Method for manufacturing carbon fiber paper, paper machine, carbon fiber paper, carbon sheet, gas diffusion electrode, and fuel cell

Abstract

To provide a carbon fiber paper body containing a small amount of iron based foreign matters each having a short major axis in particular.SOLUTION: The carbon fiber paper body production method of making paper from slurry including a carbon fiber using a paper making machine provided with a slurry feed port, a head box and paper making wire, is characterized in that the paper making machine comprises a mechanism capable of removing iron based foreign matters present in the slurry by a magnetic force.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a carbon fiber papermaking body used in fuel cells, particularly solid polymer fuel cells, and a papermaking machine used therein, as well as a carbon fiber papermaking body manufactured by the manufacturing method, a carbon sheet made from the carbon fiber papermaking body, a gas diffusion electrode having a microporous layer on the carbon sheet, and a fuel cell including the gas diffusion electrode. [Background technology]

[0002] Solid polymer fuel cells, which generate electromotive force through electrochemical reactions occurring at both electrodes by supplying a hydrogen-containing fuel gas to the anode and an oxygen-containing oxidizing gas to the cathode, are generally constructed by sequentially stacking a separator, a gas diffusion electrode, a catalyst layer, an electrolyte membrane, another catalyst layer, a gas diffusion electrode, and a separator. The gas diffusion electrode requires high gas diffusivity to diffuse the gas supplied from the separator to the catalyst layer, high drainage to discharge water generated by the electrochemical reaction to the separator, and high conductivity to extract the generated current. For this reason, gas diffusion electrodes made of a conductive porous substrate with a microporous layer formed on its surface are widely used. As porous substrates, for example, porous materials containing carbon fibers such as carbon fiber paper, carbon fiber fabrics, and felt-type carbon fiber nonwoven fabrics are preferably used, and among these, carbon fiber paper, which can be made thin, is preferably used as the porous material.

[0003] One of the functions required of gas diffusion electrodes is to improve the durability of fuel cell cells. When hydrogen and oxygen react to generate electricity in a fuel cell, water is produced, but hydrogen peroxide is also produced as a byproduct. At this time, if iron-based foreign matter is present inside the fuel cell, iron ions (Fe) derived from the iron-based foreign matter will be produced. 2+ Fe 3+ The catalyst causes hydrogen peroxide to decompose, generating radicals. These radicals decompose the perfluorosulfonic acid used in the electrolyte membrane, leading to a decrease in power generation performance. To suppress this decrease in power generation performance, it is necessary to reduce the amount of iron-based impurities in the gas diffusion electrode.

[0004] To reduce the amount of iron-based foreign matter in carbon sheets and gas diffusion electrodes, the common method involves using a metal detector during or after manufacturing to identify the location of the iron-based foreign matter and remove it. However, this method has disadvantages such as increased costs due to the introduction of metal detectors and product loss due to the removal of detected areas. Therefore, there is a need for a manufacturing method for carbon sheets and gas diffusion electrodes that suppresses the inclusion of iron-based foreign matter during manufacturing.

[0005] The manufacturing of carbon sheets and gas diffusion electrodes involves many processes, but the upstream process of making carbon fiber paper is particularly high in risk of contamination from iron-based foreign matter due to the use of large amounts of water and the use of motor-driven stirring equipment and pumps for liquid transfer. Furthermore, if iron-based foreign matter is introduced during this papermaking process, it becomes difficult to detect and remove as it penetrates the substrate and is covered by the carbon fibers during subsequent processes. Therefore, a manufacturing method was needed that prevents the introduction of iron-based foreign matter at the papermaking stage.

[0006] For example, in the papermaking process for manufacturing paper products, a method has been proposed to incorporate a foreign matter removal function into the tank that stores the slurry in which the fibers are dispersed, in order to remove iron-based foreign matter (Patent Document 1).

[0007] Furthermore, a method has been proposed to prevent the contamination of papermaking materials by removing iron-based foreign matter through a magnetic filter when supplying water used for papermaking to the papermaking process (Patent Document 2). Furthermore, a method has been proposed to prevent contamination of the papermaking body by adding a metal foreign matter removal process before dispersing the fibers (Patent Document 3). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-132848 [Patent Document 2] Japanese Patent Publication No. 2013-187138 [Patent Document 3] Japanese Patent Publication No. 2020-165019 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, while the methods described in Patent Documents 1 to 3 can remove iron-based foreign matter derived from water or raw materials, they cannot remove iron-based foreign matter derived from equipment in the papermaking process, such as the preparation of the slurry in which the fibers are dispersed or the transfer of the slurry through piping. Therefore, they could not reduce the risk of iron-based foreign matter being mixed into the paper. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a method for manufacturing a carbon fiber paper body, comprising using a paper machine equipped with a slurry supply port, a headbox, and papermaking wires to make paper from a slurry containing carbon fibers, characterized in that the paper machine has a mechanism capable of removing iron-based foreign matter from the slurry by magnetic force.

[0011] Furthermore, the present invention provides a paper machine equipped with a slurry supply port, a headbox, and a papermaking wire, which manufactures a carbon fiber paper machine by papermaking carbon fibers, and is characterized by having a mechanism for removing iron-based foreign matter in the slurry containing carbon fibers by magnetic force.

[0012] Furthermore, the present invention provides a content of 40 iron-based foreign matter particles / m² with a major axis of 20 to 100 μm. 2 The present invention provides a carbon fiber paper body, a carbon sheet characterized by comprising the carbon fiber paper body and a binder, a gas diffusion electrode having a microporous layer on at least one side of the carbon sheet, and a fuel cell including the gas diffusion electrode as a component. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a carbon fiber paper sheet with a low content of iron-based foreign matter, particularly having a small major axis, and to obtain a fuel cell with high durability in which chemical deterioration of the electrolyte membrane is suppressed.

Brief Description of the Drawings

[0014] [Figure 1] Schematic diagram of the paper machine of the present invention [Figure 2] Cross-sectional view and top view of the paper machine of the present invention from the side

Embodiments for Carrying Out the Invention

[0015] [Carbon fiber paper sheet] The carbon sheet of the present invention is composed of a porous carbon fiber paper sheet. The carbon sheet composed of the carbon fiber paper sheet is porous and can achieve both excellent gas diffusibility for diffusing the gas supplied from the separator to the catalyst and high drainage for discharging the water generated by the electrochemical reaction to the separator. In addition, the carbon fiber paper sheet is excellent in the property of absorbing dimensional changes in the plane direction of the electrolyte membrane. When a gas diffusion electrode using a carbon sheet composed of the carbon fiber paper sheet is used for a fuel cell, it is possible to suppress performance fluctuations due to temperature and humidity expansion of the electrolyte membrane and the separator even when the thickness of the gas diffusion electrode is reduced.

[0016] Examples of the carbon fiber used in the carbon fiber paper sheet of the present invention include carbon fibers such as polyacrylonitrile (PAN)-based, pitch-based, and rayon-based carbon fibers. Among them, PAN-based carbon fibers and pitch-based carbon fibers are preferably used in the present invention because of their excellent mechanical strength. Further, a flame-resistant fiber that becomes a carbon fiber by a carbonization process may be used. Also, natural fibers and synthetic fibers known in the art such as rayon fiber, acrylic fiber, and cellulose fiber may be mixed.

[0017] The carbon fibers used in the present invention preferably have an average diameter of single fibers within the range of 3 to 20 μm, more preferably within the range of 5 to 10 μm. When the average diameter of single fibers is 3 μm or more, the pore diameter becomes larger, drainage performance is improved, and flooding can be suppressed. On the other hand, when the average diameter of single fibers is 20 μm or less, it becomes easy to control the thickness range of a preferable carbon sheet and gas diffusion electrode.

[0018] The average length of single fibers of the carbon fibers used in the carbon fiber paper body of the present invention is preferably within the range of 3 to 20 mm, more preferably within the range of 5 to 15 mm. When the average length of single fibers is 3 mm or more, the carbon sheet and gas diffusion electrode have excellent mechanical strength, conductivity, and thermal conductivity. On the other hand, when the average length of single fibers is 20 mm or less, a homogeneous carbon sheet and gas diffusion electrode can be obtained.

[0019] The carbon fiber paper body may contain foreign substances containing metals. Among various metals contained as foreign substances, iron ions (Fe 2+ , Fe 3+ ) are most likely to promote the deterioration of the electrolyte membrane and thus the decrease in power generation performance (in the present invention, foreign substances containing the above iron ions are referred to as iron-based foreign substances). Therefore, generally, after manufacturing a carbon sheet or gas diffusion electrode from the carbon fiber paper body, it is necessary to identify the location of iron-based foreign substances using a metal detector and remove the relevant part, which causes product loss. Therefore, it is desirable that the content of iron-based foreign substances in the carbon fiber paper body at the time of manufacturing is low. Here, the lower limit of the major axis of the iron-based foreign substances whose content should be reduced is 20 μm because iron-based foreign substances with a major axis less than 20 μm have little concern of causing deterioration of the electrolyte membrane, and the upper limit is 100 μm considering the size of iron-based foreign substances that can actually be contained in the carbon fiber paper body. That is, it is desirable that the content of iron-based foreign substances in the range of 20 to 100 μm in major axis is low. Considering the loss of the carbon sheet or gas diffusion electrode due to the removal of iron-based foreign substances after manufacturing, the content of the iron-based foreign substances in the carbon fiber paper body is desirably 40 pieces / m 2 or less.

[0020] [Paper-making machine] The paper machine of the present invention is a device for producing carbon fiber paper, comprising a slurry supply port, a headbox, and a papermaking wire. Preferably, the paper machine forms the carbon fiber paper by separating the carbon fibers from a slurry, which is prepared by dispersing carbon fibers in an aqueous solution using a wet papermaking method, and forming it into a sheet. Preferably, the aqueous solution for dispersing the carbon fibers contains an antifoaming agent, a surfactant, and a thickening agent.

[0021] A specific example will be explained using a diagram. Slurry is transported from the raw material tank 4, which stores the slurry, through a pump 5 and piping to the paper machine via a slurry supply port. The slurry is then sent to a box-shaped device called a headbox 1, where it flows to an opening at the outlet of the headbox 1, under fluid control to ensure uniform distribution of carbon fibers in the slurry in the width direction relative to the flow direction. The opening leads to a papermaking wire 2, which is a continuously driven plastic mesh, and the slurry inside the headbox 1 is supplied onto the papermaking wire 2. A dewatering box 3, which is a liquid suction device, is installed behind the papermaking wire 2. By suctioning the slurry over the papermaking wire 2, the carbon fibers in the slurry are layered on the papermaking wire 2, and are transported in the direction of the papermaking wire 2's drive, continuously forming a wet material that is a precursor to the papermaking body.

[0022] Paper machines used in the wet papermaking method include long-wire paper machines, cylinder paper machines, and inclined paper machines. Among these, it is particularly preferable to use an inclined paper machine, which can suppress re-aggregation by reducing the carbon fiber concentration in the slurry.

[0023] [Manufacturing method for carbon fiber papermaking] The carbon fiber papermaking body of the present invention is preferably a carbon fiber papermaking body in which a slurry prepared by dispersing carbon fibers in an aqueous solution is formed into a sheet by a wet papermaking method. The aqueous solution for dispersing the carbon fibers preferably contains an antifoaming agent, a surfactant, and a thickening agent. A slurry can be obtained by dispersing the carbon fibers in the above aqueous solution, and a wet material can be obtained by the above papermaking machine.

[0024] Generally, a binder resin is applied to the wet material described above to maintain its shape as a carbon fiber papermaking body. This application can be achieved by methods such as coating the wet material with the binder resin, using various commercially available coating devices. Coating methods include spray coaters, curtain coaters, and die coaters. The coating methods described above are merely examples and are not necessarily the only options.

[0025] Carbon fiber paper can be obtained by drying a wet material coated with binder resin, with a drying temperature of 100-180°C being preferable. Commonly used drying methods include multi-cylinder dryers, Yankee dryers, and hot air drying. The drying methods exemplified above are merely examples and are not necessarily limited to these, but it is preferable to support the material with a heat-resistant belt, heat-resistant mesh, or heat-resistant felt while transporting it and drying it with hot air, as this allows for stable transport and drying.

[0026] [Removal of iron-based foreign matter] As described above, when making carbon fiber paper, the incorporation of iron-based foreign matter into the carbon fiber paper can be prevented by removing iron-based foreign matter using a magnetic mechanism before the carbon fibers are laminated. Examples of mechanisms capable of removing iron-based foreign matter using magnetism include mechanisms made of magnetic materials and mechanisms using electromagnets. The mechanism capable of removing iron-based foreign matter using magnetism can be installed anywhere on the paper machine, but it is preferable to install it in the headbox just before the carbon fibers reach the papermaking wire and lamination begins. Magnetic blocks or magnetic bars may be installed in the middle of the slurry flow path in the headbox, but this may cause turbulence in the flow velocity. Therefore, a mechanism that can be installed in the headbox, can be made of a magnetic material, and does not obstruct the flow of carbon fibers is preferably used, such as a punching plate, slice, or magnetic plate made of a magnetic material.

[0027] The punching plate is a metal plate with multiple regularly arranged holes located inside the headbox. It functions to reduce variations in basis weight in the width direction by making the flow rate uniform when spreading the slurry laterally relative to the flow direction. By making the punching plate out of a magnetic material, iron-based foreign matter in the slurry passing through the punching plate can be collected. It is preferable to install the punching plate perpendicular to the direction in which the slurry flows inside the headbox, as this allows for more efficient collection of iron-based foreign matter. When flowing slurry containing carbon fibers, if the holes are too small, the carbon fibers are more likely to clog, and if the holes are too large, the removal rate of iron-based foreign matter decreases. Therefore, it is preferable that the diameter of the holes be 2 to 3 times the length of the fibers. In addition, if the number of holes in the punching plate is increased and the perforation rate is high, the frame between the holes becomes thinner, and the carbon fibers can get caught in the frame and cause entanglement. Also, if the perforation rate is low, the flow inside the headbox becomes irregular, and the variation in basis weight in the width direction increases when the paper is made. Therefore, the perforation ratio is preferably 40-60%, and more preferably 45-55%. Furthermore, a structure in which the perforated plate can be detached is preferable because it allows for easy removal of attached iron-based foreign matter, thus improving maintainability.

[0028] A slice is a flow straightening plate installed above the papermaking wire inside the headbox. It is the same width as the papermaking wire and is fixed to the headbox at a certain angle to the papermaking wire to form a wedge-shaped flow path, which is used to control the slurry flow velocity. Since the surface of the slice that contacts the liquid surface inside the headbox is flat, making the slice out of a magnetic material allows for the removal of iron-based foreign matter without obstructing the slurry flow. Furthermore, by making the slice movable up and down using a jack, it is possible to easily remove iron-based foreign matter that has adhered after papermaking. Here, instead of designing the slice itself out of a magnetic material, a magnetic sheet may be attached to the surface of the slice that contacts the liquid surface or the surface that does not contact the liquid surface.

[0029] It is also possible to remove iron-based foreign matter from the slurry by installing a magnetic plate on the inner wall of the headbox. In this case, by installing the magnetic plate in front of the papermaking wire on the headbox, iron-based foreign matter in the slurry can be removed before fiber lamination. If the magnetic plate is detachable, the attached iron-based foreign matter can be removed by removing the magnetic plate after papermaking. Alternatively, the magnetic plate may be installed on the outer wall of the headbox. In this case, the iron-based foreign matter will stick directly to the headbox wall, so if the magnetic plate is removed after papermaking is complete, the iron-based foreign matter will peel off the headbox wall and can be easily removed during normal cleaning of the paper machine, which is preferable.

[0030] Examples of magnetic materials include ferrite magnets, neodymium magnets, and alnico magnets, but are not limited to these. Furthermore, electromagnets may be installed on surfaces that do not come into contact with the liquid surface of the slices or on the outer surface of the headbox. In this case, it is preferable to turn off the power after the papermaking process is complete to release the magnetism, which allows any attached iron-based foreign matter to detach, making cleaning easier.

[0031] [Method for manufacturing carbon sheets] The carbon sheet preferably consists of a carbon fiber papermaking body and a binder, thereby improving mechanical strength and reducing electrical resistance. The manufacturing method of the carbon sheet preferably includes a resin impregnation step of applying resin to the carbon fiber papermaking body, a pressurization step of adjusting the thickness by pressurization, a firing step of carbonizing the resin-treated carbon fiber papermaking body, and a water-repellent step of applying a water-repellent treatment after firing.

[0032] The following describes an example of a preferred manufacturing method, but the present invention is not limited to the following description.

[0033] [Resin impregnation process] In the method for producing the carbon sheet of the present invention, one preferred embodiment is to impregnate a carbon fiber papermaking body with a resin composition that serves as a binder.

[0034] In this invention, the binder in the carbon sheet refers to components other than the carbon fibers in the carbon sheet, and primarily plays a role in binding the carbon fibers together. Examples of binders include resin compositions or their carbides impregnated into the carbon fiber papermaking body. In this invention, a carbon fiber papermaking body impregnated with a resin composition that serves as a binder may be referred to as a "pre-impregnated body."

[0035] In the present invention, the resin composition used to prepare the pre-impregnated body is a resin component to which a solvent or other substances are added as needed. Here, the resin component includes a resin such as a thermosetting resin or a thermoplastic resin, and further includes additives such as carbon powder or a surfactant as needed.

[0036] The carbonization yield of the resin components in the above resin composition is preferably 40 parts by mass or more. Carbonization is the state in which carbon remains when a substance is burned in the absence of oxygen, and the carbonization yield is expressed as the ratio of the remaining carbon to the mass of the original resin components. When the carbonization yield is 40 parts by mass or more, the carbon sheet tends to have excellent mechanical properties, electrical conductivity, and thermal conductivity. There is no particular upper limit to the carbonization yield of the resin components in the resin composition, but it is usually around 60 parts by mass.

[0037] The resin components in the above resin composition are preferably thermosetting resins such as phenolic resins, epoxy resins, melamine resins, and furan resins. Among these, phenolic resins are particularly preferred due to their high carbonization yield. Carbon powder may also be added as needed.

[0038] In the present invention, methods for impregnating a carbon fiber papermaking body with a resin composition include immersing the carbon fiber papermaking body in a resin composition with added solvent, coating the carbon fiber papermaking body with a resin composition with added solvent, and forming a layer of the resin composition on a release film and transferring the layer of the resin composition to the carbon fiber papermaking body. Among these, the method of immersing the carbon fiber papermaking body in a resin composition with added solvent is particularly preferred due to its excellent productivity. Furthermore, in the case of the immersion method, the resin composition can be uniformly attached to the entire pre-impregnated body, and the binder can be uniformly attached to the entire carbon sheet obtained, thereby further improving the strength of the carbon sheet.

[0039] [Pressurization process] In this invention, the resin composition in the pre-impregnated material can be partially crosslinked by heating and pressurizing the pre-impregnated material, thereby adjusting the carbon sheet to the desired thickness and density. Methods of heating and pressurizing include using heated hot plates, rolls, or belts. By providing unwinding and winding devices before and after this heating and pressurizing apparatus, long lengths of pre-impregnated material can be continuously heated and pressurized. Additional heat treatment, such as using hot air, may be applied to further promote crosslinking of the resin composition in the pre-impregnated material.

[0040] [Firing process] In this invention, a carbon fiber paper body is impregnated with a resin composition to form a pre-impregnated body, and then fired in an inert atmosphere to carbonize the resin composition. This firing can be carried out using either a batch-type or a continuous-type heating furnace.

[0041] The maximum firing temperature is preferably within the range of 1300 to 3000°C. If the maximum temperature is 1300°C or higher, the carbonization of the resin components in the pre-impregnated material progresses, resulting in a carbon sheet with excellent conductivity and thermal conductivity. On the other hand, if the maximum temperature is 3000°C or lower, the operating cost of the heating furnace is reduced.

[0042] In this invention, a pre-impregnated material that has been carbonized may be referred to as a "carbon fiber calcined body." In other words, a carbon fiber calcined body corresponds to a carbon sheet. Furthermore, both the carbon fiber calcined body before the water-repellent treatment described below and the carbon fiber calcined body after the water-repellent treatment are considered to be carbon sheets.

[0043] [Water-repellent treatment] In the present invention, it is preferable to apply a water-repellent treatment to the carbon fiber sintered body in order to improve drainage. The water-repellent treatment can be performed by applying a water-repellent agent to the carbon fiber sintered body and heat-treating it. By applying the water-repellent treatment, a carbon sheet containing a water-repellent agent as a binder can be obtained.

[0044] As a water-repellent agent, it is preferable to use a fluorine-based polymer due to its excellent corrosion resistance. Examples of fluorine-based polymers include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0045] [Gas diffusion electrode] Next, the gas diffusion electrode of the present invention will be described.

[0046] The gas diffusion electrode of the present invention is the carbon sheet having a microporous layer on one side.

[0047] A microporous layer can be formed by applying a coating solution containing a conductive filler to at least one side of the carbon sheet. Carbon powder is preferred as the conductive filler due to its physical and chemical stability. The coating solution is a dispersion of the conductive filler in a dispersion medium such as water or an organic solvent, and may also contain a dispersion aid such as a surfactant. Water is preferred as the dispersion medium, and a nonionic surfactant is preferred as the dispersion aid. Furthermore, a water-repellent agent may be included to improve the drainage of the microporous layer.

[0048] The coating liquid can be applied to the carbon sheet using various commercially available coating devices, and it is also preferable to dry the coating liquid using a drying facility after application.

[0049] [Membrane electrode assembly] In the present invention, a membrane electrode assembly can be formed by bonding the gas diffusion electrode to at least one side of a solid polymer electrolyte membrane having catalyst layers on both sides. In this case, arranging the side with the microporous layer of the gas diffusion electrode on the catalyst layer side is preferable because it improves the drainage of the generated water, increases the contact area between the catalyst layer and the gas diffusion electrode, and reduces contact electrical resistance. The catalyst layer consists of a layer containing a solid polymer electrolyte and catalyst-supported carbon. Platinum is usually used as the catalyst.

[0050] [Fuel cell] A polymer electrolyte fuel cell can be manufactured by stacking multiple membrane electrode assemblies, each sandwiched between separators with gaskets in between, as described above. [Examples]

[0051] Next, the present invention will be specifically described with reference to examples.

[0052] <Preparation of carbon fiber papermaking> To 100 parts by mass of deionized water, 0.01 parts by mass of the defoaming agent KM-73 (manufactured by Shin-Etsu Chemical Co., Ltd.), 0.01 parts by mass of the thickening agent "Noptex®" E-R060 (manufactured by Sunopco Co., Ltd.), and 0.01 parts by mass of the surfactant "Alcox®" CP-B1 (manufactured by Meisei Chemical Industry Co., Ltd.) were added, and the mixture was stirred in a disperser for 10 minutes to prepare an aqueous solution for dispersion.

[0053] Next, 0.15 parts by mass of PAN-based carbon fiber "Torayca®" T300 (manufactured by Toray Industries, Inc.) (average single fiber diameter: 7 μm), cut to a length of 6 mm, were added to 100 parts by mass of a dispersion aqueous solution, and the mixture was stirred in a disperser for 5 minutes to prepare a slurry. The process of making carbon fiber paper from this slurry will be explained using Figures 1 and 2. The obtained slurry was filled into a raw material tank 4, and the slurry was sent to the headbox 1 of the paper machine using a pump 5. Carbon fiber paper was made by flowing the slurry onto the papermaking wire 2, which was moving at a predetermined speed. An inclined paper machine was used, with the papermaking wire 2 having an inclination angle of 20 degrees relative to the ground. At this time, the water in the slurry was discharged by a dewatering box 3 installed at the bottom of the papermaking wire 2 to promote the lamination of carbon fibers onto the papermaking wire 2.

[0054] Furthermore, a 10% by mass aqueous solution of polyvinyl alcohol was applied to the wet material coming out of the paper machine as a binder resin, and the material was heated at 180°C for 2 minutes to dry it, thereby producing a long carbon fiber paper body. The amount of polyvinyl alcohol applied was 22 parts by mass per 100 parts by mass of the carbon fiber paper body.

[0055] <Method for measuring the content of iron-based foreign matter in carbon fiber paper> A 250mm x 200mm carbon fiber paper sample was observed using an X-ray foreign matter analyzer (Hitachi High-Tech Science EA8000A) with transmitted X-rays (20kV, 35mA), and the number of iron-based foreign matter particles with a major axis of 20-100μm was counted from the captured image. Here, "major axis" refers to the major axis of the iron-based foreign matter in the captured image. For iron-based foreign matter that is not circular or elliptical, the major axis was measured as the maximum distance between any two points on the outer circumference of the iron-based foreign matter. Samples of the above size were cut from 30 different locations on the fabricated carbon fiber paper sample, and the number of iron-based foreign matter particles with a major axis of 20-100μm was counted. The average number was then calculated per square meter. Using this measurement method, the iron-based foreign matter content in the carbon fiber paper sample was found to be 40 particles / m². 2 The following criteria were considered passing.

[0056] (Example 1) A carbon fiber paper body was produced as described in <Production of Carbon Fiber Paper Body>. At this time, a punching plate 6 made of a detachable neodymium magnet, a magnet plate 9 made of a detachable neodymium magnet on the inner wall side surface, and a slice 7 made of a neodymium magnet with a variable angle of liquid attachment to the slurry liquid surface were installed above the papermaking wire in the headbox 1. The diameter of the holes in the punching plate 6 was 15 mm and the aperture ratio was 50%, and the slice immersion angle 8 of the slice 7 was set to 5 degrees so as not to hinder the flow while being immersed in the slurry. The content of iron-based foreign substances in the obtained carbon fiber paper body was 15 pieces / m 2 It was.

[0057] (Examples 2 to 7) In the papermaking process, a carbon fiber paper body was produced in the same manner as in Example 1, except that the material of the punching plate 6 installed in the headbox 1, whether the magnet plate 9 was installed, and the slice immersion angle 8 were as shown in Table 1. The slice immersion angle 8 when the bottom surface of the slice 7 touches the slurry liquid surface is 0 degrees, but in the examples where it is not immersed, the slice 7 was fixed in a state of floating from the slurry liquid surface (the state where the slice immersion angle 8 becomes -5 degrees) for papermaking. The content of iron-based foreign substances in the obtained carbon fiber paper body is shown in Table 1.

[0058] (Comparative Example 1) In the papermaking process, a carbon fiber paper body was produced in the same manner as in Example 1, except that a punching plate made of non-magnetic stainless steel was installed in the headbox 1, the magnet plate was not installed, and the slice immersion angle was set to -5 degrees. The content of iron-based foreign substances in the obtained carbon fiber paper body was 186 pieces / m 2 It was, and did not meet the passing criteria.

[0059]

Table 1

Explanation of Reference Signs

[0060] 1 Headbox 2 Papermaking wire 3. Dehydration box 4. Raw material tanks 5 pumps 6 Perforated Plates 7 slices 8 slice immersion angle 9 Magnetic Plates

Claims

1. A method for manufacturing a carbon fiber papermaking body, comprising using a papermaking machine equipped with a slurry supply port, a headbox, and papermaking wires to make paper from a slurry containing carbon fibers, wherein the papermaking machine has a mechanism made of a magnetic material that can remove iron-based foreign matter in the slurry by magnetic force, and the mechanism made of a magnetic material has a punching plate made of a magnetic material arranged inside the headbox.

2. A method for manufacturing a carbon fiber papermaking body, comprising using a papermaking machine equipped with a slurry supply port, a headbox, and papermaking wires to make paper from a slurry containing carbon fibers, wherein the papermaking machine has a mechanism made of a magnetic material that can remove iron-based foreign matter in the slurry by magnetic force, and the mechanism made of a magnetic material has slices made of a magnetic material arranged on the upper part of the papermaking wires in the headbox.

3. A method for manufacturing a carbon fiber papermaking body, comprising papermaking a slurry containing carbon fibers using a papermaking machine equipped with a slurry supply port, a headbox, and papermaking wires, wherein the papermaking machine has a mechanism made of a magnetic material that can remove iron-based foreign matter in the slurry by magnetic force, and the mechanism made of a magnetic material has a magnet plate arranged on the wall surface of the headbox.

4. The aforementioned paper machine has a mechanism that uses an electromagnet to remove the iron-based foreign matter by magnetic force. A method for manufacturing a carbon fiber paper product according to any one of claims 1 to 3, characterized by having the following features.

5. A device equipped with a slurry feed port, headbox, and papermaking wire, which is used to make paper containing carbon fiber slurry. A paper machine for manufacturing carbon fiber paper, wherein iron-based foreign matter in the slurry is removed by magnetic force. A paper machine characterized by having a mechanism made of a magnetic material in the headbox.

6. The mechanism for removing the aforementioned iron-based foreign matter by magnetic force is characterized by having a mechanism using an electromagnet. The paper machine according to claim 5.

Images