Double-interlocking polyimide electromagnetic shielding composite film and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a double-interlocking polyimide electromagnetic shielding composite film and a preparation method thereof. The preparation method comprises the following steps: dissolving 4, 4 '-diphenyl ether dianhydride and 4, 4'-diaminobiphenyl-2, 2-dicarboxylic acid in N-N dimethylacetamide, reacting at room temperature in a nitrogen atmosphere, and adding maleic anhydride to obtain a PAA solution containing MAH; the preparation method comprises the following steps: dissolving maleic anhydride in deionized water, adding an AgNWs solution, and uniformly stirring; pouring the obtained PAA solution on a glass plate, drying until the glass plate is in a semi-dry state, uniformly spraying the AgNWs mixed solution on the surface layer through a spray gun, drying in a drying oven after spraying, finally coating a layer of PAA solution, and carrying out gradient heating reaction on the composite film to form the composite film with a double-interlocking structure. The double-interlocking polyimide electromagnetic shielding film has excellent mechanical properties and stability, and can meet the use requirements in a complex environment.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a double-interlocked polyimide electromagnetic shielding composite film and its preparation method. Background Technology

[0002] Traditional metal-based electromagnetic shielding materials (such as metal foils and conductive coatings) offer good shielding effectiveness, but their working mechanism is typically limited to electromagnetic wave reflection, resulting in a single function. These materials often lack portability due to their high density and thickness, and generally exhibit drawbacks such as insufficient flexibility, susceptibility to corrosion, and shielding performance degradation upon deformation. Furthermore, their opaque nature and complex manufacturing processes make them unsuitable for meeting the comprehensive requirements of flexible electronics, wearable devices, and transparent displays, which demand materials that are lightweight, flexible, transparent, and provide highly efficient shielding.

[0003] CN120239248A discloses a flexible electromagnetic shielding film and its preparation method. The method involves mixing gallium and indium in a predetermined ratio to form a gallium-indium alloy; placing a predetermined mass of the gallium-indium alloy in an isopropanol solution and treating it with an ultrasonic cell disruption system to obtain a suspension of liquid metal particles; stirring magnetic functional nanoparticles, an electrospun polymer elastomer, and a solvent at room temperature to obtain a homogeneous electrospun solution; treating the homogeneous electrospun solution using an electrospun process to obtain a magnetic nanofiber membrane; and spraying the liquid metal particle suspension onto the magnetic nanofiber membrane using an electrostatic spraying process to obtain the flexible electromagnetic shielding film. The flexible electromagnetic shielding film provided by this invention can solve the problem of reduced stability of existing shielding materials under tension. However, this film lacks an encapsulation coating, resulting in poor environmental stability; its mechanical properties and electromagnetic shielding performance may significantly decrease in acidic or alkaline environments. Summary of the Invention

[0004] The purpose of this invention is to provide a double-interlocked polyimide electromagnetic shielding composite film, which possesses high mechanical properties, superhydrophobicity, and excellent electromagnetic shielding effect. Furthermore, the use of wet spraying and the addition of maleic anhydride for thermal cross-linking enhances the bond between the polyimide and silver nanowires, meeting the requirements of high-intensity environments.

[0005] The double-interlocking polyimide electromagnetic shielding composite film of this invention is a sandwich structure composite film. A PAA film containing MAH is used as the PI substrate layer. An AgNWs mixed solution containing MAH is uniformly sprayed onto the substrate layer by a spray gun to form an AgNWs conductive layer. Finally, a PAA solution containing MAH is coated to form a PI surface layer. The film is then placed in a high-temperature oven for thermal imidization to form a "PI-AgNWs-PI" composite film.

[0006] The preparation process of polyimide containing a capping agent (MAH) is as follows:

[0007] The specific preparation steps of the double-interlocked "PI-AgNWs-PI" composite film of the present invention are as follows: (1) Preparation of PAA containing MAH First, N / N dimethylacetamide (DMAc) solvent was added to a three-necked flask equipped with a mechanical stirrer. Then, an appropriate amount of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB) was added. After the diamine monomer was completely dissolved, 4,4'-diphenyl ether dianhydride (ODPA) was added, and the mixture was purged with nitrogen five times to ensure the apparatus was filled with nitrogen and prevent premature hydrolysis of the anhydride monomer. After the diamine and dianhydride were completely dissolved, the mixture was placed in an ice-water bath overnight. Then, an appropriate amount of MAH was added, and the reaction was continued for a period of time to obtain a PAA acid solution containing MAH.

[0008] The molar ratio of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.05~0.15.

[0009] (2) The preparation method of AgNWs mixed solution is as follows: weigh 0.3g of maleic anhydride, dissolve it completely in 4 ml of deionized water under magnetic stirring at room temperature, and then add 1 ml of silver nanowire solution and stir magnetically for 30 minutes to obtain AgNWs mixed solution.

[0010] (3) The PAA acid solution containing MAH in step (1) is poured onto a glass plate and dried for 60 min to a semi-dry state. Then, the AgNWs mixed solution prepared in step (2) is uniformly sprayed onto the semi-dry PAA acid solution film containing MAH through a spray gun. After drying for 30 min, a layer of PAA solution containing MAH is coated on top and dried for 30 min to obtain a composite film with a "PAA-AgNWs-PAA" sandwich structure.

[0011] (4) The obtained "PAA-AgNWs-PAA" sandwich structure composite film was placed in a muffle furnace and reacted by gradient heating using the thermal imidization method. After the reaction was completed, the film was removed from the muffle furnace and the reaction product was scraped off the glass plate to obtain the double interlocking sandwich structure composite film.

[0012] The temperature gradient for thermal imidization was: 90℃-1 h, 120℃-1 h, 150℃-1 h, 180℃-12 h.

[0013] This invention has the following characteristics: This invention constructs a dual-interlocking "PI-AgNWs-PI" composite film, which effectively solves the problems of easy oxidation, easy aggregation, and poor interfacial bonding of silver nanowires, and fully leverages the performance advantages of each component. Polyimide, as the coating layer, provides excellent thermal stability, mechanical strength, and flexible support; silver nanowires, as the intermediate functional layer, construct a highly efficient conductive network, endowing the material with superior electromagnetic shielding performance. This composite strategy achieves high performance while also enhancing the structural stability and lifespan of the material. Attached Figure Description

[0014] Figure 1 EDS cross-section of the “PI-AgNWs-PI” electromagnetic shielding film prepared in Example 1.

[0015] Figure 2 This is a SEM image of polyimide after AgNWs were sprayed onto it.

[0016] Figure 3 The electromagnetic shielding curve of the “PI-AgNWs-PI” electromagnetic shielding film prepared in Example 1.

[0017] Figure 4 The infrared spectra of the composite film prepared in Example 1 before and after thermal imidization are shown.

[0018] Figure 5 The image shows the AFM pattern of the composite film prepared in Example 1, which shows that AgNWs formed a uniform conductive network on the PI surface. Detailed Implementation

[0019] To more clearly illustrate the present invention, the following description, in conjunction with embodiments, provides further insight. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The experimental materials and reagents used in the following examples can be obtained commercially or through known experimental methods. Example 1

[0021] (1) Preparation of PAA solution containing MAH In the experimental procedure, 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) were pretreated in an oven at 170°C for 12 hours. Then, a three-necked flask equipped with a mechanical stirrer was vacuum filtered three times, and nitrogen was connected to one side. 20 ml of N,N-dimethylacetamide (DMAc) was added, followed by 1.413 g (5.1 mmol) of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB). After the addition was complete, the flask was vacuum filtered three more times to ensure complete removal of air. Stirring was then started, and after the 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB) was completely dissolved, 1.672 g (5 mmol) of 4,4'-diphenyl ether dianhydride (ODPA) was added in three portions. For the first addition, add half of the total amount, followed by one-quarter of the total amount each time. The first addition was 120 minutes apart, and subsequent additions were 60 minutes apart. After the dianhydride was completely added, the reaction system was placed in an ice-water bath and stirred continuously for 12 hours. After the reaction was complete, 0.025 g of maleic anhydride (MAH) (0.25 mmol) was added, and the reaction was continued for another 4 hours. The final product was a PAA acid solution containing MAH.

[0022] (2) Preparation method of AgNWs mixed solution The preparation method of AgNWs is as follows: Weigh 0.2 g of polyvinylpyrrolidone (PVP) and dissolve it completely in 25 ml of ethylene glycol (EG) under magnetic stirring at 60 °C (magnetic stirrer speed set to 150 rpm, time approximately 4 h). Add 0.25 g of AgNO3 and 3.5 g of 0.6 mmol / L FeCl3 solution sequentially to the resulting reaction solution. Stir magnetically for 5 minutes and heat the mixture to 130 °C. Prepare a three-necked flask, thermometer, etc. After the mixture reaches 130 °C, transfer it to a three-necked flask and insert a thermometer to monitor the temperature. Maintain the temperature of the mixture at 130 °C throughout the reaction. Let it stand for 5 h without stirring to grow nanowires.

[0023] The obtained product was collected and centrifuged at 4000 rpm for 10 min. Then, it was flocculated with acetone three times, washed five times with ethanol and water respectively, filtered and dried to obtain silvery-white silver nanowires.

[0024] Add 10 ml of isopropanol to a beaker, then add 0.01 g of PVP and stir magnetically until completely dissolved. Next, add 100 mg of silver nanowires to the beaker and sonicate for 15 min to obtain a silver nanowire solution.

[0025] Weigh 0.3 g of maleic anhydride and dissolve it completely in 4 ml of deionized water under magnetic stirring at room temperature. Then add 1 ml of silver nanowire solution. Stir magnetically for 30 minutes to obtain an AgNWs mixed solution.

[0026] (3) Preparation of sandwich structure composite thin films The PAA acid solution containing MAH from step (1) was cast onto a glass plate and dried for 60 min to a semi-dry state. The thickness of the PAA acid solution containing MAH sprayed was 250 μm, which decreased to 150 μm after thermal imidization. Subsequently, the AgNWs mixed solution prepared in step (2) was uniformly sprayed onto the semi-dry PAA acid solution film containing MAH using a spray gun. The thickness of the silver nanowire mixed solution sprayed was 30 μm. After drying for 30 min, another layer of PAA acid solution containing MAH was coated, with a PAA thickness of 250 μm. After drying for 30 min, a composite film with a "PAA-AgNWs-PAA" sandwich structure was obtained.

[0027] (4) Preparation of double interlocking structure thin films The obtained "PAA-AgNWs-PAA" sandwich-structured composite film was placed in a muffle furnace using a thermal imidization method, and the reaction was carried out with a gradient temperature increase. After the reaction was complete, the film was removed from the muffle furnace, and the reaction product was scraped off a glass plate, finally yielding a double-interlocked sandwich-structured composite film. The temperature gradient for thermal imidization was: 90℃-1 h, 120℃-1 h, 150℃-1 h, and 180℃-12 h.

[0028] Figure 1 The cross-sectional EDS image of the “PI-AgNWs-PI” electromagnetic shielding film prepared in Example 1 shows that Ag elements are concentrated and uniformly distributed in the middle of the composite film, and the upper and lower layers contain a small amount of Ag elements, which effectively proves that Ag elements have penetrated into the PI film.

[0029] Figure 4 Infrared spectra of the composite film prepared in Example 1 before and after thermal imidization, 1680 cm⁻¹ -1 The disappearance of the characteristic peak of the C=C double bond in MAH after thermal imidization proves the successful thermal crosslinking of MAH in the PI layer and MAH in the AgNWs layer. (1270 cm⁻¹) -1 The peak at this point is a typical CN bond characteristic peak of PVP in AgNWs, proving that AgNWs are composited in PI films. Example 2

[0030] The difference between this embodiment and Example 1 is that the molar ratio of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.075, while the other treatment methods are the same as in Example 1. Example 3

[0031] The difference between this embodiment and Example 1 is that the molar ratio of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.1. The other treatment methods are the same as in Example 1. Example 4

[0032] The difference between this embodiment and Example 1 is that the molar ratio of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.125. The other treatment methods are the same as in Example 1. Example 5

[0033] The difference between this embodiment and Example 1 is that the molar ratio of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 4,4′-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.15, while the other treatment methods are the same as in Example 1. Example 6

[0034] The difference between this embodiment and Embodiment 1 is that the thickness of the sprayed AgNWs containing MAH is 60μm, while the other treatment methods are the same as in Embodiment 1. Comparative Example 1

[0035] (1) The steps for obtaining the product PAA acid solution are the same as in Example 1.

[0036] (2) Thin film preparation The PAA acid solution containing MAH in step (1) is poured onto a glass plate and dried. The thickness of the PAA acid solution containing MAH is 250 μm. After thermal imidization, the thickness will be reduced to 150 μm.

[0037] (3) Preparation of thin films The obtained PAA film was subjected to thermal imidization in a muffle furnace, where the temperature was gradually increased. After the reaction was complete, the film was removed from the muffle furnace, and the reaction product was scraped off a glass plate to obtain the final film. Comparative Example 2

[0038] The preparation of PAA containing MAH is the same as in Example 1.

[0039] (2) Preparation method of AgNWs solution Add 1 ml of silver nanowire solution (preparation method is the same as in Example 1) to 4 ml of deionized water and stir magnetically for 30 minutes to obtain AgNWs mixed solution.

[0040] (3) Preparation of sandwich structure composite thin films The PAA acid solution containing MAH from step (1) was cast onto a glass plate and dried for 60 min to a semi-dry state. The thickness of the PAA acid solution containing MAH sprayed was 250 μm, which decreased to 150 μm after thermal imidization. Subsequently, the AgNWs solution prepared in step (2) was uniformly sprayed onto the semi-dry PAA acid solution film containing MAH using a spray gun. The thickness of the silver nanowire solution sprayed was approximately 30 μm. After drying for 30 min, another layer of PAA acid solution containing MAH was coated, with a PAA thickness of 250 μm. After drying for 30 min, a composite film with a "PAA-AgNWs-PAA" sandwich structure was obtained.

[0041] (4) The preparation of the double interlocking structure film is the same as in Example 1. Comparative Example 3

[0042] The difference between this comparative example and Example 1 is that maleic anhydride is not added to the prepared PAA-AgNWs mixed solution, and the PAA acid solution is completely dried before spraying the AgNWs mixed solution. Other treatment methods are the same as in Example 1.

[0043] (1) The preparation of PAA acid solution is as described in Example 1, except that maleic anhydride is not added to PAA compared to Example 1.

[0044] (2) Preparation method of AgNWs solution Weigh 0.3g of maleic anhydride and dissolve it completely in 4ml of deionized water under magnetic stirring at room temperature. Stir magnetically for 30 minutes to obtain an AgNWs solution.

[0045] (3) Preparation of sandwich structure composite thin films The PAA acid solution from step (1) was poured onto a glass plate and dried for 60 minutes to a semi-dry state. The thickness of the PAA acid solution sprayed was 250 μm, which would decrease to 150 μm after thermal imidization. Subsequently, the AgNWs solution prepared in step (2) was uniformly sprayed onto the semi-dry PAA acid solution film using a spray gun. The thickness of the silver nanowire solution sprayed was approximately 30 μm. After drying for 30 minutes, another layer of PAA acid solution was coated, with a PAA thickness of 250 μm. After drying for 30 minutes, a composite film with a "PAA-AgNWs-PAA" sandwich structure was obtained.

[0046] (4) The preparation of the double interlocking structure film is the same as in Example 1. Comparative Example 4

[0047] (1) The preparation of PAA containing MAH is the same as in Example 1.

[0048] (2) The preparation method of AgNWs mixed solution is the same as in Example 1.

[0049] (3) Preparation of sandwich structure composite film.

[0050] The PAA acid solution containing MAH from step (1) was cast onto a glass plate and dried. The thickness of the PAA acid solution containing MAH sprayed was 250 μm, which decreased to 150 μm after thermal imidization. Subsequently, the AgNWs mixed solution prepared in step (2) was uniformly sprayed onto the semi-dry PAA acid solution film containing MAH using a spray gun. The thickness of the silver nanowire mixed solution sprayed was 30 μm. After drying for 30 min, another layer of PAA acid solution containing MAH was coated, with a PAA thickness of 250 μm. After drying for 30 min, a composite film with a "PAA-AgNWs-PAA" sandwich structure was obtained.

[0051] (4) The preparation of the double interlocking structure film is the same as in Example 1.

[0052] The prepared polyimide composite film with a double interlocking structure was subjected to the following performance tests, and the test results are shown in Table 1. Mechanical properties: The mechanical properties of ODPA-TFDB are tested by WDT-10 electronic universal testing machine according to the national standard GB / T 1040.3-2006.

[0053] Table 1

[0054] Table 2 shows the tensile strength test results of the composite film under different bending cycles.

[0055]

[0056] Table 3 shows the percentage of electromagnetic shielding performance of the composite thin film in the X-band under different bending cycles tested by the waveguide method.

[0057]

[0058] Table 4 shows the tensile strength tests after immersion in different solvents for different times.

[0059]

[0060] Table 5 shows the percentage of electromagnetic shielding performance of the composite thin film in the X-band, tested by waveguide method after immersion in different solvents for different times.

[0061]

[0062] In summary, this application constructs a dual-interlocked "PI-AgNWs-PI" composite film, which effectively solves the problems of poor interfacial bonding and easy oxidation of silver nanowires, and fully leverages the performance advantages of each component. Polyimide, as the coating layer, provides excellent thermal stability and superior electromagnetic shielding performance. This composite strategy achieves high performance while also enhancing the material's mechanical properties, structural stability, and service life.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a double-interlocked polyimide electromagnetic shielding composite film, characterized in that, The composite film is prepared as follows: a PAA solution containing MAH is poured onto a glass plate and dried until it is semi-dry to obtain a PI substrate layer. Then, an AgNWs mixed solution is uniformly sprayed onto the surface of the PI substrate layer through a spray gun. The substrate layer is then placed in an oven to dry to obtain an AgNWs conductive layer. Finally, a layer of PAA solution containing MAH is coated to obtain a PI surface layer. The composite film is then subjected to a gradient heating reaction to form a composite film with a double interlocking structure.

2. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 1, characterized in that, In the prepared composite film with a double interlocking structure, the thickness of each PI layer is 130-140 μm, the total thickness is 300 μm, and the AgNWs layer density is 40 μm / m².

3. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 1, characterized in that, In the composite film with a double interlocking structure, the structural formula of polyimide is: 。 4. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 1, characterized in that, The method for preparing a PAA solution containing MAH is as follows: 4,4′-biphenyl dianhydride ODPA and 4,4′-diaminobiphenyl-2,2-dicarboxylic acid DCB are dissolved in NN dimethylacetamide, reacted at room temperature under a nitrogen atmosphere, placed in an ice-water bath overnight, and then maleic anhydride MAH is added to obtain a PAA solution containing MAH.

5. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 4, characterized in that, The molar ratio of 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB), 4,4'-diphenyl ether dianhydride (ODPA), and maleic anhydride (MAH) is 1.02:1:0.05; the solid content of the reaction solution is 15%.

6. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 1, characterized in that, The preparation method of AgNWs mixed solution is as follows: maleic anhydride is completely dissolved in deionized water under magnetic stirring at room temperature, and then AgNWs are added and magnetically stirred for 30 minutes to obtain AgNWs mixed solution.

7. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 6, characterized in that, The mass ratio of AgNWs to maleic anhydride is 1:30, and the concentration of the mixed solution is 2 mg / ml.

8. The method for preparing the double-interlocked polyimide electromagnetic shielding composite film according to claim 1, characterized in that, The temperature gradient for thermal imidization was as follows: 90 ℃-1 h, 120 ℃-1 h, 150 ℃-1 h, 180 ℃-12 h.

9. A double-interlocking polyimide electromagnetic shielding composite film prepared by the method according to any one of claims 1-8.

Images