Flexible electromagnetic shielding film and preparation method thereof

Abstract

The invention belongs to the technical field of electromagnetic shielding materials, and discloses a flexible electromagnetic shielding film and a preparation method thereof. The preparation method comprises the following steps: adding carbon nanotubes and polyvinylpyrrolidone into heated ethylene glycol, then sequentially adding an ethylene glycol solution of sodium chloride and an ethylene glycol solution of silver nitrate, and carrying out heat preservation reaction to obtain a carbon nanotube / silver nanowire compound; mixing with water to obtain dispersion liquid, coating a flexible substrate with the dispersion liquid, and performing hot pressing to form a conductive layer to obtain the flexible electromagnetic shielding film. The carbon nanotubes and the silver nanowires can form a cross-linked conductive network, and the carbon nanotubes and the silver nanowires are filled with each other, so that conductive paths are increased, and the electromagnetic shielding effectiveness is effectively improved. Meanwhile, the silver nanowires have excellent mechanical flexibility, the carbon nanotubes provide good mechanical support, and the flexibility and the bending resistance of the film can be improved through combination of the silver nanowires and the carbon nanotubes, so that the electromagnetic shielding film can be suitable for more scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding materials, and in particular to a flexible electromagnetic shielding film and a preparation method thereof. Background Art

[0002] With the development of electronic engineering technology, electronic devices have become widely used. While bringing convenience to people's lives, they also cause negative electromagnetic wave pollution. For example, electromagnetic waves can interfere with aircraft systems, affecting normal flight. Electromagnetic waves can also affect human health, causing varying degrees of harm to human organs and tissues, and in severe cases, even inducing cancer. Electromagnetic waves can also affect the signals of information transmission equipment such as computer networks, posing the risk of information leakage. Therefore, the research and development of electromagnetic shielding materials is of great significance to normal human life and technological progress.

[0003] Traditional electromagnetic shielding materials typically use metal foils and conductive coatings, but these have certain drawbacks. For example, while copper foil offers excellent shielding performance, its thickness typically exceeds 50 μm, making it prone to cracking when bent, severely degrading performance. While sputtered metal films significantly reduce thickness, the vacuum coating process is expensive and requires significant investment. Carbon-based composites (such as graphene / polymer systems), currently receiving widespread attention, are flexible but require the addition of large amounts of conductive fillers to achieve effective shielding. This increased brittleness and reduced bending resistance result from the addition of conductive fillers.

[0004] Therefore, there is an urgent need to develop a flexible electromagnetic shielding film that is flexible, low-cost and has good shielding performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible electromagnetic shielding film and a preparation method thereof, so as to solve the problems of high cost, complex preparation process and low film flexibility of existing electromagnetic shielding materials.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0008] (1) adding carbon nanotubes and polyvinyl pyrrolidone to heated ethylene glycol, then sequentially adding a sodium chloride solution in ethylene glycol and a silver nitrate solution in ethylene glycol, and keeping the mixture warm to react, thereby obtaining a carbon nanotube / silver nanowire composite;

[0009] (2) mixing the carbon nanotube / silver nanowire composite with water to obtain a dispersion;

[0010] (3) The dispersion is coated on a flexible substrate, and then hot-pressed to form a conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0011] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the heating temperature in step (1) is 140-180°C.

[0012] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the temperature of the insulation reaction in step (1) is 140-180° C.; and the time of the insulation reaction is 1-4 hours.

[0013] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the mass ratio of the carbon nanotubes, polyvinyl pyrrolidone, sodium chloride and silver nitrate in step (1) is 1-3:5-10:0.1-0.5:0.1-1.

[0014] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the diameter of the silver nanowires in the carbon nanotube / silver nanowire composite in step (1) is 30 to 100 nm, and the length is 10 to 80 μm.

[0015] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the concentration of the dispersion in step (2) is 0.1 to 30 g / L.

[0016] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the thickness of the conductive layer in step (3) is 5 to 30 μm.

[0017] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the coating amount of step (3) is 0.1 to 3 mL / cm 2 ; The coating is applied 1 to 20 times.

[0018] Preferably, in the above-mentioned method for preparing a flexible electromagnetic shielding film, the temperature of the hot pressing in step (3) is 60-100° C.; the pressure of the hot pressing is 0.1-10 MPa; and the time of the hot pressing is 1-3 h.

[0019] The present invention also provides a flexible electromagnetic shielding film prepared by a method for preparing the flexible electromagnetic shielding film.

[0020] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention combines carbon nanotubes and silver nanowires, coats them on a flexible substrate, and then forms a conductive layer through hot pressing. The thickness of the conductive layer can be effectively controlled by controlling the coating amount and the number of coatings, and the conductivity can be effectively controlled by controlling the ratio of carbon nanotubes to silver nanowires, thereby adjusting the electromagnetic shielding effectiveness. The carbon nanotubes and silver nanowires used in the present invention can form a cross-linked conductive network. The two fill each other, increase the conductive path, and effectively improve the electromagnetic shielding effectiveness. At the same time, the silver nanowires have excellent mechanical flexibility, and the carbon nanotubes provide good mechanical support. The combination of the two can also improve the flexibility and anti-bending performance of the film, making the electromagnetic shielding film applicable to more scenarios.

[0022] (2) The preparation method of the present invention is simple, the amount of raw materials used is small, and the electromagnetic shielding efficiency is high, which can effectively reduce the production cost of the electromagnetic shielding film and is conducive to improving market competitiveness. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0024] (1) adding carbon nanotubes and polyvinyl pyrrolidone to heated ethylene glycol, then sequentially adding a sodium chloride solution in ethylene glycol and a silver nitrate solution in ethylene glycol, and keeping the mixture warm to react, thereby obtaining a carbon nanotube / silver nanowire composite;

[0025] (2) mixing the carbon nanotube / silver nanowire composite with water to obtain a dispersion;

[0026] (3) The dispersion is coated on a flexible substrate, and then hot-pressed to form a conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0027] In the present invention, the diameter of the carbon nanotubes in step (1) is preferably 10-30 nm, more preferably 15-25 nm, and more preferably 20 nm; the length is preferably 10-100 μm, more preferably 50-90 μm, and more preferably 80 μm.

[0028] In the present invention, the molecular weight of the polyvinyl pyrrolidone in step (1) is preferably 8,000 to 15,000, more preferably 9,000 to 12,000, and even more preferably 10,000.

[0029] In the present invention, the heating temperature in step (1) is preferably 140-180°C, more preferably 150-170°C, and even more preferably 160°C.

[0030] In the present invention, the temperature of the insulation reaction in step (1) is preferably 140-180°C, more preferably 150-170°C, and more preferably 160°C; the time of the insulation reaction is preferably 1-4h, more preferably 1-3h, and more preferably 2h.

[0031] In the present invention, the mass ratio of the carbon nanotubes, polyvinyl pyrrolidone, sodium chloride and silver nitrate in step (1) is preferably 1-3:5-10:0.1-0.5:0.1-1, more preferably 1-2:6-9:0.2-0.4:0.3-0.8, and more preferably 1.5:8:0.3:0.5.

[0032] In the present invention, the usage ratio of ethylene glycol to carbon nanotubes in step (1) is preferably 100-200 mL:1-3 g, more preferably 100-150 mL:1-2 g, and even more preferably 100 mL:1.5 g.

[0033] In the present invention, the concentration of the ethylene glycol solution of sodium chloride in step (1) is preferably 1 to 10 g / L, more preferably 3 to 8 g / L, and even more preferably 7 g / L.

[0034] In the present invention, the concentration of the silver nitrate ethylene glycol solution in step (1) is preferably 0.1 to 2 g / L, more preferably 0.5 to 1 g / L, and even more preferably 0.8 g / L.

[0035] In the present invention, the diameter of the silver nanowires in the carbon nanotube / silver nanowire composite in step (1) is preferably 30 to 100 nm, more preferably 50 to 80 nm, and more preferably 65 nm; the length is preferably 10 to 80 μm, more preferably 30 to 60 μm, and more preferably 50 μm.

[0036] In the present invention, the concentration of the dispersion in step (2) is preferably 0.1 to 30 g / L, more preferably 1 to 25 g / L, and even more preferably 20 g / L.

[0037] In the present invention, the flexible substrate in step (3) is preferably a pretreated PET film; the thickness of the flexible substrate is preferably 20 μm; and the pretreatment method is: coating the PET film with a 5% by mass PVA aqueous solution to increase the adhesion of the conductive layer. The flexible substrates used in the embodiments of the present invention are all PET films that have undergone the above-mentioned pretreatment.

[0038] In the present invention, the thickness of the conductive layer in step (3) is preferably 5 to 30 μm, more preferably 10 to 29 μm, and even more preferably 21 μm.

[0039] In the present invention, the coating amount of step (3) is preferably 0.1 to 3 mL / cm 2 , more preferably 1 to 2 mL / cm 2 , more preferably 1.8 mL / cm 2 The coating is preferably applied 1 to 20 times, more preferably 5 to 10 times, and more preferably 6 times.

[0040] In the present invention, the temperature of the hot pressing in step (3) is preferably 60-100°C, more preferably 70-90°C, and more preferably 80°C; the pressure of the hot pressing is preferably 0.1-10 MPa, more preferably 1-8 MPa, and more preferably 5 MPa; the time of the hot pressing is preferably 1-3 h, more preferably 1-2 h, and more preferably 1 h.

[0041] The present invention also provides a flexible electromagnetic shielding film prepared by a method for preparing the flexible electromagnetic shielding film.

[0042] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0045] (1) Add carbon nanotubes (with a diameter of 20 nm and a length of 80 μm) and polyvinyl pyrrolidone (molecular weight of 10,000) to ethylene glycol heated to 160°C, stir at this temperature for 30 minutes, then add 7 g / L sodium chloride in ethylene glycol solution, stir at this temperature for 30 minutes, then add 0.8 g / L silver nitrate in ethylene glycol solution, the amount ratio of ethylene glycol, carbon nanotubes, polyvinyl pyrrolidone, sodium chloride, and silver nitrate is 100 mL: 1.5 g: 8 g: 0.3 g: 0.5 g, keep warm at 160°C for 2 hours, let it stand for 24 hours after the reaction is completed, wash the precipitate, and obtain a carbon nanotube / silver nanowire composite; wherein the diameter of the silver nanowire is 65 nm and the length is 50 μm;

[0046] (2) mixing the carbon nanotube / silver nanowire composite with water and ultrasonically dispersing the mixture to obtain a 20 g / L dispersion;

[0047] (3) The dispersion was coated at a rate of 1.8 mL / cm 2The flexible substrate was spin-coated and the spin coating was repeated 6 times, and then hot-pressed at 80° C. and 5 MPa pressure for 1 hour to form a 21 μm thick conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0048] The flexible electromagnetic shielding film of this embodiment has a shielding effectiveness of 94 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0049] Example 2

[0050] This embodiment provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0051] (1) Add carbon nanotubes (with a diameter of 20 nm and a length of 80 μm) and polyvinyl pyrrolidone (molecular weight of 8000) to ethylene glycol heated to 160°C, stir at this temperature for 30 minutes, then add 2 g / L sodium chloride in ethylene glycol solution, stir at this temperature for 30 minutes, then add 0.5 g / L silver nitrate in ethylene glycol solution, the amount ratio of ethylene glycol, carbon nanotubes, polyvinyl pyrrolidone, sodium chloride, and silver nitrate is 150 mL: 2 g: 5 g: 0.1 g: 0.1 g, keep warm at 160°C for 3 hours, let it stand for 24 hours after the reaction, wash the precipitate, and obtain a carbon nanotube / silver nanowire composite; wherein the diameter of the silver nanowire is 48 nm and the length is 65 μm;

[0052] (2) mixing the carbon nanotube / silver nanowire composite with water and performing ultrasonic dispersion to obtain a 1 g / L dispersion;

[0053] (3) The dispersion was coated at a rate of 2 mL / cm 2 The flexible substrate was spin-coated twice, and then hot-pressed at 70° C. and 5 MPa for 2 h to form a 13 μm thick conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0054] The flexible electromagnetic shielding film of this embodiment has a shielding effectiveness of 82 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0055] Example 3

[0056] This embodiment provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0057] (1) Add carbon nanotubes (with a diameter of 20 nm and a length of 80 μm) and polyvinyl pyrrolidone (molecular weight of 10,000) to ethylene glycol heated to 150°C, stir at this temperature for 30 minutes, then add a 3 g / L sodium chloride solution in ethylene glycol, stir at this temperature for 30 minutes, then add a 1 g / L silver nitrate solution in ethylene glycol, the amount ratio of ethylene glycol, carbon nanotubes, polyvinyl pyrrolidone, sodium chloride, and silver nitrate is 100 mL: 1 g: 6 g: 0.2 g: 0.5 g, keep the reaction at 150°C for 2 hours, let it stand for 24 hours after the reaction is completed, wash the precipitate, and obtain a carbon nanotube / silver nanowire composite; wherein the diameter of the silver nanowire is 43 nm and the length is 49 μm;

[0058] (2) mixing the carbon nanotube / silver nanowire composite with water and performing ultrasonic dispersion to obtain a 10 g / L dispersion;

[0059] (3) The dispersion was coated at a rate of 1 mL / cm 2 The flexible substrate was spin-coated and the spin coating was repeated 8 times, and then hot-pressed at 80° C. and 5 MPa pressure for 3 hours to form a 17 μm thick conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0060] The flexible electromagnetic shielding film of this embodiment has a shielding effectiveness of 91 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0061] Example 4

[0062] This embodiment provides a method for preparing a flexible electromagnetic shielding film, comprising the following steps:

[0063] (1) Add carbon nanotubes (with a diameter of 20 nm and a length of 80 μm) and polyvinyl pyrrolidone (molecular weight of 10,000) to ethylene glycol heated to 160°C, stir at this temperature for 30 minutes, then add 6 g / L sodium chloride in ethylene glycol solution, stir at this temperature for 30 minutes, then add 2 g / L silver nitrate in ethylene glycol solution, the amount ratio of ethylene glycol, carbon nanotubes, polyvinyl pyrrolidone, sodium chloride, and silver nitrate is 200 mL: 3 g: 10 g: 0.5 g: 0.5 g, keep warm at 160°C for 4 hours, let it stand for 24 hours after the reaction is completed, wash the precipitate, and obtain a carbon nanotube / silver nanowire composite; wherein the diameter of the silver nanowire is 37 nm and the length is 61 μm;

[0064] (2) mixing the carbon nanotube / silver nanowire composite with water and ultrasonically dispersing the mixture to obtain a 25 g / L dispersion;

[0065] (3) The dispersion was coated at a rate of 3 mL / cm 2The flexible substrate was spin-coated and the spin coating was repeated 9 times, and then hot-pressed at 90° C. and 5 MPa pressure for 2 hours to form a 29 μm thick conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

[0066] The flexible electromagnetic shielding film of this embodiment has a shielding effectiveness of 98 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0067] Comparative Example 1

[0068] This comparative example provides a flexible film, which is the flexible substrate of Example 1.

[0069] The flexible film of this comparative example has a shielding effectiveness of 0 against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0070] Comparative Example 2

[0071] This comparative example provides a flexible film, which is specifically described in Example 1, except that it does not contain carbon nanotubes, that is, in the preparation method, step (1) does not add carbon nanotubes, and step (2) replaces the carbon nanotube / silver nanowire composite with silver nanowires.

[0072] The flexible electromagnetic shielding film of this comparative example has a shielding effectiveness of 62 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0073] Comparative Example 3

[0074] This comparative example provides a flexible film, which is specifically described in Example 1, except that it does not contain silver nanowires, that is, in the preparation method, step (1) does not add silver nanowires, and step (2) replaces the carbon nanotube / silver nanowire composite with carbon nanotubes.

[0075] The flexible electromagnetic shielding film of this comparative example has a shielding effectiveness of 73 dB against electromagnetic waves with a frequency of 8.2 to 12.4 GHz.

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible electromagnetic shielding film, characterized in that: The following steps are involved: (1) adding carbon nanotubes and polyvinyl pyrrolidone to heated ethylene glycol, and then sequentially adding a sodium chloride solution in ethylene glycol and a silver nitrate solution in ethylene glycol, and keeping the temperature to react to obtain a carbon nanotube / silver nanowire composite; (2) mixing the carbon nanotube / silver nanowire composite with water to obtain a dispersion; (3) The dispersion is coated on a flexible substrate, and then hot-pressed to form a conductive layer on the flexible substrate, thereby obtaining the flexible electromagnetic shielding film.

2. The method for preparing a flexible electromagnetic shielding film according to claim 1, wherein: The heating temperature in step (1) is 140-180°C.

3. The method for preparing a flexible electromagnetic shielding film according to claim 2, wherein: The temperature of the insulation reaction in step (1) is 140-180° C.; the time of the insulation reaction is 1-4 hours.

4. The method for preparing a flexible electromagnetic shielding film according to claim 3, wherein: The mass ratio of the carbon nanotubes, polyvinyl pyrrolidone, sodium chloride and silver nitrate in step (1) is 1-3:5-10:0.1-0.5:0.1-1.

5. The method for preparing a flexible electromagnetic shielding film according to claim 3 or 4, characterized in that: The diameter of the silver nanowires in the carbon nanotube / silver nanowire composite in step (1) is 30 to 100 nm, and the length is 10 to 80 μm.

6. The method for preparing a flexible electromagnetic shielding film according to claim 5, characterized in that: The concentration of the dispersion in step (2) is 0.1 to 30 g / L.

7. The method for preparing a flexible electromagnetic shielding film according to claim 1 or 3, characterized in that: The thickness of the conductive layer in step (3) is 5 to 30 μm.

8. The method for preparing a flexible electromagnetic shielding film according to claim 7, characterized in that: The coating amount of step (3) is 0.1-3 mL / cm 2 ; The coating is applied 1 to 20 times.

9. The method for preparing a flexible electromagnetic shielding film according to claim 8, characterized in that: The hot pressing temperature in step (3) is 60-100° C.; the hot pressing pressure is 0.1-10 MPa; and the hot pressing time is 1-3 hours.

10. A flexible electromagnetic shielding film produced by the method for producing a flexible electromagnetic shielding film according to any one of claims 1 to 9.