Carbon fiber sheet manufacturing method and carbon fiber sheet product

Abstract

To provide a carbon fiber sheet manufacturing method capable of suppressing generation of defects and metal (particularly, iron) foreign substance contamination by preventing burning or deterioration of a heat-resistant sheet, a heat treatment furnace, and a carbon fiber sheet precursor due to oxygen.SOLUTION: A carbon fiber sheet manufacturing method manufactures a carbon fiber sheet by continuously transporting a carbon fiber sheet precursor and a heat-resistant sheet placed on the carbon fiber sheet precursor and passing them through the inside in inert atmosphere of a heat treatment furnace. The heat-resistant sheet is separated away from the carbon fiber sheet precursor at an inlet of the heat treatment furnace and placed on the carbon fiber sheet precursor in a furnace inner space of the heat treatment furnace.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carbon fiber sheet that is preferably used as a gas diffuser in a polymer electrolyte fuel cell, a methanol fuel cell, a phosphoric acid fuel cell, and a water electrolysis device (particularly a polymer electrolyte water electrolysis device). [Background technology]

[0002] Carbon fiber sheets, such as carbon paper in which short carbon fibers are bound with a resin carbide and carbon fiber nonwoven fabric in which carbon fibers are entangled, are used as gas diffusers that constitute the membrane electrode assembly in which the power generation reaction occurs in fuel cells. Cracks and chips at the edges of the carbon fiber sheet can cause deterioration of the electrolyte membrane, so the carbon fiber sheet is required to contain as few defects as possible, such as cracks and chips.

[0003] As a method for producing such a carbon fiber sheet, Patent Document 1 discloses a method in which a heat-resistant sheet is placed on a carbon fiber sheet precursor and heat treatment is performed to prevent the deposition of pyrolysis products and their contact with the carbon fiber sheet precursor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-191406 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have found that the method of Patent Document 1 has a problem in that the carbon fiber sheet precursor and the heat-resistant sheet are introduced into a heat treatment furnace with an inert atmosphere while air is present between them, resulting in burnout and wear of the heat-resistant sheet, the heat treatment furnace, and the carbon fiber sheet precursor due to oxygen contained in the air. In particular, metals (especially iron) contained in the carbon fiber sheet precursor evaporate in the heat treatment furnace and are released in pyrolysis gas, which can generate foreign particles such as precipitated particles containing metals (especially iron). If the heat-resistant sheet is burned or worn, these foreign particles fall onto the surface of the carbon fiber sheet precursor, causing holes and metal (especially iron) foreign matter contamination in the carbon fiber sheet, which is a problem.

[0006] An object of the present invention is to provide a method for producing a carbon fiber sheet that can prevent the occurrence of defects and metal (especially iron) foreign matter contamination by preventing the burning and wear of a heat-resistant sheet, a heat treatment furnace, and a carbon fiber sheet precursor caused by oxygen as described above. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a method for producing a carbon fiber sheet, in which a carbon fiber sheet precursor and a heat-resistant sheet placed on the carbon fiber sheet precursor are continuously conveyed and passed through a heat treatment furnace having an inert atmosphere to produce a carbon fiber sheet, wherein the heat-resistant sheet is separated from the carbon fiber sheet precursor at the furnace entrance of the heat treatment furnace, and is placed on the carbon fiber sheet precursor in the furnace space of the heat treatment furnace. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the occurrence of defects in the carbon fiber sheet, while preventing the heat-resistant sheet, the heat treatment furnace, and the carbon fiber sheet precursor from being burned or worn due to oxygen being brought into the heat treatment furnace, and to produce a carbon fiber sheet with few defects and metal (especially iron) foreign matter contamination. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional schematic view of a heat treatment furnace in a manufacturing apparatus for manufacturing a carbon fiber sheet using the method for manufacturing a carbon fiber sheet precursor of the present invention. [Figure 2] Schematic diagram of the heat treatment furnace 100 as seen from the inlet side of the heat treatment furnace. [Figure 3] Schematic diagram showing an embodiment in which a flame-resistant thread is connected to the end of a heat-resistant sheet and introduced into the heat treatment furnace shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will now be described in detail with reference to the drawings.

[0011] <Method of manufacturing carbon fiber sheets> First, the heat treatment furnace 100 will be described. Fig. 1 is a cross-sectional schematic diagram of a heat treatment furnace in a manufacturing apparatus for manufacturing a carbon fiber sheet using the carbon fiber sheet manufacturing method of the present invention, and Fig. 2 is a schematic diagram of the heat treatment furnace 100 as viewed from the inlet side of the heat treatment furnace.

[0012] The heat treatment furnace 100 is provided with an internal furnace space 101 through which the carbon fiber sheet precursor 10 can pass. The internal furnace space 101 has two openings, one of which is an entrance to the heat treatment furnace (hereinafter referred to as the furnace entrance) 105 and the other of which is an exit of the heat treatment furnace (hereinafter referred to as the furnace exit) 106. Heat sources 107 for raising the temperature of the internal furnace space 101 are disposed above and below the internal furnace space 101. The heat sources 107 and the internal furnace space 101 are separated by a muffle upper wall 102 and a muffle lower wall 103, and a hearth 104 along which the carbon fiber sheet precursor 10 runs is provided above the muffle lower wall 103. The internal furnace space 101 can be provided with an inert atmosphere, and is maintained in an inert gas atmosphere such as nitrogen or argon to prevent oxidation of the carbon fiber sheet 20 and the heat treatment furnace 100 itself during the heat treatment of the carbon fiber sheet precursor 10. The carbon fiber sheet precursor 10 is subjected to heat treatment while continuously traveling through the furnace space 101 and becomes the carbon fiber sheet 20.

[0013] To maintain suitable electrical conductivity of the carbon fiber sheet 20, the heat treatment temperature of the heat treatment furnace 100 (the maximum temperature inside the heat treatment furnace) is preferably 1500°C or higher. If the heat treatment temperature of the heat treatment furnace is lower than 1500°C, the degree of graphitization of the carbon fiber sheet 20 will be low, resulting in reduced electrical conductivity and thermal conductivity. If the heat treatment temperature of the heat treatment furnace is higher than 3000°C, a large amount of energy will be required for heating, and the carbon members used in the furnace will be easily worn out. The heat treatment temperature is more preferably 1800 to 2800°C, and even more preferably 1900 to 2600°C.

[0014] The materials that can be used to construct the heat treatment furnace 100 include carbon materials such as graphite, metals, and ceramics. However, carbon materials such as graphite are preferred because they are inexpensive, and carbon materials such as graphite are more preferred for the parts that reach temperatures of 1000°C or higher because of their chemical stability.

[0015] The carbon fiber sheet precursor 10 contains carbon fibers or organic fibers that can be converted into carbon fibers. In a preferred embodiment, the carbon fiber sheet precursor 10 is formed by binding carbon fibers or organic fibers that can be converted into carbon fibers with a carbonizable organic material. More preferably, the carbon fiber sheet precursor 10 is formed by papermaking short carbon fibers or short fibers of carbonizable organic fibers, impregnating and curing the paper with a carbonizable organic resin. In this case, the length of the short fibers is preferably within a range of 3 to 12 mm. A length of the short fibers within a range of 6 to 9 mm is more preferable because it ensures good dispersion during papermaking of the short fibers and allows for the production of a porous carbon fiber sheet that has high tensile strength and is tear-resistant. Alternatively, the carbon fiber sheet precursor 10 may be formed by forming a nonwoven fabric from flame-resistant PAN yarn in a dry process and calendering the nonwoven fabric with a heated roll.

[0016] The carbon fiber may be any of polyacrylonitrile (PAN)-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and phenol-based carbon fiber. Among these, it is preferable to use PAN-based carbon fiber or pitch-based carbon fiber, which can increase the bending strength and tensile strength of the obtained carbon fiber sheet 20, and it is more preferable to use PAN-based carbon fiber.

[0017] The carbonizable organic substance may be a thermosetting resin such as an epoxy resin, an unsaturated polyester resin, a phenolic resin, a polyimide resin, or a melamine resin, or a thermoplastic resin such as an acrylic resin, a polyvinylidene chloride resin, or a polytetrafluoroethylene resin, but it is preferable to use a thermosetting resin that has a high carbonization yield, and among these, it is more preferable to use a phenolic resin.

[0018] When the carbon fiber sheet is used as a fuel cell electrode substrate, the carbon fiber sheet precursor preferably contains carbon powder to improve electrical conductivity. In this case, the carbon powder preferably accounts for 1 to 50 mass % of the carbon fiber sheet precursor.

[0019] The carbon fiber sheet precursor 10 is inserted from a furnace entrance 105 and continuously moves, sliding along the hearth 104, within the furnace space 101 maintained at a high temperature toward the furnace exit 106. During this process, the carbon fiber sheet precursor 10 is heat-treated within the furnace space 101, and the organic matter described above is carbonized to form the carbon fiber sheet 20, which is then sent out of the heat treatment furnace 100 through the furnace exit 106. At this time, only one carbon fiber sheet precursor 10 may be transported, or multiple carbon fiber sheet precursors 10 may be transported simultaneously in a stacked state.

[0020] A heat-resistant sheet 108 for covering the upper surface of the carbon fiber sheet precursor 10 is disposed upstream of the furnace inlet 105. In this embodiment, the heat-resistant sheet 108 is supplied by being unwound from a roll 112 installed upstream of the heat treatment furnace. By rotating the roll 112 during heat treatment, the heat-resistant sheet 108 can be supplied and moved.

[0021] The heat-resistant sheet 108 is carried into the heat treatment furnace through a slit portion 110 of a shutter 109 provided at the entrance of the heat treatment furnace, and is placed on the carbon fiber sheet precursor 10 so as to come into contact with the carbon fiber sheet precursor 10 in the inert gas atmosphere inside the heat treatment furnace. If pyrolysis gas flows between the lower surface of the heat-resistant sheet 108 and the carbon fiber sheet precursor 10, precipitated particles and the like may be generated between the heat-resistant sheet 108 and the carbon fiber sheet precursor 10 and may adhere to the surface of the carbon fiber sheet precursor 10. Therefore, it is preferable that the heat-resistant sheet 108 be in contact with the upper surface of the carbon fiber sheet precursor 10 during transportation.

[0022] The heat-resistant sheet 108 is separated from the carbon fiber sheet precursor 10 at the furnace entrance 105 of the heat treatment furnace 100. If the heat-resistant sheet 108 is placed on the carbon fiber sheet precursor 10 upstream of the furnace entrance 105 and then carried into the heat treatment furnace 100 in that state, air may be trapped between the carbon fiber sheet precursor 10 and the heat-resistant sheet 108. If air is mixed into the furnace space 101 in this manner, it may cause wear and tear on the heat-resistant sheet 108, the heat treatment furnace 100, and the carbon fiber sheet precursor 10. Therefore, in the present invention, the heat-resistant sheet 108 is carried into the heat treatment furnace in a state separated from the carbon fiber sheet precursor 10, and is placed on the carbon fiber sheet precursor 10 in the furnace space 101.

[0023] More specifically, as shown in Fig. 2, the heat-resistant sheet 108 is preferably introduced into the furnace space 101 independently of the carbon fiber sheet precursor 10 through a slit portion 110 of a shutter 109 provided at the furnace entrance 105. Alternatively, as shown in Fig. 3, the heat-resistant sheet 108 may be introduced into the heat treatment furnace with a flame-resistant thread 111 connected to an end of the heat-resistant sheet 108.

[0024] It is preferable that the heat-resistant sheet 108 is moved in the conveying direction without being fixed in position while the carbon fiber sheet precursor 10 passes through the furnace space 101. If the heat-resistant sheet 108 remains stationary in the heat treatment furnace without moving, the heat-resistant sheet 108 may be damaged when a large number of precipitated particles from the pyrolysis gas fall on it. Furthermore, if the heat-resistant sheet 108 remains stationary for a long time in an area where the heat-resistant sheet 108 is easily worn, such as a high-temperature area, the heat-resistant sheet 108 is likely to be burned or worn. Note that moving the heat-resistant sheet in the conveying direction includes both moving the heat-resistant sheet in the direction in which the carbon fiber sheet precursor 10 advances and moving the heat-resistant sheet in the opposite direction to the direction in which the carbon fiber sheet precursor 10 advances.

[0025] However, if the heat-resistant sheet 108 is simply moved along with the carbon fiber sheet precursor 10, the heat-resistant sheet 108 must be at least as long as the carbon fiber sheet precursor 10. Therefore, it is preferable to move the heat-resistant sheet 108 in the conveying direction independently of the carbon fiber sheet precursor 10. The heat-resistant sheet 108 may be continuously moved during the heat treatment of the carbon fiber sheet precursor 10. In this case, it is preferable to move the heat-resistant sheet 108 at a speed slower than the conveying speed of the carbon fiber sheet precursor in order to shorten the required length of the heat-resistant sheet 108. A more preferable embodiment is to move the heat-resistant sheet 108 in the opposite direction to the conveying speed of the carbon fiber sheet precursor. Furthermore, in order to shorten the required length of the heat-resistant sheet 108, it is preferable to move the heat-resistant sheet 108 intermittently, independently of the carbon fiber sheet precursor 10, every time the carbon fiber sheet precursor 10 is conveyed a certain length. In particular, it is preferable to rotate the roll 112 connected to the heat-resistant sheet 108 at regular intervals every time the carbon fiber sheet precursor 10 is conveyed a certain length, and move the heat-resistant sheet 108 a certain length in the opposite direction to the advancing direction of the carbon fiber sheet precursor 10. In the furnace space 101 of the heat treatment furnace 100, the temperature is low near the furnace entrance 105, and the carbon fiber sheet precursor moves from the low-temperature side to the high-temperature side of the furnace space 101. Therefore, by moving the heat-resistant sheet 108 in the opposite direction to the direction in which the carbon fiber sheet precursor 10 moves, precipitated particles and the like that have fallen onto the heat-resistant sheet 108 can be moved toward the furnace entrance 105, preventing them from melting or evaporating. If precipitated particles and the like on the heat-resistant sheet 108 melt or evaporate in the high-temperature part of the heat treatment furnace, this can cause holes to form in the heat-resistant sheet 108.

[0026] The heat-resistant sheet 108 is preferably wider than the carbon fiber sheet precursor 10. More specifically, the width of the heat-resistant sheet 108 is preferably in the range of 1.01 to 1.50 times the width of the carbon fiber sheet precursor 10. If the width of the heat-resistant sheet 108 is more than 1.50 times the width of the carbon fiber sheet precursor 10, the width of the heat treatment furnace 100 must be increased by the width of the heat-resistant sheet 108, which is undesirable because it increases the installation costs and running costs of the heat treatment furnace 100. If the width of the heat-resistant sheet 108 is less than 1.01 times the width of the carbon fiber sheet precursor 10, precipitated particles containing metals (especially iron) may fall onto the carbon fiber sheet precursor 10 that is not covered with the heat-resistant sheet 108 when the carbon fiber sheet precursor 10 meanders.

[0027] The heat-resistant sheet 108 is not particularly limited as long as it is a material that does not decompose in the inert gas atmosphere in the heat treatment furnace 100 at temperatures ranging from 1500 to 3000°C. However, it is preferable to use a carbon fiber nonwoven fabric or a carbon fiber woven fabric. Carbon fiber nonwoven fabric can be used as the heat-resistant sheet 108 in both dry and wet processes. Dry carbon fiber nonwoven fabric can be obtained, for example, by heating polyacrylonitrile (PAN) fibers that can be carbonized to 200 to 300°C in air to obtain a nonwoven fabric from the resulting PAN flame-resistant yarn, and then heat-treating and carbonizing the resulting fabric. Wet carbon fiber nonwoven fabric is preferably a carbon fiber sheet 20 obtained by heat-treating a carbon fiber sheet precursor 10. Carbon fiber woven fabric has a rougher surface than carbon fiber nonwoven fabric, and therefore is more likely to wear down the surface of the carbon fiber sheet precursor 10 when it comes into contact with the carbon fiber sheet precursor 10, but it has excellent durability and ease of handling. Although carbon fiber nonwoven fabric is prone to wear in a heat treatment furnace and is less durable than carbon fiber woven fabric, supplying it into the heat treatment furnace without overlapping it with the carbon fiber sheet precursor 10 reduces oxygen contamination into the heat treatment furnace and suppresses wear of the heat-resistant sheet 108. Because wet carbon fiber nonwoven fabric has a smoother surface than dry carbon fiber nonwoven fabric, it is more preferable to use wet carbon fiber nonwoven fabric rather than dry carbon fiber nonwoven fabric as the heat-resistant sheet 108.

[0028] It is preferable to replace the heat-resistant sheet 108, at least for the portion inserted into the furnace, every one to three times the carbon fiber sheet precursor 10 is heat-treated (i.e., every one to three rolls if the carbon fiber sheet precursor is heat-treated one by one). If the heat-resistant sheet 108 is used repeatedly, precipitated particles and the like adhering to the upper surface of the heat-resistant sheet 108 may fall and adhere to the carbon fiber sheet precursor 10. Furthermore, if a heat-resistant sheet 108 damaged by falling precipitated particles and the like is used, the precipitated particles and the like may fall on the damaged area, causing through holes to form in the carbon fiber sheet precursor 10 or causing scorching. It is more preferable to replace the heat-resistant sheet 108 every time the carbon fiber sheet precursor 10 is heat-treated once.

[0029] The weight of the heat-resistant sheet 108 is 30 to 60 g / m 2 It is preferable that the basis weight is 30 g / m 2 If the weight is less than 60 g / m, the strength of the heat-resistant sheet 108 is weak and the heat-resistant sheet 108 may be torn, which is not preferable. 2 If the weight of the heat-resistant sheet 108 exceeds 30 to 45 g / m, when the heat-resistant sheet 108 is in contact with the carbon fiber sheet precursor 10, frictional force is applied to the carbon fiber sheet precursor 10 due to the weight of the heat-resistant sheet 108, causing cuts or chips in the carbon fiber sheet precursor 10, which may lead to breakage, and this is not preferable. 2 It is more preferable that the basis weight is 45 g / m 2 If the temperature exceeds this value, frictional force is applied to the carbon fiber sheet precursor 10 due to the weight of the heat-resistant sheet 108, and the surface of the carbon fiber sheet precursor 10 is worn away.

[0030] Before being fed to the heat treatment furnace, the carbon fiber sheet precursor 10 may be subjected to a preliminary heat treatment by passing it through a low-temperature furnace having a lower temperature than the heat treatment furnace, for example, a low-temperature furnace having a maximum temperature of 600 to 1000° C. In this case, the weight loss of the carbon fiber sheet precursor 10 tends to be greater in the low-temperature furnace, but it is possible to prevent decomposition gas generated in the low-temperature furnace from flowing to a high-temperature section and solidifying and precipitating.

[0031] <Carbon fiber sheet> The carbon fiber sheet product according to another aspect of the present invention typically has a number of metal (particularly iron) foreign particles having a major diameter of 30 μm or more of 0 to 0.02 particles / m 2 The carbon fiber sheet product is a roll-shaped material. The number of metal (especially iron) contaminants with a major axis of 30 μm or more in the carbon fiber sheet product can be confirmed by identifying the location of the metal contaminants using X-ray transmission measurement and then identifying the elements using X-ray fluorescence measurement. This can be measured using, for example, a commercially available X-ray contaminant analyzer such as the EA8000. The fewer metal (especially iron) contaminants there are, the fewer times they need to be avoided during post-processing, reducing scrap generation and making processing more efficient. In particular, when carbon fiber sheets containing iron contaminants are incorporated into solid polymer fuel cells or water electrolysis devices, OH radicals generated by contact between iron and hydrogen peroxide can accelerate deterioration of the electrolyte membrane, thereby reducing the durability of the fuel cell. In other words, iron is a metal that should be particularly avoided in solid polymer fuel cells and water electrolysis devices.

[0032] In addition, the carbon fiber sheet product has 0 to 0.02 through holes per m with a major diameter of 0.4 mm or more. 2 The number of through holes having a major diameter of 0.4 mm or more in a carbon fiber sheet product can be detected by visually observing the back surface of the carbon fiber sheet through light transmitted therethrough, and the major diameter of a through hole refers to the longest diameter in the case of an ellipse, for example, and the length of the major diameter can be measured by observing the through hole with a magnifying glass with a scale. The fewer the through holes, the fewer times the through hole area needs to be avoided during post-processing, reducing the generation of scrap and enabling more efficient processing.

[0033] The larger the area of ​​a roll of carbon fiber sheet, the more efficient post-processing such as water repellent treatment can be. The area of ​​a roll of carbon fiber sheet product, which is the product of its width and length, is 50m 2 It is preferable that the length is at least 300m, and more preferably at least 300m. 2 As described above, the method for producing a carbon fiber sheet of the present invention is more effective in producing a carbon fiber sheet of such a size. That is, in the method for producing a carbon fiber sheet of the present invention, a carbon fiber sheet precursor having an area of ​​1 roll of 50 m is used. 2It is preferable to use the above carbon fiber sheet precursors. [Example]

[0034] Specific examples of the present invention will be described below with reference to comparative examples. The conditions for the heat treatment furnace and the heat-resistant sheet were set as follows.

[0035] The heat treatment furnace was a horizontal heat treatment device as shown in Figure 1, and the carbon fiber sheet precursor was transported horizontally. In addition, a low-temperature pre-heat treatment furnace was installed before the heat treatment furnace, and the pre-heat-treated carbon fiber sheet precursor was continuously heat-treated in the heat treatment furnace at a maximum temperature of 2300°C.

[0036] The heat-resistant sheet is a carbon fiber sheet precursor that has been heat-treated separately and has a basis weight of 45 g / m. 2 A wet-laid carbon fiber nonwoven fabric with a width of 350 mm was used.

[0037] After the heat treatment of 1000 m of 300 mm wide carbon fiber sheet precursor was completed, the heat-resistant sheet was removed from the heat treatment furnace and its appearance was checked to see if any holes had occurred in the heat-resistant sheet.

[0038] The entire length of the carbon fiber sheet obtained by heat treatment was inspected using an inspection machine equipped with a light source, and the number of through holes visually confirmed by transmitted light with a major axis of 0.4 mm or more was recorded. X-ray transmission measurement was also performed over the entire length of the carbon fiber sheet, and fluorescent X-ray measurement was performed on any detected metal (especially iron) foreign matter to confirm the number of metal (especially iron) foreign matter with a major axis of 30 μm or more.

[0039] Example 1 The carbon fiber sheet precursor was supplied from under the shutter at the entrance to the heat treatment furnace, and the carbon fiber sheet used as the heat-resistant sheet was introduced through a slit in the shutter at the entrance to the heat treatment furnace. Furthermore, when a 300 mm wide, 1000 m length of carbon fiber sheet precursor was heat-treated, 0.3 m of heat-resistant sheet was wound up for every 250 m of carbon fiber sheet precursor heat-treated. After the heat treatment was completed, the heat-resistant sheet was removed from the heat treatment furnace and its appearance was inspected, confirming that no holes had formed in the heat-resistant sheet. Furthermore, when the entire length of the carbon fiber sheet obtained by heat treatment was inspected, not a single through-hole had formed, and no metal (especially iron) foreign matter was detected.

[0040] (Comparative Example 1) The carbon fiber sheet precursor was supplied from under the shutter at the entrance of the heat treatment furnace, and the carbon fiber sheet used as the heat-resistant sheet was also placed on top of the carbon fiber sheet precursor and introduced from under the shutter at the entrance of the heat treatment furnace. At this time, the slit in the shutter was closed to prevent oxygen from entering the heat treatment furnace through the slit. Furthermore, in the heat treatment of 1000 m of 300 mm wide carbon fiber sheet precursor, 0.3 m of heat-resistant sheet was wound up every 250 m of carbon fiber sheet precursor that was heat-treated. After the heat treatment was completed, the heat-resistant sheet was removed from the heat treatment furnace and its appearance was inspected, and it was found that the heat-resistant sheet had been worn down and had holes. Furthermore, when the entire length of the carbon fiber sheet obtained by the heat treatment was inspected, 11 through-holes had occurred, with a density of 0.02 / m 2 In addition, 70 iron particles with a major diameter of 30 μm or more were detected, with an average particle size of 0.02 particles / m 2 Iron foreign matter was particularly generated around the through-hole. [Explanation of symbols]

[0041] 10 Carbon fiber sheet precursor 20 carbon fiber sheets 100 Heat treatment furnace 101 Furnace space 102 Muffle upper wall 103 Muffle bottom wall 104 Hearth 105 Entrance of heat treatment furnace (furnace entrance) 106 Heat treatment furnace outlet (furnace outlet) 107 Heat source 108 Heat-resistant sheet 109 Shutter 110 Slit section 111 Flame-resistant thread 112 rolls

Claims

1. A method for producing a carbon fiber sheet, comprising: continuously transporting a carbon fiber sheet precursor, the carbon fiber sheet precursor, and a heat-resistant sheet in contact with each other, through a heat treatment furnace in an inert atmosphere to produce a carbon fiber sheet, the heat-resistant sheet is spaced apart from the carbon fiber sheet precursor at a furnace inlet of the heat treatment furnace and is in contact with the carbon fiber sheet precursor in an interior space of the heat treatment furnace, the heat-resistant sheet is moved independently of the carbon fiber sheet precursor in a transport direction of the carbon fiber sheet precursor while the carbon fiber sheet precursor passes through an inner space of the heat treatment furnace.

2. The method for producing a carbon fiber sheet according to claim 1 , wherein the heat-resistant sheet is moved intermittently every time the carbon fiber sheet precursor is transported by a certain length.

3. The method for producing a carbon fiber sheet according to claim 1 , wherein the heat-resistant sheet is continuously moved at a speed slower than a conveying speed of the carbon fiber sheet precursor.

4. The method for producing a carbon fiber sheet according to any one of claims 1 to 3, wherein the heat-resistant sheet is wider than the carbon fiber sheet precursor being transported.

5. The method for producing a carbon fiber sheet according to any one of claims 1 to 4, wherein the heat-resistant sheet is unwound from a roll installed upstream of the heat treatment furnace and supplied.

6. The method for producing a carbon fiber sheet according to any one of claims 1 to 5, wherein the heat-resistant sheet is a carbon fiber nonwoven fabric.

7. The weight of the heat-resistant sheet is 30 to 60 g / m ２ The method for producing a carbon fiber sheet according to any one of claims 1 to 6,

8. The method for producing a carbon fiber sheet according to any one of claims 1 to 7, wherein the heat-resistant sheet is replaced every time the carbon fiber sheet precursor is heat-treated one to three times.

9. The carbon fiber sheet precursor according to any one of claims 1 to 8, wherein a preliminary heat treatment is performed by passing the carbon fiber sheet precursor through a low-temperature furnace having a temperature lower than that of the heat treatment furnace before the carbon fiber sheet precursor is subjected to the heat treatment furnace.

10. The carbon fiber sheet precursor has an area of ​​50 m per roll. ２ The method for producing a carbon fiber sheet according to any one of claims 1 to 9, wherein the carbon fiber sheet precursor is used.

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