Electromagnetic shielding composite film with gradient structure and preparation method thereof

Abstract

This invention relates to the application of electromagnetic shielding composite materials, specifically to an electromagnetic shielding composite film with a gradient structure and its preparation method. Using a polymer film as the core layer, electromagnetic functional layers are sequentially deposited on both sides of the polymer core layer, and a carbon fiber felt is composited on at least one side, resulting in an electromagnetic shielding composite film with excellent electromagnetic shielding performance. The gradient multilayer structure design of this invention utilizes the principles of impedance mismatch at different interfaces and the skin effect to effectively improve the multiple reflections of electromagnetic waves between different functional layers. Furthermore, the type of polymer core layer can be changed according to different needs; using a polymer-based high-barrier film as the core layer can yield a high-barrier electromagnetic shielding packaging film that combines high barrier properties with high electromagnetic shielding.

Description

Technical Field

[0001] This invention relates to the application field of electromagnetic shielding composite materials, specifically to an electromagnetic shielding composite film with a gradient structure and its preparation method. Background Technology

[0002] Developing new, highly efficient, and multifunctional protective films is a core technology for ensuring the safety and reliability of advanced manufacturing equipment, electronic components, precision instruments, and strategic materials during manufacturing, transportation, storage, and use. Traditional packaging materials primarily function as physical barriers, protecting against moisture and corrosive gases. However, with the rapid development of the electronics industry, especially the complex environments in which precision electronic components are stored, transported, and sealed, electromagnetic fields generated in the surrounding environment can severely interfere with these components, even causing product failure and resulting in significant economic losses and incalculable consequences. In the military industry, with the rapid development of electromagnetic interference technology, particularly the high-frequency electromagnetic pulses generated by electromagnetic bombs in future warfare, which can severely damage military equipment and personnel combat effectiveness, the development of high-performance electromagnetic shielding materials is an urgent need and a future trend in the development of future weaponry and new materials.

[0003] Currently, most electromagnetic shielding packaging materials available both domestically and internationally are made of copper or aluminum foil and polymer film composites. The dense metal functional layer serves to reflect and shield electromagnetic waves. However, they generally suffer from key problems such as heavy weight, easy interlayer peeling, and easy folding that causes perforation, leading to a sharp decline in shielding performance. They are increasingly unable to meet the urgent technical needs of the rapidly developing military equipment and precision electronics industries for next-generation packaging materials that are lightweight, flexible, and have high-efficiency electromagnetic shielding.

[0004] Multilayer structures are typically composed of alternating layers of material, utilizing the multiple reflections between layers to promote polarization loss and thus achieve highly efficient electromagnetic wave shielding. The construction of multilayer structures facilitates the preparation of composite materials with multiple functions and also allows for the synergistic effect between different material layers. Gradient structures, on the other hand, are usually composed of materials with different electromagnetic properties or thicknesses, resulting in a gradually varying electromagnetic shielding effect. By using gradient structures to achieve the absorption-reflection-reabsorption process of electromagnetic waves, excellent electromagnetic shielding performance can be achieved with relatively low filler content. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic shielding composite film with a gradient structure and its preparation method. This method combines multilayer and gradient structures, constructing a "multilayer + isolation" gradient electromagnetic shielding network structure through a specific sequence, thereby endowing polymer materials with high shielding performance. Furthermore, this method is convenient to operate, highly customizable, and facilitates the construction of composite materials with multiple functions, providing a new approach for preparing highly efficient electromagnetic shielding composite materials with multifunctional properties.

[0006] To achieve the above technical objectives, the technical solution proposed by this invention is as follows:

[0007] An electromagnetic shielding composite film with a gradient structure includes a polymer core layer, electromagnetic functional layers deposited sequentially on both sides of the polymer core layer, and carbon fiber felt composited on at least one side.

[0008] The electromagnetic shielding composite film with a gradient structure has a polymer core layer material comprising: polyethylene film, polypropylene film, polyethylene terephthalate film, styrene-maleic anhydride copolymer, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, polybutylene terephthalate film, aluminized film, silicon-coated film, polyimide film, polyethylene naphthalate film, or a modified material based on the above polymer materials.

[0009] The electromagnetic shielding composite film with a gradient structure has an electromagnetic functional layer comprising: carbon black, carbon nanotubes, graphene, MXene, iron tetroxide, carbonyl iron, ultrafine metallic iron powder, nickel powder, conductive coating, conductive ink, conductive polymer magnetic coating, or one or more of aluminum plating, gold plating, silver plating, copper plating, zinc plating, and nickel plating.

[0010] The electromagnetic shielding composite film with a gradient structure has an adhesive layer between the electromagnetic functional layer and the carbon fiber felt.

[0011] The aforementioned electromagnetic shielding composite film with a gradient structure has a polyurethane adhesive layer as the adhesive layer, and a dry coating weight of 2–4 g / m³. 2 .

[0012] The electromagnetic shielding composite film with a gradient structure includes carbon fiber felt, which comprises: polyacrylonitrile-based carbon fiber felt, viscose-based carbon fiber felt, or pitch-based carbon fiber felt.

[0013] The electromagnetic shielding composite film with a gradient structure has a carbon fiber basis weight of 10-50 g / m² per unit area in the chopped carbon fiber felt. 2 .

[0014] The method for preparing the electromagnetic shielding composite film with a gradient structure includes the following steps:

[0015] (1) Depending on the type of polymer sandwich layer, different cleaning agents or plasma are used to clean the dust and oil stains on the surface of the film, and an electromagnetic functional layer is deposited on the surface of the polymer sandwich layer.

[0016] (2) Thoroughly stir the curing agent and main agent of the polyurethane adhesive. If the viscosity of the polyurethane adhesive is too high, add solvent to dilute it. Thoroughly stir during the preparation process. There should be no particulate matter. Let it stand for later use.

[0017] (3) Apply polyurethane adhesive to the electromagnetic functional layer using a dry composite coating machine. Under the premise of ensuring that the composite film will not be deformed by heat, use hot air to evaporate the solvent in the adhesive film.

[0018] (4) After the solvent in the adhesive film evaporates, attach the carbon fiber felt to the surface of the polyurethane adhesive and then place it in an oven at 40-60°C for 48 hours to cure.

[0019] The method for preparing the electromagnetic shielding composite film with a gradient structure involves depositing electromagnetic functional layers on both sides of a polymer sandwich layer, and bonding one or two electromagnetic functional layers to carbon fiber felt using polyurethane adhesive. Alternatively, electromagnetic functional layers are deposited on one side of each of the two polymer sandwich layers, and the other sides of the two polymer sandwich layers are bonded to carbon fiber felt using polyurethane adhesive.

[0020] The design concept of this invention is:

[0021] Utilizing the principle of electromagnetic wave reflection and absorption on the surface and within electromagnetic shielding materials, a conductive gradient structure is rationally constructed. Two conductive layers (electromagnetic functional layers) sandwich an insulating layer. Through multiple reflection and absorption processes, electromagnetic waves can be shielded more effectively, improving electromagnetic shielding performance. Simultaneously, the insulating polymer layer can be selected with a barrier film possessing high-efficiency blocking properties, achieving the integration of multifunctional characteristics.

[0022] This invention uses a polymer film as a sandwich layer, with electromagnetic functional layers deposited sequentially on both sides and carbon fiber felt composited on at least one side, achieving excellent electromagnetic shielding performance. The gradient multilayer structure design of this invention utilizes the principles of impedance mismatch at different interfaces and the skin effect to effectively improve the multiple reflections of electromagnetic waves between different functional layers.

[0023] The advantages and beneficial effects of this invention are:

[0024] 1. This invention, through the design of a gradient structure, can obtain a composite film with high electromagnetic shielding performance. Simultaneously, the type of polymer core layer can be changed according to different needs. For example, a polymer-based high-barrier film can be used as the core layer. Utilizing the design principle of impedance mismatch at different interfaces, multiple layers of particle size gradients, magnetic gradients, conductivity gradients, and an electromagnetic shielding network with alternating structures can be rationally constructed. This allows the composite material to not only possess excellent electromagnetic shielding performance but also to further obtain a high-barrier electromagnetic shielding packaging film that combines high barrier properties with high electromagnetic shielding.

[0025] 2. This invention designs different gradient structures, which can significantly improve the electromagnetic shielding performance of composite materials with a small amount of material, effectively leveraging the synergistic effect between different materials and greatly improving material utilization. Furthermore, the functional layers can be modified according to actual electromagnetic shielding needs, and the polymer matrix can also be selected based on specific application scenarios, such as meeting high barrier and sensing requirements, to achieve personalized processing and customization, broaden the application range, avoid material waste, reduce costs, and meet the requirements of green, environmentally friendly, and highly efficient electromagnetic shielding materials.

[0026] 3. All raw materials used in this invention can be purchased from the market, the preparation method is simple and easy to implement, it can meet the needs of large-scale production, has low equipment requirements, does not require a large amount of solvent, and can achieve zero VOC emissions, which is conducive to the promotion and application of this technology. Attached Figure Description

[0027] Figure 1 A schematic diagram of an electromagnetic shielding composite film with a gradient structure. In the diagram, 1 is carbon fiber felt, 2 is the first coating, 3 is the polymer core layer, and 4 is the second coating.

[0028] Figure 2 Electromagnetic shielding performance of gradient multilayer composite films in the frequency range of 30MHz to 3GHz. Figure (a) shows the gradient multilayer composite film of Example 1, whose composition is as follows: carbon nanotubes (CNTs), polyethylene terephthalate (PET), carbon nanotubes (CNTs), polyurethane adhesive, and carbon fiber felt (area density of 20 g / m²). 2 (b) The figure shows the gradient multilayer composite film of Example 2, whose composition is as follows: carbon nanotubes (CNT), polyethylene terephthalate (PET), carbon fiber mat (area density of 20 g / m²). 2 The components include polyurethane adhesive, polyethylene terephthalate (PET), and carbon nanotubes (CNTs). In the figure, the horizontal axis Freq. represents frequency (GHz), and the vertical axis SE represents shielding effectiveness (dB). Detailed Implementation

[0029] In practical implementation, the present invention provides an electromagnetic shielding composite film with a gradient structure and its preparation method. By designing the gradient structure, the multiple reflection-absorption effects of electromagnetic waves at different impedance matching interfaces are utilized to effectively leverage the synergistic effect between different functional layers, greatly improve the utilization rate of materials, and achieve high electromagnetic shielding performance.

[0030] The present invention will now be described more fully with reference to the embodiments. The following are merely preferred embodiments of the present invention and are not intended to limit the scope of the patent. Any equivalent structural or procedural modifications made based on the description and drawings of the present invention, or any direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

[0031] Example 1

[0032] In this embodiment, the specific preparation parameters of the electromagnetic shielding composite film with a gradient structure and its preparation method are as follows:

[0033] (1) First, use alkaline detergent, deionized water and anhydrous ethanol in sequence to clean the dust, oil and other stains on the surface of the polyvinyl alcohol (PET) film, and keep it for later use;

[0034] (2) Multi-walled carbon nanotubes (MWCNTs) were modified by using aromatic modified polyethylene glycol ether as a surfactant. The mass ratio of MWCNTs, surfactant and water solvent was 10:2.5:87.5. The MWCNTs were ultrasonically disrupted for 30 min at 300 W using an ultrasonic cell disruptor and stirred for 3 h using a magnetic stirrer to obtain an aqueous dispersion of MWCNTs.

[0035] (3) Mix 10g of waterborne polyurethane emulsion (solid content: 35wt%) with 40g of multi-walled carbon nanotube waterborne dispersion and stir magnetically for 0.5h to obtain a multi-walled carbon nanotube waterborne polyurethane mixed solution for later use.

[0036] (4) Under stirring conditions, take 0.3g of associative polyurethane thickener PU-50 and carefully add it to the above mixed solution. Continue stirring until a uniform and viscous slurry is formed to obtain MWCNT / WPU electromagnetic shielding coating.

[0037] (5) Take an appropriate amount of electromagnetic shielding coating and drop it onto the PET film that was cleaned in step (1). Use a scraper to scrape the slurry on one side of the PET film to form a wet film with uniform thickness. Then place it in an oven at 40°C to dry until the moisture is completely evaporated. The gap height between the scraper and the PET substrate is 400μm, and the thickness of the dry film is about 20μm.

[0038] (6) After the moisture in the coating has completely evaporated, repeat step (5) on the other side of the PET film and set it aside for later use.

[0039] (7) Mix the curing agent (e.g., ethylene glycol) and the main agent (e.g., polycarbonate glycol) of the polyurethane adhesive in a certain proportion, and dilute with solvent (e.g., ethyl acetate). The mass ratio of curing agent, main agent and solvent is (15-20): 100: 100. The adhesive must be mixed thoroughly during the mixing process. There should be no particulate matter. Let it stand for later use.

[0040] (8) Apply the mixed polyurethane adhesive to the composite film obtained in step (6) using a dry composite coating machine. Under the premise of ensuring that the composite film will not be deformed by heat, use hot air to evaporate the solvent in the adhesive film.

[0041] (9) After the solvent in the adhesive film has evaporated, the surface density is 20 g / m³. 2 Polyacrylonitrile-based carbon fiber felt was adhered to the surface of a polyurethane adhesive, and then cured in an oven at approximately 50°C for 48 hours to obtain a composite gradient film. (See attached image.) Figure 2 (a);

[0042] (10) The electromagnetic shielding performance of the composite gradient film was tested. The average shielding effectiveness in the frequency range of 30MHz to 3GHz was about 40dB, which corresponds to 99.99% attenuation of electromagnetic waves, meeting most military requirements.

[0043] Example 2

[0044] The difference from Example 1 is that, in this example, the specific preparation parameters for the electromagnetic shielding composite film with a gradient structure and its preparation method are as follows:

[0045] (1) First, use alkaline detergent, deionized water and anhydrous ethanol in sequence to clean the dust, oil and other stains on the surface of the polyvinyl alcohol (PET) film, and keep it for later use;

[0046] (2) Multi-walled carbon nanotubes (MWCNTs) were modified by using aromatic modified polyethylene glycol ether as a surfactant. The mass ratio of MWCNTs, surfactant and water solvent was 10:2.5:87.5. The MWCNTs were ultrasonically disrupted for 30 min at 300 W using an ultrasonic cell disruptor and stirred for 3 h using a magnetic stirrer to obtain an aqueous dispersion of MWCNTs.

[0047] (3) Mix 10g of waterborne polyurethane emulsion (solid content: 35wt%) with 40g of multi-walled carbon nanotube waterborne dispersion and stir magnetically for 0.5h to obtain a multi-walled carbon nanotube waterborne polyurethane mixed solution for later use.

[0048] (4) Under stirring conditions, take 0.3g of associative polyurethane thickener PU-50 and carefully add it to the above mixed solution. Continue stirring until a uniform and viscous slurry is formed to obtain MWCNT / WPU electromagnetic shielding coating.

[0049] (5) Take an appropriate amount of electromagnetic shielding coating and drop it onto the PET film that was cleaned in step (1). Use a scraper to scrape the slurry on one side of the PET film to form a wet film with uniform thickness. Then place it in an oven at 40°C to dry until the moisture is completely evaporated. The gap height between the scraper and the PET substrate is 400μm, and the thickness of the dry film is about 20μm. Prepare two sheets for later use.

[0050] (6) Mix the curing agent (e.g., ethylene glycol) and the main agent (e.g., polycarbonate glycol) of the polyurethane adhesive in a certain proportion, and dilute with solvent (e.g., ethyl acetate). The mass ratio of curing agent, main agent and solvent is (15-20): 100: 100. The adhesive must be mixed thoroughly during the mixing process. There should be no particulate matter. Let it stand for later use.

[0051] (7) Apply the mixed polyurethane adhesive to the insulating side of the two PET composite films obtained in step (5) using a dry laminating coating machine. While ensuring the composite film does not deform due to heat, use hot air to evaporate the solvent in the adhesive film. After the solvent in the adhesive film has evaporated, apply a film with a surface density of 20 g / m². 2 The viscose-based carbon fiber felt is sandwiched inside, and the entire assembly is then cured in an oven at approximately 50°C for 48 hours to obtain a composite gradient film. (See...) Figure 2 (b);

[0052] (8) The electromagnetic shielding performance of the composite gradient film was tested, and the average shielding effectiveness was as high as 45dB in the frequency range of 30MHz to 3GHz.

[0053] like Figure 1 As shown, the electromagnetic shielding composite film of the present invention has a gradient structure, wherein an electromagnetic functional layer (first coating 2 or second coating 4) is sequentially deposited on both sides of the polymer sandwich layer 3 and a carbon fiber felt 1 is composited on at least one side.

[0054] like Figure 2 As shown in the figure, the electromagnetic shielding performance of the gradient multilayer composite film in the frequency range of 30MHz to 3GHz can be seen that different gradient structure designs can significantly improve the electromagnetic shielding performance of the composite material. The shielding effectiveness of the two different composite films in the ultra-high frequency (UHF) band exceeds 40dB, which meets military requirements.

[0055] The results of the embodiments demonstrate that the present invention proposes an electromagnetic shielding composite film with a gradient structure and its preparation method. By designing the gradient structure, the multiple reflection-absorption effects of electromagnetic waves at different impedance matching interfaces are utilized to effectively leverage the synergistic effect between different functional layers, greatly improving material utilization and achieving high electromagnetic shielding performance. The average shielding effectiveness can reach 45dB in the frequency range of 30MHz to 3GHz. Furthermore, it can also impart electromagnetic functions to polymer films with different functional characteristics (such as high barrier properties). Multifunctional composite films can be obtained through a simple process, exhibiting advantages such as simple processing, good repeatability, and significant application effects.

Claims

1. An electromagnetic shielding composite film having a gradient structure, characterized by, The structure includes a polymer sandwich layer, electromagnetic functional layers deposited sequentially on both sides of the polymer sandwich layer, and carbon fiber felt composited on at least one side, to construct a "multi-layer + isolation" gradient electromagnetic shielding network structure, which realizes the absorption-reflection-reabsorption process of electromagnetic waves through the gradient structure. An adhesive layer is provided between the electromagnetic functional layer and the carbon fiber felt. The adhesive layer is a polyurethane adhesive layer with a dry coating amount of 2~4 g / m². 2 ; The method for preparing the electromagnetic shielding composite film with a gradient structure includes the following steps: (1) Depending on the type of polymer sandwich layer, plasma cleaning or different cleaning agents are used to clean the dust and oil stains on the surface of the film, and an electromagnetic functional layer is deposited on the surface of the polymer sandwich layer. (2) Thoroughly stir the curing agent and main agent of the polyurethane adhesive. If the viscosity of the polyurethane adhesive is too high, add solvent to dilute it. Thoroughly stir during the preparation process. There should be no particulate matter. Let it stand for later use. (3) Apply polyurethane adhesive to the electromagnetic functional layer using a dry composite coating machine. Under the premise of ensuring that the composite film will not be deformed by heat, use hot air to evaporate the solvent in the adhesive film. (4) After the solvent in the adhesive film evaporates, attach the carbon fiber felt to the surface of the polyurethane adhesive and then place it in an oven at 40~60 ℃ for 48 hours to cure. The chopped carbon fiber felt has a carbon fiber weight per unit area of 10-50 g / m 2 .

2. The electromagnetic shielding composite film having a gradient structure according to claim 1, characterized by, The polymer sandwich layer material includes: polyethylene film, polypropylene film, polyethylene terephthalate film, styrene-maleic anhydride copolymer, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, polyethylene terephthalate film, aluminized film, silicon-coated film, polyimide film, polyethylene naphthalate film, or a modified material based on the above polymer sandwich layer material.

3. The electromagnetic shielding composite film having a gradient structure according to claim 1, characterized by, The electromagnetic functional layer includes one or more of the following: carbon black, carbon nanotubes, graphene, MXene, iron tetroxide, carbonyl iron, ultrafine metallic iron powder, nickel powder, conductive coating, conductive ink, conductive polymer magnetic coating, aluminum plating, gold plating, silver plating, copper plating, zinc plating, and nickel plating.

4. The electromagnetic shielding composite film having a gradient structure according to claim 1, wherein Carbon fiber felt includes: polyacrylonitrile-based carbon fiber felt, viscose-based carbon fiber felt, or pitch-based carbon fiber felt.

5. A method for preparing an electromagnetic shielding composite thin film with a gradient structure as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Depending on the type of polymer sandwich layer, plasma cleaning or different cleaning agents are used to clean the dust and oil stains on the surface of the film, and an electromagnetic functional layer is deposited on the surface of the polymer sandwich layer. (2) Thoroughly stir the curing agent and main agent of the polyurethane adhesive. If the viscosity of the polyurethane adhesive is too high, add solvent to dilute it. Thoroughly stir during the preparation process. There should be no particulate matter. Let it stand for later use. (3) Apply polyurethane adhesive to the electromagnetic functional layer using a dry composite coating machine. Under the premise of ensuring that the composite film will not be deformed by heat, use hot air to evaporate the solvent in the adhesive film. (4) After the solvent in the adhesive film evaporates, attach the carbon fiber felt to the surface of the polyurethane adhesive and then place it in an oven at 40~60 ℃ for 48 hours to cure.

6. The method for preparing an electromagnetic shielding composite thin film with a gradient structure according to claim 5, characterized in that, Electromagnetic functional layers are deposited on both sides of the polymer sandwich layer, and the carbon fiber felt is bonded to the surface of one or two electromagnetic functional layers using polyurethane adhesive.

Images