A high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, its preparation and application

Abstract

The present invention discloses a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, as well as its preparation and application, belonging to the technical field of electromagnetic shielding materials. In the present invention, a TOCNF / CS aerogel film is placed between two hydrogel composite papers containing conductive layers, with the conductive layers facing outwards. The two identical hydrogel composite papers containing conductive layers and the TOCNF / CS aerogel film are assembled using an adhesive to obtain a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure. The combination of the hydrogel composite paper and the TOCNF / CS aerogel film in the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure of the present invention increases the distance between the conductive layers, thereby extending the transmission distance of electromagnetic waves, providing sufficient space for multiple reflections and absorptions of electromagnetic waves, and improving the electromagnetic shielding performance of the composite paper. The high-performance electromagnetic shielding composite paper with a corrugated paper-like structure prepared by the present invention has good flexibility, good mechanical properties, and excellent electromagnetic shielding performance.

Description

Technical Field

[0001] The present invention relates to a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, its preparation and application, belonging to the technical field of electromagnetic shielding materials. Background Art

[0002] Electromagnetic shielding materials can effectively alleviate the problem of electromagnetic wave pollution. Generally, the high performance of electromagnetic shielding materials can be achieved through structural design and increasing the content of conductive fillers. For example, Patent CN117106228A discloses a preparation method of a porous structure-based polydimethylsiloxane (PDMS) electromagnetic shielding composite film. Specifically, a porous PDMS film is prepared by a sugar template method, then conductive fillers are deposited on the surface of the porous PDMS film through vacuum filtration, and finally a layer of PDMS is coated for encapsulation and drying. The obtained PDMS-based electromagnetic shielding composite film has the characteristics of flexibility, low filling, and high electromagnetic shielding performance. However, its preparation process is complex and not conducive to cost savings.

[0003] Cellulose paper has a low cost and can be industrially produced; and its good flexibility and loose porous structure characteristics make it a good substrate for preparing electromagnetic shielding materials. For example, Patent CN109610229A discloses a preparation method of a self-fluffy electromagnetic shielding paper. By soaking cellulose paper in a NaBH4 solution and then taking it out and plating it in a chemical plating solution, a self-fluffy electromagnetic shielding paper is obtained. The prepared electromagnetic shielding paper exhibits an electromagnetic shielding performance greater than 60 dB in the frequency band of 9 kHz - 1.5 GHz. However, its preparation relies on chemical plating, increasing the production cost, and its electromagnetic shielding efficiency is poor in the high-frequency band. Summary of the Invention

[0004] In order to solve the problems existing in the existing electromagnetic shielding materials, such as high preparation cost, complex production process, and poor electromagnetic shielding performance, mechanical strength, and flexibility, the present invention combines the loose porous characteristics of cellulose filter paper with an aerogel film and prepares a high-performance electromagnetic shielding composite paper through a corrugated paper-like structure design. The high-performance electromagnetic shielding composite paper with a corrugated paper-like structure prepared by the present invention has conductive layers with high conductivity on both sides of the surface, and the loose porous structural characteristics of the middle cellulose filter paper and the aerogel film provide a sufficiently large spacing between the two conductive layers, which is conducive to multiple reflections and absorptions of electromagnetic waves, thereby improving the electromagnetic shielding performance.

[0005] The first object of the present invention is to provide a method for preparing a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, including the following steps:

[0006] (1) Mix the conductive filler solution and the TEMPO-oxidized nanocellulose (TOCNF) solution evenly to obtain a mixture of TEMPO-oxidized nanocellulose and conductive filler; then coat the cationic starch (CS) solution on the upper or lower surface of the cellulose filter paper first, and then coat the mixture of TOCNF and conductive filler, and dry to obtain a hydrogel composite paper containing a conductive layer.

[0007] (2) Mix the cationic starch solution and the TEMPO-oxidized nanocellulose solution to form a hydrogel, and freeze-dry it to obtain a TOCNF / CS aerogel film.

[0008] (3) Place the TOCNF / CS aerogel film between two layers of hydrogel composite papers containing conductive layers, with the conductive layers facing outwards, and assemble the two layers of the same hydrogel composite papers containing conductive layers and the TOCNF / CS aerogel film using an adhesive, and dry to obtain a high-performance electromagnetic shielding composite paper with a corrugated paper structure.

[0009] In one embodiment, the concentration of the CS solution in steps (1) and (2) is 0.5 - 1.2 wt.%, and the dispersion medium is water.

[0010] In one embodiment, the concentration of the TOCNF solution in steps (1) and (2) is 0.5 - 1.2 wt.%, and the dispersion medium is water.

[0011] In one embodiment, the concentration of the conductive filler solution in step (1) is 0.6 - 1.2 wt.%, and the dispersion medium is water.

[0012] In one embodiment, the coating amount of CS in step (1) is 0.8 - 1.6 mg / cm 2 ; the total coating amount of TOCNF and conductive filler is 0.8 - 3.6 mg / cm 2 .

[0013] In one embodiment, the mass ratio of CS, TOCNF, and conductive filler in step (1) is 1:1 - 2:0.25 - 1.25.

[0014] In one embodiment, the conductive filler in the conductive filler solution in step (1) is one or more of MXene, carbon nanotubes, silver nanowires, or graphene.

[0015] In one embodiment, the pore size of the cellulose filter paper in step (1) is 0.2 - 50 μm, and the thickness is 0.15 - 0.20 mm.

[0016] In one embodiment, the freeze-drying in step (2) is carried out at -50°C to -40°C for 36 - 60 h.

[0017] In one embodiment, the mass ratio of CS to TOCNF in step (2) is 1:1 - 2.

[0018] In one embodiment, the thickness of the TOCNF / CS aerogel film in step (2) is 0.15 - 0.48 cm.

[0019] In one embodiment, the adhesive in step (3) is a cationic starch solution, and the concentration of the cationic starch solution is 2.0 - 6.0 wt.%.

[0020] The second object of the present invention is to provide a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, which is prepared by the above method.

[0021] The third object of the present invention is to provide the application of the above method or the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure in the fields of 5G telecommunication materials, electromagnetic shielding materials, protective materials, interior decoration materials, and electronic product substrates.

[0022] The fourth object of the present invention is to provide a method for improving the electromagnetic shielding performance while maintaining the performance of cellulose filter paper, and the method includes the following steps:

[0023] (1) Mix the conductive filler solution and the TEMPO-oxidized nanofibrillated cellulose solution evenly to obtain a mixture of TEMPO-oxidized nanofibrillated cellulose and conductive filler; then, first coat the cationic starch solution on the upper or lower surface of the cellulose filter paper, and then coat the mixture of TOCNF and conductive filler, and dry to obtain a hydrogel composite paper containing a conductive layer.

[0024] (2) Mix the cationic starch solution and the TEMPO-oxidized nanofibrillated cellulose solution to form a hydrogel, and freeze-dry to obtain a TOCNF / CS aerogel film.

[0025] (3) Assemble two identical hydrogel composite papers containing a conductive layer and the TOCNF / CS aerogel film with an adhesive, with the TOCNF / CS aerogel film in the middle of the two layers of hydrogel composite papers containing a conductive layer and the conductive layer facing outward, and dry to obtain a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure.

[0026] The beneficial effects of the present invention:

[0027] (1) Due to the action of charges in the mixture of TOCNF and conductive filler adopted in the present invention, the conductive filler can be evenly dispersed, ensuring the stability of the conductive performance; the TOCNF and CS solution in the mixture of TOCNF and conductive filler can form a hydrogel, increasing the bonding force between different coatings, so that the prepared electromagnetic shielding composite paper has good mechanical properties, and the tensile strength can reach more than 10 Mpa.

[0028] (2) In the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure of the present invention, the conductive layers are located on the upper and lower surfaces, enabling electromagnetic waves to enter the interior through the conductive layers. The combination of the hydrogel composite paper and the TOCNF / CS aerogel film increases the spacing between the conductive layers, thereby extending the transmission distance of the electromagnetic waves, providing sufficient space for multiple reflections and absorptions of the electromagnetic waves, improving the electromagnetic shielding performance of the composite paper, and enabling the electromagnetic shielding performance to reach more than 60 dB.

[0029] (3) The cellulose filter paper and the aerogel TOCNF / CS aerogel film used in the present invention both have good flexibility, and the structure of the present invention will not damage the flexibility. Due to the presence of the cellulose filter paper, the composite paper has good flexibility. In addition, the hydrogen bond interaction between TOCNF and MXene is beneficial to further improving the flexibility of the composite paper.

[0030] (4) The intermediate layer of conventional multi-layer structure electromagnetic shielding materials needs to add conductive fillers, while the intermediate layer of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure prepared by the present invention does not need to add conductive fillers. While saving the conductive fillers, it also enhances the electromagnetic shielding performance of the composite paper, which is beneficial to saving the production cost of materials; and the high-performance electromagnetic shielding composite paper of the present invention has better electromagnetic shielding performance than the composite paper with a conductive layer added in the middle.

[0031] (5) The high-performance electromagnetic shielding composite paper with a corrugated paper-like structure prepared by the present invention has good flexibility, good mechanical properties, and excellent electromagnetic shielding performance. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure obtained in Example 1;

[0033] Figure 2 It is a physical diagram of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure obtained in Example 1;

[0034] Figure 3 It is a cross-sectional scanning electron microscope image and its element distribution of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure obtained in Example 2, where a is the cross-sectional scanning electron microscope image and b is the element distribution diagram. Detailed Embodiments

[0035] The following are the preferred embodiments of the present invention. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0036] Testing Methods:

[0037] 1. Electromagnetic Shielding Performance Test:

[0038] The electromagnetic shielding performance of the sample was measured in the X-band (8.2 - 12.4 GHz) using an Agilent PNA-N5244A vector network analyzer by the waveguide method. During the test, the sample was cut into a size of 22.9 mm × 10.2 mm, and the vector network analyzer was calibrated.

[0039] 2. Mechanical property test:

[0040] The mechanical properties of the sample were analyzed using an AI-7000NGD servo material multi-functional high and low temperature control testing machine. During this process, the sample was cut into a rectangle (40 mm × 15 mm), and the tensile rate was set to 10 mm·min -1 . The analysis of each sample was repeated at least three times to test the tensile strength and elongation at break of the sample.

[0041] Raw materials used in the examples:

[0042] Cellulose filter paper: medium speed, qualitative filter paper, pore size 7 - 8 μm, cut into a circle with a diameter of 4 cm, thickness 0.15 - 0.16 mm; purchased from Hangzhou Special Paper Co., Ltd.

[0043] Cationic starch (CS): purity: 99.5%; degree of substitution: 0.3; appearance: white powder; fineness ≥ 98; pH value: 7 - 11; purchased from Dezhou Runde Starch Co., Ltd.

[0044] TEMPO-oxidized nanofibrillated cellulose (TOCNF): high concentration gelatinous, specification size (L: 500 - 5000 nm; D: 10 - 20 nm (AFM); concentration: 1.2 wt.%; carboxyl content: 0.2 - 2.0 mmol / g; appearance: translucent gel; dispersion medium: water), purchased from Zhejiang Jinjiahao Green Nanomaterials Co., Ltd.

[0045] MXene:

[0046] MXene was prepared by the HCl + LiF acid etching method. First, 2.0 g of LiF was added to 40 mL of 9 mol·L -1 HCl solution and reacted at room temperature for 30 min. Then, 2.0 g of Ti3AlC2 was slowly added to the above system and stirred and reacted at 35 °C and 500 rpm for 24 h. After the reaction ended, the reaction product was centrifugally washed several times with deionized water, centrifugally washed at 3500 rpm for 5 min each time until the supernatant was neutral. Then, the centrifuged reaction product was ultrasonically treated at 200 W for 30 min. Finally, the ultrasonically treated solution was centrifuged, and the dark green supernatant was collected, which was a 1.0 wt.% MXene solution.

[0047] Silver nanowires: CAS No.: 7440-22-4, parameters (C: 10 mg / mL; length: about 20 μm; solvent: water; concentration: 1 wt.%), purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0048] Example 1

[0049] A method for preparing a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, comprising the following steps:

[0050] (1) Dissolve CS in water to prepare a CS solution with a concentration of 0.8 wt.%; dissolve high-concentration gelatinous TOCNF in water to prepare a TOCNF solution with a concentration of 0.8 wt.%; mix 2.5 g of 1.0 wt.% MXene solution with 2.5 g of 0.8 wt.% TOCNF solution evenly to obtain a mixture of TOCNF and conductive filler; then first coat 2.5 g of CS solution on the upper surface of the cellulose filter paper, and then coat 5.0 g of the mixture of TOCNF and conductive filler, and dry to obtain a hydrogel composite paper containing a conductive layer, where the coating amount of CS is 1.6 mg / cm 2 , and the total coating amount of TOCNF and conductive filler is 3.6 mg / cm 2 ;

[0051] (2) Mix 2.5 g of 0.8 wt.% TOCNF solution with 2.5 g of 0.8 wt.% CS solution to form a hydrogel, put it into a cylindrical container with a diameter of 4 cm, and freeze-dry at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.048 cm;

[0052] (3) Dissolve CS in water to prepare a solution with a concentration of 4.5 wt.% as a cationic starch adhesive; place the TOCNF / CS aerogel film between two hydrogel composite papers containing conductive layers with the conductive layers facing outwards, and assemble the two identical hydrogel composite papers containing conductive layers and the TOCNF / CS aerogel film with the cationic starch adhesive, and dry at 30 °C for 2 h to obtain a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure.

[0053] Figure 1 is a schematic structural diagram of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure obtained in Example 1; Figure 2 is a physical picture of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure obtained in Example 1.

[0054] Example 2:

[0055] Different from Example 1, in step (2), 1.25 g of 0.8 wt.% TOCNF solution was mixed with 1.25 g of 0.8 wt.% CS solution to form a hydrogel, which was placed in a round container with a diameter of 4 cm and freeze-dried at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.030 cm;

[0056] Other conditions and parameters are the same as those in Example 1.

[0057] Figure 3 Figure a is the cross-sectional scanning electron micrograph and Figure b is the elemental distribution map of the high-performance electromagnetic shielding composite paper with a corrugated paper structure obtained in Example 2. It can be seen from the figure that the Ti element (blue area) is distributed on both sides, indicating that MXene is evenly distributed on both sides of the composite paper, and there is a relatively large spacing between the conductive layers.

[0058] Example 3:

[0059] Different from Example 1, in step (2), 1.0 g of 0.8 wt.% TOCNF solution was mixed with 1.0 g of 0.8 wt.% CS solution to form a hydrogel, which was placed in a round container with a diameter of 4 cm and freeze-dried at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.015 cm;

[0060] Other conditions and parameters are the same as those in Example 1.

[0061] Example 4:

[0062] Different from Example 1, in step (1), the MXene solution was adjusted to a silver nanowire solution (concentration: 1 wt.%, solvent: water);

[0063] Other conditions and parameters are the same as those in Example 1.

[0064] Example 5:

[0065] Different from Example 1, in step (1), the masses of the added MXene solutions were adjusted to 0.5 g and 1.5 g respectively;

[0066] Other conditions and parameters are the same as those in Example 1.

[0067] Comparative Example 1:

[0068] Different from Example 1, step (2) was omitted, and two layers of hydrogel composite paper were directly assembled using cationic starch adhesive, with the side of the hydrogel composite paper with the conductive layer facing outwards.

[0069] The middle layer aerogel in Comparative Example 2 contains conductive fillers

[0070] Different from Example 1, in step (2), 2.5 g of 0.8 wt.% TOCNF solution, 2.5 g of 0.8 wt.% CS solution and 0.01 g of 1.0 wt.% MXene solution were mixed to form a hydrogel, which was placed in a round container with a diameter of 4 cm and freeze-dried at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.048 cm;

[0071] Other conditions and parameters were the same as those in Example 1.

[0072] The middle layer thickness of Comparative Example 3 was too small

[0073] Different from Example 1, in step (2), 0.75 g of 0.8 wt.% TOCNF solution and 0.75 g of 0.8 wt.% CS solution were mixed to form a hydrogel, which was placed in a round container with a diameter of 4 cm and freeze-dried at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.010 cm;

[0074] Other conditions and parameters were the same as those in Example 1.

[0075] The middle layer thickness of Comparative Example 4 was too large

[0076] Different from Example 1, in step (2), 5.0 g of 0.8 wt.% TOCNF solution and 5.0 g of 0.8 wt.% CS solution were mixed to form a hydrogel, which was placed in a round container with a diameter of 4 cm and freeze-dried at -45 °C for 48 h to form a TOCNF / CS aerogel film with a thickness of 0.086 cm;

[0077] Other conditions and parameters were the same as those in Example 1.

[0078] The middle layer of Comparative Example 5 was corrugated

[0079] Different from Example 1, in step (2), a crease roller pressing device was used to make the filter paper corrugated and assembled with the hydrogel composite paper into a corrugated paper structure electromagnetic shielding composite paper.

[0080] The interlayer bonding force of this electromagnetic shielding composite paper was weak, resulting in poor mechanical properties and making it unable to meet the requirements of electromagnetic shielding materials for practicality and durability.

[0081] Comparative Example 6

[0082] Cellulose filter paper: It was the cellulose filter paper without any treatment in Example 1.

[0083] The performances of the electromagnetic shielding composite papers prepared in Examples 1 - 5 and Comparative Examples 1 - 4 and the cellulose filter paper of Comparative Example 6 were tested, and the results are shown in Table 1:

[0084] Table 1

[0085]

[0086]

[0087] Note: The elongation at break is the ratio of the elongation at break to its initial length, expressed as a percentage. It is an indicator of the flexibility and elastic properties of the material. The larger the elongation at break, the better its flexibility and elasticity.

[0088] As can be seen from Table 1, within a certain range, as the thickness of the middle layer TOCNF / CS aerogel film increases, the electromagnetic shielding performance of the electromagnetic shielding composite paper also increases, and the mechanical strength of the paper decreases slightly. However, when the thickness of the TOCNF / CS aerogel film is too large, the electromagnetic shielding performance of the electromagnetic shielding composite paper decreases instead, and the tensile strength will decrease significantly.

[0089] In the present invention, if the pore size of the cellulose filter paper is too large, it will cause an excessive amount of the hydrogel film component on the surface to enter the interior of the paper, so that the conductive components in the hydrogel film cannot be concentrated on one side of the filter paper, affecting the spacing of the conductive layer. If the pore size of the cellulose filter paper is too small, the interfacial bonding force between the cellulose filter paper and the hydrogel film will be weak, resulting in the detachment of the hydrogel film. Therefore, the selection of the pore size of the cellulose filter paper is crucial. Only within the scope of the present invention can an electromagnetic shielding material with excellent performance be formed.

[0090] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure, characterized in that: The following steps are involved: (1) mixing a conductive filler solution and a TEMPO-oxidized nanocellulose solution uniformly to obtain a mixture of TEMPO-oxidized nanocellulose and a conductive filler; then coating the upper surface or the lower surface of the cellulose filter paper with a cationic starch solution, and then coating the TEMPO-oxidized nanocellulose and the conductive filler mixture, and drying to obtain a hydrogel composite paper containing a conductive layer; (2) Mixing the cationic starch solution with the TEMPO-oxidized nanocellulose solution to form a hydrogel, and freeze-drying to obtain a TOCNF / CS aerogel film; (3) According to the TOCNF / CS aerogel film being placed between two layers of hydrogel composite paper containing a conductive layer, with the conductive layer facing outward, two layers of the same hydrogel composite paper containing a conductive layer and the TOCNF / CS aerogel film are assembled with an adhesive and dried to obtain a high-performance electromagnetic shielding composite paper with a corrugated paper-like structure; The mass ratio of cationic starch, TEMPO oxidized nanocellulose and conductive filler in step (1) is 1:1-2:0.25-1.25; The thickness of the TOCNF / CS aerogel film described in step (2) is 0.15-0.48 cm; The pore size of the cellulose filter paper in step (1) is 0.2-50 μm and the thickness is 0.15-0.20 mm.

2. The method according to claim 1, characterized in that The coating amount of cationic starch in step (1) is 0.8-1.6 mg / cm 2 The total coating amount of TEMPO-oxidized nanocellulose and conductive filler is 0.8-3.6 mg / cm 2 .

3. The method according to claim 1, characterized in that The concentration of the cationic starch solution in step (1) and step (2) is 0.5-1.2 wt.%, and the dispersion medium is water.

4. The method according to claim 1, characterized in that The concentration of the TEMPO-oxidized nanocellulose solution in step (1) and step (2) is 0.5-1.2 wt.%, and the dispersion medium is water.

5. The method according to claim 1, characterized in that In step (2), the mass ratio of cationic starch to TEMPO-oxidized nanocellulose is 1:1-2.

6. A high-performance electromagnetic shielding composite paper with a corrugated paper structure, characterized in that: The method is prepared by any one of claims 1 to 5.

7. Application of the high-performance electromagnetic shielding composite paper with a corrugated paper-like structure as claimed in claim 6 in the fields of protective materials, interior materials and electronic product substrates.

8. The use according to claim 7, characterized in that: The protective material includes electromagnetic shielding material, and the electronic product substrate includes 5G telecommunication material.

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