A flexible composite electromagnetic shielding foam and its preparation method and application

Abstract

The application discloses a flexible composite electromagnetic shielding foam as well as a preparation method and application thereof. A simple solution ultrasonic loading method is adopted, and polyvinylpyrrolidone (PVP) is added to enhance the combination of CNTs and polyurethane foam, which is beneficial to helping the firm adhesion of CNTs on the polyurethane foam. In addition, the method introduces alkali metal salt into the carbon nanotube, forms a firm bonding effect with the graphite network, and then loads the carbon nanotube with bonded alkali metal ions on the foam in an ultrasonic mode, so as to improve the conductive performance of the flexible foam, reduce the skin thickness of the foam, and significantly improve the electromagnetic shielding efficiency of the foam. The flexible composite electromagnetic shielding foam prepared by the application has a better application prospect in electromagnetic shielding and absorption.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyurethane conductive composite materials and their preparation, and specifically relates to a flexible composite electromagnetic shielding foam and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of communication electronic technology, electromagnetic waves generated will cause electromagnetic interference (EMI) to electronic equipment, which will adversely affect the operation stability and service life of the equipment. If no shielding protection is provided, the generated electromagnetic pollution will not only endanger the normal operation of electronic equipment, but also affect human health and increase the risk of human disease. Therefore, eliminating harmful electromagnetic waves is crucial for protecting electronic communication equipment and maintaining a healthy human living environment.

[0003] Three-dimensional conductive foams have unique properties such as light weight, easy processing, low cost, and good corrosion resistance, and are expected to become a new generation of EMI shielding materials. In order to prepare conductive foams with good electromagnetic shielding performance, conductive fillers are usually introduced into the foam matrix by direct blending or solution blending methods.

[0004] However, such traditional conductive polymer composites often have some serious defects, such as strong π-π interaction between high specific surface area conductive fillers, which makes them easily aggregate and difficult to disperse uniformly in the polymer matrix. Therefore, a high load of conductive fillers is required to achieve interconnected conductive paths. However, the high load of conductive fillers inevitably weakens the mechanical strength and processing ability of the conductive polymer composite. In order to solve this shortcoming, conductive particles are loaded on the surface of the internal skeleton of the polymer foam by dip coating, so that the foam has EMI shielding function. However, the conductive particles on the surface will make the material have durability and filler content in the matrix decrease in long-term use, thereby limiting the application of this type of material in the field of electromagnetic shielding. SUMMARY

[0005] An object of the present application is to provide a preparation method of a flexible composite electromagnetic shielding foam, which improves the bonding force between the conductive filler and the surface of the foam, and the obtained flexible electromagnetic shielding foam has excellent mechanical properties, high recovery, good electromagnetic shielding efficiency, excellent stability, and excellent strain sensing performance.

[0006] To solve the above technical problems, the solution of the present application is:

[0007] A preparation method of a flexible composite electromagnetic shielding foam, the thickness of the flexible composite electromagnetic shielding foam is 1-100 mm; the preparation method comprises the following steps:

[0008] Step (1), mixing polyether polyol, deionized water, amine catalyst and silicone oil to prepare a precursor solution; adding p-xylene isocyanate TDI and tin catalyst to the precursor solution to stir rapidly, foam and cure to obtain polyurethane foam; the cell diameter of the polyurethane foam is 300-500 μm;

[0009] As preferred, the polyether polyol is polypropylene glycol (PPG) with a molecular weight of 2000;

[0010] As preferred, the stirring speed for preparing the precursor is 1600 r / min for 10-30 min;

[0011] As preferred, the rapid stirring speed for preparing the foam is 2000 r / min for 30 s;

[0012] As preferred, the curing temperature is 60℃ for 4 hours;

[0013] Step (2), adding filler to deionized water to disperse ultrasonically, then adding alkali metal salt to obtain a suspension with a filler mass content of 0.2%-0.7% after stirring uniformly; the filler includes carbon nanotube CNTs and polyvinylpyrrolidone PVP;

[0014] The PVP not only helps the dispersibility of CNTs in solution, but also helps CNTs to adhere firmly to the polyurethane foam.

[0015] As preferred, the ultrasonic dispersion is performed by a cell crusher with a power of 250 kHz for 2 hours;

[0016] As preferred, the mass ratio of the carbon nanotube CNTs to polyvinylpyrrolidone PVP is (5-10):(1-3); the mass ratio of the alkali metal salt to the filler is (4-9):(5-8); and the mass ratio of the polyether polyol to the filler is 10:(0.06-0.07);

[0017] As preferred, the alkali metal salt is one or more of cobalt salt, nickel salt and iron salt; more preferably, the alkali metal salt is one or more of cobalt acetate, nickel acetate, iron acetate, cobalt nitrate, nickel nitrate, iron nitrate, cobalt chloride, nickel chloride and iron chloride; most preferably, the alkali metal salt is iron chloride.

[0018] As preferred, the alkali metal salt is introduced into the carbon nanotube by a simple solution mixing method. This method allows the alkali metal particles to be encapsulated in the carbon nanotube to form a firm bond with the graphite network, which helps more positive and negative charges to pass through the interface between PU and CNTs.

[0019] Preferably, the stirring time is 1.5-3h and the stirring rate is 600-800r / min.

[0020] Step (3), the polyurethane foam obtained in step (1) is placed in the suspension of step (2), dried after ultrasonic treatment to obtain the flexible composite electromagnetic shielding foam.

[0021] Preferably, the ultrasonic treatment is performed by using an ultrasonic cleaner with a power of 40kHz for 30min.

[0022] Preferably, the drying temperature is 50℃ and the drying time is 4h.

[0023] Another object of the present application is to provide a flexible composite electromagnetic shielding foam prepared by the above method.

[0024] Still another object of the present application is to provide the use of the flexible composite electromagnetic shielding foam as an electromagnetic shielding material.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The present application provides a flexible composite electromagnetic shielding foam, which comprises a polyurethane porous framework, polyvinylpyrrolidone (PVP), an alkali metal salt and carbon nanotubes (CNTs), wherein the alkali metal salt, PVP and carbon nanotubes (CNTs) are uniformly distributed on the surface of the foam porous framework. In the present application, the alkali metal salt is dissolved in deionized water as a solvent, so that the alkali metal salt molecules are encapsulated inside the carbon nanotubes (CNTs) and form a firm bond with the graphite network, which is conducive to more positive and negative charges passing through the interface between the polyurethane (PU) and the CNTs, thereby improving the electrical conductivity of the flexible foam, reducing the skin thickness of the foam and improving the electromagnetic shielding efficiency. In the present application, PVP is also introduced, which not only improves the dispersibility of the carbon nanotubes in the aqueous solution, but also enhances the adhesion of the CNTs to the polyurethane foam, which is conducive to the more effective adsorption of the CNTs on the polyurethane foam.

[0027] (2) The flexible composite electromagnetic shielding foam provided by the present application has excellent resilience performance, and after 100 cycles of compression, the strength recovery and deformation recovery are maintained at 80-99% and 85-99%, respectively.

[0028] (3) The flexible composite electromagnetic shielding foam provided by the present application can adjust the content of the alkali metal filler and the carbon nanotubes on the surface of the foam by adjusting the ultrasonic time, thereby further controlling the electromagnetic shielding efficiency of the flexible composite electromagnetic shielding foam.

[0029] (4) The flexible composite electromagnetic shielding foam provided by the application has low density, suitable electrical conductivity, excellent impedance matching and loss capacity, and has a better application prospect in the field of electromagnetic shielding materials. The specific surface area of the flexible composite electromagnetic shielding foam is between 27 and 45 mg / cm 2 , the electrical conductivity is between 7.72 x 10- 5 and 1.1 S / m, and when the foam is used as an electromagnetic shielding material, the EMI SE value is between 45 and 62 dB when the thickness is 20 mm, and the effective wave absorption bandwidth is between 8 and 12 GHz. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 SEM image of the polyurethane foam prepared in Example 1;

[0031] Figure 2 SEM image of the flexible composite electromagnetic shielding foam prepared in Example 1;

[0032] Figure 3 Electromagnetic shielding performance diagram of the electromagnetic shielding foams prepared in Example 1 and Comparative Examples 1-3;

[0033] Figure 4 Wave absorption diagram of the flexible composite electromagnetic shielding foam prepared in Example 1;

[0034] Figure 5 Relative resistance change value-time evolution curve of the flexible composite electromagnetic shielding foam of Example 1 under the action of a stress with a strain of 80%;

[0035] Figure 6 Compression stress-strain curve diagram of Example 1;

[0036] Figure 7 Water immersion performance test result diagram of the electromagnetic shielding foams prepared in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0037] The application will be further described in detail below in combination with the drawings and examples. The following examples can enable those skilled in the art to more fully understand the application, but in no way limit the application.

[0038] As described above, in view of the deficiencies of the prior art, the present inventors have long studied and practiced a large amount of experiments, and have proposed the technical solution of the application. The main point is to use high-purity and uniformly dispersed multi-walled carbon nanotubes with a certain aspect ratio as conductive fillers, polyurethane foam, and alkali metal salt to prepare a flexible electromagnetic shielding foam with a conductive network, strong tensile and compression properties, and high electromagnetic shielding performance.

[0039] The present application adopts a one-step foaming method to prepare a flexible electromagnetic shielding foam with high toughness, and a simple solution-ultrasonic combined method, the process is strong in operability and low in cost.

[0040] A preparation method of a flexible composite electromagnetic shielding foam, the thickness of the flexible composite electromagnetic shielding foam is 1-100 mm; the preparation method comprises the following steps:

[0041] Step (1), 50 g of polyether polyol, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil are mixed to prepare a precursor solution, stirring at a speed of 1600 r / min for 10-30 min; TDI and tin catalyst are added to the precursor solution, stirring at a speed of 2000 r / min for 30 s, foaming, and curing at 60℃ for 4 hours to obtain a polyurethane foam; the cell diameter of the polyurethane foam is 300-500 μm; the polyether polyol is polypropylene glycol (PPG);

[0042] Step (2), 300-350 mg of filler is added to deionized water, and a cell crusher is used for ultrasonic dispersion at a power of 250 kHz for 2 h, then an alkali metal salt is added, stirring at a speed of 600-800 r / min for 1.5-3 h to obtain a suspension with a filler mass content of 0.2%-0.7%; the filler includes carbon nanotubes (CNTs) and polyvinylpyrrolidone (PVP), and the mass ratio of the two is (5-10):(1-3); the mass ratio of the alkali metal salt to the filler is (4-9):(5-8); the alkali metal salt is one or more of cobalt acetate, nickel acetate, iron acetate, cobalt nitrate, nickel nitrate, iron nitrate, cobalt chloride, nickel chloride and iron chloride;

[0043] Step (3), the polyurethane foam obtained in step (1) is placed in the suspension of step (2), and then ultrasonic cleaning machine is used for ultrasonic treatment at a power of 40 kHz for 30 min, and then the flexible composite electromagnetic shielding foam is obtained after drying at 50℃ for 4 hours.

[0044] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0045] Example 1

[0046] (1) Take 50 g of polypropylene glycol PPG, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil to prepare a precursor solution under the condition of stirring speed of 1600 r / min for 20 min; then under the condition of stirring speed of 2000 r / min, 24.86 g of p-xylene isocyanate and 0.13 g of tin catalyst are added to foam, and then cured at a temperature of 60℃ for 4 hours to obtain a polyurethane foam; the SEM image of the prepared polyurethane foam is shown in Figure 1 ;

[0047] (2) 250 mg of CNTs and 100 mg of PVP are added to deionized water and ultrasonically dispersed for 2 hours under the condition of cell crusher power of 250 kHz; a suspension with a mass content of 0.35wt% of conductive filler is obtained; 400 mg of FeCl3 is weighed and dissolved in the above suspension (i.e. the mass ratio of FeCl3 to filler is 8:7), and stirred at a stirring rate of 600 r / min for 2 h; a uniform suspension is obtained after stirring.

[0048] (3) The sample obtained in (1) is placed in the suspension in (2) and treated by ultrasonic cleaning machine at a power of 40 kHz for 45 min; after ultrasonic treatment, it is placed in a vacuum drying box at 50℃ for 4 hours to evaporate water, and a flexible composite electromagnetic shielding foam is obtained.

[0049] The SEM image of the prepared flexible composite electromagnetic shielding foam is shown in Figure 2 , which is a complete porous network structure, and many filamentous carbon nanotubes grow uniformly on the surface of the foam.

[0050] Test Example 1

[0051] The flexible composite electromagnetic shielding foam prepared in Example 1 is tested as an electromagnetic shielding material for its wave absorption performance, and the results are shown in Figure 4 ; the foam prepared by the present application shows strong wave absorption performance, and the absorption power is as high as 97.5%.

[0052] The relative resistance change value of the flexible composite electromagnetic shielding foam prepared in Test Example 1 under the action of pressure with a strain of 80% is tested to evolve with time, and the results are shown in Figure 5 .

[0053] The compression stress-strain of the flexible composite electromagnetic shielding foam prepared in Test Example 1 is tested, and the results are shown in Figure 6The resistance of the flexible composite electromagnetic shielding foam decreases with the increase of compressive strain and increases with the recovery of compressive strain. The relative resistance change value of the electromagnetic shielding foam shows the same evolution trend during the cyclic compression process, indicating that the electromagnetic shielding foam has good stability and repeatability when used as a strain sensing device.

[0054] After 100 cycles of compression, the strength recovery and deformation recovery of the flexible composite electromagnetic shielding foam are 99.4% and 99.8%, respectively; the conductivity is 1.08 S / m; when used as an electromagnetic shielding material, the addition amount is 20wt%, the electromagnetic shielding efficiency of the electromagnetic shielding composite material with a thickness of 20mm can reach 60.5dB at a wave band of 12.4GHz.

[0055] Example 2

[0056] (1) Take 50g of polypropylene glycol PPG, 1g of deionized water, 0.13g of amine catalyst and 0.55g of silicone oil to prepare a precursor solution under the condition of stirring speed of 1600r / min and time of 20min; then under the condition of stirring speed of 2000r / min, add 24.86g of p-xylene isocyanate and 0.13g of tin catalyst to foam, and then cure at a temperature of 60℃ for 4 hours to obtain a polyurethane foam; the SEM image of the prepared polyurethane foam is as shown in Figure 1

[0057] (2) Add 250mg of CNTs and 50mg of PVP to deionized water and ultrasonically disperse for 2 hours under the condition of cell crusher power of 250kHz; obtain a suspension with a mass content of conductive filler of 0.29wt%; weigh 240mg of FeCl3 and dissolve it in the above suspension (i.e. the mass ratio of FeCl3 to filler is 4:5), and stir at a stirring rate of 600r / min for 2h; after stirring, a uniform suspension is obtained.

[0058] (3) Place the sample obtained in (1) in the suspension in (2) in an ultrasonic cleaner with a power of 40kHz for 45min, and then place it in a vacuum drying box at 50℃ for 4 hours to evaporate the water, thereby obtaining a flexible composite electromagnetic shielding foam.

[0059] Example 3

[0060] ​(1) Take 50 g of polypropylene glycol PPG, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil to prepare a precursor solution under the condition of stirring speed of 1600 r / min for 20 min; then under the condition of stirring speed of 2000 r / min, add 24.86 g of p-xylene isocyanate and 0.13 g of tin catalyst to foam, and then cure at a temperature of 60°C for 4 hours to obtain a polyurethane foam; the SEM image of the prepared polyurethane foam is shown in Figure 1 ;

[0061] (2) Add 240 mg of CNTs and 72 mg of PVP to deionized water, and ultrasonically disperse under the condition of cell crusher power of 250 kHz for 2 hours; obtain a suspension with a mass content of conductive filler of 0.31 wt%; weigh 350 mg of FeCl3 and dissolve it in the above suspension (i.e. the mass ratio of FeCl3 to filler is 9:8), and stir at a stirring rate of 600 r / min for 2 h; after stirring, a uniform suspension is obtained.

[0062] (3) Place the sample obtained in (1) in the suspension in (2) in an ultrasonic cleaner with a power of 40 kHz for 45 min, and after ultrasonic treatment, place it in a vacuum drying box at 50°C for 4 hours to evaporate the water, and obtain a flexible composite electromagnetic shielding foam.

[0063] Comparative Example 1: without adding alkali metal salt

[0064] (1) Take 50 g of polypropylene glycol PPG, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil to prepare a precursor solution under the condition of stirring speed of 1600 r / min for 20 min; then under the condition of stirring speed of 2000 r / min, add 24.86 g of p-xylene isocyanate and 0.13 g of tin catalyst to foam, and then cure at a temperature of 60°C for 4 hours to obtain a polyurethane foam;

[0065] (2) Add 250 mg of CNTs and 100 mg of PVP to deionized water, and ultrasonically disperse under the condition of cell crusher power of 250 kHz for 2 hours; obtain a suspension with a filler content of 0.35 wt%;

[0066] (3) Place the sample obtained in (1) in the suspension in (2) in an ultrasonic cleaner with a power of 40 kHz for 45 min, and after ultrasonic treatment, place it in a vacuum drying box at 50°C for 4 hours to evaporate the water, and obtain a flexible composite electromagnetic shielding foam.

[0067] The strength recovery and deformation recovery of the foam containing the conductive network are 99.2% and 99.6% respectively after 100 cycles of compression; the electrical conductivity is 0.89 S / m; when used as an electromagnetic shielding material, the addition amount is 20 wt%, the thickness of the electromagnetic shielding composite material is 20 mm, and the electromagnetic shielding effectiveness at 12.4 GHz band can reach 53.6 dB.

[0068] Comparative Example 2: without adding PVP

[0069] (1) 50 g of polypropylene glycol PPG, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil were taken to prepare a precursor solution under the condition of stirring speed of 1600 r / min for 20 min; then 24.86 g of p-xylene isocyanate and 0.13 g of tin catalyst were added under the condition of stirring speed of 2000 r / min to foam, and then cured at a temperature of 60°C for 4 hours to obtain a polyurethane foam;

[0070] (2) 250 mg of CNTs were added to deionized water and ultrasonically dispersed under the condition of cell crusher power of 250 kHz for 2 hours; a suspension with a CNT content of 0.25 wt% was obtained; 370 mg of FeCl3 (mass ratio of FeCl3:CNTs is 8:5) was weighed and dissolved in the above suspension, and stirred at a stirring speed of 600 r / min for 2 h; a uniform suspension was obtained after stirring.

[0071] (3) The sample obtained in (1) was placed in the suspension in (2) and treated with ultrasonic waves in an ultrasonic cleaner at a power of 40 kHz for 45 min, and then placed in a vacuum drying box at 50°C for 4 hours to evaporate the water, thereby obtaining a foam containing a conductive network.

[0072] The strength recovery and deformation recovery of the foam containing the conductive network are 99.5% and 99.7% respectively after 100 cycles of compression; the electrical conductivity is 0.64 S / m; when used as an electromagnetic shielding material, the addition amount is 3.97 wt% less than that of Comparative Example 1, the thickness of the electromagnetic shielding composite material is 20 mm, and the electromagnetic shielding effectiveness at 12.4 GHz band can reach 44.7 dB.

[0073] Comparative Example 3: without adding PVP and alkali metal salt

[0074] (1) Take 50 g of polypropylene glycol PPG, 1 g of deionized water, 0.13 g of amine catalyst and 0.55 g of silicone oil to prepare a precursor solution under the condition of stirring speed of 1600 r / min for 20 min; then under the condition of stirring speed of 2000 r / min, 24.86 g of p-xylene isocyanate and 0.13 g of tin catalyst are added to foam, and then cured at a temperature of 60°C for 4 hours to obtain a polyurethane foam;

[0075] (2) 250 mg of CNTs is added to deionized water and ultrasonically dispersed under the condition of cell crusher power of 250 kHz for 2 hours to obtain a suspension with a mass content of 0.25 wt% of conductive filler;

[0076] (3) The sample obtained in (1) is placed in the suspension in (2) and ultrasonically treated in an ultrasonic cleaner with a power of 40 kHz for 45 min, and then placed in a vacuum drying box at 50°C for 4 hours to evaporate water, thereby obtaining a foam containing a conductive network.

[0077] After 100 cycles of compression, the strength recovery and deformation recovery of the foam containing the conductive network are 99.2% and 99.6%, respectively; the electrical conductivity is 0.47 S / m; when used as an electromagnetic shielding material, the addition amount is 4.52 wt% less than that of Comparative Example 1 under the same ultrasonic time, and the electromagnetic shielding effectiveness of the electromagnetic shielding composite material with a thickness of 20 mm at a wave band of 12.4 GHz can reach 37.5 dB.

[0078] The composite electromagnetic shielding foams prepared in Example 1 and Comparative Examples 1-3 are respectively subjected to electromagnetic shielding effectiveness test, and the results are shown in Table 1. Figure 3 As shown in Table 1, when the content of conductive filler is the same, the electromagnetic shielding effectiveness of the composite electromagnetic shielding foam prepared in Comparative Example 3 is the worst, and the electromagnetic shielding effectiveness of the composite electromagnetic shielding foam prepared in Example 1 is the best.

[0079] The composite electromagnetic shielding foams prepared in Example 1 and Comparative Examples 1-3 are respectively subjected to water immersion performance test, and the results are shown in Table 2. Figure 7 As shown in Table 2, at a time of 20 min, fillers are obviously present on the water surface of Comparative Examples 2 and 3, and the amount of fillers gradually increases with time; on the contrary, no fillers are seen in water at a time of 60 min for Example 1 and Comparative Example 1. It is further proved that the addition of polyvinylpyrrolidone PVP helps to enhance the combination of CNTs and polyurethane foam, so that CNTs are firmly adhered to the polyurethane foam.

[0080] Finally, it should be noted that the above enumeration is only specific embodiments of the present application. Obviously, the present application is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered within the scope of the present application.

Claims

1. A method for producing a flexible composite electromagnetic shielding foam having a thickness of 1 to 100 mm, characterized in that, The preparation method comprises the following steps: Step (1), mixing and stirring polyether polyol, deionized water, amine catalyst and silicone oil to prepare a precursor solution; adding p-xylene isocyanate TDI and tin catalyst to the precursor solution and stirring to foam, and obtaining polyurethane foam after curing; Step (2), adding filler to deionized water, ultrasonic dispersion, then adding alkali metal salt, stirring uniformly to obtain a suspension with a filler mass content of 0.2-0.7%; the filler comprises carbon nanotubes CNTs and polyvinylpyrrolidone PVP; the mass ratio of carbon nanotubes CNTs to polyvinylpyrrolidone PVP in the filler is (5-10):(1-3); the mass ratio of the alkali metal salt to the filler is (4-9):(5-8); Step (3), placing the polyurethane foam obtained in step (1) in the suspension obtained in step (2), ultrasonic treatment and drying to obtain the flexible composite electromagnetic shielding foam.

2. The production method according to claim 1, characterized by, The polyether polyol in step (1) is polypropylene glycol PPG.

3. The production method according to claim 1, characterized by, The stirring speed for preparing the precursor in step (1) is 500-3000 r / min, and the stirring time is 5-60 min; the stirring speed in the foaming process is 500-3000 r / min, and the stirring time is 30-500 s.

4. The method of claim 1, wherein, The mass ratio of the polyether polyol to the filler is 10:(0.06-0.07).

5. The preparation method according to claim 1, characterized in that, The alkali metal salt in step (2) is one or more of cobalt salt, nickel salt and iron salt.

6. The production method according to claim 5, wherein The alkali metal salt in step (2) is one or more of cobalt acetate, nickel acetate, iron acetate, cobalt nitrate, nickel nitrate, iron nitrate, cobalt chloride, nickel chloride and iron chloride.

7. The preparation method according to claim 1, characterized in that, The stirring time in step (2) is 1.5-3 h, and the stirring rate is 600-800 r / min.

8. A flexible, composite electromagnetic shielding foam, characterized in that, Prepared by the method of any one of claims 1-7.

9. Use of the flexible composite electromagnetic shielding foam of claim 8 as an electromagnetic shielding material.

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