JP2024122863A - Carbon fiber sheet manufacturing apparatus and manufacturing method - Google Patents

Abstract

To provide a manufacturing apparatus for long-life carbon fiber sheets by curbing denaturation and wear of a component of a carbon material due to pyrolysis gas generated during heat processing of a carbon fiber sheet precursor.SOLUTION: A manufacturing apparatus for carbon fiber sheets includes a high-temperature furnace that thermally processes carbon fibers or a carbon fiber sheet precursor including organic fibers which can be made carbon fibers, so as to make them a carbon fiber sheet, in which the high-temperature furnace contains therein a member of a carbon material with a surface coated with an organic material having a melting point of 2,000°C or higher.SELECTED DRAWING: Figure 1

Description

The present invention relates to an apparatus and method for manufacturing carbon fiber sheets that are preferably used as gas diffusers in polymer electrolyte fuel cells, methanol fuel cells, phosphoric acid fuel cells, and water electrolysis devices, and in particular as gas diffusers in polymer electrolyte fuel cells.

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 preferably used as gas diffusers that constitute the membrane electrode assemblies in which the power generation reaction occurs in fuel cells such as solid polymer fuel cells, methanol fuel cells, and phosphoric acid fuel cells, and as gas diffusers in water electrolysis devices.

The manufacturing method for producing such carbon fiber sheets generally includes a step of heat treating the carbon fiber sheet precursor in a high-temperature furnace. Here, since the manufacturing and operating costs of the high-temperature furnace are directly linked to the manufacturing cost of the carbon fiber sheet, it is desirable to use an inexpensive high-temperature furnace with low operating costs as the manufacturing device for the carbon fiber sheet.

However, repeated heat treatment of the carbon fiber sheet precursor causes wear on the components that make up the high-temperature furnace, and they need to be replaced periodically. To reduce the manufacturing costs of carbon fiber sheets, there is a need to extend the lifespan of these components.

Patent Document 1 discloses a method for heat treating a carbon fiber sheet precursor containing carbon fibers and a resin in a high-temperature furnace during the manufacturing process of a carbon fiber sheet, and describes that it is preferable that components such as heaters used in the high-temperature furnace are made of a carbon material such as graphite, which can withstand high-temperature environments and is inexpensive.

Patent document 2 discloses a method of using graphite material with a specific range of bulk density and outer surface area as a means of extending the life of heaters.

JP 2020-133006 A Japanese Unexamined Patent Publication No. 153388/1988

However, even when carbon materials such as graphite are used for the components of a high-temperature furnace as in Patent Documents 1 and 2, deterioration and wear of the carbon material components can occur, shortening the time until periodic replacement. It was found that this is due to pyrolysis gases generated when the carbon fiber sheet precursor is heat-treated.

The objective of the present invention is to provide a long-life carbon fiber sheet manufacturing device by suppressing deterioration and wear of the carbon material components caused by pyrolysis gases generated during the heat treatment of the carbon fiber sheet precursor.

The present invention for achieving the above object is as follows.
[1] An apparatus for producing a carbon fiber sheet, comprising a high-temperature furnace for heat-treating a carbon fiber sheet precursor containing carbon fibers or organic fibers that can be converted into carbon fiber to produce a carbon fiber sheet, wherein the high-temperature furnace for heat-treating the carbon fiber sheet precursor comprises a carbon material member inside the furnace, the carbon material member having a surface coated with an inorganic material having a melting point of 2,000°C or higher.
[2] The carbon fiber sheet manufacturing apparatus according to [1], wherein the inorganic material has a melting point of 2,700°C or higher.
[3] The apparatus for producing a carbon fiber sheet according to [1] or [2], wherein the inorganic material is at least one inorganic material selected from the group consisting of tantalum carbide, niobium carbide, and silicon carbide.
[4] The carbon fiber sheet manufacturing apparatus according to any one of [1] to [3], wherein the member is a heater and/or a muffle plate.
[5] The carbon fiber sheet manufacturing apparatus according to any one of [1] to [4], wherein the carbon fiber sheet precursor contains a carbonizable organic substance.
[6] A method for producing a carbon fiber sheet, using the carbon fiber sheet production apparatus according to any one of [1] to [5].
[7] The method for producing a carbon fiber sheet according to [6], in which a plurality of carbon fiber sheet precursors are stacked and simultaneously heat-treated.
[8] The method for producing a carbon fiber sheet according to [6] or [7], wherein the carbon fiber sheet is produced continuously.
[9] The method for producing a carbon fiber sheet according to [8], wherein during the heat treatment, 10 g/min or more of gas is generated from the carbon fiber sheet precursor per 50 cm of furnace width.
[10] The method for producing a carbon fiber sheet according to [6] or [7], wherein the carbon fiber sheet is produced batchwise.

The present invention provides a carbon fiber sheet manufacturing device that uses inexpensive carbon materials as components, while suppressing deterioration and wear of the carbon material components caused by pyrolysis gases generated in a high-temperature furnace, and has a long life.

FIG. 1 is a schematic cross-sectional view of an example of a continuous high-temperature furnace that is a manufacturing apparatus for a carbon fiber sheet of the present invention. FIG. 1 is a cross-sectional schematic diagram of an example of a batch-type high-temperature furnace that is a manufacturing apparatus for a carbon fiber sheet of the present invention. FIG. 2 is a schematic diagram of an example of a heater that is a component of the carbon fiber sheet manufacturing apparatus of the present invention.

A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

<Carbon fiber sheet manufacturing equipment>
Carbon fiber sheet manufacturing equipment is roughly divided into manufacturing equipment including a continuous high-temperature furnace that continuously produces a long carbon fiber sheet, and manufacturing equipment including a batch-type high-temperature furnace that batch-wise produces a single carbon fiber sheet. From the viewpoint of manufacturing cost, a manufacturing equipment including a continuous high-temperature furnace that can produce continuously is preferable, but the present invention can provide both a continuous type and a batch-type manufacturing equipment including a long-life high-temperature furnace.

A continuous high-temperature furnace 100, which is an example of the manufacturing apparatus of the present invention, is described below with reference to FIG. 1.

The high-temperature furnace 100 is provided with an in-furnace space 101 through which the carbon fiber sheet precursor 10 can pass. The in-furnace space 101 has two openings, one of which is an inlet (hereinafter referred to as the inlet) 105 of the high-temperature furnace, and the other is an outlet (hereinafter referred to as the outlet) 106 of the high-temperature furnace. Above and below the in-furnace space 101, heaters 107 are arranged to heat the in-furnace space 101. The heater 107 and the in-furnace space 101 are separated by a muffle. That is, they are separated by a muffle upper wall 102 and a muffle lower wall 103, and a hearth 104 on which the carbon fiber sheet precursor 10 runs is further provided on the muffle lower wall 103. The in-furnace space 101 can be made into an inert atmosphere, and is kept under an inert gas atmosphere filled with nitrogen, argon, or the like to prevent oxidation of the carbon fiber sheet 20 and the high-temperature furnace 100 itself during the heat treatment of the carbon fiber sheet precursor 10. The carbon fiber sheet precursor 10 is then subjected to heat treatment while traveling continuously through the furnace space 101, becoming a carbon fiber sheet 20.

A batch-type high-temperature furnace 200, which is an example of the manufacturing apparatus of the present invention, will be described with reference to FIG. 2. The batch-type high-temperature furnace 200 is provided with an in-furnace space 201 in which the carbon fiber sheet precursor 10 can be placed. The high-temperature furnace 200 has a furnace entrance door 205, and the carbon fiber sheet precursor 10 can be placed in the furnace space 201 by opening the furnace entrance door 205. Heaters 207 for heating the furnace space 201 are arranged above and below the furnace space 201. The heater 207 and the furnace space 201 are separated by a muffle. That is, they are separated by a muffle upper wall 202 and a muffle lower wall 203, and a hearth 204 for placing the carbon fiber sheet precursor 10 is further provided on the muffle lower wall 203. The furnace space 201 can be made into an inert atmosphere, and is kept under an inert gas atmosphere filled with nitrogen, argon, or the like in order to prevent oxidation of the carbon fiber sheet 20 and the high-temperature furnace 100 itself during the heat treatment of the carbon fiber sheet precursor 10. The carbon fiber sheet precursor 10 is then subjected to heat treatment to become the carbon fiber sheet 20.

To obtain suitable electrical conductivity of the carbon fiber sheet, the heat treatment temperature (maximum temperature in the high-temperature furnace) is preferably 1,500 to 2,700°C. If the heat treatment temperature is lower than 1,500°C, the degree of graphitization of the carbon fiber sheet 20 will be low, and the electrical conductivity and thermal conductivity may be reduced. If the heat treatment temperature of the high-temperature furnace is higher than 2,700°C, a large amount of energy will be required for heating and the members used in the furnace will be easily worn out. The heat treatment temperature is more preferably 1,800 to 2,600°C, and even more preferably 1,900 to 2,500°C.

The components that make up a high-temperature furnace can be made of carbon materials such as graphite, metals, or ceramics, but carbon materials such as graphite are preferred because they are inexpensive. In particular, for parts that will reach 1,000°C or higher, it is preferable to use carbon materials such as graphite because of their chemical stability.

In the present invention, the high-temperature furnace includes, inside the furnace, a carbon material member whose surface is coated with an inorganic material having a melting point of 2,000°C or higher. By coating the surface of the carbon material with an inorganic material having a melting point of 2,000°C or higher, deterioration and wear of the carbon material member caused by pyrolysis gas generated during heat treatment of the carbon fiber sheet precursor can be suppressed. The coating method is not particularly limited as long as it is a method that can form a coating layer on the surface of the carbon material, and examples of the coating method include dry methods such as PDV and CDV, and wet methods such as plating and coating.

In the present invention, the inorganic material used for the coating may have a melting point of 2,000°C or higher, but it is preferable to use an inorganic material with a melting point of 2,700°C or higher, and more preferably to use an inorganic material with a melting point of 3,000°C or higher. As inorganic materials, metals, metal carbides, silicon carbide, and boron carbide are preferred because they have high heat resistance and durability, and metal carbides, silicon carbide, and boron carbide are preferred because they are less likely to react with the coating and the material to be coated (carbon material member) over time. Among these, tantalum carbide, niobium carbide, and silicon carbide are more preferred because they are highly durable.

Among the components included in the high-temperature furnace, it is preferable that the heater and the muffle are made of a carbon material whose surface is coated with an inorganic material having a melting point of 2,000°C or higher. Here, the muffle refers to a furnace material that covers the heater so that the heater is not exposed in the furnace space, and refers to the upper wall, lower wall, side wall, etc. of the muffle in Figures 1 and 2. The heater and the muffle are easily contacted with the pyrolysis gas generated during the heat treatment of the carbon fiber sheet precursor, and are easily altered and worn out. Since the pyrolysis gas generated in the furnace space first comes into contact with the muffle, the muffle is the most easily altered and worn out of the components in the high-temperature furnace. As the muffle wears out, the pyrolysis gas is more likely to come into contact with other furnace materials, so in order to extend the life of the high-temperature furnace, it is preferable to make the muffle a carbon material whose surface is coated with an inorganic material having a melting point of 2,000°C or higher. In addition, the cross-sectional area of the heater decreases due to wear. In the area where the cross-sectional area is reduced, the electrical resistance increases, so heat is concentrated and wear is accelerated. The above coating reduces wear on the heater, thereby extending the life of the high-temperature furnace.

<Carbon fiber sheet precursor>
A carbon fiber sheet precursor applicable to the carbon fiber sheet manufacturing apparatus of the present invention will be described. The carbon fiber sheet precursor includes carbon fiber or organic fiber that can be carbonized. The carbon fiber sheet precursor is preferably configured by making short carbon fibers or short organic fibers that can be carbonized, and impregnating and curing the short fibers with a carbonizable organic material. In this case, the length of the short fibers is preferably within a range of 3 to 12 mm. If the length of the short fibers is within a range of 6 to 9 mm, good dispersibility can be obtained during papermaking of the short fibers, and a porous carbon fiber sheet that has high tensile strength and is not easily broken can be obtained, which is more preferable. Alternatively, the carbon fiber sheet precursor may be produced by making a nonwoven fabric from PAN flame-resistant yarn in a dry process and calendering the nonwoven fabric with a heated roll.

As the carbon fiber, any of polyacrylonitrile (PAN)-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and phenol-based carbon fiber can be used. 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, and it is particularly preferable to use PAN-based carbon fiber.

The organic fiber that can be made into carbon fiber is not particularly limited as long as it is an organic fiber that can be turned into carbon fiber by heat treatment during the heat treatment of the carbon fiber sheet precursor in a high-temperature furnace in which the carbon fiber sheet precursor is heat treated, but the raw materials for the carbon fiber mentioned above, such as polyacrylonitrile, coal pitch, rayon, and phenol resin fibers, can be used. It is preferable to use polyacrylonitrile fiber or pitch fiber, which can increase the bending strength and tensile strength of the obtained carbon fiber sheet, and it is particularly preferable to use polyacrylonitrile fiber.

The carbon fiber sheet precursor used in the manufacturing method of the present invention preferably contains a carbonizable organic material. The carbonizable organic material is not particularly limited as long as it is an organic material that is carbonized by heat treatment during the heat treatment of the carbon fiber sheet precursor in a high-temperature furnace in which the carbon fiber sheet precursor is heat treated. For example, thermosetting resins such as epoxy resins, unsaturated polyester resins, phenolic resins, polyimide resins, and melamine resins, and thermoplastic resins such as acrylic resins, polyvinylidene chloride resins, and polytetrafluoroethylene resins can be used, but it is preferable to use a thermosetting resin with a high carbonization yield, and it is more preferable to use a phenolic resin.

When the carbon fiber sheet is used as a gas diffuser for an electrode of a fuel cell, the carbon fiber sheet precursor preferably contains carbon powder to improve electrical conductivity. In this case, the carbon powder is preferably contained in an amount of 1 to 50 mass % when the carbon fiber sheet precursor is taken as 100 mass %.

The carbon fiber sheet precursor is subjected to a heat treatment by the manufacturing apparatus of the present invention, and if it contains organic fibers that can be converted into carbon fibers, the fibers become carbon fibers, and if it contains organic matter that can be carbonized, the organic matter is carbonized to become a carbon fiber sheet.

<Method of manufacturing carbon fiber sheet>
A method for producing a carbon fiber sheet using the carbon fiber sheet production apparatus of the present invention will be described.

When continuously producing carbon fiber sheets, for example, a continuous high-temperature furnace 100 as shown in FIG. 1 can be used. In the high-temperature furnace 100, the carbon fiber sheet precursor 10 is inserted from the furnace inlet 105 and moves continuously on the hearth 104 in the furnace space 101 maintained at high temperature toward the furnace outlet 106. The hearth 104 in FIG. 1 is plate-shaped, but it is not essential that it is plate-shaped or laid without gaps. It is possible to reduce friction and remove dust by making it lattice-shaped, rod-shaped (horizontal bars only or horizontal bars and vertical bars arranged side by side), or corrugated. It is also a preferred embodiment to divide the hearth into multiple parts and leave gaps. In this process, the carbon fiber sheet precursor 10 is heat-treated in the furnace space 101 to become a carbon fiber sheet 20, which is sent out of the high-temperature furnace 100 from the furnace outlet 106. At this time, the carbon fiber sheet precursor 10 may be heat-treated only one sheet, or multiple sheets may be stacked and heat-treated at the same time. To produce carbon fiber sheets inexpensively, it is preferable to stack multiple carbon fiber sheet precursors and heat treat them simultaneously.

To increase productivity, it is preferable to stack multiple carbon fiber sheet precursors and heat treat them at high temperature for a short time, but this also increases the amount of pyrolysis gas generated in the furnace space 101. In such cases, it is very important to use carbon material components whose surfaces are coated with an inorganic material having a melting point of 2,000°C or higher to extend the life of the high-temperature furnace. In particular, under conditions where the amount of pyrolysis gas generated per 50 cm of furnace width is 10 g/min or more, the deterioration and wear of the carbon material components is particularly rapid, so it is very important to extend the life of the high-temperature furnace. The amount of pyrolysis gas generated can be measured by the mass difference between the carbon fiber sheet precursor 10 before passing through the high-temperature furnace and the carbon fiber sheet 20 after passing through it.

When producing carbon fiber sheets in a batchwise manner, for example, a batch-type high-temperature furnace 200 as shown in FIG. 2 can be used. In the high-temperature furnace 200, the carbon fiber sheet precursor 10 is placed in the furnace space 201 with the furnace entrance door 205 open. After the furnace entrance door 205 is closed, the furnace is heated to a high temperature, and the carbon fiber sheet precursor 10 is heat-treated in the furnace space 201 to become a carbon fiber sheet. After the heat treatment is completed, the furnace is cooled, the furnace entrance door 205 is opened, and the carbon fiber sheet is removed. The carbon fiber sheet precursor 10 may be heat-treated one by one, or multiple sheets may be stacked and heat-treated at the same time. As in the case of using a continuous high-temperature furnace 100, it is preferable to heat-treat multiple sheets in a stack from the viewpoint of production costs.

Before being subjected to the above-mentioned continuous or batch-type high-temperature furnace, the carbon fiber sheet precursor 10 may be subjected to a preliminary heat treatment in a low-temperature furnace having a lower temperature than the high-temperature furnace, for example, a low-temperature furnace having a maximum temperature of 600 to 1,000°C. The preliminary heat treatment can reduce the amount of decomposition gas generated from the carbon fiber sheet precursor in the high-temperature furnace.

The following describes an embodiment of the present invention.

<Method for measuring gas generation rate>
A 10 cm square sample was taken from the carbon fiber sheet precursor before passing through the high-temperature furnace and the carbon fiber sheet after passing through the high-temperature furnace, and the mass difference between the samples was measured. The mass difference was taken as the amount of gas generated, and the value obtained by dividing the mass difference by the treatment time in the high-temperature furnace was defined as the amount of gas generated in the high-temperature furnace per unit time.

<Production of carbon fiber sheet>
The high-temperature furnace used was the continuous high-temperature furnace shown in Fig. 1. The heater and muffle, which are components of the high-temperature furnace, were made of carbon material.

Toray Industries, Inc.'s polyacrylonitrile carbon fiber "TORAYCA (registered trademark)" T300-6K (average fiber diameter: 7 μm, number of single fibers: 6,000) was cut to a length of 6 mm and continuously paper-formed using water as a paper-forming medium and polyvinyl alcohol as a binder to obtain a carbon short fiber paper body with a basis weight of 30 g/ ^m2 .

Next, the carbon short fiber paper body was impregnated with a dispersion liquid in which flake graphite having an average particle size of about 5 μm, phenol resin, and methanol were mixed, and dried at 140° C. After drying, the basis weight of the impregnated carbon short fiber paper body was increased by 50 g/m ² compared to before impregnation. Thereafter, the carbon short fiber paper body was heated at 200° C. under a pressure of 0.5 MPa to cure the phenol resin, and a carbon fiber sheet precursor was obtained.

The phenolic resin used was a mixture of resol-type phenolic resin and novolac-type phenolic resin in a mass ratio of 1:1.

Next, two of the carbon fiber sheet precursors were stacked and continuously pre-heat-treated in a low-temperature furnace with a maximum temperature of 800°C, and then continuously heat-treated in a high-temperature furnace with a maximum temperature of 2,300°C and a furnace width of 50 cm to produce a carbon fiber sheet. In addition, during the heat treatment in the high-temperature furnace, the conveying speed was adjusted so that the amount of gas generated during the production of the carbon fiber sheet was 20 g/min.

<Method of measuring heater thickness>
3 shows a schematic diagram of the heater used in the high-temperature furnace used in this embodiment. The thickness of the thinnest part 302 of the heater (the thinnest part in the cross-sectional area of the heater) was measured before the carbon fiber sheet was produced, and the thickness at that time was designated as t1. After the carbon fiber sheet was produced, the thickness of the thinnest part of the heater was measured again, and the thickness at that time was designated as t2. The rate at which the thickness of the heater was reduced was calculated by comparing t2 and t1.

(Example 1)
In the above <Manufacturing of Carbon Fiber Sheet>, a tantalum carbide layer (melting point 3,880°C) having a thickness of 100 μm was formed on the surface of the heater and muffle, which are components of the high-temperature furnace, to manufacture 200,000 ^m2 of carbon fiber sheet. After manufacture, the high-temperature furnace was dismantled, and the reduction rate of thickness was measured for the thinnest part of the heater. As a result, although the thickness had decreased by 10% compared to before manufacture began, there were no signs of the heater cracking, and it was possible to continue manufacture without replacing the heater when reassembling the high-temperature furnace.

Example 2
200,000 ^m2 of carbon fiber sheet was manufactured in the same manner as in Example 1, except that a 100 μm thick niobium carbide layer (melting point 3,490° C.) was formed on the surface of the heater and the muffle. After manufacturing, the high-temperature furnace was disassembled, and the reduction rate of thickness was measured for the thinnest part of the heater. Although the thickness had decreased by 13% compared to before the start of manufacturing, there were no signs of the heater cracking, and it was possible to continue manufacturing without replacing the heater when reassembling the high-temperature furnace.

Example 3
200,000 ^m2 of carbon fiber sheets were manufactured in the same manner as in Example 1, except that a 100 μm thick silicon carbide layer (melting point 2,730° C.) was formed on the surface of the heater and the muffle. After manufacturing, the high-temperature furnace was disassembled, and the thickness reduction rate was measured for the thinnest part of the heater. Although the thickness had decreased by 20% compared to before the start of manufacturing, there were no signs of the heater cracking, and it was possible to continue manufacturing without replacing the heater when reassembling the high-temperature furnace.

(Comparative Example 1)
A carbon fiber sheet of 200,000 ^m2 was produced in the same manner as in Example 1, except that the surfaces of the heater and the muffle were not coated with an inorganic material. After production, the high-temperature furnace was dismantled, and the reduction rate of thickness was measured at the thinnest part of the heater. As a result, the thickness was reduced by 40% compared to before the start of production, and the heater was on the verge of cracking, so production could not be continued.

10 Carbon fiber sheet precursor 20 Carbon fiber sheet 100 High-temperature furnace 101 Furnace space 102 Muffle upper wall 103 Muffle lower wall 104 Hearth 105 Inlet of high-temperature furnace (furnace inlet)
106 High temperature furnace outlet (furnace outlet)
107 heater 200 high temperature furnace 201 furnace space 202 muffle upper wall 203 muffle lower wall 204 hearth 205 furnace inlet door 206 muffle side wall 207 heater 300 heater 301 heat generating part 302 heater thinnest part

Claims (10)

A carbon fiber sheet manufacturing apparatus including a high-temperature furnace that heat-treats a carbon fiber sheet precursor that contains carbon fiber or organic fiber that can be converted into carbon fiber to form a carbon fiber sheet, the high-temperature furnace being characterized in that the high-temperature furnace contains a carbon material member inside the furnace whose surface is coated with an inorganic material having a melting point of 2,000°C or higher. The carbon fiber sheet manufacturing apparatus according to claim 1, wherein the melting point of the inorganic material is 2,700°C or higher. The carbon fiber sheet manufacturing apparatus according to claim 1, wherein the inorganic material is at least one inorganic material selected from the group consisting of tantalum carbide, niobium carbide, and silicon carbide. The carbon fiber sheet manufacturing apparatus according to claim 1, wherein the member is a heater and/or a muffle. The carbon fiber sheet manufacturing apparatus according to claim 1, wherein the carbon fiber sheet precursor contains a carbonizable organic material. A method for producing a carbon fiber sheet using the carbon fiber sheet production apparatus described in claim 1. The method for producing a carbon fiber sheet according to claim 6, in which multiple carbon fiber sheet precursors are stacked and heat-treated simultaneously. The method for producing a carbon fiber sheet according to claim 6, which produces the carbon fiber sheet continuously. The method for producing a carbon fiber sheet according to claim 8, wherein during the heat treatment, 10 g/min or more of pyrolysis gas is generated from the carbon fiber sheet precursor per 50 cm of furnace width. The method for producing a carbon fiber sheet according to claim 6, in which the carbon fiber sheet is produced in a batchwise manner.