Electromagnetic shielding film and method of manufacture

Abstract

The application relates to an electromagnetic shielding film and a preparation method, and the electromagnetic shielding film comprises a first shielding layer, a second shielding layer, a heat-conducting layer and an insulating layer arranged in sequence, the raw material of the first shielding layer comprises a thermoplastic resin A, carbon fibers and a filler A; the raw material of the second shielding layer comprises a thermoplastic resin B and a filler B, and the second shielding layer is a foaming layer. The electromagnetic shielding film provided by the application is provided with the first shielding layer and the second shielding layer, the second shielding layer can absorb the miscellaneous waves penetrating through the first shielding layer, the electromagnetic shielding efficiency is better, the second shielding layer has large-diameter micropores, the filler B can be uniformly dispersed, the filler in the heat-conducting layer and the insulating layer can be mutually synergized, the heat-conducting capacity is better, the heat energy generated by the shielding layer due to the absorption of too many electromagnetic waves can be quickly dissipated, and the overheating of electronic components is avoided.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding film preparation, specifically relating to an electromagnetic shielding film and its preparation method. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, high integration, and high power density, heat dissipation issues severely impact equipment performance, stability, and lifespan, hindering the further development of high-power-density electronic devices. Furthermore, the operation of highly densely packed electronic components generates significant electromagnetic radiation, which can cause signal interference between adjacent devices, affecting the normal operation of other precision electronic equipment, leading to decreased instrument accuracy, and potentially even the leakage of critical information. Simultaneously, electronic packaging materials typically require excellent electrical insulation to prevent short circuits. Therefore, the research and development of electronic packaging materials that combine insulation, thermal conductivity, and electromagnetic shielding functions is of great significance and holds immense commercial potential.

[0003] For example, Chinese patent CN114477157A provides a method for enhancing thermal conductivity by combining the large-area fabrication and tunable high thermal conductivity of recycled graphene oxide (RGO) with the electrical insulation properties of boron nitride to prepare a boron nitride / RGO heterojunction, achieving the preparation of fillers with high thermal conductivity and good insulation performance. However, this technology has the following drawbacks: First, the interfacial bonding between the two materials is difficult to control, and the site-specific transfer of boron nitride is difficult to achieve, resulting in a complex process. Second, whether the material has electromagnetic shielding capabilities has not been verified, and the relationship between electromagnetic shielding and insulation performance is difficult to control.

[0004] Chinese invention patent CN108129685A (patent title: Multilayer Composite Thermally Conductive Film and its Preparation Method) constructs a composite thermally conductive film with a nano-cellulose film as the middle layer, and nano-cellulose / graphene film layers or (and) nano-cellulose / boron nitride film layers sequentially coated on the top and bottom surfaces. The layers are connected by hydrogen bonds between the cellulose matrix to form an ABA three-layer structure and an ACBCA five-layer structure, exhibiting good thermal conductivity, mechanical properties, and insulation properties. However, in this technology, the nano-cellulose / graphene aqueous dispersion and the nano-cellulose / boron nitride thin aqueous dispersion are prepared only through simple mechanical blending and ultrasonic dispersion, making it difficult to achieve uniform dispersion and high doping content. The graphene and boron nitride contents are low, resulting in a low thermal conductivity of the final composite film (only 6.82300 W / (m·K)).

[0005] Therefore, there is an urgent need for a composite membrane that is simple in structure, easy to prepare, and has excellent performance, combining insulation, thermal conductivity, and electromagnetic shielding efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide an improved electromagnetic shielding film and its preparation method.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] An electromagnetic shielding film includes a first shielding layer, a second shielding layer, a thermally conductive layer, and an insulating layer arranged sequentially. The first shielding layer is made of thermoplastic resin A, carbon fiber, and filler A. The second shielding layer is made of thermoplastic resin B and filler B, and the second shielding layer is a foamed layer.

[0009] In some embodiments, the raw materials of the first shielding layer, by weight, include:

[0010] Thermoplastic resin A: 100,

[0011] Carbon fiber: 100-200

[0012] Packing material A: 10-20;

[0013] The first shielding layer can absorb or attenuate the electromagnetic energy propagation between the shielded area and the outside world.

[0014] In some embodiments, thermoplastic resin A has the properties of softening upon heating and hardening upon cooling, and does not undergo chemical reactions. This property is maintained regardless of how many times heating and cooling are repeated. Thermoplastic resin A can be one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylon, polyoxymethylene, polycarbonate, polyphenylene ether, polysulfone, rubber, and polyester. For better mechanical properties, one or more of nylon and polypropylene are preferred. Nylon is a polymer material whose macromolecular backbone contains repeating amide groups (-CO-NH-) in its main chain, and polypropylene is a polymer material whose macromolecular backbone contains repeating [CH2-CH(CH3)]n in its main chain.

[0015] In some embodiments, the carbon fiber is mainly composed of carbon elements, which is lightweight, has excellent electrical conductivity, and can absorb and attenuate the propagation of electromagnetic energy between the shielded area and the outside world. The carbon fiber can be carbon fiber powder, chopped carbon fiber, long-cut carbon fiber, carbon fiber filament, carbon fiber cloth, etc. For better electromagnetic shielding efficiency and thermal conductivity, and for the simplicity of the manufacturing process, the carbon fiber is preferably one or more of carbon fiber powder or chopped carbon fiber.

[0016] In the first shielding layer, thermoplastic resin A contains 100 to 200 parts by weight of carbon fiber per 100 parts by weight. If the amount of carbon fiber is small, the mechanical properties of the electromagnetic shielding film will be weakened, and a small amount of carbon fiber will not be conducive to the electromagnetic shielding efficiency of the film. If the amount of carbon fiber is large, the increase in electromagnetic shielding efficiency will be limited, but the manufacturing cost will increase significantly. Therefore, the preferred amount of carbon fiber in the first shielding layer is 130 to 180 parts by weight.

[0017] In the first shielding layer, the amount of filler A is 10 to 20 parts by weight. If the amount of filler A is too small, its synergistic effect with carbon fiber is weakened, resulting in poor electromagnetic shielding efficiency. If the amount of filler A is too large, it is easy for thermoplastic resin A to decompose, reducing the film strength and easily exposing the shielded area to the external environment. Therefore, the preferred amount of filler A is 12 to 18 parts by weight.

[0018] In some embodiments, the filler A is a powder, which is a powder with metal or metal oxide as the main component. It can work synergistically with carbon fiber to enhance electromagnetic shielding efficiency. The metal powder can be one or more of the following: iron powder, cobalt powder, nickel powder, copper powder, zinc powder, aluminum powder, titanium powder, vanadium powder, chromium powder, manganese powder, silver powder, platinum powder, gold powder, iron oxide, nickel oxide, cobalt oxide, copper oxide, aluminum oxide, titanium oxide, and tungsten oxide. For better electromagnetic shielding efficiency, filler A is preferably one or more of copper powder and copper oxide powder.

[0019] In some embodiments, the average particle size of the filler A powder is 10–200 nm. If the particle size is too small, it is easy to cause dust pollution; if the particle size is too large, it is not conducive to uniform mixing. Therefore, the average particle size of the filler A powder is preferably 10–100 nm.

[0020] In some embodiments, the raw materials of the second shielding layer include:

[0021] Thermoplastic resin B: 100,

[0022] Packing material B: 50-100.

[0023] The second shielding layer can absorb the remaining clutter after the first shielding layer has absorbed it, thus improving the shielding efficiency.

[0024] In some embodiments, the thermoplastic resin B comprises one or more of polystyrene, polyurethane, polyvinyl chloride, and polyethylene. Considering the synergistic effect with filler B (the dispersibility and processability of filler B in thermoplastic resin B) to enhance electromagnetic shielding efficiency, one or more of polyethylene and polyurethane are preferred.

[0025] In some embodiments, the filler B is a conductive inorganic ceramic compound, which is a functional material with ionic conductivity, electronic and hole conductivity. It has both metallic conductivity and the structural characteristics, mechanical properties and unique physicochemical properties of ceramics, such as oxidation resistance, corrosion resistance, radiation resistance and high temperature resistance. The filler B is selected from one or more of the following: metal-based conductive ceramics, oxide-based conductive ceramics, nitride-based conductive ceramics, boride-based conductive ceramics, and carbide-based conductive ceramics. Specifically, metal-based conductive ceramics include iron, nickel powder, copper powder, aluminum powder, etc.; oxide-based conductive ceramics include V₂O₅, TiO₂, Nb₂O₅, CdO, CsO, MoO₃, WO₃, BaO, SnO₂, Ta₂O₅, BaTiO₃, PbCrO₄, ZnO, Al₂O₃, MgFe₂O₄, CuFe₂O₄, Fe₃O₄, etc.; and nitride, boride, and carbide-based conductive ceramics include WC, TiC, NbC, Cr₃C₂, Mo₂C, VC, ZrC, SiC, etc. Considering the synergistic effect with thermoplastic resin B, filler B is preferably one or more of SiC ceramics and Al₂O₃ ceramics.

[0026] In some embodiments, the second shielding layer is foamed, meaning that the material of the second shielding layer itself has countless tiny pores.

[0027] In some embodiments, the porosity of the second shielding layer is 20-50%, where porosity refers to the percentage of pore volume in a bulk material to the total volume of the material in its natural state, and the porosity is tested according to GB / T 10799-2008 standard. If the porosity is too low, the pore volume in the material is small, and it cannot cover the filler B. During long-term use of electronic products, the filler B is prone to falling off, reducing thermal conductivity. If the porosity is too high, it will easily lead to pore waste. Preferably, it is 25-45%.

[0028] In some embodiments, the diameter of the micropores in the second shielding layer is 0.5–2 μm. The larger diameter micropores in the second shielding layer facilitate better absorption of electromagnetic waves transmitted through the first shielding layer and enhance thermal conductivity. The micropore diameter is the cross-sectional diameter of the pores in the second shielding layer, measured by scanning electron microscopy. For optimal electromagnetic shielding efficiency and thermal conductivity, the preferred micropore diameter in the second shielding layer is 0.8–1.5 μm.

[0029] In some implementations, the thermally conductive layer can dissipate heat rapidly. Electronic components generate heat during use, and rapid heat dissipation can extend their service life. The presence of the thermally conductive layer allows heat to reach the surface through conduction. Relying on the combined effects of thermal conduction and radiation of the thermally conductive layer, heat is quickly dissipated, causing the surface and internal temperature of the object to drop, ultimately achieving the purpose of cooling and heat dissipation.

[0030] In some embodiments, the thermally conductive layer is a particle attached to the second shielding layer, and the thermally conductive layer comprises one or more of a metal oxide and silicon nitride; the metal oxide comprises one or more of iron oxide, nickel oxide, cobalt oxide, copper oxide, aluminum oxide, titanium oxide, and tungsten oxide. The silicon nitride is an inorganic compound with the chemical formula Si3N4.

[0031] In some embodiments, the insulating layer primarily protects the heat-conducting layer, the first shielding layer, and the second shielding layer, reducing mechanical damage and chemical corrosion during use, preventing the heat-conducting layer, the first shielding layer, and the second shielding layer from moisture absorption by water vapor, and preventing electric shock to the contact conductors, thereby increasing the service life of the encapsulated electronic equipment. The insulating layer comprises a polymer and a metal oxide. The polymer is selected from one or more of polyimide, polytetrafluoroethylene, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyphenylene ether, polysulfone, rubber, and polyester. To improve the thermal conductivity of the electromagnetic shielding film and prevent damage to the shielding layer due to excessive heat accumulation from absorbing electromagnetic waves, the metal oxide is selected from one or more combinations of iron oxide, nickel oxide, cobalt oxide, copper oxide, aluminum oxide, titanium oxide, and tungsten oxide. Considering the compatibility of polymers and metal oxides, one or more of polyimide, polytetrafluoroethylene, or polyethylene are preferred.

[0032] Another technical solution adopted in this invention is:

[0033] A method for preparing the electromagnetic shielding film, comprising:

[0034] (1) Prepare a first shielding layer, a second shielding layer, a thermally conductive layer, and an insulating layer, wherein,

[0035] In preparing the first shielding layer, the raw materials for the first shielding layer are melted and made into a thin film. The film is stretched twice in the transverse and longitudinal directions to obtain the first shielding layer. Specifically, thermoplastic resin A is first heated to 150-300℃, preferably 160-280℃ (the melting point of polypropylene is 160-180℃, and the melting point of nylon PA66 is 260-280℃). After melting, carbon fiber and filler A are added. Then, the product is extruded and cast to obtain a pretreated sheet. The pretreated sheet is then stretched longitudinally and transversely to obtain the first shielding layer.

[0036] In preparing the second shielding layer, the raw materials for the second shielding layer are melted and foamed, extruded to form a foamed film, and stretched to stretch the film twice in the transverse and longitudinal directions to obtain the second shielding layer.

[0037] To prepare a thermally conductive layer, the thermally conductive layer material is sprayed onto one side of the second shielding layer to obtain the thermally conductive layer.

[0038] When preparing the insulating layer, the raw materials of the insulating layer are melted and made into a thin film. Specifically, the polymer is first heated to 100-400℃, preferably 130-330℃, melted and then metal oxide is added. Subsequently, the product is extruded and cast to obtain a pretreated sheet. The pretreated sheet is then stretched longitudinally and transversely to obtain the insulating layer.

[0039] (2) The electromagnetic shielding film is obtained by sequentially bonding the first shielding layer, the second shielding layer, the heat-conducting layer and the insulating layer together under vacuum hot pressing.

[0040] In some embodiments, the preparation method of the second shielding layer is as follows: foaming is performed using supercritical fluid foaming. The advantages of supercritical foaming are: shorter time, finer pores, stronger stress structure, more uniform pore distribution and controllable particle size, thereby enabling the product to have a lower density.

[0041] Specifically: Thermoplastic resin B and filler B are placed in a reaction vessel and heated to 170-250℃ and 10-20MPa supercritical CO2 for 1-5 hours, followed by foaming under steam at 150-200℃. The foamed film is then extruded and stretched to obtain a second shielding layer.

[0042] Supercritical fluids refer to a state where, at a specific point in the temperature and pressure of a fluid, the densities of the gas and liquid phases tend to be the same, merging into a homogeneous phase. This specific point is called the critical point of the fluid. When the temperature and pressure of any fluid exceed the critical point and reach the supercritical state, the fluid is defined as a supercritical fluid. Once a substance enters the supercritical fluid state, it exhibits a stable and special phase between the liquid and gas states, which cannot be completely classified into either the liquid or gas category, yet simultaneously possesses the properties of both. That is, on the one hand, it has the gaseous properties of low surface tension, low viscosity, and high diffusivity; on the other hand, it simultaneously possesses the liquid properties of high solubility and high density.

[0043] The second shielding layer primarily shields electromagnetic waves that pass through the first shielding layer. Due to its well-developed porous structure, the second shielding layer exhibits better thermal conductivity than the first. Electromagnetic waves passing through the first shielding layer can be absorbed by the second shielding layer. Heat dissipated from electronic components can be transferred through filler B to the first shielding layer, and then to the insulating layer, achieving rapid heat dissipation layer by layer.

[0044] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0045] The electromagnetic shielding film provided by this invention comprises a first shielding layer and a second shielding layer. The second shielding layer can absorb clutter waves that pass through the first shielding layer, resulting in better electromagnetic shielding efficiency. The second shielding layer in the electromagnetic shielding film has large-diameter micropores, which can uniformly disperse filler B. It works synergistically with the thermally conductive layer and the insulating layer, resulting in better thermal conductivity. It can quickly dissipate the heat generated by the shielding layer due to excessive absorption of electromagnetic waves, thus preventing overheating of electronic components. The electromagnetic shielding film manufacturing process of this invention does not use solvents, making it environmentally friendly and simple to manufacture. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments shown.

[0047] The first shielding layer, the second shielding layer, the thermally conductive layer, and the insulating layer were prepared separately. The raw material formula of the first shielding layer is shown in Table 1.

[0048] Table 1. Raw materials for the first shielding layer

[0049]

[0050]

[0051] The materials used for the first shielding layer in the table above are as follows:

[0052] 1. Thermoplastic resin A

[0053] A1: Polypropylene, F280 polypropylene produced by Sinopec Shanghai Petrochemical Co., Ltd.

[0054] A2: Nylon, EPR27 PA66 nylon produced by Shanghai Feimai Plastics Co., Ltd.

[0055] 2. Carbon fiber

[0056] B1: Carbon fiber powder, MLD-300 carbon fiber powder produced by Toray Industries, Inc. of Japan, with a fiber length of 130μm.

[0057] B2: Short-cut carbon fiber, T700 short-cut carbon fiber produced by Toray Industries, Inc. of Japan, with a fiber length of 2mm.

[0058] 3. Packing material A

[0059] C1: Copper powder, DK-Cu-001 nano copper powder produced by Beijing Deco Island Gold Technology Co., Ltd., with an average particle size of 50nm.

[0060] C2: Copper oxide powder, DK-CuO nano copper oxide powder produced by Beijing Deco Island Gold Technology Co., Ltd., with an average particle size of 40nm.

[0061] The method for preparing the first shielding layer is as follows:

[0062] 1. The first shielding layer (M1, M3 to M9) is made according to the formula shown in Table 1. Thermoplastic resin A is placed in a reaction vessel, heated to 160°C, melted, and then carbon fiber and filler A are added. The mixture is then extruded by a twin-screw extruder at a temperature of 160°C. The resulting product is then subjected to a casting process to obtain a pretreated sheet. The pretreated sheet is then stretched longitudinally and laterally to obtain the first shielding layer (M1, M3 to M9).

[0063] 2. The first shielding layer (M2) is made according to the formula shown in Table 1. Thermoplastic resin A is placed in a reaction vessel and heated to 260°C. After melting, carbon fiber and filler A are added. Then, it is extruded by a twin-screw extruder at a temperature of 260°C. The resulting product is subjected to a casting process to obtain a pre-treated sheet. The pre-treated sheet is then stretched longitudinally and laterally to obtain the first shielding layer M2.

[0064] The raw material formula for the second shielding layer is shown in Table 2.

[0065] Table 2. Raw materials for the second shielding layer

[0066]

[0067]

[0068] The materials used for the second shielding layer in the table above are as follows:

[0069] 1. Thermoplastic resin B

[0070] D1: Polyethylene, LD100AC polyethylene produced by Sinopec Shanghai Petrochemical Co., Ltd.

[0071] D2: Polyurethane, GMB FP3039D6 polyether polyurethane.

[0072] 2. Packing material B

[0073] E1: SiC ceramic, YM-SiC-50N SiC ceramic produced by Yumu (Ningbo) New Materials Co., Ltd., with an average particle size of 50nm.

[0074] E2: Al2O3 ceramic, alumina ceramic produced by Yixing Yalong Special Ceramics Co., Ltd.

[0075] The method for preparing the second shielding layer is as follows:

[0076] 1. The second shielding layer (N1, N3-N6) is formulated according to the method shown in Table 2. Thermoplastic resin B and filler B are placed in a reaction vessel, heated to 130°C, and immersed in supercritical CO2 at 130°C and 15MPa for 2 hours. Then, it is foamed under steam at 100°C. Subsequently, it is extruded to form a foamed film, which is then stretched twice in both the transverse and longitudinal directions to obtain the second shielding layer (N1, N3-N6). The second shielding layer (N1) has a porosity of 37% and a micropore diameter of 1.2 μm; the second shielding layer (N3) has a porosity of 23% and a micropore diameter of 1.5 μm; the second shielding layer (N4) has a porosity of 25% and a micropore diameter of 1.3 μm; the second shielding layer (N5) has a porosity of 45% and a micropore diameter of 0.8 μm; and the second shielding layer (N6) has a porosity of 21% and a micropore diameter of 1.8 μm.

[0077] 2. The second shielding layer (N2) is prepared according to the formulation shown in Table 2. Thermoplastic resin B and filler B are placed in a reaction vessel and heated to 200°C. The mixture is then immersed in supercritical CO2 at 200°C and 15 MPa for 2 hours, followed by foaming under steam at 180°C. The foamed film is then extruded and stretched twice, both laterally and longitudinally, to obtain the second shielding layer. The second shielding layer (N2) has a porosity of 43% and a micropore diameter of 0.9 μm.

[0078] 3. The second shielding layer (N7) is prepared by placing thermoplastic resin B and filler B into a reaction vessel according to the formula shown in Table 2, heating to 200°C, and then extruding to form a film. The film is stretched twice in the transverse and longitudinal directions to obtain the second shielding layer (N7). The second shielding layer (N7) is unfoamed.

[0079] The materials for the heat-conducting layer are as follows:

[0080] F1: Alumina, DK410-2 nano alumina produced by Beijing Deco Island Gold Technology Co., Ltd., with an average particle size of 20nm.

[0081] F2: Silicon nitride, DK-Si3N4-01 nano silicon nitride produced by Beijing Deco Island Gold Technology Co., Ltd., with an average particle size of 20nm.

[0082] Raw materials for the insulation layer:

[0083] Polyimide: YS-20 produced by Junhua Co., Ltd.;

[0084] Copper oxide: C112566 produced by Aladdin (Shanghai) Reagent Co., Ltd.

[0085] Polytetrafluoroethylene: P434335 produced by Aladdin (Shanghai) Reagent Co., Ltd.

[0086] Polyethylene: P434335 produced by Aladdin (Shanghai) Reagent Co., Ltd.

[0087] The method for preparing the insulating layer is as follows:

[0088] G1: Polyimide is placed in a reaction vessel and heated to 360°C. After melting, copper oxide powder filler is added, followed by twin-screw extrusion at 360°C. The resulting product is then subjected to a casting process to obtain a pretreated sheet. The pretreated sheet is then stretched longitudinally and laterally to obtain the insulating layer G1.

[0089] G2: Polytetrafluoroethylene is placed in a reaction vessel and heated to 330°C. After melting, copper oxide powder filler is added, followed by twin-screw extrusion at 330°C. The resulting product is then subjected to a casting process to obtain a pretreated sheet. The pretreated sheet is then subjected to longitudinal and transverse stretching to obtain the insulating layer G2.

[0090] G3: Polyethylene is placed in a reaction vessel and heated to 130°C. After melting, copper oxide powder filler is added, followed by twin-screw extrusion at 130°C. The resulting product is then subjected to a casting process to obtain a pretreated sheet. The pretreated sheet is then stretched longitudinally and laterally to obtain the insulation layer G2.

[0091] Examples 1-15 and Comparative Examples 1-7 are provided. The raw material formulations for Examples 1-15 and Comparative Examples 1-7 are shown in Table 3.

[0092] Table 3. Raw material formulations for Examples 1-15 and Comparative Examples 1-7

[0093]

[0094]

[0095] According to the formula described in Table 3, the thermally conductive layer is sprayed onto one side of the second shielding layer, and then the first shielding layer, the second shielding layer, the thermally conductive layer, and the insulating layer are composited to obtain an electromagnetic shielding film.

[0096] The electromagnetic shielding films of Examples 1-15 and Comparative Examples 1-7 were subjected to the following tests. Unless otherwise specified, all tests were conducted at 25°C. The main indicators are as follows:

[0097] 1. Average electromagnetic shielding effectiveness: tested according to GB / T30142-2013 standard;

[0098] 2. Tensile strength: Tested according to GB / T 1040.1-2018;

[0099] 3. Thermal conductivity: Tested according to national standard GB / T 10297-2015.

[0100] Table 4 Performance data of electromagnetic shielding films in Examples 1-15 and Comparative Examples 1-7

[0101]

[0102]

[0103] As shown in Table 4, compared with the electromagnetic shielding films of Examples 1-15 and Comparative Examples 1-7, the electromagnetic shielding films prepared in Examples 1-15 have better thermal conductivity and better electromagnetic shielding performance; the electromagnetic shielding films prepared in Examples 1-15 have superior mechanical properties and the preparation process is pollution-free, making them easy to mass-produce.

[0104] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that, The electromagnetic shielding film includes a first shielding layer, a second shielding layer, a thermally conductive layer, and an insulating layer arranged sequentially. The raw materials of the first shielding layer include thermoplastic resin A, carbon fiber, and filler A. The raw materials of the second shielding layer include thermoplastic resin B and filler B, and the second shielding layer is a foamed layer. The porosity of the second shielding layer is 20-50%, and the diameter of the micropores in the second shielding layer is 0.5-2 μm; The thermoplastic resin B includes one or more combinations of polystyrene, polyurethane, polyvinyl chloride, and polyethylene; the filler B is a conductive ceramic, which includes one or more combinations of metal-based conductive ceramics, oxide-based conductive ceramics, nitride-based conductive ceramics, boride-based conductive ceramics, and carbide-based conductive ceramics. In the preparation of the second shielding layer, the raw materials of the second shielding layer are melted and mixed with supercritical fluid, and foamed under steam to form a foamed film. By weight, the raw materials of the first shielding layer include: thermoplastic resin A: 100, carbon fiber: 100~200, filler A: 10~20; the filler A includes one or more of the following: iron, cobalt, nickel, copper, zinc, aluminum, titanium, vanadium, chromium, manganese, silver, platinum, gold, iron oxide, nickel oxide, cobalt oxide, copper oxide, aluminum oxide, titanium oxide, and tungsten oxide. The thermally conductive layer consists of particles attached to the second shielding layer, and the thermally conductive layer includes one or more of metal oxides and silicon nitride. The insulating layer comprises a polymer and a metal oxide, wherein the polymer is selected from one or more combinations of polyimide, polytetrafluoroethylene, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyphenylene ether, polysulfone, rubber, and polyester, and the metal oxide is selected from one or more combinations of iron oxide, nickel oxide, cobalt oxide, copper oxide, aluminum oxide, titanium oxide, and tungsten oxide.

2. The electromagnetic shielding film according to claim 1, characterized in that, By weight, the raw materials of the second shielding layer include: thermoplastic resin B: 100, filler B: 50~100.

3. The electromagnetic shielding film according to claim 1, characterized in that, The thermoplastic resin A includes one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylon, polyoxymethylene, polycarbonate, polyphenylene ether, polysulfone, rubber, and polyester.

4. A method for preparing an electromagnetic shielding film according to any one of claims 1 to 3, characterized in that, include: (1) Prepare a first shielding layer, a second shielding layer, a thermally conductive layer and an insulating layer, wherein when preparing the second shielding layer, the raw materials of the second shielding layer are melted and foamed to form a foamed film; (2) The electromagnetic shielding film is obtained by sequentially combining the first shielding layer, the second shielding layer, the thermally conductive layer, and the insulating layer.

5. The method for preparing the electromagnetic shielding film according to claim 4, characterized in that, In step (1), when preparing the second shielding layer, the raw materials of the second shielding layer are melted and mixed with supercritical fluid, and foamed under steam to form a foamed film.

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