JP2013080590A - Conductive sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-repellent conductive sheet capable of being produced by papermaking, high in air permeability and conductivity, and suitable for a fuel cell electrode material, and a method for producing the water-repellent conductive sheet.SOLUTION: A fluorine resin particle is deposited on aromatic polyamide pulp in a slurry including, as a raw material, the aromatic polyamide pulp, the fluorine resin particle, a carbon based conductive material and a burn-off material, then the slurry is subjected to papermaking to obtain a conductive sheet precursor, the conductive sheet precursor is subjected to hot pressing at a predetermined condition, and then the sheet is fired at a predetermined temperature. Thus, a conductive sheet including aromatic polyamide pulp, a fluorine resin fused with the aromatic polyamide pulp, and a carbon based conductive material is formed. The conductive sheet has an air permeability of 30-10,000 ml/min cmand a surface electric resistance value of 2,000 mΩ/cmor less.

Description

  The present invention relates to a conductive sheet and a manufacturing method thereof. More specifically, the present invention relates to a water-repellent conductive sheet for a fuel cell electrode material, in which a fluorine component and a conductive component are integrally made, and has high air permeability and conductivity, and a method for manufacturing the same.

  Fuel cells are classified into four types according to the type of electrolyte used: molten carbonate fuel cells, solid oxide fuel cells, phosphoric acid fuel cells, and polymer electrolyte fuel cells. Recently, development of fuel cells using enzymes and microorganisms as catalysts has been promoted.

  A unit cell constituting a solid polymer fuel cell is formed by stacking gas diffusion electrodes each having a catalyst layer on both surfaces of a thin plate-shaped polymer electrolyte membrane. The gas diffusion electrode provided with the catalyst layer is referred to as a membrane-electrode assembly (hereinafter also referred to as “MEA”). The solid polymer fuel cell has a stack structure in which a plurality of the unit cells are stacked via a separator. The polymer electrolyte membrane selectively transmits hydrogen ions (protons). The catalyst layer is mainly composed of carbon fine particles carrying a noble metal catalyst made of platinum or the like. The gas diffusion electrode is caused by the gas diffusion performance that guides the fuel gas and air to the catalyst layer and exhausts the generated gas and excess gas, the high conductivity that extracts the generated current to the outside without loss, and the generated proton Resistance to a strongly acidic atmosphere is required.

  As the material of this gas diffusion electrode, carbon fiber sheets such as carbon fiber cloth, carbon fiber felt, and carbon fiber paper are often used because of its excellent mechanical properties, acid resistance and conductivity, and light weight. .

  The following method is illustrated as a manufacturing method of a carbon fiber sheet. There is a method of manufacturing a carbon fiber sheet by processing a carbon fiber such as a filament yarn, a staple yarn, or a cut fiber by weaving or papermaking. In addition, there is a method of manufacturing a carbon fiber sheet by previously processing a flame-resistant fiber, which is a carbon fiber precursor fiber, and firing the sheet at 1000 ° C. or more (for example, Patent Document 1). Furthermore, by mixing carbon fiber and a papermaking binder to make a sheet, the resulting sheet is impregnated with a thermosetting resin such as phenol and cured, and then fired at a temperature of 1000 ° C. or higher. There is a method for producing a carbon fiber sheet (for example, Patent Document 2).

  The gas diffusion electrode is required to have a function of discharging generated water generated by the power generation reaction to the separator. The reason is that if the generated water stays in the MEA, the supply of the fuel gas to the catalyst layer is hindered (hereinafter, this phenomenon is also referred to as “flooding”). In order to promote discharge of generated water due to a power generation reaction and suppress flooding, the carbon fiber sheet constituting the gas diffusion electrode is generally provided with water repellency. As a method for imparting water repellency to a carbon fiber sheet, a conductive sheet such as a carbon fiber sheet is impregnated with a water repellent substance such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), and baked at 200 to 500 ° C. A method of performing a tying process is common (for example, Patent Document 3).

  The gas diffusion electrode is required to have a function of uniformly diffusing the fuel gas in the catalyst layer and a function of controlling the wettability in the MEA. When the fuel gas is uniformly diffused into the catalyst layer, the reaction area between the fuel gas and the catalyst layer increases. Moreover, when the wettability in the MEA is controlled, drying of the polymer electrolyte membrane is suppressed, and the electrical resistance of the polymer electrolyte membrane is reduced. As a result, a fuel cell configured using this gas diffusion electrode can generate a high voltage.

  In order to impart a function of uniformly diffusing the fuel gas to the gas diffusion electrode, it is common to provide a microporous layer (MPL) on the surface of the carbon fiber sheet. This MPL is composed of carbonaceous particles such as carbon black and a fluororesin, and has pores with an average diameter of about several μm. Compared with the carbon fiber sheet which does not have MPL, the carbon fiber sheet which has MPL can diffuse gas uniformly. In addition, since the carbon fiber sheet having MPL retains moisture, it is possible to control wettability. The MPL is formed by a method of spraying or knife coating a slurry containing carbonaceous particles and a fluorine resin at an appropriate concentration. The coating method is generally formed by coating the surface of a carbon fiber sheet (for example, Patent Document 4).

  As described above, a gas diffusion electrode for a polymer electrolyte fuel cell generally uses a water-repellent conductive sheet manufactured by performing water-repellent processing on a carbon fiber sheet and then forming MPL. Is.

  The above water-repellent conductive sheet is not only a polymer electrolyte fuel cell, but also an electrode material for a fuel cell that requires both diffusibility and drainage of fuel gas and fuel liquid such as a biofuel cell and an air zinc cell. As widely used.

  However, since the water-repellent conductive sheet is manufactured through many steps as described above, the production efficiency is poor. As a result, a fuel cell in which this sheet is used as an electrode material is expensive. Various proposals have been made for these problems.

  Patent Document 5 describes a method for producing an electrode material for a fuel cell in which a base material made of a polyarylate nonwoven fabric is immersed in a slurry in which a carbon material such as a fluororesin and carbon black is dispersed and then dried.

  Patent Document 6 discloses a fuel cell in which an acrylic resin or a vinyl acetate resin is attached to a substrate made of a glass fiber nonwoven fabric, and then a conductive paste in which PVDF, PTFE, and carbon particles are added to a solvent is applied and dried. A method for producing an electrode material is described.

  The production methods described in Patent Documents 5 and 6 have better production efficiency than conventional methods. However, since the polyarylate nonwoven fabric and the glass fiber nonwoven fabric that are the base materials have low conductivity, the fuel cell configured using this electrode material has high internal resistance. As a result, high battery performance cannot be obtained.

  Various proposals have been made as electrode materials for fuel cells having conductivity and high productivity (for example, Patent Document 7 and Patent Document 8).

  Patent Document 7 describes an electrode material for a fuel cell in which the acid resistance of the metal mesh is increased by applying a noble metal coat to the metal mesh. However, since the noble metal material used for the coat is expensive, the fuel cell is expensive. In a metal mesh not coated with a noble metal coat, metal ions eluted with corrosion deteriorate the electrolyte membrane. For this reason, the metal mesh needs to be subjected to an acid resistance treatment such as a precious metal coating.

  In Patent Document 8, an electrode material for a fuel cell manufactured by adhering carbon fibers, carbon fine particles, and a resin to a base sheet made of a woven or non-woven fabric made of inorganic fibers or organic fibers such as glass fibers or a metal mesh is disclosed. Have been described. This electrode material has higher conductivity than the electrode materials described in Patent Document 5 and Patent Document 6 because carbon fine particles are interposed between carbon fibers. However, in order to produce a highly conductive electrode material, it is necessary that a sufficient amount of carbon fibers and carbon fine particles are impregnated inside the base sheet. In order to impregnate a base sheet with a sufficient amount of carbon fibers and carbon fine particles, a predetermined resin impregnation amount is obtained by applying a thin resin solution in which carbon fibers and carbon fine particles are dispersed to the base sheet and then drying. Repeat until. However, this method is poor in production efficiency because the application and drying of the resin solution are repeated.

  Various proposals have been made for water-repellent sheets produced by papermaking. Sheets manufactured by papermaking have good production efficiency. Patent Document 9 describes a method for producing a water-repellent sheet in which aromatic polyamide and fluororesin particles are dispersed in water for papermaking. The sheet obtained by this method does not have electrical conductivity. Therefore, the fuel cell configured using this sheet has low battery performance.

  A fuel cell is usually used under various power generation conditions depending on its application and power generation method. In particular, in a high humidification-high current density region, there is a concern that the output voltage may decrease due to a decrease in the partial pressure of hydrogen and oxidant and insufficient supply of gas. For this reason, various proposals have been made as sheets in which pores are formed in the sheet to improve gas supply performance (for example, Patent Documents 10 and 11).

  Patent Document 10 describes a water-repellent conductive sheet in which a fluororesin film in which a carbon material is dispersed is prepared, and through holes are formed in the fluororesin film to form through holes. However, the drilling process requires a mechanical process such as laser irradiation or drilling. Therefore, productivity is reduced and manufacturing costs are increased. As a result, the fuel cell becomes expensive. Moreover, the fluororesin film | membrane used as a base material has low electroconductivity. Therefore, a fuel cell configured using this sheet has high internal resistance and low cell performance.

  Patent Document 11 describes a conductive sheet in which carbon fibers and a burned-out material are dispersed in water to produce a sheet, and the sheet is fired to remove the burned-out material to form pores in the sheet. Has been. However, since this conductive sheet is impregnated with a thermosetting resin, impregnated with a water repellent, and heated after the sheet is made, many steps are required and productivity is low.

JP 2003-268651 A (Claims) JP 2001-196085 A (Claims) JP-A-6-203851 (Claims) JP-A-7-220734 (Claims) JP 2008-210725 A (Claims) JP 2008-204945 A (Claims) JP 2008-103142 A (Claims) JP 2010-153222 A (Claims) JP-A-9-188767 (Claims) JP 2007-179870 A (Claims) JP 2007-335370 A (Claims)

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to be manufactured by papermaking, and to have a high air permeability and conductivity, and a water-repellent conductive sheet suitable for a fuel cell electrode material and a method for manufacturing the same Is to provide.

  In the slurry using the aromatic polyamide pulp, the fluororesin particles, the carbon-based conductive material, and the material that decomposes below the firing temperature of the sheet (hereinafter, also referred to as “burnt material”) Then, after the fluororesin particles were deposited on the aromatic polyamide pulp, the slurry was made to obtain a conductive sheet precursor. Thereafter, the conductive sheet precursor was hot pressed under predetermined conditions, and then the sheet was fired at a predetermined temperature. As a result, water repellency was imparted to the sheet, and the burned-out substance dispersed in the sheet disappeared to find that a conductive sheet having extremely high air permeability and drainage was obtained, and the present invention was completed.

  This invention which solves the said subject is the electrically conductive sheet which consists of the following structures, and its manufacturing method.

[1] A conductive sheet comprising an aromatic polyamide pulp, a fluororesin fused to the aromatic polyamide, and a carbon-based conductive material,
Air permeability is 30 to 10000 ml / min. · Cm ^2, and inter-surface conductive sheet resistance value is equal to or is 2000mΩ / cm ² or less.

  [2] The conductive sheet according to [1], wherein an average pore diameter measured by a bubble point method is 0.3 to 40 μm.

  [3] The carbon conductive material is selected from the group consisting of graphite particles, carbon black, carbon nanotubes, carbon fibers, carbon milled fibers, carbon nanofibers, carbon nanohorns, and graphenes [1] or [2] The electroconductive sheet of description.

[4] aromatic polyamide pulp;
A fluororesin deposited on the aromatic polyamide pulp;
Carbon-based conductive materials,
Burnt down substances,
A slurry containing
The slurry is made to obtain a conductive sheet precursor,
In the air, the conductive sheet precursor is hot pressed at a temperature of 120 to 250 ° C. and a contact pressure of 0.1 to 50 MPa for 1 to 300 minutes,
The method for producing a conductive sheet according to [1], wherein firing is performed in an inert gas at a firing temperature of 200 to 500 ° C.

  [5] The conductive material according to [4], wherein the burnout substance is one or more selected from the group consisting of polyvinyl alcohol, polyester, polyolefin, polyamide, acrylic resin, styrene resin, cellulose, and derivatives thereof. Sheet manufacturing method.

  [6] The method for producing a conductive sheet according to [4] or [5], wherein the pyrolysis start temperature in the inert gas of the burned substance is a substance that is lower by 30 ° C. or more than the firing temperature.

  The conductive sheet of the present invention has conductivity and air permeability, and can be suitably used as a fuel cell electrode material. Furthermore, since this sheet has water repellency, an electrode constructed using this sheet has excellent drainage properties.

  Since the conductive sheet of the present invention is integrally manufactured by a papermaking method, the productivity is high.

(Water repellent conductive sheet)
The conductive sheet of the present invention (hereinafter, also referred to as “the present conductive sheet”) includes an aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material. A fluororesin is fused to the fiber surface of the aromatic polyamide pulp. This fluororesin imparts water repellency to the conductive sheet. A carbon-based conductive material is dispersed between the fibers of the aromatic polyamide pulp. With this carbon-based conductive material, the conductive sheet is given conductivity in the thickness direction of the sheet.

  In the present invention, the air permeability of the conductive sheet is evaluated by the air permeability measured by the method described later. The greater the air permeability, the higher the air permeability of the conductive sheet.

The air permeability of the conductive sheet is 30 to 10000 ml / min. * Cm < ² >, 30-2000 ml / min. It is preferred that · cm ^2. The air permeability is 30 ml / min. -A conductive sheet of less than cm ² has low air permeability. The air permeability is 30 ml / min. When a conductive sheet of less than cm ² is used as the fuel cell electrode material, the amount of fuel gas supplied to the catalyst layer is insufficient particularly in a high current density region. As a result, the output voltage is lowered and the battery performance is lowered. The air permeability of the conductive sheet can be controlled by the type and amount of the burned-out substance used in the conductive sheet manufacturing process.

Surface between the electrical resistance of Honshirubeden sheet is preferably 2000mΩ / cm ² or less, 1000M / cm ² or less being more preferred. When a conductive sheet having an inter-surface electrical resistance exceeding 2000 mΩ / cm ² is used as the fuel cell electrode material, the cell resistance increases, the output voltage decreases, and the battery performance decreases. The inter-surface electrical resistance value of the conductive sheet can be controlled by the type and amount of the carbon-based conductive material.

  As for the average pore diameter measured by the bubble point method of this electrically conductive sheet, 0.3-40 micrometers is preferable. When the average pore diameter is less than 0.3 μm, the drainage of the sheet is poor, and flooding in which generated water stays in the electrode is likely to occur, and the battery performance is likely to be lowered. When the average pore diameter exceeds 40 μm, it becomes difficult to uniformly diffuse the fuel gas in the catalyst layer, and it is difficult to obtain high power generation performance. Furthermore, the water permeability becomes high (that is, the water shielding property is low), and a dry-out occurs in which the polymer electrolyte membrane is dried. As a result, the battery performance is lowered particularly under low temperature humidification conditions. The average pore diameter measured by the bubble point method of this conductive sheet can be controlled by the type and amount of the burned-out substance used in the conductive sheet manufacturing process.

  The thickness of the conductive sheet is preferably 50 to 500 μm, particularly preferably 100 to 400 μm. When thickness is less than 50 micrometers, the intensity | strength of a conductive sheet will become low and handleability will fall. When the thickness exceeds 500 μm, gas diffusibility and drainage are deteriorated, which causes a decrease in battery performance. The thickness of the conductive sheet can be controlled by adjusting the basis weight of the conductive sheet and the temperature and pressure when hot pressing the conductive sheet precursor.

Basis weight of Honshirubeden sheet is preferably ^{30~200g / m 2, 50~150g / m} 2 is more preferable. When the basis weight is less than 30 g / m ^2, the strength of the conductive sheet is lowered and the handleability is lowered. When the basis weight exceeds 200 g / m ² , it is difficult to obtain a conductive sheet having a predetermined thickness.

The bulk density of the conductive sheet is preferably 0.2 to 0.7 g / cm ³ . When the bulk density is less than 0.2 g / cm ³ , the strength of the conductive sheet is lowered, and the handleability is deteriorated. When the bulk density exceeds 0.7 g / cm ³ , gas diffusibility and drainage are deteriorated, which causes a decrease in battery performance.

(Carbon-based conductive material)
The carbon-based conductive material included in the conductive sheet is not particularly limited as long as the carbon content is 94% by mass or more and the specific resistance value is 100 Ω · cm or less. When carbon content is less than 94 mass%, the electroconductivity of the conductive sheet obtained will fall. Furthermore, when a battery incorporating this conductive sheet is operated for a long period of time, the conductive sheet is likely to deteriorate.

  Examples of the carbon-based conductive material that satisfies the above conditions include graphite particles, carbon black, carbon nanotubes, carbon fibers, carbon milled fibers, carbon nanofibers, carbon nanohorns, and graphene. These may be used alone or in combination of two or more.

  Examples of the carbon fiber and carbon milled fiber include PAN-based carbon fiber, pitch-based carbon fiber, and phenol-based carbon fiber. In particular, PAN-based carbon fibers are preferable. Examples of the carbon black include acetylene black and ketjen black (registered trademark) having a hollow shell structure. Of the carbon blacks, ketjen black is preferred.

  When using carbon fiber or carbon milled fiber, the fiber diameter is preferably 5 to 20 μm, particularly preferably 6 to 13 μm. In the case of carbon fibers having a flat cross section, the average value of the major axis and the minor axis is defined as the fiber diameter. When the fiber diameter is less than 5 μm, the strength of the single fiber is low, so that the strength of the obtained conductive sheet tends to be insufficient. In addition, the carbon fibers dropped from the conductive sheet may adversely affect the human body. Furthermore, the fiber strength is reduced during firing of the conductive sheet precursor, and a large amount of fine carbon fiber powder is generated. When the fiber diameter exceeds 20 μm, the shape of the outer periphery of the carbon single fiber constituting the conductive sheet rises on the sheet surface of the conductive sheet. As a result, unevenness is formed on the sheet surface, the surface smoothness of the sheet is deteriorated, and the contact electrical resistance of the sheet tends to increase due to the unevenness formed on the sheet surface.

  The average fiber length (cut length) of carbon fiber or carbon milled fiber is preferably 20 mm or less. When the average fiber length exceeds 20 mm, the uniform dispersibility of the fibers decreases, and the strength of the resulting sheet decreases.

  The average particle size of carbon black is preferably 0.5 to 20 μm. When the average particle size is less than 0.5 μm, when preparing a carbon black dispersion, the carbon black aggregates and dispersion spots tend to occur. When the average particle diameter exceeds 20 μm, the carbon black particles do not enter the inner layer portion of the sheet, so that the conductivity of the obtained conductive sheet is lowered.

  Known graphite particles can be used as the graphite particles. Of these, spherical graphite and scale-like graphite are preferable. The average particle size of the graphite particles is preferably 0.05 to 300 μm.

(Aromatic polyamide pulp)
The aromatic polyamide pulp used in the present invention (hereinafter also referred to as “aramid pulp”) has an amide bond in which 85 mol% or more of the amide bond is formed by dehydration condensation of an aromatic diamine component and an aromatic dicarboxylic acid component. Have. In the aramid pulp used in the present invention, the fibers are highly fibrillated.

  The aromatic polyamide pulp is composed of a trunk part and a fibril part in which fibers are fibrillated from the trunk part. The trunk has a fiber diameter of 3 to 70 μm and a length of 1 to 500 mm. The fiber diameter of the fibril part is 0.01-2 μm.

  The aromatic polyamide pulp in which 85 mol% or more of the amide bond is composed of an aromatic diamine component and an aromatic dicarboxylic acid component includes polyparaphenylene terephthalamide, copolyparaphenylene-3,4′oxydiphenylene-terephthalamide, polymeta Phenyleneisophthalamide, polyparabenzamide, poly-4,4'-diaminobenzanilide, polyparaphenylene-2,6-naphthalamide, copolyparaphenylene / 4,4 '-(3,3'-dimethylbiphenylene) terephthal Examples include amide, polyorthophenylene terephthalamide, polyparaphenylene phthalamide, and polymetaphenylene isophthalamide.

  In the present invention, “fibrillation” refers to a method of randomly forming short fibers having a small diameter on the fiber surface. In the present invention, fibrillation of aramid fibers is performed by a known method. For example, fibrillation is performed by adding a precipitating agent to an organic polymer solution and mixing in a system in which a shearing force is generated, as described in JP-B-35-11851 and JP-B-37-5732. . In addition, a random product is obtained by applying mechanical shearing force such as beating to a molded article having molecular orientation formed from a polymer solution exhibiting optical anisotropy described in JP-B-59-603. Fibrilization is performed by a method of forming a short fiber having a small diameter.

A BET specific surface area is used as an index of fibrillation. BET specific surface area of the aramid pulp is preferably 3~25m ² / g, particularly preferably from 5 to 20 m ² / g, more preferably 9~16m ² / g. When the BET specific surface area of the aramid pulp is less than 3 m ² / g, the entanglement between the pulps does not occur sufficiently, so the mechanical strength of the obtained conductive sheet is low. Moreover, it becomes difficult to deposit the fluororesin particles on the aramid pulp. On the other hand, when the BET specific surface area of the aramid pulp exceeds 25 m ² / g, the drainage at the time of making the conductive sheet becomes worse. Therefore, it takes a long time to produce the conductive sheet, which increases the manufacturing cost.

(Fluorine resin)
Examples of the fluororesin used in the present invention include tetrafluoroethylene resin (hereinafter abbreviated as “PTFE”), perfluoro-alkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and tetrafluoroethylene. -Ethylene copolymer resin, vinylidene fluoride resin and ethylene trifluoride chloride are exemplified. Among them, PTFE is particularly preferable because it is excellent in heat resistance and sliding characteristics.

  The average particle size of the fluororesin particles is preferably from 0.01 to 10 μm, particularly preferably from 0.1 to 1 μm. When the average particle size is less than 0.01 μm, deposition on aramid fibers becomes difficult. On the other hand, when the average particle size exceeds 10 μm, it is difficult to prepare a stable dispersion. As a result, the fluororesin tends to be unevenly distributed in the conductive sheet.

(Substances that decompose below the firing temperature)
A substance that decomposes below the firing temperature (hereinafter also referred to as “burnt substance”) is a substance that has a thermal decomposition start temperature of less than 500 ° C. in an inert atmosphere and decomposes below the firing temperature described below. In the present invention, the thermal decomposition starting temperature refers to a temperature at which weight reduction of a substance starts when the temperature of the substance is gradually raised. The burned-out material of the present invention is preferably a material having a carbon residue rate of 40% or less at an calcination temperature in an inert atmosphere, more preferably a material having a carbon residue rate of 20% or less, and a material having a carbon residue rate of 10% or less. Is more preferable. The burned-out substance is appropriately selected depending on the firing temperature. The burned-out substance is not particularly limited except that it is selected depending on the firing temperature, but is preferably a pulp-shaped or fiber-shaped organic substance having a good yield in the papermaking process and a low thermal decomposition starting temperature. Examples of the burnout substance of the present invention include polyvinyl alcohol (PVA), polyester, polyolefin, polyamide, acrylic resin, styrene resin, cellulose, and derivatives thereof. Among them, PVA, aliphatic polyester, polyolefin, aliphatic polyamide, acrylic resin, styrene resin, cellulose and derivatives thereof having a carbon residue at 500 ° C. of 40% or less are preferable, and vinylon having a carbon residue of 20% or less is preferable. , Polyethylene terephthalate (PET) and rayon are more preferable. The shape of the burned-out substance is preferably 0.1 to 100 mm in length and 0.1 to 50 μm in diameter.

  This burned-out substance decomposes and disappears in the firing step, and forms voids in the conductive sheet. When this conductive sheet is produced by blending a burned-out substance, the air permeability and drainage of the obtained conductive sheet are increased.

  The thermal decomposition starting temperature of the burned-out substance is preferably 30 ° C. or lower than the firing temperature. When the difference between the firing temperature and the decomposition temperature is less than 30 ° C., the burned-out substance does not disappear after firing and tends to remain in the sheet, and the air permeability and drainage of the sheet tend to be difficult to improve. In addition, if the burned-out substance remains in the sheet, the electrical resistance is deteriorated.

(Method for producing the water-repellent conductive sheet)
As long as the physical properties of the sheet are within the above range, the production method is not particularly limited.

<Slurry preparation process>
First, a dispersion in which aromatic polyamide pulp (hereinafter also referred to as “aramid pulp”) and fluororesin particles are dispersed (hereinafter also referred to as “aramid pulp-fluororesin dispersion”) is prepared. The aramid pulp-fluororesin dispersion can be produced by preparing a dispersion in which aramid pulp is dispersed and a dispersion in which fluororesin particles are dispersed, and mixing them. It may be prepared by adding and dispersing aramid pulp in a dispersion of fluororesin particles, or vice versa. Most preferred is a method in which aramid pulp is added and dispersed in a dispersion of fluororesin particles.

  As the dispersion medium, water is preferred.

  What is necessary is just to select suitably the mixture ratio of the aramid pulp and fluororesin in an aramid pulp-fluororesin dispersion liquid according to the final product made into the objective. The aramid pulp / fluororesin ratio (mass ratio) is preferably in the range of 10/90 to 50/50, and particularly preferably in the range of 20/80 to 40/60. When the mass ratio of the aramid pulp to the fluororesin is less than 10/90, the sheet is not sufficiently reinforced with the aramid pulp. On the other hand, when the mass ratio of the aramid pulp to the fluororesin exceeds 50/50, it is difficult to obtain a conductive sheet having sufficient water repellency due to the fluororesin.

  The dispersion of fluororesin particles can be prepared by a known method. For example, it can be prepared by radical polymerization of a raw material monomer of a fluororesin in the presence of a surfactant. Examples of the surfactant used in the dispersion of the fluororesin particles include nonionic surfactants and ionic surfactants. A commercially available dispersion of fluororesin particles can also be used as it is. Examples of commercially available dispersions of fluororesin particles include Fluon PTFE dispersion AD911L (product name) manufactured by Asahi Glass Co., Ltd. and Polyflon PTFE D-1E (product name) manufactured by Daikin Industries, Ltd.

  The dispersion of aramid pulp can be prepared by a known method such as a method conventionally used for making wood pulp. For example, various dispersers (pulpers), various beaters such as a Niagara beater, or various refiners such as a single disc refiner can be used for dispersion.

  The concentration of the aramid pulp or the fluororesin in the dispersion is not particularly limited, but it is preferable to make the concentration as high as possible within a range not impairing the fluidity of the dispersion from the viewpoint of reducing the production cost.

  Further, in order to facilitate the deposition of the fluororesin particles in the form of aramid pulp, the fluororesin particles may be dedispersed by adding a flocculant to the aramid pulp-fluororesin dispersion. The type and amount of the flocculant may be appropriately determined according to the type of surfactant used for dispersing the fluororesin particles and the specific surface area of the aramid pulp.

  It is preferable that substantially all of the fluororesin particles in the aramid pulp-fluororesin dispersion are deposited on the aramid pulp. The “substantially total amount” means an amount obtained by subtracting the outflow amount of fluororesin particles that flows out into the wastewater only when the conductive sheet is made, so that the wastewater treatment is unnecessary. Since the fluororesin particles are expensive, the fluororesin particles are not deposited on the aramid pulp, and it is not preferable from the viewpoint of economy if it flows into the waste water. Further, when the fluororesin flows into the wastewater, a wastewater treatment operation is required, which increases the manufacturing cost.

  A slurry containing an aramid pulp, a carbon-based conductive material, and a fluororesin aggregated in the aramid pulp (hereinafter, also simply referred to as “slurry”) is obtained by adding a carbon-based slurry to the aramid pulp-fluororesin dispersion prepared as described above. It can be obtained by adding a conductive substance. The order of adding the carbon-based conductive material is not limited. Therefore, the carbon-based conductive material may be added before the fluororesin particles are deposited on the aramid pulp, or may be added after the fluororesin particles are deposited. Further, a dispersion in which the carbon-based conductive material is dispersed in advance may be added, or the carbon-based conductive material may be added to the aramid pulp-fluorine resin dispersion and then dispersed by stirring.

  What is necessary is just to select suitably the mixture ratio of an aramid pulp and a carbonaceous electroconductive substance according to the target final product. The aramid pulp / carbon-based conductive substance ratio (mass ratio) is preferably in the range of 90/10 to 10/90, and particularly preferably in the range of 85/15 to 15/85. When the aramid pulp / carbon-based conductive material ratio exceeds 90/10, it is difficult to obtain conductivity due to the carbon-based conductive material. On the other hand, when the aramid pulp / carbon-based conductive material ratio is less than 10/90, it is difficult to obtain a sufficient reinforcing effect by the aramid pulp.

  The above-mentioned burned-out substance is mixed with the slurry. What is necessary is just to select the mixture ratio of a burning-out substance suitably according to the air permeability etc. which are requested | required of the target final product. The aramid pulp / burnt substance (mass ratio) is preferably 60/40 to 3/97, and particularly preferably 50/50 to 3/97. When the aramid pulp / burnt substance ratio is higher than 60/40, the resulting sheet has insufficient air permeability, and it is difficult to improve the diffusion performance and drainage of fuel gas and fuel liquid. On the other hand, when the aramid pulp / burnt material ratio is lower than 3/97, the reinforcing effect of the sheet by the aramid pulp is insufficient.

  As a method for blending the burned-out substance into the slurry, a dispersion liquid of the burned-out substance may be blended in the slurry, or the burned-out substance may be dispersed after blended in the slurry.

  In addition, for the purpose of imparting other properties such as improving the performance of the conductive sheet, a filler such as a metal oxide, an additive, or the like can be added to the slurry.

  The slurry is prepared by the method described above. In the slurry, the content ratio of the aromatic polyamide pulp, the fluororesin, the carbon-based conductive material, and the burned-out material is 4 to 36% by mass for the aromatic polyamide pulp and 4 to 36% by mass for the fluororesin. Yes, the carbon-based conductive material is preferably 4 to 73% by mass, and the burned-out material is preferably 10 to 80% by mass.

<Conductive sheet precursor production process>
The slurry prepared as above is made to obtain a conductive sheet precursor. Paper making may be performed by a known method. For example, a long net type or a round net type paper machine can be used.

<Hot press process>
Next, the conductive sheet precursor is hot pressed in air. The temperature of the hot press is 120 to 250 ° C, preferably 140 to 230 ° C, particularly preferably 160 to 200 ° C. The pressing direction of the hot press is the thickness direction of the sheet. The contact pressure during hot pressing is 0.1 to 100 MPa, preferably 1 to 50 MPa, and particularly preferably 5 to 20 MPa. The hot pressing time is 1 to 300 minutes, preferably 2.5 to 60 minutes, and particularly preferably 5 to 30 minutes. Hot pressing can be performed by a known method.

<Baking process>
Next, the hot-pressed conductive sheet precursor is fired in an inert gas. Thereby, the fluororesin particles deposited on the aramid pulp are melted and fused to the surface of the aramid pulp. Further, the burned-out substance disappears due to thermal decomposition, and a void is formed in the sheet.

  The firing temperature is 200 to 500 ° C, preferably 230 to 430 ° C. When the firing temperature is less than 200 ° C., the fluororesin particles deposited on the aramid pulp do not melt and the resulting sheet has insufficient water repellency. When the firing temperature exceeds 500 ° C., the fluororesin is decomposed and hydrofluoric acid is generated, causing problems in the apparatus and the like.

  The firing time is 10 to 120 minutes, preferably 30 to 90 minutes.

  The firing step may be performed while applying a surface pressure to the conductive sheet. The surface pressure is 1.0 kPa or less, and preferably 0.1 to 0.5 kPa. The application of the surface pressure is performed using a known method such as application of contact pressure by contact with a batch press, intermittent press, calendar press, belt press, roller or the like.

(Use of this conductive sheet)
This conductive sheet has the diffusion mobility of the reactants required for the fuel cell electrode material, the mobility of the generated substances, and the water repellency that satisfies the drainage function of the generated water. Therefore, the conductive sheet can be used as an electrode material for a fuel cell such as a gas diffusion electrode for a solid polymer fuel cell, an electrode for a biofuel cell, or an electrode for an air zinc cell. Among them, it can be suitably used for a gas diffusion electrode for a polymer electrolyte fuel cell.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

  Each physical property was measured and evaluated by the following methods.

[Unit weight]
A 10 cm square sheet was dried at 120 ° C. for 1 hour and calculated from the mass value after drying.

[Thickness]
The thickness of the sheet was measured by applying a 1.2 N load (61.9 kPa) in the sheet thickness direction using a circular pressure plate having a diameter of 5 mm. The thickness of the 10 cm square sheet surface was divided into 9 squares (that is, divided into 9 squares of about 3.33 cm square), and the thickness measurements at the center of each of the divided surfaces were averaged. Represents a value.

[Electric resistance between surfaces]
A 50 mm square conductive sheet was sandwiched between two 50 mm square (thickness 10 mm) gold-plated electrodes. At this time, the conductive sheet and the electrode were overlapped so that their corresponding sides coincided with each other. A load of 1 MPa was applied in the thickness direction of the conductive sheet with two electrodes, and the electrical resistance value R (Ω) of the conductive sheet was measured in this state. The inter-surface electrical resistance value was calculated based on the electrical resistance value R and the measurement area.

[Air permeability]
The measurement was performed according to JIS K 3832 “Bubble point test method for microfiltration membrane elements and modules”. For the measurement, a palm porometer [manufactured by PMI (Porous Material, Inc.): trade name CFP-1100AEX] was used. The air permeability per 1 cm ² under a pressure of 100 mmH ₂ O at the time of measuring the dry flow rate was defined as the air permeability.

[Average pore diameter]
The measurement was performed according to JIS K 3832 “Bubble point test method for microfiltration membrane elements and modules”. For the measurement, a palm porometer [manufactured by PMI (Porous Material, Inc.): trade name CFP-1100AEX] was used. The pore distribution of the sheet was measured by the bubble point method using the wet flow rate and the dry flow rate, and the volume average pore diameter was calculated from this pore distribution.

[Preparation of slurry dispersion]
As a para-aromatic polyamide pulp, Twaron 1094 (product name, manufactured by Teijin Aramid BV, BET specific surface area: 13.5 m ² / g, freeness: 100 ml) is mixed with ion-exchanged water and dispersed. (Hereinafter, also referred to as “dispersion A”) was prepared.

  As a nonionic dispersion of PTFE, AD911L (product name, manufactured by Asahi Glass Co., Ltd., PTFE average particle size: 0.25 μm, containing PTFE at 60% by mass) is mixed with ion-exchanged water (hereinafter referred to as “dispersion”). B ") was prepared.

  Ketjen black EC300JD (product name, manufactured by Lion Corporation, primary particle diameter 34.0 nm) was dispersed as carbon black in ion-exchanged water to prepare a dispersion (hereinafter also referred to as “dispersion C”).

  A carbon fiber (manufactured by Toho Tenax Co., Ltd., average fiber diameter 7 μm, specific gravity 1.76) was cut to a length of 3 mm and dispersed in ion-exchanged water to prepare a dispersion (hereinafter also referred to as “dispersion D”). .

  As a burned-out substance, vinylon VPB103 (product name, manufactured by Kuraray Co., Ltd., fineness 1.1 dtex, length 3 mm cut product, thermal decomposition starting temperature 340 ° C.) is dispersed in ion-exchanged water, and a dispersion (hereinafter referred to as “dispersion E” -1 ").

  As a burned-out substance, PET fiber Teijin Tetron (product name, manufactured by Teijin Fibers Ltd., average fiber diameter 10 μm, length 5 mm cut product, thermal decomposition start temperature 430 ° C.) is dispersed in ion-exchanged water, and a dispersion (hereinafter referred to as “ Dispersion E-2 ”) was also prepared.

  As a burned-out substance, rayon (manufactured by Daiwabo Rayon Co., Ltd., fineness 2.2 dtex, thermal decomposition start temperature 340 ° C.) was dispersed in ion-exchanged water to prepare a dispersion (hereinafter also referred to as “dispersion E-3”). .

[Example 1]
(1) Preparation of slurry Dispersion B and dispersion C were mixed and stirred for 20 minutes. Thereafter, the dispersion A was added to the mixed dispersion and stirred for 20 minutes. Next, dispersion D and dispersion E-1 were added to the mixed dispersion and stirred for 3 minutes to obtain a slurry. The blending ratio of each dispersion is shown in Table 1. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion C component, and 1.06 g for the dispersion D component. The dispersion E-1 component is 2.50 g.
(2) Production of conductive sheet This slurry was subjected to wet paper making to obtain a conductive sheet precursor. This conductive sheet precursor was hot-pressed for 10 minutes under the conditions of a temperature of 180 ° C. and a pressure of 150 kgf / cm ² . Thereafter, the conductive sheet precursor was baked at 400 ° C. for 60 minutes in a nitrogen gas atmosphere to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 1.

[Example 2]
A slurry was prepared in the same manner as in Example 1 except that the blending ratio of the dispersion E-1 component, which was a burned-out substance, was increased. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. The dispersion E-1 component is 15.00 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 1.

[Example 3]
A slurry was prepared in the same manner as in Example 1 except that the burned-out material was changed from vinylon to PET fiber and the baking temperature was changed to 450 ° C. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. The dispersion E-2 component is 2.50 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 1.

[Example 4]
A slurry was prepared in the same manner as in Example 1 except that the burned-out substance was changed from vinylon to rayon. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. The dispersion E-3 component is 2.50 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 2.

[Example 5]
A slurry was prepared in the same manner as in Example 1 except that the basis weight of the conductive sheet was reduced. The solid content (pure content) of each dispersion in this slurry is 0.38 g for the dispersion A component, 0.38 g for the dispersion B component, 0.59 g for the dispersion component C, and 0.53 g for the dispersion D component. The dispersion E-1 component is 1.25 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 2.

[Comparative Example 1]
A slurry was prepared in the same manner as in Example 1 except that the dispersion E-1, which was a burned-out substance, was not blended. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. It is. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 3.

[Comparative Example 2]
A slurry was prepared in the same manner as in Example 1 except that the blending ratio of the dispersion E-1 component which was a burned-out substance was decreased. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. The dispersion E-1 is 0.42 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 3.

[Comparative Example 3]
A slurry was prepared in the same manner as in Example 1 except that the blending ratio of the dispersion E-1 component, which was a burned-out substance, was increased. The solid content (pure content) of each dispersion in this slurry is 0.75 g for the dispersion A component, 0.75 g for the dispersion B component, 1.19 g for the dispersion component C, and 1.06 g for the dispersion D component. , Dispersion E-1 is 33.75 g. By the same method as in Example 1, wet papermaking, hot pressing and firing were performed to obtain a conductive sheet. The measurement results of the physical properties of this conductive sheet are shown in Table 3.

[Comparative Example 4]
A slurry was prepared in the same manner as in Example 1 except that the basis weight of the conductive sheet was set to 20 g / m ² . The solid content (pure content) of each dispersion in this slurry is 0.25 g of the dispersion A component, 0.25 g of the dispersion B component, 0.40 g of the dispersion component C, and 0.35 g of the dispersion D component. The dispersion E-1 component is 0.83 g. Although wet papermaking was performed in the same manner as in Example 1, the sheet strength was insufficient and a conductive sheet precursor could not be produced.

The conductive sheets obtained in Examples 1 to 5 have an air permeability of 30 ml / min. -It is cm < ² > or more, and all have an electrical resistance value of 2000 m [Omega] / cm < ² > or less. Accordingly, these conductive sheets are suitable as electrode materials for fuel cells.

The conductive sheets obtained in Examples 1, 2, 4, and 5 have an inter-surface electrical resistance value of 1000 mΩ / cm ² or less. Therefore, it contributes particularly to improvement of the power generation performance of the fuel cell.

The conductive sheets obtained in Comparative Examples 1 and 2 have an air permeability of 30 ml / min. · It is cm less than ^2. In a high humidification / high current density region where air permeability is required, there is a risk of insufficient fuel gas supply. Therefore, it is not suitable as a fuel cell electrode material.

  The conductive sheet obtained in Comparative Example 3 was brittle and could not retain the sheet shape.

  In Comparative Example 4, since the basis weight was low, the conductive sheet precursor was not strong enough to make paper.

Claims (6)

A conductive sheet comprising an aromatic polyamide pulp, a fluororesin fused to the aromatic polyamide, and a carbon-based conductive material,
Air permeability is 30 to 10000 ml / min. · Cm ^2, and inter-surface conductive sheet resistance value is equal to or is 2000mΩ / cm ² or less.   The conductive sheet according to claim 1, wherein an average pore diameter measured by a bubble point method is 0.3 to 40 µm.   The conductive sheet according to claim 1 or 2, wherein the carbon-based conductive material is selected from the group consisting of graphite particles, carbon black, carbon nanotubes, carbon fibers, carbon milled fibers, carbon nanofibers, carbon nanohorns, and graphene. Aromatic polyamide pulp,
A fluororesin deposited on the aromatic polyamide pulp;
Carbon-based conductive materials,
Burnt down substances,
A slurry containing
The slurry is made to obtain a conductive sheet precursor,
In the air, the conductive sheet precursor is hot pressed at a temperature of 120 to 250 ° C. and a contact pressure of 0.1 to 50 MPa for 1 to 300 minutes,
The method for producing a conductive sheet according to claim 1, wherein firing is performed at a firing temperature of 200 to 500 ° C. in an inert gas.   The conductive sheet according to claim 4, wherein the burned-out substance is one or more selected from the group consisting of polyvinyl alcohol, polyester, polyolefin, polyamide, acrylic resin, styrene resin, cellulose, and derivatives thereof. Method.   The method for producing a conductive sheet according to claim 4 or 5, wherein the pyrolysis start temperature in the inert gas of the burned-out substance is a substance that is lower by 30 ° C or more than the firing temperature.