JP2012204142A - Porous carbon electrode substrate and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous carbon electrode substrate which hardly causes a short circuit and cross leak of a reaction gas when being used in a fuel cell, and sufficiently removes a carbon short fiber and resin carbide having an insufficient binding force from a surface of the substrate, and to provide a method for manufacturing the same.SOLUTION: The method for manufacturing the porous carbon electrode substrate comprises the following steps (1)-(3) of: (1) manufacturing a carbon sheet having the carbon short fibers bound by carbon; (2) arranging a sheet having elasticity on at least one face of the carbon sheet and pressurizing the carbon sheet at a linear pressure of 5 kN/m-30 kN/m by using continuous pressurizing means; and (3) subsequently continuously removing carbon powders deposited on the carbon sheet.

Description

  The present invention relates to a porous carbon electrode substrate used for a polymer electrolyte fuel cell using liquid fuel and a method for producing the same.

  A base material using carbon fibers such as carbon fiber paper, carbon fiber cloth, and carbon fiber felt is generally used for the gas diffusion layer of the polymer electrolyte fuel cell. These base materials are not only highly conductive due to carbon fibers, but are porous materials, and are therefore suitable materials for gas diffusion layers because of high permeability of liquids such as fuel gas and generated water.

  However, the base material used as the gas diffusion layer causes fluffing, dropping, or breakage of carbon fibers due to friction or compression generated in the gas diffusion layer and electrolyte membrane joining process or stack fastening process when manufacturing the fuel cell. There is a fear. Since these dropped and broken carbon fibers are stiffer than the electrolyte membrane, they may pierce the electrolyte membrane.

By piercing the electrolyte membrane, problems such as short-circuiting between the anode and cathode, and problems such as hydrogen gas on the anode side and / or oxygen gas on the cathode side cross-leak occur, and the electromotive force of the fuel cell And the durability tended to be significantly impaired.

  By the way, as a method for reducing the damage caused by the carbon fiber sticking to the electrolyte membrane, for example, Patent Document 1 discloses in advance the surface pressure applied to the gas diffusion layer in the joining step with the electrolyte membrane and the catalyst layer and the stack fastening step. And a method for removing in advance the carbon fibers and carbides that are weakly bonded and falling off or broken. Patent Document 2 discloses a method of removing short carbon fibers having weak binding during gas diffusion layer production by blowing gas into the gas diffusion layer and simultaneously sucking it. Furthermore, Patent Document 3 discloses a method of removing carbon fibers having weak binding by applying ultrasonic treatment to a gas diffusion layer.

JP 2009-190951 A JP 2010-70433 A JP 2010-61964 A

However, in the method described in Patent Document 1, carbon powder generated in a post-process by pressing can be removed in advance, but the generated carbon powder is insufficient because the pressure applied during pressing and the post-pressing removal process are insufficient. Was not sufficiently removed, and there was a possibility that a short-circuit current would occur when used in a fuel cell.
In the method described in Patent Document 2, the surface of the gas diffusion layer can be cleaned to some extent, but carbon powder is newly generated when the gas diffusion layer is compressed, such as a bonding step with the electrolyte membrane, However, there is a problem in that a large short-circuit current is generated by being stuck into the electrolyte membrane.
Further, even if the method described in Patent Document 3 is used, there is a tendency that a problem arises in that carbon powder is generated by compression in a subsequent process.
The present invention overcomes the above-mentioned problems, and when used in a fuel cell, short-circuit and reactive gas cross-leak are unlikely to occur, and carbon short fibers and resin carbides with insufficient binding on the substrate surface are sufficient. It is an object of the present invention to provide a porous carbon electrode base material removed by the method and a method for producing the same.

The above problems are solved by the following inventions [1] to [6].
[1] A method for producing a porous carbon electrode substrate, comprising the following steps (1) to (3).
(1) A step of producing a carbon sheet in which short carbon fibers are bound by carbon.
(2) A step of placing the carbon sheet with elasticity on at least one surface of the carbon sheet and pressurizing the carbon sheet with a linear pressure of 5 kN / m to 30 kN / m using a continuous pressurizing means.
(3) Next, the process of removing the carbon powder adhering to the carbon sheet continuously.
[2] The method for producing a porous carbon electrode substrate according to [1], wherein the pressurizing means is a continuous press device provided with at least a pair of rolls, and at least one of the pair of rolls is a metal roll. .
[3] The porous carbon electrode substrate according to [1] or [2], wherein the pressurizing means is a continuous press device provided with at least a pair of rolls, and at least one of the pair of rolls is an elastic roll. Production method.
[4] The method for producing a porous carbon electrode substrate according to [3], wherein the continuous press device is a continuous press device including at least a pair of endless belts.
[5] The method for producing a porous carbon electrode substrate according to any one of [1] to [4], wherein the removal is a method by brushing and suction, or ultrasonic cleaning.
Upon crimped polyethylene sheet and force lap 50 g / cm ^2, the number of short carbon fibers attached to the peeled polyethylene sheet is 0.1 present 10 present / cm ^2, was deposited in the number of short carbon fibers Porous carbon electrode substrate with less number of carbides.

  It is possible to obtain a porous carbon electrode base material in which short carbon and reactive gas cross-leakage are hardly generated when used in a fuel cell, and carbon short fibers and resin carbide insufficiently bonded on the surface of the base material are sufficiently removed. it can.

Hereinafter, the present invention will be described in detail.
The present invention is a method for producing a porous carbon electrode substrate, comprising the following steps (1) to (3).
(1) A step of producing a carbon sheet in which short carbon fibers are bound by carbon.
(2) A step of placing the carbon sheet with elasticity on at least one surface of the carbon sheet and pressurizing the carbon sheet with a linear pressure of 5 kN / m to 30 kN / m using a continuous pressurizing means.
(3) Next, the process of removing the carbon powder adhering to the carbon sheet continuously.

  First, in the first step, a carbon sheet in which short carbon fibers are bound by carbon is manufactured. Specifically, the short carbon fibers and the binder for binding the short carbon fibers are dispersed in water and made, then the paper is impregnated with a phenol resin and then carbonized. Hereinafter, the manufacturing method will be described in detail.

The short carbon fiber can be used regardless of the raw material, but one or more selected from polyacrylonitrile (hereinafter abbreviated as PAN) carbon fiber, pitch carbon fiber, rayon carbon fiber, and phenolic carbon fiber. It is preferable that the carbon fiber is included, and it is more preferable to include the PAN-based carbon fiber or the pitch-based carbon fiber. The average diameter of the short carbon fibers is preferably about 3 to 30 μm, more preferably 4 to 20 μm, and still more preferably 4 to 8 μm. Within this range, the surface smoothness and conductivity as a porous carbon electrode substrate are good.
The average length of the short carbon fibers is preferably 2 to 12 mm, and more preferably 3 to 9 mm. Within this range, the dispersibility during papermaking and the mechanical strength as a porous carbon electrode substrate are increased.

  The polyacrylonitrile-based carbon fiber is manufactured using a polymer mainly composed of acrylonitrile as a raw material. Specifically, a spinning process for spinning acrylonitrile fibers, a flameproofing process for heating and firing the fibers in an air atmosphere at 200 to 400 ° C. to convert them into oxidized fibers, and in an inert atmosphere such as nitrogen, argon, helium, etc. In addition, the carbon fiber can be obtained through a carbonization step of carbonizing by heating to 300 to 2500 ° C., and is suitably used as a composite material reinforcing fiber. Therefore, it is possible to form a carbon sheet having a higher strength and a higher mechanical strength than other carbon fibers.

  As a papermaking method for producing a carbon sheet, a wet method in which short carbon fibers are dispersed in a liquid medium for papermaking, or a dry method in which short carbon fibers are dispersed in air to be deposited can be applied. Moreover, it is preferable to mix an appropriate amount of an organic polymer substance as a binder for binding carbon fibers together. By mixing the organic polymer substance, the strength of the carbon sheet can be maintained, and the carbon fiber can be prevented from peeling off from the carbon sheet during the production or the orientation of the carbon fiber can be prevented from changing.

The organic polymer compound is preferably polyvinyl alcohol, or an acrylonitrile-based polymer pulp or short fiber. Acrylonitrile-based polymer pulps or short fibers are particularly preferred because their own fired product serves as a conductor. Polyvinyl alcohol is preferable as a binder because it has excellent binding power in the paper making process, and the short carbon fibers do not fall off.
Polyvinyl alcohol is mostly decomposed and volatilized in the final stage of carbonization process for producing an electrode substrate to form pores. The presence of these pores is preferable because the permeability of water and gas is improved.

  A pulp-like material has a structure in which a large number of fibrils having a diameter of several μm or less are branched from a fibrous trunk, and a sheet-like material made from this pulp-like material has an efficient entanglement between fibers and is thin. -Even if it is a toroid, it has the advantage that it is excellent in its handleability. Moreover, the short fiber of an acrylonitrile-type polymer can be obtained by cutting the fiber yarn which consists of an acrylonitrile-type polymer, or the fiber tow into predetermined length.

  The content of the organic polymer compound in the carbon sheet is preferably in the range of 5 to 40% by mass. More preferably, it is the range of 15-30 mass%. In order to reduce the electrical resistance of the electrode base material obtained by impregnating the carbon sheet with resin and firing, it is better that the content of the polymer compound is small, and the content is preferably 40% by mass or less. From the viewpoint of maintaining the strength and shape of the carbon sheet, the content is preferably 5% by mass or more.

  There are two methods for mixing pulp fibers or short fibers of these organic polymer compounds into carbon fibers: stirring and dispersing together with carbon fibers in water and mixing directly. The method of diffusing and dispersing with is preferable.

  After paper making a carbon sheet, hot pressing with a heating and pressing roll can make the orientation and thickness of the carbon fiber uniform and minimize the fluff peculiar to the carbon fiber. The heating temperature of the heating and pressing roll is preferably 100 ° C to 150 ° C, and the pressure is preferably 0.5 MPa to 20 MPa.

  In the present invention, a carbon sheet containing short carbon fibers described above is impregnated with a thermosetting resin, cured by heating and pressing, and then carbonized to obtain a porous carbon electrode substrate for a fuel cell.

  The thermosetting resin used in the present invention is preferably a substance that exhibits adhesiveness or fluidity at room temperature and remains as a conductive substance even after carbonization, and a phenol resin, a furan resin, or the like can be used. As the phenol resin, a resol type phenol resin obtained by reaction of phenols and aldehydes in the presence of an alkali catalyst can be used. In addition, a novolac type phenolic resin showing solid heat-fusibility, which is produced by a reaction of phenols and aldehydes under an acidic catalyst by a known method, can be dissolved and mixed in a resol type flowable phenolic resin. In this case, a self-crosslinking type containing a curing agent such as hexamethylenediamine is preferred.

  As phenols, for example, phenol, resorcin, cresol, xylol and the like are used. As aldehydes, for example, formalin, paraformaldehyde, furfural and the like are used. Moreover, these can be used as a mixture. These can also use a commercial item as a phenol resin.

  A desirable ratio of the resin in the resin-impregnated carbon sheet used in the present invention is 30% by mass to 70% by mass. 30 mass% or more is preferable at the point that the structure of a porous carbon electrode base material becomes dense and the intensity | strength of the electrode base material obtained is high. Moreover, it is preferable to set it as 70 mass% or less at the point of maintaining the porosity and gas permeability of the electrode base material obtained. Here, the resin-impregnated carbon sheet refers to a sheet obtained by impregnating a carbon sheet before heating and pressurization, and when a solvent is used during resin impregnation, it refers to a sheet from which the solvent has been removed.

  In the thermosetting resin impregnation step, a conductive substance can be mixed into the thermosetting resin. Examples of the conductive material include carbonaceous milled fiber, carbon black, acetylene black, and isotropic graphite powder. The mixing amount when the conductive substance is mixed in the resin is preferably 1% by mass to 10% by mass with respect to the resin. If the mixing amount is less than 1% by mass, it is disadvantageous in that the effect of improving the conductivity is small, and if it exceeds 10% by mass, the effect of improving the conductivity tends to saturate, and the cost increases. It is disadvantageous in terms.

  As a method of impregnating a carbon sheet with a resin or a mixture of a resin and a conductor, a method using a drawing device or a method of stacking a thermosetting resin film on a carbon sheet is preferable. In the method using a squeezing device, a carbon sheet is impregnated in a resin solution or mixed solution, and the squeezing device is used to uniformly apply the intake liquid to the entire carbon sheet. It is a method to do. If the viscosity is relatively low, a spray method or the like can also be used.

  In the method using a thermosetting resin film, first, a thermosetting resin is once coated on a release paper to obtain a thermosetting resin film. Thereafter, the film is laminated on a carbon sheet and subjected to heat and pressure treatment to transfer a thermosetting resin.

  The heating and pressing step in the present invention is preferably performed continuously over the entire length of the carbon sheet from the viewpoint of productivity. Moreover, it is preferable to perform preheating prior to heating and pressurization. In this preheating step, the thermosetting resin is softened, and in the subsequent heating and pressing step, the thickness of the electrode base material can be well controlled by pressing. An electrode base material having a desired thickness and density can be obtained by pressing the preheated resin-impregnated carbon sheet at a temperature higher by 50 ° C. or more than the preheating temperature. Moreover, in order to obtain an electrode base material having a desired thickness and density, a plurality of resin-impregnated carbon sheets may be stacked and heated and pressurized.

  The heating and pressing described above is preferably performed using a continuous heating roll press apparatus or a continuous heating press apparatus having a pair of endless belts. In the latter continuous heating press apparatus, since the base material is sent out by a belt, the base material is hardly tensioned. Therefore, destruction of the base material during production hardly occurs and the process passability is excellent. Moreover, the former continuous heating roll press apparatus has a simple structure and a low running cost. As described above, the two heating and pressurizing methods are suitable methods for continuously curing the resin, and are preferably used for producing the electrode substrate of the present invention.

The pressurizing pressure when using the above-described continuous press device is preferably 1.5 × 10 ⁴ to 1 × 10 ⁵ N / m. Heating and pressurization is a process necessary for sufficiently impregnating the resin in the fiber and increasing the bending strength.

By pressurizing at 1.5 × 10 ⁴ N / m or more when the resin is thermally cured, sufficient conductivity and flexibility can be produced. Moreover, by pressurizing at 1 × 10 ⁵ N / m or less, the vapor generated from the resin can be released to the outside sufficiently at the time of curing, and the generation of cracks can be suppressed.

  The heating temperature in the heat and pressure treatment is preferably 140 ° C. or higher from the viewpoint of the curing treatment time or productivity, and is preferably 320 ° C. or lower from the viewpoint of cost for equipment such as a heat and pressure apparatus. More preferably, it is the range of 160-300 degreeC. The preheating temperature is preferably in the range of 100 to 180 ° C.

  In the present invention, it is preferable that the carbonization following the resin curing is continuously performed over the entire length of the carbon sheet. If the electrode base material is long, not only the productivity of the electrode base material is increased, but also MEA production in the subsequent steps can be performed continuously, which can greatly contribute to cost reduction of the fuel cell. Specifically, the carbonization is preferably performed by continuous firing over the entire length of the carbon sheet in a temperature range of 1000 to 3000 ° C. in an inert treatment atmosphere. In the carbonization of the present invention, a pretreatment by firing in an inert atmosphere of about 300 to 800 ° C., which is performed before a carbonization treatment in a temperature range of 1000 to 3000 ° C. in an inert atmosphere, is performed. You can go.

  Next, in the second step, the carbon sheet obtained as described above is arranged with an elastic sheet on at least one surface of the carbon sheet, and a linear pressure of 5 kN / m˜ Pressurize at 30 kN / m.

  The porous carbon electrode substrate is usually pressurized when adhered to a polymer electrolyte membrane or a catalyst layer, or when incorporated into a fuel cell. At this time, the short carbon fibers that fall off the porous carbon electrode base material and the carbon powder that binds the short carbon fibers cause damage to the polymer electrolyte membrane. Therefore, by passing through the second step, carbon short fibers that fall off the porous carbon electrode substrate by pressurization and carbon binding carbon short fibers can be removed in advance, and the polymer electrolyte membrane can be obtained. Damage can be reduced.

  In a membrane-electrode assembly or a polymer electrolyte fuel cell, by disposing such a porous carbon electrode substrate according to the present invention, when the membrane-electrode assembly is assembled, the polymer electrolyte fuel cell In pressurization during production or power generation, damage caused to the polymer electrolyte membrane by the carbon short fiber and the carbon component binding the carbon short fiber can be reduced.

Here, the “continuous pressurizing means” refers to a method of continuously pressurizing a sheet while transporting it using, for example, a continuous roll press or a continuous press apparatus having a pair of endless belts. By pressurizing with such an apparatus, the carbon sheet can be processed continuously, and the productivity is high. The press method that performs batch press intermittently is a problem that a high load is applied to the edge part of the press panel surface, the press mark is transferred to the carbon sheet, and the carbon sheet breaks in some cases, the duplicate press However, this method is not a preferable method.
In the present invention, the above-described continuous press apparatus is used and pressurization is performed with linear pressure. Specifically, the line pressure is increased from 5 kN / m to 30 kN / m. Thereby, pressure can be uniformly applied to the carbon sheet, and pressure unevenness applied to the carbon sheet due to thickness unevenness of the carbon sheet that may occur in the pressing method that applies surface pressure can be avoided.

  Moreover, when pressurizing continuously, the sheet | seat which has elasticity is arrange | positioned on the at least single side | surface of a carbon sheet, and a press process is performed simultaneously. Thereby, the surface area with respect to a carbon sheet becomes good, and a pressure can be uniformly provided with respect to a carbon sheet.

  Here, the “elastic sheet” refers to a sheet that has a lower compression elastic modulus than the carbon sheet and acts as a cushioning material by being disposed between the press surface and the carbon sheet during compression. Examples of the elastic sheet include a release paper having a release material applied to the surface, a Teflon (registered trademark) sheet, and a sheet made of silicon rubber. A sheet having an elastic modulus in the range of 1 to 50 GPa is preferable. If the sheet has a compression elastic modulus of 50 GPa or more, the rigidity is too high, so that the buffering action does not work and improvement per surface cannot be expected. In addition, if the sheet is 1 GPa or less, it is integrated with the carbon sheet during pressing, and the sheet cannot be peeled off.

  Moreover, when using a roll press machine as a continuous press apparatus, it is preferable to set at least one of a pair of rolls as a metal roll. This is because the use of a metal roll makes it possible to apply a uniform pressure since the roll has high rigidity. Further, at least one of the pair of rolls can be an elastic roll. Here, the “elastic roll” is a roll in which a material having a lower elastic coefficient than a metal such as rubber or silicon is arranged on the outer periphery of the roll.

  Next, in the third step, the carbon powder adhering to the pressurized carbon sheet is removed. The carbon sheet after pressurization has a lot of carbon powder or the like attached thereto. Examples of the method for removing the adhering carbon powder include a method of sweeping with a brush, a method of suction, a method of ultrasonic cleaning, and the like. From the viewpoint of removing the generated carbon powder continuously and efficiently, a method of sucking the carbon powder while sweeping with a brush or the like, or ultrasonic cleaning is preferable. In any case, carbon powder and the like adhering to the porous carbon electrode substrate can be removed continuously after pressing, so that no loss occurs and productivity is high.

The porous carbon electrode substrate obtained as described above is a substrate having the following characteristics.
Upon crimped polyethylene sheet and force lap 50 g / cm ^2, the number of short carbon fibers attached to the peeled polyethylene sheet is 0.1 present 10 present / cm ^2, was deposited in the number of short carbon fibers Porous carbon electrode substrate with less number of carbides.
In other words, the number of short carbon fibers attached after crimping / peeling to a polyethylene sheet is small, and fuel cells using such porous carbon electrode base materials are less likely to cause short circuits and cross-leakage of reactive gases, and are extremely durable. Very expensive.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Measurement method of leakage current]
The perforated sulfonic acid polymer electrolyte membrane (thickness: 30 μm) is placed so that the obtained porous carbon electrode substrate is in contact with it, and it is sandwiched between gold-plated copper plate electrodes and heated to 3.5 MPa. After pressurization, a digital multimeter TR6487 (manufactured by Advantest) was used to measure leakage current due to damage to the polymer electrolyte membrane. The potential difference between the electrodes at this time was 0.6V.

[Measurement method of the number of short carbon fibers attached after pressure bonding / peeling with polyethylene sheet]
A PE film was disposed on the upper surface of the porous carbon electrode substrate, and a weight was placed on the PE film, whereby a pressure of 50 g / cm 2 was applied to the porous carbon electrode substrate. After applying pressure for 1 minute, the weight, the PE film was removed from the porous carbon electrode substrate, and the number of short carbon fibers attached to the PE film was observed with a microscope. Observation was performed 5 times for each sample, and the average value per 1 cm ² was defined as the number of carbon short fibers attached.

[Measurement of compression modulus of elastic sheet used]
Release paper and Teflon (registered trademark), which are elastic sheets used in the examples
The compression modulus of the sheet was measured. Shimadzu Micro Auto MST-I (manufactured by Shimadzu Corporation) was used as a compression tester. A test force was applied to a sample having a diameter of 25 mm, and the behavior of stress against compressive strain was measured. The change in stress relative to the compressive strain in the stress range of 0 to 3.0 MPa was recorded as the compressive elastic modulus. In order to determine an accurate elastic modulus, the compression test was performed 5 times, and the average value was used as the elastic modulus of each sample. The elastic modulus of the release paper used in the present invention was 1.59 GPa, and the elastic modulus of the Teflon (registered trademark) sheet was 2.79 GPa.

[Example 1]
As carbon short fibers, 100 parts by mass of PAN-based carbon short fibers having an average diameter of 7 μm cut to a length of 3 mm and polyvinyl alcohol (PVA) fibers having a length of 3 mm (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) 11 After mass parts were dispersed in water and continuously formed on a wire mesh, they were dried to obtain carbon fiber paper.
100 parts by mass of this carbon fiber paper is impregnated with a methanol solution of a phenol resin (trade name: Phenolite J-325, manufactured by Dainippon Ink and Chemicals), and the methanol is sufficiently dried at room temperature, so that the nonvolatile content of the phenol resin A phenol resin-impregnated carbon sheet with 84 parts by mass of was obtained.
Two of the phenol resin-impregnated carbon sheets were stacked and roll-pressed with a linear force of 8 × 10 ⁴ N / m at a temperature of 250 ° C. to cure the phenol resin. Then, it carbonized continuously at 1900 degreeC in inert gas (nitrogen) atmosphere, and obtained the carbon sheet which consists of a paper body of the carbon short fiber whose thickness is 220 micrometers and whose bulk density is 0.26 g / cm < ² >.

By releasing release paper (Koutei WBE90R-DT manufactured by Lintec Corporation) from both sides of this carbon sheet and continuously applying pressure at a linear pressure of 17.5 kN / m with a roll press device comprising a pair of metal rolls. A porous carbon electrode substrate was obtained. The obtained porous carbon electrode base material was continuously subjected to ultrasonic cleaning for 1 minute by passing through a treatment tank filled with ion-exchanged water, and then removed. After ultrasonic cleaning and drying, the porous carbon electrode substrate was wound up in a roll shape. The leakage current of the porous carbon electrode substrate was evaluated. The obtained porous carbon electrode substrate had a leakage current as low as 4.3 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 2.2 per 1 cm ² .

[Example 2]
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the ultrasonic cleaning time was 3 minutes. The obtained porous carbon electrode substrate had a low leakage current of ^2.5 mA / cm ² and exhibited good characteristics. The number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 2.6 per 1 cm ² .

Example 3
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the ultrasonic cleaning time was changed to 5 minutes. The obtained porous carbon electrode substrate had a low leakage current of 4.8 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhered after pressure bonding / peeling with the polyethylene sheet was as small as 3.1 per 1 cm ² .

Example 4
Porous carbon electrode substrate in the same manner as in Example 1 except that it was removed by collecting dust from both sides of the porous carbon electrode substrate with a rotary brush and a suction power of 70 W instead of performing ultrasonic cleaning. Got. The obtained porous carbon electrode substrate had a low leakage current of 2.0 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 3.2 per 1 cm ² .

Example 5
Porous carbon electrode substrate in the same manner as in Example 1 except that it was removed by collecting dust from both sides of the porous carbon electrode substrate at a suction power of 300 W instead of ultrasonic cleaning. Got. The obtained porous carbon electrode substrate had a leakage current as low as 2.2 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 1.8 per 1 cm ² .

Example 6
Porous carbon electrode substrate in the same manner as in Example 1 except that it was removed by collecting dust from both sides of the porous carbon electrode substrate with a rotary brush and a suction power of 500 W instead of performing ultrasonic cleaning. Got. The obtained porous carbon electrode substrate had a low leakage current of 3.8 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 2.2 per 1 cm ² .

Example 7
Of the pair of press rolls used for pressing the carbon sheet, one was a rubber roll, the other was a metal roll, and a Teflon (registered trademark) sheet was used instead of the release paper. In the same manner as in Example 1, a porous carbon electrode substrate was obtained. The obtained porous carbon electrode substrate had a low leakage current of 3.0 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 1.7 per 1 cm ² .

Example 8
A porous carbon electrode substrate was obtained in the same manner as in Example 4 except that one of the pair of press rolls used for pressing the carbon sheet was a rubber roll and the other was a metal roll. The obtained porous carbon electrode substrate had a low leakage current of 3.0 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 0.6 per 1 cm ² .

Example 9
The carbon sheet was pressed by a continuous press machine equipped with a pair of stainless steel belts, and a Teflon (registered trademark) sheet (trade name: Skyved Tape, manufactured by Chukoh Chemical Industry Co., Ltd.) was used instead of the release paper. A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that it was. The obtained porous carbon electrode base material had a leakage current as low as 2.3 mA / cm ² and exhibited good characteristics. The number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 2.6 per 1 cm ² .

Example 10
A porous carbon electrode substrate was obtained in the same manner as in Example 4 except that the carbon sheet was pressed by a continuous press apparatus equipped with a pair of stainless steel belts. The obtained porous carbon electrode substrate had a low leakage current of 2.0 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 3.4 per 1 cm ² .

Example 11
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the linear pressure during pressing was 5.8 kN / m. The obtained porous carbon electrode substrate had a low leakage current of 4.4 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 3.3 per 1 cm ² .

Example 12
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the linear pressure during pressing was 11.7 kN / m. The obtained porous carbon electrode substrate had a low leakage current of 4.3 mA / cm ² and exhibited good characteristics. The number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 3.9 per 1 cm ² .

Example 13
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the linear pressure during pressing was 20.4 kN / m. The obtained porous carbon electrode substrate had a low leakage current of 4.5 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 3.6 per 1 cm ² .

Example 14
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that release paper was used only on one side of the carbon sheet in the press treatment. The obtained porous carbon electrode substrate had a low leakage current of 8.9 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 8.8 per 1 cm ² .

Example 15
A porous carbon electrode substrate was obtained in the same manner as in Example 8 except that the release paper was used only on one side of the carbon sheet in the press treatment. The obtained porous carbon electrode substrate had a low leakage current of 6.3 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 5.6 per 1 cm ² .

Example 16
A porous carbon electrode substrate was obtained in the same manner as in Example 9 except that the release paper was used only on one side of the carbon sheet in the press treatment. The obtained porous carbon electrode substrate had a low leakage current of 8.2 mA / cm ² and exhibited good characteristics. Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as small as 8.1 per 1 cm ² .

[Comparative Example 1]
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the press treatment and removal were not performed. The obtained porous carbon electrode base material showed a high leakage current of 13.8 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 13.2 per 1 cm ² .

[Comparative Example 2]
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the press treatment was not performed. The obtained porous carbon electrode substrate showed a high leak current of 11.3 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 11.2 per 1 cm ² .

[Comparative Example 3]
A porous carbon electrode substrate was obtained in the same manner as in Example 4 except that the press treatment was not performed. The obtained porous carbon electrode substrate showed a high leak current of 10.5 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 11.5 per 1 cm ² .

[Comparative Example 4]
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the removal was not performed. The obtained porous carbon electrode substrate showed a high leak current of 10.8 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 11.8 per 1 cm ² .

[Comparative Example 5]
A porous carbon electrode substrate was obtained in the same manner as in Example 4 except that the release paper was not used in the press treatment. The obtained porous carbon electrode base material showed a high leak current of 10.3 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 12.6 per 1 cm ² .

[Comparative Example 6]
A porous carbon electrode substrate was obtained in the same manner as in Example 10 except that the release paper was not used in the press treatment. The obtained porous carbon electrode base material showed a high leak current of 10.1 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 11.2 per 1 cm ² .

[Comparative Example 7]
A porous carbon electrode substrate was obtained in the same manner as in Example 1 except that the carbon sheet was passed through a batch press apparatus having a pair of flat plates and intermittently pressed. The obtained porous carbon electrode base material showed a high leak current of 10.2 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 12.6 per 1 cm ² .

[Comparative Example 8]
The carbon sheet was passed through a batch press apparatus having a pair of flat plates, and the press process was intermittently performed, and the suction process was performed while performing a gas blowing process as a removal method, as in Example 1. Thus, a porous carbon electrode substrate was obtained. The obtained porous carbon electrode base material showed a high leak current of 10.3 mA / cm ² . Further, the number of short carbon fibers adhering after pressure bonding / peeling with the polyethylene sheet was as large as 11.6 per cm ² .

Table 1 shows the results of the measured leakage current and the like.

  From the results shown in Table 1, even if the carbon sheet has a certain degree of roughness on the surface, the carbon sheet is pressed with linear pressure at the same time as the release sheet, Teflon (registered trademark) sheet or the like. Since pressure is applied, the weak binding portion of the carbon sheet is uniformly destroyed and removed. Moreover, it was obtained in Examples 1 to 16 that the carbon short fibers and resin carbide fragments / powder produced by destruction / removal were continuously and efficiently removed by ultrasonic cleaning or suction treatment. It is clear from the fact that all the porous carbon electrode base materials show a low leakage current and that the number of short carbon fibers attached after the pressure bonding / peeling with the polyethylene sheet is small. Since the porous carbon electrode base material of the present invention is a continuous product, not only is post-roll roll post-processing easy, but the fuel cell using the porous carbon electrode base material is short-circuited or cross leaks of the reaction gas. Is less likely to occur and is extremely durable.

Claims (6)

The manufacturing method of the porous carbon electrode base material including the process of the following (1)-(3).
(1) A step of producing a carbon sheet in which short carbon fibers are bound by carbon.
(2) A step of placing the carbon sheet with elasticity on at least one surface of the carbon sheet and pressurizing the carbon sheet with a linear pressure of 5 kN / m to 30 kN / m using a continuous pressurizing means.
(3) Next, the process of removing the carbon powder adhering to the carbon sheet continuously.   2. The method for producing a porous carbon electrode substrate according to claim 1, wherein the pressurizing means is a continuous press device provided with at least a pair of rolls, and at least one of the pair of rolls is a metal roll.   3. The method for producing a porous carbon electrode substrate according to claim 1, wherein the pressurizing means is a continuous press apparatus including at least a pair of rolls, and at least one of the pair of rolls is an elastic roll.   The method for producing a porous carbon electrode substrate according to claim 3, wherein the continuous press device is a continuous press device including at least a pair of endless belts.   The manufacturing method of the porous carbon electrode base material in any one of Claims 1-4 whose removal is the method by brushing and suction, or ultrasonic cleaning. Upon crimped polyethylene sheet and force lap 50 g / cm ^2, the number of short carbon fibers attached to the peeled polyethylene sheet is 0.1 present 10 present / cm ^2, was deposited in the number of short carbon fibers Porous carbon electrode substrate with less number of carbides.