Electromagnetic shielding composite material and method for manufacturing the same

Abstract

The application provides an electromagnetic shielding composite material and a preparation method thereof. The electromagnetic shielding composite material comprises a conductive film with a corrugated structure, a bonding layer and an elastic substrate layer, and the bonding layer comprises a molecular adhesion promoter. The electromagnetic shielding composite material provided by the application has excellent stretchability and electromagnetic shielding performance, because the surface of the conductive film is modified by the bonding layer, and the conductive film with the corrugated structure can be combined with the elastic substrate layer through chemical bonds. The preparation method of the electromagnetic shielding composite material provided by the application has simple preparation steps, low preparation cost and wide application range.

Description

Technical Field

[0001] This application relates to the field of electromagnetic shielding technology, and in particular to an electromagnetic shielding composite material and its preparation method. Background Technology

[0002] With the rapid development of electronic information technology, the Internet of Things (IoT) era is changing modern lifestyles, especially the application of miniaturized, portable, and wireless wearable electronic devices in the fields of human health and medicine, which is changing people's lifestyles and improving their quality of life. However, the emission, distribution, and use of electrical energy by electronic devices generate electromagnetic interference, which not only disrupts the normal operation of other electronic devices but also has adverse effects on health. Therefore, wearable electronic devices need to integrate electromagnetic shielding devices to eliminate the adverse effects of electromagnetic interference. This requires electromagnetic shielding materials to not only have good electromagnetic shielding performance but also excellent tensile properties to withstand external forces (i.e., the electromagnetic shielding performance of the electromagnetic shielding device does not change much under external forces and can still meet its functional requirements). Currently, metal materials are the main materials for electromagnetic shielding devices, but metal films have extremely poor ability to withstand mechanical forces such as tension, compression, and bending, which is insufficient to meet the requirements of wearable electromagnetic shielding electronic devices. Therefore, designing and fabricating conductive thin film materials with good resistance to external mechanical forces and excellent electromagnetic shielding performance is of great significance for the development of wearable electronic devices. Summary of the Invention

[0003] The purpose of this application is to provide an electromagnetic shielding composite material and its preparation method, so as to obtain an electromagnetic shielding material with both excellent stretchability and electromagnetic shielding performance. The specific technical solution is as follows:

[0004] The first aspect of this application provides an electromagnetic shielding composite material comprising a conductive thin film having a corrugated structure, a bonding layer, and an elastic substrate layer, wherein the bonding layer comprises a molecular adhesion promoter.

[0005] In some embodiments, the molecular adhesion promoter is (3-mercaptopropyl)trimethoxysilane.

[0006] In some embodiments, the conductive film is a unidirectional or bidirectional wrinkled structure.

[0007] In some embodiments, the planar area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film.

[0008] 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.

[0009] In some embodiments, the material of the elastic base layer is selected from at least one of polydimethylsiloxane and Ecoflex.

[0010] In some embodiments, the thickness of the conductive film is 3nm-500nm, preferably 5nm-200nm, the thickness of the bonding layer is 0.5nm-1nm, and the thickness of the elastic substrate layer is 500µm-2mm.

[0011] In some implementations, the strain of the electromagnetic shielding composite material is 0-40%.

[0012] The second aspect of this application provides a method for preparing the electromagnetic shielding composite material provided in the first aspect of this application, which includes the following steps:

[0013] S1. Prepare a sacrificial layer on a pre-stretched shape memory polymer substrate;

[0014] S2. Prepare a smooth conductive film on the surface of the sacrificial layer;

[0015] S3. Heat the shape memory polymer substrate to shrink the flat conductive film and form a conductive film with a wrinkled structure;

[0016] S4. The molecular adhesion promoter is applied to the surface of the conductive film with the wrinkled structure to obtain the bonding layer;

[0017] S5. Prepare an elastic base layer on the surface of the bonding layer;

[0018] S6. Dissolve the sacrificial layer, separate the shape memory polymer substrate, and obtain the electromagnetic shielding composite material.

[0019] In some embodiments, 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.

[0020] In some embodiments, the method for preparing the elastic substrate layer includes: adding a polymer monomer and a curing agent in a mass ratio of (8-12):1, and holding at 60-80°C for 3-5 hours.

[0021] In some embodiments, the method for preparing the sacrificial layer is selected from spin coating or dip coating; the method for preparing the planar conductive thin film is selected from physical vapor deposition, solution deposition or atomic layer deposition.

[0022] In some implementations, 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.

[0023] In some embodiments, the shape memory polymer is selected from polystyrene, polyurethane, or trans-1,4-polyisoprene.

[0024] In some embodiments, the heating includes a heating temperature of 110-160°C and a heating time of 5-20 minutes.

[0025] In some implementations, the thickness of the sacrificial layer is ≤1000nm.

[0026] In some embodiments, the sacrificial layer material is photoresist, and the solvent for dissolution is acetone;

[0027] Alternatively, the sacrificial layer material is selected from at least one of polyvinylpyrrolidone and polyvinyl alcohol, and the solvent for dissolution is water.

[0028] This application provides an electromagnetic shielding composite material and its preparation method. The electromagnetic shielding composite material includes a conductive thin film with a wrinkled structure, a bonding layer, and an elastic base layer. The bonding layer includes a molecular adhesion promoter. The electromagnetic shielding composite material provided in this application modifies the surface of the conductive thin film through the bonding layer. The conductive thin film with a wrinkled structure can bond with the elastic base layer through chemical bonds, giving the electromagnetic shielding composite material, comprising the conductive thin film with a wrinkled structure, the bonding layer, and the elastic base layer, excellent tensile properties and electromagnetic shielding performance. The preparation method of the electromagnetic shielding composite material provided in this application is simple in preparation steps, low in preparation cost, and has a wide range of applications. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0030] Figure 1 The bidirectional pleated structure of the electromagnetic shielding composite material of Example 1 is shown;

[0031] Figure 2 The electromagnetic shielding effectiveness curves of the electromagnetic shielding composite material of Example 1 and the electromagnetic shielding composite material of Comparative Example 1 are shown.

[0032] Figure 3The electromagnetic shielding effectiveness curves of the electromagnetic shielding composite material of Example 1 are shown at strains of 0%, 15%, and 30%. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0034] The first aspect of this application provides an electromagnetic shielding composite material, comprising a conductive film with a wrinkled structure, a bonding layer, and an elastic substrate layer, wherein the bonding layer includes a molecular adhesion promoter. The electromagnetic shielding composite material provided by this application modifies the surface of the conductive film using a molecular adhesion promoter (i.e., molecules with self-assembly properties that form a bonding layer), enabling the wrinkled conductive film to bond with the elastic substrate layer through chemical bonds. This results in the high ductility of the wrinkled conductive film itself and the high-strength chemical bond between the conductive film and the elastic substrate layer, improving the electromagnetic shielding composite material's resistance to external mechanical forces such as tension, compression, and bending. Simultaneously, the wrinkled conductive film provides more contacts, offering more channels for electron flow and reducing the sheet resistance of the conductive film. Therefore, the electromagnetic shielding composite material of this application, comprising a wrinkled conductive film, a bonding layer, and an elastic substrate layer, simultaneously possesses excellent tensile strength and electromagnetic shielding performance.

[0035] In some embodiments, the molecular adhesion promoter is (3-mercaptopropyl)trimethoxysilane (MPTMS). This application modifies the surface of the conductive film using the aforementioned type of molecular adhesion promoter, enabling the conductive film to form chemical bonds with the elastic substrate layer, thereby improving the stretchability and stability of the electromagnetic shielding composite material.

[0036] In some embodiments, the conductive film is a unidirectional or bidirectional wrinkled structure. In this application, "unidirectional" refers to a single length direction or a single width direction, and "bidirectional" refers to both the length and width directions.

[0037] In some embodiments, the planar area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film. For example, the planar area of ​​the conductive film can be 10%, 12%, 16%, 20%, 24%, 30%, 36%, 40%, 42%, 46%, 50% of the surface area of ​​the conductive film, or a range of any two of these values. In this application, the planar area of ​​the conductive film refers to the maximum area of ​​the plane in which the corrugated conductive film is projected perpendicularly in both the length and width directions; the surface area of ​​the conductive film refers to the product of the length and width of the corrugated conductive film when it is a flat conductive film. By controlling the ratio of the planar area of ​​the conductive film to the surface area of ​​the conductive film within the above range, this application enables the electromagnetic shielding composite material to have better stretchability and electromagnetic shielding performance.

[0038] In some embodiments, the conductive film is made of at least one material selected from gold and its alloys, silver and its alloys, copper and its alloys, and aluminum and its alloys. The conductive film with a corrugated structure selected from the above-mentioned material types in this application has high electromagnetic shielding strength and good ductility, giving the electromagnetic shielding composite material good stretchability and electromagnetic shielding performance.

[0039] In some embodiments, the material of the elastic substrate layer is selected from at least one of polydimethylsiloxane (PDMS) and Ecoflex. In this application, Ecoflex is a silicone material prepared by mixing renewable raw materials such as polylactic acid (PLA) and starch. This application does not particularly limit the source of PDMS and Ecoflex, as long as they can achieve the purpose of this application, for example, they can be obtained through commercial purchase. By using the above-mentioned elastic substrate layer and the conductive film with a wrinkled structure to chemically bond, this application enables the electromagnetic shielding composite material to have good stretchability and electromagnetic shielding performance.

[0040] In some embodiments, the thickness of the conductive film is 3nm-500nm, preferably 5nm-200nm, the thickness of the bonding layer is 0.5nm-1nm, and the thickness of the elastic substrate layer is 500µm-2mm. For example, the thickness of the conductive film can be 3nm, 5nm, 10nm, 20nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, or any two of these values; the thickness of the bonding layer can be 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, or any two of these values; and the thickness of the elastic substrate layer can be 500µm, 600µm, 800µm, 900µm, 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm, or any two of these values. By adjusting the thickness of the conductive film, bonding layer, and elastic substrate layer within the aforementioned range, this application can balance the electromagnetic shielding performance and mechanical tensile properties of the electromagnetic shielding composite material, enabling the electromagnetic shielding composite material to simultaneously possess excellent tensile properties and electromagnetic shielding performance.

[0041] In some embodiments, the strain of the electromagnetic shielding composite material is 0-40%. For example, the strain of the electromagnetic shielding composite material can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a range of any two of these values. The electromagnetic shielding composite material with strain controlled within the above range exhibits good tensile properties while also maintaining good electromagnetic shielding performance.

[0042] The second aspect of this application provides a method for preparing the electromagnetic shielding composite material provided in the first aspect of this application, which includes the following steps:

[0043] S1. Prepare a sacrificial layer on a pre-stretched shape memory polymer substrate;

[0044] S2. Prepare a smooth conductive film on the surface of the sacrificial layer;

[0045] S3. Heat the shape memory polymer substrate to shrink the flat conductive film and form a conductive film with a wrinkled structure;

[0046] S4. The molecular adhesion promoter is applied to the surface of the conductive film with the wrinkled structure to obtain the bonding layer;

[0047] S5. Prepare an elastic base layer on the surface of the bonding layer;

[0048] S6. Dissolve the sacrificial layer, separate the shape memory polymer substrate, and obtain the electromagnetic shielding composite material.

[0049] The method for preparing the electromagnetic shielding composite material provided in this application involves preparing a sacrificial layer on a pre-stretched shape memory polymer substrate, then preparing a flat conductive film on the surface of the sacrificial layer. Subsequently, the conductive film forms a wrinkled structure by shrinking the shape memory polymer substrate. A molecular adhesion promoter is used to modify the surface of the conductive film in the bonding layer, enabling the conductive film to form chemical bonds with the elastic substrate layer. The sacrificial layer is then dissolved in a solvent, and the shape memory polymer substrate is separated to obtain the stretchable electromagnetic shielding composite material of this application. The method for preparing the electromagnetic shielding composite material provided in this application has simple preparation steps, low preparation cost, and is applicable to various conductive film materials, thus having a wide range of applications. The resulting electromagnetic shielding composite material simultaneously possesses excellent stretchability and electromagnetic shielding performance.

[0050] In some embodiments, 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.

[0051] In some embodiments, shrinking the flat conductive film includes: fixing the width direction of the shape memory polymer substrate and shrinking the flat conductive film unidirectionally along the length direction perpendicular to it; further, the unidirectional shrinkage is such that 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 of any two of these values; in some embodiments, M2=M1.

[0052] In some embodiments, shrinking the flat conductive film includes: fixing the length direction of the shape memory polymer substrate and unidirectionally shrinking the flat conductive film along the width direction perpendicular to it; further, the unidirectional shrinkage is such that the width before shrinkage to the width after shrinkage, N2, is (2-5):1, for example, N2 can be 2:1, 3:1, 4:1, 5:1 or a range of any two of these values; in some embodiments, N2=N1.

[0053] In some embodiments, shrinking the flat conductive film includes: not fixing the shape memory polymer substrate, allowing the flat conductive film to shrink freely in both the length and width directions; further, in the bidirectional free shrinkage, the ratio of the length before shrinkage to the length after shrinkage, M2, is (2-5):1, and the ratio of the width before shrinkage to the width after shrinkage, N2, 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.

[0054] In some embodiments, the strain of the electromagnetic shielding composite material is 0-40%. This application can control the strain of the electromagnetic shielding composite material through stretching. In some embodiments, shrinking the flat conductive film includes: fixing one direction (denoted as the x-direction) of the shape memory polymer substrate and causing the flat conductive film to shrink unidirectionally along another direction perpendicular to it (denoted as the y-direction), wherein the strain is unidirectional stretching along the y-direction. In some embodiments, shrinking the flat conductive film includes: not fixing the shape memory polymer substrate and causing the flat conductive film to shrink bidirectionally, wherein the strain can be unidirectional stretching along the x-direction, unidirectional stretching along the y-direction, or bidirectional stretching along both the x and y directions. This application does not have any particular limitation on these aspects; as long as the purpose of this application can be achieved, different directions of strain stretching can be applied as needed.

[0055] In this application, the shape memory polymer substrate loaded with the sacrificial layer and the flat conductive film obtained in the heating step S2 is adjusted by controlling the shrinkage mode of the shape memory polymer substrate and adjusting the structure of the conductive film, thereby obtaining a conductive film with a unidirectional or bidirectional wrinkled structure.

[0056] In some embodiments, the heating includes a heating temperature of 110-160°C and a heating time of 5-20 minutes. For example, the heating temperature can be 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, or a range of any two of these values, and the heating time can be 5 minutes, 6 minutes, 8 minutes, 10 minutes, 12 minutes, 15 minutes, 18 minutes, 20 minutes, or a range of any two of these values.

[0057] In some embodiments, the preparation method of the elastic substrate layer includes: adding a polymer monomer and a curing agent in a mass ratio of (8-12):1, and holding at 60-80°C for 3-5 hours. This application does not particularly limit the source of the polymer monomer and curing agent used to prepare the elastic substrate layer, as long as they can achieve the purpose of this application; for example, they can be obtained through commercial purchase. When the elastic substrate layer is PDMS, for example, the commercially available SYLGARD 184 silicone elastomer kit includes a polymer monomer and a curing agent, and PDMS is composed of a base (polymer monomer) / curing agent mixture. When the elastic substrate layer is Ecoflex, for example, Ecoflex is composed of a commercially available Ecoflex 0030 base (polymer monomer) and Ecoflex curing agent mixture.

[0058] In some embodiments, the method for preparing the sacrificial layer is selected from spin coating or dip coating; the method for preparing the planar conductive thin film is selected from physical vapor deposition (such as magnetron sputtering), solution deposition or atomic layer deposition.

[0059] In some embodiments, 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. In this application, for the same shape memory polymer, M1 and N1 are fixed; in some embodiments, M2=M1 and N2=N1.

[0060] In some embodiments, the shape memory polymer is selected from at least one of polystyrene (PS), polyurethane, or trans-1,4-polyisoprene (TPI).

[0061] In some embodiments, the thickness of the sacrificial layer is ≤1000nm, preferably 2-500nm. For example, the thickness of the sacrificial layer can be 2nm, 10nm, 20nm, 50nm, 100nm, 200nm, 300nm, 500nm, 600nm, 800nm, 1000nm, or a range of any two of these values. The inventors have found that if the thickness of the sacrificial layer is too high, such as above 1000nm, the conductive film will crack; if the thickness of the sacrificial layer is too low, such as below 2nm, the sacrificial layer is too thin and difficult to form a film, making it difficult for the conductive film to detach from the shape memory polymer substrate. By controlling the thickness of the sacrificial layer within the above range, a stable electromagnetic shielding composite material can be obtained.

[0062] 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 this application, the sacrificial layer is dissolved by a solution method, thereby separating and removing the shape memory polymer substrate to obtain the electromagnetic shielding composite material comprising a conductive film, a bonding layer, and an elastic substrate layer with a wrinkled structure.

[0063] A third aspect of this application provides an electronic device comprising the electromagnetic shielding composite material provided in the first aspect of this application or the electromagnetic shielding composite material prepared according to the preparation method provided in the second aspect of this application.

[0064] In this application, the term "about" is defined as close to as understood by one of ordinary skill in the art. In some embodiments, the term is defined as less than 10%, preferably less than 5%, more preferably less than 1%, and even more preferably less than 0.5%.

[0065] Example

[0066] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0067] Test methods and equipment:

[0068] Electromagnetic shielding value test:

[0069] The steps for testing electromagnetic shielding strength using a vector network analyzer (VNA, Agilent N5247A, Shenzhen McKerry Instrument Co., LTD, China) are as follows:

[0070] 1. Prepare and calibrate the equipment: Ensure that both the VNA and the electromagnetic shielding composite material are in good working order;

[0071] 2. VNA settings: According to the device manual, set the appropriate frequency range and power level. The frequency range for this test is 8.2-12.4GHz.

[0072] 3. Sample installation: Place the electromagnetic shielding composite material in the test area of ​​the VNA, ensuring that its position is fixed and free from interference from impurities;

[0073] 4. Connect the probe: Connect the VNA probe to both ends of the electromagnetic shielding composite material sample, ensuring good contact;

[0074] 5. Conduct tests: Start the VNA and record the transmission parameters (such as S-parameters) at different frequencies.

[0075] 6. Data Analysis: Use VNA software to analyze the test data, calculate the electromagnetic shielding effect of the electromagnetic shielding composite material, obtain the electromagnetic shielding effectiveness curve of the electromagnetic shielding composite material, and obtain the electromagnetic shielding value of the electromagnetic shielding composite material.

[0076] Testing the planar area of ​​conductive thin films:

[0077] Using a ruler, measure the length L2 and width W2 of the conductive film with a unidirectional or bidirectional wrinkled structure projected perpendicularly in the length and width directions, and obtain the planar area of ​​the conductive film = L2 × W2.

[0078] Testing the surface area of ​​conductive thin films:

[0079] Using a ruler, measure the length L1 and width W1 of the flat conductive film to obtain the surface area of ​​the conductive film = L1 × W1.

[0080] Example 1

[0081] S1. A pre-stretched shape memory polymer PS substrate (Polystyrene, Graphix shrink film, Graphix, Maple Heights, OH, USA) with a length-to-length ratio of 2.5:1 and a width-to-width ratio of 2.5:1. A photoresist with a thickness of approximately 500 nm is spin-coated onto the pre-stretched PS substrate as a sacrificial layer at a spin speed of 5000 rpm and a spin time of 37 s.

[0082] S2. A flat Au conductive film with a thickness of 50 nm is prepared on the surface of the sacrificial layer obtained in step S1 by magnetron sputtering;

[0083] S3. Heat the PS substrate with the sacrificial layer and flat conductive film obtained in step S2 at 130℃ for 10 min. Do not fix the PS substrate with the sacrificial layer and flat conductive film, so that the flat conductive film can freely shrink along the length and width directions of the PS substrate to obtain a conductive film with a bidirectional wrinkled structure. The ratio of its length before shrinkage to its length after shrinkage is 2.5:1, and the ratio of its width before shrinkage to its width after shrinkage is 2.5:1.

[0084] S4. A bonding layer with a thickness of 0.7 nm was obtained by coating the surface of a conductive film with a bidirectional wrinkled structure with a molecular adhesion promoter (3-mercaptopropyl)trimethoxysilane (MPTMS).

[0085] S5. Pour a polymer PDMS monomer and curing agent (SYLGARD 184 silicone elastomer kit) at a mass ratio of 10:1 onto the surface of the bonding layer, and keep it at 70°C for 4 hours to cure the PDMS precursor into an elastomer, forming a PDMS elastic base layer with a thickness of 1 mm on the surface of the bonding layer.

[0086] S6. Immerse the sample obtained in step S5 in the solvent acetone to dissolve the photoresist sacrificial layer, separate the PS substrate, and obtain the electromagnetic shielding composite material, which includes an Au conductive film with a bidirectional wrinkled structure, an MPTMS bonding layer and a PDMS elastic substrate layer. The planar area of ​​the Au conductive film accounts for 16% of its surface area and the strain is 0%.

[0087] Using a tensile tester with an accuracy of 0.01 mm developed in the laboratory, the electromagnetic shielding composite material was stretched to strains of 15% and 30%, respectively.

[0088] Example 2

[0089] Except for step S3, which uses the steps described below, the rest is the same as in Example 1, resulting in an electromagnetic shielding composite material, comprising an Au conductive film with a unidirectional wrinkled structure, an MPTMS bonding layer, and a PDMS elastic substrate layer. The planar area of ​​the Au conductive film accounts for 40% of its surface area, and the strain is 0%.

[0090] S3. Heat the PS substrate with the sacrificial layer and flat conductive film obtained in step S2 at 130°C for 10 min. Fix the width direction of the PS substrate with the sacrificial layer and flat conductive film, and make the flat conductive film shrink unidirectionally along the length direction of the PS substrate to obtain a conductive film with a unidirectional wrinkled structure. The ratio of its length before shrinkage to its length after shrinkage is 2.5:1.

[0091] Using a tensile tester with an accuracy of 0.01 mm developed in the laboratory, electromagnetic shielding composite materials were stretched to strains of 15% and 30%, respectively, with the stretching direction being the length direction.

[0092] Examples 3-7

[0093] Except for adjusting the corresponding preparation parameters according to Table 1, everything else is the same as in Example 1.

[0094] Comparative Example 1

[0095] S1. Pre-stretched shape memory polymer PS substrate (Graphix shrink film, Graphix, MapleHeights, OH, USA), with a pre-stretched length to unstretched length ratio of 2.5:1 and a pre-stretched width to unstretched width ratio of 2.5:1;

[0096] S2. A flat conductive Au film with a thickness of 50 nm is prepared on the surface of the PS substrate obtained in step S1 by magnetron sputtering, resulting in an electromagnetic shielding composite material including the flat conductive Au film and the PS substrate.

[0097] Comparative Example 2

[0098] Except for skipping step S3, i.e. directly preparing the bonding layer on the flat conductive film obtained in step S2 according to step S4, the rest is the same as in Example 1, and an electromagnetic shielding composite material is obtained, including an Au flat conductive film, an MPTMS bonding layer and a PDMS elastic substrate layer, wherein the planar area of ​​the Au flat conductive film accounts for 100% of its surface area.

[0099] Comparative Example 3

[0100] Except for skipping step S4, i.e. not coating the conductive film obtained in step S3 with a bonding layer, and directly preparing the PDMS elastic substrate layer according to step S5, the rest is the same as in Example 1, resulting in an electromagnetic shielding composite material, including an Au conductive film with a bidirectional pleated structure and a PDMS elastic substrate layer.

[0101] The preparation parameters and performance test results of the electromagnetic shielding composite materials of each embodiment and comparative example are shown in Table 1.

[0102] Table 1

[0103]

[0104] Note: " / " indicates that there is no corresponding parameter.

[0105] The electromagnetic shielding composite material of Example 1 was examined using a scanning electron microscope (manufacturer: JEOL Ltd., Tokyo, Japan, model: JSM-7000F) to obtain its microstructure as shown below. Figure 1 As shown, its bidirectional pleated structure is visible. The electromagnetic shielding effectiveness curves of the electromagnetic shielding composite material of Example 1 and the electromagnetic shielding composite material of Comparative Example 1 in the 8.2-12.4 GHz frequency band are shown below. Figure 2 As shown, the electromagnetic shielding value of the electromagnetic shielding composite material in Comparative Example 1 is relatively low, approximately 38 dB; the electromagnetic shielding value of the electromagnetic shielding composite material in Example 1, including the bidirectional wrinkled film, is approximately 55 dB, which is 45% higher than that in Comparative Example 1. The results indicate that the electromagnetic shielding composite material of this application can effectively cancel interfering electromagnetic waves and has excellent electromagnetic shielding performance. The electromagnetic shielding effectiveness curves of the electromagnetic shielding composite material in Example 1 at strains of 0%, 15%, and 30% are shown in the figure. Figure 3 As shown, the electromagnetic shielding values ​​of the electromagnetic shielding composite material of Example 1 with strains of 0%, 15%, and 30% are approximately 55 dB, 52.5 dB, and 51 dB, respectively. This indicates that the electromagnetic shielding value under tension is only 4.5% and 7.2% lower than that under non-tension conditions, demonstrating that the electromagnetic shielding composite material of this application has good stretchability. The inventors discovered that the electromagnetic shielding composite material obtained in Comparative Example 2 has an electromagnetic shielding value of 0. This is because the flat conductive film itself is too brittle; without any shrinkage, even a slight external force will cause cracks, resulting in the failure of its electromagnetic shielding performance. According to Table 1 and... Figures 2-3 The results show that the electromagnetic shielding composite material prepared according to the method of this application can simultaneously possess excellent tensile properties and electromagnetic shielding properties.

[0106] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0107] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0108] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electromagnetic shielding composite material, comprising a conductive thin film having a wrinkled structure, a bonding layer, and an elastic substrate layer, wherein the bonding layer comprises a molecular adhesion promoter; The electromagnetic shielding composite 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. Heat the shape memory polymer substrate to shrink the flat conductive film and form a conductive film with a wrinkled structure; S4. The molecular adhesion promoter is applied to the surface of the conductive film with the wrinkled structure to obtain the bonding layer; S5. Prepare the elastic base layer on the surface of the bonding layer; S6. Dissolve the sacrificial layer, separate the shape memory polymer substrate, and obtain the electromagnetic shielding composite material.

2. The electromagnetic shielding composite material according to claim 1, wherein, The molecular adhesion promoter is (3-mercaptopropyl)trimethoxysilane.

3. The electromagnetic shielding composite material according to claim 1, wherein, The conductive film has a unidirectional or bidirectional wrinkled structure.

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

5. The electromagnetic shielding composite material according to claim 1, 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.

6. The electromagnetic shielding composite material according to claim 1, wherein, The material of the elastic base layer is selected from at least one of polydimethylsiloxane and Ecoflex.

7. The electromagnetic shielding composite material according to claim 1, wherein, The thickness of the conductive film is 3nm-500nm, the thickness of the bonding layer is 0.5nm-1nm, and the thickness of the elastic substrate layer is 500μm-2mm.

8. The electromagnetic shielding composite material according to claim 7, wherein, The thickness of the conductive film is 5nm-200nm.

9. The electromagnetic shielding composite material according to any one of claims 1-8, wherein, The strain of the electromagnetic shielding composite material is 0-40%.

10. The electromagnetic shielding composite 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.

11. The electromagnetic shielding composite material according to claim 1, wherein, The preparation method of the elastic base layer includes: adding a polymer monomer and a curing agent in a mass ratio of (8-12):1, and keeping it at 60-80℃ for 3-5 hours.

12. The electromagnetic shielding composite material according to claim 1, wherein, The method for preparing the sacrificial layer is selected from spin coating or dip coating; the method for preparing the planar conductive thin film is selected from physical vapor deposition, solution deposition or atomic layer deposition.

13. The electromagnetic shielding composite material according to claim 1, 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.

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

15. The electromagnetic shielding composite material according to any one of claims 1, 10-14, wherein, The heating includes a heating temperature of 110-160℃ and a heating time of 5-20 minutes.

16. The electromagnetic shielding composite material according to any one of claims 1, 10-14, wherein, The thickness of the sacrificial layer is ≤1000nm.

17. The electromagnetic shielding composite material according to any one of claims 1, 10-14, 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.

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