A flexible electromagnetic shielding film material with a bionic multi-layer structure that can be adjusted to an isolation structure and its preparation method

Abstract

The present invention discloses a flexible electromagnetic shielding film material with a bionic multi-layer structure that can be regulated into an isolation structure and a preparation method thereof. The flexible electromagnetic shielding film material uses a vacuum filtration technique to alternately form films of responsive castor oil-based waterborne polyurethane and electromagnetic shielding fillers in sequence, and forms a multi-layer structure integrated material relying on hydrogen bonds and electrostatic forces, with a total thickness of 20-30 μm. In the components of the flexible electromagnetic shielding material, the responsive castor oil-based waterborne polyurethane accounts for 97-99 wt%, and the electromagnetic shielding filler accounts for 1-3 wt%. The flexible electromagnetic shielding film material of the present invention can obtain good electromagnetic shielding effect with a film thickness of only 20-30 μm. The electromagnetic shielding efficiency in the X-band can reach 20-80 dB, and the decrease in the electromagnetic shielding efficiency after being converted into an isolation structure does not exceed 13%. Moreover, the electromagnetic shielding film has excellent fire safety performance with low heat release.

Description

Technical Field

[0001] The present invention relates to a flexible electromagnetic shielding film material with a bionic multi-layer structure that can be adjusted to an isolation structure and a preparation method thereof, belonging to the field of electromagnetic shielding. Background Art

[0002] Currently, human communication is gradually developing towards high-frequency bands (1 - 30 GHz) represented by 5G and satellite communication, and the 8.2 - 12.4 GHz (X-band) plays an important role in communication. Generally, it is considered that a shielding effectiveness of the material higher than 20 dB can meet general civilian needs, while commercial electromagnetic shielding products need to reach at least 30 dB. Generally speaking, an effectiveness value above 50 dB belongs to high electromagnetic shielding materials, and aerospace-grade electromagnetic shielding materials are even required to reach above 70 dB. Therefore, traditional metal electromagnetic shielding materials represented by the Faraday cage cannot well meet the new requirements for electromagnetic shielding materials such as high-frequency shielding, broadband action, and lightweight structure, and metal materials have disadvantages such as easy oxidation, high density, and high processing difficulty.

[0003] Polymer-based electromagnetic shielding nanocomposites provide an alternative to the traditional metal shielding mode. By means of filler modification and structural design, etc., the electromagnetic shielding effectiveness and frequency band of the composite material can be adjusted. In addition, the excellent processing performance and lightweight advantages of the polymer matrix also effectively broaden the forefront applications of electromagnetic shielding composites. Since the conductivity of highly doped conductive polymers belongs to the metal range (10 - 10 5 S / cm), it has the characteristic of total reflection of electromagnetic waves, that is, the electromagnetic shielding effect. Therefore, the application of conductive polymers in electromagnetic shielding technology has attracted wide attention. For example, the composite of polyaniline and polyethylene (PE) or polymethyl methacrylate (PMMA) developed by Drmecon Company in Germany has a shielding efficiency exceeding 25 dB at a frequency of 1 GHz, and its performance is better than that of traditional carbon powder / polymer composite materials. However, since a large amount of conductive polymers need to be added to have good shielding effectiveness, it will cause damage to the mechanical properties of the polymer matrix. When performing shielding behavior in the high-frequency band, the materials used need to have high conductivity or high magnetic permeability or the synergistic effect of both. This is because when electromagnetic waves pass through the interior of the material, they are converted into heat energy, thus showing absorption effectiveness. The higher the conductivity of the material, the greater the magnetic permeability, the greater the absolute thickness, and the higher the electromagnetic wave frequency, the greater the absorption loss, and the more electromagnetic waves are converted into heat energy. First, a large amount of heat energy will hit the magnetic loss, and second, it will trigger a thermal disaster of the polymer matrix and induce a fire accident. Therefore, the flame retardancy or fire safety problem of polymer-based electromagnetic shielding nanocomposites cannot be ignored.

[0004] In view of the above analysis, the future development trend still points towards new two-dimensional materials with high-efficiency electromagnetic shielding and flame retardant potential, such as graphene and MXene. Thanks to the rich surface functional groups of MXene, which are very similar to substances in nature and are prone to intermolecular interactions, forming strong microscopic-scale interactions such as hydrogen bonds. Therefore, the method of using a biomimetic multi-layer structure is a feasible preparation mechanism.

[0005] The isolation structure is a common configuration in polymer electromagnetic shielding composites and is a key research object in the field of conductive polymer composites. This structure can significantly reduce the percolation value of conductive composites, thereby achieving the purpose of efficiently improving the electromagnetic shielding efficiency. However, the current preparation method of this structure is relatively stringent. Generally, conductive or electromagnetic shielding fillers and polymer matrices are pre-assembled and fixed into a certain-size configuration, and then extruded into corresponding plates or other shapes under high temperature and high pressure. This approach depends on the properties of the polymer. For example, commonly used thermoplastic polystyrene (PS), polypropylene (PP), etc. all need to be heated to at least above 130 °C and combined with an external force pressure of 10 - 20 MPa to form a strong interaction force between the filler and the polymer. However, the problem of easy filler detachment still cannot be avoided in this mode, and it is only suitable for the field of thermoplastic composites. The biomimetic multi-layer structure, on the other hand, can well maintain the properties of each original component itself, has the same level of electromagnetic shielding advantage as the isolation structure, and can avoid the decrease in electromagnetic shielding performance caused by the mutual interference between the polymer matrix and the electromagnetic shielding filler. However, the biomimetic multi-layer structure is stable and once damaged, it is difficult to return to its original state, resulting in the failure of the material's performance. The polymer matrices selected for common polymer electromagnetic shielding composites are all thermoplastic polymer materials, and a mixed system can be prepared by the method of melt mixing. However, once a thermosetting polymer material with better dimensional stability and comprehensive performance is made into an electromagnetic shielding composite, it cannot be processed twice or multiple times. Moreover, under external forces, such as scratches, breakage, and damage, the electromagnetic shielding performance drops significantly and cannot be repaired or recycled. After damage, the electromagnetic shielding performance drops significantly, causing trouble for the preparation of high-performance and high-stability thermosetting polymer electromagnetic shielding composites. Therefore, developing a thermosetting polymer electromagnetic shielding composite with a controllable structure, which can be transformed from a multi-layer structure to an isolation structure and still maintain high-efficiency electromagnetic shielding performance, can be widely applied in the fields of military, aerospace, electronics, and electricity, and has great application value. Summary of the Invention

[0006] The present invention aims at the deficiencies of the above-mentioned existing technologies and provides a flexible electromagnetic shielding material with a biomimetic multi-layer structure that can be adjusted to an isolation structure and its preparation method, successfully preparing a thermosetting biomimetic flexible electromagnetic shielding film that can be converted from a multi-layer structure to an isolation structure.

[0007] Through molecular design, the present invention synthesizes a castor oil-based waterborne polyurethane with thermosetting recyclable characteristics. Utilizing the responsive behavior of dynamic disulfide bonds in the molecular chain segments and the vacuum sand core filtration technology, the synthesized polymer matrix and electromagnetic shielding fillers are alternately formed into films in sequence, successfully preparing a flexible bionic film with extremely high electromagnetic shielding efficiency and structural controllability. In the case where the multi-layer structure electromagnetic shielding material is broken by external forces, it can be transformed into an isolation structure within 1 - 30 minutes at a certain temperature under a pressure of 5 MPa. The electromagnetic shielding film prepared by the present invention has a thickness of only 20 - 30 μm, and when used in flexible electronic products, it will not significantly increase the volume of the electronic products; it has excellent fire resistance, and compared with pure castor oil-based waterborne polyurethane, the peak value of its heat release rate has decreased by 32.59%; the shielding efficiency of this electromagnetic shielding film in the multi-layer structure can reach a wide range of 20 - 80 dB, and after the configuration is converted into an isolation structure, the decline rate does not exceed 13%, thereby increasing the possibility of its multiple cycle applications in military and aerospace fields and electronic products.

[0008] The flexible electromagnetic shielding material with a bionic multi-layer structure that can be adjusted to an isolation structure in the present invention has a component ratio of 97 - 99 wt% of responsive castor oil-based waterborne polyurethane and 1 - 3 wt% of electromagnetic shielding filler.

[0009] The responsive castor oil-based waterborne polyurethane is prepared by a method including the following steps:

[0010] First, castor oil (7.0 g), isophorone diisocyanate, and N-methyldiethanolamine are mixed in a three-necked round-bottom flask and stirred at 78 °C for 10 minutes; then, a drop of dibutyltin dilaurate (DBTDL) is added to the prepolymer and stirring is maintained until the prepolymer becomes a white paste and can hardly flow; subsequently, methyl ethyl ketone (MEK) is added to the system to reduce the viscosity. After the prepolymer is dissolved in MEK, the disulfide bond compound is quickly added, and stirring reaction is continued at 78 °C for 2 h; then the heating is removed. When the reactant cools to room temperature, glacial acetic acid (HAc) is added with stirring to neutralize for 30 minutes; 62 mL of distilled water is added to the system and emulsified and dispersed vigorously for two hours; finally, MEK is removed by rotary evaporation to obtain a thermosetting cationic waterborne polyurethane-polyurea emulsion (30% DTDA-WPUU) with a solid content of ~20 wt%.

[0011] Among them, the molar ratio of -OH in castor oil (CO), -NCO group in isophorone diisocyanate (IPDI), and -OH in N-methyldiethanolamine (MDEA) is 1:1.70:0.69; among them, 30 wt% of castor oil is replaced by an equivalent molar amount of disulfide bond compound to realize the preparation of a polymer with disulfide bonds in the main chain.

[0012] The reactant ratios involved in the preparation of responsive castor oil-based waterborne polyurethane mainly affect the hardness and softness of the polymer and have no effect on the electromagnetic shielding performance of the final material.

[0013] The disulfide compound is selected from one of 2,2'-diaminodiphenyl disulfide, 4,4'-diaminodiphenyl disulfide, bis(6-hydroxy-2-naphthyl) disulfide, and 3,3'-dihydroxydiphenyl disulfide.

[0014] The electromagnetic shielding filler is selected from one of titanium carbide, titanium carbonitride, silver nanowires, carbon nanotubes, graphene, etc. The electromagnetic shielding filler accounts for 1 wt% - 3 wt% of the total mass of the flexible film.

[0015] The preparation method of the flexible electromagnetic shielding material with a bionic multi-layer structure that can be regulated into an isolation structure according to the present invention uses castor oil-based waterborne polyurethane as the substrate. Starting from the bionic multi-layer structure, independent sub-films are sequentially prepared by vacuum filtration, and an integrated material is formed by relying on hydrogen bonds and electrostatic forces. The specific steps are as follows:

[0016] Step 1: Prepare an aqueous dispersion of the electromagnetic shielding filler by ultrasonic dispersion with a concentration of 1 wt% to obtain an electromagnetic shielding nanofiller dispersion for standby.

[0017] Step 2: Dilute the responsive castor oil-based waterborne polyurethane emulsion with deionized water to a concentration of 2 wt% to obtain a polymer dispersion for standby.

[0018] Step 3: Sequentially and alternately add the two raw material components obtained in Steps 1 and 2 into a vacuum filtration device, and filter under vacuum conditions for 6 h to form an alternating multi-layer structure with a total of five layers (2 layers of polymer matrix layer and 3 layers of electromagnetic shielding filler), obtaining an electromagnetic shielding film with a certain humidity. Then dry it in an oven at 60 °C to obtain the bionic flexible electromagnetic shielding film.

[0019] The thickness of the electromagnetic shielding film prepared by the present invention is only 20 - 30 μm. The thickness of the polymer matrix layer is the main source of the thickness of the invention, and its thickness range is 5 - 10 μm. If the polymer matrix layer is too thick, the electromagnetic shielding performance will decrease, and the optimal size is 10 μm; the thickness of the electromagnetic shielding filler layer is 1 - 5 μm; the finally prepared electromagnetic shielding film has a thickness of only 20 - 30 μm, which is both thin and efficient.

[0020] The condition for the multi-layer structure electromagnetic shielding film material obtained to be transformed into an isolation structure is: under an external pressure of 5 MPa in a flat vulcanizer, hot press at 40 - 80 °C for 1 - 10 min to convert from the multi-layer structure to the isolation structure.

[0021] Once a thermosetting polymer material with better dimensional stability and comprehensive performance is made into an electromagnetic shielding composite material, it cannot be processed secondarily or multiple times. Moreover, under external forces such as scratches, breakage, and damage, the electromagnetic shielding performance drops significantly and cannot be repaired or recycled. The method of the present invention has a wide range of applications and can be used to construct thermosetting polymer composite materials with a multi-layer structure between various electromagnetic shielding fillers and synthesized castor oil-based waterborne polyurethane. The method of the present invention can significantly improve the electromagnetic shielding efficiency, solve the problem of secondary (multiple) processing of thermosetting materials, realize the efficient transformation from a multi-layer structure to an isolation structure, and still maintain high-efficiency electromagnetic shielding performance after the structure transformation.

[0022] Compared with the existing technology, the beneficial effects of the present invention are reflected in:

[0023] 1. The preparation process of the present invention is simple. Water is used as the solvent during the preparation process, and natural product castor oil is used as the main raw material, without generating other toxic and harmful by-products, meeting the requirements of green environmental protection and sustainable development;

[0024] 2. The electromagnetic shielding film prepared by the present invention has an ultra-thin structure, with a thickness range of 20 - 30 μm, having the characteristics of light weight, and excellent fire resistance (compared with the pure responsive castor oil-based waterborne polyurethane film material, the peak heat release drops by more than 30%), and is suitable for preparing high-fire-safety electronic products and low-specific-gravity electromagnetic shielding products;

[0025] 3. Under relatively mild industrial conditions (5 MPa, 40 - 80 °C, 1 - 10 min), due to the responsive behavior of the dynamic disulfide bonds in the polymer, the electromagnetic shielding film prepared by the present invention undergoes a sulfur exchange reaction under thermal and pressure stimuli, enabling the secondary processing and structure conversion of the thermosetting composite material, transforming from a multi-layer structure to an isolation structure, such that the decrease in electromagnetic shielding efficiency does not exceed 13%, making the multi-layer structure electromagnetic shielding film material prepared by the present invention applicable to military and aerospace fields and electronic products, meeting the requirements of multiple cyclic applications. Description of the Drawings

[0026] Figure 1 It is the flow chart and corresponding structural formula of the castor oil-based waterborne polyurethane prepared in the embodiment.

[0027] Figure 2It is the shielding effectiveness curve of the electromagnetic shielding film 1 prepared in Example 1 in the X band (taking titanium carbide as an example and with different dosages of titanium carbide). Among them, (a) total shielding effectiveness, (b) absorption effectiveness, (c) reflection effectiveness, (d) power coefficient (0.4MXM represents that titanium carbide accounts for 0.25 wt% of the electromagnetic shielding film, 0.8MXM represents that titanium carbide accounts for 0.50 wt% of the electromagnetic shielding film, 1.6MXM represents that titanium carbide accounts for 1.00 wt% of the electromagnetic shielding film, 3.2MXM represents that titanium carbide accounts for 2.00 wt% of the electromagnetic shielding film).

[0028] Figure 3 It is a schematic diagram of the structural transformation of the electromagnetic shielding film 1 prepared in Example 1 (taking titanium carbide as an example). Specific embodiments

[0029] To further illustrate the technical solution of the present invention, the preferred implementation schemes of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0030] In the following embodiments of the present invention, the responsive castor oil-based waterborne polyurethane is prepared by a method including the following steps:

[0031] First, castor oil (7.0 g), isophorone diisocyanate and N-methyldiethanolamine are mixed in a three-necked round-bottom flask and stirred at 78 °C for 10 minutes; then, a drop of dibutyltin dilaurate (DBTDL) is added to the prepolymer and stirring is continued until the prepolymer becomes a white paste and can hardly flow; subsequently, methyl ethyl ketone (MEK) is added to the system to reduce the viscosity. After the prepolymer is dissolved in MEK, DTDA is quickly added, and the reaction is continued with stirring at 78 °C for 2 h; then the heating is removed. When the reactant cools to room temperature, glacial acetic acid (HAc) is added with stirring and neutralized for 30 minutes; 62 mL of distilled water is added to the system and emulsified and dispersed vigorously for two hours; finally, MEK is removed by rotary evaporation to obtain a thermosetting cationic waterborne polyurethane-polyurea emulsion (30% DTDA-WPUU) with a solid content of ~20 wt%.

[0032] Among them, the molar ratio of -OH in castor oil (CO), -NCO group in isophorone diisocyanate (IPDI) and -OH in N-methyldiethanolamine (MDEA) is 1:1.70:0.69; among them, castor oil is replaced by 30 wt% of an equivalent molar amount of 2,2'-diaminodiphenyl disulfide (DTDA) to achieve the preparation of a polymer with disulfide bonds in the main chain.

[0033] The reactant ratios involved in the preparation of responsive castor oil-based waterborne polyurethane mainly affect the hardness and softness of the polymer and have no effect on the electromagnetic shielding performance of the final material. Since the present invention describes a flexible electromagnetic shielding material, a ratio with both excellent flexibility and strength is selected for the application; if the ratio is increased, the strength of the electromagnetic shielding film material will become too high and hard, and the flexibility will decrease; if the ratio is decreased, the comprehensive mechanical properties of the material will deteriorate, which is not conducive to practical applications.

[0034] Example 1:

[0035] This bionic structure-tunable electromagnetic shielding film is an electromagnetic shielding film prepared from castor oil-based waterborne polyurethane (the preparation process is shown in Figure 1 ), solvent water, and electromagnetic shielding filler by vacuum filtration; the specific preparation steps are as follows:

[0036] Step 1: Titanium carbide nanosheets were prepared by liquid-phase chemical etching method, and an aqueous dispersion of titanium carbide was prepared by ultrasonic dispersion with a concentration of 1 wt%, and the obtained electromagnetic shielding nanofiller dispersion was reserved for use; the mass usage amounts of titanium carbide were 0.02 g, 0.04 g, and 0.06 g respectively.

[0037] Step 2: Responsive castor oil-based waterborne polyurethane was prepared and diluted with deionized water to a concentration of 2 wt% to obtain a polymer dispersion for standby use, and the usage amounts of castor oil-based waterborne polyurethane were 1.98 g, 1.96 g, and 1.94 g respectively.

[0038] Step 3: The two raw material components obtained in Steps 1 and 2 were alternately added to a vacuum filtration device in turn, and vacuum filtration was carried out for 6 h under vacuum conditions to form an alternating multi-layer model with a total of five layers (2 layers of polymer matrix layer and 3 layers of electromagnetic shielding filler). The usage amount of titanium carbide in the whole multi-layer flexible film was set at 1.00 wt%, 2.00 wt%, and 3.00 wt% in gradient in turn. After obtaining an electromagnetic shielding film with a certain humidity, it was dried in an oven at 60 °C to obtain a bionic flexible electromagnetic shielding film;

[0039] Step 4: The multi-layer structure obtained in Step 3 was fragmented, and then hot-pressed by a flat vulcanizer. It could be converted into an isolation structure at 60 °C, 5 MPa, and 5 min. The microstructures of the electromagnetic shielding films before and after fragmentation were characterized ( Figure 3 ).

[0040] From Figure 1 's synthesis route diagram, it can be seen that the chain segments of the waterborne polyurethane have dynamic disulfide bonds. From Figure 2 it can be seen that the material has excellent and tunable electromagnetic shielding performance. From Figure 3As can be seen from Table 1, the electromagnetic shielding film 1 can achieve structural regulation at 60 °C, 5 MPa, and for 5 minutes, and the shielding performance only drops by 6 dB, indicating that the electromagnetic shielding film has the properties of structural conversion and multiple processing. It can also be seen from Table 1 that the type of electromagnetic shielding filler used has no direct relationship with the smoothness of structural conversion.

[0041] Example 2:

[0042] This bionic structure-tunable electromagnetic shielding film is an electromagnetic shielding film prepared from castor oil-based waterborne polyurethane, solvent water, and electromagnetic shielding filler by vacuum filtration; the specific preparation steps are as follows:

[0043] Step 1: Prepare an aqueous dispersion of carbon nanotubes by ultrasonic dispersion for 24 h, with a concentration of 1 wt%, to obtain an electromagnetic shielding nanofiller dispersion for standby; the mass usage amounts of carbon nanotubes are 0.02 g, 0.04 g, and 0.06 g respectively.

[0044] Step 2: Prepare a responsive castor oil-based waterborne polyurethane, dilute its concentration to 2 wt% with deionized water, and obtain a polymer dispersion for standby; the usage amounts of castor oil-based waterborne polyurethane are 1.98 g, 1.96 g, and 1.94 g respectively.

[0045] Step 3: Add the two raw material components obtained in Steps 1 and 2 to the vacuum filtration device alternately, and filter under vacuum for 6 h to form an alternating multilayer model with a total of five layers (2 layers of polymer matrix layer and 3 layers of electromagnetic shielding filler). The usage amounts of gradient carbon nanotubes in the entire multilayer flexible film are set to 1.00 wt%, 2.00 wt%, and 3.00 wt% in sequence. After obtaining an electromagnetic shielding thin film with a certain humidity, dry it in an oven at 60 °C to obtain a bionic flexible electromagnetic shielding thin film;

[0046] Step 4: Fragment the multilayer structure obtained in Step 3, and then hot press it with a flat vulcanizer. It can be converted into an isolation structure at 40 °C, 5 MPa, and for 10 minutes.

[0047] As can be seen from Table 1, the shielding efficiency of the electromagnetic shielding film 2 is lower than that of the electromagnetic shielding film 1 under the same filler usage amount, indicating that the electromagnetic shielding effect of carbon nanotubes is inferior to that of two-dimensional material titanium carbide. After being hot pressed and reformed into an isolation structure, its electromagnetic shielding efficiency still exceeds 20 dB, reaching the commercial level. However, the decline amplitude is lower than that using titanium carbide, which is due to the fact that the conductivity of carbon nanotubes is not sensitive to air oxidation.

[0048] Example 3:

[0049] The bionic structure - adjustable electromagnetic shielding film in this implementation is an electromagnetic shielding film prepared from castor - oil - based waterborne polyurethane as the polymer substrate, solvent water, and electromagnetic shielding fillers through the method of vacuum sand - core filtration. The specific preparation steps are as follows:

[0050] Step 1: Prepare an aqueous dispersion of graphene by ultrasonic dispersion for 24 h with a concentration of 1 wt%, and obtain an electromagnetic shielding nano - filler dispersion for standby. The mass usage amounts of graphene are 0.02 g, 0.04 g, and 0.06 g respectively.

[0051] Step 2: Prepare a responsive castor - oil - based waterborne polyurethane, dilute its concentration to 2 wt% with deionized water, and obtain a polymer dispersion for standby. The usage amounts of castor - oil - based waterborne polyurethane are 1.98 g, 1.96 g, and 1.94 g respectively.

[0052] Step 3: Add the two raw material components obtained in Steps 1 and 2 alternately into a vacuum filtration device, and filter under vacuum conditions for 6 h to form an alternating multi - layer model with a total of five layers (2 layers of polymer matrix and 3 layers of electromagnetic shielding filler). Sequentially set the gradient of the graphene dosage in the entire multi - layer flexible film to 1.00 wt%, 2.00 wt%, and 3.00 wt%. After obtaining an electromagnetic shielding film with a certain humidity, dry it in an oven at 60 °C to obtain a bionic flexible electromagnetic shielding film.

[0053] Step 4: Fragment the multi - layer structure obtained in Step 3, and then hot - press it through a flat vulcanizer. It can be converted into an isolation structure at 80 °C, 5 MPa, and for 1 min.

[0054] As can be seen from Table 1, the shielding effectiveness of electromagnetic shielding film 3 is inferior to that of electromagnetic shielding film 1 under the same filler dosage, indicating that the electromagnetic shielding effect of graphene is inferior to that of titanium carbide. However, since graphene belongs to two - dimensional materials, the formed conductive network is better and it is easier to be converted into an isolation structure. Therefore, its electromagnetic shielding effectiveness is better than that using carbon nanotubes. After being hot - pressed and re - formed into an isolation structure, its electromagnetic shielding effectiveness still exceeds 20 dB, and the decline amplitude does not exceed 13%, reaching the optimal commercial level, and it can shield 99.9% of electromagnetic waves. But the decline amplitude is lower than that using titanium carbide, which is due to the fact that the conductivity of graphene is also insensitive to air oxidation.

[0055] Table 1 The formulation of electromagnetic shielding films and the electromagnetic shielding effectiveness before and after structural transformation

[0056]

Claims

1. A flexible electromagnetic shielding film material with a bionic multi-layer structure that can be adjusted to an isolation structure, characterized in that: In the flexible electromagnetic shielding material with a bionic multi-layer structure that can be adjusted to an isolation structure, the proportion of responsive castor oil-based waterborne polyurethane in its components is 97-99 wt%, and the proportion of electromagnetic shielding filler is 1-3 wt%; The flexible electromagnetic shielding film material uses the vacuum filtration technology to alternately form films of responsive castor oil-based waterborne polyurethane and electromagnetic shielding filler in sequence, and forms a multi-layer structure integrated material relying on hydrogen bonds and electrostatic forces, with a total thickness of 20-30 μm; The responsive castor oil-based waterborne polyurethane is obtained by a method including the following steps: First, mix castor oil, isophorone diisocyanate and N-methyldiethanolamine in a three-necked round-bottom flask and stir at 78 °C for 10 minutes; then, add dibutyltin dilaurate to the prepolymer and keep stirring until the prepolymer is a white paste and hardly flows; subsequently, add methyl ethyl ketone to the system to reduce the viscosity. After the prepolymer is dissolved in methyl ethyl ketone, the disulfide compound is quickly added, and the stirring reaction is continued at 78 °C for 2 h; then remove the heating. When the reactant cools to room temperature, add glacial acetic acid to neutralize under stirring; add distilled water to the system for emulsification and dispersion; finally, remove methyl ethyl ketone by rotary evaporation to obtain a thermosetting cationic waterborne polyurethane-polyurea emulsion; The disulfide compound is selected from one of 2, 2'-diaminodiphenyl disulfide, 4, 4'-diaminodiphenyl disulfide, bis(6-hydroxy-2-naphthyl) disulfide, 3, 3'-dihydroxydiphenyl disulfide; The electromagnetic shielding filler is selected from one of titanium carbide, titanium carbonitride, silver nanowires, carbon nanotubes, graphene; The condition for the obtained multi-layer structure electromagnetic shielding film material to be transformed into an isolation structure is: under an external pressure of 5 MPa in a flat vulcanizer, hot press at 40-80 °C for 1-10 min to convert from a multi-layer structure to an isolation structure.

2. The flexible electromagnetic shielding film material with a bionic multi-layer structure that can be adjusted to an isolation structure according to claim 1, characterized in that: In the multi-layer structure, there are 2 layers of responsive castor oil-based waterborne polyurethane layer and 3 layers of electromagnetic shielding filler layer.

3. The flexible electromagnetic shielding film material with a bionic multi-layer structure that can be adjusted to an isolation structure according to claim 1, characterized in that: The molar ratio of -OH in castor oil, -NCO group in isophorone diisocyanate and -OH in N-methyldiethanolamine is 1:1.70:0.69; among them, 30 wt% of castor oil is replaced by an equivalent molar amount of disulfide compound to realize the preparation of a polymer with disulfide bonds in the main chain.

4. A method for preparing a flexible electromagnetic shielding film material of a bionic multi-layer structure adjustable to an isolation structure according to any one of claims 1-3, characterized in that Including the following steps: Step 1: Prepare an aqueous dispersion of electromagnetic shielding filler by ultrasonic dispersion, with a concentration of 1 wt%, and obtain an electromagnetic shielding nano-filler dispersion for standby; Step 2: Dilute the responsive castor oil-based waterborne polyurethane emulsion with deionized water to a concentration of 2 wt% to obtain a polymer dispersion for standby; Step 3: The two raw material components obtained in Steps 1 and 2 are alternately added into a vacuum filtration device in sequence, and vacuum filtration is carried out for 6 h to form an alternating multi-layer structure with a total of five layers, including 2 polymer matrix layers and 3 electromagnetic shielding filler layers, obtaining an electromagnetic shielding film with a certain humidity, and then drying it in an oven to obtain a bionic flexible electromagnetic shielding film.

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