Flexible electromagnetic shielding film and preparation method thereof

Abstract

The invention relates to the technical field of electromagnetic shielding materials, and particularly discloses a flexible electromagnetic shielding film and a preparation method thereof. The flexible electromagnetic shielding film comprises a substrate layer, a silver nanowire-chitosan gel layer and a SiO2-TiO2 hybrid layer which are sequentially arranged from inside to outside, and the silver nanowire-chitosan gel layer comprises gelatin (dry weight) and a silver nanowire-chitosan composite material with the mass ratio of 1: (5-20). The preparation method of the flexible electromagnetic shielding film can be used for producing the flexible electromagnetic shielding film, and has the advantages that the electromagnetic shielding effectiveness, flexibility and environmental stability of the electromagnetic shielding film are synergistically improved at the same time, and the electromagnetic shielding film has high electromagnetic shielding effectiveness, excellent flexibility and environmental stability.

Description

Technical Field

[0001] This application relates to the technical field of electromagnetic shielding materials, and in particular to a flexible electromagnetic shielding film and its preparation method. Background Technology

[0002] Electromagnetic shielding materials are key functional materials for preventing electromagnetic interference in modern electronic devices. Traditional metal-based electromagnetic shielding materials (such as copper foil and metal sputtered films) can achieve high electromagnetic shielding effectiveness due to their excellent conductivity, but they have drawbacks such as large thickness, poor flexibility, and high cost.

[0003] To overcome the limitations of metal-based materials, carbon-based composite materials (such as graphene / polymer composites) have attracted widespread attention due to their lightweight and highly designable properties. However, to achieve electromagnetic shielding effectiveness, existing carbon-based composite materials typically require the addition of high-volume-fraction conductive fillers (such as graphene and carbon nanotubes). High filler loading not only significantly increases material brittleness but also makes the conductive network prone to fracture during mechanical deformations such as bending and stretching, leading to conductivity degradation or even failure, making it difficult to meet the reliability requirements of flexible electronic devices.

[0004] Silver wire nanoparticles are considered important candidates for constructing next-generation flexible electromagnetic shielding composite materials due to their high conductivity and low density. However, existing silver wire nanoparticle-based materials mostly employ a single conductive network structure, lacking a multi-level synergistic conductive network design, resulting in insufficient stability of the conductive network under complex deformation conditions. More importantly, silver wire nanoparticles are prone to oxidation in humid and hot environments (high temperature and high humidity conditions), leading to a sharp decline in conductivity or even complete failure, severely limiting their application in harsh environments or long-term use scenarios.

[0005] Therefore, how to simultaneously improve the electromagnetic shielding effectiveness, flexibility, and environmental stability of electromagnetic shielding films, and solve the technical bottlenecks of existing materials' conductive networks being prone to breakage and having poor stability, has become a core issue that urgently needs to be addressed in the field of electromagnetic shielding composite materials. Summary of the Invention

[0006] In order to simultaneously improve the electromagnetic shielding effectiveness, flexibility and environmental stability of the electromagnetic shielding film, and solve the problems of easy breakage and poor stability of the conductive network, this application provides a flexible electromagnetic shielding film that combines high electromagnetic shielding effectiveness, excellent flexibility and environmental stability.

[0007] In a first aspect, this application provides a flexible electromagnetic shielding film, which adopts the following technical solution:

[0008] A flexible electromagnetic shielding film includes a base layer, a silver nanowire-chitosan gel layer, and a SiO2-TiO2 hybrid layer arranged sequentially from the inside out. The silver nanowire-chitosan gel layer comprises gelatin (dry weight) and a silver nanowire-chitosan composite material in a mass ratio of 1:(5-20). The silver nanowire-chitosan composite material is prepared by the following steps:

[0009] Dissolve AgNO3 in deionized water to prepare a 0.2 mol / L-0.4 mol / L AgNO3 solution, and then purge with nitrogen gas to remove oxygen.

[0010] Chitosan was dissolved in a 1%-1.5% acetic acid solution and stirred until completely dissolved. The pH was then adjusted to 4.0 to obtain a chitosan solution.

[0011] Slowly add AgNO3 solution dropwise to chitosan solution, maintaining the temperature at 60-80℃;

[0012] Then, a reducing agent is added, wherein the molar ratio of the reducing agent to AgNO3 is (1.2-1.5):1, and the reaction is stirred continuously for 2-4 hours to generate a silver nanowire-chitosan composite material.

[0013] The gelatin is dispersed in the silver nanowire-chitosan composite material. In this application, "dry weight" refers to the weight after drying to constant weight.

[0014] By employing the above technical solution, controlling the dropping rate of the AgNO3 solution and maintaining a temperature of 60℃-80℃ during the preparation of the silver nanowire-chitosan composite material (AgNWs@CS) helps to balance the mechanical strength and flexibility of the silver nanowire-chitosan composite material. The silver nanowire-chitosan gel layer (AgNWs@CS-gel) uses a blend of gelatin and the silver nanowire-chitosan composite material (AgNWs@CS). Since the molecular chains of gelatin are rich in amino, carboxyl, and hydroxyl groups, while the chitosan chains of the silver nanowire-chitosan composite material are rich in amino and hydroxyl groups, the mixture forms an extremely dense and strong hydrogen bond network, enhancing flexibility. Furthermore, the cationic properties of chitosan in the silver nanowire-chitosan composite material inhibit silver ion oxidation. The SiO2-TiO2 hybrid layer further isolates oxygen and moisture, improving weather resistance and hydrophobicity, inhibiting AgNWs oxidation, maintaining long-term stability, and extending the lifespan of the electromagnetic shielding film device.

[0015] Optionally, the mass ratio of the gelatin and silver nanowire-chitosan composite material can be 1:5, 1:8, 1:10, 1:13, 1:15, 1:18, 1:20, etc.

[0016] Optionally, the chitosan has a molecular weight of 100kDa-150kDa and a degree of deacetylation ≥90%, and the reducing agent is...

[0017] NaBH4.

[0018] By employing the above technical solution and controlling the molecular weight of chitosan within the range of 100kDa-150kDa, the integrity of the core-shell structure of the silver nanowire-chitosan composite material can be enhanced, maintaining the continuity of the conductive network and improving SE and flexibility. If the molecular weight of chitosan is below this range, the molecular chains are short, the coating layer is thin and incomplete, and the formed network is fragile. If the molecular weight of chitosan is above this range, excessively long molecular chains may lead to excessively high solution viscosity and poor film uniformity.

[0019] Optionally, the SiO2-TiO2 hybrid layer is formed by coating with a SiO2-TiO2 hybrid solution, which is prepared by the following steps:

[0020] Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of (4-6):(1-3) and slowly added dropwise to ethanol. Nitrogen gas was passed through the mixture while stirring, and HCl was added to adjust the pH to 2.0. The hydrolysis reaction was carried out at a temperature of 35℃-45℃ for 2 hours, during which hydrolysis and condensation occurred simultaneously to form a SiO2-TiO2 hybrid solution.

[0021] Optionally, the substrate layer is made of polyethylene terephthalate or transparent polyimide.

[0022] Optionally, the thickness of the substrate layer is 50-100 μm, the thickness of the silver nanowire-chitosan gel layer is 10-30 μm, and the thickness of the SiO2-TiO2 hybrid layer is 50-100 nm.

[0023] Optionally, the thickness of the substrate layer can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc., the thickness of the silver nanowire-chitosan gel layer can be 10μm, 15μm, 20μm, 25μm, 30μm, etc., and the thickness of the SiO2-TiO2 hybrid layer can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc.

[0024] Secondly, this application provides a method for preparing a flexible electromagnetic shielding film, which adopts the following technical solution:

[0025] A method for preparing a flexible electromagnetic shielding film includes the following steps:

[0026] S1: The silver nanowire-chitosan composite material is centrifuged, washed, and freeze-dried for later use;

[0027] S2: Dissolve gelatin in deionized water, add freeze-dried silver nanowire-chitosan composite material, ultrasonically disperse, add crosslinking agent, stir and mix well, coat on the surface of the substrate, and dry at 60℃-80℃ to form a film, forming a silver nanowire-chitosan gel layer.

[0028] S3: A SiO2-TiO2 hybrid solution was coated on the surface of the silver nanowire-chitosan gel layer, and the SiO2-TiO2 hybrid layer was obtained after curing.

[0029] By employing the above technical solution, unreacted Ag can be removed by centrifugation and washing of the silver nanowire-chitosan composite material. + Freeze-drying of the silver nanowire-chitosan composite material and byproducts can further optimize the porosity of the composite material and enhance the synergistic effect of electromagnetic wave reflection and absorption.

[0030] Optionally, the freeze-drying parameters in S1 are: cooling to -50°C at a cooling rate of 10°C / min and maintaining the temperature for 24-72 hours.

[0031] By adopting the above technical solution, the silver nanowire-chitosan composite material can be completely frozen by cooling to -50℃ at a rate of 10℃ / min and holding it for a period of time. Then, it can be sublimated and dried under low temperature and low pressure. This allows the silver nanowire-chitosan composite material to be rapidly cryogenically cooled to form a rich micro-nano porous structure, which can reflect and scatter incident electromagnetic waves multiple times.

[0032] Optionally, the concentration of gelatin in S2 is 8wt%-15wt%.

[0033] By adopting the above technical solution and controlling the gelatin concentration within the range of 8wt%-15wt%, a continuous and uniform gel matrix can be formed. When the gelatin concentration is too high (above 15wt%), it will cause enhanced light scattering and easily lead to the final electromagnetic shielding film becoming hard and brittle. When the gelatin concentration is too low (below 8wt%), it will easily lead to increased brittleness of the silver nanowire-chitosan gel layer matrix, decreased conductive network density, and significantly reduced SE and mechanical properties.

[0034] Optionally, the crosslinking agent in S2 is 0.1wt%-1wt% glutaraldehyde.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. The silver nanowire-chitosan gel layer (AgNWs@CS-gel) utilizes a blend of gelatin and a silver nanowire-chitosan composite material (AgNWs@CS). Since gelatin's molecular chains are rich in amino, carboxyl, and hydroxyl groups, while chitosan chains are also rich in amino and hydroxyl groups, their combination forms an extremely dense and strong hydrogen bond network, enhancing flexibility. The SiO2-TiO2 hybrid layer further isolates oxygen and moisture, inhibiting AgNWs oxidation, maintaining long-term stability, and extending the lifespan of the electromagnetic shielding device.

[0037] 2. By controlling the molecular weight of chitosan within the range of 100kDa-150kDa, the coating integrity of the shell-core structure of the silver nanowire-chitosan composite material can be enhanced, maintaining the continuity of the conductive network and improving SE and flexibility. If the molecular weight of chitosan is below this range, the molecular chains are short, the coating layer is thin and incomplete, and the formed network is fragile. If the molecular weight of chitosan is above this range, the molecular chains are too long, resulting in excessively high solution viscosity and poor film uniformity.

[0038] 3. By controlling the gelatin concentration within the range of 8wt%-15wt%, a continuous and uniform gel matrix can be formed. When the gelatin concentration is too high (above 15wt%), it will cause enhanced light scattering and easily lead to the final electromagnetic shielding film becoming hard and brittle. When the gelatin concentration is too low (below 8wt%), it will easily lead to increased brittleness of the silver nanowire-chitosan gel layer matrix, decreased conductive network density, and significantly reduced SE and mechanical properties. Detailed Implementation

[0039] Experimental methods in the following embodiments of this application that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products.

[0040] Example

[0041] Example 1

[0042] A flexible electromagnetic shielding film includes a base layer, a silver nanowire-chitosan gel layer, and a SiO2-TiO2 hybrid layer arranged sequentially from the inside out. The base layer is made of polyethylene terephthalate and has a thickness of 80 μm. The silver nanowire-chitosan gel layer has a thickness of 20 μm, and the SiO2-TiO2 hybrid layer has a thickness of 80 nm.

[0043] A method for preparing a flexible electromagnetic shielding film includes the following steps:

[0044] S1: Dissolve AgNO3 in deionized water to prepare a 0.3 mol / L AgNO3 solution, and then purge with nitrogen gas to remove oxygen;

[0045] Chitosan with a molecular weight of 150 kDa and a mass percentage of 2 wt% (degree of deacetylation ≥ 90%) was dissolved in 1% acetic acid solution and stirred for 2 hours until completely dissolved. The pH was then adjusted to 4.0 to obtain a chitosan solution.

[0046] The AgNO3 solution was slowly added dropwise to the chitosan solution at a rate of 1 mL / min, while maintaining the temperature at 70 °C.

[0047] Then, 0.05 mol / L NaBH4 was added as a reducing agent, and the molar ratio of the reducing agent to AgNO3 was 1.2:1. The reaction was stirred continuously for 3 hours to generate silver nanowire-chitosan composite material (AgNWs@CS).

[0048] The silver nanowire-chitosan composite material was centrifuged at 8000 rpm for 10 min and then washed three times to remove unreacted Ag. + The byproducts and other products were freeze-dried at a cooling rate of 10℃ / min to -50℃ and maintained for 48 hours for later use.

[0049] S2: Dissolve 10wt% gelatin in deionized water, add freeze-dried silver nanowire-chitosan composite material, the mass ratio of gelatin (dry weight) to silver nanowire-chitosan composite material is 1:20, ultrasonically disperse for 30 min, then add 0.5wt% glutaraldehyde as crosslinking agent, stir and mix well, coat on the surface of the substrate layer, and dry at 70℃ to form a silver nanowire-chitosan gel layer with a thickness of 20μm;

[0050] S3: Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of 5:2 and slowly added dropwise to ethanol. Nitrogen gas was introduced while stirring, and HCl was added to adjust the pH to 2.0. The hydrolysis reaction was carried out at 40℃ for 2 hours, with simultaneous hydrolysis and condensation to form a SiO2-TiO2 hybrid solution. The SiO2-TiO2 hybrid solution was coated on the surface of the silver nanowire-chitosan gel layer and cured to obtain a SiO2-TiO2 hybrid layer with a thickness of 80 nm.

[0051] Example 2

[0052] A flexible electromagnetic shielding film includes a base layer, a silver nanowire-chitosan gel layer, and a SiO2-TiO2 hybrid layer arranged sequentially from the inside out. The base layer is made of polyethylene terephthalate and has a thickness of 80 μm. The silver nanowire-chitosan gel layer has a thickness of 20 μm, and the SiO2-TiO2 hybrid layer has a thickness of 80 nm.

[0053] A method for preparing a flexible electromagnetic shielding film includes the following steps:

[0054] S1: Dissolve AgNO3 in deionized water to prepare a 0.3 mol / L AgNO3 solution, and then purge with nitrogen gas to remove oxygen;

[0055] Chitosan with a molecular weight of 100 kDa and a mass percentage of 2 wt% (degree of deacetylation ≥ 90%) was dissolved in a 1% acetic acid solution and stirred for 2 hours until completely dissolved. The pH was then adjusted to 4.0 to obtain a chitosan solution.

[0056] The AgNO3 solution was slowly added dropwise to the chitosan solution at a rate of 1 mL / min, while maintaining the temperature at 70 °C.

[0057] Then, 0.05 mol / L NaBH4 was added as a reducing agent, and the molar ratio of the reducing agent to AgNO3 was 1.2:1. The reaction was stirred continuously for 3 hours to generate silver nanowire-chitosan composite material (AgNWs@CS).

[0058] The silver nanowire-chitosan composite material was centrifuged at 8000 rpm for 10 min and then washed three times to remove unreacted Ag. + The byproducts and other products were freeze-dried at a cooling rate of 10℃ / min to -50℃ and maintained for 48 hours for later use.

[0059] S2: Dissolve 8 wt% gelatin in deionized water, add freeze-dried silver nanowire-chitosan composite material, the mass ratio of gelatin to silver nanowire-chitosan composite material is 1:20, ultrasonically disperse for 30 min, then add 0.5 wt% glutaraldehyde as crosslinking agent, stir and mix well, coat on the surface of the substrate layer, and dry at 70℃ to form a film, forming a silver nanowire-chitosan gel layer with a thickness of 20 μm;

[0060] S3: Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of 5:2 and slowly added dropwise to ethanol. Nitrogen gas was introduced while stirring, and HCl was added to adjust the pH to 2.0. The hydrolysis reaction was carried out at 40℃ for 2 hours, with simultaneous hydrolysis and condensation to form a SiO2-TiO2 hybrid solution. The SiO2-TiO2 hybrid solution was coated on the surface of the silver nanowire-chitosan gel layer and cured to obtain a SiO2-TiO2 hybrid layer with a thickness of 80 nm.

[0061] Example 3

[0062] A flexible electromagnetic shielding film includes a base layer, a silver nanowire-chitosan gel layer, and a SiO2-TiO2 hybrid layer arranged sequentially from the inside out. The base layer is made of polyethylene terephthalate and has a thickness of 80 μm. The silver nanowire-chitosan gel layer has a thickness of 20 μm, and the SiO2-TiO2 hybrid layer has a thickness of 80 nm.

[0063] A method for preparing a flexible electromagnetic shielding film includes the following steps:

[0064] S1: Dissolve AgNO3 in deionized water to prepare a 0.3 mol / L AgNO3 solution, and then purge with nitrogen gas to remove oxygen;

[0065] Chitosan with a molecular weight of 120 kDa and a mass percentage of 2 wt% (degree of deacetylation ≥ 90%) was dissolved in 1% acetic acid solution and stirred for 2 hours until completely dissolved. The pH was then adjusted to 4.0 to obtain a chitosan solution.

[0066] The AgNO3 solution was slowly added dropwise to the chitosan solution at a rate of 1 mL / min, while maintaining the temperature at 70 °C.

[0067] Then, 0.05 mol / L NaBH4 was added as a reducing agent, and the molar ratio of the reducing agent to AgNO3 was 1.2:1. The reaction was stirred continuously for 3 hours to generate silver nanowire-chitosan composite material (AgNWs@CS).

[0068] The silver nanowire-chitosan composite material was centrifuged at 8000 rpm for 10 min and then washed three times to remove unreacted Ag. + The byproducts and other products were freeze-dried at a cooling rate of 10℃ / min to -50℃ and maintained for 48 hours for later use.

[0069] S2: Dissolve 15wt% gelatin in deionized water, add freeze-dried silver nanowire-chitosan composite material, the mass ratio of gelatin to silver nanowire-chitosan composite material is 1:20, ultrasonically disperse for 30 min, then add 0.5wt% glutaraldehyde as a crosslinking agent, stir and mix well, coat on the surface of the substrate, and dry at 70℃ to form a film, forming a silver nanowire-chitosan gel layer with a thickness of 20μm;

[0070] S3: Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of 5:2 and slowly added dropwise to ethanol. Nitrogen gas was introduced while stirring, and HCl was added to adjust the pH to 2.0. The hydrolysis reaction was carried out at 40℃ for 2 hours, with simultaneous hydrolysis and condensation to form a SiO2-TiO2 hybrid solution. The SiO2-TiO2 hybrid solution was coated on the surface of the silver nanowire-chitosan gel layer and cured to obtain a SiO2-TiO2 hybrid layer with a thickness of 80 nm.

[0071] Comparative Example

[0072] Comparative Example 1

[0073] A flexible electromagnetic shielding film differs from Example 1 in that, in S1, chitosan with a molecular weight of 50kDa is used to replace chitosan with a molecular weight of 100kDa in an equal amount, while the rest are the same.

[0074] Comparative Example 2

[0075] A flexible electromagnetic shielding film differs from Example 1 in that, in S1, chitosan with a molecular weight of 200kDa is used to replace chitosan with a molecular weight of 100kDa in an equal amount, while the rest are the same.

[0076] Comparative Example 3

[0077] A flexible electromagnetic shielding film differs from Example 1 in that, in S2, gelatin with a concentration of 5 wt% is used to replace gelatin with a concentration of 10 wt%, while the other steps are the same.

[0078] Comparative Example 4

[0079] A flexible electromagnetic shielding film differs from Example 1 in that, in S2, gelatin with a concentration of 20wt% is used to replace gelatin with a concentration of 10wt%, while the other steps are the same.

[0080] Comparative Example 5

[0081] A flexible electromagnetic shielding film differs from Example 1 in that the thickness of the SiO2-TiO2 hybrid layer is 0, i.e., step S3 is not performed.

[0082] Comparative Example 6

[0083] A method for preparing a flexible electromagnetic shielding film differs from Example 1 in that, in S1, the generated silver nanowire-chitosan composite material was not freeze-dried after centrifugal washing; its drying conditions were 10 hours at 80°C, while the rest were the same.

[0084] Comparative Example 7

[0085] A flexible electromagnetic shielding film, differing from Example 1 in that the amount of chitosan used is 0, and an equal amount of silver nanowires replaces the silver nanowire-chitosan composite material. Its preparation method is as follows:

[0086] S1: After centrifuging the silver nanowires at 8000 rpm for 10 min, wash them 3 times, cool them to -50℃ at a cooling rate of 10℃ / min, and freeze-dry them for 48 h for later use.

[0087] S2: Dissolve 10wt% gelatin in deionized water, add the freeze-dried silver nanowires, the mass ratio of gelatin to silver nanowires is 1:20, ultrasonically disperse for 30 min, then add 0.5wt% glutaraldehyde as a crosslinking agent, stir and mix well, coat it on the surface of the substrate, and dry it at 70℃ to form a silver nanowire-gelatin gel layer with a thickness of 20μm;

[0088] S3: Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of 5:2 and slowly added dropwise to ethanol. Nitrogen gas was introduced while stirring, and HCl was added to adjust the pH to 2.0. The hydrolysis reaction was carried out at 40℃ for 2 hours, with simultaneous hydrolysis and condensation to form a SiO2-TiO2 hybrid solution. The SiO2-TiO2 hybrid solution was coated on the surface of the formed silver nanowire-gelatin gel layer. After curing, a SiO2-TiO2 hybrid layer with a thickness of 80 nm was obtained.

[0089] Comparative Example 8

[0090] A flexible electromagnetic shielding film differs from Example 1 in that an equal amount of polyacrylamide is used to replace chitosan, while the other steps are the same.

[0091] The experimental parameters of Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0092] Table 1. Experimental parameters of Examples 1-3 and Comparative Examples 1-5

[0093] Chitosan molecular weight Gelatin concentration Surface coating Example 1 150kDa 10wt% <![CDATA[SiO2 / TiO2]]> Example 2 100kDa 8wt% <![CDATA[SiO2 / TiO2]]> Example 3 120kDa 15wt% <![CDATA[SiO2 / TiO2]]> Comparative Example 1 50kDa 10wt% <![CDATA[SiO2 / TiO2]]> Comparative Example 2 200kDa 10wt% <![CDATA[SiO2 / TiO2]]> Comparative Example 3 150kDa 5wt% <![CDATA[SiO2 / TiO2]]> Comparative Example 4 150kDa 20wt% <![CDATA[SiO2 / TiO2]]> Comparative Example 5 150kDa 10wt% none

[0094] Performance testing experiment

[0095] The electromagnetic shielding performance of the electromagnetic shielding films of Examples 1-3 and Comparative Examples 1-8 was tested according to the test method in ASTM D4935-18. The test results are shown in Table 2.

[0096] Table 2. Test results of electromagnetic shielding films in Examples 1-3 and Comparative Examples 1-8

[0097] SE (dB) Elongation at break Rate of change of resistance Light transmittance Example 1 52 150% <5% 85% Example 2 50 >130% <7% 85% Example 3 51 >135% <6% 83% Comparative Example 1 47 <90% <20% 83% Comparative Example 2 48 <130% <10% 80% Comparative Example 3 42 <80% >20% 78% Comparative Example 4 50 <100% <8% 75% Comparative Example 5 52 150% >35% 85% Comparative Example 6 45 <120% >12% 80% Comparative Example 7 38 <100% >40% 70% Comparative Example 8 40 <90% >40% 75%

[0098] Combining Examples 1-3 and Comparative Examples 1-2 with the test results in Table 2, it can be seen that there is no significant substantial difference in the experimental results of Examples 1-3. Example 1 is the preferred example, and Examples 1-3 are all superior to Comparative Examples 1-2. The reason for this may be that Example 1 of this application, by controlling the molecular weight of chitosan within the range of 100kDa-150kDa, can enhance the coating integrity of the core-shell structure of the silver nanowire-chitosan composite material, maintain the continuity of the conductive network, and improve SE and flexibility. If the molecular weight of chitosan is lower than this range (as in Comparative Example 1), the molecular chains are short, the coating layer is thin and incomplete, and the formed network is fragile. If the molecular weight of chitosan is higher than this range (as in Comparative Example 2), the molecular chains may be too long, which may lead to excessively high solution viscosity and poor film uniformity.

[0099] Combining the test results of Example 1 and Comparative Examples 3-4 with those in Table 2, it can be seen that Example 1 is superior to Comparative Examples 3-4. The reason for this may be that Example 1 of this application, by controlling the gelatin concentration within the range of 8wt%-15wt%, can form a continuous and uniform gel matrix. When the gelatin concentration is too high (as in Comparative Example 4), it will cause enhanced light scattering and easily lead to the final electromagnetic shielding film becoming hard and brittle. When the gelatin concentration is too low (as in Comparative Example 3), it will easily lead to increased brittleness of the silver nanowire-chitosan gel layer matrix, decreased conductive network density, and significantly reduced SE and mechanical properties.

[0100] Based on the test results in Table 2, it can be seen that Example 1 is superior to Comparative Example 5. The reason for this is that the SiO2-TiO2 hybrid layer on the surface of Example 1 can further isolate oxygen and moisture, improve weather resistance and hydrophobicity, inhibit AgNWs oxidation, maintain long-term stability, and extend the life of electromagnetic shielding film devices.

[0101] Combining Example 1 and Comparative Example 6 with the test results in Table 2, it can be seen that Example 1 is superior to Comparative Example 6. The reason for this is that Example 1 of this application uses freeze-drying, which can further optimize the porosity of the silver nanowire-chitosan composite material. Rapid deep freezing of the silver nanowire-chitosan composite material can form a rich micro-nano pore structure, which can reflect and scatter incident electromagnetic waves multiple times, thereby enhancing the electromagnetic wave reflection-absorption synergistic effect.

[0102] Combining the results of Example 1 and Comparative Examples 7-8 with the test results in Table 2, it can be seen that Example 1 is superior to Comparative Examples 7-8. The reason for this may be that the silver nanowire-chitosan gel layer (AgNWs@CS-gel) uses a blend of gelatin and silver nanowire-chitosan composite material (AgNWs@CS). Since the molecular chains of gelatin are rich in amino, carboxyl, and hydroxyl groups, while the chitosan chains of the silver nanowire-chitosan composite material are rich in amino and hydroxyl groups, the mixture forms an extremely dense and strong hydrogen bond network, improving flexibility. The SiO2-TiO2 hybrid layer can further isolate oxygen and moisture, improving weather resistance and hydrophobicity, inhibiting AgNWs oxidation, maintaining long-term stability, and extending the lifespan of the electromagnetic shielding film device. When sodium polyacrylate is used to replace chitosan (as in Comparative Example 8), although it has cationic properties, the molecular forces between polyacrylamide and gelatin are mainly weak hydrogen bonds and van der Waals forces. The interaction between amide bonds is far less strong than the synergistic effect of the multifunctional groups between chitosan and gelatin.

[0103] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A flexible electromagnetic shielding film, characterized in that: The structure comprises, from the inside out, a base layer, a silver nanowire-chitosan gel layer, and a SiO2-TiO2 hybrid layer. The silver nanowire-chitosan gel layer comprises gelatin (dry weight) and a silver nanowire-chitosan composite material in a mass ratio of 1:(5-20). The silver nanowire-chitosan composite material is prepared by the following steps: Dissolve AgNO3 in deionized water to prepare a 0.2 mol / L-0.4 mol / L AgNO3 solution, and then purge with nitrogen gas to remove oxygen. Chitosan was dissolved in a 1%-1.5% acetic acid solution and stirred until completely dissolved. The pH was then adjusted to 4.0 to obtain a chitosan solution. Slowly add AgNO3 solution dropwise to chitosan solution while maintaining the temperature at 60℃-80℃; Then, a reducing agent is added, wherein the molar ratio of the reducing agent to AgNO3 is (1.2-1.5):1, and the reaction is stirred continuously for 2-4 hours to generate a silver nanowire-chitosan composite material.

2. The flexible electromagnetic shielding film according to claim 1, characterized in that: The chitosan has a molecular weight of 100kDa-150kDa and a degree of deacetylation ≥90%, and the reducing agent is NaBH4.

3. The flexible electromagnetic shielding film according to claim 1, characterized in that: The SiO2-TiO2 hybrid layer is formed by coating with a SiO2-TiO2 hybrid solution, which is prepared by the following steps: Tetrabutyl orthosilicate and tetrabutyl titanate were mixed as precursors at a volume ratio of (4-6):(1-3) and slowly added dropwise to ethanol. Nitrogen gas was passed through the mixture while stirring, and HCl was added to adjust the pH to 2.

0. The hydrolysis reaction was carried out at a temperature of 35℃-45℃ for 2 hours, during which hydrolysis and condensation occurred simultaneously to form a SiO2-TiO2 hybrid solution.

4. The flexible electromagnetic shielding film according to claim 1, characterized in that: The base layer is made of polyethylene terephthalate or transparent polyimide.

5. The flexible electromagnetic shielding film according to claim 1, characterized in that: The thickness of the substrate layer is 50-100 μm, the thickness of the silver nanowire-chitosan gel layer is 10-30 μm, and the thickness of the SiO2-TiO2 hybrid layer is 50-100 nm.

6. A method for preparing a flexible electromagnetic shielding film according to any one of claims 1-5, characterized in that: Includes the following steps: S1: The silver nanowire-chitosan composite material is centrifuged, washed, and freeze-dried for later use; S2: Dissolve gelatin in deionized water, add freeze-dried silver nanowire-chitosan composite material, ultrasonically disperse, add crosslinking agent, stir and mix well, coat on the surface of the substrate, and dry at 60℃-80℃ to form a film, forming a silver nanowire-chitosan gel layer. S3: A SiO2-TiO2 hybrid solution was coated on the surface of the silver nanowire-chitosan gel layer, and the SiO2-TiO2 hybrid layer was obtained after curing.

7. The method for preparing a flexible electromagnetic shielding film according to claim 6, characterized in that: The parameters for freeze drying in S1 are: cooling to -50℃ at a cooling rate of 10℃ / min and maintaining the temperature for 24h-72h.

8. The method for preparing a flexible electromagnetic shielding film according to claim 6, characterized in that: The concentration of gelatin in S2 is 8wt%-15wt%.

9. The method for preparing a flexible electromagnetic shielding film according to claim 6, characterized in that: The crosslinking agent in S2 is 0.1wt%-1wt% glutaraldehyde.