Sandwich structure high-efficiency electromagnetic shielding film and preparation method thereof

Abstract

This invention relates to a sandwich-structured high-efficiency electromagnetic shielding film and its preparation method. The preparation method includes the following steps: providing a dispersion of single-walled carbon nanotubes and a dispersion of silver nanowires; alternately pouring the single-walled carbon nanotube dispersion and the silver nanowire dispersion into a funnel with filter paper in a vacuum filtration device for filtration to obtain a composite film; removing the composite film and drying it, and peeling off the filter paper to obtain the sandwich-structured high-efficiency electromagnetic shielding film. This invention controls the spacing between the composite film layers by controlling the filtration quality of the single-layer dispersion. A larger interlayer spacing allows electromagnetic waves to be reflected and absorbed multiple times, thereby enhancing the electromagnetic shielding performance of the material. Furthermore, multiple electromagnetic absorptions can prevent secondary electromagnetic pollution, thus achieving a good green shielding effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic shielding materials, and particularly relates to a sandwich structure high-efficiency electromagnetic shielding film and a preparation method thereof. BACKGROUND

[0002] With the advent of the 5G era and the integration of electronic devices, electromagnetic interference is intensified, causing information leakage, affecting the normal operation of the device, 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 electromagnetic interference shielding material can effectively control harmful electromagnetic radiation. Therefore, all types of materials are being developed, including printed inks, metal meshes, independent films, and lightweight aerogels. Among these materials, films are one of the most widely used materials because they can meet the requirements of complex application scenarios such as wideband, lightweight, ultrathin, etc. Due to these characteristics, many shielding films, including carbon and MXene films, have been created. Carbon-based shielding materials (such as graphite, graphene, carbon fibers, 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 films and causing polarization loss to reduce electromagnetic waves. The electromagnetic interference shielding effectiveness (EMI SE) of CNT / epoxy composites is 8 dB at a thickness of 4.25 mm, and SE / t (thickness) is 1.9 dB mm -1 . Due to the limited electrical conductivity of pure CNTs, the shielding material must be relatively thick to achieve satisfactory performance. Silver nanowires (AgNWs) are considered a potential metal-based material for electromagnetic interference shielding applications because of its ultrathin characteristics and excellent electrical conductivity of high-concentration carriers, and it will cause considerable ohmic loss to attenuate electromagnetic waves. The EMI SE of AgNWs / MWCNT / cellulose composite paper is 24.8 dB, and SE / t is 3757 dB mm -1 , the EMI SE of AgNWs / MWCNT / PVDF fabric is 34 dB, and SE / t is 87 dB mm -1 , which shows that the combination of carbon nanotubes and AgNWs is valuable. When introducing two shielding fillers, a controllable structural design is particularly important in order to fully exploit the performance of each component.

[0005] Fang et al. developed AgNWs / PANI composite films and proved that the layered composite film has better conductivity in the x-band than the directly mixed composite film. Pradip et al. synthesized a three-layer reduced graphene oxide (rGO) / AgNWs / rGO flexible composite film (8 mm) with an x-band EMI SE of 38 dB. It has been proved that a better EMI SE can be obtained by adopting a layered structure design. However, the composite films in the prior art are mostly compact multi-layer structures, which cannot occur scattering and multiple reflections, cannot effectively produce synergistic effects of dielectric loss and magnetic loss, and cannot improve the loss capability of electromagnetic waves. SUMMARY

[0006] Based on this, the purpose of the present application is to provide a sandwich structure high-efficiency electromagnetic shielding film and a preparation method thereof, which can control the spacing between the layers of the composite film by controlling the single-layer dispersion extraction quality, so that the electromagnetic waves can be reflected and absorbed multiple times to enhance the electromagnetic shielding performance of the material, and multiple electromagnetic absorptions can also prevent secondary pollution of electromagnetic waves, thereby achieving good green shielding effect.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] The present application first provides a preparation method of a sandwich structure high-efficiency electromagnetic shielding film, which comprises the following steps:

[0009] S1. providing a single-walled carbon nanotube dispersion and a silver nanowire dispersion;

[0010] S2. alternately pouring the single-walled carbon nanotube dispersion and the silver nanowire dispersion into a funnel with filter paper of an extraction device for extraction to obtain a composite film;

[0011] S3. taking out the composite film and drying, and peeling off the filter paper to obtain a sandwich structure high-efficiency electromagnetic shielding film.

[0012] The present application can control the spacing between the layers of the composite film by controlling the single-layer dispersion extraction quality, so that the electromagnetic waves can be reflected and absorbed multiple times to enhance the electromagnetic shielding performance of the material, and multiple electromagnetic absorptions can also prevent secondary pollution of electromagnetic waves, thereby achieving good green shielding effect.

[0013] As a further improvement of the above-mentioned scheme of the present application, the single extraction amount of the single-walled carbon nanotube dispersion is consistent; and / or, the single extraction amount of the silver nanowire dispersion is 1.5-2.5 times of the single extraction amount of the single-walled carbon nanotube dispersion.

[0014] As a further improvement of the above-mentioned scheme of the present application, the single-walled carbon nanotube dispersion is obtained by dispersing single-walled carbon nanotubes in ethanol.

[0015] As a further improvement of the above-mentioned scheme of the present application, the concentration of the single-walled carbon nanotube dispersion is 0.5-1 mg / mL.

[0016] As a further improvement of the above-mentioned scheme of the present application, the silver nanowire dispersion is obtained by dispersing the silver nanowire dispersion in deionized water.

[0017] As a further improvement of the above-mentioned scheme of the present application, the concentration of the silver nanowire dispersion is 0.5-1 mg / mL.

[0018] As a further improvement of the above-mentioned scheme of the present application, the silver nanowire is prepared by mixing polyvinylpyrrolidone, potassium bromide and ethylene glycol and heating, adding silver chloride, continuously stirring, and then dropping silver nitrate solution drop by drop for reaction; after the reaction is completed, filtering to obtain silver nanowire.

[0019] As a further improvement of the above-mentioned scheme of the present application, the ratio of the use amount of polyvinylpyrrolidone, 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, the dropping speed of the silver nitrate solution is 0.006-0.06 mL / s; the heating is heating to 160-180℃, and the reaction is carried out at 160-180℃ for 90-120 min.

[0020] As a further improvement of the above-mentioned scheme of the present application, in step S4, the drying is carried out at 50-70℃ for 4-6 h.

[0021] The present application also provides a sandwich structure high-efficiency electromagnetic shielding film prepared by the above-mentioned preparation method.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The application utilizes the sandwich structure composite film prepared by single-walled carbon nanotube dispersion and silver nanowire dispersion through filtration technology, controls the spacing between the composite film layers by controlling the filtration quality of the single-layer dispersion, controls the reduction of the filtration quality of the single-layer dispersion, and the spacing between the film layers gradually increases, because the filtration quality of the single-layer dispersion is small, and the single-walled carbon nanotube in the microstructure is fibrous, which can support the whole single layer, so the lighter the filtration quality of the single-layer dispersion, the more the fiber can support the single layer, thereby regulating the layer spacing, thereby achieving the effect of increasing the effective area, and the larger layer spacing can make the electromagnetic wave reflect and absorb 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 good green shielding effect, and improving the electromagnetic shielding performance of the composite film.

[0024] The silver nanowire introduced in the application forms a three-dimensional conductive network, and the single-walled carbon nanotube has effective electromagnetic absorption capacity, so that efficient green electromagnetic shielding can be achieved, and both materials have excellent mechanical properties, and the efficient electromagnetic shielding effect can still be guaranteed after 1000 times of bending.

[0025] The sandwich structure efficient electromagnetic shielding composite film prepared by the preparation method of the application has excellent electromagnetic shielding performance and green shielding efficiency, is environmentally friendly and safe, and has a broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM image of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 1;

[0027] Figure 2 Electromagnetic interference shielding efficiency diagram of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 1;

[0028] Figure 3 SEM image of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 2;

[0029] Figure 4 Electromagnetic interference shielding efficiency diagram of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 2;

[0030] Figure 5 SEM image of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 3;

[0031] Figure 6 Electromagnetic interference shielding efficiency diagram of the sandwich structure efficient electromagnetic shielding composite film prepared in Example 3;

[0032] Figure 7The electromagnetic interference shielding effectiveness comparison chart of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in Example 3 before and after being folded 1000 times. DETAILED DESCRIPTION

[0033] For the purpose of facilitating the understanding of the present application, the present application will be described in more detail below in conjunction with specific embodiments. However, the present application can be realized 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 application more thorough and comprehensive.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0035] Example 1

[0036] The present embodiment proposes a preparation method of a sandwich structure high-efficiency electromagnetic shielding film, which comprises the following steps:

[0037] 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℃, then add 0.1 g of AgCl, continuously stir for 3 min, then drop 4 ml of AgNO3 solution (concentration is 110 mg mL -1 ) into the round-bottom flask drop by drop at a rate of 0.006 mL / s, keep at 170℃ for 120 min, to obtain an AgNWs solution. Centrifuge the supernatant at 2000 rpm for 2 hours to obtain a precipitate, which is silver nanowires.

[0038] S2. Mix single-walled carbon nanotubes and ethanol according to 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.

[0039] S3. First, put a PVDF filter membrane in the Buchner funnel of the pre-prepared VAF filtration device, pour 6 mL of the SWCNT dispersion into the Buchner funnel (diameter is 5 cm) for filtration; after the solvent is filtered out, pour 12 mL of the AgNWs dispersion into the Buchner funnel for filtration; after the filtration is completed, pour 6 mL of the 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.

[0040] S4. Put the prepared composite film into a 70°C oven for drying for 5h, and the PVDF filter film will automatically fall off, thus obtaining the sandwich-structured high-efficiency electromagnetic shielding composite film.

[0041] Figure 1 The SEM image of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example shows that the interlayer spacing between the uppermost layer and the intermediate layer, and the interlayer spacing between the intermediate layer and the lowermost layer of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example are both about 15μm.

[0042] Figure 2 The electromagnetic interference shielding effectiveness EMI SE of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example is shown in Table 1. Figure 2 It can be seen that the electromagnetic shielding performance of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example can reach about 60dB.

[0043] Example 2

[0044] The present example adopts the same implementation as Example 1, and the difference from Example 1 is that the step S3 of the present example is specifically as follows: first, put a PVDF filter film into the Buchner funnel (with a diameter of 5cm) of the VAF filtration device prepared in advance, pour 4mL of SWCNT dispersion into the Buchner funnel for filtration; after the solvent is filtered out, pour 6mL of AgNW dispersion into the Buchner funnel for filtration; after the filtration is completed, pour 4mL of SWCNT dispersion into the Buchner funnel for the last filtration; after the filtration is completed, the composite film attached to the PVDF filter film is obtained.

[0045] Figure 3 The SEM image of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example shows that the interlayer spacing between the uppermost layer and the intermediate layer, and the interlayer spacing between the intermediate layer and the lowermost layer of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example are both about 30μm.

[0046] Figure 4 The electromagnetic shielding effectiveness value EMI SE of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example is shown in Table 1. Figure 4 It can be seen that the electromagnetic shielding performance of the sandwich-structured high-efficiency electromagnetic shielding composite film obtained in the present example can reach about 65dB.

[0047] Example 3

[0048] The embodiment and the embodiment 1 adopt the same implementation, and the difference between the embodiment and the embodiment 1 is that the step S3 of the embodiment is specifically as follows: a PVDF filter membrane is first placed in a Buchner funnel (with a diameter of 5 cm) of a VAF filtration device prepared in advance, 3 mL of the SWCNT dispersion is poured into the Buchner funnel for filtration; after the solvent is filtered out, 4 mL of the AgNW dispersion is poured into the Buchner funnel for filtration; after the filtration is completed, 3 mL of the SWCNT dispersion is poured into the Buchner funnel for the last filtration; and after the filtration is completed, the composite film attached to the PVDF filter membrane is obtained.

[0049] Figure 5 The SEM image of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in the embodiment is measured by a scale, and the interlayer spacing between the uppermost layer and the intermediate layer and the interlayer spacing between the intermediate layer and the lowermost layer of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in the embodiment are both about 40 μm.

[0050] Figure 6 The electromagnetic shielding effectiveness value EMISE of the sandwich structure high-efficiency electromagnetic shielding composite film obtained in the embodiment is measured from Figure 6 It can be seen that the electromagnetic shielding performance of the sandwich structure high-efficiency electromagnetic shielding composite film prepared in the embodiment can reach about 75 dB.

[0051] The sandwich structure high-efficiency electromagnetic shielding composite film obtained in the embodiment is manually folded 1000 times, and then the electromagnetic shielding effectiveness value EMISE of the folded sandwich structure high-efficiency electromagnetic shielding composite film is measured, and the value is Figure 7 It can be seen that the sandwich structure high-efficiency electromagnetic shielding composite film obtained in the embodiment has excellent electromagnetic shielding performance. Figure 7 It can be seen that under 1000 times of bending, the high-efficiency electromagnetic shielding effect can still be ensured.

[0052] As can be seen from the above, the sandwich structure high-efficiency electromagnetic shielding composite film prepared by the preparation method of adjusting the interlayer spacing has excellent electromagnetic shielding performance and green shielding efficiency, is environmentally friendly and safe, and has a broad application prospect.

[0053] The technical features of the above-described embodiments can be combined in any manner, and in order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered that it is within the scope of the present disclosure.

[0054] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a sandwich-structured high-efficiency electromagnetic shielding thin film, characterized in that, It includes the following steps: S1. Provides single-walled carbon nanotube dispersions and silver nanowire dispersions; S2. The single-walled carbon nanotube dispersion and the silver nanowire dispersion are alternately poured into a funnel with filter paper in a vacuum filtration device for vacuum filtration to obtain a composite film; the single filtration volume of the silver nanowire dispersion is 1.5-2.5 times that of the single filtration volume of the single-walled carbon nanotube dispersion. S3. Remove the composite film and dry it, then peel off the filter paper to obtain the sandwich structure high-efficiency electromagnetic shielding film.

2. The method for preparing the sandwich-structured high-efficiency electromagnetic shielding film according to claim 1, characterized in that, The amount of material filtered in a single pass of the single-walled carbon nanotube dispersion remains consistent.

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

6. The method for preparing the sandwich-structured 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 the sandwich-structured high-efficiency electromagnetic shielding film according to claim 5, characterized in that, The silver nanowires are prepared by mixing polyvinylpyrrolidone, potassium bromide, and ethylene glycol and heating them, adding silver chloride, stirring continuously, and then adding silver nitrate solution dropwise to react; after the reaction is completed, the mixture is filtered to obtain silver nanowires.

8. The method for preparing the sandwich-structured high-efficiency electromagnetic shielding film according to claim 7, characterized in that, The ratio of polyvinylpyrrolidone, 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 rate of the silver nitrate solution is 0.006-0.06 mL / s; the heating is to 160-180 °C, and the reaction is carried out at 160-180 °C for 90-120 min.

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

10. A sandwich-structured high-efficiency electromagnetic shielding film, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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