A composite film with insulation, heat conduction and electromagnetic shielding functions, a preparation method and application thereof

Abstract

The application discloses a composite film with insulation, heat conduction and electromagnetic shielding functions, a preparation method and application, and the composite film is composed of an upper layer, a middle layer and a lower layer; the middle layer is a graphene / aramid nanofiber composite material with a content of 50-80 wt%; and the upper layer and the lower layer are both boron nitride nanosheet / aramid nanofiber composite materials with a content of 70 wt%. Through the above scheme, the boron nitride and the graphene play their respective roles and complement each other, and the composite film has the advantages of simple structure, simple preparation process, excellent performance and the like, and has high practical value and popularization value in the technical field of new material technology.

Description

Technical Field

[0001] This invention relates to the technical field of new materials technology, and in particular to a composite film that combines insulation, thermal conductivity and electromagnetic shielding functions, its preparation method and application. 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] Thermally / conductively conductive polymer composites are widely used in the fields of thermal management and electromagnetic shielding of electronic devices due to their lightweight, ease of processing, corrosion resistance, good fatigue resistance, and excellent overall performance. Since the exfoliation of monolayer graphene (GNS), GNS, with its superior properties, has rapidly become one of the ideal fillers for thermally and electrically conductive composites. The thermal conductivity of monolayer GNS can reach up to 5300 W / (m·K), which is currently the highest intrinsic thermal conductivity of any material. While its excellent electrical conductivity endows GNS composites with excellent electromagnetic shielding capabilities, it also limits its application in many electrical insulation fields. Boron nitride nanosheets (BNNS) have attracted widespread attention from researchers due to their excellent physical properties, thermal stability, and chemical stability. At the same time, their excellent thermal conductivity (approximately 300 W / (m·K)) and good insulation properties make them promising candidates for application in the field of electronic packaging materials. However, the thermal conductivity of BNNS is still significantly lower than that of GNS. The thermal conductivity of BNNS-based polymer composites is difficult to exceed 30 W / (m·K), and they do not possess electromagnetic shielding capabilities. Furthermore, the difficulty in preparing stable dispersions of GNS and BNNS limits their application in traditional solution processing. Therefore, leveraging the individual functions of BNNS and GNS and synergistically complementing each other is key to achieving the multifunctional integration of insulation, thermal conductivity, and electromagnetic shielding in polymer composites, thus meeting the thermal management and electromagnetic shielding requirements of high-power electronic devices.

[0004] For example, the Chinese invention patent "Patent Publication No.: CN114477157A, Title: A Method for Enhancing the Thermal Conductivity of Reduced Graphene Oxide" comprehensively utilizes the large-area fabrication and tunable high thermal conductivity of reduced graphene oxide (RGO) with the electrical insulation properties of boron nitride (h-BN) to prepare an h-BN / RGO heterojunction. Its thermal conductivity is nearly 18 times higher than that of graphene oxide, achieving the preparation of fillers with high thermal conductivity and good insulation properties. 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 possesses electromagnetic shielding capabilities has not been verified, and the relationship between electromagnetic shielding and insulation performance is difficult to control.

[0005] For example, the Chinese invention patent "Patent Publication No.: CN108129685B, Title: Multilayer Composite Thermally Conductive Film and its Preparation Method" constructs a composite thermally conductive film with a nanocellulose film as the middle layer, and nanocellulose / graphene film layers or (and) nanocellulose / boron nitride film layers successively coated on the top and bottom sides. The layers are connected by hydrogen bonds between the cellulose matrix to form an ABA three-layer structure and an ACBCA five-layer structure, which have good thermal conductivity, mechanical properties, and insulation properties. However, this technology has the following drawbacks: First, the nanocellulose / graphene aqueous dispersion and the nanocellulose / boron nitride thin aqueous dispersion are prepared by simple mechanical blending and ultrasonic dispersion, which makes it difficult to achieve uniform dispersion and high doping content (graphene and boron nitride content is only 6-10%). Therefore, the final composite film has a low thermal conductivity (only 6.82300 W / (m·K)). Second, the multilayer film is composited by vacuum filtration, and its interfacial bonding is weak.

[0006] Therefore, there is an urgent need to propose a composite film with simple structure, simple preparation process, and excellent performance that combines insulation, thermal conductivity, and electromagnetic shielding functions, as well as its preparation method and application. Summary of the Invention

[0007] To address the above problems, the present invention aims to provide a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, its preparation method, and its application. The technical solution adopted by the present invention is as follows:

[0008] Part 1: This technology provides a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, consisting of an upper layer, a middle layer, and a lower layer; the middle layer is a graphene / aramid nanofiber composite material with a content of 50-80 wt%; the upper and lower layers are both boron nitride nanosheets / aramid nanofiber composite materials with a content of 70 wt%.

[0009] Part Two: This technology provides a method for preparing a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, comprising the following steps:

[0010] Step S01: Prepare an aramid nanofiber dispersion for later use;

[0011] Step S02: Graphene is added to dimethyl sulfoxide solvent and ultrasonically dispersed to obtain a graphene / dimethyl sulfoxide solution; the mass ratio of graphene to dimethyl sulfoxide solvent is 0.1:66.

[0012] Step S03: The graphene / dimethyl sulfoxide solution from step S02 is added to the aramid nanofiber dispersion from step S01 at a mass ratio of 66:15.2 to 264:15.2, and the mixture is stirred and ultrasonically treated to obtain a graphene / aramid nanofiber mixture containing black flocculent matter.

[0013] Step S04: Protonate and filter the graphene / aramid nanofiber mixture 4-5 times to remove the dimethyl sulfoxide solvent remaining in the flocculent.

[0014] Step S05: After removing the dimethyl sulfoxide solvent remaining in the flocculent, the flocculent is sheared to obtain a stable graphene / aramid nanofiber mixture for later use.

[0015] Step S06: Replace the graphene in steps S02 to S05 with boron nitride nanosheets to prepare a boron nitride nanosheet / aramid nanofiber mixture for later use.

[0016] Step S07: Vacuum filter the graphene / aramid nanofiber mixture obtained in step S05 to obtain a graphene / aramid nanofiber composite membrane.

[0017] Step S08: Apply a pressure of 10 MPa to the graphene / aramid nanofiber composite film to press it, thereby obtaining a graphene / aramid nanofiber composite film with a dense structure and smooth surface.

[0018] Step S09: At 80°C, a dense and smooth graphene / aramid nanofiber composite film is fixed on a heating stage; the boron nitride nanosheet / aramid nanofiber mixture obtained in step S06 is sprayed onto both sides of the dense and smooth graphene / aramid nanofiber composite film; and the composite film is dried to obtain the composite film.

[0019] Part Three: This technology provides an application of a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions. The composite film is used in heat dissipation and electromagnetic shielding components in electronic components and printed circuit equipment.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention cleverly utilizes the “sandwich” structure to give full play to the respective roles of boron nitride (BNNS) and graphene (GNS) and to complement each other’s advantages. The thermal conductivity and insulation properties of BNNS are well coordinated with the high electrical conductivity and thermal conductivity properties of GNS, thus realizing the integrated preparation of composite material insulation, thermal conductivity and electromagnetic shielding.

[0022] (2) This invention ingeniously utilizes the abundant surface functional groups of aramid nanofibers (ANF) and the π-π interactions of benzene rings to achieve a good combination of ANF with GNS and BNNS. The carbonyl and amide bonds in ANF can form stable hydrogen bond structures with GNS and BNNS. Simultaneously, due to the large aspect ratio of ANF, a steric hindrance effect is generated, and the extremely strong electronegativity of ANF can generate electrostatic repulsion, thereby suppressing the aggregation of GNS and BNNS, and preparing stable GNS / ANF and BNNS / ANF aqueous dispersions. This method achieves high filling of GNS and BNNS in composite materials, thus realizing the preparation of composite materials with high thermal conductivity and high electromagnetic shielding performance. At the same time, aramid nanofibers, as the main matrix material, also provide good mechanical properties.

[0023] (3) This invention utilizes ANF to modify the surface of GNS and BNNS, forming a long-term stable aqueous dispersion of GNS and BNNS. Compared with chemical modification methods, this method avoids damage to the surface structure of GNS and BNNS. Compared with traditional physical modification, this method does not require the use of dispersants to coat GNS and BNNS, thereby mitigating the adverse effects of excessive dispersant coating on the performance of GNS and BNNS. In addition, the aqueous dispersion of GNS and BNNS has good long-term stability, facilitating subsequent processing and application.

[0024] In summary, this invention has the advantages of simple structure, simple preparation process, and excellent performance, and has high practical and promotional value in the field of new materials technology. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of protection. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a logic flowchart of the present invention.

[0027] Figure 2 This is a cross-sectional SEM image of the GNS / ANF composite membrane according to the first embodiment of the present invention.

[0028] Figure 3 The images shown are cross-sectional SEM images of the BGB / ANF composite membranes in the second to fourth embodiments of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0030] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0031] The terms "first" and "second," etc., used in the specification and claims of this embodiment are used to distinguish different objects, not to describe a specific order of objects. For example, "first target object" and "second target object," etc., are used to distinguish different target objects, not to describe a specific order of target objects.

[0032] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0033] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more. For example, multiple processing units means two or more processing units; multiple systems means two or more systems.

[0034] like Figures 1 to 3 As shown, this embodiment provides a method for preparing a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, including the following steps:

[0035] Step 1: Add poly(p-phenylene terephthalamide) fibers to a mixed solution of potassium hydroxide, dimethyl sulfoxide, and water, and magnetically stir to deprotonate and obtain the desired aramid nanofiber (ANF) dispersion. The mass concentration of potassium hydroxide in the mixed solution is 1.0 wt%. The volume ratio of dimethyl sulfoxide to deionized water is 25:1. The mass ratio of poly(p-phenylene terephthalamide) fibers, potassium hydroxide, dimethyl sulfoxide, and water is 1.2:1.8:176:6.4.

[0036] Step 2: Weigh 0.1g of graphene (GNS) into a beaker containing 66g of dimethyl sulfoxide (DMSO), and sonicate it for 10 minutes using a probe sonication device at a power of 600W; finally, obtain the GNS / DMSO solution.

[0037] Step 3: Add the GNS / DMSO solution obtained in Step 2 to the ANF dispersion obtained in Step 1 at a mass ratio of 66:15.2 to 264:15.2, and treat it simultaneously with ultrasound at 300 r / min and 80 W for 30 min to finally obtain a GNS / ANF mixture containing black flocculent matter.

[0038] Step 4: Protonation process. Slowly pour the GNS / ANF mixture containing flocculents obtained in Step 3 into deionized water and stir the mixture until all the GNS / ANF flocculents float to the surface. Then filter and wash 4-5 times to remove the DMSO solvent remaining in the GNS / ANF flocculents.

[0039] Step 5: Shear the GNS / ANF flocculents at a rate of 10,000 r / min using a shearing machine. After 10 min, a stable GNS / ANF aqueous dispersion is obtained.

[0040] Step 6: Prepare BNNS / ANF aqueous dispersion using a method similar to steps 2-5.

[0041] Step 7: Prepare a GNS / ANF composite membrane from the GNS / ANF mixture obtained in Step 5 using vacuum filtration. To ensure that the obtained GNS / ANF composite membrane has a uniform thickness and is free of air gaps, first remove any remaining air bubbles from the GNS / ANF mixture, then slowly pour it into the vacuum filtration apparatus. After filtration for 5 hours, the GNS / ANF composite membrane is obtained.

[0042] Step 8: The GNS / ANF composite membrane obtained by vacuum filtration is treated with a pressure of 10 MPa to finally obtain a GNS / ANF composite membrane with a dense structure and smooth surface.

[0043] Step 9: Fix the GNS / ANF composite film on a heating table at 80°C, and spray equal amounts of the BNNS / ANF mixture obtained in Step 6 onto both sides of the GNS / ANF composite film with a spray gun. After the mixture is dried, a multilayer BGB / ANF composite material is obtained.

[0044] To verify the performance of the composite membrane in this embodiment, the following embodiments are introduced:

[0045] Example 1

[0046] The main raw materials were prepared in the following percentages by mass: graphene (GNS) 80% and aramid nanofibers (ANF) 20%. In step 3, the mass ratio of GNS / DMSO solution to ANF dispersion was 264:15.2.

[0047] Example 2

[0048] The main raw materials are prepared in the following percentages by mass: graphene (GNS) 80%; aramid nanofibers (ANF) 20%, to prepare GNS / ANF composite membrane.

[0049] The main raw materials are prepared in the following percentages by mass: boron nitride nanosheets (BNNS) 70%; aramid nanofibers (ANF) 30%, to prepare a BNNS / ANF mixture.

[0050] A BGB / ANF composite film was prepared by using a thermally conductive GNS / ANF composite material with a middle layer containing 80 wt% GNS and an insulating BNNS / ANF composite material with a 70 wt% BNNS content sprayed on top and bottom with a thickness ratio of 1:6:1.

[0051] Example 3

[0052] The thickness ratio of the three layers is 1:3:1, and the rest is the same as in Example 2.

[0053] Example 4

[0054] The thickness ratio of the three layers is 1:2:1, and the rest is the same as in Example 2.

[0055] Comparative Example 1

[0056] This example is a control sample; no GNS was added, and the pure ANF membrane was prepared in the same manner as in Example 1.

[0057] Thermal conductivity: To investigate the thermal conductivity of the prepared GNS / ANF composite film and BGB / ANF trilayer composite film, the in-plane and out-of-plane thermal conductivity coefficients were measured using a laser thermal conductivity meter (LFA467, Netzsch GmbH, Germany). The results are shown in Table 1.

[0058] Table 1 Thermal conductivity, electromagnetic shielding performance, and breakdown strength of GNS / ANF composite film and BGB / ANF composite film

[0059]

[0060] Compared to Comparative Example 1, the introduction of GNS significantly increases the in-plane thermal conductivity of the GNS / ANF composite film, reaching 122.46 W / (m·K), which is 54.4 times that of the pure ANF film. At this point, the thermal conductivity channels of GNS are almost fully formed, and heat is efficiently transferred through lattice vibrations. Under the influence of vacuum filtration attraction, the layered GNS structure is orderly stacked along the planar direction, and an in-plane thermal conductivity network is efficiently formed. In step 8, a certain pressure is first applied to densify the microscopic thermal and electrical conductivity channels and reduce the interfacial thermal resistance and interfacial resistance. In addition, the thermal conductivity of the three-layer BGB / ANF composite film is slightly lower than that of the GNS / ANF composite film with the same GNS content, and its thermal conductivity gradually decreases with the increase of the insulating layer thickness. This is mainly because the intrinsic thermal conductivity of BNNS is lower than that of GNS. However, the thermal conductivity of the three-layer composite film is still at an extremely high level. This is because the three layers are made of the same matrix, which makes the interface bonding good and the interface thermal resistance low. Even in Example 4, it still exhibits excellent thermal conductivity, with an in-plane thermal conductivity of over 86.49 W / (m·K).

[0061] Electromagnetic Shielding Performance: To investigate the electromagnetic shielding performance of the prepared GNS / ANF composite film and BGB / ANF three-layer composite film, the electromagnetic shielding performance (EMI SE) at 8.3 GHz was tested using an Agilent N5247A vector network analyzer (Agilent, USA). The results are shown in Table 1. Compared to Comparative Example 1, the introduction of GNS endowed the composite film of Example 1 with excellent electromagnetic shielding performance, achieving a shielding capability of 41.7 dB for electromagnetic waves at 8.3 GHz. This is because, under the influence of vacuum filtration attraction, the layered GNS structure is orderly stacked along the planar direction, forming a multilayer structure that effectively enhances interface polarization and promotes multiple reflections of electromagnetic waves. In addition, the three-layer BGB / ANF composite film exhibited excellent electromagnetic shielding performance, with Examples 2-4 all reaching above 43 dB, and the electromagnetic shielding performance remained essentially unchanged with increasing insulation layer thickness.

[0062] Electrical insulation performance: To investigate the electrical insulation properties of the prepared BGB / ANF three-layer composite film, a withstand voltage tester (Chroma 19057-20) was used to conduct electrical breakdown tests in a uniformly accelerated voltage manner. The structure is shown in Table 1. As the thickness ratio of the insulating layer BNNS / ANF composite film increases, the breakdown field strength of the multilayer BGB / ANF composite film shows an increasing trend. When the thickness ratio of the thermally conductive layer GNS / ANF composite film to the insulating layer BNNS / ANF composite film is 1:2:1, its breakdown field strength reaches 70.7 kV / mm. This is mainly because the high bandgap of BNNS can inhibit the growth of electrical trees in a high electric field.

[0063] In summary, this embodiment provides a multifunctional composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, exhibiting high thermal conductivity, electromagnetic shielding performance, and breakdown strength. The material consists of two insulating and thermally conductive layers and one conductive and thermally conductive layer, with the two insulating and thermally conductive layers located on either side of the conductive and thermally conductive layer, forming an integrated sandwich structure. In the insulating and thermally conductive layer, BNNS is distributed within the polymer matrix to form an insulating and thermally conductive network; in the conductive and thermally conductive layer, GNS is distributed within the polymer matrix to form a conductive and thermally conductive network. Both the insulating and conductive and the conductive and thermally conductive layers are based on aramid nanofibers, resulting in good interfacial bonding. The conductive and thermally conductive layer in the three-layer multifunctional composite film imparts high thermal conductivity and electromagnetic shielding performance to the composite material, while the insulating and thermally conductive layer imparts high thermal conductivity and electrical insulation performance. The sandwich structure cleverly achieves synergistic properties and functional integration of BNNS and GNS, enabling the integrated fabrication of composite materials with both insulation, thermal conductivity, and electromagnetic shielding functions. The material preparation process is simple, the technology is easy to master, the production cost is low, and mass production is easily achievable, making it highly valuable for widespread application.

[0064] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any changes made based on the design principles of the present invention, or any non-creative modifications made thereon, shall fall within the scope of protection of the present invention.

Claims

1. A composite film having both insulation and electromagnetic shielding functions, characterized by comprising a thermally conductive and electrically insulating resin layer and a magnetic material layer. The upper layer, the middle layer and the lower layer are composed of; the middle layer is graphene / aramid nanofiber composite material with a content of 50-80wt%; the upper layer and the lower layer are both boron nitride nanosheet / aramid nanofiber composite material with a content of 70wt%; the preparation method of the composite film comprises the following steps: Step S01, prepare aramid nanofiber dispersion liquid for standby; Step S02, graphene is added to dimethyl sulfoxide solvent for ultrasonic dispersion treatment to obtain graphene / dimethyl sulfoxide solution; Step S03, the graphene / dimethyl sulfoxide solution in step S02 is added to the aramid nanofiber dispersion liquid in step S01 according to the mass ratio of 66:15.2-264:15.2, stirring and ultrasonic treatment, to obtain graphene / aramid nanofiber mixed liquid containing black flocculent; Step S04, the graphene / aramid nanofiber mixed liquid is sequentially protonated, filtered and washed 4-5 times to remove the residual dimethyl sulfoxide solvent in the flocculent; Step S05, the flocculent after removing the residual dimethyl sulfoxide solvent is sheared to obtain a stable graphene / aramid nanofiber mixed liquid for standby; Step S06, replace the graphene in steps S02 to S05 with boron nitride nanosheet to prepare boron nitride nanosheet / aramid nanofiber mixed liquid for standby; Step S07, the graphene / aramid nanofiber mixed liquid obtained in step S05 is vacuum filtered to obtain graphene / aramid nanofiber composite film; Step S08, the graphene / aramid nanofiber composite film is pressed by applying a pressure of 10Mpa to obtain a graphene / aramid nanofiber composite film with compact structure and smooth surface; Step S09, the graphene / aramid nanofiber composite film with compact structure and smooth surface is fixed on a heating table at 80℃; the two sides of the graphene / aramid nanofiber composite film with compact structure and smooth surface are respectively sprayed with the boron nitride nanosheet / aramid nanofiber mixed liquid obtained in step S06; and the composite film is obtained after drying.

2. The composite film according to claim 1, wherein the film has a thickness of 10 to 1000 μm. The thickness ratio of the upper layer, the middle layer and the lower layer is 1:2:1-1:6:

1.

3. The composite film with insulation, heat conduction and electromagnetic shielding functions according to claim 1 or 2, characterized in that, The thickness of the composite film is 60-70μm.

4. A method for preparing a composite film that combines insulation, thermal conductivity, and electromagnetic shielding functions, characterized in that, The preparation method comprises the following steps: Step S01, prepare aramid nanofiber dispersion liquid for standby; Step S02, graphene is added to dimethyl sulfoxide solvent for ultrasonic dispersion treatment to obtain graphene / dimethyl sulfoxide solution; Step S03, the graphene / dimethyl sulfoxide solution in step S02 is added to the aramid nanofiber dispersion liquid in step S01 according to the mass ratio of 66:15.2-264:15.2, stirring and ultrasonic treatment, to obtain graphene / aramid nanofiber mixed liquid containing black flocculent; Step S04, the graphene / aramid nanofiber mixed liquid is sequentially protonated, filtered and washed 4-5 times to remove the residual dimethyl sulfoxide solvent in the flocculent; Step S05, the flocculent after removing the residual dimethyl sulfoxide solvent is sheared to obtain a stable graphene / aramid nanofiber mixed liquid for standby; Step S06, replace the graphene in steps S02 to S05 with boron nitride nanosheet to prepare boron nitride nanosheet / aramid nanofiber mixed liquid for standby; Step S06, replace the graphene in steps S02 to S05 with boron nitride nanosheet to prepare boron nitride nanosheet / aramid nanofiber mixed solution, ready for use; Step S07, vacuum filtration of the graphene / aramid nanofiber mixed solution obtained in step S05 to obtain a graphene / aramid nanofiber composite film; Step S08, press the graphene / aramid nanofiber composite film under a pressure of 10 MPa to obtain a graphene / aramid nanofiber composite film with a compact structure and a smooth surface; Step S09, fix the graphene / aramid nanofiber composite film with a compact structure and a smooth surface on a heating table at 80℃; spray the boron nitride nanosheet / aramid nanofiber mixed solution obtained in step S06 on both sides of the graphene / aramid nanofiber composite film with a compact structure and a smooth surface; and dry to obtain a composite film.

5. The method of claim 4, wherein the composite film is prepared by the steps of: (a) preparing a solution of the conductive polymer and the thermally conductive polymer; (b) coating the solution on a substrate; (c) drying the coated solution; and (d) removing the substrate. The preparation of aramid nanofiber dispersion liquid comprises the following steps: The poly-p-phenyleneterephthalamide fiber is added to a mixed solution composed of potassium hydroxide, dimethyl sulfoxide and water, and the proton is removed by magnetic stirring to obtain the required aramid nanofiber dispersion liquid; the mass concentration of potassium hydroxide in the mixed solution is 1.0wt%; the volume ratio of dimethyl sulfoxide to deionized water is 25:1; and the mass ratio of poly-p-phenyleneterephthalamide fiber, potassium hydroxide, dimethyl sulfoxide and water is 1.2:1.8:176:6.

4.

6. The method for preparing a composite film with insulating, thermally conductive, and electromagnetic shielding functions according to claim 4, characterized in that, In step S02, the ultrasonic power of the ultrasonic dispersion treatment is 300W, and the dispersion time is 10min.

7. The method for preparing a composite film with insulating, thermally conductive, and electromagnetic shielding functions according to claim 4, characterized in that, In step S02, the rotation speed of the ultrasonic dispersion treatment is 300r / min, the ultrasonic power is 80W, and the dispersion time is 30min.

8. The method of claim 4, wherein the composite film is prepared by the steps of: (a) preparing a solution of the conductive polymer and the thermally conductive polymer; (b) coating the solution on a substrate; (c) drying the coated solution; and (d) removing the substrate. In step S05, the rotation speed of the required shearing machine is 10000r / min, and the dispersion time is 10min.

9. Use of a composite film having both insulation and electromagnetic shielding functions, characterized by, The composite film is used as a heat dissipation and conduction component and an electromagnetic shielding component in electronic components and printed circuit devices.

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