JP6691924B2 - Conductive porous sheet, polymer electrolyte fuel cell, and method for producing conductive porous sheet - Google Patents

Description

  The present invention relates to a conductive porous sheet, a polymer electrolyte fuel cell, and a method for manufacturing a conductive porous sheet.

  BACKGROUND ART Conventionally, a conductive porous sheet utilizes its conductivity and porosity, as a base material for a gas diffusion electrode for a fuel cell, an electrode of an electric double layer capacitor, or an electrode of a lithium ion secondary battery. Is being considered for use.

  As such a conductive porous sheet, a fiber web is prepared by mixing carbon fibers and a binder for papermaking, and the fiber web is impregnated with a thermosetting resin such as a phenol resin, and after curing, the temperature is 1000 ° C. or higher. A carbon fiber sheet produced by firing at a temperature is known. Although this carbon fiber sheet had excellent conductivity, it had a small surface area because the fibers were bonded together using a thermosetting resin such as phenol resin.

As a conductive porous body capable of solving such a problem, the applicant of the present application has stated that “a conductive material in which fibrous substances having a first conductive material and a second conductive material connecting the first conductive material are aggregated together. It is a porous body, and the conductive porous body has a specific surface area of 100 m ² / g or more and a thickness maintenance rate after applying a pressure of 2 MPa of 60% or more. Document 1) was proposed. Although this conductive porous body had a large specific surface area, it was inferior in flexibility such as breaking by a slight bending and inferior in handling property.

  As a carbon fiber nonwoven fabric having improved handling properties, a non-woven fabric obtained by electrospinning a composition containing a polymer substance capable of electrospinning, an organic compound different from the polymer substance, and a transition metal is used. A flexible carbon fiber non-woven fabric characterized by being carbonized. "(Patent Document 2). Although this carbon fiber nonwoven fabric was certainly flexible, it was inferior in mechanical strength and electroconductivity.

International Publication No. 2015/146984 International Publication No. 2011/070893

  The present invention has been made under such circumstances, with an excellent handling property due to excellent flexibility, a conductive porous sheet having excellent mechanical strength and conductivity, and a method for producing the same. To do. Moreover, it aims at providing the polymer electrolyte fuel cell using this electroconductive porous sheet.

The present invention is
[1] A conductive porous sheet, which is mainly composed of carbon fibers, wherein the carbon fibers are bonded at intersections, and the conductive porous sheet does not break in a three-point bending test,
[2] The conductive porous sheet according to [1], wherein the carbon fiber is curved.
[3] A conductive porous sheet according to [1] or [2], which has a breaking strength of 0.30 MPa or more,
[4] The conductive porous sheet according to any one of [1] to [3], which is used as a base material for electrodes.
[5] A polymer electrolyte fuel cell, comprising the conductive porous sheet according to any one of [1] to [4] as a substrate for a gas diffusion electrode,
[6] A step of forming a precursor fiber that includes a first carbonizable organic material and a second carbonizable organic material that is an organic material different from the first carbonizable organic material, and the first carbonization can be performed at an intersection of the precursor fibers A step of forming a precursor fiber sheet mainly composed of precursor fibers by joining with an organic material or a second carbonizable organic material; carbonizing the precursor fibers constituting the precursor fiber sheet in a state of being joined at their intersections The present invention relates to a method for producing a conductive porous sheet that does not break in a three-point bending test, including a step of forming a curved carbon fiber.

  The conductive porous sheet of [1] of the present invention has flexibility that does not break even in a three-point bending test, and thus is excellent in handleability. Further, since the carbon fibers are joined at the intersections, not only the mechanical strength is excellent, but also the conductivity is excellent.

  In the conductive porous sheet of [2] of the present invention, since the carbon fiber is curved, when the conductive porous sheet is bent, the curved portion of the carbon fiber is stretched, which is excellent in flexibility. Since the curved portion of the carbon fiber is simply stretched, the crossing point where the carbon fibers are joined is not easily broken, so that it is difficult to break when bent.

  The conductive porous sheet [3] of the present invention has excellent mechanical strength with a breaking strength of 0.30 MPa or more.

  Since the conductive porous sheet of [4] of the present invention is excellent in flexibility, mechanical strength and conductivity, it can exhibit excellent electrode performance when used as a base material for electrodes.

  The polymer electrolyte fuel cell of [5] of the present invention includes the conductive porous sheet as a gas diffusion electrode substrate. The conductive porous sheet is excellent in conductivity and mechanical strength, and further has excellent flexibility that is hard to break even when bent, and is hard to be broken even when stretched by swelling and shrinking of the solid polymer film. , Can generate stable power generation performance.

  In the method for manufacturing a conductive porous sheet according to [6] of the present invention, after joining the intersections of the precursor fibers, the precursor is carbonized in the joined state at the intersections to form curved carbon fibers. It is possible to manufacture a conductive porous sheet having excellent mechanical strength and conductivity.

Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Example 1. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Example 2. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Example 3. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Example 4. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 1. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 2. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 3. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 4. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 5. Electron micrograph (2000 times) of the main surface of the conductive porous sheet of Comparative Example 6. Electron micrograph (50,000 times) showing the state of joining at the intersection of carbon fibers Electron micrograph (50,000 times) showing the state where the intersections of carbon fibers are not joined

  Since the conductive porous sheet of the present invention is mainly composed of carbon fibers and is bonded at the intersections of the carbon fibers, it has excellent mechanical strength and conductivity. In addition, since it has the flexibility not to break in the three-point bending test, it is excellent in handleability.

  The carbon fiber used in the present invention can be, for example, a PAN-based carbon fiber. In addition, the carbon fiber can include a conductive material. When the conductive material is contained in this way, the conductivity and mechanical strength are more excellent, which is preferable. Such conductive materials include, for example, fullerenes, carbon nanotubes, carbon nanohorns, graphite, graphene, vapor grown carbon fibers, carbon black, metals (eg, gold, platinum, titanium, nickel, aluminum, silver, zinc, iron). , Copper, manganese, cobalt, stainless steel, etc.), and one or more selected from the group of metal oxides of the above metals. Among these, carbon nanotubes are preferable because they are excellent in conductivity, more easily aligned in the length direction in the carbon fiber, and can enhance conductivity and mechanical strength. Furthermore, when carbonized, a difference occurs between the shrinkage rate in the portion where the carbon nanotubes are present and the shrinkage rate in the portion where the carbon nanotubes are not present, and it tends to be a curved carbon fiber. It is preferable to contain the carbon nanotubes because the curved portion is easily stretched when bent and is excellent in flexibility. The suitable carbon nanotube may be a single-wall carbon nanotube, a multi-wall carbon nanotube, or a coiled carbon nanotube.

  The size of the suitable conductive material is not particularly limited, but when the conductive material is in the form of particles, the average particle size is preferably 5 nm to 50 μm so that carbon fibers are easily formed, The thickness is more preferably 20 nm to 25 μm, further preferably 30 nm to 10 μm. The above lower limits and the respective upper limits can be arbitrarily combined as desired. This "average particle size" basically represents the number average particle size of particles obtained from a particle size distribution meter by the dynamic light scattering method, but for example, a state called aggregate or structure of carbon black or the like was formed. When it is difficult to measure the particles by the above-mentioned dynamic light scattering method, an electron micrograph of the particles is taken, and the arithmetic average value of the diameters of 50 particles shown in the electron micrograph is taken as the average particle size. .. In this case, when the shape of the particle is non-circular on the photograph, the diameter of the circle having the same area as the area of the particle on the photograph is regarded as the diameter of the particle.

  When the conductive material has a fiber shape, the fiber diameter is preferably 10 nm to 5000 nm, more preferably 10 nm to 1000 nm, even more preferably 10 nm to 500 nm, further preferably 10 nm to 250 nm. It is more preferable that there is. The above lower limits and the respective upper limits can be arbitrarily combined as desired. The fiber length is preferably a fiber length having an aspect ratio of 1000 or less, more preferably 500 or less, so that the fiber length is easily dispersed in the carbon fiber.

  When the carbon fiber contains a conductive material as described above, the amount of the conductive material is not particularly limited, but in order to have excellent conductivity, mechanical strength and flexibility, 1 mass in the carbon fiber is used. % Or more, preferably 5 mass% or more, more preferably 10 mass% or more. On the other hand, since the flexibility tends to be low, the content is preferably 80% by mass or less, more preferably 50% by mass or less, and further preferably 40% by mass or less. The above lower limits and the respective upper limits can be arbitrarily combined as desired.

  The carbon fiber of the present invention is preferably curved regardless of whether it contains a conductive material or not. When the carbon fiber is curved, even if the carbon fibers are bonded at the intersection, when the conductive porous sheet is bent, the curved portion of the carbon fiber is stretched, which is excellent in flexibility. This is because the intersection of the carbon fibers joined together is less likely to be broken just by extending the curved portion of the carbon fiber, and thus is less likely to be broken when bent.

  It is preferable that the carbon fiber of the present invention is excellent in mechanical strength and conductivity when there are no voids inside the fiber. The phrase “there are no voids inside the fiber” means that the cross section of the conductive porous sheet in the thickness direction has a continuous contour, and the entire cross section of the carbon fiber whose cross-sectional shape is clear is 1 to 3 Observation of carbon fibers in the visual field was carried out at 10 locations, and it means that the number of carbon fibers in which voids are not observed is 70% or more. Incidentally, the carbon fiber contains a conductive material as described above, when the conductive porous sheet is cut in the thickness direction, the voids that are apparently formed by dropping the conductive material are Not included. Even if the conductive material itself is porous and contains voids, the conductive material is discontinuous and has a small effect on the mechanical strength of the carbon fiber, so the carbon fiber contains the conductive material containing voids. However, it is considered that there is no void inside the fiber. Incidentally, the carbon fiber is preferably a carbon fiber mainly composed of a conductive porous sheet "there is no void inside the fiber", that is, the carbon fiber joined at the intersection is "there is no void inside the fiber", Since carbon fibers which are not joined have little influence on the mechanical strength of the conductive porous sheet, there may or may not be voids inside the fibers.

  The average fiber diameter of the carbon fiber of the present invention is not particularly limited, but is preferably 50 μm or less, more preferably 30 μm or less, and further preferably 20 μm or less. This is because when the average fiber diameter exceeds 50 μm, the number of contact points between carbon fibers in the conductive porous sheet is small, and the mechanical strength and conductivity of the conductive porous sheet tend to be poor. The lower limit of the average fiber diameter of the carbon fibers is not particularly limited, but it is realistically 0.1 μm or more. The above lower limit and each upper limit can be arbitrarily combined as desired.

  The "average fiber diameter" in the present invention means the arithmetic average value of the fiber diameters at 40 points of the carbon fiber, and the "fiber diameter" is the width orthogonal to the length direction when observing the carbon fiber in a micrograph. is there.

  The carbon fibers are preferably continuous so as to have excellent conductivity. Such continuous carbon fibers are obtained by, for example, spinning a continuous precursor fiber by an electrostatic spinning method or a spunbond method using a spinning solution containing a carbonizable organic material, and then carbonizing the carbonizable organic material. Can be manufactured.

  Although the conductive porous sheet of the present invention is mainly composed of carbon fibers, it can be composed of two or more kinds of carbon fibers. For example, presence / absence of conductive material, difference in conductive material (type, shape, size, length, etc.), difference in content of conductive material, presence / absence of voids in carbon fiber, average fiber diameter, fiber length, etc. It can be composed of two or more kinds of carbon fibers that differ in at least one point.

  Since the conductive porous sheet of the present invention is mainly composed of the carbon fiber as described above, it has excellent conductivity. The "main body" in the present invention means that the carbon fibers occupy 50 mass% or more of the conductive porous sheet, but the higher the proportion of the carbon fibers, the more excellent the conductivity is. The porous sheet preferably occupies 70 mass% or more, more preferably 90 mass% or more, and most preferably 100 mass% carbon fiber.

  In addition to carbon fibers, examples of materials that can be used to form the conductive porous sheet include fullerenes, carbon nanotubes, carbon nanohorns, graphite, graphene, vapor grown carbon fibers, carbon black, and fine particles of metal or metal oxides; rayon. , Recycled fibers such as polynosic and cupra, semi-synthetic fibers such as acetate fibers, nylon fibers, vinylon fibers, fluorine fibers, polyvinyl chloride fibers, polyester fibers, acrylic fibers, polyethylene fibers, polyolefin fibers or polyurethane fibers, and other synthetic fibers, Inorganic fibers such as glass fibers and ceramic fibers, plant fibers such as cotton and hemp, animal fibers such as wool and silk; activated carbon powder (for example, steam activated carbon, alkali-treated activated carbon, acid-treated activated carbon), inorganic particles (for example, , Manganese dioxide, Iron oxide, copper oxide, nickel oxide, cobalt oxide, zinc oxide, titanium-containing oxide, zeolite, catalyst-supporting ceramics, silica, etc.), ion-exchange resin powder, plant seeds and other non-conductive materials; it can.

  The conductive porous sheet of the present invention is excellent in mechanical strength and conductivity because the carbon fibers are bonded at the intersections. In addition, it is preferable that the carbon fibers are bonded to each other by using a carbide of an organic material so that the carbon fibers are excellent in adhesion and the conductivity is excellent. For example, an organic fiber containing two or more kinds of carbonizable organic materials is used, and the organic fibers are bonded by one or more kinds of carbonizable organic material and then carbonized, so that the carbon fibers are bonded at an intersection. It can be a porous sheet.

  The state in which such carbon fibers are joined at the intersection can be confirmed by an electron micrograph. For example, FIG. 11 is an electron micrograph (50000 times) of the main surface of the conductive porous sheet, which confirms that the carbon fibers are bonded to each other because a water-like film can be observed at the intersections of the carbon fibers. it can. On the other hand, FIG. 12 is an electron micrograph (50000 times) of the main surface of the conductive porous sheet, but it is not possible to observe the web-like film at the intersection of the carbon fibers. Can be confirmed.

  As long as the conductive porous sheet of the present invention is mainly composed of carbon fibers, it may have a single-layer structure or may have a multi-layer structure of two or more layers, and the content ratio of carbon fibers gradually increases. It may change. For example, it may have a multilayer structure having two or more layers made of carbon fibers having different fiber diameters.

  Further, the carbon fiber abundance ratio may be different on the main surface of the conductive porous sheet. For example, on the main surface of the conductive porous sheet, there is a region mainly composed of carbon fibers having a small fiber diameter and a region mainly composed of carbon fibers having a large fiber diameter, and any one of the regions has a dot shape, a linear shape and a It may have a curved shape (circular shape, etc.). Furthermore, the abundance ratio of carbon fibers may be gradually changed on the main surface of the conductive porous sheet.

  The form of the conductive porous sheet of the present invention is not particularly limited, but may be, for example, a non-woven fabric form in which fibers are randomly oriented, or a woven or knitted form in which fibers are regularly oriented. In particular, the non-woven fabric form is preferable because it has many intersections between carbon fibers, is excellent in conductivity, has fine voids, and has a high porosity, and is preferably the non-woven fabric form only.

The conductive porous sheet of the present invention is mainly composed of the carbon fiber as described above, but has the flexibility not to be broken in the three-point bending test and is excellent in the handling property. The "three-point bending test" in the present invention is performed by the following procedure using a load-displacement measuring unit (made by Imada Co., Ltd., FSA-1KE-5N + GA-10N).
(1) The conductive porous sheet was cut, and 5 test pieces (flow direction test pieces) of 50 mm (flow direction during manufacturing of the conductive porous sheet) x 10 mm [width direction (direction orthogonal to the flow direction)] were cut. And 50 mm [width direction] × 10 mm (flow direction during production of the conductive porous sheet) test pieces (width direction test pieces) are sampled.
(2) The fulcrums are arranged so that the distance between the metal rod-shaped fulcrums having the rounded ends of 2 ± 0.2 mm is 16 mm.
(3) The test piece is arranged so as to straddle the fulcrums.
(4) A rod-shaped metallic pressure wedge having a roundness of 5 ± 0.1 mm at its tip was applied to the center portion between the fulcrums of the test piece (a point 8 mm from one fulcrum) at a speed of 1 mm / min. Then, it is pushed from above the test piece into the fulcrum until the distance between the initial position of the upper surface or the lower surface of the test piece and the bent position becomes 4 mm. At this time, the indentation length and the stress are sequentially measured, and when the stress drops rapidly, the indentation length at this time is defined as the bending deflection amount (mm). If the stress does not drop sharply even when pushed to 4 mm, the bending deflection amount is judged to be over 4 mm. (5) The bending deflection amount is measured for each of the five flow direction test pieces and the five width direction test pieces, and the maximum bending bending amount and the minimum value among the five flow direction test pieces are shown. The arithmetic mean value of the three flow direction test pieces excluding the bending deflection amount, and the three pieces excluding the bending deflection amount showing the maximum value and the bending deflection amount showing the minimum value among the five width direction test pieces The arithmetic mean value of the three widthwise test pieces is calculated. As a result, a larger value of the arithmetic mean value of the bending deflection amount is adopted as the "bending deflection amount".
(6) When the bending deflection amount exceeds 4 mm, it is determined that the conductive porous sheet of the test piece is “not broken”.

The basis weight of the conductive porous sheet of the present invention is not particularly limited, but the basis weight is preferably 0.5 to 500 g / m ² , and preferably 1 to 400 g so as to have excellent mechanical strength and conductivity. more preferably from / ^{m 2,} more preferably in the range of 5~300g / ^{m 2,} and even more preferably 5 to 200 g / ^{m 2.} The thickness is not particularly limited, but is preferably 1 to 2000 μm, more preferably 3 to 1000 μm, further preferably 5 to 500 μm, and further preferably 10 to 300 μm. In addition, each lower limit and each upper limit in the above basis weight and thickness can be arbitrarily combined as desired. The "unit weight" in the present invention is a value obtained by measuring the mass of a sample obtained by cutting a conductive porous sheet into 10 cm square pieces, and converting the mass into a mass of 1 m ² , and "thickness" is a thickness gauge. (Manufactured by Mitutoyo Corporation: Code No. 547-401: measuring force of 3.5 N or less).

Conductive porous sheet of the invention are excellent in electrical conductivity, the degree is preferably an electric resistance of 20 m [Omega · cm ² or less, more preferably at 15mΩ · cm ² or less, 10 m [Omega · cm ² less more preferably in the range, further preferably at 8mΩ · cm ² or less, and even more preferably 6mΩ · cm ² or less. This "electrical resistance" is obtained by sandwiching a conductive porous sheet (25 cm ² ) cut into 5 cm squares from both sides with gold-plated metal plates, and applying a current of 1 A (2 A) under pressure in the stacking direction of the metal plates at 2 MPa. The voltage (V) is measured while I) is applied. Subsequently, it is a value obtained by calculating the resistance (R = V / I) and further multiplying it by the area (25 cm ² ) of the conductive porous sheet.

  Further, the conductive porous sheet of the present invention is excellent in mechanical strength, but the breaking strength thereof is preferably 0.30 MPa or more, more preferably 0.40 MPa or more, and 0.50 MPa. More preferably, it is more preferably 0.60 MPa or more. This breaking strength is the quotient obtained by dividing the breaking load by the cross-sectional area of the conductive porous sheet, the breaking load is the value measured under the following conditions, and the cross-sectional area is the width of the conductive porous sheet (test piece) at the time of measurement. And the value obtained from the product of thickness. The breaking load was measured for 10 flow direction test pieces and 10 width direction test pieces, and the arithmetic mean value of the 20 test pieces was taken as the breaking load.

Test piece: 50 mm (flow direction at the time of manufacturing the test piece) x 5 mm [width direction (direction orthogonal to the flow direction)] 10 test pieces (flow direction test piece), 50 mm [width direction] x 5 mm (test piece Of 10 pieces in the flow direction at the time of manufacturing) (width-direction test piece)
Distance between chucks: 20 mm
Tensile speed: 20 mm / min.

The conductive porous sheet of the present invention is mainly composed of carbon fiber, but it is preferable that the relative apparent Young's modulus is 100 [MPa / (g / cm ³ )] or more. High relative apparent Young's modulus means high rigidity, and since it is a conductive porous sheet with high rigidity, it has excellent dimensional stability, and it is easy to handle by itself and rolled into a roll shape. It has the advantage that it can be stored and transported. For example, when such a conductive porous sheet having a high relative Young's modulus is used as a base material for an electrode of a polymer electrolyte fuel cell, it is possible to suppress swelling and shrinkage of the polymer solid membrane, so that the solid polymer It is possible to prevent cracks due to swelling and contraction of the molecular film.

The specific apparent Young's modulus is a value obtained by dividing the apparent Young's modulus, which is an index of the rigidity of the conductive porous sheet, by the apparent density of the conductive porous sheet, as can be understood from the measuring method described later. .. In other words, even if the apparent Young's modulus is the same, it is said that when the apparent density is high and when the apparent density is low, the lower apparent density has the same apparent Young's modulus even though the amount of carbon fibers is smaller. This means that the rigidity of each carbon fiber is high, and therefore, the apparent Young's modulus of the conductive porous sheet is expressed by the relative apparent Young's modulus which is a value obtained by dividing the apparent Young's modulus by the apparent density. ing. Since the higher the relative apparent Young's modulus is, the higher the rigidity of each carbon fiber is, the pressure is more preferably 200 [MPa / (g / cm ³ )] or more, and 300 [MPa / (g / cm ³ )]. More preferably, it is more preferably 400 [MPa / (g / cm ³ )] or more, still more preferably 500 [MPa / (g / cm ³ )] or more, 550 [MPa / (G / cm ³ )] or more, more preferably 600 [MPa / (g / cm ³ )] or more. On the other hand, when the relative apparent Young's modulus is too high, the rigidity of the carbon fiber is too high, which may have an adverse effect such as damage to the solid polymer membrane. Therefore, 2000 [MPa / (g / cm ³ )] The following is preferable. The above-mentioned lower and upper limits can be arbitrarily combined if desired.

The "specific apparent Young's modulus" is a value obtained by the following procedure.
(1) The apparent density (g / cm ³ ) is calculated by dividing the basis weight (g / cm ² ) of the conductive porous sheet to be evaluated by the thickness (cm).
(2) 10 pieces of vertical direction test pieces obtained by cutting the conductive porous sheet into a rectangular shape having a size of 50 mm in the flow direction at the time of manufacturing the conductive porous sheet and 5 mm in the width direction (direction orthogonal to the flow direction), Also, 10 transverse direction test pieces cut into a rectangular shape of 50 mm in the width direction and 5 mm in the flow direction are collected.
(3) The tensile shear test of each of the test pieces was performed by using a small tensile tester (TSM-41-cre manufactured by Search Co.) with a chuck distance of 20 mm and a pulling speed of 20 mm / min. Under the conditions of, draw a load-elongation curve for each.
(4) The load (N) at the maximum load change point (maximum tangent angle) near the origin in each load-elongation curve (the maximum point of the tangent angle) is taken as the cross-sectional area [thickness of the test piece before the tensile shear test. (T) × 5] (unit: mm ² ) to calculate the tensile stress (MPa).
(5) The apparent Young's modulus is obtained by dividing the tensile stress by the strain (dimensionless) at the maximum point [extension length (mm) of test piece / initial test piece length (mm)].
(6) The arithmetic average value of the apparent Young's moduli of 20 test pieces is calculated to be the "average apparent Young's modulus".
(7) The "average apparent Young's modulus" is calculated by dividing the average apparent Young's modulus by the apparent density.

  Further, when the conductive porous sheet of the present invention is used as a gas diffusion electrode substrate of a polymer electrolyte fuel cell and a gas diffusion layer is formed, when the surface smoothness is low, a conductive porous sheet is obtained. The conductive porous sheet may pierce the other material (in the case of a solid polymer fuel cell, a solid polymer membrane in the case of contact), which may damage the other material. In the case of a solid fuel cell, a gap is created between the solid polymer membrane and / or the separator) and the conductive porous sheet, resulting in poor adhesion. , Power generation performance) tends to be difficult to exert. Therefore, the surface of the conductive porous sheet is preferably smooth so that other materials are less likely to be damaged and sufficient performance can be easily exhibited. Specifically, the “average arithmetic average surface roughness” on the main surface of the conductive porous sheet is preferably 0.01 μm to 20 μm, more preferably 0.1 μm to 10 μm, and 0.1 μm to 5 μm. Is more preferable, and 0.1 to 4 μm is further preferable. The above lower limits and the respective upper limits can be arbitrarily combined as desired. This "average arithmetic average surface roughness" is obtained by cutting a conductive porous sheet into 5 cm square pieces to prepare a sample, and measuring a roughness (three-dimensional) parameter according to ISO25178 with a laser microscope (Olympus OLS4100). After measuring the arithmetic mean surface roughness (Sa) for each of the five evaluation regions (260 μm × 260 μm) in the sample, the value obtained by further averaging the values of each arithmetic mean surface roughness (Sa) is meant. To do.

  Further, the conductive porous sheet of the present invention preferably has a porosity of 50% or more so that the voids can be effectively utilized. When a conductive porous sheet having such a porosity is used as an electrode base material of a polymer electrolyte fuel cell, for example, a fuel cell having excellent drainage and gas diffusibility and high power generation performance can be manufactured. Since the higher the porosity is, the more the voids are, and the voids can be utilized more effectively, the porosity is more preferably 60% or more, further preferably 70% or more, and 80% or more. Is more preferable, and 90% or more is further preferable. On the other hand, if it exceeds 99%, the morphological stability of the conductive porous sheet tends to be extremely lowered, so that it is preferably 99% or less. The above-mentioned lower and upper limits can be arbitrarily combined if desired.

The porosity P (unit:%) is a value obtained from the following equation.
P = 100- (Fr1 + Fr2 + ... + Frn)
Here, Frn represents the filling rate (unit:%) of the component n that constitutes the conductive porous sheet, and is a value obtained from the following formula.
Frn = [M × Prn / (T × SGn)] × 100
Here, M is the mass per unit of the conductive porous sheet (unit: g / cm ² ), T is the thickness of the conductive porous sheet (cm), Prn is the component n in the conductive porous sheet (for example, carbon fiber). ), SGn means the specific gravity (unit: g / cm ³ ) of the component n.

  Since the conductive porous sheet of the present invention is not only excellent in mechanical strength and conductivity, but also flexible and excellent in handleability, it can be suitably used as a substrate for electrodes. For example, when used as an electrode of a lithium ion secondary battery or an electric double layer capacitor, a secondary battery or capacitor having a large capacity can be manufactured. Further, when used as a base material for a gas diffusion electrode of a polymer electrolyte fuel cell, a polymer electrolyte fuel cell capable of exhibiting excellent power generation performance can be produced.

  Thus, when the conductive porous sheet of the present invention is provided as a substrate for a gas diffusion electrode of a polymer electrolyte fuel cell, since the conductive porous sheet of the present invention is porous, voids between carbon fibers are present. If nothing is filled in, the material is excellent in the drainage property in the thickness direction and the surface direction of the gas diffusion electrode substrate (conductive porous sheet) and also in the diffusibility of the supplied gas.

  When the voids between the carbon fibers of the gas diffusion electrode substrate (conductive porous sheet) contain a fluororesin and / or carbon, the former fluororesin causes the liquid water to flow. Since it is easily extruded, it has excellent drainage properties, and since it contains the latter carbon, it has excellent conductivity.

  Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), and tetrafluorine. Ethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride / tetrafluoroethylene / hexafluoro Examples thereof include a propylene copolymer, and a copolymer of various monomers constituting the resin.

  Examples of carbon include carbon fibers, fullerenes, carbon nanotubes, carbon nanohorns, graphite, graphene, vapor grown carbon fibers, and carbon black.

  The polymer electrolyte fuel cell of the present invention can be exactly the same as the conventional polymer electrolyte fuel cell except that the above-mentioned conductive porous sheet is provided as the substrate for the gas diffusion electrode. That is, a cell in which a bonded body of a gas diffusion electrode having a catalyst supported on the surface of a gas diffusion electrode substrate (conductive porous sheet) as described above and a solid polymer membrane is sandwiched between a pair of bipolar plates. It has a structure in which a plurality of units are laminated.

  Such a conductive porous sheet of the present invention is a step of forming a precursor fiber containing, for example, a first carbonizable organic material and a second carbonizable organic material composed of an organic material different from the first carbonizable organic material. A step of joining a cross point of the precursor fiber with a first carbonizable organic material or a second carbonizable organic material to form a precursor fiber sheet mainly composed of the precursor fiber, and a precursor fiber constituting the precursor fiber sheet, A conductive porous sheet that does not break in the three-point bending test can be manufactured by the step of carbonizing the bonded carbon fibers at the intersections to form curved carbon fibers. According to this manufacturing method, after joining the intersections of the precursor fibers, since the carbon fibers are carbonized in the joined state at the intersections to form curved carbon fibers, flexibility, mechanical strength, and excellent conductivity Perforated sheets can be manufactured.

  More specifically, first, a first carbonizable organic material and a second carbonizable organic material made of an organic material different from the first carbonizable organic material are prepared. The first carbonizable organic material and the second carbonizable organic material are not particularly limited, and examples thereof include phenol resin, urea resin, melamine resin, unsaturated polyester resin, epoxy resin, xylene resin, urethane resin, silicone. Resin, thermosetting polyimide resin, thermosetting polyimide resin, thermosetting resin such as thermosetting polyamide resin; polystyrene resin, polyester resin, polyolefin resin, polyimide resin, polyamide resin, polyamideimide resin, polyvinyl acetate resin, Thermoplastic resins such as vinyl chloride resin, fluororesin, polyacrylonitrile resin, acrylic resin, polyether resin, polyvinyl alcohol, polyvinylpyrrolidone, pitch, polyamino acid resin, polybenzimidazole resin; cellulose (polysaccharide), tar; Mention may be made of a copolymer of a monomer of the resin component (e.g., acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer).

  Among these, it is preferable that the first carbonizable organic material or the second carbonizable organic material contains a thermosetting resin. When the thermosetting resin is contained, as described below, the intersections of the precursor fibers containing the first carbonizable organic material and the second carbonizable organic material are joined by the thermosetting resin, and at the time of carbonization, This is because it is easy to maintain the joined state. In particular, a phenol resin and / or an epoxy resin is preferable because it has excellent conductivity after carbonization in addition to the above-mentioned action.

  Further, as the first carbonizable organic material or the second carbonizable organic material, it is preferable to use a carbonizable organic material having a carbonization process or a carbonization rate different from that of the thermosetting resin. That is, by including the first or second carbonizable organic material having a different carbonization process, not only the spinnability is improved, but also the chemical change mechanism (optimum temperature, time, decomposition, etc.) in the carbonization process is different, This is because a difference in contraction rate, fluidity and the like causes a curve at the time of carbonization to easily form a curved carbon fiber. For example, a thermosetting resin such as a phenol resin and / or an epoxy resin as the first carbonizable organic material or the second carbonizable organic material, and a polyacrylonitrile resin as the second carbonizable organic material or the first carbonizable organic material. When a thermoplastic resin such as pitch is used, since the shrinkage rate at the time of carbonization is different, curved carbon fibers can be formed. In particular, the polyacrylonitrile resin has a high carbonization rate and easily forms a carbon fiber having no voids inside the fiber, and thus is suitable as the first carbonizable organic material or the second carbonizable organic material.

  In addition, it is preferable to prepare a conductive material so that the carbon fiber has excellent conductivity and mechanical strength, and that the carbon fiber can be easily formed. The conductive material may be the conductive material described above, and is preferably carbon nanotube. That is, at the time of carbonization, a difference occurs between the shrinkage rate in the portion where the carbon nanotubes are present and the shrinkage rate in the portion where the carbon nanotubes are not present, and it tends to become a curved carbon fiber. It has excellent flexibility because the curved part is easily stretched even when bent.

  In addition to the first carbonizable organic material or the second carbonizable organic material as described above, silicone such as polydimethylsiloxane or metal alkoxide (methoxide such as silicon, aluminum, titanium, zirconium, boron, tin or zinc). , Ethoxide, propoxide, butoxide, etc.) can be used in combination.

  After preparing the materials as described above, a spinning solution containing the first carbonizable organic material and the second carbonizable organic material as described above is prepared to form a precursor fiber. Preferably, a spinning solution that also contains a conductive material is prepared. In some cases, a spinning solution containing silicone and an inorganic polymer is prepared.

  The solvent that constitutes the spinning solution is not particularly limited as long as it is a solvent that can dissolve the first carbonizable organic material and the second carbonizable organic material, and examples thereof include acetone, methanol, ethanol, propanol, and isopropanol. , Tetrahydrofuran, dimethylsulfoxide, 1,4-dioxane, pyridine, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, formic acid, toluene, benzene, cyclohexane, cyclohexanone, tetrachloride Carbon, methylene chloride, chloroform, trichloroethane, ethylene carbonate, diethyl carbonate, propylene carbonate, water and the like can be mentioned, and they can be a single solvent or a mixed solvent of these solvents. In addition, a poor solvent can be added as long as the spinnability is not a problem.

  The solid content concentration in the spinning solution is not particularly limited, but is preferably 1 to 50 mass%, more preferably 5 to 30 mass%. This is because if it is less than 1 mass%, the productivity is extremely reduced, and if it exceeds 50 mass%, spinning tends to be unstable. The above lower limits and the respective upper limits can be arbitrarily combined as desired.

  Further, since the solid content mass ratio of the first carbonizable organic material and the second carbonizable organic material in the spinning solution varies depending on the combination of the first carbonizable organic material and the second carbonizable organic material, it is not particularly limited. However, for example, when the first carbonizable organic material is a high carbonization organic material such as polyacrylonitrile resin and the second carbonizable organic material is a thermosetting resin such as epoxy resin, The first carbonizable organic material and the second carbonizable organic material are excellent in electrical conductivity, and the second carbonizable organic material has excellent mechanical strength, electrical conductivity, and flexibility due to bending. The solid content ratio with the 2 carbonizable organic material is preferably 40 to 90:60 to 10, more preferably 50 to 80:50 to 20, and more preferably 50 to 70:50 to 30. There further preferred. The above lower limits and the respective upper limits can be arbitrarily combined as desired.

  In addition to the first carbonizable organic material and the second carbonizable organic material, when a suitable conductive material is contained, the first carbonizable organic material and 2 It is preferable to include a conductive material in a mass of 1 to 90, more preferably to include a conductive material in a mass of 5 to 50, more preferably 10 to 100 based on the total mass of solid content of the carbonizable organic material. It is more preferred to include a mass of conductive material of -40. The above lower limits and the respective upper limits can be arbitrarily combined as desired.

  Then, a spinning solution containing the first carbonizable organic material and the second carbonizable organic material as described above is spun to form a precursor fiber. As a method for forming this precursor fiber, for example, a dry spinning method, an electrostatic spinning method, and a gas parallel to a spinning solution discharged from a liquid discharging section as disclosed in JP-A-2009-287138. And a spinning solution is applied with a linear shearing force to form a fiber. Among these, the electrostatic spinning method or the spinning method disclosed in JP-A-2009-287138 is preferable because it is easy to spin a precursor fiber having an average fiber diameter of 3 μm or less and a small fiber diameter. Further, the dry spinning method or the electrostatic spinning method is preferable because continuous precursor fibers can be spun. In particular, the electrospinning method is suitable because the precursor fiber having a continuous fiber length can be spun in addition to the small fiber diameter. The precursor fiber spun by the above-described method can be directly collected by the collector to form a sheet-shaped precursor fiber.

  The “precursor fiber” in the present invention means a fiber in a state where neither the first carbonizable organic material nor the second carbonizable organic material is carbonized, and the first carbonizable organic material and the second carbonizable organic material. Since all of the possible organic materials are carbonized to form carbon fibers, they are referred to as precursor fibers in the sense of fibers that are the basis of carbon fibers.

  After forming the precursor fibers in this way, the intersections of the precursor fibers are joined with the first carbonizable organic material or the second carbonizable organic material to form a precursor fiber sheet mainly composed of the precursor fibers. Therefore, first, a sheet in which precursor fibers are assembled is formed. The sheet in which the precursor fibers are gathered can be formed, for example, by directly collecting the spun precursor fibers with a collector, and the spun precursor fibers are wound as continuous fibers and then cut into a desired fiber length. After forming into short fibers, it can be formed by a dry method such as a card method, an air-laying method, or a wet method, or can be formed by weaving or knitting by a conventional method using continuous precursor fibers. You can also Among these, the method of directly collecting the spun precursor fiber with a collector is preferable because it can be a precursor fiber having a continuous fiber length and is excellent in productivity.

  The intersections of the precursor fibers forming the sheet in which the precursor fibers are assembled are joined with the first carbonizable organic material or the second carbonizable organic material. This joining method is not particularly limited. For example, as described above, when the first carbonizable organic material or the second carbonizable organic material contains a thermosetting resin, the thermosetting resin is To cure, a heat treatment can be performed at the temperature at which the thermosetting resin is thermoset to bond. Since the thermosetting conditions such as the heat treatment temperature and the time vary depending on the thermosetting resin, they are appropriately adjusted according to the thermosetting resin. Further, a solvent capable of dissolving the first carbonizable organic material or the second carbonizable organic material was applied to the sheet in which the precursor fibers were assembled to dissolve the first carbonizable organic material or the second carbonizable organic material. After that, the solvent can be dried and removed to bond. Since the plasticizing joining conditions such as the kind of the solvent, the amount of the solvent applied, the solvent temperature, the drying temperature, and the drying time are different depending on the first carbonizable organic material or the second carbonizable organic material, 2 It is appropriately adjusted depending on the carbonizable organic material.

  Although it is possible to bond the intersections of the precursor fibers with a binder, when the binder is used, the binder fills the voids formed by the precursor fibers, or the binder needs to be around the intersections of the precursor fibers. Since there is a case in which the voids of the conductive porous sheet obtained as a result are covered with the above, and the resulting voids cannot be fully utilized, it is preferable to bond them by the first carbonizable organic material or the second carbonizable organic material forming the precursor fiber. preferable. For example, when a conductive porous sheet is used as a substrate for a gas diffusion electrode, gas or liquid water permeability tends to decrease.

  The precursor fiber sheet mainly composed of the precursor fiber can be formed by the method as described above. However, when a material other than the precursor fiber is contained, when the precursor fiber is spun, a sheet in which the precursor fiber is assembled is formed. A material other than the precursor fibers can be applied when forming the sheet or after forming the sheet in which the precursor fibers are assembled. For example, a carbon fiber nanotube-mixed precursor fiber sheet can be formed by spraying carbon nanotubes onto a stream of spun precursor fibers.

  Then, the precursor fibers constituting the precursor fiber sheet are carbonized in the state of being bonded at the intersections thereof to produce curved conductive carbon fibers, and a conductive porous sheet that does not break in a three-point bending test is manufactured. In the present invention, after joining the intersections of the precursor fibers, carbonized in the state of being joined at the intersections to form a curved carbon fiber, so that the conductive porous sheet has excellent flexibility, mechanical strength, and conductivity. Can be manufactured. That is, the precursor fiber contains the first carbonizable organic material and the second carbonizable organic material, and has different contraction rates when carbonized, so that the precursor fiber becomes a curved carbon fiber.

  This carbonization is not particularly limited as long as it can carbonize the first carbonizable organic material and the second carbonizable organic resin, and is not particularly limited. For example, in an inert gas atmosphere of nitrogen, helium, argon or the like, the maximum temperature is 800 to 3000 ° C. It can be performed by heating. The rate of temperature increase is preferably 5 to 100,000 ° C./min, more preferably 5 to 1000 ° C./min. Further, the holding time at the maximum temperature is preferably 3 hours or less, more preferably 1 to 120 minutes. In addition, in each of these parameters, the above-mentioned respective lower limits and respective upper limits can be arbitrarily combined as desired.

  The conductive porous sheet of the present invention can be produced by the method as described above, but in the case of containing a polyacrylonitrile resin as the first carbonizable organic material or the second carbonizable organic material constituting the precursor fiber. In order to maintain the fiber shape after the carbonization treatment, the infusibilizing step may be performed before the carbonization treatment. This infusibilization can be carried out by heating in an oxidizing atmosphere at a temperature of 200 to 300 ° C. for 10 to 120 minutes. The heating for infusibilization can be performed twice or more under the condition of different temperature or time.

  The conductive porous sheet of the present invention preferably has many voids with a porosity of 50% or more, but such a conductive porous sheet with high porosity has carbon fibers having an average fiber diameter of 0.1 μm to 50 μm. If it is mainly composed of, it is easy to satisfy the porosity. Precursor fibers, which are the basis of carbon fibers having such an average fiber diameter, can be easily manufactured by, for example, an electrostatic spinning method or a spinning method disclosed in Japanese Patent Application Laid-Open No. 2009-287138. Further, when a binder is used to bond the intersections of the precursor fibers, the binder fills the voids between the precursor fibers or covers the periphery of the intersections of the precursor fibers more than necessary, and the porosity tends to be low. Therefore, if the first carbonizable organic material or the second carbonizable organic material forming the precursor fiber is used for bonding without using a binder, the porosity can be easily satisfied.

  In addition, the conductive porous sheet of the present invention can be imparted or improved with physical properties suitable for each application by various post-processing. For example, when the conductive porous sheet of the present invention is used as a base material for a gas diffusion electrode of a polymer electrolyte fuel cell, in order to enhance the water repellency of the conductive porous sheet and enhance the drainage property and the gas diffusion property, The conductive porous sheet may be dipped in a fluorine-based dispersion such as tetrafluoroethylene dispersion to give a fluorine-based resin, and then sintered at a temperature of 300 to 350 ° C.

  Furthermore, the carbon fiber having no voids inside is easily manufactured by using an organic material having a high carbonization rate for both the first carbonizable organic material and the second carbonizable organic material. In other words, since the amount of organic material that disappears during carbonization is small, it is easy to manufacture carbon fibers having no voids inside. Examples of the first carbonizable organic material or the second carbonizable organic material having a high carbonization rate include polyacrylonitrile, epoxy resin, and phenol resin.

Furthermore, the conductive conductive porous sheet having a specific apparent Young's modulus of 100 MPa / (g / cm ³ ) or more is easily manufactured by forming the carbon fiber from a rigid material. That is, it is easy to manufacture by using a thermosetting resin, particularly an epoxy resin or a phenol resin, as the first carbonizable organic material and / or the second carbonizable organic material.

  Further, the average arithmetic average surface roughness on the main surface is 0.01 μm to 20 μm (preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 5 μm, and 0.1 to 4 μm). More preferably), the conductive porous sheet is, for example, by using carbon fibers having an average fiber diameter of 20 μm or less, making the conductive porous sheet a non-woven fabric, and / or keeping the conductive porous sheet static. Direct production by the electrospinning method or the method disclosed in JP-A-2009-287138 facilitates production. The lower limit and the upper limit in the average arithmetic average surface roughness can be arbitrarily combined as desired.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Preparation of first spinning solution>
Polyacrylonitrile (= PAN, first carbonizable organic material) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solution having a solid content concentration of 20 mass%.

  Then, a second carbonizable organic material (= EP) containing cresol novolac epoxy resin as a main component and novolac type phenolic resin as a curing agent is added to the solution and mixed, and after stirring, DMF is further added to dilute. Then, the first spinning solution having a solid content mass ratio of PAN: EP of 70:30 and a solid content concentration of 25 mass% was prepared.

<Preparation of second spinning solution>
Polyacrylonitrile (= PAN, first carbonizable organic material) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solution having a solid content concentration of 20 mass%.

  Then, as a conductive material, carbon nanotubes synthesized by a CVD method [= CNT, trade name: VGCF-H (manufactured by Showa Denko KK), fiber diameter: 150 nm, aspect ratio: 40, multi-walled carbon nanotube] are described above. A dispersion was prepared by mixing with the solution.

  Then, a second carbonizable organic material (= EP) having cresol novolac epoxy resin as a main component and novolac type phenolic resin as a curing agent is added to the dispersion liquid and mixed, and after stirring, DMF is further added to dilute. Then, a second spinning solution having a solid content mass ratio of CNT: PAN: EP of 10:60:30 and a solid content concentration of 25 mass% was prepared.

<Preparation of third spinning solution>
Similar to the second spinning solution, except that carbon black (= CB, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Denka Black granular product, average particle size: 35 nm) is used instead of the carbon nanotube (CNT). To prepare a third spinning solution having a solid content mass ratio of CB: PAN: EP of 10:60:30 and a solid content concentration of 20 mass%.

<Preparation of Fourth Spinning Liquid>
Polyacrylonitrile was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to prepare a fourth spinning solution having a solid content concentration of 16 ass%.

<Preparation of fifth spinning solution>
Polyacrylonitrile (= PAN), phenol resin (= PH, Gunei Chemical Industry PSK-2320), Titanium (IV) butoxide (= TI, manufactured by Aldrich) are dissolved in N, N-dimethylformamide (DMF). Then, a fifth spinning solution having a solid content mass ratio of PAN: PH: TI of 44:44:12 and a solid content concentration of 25 mass% was prepared.

<Preparation of sixth spinning solution>
Vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer (= THV, first carbonizable organic material) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solid content concentration of 10 mass. % Solution was obtained.

  Then, as a conductive material, carbon nanotubes (CNT) synthesized by a CVD method [trade name: VGCF-H (manufactured by Showa Denko KK), fiber diameter: 150 nm, aspect ratio: 40, multi-walled carbon nanotubes] are described above. After mixing with the solution and stirring, DMF was further added for dilution to obtain a dispersion solution in which carbon nanotubes were dispersed.

  Then, a second carbonizable organic material (= EP) having a cresol novolac epoxy resin as a main component and a novolac type phenolic resin as a curing agent is added to the dispersion solution, and a solid content mass ratio of CNT: THV: EP is 40 :. At 30:30, a sixth spinning solution having a solid content concentration of 20 mass% was prepared.

<Preparation of seventh spinning solution>
Polyacrylonitrile (= PAN) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solution having a solid content concentration of 18 mass%.

  Then, as a conductive material, carbon nanotubes (CNT) synthesized by a CVD method [trade name: VGCF-H (manufactured by Showa Denko KK), fiber diameter: 150 nm, aspect ratio: 40, multi-walled carbon nanotubes] are described above. After mixing with the solution and stirring, DMF was further added for dilution to obtain a dispersion solution in which carbon nanotubes were dispersed.

  Then, a second carbonizable organic material (= EP) having a bisphenol A type epoxy resin as a main agent and a novolac type phenol resin as a curing agent is added to the dispersion solution, and a solid content mass ratio of CNT: PAN: EP is 10. : 60:30, a seventh spinning solution having a solid content concentration of 25 mass% was prepared.

(Example 1)
Precursor continuous fibers are spun by the electrostatic spinning method under the following conditions and directly accumulated on a stainless steel drum, which is a counter electrode, consisting of only the precursor continuous fibers, and the intersections of the fibers are joined together. A non-woven fabric type precursor fiber aggregate sheet was formed.

(Electrostatic spinning conditions)
Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge rate: 5 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: 10kV
Temperature / humidity: 25 ° C / 30% RH

  Next, the precursor fiber aggregated sheet was heat-treated in a hot air dryer at a temperature of 150 ° C. for 1 hour to cure the epoxy resin, and a precursor fiber sheet in which the intersections of the fibers were joined was obtained.

  Subsequently, the precursor fiber sheet is subjected to an oxidation treatment in air at a temperature of 220 ° C. for 30 minutes and at a temperature of 260 ° C. for 1 hour to infusibilize the PAN forming the precursor continuous fiber, thereby making the infusible precursor fiber. It was a sheet.

Then, the infusibilized precursor fiber sheet is subjected to carbonization and firing treatment (temperature rising rate: 10 ° C./min) for 1 hour at a temperature of 1300 ° C. in a nitrogen gas atmosphere using a vacuum displacement type electric furnace to obtain a precursor continuous fiber. The PAN and EP constituting the above are carbonized into continuous carbon fibers, and the conductive porous sheet is formed of only continuous carbon fibers and has a non-woven structure and is bonded at the intersections of continuous carbon fibers (weight: 6.5 g / m ² , thickness: 65 μm, fiber diameter: 1.1 μm, porosity: 91%). An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed. As a result, as shown in FIG. 1, the continuous carbon fibers were in a curved state even between the intersections of the fibers. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids.

(Example 2)
In the same manner as in Example 1 except that the second spinning solution was used as the spinning solution, a conductive porous sheet having a monolayer structure consisting of only continuous carbon fibers and having a nonwoven fabric structure, which was joined at the intersection of the continuous carbon fibers ( A fabric weight: 10 g / m ² , thickness: 84 μm, fiber diameter: 0.7 μm, porosity: 94%) was produced. An electron micrograph (magnification: 2000) of the main surface of this conductive porous sheet was taken and observed. As shown in FIG. 2, the continuous carbon fibers were in a curved state even between the intersections of the fibers. In addition, the continuous carbon fiber was in a solid state without voids inside the fiber, and the mass ratio of CNT in the continuous carbon fiber was 12 mass%.

(Example 3)
Except that the PAN constituting the precursor continuous fiber was not infusibilized without performing an oxidation treatment, in the same manner as in Example 2, one-layer carbon continuous fibers composed of only continuous carbon fibers and having a nonwoven fabric structure A conductive porous sheet (unit weight: 10 g / m ² , thickness: 84 μm, fiber diameter: 0.7 μm, porosity: 94%) joined at the intersection of was prepared. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed, and as shown in FIG. 3, the continuous carbon fibers were in a curved state even between the intersections of the fibers. In addition, the continuous carbon fiber was in a solid state without voids inside the fiber, and the mass ratio of CNT in the continuous carbon fiber was 12 mass%.

(Example 4)
In the same manner as in Example 1 except that the third spinning solution was used as the spinning solution, a conductive porous sheet having a monolayer structure composed of only continuous carbon fibers and having a nonwoven fabric structure, which was joined at the intersection of continuous carbon fibers ( A fabric weight: 5.6 g / m ² , thickness: 34 μm, fiber diameter: 0.8 μm, porosity: 91%) was produced. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed, and as shown in FIG. 4, the continuous carbon fibers were in a curved state even between the intersections of the fibers. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids, and the mass ratio of carbon black in the continuous carbon fiber was 12 mass%.

(Comparative Example 1)
Using a fourth spinning solution as the spinning solution and spinning under the following electrostatic spinning conditions, in the same manner as in Example 1, consisting of only PAN precursor continuous fibers and having a non-woven fabric form in which the intersections of the fibers were not joined. A precursor fiber aggregated sheet was formed.

(Electrostatic spinning conditions)
Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge rate: 1 g / hour Distance between nozzle tip and stainless steel drum: 8 cm
Applied voltage: 10kV
Temperature / humidity: 25 ° C / 30% RH

Next, the precursor fiber aggregated sheet is subjected to an oxidation treatment in air at a temperature of 220 ° C. for 30 minutes and at a temperature of 260 ° C. for 1 hour to infusibilize the PAN constituting the precursor continuous fiber, and then the vacuum substitution type Using an electric furnace, under a nitrogen gas atmosphere, a carbonization and calcination treatment (temperature rising rate: 10 ° C./min) at a temperature of 1300 ° C. for 1 hour was carried out to carbonize PAN constituting the precursor continuous fiber into a carbon continuous fiber, A conductive porous sheet made of only continuous carbon fibers and having a non-woven fabric structure, in which the intersections of continuous carbon fibers are not joined (unit weight: 5 g / m ² , thickness: 20 μm, fiber diameter: 0.3 μm, Porosity: 86%) was produced. An electron micrograph (× 2000) of the principal surface of this conductive porous sheet was taken and observed, and as shown in FIG. 5, the continuous carbon fibers were linear. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids.

(Comparative example 2)
Before carrying out the oxidation treatment, the precursor fiber assembly sheet is dipped in a DMF / water mixed solution adjusted to a concentration of 7 mass% and squeezed between a pair of rolls, and then in an oven set to a temperature of 80 ° C. for 10 minutes. Then, only the carbon continuous fiber was prepared in the same manner as in Comparative Example 1 except that the mixed solvent was removed by subsequent heat treatment in an oven set to a temperature of 160 ° C. to bond the intersections of the PAN precursor continuous fibers. Consisting of a single layer structure having a non-woven fabric, a conductive porous sheet in which the intersections of continuous carbon fibers are joined (unit weight: 5 g / m ² , thickness: 18 μm, fiber diameter: 0.3 μm, porosity: 85%) Was produced. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed. As shown in FIG. 6, the continuous carbon fibers were linear. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids.

(Comparative example 3)
Using a fifth spinning solution as the spinning solution and spinning under the following electrostatic spinning conditions, the same procedure as in Example 1 was repeated except that carbon continuous fibers alone were formed, and continuous carbon fibers having a single-layer structure and having a nonwoven fabric structure were used. A conductive porous sheet (unit weight: 8 g / m ² , thickness: 62 μm, fiber diameter: 0.6 μm, porosity: 93%) in which the intersection points of No. were not joined was produced. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed, and as shown in FIG. 7, the continuous carbon fibers were linear. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids.

(Electrostatic spinning conditions)
Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge rate: 1 g / hour Distance between nozzle tip and stainless steel drum: 8 cm
Applied voltage: 10kV
Temperature / humidity: 25 ° C / 40% RH

(Comparative example 4)
In the same manner as in Comparative Example 3 except that the PAN constituting the precursor continuous fiber was not infusibilized without performing an oxidation treatment, carbon continuous fibers composed of only continuous carbon fibers and having a non-woven fabric structure, having continuous carbon fibers A conductive porous sheet (unit weight: 8 g / m ² , thickness: 62 μm, fiber diameter: 0.6 μm, porosity: 93%) in which the intersection points of No. were not joined was produced. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed, and as shown in FIG. 8, the continuous carbon fibers were linear. In addition, the continuous carbon fiber was in a state in which the inside of the fiber was solid without voids.

(Comparative example 5)
Precursor continuous fibers are spun by the electrospinning method using the sixth spinning solution under the following conditions and directly accumulated on a stainless steel drum which is a counter electrode to consist of only the precursor continuous fibers, and the intersections of the fibers are joined. A non-woven fabric type precursor fiber aggregate sheet was formed.

(Electrostatic spinning conditions)
Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge rate: 4 g / hour Distance between nozzle tip and stainless steel drum: 14 cm
Applied voltage: 10kV
Temperature / humidity: 25 ° C / 30% RH

  Next, the precursor fiber aggregated sheet was heat-treated in a hot air dryer at a temperature of 150 ° C. for 1 hour to cure the epoxy resin and obtain a precursor fiber sheet in which the intersections of the fibers were joined.

Then, the precursor fiber sheet is subjected to carbonization and firing treatment (temperature rising rate: 10 ° C./minute) for 1 hour at a temperature of 800 ° C. in an argon gas atmosphere using a tubular furnace, and THV constituting the precursor continuous fiber and While carbonizing EP, most of THV is eliminated to form a carbon continuous fibrous material, which is composed of only carbon continuous fibrous material (CNT: mass ratio of total amount of EP carbide and THV carbide = 52:48). A conductive porous sheet (unit weight: 20 g / m ² , thickness: 40 μm, average fiber diameter: 1.3 μm, porosity: 73%) having a single-layer structure and having continuous carbon fibrous materials joined together at an intersection did. An electron micrograph (× 2000) of the main surface of this conductive porous sheet was taken and observed, and as shown in FIG. 9, CNTs oriented in the length direction of the continuous carbon fibrous material were dispersed throughout. The carbonaceous continuous fibrous material in a porous and continuous state in which the CNTs are partially connected and bonded with EP carbide and THV carbide, and the crossing points of the continuous carbonaceous fibrous materials are EP carbide and THV. It was in a state of being bonded by carbide.

(Comparative example 6)
Precursor continuous fibers are spun by the electrostatic spinning method under the following conditions by the seventh spinning solution and directly accumulated on a stainless steel drum which is a counter electrode, and only the precursor continuous fibers are formed. A non-woven fabric type precursor fiber aggregate sheet was formed.

(Electrostatic spinning conditions)
Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge rate: 4 g / hour Distance between nozzle tip and stainless steel drum: 14 cm
Applied voltage: 17kV
Temperature / humidity: 25 ° C / 35% RH

  Next, the precursor fiber aggregated sheet was heat-treated in a hot air dryer at a temperature of 150 ° C. for 1 hour to cure the epoxy resin and obtain a precursor fiber sheet in which the intersections of the fibers were joined.

  Subsequently, the precursor fiber sheet is subjected to an oxidation treatment in air at a temperature of 220 ° C. for 30 minutes and at a temperature of 260 ° C. for 1 hour to infusibilize the PAN forming the precursor continuous fiber and to partially remove EP. A fluidized infusible precursor fiber sheet was obtained.

Then, the infusible precursor fiber sheet is subjected to carbonization and firing treatment (temperature rising rate: 10 ° C./min) at a temperature of 800 ° C. for 1 hour in a tubular furnace in a nitrogen atmosphere to form a PAN constituting a precursor continuous fiber. And EP are carbonized (the mass ratio of the total amount of CNT: PAN carbide and EP carbide = 14: 86), and the conductive porous sheet having a one-layer structure having a non-woven fabric structure and joined at the intersection of continuous carbon fibrous materials (weight: 5 g / m ² , thickness: 15 μm, average fiber diameter: 0.8 μm, porosity: 82%) were produced. An electron micrograph (× 2000) of the main surface of this electrically conductive porous sheet was taken and observed. As shown in FIG. 10, when carbonized, the PAN carbide that had become porous due to the difference in resin flow and carbonization process. A continuous carbon fibrous material composed of EP carbide was observed.

(Evaluation of conductive porous sheet)
With respect to the conductive porous sheets of Examples 1 to 4 and Comparative Examples 1 to 6, the three-point bending test (bending flexure amount), the electrical resistance, the breaking strength, and the relative apparent Young's modulus were measured by the methods described above. .. The results are shown in Table 1.

  In the conductive porous sheets of Comparative Examples 1 and 2, when the pressure wedge was pushed in by 1.5 mm, the stress dropped sharply and ruptured. It was considered that this is because the carbon fibers were not curved. Further, the conductive porous sheet of Comparative Example 1 had a relatively high electric resistance. It was considered that this was because the carbon fibers were not joined at the intersections.

  Further, the conductive porous sheets of Comparative Examples 3 to 4 had relatively high electric resistance and low mechanical strength. This was considered to be because the intersections of carbon fibers were not joined.

  Further, in the conductive porous sheet of Comparative Example 5, when the pressure wedge was pushed in by 3.0 mm, the stress drastically dropped and was broken. It was considered that this is because the carbon fibers were porous and the content ratio of the conductive material was high.

  In the conductive porous sheet of Comparative Example 6, the fibrous material was porous, so the fibers were brittle, and when the pressure wedge was pressed by 2.6 mm or more, the stress was sharply reduced and the sheet was broken.

  On the other hand, the results of Examples 1 to 4 show that the conductive porous sheet of the present invention is excellent in flexibility and mechanical strength and conductivity even though it is made of rigid carbon fiber. It was a thing. The excellent flexibility is due to the fact that the carbon fibers are curved between the intersections where the carbon fibers are joined, so that the stress against bending can be dispersed, and the mechanical strength and the electrical conductivity are excellent. Was thought to be because the intersections of the carbon fibers were joined together.

The conductive porous sheet of the present invention is excellent in mechanical strength, conductivity, and flexibility, and can be suitably used as a base material for electrodes. For example, it is useful as an electrode of a lithium ion secondary battery or an electric double layer capacitor, and as a base material for a gas diffusion electrode of a polymer electrolyte fuel cell.
Although the present invention has been described above according to the specific embodiments, modifications and improvements obvious to those skilled in the art are included in the scope of the present invention.

Claims (6)

  A conductive porous sheet, which is mainly composed of carbon fibers, and in which the carbon fibers are bonded at intersections, and the conductive porous sheet does not break in a three-point bending test.   The conductive porous sheet according to claim 1, wherein the carbon fiber is curved.   Breaking strength is 0.30 MPa or more, The electroconductive porous sheet according to claim 1 or 2 characterized by things.   The conductive porous sheet according to claim 1, which is used as a base material for electrodes.   A polymer electrolyte fuel cell, comprising the conductive porous sheet according to any one of claims 1 to 4 as a substrate for a gas diffusion electrode. Forming a precursor fiber comprising a first carbonizable organic material and a second carbonizable organic material composed of an organic material different from the first carbonizable organic material;
Bonding the intersections of the precursor fibers with a first carbonizable organic material or a second carbonizable organic material to form a precursor fiber sheet mainly composed of precursor fibers;
A step of carbonizing the precursor fibers constituting the precursor fiber sheet in a state of being bonded at the intersections thereof to form curved carbon fibers,
And a method for producing a conductive porous sheet which does not break in a three-point bending test.