comparison chart of the electromagnetic interference shielding effectiveness of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 3 before and after folding 1000 times. DETAILED DESCRIPTION

[0022] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0024] Example 1 This embodiment provides a method for preparing a sandwich structure high-efficiency electromagnetic shielding film, which comprises the following steps: S1. Pour 1.336 g of PVP, 20 mg of KBr and 40 mL of ethylene glycol EG into a round-bottom flask, place the round-bottom flask in an oil bath, heat to 170 °C, add 0.1 g of AgCl, stir continuously for 3 min, and then drop 4 ml of AgNO3 solution (concentration of 110 mg mL -1 ), kept at 170°C for 120 min to obtain AgNWs solution. The supernatant was centrifuged at 2000 rpm for 2 h to obtain a precipitate, which was silver nanowires.

[0025] S2. Mix single-walled carbon nanotubes and ethanol in a mass volume ratio of 1 mg:1 mL and ultrasonically disperse for 20 minutes to obtain a SWCNT dispersion with a concentration of 1 mg / mL; disperse the silver nanowires obtained in step S1 in deionized water to obtain an AgNWs dispersion with a concentration of 1 mg / mL.

[0026] S3. First, place a PVDF filter membrane in the Buchner funnel of the pre-assembled VAF filtration device, and pour 6 mL of SWCNT dispersion into the Buchner funnel (with a diameter of 5 cm) for filtration; after the solvent is drained, pour 12 mL of AgNWs dispersion into the Buchner funnel for filtration; after the filtration is completed, pour another 6 mL of SWCNT dispersion into the Buchner funnel for the last filtration; after the filtration is completed, a composite film attached to the PVDF filter membrane is obtained.

[0027] S4. Place the prepared composite film in a 70°C oven and dry it for 5 hours. The film will fall off the PVDF filter membrane by itself, and a sandwich structure high-efficiency electromagnetic shielding composite film will be obtained.

[0028] Figure 1 This is a SEM image of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment. Using a scale ruler, it is measured that the interlayer spacing between the top layer and the middle layer of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment is about 15μm, and the middle layer is tightly connected to the bottom layer.

[0029] Figure 2 The electromagnetic interference shielding effectiveness EMI SE of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment is as follows: Figure 2 It can be seen that the electromagnetic shielding performance of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in this embodiment can reach about 60 dB.

[0030] Example 2 This embodiment adopts the same implementation method as that of Embodiment 1, and the difference from Embodiment 1 is that step S3 of this embodiment is specifically as follows: first, a PVDF filter membrane is placed in a Buchner funnel (with a diameter of 5 cm) of a pre-assembled VAF filtration device, and 4 mL of SWCNT dispersion is poured into the Buchner funnel for filtration; after the solvent is drained, 6 mL of AgNW dispersion is poured into the Buchner funnel for filtration; after the filtration is completed, 4 mL of SWCNT dispersion is poured into the Buchner funnel for the last filtration; after the filtration is completed, a composite film attached to the PVDF filter membrane is obtained.

[0031] Figure 3 This is a SEM picture of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment. Using a scale ruler to measure the interlayer spacing between the top layer and the middle layer, and between the middle layer and the bottom layer of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment are both about 30μm.

[0032] Figure 4 is the electromagnetic shielding effectiveness value EMISE of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment, from Figure 4 It can be seen that the electromagnetic shielding performance of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in this embodiment can reach about 65dB.

[0033] Example 3 This embodiment adopts the same implementation method as that of Embodiment 1, and the difference from Embodiment 1 is that step S3 of this embodiment is specifically as follows: first, a PVDF filter membrane is placed in a Buchner funnel (with a diameter of 5 cm) of a pre-assembled VAF filtration device, and 3 mL of SWCNT dispersion is poured into the Buchner funnel for filtration; after the solvent is drained, 4 mL of AgNW dispersion is poured into the Buchner funnel for filtration; after the filtration is completed, 3 mL of SWCNT dispersion is poured into the Buchner funnel for the last filtration; after the filtration is completed, a composite film attached to the PVDF filter membrane is obtained.

[0034] Figure 5 This is a SEM picture of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment. Using a scale ruler to measure the interlayer spacing between the top layer and the middle layer, and between the middle layer and the bottom layer of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment is about 40μm.

[0035] Figure 6 is the electromagnetic shielding effectiveness value EMISE of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment, from Figure 6 It can be seen that the electromagnetic shielding performance of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in this embodiment can reach about 75 dB.

[0036] The sandwich structure high-efficiency electromagnetic shielding composite film obtained in this embodiment is manually folded 1000 times, and then the electromagnetic shielding effectiveness value EMI SE of the folded sandwich structure high-efficiency electromagnetic shielding composite film is measured to obtain Figure 7 ,from Figure 7 It can be seen that after 1000 bends, efficient electromagnetic shielding effect can still be guaranteed.

[0037] In summary, the sandwich structure high-efficiency electromagnetic shielding composite film prepared by the preparation method with adjustable interlayer spacing of the present invention has excellent electromagnetic shielding performance and green shielding efficiency, is environmentally friendly and safe, and has broad application prospects.

[0038] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a sandwich structure high-efficiency electromagnetic shielding film, characterized in that: It includes the following steps: S1. providing a single-walled carbon nanotube dispersion and a silver nanowire dispersion; S2. The single-walled carbon nanotube dispersion and the silver nanowire dispersion are alternately poured into a funnel with filter paper in a filtration device for filtration to obtain a composite film; S3. Take out the composite film and dry it, peel off the filter paper, and obtain a sandwich structure high-efficiency electromagnetic shielding film.

2. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 1, characterized in that: The single filtration volume of the single-walled carbon nanotube dispersion remains consistent; and / or the single filtration volume of the silver nanowire dispersion is 1.5-2.5 times the single filtration volume of the single-walled carbon nanotube dispersion.

3. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 1, characterized in that: The single-walled carbon nanotube dispersion is obtained by dispersing single-walled carbon nanotubes in ethanol.

4. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 3, characterized in that: The concentration of the single-walled carbon nanotube dispersion is 0.5-1 mg / mL.

5. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 1, characterized in that: The silver nanowire dispersion is obtained by dispersing the silver nanowire dispersion in deionized water.

6. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 5, characterized in that: The concentration of the silver nanowire dispersion is 0.5-1 mg / mL.

7. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 5, characterized in that: The preparation method of the silver nanowires comprises: mixing polyvinyl pyrrolidone, potassium bromide and ethylene glycol and heating them, adding silver chloride, stirring continuously, and then dripping a silver nitrate solution dropwise for reaction; filtering after the reaction is completed to obtain the silver nanowires.

8. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 7, characterized in that: The dosage ratio of polyvinyl pyrrolidone, potassium bromide, ethylene glycol, silver chloride and silver nitrate solution is 1.336-2.672 g: 20-200 mg: 40-80 mL: 0.1-0.2 g: 4-8 mL; and / or, the concentration of the silver nitrate solution is 100-1100 mg / mL, and the dropping speed of the silver nitrate solution is 0.006-0.06 mL / s; the heating is heating to 160-180° C., and the reaction is reacted at 160-180° C. for 90-120 min.

9. The method for preparing a sandwich structure high-efficiency electromagnetic shielding film according to claim 1, characterized in that: In step S4, the drying is performed at 50-70° C. for 4-6 hours.

10. A sandwich structure high efficiency electromagnetic shielding film, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 9.

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