Composite flexible transparent electromagnetic shielding film and preparation method and application thereof

Abstract

The application discloses a kind of composite flexible transparent electromagnetic shielding film, including substrate, conductive film layer, MXene layer, protective layer in turn;Conductive film layer, MXene layer is arranged with interval;Substrate is PET polyester film, conductive film layer is silver nanowire, MXene layer is two-dimensional sheet MXene with multilayer structure, and protective layer is made of polymethyl methacrylate.The application further discloses a kind of preparation method of composite flexible transparent electromagnetic shielding film and its application in electronic touch screen.The preparation condition of the application is simple, and operability is strong, by regulating the alternate coating layer of silver nanowire layer and MXene layer, the transmittance and shielding effectiveness of electromagnetic shielding film are adjusted, and the more the layer is, the transmittance and shielding effectiveness are gradually smaller.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electromagnetic shielding films, in particular to a composite flexible transparent electromagnetic shielding film and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development and popularization of electronic equipment, especially the rapid development of 5G technology, along with the improvement of transmission speed, the interference problems of parts in high-frequency equipment and between equipment gradually highlight. In addition, new environmental pollution problems such as electromagnetic information leakage, electromagnetic environmental pollution and electromagnetic interference will also cause various precision electronic equipment to malfunction, and even can cause serious safety accidents. High-performance electromagnetic wave shielding materials have become the key technology to solve electromagnetic wave pollution. Therefore, in view of the urgent need for electromagnetic protection, many metal materials are the most widely used electromagnetic shielding materials at present, such as copper. However, the physical performance of metal shielding materials is not strong, easy to corrode, and low in transmittance. In addition, based on the internal structure of the material, the metal shielding material is mostly through reflection of electromagnetic waves to achieve electromagnetic shielding. This leads to its inability to meet the needs of small and thin electronic equipment in civilian or military use. It is urgent to develop a high-transmittance and high-shielding-effect electromagnetic shielding material.

[0003] A MXene / silver nanowire composite electromagnetic shielding film is disclosed in Chinese Patent No. 201911420173.8, which combines one-dimensional conductor silver nanowires with two-dimensional reflector MXene with conductivity to form a composite electromagnetic shielding film through the action of a binder, which not only increases the conductivity of the composite electromagnetic shielding film, but also improves the multiple reflection effect of the composite electromagnetic shielding film. However, the application uses a filtration method to prepare the film, which is limited by the size of the current vacuum equipment and the required filter membrane, and the size and shape of the prepared film are limited, making it difficult to prepare a large-area electromagnetic shielding film. SUMMARY

[0004] The purpose of the application is to overcome the shortcomings of the prior art, and the purpose of the application is to provide a composite flexible transparent electromagnetic shielding film, the purpose of the application is to provide a preparation method of a composite flexible transparent electromagnetic shielding film, and the purpose of the application is to provide an application of a composite flexible transparent electromagnetic shielding film in an electronic touch screen.

[0005] Technical scheme: the composite flexible transparent electromagnetic shielding film comprises a substrate, a conductive film layer, a MXene layer and a protective layer in sequence, the conductive film layer and the MXene layer are arranged in intervals, the substrate is a PET polyester film, the conductive film layer is silver nanowires, the MXene layer is a two-dimensional sheet MXene with a multi-layer structure, and the protective layer is made of polymethyl methacrylate.

[0006] Further, the thickness of the substrate is 0.5-2 mm, the thickness of the single layer of the MXene layer is 10-100 nm, the thickness of the single layer of the conductive film layer is 10-50 μm, and the thickness of the protective layer is 100-250 nm.

[0007] The preparation method of the composite flexible transparent electromagnetic shielding film comprises the following steps:

[0008] (a) peeling off the release film on the surface of the PET polyester film, plasma cleaning the surface of the film, and fixing the film on a coating table as a substrate;

[0009] (b) distributing the silver nanowire solution horizontally on the surface of the substrate, uniformly pulling down the solution with a Meyer rod, and vacuum drying to obtain a conductive film layer;

[0010] (c) uniformly spraying the MXene solution on the surface of the conductive film layer obtained in step (b), and drying to form a MXene layer;

[0011] (d) continuing to alternately perform steps (b) and (c), and adjusting the transmittance and shielding effectiveness by controlling the number of times of alternately coating the silver nanowire solution and the MXene solution;

[0012] (e) spin-coating the PMMA (polymethyl methacrylate) acetone solution on the film obtained in step (d), and cooling at 30-45 ℃ to obtain a protective layer.

[0013] Further, in step (a), the power of the plasma cleaning is 80-110 W, and the treatment time is 0.5-5.0 min.

[0014] Further, in step (b), the concentration of the silver nanowire solution is 0.5-5 mg / mL, and the silver nanowire solution is prepared by centrifuging and dissolving silver nanowires in a mixed solution of water and isopropanol. When the concentration of the silver nanowire solution is less than 0.5 mg / mL, the silver nanowires are difficult to connect into a network, the conductivity of the obtained conductive film is poor, and the electromagnetic shielding effectiveness is low. When the concentration of the silver nanowire solution is greater than 5 mg / mL, the silver nanowire concentration is too high, which reduces the uniformity of the film and the transmittance of the electromagnetic shielding film, affecting its application in the field of electronic touch screens. The volume ratio of water to isopropanol is 1:4. The pulling-down speed of the Meyer rod is 1-5 cm / s, the vacuum drying temperature is 30-60 ℃, and the time is 1-5 min. When the pulling-down speed of the Meyer rod is less than 1 cm / s, the solution backflows, affecting the uniformity of the film. When the pulling-down speed of the Meyer rod is greater than 5 cm / s, the liquid is difficult to uniformly form a film, and the formed cavities reduce the usability of the film. When the vacuum drying temperature is less than 30 ℃, the drying is too slow, causing disturbance of the solution and reducing the uniformity of the film. When the vacuum drying temperature is greater than 60 ℃, the solution is not uniformly dispersed and connected in time, reducing the uniformity of the film.

[0015] Further, in step (c), the concentration of the MXene solution is 0.3-5 mg / mL, the diameter of the spray gun is 0.2-0.3 mm, the distance is 5-15 cm, and the air pressure is 1-2 atm, and the spray is serpentine. If the concentration of the MXene solution is less than 0.3 mg / mL, the MXene is too dispersed, and it is difficult to improve the electromagnetic shielding properties of the film. If the concentration of the MXene solution is greater than 5 mg / mL, the transmittance of the film is rapidly reduced, which affects its practicability in electronic touch screens.

[0016] Further, in step (d), the number of alternating coating times is 2-8.

[0017] Further, in step (e), the mass percentage of polymethyl methacrylate in the acetone solution is 14-16 wt%, the spin coating speed is 1500-3600 rpm, the spin coating time is 1 min, and the cooling time is 10 min. If the mass percentage of polymethyl methacrylate is less than 14 wt%, the concentration is too low, and it is difficult to protect the conductive layer. If the mass percentage of polymethyl methacrylate is greater than 16 wt%, the conductivity of polymethyl methacrylate is poor, and a high concentration will reduce the conductivity of the film. If the spin coating speed is less than 1500 rpm, the film is not uniform, with a high concentration in the center and a low concentration at the edge. If the spin coating speed is greater than 3600 rpm, the solution is wasted, and the cost is increased.

[0018] The application of the composite flexible transparent electromagnetic shielding film in an electronic touch screen.

[0019] Preparation principle: Silver nanowires, as one-dimensional metal nanomaterials, have a high aspect ratio, good conductivity, and can be uniformly dispersed in water, ethanol, isopropanol and other volatile solvents. A silver nanowire network is formed by crossing, and a high-transmittance film is obtained. In addition, based on its high conductivity, it also has high shielding effectiveness. MXenes material has a multi-layer structure, which is beneficial to interlayer electromagnetic absorption and helps to further improve the electromagnetic shielding performance. It also has high capacitance, high conductivity, superior stability and flexibility. Covering the silver nanowire layer will promote the linking between silver wires, further enhance the conductivity, and also serve as a protective layer to prevent silver nanowires from oxidizing.

[0020] Advantages: Compared with the prior art, the present application has the following outstanding features:

[0021] 1. The preparation conditions are simple and the operability is strong. By adjusting the number of alternating coating layers of the silver nanowire layer and the MXene layer, the transmittance and shielding effectiveness of the electromagnetic shielding film can be adjusted. The more the number of layers, the smaller the transmittance and shielding effectiveness.

[0022] 2. The size and shape of the flexible substrate can be cut and quickly adjusted to expand the application range of the electromagnetic shielding film.

[0023] 3. The obtained electromagnetic shielding film has high transmittance of visible light and high shielding effectiveness, and is widely used in the fields of light transmission electromagnetic protection, etc. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the preparation principle diagram of the present application;

[0025] Figure 2 is the structural schematic diagram of the present application;

[0026] Figure 3 is the scanning electron microscope diagram of the electromagnetic shielding film of the present application;

[0027] Figure 4 is the transmittance, sheet resistance and number of layers of the electromagnetic shielding film obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0028] In each of the following examples, the aspect ratio of the silver nanowire is 1000, and the purity is 90%.

[0029] Example 1

[0030] As Figure 1 A preparation method of a composite flexible transparent electromagnetic shielding film, comprising the following steps:

[0031] Step one, centrifuge silver nanowires with a concentration of 1 mg / mL at 2500 rpm for 8 min, and then disperse them in 1 mL of a mixed solution of deionized water and isopropanol at a ratio of 1:4, and shake gently to mix the solution evenly.

[0032] Step two, peel off the release protective film on the surface of the PET polyester film, and place it flat in a plasma cleaning machine, with the cleaning surface facing upwards and the power of the plasma cleaning being 110 W, for 2 min to obtain a PET polyester film with a hydrophilic surface. Take out the film and fix it on a coating table as a substrate 1.

[0033] Step three, distribute 800 μL of silver nanowire solution horizontally on the upper end of the substrate 1, and use a Meyer rod to pull it down evenly from top to bottom to the bottom end of the substrate 1 at a speed of 5 cm / s. Then place the film in a 60°C vacuum drying oven for drying for 5 min to obtain a conductive film layer 2 (silver nanowire layer).

[0034] Step four, the obtained silver nanowire film is fixed on the coating table, a MXene solution with a concentration of 2 mg / mL is uniformly sprayed on the surface of the silver nanowire layer obtained in step three, the diameter of the spray gun is 0.2 mm, the distance is 10 cm, the air pressure is 2 atmospheres, the spraying is serpentine, and the film is placed at room temperature for drying to form a MXene layer 3, thereby obtaining a silver nanowire-MXene composite electromagnetic shielding film.

[0035] Step five, the film obtained in step four is placed on the coating table, and steps three and four are repeated to continue spraying the silver nanowire layer and the MXene layer 3 alternately for 8 times, and the diameter of the spray gun and the air pressure are the same as in step four, and the spraying is serpentine.

[0036] Step six, the polymethyl methacrylate solution is diluted with acetone to a final concentration of 15 wt%, and the acetone solution of PMMA is spin-coated on the film obtained in step five at a spin-coating speed of 3600 rpm for 1 min, and then cooled at 30°C for 10 min to obtain a protective layer 4.

[0037] As Figure 2 , the composite flexible transparent electromagnetic shielding film prepared in this embodiment is provided on a PET polyester film substrate 1 with a thickness of 1 mm, and the conductive film layer 2 and the MXene layer 3 are repeatedly arranged, the conductive film layer 2 is silver nanowire, the MXene layer 3 is two-dimensional sheet-shaped MXene with a multi-layer structure, the thickness of a single MXene layer 3 is 50 nm, the thickness of a single conductive film layer 2 is 50 μm, and the PMMA protective layer 4 with a thickness of 140 nm is arranged on the top MXene layer 3. The silver nanowires are uniformly distributed on the surface of the film, and the MXene is distributed in the form of sheets above the silver nanowires. With the increase of the number of alternating spraying, the transmittance of the obtained film continues to decrease, and the conductivity increases. When the number of spraying is 8, the electromagnetic shielding performance is 35 dB. The composite flexible transparent electromagnetic shielding film obtained in this embodiment can be used for electronic touch screens.

[0038] Example 2

[0039] A method for preparing a composite flexible transparent electromagnetic shielding film, comprising the following steps:

[0040] Step one, centrifuge silver nanowires with a concentration of 2 mg / mL at 2500 rpm for 8 min, and then disperse them in 3 mL of a mixed solution of deionized water and isopropanol at a ratio of 1:4, and mix the solution uniformly by shaking.

[0041] Step two, peel off the release protective film on the surface of the PET polyester film, place it flat in a plasma cleaning machine, and clean the surface with a power of 80 W for 5 min to obtain a PET polyester film with a hydrophilic surface. Take out the film and fix it on the coating table as a substrate 1.

[0042] Step three, 1000 μL of silver nanowire solution was distributed horizontally on the upper end of the substrate 1, and was pulled down uniformly from top to bottom to the bottom end of the substrate 1 by using a Meyer rod at a pulling speed of 1 cm / s. Then the film was dried in a vacuum drying oven at 45°C for 5 min to obtain a conductive film layer 2 (silver nanowire layer).

[0043] Step four, the obtained silver nanowire film was fixed on a coating table, and a MXene solution with a concentration of 1.5 mg / mL was uniformly sprayed on the surface of the silver nanowire layer obtained in step three. The diameter of the spray gun was 0.2 mm, the distance was 5 cm, the air pressure was 2 atmospheres, and the film was dried at room temperature to form a MXene layer 3, thereby obtaining a silver nanowire-MXene composite electromagnetic shielding film.

[0044] Step five, the film obtained in step four was placed on the coating table, and steps three and four were repeated to continue spraying the silver nanowire layer and the MXene layer 3 alternately for two times. The diameter of the spray gun and the air pressure were the same as in step four, and the film was sprayed in a serpentine manner.

[0045] Step six, the polymethyl methacrylate solution was diluted with acetone to a final concentration of 15 wt%, and the acetone solution of PMMA was spin-coated on the film obtained in step five at a spin-coating speed of 1500 rpm for 1 min, and then cooled at 45°C for 10 min to obtain a protective layer 4.

[0046] The composite flexible transparent electromagnetic shielding film prepared in this example has a thickness of 0.5 mm, and the PET polyester film substrate 1 is repeatedly provided with a conductive film layer 2 and a MXene layer 3. The conductive film layer 2 is silver nanowire, and the MXene layer 3 is two-dimensional sheet-shaped MXene with a multi-layer structure. The thickness of a single MXene layer 3 is 30 nm, and the thickness of a single conductive film layer 2 is 20 μm. On the top MXene layer 3, there is a PMMA protective layer 4 with a thickness of 160 nm.

[0047] Example 3

[0048] A method for preparing a composite flexible transparent electromagnetic shielding film, comprising the following steps:

[0049] Step one, silver nanowires with a concentration of 0.5 mg / mL were centrifuged at 2500 rpm for 8 min, and then dispersed in 1 mL of a mixed solution of deionized water and isopropyl alcohol at a ratio of 1:4. The solution was mixed uniformly by gentle shaking.

[0050] Step two, the release protection film on the surface of the PET polyester film was peeled off, and the film was placed flat in a plasma cleaning machine. The power of the plasma cleaning was 100 W, and the time was 2 min to obtain a PET polyester film with a hydrophilic surface. The film was taken out and fixed on a coating table as a substrate 1.

[0051] Step three, 1200 μL of silver nanowire solution was distributed horizontally on the upper end of the substrate 1, and was pulled down uniformly from top to bottom to the bottom end of the substrate 1 by using a Meyer rod at a speed of 3 cm / s. Then the film was dried in a vacuum drying oven at 60°C for 5 min to obtain a conductive film layer 2 (silver nanowire layer).

[0052] Step four, the obtained silver nanowire film was fixed on a coating table, and a MXene solution with a concentration of 0.3 mg / mL was uniformly sprayed on the surface of the silver nanowire layer obtained in step three. The diameter of the spray gun was 0.2 mm, the distance was 15 cm, the air pressure was 2 atmospheres, and the film was dried at room temperature to form a MXene layer 3, thereby obtaining a silver nanowire-MXene composite electromagnetic shielding film.

[0053] Step five, the film obtained in step four was placed on the coating table, and steps three and four were repeated to continue spraying the silver nanowire layer and the MXene layer 3 alternately for 8 times. The diameter of the spray gun and the air pressure were the same as in step four, and the film was sprayed in a serpentine manner.

[0054] Step six, the polymethyl methacrylate solution was diluted with acetone to a final concentration of 15 wt%, and the acetone solution of PMMA was spin-coated on the film obtained in step five at a speed of 3000 rpm for 1 min and cooled at 35°C for 10 min to obtain a protective layer 4.

[0055] The composite flexible transparent electromagnetic shielding film prepared in this example has a thickness of 1.5 mm PET polyester film substrate 1, and is provided with a conductive film layer 2 and a MXene layer 3. The conductive film layer 2 is silver nanowire, and the MXene layer 3 is two-dimensional sheet MXene with a multi-layer structure. The thickness of a single MXene layer 3 is 10 nm, and the thickness of a single conductive film layer 2 is 40 μm. On the top MXene layer 3, there is a PMMA protective layer 4 with a thickness of 200 nm.

[0056] Example 4

[0057] A method for preparing a composite flexible transparent electromagnetic shielding film, comprising the following steps:

[0058] Step one, silver nanowires with a concentration of 5 mg / mL were centrifuged at 2500 rpm for 8 min, and then dispersed in 1 mL of a mixed solution of deionized water and isopropyl alcohol at a ratio of 1:4. The solution was mixed uniformly by gentle shaking.

[0059] Step two, the release protection film on the surface of the PET polyester film was peeled off, and the film was placed flat in a plasma cleaning machine. The power of the plasma cleaning was 90 W, and the time was 5 min to obtain a PET polyester film with a hydrophilic surface. The film was taken out and fixed on a coating table as a substrate 1.

[0060] Step three, 900 μL of silver nanowire solution was distributed horizontally on the upper end of the substrate 1, and was pulled down uniformly from top to bottom to the bottom end of the substrate 1 by using a Meyer rod at a pulling speed of 4 cm / s. Then the film was dried in a vacuum drying oven at 50°C for 5 min to obtain a conductive film layer 2 (silver nanowire layer).

[0061] Step four, the obtained silver nanowire film was fixed on a coating table, and a MXene solution with a concentration of 2 mg / mL was sprayed uniformly on the surface of the silver nanowire layer obtained in step three. The diameter of the spray gun was 0.2 mm, the distance was 8 cm, the air pressure was 2 atmospheres, and the film was dried at room temperature to form a MXene layer 3, thereby obtaining a silver nanowire-MXene composite electromagnetic shielding film.

[0062] Step five, the film obtained in step four was placed on the coating table, and steps three and four were repeated to continue spraying the silver nanowire layer and the MXene layer 3 alternately for two times. The diameter of the spray gun and the air pressure were the same as in step four, and the film was sprayed in a serpentine manner.

[0063] Step six, the polymethyl methacrylate solution was diluted with acetone to a final concentration of 16 wt%, and the acetone solution of PMMA was spin-coated on the film obtained in step five at a spin-coating speed of 3600 rpm for 1 min, and then cooled at 30°C for 10 min to obtain a protective layer 4.

[0064] The composite flexible transparent electromagnetic shielding film prepared in this example has a thickness of 0.5 mm, and the PET polyester film substrate 1 is repeatedly provided with a conductive film layer 2 and a MXene layer 3. The conductive film layer 2 is silver nanowire, and the MXene layer 3 is two-dimensional sheet-shaped MXene with a multi-layer structure. The thickness of a single MXene layer 3 is 50 nm, and the thickness of a single conductive film layer 2 is 10 μm. On the topmost MXene layer 3, there is a PMMA protective layer 4 with a thickness of 100 nm.

[0065] Example 5

[0066] A method for preparing a composite flexible transparent electromagnetic shielding film, comprising the following steps:

[0067] Step one, silver nanowires with a concentration of 4 mg / mL were centrifuged at 2500 rpm for 8 min, and then dispersed in 2 mL of a mixed solution of deionized water and isopropyl alcohol at a ratio of 1:4. The solution was mixed uniformly by gentle shaking.

[0068] Step two, the release protective film on the surface of the PET polyester film was peeled off, and the film was placed flat in a plasma cleaning machine. The power of the plasma cleaning was 95 W, and the time was 0.5 min to obtain a PET polyester film with a hydrophilic surface. The film was taken out and fixed on a coating table as a substrate 1.

[0069] Step three, 1100 μL of silver nanowire solution was distributed horizontally on the upper end of the substrate 1, and was pulled down uniformly from top to bottom to the bottom end of the substrate 1 by a Meyer rod at a speed of 2 cm / s. Then the film was dried in a vacuum drying oven at 30°C for 1 min to obtain a conductive film layer 2 (silver nanowire layer).

[0070] Step four, the obtained silver nanowire film was fixed on a coating table, and a MXene solution with a concentration of 5 mg / mL was sprayed uniformly on the surface of the silver nanowire layer obtained in step three. The diameter of the spray gun was 0.3 mm, the distance was 12 cm, the air pressure was 1 atmosphere, and the film was dried at room temperature to form a MXene layer 3, thereby obtaining a silver nanowire-MXene composite electromagnetic shielding film.

[0071] Step five, the film obtained in step four was placed on a coating table, and steps three and four were repeated to continue spraying the silver nanowire layer and the MXene layer 3 alternately for 2 times. The diameter of the spray gun and the air pressure were the same as in step four, and the film was sprayed in a serpentine manner.

[0072] Step six, the polymethyl methacrylate solution was diluted with acetone to a final concentration of 16 wt%, and the acetone solution of PMMA was spin-coated on the film obtained in step five at a speed of 2000 rpm for 1 min and cooled at 40°C for 10 min to obtain a protective layer 4.

[0073] The composite flexible transparent electromagnetic shielding film prepared in this example has a thickness of 2 mm, and the PET polyester film substrate 1 is repeatedly provided with a conductive film layer 2 and a MXene layer 3. The conductive film layer 2 is silver nanowire, and the MXene layer 3 is two-dimensional sheet-shaped MXene with a multi-layer structure. The thickness of a single MXene layer 3 is 100 nm, and the thickness of a single conductive film layer 2 is 50 μm. On the topmost MXene layer 3, there is a PMMA protective layer 4 with a thickness of 250 nm.

[0074] Comparative Example 1

[0075] The remaining steps of this comparative example are the same as those of Example 1, except that the diameter of the spray gun used in step four and step five is 0.1 mm. It is found that the film forming efficiency is too low when the spray diameter is too small, which is not suitable for industrial production.

[0076] Comparative Example 2

[0077] The remaining steps of this comparative example are the same as those of Example 1, except that the diameter of the spray gun used in step four and step five is 0.4 mm. It is found that the uniformity of the film is not good when the spray diameter is too large.

[0078] Comparative Example 3

[0079] The remaining steps of this comparative example are the same as those of Example 1, except that the spraying diameter in the fourth and fifth steps is 3 cm. It is found that the sprayed lines are concentrated and the central position has too high a concentration, making it difficult to form a uniform film.

[0080] Comparative Example 4

[0081] The remaining steps of this comparative example are the same as those of Example 1, except that the spraying diameter in the fourth and fifth steps is 18 cm. It is found that the sprayed silver nanowires are too dispersed and a large amount of spraying is required to form a silver wire network, resulting in waste of raw materials.

[0082] Comparative Example 5

[0083] The remaining steps of this comparative example are the same as those of Example 1, except that the spin coating speed in the sixth step is 1300 rpm. It is found that the film formation is not uniform, with a high concentration in the center of the film and a low concentration at the outer edge of the film.

[0084] Comparative Example 6

[0085] The remaining steps of this comparative example are the same as those of Example 1, except that the spin coating speed in the sixth step is 3700 rpm. It is found that the solution is wasted, greatly increasing the cost.

Claims

1. A method for preparing a composite flexible transparent electromagnetic shielding film, characterized in that, Includes the following steps: (a) Peel off the release film from the surface of the PET polyester film, clean the film surface with plasma, and then fix it on the coating table as a substrate (1). (b) The silver nanowire solution was laterally distributed on the surface of the substrate (1), uniformly pulled down with a Mayer rod, and vacuum dried to obtain a conductive thin film layer (2). (c) The MXene solution is uniformly sprayed onto the surface of the conductive thin film layer (2) obtained in step (b), and dried to form the MXene layer (3). (d) Continue alternating steps (b) and (c) to adjust the transmittance and shielding effectiveness by controlling the number of alternating coatings of silver nanowire solution and MXene solution; (e) Spin-coat a polymethyl methacrylate acetone solution onto the film obtained in step (d), and cool at 30~45°C to obtain a protective layer (4). In step (b), the concentration of the silver nanowire solution is 0.5~5 mg / mL, and the silver nanowire solution is prepared by centrifuging and dissolving silver nanowires in a mixed solution of water and isopropanol. In step (b), the pulling speed of the Mayer rod is 1~5 cm / s, the vacuum drying temperature is 30~60℃, and the time is 1~5 min; In step (c), the concentration of the MXene solution is 0.3~5 mg / mL, the diameter of the spray gun is 0.2~0.3 mm, the distance is 5~15 cm, the air pressure is 1~2 atmospheres, and the spraying is done in a serpentine pattern. In step (d), the alternating coating is performed 2 to 8 times; In step (e), the acetone solution of polymethyl methacrylate contains 14-16 wt% polymethyl methacrylate and the spin coating speed is 1500-3600 rpm.

2. The method for preparing a composite flexible transparent electromagnetic shielding film according to claim 1, characterized in that: The composite flexible transparent electromagnetic shielding film comprises, in sequence, a substrate (1), a conductive film layer (2), an MXene layer (3), and a protective layer (4); the conductive film layer (2) and the MXene layer (3) are arranged at intervals; the substrate (1) is a PET polyester film, the conductive film layer (2) is silver nanowires, the MXene layer (3) is a two-dimensional sheet-like MXene with a multi-layer structure, and the protective layer (4) is made of polymethyl methacrylate.

3. The method for preparing a composite flexible transparent electromagnetic shielding film according to claim 1, characterized in that: The thickness of the substrate (1) is 0.5~2mm, the thickness of the single layer of the MXene layer (3) is 10~100nm, the thickness of the single layer of the conductive thin film layer (2) is 10~50µm, and the thickness of the protective layer (4) is 100~250nm.

4. The method for preparing a composite flexible transparent electromagnetic shielding film according to claim 3, characterized in that: In step (a), the plasma cleaning power is 80~110 W and the processing time is 0.5~5.0 min.

5. The application of the composite flexible transparent electromagnetic shielding film obtained by the preparation method according to any one of claims 1 to 4 in electronic touch screens.

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