Electromagnetic shielding composite material and preparation method thereof

Abstract

The invention provides an electromagnetic shielding composite material and a preparation method thereof, the electromagnetic shielding composite material comprises a conductive film with a wrinkle structure, a binding layer and an elastic substrate layer, and the binding layer comprises a molecular adhesion promoter. According to the electromagnetic shielding composite material provided by the invention, the surface of the conductive film is modified through the bonding layer, and the conductive film with a wrinkle structure can be bonded with the elastic substrate layer through a chemical bond; therefore, the electromagnetic shielding composite material comprising the conductive film with the wrinkle structure, the bonding layer and the elastic substrate layer has excellent tensile property and electromagnetic shielding property. The preparation method of the electromagnetic shielding composite material is simple in preparation step, low in preparation cost and wide in application range.

Description

Technical Field

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

[0002] With the rapid development of electronic information technology, the era of the Internet of Things is changing the modern lifestyle, 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 will generate electromagnetic interference, which not only disrupts the normal operation of other electronic devices, but also has an adverse effect on physical health. Therefore, it is necessary to integrate electromagnetic shielding functional devices in wearable electronic devices to eliminate the adverse effects of electromagnetic interference. This requires that the electromagnetic shielding material not only has good electromagnetic shielding performance, but also has excellent tensile properties to withstand external forces (that is, the electromagnetic shielding performance of the electromagnetic shielding device under the action of external forces does not change much and can still meet its functional requirements). At present, metal materials are the main materials of electromagnetic shielding devices, but the ability of metal films to withstand mechanical external forces such as stretching, compression, and bending is extremely poor, which is not enough to meet the requirements of wearable electromagnetic shielding electronic devices. Therefore, designing and preparing conductive film materials with good resistance to external mechanical forces and excellent electromagnetic shielding properties is of great significance to 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 a preparation method thereof, so as to obtain an electromagnetic shielding material having both excellent stretchability and electromagnetic shielding performance. The specific technical solution is as follows:

[0004] A first aspect of the present application provides an electromagnetic shielding composite material, which includes a conductive film with a pleated structure, a bonding layer and an elastic base layer, wherein the bonding layer includes a molecular adhesion promoter.

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

[0006] In some embodiments, the conductive film has a unidirectional corrugated structure or a bidirectional corrugated 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 base layer is 500µm-2mm.

[0011] In some embodiments, the electromagnetic shielding composite material has a strain of 0-40%.

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

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

[0014] S2. Preparing a flat conductive film on the surface of the sacrificial layer;

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

[0016] S4. Using the molecular adhesion promoter to coat the surface of the conductive film having a folded structure to obtain the bonding layer;

[0017] S5. Preparing an elastic base layer on the surface of the binding layer;

[0018] S6. Dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining the electromagnetic shielding composite material.

[0019] 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.

[0020] In some embodiments, the preparation method of the elastic base layer comprises: adding a polymer monomer and a curing agent in a mass ratio of (8-12):1, and keeping the mixture 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 flat conductive film is selected from physical vapor deposition, solution method or atomic layer deposition.

[0022] 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.

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

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

[0025] In some embodiments, the sacrificial layer has a thickness of ≤ 1000 nm.

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

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

[0028] The present application provides an electromagnetic shielding composite material and a preparation method thereof, wherein the electromagnetic shielding composite material comprises a conductive film with a pleated structure, a bonding layer and an elastic base layer, wherein the bonding layer comprises a molecular adhesion promoter. The electromagnetic shielding composite material provided by the present application modifies the surface of the conductive film by means of a bonding layer, and the conductive film with a pleated structure can be bonded to the elastic base layer through chemical bonds, so that the electromagnetic shielding composite material comprising a conductive film with a pleated structure, a bonding layer and an elastic base layer in the present application has excellent stretchability and electromagnetic shielding performance. The preparation method of the electromagnetic shielding composite material provided by the present application has simple preparation steps, low preparation cost and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] Figure 1 The bidirectional wrinkled 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 when the strains are 0%, 15%, and 30%, respectively. DETAILED DESCRIPTION

[0033] 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.

[0034] The first aspect of the present application provides an electromagnetic shielding composite material, which includes a conductive film with a pleated structure, a bonding layer and an elastic base layer, and the bonding layer includes a molecular adhesion promoter. The electromagnetic shielding composite material provided by the present application modifies the surface of the conductive film by a molecular adhesion promoter (i.e., a molecule with self-assembly performance, forming a film to form a bonding layer), so that the conductive film with a pleated structure can be combined with the elastic base layer through a chemical bond, and the high ductility of the conductive film with a pleated structure and the high-strength chemical bond between the conductive film and the elastic base layer can improve the ability of the electromagnetic shielding composite material to resist external mechanical forces such as stretching, compression, and bending. At the same time, the conductive film with a pleated structure can make the conductive film have more contacts, provide more channels for the flow of electrons, thereby reducing the square resistance of the conductive film, so that the electromagnetic shielding composite material including the conductive film with a pleated structure, the bonding layer and the elastic base layer in the present application has excellent tensile properties and electromagnetic shielding properties that can withstand external forces.

[0035] In some embodiments, the molecular adhesion promoter is (3-mercaptopropyl) trimethoxysilane (MPTMS). The present application uses the above-mentioned molecular adhesion promoter to modify the surface of the conductive film so that the conductive film can form a chemical bond with the elastic base layer, thereby improving the stretchability and stability of the electromagnetic shielding composite material.

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

[0037] In some embodiments, the plane area of ​​the conductive film is 10-50% of the surface area of ​​the conductive film. For example, the plane area of ​​the conductive film may be 10%, 12%, 16%, 20%, 24%, 30%, 36%, 40%, 42%, 46%, 50% of the surface area of ​​the conductive film, or a range consisting of any two of these values. In the present application, the plane area of ​​the conductive film refers to the maximum area value of the plane of the vertical projection of the length and width directions of the conductive film with a pleated structure; the surface area of ​​the conductive film refers to the product of the length and width of the conductive film with a pleated structure 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 enable the electromagnetic shielding composite material to have better stretchability and electromagnetic shielding performance.

[0038] 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 conductive film with a pleated structure selected from the above-mentioned material types in the present application has high electromagnetic shielding strength and good ductility, so that the electromagnetic shielding composite material has good stretchability and electromagnetic shielding performance.

[0039] In some embodiments, the material of the elastic base layer is selected from at least one of polydimethylsiloxane (PDMS) and Ecoflex. In the present application, Ecoflex is a silica gel prepared by mixing renewable raw materials such as polylactic acid (PLA) and starch. The present application does not specifically limit the sources of PDMS and Ecoflex, as long as the purpose of the present application can be achieved, for example, they can be purchased commercially. The present application uses an elastic base layer of the above-mentioned material type and a conductive film with a pleated structure to combine with chemical bonds, which can make the electromagnetic shielding composite material have better 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 base 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 a range consisting of any two of the values; the thickness of the bonding layer can be 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, or a range consisting of any two of the values; the thickness of the elastic base layer can be 500µm, 600µm, 800µm, 900µm, 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm, or a range consisting of any two of the values. The present application regulates the thickness of the conductive film, the bonding layer and the elastic base layer within the above range, which can take into account both the electromagnetic shielding performance and the mechanical tensile performance of the electromagnetic shielding composite material, so that the electromagnetic shielding composite material can have excellent stretchability and electromagnetic shielding performance at the same time.

[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 consisting of any two of these values. The electromagnetic shielding composite material with strain regulated in the present application within the above range has good stretchability and can also take into account good electromagnetic shielding performance.

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

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

[0044] S2. Preparing a flat conductive film on the surface of the sacrificial layer;

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

[0046] S4. Using the molecular adhesion promoter to coat the surface of the conductive film having a folded structure to obtain the bonding layer;

[0047] S5. Preparing an elastic base layer on the surface of the binding layer;

[0048] S6. Dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining the electromagnetic shielding composite material.

[0049] The preparation method of the electromagnetic shielding composite material provided by the present application is to prepare a sacrificial layer on a pre-stretched shape memory polymer substrate, and then prepare a flat conductive film on the surface of the sacrificial layer, and then the conductive film is formed into a pleated structure by the contraction of the shape memory polymer substrate, and the bonding layer uses a molecular adhesion promoter to modify the surface of the conductive film so that the conductive film and the elastic substrate layer can form a chemical bond to combine, and then the sacrificial layer is dissolved by a solvent, and the shape memory polymer substrate is separated to obtain the stretchable electromagnetic shielding composite material of the present application. The preparation method of the electromagnetic shielding composite material provided by the present application has simple preparation steps and low preparation cost, and can be applied to a variety of conductive film materials and has a wide range of applications. The prepared electromagnetic shielding composite material can have excellent stretchability and electromagnetic shielding performance at the same time.

[0050] 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.

[0051] In some embodiments, shrinking the flat conductive film includes: fixing the width direction of the shape memory polymer substrate so that the flat conductive film shrinks 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 values ​​therein; 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 so that the flat conductive film shrinks unidirectionally along a width direction perpendicular thereto; further, in the unidirectional shrinkage, a ratio N2 of a width before shrinkage to a 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.

[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 directions along the length direction and the width direction; 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 the values ​​therein, and N2 can be 2:1, 3:1, 4:1, 5:1 or a range consisting of any two of the values ​​therein.

[0054] In some embodiments, the strain of the electromagnetic shielding composite material is 0-40%. The present application can regulate the strain of the electromagnetic shielding composite material by stretching; in some embodiments, the shrinking of the flat conductive film includes: fixing one direction of the shape memory polymer substrate (recorded as the x direction), causing the flat conductive film to shrink unidirectionally along another direction perpendicular thereto (recorded as the y direction), and the strain is unidirectional stretching along the y direction; in some embodiments, the shrinking of the flat conductive film includes: not fixing the shape memory polymer substrate, causing the flat conductive film to shrink bidirectionally, and the strain can be unidirectional stretching along the x direction, unidirectional stretching along the y direction, or bidirectional stretching along the x and y directions. The present application has no special limitation on it, as long as the purpose of the present application can be achieved, and strain stretching in different directions can be performed as needed.

[0055] In the present application, the shape memory polymer substrate loaded with the sacrificial layer and the flat conductive film obtained by the heating step S2 is used to regulate the shrinkage mode of the shape memory polymer substrate and adjust the structure of the conductive film, thereby obtaining a conductive film with a unidirectional corrugated structure or a bidirectional corrugated structure.

[0056] In some embodiments, the heating includes a heating temperature of 110-160° C. and a heating time of 5-20 min. For example, the heating temperature can be 110° C., 120° C., 130° C., 140° C., 150° C., 160° C., or a range consisting of any two values ​​therein, 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 values ​​therein.

[0057] In some embodiments, 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 warm at 60-80°C for 3-5h. The present application does not particularly limit the sources of the polymer monomer and curing agent for preparing the elastic base layer, as long as the purpose of the present application can be achieved, for example, they can be obtained through commercial purchase; when the elastic base layer is PDMS, exemplarily, the commercially available SYLGARD 184 silicone elastomer kit includes polymer monomers and curing agents, and PDMS is composed of a base (polymer monomer) / curing agent mixture; when the elastic base layer is Ecoflex, exemplarily, 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 flat conductive film is selected from physical vapor deposition (such as magnetron sputtering), solution method or atomic layer deposition.

[0059] 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.

[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, the thickness of the sacrificial layer is 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 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 shape memory polymer substrate. By regulating the thickness of the sacrificial layer within the above range, an electromagnetic shielding composite material with stable quality 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 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, and obtaining the electromagnetic shielding composite material of the present application including a conductive film with a folded structure, a bonding layer and an elastic substrate layer.

[0063] The third aspect of the present application provides an electronic device, which includes the electromagnetic shielding composite material provided by the first aspect of the present application or the electromagnetic shielding composite material prepared according to the preparation method provided by the second aspect of the present application.

[0064] 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%.

[0065] Example

[0066] 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.

[0067] Test methods and equipment:

[0068] Electromagnetic shielding value test:

[0069] 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:

[0070] 1. Prepare and calibrate equipment: Make sure both the VNA and the electromagnetic shielding composite material are in good working condition;

[0071] 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;

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

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

[0074] 5. Perform the test: 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] Test of the plane area of ​​conductive film:

[0077] The length L2 and width W2 of the vertical projection of the conductive film with a unidirectional corrugated structure or a bidirectional corrugated structure in the length direction and the width direction are measured by a ruler, and the plane area of ​​the conductive film = L2×W2 is obtained.

[0078] Test of conductive film surface area:

[0079] 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.

[0080] Example 1

[0081] S1. Pre-stretched shape memory polymer PS substrate (Polystyrene, 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 500 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;

[0082] 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;

[0083] 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 along the length and width directions of the PS substrate, thereby obtaining a conductive film with a bidirectional pleated structure, wherein the ratio of the length before shrinkage to the length after shrinkage is 2.5:1, and the ratio of the width before shrinkage to the width after shrinkage is 2.5:1;

[0084] S4. The molecular adhesion promoter (3-mercaptopropyl) trimethoxysilane (MPTMS) was used to modify the surface of the conductive film with a bidirectional fold structure to obtain a bonding layer with a thickness of 0.7 nm;

[0085] S5. Pour the monomer and curing agent of polymer PDMS (SYLGARD 184 silicone elastomer kit) in a mass ratio of 10:1 on the surface of the bonding layer, keep it at 70°C for 4 hours, cure the PDMS precursor into an elastomer, and form 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 solvent acetone to dissolve the sacrificial photoresist layer and separate the PS substrate to obtain an electromagnetic shielding composite material, including an Au conductive film with a bidirectional pleated structure, an MPTMS bonding layer and a PDMS elastic substrate layer, wherein 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 that step S3 adopts the following steps, the rest is the same as Example 1 to obtain an electromagnetic shielding composite material, including an Au conductive film with a unidirectional wrinkled structure, an MPTMS bonding layer and a PDMS elastic base layer, the plane area of ​​the Au conductive film accounts for 40% of its surface area, and the strain is 0%;

[0090] S3. Heat the PS substrate loaded with a sacrificial layer and a flat conductive film obtained in step S2 at 130°C for 10 minutes, fix the width direction of the PS substrate loaded with a sacrificial layer and a 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 corrugated structure, wherein 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, the electromagnetic shielding composite material was stretched to a strain of 15% and 30% respectively, with the stretching direction being the length direction.

[0092] Embodiment 3-7

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

[0094] Comparative Example 1

[0095] S1. Pre-stretched shape memory polymer PS substrate (Graphix shrink film, Graphix, MapleHeights, OH, USA), the length ratio after pre-stretching to the length before pre-stretching is 2.5:1, and the width ratio after pre-stretching to the width before pre-stretching is 2.5:1;

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

[0097] Comparative Example 2

[0098] Except that step S3 is not performed, that is, a bonding layer is directly prepared according to step S4 on the flat conductive film obtained in step S2, the rest is the same as Example 1, and an electromagnetic shielding composite material is obtained, including an Au flat conductive film, an MPTMS bonding layer and a PDMS elastic base layer, and the planar area of ​​the Au flat conductive film accounts for 100% of its surface area.

[0099] Comparative Example 3

[0100] Except that step S4 is not performed, that is, a bonding layer is not coated on the conductive film obtained in step S3, and the PDMS elastic base layer is directly prepared according to step S5, the rest is the same as Example 1 to obtain an electromagnetic shielding composite material, including an Au conductive film with a bidirectional pleated structure and a PDMS elastic base layer.

[0101] The preparation parameters and performance test results of the electromagnetic shielding composite materials of various embodiments and comparative examples are shown in Table 1.

[0102] Table 1

[0103] Note: “ / ” means no corresponding parameter.

[0104] The electromagnetic shielding composite 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 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 in FIG. Figure 2 As shown, it can be seen that the electromagnetic shielding value of the electromagnetic shielding composite material of comparative example 1 is relatively low, about 38dB; the electromagnetic shielding value of the electromagnetic shielding composite material of embodiment 1 including the bidirectional pleated film is about 55dB, which is 45% higher than that of comparative example 1. The results show that the electromagnetic shielding composite material of the present application can effectively offset the interference electromagnetic waves and has excellent electromagnetic shielding performance. The electromagnetic shielding effectiveness curves of the electromagnetic shielding composite material of embodiment 1 at strains of 0%, 15%, and 30% are shown in FIG. Figure 3 As shown, it can be seen that the electromagnetic shielding values ​​of the electromagnetic shielding composite material of Example 1 with strains of 0%, 15%, and 30% are approximately 55dB, 52.5dB, and 51dB, respectively. It can be seen that the electromagnetic shielding values ​​in the stretched state are only reduced by 4.5% and 7.2% compared with the non-stretched state. It can be seen that the electromagnetic shielding composite material of the present application has good stretchability. The inventors found that the electromagnetic shielding composite material prepared in Comparative Example 2 has an electromagnetic shielding value of 0. The reason is that the flat conductive film itself is too brittle. Without any shrinkage, a slight external force will cause it to crack, making its electromagnetic shielding performance ineffective. According to Table 1 and Figure 2-Figure 3 It can be seen from the results that the electromagnetic shielding composite material prepared according to the preparation method of the present application can have excellent stretchability and electromagnetic shielding performance at the same time.

[0105] 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.

[0106] 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.

[0107] 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 composite material, comprising a conductive film with a pleated structure, a bonding layer and an elastic base layer, wherein the bonding layer comprises a molecular adhesion promoter.

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 corrugated structure or a bidirectional corrugated structure.

4. The electromagnetic shielding composite material according to claim 1, wherein: The plane 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, preferably 5nm-200nm, the thickness of the bonding layer is 0.5nm-1nm, and the thickness of the elastic base layer is 500µm-2mm.

8. The electromagnetic shielding composite material according to any one of claims 1 to 7, wherein: The strain of the electromagnetic shielding composite material is 0-40%.

9. A method for preparing an electromagnetic shielding composite material according to any one of claims 1 to 8, 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 structure; S4. Using the molecular adhesion promoter to coat the surface of the conductive film having a folded structure to obtain the bonding layer; S5. Preparing an elastic base layer on the surface of the binding layer; S6. Dissolving the sacrificial layer, separating the shape memory polymer substrate, and obtaining the electromagnetic shielding composite material.

10. The preparation method according to claim 9, 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.

11. The preparation method according to claim 9, wherein: The preparation method of the elastic base layer comprises: adding a polymer monomer and a curing agent in a mass ratio of (8-12):1, and keeping the temperature at 60-80°C for 3-5 hours.

12. The preparation method according to claim 9, wherein: The sacrificial layer is prepared by a method selected from spin coating or dip coating; the flat conductive film is prepared by a method selected from physical vapor deposition, solution method or atomic layer deposition.

13. The preparation method according to claim 9, 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.

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

15. The preparation method according to any one of claims 9 to 14, wherein The heating includes a heating temperature of 110-160° C. and a heating time of 5-20 min.

16. The preparation method according to any one of claims 9 to 14, wherein The thickness of the sacrificial layer is ≤1000nm.

17. The preparation method according to any one of claims 9 to 14, 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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