Surface treatment method of carbon fibers for carbon paper

Abstract

The application provides a surface treatment method of carbon fibers for carbon paper, and belongs to the technical field of carbon fiber materials. The method is characterized in that: the original sizing agent on the surface of the carbon fibers is removed without damaging the carbon fiber matrix by using a sintering process, then electrolytic treatment is performed to change the hydrophobicity of the surface of the carbon fibers, and then a new conductive sizing agent is coated on the carbon fiber matrix, so that the surface conductive performance of the carbon fibers is enhanced, the hydrophilicity is good, and the carbon fibers are more easily dispersed, and the carbon fibers are suitable for being used as raw materials of carbon paper.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber material technology, and specifically relates to a surface treatment method for carbon fiber used in carbon paper. Background Technology

[0002] Carbon paper is a commonly used GDL (gas diffusion layer) substrate material in proton exchange membrane fuel cell electrodes, mainly because it not only has a uniform porous thin-layer structure, good porosity and permeability, but also has good electrical conductivity, chemical stability and thermal stability due to its main raw material being carbon fiber.

[0003] Currently, carbon paper blanks are prepared using both wet and dry processes. The more widely used wet papermaking technology involves mixing a binder solution with chopped carbon fibers, forming the mixture on a paper machine using papermaking techniques, drying it to bond the chopped fibers together, then impregnating it with a dilute solution such as phenolic resin. After curing and carbonization, carbon fiber-based paper material (raw carbon paper) is obtained. The advantage of wet papermaking is its flexibility; the binder leaves numerous pores after carbonization, acting as a pore-forming agent.

[0004] However, during production, it was found that commercially available carbon fiber filaments are sized carbon fibers coated with a uniform and dense layer of cured resin. This results in good bundle properties of the sized carbon fibers, providing excellent interfacial properties and bundle properties for the subsequent preparation of carbon fiber prepregs. However, this type of commercially available carbon fiber is not suitable as a matrix for carbon paper. This is because the hydrophobic interface and bundle properties after sizing make it difficult to disperse chopped carbon fibers in the dispersant. Therefore, the resulting carbon fiber preform may exhibit uneven dispersion of chopped carbon fibers, uneven porosity, and uneven thickness, leading to a lower yield rate. Furthermore, since the sizing agent is a non-conductive resin-based agent, the conductivity of the sized carbon fibers will also decrease, thus affecting the conductivity of the carbon paper preform.

[0005] Therefore, if commercially available carbon fiber filaments can be processed to become carbon fibers with good dispersibility, hydrophilicity, and enhanced conductivity, they will be more suitable for use as raw materials for carbon paper. Summary of the Invention

[0006] To address the issue that currently commercially available carbon fiber filaments are unsuitable as raw materials for carbon paper, this invention provides a surface treatment method for carbon fibers used in carbon paper. This method involves removing the original sizing agent from the carbon fiber surface without damaging the carbon fiber matrix using a sintering process, then altering the hydrophobicity of the carbon fiber surface through electrolytic treatment, and finally coating the carbon fiber matrix with a new conductive slurry. This process enhances the conductivity and hydrophilicity of the carbon fiber surface, making it easier to disperse and suitable for use as a raw material for carbon paper.

[0007] The present invention provides a surface treatment method for carbon fiber for carbon paper, comprising the following steps:

[0008] S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace;

[0009] S2: Cleaning: Clean the sintered carbon fiber;

[0010] S3: Electrolysis: Electrolysis is performed on the cleaned carbon fiber.

[0011] S4: Steam drying: Drying the electrolytically treated carbon fibers in a steam pipe;

[0012] S5: Sizing: The dried carbon fiber is sized with an alcoholic solution of polyvinylpyrrolidone (PVP) K90 or K30.

[0013] S6: Hot roller drying: The sized carbon fiber is dried using steam-heated rollers.

[0014] Preferably, the carbon fiber is unwound before step S1 and wound after step S6.

[0015] Preferably, in step S1, the furnace temperature is 350~450℃ and the sintering time is 15~25min.

[0016] Preferably, in step S2, the carbon fiber is cleaned by countercurrent spraying of deionized water for 3 minutes.

[0017] Preferably, in step S3, the carbon fiber is electrolyzed in an aqueous solution of ammonium sulfate with a mass concentration of 3-10%, at an electrolysis temperature of 30°C and a current density of 0.03-0.06 A / m. 2 Electrolysis time is 6~30 seconds.

[0018] Preferably, in step S4, the steam temperature is 180°C and the drying time is 30~60 seconds.

[0019] Preferably, in step S5, the mass concentration of the alcohol solution of polyvinylpyrrolidone (PVP) K90 or K30 is 2-6%.

[0020] Preferably, in step S6, the drying temperature is 80°C and the drying time is 3~10 seconds.

[0021] The main principle of the surface treatment method for carbon fiber for carbon paper of the present invention is as follows:

[0022] Commercially available carbon fibers are shipped with a layer of hydrophobic slurry on their surface. This slurry needs to be removed, which is detrimental to carbon paper production, requiring sintering of the carbon fibers. An inert atmosphere furnace is used for sintering because burning in air would oxidize the carbon fibers and cause them to lose their mechanical properties. The inert atmosphere can be nitrogen, argon, etc. Cleaning removes any remaining burnt slurry residue from the carbon fibers. Electrolysis modifies the carbon fiber surface, creating a hydrophilic interface and changing it from hydrophobic to hydrophilic. After electrolytic modification, the carbon fiber tubes are dried using steam drying. This method is cleaner and avoids contaminating the hydrophilic surface of the carbon fibers after electrolysis. Furthermore, the surface of the carbon fibers after electrolysis has many tiny fibers; drying these fibers in a conventional environment can easily cause static electricity and entanglement, which is avoided by steam drying. Sizing involves coating the carbon fiber matrix with a new conductive slurry, enhancing the surface conductivity and further increasing hydrophilicity, making it easier to disperse and suitable for use as a carbon paper raw material. Choosing an alcohol solution of polyvinylpyrrolidone (PVP) K90 or K30 as the sizing agent results in better conductivity than the original bisphenol A epoxy resin sizing agent. After sizing, the carbon fibers are dried using steam-heated rollers, resulting in uniform temperature distribution and the carbon fibers forming a strip of a certain width on the roller surface without twisting, making them easy to disperse in the dispersant when making carbon paper.

[0023] The surface treatment method for carbon fiber for carbon paper of the present invention has the following beneficial effects:

[0024] The surface treatment method for carbon fibers used in carbon paper of the present invention removes the original sizing agent on the surface of carbon fibers without damaging the carbon fiber matrix by using a sintering process, then changes the hydrophobicity of the carbon fiber surface by electrolytic treatment, and then coats a new conductive slurry on the carbon fiber matrix. This method enhances the conductivity of the carbon fiber surface, improves its hydrophilicity, and makes it easier to disperse, making it suitable for use as a raw material for carbon paper. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the surface treatment method for carbon fiber for carbon paper according to an embodiment of the present invention;

[0026] Figure 2 A scanning electron microscope image of the surface of carbon fiber without any surface treatment;

[0027] Figure 3 A scanning electron microscope image of a cross-section of carbon fiber without any surface treatment;

[0028] Figure 4 This is a scanning electron microscope image of the carbon fiber surface after surface treatment in Embodiment 1 of the present invention;

[0029] Figure 5This is a scanning electron microscope image of the cross-section of carbon fiber after surface treatment in Embodiment 1 of the present invention. Detailed Implementation

[0030] A surface treatment method for carbon fiber for carbon paper includes the following steps:

[0031] S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace;

[0032] S2: Cleaning: Clean the sintered carbon fiber;

[0033] S3: Electrolysis: Electrolysis is performed on the cleaned carbon fiber.

[0034] S4: Steam drying: Drying the electrolytically treated carbon fibers in a steam pipe;

[0035] S5: Sizing: The dried carbon fiber is sized with an alcoholic solution of polyvinylpyrrolidone (PVP) K90 or K30.

[0036] S6: Hot roller drying: The sized carbon fiber is dried using steam-heated rollers.

[0037] In one embodiment, the carbon fiber is unwound before step S1 and wound after step S6.

[0038] In one embodiment, in step S1, the furnace temperature is 350–450°C and the sintering time is 15–25 min.

[0039] In one embodiment, in step S2, the carbon fiber is cleaned by countercurrent spraying of deionized water for 3 minutes.

[0040] In one embodiment, in step S3, the carbon fiber is electrolyzed in an ammonium sulfate aqueous solution with a mass concentration of 3-10%, at an electrolysis temperature of 30°C, a current density of 0.03-0.06 A / m², and an electrolysis time of 6-30 s.

[0041] In one embodiment, in step S4, the steam temperature is 180°C and the drying time is 30–60 seconds.

[0042] In one embodiment, in step S5, the mass concentration of the alcoholic solution of polyvinylpyrrolidone (PVP) K90 or K30 is 2-6%.

[0043] In one embodiment, in step S6, the drying temperature is 80°C and the drying time is 3-10 seconds.

[0044] The present invention will be further described in detail below with reference to specific embodiments.

[0045] Example 1

[0046] Follow these steps to perform surface treatment on carbon fiber for carbon paper:

[0047] S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace at a temperature of 380℃ for 25 minutes.

[0048] S2: Cleaning: The sintered carbon fiber is cleaned by using deionized water in a counter-current spraying method for 3 minutes.

[0049] S3: Electrolysis: The cleaned carbon fibers are electrolyzed in a 6% ammonium sulfate aqueous solution at a temperature of 30℃, a current density of 0.04A / m2, and an electrolysis time of 20s.

[0050] S4: Steam drying: The electrolytically treated carbon fibers are dried in a steam pipe at a steam temperature of 180℃ for 45 seconds.

[0051] S5: Sizing: The dried carbon fibers are sized with an alcoholic solution of polyvinylpyrrolidone (PVP K90), the mass concentration of which is 4%.

[0052] S6: Hot roller drying: The sized carbon fiber is dried using a steam-heated roller at a temperature of 80℃ for 10 seconds.

[0053] In this embodiment, the carbon fiber is unwound before step S1 and wound after step S6.

[0054] Example 2

[0055] Follow these steps to perform surface treatment on carbon fiber for carbon paper:

[0056] S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace at a temperature of 450℃ for 15 minutes.

[0057] S2: Cleaning: The sintered carbon fiber is cleaned by using deionized water in a counter-current spraying method for 3 minutes.

[0058] S3: Electrolysis: The cleaned carbon fibers are electrolyzed in a 10% ammonium sulfate aqueous solution at a temperature of 30℃, a current density of 0.03A / m2, and an electrolysis time of 6s.

[0059] S4: Steam drying: The electrolytically treated carbon fibers are dried in a steam pipe at a steam temperature of 180℃ for 50 seconds.

[0060] S5: Sizing: The dried carbon fibers are sized with an alcoholic solution of polyvinylpyrrolidone (PVP K90), the mass concentration of which is 6%.

[0061] S6: Hot roller drying: The sized carbon fiber is dried using a steam-heated roller at a temperature of 80℃ for 8 seconds.

[0062] In this embodiment, the carbon fiber is unwound before step S1 and wound after step S6.

[0063] Example 3

[0064] Follow these steps to perform surface treatment on carbon fiber for carbon paper:

[0065] S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace at a temperature of 350℃ for 25 minutes.

[0066] S2: Cleaning: The sintered carbon fiber is cleaned by using deionized water in a counter-current spraying method for 3 minutes.

[0067] S3: Electrolysis: The cleaned carbon fibers are electrolyzed in a 3% ammonium sulfate aqueous solution at a temperature of 30℃, a current density of 0.06A / m2, and an electrolysis time of 25s.

[0068] S4: Steam drying: The electrolytically treated carbon fibers are dried in a steam pipe at a steam temperature of 180℃ for 45 seconds.

[0069] S5: Sizing: The dried carbon fibers are sized with an alcoholic solution of polyvinylpyrrolidone (PVP K30), the mass concentration of which is 3%.

[0070] S6: Hot roller drying: The sized carbon fiber is dried using a steam-heated roller at a temperature of 80℃ for 10 seconds.

[0071] In this embodiment, the carbon fiber is unwound before step S1 and wound after step S6.

[0072] The carbon fibers from Examples 1-3 were subjected to tests for hydrophilicity, conductivity, and dispersibility. The specific methods are as follows: 2.0g of treated carbon fibers were taken and cut into lengths of about 5mm. Sodium carboxymethyl cellulose (2% concentration) was used as the dispersant. After dissociation by a fiber dissociator for 30 minutes, the dispersion state of the carbon fibers was observed. Then, carbon paper was made into carbon paper using a paper forming device. The static water contact angle of the carbon paper was tested using a contact angle measuring instrument. The planar resistivity of the carbon paper was tested using a four-probe resistance measurement method. The results are shown in Table 1.

[0073] Table 1. Test results of carbon fiber properties after surface treatment

[0074] carbon fiber Contact angle of hydrophilic surface (°) Planar resistivity (mΩ·cm) Dispersion performance Example 1 33 42 Evenly dispersed Example 2 38 51 Evenly dispersed Example 3 40 63 Evenly dispersed

[0075] Carbon fibers that underwent surface treatment as described in Example 1 and untreated carbon fibers (Toray Carbon T300-3K from Japan) were tested using a scanning electron microscope. The scanning electron microscope images are shown below. Figures 2-5 .in, Figure 2 and Figure 3 The images show SEM images of the surface and cross-section of untreated carbon fibers. As can be seen from the images, the fiber surface is smooth and the cross-section is approximately circular or elliptical. Figure 4 The image shown is a surface SEM image of the surface-treated carbon fiber from Example 1. It can be seen that a sizing agent is adhered to the surface of the carbon fiber. Figure 5 The image shows a cross-sectional SEM image of the surface-treated carbon fiber in Example 1. It can be seen that the surface of the carbon fiber is also covered with a sizing agent. This sizing agent is a newly applied conductive sizing agent, and the sizing agent is not a hydrophobic sphere, but a hydrophilic irregular sheet. Carbon fibers in this state are easier to disperse in the subsequent papermaking process.

[0076] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A surface treatment method for carbon fiber for carbon paper, characterized in that, Includes the following steps: S1: Sintering: The carbon fiber is sintered in an inert atmosphere furnace; S2: Cleaning: Clean the sintered carbon fiber; S3: Electrolysis: The cleaned carbon fibers are electrolyzed in a 3-10% (w / w) ammonium sulfate aqueous solution at a temperature of 30°C and a current density of 0.03-0.06 A / m. 2 Electrolysis time: 6–30 seconds; S4: Steam drying: Drying the electrolytically treated carbon fibers in a steam pipe; S5: Sizing: The dried carbon fiber is sized with an alcoholic solution of polyvinylpyrrolidone (PVP) K90 or K30. S6: Hot roller drying: The sized carbon fiber is dried using steam-heated rollers.

2. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, The carbon fiber is unwound before step S1 and wound after step S6.

3. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, In step S1, the furnace temperature is 350~450℃ and the sintering time is 15~25min.

4. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, In step S2, the carbon fiber is cleaned by countercurrent and spraying of deionized water for 3 minutes.

5. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, In step S4, the steam temperature is 180℃ and the drying time is 30~60S.

6. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, In step S5, the mass concentration of the alcohol solution of polyvinylpyrrolidone (PVP) K90 or K30 is 2-6%.

7. The surface treatment method for carbon fiber for carbon paper according to claim 1, characterized in that, In step S6, the drying temperature is 80℃ and the drying time is 3~10s.

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