Preparation method of high-orientation graphene aggregate flexible film for electromagnetic shielding

Abstract

The invention provides a preparation method of a high-orientation graphene aggregate flexible film for electromagnetic shielding. According to the preparation method, a confinement growth container is adopted for orientation and confinement, so that the graphene aggregate with high orientation arrangement and oriented growth is obtained, the high-orientation graphene aggregate flexible film can be obtained in combination with subsequent simple mechanical pressing, and the preparation method is simple and low in cost and has potential large-scale production advantages. According to the directionally grown graphene aggregate obtained in the invention, impurities introduced in the preparation process can be completely removed in combination with temperature treatment, so that the intrinsic high conductivity advantage of graphene is maximized. Compared with a traditional electromagnetic shielding material, the high-orientation graphene aggregate flexible thin film prepared by the preparation method disclosed by the invention keeps excellent conductivity under the condition of extremely good flexibility, the highest conductivity can reach 4.072 * 10 < 5 > S / m, the electromagnetic wave shielding performance is extremely good, the high-orientation graphene aggregate flexible thin film can be stably kept at about 105dB at 8-12Hz, and meanwhile, the high-orientation graphene aggregate flexible thin film has good shielding bandwidth.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding films, and specifically to a preparation method of a highly oriented graphene aggregate flexible film for electromagnetic shielding. Background Art

[0002] With the rapid development of 5G digital cellular networks, the application of electromagnetic waves mainly in the GHz range has brought great convenience to life. However, the problem of negative electromagnetic interference (EMI) caused by widely popular wireless communication devices and electronic components has become increasingly serious. This has seriously affected the normal operation and health status of the interfered electronic devices and living organisms. Therefore, protective measures against electromagnetic interference are very important, which has directly promoted the rapid development of electromagnetic shielding films. Among them, using highly conductive materials as the shielding body will generate a large number of free charges to form a continuous conductive path on the surface of the medium, interact with the EMW and generate an induced counter field, causing strong reflection of electromagnetic waves to achieve the shielding effect. Therefore, the development of highly conductive electromagnetic shielding materials has received extensive attention.

[0003] As an emerging sp2 two-dimensional material, graphene nanosheets have extremely high conductivity. How to assemble graphene into macroscopic graphene films to fully utilize its high conductivity advantage for EMI shielding has received extensive attention. Among them, methods such as CVD method, wet assembly of graphene oxide combined with high-temperature / chemical thermal reduction, graphite intercalation compounds combined with high-temperature exfoliation / dispersant ultrasonic dispersion, etc. have all been proven to be able to successfully prepare and assemble graphene films and can be applied to electromagnetic shielding. However, these methods still have the problems of high cost and complex processes, which increase the cost of large-scale production and application of graphene films. More importantly, the preparation of traditional graphene films usually has problems such as a large degree of defects caused by ultrasonic exfoliation and difficulty in removing impurity solvents, which seriously affect the intrinsic high conductivity of graphene and its application value in the field of electromagnetic shielding.

[0004] Graphene aggregates, as a macroscopic 3D graphene structure, can be obtained through simple oxidation intercalation and interlayer exfoliation. Graphene existing in the form of aggregates can retain its intrinsic high conductivity advantage, while avoiding the high-concentration defects caused by excessive oxidation and the introduction of additional impurity solvents, thus avoiding the common problems in the current assembly of graphene films. Therefore, it is particularly important to orient graphene aggregates as assembly monomers and combine mechanical pressing to prepare macroscopic graphene films to improve the serious problems of current traditional graphene films. Summary of the Invention

[0005] The present invention provides a highly oriented graphene aggregate flexible film for electromagnetic shielding, its preparation method and application, to solve the problems raised in the above background art.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for preparing a highly oriented graphene aggregate flexible film, comprising the following steps: Step (1), mixing raw graphite, persulfate and concentrated sulfuric acid to obtain a slurry; placing the slurry in a confined growth container in a tiled manner, standing and reacting to obtain a directionally grown graphene aggregate; Step (2), removing residual chemical reagents in the directionally grown graphene aggregate by high-temperature impurity removal to obtain a directionally grown graphene aggregate foam; Step (3), mechanically pressing the directionally grown graphene aggregate foam to obtain the highly oriented graphene aggregate flexible film.

[0008] Further, the volume-mass ratio of the raw graphite, persulfate and concentrated sulfuric acid in Step (1) is: 1-3 g: 3-5 g: 1-2 mL.

[0009] Further, in Step (1), the raw graphite is flake graphite or massive graphite; the persulfate includes potassium peroxymonosulfate and / or ammonium persulfate.

[0010] Further, the confined growth container in Step (1) is specifically a cylindrical and hollow quartz container, and a plurality of circular holes are uniformly distributed at the bottom of the container. After depositing the slurry at the bottom of the container, a quartz wafer is horizontally covered on the surface of the slurry; preferably, the specific dimensions of the container are a bottom diameter of 30 mm and a height of 20 mm; the size of the circular holes is a diameter of 0.5 mm; the size of the quartz wafer includes a diameter of 30 mm and a thickness of 0.5 mm, 1 mm, 1.5 mm, 2 mm or 2.5 mm.

[0011] Further, the tiling in Step (1) specifically includes: at a rotation speed of 3000-4000 rpm, spin-coating the slurry for 15-30 seconds, and then performing vacuum filtration for 3-5 s at a pressure of -0.1 Mpa through the circular holes reserved at the bottom of the growth container.

[0012] Further, the standing reaction in Step (1) is specifically a reaction at a temperature of 25°C to 80°C for 7 h to 24 h.

[0013] Further, the high-temperature impurity removal in Step (2) specifically includes: in an argon atmosphere, heating from 25°C to 450°C, 550°C or 650°C at a heating rate of 7°C / min, and holding for 90 min.

[0014] Further, the mechanical pressing in Step (3) is specifically a pressure holding for 60 min at a pressure of 15-30 Mpa.

[0015] The present invention also provides a highly oriented graphene aggregate flexible film prepared by the method for preparing a highly oriented graphene aggregate flexible film as described above.

[0016] The present invention also provides the application of the highly oriented graphene aggregate flexible film as described above in the field of electromagnetic shielding.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0018] The method for preparing a highly oriented graphene aggregate flexible film provided by the present invention uses a confinement growth container for orientation and confinement, thereby obtaining a highly oriented graphene aggregate with oriented growth. By combining subsequent simple mechanical pressing, a highly oriented graphene aggregate flexible film can be obtained. The preparation method is simple and the cost is low, having the potential for large-scale production advantages.

[0019] In the present invention, the obtained graphene aggregate with oriented growth can completely remove the impurities introduced during the preparation process by combining temperature treatment, thereby maximizing the intrinsic high conductivity advantage of graphene. Compared with traditional electromagnetic shielding materials, the highly oriented graphene aggregate flexible film prepared by the present invention maintains excellent electrical conductivity while having excellent flexibility. The highest electrical conductivity can reach 4.072×10 5 S / m, and excellent electromagnetic wave shielding performance, which can be stably maintained at about 105 dB in the range of 8 - 12 Hz, and at the same time has a good shielding bandwidth.

[0020] The present invention broadens the uses of graphene aggregates and improves the practical application value of graphene aggregates. The highly oriented graphene aggregates obtained by confinement growth have high density. After mechanical pressing, a highly compact graphene layered structure can be obtained, which endows the film with extremely high electrical conductivity and EMI SE ability. The highly oriented graphene aggregate foam obtained by the present invention can obtain a graphene aggregate film through mechanical pressing. Compared with traditional graphene assembly methods, mechanical ultrasonic treatment is avoided, and the large-size structure of graphene is retained, which can maximize its high conductivity advantage.

[0021] The highly oriented graphene aggregate flexible film developed by the present invention through confinement growth combined with mechanical pressing can control its thickness to be only between 40 and 60 microns, fully meeting the actual application in small and ultra-thin devices. By adjusting the size of the confinement growth container, the thickness of the highly oriented graphene aggregate flexible film can be controlled to be suitable for different application scenarios. Description of the Drawings

[0022] One or more embodiments are illustrated by the pictures in the corresponding drawings. These illustrative descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation.

[0023] Figure 1 SEM images of the GAs compression films prepared in Example 1 and Example 2 of the present invention;

[0024] Figure 2 Comparison of the conductivity of the GAs compression films prepared in Example 1 and Example 2 of the present invention;

[0025] Figure 3 Comparison of the Raman spectra of the GAs foams with oriented growth in Example 1 and Example 3 of the present invention;

[0026] Figure 4 Comparison of the conductivity of the mechanically pressed GAs films prepared in Example 1 and Example 4 of the present invention

[0027] Figure 5 Comparison of the EMI SE of the GAs compression films in Example 1 and Example 5 of the present invention;

[0028] Figure 6 SEM comparison of the cross-sections of the GAs foams in Example 1 and Example 6 of the present invention. Detailed implementation manners

[0029] In view of the problems existing in the prior art, the present invention provides a highly oriented graphene aggregate flexible film for electromagnetic shielding, its preparation method and application.

[0030] Among them, a preparation method of a highly oriented graphene aggregate flexible film includes the following steps:

[0031] Step 1: Mix potassium persulfate, concentrated sulfuric acid, and raw graphite evenly into a slurry state, then transfer the slurry to a confined growth container and horizontally cover a quartz wafer on the surface of the slurry as a confinement means. At the same time, perform vacuum filtration through the round holes reserved at the bottom of the container to promote the deposition and spreading of the raw graphite in the slurry. Transfer the reaction system to a specific temperature and let it stand. After the room-temperature exfoliation is completed, obtain graphene aggregates with oriented growth.

[0032] Step 2: Transfer the graphene aggregates with oriented growth to an argon environment and perform high-temperature treatment to remove residual impurities to obtain graphene aggregate foams with oriented growth.

[0033] Step 3: Mechanically press and hold the pressure of the graphene aggregate foams with oriented growth to obtain a graphene aggregate shielding film with high-orientation arrangement of the lamellae.

[0034] Among them, in Step 1, the persulfate is potassium persulfate or ammonium persulfate; the raw graphite can be flake graphite.

[0035] Among them, the dosages in step 1 are as follows: 1 g of flake graphite, 3 g of persulfate, and 2 mL of concentrated sulfuric acid.

[0036] Among them, the confinement growth container in step 1 is a quartz growth container with 30 circular holes (diameter 0.5 mm) distributed at the bottom, the bottom diameter is 30 mm, the height is 20 mm, and the diameter of the circular quartz wafer vertically covering the surface of the material is 30 mm, and the thickness is 0.5 mm, 1 mm, 1.5 mm, 2 mm or 2.5 mm.

[0037] Among them, the auxiliary paving means of the graphite raw material in step 1 is spin coating (3000 - 4000 rpm) and vacuum filtration deposition paving (-0.1 Mpa).

[0038] Among them, the high-temperature condition in step 2 starts from an initial temperature of 25°C, and is heated to 350°C, 450°C, 550°C or 650°C at a heating rate of 7°C / min and held for 90 min.

[0039] Among them, the mechanical pressing condition in step 3 is any pressure of 15 - 30 Mpa and the pressure is held for 60 min.

[0040] The present invention will be described in detail below in conjunction with specific embodiments.

[0041] Example 1:

[0042] A preparation method of a highly oriented graphene aggregate flexible film, comprising the following steps:

[0043] First, 1 g of flake graphite, 3 g of ammonium persulfate and 2 mL of concentrated sulfuric acid are stirred evenly to form a mixed slurry;

[0044] The slurry is transferred into a confinement growth container, spin-coated at 3000 rpm, and vacuum filtered at -0.1 Mpa to assist the deposition of the slurry;

[0045] The reaction container is transferred to a room temperature (25°C) environment, and left to stand and exfoliate at room temperature. The C-axis confinement quartz wafer is slowly lifted, and after 24 h, a directionally grown graphene aggregate is obtained;

[0046] The obtained graphene aggregate is heated from an initial temperature of 25°C to 350°C at a heating rate of 7°C / min in an argon environment and held at the target temperature for 90 min to obtain a highly oriented graphene aggregate foam.

[0047] The obtained graphene aggregate foam is mechanically pressed at a pressure of 30 Mpa and the pressure is held for 60 min to obtain a highly oriented graphene aggregate film.

[0048] From Figure 1As can be seen from the right, the GAs compression film pressed at 30 Mpa has good compactness, a highly ordered interlayer structure, a flat surface, and no unevenness;

[0049] From Figure 2 it can be seen that the high pressure of 30 Mpa can well promote the electrical conductivity of the GAs compression film;

[0050] From Figure 3 it can be seen that the GAs foam obtained by high-temperature impurity removal in an argon environment has good structural integrity and a very low overall defect degree;

[0051] From Figure 4 it can be seen that the impurity removal temperature of 350 °C can maximize the removal of strong acid / oxidant impurities in the exfoliation system, thus maximizing the advantage of the intrinsic high electrical conductivity of the film;

[0052] From Figure 5 it can be seen that the exfoliation system ratio of 1:3:2 can fully exfoliate NG into GAs, thereby maximizing the electromagnetic shielding performance of the subsequent compression film, and reaching the level of 105 dB;

[0053] From Figure 6 it can be seen that after applying the confinement effect in the C-axis direction, the GAs as a whole exhibits a high-orientation growth state;

[0054] Example 2:

[0055] A preparation method of a highly oriented graphene aggregate flexible film includes the following steps:

[0056] First, 1 g of flake graphite, 3 g of ammonium persulfate and 2 mL of concentrated sulfuric acid are stirred evenly into a mixed slurry;

[0057] The slurry is transferred into a confinement growth container, spin-coated at 3000 rpm, and vacuum filtration is carried out at -0.1 Mpa to assist the deposition of the slurry;

[0058] The reaction container is transferred to a room temperature (25 °C) environment, and static exfoliation is carried out at room temperature. The confinement quartz wafer covering the surface of the slurry is slowly lifted up, and oriented graphene aggregates are obtained after 24 h;

[0059] The obtained graphene aggregates are heated from an initial temperature of 25 °C to 350 °C at a heating rate of 7 °C / min in an argon environment, and kept at the target temperature for 90 min to obtain highly oriented graphene aggregate foam.

[0060] The obtained graphene aggregate foam is mechanically pressed at a pressure of 10 Mpa and kept under pressure for 60 min to obtain a highly oriented graphene aggregate film.

[0061] From Figure 1As can be seen from the left, due to the relatively low mechanical pressure applied in the vertical direction, the film exhibits significantly larger interlayer pores, has a certain degree of orientation, but a relatively low density, indicating that pressure plays an important role in the film structure during mechanical pressing.

[0062] Example Three:

[0063] A method for preparing a highly oriented graphene aggregate flexible film, comprising the following steps:

[0064] First, 1 g of flake graphite, 3 g of ammonium persulfate, and 3 mL of concentrated sulfuric acid are stirred evenly to form a mixed slurry;

[0065] The slurry is transferred into a confined growth container, spin-coated at 3000 rpm, and vacuum filtration is carried out at -0.1 Mpa to assist the deposition of the slurry;

[0066] The reaction container is transferred to a room temperature (25 °C) environment, and static peeling is carried out at room temperature. The quartz wafer covering the surface of the slurry is slowly lifted, and oriented graphene aggregates are obtained after 24 h;

[0067] The obtained graphene aggregates are heated from an initial temperature of 25 °C to 350 °C at a heating rate of 7 °C / min in an air environment and held at the target temperature for 90 min to obtain highly oriented graphene aggregate foams.

[0068] The obtained graphene aggregate foams are mechanically pressed at a pressure of 10 Mpa and held for 60 min to obtain highly oriented graphene aggregate films.

[0069] From Figure 3 It can be seen that due to the fact that the impurity removal atmosphere is air, the presence of oxygen at high temperatures causes certain oxidative damage to the structure of the GAs foams, indirectly leading to a significant increase in the D peak of the Raman spectrum;

[0070] Example Four:

[0071] A method for preparing a highly oriented graphene aggregate flexible film, comprising the following steps:

[0072] First, 1 g of flake graphite, 3 g of ammonium persulfate, and 2 mL of concentrated sulfuric acid are stirred evenly to form a mixed slurry;

[0073] The slurry is transferred into a confined growth container, spin-coated at 3000 rpm, and vacuum filtration is carried out at -0.1 Mpa to assist the deposition of the slurry;

[0074] The reaction container is transferred to a room temperature (25 °C) environment, and static peeling is carried out at room temperature. The quartz wafer covering the surface of the slurry is slowly lifted, and oriented graphene aggregates are obtained after 24 h;

[0075] The obtained graphene aggregates are heated from an initial temperature of 25 °C to 150 °C at a heating rate of 7 °C / min in an air environment and held at the target temperature for 90 min to obtain a highly oriented graphene aggregate foam.

[0076] The obtained graphene aggregate foam is mechanically pressed at a pressure of 30 MPa and held under pressure for 60 min to obtain a highly oriented graphene aggregate film.

[0077] From Figure 4 It can be seen that due to the relatively low impurity removal temperature (150 °C), the oxidant remaining on the surface of the GAs foam cannot be fully removed. After remaining between the layers, it has an obvious negative impact on the conductivity of the constructed GAs film, indicating that the impurity removal temperature plays an important role in demonstrating the high conductivity advantage of the film.

[0078] Example Five:

[0079] A method for preparing a highly oriented graphene aggregate flexible film includes the following steps:

[0080] First, 1 g of flake graphite, 1 g of ammonium persulfate, and 3 mL of concentrated sulfuric acid are stirred evenly to form a mixed slurry.

[0081] The slurry is transferred into a confined growth container, spin-coated at 3000 rpm, and vacuum filtered at -0.1 MPa to assist the deposition of the slurry.

[0082] The reaction container is transferred to an Ar (25 °C) environment and left standing at room temperature for exfoliation. The quartz wafer covering the surface of the slurry is slowly lifted. After 24 h, a directionally grown graphene aggregate is obtained.

[0083] The obtained graphene aggregates are heated from an initial temperature of 25 °C to 450 °C at a heating rate of 7 °C / min in an air environment and held at the target temperature for 90 min to obtain a highly oriented graphene aggregate foam.

[0084] The obtained graphene aggregate foam is mechanically pressed at a pressure of 30 MPa and held under pressure for 60 min to obtain a highly oriented graphene aggregate film.

[0085] From Figure 5 It can be seen that due to the relatively low content of the oxidant in the oxidation exfoliation system, the exfoliation of the GAs lamellae cannot be fully completed, resulting in a significant decrease in the EMI SE performance of the constructed film.

[0086] Example Six:

[0087] A method for preparing a highly oriented graphene aggregate flexible film includes the following steps:

[0088] First, 1 g of flake graphite, 3 g of ammonium persulfate, and 3 mL of concentrated sulfuric acid are stirred evenly to form a mixed slurry;

[0089] Transfer the slurry into the confined growth container without applying additional auxiliary deposition treatment.

[0090] Transfer the reaction container to an Ar (25 °C) environment, let it stand at room temperature for peeling. The quartz wafer covering the surface of the slurry is slowly lifted up. After 24 h, graphene aggregates with oriented growth are obtained.

[0091] The obtained graphene aggregates are heated from an initial temperature of 25 °C to 450 °C at a heating rate of 7 °C / min in an air environment and kept at the target temperature for 90 min to obtain highly oriented graphene aggregate foam.

[0092] Press the obtained graphene aggregate foam mechanically at a pressure of 10 Mpa and keep the pressure for 60 min to obtain a highly oriented graphene aggregate film.

[0093] As can be seen from Figure 6 b, due to the lack of the restrictive effect of the quartz wafer covering the surface of the slurry, obvious orientation disorder occurred in the growth and peeling process of GAs, and it was impossible to construct and form GAs foam with highly oriented arrangement. This indicates that the confinement effect of the C-axis plays an important role in obtaining GAs foam by the highly oriented confinement growth method. In contrast Figure 6 a, obvious orientation arrangement of GAs foam was obtained after covering the confined quartz wafer on the surface of the slurry.

[0094] Those of ordinary skill in the art can understand that the above embodiments are specific examples for implementing the present invention. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present invention. Any person skilled in the art can make their respective changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for preparing a highly oriented graphene aggregate flexible film for electromagnetic shielding, characterized in that: The following steps are involved: Step (1), mixing raw graphite, persulfate and concentrated sulfuric acid to obtain a slurry; placing the slurry in a confined growth container in a flat manner, standing for reaction, and obtaining a directed growth graphene aggregate; Step (2), removing the residual chemical reagents in the oriented graphene aggregates by high-temperature impurity removal to obtain oriented graphene aggregate foam; Step (3), mechanically pressing the directionally grown graphene aggregate foam to obtain the highly oriented graphene aggregate flexible film.

2. The method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to claim 1, characterized in that: The original graphite, persulfate and concentrated sulfuric acid described in step (1) are 1-3 g: 3-5 g: 1-2 mL.

3. The method for preparing a highly oriented graphene aggregate flexible film for electromagnetic shielding according to claim 1, characterized in that: In step (1), the original graphite is flake graphite or block graphite; the persulfate includes potassium hydrogen persulfate and / or ammonium persulfate.

4. The method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to claim 1, characterized in that: The confined growth container in step (1) is specifically a cylindrical and hollow quartz container, the bottom of which is evenly distributed with a plurality of circular holes, and after the slurry is deposited on the bottom of the container, a quartz disc is horizontally covered on the surface of the slurry; Preferably, the specific dimensions of the container are a bottom diameter of 30 mm and a height of 20 mm; the size of the circular hole is a diameter of 0.5 mm; the dimensions of the quartz disc include a diameter of 30 mm and a thickness of 0.5 mm, 1 mm, 1.5 mm, 2 mm or 2.5 mm.

5. The method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to claim 4, characterized in that: The paving process described in step (1) specifically includes: spin coating the slurry at a rotation speed of 3000-4000 rpm for 15-30 seconds, and then vacuum filtering the slurry from the circular hole reserved at the bottom of the growth container at a pressure of -0.1 MPa for 3-5 seconds.

6. The method for preparing a highly oriented graphene aggregate flexible film for electromagnetic shielding according to claim 1, characterized in that: The static reaction described in step (1) is specifically carried out at a temperature of 25° C. to 80° C. for 7 h to 24 h.

7. The method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to claim 1, characterized in that: The high-temperature impurity removal described in step (2) specifically includes: heating from 25°C to 450°C, 550°C or 650°C at a heating rate of 7°C / min in an argon environment, and keeping the temperature for 90 minutes.

8. The method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to claim 1, characterized in that: The mechanical pressing described in step (3) is specifically to maintain the pressure at 15-30 MPa for 60 minutes. 9 . A flexible film of highly oriented graphene aggregates for electromagnetic shielding obtained by the method for preparing a flexible film of highly oriented graphene aggregates for electromagnetic shielding according to any one of claims 1 to 8 .

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