JP2004176245A - Method for making of carbon fiber sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making carbon fiber sheet suppressing surface defects such as wrinkles and ups and downs, etc. <P>SOLUTION: The method for making carbon fiber sheet 10 by baking a precursor fiber sheet 2 on a bed 5 of a heating furnace 6 while continuously pulling, the precursor fiber sheet 2 is kept in a tension satisfying the following formula ¾T1-T2¾≤30N/m, wherein T1 is a tension in pulling direction of the precursor sheet 2 and T2 is a tension in a direction orthogonalizing to the pulling direction. <P>COPYRIGHT: (C)2004,JPO

Description

      The present invention relates to a method for producing a sheet of carbon fiber woven fabric, nonwoven fabric, paper and the like.

  Sheets such as carbon fiber woven fabric, non-woven fabric, and paper are used for a wide variety of applications such as molding CFRP (carbon fiber reinforced plastic), repairing and reinforcing concrete structures, radio wave absorbers, and fuel cell electrodes. ing.

  By the way, as is well known, carbon fibers are prepared by firing raw material fibers (precursors) such as polyacrylonitrile fibers in a relatively low-temperature oxidizing atmosphere of about 200 to 400 ° C. to make them flame-resistant (flame-resistant). And then carbonized by firing in an inert atmosphere at a high temperature of 1,000 ° C. or higher. A carbon fiber sheet, for example, a woven fabric may be woven with the carbon fiber thus produced as a woven yarn. However, weaving is difficult because the carbon fiber is brittle and easily fluffed. Also, since it is inefficient to fire the raw material fibers and the oxidized fibers one by one, the raw fibers and the oxidized fibers are made into a woven fabric in advance, and then baked to form a carbon fiber woven fabric. (For example, see Patent Document 1).

However, when the raw fiber is subjected to the oxidization treatment in the form of a woven fabric having a high yarn density, the oxidization treatment involves an exothermic reaction, so that the woven fabric stores heat, and it is extremely difficult to control the temperature stably. Quality unevenness easily occurs in the fabric. In addition, when carbonizing the flame-resistant fabric, it is said that it is preferable that the flame-resistant fabric is fired under no tension because it generally has low strength.However, it is extremely difficult to keep the fabric under no tension at all. It is. Therefore, the fire-resistant fabric is baked while being transported in the heating furnace using a transport roll installed inside or outside the furnace, but surface defects such as wrinkles and undulations due to variations in the transport tension are likely to occur. If the carbon fiber woven fabric has surface defects such as wrinkles and undulations, for example, when it is used as an electrode of a polymer electrolyte fuel cell, poor adhesion to a proton exchange membrane occurs and the cell characteristics are greatly reduced. There is.
Japanese Patent Publication No. 61-11323

  An object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a method for manufacturing a carbon fiber sheet that can suppress the occurrence of surface defects such as wrinkles and undulations.

In order to achieve the above object, the present invention is to produce a carbon fiber sheet by firing while continuously pulling the precursor fiber sheet on the hearth of the heating furnace, during firing, the precursor fiber sheet, When the tension in the tension direction of the precursor fiber sheet is T1 and the tension in the direction perpendicular to the tension direction is T2, the following equation is obtained.
| T1-T2 | ≦ 30 N / m
Preferably, the following formula:
| T1-T2 | ≦ 20 N / m
And a method for producing a carbon fiber sheet, characterized by maintaining under a tension satisfying the following. The tensions T1 and T2 are preferably low, and are preferably 20 N / m or less, and more preferably 10 N / m or less. When the relationship is out of the range of the above equation, the dispersion of each of the tensions T1 and T2 is reduced. They remain on the surface of the carbon fiber sheet as surface defects such as wrinkles and undulations.

  As the precursor fiber, polyacrylonitrile-based flame-resistant fiber obtained by flame-resistant polyacrylonitrile-based fiber, rayon fiber, phenol fiber, infusible pitch fiber, etc. can be used. It is preferably a polyacrylonitrile-based oxidized fiber from which excellent carbon fibers and, eventually, a carbon fiber sheet can be obtained.

  As a sheet made of such precursor fibers, an oxidized fiber fabric such as a woven fabric, a nonwoven fabric, and paper can be used. These flame-resistant fiber fabrics include 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. The resin may be impregnated. In that case, the resin may be in an uncured or unsolidified state, but such a resin shrinks with the carbonization during firing, and the surface of the obtained carbon fiber sheet may be roughened. It is preferable that the resin be cured or solidified prior to the treatment. Further, these resins may be contained in the precursor fiber sheet as a fibrous material. Further, as the precursor fiber sheet, paper formed by binding chopped carbon fiber (short fibers) or the like with a binder such as a phenol resin or a PVA resin can also be used.

The relationship between the tension T1 in the tension direction of the precursor fiber sheet and the tension T2 in the direction orthogonal to the tension direction is represented by the following equation:
| T1-T2 | ≦ 30 N / m
Preferably, the following formula:
| T1-T2 | ≦ 20 N / m
A preferred method for maintaining under a certain tension is to use, as a heating furnace, a heating furnace having a hearth with an upwardly convex surface in a cross section orthogonal to the tensile direction of the precursor fiber sheet, and dragging over the furnace. That is. In this way, in the tensile direction of the precursor fiber sheet, a tension T1, which is obtained by adding the initial tension at the entrance of the heating furnace to the tension generated by friction with the hearth, is generated, and the tension T1 is upward in the direction orthogonal to the tensile direction. By dragging on the convex hearth, a tension T2 is generated by adding initial tension to tension generated by friction with the hearth and gravity.

  The hearth shape is not limited to the above, and may be a flat plate. The tension T1 and T2 may be adjusted by imparting anisotropy to the friction coefficient between the precursor fiber sheet and the hearth by performing surface processing on the flat plate.

Another preferred method is to use a combination of a helical wire (hereinafter, referred to as a helical material) and a rod-shaped wire (hereinafter, referred to as a rod) as a hearth and drag it over the hearth.
By doing so, tensions T1 and T2 generated by friction with the spiral material are generated in the initial tension in the tensile direction of the precursor fiber sheet and in a direction perpendicular to the tensile direction, respectively. The combination of pitches changes the tension direction of the precursor sheet and the angle of the helical material facing in the direction perpendicular to the tension direction, so that the friction coefficient in the tension direction and the friction coefficient in the direction perpendicular to the tension direction can be adjusted. It becomes possible, and T1 and T2 can be controlled. In this case, it is preferable to use a heat-resistant metal such as SUS310S or a material such as carbon fiber reinforced carbon depending on the temperature range of the heating furnace.

  Further, the precursor fiber sheet may be fired by stacking a plurality of layers, or the muffle is divided into multiple stages in the vertical direction, and the precursor fiber sheet is fired while continuously pulling the furnace fiber in the respective sections. May be. By doing so, the processing amount per unit time can be increased.

Further, as a heating furnace, a belt is provided in a positional relationship for supporting the precursor fiber sheet from below in the muffle, and the belt speed V1 and the transport speed V2 of the precursor fiber sheet are represented by the following formula:
V1 <V2
By maintaining the condition that satisfies the following condition, the tension difference of the above-described equation may be generated.
In this case, as the belt provided in the muffle, for example, a heating furnace having a maximum temperature of less than 1000 ° C. is made of a heat-resistant metal such as SUS310S, and a heating furnace having a temperature of 1000 ° C. or more is made of ceramics, graphite, carbon fiber reinforced carbon, or the like. It is preferable that the mounting position is part of the inside of the muffle, but it is preferable that the mounting position be provided over the entire length. Further, the belt may be stationary or may be moving. The point is that the difference in the two speeds between the precursor fiber sheet and the belt passing above should generate a tension difference that satisfies the above relationship. In addition, when a belt is provided in the furnace, not only the above-described tension difference but also easy passage of the precursor fiber sheet in the furnace, and products such as scales generated at the time of firing and adhering to the hearth are removed. , Can be continuously removed outside the furnace. In this case, it is more preferable to use a combination of the above-mentioned helical material and rod material as the belt, and to drag over the belt.

  Also, even if V1 is reduced, the dynamic frictional force acting between the precursor fiber sheet and the belt does not change. Therefore, when V1 is reduced, the heat load on the heating furnace is reduced, and the power consumption of the heating furnace is reduced. It is possible to do.

  In addition, a pin tenter, a clamp tenter, or the like may be used to apply the tension T2 in the width direction in order to generate a tension difference that satisfies the above relationship. In this case, it is important to use heat-resistant metals, ceramics, and carbon materials depending on the temperature range of the heating furnace as in the case of the belt.

The present invention provides a method for manufacturing a carbon fiber sheet by firing a precursor fiber sheet while continuously pulling the precursor fiber sheet on a hearth of a heating furnace.During firing, the precursor fiber sheet is stretched in the tensile direction of the precursor fiber sheet. When the tension in the direction perpendicular to the tension direction is T1 and the tension in the direction perpendicular to the tension direction is T2,
| T1-T2 | ≦ 30 N / m
Is maintained under a tension that satisfies the following condition, so that a carbon fiber sheet free from surface defects such as wrinkles and undulations can be obtained as is clear from the comparison between the examples and comparative examples.

  FIG. 1 shows a state in which the production method of the present invention is being carried out. A precursor fiber sheet 2 carried by a carry-in roll 1 is passed through a tension meter 3 and a guide roll 4 to form a muffle 7 in a heating furnace 6. Introduced within. The carbon fiber sheet 11 obtained by firing in the heating furnace 6 is conveyed to the next step, for example, a roll-up step, via a guide roll 8, a tensiometer 9, and an unloading roll 10. The heating furnace 6 includes a muffle 7 and a hearth 5 having an upwardly convex surface when viewed in a cross section orthogonal to the pulling direction of the precursor fiber sheet 2 by the unloading roll 10 as shown in a cross-sectional view in FIG. It has.

  Now, the precursor fiber sheet 2 is baked while being conveyed while being pulled on the hearth 5 in the muffle 7 of the heating furnace 6, and becomes the carbon fiber sheet 11. At this time, in the tensile direction, A tension T1 consisting of an initial tension at the entrance of the heating furnace and a tension generated by friction between the precursor fiber sheet 2 and the hearth 5 is generated. On the other hand, when a cross section orthogonal to the tensile direction of the precursor fiber sheet 2 is viewed, the furnace fiber 5 having the upwardly convex surface is used, so that the precursor fiber sheet 2 is as shown in FIGS. 2 and 3. In the width direction orthogonal to the tension direction of the precursor fiber sheet 2, the initial tension, the precursor fiber sheet 2 and the furnace are conveyed while bending in a convex shape in the width direction orthogonal to the tension direction. T2 is generated, which consists of the friction caused by the friction with the floor 5 and the weight of the precursor fiber sheet 2. Therefore, while monitoring the tension in the tension direction with the tensiometers 3 and 9, the speeds of the carry-in roll 1 and the carry-out roll 10 are controlled such that | T1-T2 | becomes 30 N / m or less, preferably 20 N / m or less. . That is, the precursor fiber sheet 2 is fired while being continuously pulled on the hearth 5 in the muffle 7 of the heating furnace 6 to become the carbon fiber sheet 11, but the precursor fiber sheet 2 is pulled during firing. The absolute value | T1−T2 | of the difference between the tension T1 in the directional direction and the tension T2 in the width direction is maintained at a tension of 30 N / m or less, preferably 20 N / m or less. Note that the tension T2 in the width direction is obtained as a calculated value based on the following inequality.

0 ≦ T2 ≦ waaggμ / 2,000
Here, w: width (m) of the precursor fiber sheet
a: Weight of precursor fiber sheet (g / m ² )
g: Gravitational acceleration (m / sec ² )
μ: dynamic friction coefficient between the precursor fiber sheet and the hearth surface In the above description, the inside of the heating furnace is usually maintained under an inert atmosphere such as nitrogen gas, argon gas or the like. May be kept below. The furnace temperature is usually in the range of about 300 to 3,000 ° C. However, by providing a gradient in the furnace temperature along the tensile direction of the precursor fiber sheet, or by dividing the heating furnace into two, the firing is divided into two stages, namely, pre-carbonization treatment and carbonization treatment. You can do it too. In this case, the furnace temperature is set to be in the range of about 300 to 1,200 ° C. in the pre-carbonization treatment, and in the range of about 1,200 to 3,000 ° C. in the carbonization treatment. When such a two-stage baking is performed, a large amount of decomposition gas is generated, and the degree of involvement in the surface quality such as wrinkles and undulations of the surface of the obtained carbon fiber sheet and the pre-carbonization treatment in which shrinkage due to carbonization proceeds is large. It is also possible to change the tension conditions between the carbonization process. In some cases, the design of the heating furnace is facilitated. In consideration of the depletion, damage, and ambient temperature of the furnace body due to the decomposition gas, it is preferable to use a metal-based material for the pre-carbonization treatment and a graphite-based material or a ceramic-based material for the carbonization treatment. .

The present invention is particularly suitable for obtaining a relatively thin carbon fiber sheet having a thickness of about 0.05 to 2 mm and a basis weight of about 30 to 300 g / m ² , in which surface defects such as wrinkles and undulations are likely to occur. . Further, the carbon fiber sheet obtained by the present invention can be used for various applications as described above, but the electrode material of a polymer electrolyte fuel cell in which surface defects such as wrinkles and undulations have a great effect on cell characteristics. It is particularly suitable as

Examples 1 to 5 and Comparative Example 1
As the precursor fiber sheet, a polyacrylonitrile-based oxidized fiber woven fabric having a width of 500 mm, a thickness of 0.285 mm, and a basis weight of 140 g / m ² was used.

  Two heating furnaces 6 shown in FIGS. 1 to 3 are arranged in series on the above-described woven fabric, and a maximum temperature of 650 ° C. is pre-carbonized and a maximum temperature is 1,950 ° C. in a nitrogen gas atmosphere. (Two-stage firing) to obtain a carbon fiber woven fabric as a carbon fiber sheet. The effective furnace length of the heating furnace 6 was 3 m, and the furnace floor 5 used had an upwardly convex surface with a radius of curvature of 2,000 mm in a cross section orthogonal to the tensile direction of the oxidized fiber woven fabric. Further, the transport speed was set to 0.2 m / min, and the carry-in roll 1 and the carry-out roll 10 were controlled to change the tension T1 in the tension direction of the oxidized fiber woven fabric in the range of 3 to 50 N / m. The tension T2 in the width direction was 0.1 N / m or less. The surface of the obtained carbon fiber fabric was visually inspected for wrinkles or undulations. Table 1 shows the observation results.

Next, a mixture of carbon black powder and polytetrafluoroethylene powder (carbon black powder content: 80% by weight) was applied to the surface of the obtained carbon fiber fabric so that the basis weight was 2 mg / cm ^2. Then, heat treatment was performed at 380 ° C. in the air to obtain a carbon fiber fabric with a carbon layer. On the other hand, a mixture of a carbon powder carrying platinum as a catalyst and a “Nafion” powder was applied to both surfaces of a proton exchange membrane “Nafion” 112 manufactured by DuPont, USA, so that the basis weight of platinum was 0.5 mg / m ^2. As a result, a membrane-catalyst sheet was obtained.

  Next, the membrane-catalyst sheet is sandwiched between the two carbon fiber fabrics with a carbon layer so that the carbon layer is on the membrane-catalyst sheet side, and pressurized and heated at 130 ° C. under a pressure of 3 MPa to integrally form To obtain a membrane-electrode assembly for a polymer electrolyte fuel cell.

Next, the membrane-electrode assembly was sandwiched between grooved separators, and operated as a fuel cell using a fuel cell measuring unit 890-500W manufactured by Scribna Corporation (power generation). The adhesion to the layered carbon fiber fabric was visually observed. The operating conditions at the time of evaluation were a battery temperature of 70 ° C., a hydrogen gas humidification temperature of 80 ° C., an air humidification temperature of 60 ° C., and a gas pressure of atmospheric pressure. At a current density of 0.7 A / cm ² , the hydrogen utilization was 70% and the air utilization was 40%.

  Table 1 shows the evaluation results. The adhesion between the proton exchange membrane and the carbon fiber woven fabric with a carbon layer is important that the fuel cell does not peel off during operation as a fuel cell. Rejected.

Example 6
A carbon fiber woven fabric was obtained in the same manner as in Examples 1 to 5 and Comparative Example 1 except that the hearth 5 was removed from the muffle 7 in the heating furnace 6 and fired while pulling on the bottom surface (plane) of the muffle. The tension T1 in the tensile direction of the oxidized fiber woven fabric was 12 N / m. Further, the tension T2 in the width direction was 0.08 N / m or less because the hearth 5 was not convex upward. The surface of the obtained carbon fiber fabric was visually inspected for wrinkles or undulations. Table 1 shows the observation results.

  Hereinafter, in the same manner as in Examples 1 to 5 and Comparative Example 1, a membrane-electrode assembly was prepared, and the battery characteristics were further evaluated. Table 1 shows the evaluation results.

Examples 7 and 8
The hearth 5 is removed from the muffle 7 in the heating furnace 6, and the combination of the belt speed V1 and the conveyance speed V2 of the oxidized fiber woven fabric is V1 = 0 m / min (stationary) on the belt made of the spiral material and the bar material. , V2 = 0.2 m / min, V1 = 0.2 m / min, and V2 = 0.5 m / min. Obtained. The tension T1 in the tensile direction of the oxidized fiber woven fabric was 14 N / m. Further, the tension T2 in the width direction was 0.2 N / m or less from the friction coefficient between the oxidized fiber woven fabric and the belt. The surface of the obtained carbon fiber fabric was visually inspected for wrinkles or undulations. Table 1 shows the observation results.

  Hereinafter, in the same manner as in Examples 1 to 5 and Comparative Example 1, a membrane-electrode assembly was prepared, and the battery characteristics were further evaluated. Table 1 shows the evaluation results.

Comparative Example 2
A carbon fiber fabric was obtained in the same manner as in Examples 1 to 5 and Comparative Example 1 except that the hearth 5 was removed from the muffle 7 in the heating furnace 6. Since the hearth 5 was removed, the oxidized fiber woven fabric was conveyed in the heating furnace 6 while being bent by its own weight so as to draw a parabola. The tension T1 in the tensile direction of the oxidized fiber woven fabric was 100 N / m. The tension T2 in the width direction was almost 0 because there was no hearth in the heating furnace. The surface of the obtained carbon fiber fabric was visually inspected for wrinkles or undulations. Table 1 shows the observation results.

  Hereinafter, in the same manner as in Examples 1 to 5 and Comparative Example 1, a membrane-electrode assembly was prepared, and the battery characteristics were further evaluated. Table 1 shows the evaluation results.

Comparative Example 3
A carbon fiber woven fabric was obtained in the same manner as in Examples 1 to 5 and Comparative Example 1 except that the heating furnace 6 was a vertical furnace which was perpendicular to the ground. Since the furnace was a vertical furnace, there was no hearth in the muffle, and the oxidized fiber woven fabric did not come into contact with the furnace wall. A tension of 33 N / m was applied as a tension T1 to the flame-resistant fiber fabric by its own weight. Although the tension T2 in the width direction was almost 0 because the hearth was not present in the heating furnace, the carbon fiber fabric fluttered due to the convection of the inert atmosphere in the furnace. The surface of the obtained carbon fiber fabric was visually inspected for wrinkles or undulations. Table 1 shows the observation results.

  Hereinafter, in the same manner as in Examples 1 to 5 and Comparative Example 1, a membrane-electrode assembly was prepared, and the battery characteristics were further evaluated. Table 1 shows the evaluation results.

表１から明らかなように、本発明によれば、固体高分子型燃料電池の電池特性の低下を招くような、皺や起伏等の表面欠陥のない炭素繊維シートを得ることができる。

As is clear from Table 1, according to the present invention, it is possible to obtain a carbon fiber sheet free from surface defects such as wrinkles and undulations, which causes deterioration of the cell characteristics of the polymer electrolyte fuel cell.

  The present invention can be applied not only to the electrode material of the polymer electrolyte fuel cell but also to various electrodes and radio wave absorbers, but the application range is not limited to these.

FIG. 1 is a schematic vertical sectional view showing one embodiment of a heating furnace used for carrying out the present invention. FIG. 2 is a cross-sectional view of the inside of the muffle of the heating furnace shown in FIG. 1. FIG. 2 is a schematic perspective view of a hearth in a muffle, showing a state in which a precursor fiber sheet is fired using the heating furnace shown in FIG. 1. FIG. 4 is a cross-sectional view in a muffle showing a state in which a plurality of precursor fiber sheets are fired while being stacked. It is a cross section inside a muffle which shows a mode that a plurality of precursor fiber sheets are calcined using a multi-stage muffle divided up and down. 1 is a partial front view of a hearth (or a belt) in which a spiral material and a bar material are combined for use in carrying out the present invention.

Explanation of reference numerals

Reference Signs List 1 carry-in roll 2 precursor fiber sheet 3 tensiometer 4 guide roll 5 hearth 6 heating furnace 7 muffle 8 guide roll 9 tensiometer 10 carry-out roll 11 carbon fiber sheet 12 multi-stage muffle 13 spiral material 14 rod material

Claims (11)

When the precursor fiber sheet is fired while continuously pulling it on the hearth of the heating furnace to produce a carbon fiber sheet, during firing, the precursor fiber sheet is subjected to a tension T1 in the tensile direction of the precursor fiber sheet. , When the tension in the direction perpendicular to the tension direction is T2,
| T1-T2 | ≦ 30 N / m
A method for producing a carbon fiber sheet, wherein the carbon fiber sheet is maintained under a tension satisfying the following. The tension T1 and the tension T2 are expressed by the following equation:
| T1-T2 | ≦ 20 N / m
The method for producing a carbon fiber sheet according to claim 1, wherein the tension is maintained under the following condition. The method for producing a carbon fiber sheet according to claim 1 or 2, wherein an oxidized fiber cloth is used as the precursor fiber sheet. The method for producing a carbon fiber sheet according to claim 3, wherein a woven fabric, a nonwoven fabric, or paper is used as the flame-resistant fiber fabric. The method for producing a carbon fiber sheet according to claim 1 or 2, wherein a paper obtained by binding carbon fibers with a binder is used as the precursor fiber sheet. The method for producing a carbon fiber sheet according to any one of claims 3 to 5, wherein a resin fiber impregnated, cured or solidified is used as the precursor fiber sheet. The method for producing a carbon fiber sheet according to any one of claims 1 to 6, wherein a heating furnace having a hearth having an upwardly convex surface in a cross section orthogonal to the tensile direction of the precursor fiber sheet is used as the heating furnace. . The method for producing a carbon fiber sheet according to any one of claims 1 to 7, wherein a combination of a helical wire and a rod-shaped wire is used as a heating furnace as a heating furnace. The method for producing a carbon fiber sheet according to any one of claims 1 to 8, wherein the precursor fiber sheet is fired while a plurality of layers are stacked. The carbon fiber sheet according to any one of claims 1 to 9, wherein, as a heating furnace, the inside of the muffle is vertically divided into multiple stages, and the precursor fiber sheet is fired while continuously pulling the furnace floor in each section. Manufacturing method. As a heating furnace, a belt is provided in a positional relationship that supports the precursor fiber sheet from below in the heating furnace, and the belt speed V1 and the transport speed V2 of the precursor fiber sheet are represented by the following formula:
V1 <V2
The method for producing a carbon fiber sheet according to any one of claims 1 to 9, wherein the condition is satisfied.

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