A thermally conductive and electromagnetically shielding multilayer composite film, its preparation method and application

Abstract

This invention discloses a thermally conductive and electromagnetically shielding multilayer composite film, its preparation method, and its applications. The thermally conductive and electromagnetically shielding multilayer composite film of this invention comprises an insulating and thermally conductive layer, a magnetic shielding layer, a conductive shielding layer, and an insulating and thermally conductive layer stacked sequentially. The insulating and thermally conductive layer is a cellulose film containing thermally conductive fillers; the magnetic shielding layer is a cellulose film containing magnetic fillers and expanded microspheres; and the conductive shielding layer is a cellulose film containing conductive fillers and expanded microspheres. The thermally conductive and electromagnetically shielding multilayer composite film of this invention has advantages such as excellent in-plane thermal conductivity, excellent electromagnetic shielding performance, high mechanical strength, and small thickness. Furthermore, its preparation process is simple and environmentally friendly, and it has broad application prospects in fields such as 5G communication, consumer electronics, new energy batteries, and national defense.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic protection technology, specifically to a thermally conductive electromagnetic shielding multilayer composite film, its preparation method, and its application. Background Technology

[0002] With the rapid development of the electronics and communications industries, various electronic communication products are becoming increasingly miniaturized, integrated, and high-powered, bringing numerous conveniences to people's production and lives. However, this has also led to problems such as poor heat dissipation of electronic components and communication equipment, and electromagnetic interference, ultimately resulting in decreased operational stability and shortened lifespan of electronic devices. Furthermore, the large amounts of electromagnetic radiation in the living environment can pose potential health hazards. Electromagnetic shielding films are electronic material films used to reduce electromagnetic interference or radiation, and they have a very broad application prospect in the field of electromagnetic protection. However, existing electromagnetic shielding films mainly rely on reflective electromagnetic shielding to function, without directly absorbing or eliminating electromagnetic radiation, which can easily cause secondary electromagnetic pollution and cannot fully meet the requirements of practical applications.

[0003] Therefore, developing an absorptive electromagnetic shielding film that combines excellent thermal conductivity and electromagnetic shielding properties is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a thermally conductive and electromagnetically shielding multilayer composite film, its preparation method, and its application.

[0005] The technical solution adopted in this invention is:

[0006] A thermally conductive and electromagnetically shielding multilayer composite film comprises an insulating and thermally conductive layer, a magnetic shielding layer, a conductive shielding layer, and an insulating and thermally conductive layer stacked sequentially; the insulating and thermally conductive layer is a cellulose membrane containing thermally conductive fillers; the magnetic shielding layer is a cellulose membrane containing magnetic fillers and expanded microspheres; and the conductive shielding layer is a cellulose membrane containing conductive fillers and expanded microspheres.

[0007] Preferably, the thermally conductive and electromagnetically shielding multilayer composite film comprises the following components by mass percentage:

[0008] Thermally conductive filler: 5%–30%;

[0009] Conductive filler: 10%–25%;

[0010] Magnetic filler: 20%–60%;

[0011] Expanded microspheres: 15%–30%;

[0012] Cellulose: 10%–30%.

[0013] More preferably, the thermally conductive and electromagnetically shielding multilayer composite film comprises the following components by mass percentage:

[0014] Thermally conductive filler: 10%–20%;

[0015] Conductive filler: 15%–25%;

[0016] Magnetic filler: 20%–35%;

[0017] Expanded microspheres: 15%–25%;

[0018] Cellulose: 10%–25%.

[0019] Preferably, the thermally conductive filler is at least one of hexagonal boron nitride powder, carbon fiber powder, and aluminum oxide powder.

[0020] Preferably, the particle size of the thermally conductive filler is 1μm to 100μm.

[0021] Preferably, the conductive filler is at least one of graphene powder, MXene powder, and fullerene powder.

[0022] Preferably, the MXene powder is at least one of titanium carbide MXene powder, zirconium carbide MXene powder, and manganese carbide MXene powder.

[0023] Preferably, the particle size of the conductive filler is 1 μm to 10 μm.

[0024] Preferably, the magnetic filler is at least one of iron(III) oxide powder, iron-silicon-aluminum powder, and carbonyl iron powder.

[0025] Preferably, the particle size of the magnetic filler is 1 μm to 50 μm.

[0026] Preferably, the expanded microspheres are hollow polyacrylate microspheres.

[0027] Preferably, the hollow polyacrylate microspheres have a particle size of 6μm to 15μm, an expansion temperature of 80℃ to 135℃, and an expansion ratio of 2 to 5 times.

[0028] Preferably, the expanded microspheres have undergone plasma surface modification treatment.

[0029] More preferably, the expanded microspheres undergo peroxy plasma surface modification treatment.

[0030] Preferably, the cellulose is at least one of carboxymethyl cellulose, bacterial cellulose, and hydroxypropyl methyl cellulose.

[0031] Preferably, the mass ratio of thermally conductive filler to cellulose in the insulating and thermally conductive layer is 1 to 5:1.

[0032] Preferably, the thickness of the insulating and thermally conductive layer is 10 μm to 100 μm.

[0033] Preferably, the mass ratio of magnetic filler, expanded microspheres, and cellulose in the magnetic shielding layer is 2-7:2-5:1.

[0034] Preferably, the thickness of the magnetic shielding layer is 20μm to 150μm.

[0035] Preferably, the mass ratio of conductive filler, expanded microspheres, and cellulose in the conductive shielding layer is 10:1-5:1-5.

[0036] Preferably, the thickness of the conductive shielding layer is 10μm to 70μm.

[0037] A method for preparing a thermally conductive and electromagnetically shielding multilayer composite film as described above includes the following steps:

[0038] 1) Surface-modified expandable microspheres were obtained by surface treatment with plasma.

[0039] 2) The conductive filler, surface-modified expanded microspheres and cellulose are dispersed in water to form a dispersion, which is then filtered to form a conductive shielding layer. The magnetic filler, surface-modified expanded microspheres and cellulose are then dispersed in water to form a dispersion, which is then coated on one side of the conductive shielding layer and dried to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0040] Alternatively, magnetic filler, surface-modified expanded microspheres and cellulose are dispersed in water to form a dispersion, which is then filtered to form a magnetic shielding layer. Conductive filler, surface-modified expanded microspheres and cellulose are then dispersed in water to form a dispersion, which is then coated on one side of the magnetic shielding layer and dried to form a conductive shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0041] 3) Disperse the thermally conductive filler and cellulose with water to form a dispersion, then coat it on both sides of the conductive shielding layer-magnetic shielding layer composite structure and dry it to form an insulating and thermally conductive layer. Then perform heat treatment to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0042] Preferably, a method for preparing a thermally conductive and electromagnetically shielding multilayer composite film as described above includes the following steps:

[0043] 1) Surface-modified expandable microspheres were obtained by surface treatment with plasma.

[0044] 2) The conductive filler, surface-modified expanded microspheres and cellulose are mixed with water and stirred and ultrasonically dispersed to form a dispersion. The dispersion is then filtered and dried to form a conductive shielding layer. The magnetic filler, surface-modified expanded microspheres and cellulose are mixed with water and stirred to form a dispersion. The dispersion is then coated on one side of the conductive shielding layer and dried to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0045] Alternatively, magnetic filler, surface-modified expanded microspheres and cellulose are mixed with water and stirred to form a dispersion, which is then filtered and dried to form a magnetic shielding layer. Conductive filler, surface-modified expanded microspheres and cellulose are mixed with water and stirred and ultrasonically dispersed to form a dispersion, which is then coated on one side of the magnetic shielding layer and dried to form a conductive shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0046] 3) Add water to the thermally conductive filler and cellulose to make a dispersion, then coat it on both sides of the conductive shielding layer-magnetic shielding layer composite structure and dry it to form an insulating and thermally conductive layer. Then perform heat treatment to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0047] Preferably, the plasma in step 1) is oxygen plasma.

[0048] Preferably, the surface treatment time in step 1) is 10 min to 60 min.

[0049] Preferably, the stirring and dispersion in step 2) is carried out at a mixer speed of 300 rpm to 800 rpm, and the stirring and dispersion time is 30 min to 180 min.

[0050] Preferably, the coating method in step 2) is spin coating.

[0051] Preferably, the spin coating is performed at a spin coating speed of 1000 rpm to 3000 rpm and the spin coating time is 5 s to 30 s.

[0052] Preferably, the drying in step 2) is carried out at a temperature of 40℃ to 100℃ for a time of 10 min to 180 min.

[0053] Preferably, the stirring and dispersion in step 3) is carried out at a mixer speed of 300 rpm to 800 rpm, and the stirring and dispersion time is 30 min to 180 min.

[0054] Preferably, the coating method in step 3) is spin coating.

[0055] Preferably, the spin coating is performed at a spin coating speed of 1000 rpm to 3000 rpm and the spin coating time is 5 s to 30 s.

[0056] Preferably, the drying in step 3) is carried out at a temperature of 40℃ to 100℃ for a time of 10 min to 180 min.

[0057] Preferably, the heat treatment in step 3) is carried out at a temperature of 60℃ to 140℃ for a time of 20 min to 100 min.

[0058] More preferably, the heat treatment in step 3) is carried out at a temperature of 80℃ to 120℃ for a time of 30 min to 60 min.

[0059] An electronic device comprising the aforementioned thermally conductive and electromagnetically shielding multilayer composite film.

[0060] Preferably, the electronic device is a communication device.

[0061] The beneficial effects of this invention are: the thermally conductive and electromagnetically shielding multilayer composite film of this invention has the advantages of excellent in-plane thermal conductivity, excellent electromagnetic shielding performance, high mechanical strength, and small thickness. Moreover, its preparation process is simple and environmentally friendly, and it has a very broad application prospect in the fields of 5G communication, consumer electronics, new energy batteries, and national defense.

[0062] Specifically:

[0063] 1) The thermally conductive electromagnetic shielding multilayer composite film of the present invention contains expanded microspheres. The particle size of the expanded microspheres can be controlled by adjusting the temperature. The increased volume of the expanded microspheres can form large pores inside the composite film, which enhances the multiple reflections of electromagnetic waves inside the composite film. Thus, the electromagnetic shielding mechanism can be transformed from a reflective shielding to an absorptive shielding, realizing the control of electromagnetic shielding type by temperature.

[0064] 2) The thermally conductive and electromagnetically shielding multilayer composite film of the present invention adopts a multilayer structure design. Different layers can respectively achieve the functions of conductive shielding, magnetic shielding, and in-plane thermal conductivity. Furthermore, by changing the composition and amount of functional fillers, the in-plane thermal conductivity and electromagnetic shielding effectiveness of the composite film can be adjusted within a wide range, with the highest in-plane thermal conductivity reaching 6.22 W·m. -1 ·K -1 The electromagnetic shielding effectiveness (EMI SE) can reach up to 45.0 dB;

[0065] 3) The preparation process of the thermally conductive electromagnetic shielding multilayer composite film of the present invention is simple, with no VOC emissions throughout the process, making it green and environmentally friendly, and suitable for large-scale industrial production and application. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of the structure of the thermally conductive electromagnetic shielding multilayer composite film of the present invention.

[0067] Explanation of the symbols in the attached diagram: 10, insulating and thermally conductive layer; 20, magnetic shielding layer; 30, conductive shielding layer; 40, insulating and thermally conductive layer.

[0068] Figure 2 The graph shows the electromagnetic shielding effectiveness test results of the multilayer composite film and the thermally conductive electromagnetically shielding multilayer composite film in Examples 1-5 and Comparative Examples 1-2.

[0069] Figure 3 The graph shows the electromagnetic shielding absorption and reflection ratio test results of the multilayer composite film and the thermally conductive electromagnetic shielding multilayer composite film in Examples 1-5 and Comparative Examples 1-2.

[0070] Figure 4 The graph shows the test results of the thermal conductivity of the thermally conductive electromagnetic shielding multilayer composite film in Examples 1-5 and Comparative Examples 1-2. Detailed Implementation

[0071] The present invention will be further explained and described below with reference to specific embodiments.

[0072] Example 1:

[0073] A thermally conductive and electromagnetically shielding multilayer composite film (structural schematic diagram shown) Figure 1 As shown in the table below, its composition is as follows:

[0074] Table 1. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0075]

[0076] Note:

[0077] Iron-silicon-aluminum powder: Jiangsu Baona Electromagnetic New Material Co., Ltd., grade BNWFA-150, with iron, silicon and aluminum content of 85%, 9.6% and 5.4% by mass, respectively.

[0078] Polyacrylate hollow microspheres: Akzo Nobel NV, grade 031DU40.

[0079] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0080] 1) Place the hollow polyacrylate microspheres into a plasma treatment machine, set the power to 100W, the oxygen flow rate to 30mL / min, and treat for 20min to obtain surface-modified expanded microspheres.

[0081] 2) Ti3C2-MXene, surface-modified expanded microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:2:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 60 min to obtain a conductive shielding layer (42 μm thick).

[0082] 3) Mix iron-silicon-aluminum powder, surface-modified expanded microspheres, carboxymethyl cellulose and deionized water in a mass ratio of 5:2:1:20, and then stir for 2 hours at a speed of 400 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 50℃ for 15 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0083] 4) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 1:1:40, and stir for 2 hours at a speed of 600 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 50°C for 30 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 100 μm). Then heat treat at 60°C for 30 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0084] In this embodiment, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 105 μm, of which the thickness of the insulating and thermally conductive layer is 17.5 μm, the thickness of the magnetic shielding layer is 28 μm, and the thickness of the conductive shielding layer is 42 μm.

[0085] Example 2:

[0086] A thermally conductive and electromagnetically shielding multilayer composite film (structural schematic diagram shown) Figure 1 As shown in the table below, its composition is as follows:

[0087] Table 2. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0088]

[0089] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0090] 1) Place the hollow polyacrylate microspheres into a plasma treatment machine, set the power to 100W, the oxygen flow rate to 30mL / min, and treat for 20min to obtain surface-modified expanded microspheres.

[0091] 2) Ti3C2-MXene, surface-modified expanded microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:2:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 60 min to obtain a conductive shielding layer (45 μm thick).

[0092] 3) Mix iron-silicon-aluminum powder, surface-modified expanded microspheres, carboxymethyl cellulose and deionized water in a mass ratio of 5:2:1:20, and then stir for 2 hours at a speed of 400 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 10 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0093] 4) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 1:1:40, and stir for 2 hours at a speed of 600 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 15 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 110 μm). Then heat treat at 80℃ for 30 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0094] In this embodiment, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 140 μm, wherein the thickness of the insulating and thermally conductive layer is 20 μm, the thickness of the magnetic shielding layer is 45 μm, and the thickness of the conductive shielding layer is 55 μm.

[0095] Example 3:

[0096] A thermally conductive and electromagnetically shielding multilayer composite film (structural schematic diagram shown) Figure 1 As shown in the table below, its composition is as follows:

[0097] Table 3. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0098]

[0099] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0100] 1) Place the hollow polyacrylate microspheres into a plasma treatment machine, set the power to 100W, the oxygen flow rate to 30mL / min, and treat for 20min to obtain surface-modified expanded microspheres.

[0101] 2) Ti3C2-MXene, surface-modified expanded microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:2:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 60 min to obtain a conductive shielding layer (50 μm thick).

[0102] 3) Mix iron-silicon-aluminum powder, surface-modified expanded microspheres, carboxymethyl cellulose and deionized water in a mass ratio of 5:2:1:20, and then stir for 2 hours at a speed of 400 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 10 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0103] 4) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 2:1:40, and stir for 2 hours at a speed of 600 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 15 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 115 μm). Then heat treat at 80℃ for 40 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0104] In this embodiment, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 150 μm, of which the thickness of the insulating and thermally conductive layer is 22.5 μm, the thickness of the magnetic shielding layer is 47 μm, and the thickness of the conductive shielding layer is 58 μm.

[0105] Example 4:

[0106] A thermally conductive and electromagnetically shielding multilayer composite film (structural schematic diagram shown) Figure 1 As shown in the table below, its composition is as follows:

[0107] Table 4. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0108]

[0109] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0110] 1) Place the hollow polyacrylate microspheres into a plasma treatment machine, set the power to 100W, the oxygen flow rate to 30mL / min, and treat for 20min to obtain surface-modified expanded microspheres.

[0111] 2) Ti3C2-MXene, surface-modified expanded microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:2:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 50 min to obtain a conductive shielding layer (48 μm thick).

[0112] 3) Mix iron-silicon-aluminum powder, surface-modified expanded microspheres, carboxymethyl cellulose and deionized water in a mass ratio of 7:3:1:20, and then stir for 2 hours at a speed of 500 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 10 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0113] 4) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 2:1:40, and stir for 2 hours at a speed of 700 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 15 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 140 μm). Then heat treat at 80℃ for 40 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0114] In this embodiment, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 180 μm, of which the thickness of the insulating and thermally conductive layer is 27.5 μm, the thickness of the magnetic shielding layer is 67 μm, and the thickness of the conductive shielding layer is 58 μm.

[0115] Example 5:

[0116] A thermally conductive and electromagnetically shielding multilayer composite film (structural schematic diagram shown) Figure 1 As shown in the table below, its composition is as follows:

[0117] Table 5. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0118]

[0119] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0120] 1) Place the hollow polyacrylate microspheres into a plasma treatment machine, set the power to 100W, the oxygen flow rate to 30mL / min, and treat for 20min to obtain surface-modified expanded microspheres.

[0121] 2) Ti3C2-MXene, surface-modified expanded microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:2:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 60 min to obtain a conductive shielding layer (50 μm thick).

[0122] 3) Mix iron-silicon-aluminum powder, surface-modified expanded microspheres, carboxymethyl cellulose and deionized water in a mass ratio of 7:3:1:20, and then stir for 2 hours at a speed of 500 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 10 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0123] 4) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 3:1:40, and stir for 2 hours at a speed of 700 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 70℃ for 20 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 155 μm). Then heat treat at 80℃ for 60 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0124] In this embodiment, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 190 μm, wherein the thickness of the insulating and thermally conductive layer is 30 μm, the thickness of the magnetic shielding layer is 70 μm, and the thickness of the conductive shielding layer is 60 μm.

[0125] Comparative Example 1:

[0126] A thermally conductive and electromagnetically shielding multilayer composite film, the composition of which is shown in the table below:

[0127] Table 6. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0128]

[0129] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0130] 1) Ti3C2-MXene, carboxymethyl cellulose, and deionized water were mixed at a mass ratio of 10:5:500. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 60 min to obtain a conductive shielding layer (40 μm thick).

[0131] 2) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 1:1:40, and stir for 2 hours at a speed of 500 rpm to obtain a dispersion. Spread the conductive shielding layer on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 50°C for 20 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer over and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 88 μm). Then heat treat at 60°C for 30 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0132] In this comparative example, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 88 μm, of which the thickness of the insulating and thermally conductive layer is 24 μm and the thickness of the conductive shielding layer is 40 μm.

[0133] Comparative Example 2:

[0134] A thermally conductive and electromagnetically shielding multilayer composite film (structure same as in Example 1) has the following composition as shown in the table below:

[0135] Table 7. Composition of a thermally conductive and electromagnetically shielding multilayer composite film.

[0136]

[0137] The preparation method of the above-mentioned thermally conductive and electromagnetically shielding multilayer composite film is as follows:

[0138] 1) Ti3C2-MXene, polyacrylate hollow microspheres, carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 10:5:5:1000. The mixture was stirred at 500 rpm for 30 min and then sonicated for 20 min. This process of stirring and sonication was repeated three times to obtain a dispersion. The dispersion was then vacuum filtered for 2 h and vacuum dried at 40 °C for 50 min to obtain a conductive shielding layer (45 μm thick).

[0139] 2) Iron-silicon-aluminum powder, polyacrylate hollow microspheres, carboxymethyl cellulose and deionized water were mixed in a mass ratio of 3:1:1:20 and stirred for 2 hours at a speed of 500 rpm to obtain a dispersion. The conductive shielding layer was spread on a benchtop spin coater, the dispersion was added dropwise, the spin coating speed was controlled at 2000 rpm, the spin coating was carried out for 10 seconds, and then baked at 50℃ for 15 minutes to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure.

[0140] 3) Mix hexagonal boron nitride powder, carboxymethyl cellulose, and deionized water at a mass ratio of 1:1:40, and stir for 2 hours at a speed of 600 rpm to obtain a dispersion. Spread the conductive shielding layer-magnetic shielding layer composite structure on a benchtop spin coater, add the dispersion dropwise, control the spin coating speed at 2000 rpm, spin coat for 10 seconds, and then bake at 50°C for 20 minutes to form an insulating and thermally conductive layer. Then flip the conductive shielding layer-magnetic shielding layer composite structure and repeat the above operation to prepare an insulating and thermally conductive layer to obtain a multilayer composite film (thickness of 106 μm). Then heat treat at 60°C for 30 minutes to obtain a thermally conductive electromagnetic shielding multilayer composite film.

[0141] In this comparative example, the total thickness of the thermally conductive and electromagnetically shielding multilayer composite film is 110 μm, of which the thickness of the insulating and thermally conductive layer is 18.5 μm, the thickness of the magnetic shielding layer is 25 μm, and the thickness of the conductive shielding layer is 48 μm.

[0142] Performance testing:

[0143] The electromagnetic shielding effectiveness test results of the multilayer composite films (before heat treatment) and the thermally conductive electromagnetically shielding multilayer composite films (after heat treatment) in Examples 1-5 and Comparative Examples 1-2 are as follows: Figure 2 (a is before heat treatment, b is after heat treatment) as shown.

[0144] The electromagnetic shielding absorption and reflection ratio test results of the multilayer composite films (before heat treatment) and thermally conductive electromagnetic shielding multilayer composite films (after heat treatment) in Examples 1-5 and Comparative Examples 1-2 are as follows: Figure 3 (a is before heat treatment, b is after heat treatment) as shown.

[0145] The thermal conductivity test results of the thermally conductive electromagnetic shielding multilayer composite films in Examples 1-5 and Comparative Examples 1-2 are as follows: Figure 4 As shown.

[0146] The test results of the thermal conductivity and electromagnetic shielding performance of the multilayer composite films (before heat treatment) and the thermally conductive and electromagnetically shielding multilayer composite films (after heat treatment) in Examples 1-5 and Comparative Examples 1-2 are shown in the table below:

[0147] Table 8 Test results of thermal conductivity and electromagnetic shielding performance of multilayer composite films and thermally conductive and electromagnetically shielding multilayer composite films.

[0148]

[0149] Note:

[0150] In-plane thermal conductivity: Referring to "ISO 22007-2 standard and transient planar heat source test method for thermal diffusivity", the samples were tested using a TPS2500S thermal constant analyzer from Hotdisk, Sweden. During the test, the probe was placed in the middle of the sample to be tested, ensuring that the sample and the probe were in close contact. Each sample was tested 3 times, and then the average value was taken.

[0151] EMI SE (Electromagnetic Shielding Effectiveness): The electromagnetic parameters of the sample were tested using a Rohde & Schwarz ZNA-43 vector network analyzer and the waveguide method was employed to calculate the electromagnetic shielding effectiveness of the sample. The test frequency range was 8.2 GHz to 12.4 GHz.

[0152] Depend on Figures 2-4 As shown in Table 8:

[0153] a) The thermally conductive and electromagnetically shielding multilayer composite film in Examples 1 to 5 (composed of a magnetic shielding layer containing iron-silicon-aluminum powder, a conductive shielding layer containing Ti3C2-MXene, and an insulating and thermally conductive layer containing hexagonal boron nitride powder) has excellent thermal conductivity and electromagnetic shielding performance.

[0154] b) After heat treatment, the absorption / reflection ratio of the electromagnetic shielding performance of the multilayer composite films in Examples 2 to 5 (i.e., the final thermally conductive electromagnetic shielding multilayer composite film) all increased.

[0155] c) Compared with the thermally conductive electromagnetic shielding multilayer composite films in Examples 1-5, the thermally conductive electromagnetic shielding multilayer composite film in Comparative Example 1 lacks modified expanded microspheres and a magnetic shielding layer. Compared with the thermally conductive electromagnetic shielding multilayer composite films in Examples 1-5, the thermally conductive electromagnetic shielding multilayer composite film in Comparative Example 2 has a relatively lower content of conductive filler and magnetic filler, an increased content of cellulose, and the heat treatment temperature does not reach the microsphere expansion temperature, so it does not cause a significant increase in the volume of microspheres. Therefore, the electromagnetic shielding effectiveness is low.

[0156] d) Compared with the thermally conductive electromagnetic shielding multilayer composite films in Examples 2 to 5, the heat treatment temperature of the thermally conductive electromagnetic shielding multilayer composite film in Example 1 did not reach the microsphere expansion temperature, the change in the pore size of the film was not significant, and the difference before and after heat treatment was not obvious. It is still a reflective electromagnetic shielding method.

[0157] e) Compared with the thermally conductive electromagnetic shielding multilayer composite film in Example 2, the thermally conductive electromagnetic shielding multilayer composite film in Example 3 has increased the content of hexagonal boron nitride powder, a thermally conductive filler in the insulating and thermally conductive layer, and the thermal conductivity of the composite film is improved.

[0158] f) Compared with the thermally conductive electromagnetic shielding multilayer composite film in Example 3, the thermally conductive electromagnetic shielding multilayer composite film in Example 4 has a higher content of magnetic filler iron-silicon-aluminum powder and expanded microspheres in the magnetic shielding layer, and the total electromagnetic shielding effectiveness and absorption effectiveness / reflection effectiveness ratio of the composite film are both increased.

[0159] g) Compared with the thermally conductive electromagnetic shielding multilayer composite film in Example 4, the thermally conductive electromagnetic shielding multilayer composite film in Example 5 has increased the content of hexagonal boron nitride powder, a thermally conductive filler, and the heat treatment time in the insulating and thermally conductive layer. The electromagnetic shielding effectiveness, absorption effectiveness / reflection effectiveness ratio, and thermal conductivity of the composite film are all increased.

[0160] In summary, the thermally conductive and electromagnetically shielding multilayer composite film of the present invention possesses excellent thermal conductivity and electromagnetic shielding performance. This is because the spin-coating method facilitates the orientation of the thermally conductive filler within the layers, thereby easily forming thermally conductive pathways in the insulating and thermally conductive layer, improving the in-plane thermal conductivity of the composite film. The magnetic filler added to the composite film can provide magnetic loss, and the conductive filler can form conductive pathways in the conductive shielding layer, significantly improving the conductivity of the composite film and providing dielectric loss. The expanded microspheres can increase the porosity in the composite film, thereby achieving multiple reflection losses of electromagnetic waves within the thin film. Furthermore, the preparation process of this thermally conductive and electromagnetically shielding multilayer composite film is simple, safe, and environmentally friendly, and it can be widely used in fields such as 5G communication, consumer electronics, new energy batteries, and national defense.

[0161] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A thermally conductive and electromagnetically shielding multilayer composite film, characterized in that, The composition includes an insulating and thermally conductive layer, a magnetic shielding layer, a conductive shielding layer, and an insulating and thermally conductive layer stacked sequentially. The insulating and thermally conductive layer is a cellulose membrane containing thermally conductive filler; the mass ratio of the thermally conductive filler to cellulose in the insulating and thermally conductive layer is 1–5:

1. The magnetic shielding layer is a cellulose membrane containing magnetic filler and expanded microspheres; the mass ratio of the magnetic filler, expanded microspheres, and cellulose in the magnetic shielding layer is 2–7:2–5:

1. The conductive shielding layer is a cellulose membrane containing conductive filler and expanded microspheres; the conductive shielding layer contains conductive filler, expanded microspheres, and cellulose... The mass ratio of the components is 10:1 to 5:1 to 5; the expanded microspheres are hollow polyacrylate microspheres; the particle size of the hollow polyacrylate microspheres is 6 μm to 15 μm, the expansion temperature is 80℃ to 135℃, and the expansion ratio is 2 to 5 times; the expanded microspheres have undergone plasma surface modification treatment; the thermally conductive and electromagnetically shielding multilayer composite film contains the following components by mass percentage: thermally conductive filler: 5% to 30%; conductive filler: 10% to 25%; magnetic filler: 20% to 60%; expanded microspheres: 15% to 30%; cellulose: 10% to 30%.

2. The thermally conductive and electromagnetically shielding multilayer composite film according to claim 1, characterized in that: The thermally conductive filler is at least one of hexagonal boron nitride powder, carbon fiber powder, and aluminum oxide powder; the conductive filler is at least one of graphene powder, MXene powder, and fullerene powder; and the magnetic filler is at least one of iron oxide powder, iron-silicon-aluminum powder, and carbonyl iron powder.

3. The thermally conductive and electromagnetically shielding multilayer composite film according to claim 2, characterized in that: The thermally conductive filler has a particle size of 1μm to 100μm; the conductive filler has a particle size of 1μm to 10μm; and the magnetic filler has a particle size of 1μm to 50μm.

4. The thermally conductive and electromagnetically shielding multilayer composite film according to claim 1, characterized in that: The cellulose is at least one of carboxymethyl cellulose, bacterial cellulose, and hydroxypropyl methyl cellulose.

5. The thermally conductive and electromagnetically shielding multilayer composite film according to claim 1, characterized in that: The thickness of the insulating and thermally conductive layer is 10μm to 100μm; the thickness of the magnetic shielding layer is 20μm to 150μm; and the thickness of the conductive shielding layer is 10μm to 70μm.

6. A method for preparing a thermally conductive and electromagnetically shielding multilayer composite film as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Surface-modified expandable microspheres were obtained by surface treatment with plasma. 2) The conductive filler, surface-modified expanded microspheres and cellulose are dispersed in water to form a dispersion, which is then filtered to form a conductive shielding layer. The magnetic filler, surface-modified expanded microspheres and cellulose are then dispersed in water to form a dispersion, which is then coated on one side of the conductive shielding layer and dried to form a magnetic shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure. Alternatively, magnetic filler, surface-modified expanded microspheres and cellulose are dispersed in water to form a dispersion, which is then filtered to form a magnetic shielding layer. Conductive filler, surface-modified expanded microspheres and cellulose are then dispersed in water to form a dispersion, which is then coated on one side of the magnetic shielding layer and dried to form a conductive shielding layer, thus obtaining a conductive shielding layer-magnetic shielding layer composite structure. 3) Disperse the thermally conductive filler and cellulose with water to form a dispersion, then coat it on both sides of the conductive shielding layer-magnetic shielding layer composite structure and dry it to form an insulating and thermally conductive layer. Then perform heat treatment to obtain a thermally conductive electromagnetic shielding multilayer composite film.

7. An electronic device, characterized in that, It includes the thermally conductive electromagnetic shielding multilayer composite film as described in any one of claims 1 to 5.

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