A multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste and its preparation method

Abstract

This invention relates to the field of electromagnetic functional materials, specifically disclosing a multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste and its preparation method. From bottom to top, it comprises: a flexible substrate layer, a micron-sized sheet aluminum electromagnetic shielding coating, and an environmental protection layer. The flexible substrate layer is a polymer-based composite film reinforced with ultra-high molecular weight polymer fibers. The micron-sized sheet aluminum electromagnetic shielding coating is a highly oriented coating obtained by scraping micron-sized sheet aluminum paste. The environmental protection layer is an acrylic polyvinylidene fluoride organic polymer coating. The micron-sized sheet is obtained using an improved wet ball milling process, significantly reducing the process flow. The micron-sized sheet aluminum coating achieves a highly oriented arrangement of micron-sized sheet aluminum through a scraping method using transverse shear force, improving electromagnetic shielding effectiveness. This invention, through its multilayer structure design, enables the electromagnetic shielding film to possess advantages such as strong electromagnetic shielding effectiveness, flexibility, low cost, and environmental resistance, demonstrating significant engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional materials, and specifically relates to a multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste and its preparation method. Background Technology

[0002] Electromagnetic shielding materials are an important class of electromagnetic functional materials, widely used in electronic devices, electromagnetic radiation protection, radar stealth, and other fields. They provide highly efficient reflection and shielding against external electromagnetic waves, thereby achieving electromagnetic protection for internal electronic components, personnel, and critical equipment. Existing electromagnetic shielding materials are mostly metal films and metal meshes, which suffer from key drawbacks such as susceptibility to rust in humid environments, corrosion in acidic and alkaline environments, and high density and weight, posing numerous challenges to practical applications.

[0003] Currently, electromagnetic shielding composite materials have been developed. These materials involve coating a substrate with a metallic coating, which uses metal powders such as platinum, silver, and copper, along with conductive fillers like carbon nanotubes or graphene, mixed with a polymer matrix to create a conductive coating. This coating is then sprayed onto the surface of the component requiring electromagnetic protection to achieve the shielding effect. However, platinum, silver, carbon nanotubes, and graphene are expensive. Commonly used spherical and tubular conductive fillers have small specific surface areas, making it difficult to achieve good overlap. They also have high conductivity and permeation thresholds (requiring higher filler concentrations to achieve significant conductivity), resulting in large filler usage, poor coating mechanical properties, and high coating costs. Sheet-like microstructured metallic conductive fillers offer significant advantages in terms of large specific surface area and large lateral dimensions, effectively solving the above problems. However, common sheet-like silver... Precious metals such as silver-coated sheet materials are costly and have complex preparation processes. The ball milling process, in particular, involves multiple steps including ball milling, pressure filtration, dispersion, washing, re-pressure filtration, and drying to obtain micron-sized sheet powder suitable for coating preparation. This process is lengthy and inefficient. Furthermore, traditional powder conductive phase / resin matrix conductive coatings are applied by spraying, which makes it difficult to ensure uniform coating thickness. The random arrangement of the micron-sized sheet conductive fillers also fails to fully utilize their high in-plane conductivity, thus affecting the shielding effect. Current research reports on applying a movable strong magnetic field to achieve consistent in-plane orientation, but this method is only suitable for fillers containing magnetic materials. Therefore, there is an urgent need for innovative coating application methods to achieve in-plane orientation and good conductive overlap of the sheet conductive fillers. Thus, there is a pressing need for innovative methods to prepare low-cost metal sheet-like microstructure conductive coatings. Based on low-cost metal materials, this involves simplifying the ball milling process, improving the conductive coating preparation method, and optimizing the coating structure to achieve low cost, lightweight, and improved overall environmental resistance of electromagnetic shielding coating materials. Summary of the Invention

[0004] To address the above shortcomings, this invention provides a multi-layer electromagnetic shielding film material based on micron-sized sheet aluminum paste, which has advantages such as lightweight, good environmental resistance, and excellent electromagnetic shielding performance. It solves the problems of existing electromagnetic shielding materials being prone to rusting and corrosion, having high density, and being costly. The specific technical solution is as follows:

[0005] A multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste comprises, from bottom to top: a flexible substrate layer, a micron-sized sheet aluminum electromagnetic shielding coating, and an environmental protection layer. The flexible substrate layer is an ultra-high molecular weight polymer fiber reinforced polymer matrix composite film; the micron-sized sheet aluminum electromagnetic shielding coating is a highly oriented micron-sized sheet aluminum coating prepared by scraping micron-sized sheet aluminum paste; and the environmental protection layer is an acrylic polyvinylidene fluoride organic polymer coating.

[0006] This invention relates to a multi-layer electromagnetic shielding membrane based on micron-sized sheet aluminum paste. The flexible substrate layer is an ultra-high molecular weight polymer fiber-reinforced polymer matrix composite film, which enhances the membrane's tensile and other mechanical load-bearing capacity. The highly oriented micron-sized sheet aluminum coating has a strong ability to reflect and shield electromagnetic waves. An acrylic polyvinylidene fluoride organic polymer coating is set on the surface of the electromagnetic shielding layer, which can protect the micron-sized sheet aluminum electromagnetic shielding coating and enhance the environmental aging resistance of the multi-layer electromagnetic shielding membrane. Through the multi-layer structure design, this invention enables the electromagnetic shielding membrane to have advantages such as strong electromagnetic shielding effectiveness, flexibility, and low cost.

[0007] Preferably, in the above-mentioned multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste, the flexible substrate layer is a thin film of ultra-high molecular weight polyethylene fiber or aramid fiber reinforced polyethylene composite material with a thickness of 0.2~1mm.

[0008] Preferably, in the above-mentioned multi-layer electromagnetic shielding film material based on micron-sized sheet aluminum paste, the micron-sized sheet aluminum electromagnetic shielding coating has a sheet aluminum particle size of 5~20μm and a shape of one or more of the following: round, disc-shaped, or maple leaf-shaped. The sheet aluminum powder is highly oriented along the in-plane direction of the substrate by means of transverse shear force through a scraping method, and the coating thickness is 5~50μm.

[0009] Preferably, in the above-mentioned multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste, the thickness of the environmental protection layer is 5~20μm.

[0010] On the other hand, the present invention also provides a method for preparing the above-mentioned multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste, comprising the following steps:

[0011] (1) Preparation of flake aluminum powder: Micron-sized flake aluminum powder was prepared by wet ball milling. Micron-sized aluminum powder was used as raw material, and ball milling aid and ball milling beads were added together for ball milling to obtain an aqueous dispersant of flake aluminum particles. After ball milling, micron-sized flake aluminum powder was obtained by pressure filtration and drying.

[0012] (2) Preparation of micron-sized sheet aluminum paste: Add the micron-sized sheet aluminum powder prepared in step (1) into the polymer dispersion matrix and stir continuously until the micron-sized sheet aluminum powder is uniformly dispersed in the polymer resin matrix to obtain micron-sized sheet aluminum paste.

[0013] (3) Preparation of micron-sized aluminum electromagnetic shielding coating: The highly oriented micron-sized aluminum coating is prepared by scraping method. The micron-sized aluminum paste prepared in step (2) is used as the coating raw material. The micron-sized aluminum paste is scraped onto the surface of the flexible substrate layer by scraping method and then heated and cured to obtain the highly oriented micron-sized aluminum coating, which is the micron-sized aluminum electromagnetic shielding coating.

[0014] (4) Preparation of environmental protection layer: On the surface of the micron sheet aluminum electromagnetic shielding coating obtained in step (3), an acrylic polyvinylidene fluoride coating is uniformly sprayed and heated to cure, so as to obtain a multi-layer electromagnetic shielding film material based on micron sheet aluminum paste.

[0015] Preferably, in the above preparation method, in step (1), the particle size of the micron-sized aluminum powder is 2~20μm.

[0016] Preferably, in the above preparation method, in step (1), the ball milling aid is one or both of n-propanol and propylene glycol, and the ratio of micron-sized aluminum powder to ball milling aid is 1g:1~2mL; the ball milling parameters are: ball-to-material ratio 10~20:1, ball milling speed 300~500rpm, and ball milling time 24~48h. The selected ball milling aid is an aqueous aid, which can reduce the adhesion between the ball milling beads and the micron-sized aluminum particles during the ball milling process and improve the ball milling efficiency. At the same time, the ball milling aid used can also be used as an aqueous dispersant for ball milling, so that good dispersion and surface washing can be achieved simultaneously after ball milling.

[0017] Preferably, in the above preparation method, in step (2), the polymer matrix is ​​one or more of polyurethane, polyimide, polyvinyl alcohol, and epoxy resin, and the mass ratio of micron-sized sheet aluminum powder to polymer matrix is ​​2:8 to 4:6.

[0018] Preferably, in the above preparation method, in step (3), the curing temperature after scraping is 60~90℃ and the curing time is 2~6h.

[0019] Preferably, in the above preparation method, in step (4), the acrylic polyvinylidene fluoride weather-resistant layer is sprayed by a spray gun, and the curing temperature in the drying oven is 60~80℃, and the time is 3~6h.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. In the multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste of the present invention, the flexible substrate layer can enhance the tensile and other mechanical load bearing capacity of the film material, the highly oriented micron-sized sheet aluminum coating has a strong ability to reflect and shield electromagnetic waves, and the acrylic polyvinylidene fluoride organic polymer coating is set on the surface of the electromagnetic shielding layer to protect the micron-sized sheet aluminum electromagnetic shielding coating and enhance the environmental aging resistance of the multilayer electromagnetic shielding film material. Through the multilayer structure design, the present invention enables the electromagnetic shielding film material to have the advantages of strong electromagnetic shielding effectiveness, flexibility, low cost, and environmental resistance, and has good engineering application value.

[0022] 2. In the preparation method of the multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste of the present invention, the micron-sized sheets are obtained by an improved wet ball milling process, and an improved water-based ball milling / dispersing agent is used, which significantly reduces the process flow. The micron-sized sheet aluminum coating process utilizes transverse shear force to achieve a high orientation arrangement of micron-sized sheet aluminum, thereby improving electromagnetic shielding effectiveness. The preparation process is simple, does not involve special equipment, and has low preparation cost.

[0023] 3. This invention selects low-cost, oxidation-resistant aluminum as the metallic conductive filler. By improving the ball milling process and combining the ball milling and dispersion washing processes, the preparation process of micron-sized sheet aluminum is significantly reduced, improving preparation efficiency. An innovative scraping coating method is used to achieve highly oriented arrangement and conductive overlap of micron-sized sheet aluminum, enhancing the electromagnetic shielding capability of the coating while reducing the required metal layer thickness compared to the shielding film obtained by aluminum foil coating. A multi-layer structure with a flexible substrate and an environmental protection layer is designed to improve the flexibility and environmental resistance of the coating, achieving a comprehensive improvement in the flexibility, low cost, lightweight, and environmental resistance of the electromagnetic shielding material. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is an exploded structural diagram of the multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste according to the present invention.

[0026] Figure 2 These are scanning electron microscope images of the highly oriented micron-sized sheet-like aluminum coating prepared in Example 1 of this invention;

[0027] Figure 3 This is a photograph of the multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste prepared in Example 1 of this invention;

[0028] Figure 4 These are the electromagnetic shielding performance test results of the multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste prepared in Example 1 of this invention;

[0029] Figure 5 These are the electromagnetic shielding performance test results of the multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste prepared in Example 2 of this invention;

[0030] Legend: 1- Flexible substrate layer, 2- Micron-sized sheet aluminum electromagnetic shielding coating, 3- Environmental protection layer. Detailed Implementation

[0031] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0032] Example 1

[0033] A multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste, such as Figure 1 As shown, from bottom to top, it includes: a flexible substrate layer 1, a micron-sized sheet aluminum electromagnetic shielding coating 2, and an environmental protection layer 3. The flexible substrate layer is a thin film of ultra-high molecular weight polyethylene fiber reinforced polyethylene composite material with a thickness of 0.2 mm; the micron-sized sheet aluminum electromagnetic shielding coating is a highly oriented micron-sized sheet aluminum coating prepared by scraping micron-sized sheet aluminum slurry with a thickness of 5 μm; and the environmental protection layer is an acrylic polyvinylidene fluoride organic polymer coating with a thickness of 5 μm.

[0034] A method for preparing a multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste includes the following steps:

[0035] (1) Preparation of flake aluminum powder: Aluminum powder with an average particle size of 2 μm was used as raw material and ball milled together with n-propanol. The ratio of aluminum powder to n-propanol was 1g:1.5mL. The ball milling parameters were: ball-to-material ratio of 15:1, ball milling speed of 450rpm, and ball milling time of 36h. The ball milling mixture was then poured out, filtered by pressure, and dried at 80℃ to obtain micron-sized flake aluminum powder.

[0036] (2) Preparation of micron-sized sheet aluminum paste: The micron-sized sheet aluminum powder prepared in step (1) is added to an aqueous polyurethane solution (manufacturer: McLean, model: W909579). The mass ratio of micron-sized sheet aluminum powder to polyurethane is 4:6. The mixture is stirred slowly and continuously until the micron-sized sheet aluminum powder is uniformly dispersed in the polymer resin matrix to obtain micron-sized sheet aluminum paste.

[0037] (3) Preparation of highly oriented micron-scale aluminum coating: Using ultra-high molecular weight polyethylene fiber reinforced polyethylene composite film as substrate, and micron-scale aluminum paste prepared in step (2) as coating material, the coating is applied by scraping along the direction of the substrate film using a scraper, and then dried and cured. The drying and curing temperature is 80℃ and the curing time is 4h to obtain a highly oriented micron-scale aluminum coating.

[0038] (4) Preparation of environmental protection layer: On one side of the film obtained in step (2) with the highly oriented micron-sized sheet aluminum shielding coating, an acrylic polyvinylidene fluoride coating is uniformly sprayed, and finally transferred to an oven for heating and curing. The curing temperature is 70℃ and the time is 4h, to obtain a multilayer electromagnetic shielding film material based on micron-sized sheet aluminum paste (see photo of the film material). Figure 3 ).

[0039] The scanning electron microscope image of the highly oriented micron-sized sheet-like aluminum coating prepared in this embodiment is shown below. Figure 2 As shown in the figure, the micron-sized aluminum flakes in the coating are uniformly oriented. The electromagnetic shielding performance of the multilayer electromagnetic shielding film of this invention was tested using the focusing lens test method. The test results are shown in [Figure number missing]. Figure 4 As shown in the figure, the multi-layer electromagnetic shielding film of this embodiment has a transmittance of less than -40dB in the 4~18GHz frequency band, and has excellent electromagnetic shielding performance.

[0040] Example 2

[0041] A multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste, such as Figure 1As shown, from bottom to top, it includes: a flexible substrate layer 1, a micron-sized sheet aluminum electromagnetic shielding coating 2, and an environmental protection layer 3. The flexible substrate layer is an ultra-high molecular weight aramid fiber reinforced polyethylene composite film with a thickness of 1 mm; the micron-sized sheet aluminum electromagnetic shielding coating is a highly oriented micron-sized sheet aluminum coating prepared by scraping micron-sized sheet aluminum paste with a thickness of 5 μm; and the environmental protection layer is an acrylic polyvinylidene fluoride organic polymer coating with a thickness of 20 μm.

[0042] A method for preparing a multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste includes the following steps:

[0043] (1) Preparation of flake aluminum powder: Aluminum powder with an average particle size of 5 μm was used as raw material and mixed with propylene glycol ball milling / dispersing agent and added to a ball mill for ball milling. The ratio of aluminum powder to n-propanol was 1 g: 1.5 mL. The ball milling parameters were: ball-to-material ratio of 15:1, ball milling speed of 450 rpm, and ball milling time of 36 h. The ball milled mixture was then poured out, filtered by pressure, and dried at 80 °C to obtain micron-sized flake aluminum powder.

[0044] (2) Preparation of micron-sized sheet aluminum paste: Add the micron-sized sheet aluminum powder prepared in step (1) to a polyvinyl alcohol aqueous solution. The mass ratio of the micron-sized sheet aluminum powder to polyvinyl alcohol is 2:8. Stir slowly and continuously until the micron-sized sheet aluminum powder is uniformly dispersed in the polymer resin matrix to obtain micron-sized sheet aluminum paste.

[0045] (3) Preparation of highly oriented micron-sized sheet aluminum coating: Using ultra-high molecular weight aramid fiber reinforced polyethylene composite film as substrate, and micron-sized sheet aluminum paste prepared in step (2) as coating material, the coating is applied by scraping along the direction of the substrate film using a scraper, and then dried and cured. The drying and curing temperature is 80℃ and the curing time is 4h to obtain a highly oriented micron-sized sheet aluminum coating.

[0046] (4) Preparation of environmental protection layer: On one side of the film obtained in step (2) with a highly oriented micron-sized sheet aluminum shielding coating, an acrylic polyvinylidene fluoride coating is uniformly sprayed, and finally transferred to an oven for heating and curing. The curing temperature is 70°C and the time is 4 hours to obtain a multi-layer electromagnetic shielding film material based on micron-sized sheet aluminum paste.

[0047] The electromagnetic shielding performance of the multilayer electromagnetic shielding film prepared in this example was tested using the focusing lens test method. The test results are shown in [Figure number missing]. Figure 5 Within the 4~18GHz frequency band, the electromagnetic wave transmittance is generally below -41dB, and the electromagnetic wave energy shielding efficiency is greater than 99.99%, demonstrating excellent electromagnetic shielding performance.

[0048] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste, characterized in that, From bottom to top, the structure comprises: a flexible substrate layer, a micron-sized sheet aluminum electromagnetic shielding coating, and an environmental protection layer. The flexible substrate layer is an ultra-high molecular weight polymer fiber-reinforced polymer matrix composite film with a thickness of 0.2–1 mm. The micron-sized sheet aluminum electromagnetic shielding coating is a highly oriented micron-sized sheet aluminum coating prepared by scraping micron-sized sheet aluminum slurry. The sheet aluminum particle size is 5–20 μm, the coating thickness is 5–50 μm, and the sheet aluminum powder is highly oriented along the in-plane direction of the substrate. The environmental protection layer is composed of acrylic acid. Acrylic acid polyvinylidene fluoride organic polymer coating; the flake aluminum powder is prepared by wet ball milling. Micron-sized aluminum powder is used as raw material, and ball milling is carried out together with ball milling aid and ball milling beads. The ball milling aid is one or two of n-propanol and propylene glycol. The ratio of micron-sized aluminum powder to ball milling aid is 1g:1~2mL. Good dispersion and surface washing are achieved simultaneously after ball milling to obtain an aqueous dispersant of flake aluminum particles. After ball milling, micron-sized flake aluminum powder is obtained by pressure filtration and drying.

2. The multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste according to claim 1, characterized in that, The flexible substrate layer is a thin film of polyethylene composite material reinforced with ultra-high molecular weight polyethylene fiber or aramid fiber.

3. The multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste according to claim 1, characterized in that, The micron-sized sheet-like aluminum electromagnetic shielding coating has one or more shapes, such as circular, disc-shaped, or maple leaf-shaped.

4. The multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste according to claim 1, characterized in that, The thickness of the environmental protection layer is 5~20μm.

5. A method for preparing a multilayer electromagnetic shielding film based on micron-sized sheet aluminum paste as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of micron-sized sheet aluminum paste: Micron-sized sheet aluminum powder is added to a polymer dispersion matrix and stirred continuously until the micron-sized sheet aluminum powder is uniformly dispersed in the polymer resin matrix to obtain micron-sized sheet aluminum paste. (2) Preparation of micron-sized aluminum electromagnetic shielding coating: The highly oriented micron-sized aluminum coating is prepared by scraping method. The micron-sized aluminum paste prepared in step (1) is used as the coating raw material. The micron-sized aluminum paste is scraped onto the surface of the flexible substrate layer by scraping method and then heated and cured to obtain the highly oriented micron-sized aluminum coating, which is the micron-sized aluminum electromagnetic shielding coating. (3) Preparation of environmental protection layer: On the surface of the micron sheet aluminum electromagnetic shielding coating obtained in step (2), an acrylic polyvinylidene fluoride coating is uniformly sprayed and heated to cure, so as to obtain a multi-layer electromagnetic shielding film material based on micron sheet aluminum paste.

6. The preparation method according to claim 5, characterized in that, In step (1), the polymer matrix is ​​one or more of polyurethane, polyimide, polyvinyl alcohol, and epoxy resin, and the mass ratio of micron-sized sheet aluminum powder to polymer matrix is ​​2:8 to 4:

6.

7. The preparation method according to claim 5, characterized in that, In step (2), the curing temperature after scraping is 60~90℃ and the curing time is 2~6h.

8. The preparation method according to claim 5, characterized in that, In step (3), the acrylic polyvinylidene fluoride weather-resistant layer is sprayed by a spray gun, and the curing temperature in the drying oven is 60~80℃ for 3~6h.

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