Electromagnetic shielding material and preparation method thereof

Abstract

The invention provides an electromagnetic shielding material and a preparation method thereof, the electromagnetic shielding material comprises a self-supporting conductive film with a fold topological structure, and the thickness of the conductive film is 20-500 nm. The electromagnetic shielding material provided by the invention is high in unit area electromagnetic shielding strength, small in specific surface area, easy to integrate and adjustable in unit area electromagnetic shielding strength. The preparation method of the electromagnetic shielding material provided by the invention is simple in preparation steps and low in preparation cost.

Description

Technical Field

[0001] The present application relates to the field of electromagnetic shielding technology, and in particular to an electromagnetic shielding material and a preparation method thereof. Background Art

[0002] With the rapid development of electronic communications and artificial intelligence technology, the development of electronic devices tends to be highly functionally diversified and integrated, which inevitably leads to the problem of electromagnetic interference. The electromagnetic interference of portable and wearable thin-film electronic devices will not only disrupt the normal operation of electronic devices and systems, seriously undermine the security and stability of information exchange, but also damage people's health. Therefore, the research on thin-film electromagnetic shielding materials is of great significance to solving the signal interference in the integration of electronic devices. However, thin-film electromagnetic shielding materials have the problems of low electromagnetic shielding efficiency per unit area, large occupied area, and high preparation cost. Therefore, it is urgent to develop a simple and low-cost preparation method to improve the electromagnetic shielding efficiency of electromagnetic shielding materials per unit area and adapt to the design and production of refined and integrated thin-film electronic devices. Summary of the invention

[0003] The purpose of this application is to provide an electromagnetic shielding material and a preparation method thereof, so as to obtain an electromagnetic shielding material with high electromagnetic shielding strength per unit area through a simple process and low-cost preparation method. The specific technical solution is as follows:

[0004] A first aspect of the present application provides an electromagnetic shielding material, which includes a self-supporting conductive film with a corrugated topological structure, wherein the thickness of the conductive film is 20nm-500nm, preferably 20nm-200nm.

[0005] In some embodiments, the conductive film has a unidirectional corrugated topology or a bidirectional corrugated topology.

[0006] In some embodiments, the planar area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film.

[0007] In some embodiments, the material of the conductive film is selected from at least one of gold and its alloys, silver and its alloys, copper and its alloys, and aluminum and its alloys.

[0008] The second aspect of the present application provides a method for preparing the electromagnetic shielding material provided in the first aspect of the present application, which comprises the following steps:

[0009] S1. Preparing a sacrificial layer on a pre-stretched shape memory polymer substrate;

[0010] S2. Preparing a flat conductive film on the surface of the sacrificial layer;

[0011] S3. heating the shape memory polymer substrate to shrink the flat conductive film to form a conductive film having a wrinkled topological structure;

[0012] S4. dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining an electromagnetic shielding material including a self-supporting conductive film with a wrinkled topological structure.

[0013] In some embodiments, in step S3, shrinking the flat conductive film includes: fixing one direction of the shape memory polymer substrate to shrink the flat conductive film unidirectionally along another direction perpendicular thereto; or, not fixing the shape memory polymer substrate to shrink the flat conductive film bidirectionally.

[0014] In some embodiments, the heating comprises a heating temperature of 120-160° C. and a heating time of 5-20 min.

[0015] In some embodiments, the flat conductive film is prepared by a method selected from physical vapor deposition, solution deposition or atomic layer deposition.

[0016] In some embodiments, in step S1, the pre-stretched shape memory polymer has a length ratio M1 after pre-stretching to a length ratio before pre-stretching of (2-5):1, and a width ratio N1 after pre-stretching to a width ratio before pre-stretching of (2-5):1.

[0017] In some embodiments, the shape memory polymer is selected from polystyrene, polyurethane, or trans-1,4-polyisoprene.

[0018] In some embodiments, the sacrificial layer is prepared by a method selected from spin coating or dip coating.

[0019] In some embodiments, the sacrificial layer has a thickness of ≤ 1000 nm.

[0020] In some embodiments, the sacrificial layer material is photoresist, and the dissolving solvent is acetone;

[0021] Alternatively, the sacrificial layer material is selected from at least one of polyvinyl pyrrolidone and polyvinyl alcohol, and the dissolving solvent is water.

[0022] The present application provides an electromagnetic shielding material and a preparation method thereof, wherein the electromagnetic shielding material comprises a self-supporting conductive film having a pleated topological structure, and the thickness of the conductive film is 20nm-500nm. The electromagnetic shielding material provided by the present application has high electromagnetic shielding strength per unit area, small specific surface area, easy integration, and adjustable electromagnetic shielding strength per unit area. The preparation method of the electromagnetic shielding material provided by the present application has simple preparation steps and low preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0024] Figure 1 The microstructure of the electromagnetic shielding material of Example 1 is shown;

[0025] Figure 2 The electromagnetic shielding effectiveness curves of the electromagnetic shielding materials of Example 1 and Comparative Example 1 are shown;

[0026] Figure 3 The electromagnetic shielding effectiveness curves of the electromagnetic shielding materials of Example 2 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0027] 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, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0028] The first aspect of the present application provides an electromagnetic shielding material, which includes a self-supporting conductive film with a corrugated topological structure, and the thickness of the conductive film is 20nm-500nm, preferably 20nm-200nm. For example, the thickness of the conductive film can be 20nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm or a range consisting of any two of the values. The electromagnetic shielding material provided by the present application, which includes a conductive film with a corrugated topological structure, has high electromagnetic shielding strength per unit area, small specific surface area, easy integration, and adjustable electromagnetic shielding strength per unit area.

[0029] In some embodiments, the conductive film has a unidirectional corrugated topology or a bidirectional corrugated topology. In the present application, the "unidirectional" refers to a single length direction or a single width direction; the "bidirectional" refers to both the length direction and the width direction. The present application can adjust the electromagnetic shielding strength per unit area of ​​the electromagnetic shielding material by controlling the unidirectional corrugated topology or the bidirectional corrugated topology of the conductive film.

[0030] In some embodiments, the plane area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film. In the present application, the plane area of ​​the conductive film refers to the maximum area value of the plane in the length direction and the width direction of the self-supporting conductive film with a pleated topological structure; the surface area of ​​the conductive film refers to the self-supporting conductive film with a pleated topological structure, the product of its length and width when it is a flat conductive film. The present application regulates the ratio of the plane area of ​​the conductive film to the surface area of ​​the conductive film within the above range, which can make the electromagnetic shielding material per unit area have a higher electromagnetic shielding performance. The present application can adjust the electromagnetic shielding strength per unit area of ​​the electromagnetic shielding material by controlling the ratio of the plane area of ​​the conductive film to the surface area of ​​the conductive film.

[0031] In some embodiments, the material of the conductive film is selected from at least one of gold and its alloys, silver and its alloys, copper and its alloys, and aluminum and its alloys. The self-supporting conductive film with a pleated topological structure selected from the above-mentioned material types in the present application has a high electromagnetic shielding strength, so that the electromagnetic shielding material per unit area has good electromagnetic shielding performance.

[0032] The second aspect of the present application provides a method for preparing the electromagnetic shielding material provided in the first aspect of the present application, which comprises the following steps:

[0033] S1. Preparing a sacrificial layer on a pre-stretched shape memory polymer substrate;

[0034] S2. Preparing a flat conductive film on the surface of the sacrificial layer;

[0035] S3. heating the shape memory polymer substrate to shrink the flat conductive film to form a conductive film having a wrinkled topological structure;

[0036] S4. dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining an electromagnetic shielding material including a self-supporting conductive film with a wrinkled topological structure.

[0037] The present application provides a method for preparing an efficient flexible electromagnetic shielding material based on a pleated topological structure, which has a simple process and low cost, and can obtain an electromagnetic shielding material with high electromagnetic shielding strength per unit area to adapt to the design and production of refined and integrated thin-film electronic devices, and the electromagnetic shielding strength per unit area of ​​the electromagnetic shielding material is adjustable.

[0038] In some embodiments, in step S3, shrinking the flat conductive film includes: fixing one direction of the shape memory polymer substrate to shrink the flat conductive film unidirectionally along another direction perpendicular thereto; or, not fixing the shape memory polymer substrate to shrink the flat conductive film bidirectionally.

[0039] In some embodiments, shrinking the flat conductive film comprises: fixing the width direction of the shape memory polymer substrate, shrinking the flat conductive film unidirectionally along the length direction perpendicular thereto. Further, in the unidirectional shrinkage, the ratio M2 of the length before shrinkage to the length after shrinkage is (2-5):1, for example, M2 can be 2:1, 3:1, 4:1, 5:1 or a range consisting of any two of these values; in some embodiments, M2=M1.

[0040] In some embodiments, shrinking the flat conductive film includes: fixing the length direction of the shape memory polymer substrate, shrinking the flat conductive film unidirectionally along a width direction perpendicular thereto. Further, in the unidirectional shrinkage, the ratio N2 of the width before shrinkage to the width after shrinkage is (2-5):1, for example, N2 can be 2:1, 3:1, 4:1, 5:1 or a range consisting of any two of these values; in some embodiments, N2=N1.

[0041] In some embodiments, shrinking the flat conductive film comprises: not fixing the shape memory polymer substrate, and allowing the flat conductive film to shrink freely in both length and width directions. Further, in the free shrinkage in both directions, the ratio M2 of the length before shrinkage to the length after shrinkage is (2-5):1, and the ratio N2 of the width before shrinkage to the width after shrinkage is (2-5):1, for example, M2 can be 2:1, 3:1, 4:1, 5:1, or a range consisting of any two of these values, and N2 can be 2:1, 3:1, 4:1, 5:1, or a range consisting of any two of these values.

[0042] In the present application, the shape memory polymer substrate loaded with the sacrificial layer and the flat conductive film obtained in the heating step S2 is used to regulate the shrinkage mode of the shape memory polymer substrate and adjust the wrinkle topology of the conductive film, thereby obtaining a conductive film with a unidirectional wrinkle topology or a bidirectional wrinkle topology.

[0043] In some embodiments, the heating comprises a heating temperature of 120-160° C. and a heating time of 5-20 min. For example, the heating temperature can be 120° C., 130° C., 140° C., 150° C., 160° C., or a range consisting of any two of the values, and the heating time can be 5 min, 6 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, or a range consisting of any two of the values.

[0044] In some embodiments, the flat conductive film is prepared by a method selected from physical vapor deposition (such as magnetron sputtering), solution deposition or atomic layer deposition.

[0045] In some embodiments, in step S1, the length ratio M1 of the pre-stretched shape memory polymer after pre-stretching to the length ratio before pre-stretching is (2-5): 1, and the width ratio N1 of the pre-stretched shape memory polymer after pre-stretching to the width ratio before pre-stretching is (2-5): 1. In the present application, for the same shape memory polymer, M1 and N1 are fixed; in some embodiments, M2=M1, N2=N1.

[0046] In some embodiments, the shape memory polymer is selected from polystyrene (PS), polyurethane, or trans-1,4-polyisoprene (TPI).

[0047] In some embodiments, the sacrificial layer is prepared by a method selected from spin coating or dip coating.

[0048] In some embodiments, the thickness of the sacrificial layer is ≤1000nm, and preferably, the thickness of the sacrificial layer is 2nm-500nm. For example, the thickness of the sacrificial layer can be 2nm, 10nm, 20nm, 50nm, 100nm, 200nm, 300nm, 500nm, 600nm, 800nm, 1000nm or a range consisting of any two of these values. The inventors found that if the thickness of the sacrificial layer is too high, such as higher than 1000nm, cracks will occur in the conductive film; if the thickness of the sacrificial layer is too low, such as lower than 2nm, the sacrificial layer is too thin and difficult to form a film, which will make the conductive film difficult to fall off from the substrate. By regulating the thickness of the sacrificial layer within the above range, an electromagnetic shielding material with stable quality can be obtained.

[0049] In some embodiments, the sacrificial layer material is a photoresist, and the dissolving solvent is acetone; or, the sacrificial layer material is selected from at least one of polyvinyl pyrrolidone and polyvinyl alcohol, and the dissolving solvent is water. In the present application, the sacrificial layer is dissolved by a solution method, thereby separating and removing the shape memory polymer substrate, obtaining a self-supporting conductive film with a wrinkled topological structure, and obtaining the electromagnetic shielding material described in the present application.

[0050] In this application, the term "about" is defined as close to as understood by those of ordinary skill in the art. In some embodiments, the term is defined as within 10%, preferably within 5%, more preferably within 1%, and further preferably within 0.5%.

[0051] Example

[0052] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0053] Test methods and equipment:

[0054] Determination of electromagnetic shielding value:

[0055] The steps for testing the electromagnetic shielding strength using a vector network analyzer (VNA, Agilent N5247A, Shenzhen McKerry Instrument Co., LTD, China) are as follows:

[0056] 1. Prepare and calibrate equipment: Make sure the VNA and electromagnetic shielding materials are in good working condition.

[0057] 2. Set up the VNA: According to the equipment manual, set the appropriate frequency range and power level. The frequency range of this test is 8.2-12.4GHz.

[0058] 3. Sample installation: Place the electromagnetic shielding material in the test area of ​​the VNA, ensuring that its position is fixed and free of impurities.

[0059] 4. Connect the probe: Connect the VNA probe to both ends of the electromagnetic shielding material sample to ensure good contact.

[0060] 5. Perform the test: Start the VNA and record the transmission parameters (such as S parameters) at different frequencies.

[0061] 6. Data analysis: Use VNA software to analyze the test data, calculate the electromagnetic shielding effect of the electromagnetic shielding material, obtain the electromagnetic shielding effectiveness curve of the electromagnetic shielding material, and obtain the electromagnetic shielding value of the electromagnetic shielding material.

[0062] Determination of surface area of ​​conductive film:

[0063] The length L1 and width W1 of the flat conductive film were measured using a ruler, and the surface area of ​​the conductive film was obtained as L1×W1.

[0064] Determination of the plane area of ​​conductive film:

[0065] The maximum length L2 and the maximum width W2 of the conductive film with a unidirectional corrugated topological structure or a bidirectional corrugated topological structure in the same plane are measured by a ruler, and the plane area of ​​the conductive film is obtained as L2×W2.

[0066] Example 1

[0067] S1. Pre-stretched PS substrate (Graphix shrink film, Graphix, Maple Heights, OH, USA), the length ratio after pre-stretching to the length ratio before pre-stretching is 2.5:1, the width ratio after pre-stretching to the width ratio before pre-stretching is 2.5:1, and a photoresist with a thickness of about 400 nm is spin-coated on the pre-stretched PS substrate as a sacrificial layer. The spin-coating speed is 5000 rpm and the spin-coating time is 37 s;

[0068] S2. A flat Au conductive film having a thickness of 50 nm is prepared on the surface of the sacrificial layer obtained in step S1 by magnetron sputtering;

[0069] S3. The PS substrate loaded with the sacrificial layer and the flat conductive film obtained in step S2 is heated at 130° C. for 10 min, and the width direction of the PS substrate loaded with the sacrificial layer and the flat conductive film is fixed, so that the flat conductive film shrinks unidirectionally along the length direction of the PS substrate, thereby obtaining a conductive film with a unidirectional wrinkled topological structure;

[0070] S4. Immerse the sample obtained in step S3 in solvent acetone to dissolve the photoresist and separate the PS substrate to obtain an electromagnetic shielding material: a self-supporting Au conductive film with a unidirectional wrinkled topological structure, wherein the ratio of its length before shrinkage to its length after shrinkage is 2.5:1, and the plane area accounts for 40% of its surface area.

[0071] Example 2

[0072] S1-S2: Same as Example 1;

[0073] S3. The PS substrate loaded with the sacrificial layer and the flat conductive film obtained in step S2 is heated at 130° C. for 10 min, and the PS substrate loaded with the sacrificial layer and the flat conductive film is not fixed, so that the flat conductive film can freely shrink in both directions along the length and width directions of the PS substrate, thereby obtaining a conductive film having a bidirectional wrinkled topological structure;

[0074] S4. Immerse the sample obtained in step S3 in solvent acetone to dissolve the photoresist and separate the PS substrate to obtain an electromagnetic shielding material: a self-supporting Au conductive film with a bidirectional pleated topological structure, wherein the ratio of its length before contraction to its length after contraction is 2.5:1, the ratio of its width before contraction to its width after contraction is 2.5:1, and the plane area accounts for 16% of its surface area.

[0075] Embodiment 3-6

[0076] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as Example 1.

[0077] Comparative Example 1

[0078] S1-S2: Same as Example 1;

[0079] S3. Immerse the sample obtained in step S2 in the solvent acetone to dissolve the photoresist, separate the PS substrate, and obtain the electromagnetic shielding material: Au flat conductive film.

[0080] Comparative Examples 2-5

[0081] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as Comparative Example 1.

[0082] The preparation parameters and performance test results of the electromagnetic shielding materials of each embodiment and comparative example are shown in Table 1, wherein, based on the same conductive film material, the improvement rate of the electromagnetic shielding value of the flat conductive film = (electromagnetic shielding value of the electromagnetic shielding material of the embodiment - the electromagnetic shielding value of the flat conductive film of the comparative example) / electromagnetic shielding value of the flat conductive film of the comparative example × 100%.

[0083] Table 1

[0084] Note: “ / ” indicates no corresponding preparation parameters.

[0085] The electromagnetic shielding material of Example 1 was examined using a scanning electron microscope (manufacturer: JEOL Ltd., Tokyo, Japan, model: JSM-7000F), and its microstructure was obtained as follows: Figure 1 As shown, it can be seen that it has a unidirectional wrinkled topological structure. The electromagnetic shielding values ​​of the electromagnetic shielding materials of Example 1, Example 2 and Comparative Example 1 were measured respectively, and the electromagnetic shielding effectiveness curves of each electromagnetic shielding material in the 8.2-12.4 GHz frequency band were obtained as shown in Figure 2 and Figure 3 As shown, it can be seen that between 8.2-12.4GHz, the electromagnetic shielding value of the electromagnetic shielding material of the flat conductive film of Comparative Example 1 is the lowest, about 38dB; the electromagnetic shielding value of the electromagnetic shielding material of the unidirectional shrink film of Example 1 is 43dB; the electromagnetic shielding value of the electromagnetic shielding material of the bidirectional shrink film of Example 2 is 55dB; the plane areas of the electromagnetic shielding materials of Examples 1 and 2 are reduced to 40% and 16% of their surface areas, respectively, while the electromagnetic shielding values ​​are increased by 13% and 45% compared with Comparative Example 1, respectively. According to Table 1 and Figure 2-Figure 3 It can be seen from the results that the electromagnetic shielding material prepared according to the preparation method of the present application can greatly improve the electromagnetic shielding strength per unit area of ​​the electromagnetic shielding material and has excellent electromagnetic shielding performance.

[0086] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such process, method or article.

[0087] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0088] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electromagnetic shielding material, comprising a self-supporting conductive film with a corrugated topological structure, wherein the thickness of the conductive film is 20nm-500nm, preferably 20nm-200nm.

2. The electromagnetic shielding material according to claim 1, wherein: The conductive film has a unidirectional corrugated topological structure or a bidirectional corrugated topological structure.

3. The electromagnetic shielding material according to claim 1, wherein: The plane area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film.

4. The electromagnetic shielding material according to any one of claims 1 to 3, wherein: The material of the conductive film is selected from at least one of gold and its alloys, silver and its alloys, copper and its alloys, and aluminum and its alloys.

5. A method for preparing an electromagnetic shielding material according to any one of claims 1 to 4, comprising the following steps: S1. Preparing a sacrificial layer on a pre-stretched shape memory polymer substrate; S2. Preparing a flat conductive film on the surface of the sacrificial layer; S3. heating the shape memory polymer substrate to shrink the flat conductive film to form a conductive film having a wrinkled topological structure; S4. dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining an electromagnetic shielding material including a self-supporting conductive film with a wrinkled topological structure.

6. The preparation method according to claim 5, wherein: In step S3, shrinking the flat conductive film comprises: fixing one direction of the shape memory polymer substrate to shrink the flat conductive film unidirectionally along another direction perpendicular thereto; or not fixing the shape memory polymer substrate to shrink the flat conductive film bidirectionally.

7. The preparation method according to claim 5, wherein: The heating includes a heating temperature of 120-160° C. and a heating time of 5-20 min.

8. The preparation method according to claim 5, wherein: The flat conductive film is prepared by a method selected from physical vapor deposition, solution method or atomic layer deposition.

9. The preparation method according to any one of claims 5 to 8, wherein In step S1, the pre-stretched shape memory polymer has a length ratio M1 after pre-stretching to a length ratio before pre-stretching of (2-5):1, and a width ratio N1 after pre-stretching to a width ratio before pre-stretching of (2-5):

1.

10. The preparation method according to claim 9, wherein: The shape memory polymer is selected from polystyrene, polyurethane or trans-1,4-polyisoprene.

11. The preparation method according to any one of claims 5 to 8, wherein: The sacrificial layer is prepared by a method selected from a spin coating method or a dip coating method.

12. The preparation method according to claim 11, wherein The thickness of the sacrificial layer is ≤1000nm.

13. The preparation method according to claim 11, wherein The sacrificial layer material is photoresist, and the dissolving solvent is acetone; Alternatively, the sacrificial layer material is selected from at least one of polyvinyl pyrrolidone and polyvinyl alcohol, and the dissolving solvent is water.

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