Preparation method and application of flame-retardant electromagnetic shielding paper

Abstract

The invention provides a preparation method and application of flame-retardant electromagnetic shielding paper, and relates to the technical field of functional paper preparation.According to the method, carbon fiber / cellulose paper is formed firstly, then MXene suspension liquid is sprayed to the surface of the carbon fiber / cellulose paper, finally, a zein solution is used for soaking treatment, and in the process, MXene and carbon fibers are introduced, so that the flame-retardant electromagnetic shielding paper is obtained. The performance characteristics of the two can be combined together, and the electromagnetic shielding paper can be endowed with the high-strength characteristic by utilizing the synergistic effect of the two; the zein solution is used for treating the paper, so that the strength and the stability of the paper can be improved while the paper is endowed with waterproofness. Through the method, the flame-retardant electromagnetic shielding paper with high strength, waterproofness, conductivity and stability is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of functional paper preparation, and particularly to a preparation method and application of a flame-retardant electromagnetic shielding paper. Background Art

[0002] With the continuous upgrading and large-scale use of 5G and 6G communication technologies in the GHz band, electromagnetic pollution has become the fourth major hazard after water pollution, noise pollution, and air pollution, seriously affecting the stable operation of precision equipment and human physical health. The electromagnetic radiation generated by the highly integrated circuits of electronic devices can not only cause functional failures of nearby devices, but also interfere with the normal operation of their own devices. According to a recent report by the World Health Organization, electromagnetic radiation may cause symptoms such as headaches, depression, and fatigue. Therefore, electromagnetic pollution has become one of the urgent problems to be solved at present.

[0003] Electromagnetic shielding materials reduce interference and radiation to the protected target, thereby blocking the interference of electromagnetic waves to the protected target. Commonly used electromagnetic shielding materials are mainly metals or metal alloy materials, such as products made of copper, aluminum, silver, tungsten, iron, stainless steel, etc. The electromagnetic shielding performance of metal products mainly depends on their thickness and metal type. The greater the thickness of the metal product, the better the electromagnetic shielding effect. Although metal products show good absorption and reflection effects in electromagnetic shielding, metal products have disadvantages such as large mass and high processing difficulty. In addition to metal products, wave-absorbing materials are also commonly used electromagnetic shielding materials. For example, polymer materials, carbon black, carbon fiber, etc., have characteristics such as light weight and good wave-absorbing performance. However, how to efficiently disperse and enhance these wave-absorbing materials is one of the key problems to be overcome in the preparation of high-performance electromagnetic shielding materials. In addition, carbon fiber-based electromagnetic shielding materials have the problem of high brittleness and are difficult to maintain the integrity of the morphological structure during repeated use.

[0004] In addition, during the use of electromagnetic shielding materials, they will come into contact with electronic devices and are prone to overheating or catching fire. Good flame retardancy is one of the essential important functions of electromagnetic shielding materials. In addition, electromagnetic shielding in a high-humidity environment will also become normal, which requires that electromagnetic shielding materials have good water resistance and can show good strength in a wet environment. Therefore, the development of high-strength and flame-retardant electromagnetic shielding materials plays an important role and significance in solving the problem of electromagnetic pollution.

[0005] In view of this, it is necessary to design an improved preparation method and application of a flame-retardant electromagnetic shielding paper to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of a flame-retardant electromagnetic shielding paper.

[0007] To achieve the above-mentioned invention object, the present invention provides a preparation method of a flame-retardant electromagnetic shielding paper, comprising the following steps:

[0008] S1. Dispersing carbon fibers in a cellulose suspension to obtain a carbon fiber suspension; diluting the carbon fiber suspension, and performing suction filtration to obtain a wet paper web of carbon fiber / cellulose;

[0009] S2. Spraying an MXene suspension on the surface of the wet paper web of carbon fiber / cellulose obtained in step S1, and then performing hot pressing treatment to obtain an MXene / carbon fiber / cellulose composite paper;

[0010] S3. Immersing the MXene / carbon fiber / cellulose composite paper prepared in step S2 in a zein solution, and performing secondary hot pressing treatment to obtain the flame-retardant electromagnetic shielding paper.

[0011] Preferably, in step S2, the concentration of the MXene suspension is 0.1-1.0 wt%, and the spraying amount of the MXene suspension on the surface of the wet paper web of carbon fiber / cellulose is 10-100 mL.

[0012] Preferably, in step S1, the mass fraction of the carbon fibers is 0.1-0.8 wt%.

[0013] Preferably, the mass percentage of cellulose in the cellulose suspension is 0.1-0.5 wt%.

[0014] Preferably, in step S2, the temperature of the hot pressing treatment is 70-180 °C, the pressure is 0.5-2.0 MPa, and the time is 5-20 min.

[0015] Preferably, in step S3, the temperature of the secondary hot pressing treatment is 70-180 °C, the pressure is 0.5-2.0 MPa, and the time is 5-20 min.

[0016] Preferably, the concentration of the zein solution is 1-20 wt%, and the immersion time is 3-10 min.

[0017] Preferably, in step S1, the dilution process is carried out as follows: adding water or ethanol to the carbon fiber dispersion liquid, and the dilution multiple is 1-5 times.

[0018] Particularly, the flame-retardant electromagnetic shielding paper prepared by using the preparation method provided by the present invention can be applied to the field of electromagnetic shielding.

[0019] The beneficial effects of the present invention are:

[0020] The preparation method of the flame-retardant electromagnetic shielding paper provided by the present invention is to first form a carbon fiber / cellulose paper, then spray an MXene suspension on its surface, and finally soak it with a zein solution. By introducing MXene and carbon fiber in this process, not only can the performance characteristics of the two be combined together, but also the synergistic effect between the two can be utilized to endow the electromagnetic shielding paper with high strength characteristics. By treating the paper with a zein solution, while endowing the paper with waterproofness, the strength and stability of the paper can be improved. Through the above method, a flame-retardant electromagnetic shielding paper with high strength, waterproofness, conductivity and high stability is prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the tensile strength diagram of the flame-retardant electromagnetic shielding paper prepared in Example 1 of the present invention;

[0022] Figure 2 It is the electromagnetic shielding diagram of the paper prepared in Example 1;

[0023] Figure 3 It is the average electromagnetic loss value diagram of the paper prepared in Example 1;

[0024] Figure 4 It is the conductive effect diagram of the flame-retardant electromagnetic shielding paper prepared in Example 1 of the present invention;

[0025] Figure 5 It is the optical photo of the flame-retardant electromagnetic shielding paper prepared in Example 1 of the present invention when hanging a heavy object;

[0026] Figure 6 It is the flame retardancy test diagram of the flame-retardant electromagnetic shielding paper prepared in Example 1 of the present invention;

[0027] Figure 7 It is the tensile strength curve diagram of the electromagnetic shielding paper prepared in Examples 2 to 4 of the present invention;

[0028] Figure 8 It is the current-voltage curve diagram of the electromagnetic shielding paper prepared in Examples 2 to 4 of the present invention;

[0029] Figure 9 It is the electromagnetic shielding diagram of the electromagnetic shielding paper prepared in Examples 2 to 4 of the present invention;

[0030] Figure 10 It is the average electromagnetic loss value diagram of the electromagnetic shielding paper prepared in Examples 2 to 4 of the present invention;

[0031] Figure 11 It is the tensile strength diagram of the MXene / carbon fiber / cellulose composite paper prepared in Comparative Example 1;

[0032] Figure 12 It is the electromagnetic shielding diagram of the paper prepared in Comparative Example 1;

[0033] Figure 13 Graph of the average electromagnetic loss value of the paper prepared in Comparative Example 1;

[0034] Figure 14 Optical photographs of the papers prepared in Example 1 and Comparative Example 1 immersed in water. Detailed implementation manners

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0037] In addition, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0038] The preparation method of the flame-retardant electromagnetic shielding paper provided by the present invention comprises the following steps:

[0039] S1. Dispersing carbon fibers in a cellulose suspension to obtain a carbon fiber suspension; after diluting the carbon fiber suspension, performing suction filtration to obtain a wet paper web of carbon fiber / cellulose;

[0040] S2. Spraying an MXene suspension on the surface of the wet paper web of carbon fiber / cellulose obtained in step S1, and then performing hot pressing treatment to obtain an MXene / carbon fiber / cellulose composite paper;

[0041] S3. Immersing the MXene / carbon fiber / cellulose composite paper prepared in step S2 in a zein solution, and performing secondary hot pressing treatment to obtain the flame-retardant electromagnetic shielding paper.

[0042] In the above technical solution, by preparing paper with carbon fiber and MXene together, the flexibility and strength characteristics of MXene and the strength characteristics of carbon fiber can be fully utilized to endow the electromagnetic shielding paper with high strength characteristics. By regulating the concentration of the carbon fiber suspension, the uniform distribution of carbon fibers in the solution can be ensured. This is because both carbon fibers and cellulose molecules contain polar hydroxyl groups, and hydrogen bonds can be formed between them. The formation of hydrogen bonds is conducive to the uniform dispersion of carbon fibers in the cellulose solution and prevents the aggregation of carbon fibers. At the same time, the solvent molecules in the cellulose suspension will form a solvation layer around the carbon fibers and cellulose molecules, which can reduce the direct contact and mutual collision between carbon fibers and between carbon fibers and cellulose molecules, reducing the possibility of their aggregation and helping the carbon fibers to maintain a uniformly dispersed state in the solution. Under the above actions, the uniform distribution of carbon fibers in the paper can be ensured, and the integrity of the paper can be ensured. By using the spraying method to load MXene on the paper surface, the efficient adhesion of MXene on the paper surface can be ensured, providing excellent mechanical properties for the paper. This is because: some MXene will be embedded in the structures of cellulose and carbon fiber to form a skeleton structure, effectively improving the stability of MXene. By treating the paper with zein solution, on the one hand, a protective film can be formed on the paper surface by using its film-forming property to prevent the MXene on the paper from falling off. At the same time, the formation of the protective film can further enhance the electrostatic interaction between MXene and carbon fiber, making MXene stably exist in the paper to improve the integrity and overall strength of the paper. On the other hand, the zein film layer itself has a certain strength, which can further improve the strength of the paper; secondly, zein has a certain hydrophobicity, and treating the paper with it can endow the paper with certain waterproof properties.

[0043] As an embodiment of the present invention, in step S1, the preparation method of the cellulose suspension is as follows: Mix sodium hydroxide, urea and water according to a mass ratio of 7:12:81, stir and cool down to -12°C. When the solution becomes clear and transparent, add an appropriate amount of cellulose and stir at -12°C for 30 minutes to obtain a cellulose suspension, and the mass percentage of cellulose in the cellulose suspension is 0.1-0.5 wt%.

[0044] As an embodiment of the present invention, in step S1, the length of the carbon fiber is 2-8 mm, and the mass percentage of the carbon fiber in the carbon fiber dispersion is 0.1-0.8 wt%.

[0045] As an embodiment of the present invention, in step S1, the vacuum filtration is carried out as follows: Vacuum filtration is carried out using a 0.45 μm filter membrane.

[0046] As an embodiment of the present invention, in step S1, the dilution process is carried out as follows: water or ethanol is added to the carbon fiber dispersion liquid, and the dilution multiple is 1 - 5 times.

[0047] As an embodiment of the present invention, in step S2, the MXene suspension is a single-layer Ti 3 C 2 T x MXene is dispersed in water to obtain it, and its concentration is 0.1 - 1.0 wt%, and the spraying amount of the MXene suspension on the surface of the carbon fiber / cellulose wet paper web is 10 - 100 mL.

[0048] As an embodiment of the present invention, in step S2, the temperature of the hot pressing treatment is 70 - 180 °C, the pressure is 0.5 - 2.0 MPa, and the time is 5 - 20 min.

[0049] As an embodiment of the present invention, in step S3, the zein solution is obtained by dissolving zein in an ethanol solution, the mass percentage of the ethanol solution is 60 - 90%, the concentration of the zein solution is 1 - 20 wt%, and the soaking time is 3 - 10 min.

[0050] As an embodiment of the present invention, in step S3, the temperature of the secondary hot pressing treatment is 70 - 180 °C, the pressure is 0.5 - 2.0 MPa, and the time is 5 - 20 min.

[0051] The preparation method and application of the flame-retardant electromagnetic shielding paper proposed by the present invention are further described below in conjunction with specific embodiments:

[0052] Example 1

[0053] In this example, a flame-retardant electromagnetic shielding paper was prepared, and the preparation method included the following steps:

[0054] S1. Sodium hydroxide, urea and water were mixed according to a mass ratio of 7:12:8, stirred and cooled to -12 °C. When the solution became clear and transparent, 1.0 g of cellulose was added and stirred at -12 °C for 30 min to obtain a cellulose suspension; carbon fibers were dispersed in the cellulose suspension and stirred for 20 min to obtain a carbon fiber suspension; 100 mL of water was added to 100 mL of the carbon fiber suspension for dilution, and suction filtration was carried out to obtain a wet paper web of carbon fiber / cellulose; among them, the mass fraction of carbon fibers in the carbon fiber suspension was 0.4 wt%;

[0055] S2. Apply 30 mL of an MXene suspension with a concentration of 0.2 mg / mL onto the surface of the wet paper web of carbon fiber / cellulose obtained in step S1, and then perform hot pressing treatment to obtain an MXene / carbon fiber / cellulose composite paper. Among them, the conditions for the hot pressing treatment are: temperature 150 °C, pressure 1.0 MPa, and time 15 min;

[0056] The MXene suspension is a single-layer Ti 3 C 2 T x MXene dispersed in water and is obtained by the following preparation method:

[0057] Mix 1 g of lithium fluoride (LiF) with 20 mL of 9M hydrochloric acid, and stir well at room temperature for 10 min to form a uniform etching solution; Weigh 1 g of Ti 3 AlC 2 Add the powder in small amounts and multiple times to the above LiF-HCl etching solution, and magnetically stir the reaction in a constant temperature water bath at 35 °C for 24 h. After the etching is completed, centrifuge the etching solution (4000 rpm, 8 min / time). After one cycle, pour off the upper etching solution and collect the bottom precipitate; Wash the precipitate with deionized water, centrifuge (4000 rpm, 8 min / time), wash and centrifuge with deionized water 4 - 5 times (the upper layer liquid gradually becomes turbid from clear), centrifuge until the pH of the supernatant > 6 (or completely neutral), and collect the bottom precipitate; Add deionized water to the precipitate (20 mL per tube), and ultrasonicate for 30 min (ice water bath) under nitrogen protection. After the ultrasonication is completed, centrifuge the solution at 4000 rpm for 1 hour, and collect the upper black liquid; Take 2 - 4 mL of the black liquid and perform vacuum filtration, and naturally dry it into a film to obtain a single-layer Ti 3 C 2 T x MXene; Before use, disperse the single-layer Ti 3 C 2 T x MXene in water, and then the MXene suspension is obtained;

[0058] S3. Add 10 g of zein to an ethanol solution with an ethanol concentration of 85% and stir until the zein is dissolved to obtain a zein solution; Immerse the MXene / carbon fiber / cellulose composite paper prepared in step S2 in the zein solution for 10 min, and use a flat vulcanizer to hot press the soaked paper at 150 °C and 1.0 MPa for 15 min, then the flame-retardant electromagnetic shielding paper is prepared. It should be noted that the reagents and raw materials used in the embodiments of the present invention can be obtained by purchasing in the market without special instructions.

[0059] The tensile strength diagram of the flame-retardant electromagnetic shielding paper prepared in this example is as Figure 1As shown, the maximum tensile strength of the paper can reach 28 MPa; in the frequency range of 8.20 to 12.4 GHz, the total electromagnetic shielding effectiveness is 47.4 dB, of which the reflection shielding effectiveness is 12.7 dB and the absorption shielding effectiveness is 34.7 dB, as Figure 2 shown; the average electromagnetic loss value diagram of the paper is as Figure 3 shown. After forming an electric current loop with the above-mentioned flame-retardant electromagnetic shielding paper, a battery, a small light bulb, and wires, the small light bulb can emit light, and the result is as Figure 4 shown. This conclusion shows from the side that the electromagnetic shielding paper has certain electrical conductivity; in addition, in this embodiment, the tensile strength is also illustrated by using a flame-retardant electromagnetic shielding paper (5.0 cm long and 1.5 cm wide) to hang a 3 kg weight. The optical photo of the paper when hanging the heavy object is as Figure 5 (the red circle part in the figure indicates the flame-retardant electromagnetic shielding paper) shown. This conclusion further verifies that the flame-retardant electromagnetic shielding paper has excellent tensile properties; the limiting oxygen index of the flame-retardant electromagnetic shielding paper is 28%, and in the combustion test, there is no open flame on the electromagnetic shielding paper and it self-extinguishes when removed from the fire, as Figure 6 shown, indicating that the paper has an obvious inhibitory ability to combustion and exhibits good flame-retardant effects.

[0060] Examples 2 to 4

[0061] The differences between Examples 2 to 4 and Example 1 are only as follows: in step S1, the mass fraction of carbon fibers in the carbon fiber suspension is different from that in Example 1, and the treatments of steps S2 and S3 are not carried out. The mass fractions of carbon fibers in the carbon fiber suspensions of Examples 1 to 4 are set as shown in Table 1. The tensile strength curve diagrams of the electromagnetic shielding papers prepared in Examples 2 to 4 are as Figure 7 shown. It can be seen from the figure that the electromagnetic shielding paper prepared in Example 1 exhibits good strength performance, its maximum tensile strength is close to 40 MPa, and the breaking length is higher than 2.0%. However, the tensile strength of Example 4 is the lowest because when the mass fraction of carbon fibers is 8 wt%, the dispersion effect of carbon fibers becomes poor, and some carbon fibers agglomerate into clusters and finally remain in the paper, resulting in a significant decrease in the tensile strength of the paper compared with Example 1. Its maximum tensile strength only maintains at about 6.0 MPa, and the breaking length is lower than 1.0%; the current-voltage curve diagram of the electromagnetic shielding paper is as Figure 8 shown. The results show that as the voltage increases, the current of the paper shows an upward trend, and the resistance of Example 2 is the smallest, indicating that the electromagnetic shielding paper prepared under this condition has the best electrical conductivity. Further measurement shows that its resistivity is 0.077 Ω·cm; the electromagnetic shielding diagram of the electromagnetic shielding paper is as Figure 9 shown, and the average electromagnetic loss value diagram of the electromagnetic shielding paper is as Figure 10As shown, the results indicate that the electromagnetic shielding paper prepared in Example 4 has the best electromagnetic shielding performance. Its total electromagnetic shielding effectiveness within the frequency range of 8.20 to 12.4 GHz is 45.6 dB, where the reflection shielding effectiveness is 12.3 dB and the absorption shielding effectiveness is 33.3 dB.

[0062] Table 1 Mass fraction of carbon fibers in the carbon fiber suspension of Examples 1 to 4

[0063] Item Carbon fiber mass fraction (wt%) Resistivity (Ω·cm) Example 1 0.4 0.128 Example 2 0.1 0.584 Example 3 0.2 0.244 Example 4 0.8 0.077

[0064] Examples 5 to 7

[0065] The differences between Examples 5 to 7 and Example 1 are only as follows: In step S2, the concentration of the MXene suspension used is different from that in Example 1, and the treatment of step S3 is not carried out. Other experimental parameters are the same as those in Example 1 and will not be elaborated here. The performance comparison of the electromagnetic shielding paper prepared under the MXene suspension concentration settings and corresponding conditions in Example 1 and Examples 5 to 8 is shown in Table 2. It can be seen from the data in the table that as the concentration of the MXene suspension increases, the resistivity of the paper gradually decreases. This is because more MXene constructs a conductive network structure.

[0066] Table 2 Performance comparison of the electromagnetic shielding paper prepared under the MXene suspension concentration settings and corresponding conditions in Example 1 and Examples 5 to 8

[0067]

[0068] Comparative Example 1

[0069] The difference between Comparative Example 1 and Example 1 is only that the paper is not treated with zein solution. Other experimental parameters are the same as those in Example 1 and will not be elaborated here. The tensile strength diagram of the MXene / carbon fiber / cellulose composite paper prepared in Comparative Example 1 is as Figure 11 shown. Its maximum tensile strength is 8.0 MPa, and the breaking length is less than 2.0%, far lower than 28 MPa of Example 1. This is because during the process of treating the paper with zein solution in Example 1, zein can form a film layer on the paper surface, which can improve the strength of the paper to a certain extent. At the same time, the film layer can further enhance the connection stability between MXene and carbon fibers, enabling MXene to stably exist in the paper to improve the integrity and overall strength of the paper. The electromagnetic shielding diagrams and average electromagnetic loss value diagrams of the papers prepared in Comparative Example 1 and Example 1 are as Figure 12 and Figure 13As shown, it can be seen from the figure that the total electromagnetic shielding efficiency of the MXene / carbon fiber / cellulose composite paper prepared in Comparative Example 1 is 44.8 dB in the frequency range of 8.20 to 12.4 GHz, of which the reflection shielding efficiency is 11.7 dB and the absorption shielding efficiency is 33.1 dB. The shielding efficiency of this is not much different from that of the electromagnetic shielding paper in Example 1. This is because zein has poor conductivity, and the soaking and hot pressing treatment of zein do not change the conductivity of the electromagnetic shielding paper. The optical photo of the paper soaked in water is as Figure 14 As shown, it can be seen from the figure that after soaking in water for 10 h, the whole paper is damaged, and the black MXene and carbon fibers fall off, affecting the conductivity and electromagnetic shielding ability of the paper. After soaking in water for 10 h, the overall shape of the electromagnetic shielding paper treated with zein solution in Example 1 does not change significantly, and the water becomes slightly turbid. This shows that treating the paper with zein solution can enhance the stability of the paper as a whole and prevent the paper from changing its shape under conditions such as soaking in water and bending.

[0070] Comparative Example 2

[0071] The difference between Comparative Example 2 and Example 1 is only that: the MXene suspension is not sprayed, and other experimental parameters are the same as those in Example 1, which will not be elaborated here. It was found during the experiment that the conductivity and electromagnetic shielding ability of the paper prepared in Comparative Example 2 are both inferior to those in Example 1. This is because MXene itself has good conductivity and electromagnetic shielding ability, and without the filling of Mxene between the fibers and carbon fibers, the conductivity and electromagnetic shielding of the paper only rely on the network structure formed by the internal carbon fibers, so the conductivity and electromagnetic shielding ability are reduced.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flame retardant electromagnetic shielding paper, characterized in that: The steps include: S1, dispersing carbon fiber in a cellulose suspension to obtain a carbon fiber suspension; diluting the carbon fiber suspension and filtering to obtain a carbon fiber / cellulose wet paper web; S2, spraying the MXene suspension on the surface of the carbon fiber / cellulose wet paper web obtained in step S1, and then subjecting the paper to a hot press treatment to obtain a MXene / carbon fiber / cellulose composite paper; S3. Soaking the MXene / carbon fiber / cellulose composite paper obtained in step S2 in a zein solution, and subjecting the paper to secondary hot pressing to obtain a flame-retardant electromagnetic shielding paper.

2. The preparation method according to claim 1, characterized in that: In step S2, the concentration of the MXene suspension is 0.1-1.0 wt%, and the spraying amount of the MXene suspension on the surface of the carbon fiber / cellulose wet paper web is 10-100 mL.

3. The preparation method according to claim 1, characterized in that: In step S1, the mass fraction of the carbon fiber is 0.1-0.8wt%.

4. The preparation method according to claim 1, characterized in that: The mass percentage of cellulose in the cellulose suspension is 0.1-0.5wt%.

5. The preparation method according to claim 1, characterized in that: In step S2, the temperature of the hot pressing treatment is 70-180°C, the pressure is 0.5-2.0 MPa, and the time is 5-20 min.

6. The preparation method according to claim 1, characterized in that: In step S3, the secondary hot pressing treatment is performed at a temperature of 70-180°C, a pressure of 0.5-2.0 MPa, and a time of 5-20 min.

7. The preparation method according to claim 1, characterized in that: The concentration of the zein solution is 1-20wt%, and the soaking time is 3-10min.

8. The preparation method according to claim 1, characterized in that: In step S1, the dilution process is performed as follows: water or ethanol is added to the carbon fiber dispersion, and the dilution multiple is 1-5 times.

9. A flame retardant electromagnetic shielding paper prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the flame-retardant electromagnetic shielding paper according to claim 9 in the field of electromagnetic shielding.

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