Electromagnetic shielding material and method for manufacturing the same

Abstract

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

Description

TECHNICAL FIELD

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

[0002] With the rapid development of electronic communication and artificial intelligence technology, the development of electronic devices tends to be highly functional and integrated, which inevitably causes electromagnetic interference problems. The electromagnetic interference of portable and wearable thin film electronic devices not only disturbs the normal operation of electronic devices and systems, seriously damages the safety and stability of information exchange, but also harms people's health. Therefore, the research on thin film electromagnetic shielding materials is of great significance to solve the signal interference in the integration of electronic devices. However, the thin film electromagnetic shielding material has 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 process and low-cost preparation method to improve the electromagnetic shielding efficiency per unit area of the electromagnetic shielding material and adapt to the design and production of fine and integrated thin film electronic devices. SUMMARY

[0003] The purpose of the present 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 by a simple process and low-cost preparation method. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides an electromagnetic shielding material, which comprises a self-supportable conductive thin film with a pleated topological structure, the thickness of the conductive thin film is 20-500nm, preferably 20-200nm.

[0005] In some embodiments, the conductive thin film is a one-way pleated topological structure or a two-way pleated topological structure.

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

[0007] In some embodiments, the material of the conductive thin 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 preparation method of 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 thin film on the surface of the sacrificial layer;

[0011] S3. heating the shape memory polymer substrate to make the flat conductive film shrink, forming a conductive film with a pleated topological structure;

[0012] S4. dissolving the sacrificial layer to separate the shape memory polymer substrate, obtaining an electromagnetic shielding material comprising a self-supportable conductive film with a pleated topological structure.

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

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

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

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

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

[0018] In some embodiments, the method for preparing the sacrificial layer is selected from spin coating or dip coating.

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

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

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

[0022] The present application provides an electromagnetic shielding material and a preparation method thereof, the electromagnetic shielding material comprising a self-supportable conductive film with a pleated topological structure, and the thickness of the conductive film is 20-500nm. 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 DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art 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 efficiency curve of the electromagnetic shielding material of Example 1 and Comparative Example 1 is shown;

[0026] Figure 3 The electromagnetic shielding efficiency curve of the electromagnetic shielding material of Example 2 and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some 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 are within the scope of protection of the present application.

[0028] The first aspect of the present application provides an electromagnetic shielding material comprising a self-supportable conductive film with a pleated topological structure, the thickness of the conductive film being 20-500 nm, preferably 20-200 nm. For example, the thickness of the conductive film can be 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or a range between any two of the above values. The electromagnetic shielding material provided by the present application comprising a conductive film with a pleated 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 one-way pleated topological structure or a two-way pleated topological structure. In the present application, the "one-way" refers to a single length direction or a single width direction; the "two-way" refers to both the length direction and the width direction. The present application can realize the adjustment of the electromagnetic shielding strength per unit area of the electromagnetic shielding material by controlling the one-way pleated topological structure or the two-way pleated topological structure of the conductive film.

[0030] In some embodiments, the planar area of the conductive film is 10-50% of the surface area of the conductive film. In the present application, the planar area of the conductive film refers to the maximum area value of the self-supportable conductive film with a wrinkled topological structure in the plane of the length direction and the width direction; the surface area of the conductive film refers to the product of the length and the width of the self-supportable conductive film with a wrinkled topological structure when the conductive film is flat. The present application regulates the ratio of the planar area of the conductive film to the surface area of the conductive film within the above range, which can make the unit area of the electromagnetic shielding material have higher electromagnetic shielding performance. The present application can adjust the unit area electromagnetic shielding strength of the electromagnetic shielding material by controlling the ratio of the planar 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 present application selects the self-supportable conductive film with a wrinkled topological structure from the above-mentioned material categories, which has higher electromagnetic shielding strength, so that the unit area of the electromagnetic shielding material has better electromagnetic shielding performance.

[0032] The second aspect of the present application provides a preparation method of the electromagnetic shielding material provided by 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 make the flat conductive film shrink and form a conductive film with a wrinkled topological structure;

[0036] S4. Dissolving the sacrificial layer and separating the shape memory polymer substrate to obtain an electromagnetic shielding material comprising a self-supportable conductive film with a wrinkled topological structure.

[0037] The present application provides a preparation method of a high-efficiency flexible electromagnetic shielding material based on a wrinkled topological structure, which has simple process and low cost, can obtain an electromagnetic shielding material with high unit area electromagnetic shielding strength, is suitable for the design and production of fine and integrated thin film electronic devices, and the unit area electromagnetic shielding strength of the electromagnetic shielding material is adjustable.

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

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

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

[0041] In some embodiments, the shrinking of the flat conductive film comprises: not fixing the shape memory polymer substrate, and bidirectionally freely shrinking the flat conductive film along the length direction and the width direction. Further, the bidirectional free shrinking has a length ratio M2 of (2-5): 1 between the length before shrinking and the length after shrinking, and a width ratio N2 of (2-5): 1 between the width before shrinking and the width after shrinking, for example, M2 can be 2:1, 3:1, 4:1, 5:1 or a range between any two of the values, and N2 can be 2:1, 3:1, 4:1, 5:1 or a range between any two of the values.

[0042] In the present application, the shape memory polymer substrate loaded with the sacrificial layer and the flat conductive film obtained after the heating step S2 is controlled to shrink in a certain way, so as to adjust the wrinkle topology of the conductive film, thereby obtaining a conductive film with unidirectional wrinkle topology or bidirectional wrinkle topology.

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

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

[0045] In some embodiments, in step S1, the pre-stretched shape memory polymer has a length ratio M1 of (2-5):1 after pre-stretching to the length before pre-stretching, and a width ratio N1 of (2-5):1 after pre-stretching to the width before pre-stretching. In the present application, M1 and N1 are fixed for the same kind of shape memory polymer; in some embodiments, M2=M1 and 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 method for preparing the sacrificial layer is selected from spin coating or dip coating.

[0048] In some embodiments, the thickness of the sacrificial layer is ≤1000 nm, preferably, the thickness of the sacrificial layer is 2 nm-500 nm. For example, the thickness of the sacrificial layer can be 2 nm, 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 600 nm, 800 nm, 1000 nm, or a range between any two of the aforementioned values. The inventors have found that if the thickness of the sacrificial layer is too high, such as higher than 1000 nm, cracks will occur in the conductive film; if the thickness of the sacrificial layer is too low, such as lower than 2 nm, the sacrificial layer is too thin to form a film, and the conductive film will not easily fall off from the substrate. Controlling the thickness of the sacrificial layer within the aforementioned range can obtain an electromagnetic shielding material with stable quality.

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

[0050] In the present application, the term "about" is defined as approximately as understood by one 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] Examples

[0052] Hereinafter, examples and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations are performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are mass-based.

[0053] Test methods and equipment:

[0054] Measurement of electromagnetic shielding value:

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

[0056] 1. Preparation and calibration of equipment: Ensure that the VNA and electromagnetic shielding material are in good working condition.

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

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

[0059] 4. Connect the probe: Connect the probe of the VNA to both ends of the electromagnetic shielding material sample, ensuring 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 the 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] Measurement of the surface area of the conductive film:

[0063] Measure the length L1 and width W1 of the flat conductive film with a ruler, and obtain the surface area of the conductive film = L1 x W1.

[0064] Measurement of the planar area of the conductive film:

[0065] Measure the maximum length L2 and maximum width W2 of the conductive film with a one-way fold topology or a two-way fold topology on the same plane with a ruler, and obtain the planar area of the conductive film = L2 x W2.

[0066] Example 1

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

[0068] S2. Preparing a 50 nm-thick Au flat conductive film on the surface of the sacrificial layer obtained in step S1 by magnetron sputtering;

[0069] S3. Heating the PS substrate loaded with the sacrificial layer and the flat conductive film obtained in step S2 at 130°C for 10 min, fixing the width direction of the PS substrate loaded with the sacrificial layer and the flat conductive film, and allowing the flat conductive film to unidirectionally shrink along the length direction of the PS substrate to obtain a conductive film with a unidirectional wrinkle topological structure;

[0070] S4. Immersing the sample obtained in step S3 in a solvent of acetone to dissolve away the photoresist and separate the PS substrate to obtain an electromagnetic shielding material: a self-supportable Au conductive film with a unidirectional wrinkle topological structure, with a ratio of 2.5:1 between the length before shrinkage and the length after shrinkage, and a planar area accounting for 40% of the surface area thereof.

[0071] Example 2

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

[0073] S3. Heating the PS substrate loaded with the sacrificial layer and the flat conductive film obtained in step S2 at 130°C for 10 min without fixing the PS substrate loaded with the sacrificial layer and the flat conductive film, and allowing the flat conductive film to bidirectionally freely shrink along the length and width directions of the PS substrate to obtain a conductive film with a bidirectional wrinkle topological structure;

[0074] S4. Immersing the sample obtained in step S3 in a solvent of acetone to dissolve away the photoresist and separate the PS substrate to obtain an electromagnetic shielding material: a self-supportable Au conductive film with a bidirectional wrinkle topological structure, with a ratio of 2.5:1 between the length before shrinkage and the length after shrinkage, a ratio of 2.5:1 between the width before shrinkage and the width after shrinkage, and a planar area accounting for 16% of the surface area thereof.

[0075] Examples 3-6

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

[0077] Comparative Example 1

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

[0079] S3. The sample obtained in step S2 was immersed in solvent acetone to dissolve away the photoresist, and the PS substrate was separated to 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 was the same as Comparative Example 1.

[0082] The preparation parameters and performance test results of the electromagnetic shielding materials of each example 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 relatively flat conductive film electromagnetic shielding material = (electromagnetic shielding value of the electromagnetic shielding material of the example - electromagnetic shielding value of the flat conductive film of the comparative example) / electromagnetic shielding value of the flat conductive film of the comparative example x 100%.

[0083] Table 1

[0084]

[0085] Note: " / " means no corresponding preparation parameter.

[0086] The scanning electron microscope (manufacturer: JEOL Ltd., Tokyo, Japan, model: JSM-7000F) was used to detect the electromagnetic shielding material of Example 1, and the microstructure thereof was obtained as shown in Figure 1 It can be seen that it has a one-way wrinkle topological structure. The electromagnetic shielding values of the electromagnetic shielding materials of Example 1, Example 2 and Comparative Example 1 were determined, and the electromagnetic shielding efficiency curves of each electromagnetic shielding material in the frequency band of 8.2-12.4 GHz were obtained as shown in Figure 2 and Figure 3 It can be seen that, between 8.2-12.4 GHz, the electromagnetic shielding material of the flat conductive film of Comparative Example 1 has the lowest electromagnetic shielding value, about 38 dB; the electromagnetic shielding material of the one-way shrink film of Example 1 has an electromagnetic shielding value of 43 dB; the electromagnetic shielding material of the two-way shrink film of Example 2 has an electromagnetic shielding value of 55 dB; the planar area of the electromagnetic shielding materials of Example 1 and Example 2 is reduced to 40% and 16% of the surface area, respectively, and the electromagnetic shielding values are increased by 13% and 45% compared with Comparative Example 1, respectively. According to the results of Table 1 and Figures 2-3 It can be seen from the results of Table 1 and

[0087] It should be noted that, in the present document, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0088] Each of the embodiments in the present specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments.

[0089] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electromagnetic shielding material comprising a self-supporting conductive film having a corrugated topology; The electromagnetic shielding material is prepared by the following method: S1. Prepare a sacrificial layer on a pre-stretched shape memory polymer substrate; S2. Prepare a smooth conductive film on the surface of the sacrificial layer; S3. Heating the shape memory polymer substrate causes the flat conductive film to shrink, forming a conductive film with a wrinkled topology; S4. Dissolve the sacrificial layer, separate the shape memory polymer substrate, and obtain the electromagnetic shielding material.

2. The electromagnetic shielding material according to claim 1, wherein, The thickness of the conductive film is 20nm-500nm.

3. The electromagnetic shielding material according to claim 2, wherein, The thickness of the conductive film is 20nm-200nm.

4. The electromagnetic shielding material according to claim 1, wherein, The conductive film has a unidirectional or bidirectional wrinkled topology.

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

6. The electromagnetic shielding material according to any one of claims 1-5, 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.

7. The electromagnetic shielding material according to claim 1, wherein, In step S3, shrinking the flat conductive film includes: fixing one direction of the shape memory polymer substrate and causing the flat conductive film to shrink unidirectionally in another direction perpendicular to it; or, not fixing the shape memory polymer substrate and causing the flat conductive film to shrink bidirectionally.

8. The electromagnetic shielding material according to claim 1, wherein, The heating includes a heating temperature of 120-160℃ and a heating time of 5-20 minutes.

9. The electromagnetic shielding material according to claim 1, wherein, The method for preparing the flat conductive thin film is selected from physical vapor deposition, solution deposition, or atomic layer deposition.

10. The electromagnetic shielding material according to any one of claims 1, 7-9, wherein, In step S1, the pre-stretched shape memory polymer has a length-to-length ratio M1 of (2-5):1 and a width-to-width ratio N1 of (2-5):

1.

11. The electromagnetic shielding material according to claim 10, wherein, The shape memory polymer is selected from polystyrene, polyurethane, or trans-1,4-polyisoprene.

12. The electromagnetic shielding material according to any one of claims 1, 7-9, wherein, The method for preparing the sacrificial layer is selected from spin coating or dip coating.

13. The electromagnetic shielding material according to claim 12, wherein, The thickness of the sacrificial layer is ≤1000nm.

14. The electromagnetic shielding material according to claim 12, wherein, The sacrificial layer material is photoresist, and the solvent for dissolution is acetone; Alternatively, the sacrificial layer material is selected from at least one of polyvinylpyrrolidone and polyvinyl alcohol, and the solvent for dissolution is water.

Images