Elastic metal film with high electromagnetic shielding performance and preparation method and application thereof

Abstract

The invention belongs to the technical field of electromagnetic interference shielding materials, and discloses an elastic metal film with high electromagnetic shielding performance and a preparation method and application thereof, and the preparation method comprises the following steps: preparing a PU film from a precursor solution of polyurethane through electrostatic spinning; carrying out hot pressing on the PU film, and then dipping the PU film in a polydopamine solution for a set time for modification; after modification is completed, the modified PU film is washed and dried and then soaked in a chemical copper plating solution, a borane dimethylamine complex DMAB is added to serve as a reducing agent, and chemical metal plating is conducted; and after the reaction is finished, cleaning and drying. The elastic metal film is a porous honeycomb-shaped film, has the advantages of light weight, stretchability, flexibility, good air permeability, adjustable shielding performance, infrared stealth, bidirectional heat management, sun protection and the like, and has a wide application range.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic interference shielding materials technology, specifically relating to an elastic metal film with high electromagnetic shielding performance, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With the popularization of electronic devices and communication technologies, electromagnetic interference (EMI) problems are becoming increasingly serious, which not only affect equipment operation but may also endanger health. Therefore, there is an urgent need for high-performance EMI shielding materials.

[0004] While traditional metallic materials offer good conductivity and shielding properties, their heavy weight and poor flexibility make them unsuitable for modern applications. Current research focuses on lightweight, flexible, and mechanically sound porous honeycomb structures, which offer low density, good air permeability, and enhanced shielding performance (SE) through multiple reflections.

[0005] Highly conductive, high aspect ratio metal nanofibers are ideal for constructing such lightweight, highly shielding materials. However, the weak interfiber forces result in low mechanical strength. While commonly used adhesives / crosslinking agents can enhance these forces, they significantly reduce conductivity, thereby weakening the shielding performance.

[0006] Electroless metallization (electrodeposition) is a simple, energy-efficient, and environmentally friendly surface treatment method that can form a high-quality metal coating on a substrate. Using this method to coat metal onto polymer nanofiber membranes can create a porous structure while maintaining the high conductivity of the metal. However, this method still faces challenges: weak bonding between the metal and polymer reduces stability; overlapping at fiber interfaces increases contact resistance; and the rigidity of the metal itself limits the application of flexible materials. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an elastic metal film with high electromagnetic shielding performance, its preparation method, and its applications. This elastic metal film is a porous honeycomb film, possessing advantages such as lightweight, stretchability, flexibility, good air permeability, adjustable shielding performance, infrared stealth, bidirectional thermal management, and sun protection, thus having a wide range of applications.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing an elastic metal thin film with high electromagnetic shielding performance, comprising the following steps: PU films were prepared by electrospinning a polyurethane precursor solution. After hot pressing, the PU film is impregnated in a polydopamine solution for a set time to modify it; After modification, the modified PU film is washed and dried, then immersed in a chemical copper plating solution, and DMAB (borane dimethylamine complex) is added as a reducing agent for chemical metal plating. After the reaction is complete, clean and dry.

[0009] Secondly, the present invention provides an elastic metal film with high electromagnetic shielding performance, which is prepared by the aforementioned preparation method.

[0010] Thirdly, the present invention provides the application of the elastic metal film with high electromagnetic shielding performance in the fields of electromagnetic wave shielding, infrared stealth, thermal insulation, sun protection, and wearable flexible electronics.

[0011] The beneficial effects achieved by one or more embodiments of the present invention are as follows: The elastic metal film with high electromagnetic shielding performance prepared by this invention uses pDA for pretreatment, selects DMAB as a reducing agent, and carries out a reduction reaction at room temperature to ensure that small copper nanoparticles grow uniformly on polymer nanofibers, thus ensuring the stability, excellent conductivity, and mechanical properties of the metal film. This elastic metal film still exhibits excellent conductivity and shielding performance when deformed, solving the problems of traditional metal foils being difficult to deform and lacking flexibility.

[0012] The high elasticity of the PU substrate and the uniform, dense metal layer firmly "locked" onto the PU fibers ensure the elasticity and stability of the metal film during stretching. Furthermore, the inherent porosity of the electrospun film gives the metal film low density and breathability. This metal film relies on the optical properties of copper on the fiber surface, exhibiting high reflectivity in both solar and mid-to-far infrared bands, thus achieving multifunctionality such as infrared stealth, two-way thermal management, and sun protection.

[0013] This invention employs electrospinning and chemical plating to produce an ultralight, flexible metal film with high electromagnetic shielding performance. The preparation process is simple, requires no complex equipment, is environmentally friendly, has low production costs, and high yield. The fiber diameter can be controlled by adjusting the syringe pump needle diameter, extrusion speed, voltage, and the distance between the needle and receiver; the thickness of the PU film can be controlled by adjusting the electrospinning time; and the thickness of the metal layer on the fiber surface can be controlled by adjusting the chemical plating time, thereby adjusting the conductivity and electromagnetic shielding performance of the metal film.

[0014] The elastic metal film with high electromagnetic shielding performance prepared by this invention possesses good mechanical and electromagnetic shielding properties and can be used to prepare wearable electromagnetic shielding textiles. This electronic textile can be applied in fields such as flexible wearable devices and wearable electromagnetic shielding materials. The textile maintains the performance and reliability of the device under various deformations. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 Scanning electron microscope (SEM) images of the highly elastic and porous PU electrospun films prepared for Examples 1, 2, 3, 4 and 5.

[0017] Figure 2 Scanning electron microscope (SEM) images of the hot-pressed electrospun PU films prepared in Examples 2, 3, 4 and 5.

[0018] Figure 3 The image shows a scanning electron microscope (SEM) image of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 3.

[0019] Figure 4 The energy spectrum of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 3 is shown.

[0020] Figure 5 This is a physical illustration of the elastic metal film with high electromagnetic shielding performance prepared in Example 3.

[0021] Figure 6 The electromagnetic shielding performance diagrams are for the elastic metal films with high electromagnetic shielding performance prepared in Examples 1 and 4.

[0022] Figure 7 The XRD diffraction pattern of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 4 is shown.

[0023] Figure 8 The Fourier transform infrared (FTIR) spectrum of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 4 is shown.

[0024] Figure 9 The stress-strain curve of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 4 is shown.

[0025] Figure 10 Electromagnetic shielding performance diagrams of the elastic metal films with high electromagnetic shielding performance prepared in Examples 2, 3, 4 and 5.

[0026] Figure 11 The image shows the bending stability test results of the elastic metal film with high electromagnetic shielding performance prepared in Example 3.

[0027] Figure 12The image shows the tensile stability test results of the elastic metal film with high electromagnetic shielding performance prepared in Example 3.

[0028] Figure 13 Infrared imaging of human skin covered by an elastic metal film with high electromagnetic shielding performance prepared in Example 3.

[0029] Figure 14 The graph shows the thermal insulation performance of the elastic metal film with high electromagnetic shielding properties prepared in Example 3 under cold conditions.

[0030] Figure 15 The graph shows the cold-keeping performance of the elastic metal film with high electromagnetic shielding properties prepared in Example 3 under hot conditions.

[0031] Figure 16 The ultraviolet protection factor (UPF) of the elastic metal film with high electromagnetic shielding performance prepared in Example 3.

[0032] Figure 17 The images show a comparison of the hydrophilicity and hydrophobicity of the substrates before metallization for the elastic metal films with high electromagnetic shielding performance prepared in Example 3 and Comparative Example 1. HLPU@pDA is the substrate corresponding to Example 3; HLPU is the substrate corresponding to Comparative Example 1. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] In a first aspect, the present invention provides a method for preparing an elastic metal thin film with high electromagnetic shielding performance, comprising the following steps: PU films were prepared by electrospinning a polyurethane precursor solution. After hot pressing, the PU film is impregnated in a polydopamine solution for a set time to modify it; After modification, the modified PU film is washed and dried, then immersed in a chemical copper plating solution, with borane dimethylamine complex added as a reducing agent for chemical metal plating. After the reaction is complete, clean and dry.

[0035] Using PU film as the substrate for chemical metal plating is beneficial for obtaining elastic metal films in the future.

[0036] Before electroless metal plating onto polymer nanofibers, a hot press is used to apply pressure and temperature to the film, causing the molten polymer nanofibers to cross-link and achieve strong connections at the fiber-to-fiber junctions, which further improves the mechanical strength of the polyurethane film. Simultaneously, in the subsequent electroless plating solution, metallic copper uniformly coats the polyurethane nanofibers and the strong connection points between them, resulting in a tightly bonded metal nanolayer, rather than simple contact between metal layers on the fiber surface. This effectively reduces the contact resistance between conductive layers and improves shielding performance.

[0037] pDA pretreatment can form an adhesion layer on the surface of PU fibers, enhancing the bonding force between the copper plating and the PU film substrate.

[0038] After fixing the substrate film with a frame and fixture, immersing it in the electroless copper plating solution allows the substrate to spread out in the solution, resulting in a more uniform plating layer. Borane dimethylamine complex (DMAB) is selected as the reducing agent for electroless copper plating, and the reduction reaction is mild and controllable, resulting in a copper layer with fine crystals, low porosity, and better conductivity and mechanical properties. A reduction reaction is carried out at room temperature to limit the growth of copper nanoparticles and prevent the formation of large metal crystals, thereby obtaining a dense metal layer with low roughness.

[0039] In some embodiments, the polyurethane precursor solution comprises polyurethane, acetone, and N,N-dimethylformamide (DMF), wherein the mass percentage of polyurethane is 10-20%, and the volume ratio of acetone to DMF is 1:0.8-1.2.

[0040] Polyurethane is a polar polymer containing numerous urethane and urea bonds, requiring highly polar solvents for dissolution. While DMF alone offers good solubility, its high boiling point results in slow solvent evaporation during spinning, causing fibers to adhere to the collector before solidification, leading to film formation rather than independent fibers. Acetone, with its low boiling point and rapid evaporation, is a moderately polar solvent and does not readily dissolve high molecular weight polyurethane. Using acetone alone can result in gel particles that clog the spinning needles or produce beaded fibers. Therefore, using both acetone and DMF as solvents allows DMF to ensure the molecular chains fully expand and dissolve, while acetone accelerates evaporation and reduces surface tension, resulting in an ideal PU electrospun film.

[0041] Preferably, the polyurethane is of type 685AU.

[0042] In some embodiments, the hot pressing temperature is 60-80°C, the hot pressing pressure is 20-30 MPa, and the hot pressing time is 5-15 min.

[0043] In some embodiments, the polydopamine solution is obtained by quantitatively dissolving dopamine hydrochloride in Tris-hydrochloric acid buffer (10 mM, pH 8.5).

[0044] In some embodiments, the hot-pressed PU film is immersed in a polydopamine solution for 12-24 hours.

[0045] Preferably, the hot-pressed PU film is immersed in a polydopamine solution, then placed in clean water and ultrasonically removed to remove excess pDA agglomerates, and then dried.

[0046] In some embodiments, the preparation method of the chemical copper plating solution is as follows: copper chloride, disodium ethylenediaminetetraacetate, disodium ethylenediaminetetraacetate dihydrate and boric acid are mixed in proportion and dissolved in water, and then alkali is added to adjust the solution to neutral.

[0047] Preferably, the concentration of copper chloride is 30-70 mM, the concentrations of disodium ethylenediaminetetraacetate and disodium ethylenediaminetetraacetate dihydrate are 30-70 mM, and the concentration of boric acid is 80-120 mM.

[0048] Preferably, the alkali is KOH.

[0049] Secondly, the present invention provides an elastic metal film with high electromagnetic shielding performance, which is prepared by the aforementioned preparation method.

[0050] Thirdly, the present invention provides the application of the elastic metal film with high electromagnetic shielding performance in the fields of electromagnetic wave shielding, infrared stealth, thermal insulation, sun protection, or wearable flexible electronics.

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0052] Example 1 A method for preparing an elastic metal thin film with high electromagnetic shielding performance includes the following steps: (1) Preparation of electrospinning precursor solution: Mix 10 ml acetone and 10 ml DMF evenly as the mixed solvent in the electrospinning precursor solution; then add 3 g polyurethane particles to the mixed solvent and stir at room temperature for 8 hours. (2) Preparation of PU electrospun membrane: Pour the above-mentioned uniformly mixed precursor solution into a syringe, select a flat receiver, and wrap a layer of tin foil on its surface. Fix them respectively in the corresponding positions of the electrospinning machine. The voltage applied to the needle is 13 kV, the distance between the needle and the flat receiver is 15 cm, and the extrusion speed of the syringe is 0.3 ml / h. Finally, peel off the obtained fiber membrane from the tin foil.

[0053] (3) Preparation of pDA pretreatment solution: Dopamine hydrochloride powder was quantitatively dissolved in 10 mM Tris-HCl (pH 8.5) to form a 2 g / L transparent solution.

[0054] (4) Preparation of PU@pDA membrane: After the pretreatment solution is mixed evenly, the PU electrospun membrane is placed in the solution and stirred for 24 hours. Then, excess pDA agglomerates are removed by ultrasonication and then placed in a vacuum oven at 40°C for 12 hours to dry.

[0055] (5) Preparation of electroless copper plating solution: A precursor solution for electroless copper plating was obtained by quantitatively dissolving 50 mM CuCl2·2H2O, 50 mM EDTA-2Na·2H2O, and 100 mM boric acid. After the solution was mixed evenly, 3 mM KOH was added dropwise until the pH of the solution became 7. CuCl2·2H2O served as the main salt to provide copper ions, EDTA-2Na·2H2O served as a complexing agent, and boric acid and KOH served as pH adjusters.

[0056] (6) Preparation of PU@pDA / Cu metal film: Make a frame with a similar shape to the base film, use a clamp to fix the film on the frame, immerse it in the chemical copper plating solution so that the film can spread out in the solution, soak for 10 min to allow the solution to fully wet the sample surface.

[0057] Subsequently, 100 mM reducing agent borane dimethylamine complex (DMAB) was added to the above reaction chamber, and the reaction was carried out at room temperature for 24 h to obtain a metal content of 2.4 mg / cm³. 2 Stretchable metal film.

[0058] After the reaction is complete, remove the frame and fixture used to fix the sample, and clean the sample membrane with deionized water to obtain a copper-coated polyurethane nanofiber membrane (PU@pDA / Cu).

[0059] Finally, place the washed sample in a vacuum oven at 40°C for 24 hours to dry completely, and then seal it in a vacuum packaging bag for storage.

[0060] Example 2 A method for preparing an elastic metal thin film with high electromagnetic shielding performance includes the following steps: (1) Preparation of electrospinning precursor solution: Mix 10 ml acetone and 10 ml DMF evenly as solvent in electrospinning precursor solution, then add 3 g polyurethane particles and stir at room temperature for 8 hours.

[0061] (2) Preparation of PU electrospun membrane: Pour the above-mentioned uniformly mixed precursor solution into a syringe, select a flat receiver, and wrap a layer of tin foil on its surface. Fix them respectively in the corresponding positions of the electrospinning machine. The voltage applied to the needle is 13 kV, the distance between the needle and the flat receiver is 15 cm, and the extrusion speed of the syringe is 0.3 ml / h. Finally, peel off the obtained fiber membrane from the tin foil.

[0062] (3) Preparation of hot-pressed PU (HLPU) electrospun film: The above PU electrospun film is placed between the upper and lower clamps of the hot press, the applied temperature is 70 ℃, the loading pressure is 29 MPa, and the loading time is controlled at 10 min.

[0063] (4) Preparation of pDA pretreatment solution: Dopamine hydrochloride powder was quantitatively dissolved in 10 mM Tris-HCl (pH 8.5) to form a 2 g / L transparent solution.

[0064] (5) Preparation of HLPU@pDA membrane: After the pretreatment solution is mixed evenly, the hot-pressed PU electrospun membrane is placed into the solution and stirred for 24 h. After that, excess pDA agglomerates are removed by ultrasonication and then placed in a vacuum oven at 40 ℃ for 12 h to dry.

[0065] (6) Preparation of electroless copper plating solution: A precursor solution for electroless copper plating was obtained by quantitatively dissolving 50 mM CuCl2·2H2O, 50 mM EDTA-2Na·2H2O, and 100 mM boric acid. After the solution was mixed evenly, 3 mM KOH was added dropwise until the pH of the solution became 7. CuCl2·2H2O served as the main salt to provide copper ions, EDTA-2Na·2H2O served as a complexing agent, and boric acid and KOH served as pH adjusters.

[0066] (7) Preparation of HLPU@pDA / Cu metal film: Make a frame with a similar shape to the substrate film, use a clamp to fix the film on the frame, and immerse it in the chemical copper plating solution so that the film can spread out in the solution; The sample was soaked for 10 min to allow the solution to fully wet the sample surface. Then, 100 mM reducing agent (DMAB) was added to the reaction chamber, and the reaction was carried out at room temperature for 60 h, yielding a metal content of 3.6 mg / cm³. 2 Stretchable metal film.

[0067] After the reaction is complete, remove the frame and fixture used to fix the sample, and clean the sample membrane with deionized water to obtain a copper-coated polyurethane nanofiber membrane.

[0068] Finally, place the washed sample in a vacuum oven at 40°C for 24 hours to dry completely, and then seal it in a vacuum packaging bag for storage.

[0069] Example 3 A method for preparing an elastic metal thin film with high electromagnetic shielding performance includes the following steps: (1) Preparation of the precursor solution for electrospinning: Mix 10 ml of acetone and 10 ml of DMF evenly as the solvent in the precursor solution for electrospinning. Then add 3 g of polyurethane particles and stir at room temperature for 8 hours.

[0070] (2) Preparation of PU electrospun membrane: Pour the above-mentioned uniformly mixed precursor solution into a syringe, select a flat receiver, and wrap a layer of tin foil on its surface. Fix them respectively in the corresponding positions of the electrospinning machine. The voltage applied to the needle is 13 kV, the distance between the needle and the flat receiver is 15 cm, and the extrusion speed of the syringe is 0.3 ml / h. Finally, peel off the obtained fiber membrane from the tin foil.

[0071] (3) Preparation of hot-pressed PU (HLPU) electrospun film: The above PU electrospun film is placed between the upper and lower clamps of the hot press, the applied temperature is 70℃, the loading pressure is 29 MPa, and the loading time is controlled at 10 min.

[0072] (4) Preparation of pDA pretreatment solution: Dopamine hydrochloride powder was quantitatively dissolved in 10 mM Tris-HCl (pH 8.5) to form a 2 g / L transparent solution.

[0073] (5) Preparation of HLPU@pDA membrane: After the pretreatment solution is mixed evenly, the hot-pressed PU electrospun membrane is placed into the solution and stirred for 24 h. The excess pDA agglomerates are removed by ultrasonication, and then placed in a vacuum oven at 40℃ for 12 h to dry.

[0074] (6) Preparation of electroless copper plating solution: A precursor solution for electroless copper plating was obtained by quantitatively dissolving 50 mM CuCl2·2H2O, 50 mM EDTA-2Na·2H2O, and 100 mM boric acid. After the solution was mixed evenly, 3 mM KOH was added dropwise until the pH of the solution became 7. CuCl2·2H2O served as the main salt to provide copper ions, EDTA-2Na·2H2O served as a complexing agent, and boric acid and KOH served as pH adjusters.

[0075] (7) Preparation of HLPU@pDA / Cu metal film: Prepare the substrate film after hot pressing and pretreatment, fix the film with a clamp, and immerse it in the chemical copper plating solution. Immerse for 10 min to allow the solution to fully wet the sample surface.

[0076] Subsequently, 100 mM reducing agent (DMAB) was added to the above reaction chamber, and the reaction was carried out at room temperature for 48 h to obtain a metal content of 2.9 mg / cm³. 2 Stretchable metal film.

[0077] After the reaction is complete, remove the sample and rinse it thoroughly with deionized water. Finally, place the cleaned sample in a vacuum oven at 40°C for 24 hours to dry completely, then seal it in a vacuum-sealed bag for storage.

[0078] SEM images and energy dispersive spectroscopy (EDS) spectra of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 3 are shown below. Figure 3 and Figure 4 As shown, the results indicate that a uniform copper metal layer was successfully formed on the fiber surface.

[0079] Figure 5 The image shows a physical picture of the elastic metal film of Embodiment 3 of the present invention, as well as its stretchability, flexibility and foldability. The results show that this metal film is different from traditional metal foil. It can adapt to various deformations, such as stretching, bending and folding, while maintaining the stability of its performance.

[0080] Example 4 A method for preparing an elastic metal thin film with high electromagnetic shielding performance includes the following steps: (1) Preparation of the precursor solution for electrospinning: Mix 10 ml of acetone and 10 ml of DMF evenly as the solvent in the precursor solution for electrospinning. Then add 3 g of polyurethane particles and stir at room temperature for 8 hours.

[0081] (2) Preparation of PU electrospun membrane: Pour the above-mentioned uniformly mixed precursor solution into a syringe, select a flat receiver, and wrap a layer of tin foil on its surface. Fix them respectively in the corresponding positions of the electrospinning machine. The voltage applied to the needle is 13 kV, the distance between the needle and the flat receiver is 15 cm, and the extrusion speed of the syringe is 0.3 ml / h. Finally, peel off the obtained fiber membrane from the tin foil.

[0082] (3) Preparation of hot-pressed PU (HLPU) electrospun film: The above PU electrospun film is placed between the upper and lower clamps of the hot press, the applied temperature is 70℃, the loading pressure is 29 MPa, and the loading time is controlled at 10 min.

[0083] (4) Preparation of pDA pretreatment solution: Dopamine hydrochloride powder was quantitatively dissolved in 10 mM Tris-HCl (pH 8.5) to form a 2 g / L transparent solution.

[0084] (5) Preparation of HLPU@pDA membrane: After the pretreatment solution is mixed evenly, the hot-pressed PU electrospun membrane is placed into the solution and stirred for 24 h. The excess pDA agglomerates are removed by ultrasonication, and then placed in a vacuum oven at 40℃ for 12 h to dry.

[0085] (6) Preparation of electroless copper plating solution: A precursor solution for electroless copper plating was obtained by quantitatively dissolving 50 mM CuCl2·2H2O, 50 mM EDTA-2Na·2H2O, and 100 mM boric acid. After the solution was mixed evenly, 3 mM KOH was added dropwise until the pH of the solution became 7. CuCl2·2H2O served as the main salt to provide copper ions, EDTA-2Na·2H2O served as a complexing agent, and boric acid and KOH served as pH adjusters.

[0086] (7) Preparation of HLPU@pDA / Cu metal film: After hot pressing and pretreatment, the substrate film was fixed with a clamp and then immersed in a chemical copper plating solution. The film was immersed for 10 min to allow the solution to fully wet the sample surface. Then, 100 mM reducing agent (DMAB) was added to the reaction chamber, and the reaction was carried out at room temperature for 24 h to obtain a metal content of 2.4 mg / cm³. 2 The stretchable metal film was removed after the reaction was complete. The sample, washed with deionized water, was placed in a vacuum oven at 40°C for 24 hours to dry completely. After drying, it was sealed in a vacuum packaging bag for storage.

[0087] The EMI shielding performance of the elastic metal films prepared in Examples 1 and 4 of this invention was tested as follows: Figure 6 As shown, the results indicate that hot pressing can achieve strong connections at the fiber-to-fiber junctions. After chemical plating, copper metal is uniformly coated on the strong connection points between the PU nanofibers and fibers, resulting in tightly connected metal nanolayers, rather than simple contact between metal layers on the fiber surface. This effectively reduces the contact resistance between conductive layers and improves the EMI shielding performance of the metal film.

[0088] Figure 7 The XRD diffraction pattern of the elastic metal film with high electromagnetic shielding performance prepared in Example 4 of this invention shows that the main peaks of XRD are near 43° and 50°, which correspond to the (111) and (200) crystal planes of pure copper, respectively, confirming that the surface of the nanofibers was successfully coated with a pure copper coating with good crystallinity.

[0089] Figure 8 The FTIR of the elastic metal film with high electromagnetic shielding performance prepared in Example 4 of this invention shows that the PU film has high electromagnetic shielding performance at 1707, 1533, 1224, 1078, 813, and 513 cm⁻¹. -1The peaks at these locations correspond to C=O, CN and NH, COC, CO, CH, CN bonds, respectively. The amino group (-NH2) of PDA and the urethane ester (-NH-COO-) of PU form hydrogen bonds or covalent crosslinks, altering the CN vibration mode and thus intensifying the peak. During PDA polymerization, some unoxidized dopamine alkyl chains (-CH2-) may be retained or aromatic rings (CH) may form; these CH vibrations superimpose on the original CH peaks of PU, leading to increased peak intensity. After electroless metal plating, the intensities of all peaks significantly decreased, and some peaks were masked. This is because the metal plating reflects infrared light, which also confirms successful metal coating.

[0090] The stress-strain curves of the elastic metal thin film with high electromagnetic shielding performance prepared in Example 4 are as follows: Figure 9 As shown, the results indicate that the metal plating still maintains good stretchability and tensile strength.

[0091] Example 5 A method for preparing an elastic metal thin film with high electromagnetic shielding performance includes the following steps: (1) Preparation of the precursor solution for electrospinning: Mix 10 ml of acetone and 10 ml of DMF evenly as the solvent in the precursor solution for electrospinning. Then add 3 g of polyurethane particles and stir at room temperature for 8 hours.

[0092] (2) Preparation of PU (HLPU) electrospun membrane: Pour the above-mentioned uniformly mixed precursor solution into a syringe, select a flat receiver, and wrap a layer of tin foil on its surface. Fix them respectively in the corresponding positions of the electrospinning machine. The voltage applied to the needle is 13 kV, the distance between the needle and the flat receiver is 15 cm, and the extrusion speed of the syringe is 0.3 ml / h. Finally, peel off the obtained fiber membrane from the tin foil.

[0093] (3) Preparation of hot-pressed PU (HLPU) electrospun film: The above PU electrospun film is placed between the upper and lower clamps of the hot press, the applied temperature is 70℃, the loading pressure is 29 MPa, and the loading time is controlled at 10 min.

[0094] (4) Preparation of pDA pretreatment solution: Dopamine hydrochloride powder was quantitatively dissolved in 10 mM Tris-HCl (pH 8.5) to form a 2 g / L transparent solution.

[0095] (5) Preparation of HLPU@pDA membrane: After the pretreatment solution is mixed evenly, the hot-pressed PU electrospun membrane is placed into the solution and stirred for 24 h. The excess pDA agglomerates are removed by ultrasonication, and then placed in a vacuum oven at 40℃ for 12 h to dry.

[0096] (6) Preparation of electroless copper plating solution: A precursor solution for electroless copper plating was obtained by quantitatively dissolving 50 mM CuCl2·2H2O, 50 mM EDTA-2Na·2H2O, and 100 mM boric acid. After the solution was mixed evenly, 3 mM KOH was added dropwise until the pH of the solution became 7. Among them, CuCl2·2H2O served as the main salt to provide copper ions, EDTA-2Na·2H2O served as a complexing agent, and boric acid and KOH served as pH adjusters.

[0097] (7) Preparation of HLPU@pDA / Cu metal film: After hot pressing and pretreatment, the substrate film was fixed with a clamp and then immersed in a chemical copper plating solution. After immersion for 10 min, 100 mM reducing agent (DMAB) was added, and the reaction was carried out at room temperature for 9 h to obtain a metal content of 1.6 mg / cm³. 2 The stretchable metal film was removed after the reaction was complete. The sample, washed with deionized water, was placed in a vacuum oven at 40 °C and dried for 24 h. After it was completely dry, it was removed.

[0098] Figure 1 The images are SEM images of the PU electrospun fiber membranes prepared in step (2) of Examples 1, 2, 3, 4 and 5 of the present invention. The five examples used the same PU electrospun fiber membrane.

[0099] Figure 2 The images are SEM images of the PU electrospun fiber membranes prepared by hot pressing in step (3) of Examples 2, 3, 4 and 5 of the present invention. The results show that hot pressing can achieve strong connection at the fiber junction.

[0100] The electromagnetic shielding performance of the elastic metal films prepared in Examples 2, 3, 4, and 5 are shown in the figure below. Figure 10 As shown, the results indicate that the EMI shielding performance of the metal film can be adjusted by changing the metal content on the nanofibers. As the reaction time in the chemical plating solution increases, the isolated small crystals gradually coalesce to form a continuous metal layer, and the conductivity and shielding performance are significantly improved.

[0101] The bending stability and tensile stability of the elastic metal film with high electromagnetic shielding performance prepared in Example 3 were tested as follows: Figure 11 and Figure 12 As shown, when the sample was attached to a finger and subjected to 2000 bending cycles, the fabric's electrical resistance remained stable. Furthermore, the sample's conductivity remained stable when stretched within a certain strain range.

[0102] Infrared imaging of the elastic metal film prepared in Example 3 covering human skin is shown below. Figure 13As shown, a glove made of the metal film was worn on the hand, and an infrared camera was used to take an infrared image. The results showed that due to its extremely high reflectivity in the 8-14 μm range (the main band of Earth's thermal radiation), it can effectively shield the target's own thermal radiation, allowing it to blend into the low-temperature background in thermal imaging and achieve the effect of infrared stealth.

[0103] Figure 14 and Figure 15 The graph shows the thermal insulation performance of the elastic metal film with high electromagnetic shielding properties prepared in Example 3 under cold and hot environments. Attaching the prepared metal film to the inside of clothing can effectively reduce heat loss and minimize the impact of the external environment on the human body.

[0104] The ultraviolet protection factor (UPF) of the elastic metal film with high electromagnetic shielding performance prepared in Example 3 is as follows: Figure 16 As shown in the figure. The results indicate that the elastic metal film has excellent sun protection capabilities.

[0105] Comparative Example 1 The difference from Example 3 is that steps (4) and (5) are omitted, while everything else is the same as Example 3.

[0106] Comparative Example 2 The difference from Example 3 is that the reducing agent DMAB in step (7) is replaced with formaldehyde, while everything else is the same as in Example 3.

[0107] The elastic metal films with high electromagnetic shielding performance prepared in Examples 3 and 1, before metal plating, exhibited similar hydrophilicity and hydrophobicity of the substrates. Figure 17 As shown. In Comparative Example 1, because steps (4) and (5) were omitted, the hydrophobicity of the PU electrospun film could not be changed, and thus copper plating could not be achieved in the chemical plating solution.

[0108] The EMI shielding performance of the elastic metal films prepared in Examples 3 and 1 of this invention was tested as follows: Figure 6 As shown, the results indicate that hot pressing can achieve strong connections at the fiber-to-fiber junctions. After chemical plating, copper metal is uniformly coated on the strong connection points between the PU nanofibers and fibers, resulting in tightly connected metal nanolayers, rather than simple contact between metal layers on the fiber surface. This effectively reduces the contact resistance between conductive layers and improves the EMI shielding performance of the metal film.

[0109] Compared with the elastic metal film with high electromagnetic shielding performance prepared in Example 3 and Comparative Example 2, Comparative Example 3 uses formaldehyde as a reducing agent, which is toxic and carcinogenic, harmful to human health and the environment. Moreover, formaldehyde only has sufficient reducing power in an alkaline environment and usually needs to be used under strongly alkaline conditions (pH>11).

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an elastic metal thin film with high electromagnetic shielding performance, characterized in that: Includes the following steps: PU films were prepared by electrospinning a polyurethane precursor solution. After hot pressing, the PU film is impregnated in a polydopamine solution for a set time to modify it; After modification, the modified PU film is washed and dried, then immersed in a chemical copper plating solution, with borane dimethylamine complex added as a reducing agent for chemical metal plating. After the reaction is complete, clean and dry.

2. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 1, characterized in that: The precursor solution of polyurethane includes polyurethane, acetone and N,N-dimethylformamide (DMF), with polyurethane accounting for 10-20% by mass and the volume ratio of acetone to DMF being 1:0.8-1.

2.

3. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 1, characterized in that: The hot pressing temperature is 60-80℃, the hot pressing pressure is 20-30MPa, and the hot pressing time is 5-15min.

4. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 1, characterized in that: The polydopamine solution was obtained by quantitatively dissolving dopamine hydrochloride in Tris-hydrochloric acid buffer.

5. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 1, characterized in that: The hot-pressed PU film is immersed in polydopamine solution for 12-24 hours.

6. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 5, characterized in that: After hot-pressing, the PU film is immersed in a polydopamine solution, then placed in clean water and ultrasonically removed to remove excess pDA agglomerates, and then dried.

7. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 1, characterized in that: The preparation method of the chemical copper plating solution is as follows: copper chloride, disodium ethylenediaminetetraacetate, disodium ethylenediaminetetraacetate dihydrate and boric acid are mixed in proportion and dissolved in water, and then alkali is added to adjust the solution to neutral.

8. The method for preparing an elastic metal thin film with high electromagnetic shielding performance according to claim 7, characterized in that: The concentration of copper chloride is 30-70 mM, the concentration of disodium ethylenediaminetetraacetate and disodium ethylenediaminetetraacetate dihydrate is 30-70 mM, and the concentration of boric acid is 80-120 mM.

9. An elastic metal film with high electromagnetic shielding performance, characterized in that: It is prepared by any one of the preparation methods described in claims 1-8.

10. The application of the elastic metal film with high electromagnetic shielding performance as described in claim 9 in the fields of electromagnetic wave shielding, infrared stealth, thermal insulation, sun protection, or wearable flexible electronics.

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