Electromagnetic shielding composite film with mushroom-shaped array microstructure on surface and preparation method thereof

Abstract

The application belongs to the technical field of electromagnetic shielding composite film materials, and discloses an electromagnetic shielding composite film with a mushroom-shaped array microstructure on the surface and a preparation method thereof. The electromagnetic shielding composite film comprises a polymer base film, and a mushroom-shaped array microstructure layer and a conductive layer are sequentially arranged on the surface of the polymer base film from bottom to top. The preparation steps are as follows: (1) washing and drying a polymer raw material, and hot-pressing to prepare a polymer base film; (2) sequentially stacking the polymer base film, a perforated plate and a screen mesh from bottom to top, and hot-pressing to obtain a polymer base film with a mushroom-shaped array microstructure layer on the surface; (3) performing surface activation treatment; and (4) spraying a conductive filler dispersion liquid to obtain the target product. The base material and the conductive component can be flexibly selected, and the diversified use requirements can be met. The high-temperature oxidation and thermal damage caused by the laser etching process can be effectively avoided, and the functions of electromagnetic shielding, infrared stealth and light-heat conversion can be integrated.

Description

Technical Field

[0001] This invention belongs to the technical field of electromagnetic shielding composite film materials, specifically relating to an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface and its preparation method. Background Technology

[0002] Radiation pollution has become a significant issue affecting the stability of electronic devices, information security, and human health. Traditional electromagnetic shielding materials are primarily metal-based, which suffer from drawbacks such as high density, poor corrosion resistance, insufficient flexibility, and difficulty in adapting to flexible and wearable applications. In recent years, flexible polymer-based electromagnetic shielding composite films have become a research hotspot; however, existing technologies mostly employ planar structural designs, resulting in problems such as a single electromagnetic shielding mechanism, limited shielding effectiveness, and low functional integration.

[0003] In terms of microstructure construction, while methods such as laser etching and photolithography can achieve surface patterning, they suffer from drawbacks such as expensive equipment, complex processes, susceptibility to material oxidation and thermal damage at high temperatures, and difficulty in large-scale production. Furthermore, most shielding films only possess a single protective function, failing to meet the demands of high-end applications for multi-functional integration, including electromagnetic shielding, infrared stealth, and photothermal conversion. Therefore, developing a flexible electromagnetic shielding composite film that is simple to process, has adjustable performance, integrates multiple functions, and can be mass-produced is of significant research value and application importance. Summary of the Invention

[0004] To overcome the shortcomings of existing electromagnetic shielding composite films, such as simple structure, insufficient shielding performance, complex preparation process, single function, and easy material damage at high temperatures, the present invention aims to provide an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface includes a polymer substrate film, on the surface of which a mushroom-shaped array microstructure layer and a conductive layer are sequentially constructed from bottom to top; the polymer substrate is a thermoplastic polymer substrate.

[0006] Preferably, the thermoplastic polymer substrate is TPAE (thermoplastic polyamide elastomer), TPU (thermoplastic polyurethane), PP (polypropylene), PA (polyamide), PVA (polyvinyl alcohol), or PE (polyethylene); the conductive layer is one or more of MXene, AgNWs (silver nanowires), and CNTs (carbon nanotubes).

[0007] A method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface includes the following steps: (1) After cleaning and drying the polymer raw materials, hot pressing is used to prepare a polymer substrate film; (2) Constructing a mushroom-shaped array microstructure layer on the surface of the polymer substrate film obtained in step (1): From bottom to top, the polymer substrate film, perforated plate and screen obtained in step (1) are stacked in sequence, hot-pressed, and then the screen and perforated plate are peeled off to obtain a polymer substrate film with a mushroom-shaped array microstructure layer on the surface; the material of the perforated plate and screen must ensure that its temperature and pressure resistance is compatible with the hot pressing in this step (i.e. the material of the perforated plate and screen can withstand the hot pressing conditions). (3) Perform surface-active treatment on the polymer substrate film obtained in step (2); (4) Spray the conductive filler dispersion corresponding to the conductive layer onto the surface of the polymer substrate film obtained in step (3) to obtain the target product.

[0008] Preferably, in step (2), the perforated plate includes a rectangular plate with a plurality of through holes arranged in an array structure; wherein, the thickness of the rectangular plate is less than the thickness of the polymer substrate film obtained in step (1).

[0009] Furthermore, the through hole is circular with a diameter of 0.1~0.3mm and a hole spacing of 0.1~0.3mm; the thickness of the rectangular plate is less than the thickness of the polymer substrate film obtained in step (1) by 0.3~0.6mm.

[0010] Preferably, in step (2), the mesh size of the sieve is 1000~2000 mesh.

[0011] Preferably, in step (2), a vacuum hot press is used for hot pressing. The parameters of the vacuum hot press are: the upper mold temperature and the lower mold temperature are both 50~150℃, and the pressure is 5~30kgf / cm. 2 The heat preservation time is 3~10min, the pressure holding time is 3~10min, and the mold opening temperature is room temperature~80℃.

[0012] Preferably, in step (1), after the polymer raw materials are cleaned and dried, they are uniformly filled into the mold frame and then hot-pressed using a vacuum hot press to prepare a polymer substrate film. The material of the mold frame must ensure that its temperature and pressure resistance is compatible with the hot pressing described in this step (i.e., the material of the mold frame can withstand the hot pressing conditions), and the thickness of the mold frame must be compatible with the thickness of the polymer substrate film to be prepared. The parameters of the vacuum hot press are: upper mold temperature and lower mold temperature are both 50~150℃, and the pressure is 5~30 kgf / cm². 2 The heat preservation time is 3~10min, the pressure holding time is 3~10min, and the mold opening temperature is room temperature~80℃.

[0013] Preferably, in step (3), a plasma instrument is used for surface activity treatment, the gas used is oxygen, the treatment time is 30~80s, and the radio frequency power is 45~120W.

[0014] Preferably, in step (4), the conductive filler dispersion corresponding to the conductive layer is sprayed onto the surface of the polymer substrate film, with each 16cm layer... 2 10-60 mL of conductive filler dispersion is sprayed onto the surface of a polymer substrate film at a spraying pressure of 0.3-0.6 MPa and a spraying distance of 3-10 cm. The solvent of the conductive filler dispersion is water, anhydrous ethanol, or a mixture of the two, and the concentration of the conductive filler dispersion is 0.75-2 mg / mL.

[0015] The preparation principle of this invention is as follows: This invention uses a polymer material as a flexible substrate. First, a regular mushroom-shaped array microstructure is constructed on the substrate surface. Then, surface activation treatment is performed to enhance surface activity and hydrophilicity, and strengthen interfacial bonding. Finally, a conductive layer is constructed. The mushroom-shaped array microstructure can significantly increase the specific surface area, providing multiple reflection and scattering paths for electromagnetic waves, and extending the transmission path to enhance attenuation. The conductive layer, with its high conductivity, constructs an efficient conductive loss network. The two work together to form a dual shielding mechanism of "microstructure multiple scattering + conductive loss". At the same time, relying on the photothermal properties of the conductive layer and the infrared modulation capability of the microstructure, the film has multiple functions including electromagnetic shielding, infrared stealth, and photothermal conversion. The process is simple, the bonding is strong, and the performance is excellent.

[0016] Beneficial effects: (1) The present invention can flexibly select various polymer substrates such as TPAE, TPU, PP, PA, PVA, PE, etc. according to actual application scenarios, and combine them with different conductive layers such as MXene, AgNWs, CNTs, etc. to meet diverse application needs and has strong universality. (2) By changing the thickness of the conductive layer, the electromagnetic shielding effectiveness can be continuously adjusted from low to high, which can accurately match the usage requirements of different frequency bands and different protection levels. It can meet the differentiated requirements of shielding strength in different fields such as electronic equipment, military camouflage, and smart wearables, and has a high degree of freedom in performance adjustment. (3) The present invention uses template hot pressing method to achieve efficient preparation of mushroom array microstructure, effectively avoiding problems such as oxidation of conductive filler, thermal degradation of substrate, structural deformation and performance decay caused by high temperature of laser. It can retain the intrinsic properties of substrate and conductive layer to the greatest extent, improve the structural stability and functional reliability of composite film, and integrate electromagnetic shielding, infrared stealth and photothermal conversion functions. (4) By constructing an array of mushroom-shaped microstructures on the substrate surface, the present invention significantly increases the specific surface area and the number of internal interfaces of the material, providing multiple reflection and scattering paths for electromagnetic waves, effectively extending the transmission distance of electromagnetic waves inside the material, and improving the absorption and conversion efficiency. Attached Figure Description

[0017] Figure 1 The following are SEM images of the composite film obtained in Example 1: (a) is a longitudinal section SEM image, (b) is a top view SEM image, and (c) is a partial enlarged view of (a).

[0018] Figure 2 SEM images of the composite films obtained in Examples 1-4: (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4.

[0019] Figure 3 The following are SEM images of the composite film obtained in Comparative Example 1: (a) is a top view SEM image, (b) is a partial enlarged view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image.

[0020] Figure 4 The following are SEM images of the composite film obtained in Comparative Example 2: (a) is a top view SEM image, (b) is a partial enlarged view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image.

[0021] Figure 5 The following are SEM images of the composite film obtained in Comparative Example 3: (a) is a top view SEM image, (b) is a partial magnified view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image.

[0022] Figure 6 The electromagnetic shielding performance (a) of the composite films obtained in Examples 1-4 in the X-band and the corresponding SE A SE R SE T Value statistics chart (b).

[0023] Figure 7 The chart shows the statistical values ​​of R, T, and A for the composite films obtained in Examples 1-4.

[0024] Figure 8 The electromagnetic shielding performance (a) of the composite films obtained in Example 2 and Comparative Examples 1-4 in the X-band and the corresponding SE A SE R SE T Value statistics chart (b).

[0025] Figure 9 The chart shows the statistical values ​​of R, T, and A for the composite films obtained in Example 2 and Comparative Examples 1-4.

[0026] Figure 10 The results are the photothermal conversion performance test results of the composite thin film obtained in Example 3.

[0027] Figure 11 The diagram shows the infrared stealth performance test results (b-c) of the composite film obtained in Example 3. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0029] Example 1 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface, the preparation process is as follows: (1) Preparation of TPAE thin film After cleaning and drying the TPAE granules, take 2.5g of the cleaned TPAE granules and evenly fill them into a 304 stainless steel mold frame with dimensions of 70mm × 70mm × 0.5mm (length × width × thickness). Place the mold frame in a vacuum hot press, evacuate the vacuum, and set the upper and lower mold temperatures to 140℃ and the pressure to 14kgf / cm². 2 The constant temperature time is 5 minutes, the constant pressure time is 5 minutes, and after hot pressing, the mold is opened when it is naturally cooled to 80°C to obtain TPAE film. (2) Constructing mushroom-shaped array microstructures on the surface of TPAE thin film From bottom to top, the TPAE film prepared in step (1), the 304 stainless steel perforated plate, and the 304 stainless steel screen are stacked sequentially and placed in a vacuum hot press. A vacuum is drawn, and the temperature of the upper and lower molds is set to 90℃ and the pressure to 14kgf / cm². 2 The constant temperature time is 5 minutes, and the constant pressure time is 5 minutes. After hot pressing, the film is opened when it is naturally cooled to 40°C. The perforated plate and screen are peeled off to obtain a 70mm×70mm (length×width) TPAE film with a mushroom-shaped array microstructure on the surface. This film is then cut into three identical 23mm×70mm (width×length) rectangular films for subsequent spraying. The perforated plate consists of a rectangular plate with dimensions of 70mm×70mm×0.1mm (length×width×thickness). The rectangular plate has several circular through holes arranged in an array structure. The through hole diameter is 0.2mm and the hole spacing is 0.2mm. The screen has a mesh size of 2000. (3) Surface-active treatment of TPAE film The TPAE film obtained in step (2) was placed in a plasma processor for treatment. The gas used was O2, the treatment time was 60s, and the radio frequency power was 75W. (4) Applying a conductive layer to the surface of the TPAE film. A monolayer MXene / water dispersion with a concentration of 4 mg / mL was prepared by conventional LiF / HCl in-situ etching. 5 mL of MXene / water dispersion and 5 mL of anhydrous ethanol were placed in the same beaker and mixed. The mixture was ultrasonically dispersed for 10 min to obtain 10 mL of MXene dispersion. The dispersion was then sprayed (spraying pressure 0.5 MPa, spraying distance 5 cm) onto the 23 mm × 70 mm TPAE film obtained in step (3) to obtain the target product.

[0030] Example 2 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a mushroom-shaped array microstructure on the surface differs from Example 1 in that: in step (4), 10 mL of MXene / water dispersion and 10 mL of anhydrous ethanol are placed in a beaker, ultrasonically dispersed for 10 min to obtain 20 mL of MXene dispersion, and then sprayed to obtain the target product.

[0031] Example 3

[0032] A method for preparing a TPAE / MXene electromagnetic shielding composite film with a mushroom-shaped array microstructure on the surface differs from Example 1 in that: in step (4), 15 mL of MXene / water dispersion and 15 mL of anhydrous ethanol are placed in a beaker, ultrasonically dispersed for 10 min to obtain 30 mL of MXene dispersion, and the target product is obtained after spraying.

[0033] Example 4 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a mushroom-shaped array microstructure on the surface differs from Example 1 in that: in step (4), 30 mL of MXene / water dispersion and 30 mL of anhydrous ethanol are placed in a beaker, ultrasonically dispersed for 10 min to obtain 60 mL of MXene dispersion, and the target product is obtained after spraying.

[0034] Comparative Example 1 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a triangular pyramidal array microstructure on its surface, the preparation process is as follows: (1) Same as step (1) in Example 2; (2) Constructing a triangular pyramidal array microstructure on the surface of a TPAE thin film (2.1) Use an infrared laser marking machine to print a triangular pyramid groove array template on a 32mm×32mm (length×width) stainless steel plate: (2.1.1) Draw closed equilateral triangles with a side length of 0.2mm; (2.1.2) Open the fill window, select the loop fill, set the laser line spacing to 0.01mm, the laser power to 20W, the laser frequency to 20kHz, the number of fill layers to 6, and set the parameters for each layer as follows: the side length of the first layer triangle is 0.2mm, the number of processing times is 10, and the laser speed is 2500mm / s; the side length of the second layer triangle is 0.1654mm, the number of processing times is 10, and the laser speed is 2500mm / s. Number 10, laser speed 2500mm / s; third layer triangle side length is 0.1307mm, processing times 10, laser speed 2500mm / s; fourth layer triangle side length is 0.0961mm, processing times 15, laser speed 3000mm / s; fifth layer triangle side length is 0.0614mm, processing times 15, laser speed 3000mm / s; sixth layer triangle side length is 0.0268mm, processing times 15, laser speed 3000mm / s; (2.1.3) Select a single triangle with fill to generate an array; (2.1.4) Start laser printing; (2.2) After cleaning and drying the stainless steel plate laser-cut in step (2.1), the TPAE film obtained in step (1) is stacked on top of the stainless steel plate from bottom to top, with the grooved surface of the stainless steel plate in contact with the TPAE film. The plate is then placed in a vacuum hot press, a vacuum is drawn, and the upper and lower mold temperatures are set to 90℃ and the pressure to 14kgf / cm². 2 The constant temperature time is 5 minutes and the constant pressure time is 5 minutes. After hot pressing, the mold is opened when it is naturally cooled to 40°C, and the stainless steel plate is peeled off to obtain a TPAE film with a triangular pyramid array microstructure on the surface. (3) Same as step (3) in Example 2; (4) Same as step (4) in Example 2.

[0035] Comparative Example 2 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a square pyramidal array microstructure on its surface, the preparation process is as follows: (1) Same as step (1) in Example 2; (2) Constructing a pyramidal array microstructure on the surface of a TPAE thin film (2.1) Use an infrared laser marking machine to print a quadrangular pyramidal groove array template on a 32mm×32mm (length×width) stainless steel plate: (2.1.1) Draw a closed square with a side length of 0.2mm; (2.1.2) Open the fill window, select the loop fill, set the laser line spacing to 0.01mm, the laser power to 20W, the laser frequency to 20kHz, the number of fill layers to 6, and set the parameters for each layer as follows: the side length of the first layer square is 0.2mm, the number of processing times is 10, and the laser speed is 2500mm / s; the side length of the second layer square is 0.1654mm, and the number of processing times is 10. 10, laser speed 2500mm / s; the third layer square has a side length of 0.1307mm, 10 processing times, laser speed 2500mm / s; the fourth layer square has a side length of 0.0961mm, 15 processing times, laser speed 3000mm / s; the fifth layer square has a side length of 0.0614mm, 15 processing times, laser speed 3000mm / s; the sixth layer square has a side length of 0.0268mm, 15 processing times, laser speed 3000mm / s; (2.1.3), select a single square with fill to generate an array; (2.1.4), start laser printing; (2.2) After cleaning and drying the stainless steel plate laser-cut in step (2.1), the TPAE film obtained in step (1) is stacked on top of the stainless steel plate from bottom to top, with the grooved surface of the stainless steel plate in contact with the TPAE film. The plate is then placed in a vacuum hot press, a vacuum is drawn, and the upper and lower mold temperatures are set to 90℃ and the pressure to 14kgf / cm². 2 The constant temperature time is 5 minutes and the constant pressure time is 5 minutes. After hot pressing, the mold is opened when it is naturally cooled to 40°C, and the stainless steel plate is peeled off to obtain a TPAE film with a four-sided pyramidal array microstructure on the surface. (3) Same as step (3) in Example 2; (4) Same as step (4) in Example 2.

[0036] Comparative Example 3 A method for preparing a TPAE / MXene electromagnetic shielding composite film with a cylindrical array microstructure on the surface. The method differs from that in Example 2 in that: in step (2), the sieve is not stacked, that is, the TPAE film and the perforated plate are stacked from bottom to top and placed in a vacuum hot press for hot pressing.

[0037] Comparative Example 4 A method for preparing a smooth TPAE / MXene electromagnetic shielding composite film, the preparation method differs from that in Example 2 in that step (2) is omitted, that is, the TPAE film obtained in step (1) is directly subjected to steps (3) and (4).

[0038] Characterization results The morphology of the electromagnetic shielding composite film was characterized using a scanning electron microscope; the electromagnetic shielding performance of the electromagnetic shielding composite film was characterized using a vector network analyzer; and the electroheating and infrared stealth performance of the electromagnetic shielding composite film were characterized using an infrared camera.

[0039] (a) Structural characterization Figure 1 The following are SEM images of the composite film obtained in Example 1: (a) is a longitudinal section SEM image, (b) is a top view SEM image, and (c) is a magnified view of (a). It can be seen that a mushroom-shaped array microstructure was successfully constructed on the surface of the TPAE film using a vacuum hot press. The pattern is neatly arranged and complete. After spraying MXene, a uniform layer of MXene nanosheets is deposited on the surface of the mushroom-shaped array microstructure, forming a conductive network through mutual contact.

[0040] Figure 2 SEM images of the composite films obtained in Examples 1-4 are shown: (a) Example 1, (b) Example 2, (c) Example 3, and (d) Example 4. It can be seen that the thickness of the MXene layer deposited on the TPAE film surface increases with the increase in the volume of MXene dispersion liquid. After multiple measurements and averaging, the MXene layer thicknesses of the composite films obtained in Examples 1-4 are 0.6 μm, 1.6 μm, 2.3 μm, and 4.0 μm, respectively.

[0041] Figure 3 The following are SEM images of the composite film obtained in Comparative Example 1: (a) is a top-view SEM image, (b) is a magnified view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image. It can be seen that a triangular pyramidal array microstructure is formed on the surface of the TPAE film, with uniform height and size. After spraying the surface with the same volume of MXene dispersion as in Example 2, and taking the average of multiple measurements, the thickness of the MXene layer on the surface is comparable to that in Example 2, at 1.75 μm.

[0042] Figure 4 The following are SEM images of the composite film obtained in Comparative Example 2: (a) is a top-view SEM image, (b) is a magnified view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image. It can be seen that a quadrangular pyramidal array microstructure is formed on the TPAE surface, with uniform height and size. After spraying the surface with the same volume of MXene dispersion as in Example 2, and taking the average of multiple measurements, the thickness of the MXene layer on the surface is comparable to that in Example 2, at 1.9 μm.

[0043] Figure 5The following are SEM images of the composite film obtained in Comparative Example 3: (a) is a top-view SEM image, (b) is a magnified view of (a), (c) is one of the longitudinal section SEM images, and (d) is another longitudinal section SEM image. It can be seen that TPAE enters the pores of the perforated plate at high temperature, forming a cylindrical array microstructure with uniform height and size. After spraying the surface with the same volume of MXene dispersion as in Example 2, multiple measurements were taken and the average value was calculated. It can be seen that the thickness of the surface MXene layer is comparable to that in Example 2, with an MXene layer thickness of 1.6 μm.

[0044] (ii) Performance Characterization (2.1) Electromagnetic shielding performance Figure 6 The electromagnetic shielding performance curves (a) of the composite films obtained in Examples 1-4 in the X-band and the corresponding SE values ​​are shown. A SE R SE T The value statistics are shown in Figure (b). It can be seen that as the volume of MXene dispersion increases, the electromagnetic shielding performance of the composite film increases, from 18.7 dB at 10 mL to 45.28 dB at 60 mL. This indicates that as the thickness of the surface MXene layer increases, the conductivity of the film improves, forming a more complete conductive network, thereby achieving an increased electromagnetic shielding effect.

[0045] Figure 7 The chart shows the statistical values ​​of R, T, and A for the composite films obtained in Examples 1-4. It can be seen that the R value of all composite films is close to 1, indicating that their electromagnetic shielding mainly relies on the reflection effect. The mushroom-shaped array microstructure constructed on the TPAE substrate significantly increases the effective specific surface area of ​​the film, introducing abundant scattering interfaces and providing multiple reflection and scattering sites for electromagnetic waves. Incident electromagnetic waves can undergo multiple reflections and scatterings between and within the mushroom-shaped microstructure units, extending the transmission path of electromagnetic waves within the material and enhancing the electromagnetic attenuation effect, thereby achieving efficient electromagnetic shielding. Furthermore, the unique layered stacking structure of MXene material itself provides a structural basis for multiple reflections of electromagnetic waves on the surface and between layers of MXene sheets, causing repeated reflection losses at the interlayer interfaces. Therefore, as the thickness of the composite film increases, the reflection effect of the layered structure on electromagnetic waves is further enhanced, macroscopically manifested as a gradual increase in the reflection coefficient R with increasing thickness.

[0046] Figure 8 The electromagnetic shielding performance curves (a) of the composite films obtained in Example 2 and Comparative Examples 1-4 in the X-band and the corresponding SE values ​​are shown. A SE R SE TValue statistics (b). It can be seen that compared to the planar composite film (Comparative Example 4), the shielding performance of all samples with microstructures is improved. The triangular pyramid, square pyramid, cylindrical, and mushroom-shaped array microstructures show improvements of 108.4%, 115.6%, 131.8%, and 143.1%, respectively. At the same MXene layer thickness, the composite film with the mushroom-shaped array microstructure on the surface exhibits a higher SE. T This is because: surface microstructures introduce more interfaces and multiple reflection paths within the material, extending the propagation distance of electromagnetic waves and giving them more opportunities to be absorbed and converted; the more complex the pattern, the greater the effective specific surface area, and the more interfaces and reflection paths, the more it helps improve the material's shielding performance.

[0047] Figure 9 The chart shows the statistical values ​​of R, T, and A for the composite films obtained in Example 2 and Comparative Examples 1-4. It can be seen that the more complex the microstructure of the sample surface, the closer the reflectance coefficient R is to 1.

[0048] (2.2) Photothermal conversion performance The composite film obtained in Example 3 was cut into 23mm × 23mm square samples and placed on an insulating substrate to reduce heat loss due to lateral heat conduction. A xenon lamp was used to vertically irradiate the sample surface to simulate sunlight, and an infrared camera was used to measure and record the temperature change of the sample surface. Different light intensities (50mW / cm²) were achieved by adjusting the xenon lamp output power. 2 100mW / cm 2 150mW / cm 2 200mW / cm 2 Regulation of ). Figure 10 The results show the photothermal conversion performance of the composite film obtained in Example 3. The test results indicate that the steady-state surface temperature of the composite film increases significantly with increasing light intensity, reaching 200 mW / cm². 2 Under irradiation conditions, the steady-state temperature of the film can reach 64℃, which fully demonstrates that the composite film has excellent photothermal response characteristics and energy conversion capabilities.

[0049] (2.3) Infrared stealth performance like Figure 11 As shown in (a), the composite film obtained in Example 3 was cut into several samples and placed on a hot stage. The surface temperature of the samples was recorded using an infrared camera. By changing the set temperature of the hot stage (50°C, 100°C, 150°C), the temperature change of the sample surface as fed back by the infrared camera under different set temperatures of the hot stage was investigated. The results are as follows. Figure 11As shown in (b), it can be seen that: (i) at the three set temperatures of the hot stage, the surface temperature of the composite film sample obtained in Example 3 reached a steady state at approximately 300 s; (ii) as the set temperature of the hot stage increased, the surface temperature of the composite film gradually increased, but remained far below the set temperature of the hot stage, indicating that it has good infrared stealth capability. To further observe the infrared stealth performance directly, the composite film sample obtained in Example 3 was placed on the surface of a model (an aircraft model at 46.5°C and a human hand at 34.5°C) at a certain temperature in an air environment. After 300 s, the model temperature, sample temperature, and background temperature (air temperature around the model) were measured and recorded using an infrared camera. The results are as follows: Figure 11 As shown in (c), it can be seen that the temperature of the sample surface is close to the background temperature (28.0℃ and 26.9℃ respectively in the figure), which intuitively proves its excellent infrared stealth performance.

Claims

1. An electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface, characterized in that: It includes a polymer substrate film, on the surface of which a mushroom-shaped array of microstructure layers and a conductive layer are sequentially constructed from bottom to top; the polymer substrate is a thermoplastic polymer substrate.

2. The electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 1, characterized in that: The thermoplastic polymer substrate is TPAE, TPU, PP, PA, PVA or PE; the conductive layer is one or more of MXene, AgNWs, and CNTs.

3. A method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 1 or 2, characterized in that, Includes the following steps: (1) After cleaning and drying the polymer raw materials, hot pressing is used to prepare a polymer substrate film; (2) Constructing a mushroom-shaped array microstructure layer on the surface of the polymer substrate film obtained in step (1): From bottom to top, the polymer substrate film, perforated plate and screen obtained in step (1) are stacked in sequence, hot-pressed, and then the screen and perforated plate are peeled off to obtain a polymer substrate film with a mushroom-shaped array microstructure layer on the surface; the material of the perforated plate and screen must ensure that its temperature and pressure resistance is compatible with the hot pressing in this step; (3) Perform surface-active treatment on the polymer substrate film obtained in step (2); (4) Spray the conductive filler dispersion corresponding to the conductive layer onto the surface of the polymer substrate film obtained in step (3) to obtain the target product.

4. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 3, characterized in that: In step (2), the perforated plate includes a rectangular plate with a plurality of through holes arranged in an array structure; wherein the thickness of the rectangular plate is less than the thickness of the polymer substrate film obtained in step (1).

5. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 4, characterized in that: The through hole is circular with a diameter of 0.1~0.3mm and a hole spacing of 0.1~0.3mm; the thickness of the rectangular plate is less than the thickness of the polymer substrate film obtained in step (1) by 0.3~0.6mm.

6. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 4, characterized in that: In step (2), the mesh size of the sieve is 1000~2000 mesh.

7. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 3, characterized in that: In step (2), a vacuum hot press is used for hot pressing. The parameters of the vacuum hot press are: the temperature of the upper mold and the temperature of the lower mold are both 50~150℃, and the pressure is 5~30kgf / cm. 2 The heat preservation time is 3~10min, the pressure holding time is 3~10min, and the mold opening temperature is room temperature~80℃.

8. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 3, characterized in that: In step (1), after cleaning and drying the polymer raw materials, they are uniformly filled into the mold frame and then hot-pressed using a vacuum hot press to prepare a polymer substrate film. The material of the mold frame must ensure its temperature and pressure resistance is compatible with the hot pressing process described in this step, and the thickness of the mold frame must be compatible with the thickness of the polymer substrate film to be prepared. The parameters of the vacuum hot press are: upper mold temperature and lower mold temperature both 50~150℃, and pressure 5~30 kgf / cm². 2 The heat preservation time is 3~10min, the pressure holding time is 3~10min, and the mold opening temperature is room temperature~80℃.

9. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 3, characterized in that: In step (3), a plasma instrument is used for surface activity treatment. The gas used is oxygen, the treatment time is 30~80s, and the radio frequency power is 45~120W.

10. The method for preparing an electromagnetic shielding composite film with a mushroom-shaped array microstructure on its surface as described in claim 3, characterized in that: In step (4), the conductive filler dispersion corresponding to the conductive layer is sprayed onto the surface of the polymer substrate film, every 16 cm. 2 10-60 mL of conductive filler dispersion is sprayed onto the surface of a polymer substrate film at a spraying pressure of 0.3-0.6 MPa and a spraying distance of 3-10 cm. The solvent of the conductive filler dispersion is water, anhydrous ethanol, or a mixture of the two, and the concentration of the conductive filler dispersion is 0.75-2 mg / mL.

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