Carbon fiber surface treatment device, chopped carbon fiber preparation system and carbon fiber paper preparation method

Abstract

The invention belongs to the technical field of carbon fiber surface treatment, and particularly relates to a carbon fiber surface treatment device, a chopped carbon fiber preparation system and a carbon fiber paper preparation method. In order to solve the problems of a fiber network structure, non-uniform pore distribution between fibers, random fiber overlapping points, adhesion between the fibers and the like, a discontinuous surface treatment mode is adopted, and a structure in which active site areas and non-active site areas appear periodically at intervals is formed on the surface of the carbon fiber; the chopped fibers are dispersed to prepare the carbon fiber paper, and due to the existence of the anionic surfactant, active sites on the chopped carbon fibers tend to gather towards surfactant groups more easily under the action of the double electric layer effect of particles; after dehydration and paper forming are completed, the active sites are in lap joint to form fiber connection points, and controllable lap joint of fibers at the active sites is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber surface treatment, and in particular relates to a carbon fiber surface treatment device, a chopped carbon fiber preparation system, and a carbon fiber paper preparation method. Background Art

[0002] Using chopped carbon fibers as papermaking raw materials, wet-forming techniques can produce functional materials with sheet properties, commonly referred to as carbon fiber paper and carbon fiber paper-based functional materials. By adjusting the type and amount of carbon fibers in the carbon fiber paper, paper-based composite materials with different functions can be produced. These functional materials are characterized by being light, thin, and flexible, with excellent mechanical properties and thermal and electrical conductivity. Therefore, as a high-performance, multifunctional material, carbon fiber paper-based functional materials have broad development prospects in areas such as electrical conductivity, electromagnetic shielding, friction, and electrodes.

[0003] Specifically, carbon fiber paper can form a good conductive network structure through the overlap between short fibers, and effectively reduce the penetration of electromagnetic signals by increasing the reflection and absorption of electromagnetic waves. As long as a layer of carbon fiber paper-based material is completely coated on the outside of the space, a good carrier of shielding material can be formed to greatly improve the material's wave absorption and shielding performance. Carbon fiber can be used to prepare thermoplastic resin composites through wet papermaking process. As a reinforcing phase of the composite material, it can achieve a significant improvement in the mechanical properties of the material. At the same time, it has many excellent properties such as isotropy, light weight, and rapid preparation. Through wet papermaking and high-temperature graphitization, carbon fiber paper can be processed into a gas diffusion layer for fuel cells with uniform porosity, high conductivity, and electrical corrosion resistance, or used as an electrode material for hydrogen production by electrolysis of water. It has a wide range of uses in the hydrogen energy industry.

[0004] However, the surface of carbon fiber is chemically inert. On the one hand, this gives carbon fiber good stability and high environmental adaptability, and is resistant to strong acids, strong alkalis, and even high electrochemical corrosion. On the other hand, this leads to technical difficulties in the wet forming process of carbon fiber, such as the easy aggregation of fibers in water, resulting in low paper uniformity, and weak bonding between fibers, resulting in weak paper strength. In addition, carbon fiber is an inorganic fiber material prepared by high-temperature (1600-2000℃) carbonization and traction stretching. It cannot be separated and broomed to produce active sites through papermaking beating, and there is a problem of poor fiber interweaving. In order to optimize the interface characteristics and overall performance of the composite material, it is necessary to adjust the microstructure of the interface between the two and conduct a comprehensive optimization design.

[0005] In existing carbon fiber paper-based functional materials, the carbon fiber surface serves as a link for transmitting and dispersing stress, and the interfacial bonding determines the final effect of carbon fiber reinforcement. However, the carbon fiber surface is smooth, has low chemical activity, and low surface energy, which makes it difficult for the interface performance to meet the needs of actual applications. Currently commonly used carbon fiber surface treatment methods include: magnetron sputtering modification, sizing agent coating, high-temperature vapor deposition, electrochemical oxidation, plasma polymerization, grafting modification, etc. As for the electrochemical oxidation treatment scheme, the carbon fiber is usually immersed in an electrolyte solution, and a conductive electrode is placed in the solution as a cathode. The carbon fiber is connected to a power supply as an anode, and a certain voltage is applied between the anode and the cathode. A constant current is formed through the electrolyte, so that the electrolyte electrochemically oxidizes the carbon fiber to increase the oxygen-containing functional groups on the carbon fiber surface. At present, the carbon fiber surface treatment methods all adopt uniform and indifferent surface modification technology for the carbon fiber surface. In the preparation process of carbon fiber paper, the active sites on the chopped fibers after surface treatment are uniform and indifferent, due to the stirring and dispersion of the papermaking pulp and the disturbance of the dehydration fluid in the wet papermaking process. Summary of the Invention

[0006] To address the above-mentioned issues, the present invention provides a carbon fiber surface treatment device, a chopped carbon fiber preparation system, and a carbon fiber paper preparation method. The present invention utilizes an electrochemical oxidation treatment scheme to surface treat the carbon fibers, applying a discontinuous voltage for treatment to form a layout in which active sites on the fiber surface are spaced apart from non-treated segments (non-active sites). Furthermore, by controlling the chopped length, the active sites on the surface of the chopped carbon fibers are discontinuously and periodically evenly distributed. Furthermore, carbon fiber paper is prepared through wet dispersion and papermaking, and the chopped carbon fibers are loosened and dispersed using a surfactant solution. The adsorption and positioning effect of the surfactant allows for controlled overlap of the chopped fibers at the active sites, thereby improving the performance uniformity of the carbon fiber paper. Furthermore, various composite material molding technologies can be used to effectively improve the conductivity, air permeability, and mechanical properties.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a surface treatment device for carbon fiber, comprising a reaction tank and an electrolyte tank, wherein a baffle is provided in the reaction tank, the baffle dividing the reaction tank into a front section and a rear section, wherein a positive electrode plate and a negative electrode plate are respectively provided in the front section and the rear section, and the positive electrode plate and the negative electrode plate are respectively connected to the positive and negative poles of a DC power supply; the electrolyte tank is filled with electrolyte, and the electrolyte is pumped out to the front section of the reaction tank by a liquid supply pump, overflows over the baffle to the rear section of the reaction tank, and then flows to the electrolyte tank through a reflux pipeline provided with a control valve, and the carbon fiber is located above the reaction tank and contacts with the electrolyte that overflows over the baffle.

[0008] Furthermore, the distance between the positive plate and the negative plate is 1.5 mm.

[0009] Furthermore, the height of the reaction tank is higher than the baffle.

[0010] In a second aspect, the present invention provides a system for preparing chopped carbon fibers based on the surface treatment device, comprising an unwinding device, a surface treatment device, a front transmission roller, a rear transmission roller, a drying furnace, and a slitting device, which are arranged in sequence; The slicing device includes an upper pressing roller, a lower pressing roller and a cutting blade. The upper pressing roller and the lower pressing roller transmit the carbon fiber to the cutting blade to obtain chopped carbon fiber. A cutting pressing roller is provided below the cutting blade.

[0011] In a third aspect, the present invention provides a method for preparing carbon fiber paper using the system, comprising the following steps: Step 1: The carbon fibers are continuously passed through a surface treatment device via an unwinding device and a front transmission roller to achieve electrochemical oxidation surface treatment of the carbon fibers. The carbon fibers are then fed into a drying furnace via a rear transmission roller for drying, and then into a shredding device to obtain chopped carbon fibers. Step 2: Dispersing the chopped carbon fibers in a surfactant solution, followed by dehydration, glue spraying, and drying to complete the preparation of carbon fiber paper. The prepared carbon fiber paper can be further used as a prefabricated material for carbon fiber paper-based functional materials.

[0012] Furthermore, the carbon fibers continuously pass through the surface treatment device and the chopped carbon fiber preparation system at a speed of 0.1 to 1 m / min.

[0013] Furthermore, the voltage loading time of the electrochemical oxidation surface treatment adopts a discontinuous and periodic treatment mode, that is, the voltage is applied to the carbon fiber surface for a period of time, and the voltage is stopped for another period of time without surface treatment. Since the carbon fiber passes through the surface treatment device continuously, periodic active site areas and inactive site areas are formed on the carbon fiber surface. The voltage loading time period is composed of the treatment time and the interval time, and the ratio of the treatment time to the interval time is 1:1.5~3.5. During the electrochemical oxidation surface treatment process, the current density is controlled in the range of 0.1-0.75mA / cm 2 .

[0014] Furthermore, the electrolyte in the surface treatment device uses deionized water as a solvent, and the electrolyte includes one of ammonium bicarbonate and ammonium acetate, with a concentration range of 0.8-2.5wt%; Furthermore, the drying temperature of the drying furnace is 100°C-200°C; Furthermore, the carbon fiber is selected from unsized carbon fiber or commercial carbon fiber that has been desized, and its dimensional diameter is 3-10 μm.

[0015] Furthermore, the slitting device transmits the carbon fiber through the upper and lower pressure rollers and then transmits it to the cutting head. The fiber is cut by the shear force continuously generated by the head, and the cutting frequency can be adjusted to control the length of the short carbon fiber. The length of the short carbon fiber is 5mm~10mm; Surface treatment interval cycle × fiber running speed = surface treatment length interval; the length of the carbon fiber after chopped should meet the following conditions: surface treatment length interval × 2 < carbon fiber chopped length < surface treatment length interval × 4, that is, to ensure that each section of chopped carbon fiber surface has at least 2 active site areas and 2 inactive site areas, and to ensure that the fiber length can be effectively decomposed and dispersed.

[0016] Furthermore, the solvent in the surfactant solution is deionized water, and the surfactant is an anionic surfactant, including one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, fatty acid soap, and dioctyl sodium sulfosuccinate, with a concentration of 0.05-0.18wt%.

[0017] Furthermore, the glue used for the spray glue is one of carboxymethyl cellulose, polyvinyl alcohol, and polyacrylic acid, with a concentration of 0.1~0.5wt%.

[0018] Compared with the prior art, the present invention has the following advantages: Due to the use of a discontinuous surface treatment method, it is inevitable that the active site area and the inactive site area on the carbon fiber surface will appear periodically; the short fibers are dispersed to prepare carbon fiber paper. Due to the presence of anionic surfactants, under the action of the double layer effect of the particles, the active sites on the short carbon fibers are more likely to tend to aggregate with surfactant groups; after dehydration into paper, the active sites are overlapped to form fiber connection points. Due to the fixed structure of the active site area and the inactive site area, the fiber network structure formed in this way is more uniform, effectively reducing the uneven distribution of pores between fibers, random fiber overlap points, adhesion between fibers and other problems, and can provide a good prefabricated material for the further preparation of carbon fiber paper-based functional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the surface treatment device for carbon fiber; Figure 2 Schematic diagram of the structure of the chopped carbon fiber preparation system; Figure 3 This is a microscope photo of Example 2; Figure 4 This is a microscope photo of Comparative Example 2; Figure 5 This is a schematic diagram of the fiber splicing structure of Example 2; Figure 6 This is a schematic diagram of the fiber overlap structure of comparative example 2. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical solution of the present invention, the present invention is further described below through examples. Example

[0021] like Figure 1 As shown, a surface treatment device for carbon fiber of this embodiment includes a reaction tank 11 and an electrolyte tank 14, wherein a baffle 115 is provided in the reaction tank 11, and the baffle 15 divides the reaction tank 11 into a front section and a rear section, wherein a positive electrode plate 111 and a negative electrode plate 112 are respectively provided in the front section and the rear section, and the positive electrode plate 111 and the negative electrode plate 112 are respectively connected to the positive and negative poles of a DC power supply 16; the electrolyte tank 14 is filled with an electrolyte 15, and the electrolyte 15 is pumped out to the front section of the reaction tank 11 by a liquid supply pump 113, overflows over the baffle 115 to the rear section of the reaction tank 11, and then flows to the electrolyte tank 14 through a reflux line provided with a control valve 114, and the carbon fiber 5 is located above the reaction tank 11 and contacts with the electrolyte 15 that overflows over the baffle 115.

[0022] In this embodiment, the distance between the positive electrode plate 111 and the negative electrode plate 112 is 1.5 mm, and the height of the reaction tank 11 is 0.8 mm higher than the baffle 115 .

[0023] The working process of the surface treatment device is as follows: The structure of the reaction tank 11 is divided into two sections, front and back, separated by a baffle 115 in the middle. The liquid supply pump 113 can pump the electrolyte 15 from the electrolyte tank 14 to the front section of the reaction tank 11, and then overflow over the baffle 115 to the rear section of the reaction tank 11, and then flow back to the electrolyte tank 14 along the pipeline; a control valve 114 is connected to the return pipeline. By adjusting the flow rate of the liquid supply pump 113 and the opening of the control valve 114, the electrolyte can overflow in the reaction tank 11 and the liquid level can be stabilized without overflowing the reaction tank 11; the front and back of the reaction tank 11 are also equipped with positive plates 111 and negative plates 112 respectively. The positive plate 111 is connected to the positive pole of the DC power supply 116, and the negative plate 112 is connected to the negative pole of the DC power supply 116. In this way, when the reaction tank 111 is full of electrolyte 15, a certain voltage is applied between the positive plate 111 and the negative plate 112 to form a constant current with a certain current density. The carbon fiber tow passes over the reaction tank 11. By utilizing the surface tension of the electrolyte 15 and the strong hydrophobicity of the surface of the carbon fiber 5, the carbon fiber 5 can be immersed in the electrolyte 15 in a point contact manner. Through electrochemical oxidation, an active site area can be formed on the surface of the carbon fiber 5. The oxygen surface functional groups in this area are effectively increased, becoming a strong binding site for chemical bonds.

[0024] like Figure 2As shown, the short-cut carbon fiber preparation system of this embodiment includes an unwinding device 21, a surface treatment device 1, a front transmission pressure roller 22, a rear transmission pressure roller 23, a drying furnace 3 and a slitting device 4 arranged in sequence; The slitting device 4 includes an upper pressing roller 41, a lower pressing roller 42 and a cutting head 43. The upper pressing roller 41 and the lower pressing roller 42 transmit the carbon fiber 5 to the cutting head 43 to obtain short-cut carbon fiber 51. A cutting pressing roller 44 is provided below the cutting head 43. Example

[0025] A method for preparing carbon fiber paper according to this embodiment, using the system described in Example 1, includes the following steps: Step 1: The carbon fibers 5 are continuously passed through the surface treatment device 1 through the unwinding device 21 and the front transmission roller 22 to achieve electrochemical oxidation surface treatment of the carbon fibers, and then the carbon fibers 5 are sent to the drying furnace 3 for drying through the rear transmission roller 23; Step 2: Then, the carbon fibers 5 are cut into short pieces by the shredding device 4 to obtain chopped carbon fibers 51. Step 3: Dispersing the chopped carbon fibers 51 in a surfactant solution, followed by dehydration, glue spraying, and drying to complete the preparation of the carbon fiber paper.

[0026] Specifically, 1.0 wt% of ammonium bicarbonate electrolyte is pre-configured in the electrolyte tank 14; the flow rate of the liquid supply pump 113 and the opening of the control valve 114 are adjusted to achieve the effect that the electrolyte 15 in the reaction tank 11 can overflow and the liquid level can be stable so as not to overflow the reaction tank 11. The unsized carbon fiber is placed on the unwinding device 21, and the front transmission roller 22 and the rear transmission roller 23 are used to keep the carbon fiber 5 at a certain tension and continuously pass through the surface treatment device 1; the surface tension of the electrolyte 15 and the strong hydrophobicity of the surface of the carbon fiber 5 are used to make the carbon fiber and the electrolyte form point contact and be immersed in the electrolyte; the voltage loading time adopts a non-continuous and periodic treatment method to form periodic active site areas and inactive site areas on the surface of the carbon fiber 5. The period of the voltage loading time is composed of the treatment time and the interval time, that is, the DC power supply 16 is turned on intermittently and the current density is controlled to 0.4 mA / cm 2 The carbon fiber 5 is surface treated by electrochemical oxidation, the surface treatment interval period is 0.3s, the ratio of treatment time to interval time is 1:2 (i.e., the treatment time is 0.1s, and the interval time is 0.2s), and the running speed of the carbon fiber 5 is synchronously controlled to be 0.5m / min, and then the carbon fiber 5 is dried at a drying temperature of 120℃.

[0027] The dried carbon fibers 5 are chopped to a length of 8 mm, and the chopped carbon fibers are collected.

[0028] The chopped carbon fibers are dispersed in a surfactant solution (sodium lauryl sulfate, 0.12 wt%). After being evenly dispersed, they are dehydrated and then evenly sprayed with 0.3 wt% carboxymethyl cellulose glue. Finally, the carbon fiber paper is prepared after drying.

[0029] Examples 3-8 During the preparation process, parameters such as the electrolyte and its concentration, current density, treatment cycle and ratio, operating speed, chopped carbon fiber length, surfactant and concentration were changed. Other conditions were the same as those in Example 2 for carbon fiber surface treatment and preparation of carbon fiber paper. The specific preparation conditions are shown in Table 1.

[0030] Comparative Example 1 During the preparation process, step 1 was not used, and the carbon fibers were directly chopped. Other conditions were the same as those in Example 2 for carbon fiber surface treatment and preparation of carbon fiber paper. The specific preparation conditions are shown in Table 1.

[0031] Comparative Example 2 During the preparation process, intermittent surface treatment was not used. Instead, a constant current density was continuously applied to complete the surface treatment. Other conditions were the same as those in Example 2 for the carbon fiber surface treatment and the preparation of carbon fiber paper. The specific preparation conditions are shown in Table 1.

[0032] Table 1 Process parameters Example Electrolyte / concentration (wt%) <![CDATA[Current density (A / cm 2 )]]> Processing cycle (s) Processing time: Interval time Running speed (m / min) Short cut length (mm) Surfactant / concentration (wt%) Example 2 Ammonium bicarbonate / 1.0 0.4 0.3 1：2 0.5 8 Sodium lauryl sulfate / 0.12 Example 3 Ammonium acetate / 1.5 0.25 0.8 1：1.5 0.2 6 Sodium dodecylbenzenesulfonate / 0.05 Example 4 Ammonium bicarbonate / 2.5 0.75 0.1 1：1.5 0.8 5 Fatty acid soap / 0.18 Example 5 Ammonium acetate / 1.2 0.3 0.15 1：2.5 1 7 Sodium dioctyl sulfosuccinate / 0.15 Example 6 Ammonium bicarbonate / 1.6 0.1 1 1：2 0.1 6 Sodium dodecylbenzenesulfonate / 0.10 Example 7 Ammonium acetate / 1.8 0.6 0.15 1：3.5 1.5 10 Sodium lauryl polyoxyethylene ether sulfate / 0.08 Example 8 Ammonium bicarbonate / 2.0 0.5 0.5 1：3 0.3 9 Sodium dodecylbenzenesulfonate / 0.13 Comparative Example 1 none none none none none 8 Sodium lauryl sulfate / 0.12 Comparative Example 2 Ammonium bicarbonate / 1.0 0.4 none none 0.5 8 Sodium lauryl sulfate / 0.12 The carbon fiber papers prepared in Examples 2-8 and Comparative Examples 1-2 were further subjected to performance tests, including testing the electrical conductivity of the carbon fiber papers using a four-probe tester, testing the tensile properties of the carbon fiber papers using a tensile tester, and testing the coefficient of dispersion of air permeability at different locations of the carbon fiber papers using an air permeability meter (the results are shown in Table 2). The morphological differences between the carbon fiber papers prepared in Example 2 and Comparative Example 2 were observed under a microscope.

[0033] Table 2 Test results Example Resistivity (Ω·cm) Tensile strength (N / m) Coefficient of dispersion of air permeability (%) Example 2 0.129 350.75 8.90 Example 3 0.122 374.55 11.86 Example 4 0.118 400.14 9.14 Example 5 0.135 386.57 6.77 Example 6 0.127 356.12 10.03 Example 7 0.122 340.22 9.74 Example 8 0.120 366.01 9.09 Comparative Example 1 - - - Comparative Example 2 0.260 265.94 19.15 As can be seen from Table 2, due to the telephone oxidation treatment of the carbon fibers using the discontinuous periodic surface treatment used in the present invention, the fiber connection points are more uniform and stable, which is conducive to forming a good conductive network structure. The prepared carbon fiber paper has good conductivity and a resistivity of less than 0.14 Ω·cm. Further, from the perspective of tensile strength, the uniform and stable fiber network structure helps to eliminate adhesion and defective structures between fibers, making the force that destroys this network structure more significant, and the tensile strength reaches more than 340 N / m. The uniform network structure is also reflected in the stability of air permeability. The pore structure between the fibers can form an airflow channel for gas to pass through the carbon fiber paper. This structure is more uniform, and the difference in air permeability between points is also smaller. The good airflow distribution effect provides a uniform diffusion channel for gas conduction, thereby improving the efficiency and stability of the reaction gas.

[0034] In Comparative Example 1, since no surface treatment was performed, the carbon fiber surface was mainly inert. Although the same surfactant was added to the preparation of the carbon fiber paper for loosening and dispersion, a uniform fiber overlap effect could not be formed, and the fibers were severely agglomerated, which ultimately led to poor performance of the carbon fiber paper and even the inability to complete the preparation of the carbon fiber paper.

[0035] Comparative Example 2 does not use an intermittent periodic surface treatment method. Although the surfactant can form a relatively uniform carbon fiber paper, the positions of the fiber overlap points are irregular and uncontrollable, which means that there are multiple fibers adhering to each fiber overlap point, uneven pore distribution, and defects in the carbon fiber paper. It can also be seen from the dispersion coefficient of conductivity, tensile strength, and air permeability that Comparative Example 2 has a significant gap with Example 2. Further, from the microscopic photos of Example 2 and Comparative Example 2 ( Figure 3 and Figure 4 ), the fiber overlap points in Example 2 are relatively uniform, the pore size distribution is reasonable, the fiber orientation is also relatively uniform, and there is no obvious orientation; while although Comparative Example 2 can also form pores within a certain range, the pore distribution is uneven, and some small pores are relatively concentrated, which is exactly the effect caused by the uneven distribution of fiber overlap points; so this uneven distribution can further affect the conductivity and mechanical properties of the fiber.

[0036] Figure 5 52 represents the active site region, and 53 represents the inactive site region. It can be seen that in Example 2, due to the regularly spaced surface treatment, the active site regions on the fiber surface appear at equal intervals. Under the action of the surfactant, the fiber active sites are more likely to aggregate and form fiber overlap points. A uniform fiber network structure is also easily formed after papermaking.

[0037] Figure 652 represents the active site region. It can be seen that in Comparative Example 2, due to the continuous surface treatment, the active sites on the fiber surface are evenly distributed; under the action of the surfactant, the fiber overlap points are randomly distributed, which can easily lead to a high concentration of fibers in some areas and a low distribution of fibers in others. Adhesion between multiple fibers may also occur. Furthermore, the fiber network structure after papermaking also has the problem of uneven pore size distribution.

[0038] In summary, the present invention aims at the characteristics of carbon fiber paper, improves the surface treatment method of carbon fiber by electrochemical oxidation, that is, changes the continuous treatment to periodic interval treatment, and wet-forms the paper through a surfactant solution, thereby improving the uniformity of the lap joints of the chopped fibers of the carbon fiber paper, and further improving the conductivity, air permeability uniformity, mechanical properties and other properties of the carbon fiber paper-based functional material.

Claims

1. A surface treatment device for carbon fiber, characterized in that: The invention comprises a reaction tank (11) and an electrolyte tank (14). A baffle (115) is provided in the reaction tank (11). The baffle (15) divides the reaction tank (11) into a front section and a rear section. A positive electrode plate (111) and a negative electrode plate (112) are provided in the front section and the rear section, respectively. The positive electrode plate (111) and the negative electrode plate (112) are connected to the positive and negative electrodes of a DC power supply (16), respectively. The electrolyte tank (14) contains an electrolyte (15). The electrolyte (15) is pumped out to the front section of the reaction tank (11) by a liquid supply pump (113), overflows over the baffle (115) to the rear section of the reaction tank (11), and then returns to the electrolyte tank (14) through a return line provided with a control valve (114). The carbon fiber (5) is located above the reaction tank (11) and contacts the electrolyte (15) overflowing over the baffle (115).

2. The surface treatment device for carbon fiber according to claim 1, characterized in that: The distance between the positive electrode plate (111) and the negative electrode plate (112) is 1.5 mm.

3. The surface treatment device for carbon fiber according to claim 1, characterized in that: The height of the reaction tank (11) is higher than the baffle (115).

4. A system for preparing chopped carbon fibers based on the surface treatment device according to any one of claims 1 to 3, characterized in that: It comprises an unwinding device (21), a surface treatment device (1), a front transmission pressure roller (22), a rear transmission pressure roller (23), a drying furnace (3) and a slitting device (4) which are arranged in sequence; The slicing device (4) comprises an upper pressing roller (41), a lower pressing roller (42) and a cutting blade (43). The upper pressing roller (41) and the lower pressing roller (42) transmit the carbon fibers (5) to the cutting blade (43) to obtain chopped carbon fibers (51). A cutting pressing roller (44) is provided below the cutting blade (43).

5. A method for preparing carbon fiber paper using the system according to claim 4, characterized in that: The following steps are involved: Step 1, the carbon fiber (5) is continuously passed through the surface treatment device (1) via the unwinding device (21) and the front transmission pressure roller (22) to achieve electrochemical oxidation surface treatment of the carbon fiber, and then the carbon fiber (5) is sent to the drying furnace (3) for drying via the rear transmission pressure roller (23), and then enters the shredding device (4) to obtain short-cut carbon fiber (51); Step 2: Dispersing the chopped carbon fibers (51) in a surfactant solution, followed by dehydration, glue spraying, and drying to complete the preparation of carbon fiber paper.

6. The method for preparing carbon fiber paper according to claim 5, characterized in that: The carbon fibers (5) continuously pass through the surface treatment device (1) and the chopped carbon fiber preparation system at a speed of 0.1 to 1 m / min.

7. The method for preparing carbon fiber paper according to claim 5, characterized in that: The voltage loading time of the electrochemical oxidation surface treatment adopts a discontinuous and periodic treatment mode, forming a periodic active site area and an inactive site area on the surface of the carbon fiber (5), and the voltage loading time period is composed of the treatment time and the interval time, and the ratio of the treatment time to the interval time is 1:1.5~3.5; during the electrochemical oxidation surface treatment, the current density is controlled in the range of 0.1-0.75mA / cm 2 .

8. The method for preparing carbon fiber paper according to claim 5, characterized in that: The electrolyte (15) in the surface treatment device (1) uses deionized water as a solvent, and the electrolyte includes one of ammonium bicarbonate and ammonium acetate, with a concentration range of 0.8-2.5wt%; The drying temperature of the drying furnace (3) is 100°C-200°C; The carbon fiber (5) is selected from unsized carbon fiber or commercial carbon fiber that has been desized and has a dimensional diameter of 3 to 10 μm.

9. The method for preparing carbon fiber paper according to claim 7, characterized in that: The length of the chopped carbon fiber (51) is 5 mm to 10 mm; the length of the carbon fiber after chopped should meet the following conditions: surface treatment length interval × 2 < carbon fiber chopped length < surface treatment length interval × 4, surface treatment interval period × fiber running speed = surface treatment length interval, and its surface has at least 2 active site areas and 2 inactive site areas.

10. The method for preparing carbon fiber paper according to claim 5, characterized in that: The surfactant solution comprises deionized water as the solvent, an anionic surfactant including one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, fatty acid soap, and sodium dioctyl sulfosuccinate, with a concentration of 0.05-0.18 wt %; The glue used for the spray glue is one of carboxymethyl cellulose, polyvinyl alcohol, and polyacrylic acid, with a concentration of 0.1-0.5wt%.

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