Electromagnetic shielding porous film and preparation method thereof

Abstract

The invention discloses an electromagnetic shielding porous film and a preparation method thereof, and the method comprises the following steps: firstly, preparing a film from a two-dimensional nano material or a composite nano material of a one-dimensional nano material and the two-dimensional nano material, and then carrying out supercritical foaming on the film to prepare the electromagnetic shielding porous film. The film is prepared by taking a nano material as a raw material, the porous film is obtained through supercritical foaming, and the porous film not only can reduce the interface impedance mismatching between the material and air, so that electromagnetic waves are easy to sink into the composite film, but also provides a multiple reflection / scattering interface for the electromagnetic waves, so that the propagation path of the electromagnetic waves is greatly increased; the composite material can effectively attenuate electromagnetic waves, has excellent electromagnetic shielding effectiveness, and is simple in preparation method, pollution-free in process and suitable for the technical field of electromagnetic shielding.

Description

Technical Field

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

[0002] The porous nanomaterial composite film has a rich pore structure, which can not only reduce the interface impedance mismatch between the material and the air, making it easy for electromagnetic waves to "fall" into the composite film, but also provide multiple reflection / scattering interfaces for electromagnetic waves, greatly increasing the propagation path of electromagnetic waves and effectively attenuating electromagnetic waves. In addition, the presence of the porous structure reduces the density of the material, realizes the lightweight of the film, and can be applied in the field of electromagnetic shielding technology.

[0003] At present, the commonly used methods for preparing porous composite films are chemical foaming methods such as hydrazine hydrate reduction foaming, thermal reduction foaming, acid-base neutralization foaming, and physical sacrificial template methods. However, these methods all have certain defects in the production process, such as cumbersome steps, long time consumption, high pollution of toxic reduction reagents, high conditions and high equipment requirements, etc., which makes it difficult to truly promote the application of porous composite materials. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing an electromagnetic shielding porous film in view of the deficiencies of the above-mentioned prior art. The method uses nanomaterials as raw materials to prepare a film, and obtains a porous film through supercritical foaming. The porous film greatly increases the propagation path of electromagnetic waves, effectively attenuates electromagnetic waves, has excellent electromagnetic shielding effectiveness, and the preparation method is simple and the process is pollution-free, which solves the problem that the preparation process of the electromagnetic shielding porous film is cumbersome and the preparation process is highly polluting.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an electromagnetic shielding porous film, characterized in that the method first uses two-dimensional nanomaterials or a composite of one-dimensional nanomaterials and two-dimensional nanomaterials to prepare a film, and then supercritically foams the film to prepare an electromagnetic shielding porous film.

[0006] In the supercritical foaming process of the present invention, the fluid gas in the supercritical state is injected into the high-pressure foaming device so that the gas component is uniformly diffused into the film, and then the pressure is released to generate a large pressure drop inside and outside the film, so that the gas phase changes to form a large number of bubble nuclei and continue to grow. In the subsequent shaping process, the bubbles inside the film grow and form, and finally a porous film with microporous foaming is obtained. Based on the difference in the raw materials for preparing the film, the performance improvement direction of the corresponding porous film is diversified, and the improvement of electrical conductivity and mechanical properties is usually more significant. In addition, unlike the existing supercritical technology only applied to polymer foaming, the present invention uses two-dimensional nanomaterials or a film prepared by combining one-dimensional nanomaterials with two-dimensional nanomaterials to adsorb supercritical gas fluid through interlayer, and the fluid is easier to diffuse, the pressure holding time is shorter, and the temperature required for adsorption saturation is low, and there is no need to reach the glass transition temperature or viscosity flow temperature of the polymer, which further simplifies the preparation process.

[0007] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the supercritical foaming process is: placing the film in a high-pressure foaming device, setting the target temperature, and filling the high-pressure foaming device with a supercritical fluid until the target pressure is reached, and then standing for a preset time, and releasing the pressure to obtain an electromagnetic shielding porous film. Compared with conventional polymer foaming, the film foaming steps of the present invention are simple, no gradient pressure increase or temperature increase is required, and the pressure holding time is short.

[0008] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the target temperature is 20°C to 40°C, the target pressure is 10MPa to 25MPa, and the preset time is 0.5h to 5h. Compared with conventional polymer foaming, the film foaming temperature of the present invention is lower and the time is shorter.

[0009] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the pressure relief temperature is 5°C to 50°C, and the pressure relief rate is 1MPa / min to 20MPa / min. By controlling the pressure relief temperature and rate, the foaming speed is controlled to prevent CO2 from condensing too quickly to form large holes or broken holes locally, or the foaming rate is too slow to cause most of the CO2 to diffuse and escape, and the foaming is not obvious.

[0010] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the supercritical fluid is carbon dioxide or nitrogen.

[0011] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the method for preparing the film is a vacuum-assisted filtration method, a doctor blade method, a spraying method or a casting method.

[0012] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the one-dimensional nanomaterial is derived from silver nanowires, copper nanowires, carbon nanotubes, carbon nanofibers, cellulose nanofibers, and aramid nanofibers.

[0013] The above-mentioned method for preparing an electromagnetic shielding porous film is characterized in that the two-dimensional nanomaterial is derived from graphene, exfoliated expanded graphite sheets, carbon nanosheets, and MXene.

[0014] The one-dimensional nanomaterials and two-dimensional nanomaterials used to prepare the thin film in the present invention have a wide range of sources, indicating that the preparation method of the present invention has universal applicability in nano-assembled thin films.

[0015] Meanwhile, the present invention also discloses an electromagnetic shielding porous film, which is characterized in that it is prepared by the above method.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention first prepares a film using nanomaterials as raw materials, and then performs supercritical foaming on the film to form a porous structure. The porous structure can not only reduce the interface impedance mismatch between the porous film and the air, making it easy for electromagnetic waves to "fall" into the film, but also provide multiple reflection / scattering interfaces for electromagnetic waves, greatly increasing the propagation path of electromagnetic waves, effectively attenuating electromagnetic waves, and having excellent electromagnetic shielding performance.

[0018] 2. The preparation method of the present invention is simple and pollution-free during the preparation process, which solves the problems of the existing electromagnetic shielding porous film preparation process being complicated, time-consuming, highly polluting, requiring strict conditions and having high equipment requirements.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of the preparation method of the electromagnetic shielding porous film.

[0021] Figure 2 This is a microstructure diagram of the electromagnetic shielding porous film prepared in Example 3 of the present invention.

[0022] Figure 3 This is a test curve diagram of the electromagnetic shielding performance of the electromagnetic shielding porous film prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0024] For the following defined terms, these definitions shall apply unless a different definition is given in the claims or elsewhere in this specification. All numerical values, whether or not explicitly indicated, are defined herein as modified by the term "about". The term "about" generally refers to a numerical range that a person of ordinary skill in the art considers to be equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A numerical range indicated by a lower value and a higher value is defined to include all numerical values ​​included in the numerical range and all subranges included in the numerical range.

[0025] The following examples describe the technical scheme of the present application in more detail, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the present disclosure are obvious to those skilled in the art. The reagents used in the examples can be obtained commercially or synthesized according to conventional methods and can be used directly without further treatment, and the instruments and devices used in the examples can be obtained commercially.

[0026] Example 1

[0027] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 25°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 25MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 5MPa / min, and the pressure relief temperature is maintained at 20°C to obtain an electromagnetic shielding porous film.

[0028] The film preparation material in this embodiment can also be two-dimensional nanomaterial graphene, exfoliated expanded graphite sheets or carbon nanosheets, or can also be a composite nanomaterial of one-dimensional nanomaterial and two-dimensional nanomaterial, and the one-dimensional nanomaterial is derived from silver nanowires, copper nanowires, carbon nanotubes, carbon nanofibers, cellulose nanofibers, aramid nanofibers, and the two-dimensional nanomaterial is derived from graphene, exfoliated expanded graphite sheets, carbon nanosheets, and MXene.

[0029] The film preparation method in this embodiment may also be a scraping method, a spraying method or a casting method, and the supercritical fluid used may also be nitrogen.

[0030] Example 2

[0031] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 20°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 20MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 5MPa / min, and the pressure relief temperature is maintained at 15°C to obtain an electromagnetic shielding porous film.

[0032] Example 3

[0033] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 25°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 15MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 5MPa / min, and the pressure relief temperature is maintained at 5°C to obtain an electromagnetic shielding porous film.

[0034] Figure 2 The microstructure of the electromagnetic shielding porous film prepared in this embodiment is shown in FIG. Figure 2 It can be seen that the electromagnetic shielding porous film has a rich pore structure and has no collapse.

[0035] Example 4

[0036] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 25°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 10MPa is reached and allowed to stand for 0.5h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 5MPa / min, and the pressure relief temperature is maintained at 30°C to obtain an electromagnetic shielding porous film.

[0037] Example 5

[0038] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 35°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure reaches 20MPa and allowed to stand for 5 hours, and then the air outlet is opened to release the pressure at a rate of 5MPa / min to the high-pressure foaming device, and the pressure relief temperature is maintained at 20°C to obtain an electromagnetic shielding porous film.

[0039] Example 6

[0040] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 40°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 20MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 5MPa / min, and the pressure relief temperature is maintained at 15°C to obtain an electromagnetic shielding porous film.

[0041] Example 7

[0042] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 35°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 20MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure on the high-pressure foaming device at a rate of 1MPa / min, and the pressure relief temperature is maintained at 10°C to obtain an electromagnetic shielding porous film.

[0043] Example 8

[0044] like Figure 1 As shown, the specific process of this embodiment is: a film is prepared by vacuum-assisted filtration using MXene nanosheets, and then the film is placed in a high-pressure foaming device, the target temperature is set to 35°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 20MPa is reached and allowed to stand for 1h, and then the air outlet is opened to release the pressure at a rate of 20MPa / min to the high-pressure foaming device, and the pressure relief temperature is maintained at 50°C to obtain an electromagnetic shielding porous film.

[0045] Example 9

[0046] like Figure 1 As shown, the specific process of this embodiment is: MXene nanosheets and aramid nanofibers with a mass ratio of 8:2 are used to prepare a film by vacuum-assisted filtration, and then the film is placed in a high-pressure foaming device, the target temperature is set to 35°C, and supercritical CO2 fluid is filled into the high-pressure foaming device until the target pressure of 20MPa is reached and it is allowed to stand for 2h, and then the air outlet is opened to release the pressure of the high-pressure foaming device at a rate of 5MPa / min, and the pressure release temperature is maintained at 20°C to obtain an electromagnetic shielding porous film.

[0047] The electromagnetic shielding porous films prepared in Examples 1 to 9 of the present invention were respectively tested for X-band (8.2 GHz to 12.4 GHz) electromagnetic shielding performance using a vector network analyzer. The test results are shown in Table 1 below.

[0048] Table 1 Electromagnetic shielding effectiveness of different electromagnetic shielding porous films

[0049] sample Thickness(mm) <![CDATA[Density (g / cm 3 )]]> Electromagnetic shielding effectiveness (dB) Example 1 0.031 0.31 77.8 Example 2 0.028 0.33 74.2 Example 3 0.026 0.34 72.3 Example 4 0.019 0.40 63.4 Example 5 0.027 0.34 71.3 Example 6 0.022 0.37 68.4 Example 7 0.018 0.41 64.1 Example 8 0.017 0.43 62.5 Example 9 0.028 0.31 69.3

[0050] As can be seen from Table 1, compared with the conventional dense film density (all greater than 1g / cm 3 ), the density of the electromagnetic shielding porous films prepared in Examples 1 to 9 of the present invention are significantly reduced, and the electromagnetic shielding effectiveness exceeds the commercial application requirement of 20dB.

[0051] Figure 3 This is a test curve of the electromagnetic shielding performance of the electromagnetic shielding porous film prepared in Example 3 of the present invention. Figure 3 It can be seen that the average value of the electromagnetic shielding effectiveness (dB) of the electromagnetic shielding porous film is about 72.3.

[0052] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an electromagnetic shielding porous film, characterized in that: The method firstly adopts two-dimensional nanomaterials or composites one-dimensional nanomaterials with two-dimensional nanomaterials to prepare a film, and then performs supercritical foaming on the film to prepare an electromagnetic shielding porous film.

2. The method for preparing an electromagnetic shielding porous film according to claim 1, characterized in that: The supercritical foaming process is: placing the film in a high-pressure foaming device, setting a target temperature, and filling the high-pressure foaming device with a supercritical fluid until the target pressure is reached, then standing for a preset time, and releasing the pressure to obtain an electromagnetic shielding porous film.

3. The method for preparing an electromagnetic shielding porous film according to claim 2, characterized in that: The target temperature is 20°C to 40°C, the target pressure is 10MPa to 25MPa, and the preset time is 0.5h to 5h.

4. The method for preparing an electromagnetic shielding porous film according to claim 2, characterized in that: The pressure relief temperature is 5°C to 50°C, and the pressure relief rate is 1MPa / min to 20MPa / min.

5. The method for preparing an electromagnetic shielding porous film according to claim 2, characterized in that: The supercritical fluid is carbon dioxide or nitrogen.

6. The method for preparing an electromagnetic shielding porous film according to claim 1, characterized in that: The method for preparing the film is vacuum assisted filtration, blade coating, spray coating or casting.

7. The method for preparing an electromagnetic shielding porous film according to claim 1, characterized in that: The one-dimensional nanomaterial is derived from silver nanowires, copper nanowires, carbon nanotubes, carbon nanofibers, cellulose nanofibers, and aramid nanofibers.

8. The method for preparing an electromagnetic shielding porous film according to claim 1, characterized in that: The two-dimensional nanomaterial is derived from graphene, exfoliated expanded graphite sheets, carbon nanosheets, and MXene.

9. An electromagnetic shielding porous film, characterized in that: The method is prepared by any one of claims 1 to 8.

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