Carbon fiber paper and method of making the same

Abstract

The application relates to the technical field of carbon fiber materials, and discloses a carbon fiber paper and a preparation method thereof, the preparation method of the carbon fiber paper comprises the following steps: (1) preparing a chopped carbon fiber slurry with a length of 3-12 mm; (2) forming and drying the slurry to obtain a raw paper; (3) preparing an active raw paper by sizing the raw paper; (4) resin impregnation and heat curing to obtain a precursor paper; (5) carbonization and graphitization to obtain the carbon fiber paper; wherein sizing is carried out in step (3) by using a sizing agent, and the sizing agent comprises at least one of a polyvinyl acetal modified thermoplastic resin, a polyurethane resin and a cellulose ether. In the application, the sizing agent serves as an adhesive, an adsorbent and a resin flow promoter, and can improve the air permeability of the carbon fiber paper while maintaining the strength of the carbon fiber paper.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber materials technology, specifically to a carbon fiber paper and its preparation method. Background Technology

[0002] One of the key technologies for proton exchange membrane fuel cells to realize hydrogen energy applications is the gas diffusion layer, which is composed of a carbon fiber paper substrate layer and a microporous layer. This layer is a key component for realizing the transport of reactants (hydrogen, oxygen / air), the removal of products (water), electron conduction, and heat dissipation. It is also the site of electrode electrochemical reactions and plays an important role in improving the performance of fuel cells.

[0003] CN200480008038.8 discloses a porous carbon substrate and its preparation method, which can be used as a gas diffusion layer material, membrane-electrode bonding product, and fuel cell. The porous carbon-based material of this invention comprises chopped carbon fibers and carbonized resin, with the chopped carbon fibers bonded by the carbonized resin. This aims to solve the cracking problem at the interface between the carbon fibers and the resin-carbon bonded together, enabling continuous roll-to-roll production of the carbon-based material. Furthermore, a water-repellent material is added to the porous carbon substrate to obtain a usable gas diffusion layer material.

[0004] CN202010760099.0 discloses a method for preparing carbon fiber paper precursors for fuel cell gas diffusion layers. This patent uses a wet papermaking process, adding a small amount of nanocellulose to improve the dispersion of carbon fibers, enhance the overall mechanical strength and structural stability of the carbon fiber paper, and utilize the characteristic that nanocellulose does not damage the porous structure of carbon fiber paper to give it good air permeability. CN202010892768.X discloses a method for producing carbon fiber paper for hydrogen fuel cell gas diffusion layers, using a low-concentration inclined wire forming paper machine to prepare the finished carbon fiber paper. However, the preparation process involves carbon fiber acid washing modification and alkaline reagent adjustment of paper pulp. Although it emphasizes the recycling of waste liquid and reduces preparation costs, it will inevitably put pressure on environmental protection. CN202110706943.6 discloses a method for preparing carbon fiber paper. The preparation method still adopts the basic process of wet papermaking. In particular, this invention effectively improves the structural uniformity and strength of carbon fiber paper by adding aramid fibers; secondly, it introduces mesophase pitch to improve the electrical and thermal conductivity of carbon fiber paper. CN202110433990.8 discloses a carbon fiber paper, its preparation method and application. This patent obtains different carbon fiber paper precursors by wet papermaking from short-cut carbon fibers of different lengths. The different carbon fiber precursors obtained are impregnated with phenolic resin solutions, and then superimposed and bonded to obtain carbon fiber paper with high porosity, good conductivity and tensile strength.

[0005] The common feature of the aforementioned existing technologies is to improve the overall performance of carbon fiber paper. However, while increasing conductivity or strength, the permeability of the carbon fiber paper often decreases. When the content, specifications, papermaking, and graphitization processes of chopped carbon fibers are consistent, resin carbon is the key factor affecting the performance of carbon fiber paper. Higher resin carbon content results in better adhesion to the carbon fibers, and better strength, electrical conductivity, and thermal conductivity of the carbon fiber paper. However, excessive resin carbon can cause pore blockage, reducing the permeability and porosity of the carbon fiber paper, thus affecting the electrochemical performance of fuel cells. Summary of the Invention

[0006] In order to overcome the problem that existing technologies cannot balance the strength, electrical conductivity, thermal conductivity and air permeability and porosity of carbon fiber paper, this invention provides a carbon fiber paper and its preparation method, which can improve the air permeability of carbon fiber paper while maintaining its strength.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing carbon fiber paper, comprising the following steps:

[0008] (1) Prepare short-cut carbon fiber slurry with a length of 3-12 mm;

[0009] (2) The pulp is wire-fed, formed, and dried to obtain the base paper;

[0010] (3) Preparation of active base paper by sizing base paper;

[0011] (4) Resin impregnation and thermosetting yield precursor paper;

[0012] (5) Carbonization and graphitization yield carbon fiber paper;

[0013] In step (3), a sizing agent is used for sizing, wherein the sizing agent comprises at least one of polyvinyl acetal modified thermoplastic resin, polyurethane resin and cellulose ether.

[0014] A second aspect of the present invention provides a carbon fiber paper prepared according to the method provided in the first aspect of the present invention.

[0015] In the above technical solution, the sizing agent firstly acts as a binder, improving the tensile strength, tear resistance, and other mechanical properties of the base paper; secondly, it acts as an adsorbent, forming hydrogen bonds with the resin used in subsequent impregnation processes, adsorbing more resin, and thus obtaining more resin carbon after carbonization and graphitization to bond the chopped carbon fibers, giving the carbon fiber paper higher tensile strength, electrical conductivity, and thermal conductivity; thirdly, it acts as a resin flow promoter, promoting resin flow along the carbon fiber surface during thermosetting, ensuring that over 85% of the resin is cured at the intersections of the chopped carbon fibers, thereby forming a three-dimensional network porous structure after carbonization and graphitization, significantly improving the air permeability of the carbon fiber paper. Therefore, through the above technical solution, the present invention can improve the air permeability of carbon fiber paper while maintaining its strength. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The first aspect of this invention provides a method for preparing carbon fiber paper, comprising the following steps:

[0018] (1) Prepare short-cut carbon fiber slurry with a length of 3-12 mm;

[0019] (2) The pulp is wire-fed, formed, and dried to obtain the base paper;

[0020] (3) Preparation of active base paper by sizing base paper;

[0021] (4) Resin impregnation and thermosetting yield precursor paper;

[0022] (5) Carbonization and graphitization yield carbon fiber paper;

[0023] In step (3), a sizing agent is used for sizing, wherein the sizing agent comprises at least one of polyvinyl acetal modified thermoplastic resin, polyurethane resin and cellulose ether.

[0024] This invention allows for a wide range of solvent choices in the sizing agent, including common organic solvents in the art such as ethanol, acetone, butanone, N,N-dimethylformamide, cyclohexanone, ethyl acetate, tetrahydrofuran, and toluene. According to this invention, ethanol is preferred as the solvent.

[0025] This invention offers a wide range of options for the concentration of the sizing agent. According to a preferred embodiment of the invention, the concentration of the sizing agent is 0.1-10 wt%, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wt%, more preferably 1-5 wt%. The concentration of the sizing agent is the sum of the mass concentrations of one or more of the following: polyvinyl acetal-modified thermoplastic resin, polyurethane resin, and cellulose ether.

[0026] According to a preferred embodiment of the present invention, the sizing agent used in step (3) comprises a first sizing agent and a second sizing agent, wherein the first sizing agent comprises a polyvinyl acetal modified thermoplastic resin and the second sizing agent comprises a polyurethane resin and / or a cellulose ether.

[0027] The inventors of this invention have discovered that polyvinyl acetal modified thermoplastic resin, when combined with polyurethane resin and cellulose ether, can further enhance the ability of the sizing agent to adsorb phenolic resin during the impregnation process, and further promote the flow of phenolic resin along the carbon fiber surface during the thermosetting process.

[0028] According to the present invention, preferably, the mass ratio of the first sizing agent and the second sizing agent is 1:0.1-10.

[0029] According to the present invention, more preferably, the mass ratio of the first sizing agent and the second sizing agent is 1:0.5-1.

[0030] According to a preferred embodiment of the present invention, the second sizing agent comprises a polyurethane resin and a cellulose ether.

[0031] The inventors of this invention have discovered that the combination of polyvinyl acetal modified thermoplastic resin, polyurethane resin, and cellulose ether, compared to the combination of polyvinyl acetal modified thermoplastic resin with polyurethane resin and cellulose ether in pairs, can further enhance the ability of the sizing agent to adsorb phenolic resin and further promote the flow of phenolic resin along the carbon fiber surface during the thermosetting process.

[0032] According to the present invention, preferably, the mass ratio of polyurethane resin to cellulose ether is 1:0.1-10.

[0033] According to the present invention, more preferably, the mass ratio of polyurethane resin to cellulose ether is 1:0.5-2.

[0034] According to a preferred embodiment of the present invention, the polyvinyl acetal modified thermoplastic resin is obtained by mixing polyvinyl acetal and thermoplastic resin in an organic solvent, wherein the mass ratio of polyvinyl acetal to thermoplastic resin is 1:1-5, more preferably 1:1.5-3.

[0035] According to the present invention, preferably, the polyvinyl acetal is selected from at least one of polyvinyl formal, polyvinyl acetal, polyvinyl propionate, and polyvinyl butyral, and more preferably polyvinyl butyral.

[0036] In this invention, polyvinyl butyral has better flexibility and adhesion, which enables polyvinyl butyral-modified thermoplastic resin to have better mechanical properties.

[0037] According to the present invention, preferably, the thermoplastic resin is a thermoplastic phenolic resin.

[0038] This invention allows for a wide range of choices of polyurethane resins. According to this invention, the polyurethane resin is preferably a waterborne polyurethane, and more preferably an anionic waterborne polyurethane.

[0039] This invention allows for a wide range of choices regarding cellulose ethers. According to this invention, the cellulose ether is preferably anionic, and more preferably carboxymethyl cellulose (sodium).

[0040] This invention does not particularly limit the type of chopped carbon fiber, and those skilled in the art can choose conventionally. According to a preferred embodiment of the invention, the chopped carbon fiber is chopped polyacrylonitrile-based carbon fiber.

[0041] According to a preferred embodiment of the present invention, the chopped carbon fiber slurry is an aqueous slurry, and the chopped carbon fiber slurry further includes a binder and a dispersant. The present invention does not particularly limit the specific type or content of the binder and dispersant.

[0042] According to the present invention, preferably, the adhesive is short-cut polyvinyl alcohol fibers with a length of 2-4 mm.

[0043] According to the present invention, preferably, the content of the binder is 10-30 wt% of chopped carbon fibers.

[0044] According to the present invention, preferably, the dispersant is polyethylene oxide.

[0045] According to the present invention, preferably, the mass ratio of the chopped carbon fibers to the dispersant is 1:4-10.

[0046] The present invention does not particularly limit the method of pulp forming on the wire in step (2), and those skilled in the art can choose conventionally. According to a specific embodiment of the present invention, the method of pulp forming on the wire is inclined wire papermaking.

[0047] According to the present invention, preferably, the online concentration of the chopped carbon fiber slurry is 0.01-0.1 wt%.

[0048] In this invention, the "online concentration" refers to the mass concentration of carbon fibers in the slurry.

[0049] This invention does not particularly limit the dehydration and drying methods for the slurry after it has been formed on the wire mesh; those skilled in the art can choose conventional methods. According to one specific embodiment of the invention, the dehydration method is roller pressing. According to another specific embodiment of the invention, the drying method is cylinder drying. Preferably, the drying temperature is 80-120℃, and the drying time is 0.5-10 min.

[0050] The sizing method in step (3) of the present invention can be any of the methods conventionally used in the art, preferably spraying or immersion.

[0051] According to a preferred embodiment of the present invention, spraying is used for sizing, with a spraying speed of 50-250 ml / min, a spraying time of 2-10 min, and a spraying temperature of 10-50℃.

[0052] According to the present invention, preferably, the spraying is followed by hot air drying, the hot air temperature is 100-150℃, the hot air velocity is 5-30m / min, and the drying time is 10-60min.

[0053] According to another preferred embodiment of the present invention, immersion sizing is adopted, preferably, the immersion time is 5-10 min and the temperature is 10-50℃.

[0054] According to the present invention, preferably, it further includes rolling and pressing after impregnation to remove excess sizing agent.

[0055] The present invention does not have any particular limitation on the impregnation solution for impregnating the active base paper in step (4). Those skilled in the art can choose conventionally, such as thermosetting resin solution.

[0056] According to one specific embodiment of the present invention, the thermosetting resin is selected from thermosetting phenolic resins.

[0057] According to a preferred embodiment of the present invention, in step (4), the reactive base paper is impregnated with a thermosetting phenolic resin solution. The solvent in the thermosetting phenolic resin solution has a wide range of choices and can be a common organic solvent, such as acetone, ethanol, etc.

[0058] According to the present invention, preferably, the concentration of the thermosetting phenolic resin solution is 2-20 wt%, and the impregnation time is 10-30 min.

[0059] According to the present invention, preferably, the impregnation is followed by hot air drying, with the hot air temperature being 60-120°C, the hot air velocity being 5-30 m / min, and the drying time being 2-15 min.

[0060] The present invention does not particularly limit the method of thermosetting in step (4). According to a specific embodiment of the present invention, a press is used for thermosetting. Preferably, the thermosetting pressure is 5-30 MPa, the thermosetting temperature is 150-200℃, and the thermosetting time is 5-15 min.

[0061] The present invention does not impose any particular limitations on the carbonization temperature, heating rate, or time in step (5). According to a preferred embodiment of the present invention, carbonization is carried out in an inert atmosphere such as nitrogen or argon, the carbonization temperature is 800-1250℃, the heating rate is 2-20℃ / min, and the carbonization temperature is reached and then held for 1-2 hours.

[0062] The present invention does not impose any particular limitations on the graphitization temperature, heating rate, and time in step (5). According to a preferred embodiment of the present invention, graphitization is carried out in an inert atmosphere such as nitrogen or argon at a temperature of 1800-2600°C, a heating rate of 20-50°C / min, and a holding time of 1-3 hours after reaching the graphitization temperature.

[0063] A second aspect of the present invention provides a carbon fiber paper prepared according to the method provided in the first aspect of the present invention.

[0064] Preferably, the thickness of the carbon fiber paper is 190-260 μm.

[0065] Preferably, the porosity of the carbon fiber paper is 80-95%.

[0066] Preferably, the air permeability of the carbon fiber paper is 2400-3000 (mL·mm) / (cm). 2 ·h·mmAq).

[0067] Preferably, the in-plane resistivity of the carbon fiber paper is 2-5 mΩ·cm.

[0068] Preferably, the normal resistivity of the carbon fiber paper is 3-6 mΩ·cm.

[0069] Preferably, the tensile strength of the carbon fiber paper is 18-30 MPa.

[0070] The carbon fiber paper prepared by the method provided by this invention has high air permeability while maintaining a certain strength and meeting the conductivity requirements.

[0071] The parameters of the carbon fiber mentioned above were determined in accordance with Part 7 of GB / T20042.7-2014 Proton Exchange Membrane Fuel Cells: Test Methods for Carbon Paper Properties.

[0072] The present invention will be described in detail below through embodiments.

[0073] In the following examples, the polyacrylonitrile-based carbon fiber was purchased from Shanghai Petrochemical Company, and the short-cut polyvinyl alcohol fiber with the grade SCF35S was purchased from Anhui Wanwei Group Co., Ltd. as water-soluble polyvinyl alcohol fiber with a fineness of 2.2 dtex.

[0074] Polyvinyl butyral was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0075] The thermoplastic phenolic resin was purchased from Hongxing Chemical Industry and Commerce Company in Zhengzhou Economic and Technological Development Zone, and its grade was 5400.

[0076] The waterborne polyurethane was purchased from Covestro, and its brand name was Dispercoll U8755.

[0077] The thermosetting phenolic resin was purchased from Jining Huakai Resin Co., Ltd., and its grade was 381A.

[0078] The polyethylene oxide was purchased from Sinopharm Chemical Reagent Co., Ltd., with a weight-average molecular weight of 8,000,000 Da;

[0079] For the method of measuring the parameters of carbon fiber paper, please refer to the detailed implementation section.

[0080] Example 1

[0081] Prepare carbon fiber paper according to the following steps:

[0082] (1) Preparation of short-cut carbon fiber slurry

[0083] Ten parts by weight of 3 mm chopped polyacrylonitrile-based carbon fibers and one part by weight of 2 mm chopped polyvinyl alcohol fibers were uniformly dispersed in a 0.1 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.01 wt%.

[0084] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0085] The slurry obtained in step (1) is formed on a wire mesh using the conventional papermaking process. Then, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 80°C for 10 minutes to obtain the base paper.

[0086] (3) Preparation of active base paper by sizing base paper

[0087] First, polyvinyl butyral and thermoplastic phenolic resin in a mass ratio of 1:1.5 are dissolved in ethanol to obtain polyvinyl butyral-modified thermoplastic phenolic resin. Then, the polyvinyl butyral-modified thermoplastic phenolic resin is dissolved in ethanol to obtain a sizing agent with a concentration of 5 wt%. The base paper obtained in step (2) is then impregnated in a sufficient amount of the above sizing agent for 5 minutes at an impregnation temperature of 20°C. Finally, excess sizing agent is rolled and pressed to obtain active base paper.

[0088] (4) Resin impregnation and thermosetting yield precursor paper

[0089] The active base paper obtained in step (3) was impregnated in a 20wt% thermosetting phenolic resin ethanol solution for 10 min, and then dried in hot air at 60℃ for 15 min with a hot air velocity of 15 m / s; then it was heat-cured using a press at a pressure of 5 MPa and a temperature of 150℃ to obtain the precursor paper.

[0090] (5) Carbonization and graphitization yield carbon fiber paper.

[0091] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 800℃, and a carbonization time of 1 hour (excluding heating time). Then, graphitization was carried out under argon atmosphere, starting from the carbonization temperature and heating at a rate of 20℃ / min, with a graphitization temperature of 2600℃, and held for 1 hour to finally obtain carbon fiber paper.

[0092] The obtained carbon fiber paper has a thickness of 200 μm, a porosity of 91%, and an air permeability of 2926 (mL·mm) / (cm). 2 The resistivity is 2.7 mΩ·cm (·h·mmAq), the in-plane resistivity is 3.4 mΩ·cm, and the tensile strength is 20 MPa.

[0093] Example 2

[0094] Prepare carbon fiber paper according to the following steps:

[0095] (1) Preparation of short-cut carbon fiber slurry

[0096] Ten parts by weight of 12 mm long chopped carbon fibers and three parts by weight of 4 mm long chopped polyethylene fibers were uniformly dispersed in a 0.5 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.1 wt%.

[0097] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0098] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 120°C for 0.5 minutes to obtain the base paper.

[0099] (3) Preparation of active base paper by sizing base paper

[0100] First, polyvinyl butyral and thermoplastic phenolic resin in a mass ratio of 1:3 were dissolved in ethanol to obtain polyvinyl butyral-modified thermoplastic phenolic resin. Then, waterborne polyurethane and polyvinyl butyral-modified thermoplastic phenolic resin in a mass ratio of 1:1 were dissolved in N,N-dimethylformamide to obtain a sizing agent with a concentration of 2wt%. The base paper obtained in step (2) was then sprayed with the above sizing agent at a spraying speed of 250 ml / min and a spraying temperature of 20°C. Then, it was dried with hot air for 2 min at a hot air temperature of 150°C and a hot air velocity of 30 m / min to obtain active base paper.

[0101] (4) Resin impregnation and thermosetting yield precursor paper

[0102] The active base paper obtained in step (3) was impregnated in a 2wt% thermosetting phenolic resin ethanol solution for 30 min, and then dried with hot air at 120℃ for 2 min at a hot air velocity of 15 m / s; then it was heat-cured using a press at a pressure of 30 MPa and a temperature of 200℃ to obtain the precursor paper.

[0103] (5) Carbonization and graphitization yield carbon fiber paper.

[0104] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1250℃, and a carbonization time of 1 hour (excluding heating time). Second, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 50℃ / min, with a graphitization temperature of 1800℃, and held for 3 hours to finally obtain carbon fiber paper.

[0105] The obtained carbon fiber paper has a thickness of 220 μm, a porosity of 84%, an air permeability of 2621 (mL·mm) / (cm2·h·mmAq), an in-plane resistivity of 3.8 mΩ·cm, a normal resistivity of 4.4 mΩ·cm, and a tensile strength of 27 MPa.

[0106] Example 3

[0107] Prepare carbon fiber paper according to the following steps:

[0108] (1) Preparation of short-cut carbon fiber slurry

[0109] Ten parts by weight of 12 mm long chopped carbon fibers and three parts by weight of 4 mm long chopped polyethylene fibers were uniformly dispersed in a 0.5 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.1 wt%.

[0110] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0111] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 120°C for 0.5 minutes to obtain the base paper.

[0112] (3) Preparation of active base paper by sizing base paper

[0113] First, polyvinyl butyral and thermoplastic phenolic resin in a mass ratio of 1:1.5 are dissolved in ethanol to obtain polyvinyl butyral-modified thermoplastic phenolic resin. Then, waterborne polyurethane and polyvinyl butyral-modified thermoplastic phenolic resin in a mass ratio of 1:1 are dissolved in acetone to obtain a sizing agent with a concentration of 2.0 wt%. The base paper obtained in step (2) is then impregnated in a sufficient amount of the above sizing agent for 10 minutes at an impregnation temperature of 20°C. Finally, excess sizing agent is rolled and pressed to obtain active base paper.

[0114] (4) Resin impregnation and thermosetting yield precursor paper

[0115] The active base paper obtained in step (3) was impregnated in a 2 wt% thermosetting phenolic resin ethanol solution for 30 min, and then dried with hot air at 120°C for 2 min at a hot air velocity of 15 m / s. It was then thermo-cured using a press at a pressure of 30 MPa and a temperature of 200°C to obtain the precursor paper.

[0116] (5) Carbonization and graphitization yield carbon fiber paper.

[0117] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1250℃, and a carbonization time of 1 hour (excluding heating time). Second, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 50℃ / min, with a graphitization temperature of 1800℃, and held for 3 hours to finally obtain carbon fiber paper.

[0118] The obtained carbon fiber paper has a thickness of 250 μm, a porosity of 90%, an air permeability of 2442 (mL·mm) / (cm2·h·mmAq), an in-plane resistivity of 4.5 mΩ·cm, a normal resistivity of 5.4 mΩ·cm, and a tensile strength of 24 MPa.

[0119] Example 4

[0120] Prepare carbon fiber paper according to the following steps:

[0121] (1) Preparation of short-cut carbon fiber slurry

[0122] Ten parts by weight of 3 mm chopped carbon fibers and one part by weight of 2 mm chopped polyethylene fibers were uniformly dispersed in a 0.1 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.1 wt%.

[0123] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0124] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 80°C for 10 minutes to obtain the base paper.

[0125] (3) Preparation of active base paper by sizing base paper

[0126] A waterborne polyurethane and sodium carboxymethyl cellulose were dissolved in water at a mass ratio of 1:1 to obtain a sizing agent with a concentration of 1.0 wt%. The base paper obtained in step (2) was then sprayed with the above sizing agent at a spraying speed of 50 ml / min and a spraying temperature of 20°C. Then, it was dried with hot air for 2 min at a hot air temperature of 100°C and a hot air velocity of 5 m / min to obtain an active base paper.

[0127] (4) Resin impregnation and thermosetting yield precursor paper

[0128] The active base paper obtained in step (3) was impregnated in a 20wt% thermosetting phenolic resin ethanol solution for 10 min, and then dried with hot air at 60℃ for 15 min at a hot air velocity of 15 m / s. It was then thermo-cured using a press at a pressure of 5 MPa and a temperature of 150℃ to obtain the precursor paper.

[0129] (5) Carbonization and graphitization yield carbon fiber paper.

[0130] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 800℃, and a carbonization time of 1 hour (excluding heating time). Second, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 20℃ / min, with a graphitization temperature of 2600℃, and held for 1 hour to finally obtain carbon fiber paper.

[0131] The obtained carbon fiber paper has a thickness of 230 μm, a porosity of 85%, an air permeability of 2389 (mL·mm) / (cm2·h·mmAq), an in-plane resistivity of 3.5 mΩ·cm, a normal resistivity of 4.4 mΩ·cm, and a tensile strength of 16 MPa.

[0132] Example 5

[0133] Prepare carbon fiber paper according to the following steps:

[0134] (1) Preparation of short-cut carbon fiber slurry

[0135] Ten parts by weight of 6 mm chopped carbon fibers and two parts by weight of 3 mm chopped polyethylene fibers were uniformly dispersed in a 0.2 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.05 wt%.

[0136] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0137] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 90°C for 8 minutes to obtain the base paper.

[0138] (3) Preparation of active base paper by sizing base paper

[0139] A waterborne polyurethane and sodium carboxymethyl cellulose were dissolved in water at a mass ratio of 1:1 to obtain a sizing agent with a concentration of 1.0 wt%. The base paper obtained in step (2) was then sprayed with the above sizing agent at a spraying speed of 100 ml / min and a spraying temperature of 20°C. Then, it was dried with hot air for 2 min at a hot air temperature of 120°C and a hot air velocity of 15 m / min to obtain an active base paper.

[0140] (4) Resin impregnation and thermosetting yield precursor paper

[0141] The active base paper obtained in step (3) was impregnated in a 15wt% thermosetting phenolic resin ethanol solution for 20 min, and then dried with hot air at 80℃ for 10 min at a hot air velocity of 15 m / s. It was then thermo-cured using a press at a pressure of 10 MPa and a temperature of 170℃ to obtain the precursor paper.

[0142] (5) Carbonization and graphitization yield carbon fiber paper.

[0143] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1000℃, and a carbonization time of 1 hour (excluding heating time). Second, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 30℃ / min, with a graphitization temperature of 2200℃, and held for 2 hours to finally obtain carbon fiber paper.

[0144] The obtained carbon fiber paper has a thickness of 220 μm, a porosity of 89%, an air permeability of 2934 (mL·mm) / (cm2·h·mmAq), an in-plane resistivity of 4.2 mΩ·cm, a normal resistivity of 5.1 mΩ·cm, and a tensile strength of 19 MPa.

[0145] Example 6

[0146] Prepare carbon fiber paper according to the following steps:

[0147] (1) Preparation of short-cut carbon fiber slurry

[0148] Ten parts by weight of 9 mm chopped carbon fibers and 2.5 parts by weight of 4 mm chopped polyethylene fibers were uniformly dispersed in a 0.3 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.06 wt%.

[0149] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0150] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 100°C for 4 minutes to obtain the base paper.

[0151] (3) Preparation of active base paper by sizing base paper

[0152] Aqueous polyurethane was dissolved in acetone to obtain a sizing agent with a concentration of 1.5 wt%. The base paper obtained in step (2) was then sprayed with the above sizing agent at a spraying speed of 150 ml / min and a spraying temperature of 20°C. Then, it was dried with hot air for 2 min at a hot air temperature of 135°C and a hot air velocity of 20 m / min to obtain active base paper.

[0153] (4) Resin impregnation and thermosetting yield precursor paper

[0154] The active base paper obtained in step (3) was impregnated in a 10 wt% thermosetting phenolic resin ethanol solution for 25 min, and then dried with hot air at 100°C for 6 min at a hot air velocity of 15 m / s. It was then thermo-cured using a press at a pressure of 20 MPa and a temperature of 180°C to obtain the precursor paper.

[0155] (5) Carbonization and graphitization yield carbon fiber paper.

[0156] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 100℃, and a carbonization time of 1 hour (excluding heating time). Second, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 40℃ / min, with a graphitization temperature of 2000℃ and a holding time of 2.5 hours, finally obtaining carbon fiber paper.

[0157] The obtained carbon fiber paper has a thickness of 190 μm, a porosity of 87%, an air permeability of 2758 (mL·mm) / (cm2·h·mmAq), an in-plane resistivity of 3.7 mΩ·cm, a normal resistivity of 4.3 mΩ·cm, and a tensile strength of 24 MPa.

[0158] Example 7

[0159] Prepare carbon fiber paper according to the following steps:

[0160] (1) Preparation of short-cut carbon fiber slurry

[0161] Ten parts by weight of 9 mm long short-cut polyacrylonitrile-based carbon fibers and 2.5 parts by weight of 4 mm long short-cut polyvinyl alcohol fibers were uniformly dispersed in a 0.3 wt% polyethylene oxide aqueous solution to prepare a short-cut carbon fiber slurry with a short-cut carbon fiber concentration of 0.06 wt%.

[0162] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0163] The slurry obtained in step (1) is formed on a wire mesh using the conventional papermaking process. Then, it is dewatered by pressing with rollers and dried in a drying cylinder at 100°C for 4 minutes to obtain the base paper.

[0164] (3) Preparation of active base paper by sizing base paper

[0165] Aqueous polyurethane was dissolved in water to obtain a sizing agent with a concentration of 2 wt%. The base paper obtained in step (2) was then impregnated in a sufficient amount of the above sizing agent for 8 minutes at a temperature of 20°C. Excess sizing agent was then rolled and pressed to obtain active base paper.

[0166] (4) Resin impregnation and thermosetting yield precursor paper

[0167] The active base paper obtained in step (3) was impregnated in a 10wt% thermosetting phenolic resin ethanol solution for 25 min, and then dried in hot air at 100℃ for 6 min with a hot air velocity of 15 m / s; then it was heat-cured using a press at a pressure of 20 MPa and a temperature of 180℃ to obtain the precursor paper.

[0168] (5) Carbonization and graphitization yield carbon fiber paper.

[0169] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1100℃, and a carbonization time of 1 hour (excluding heating time). Then, graphitization was carried out under argon atmosphere, starting from the carbonization temperature and heating at a rate of 40℃ / min, with a graphitization temperature of 2000℃ and a holding time of 2.5 hours, finally obtaining carbon fiber paper.

[0170] The obtained carbon fiber paper has a thickness of 180 μm, a porosity of 84%, and an air permeability of 2143 (mL·mm) / (cm). 2 The resistivity is 3.7 mΩ·cm (·h·mmAq), the in-plane resistivity is 3.7 mΩ·cm, the normal resistivity is 3.9 mΩ·cm, and the tensile strength is 22 MPa.

[0171] Example 8

[0172] Prepare carbon fiber paper according to the following steps:

[0173] (1) Preparation of short-cut carbon fiber slurry

[0174] Ten parts by weight of 6 mm chopped polyacrylonitrile-based carbon fibers and two parts by weight of 3 mm chopped polyvinyl alcohol fibers were uniformly dispersed in a 0.2 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a chopped carbon fiber concentration of 0.05 wt%.

[0175] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0176] The slurry obtained in step (1) is formed on a wire mesh using the conventional papermaking process. Then, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 90°C for 8 minutes to obtain the base paper.

[0177] (3) Preparation of active base paper by sizing base paper

[0178] Sodium carboxymethyl cellulose was dissolved in water to obtain a sizing agent with a concentration of 1.5 wt%. The base paper obtained in step (2) was then impregnated in a sufficient amount of the above sizing agent for 7 minutes at a temperature of 20°C. Excess sizing agent was then rolled and pressed to obtain active base paper.

[0179] (4) Resin impregnation and thermosetting yield precursor paper

[0180] The active base paper obtained in step (3) was impregnated in a 15wt% thermosetting phenolic resin ethanol solution for 20 min, and then dried in hot air at 80℃ for 10 min with a hot air velocity of 15 m / s; then it was heat-cured using a press at a pressure of 10 MPa and a temperature of 170℃ to obtain the precursor paper.

[0181] (5) Carbonization and graphitization yield carbon fiber paper.

[0182] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1000℃, and a carbonization time of 1 hour (excluding heating time). Then, graphitization was carried out under argon atmosphere, starting from the carbonization temperature and heating at a rate of 30℃ / min, with a graphitization temperature of 2200℃, and held for 2 hours to finally obtain carbon fiber paper.

[0183] The obtained carbon fiber paper has a thickness of 190 μm, a porosity of 86%, and an air permeability of 2677 (mL·mm) / (cm). 2 The resistivity is 3.3 mΩ·cm (·h·mmAq), the in-plane resistivity is 3.3 mΩ·cm, the normal resistivity is 3.8 mΩ·cm, and the tensile strength is 21 MPa.

[0184] Example 9

[0185] Prepare carbon fiber paper according to the following steps:

[0186] (1) Preparation of short-cut carbon fiber slurry

[0187] Ten parts by weight of 12 mm long chopped carbon fibers and three parts by weight of 4 mm long chopped polyethylene fibers were uniformly dispersed in a 0.5 wt% aqueous solution of polyethylene oxide to prepare a chopped carbon fiber slurry with a net concentration of 0.1%.

[0188] (2) The pulp is wire-fed, dried and formed to obtain the base paper.

[0189] The slurry obtained in step (1) is formed on a wire mesh using a conventional papermaking process. Subsequently, it is dewatered by pressing with rollers and dried in a drying cylinder at a temperature of 120°C for 0.5 minutes to obtain the base paper.

[0190] (3) Preparation of active base paper by sizing base paper

[0191] First, polyvinyl butyral and thermoplastic phenolic resin in a mass ratio of 1:3 are dissolved in ethanol to obtain polyvinyl butyral modified thermoplastic phenolic resin. Then, polyvinyl butyral modified thermoplastic phenolic resin, waterborne polyurethane, and sodium carboxymethyl cellulose in a mass ratio of 1:0.5:0.5 are dissolved in acetone to obtain a sizing agent with a concentration of 2.0 wt%. The base paper obtained in step (2) is impregnated in a sufficient amount of the above sizing agent for 10 minutes at an impregnation temperature of 20°C. Then, excess sizing agent is rolled and pressed to obtain active base paper.

[0192] (4) Resin impregnation and thermosetting yield precursor paper

[0193] The active base paper obtained in step (3) was impregnated in a 2 wt% phenolic resin ethanol solution for 30 min, and then dried with hot air at 120°C for 2 min at a hot air velocity of 15 m / s. It was then heat-cured using a press at a pressure of 30 MPa and a temperature of 200°C to obtain the precursor paper.

[0194] (5) Carbonization and graphitization yield carbon fiber paper.

[0195] The precursor paper obtained in step (4) was subjected to carbonization and graphitization. First, carbonization was carried out under nitrogen atmosphere at a heating rate of 5℃ / min, a carbonization temperature of 1250℃, and a carbonization time of 1 hour (excluding heating time). Then, graphitization was carried out under high-purity nitrogen atmosphere, starting from the carbonization temperature and heating at a rate of 50℃ / min, with a graphitization temperature of 1800℃, and held for 3 hours to finally obtain carbon fiber paper.

[0196] The obtained carbon fiber paper has a thickness of 235 μm, a porosity of 90%, and an air permeability of 2513 (mL·mm) / (cm). 2 The resistivity is 4.1 mΩ·cm (·h·mmAq), the in-plane resistivity is 4.9 mΩ·cm, and the tensile strength is 22 MPa.

[0197] Example 10

[0198] Carbon fiber paper was prepared in accordance with the method of Example 3, except that the mass ratio of waterborne polyurethane and polyvinyl butyral modified thermoplastic phenolic resin was 0.1:1.

[0199] The obtained carbon fiber paper has a thickness of 207 μm, a porosity of 93%, and an air permeability of 2737 (mL·mm) / (cm). 2 The resistivity is 3.0 mΩ·cm (·h·mmAq), the in-plane resistivity is 3.0 mΩ·cm, the normal resistivity is 3.6 mΩ·cm, and the tensile strength is 20 MPa.

[0200] Example 11

[0201] Carbon fiber paper was prepared in accordance with the method of Example 3, except that the mass ratio of waterborne polyurethane and polyvinyl butyral modified thermoplastic phenolic resin was 0.5:1.

[0202] The obtained carbon fiber paper has a thickness of 214 μm, a porosity of 91%, and an air permeability of 2621 (mL·mm) / (cm). 2 The resistivity is 3.4 mΩ·cm (·h·mmAq), the in-plane resistivity is 3.7 mΩ·cm, the normal resistivity is 3.7 mΩ·cm, and the tensile strength is 23 MPa.

[0203] Example 12

[0204] Carbon fiber paper was prepared according to the method of Example 9, except that the mass ratio of polyvinyl butyral modified thermoplastic phenolic resin, waterborne polyurethane, and sodium carboxymethyl cellulose was 1:0.5:0.25. The resulting carbon fiber paper had a thickness of 240 μm, a porosity of 90%, and an air permeability of 2512 (mL·mm) / (cm). 2 The resistivity is 4.2 mΩ·cm (·h·mmAq), the in-plane resistivity is 4.9 mΩ·cm, and the tensile strength is 21 MPa.

[0205] Example 13

[0206] Carbon fiber paper was prepared according to the method of Example 9, except that the mass ratio of polyvinyl butyral modified thermoplastic phenolic resin, waterborne polyurethane, and sodium carboxymethyl cellulose was 1:0.5:1. The resulting carbon fiber paper had a thickness of 227 μm, a porosity of 89%, and an air permeability of 2712 (mL·mm) / (cm). 2 The resistivity is 3.7 mΩ·cm (·h·mmAq), the in-plane resistivity is 4.0 mΩ·cm, and the tensile strength is 22 MPa.

[0207] As can be seen from the above embodiments, the carbon fiber paper prepared by the method provided by the present invention has high air permeability while maintaining a certain strength and meeting the conductivity requirements.

[0208] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing carbon fiber paper, characterized in that, Includes the following steps: (1) Prepare short-cut carbon fiber slurry with a length of 3-12 mm; (2) The pulp is wire-fed, formed, and dried to obtain the base paper; (3) Preparation of active base paper by sizing base paper; (4) Resin impregnation and thermosetting yield precursor paper; (5) Carbonization and graphitization yield carbon fiber paper; In step (3), a sizing agent is used for sizing, wherein the sizing agent comprises at least one of polyvinyl acetal modified thermoplastic resin, polyurethane resin and cellulose ether.

2. The method according to claim 1, wherein, The concentration of the sizing agent is 0.1-10 wt%, preferably 1-5 wt%.

3. The method according to claim 1 or 2, wherein, The sizing agent mentioned in step (3) includes a first sizing agent and a second sizing agent. The first sizing agent includes polyvinyl acetal modified thermoplastic resin, and the second sizing agent includes polyurethane resin and / or cellulose ether. Preferably, the mass ratio of the first sizing agent to the second sizing agent is 1:0.1-10.

4. The method according to claim 3, wherein, The second sizing agent contains polyurethane resin and cellulose ether; Preferably, the mass ratio of polyurethane resin to cellulose ether in the second sizing agent is 1:0.1-10.

5. The method according to any one of claims 1-4, wherein, Polyvinyl acetal modified thermoplastic resin is obtained by mixing polyvinyl acetal and thermoplastic resin in an organic solvent, wherein the mass ratio of polyvinyl acetal to thermoplastic resin is 1:1-5. Preferably, the polyvinyl acetal is selected from at least one of polyvinyl formal, polyvinyl acetal, polyvinyl propionate, and polyvinyl butyral, and more preferably polyvinyl butyral. Preferably, the thermoplastic resin is a thermoplastic phenolic resin.

6. The method according to any one of claims 1-5, wherein, The chopped carbon fiber slurry also contains a binder; preferably, the binder is chopped polyvinyl alcohol fiber with a length of 2-4 mm; preferably, the content of the binder is 10-30 wt% of the chopped carbon fiber. And / or, the chopped carbon fiber slurry further includes a dispersant; preferably, the dispersant is polyethylene oxide; preferably, the mass ratio of the chopped carbon fiber to the dispersant is 1:4-10.

7. The method according to any one of claims 1-6, wherein, The wire mesh forming process described in step (2) includes forming a wire mesh from chopped carbon fiber slurry. Preferably, the online concentration of the chopped carbon fiber slurry is 0.01-0.1 wt%. Preferably, the drying temperature is 80-120℃ and the drying time is 0.5-10min.

8. The method according to any one of claims 1-7, wherein, In step (3), the base paper is coated with a sizing agent by spraying and then dried with hot air to obtain active base paper; Preferably, the spraying speed is 50-250 mL / min, the spraying time is 2-10 min, and the spraying temperature is 10-50℃; Preferably, the hot air temperature is 100-150℃ and the hot air velocity is 5-30m / min.

9. The method according to any one of claims 1-7, wherein, In step (3), the base paper is impregnated with sizing and then rolled and pressed to obtain active base paper; Preferably, the immersion time is 5-10 minutes and the temperature is 10-50℃.

10. The method according to any one of claims 1-9, wherein, In step (4), the resin is a phenolic resin; Preferably, in step (4), the active base paper is impregnated with a phenolic resin solution; Preferably, the concentration of the phenolic resin solution is 2-20 wt%, and the impregnation time is 10-30 min; Preferably, the thermosetting pressure is 5-30 MPa, the thermosetting temperature is 150-200℃, and the thermosetting time is 5-15 min.

11. The method according to any one of claims 1-10, wherein, In step (5), the carbonization temperature is 800-1250℃, the heating rate is 2-20℃ / min, and the carbonization temperature is reached and then held for 1-2 hours. And / or, the graphitization temperature is 1800-2600℃, the heating rate is 20-50℃ / min, and the temperature is held for 1-3 hours after reaching the graphitization temperature.

12. A carbon fiber paper prepared by the method according to any one of claims 1-11.