JP2018204150A - Carbon fiber sheet, gas diffusion electrode, membrane-electrode assembly, polymer electrolyte fuel cell, and method for producing carbon fiber sheet - Google Patents

Abstract

To provide: a carbon fiber sheet which is excellent in flexibility and excellent in handleability; a gas diffusion electrode; a membrane-electrode assembly; a polymer electrolyte fuel cell; and a method for producing the carbon fiber sheet.SOLUTION: In a carbon fiber sheet according to the present invention, particles or particle aggregates are present between carbon fibers. The carbon fiber sheet includes, as the particles or particle aggregates, large-sized particles or large-sized particle aggregates having a diameter larger than the average fiber diameter of the carbon fibers between the carbon fibers in a thickness direction. In a gas diffusion electrode, a membrane-electrode assembly, and a polymer electrolyte fuel cell according to the present invention, the carbon fiber sheet is used. A method for producing the carbon fiber sheet according to the present invention includes the steps of: using a spinning solution containing a carbonizable resin to spin a precursor carbon fiber; supplying the particles or particle aggregates to the precursor carbon fiber; forming a precursor carbon fiber sheet in which the particles or particle aggregates are present between the precursor carbon fibers in a thickness direction; and carbonizing the precursor carbon fibers forming the precursor carbon fiber sheet.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon fiber sheet, a gas diffusion electrode, a membrane-electrode assembly, a solid polymer fuel cell, and a method for producing a carbon fiber sheet.

  Conventionally, carbon fiber sheets have been used as a base material for gas diffusion electrodes for fuel cells, as an electrode for electric double layer capacitors, or as an electrode for lithium ion secondary batteries by utilizing their conductivity and porosity. Use is under consideration.

  As such a carbon fiber sheet, after making a fiber web in which carbon fibers and a papermaking binder are mixed, the fiber web is impregnated with a thermosetting resin such as a phenol resin and cured, and then a temperature of 1000 ° C. or higher. A carbon fiber sheet produced by firing at a known temperature is known. Considering the mass productivity of the carbon fiber sheet, it is desirable that the carbon fiber sheet has flexibility that can be wound in a roll shape, but the carbon fiber sheet is excellent in conductivity, but is wound in a roll shape. However, the flexibility was insufficient and the handleability was poor.

  In addition, the applicant of the present application stated that “a gas diffusion electrode substrate made of a glass nonwoven fabric in which a binder containing acrylic resin and / or vinyl acetate resin is attached to glass fiber, carbon black, polytetrafluoroethylene resin or polyfluorinated resin”. A gas diffusion electrode obtained by depositing and firing a conductive paste containing vinylidene resin "(Patent Document 1) has been proposed. However, the glass fiber has high rigidity, and the conductive paste is deposited and fired. Further, since the rigidity is higher, the flexibility is insufficient and the handleability is poor.

As a carbon fiber sheet capable of solving such a problem of flexibility, the applicant of the present application states that “a conductive material including a fibrous material having a first conductive material and a second conductive material connecting between the first conductive material. A conductive porous body, wherein the conductive porous body has a specific surface area of 100 m ² / g or more, a bending strength of 10 MPa or more, and a bending deflection of 1 mm or more. (Patent Document 2). This conductive porous body had a certain degree of flexibility, but was insufficient in flexibility and poor in handleability.

JP 2008-204945 A

JP 2017-59309 A

  The present invention has been made under such circumstances. The carbon fiber sheet, the gas diffusion electrode, the membrane-electrode assembly, the solid polymer fuel cell, and the carbon fiber sheet, which are excellent in flexibility and handleability, are provided. An object is to provide a manufacturing method.

  The carbon fiber sheet of the present invention is a carbon fiber sheet in which particles or particle aggregates are present between carbon fibers, and the particles or particle aggregates are large particles or large particles having a diameter larger than the average fiber diameter of carbon fibers. Particle aggregates are included between the carbon fibers in the thickness direction.

  In the carbon fiber sheet of the present invention, large particles or large particle aggregates are present in the thickness direction of the carbon fiber sheet, the large particles or large particle aggregates have a substantially spherical shape, or large particles or large particles. The particle agglomerates are in point contact with the carbon fibers, the large particles or the large particle agglomerates and the carbon fibers are not formed, and / or the large particles or the large particle agglomerates. It is preferable that the aggregate has conductivity.

  Moreover, the carbon fiber sheet of this invention can use suitably the said carbon fiber sheet in which a large particle or a large particle aggregate has electroconductivity as a base material for gas diffusion electrodes.

  Furthermore, a gas diffusion electrode in which a catalyst is supported on the carbon fiber sheet, a membrane-electrode assembly including the gas diffusion electrode, and a polymer electrolyte fuel cell including the gas diffusion electrode.

  The method for producing a carbon fiber sheet of the present invention includes a step of spinning a precursor carbon fiber using a spinning solution containing a carbonizable resin, a step of supplying particles or particle aggregates to the precursor carbon fiber, and a thickness direction. The step of forming a precursor carbon fiber sheet in which particles or particle aggregates exist between the precursor carbon fibers, carbonizing the precursor carbon fibers constituting the precursor carbon fiber sheet, and the average of the carbon fibers between the carbon fibers in the thickness direction A carbon fiber sheet containing large particles or large particle aggregates having a diameter larger than the fiber diameter.

  The step of supplying the particles or particle aggregates to the precursor carbon fibers is performed by spraying the dispersion liquid containing the particles or particle aggregates onto the precursor carbon fibers, in particular, a dispersion liquid including the particles or particle aggregates. It is preferable to carry out by fragmenting into droplets having a charge and spraying onto the precursor carbon fiber.

  The step of spinning the precursor carbon fiber is preferably carried out by an electrostatic spinning method, and the large particles or large particle aggregates are preferably conductive.

  Since the present invention has a large particle or large particle aggregate having a diameter larger than the average fiber diameter of the carbon fiber between the carbon fibers in the thickness direction, there are few contacts between the carbon fibers, The presence of large particles or large particle aggregates allows the carbon fiber to bend along the large particles or large particle aggregates, which is considered to have excellent flexibility and handleability. . Moreover, since the large particles or large particle aggregates act like a pillar in a house, there is also an effect that they are not easily damaged by pressure in the thickness direction.

  When large particles or large particle aggregates are present in the thickness direction of the carbon fiber sheet, the flexibility is superior.

  When the large particle or large particle aggregate has a substantially spherical shape, the contact area between the large particle or large particle aggregate and the carbon fiber is small, and the degree of freedom of the carbon fiber is not so limited, so the carbon fiber sheet is flexible. It is superior to the nature.

  When large particles or large particle aggregates are present in a point contact with carbon fibers, the contact area between the large particles or large particle aggregates and the carbon fibers is small, and the degree of freedom of the carbon fibers is very limited. Therefore, the carbon fiber sheet is superior in flexibility.

  If a film is not formed between the large particles or large particle aggregates and the carbon fibers, the degree of freedom of the carbon fibers is not so limited, so the carbon fiber sheet is superior in flexibility. Moreover, the space | gap of a carbon fiber sheet can be utilized effectively. For example, it is excellent in gas diffusibility and water permeability.

  When the large particles or large particle aggregates have conductivity, the carbon fiber sheet is excellent in conductivity, and therefore can be suitably used for applications that require conductivity.

  Since the carbon fiber sheet in which the large particles or the large particle aggregates have conductivity is excellent in conductivity, it is suitable as a base material for a gas diffusion electrode.

  The gas diffusion electrode has a large solid particle or large particle agglomerate having conductivity, and a carbon fiber sheet having excellent conductivity, so that the catalyst is supported. Therefore, the gas diffusion electrode has low electrical resistance and can exhibit sufficient power generation performance. A molecular fuel cell can be manufactured.

  Since the membrane-electrode assembly includes the gas diffusion electrode, it is possible to manufacture a polymer electrolyte fuel cell that has low electric resistance and can exhibit sufficient power generation performance.

  Since the polymer electrolyte fuel cell includes the gas diffusion electrode, it has a low electric resistance and can exhibit sufficient power generation performance.

  Since the carbon fiber sheet manufacturing method of the present invention supplies particles or particle aggregates to precursor carbon fibers, the carbon fiber sheet includes large particles or large particle aggregates between carbon fibers in the thickness direction. Can be manufactured. That is, it is possible to produce a carbon fiber sheet that is excellent in flexibility and easy to handle.

  In addition, when the dispersion liquid containing particles or particle aggregates is sprayed onto the precursor carbon fibers, it is easy to produce a carbon fiber sheet in which a film is not formed between the large particles or large particle aggregates and the carbon fibers.

  In addition, when a dispersion liquid containing particles or particle aggregates is fragmented into charged droplets and sprayed onto the precursor carbon fiber, the large particles or large particle aggregates have a substantially spherical shape, and the large particles or large particle aggregates. It is easy to produce a carbon fiber sheet in which the aggregates are in point contact with the carbon fibers and no film is formed between the large particles or large particle aggregates and the carbon fibers.

  Further, when the precursor carbon fiber is spun by an electrostatic spinning method, the precursor carbon fiber is thin and has a uniform fiber diameter, and can be spun continuously. Therefore, it is possible to produce a carbon fiber sheet that is excellent in conductivity, has a large surface area, and can effectively use the carbon fiber surface.

  Furthermore, if the large particles or large particle aggregates have conductivity, a carbon fiber sheet having excellent conductivity can be produced.

Electron micrograph (2500 times magnification) in a cross section in the thickness direction of the carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Magnified electron micrograph (20000 times) of the carbon particle aggregate of the carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Electron micrograph (5000 times) on the surface of the carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Electron micrograph (2500 times magnification) in a cross section in the thickness direction of the carbon continuous fiber nonwoven fabric provided with ketjen black in Comparative Example 3 Magnified electron micrograph (magnified 20000 times) of carbon particle aggregates of carbon continuous fiber nonwoven fabric with ketjen black in Comparative Example 3 Electron micrograph on the surface of a carbon continuous fiber nonwoven fabric to which ketjen black was applied in Comparative Example 3 (5000 times)

  In the carbon fiber sheet of the present invention, the presence of large particles or large particle aggregates having a diameter larger than the average fiber diameter of the carbon fibers between the carbon fibers in the thickness direction allows the contact between the carbon fibers. The carbon fiber can be curved along the large particles or large particle aggregates due to the presence of large particles or large particle aggregates due to the low degree of freedom of the carbon fibers and the presence of large particles or large particle aggregates. Since there is room to follow the deformation when the fiber sheet is bent, it is considered that the flexibility is excellent and the handling property is excellent. Moreover, since the large particles or large particle aggregates act like a pillar in a house, there is also an effect that they are not easily damaged by pressure in the thickness direction. The “thickness direction” means a direction parallel to a straight line perpendicular to both surfaces, and “both surfaces” are the surface of the carbon fiber sheet having the largest area and face the surface. Means a face.

  The carbon fiber of the present invention can be, for example, a PAN-based carbon fiber. The carbon fiber can contain a conductive material. Thus, when a conductive material is included, conductivity and mechanical strength are more excellent. Such conductive materials include, for example, fullerene, carbon nanotube, carbon nanohorn, graphite, graphene, vapor grown carbon fiber, carbon black, metal (for example, gold, platinum, titanium, nickel, aluminum, silver, zinc, iron , Copper, manganese, cobalt, stainless steel, etc.), one type selected from the group of metal oxides of the metal, or two or more types. Among these, carbon nanotubes are preferable because they are excellent in electrical conductivity, are easily oriented in the length direction in carbon fibers, and can increase electrical conductivity and mechanical strength.

  When the carbon fiber of the present invention is in a state having no voids inside the fiber, it is suitable because it is excellent in mechanical strength and conductivity. This “there is no void inside the fiber” means that the cross-section in the thickness direction of the carbon fiber sheet has a continuous contour and the cross-sectional shape of the carbon fiber with a clear cross-sectional shape is within 1 to 3 This means that the number of carbon fibers in which no voids are observed is 70% or more. In addition, the carbon fiber contains the conductive material as described above, and when the carbon fiber sheet is cut in the thickness direction, the void that is apparently formed by dropping the conductive material is included in the void. Absent. Even if the conductive material itself is porous and contains voids, the conductive material is discontinuous and has little influence on the mechanical strength of the carbon fiber, so the carbon fiber contains a conductive material containing voids. However, it is considered that there are no voids inside the fiber.

  The average fiber diameter of the carbon fiber of the present invention is not particularly limited, so that the mechanical strength of the carbon fiber itself is excellent, and there are some contact points between the carbon fibers, the mechanical strength of the carbon fiber sheet, In order to be excellent in conductivity, the thickness is preferably 10 nm to 20 μm, more preferably 50 nm to 10 μm, and still more preferably 100 nm to 5 μm.

  The “average fiber diameter” in the present invention means an arithmetic average value of the fiber diameters at 40 points of the carbon fiber, and the “fiber diameter” is a width orthogonal to the length direction when the carbon fiber is observed with a micrograph. means.

  In addition, it is preferable that carbon fiber is a continuous fiber so that it may be excellent in electroconductivity. In addition, when using the carbon fiber sheet of this invention as a base material for gas diffusion electrodes, there exists an effect that there is substantially no fiber edge part of carbon fiber and a solid polymer film is not damaged. The carbon fiber which is such a continuous fiber, for example, after spinning a continuous precursor carbon fiber using a spinning solution containing a carbonizable organic material (for example, an electrostatic spinning method, a spunbond method, etc.) It can be produced by carbonizing a carbonizable organic material (precursor carbon fiber). “Continuous fiber” means an electron micrograph when a photo of a carbon fiber sheet using an electron microscope is taken at a magnification at which one side of the taken image is about 60 times the average fiber diameter of the carbon fiber. It means that the number of carbon fiber ends per sheet is 0.3 or less. That is, it means that the total number of carbon fiber ends in 20 electron micrographs is divided by the number of photographs (20), and the number of carbon fiber ends per electron micrograph is 0.3 or less. In addition, the photography is performed in the location which is continuously different in the center part of the surface which does not include the cut part of the carbon fiber sheet. For example, when checking whether carbon fibers having an average fiber diameter of 1 μm are continuous fibers, photography using an electron microscope is performed at different locations in the center of the surface not including the cut portion of the carbon fiber sheet. , The number of ends of the carbon fiber per electron micrograph is calculated by performing 20 sheets (4 rows x 5 columns) at a magnification (2500 times) at which one side of the photographed image is about 60 μm, and if it is 0.3 or less For example, it can be considered as a continuous fiber.

  The carbon fiber sheet of this invention does not need to be comprised from one type of carbon fiber, and can be comprised from two or more types of carbon fibers. For example, it can be composed of two or more types of carbon fibers that differ in at least one point selected from the presence or absence of a conductive material, the type of conductive material, the presence or absence of voids inside the carbon fiber, the average fiber diameter, the fiber length, and the like. .

  The carbon fibers constituting the carbon fiber sheet of the present invention are preferably joined together so that the mechanical strength is excellent and the conductivity is excellent. In addition, it is preferable that the carbon fibers are bonded to each other with a carbide of an organic material so that the carbon fibers are excellent in adhesiveness and mechanical strength and conductivity are excellent. Such a carbon fiber sheet can be obtained, for example, by carbonizing a fiber sheet containing organic fibers containing a carbonizable organic material. The state in which such carbon fibers are bonded to each other can be confirmed by an electron micrograph. For example, FIG. 2 is an enlarged electron micrograph of the carbon particle aggregate of the carbon fiber sheet, and it can be confirmed that the carbon fibers are bonded to each other.

  The carbon fiber sheet of the present invention has particles or particle aggregates in addition to the carbon fibers as described above, and large particles or large particle aggregates having a diameter larger than the average fiber diameter of the carbon fibers. The carbon fibers are included between the carbon fibers in the thickness direction, the bonding between the carbon fibers is hindered, and there are few contact points between the carbon fibers, and because the large particles or large particle aggregates are present, Since it can be curved along the large particles or large particle aggregates, it is considered to have excellent flexibility and handleability. That is, there are few contact points between the carbon fibers, the degree of freedom of the carbon fibers is relatively high, and if the carbon fibers are curved, there is room to follow the deformation when the carbon fiber sheet is bent. This carbon fiber is considered to be excellent in flexibility.

  Thus, if the large particles or large particle aggregates constituting the carbon fiber sheet of the present invention have a diameter larger than the average fiber diameter of the carbon fibers, the bonding of the carbon fibers is hindered and the flexibility is excellent. Although it is a carbon fiber sheet, the diameter of the large particle or large particle aggregate is preferably 1.5 times or more the average fiber diameter of the carbon fiber so that the bonding between the carbon fibers can be surely prevented. It is more preferably 2.0 times or more, and further preferably 2.5 times or more. On the other hand, if the diameter of the large particle or large particle aggregate is too large, the bonding between the carbon fibers is almost lost, and the mechanical strength, conductivity, etc. of the carbon fiber sheet tend to be remarkably deteriorated. The diameter of the particle aggregate is preferably 60 times or less of the average fiber diameter of the carbon fibers, more preferably 50 times or less, and still more preferably 40 times or less. The diameter of the large particle or large particle aggregate is not particularly limited as long as it is larger than the average fiber diameter of the carbon fiber, but is preferably 0.1 μm to 1000 μm, and is 0.5 μm to 100 μm. Is more preferably 1 μm to 30 μm, further preferably 1 μm to 10 μm.

  The “diameter” of the large particle or large particle aggregate is the diameter of 50 large particles or large particle aggregates taken in an electron micrograph taken in a cross section in the thickness direction of the carbon fiber sheet. Arithmetic mean value. When the shape of the large particle or large particle aggregate is non-circular on the photograph, the diameter of the circle having the same area as that of the large particle or large particle aggregate on the photograph is the large particle or large particle. Considered as the diameter of the particle aggregate.

The material constituting the large particle or large particle aggregate of the present invention may be conductive or non-conductive, but when utilizing the conductivity of carbon fiber, the conductive large particle or Large particle aggregates are preferred. The former conductive material means a material having an electric resistivity of 10 ³ Ω · cm or less, such as carbon (for example, ketjen black, acetylene black, carbon black, carbon nanotube, carbon nanofiber, fullerene, carbon nanohorn, Graphite, graphene, etc.), metal (silver, aluminum, nickel, gold, palladium, platinum, cadmium, cobalt, copper, iron, zinc, etc.), conductive metal oxide (tin oxide doped indium oxide, tin oxide, zinc oxide, etc.) Carbon is preferable from the viewpoints of chemical resistance and conductivity, and it is particularly preferable to use conductive carbon such as ketjen black and acetylene black.

On the other hand, the latter non-conductive material means a material having an electrical resistivity exceeding 10 ³ Ω · cm. For example, non-conductive metal oxides (for example, silicon oxide, aluminum oxide, iron oxide, manganese dioxide, copper oxide) , Nickel oxide, cobalt oxide, zinc oxide, titanium-containing oxide, zeolite, catalyst-supporting ceramics, etc.), organic resins (polyamide resins, polyester resins, polyolefin resins, fluorine resins, etc.), activated carbon powders (for example, Steam activated carbon, alkali-treated activated carbon, acid-treated activated carbon, etc.), ion-exchange resin powder, plant seeds and the like.

  The shape of the large particle or large particle aggregate of the present invention is not particularly limited. For example, it is substantially spherical (substantially spherical or true spherical), fibrous, needle-like (for example, tetrapot-like), flat plate-like. Polyhedron shape, feather shape, and irregular shape. Among these, a substantially spherical shape is a preferable shape because the contact area with the carbon fiber is small and the degree of freedom of the carbon fiber is difficult to decrease.

  The preferred substantially spherical shape means that the aspect ratio measured by the following method is 2.0 or less, preferably 1.5 or less, and preferably 1.2 or less. More preferred.

(aspect ratio)
(1) In the electron micrograph on the surface of the carbon fiber sheet, large particles or large particle aggregates that can clearly observe the entire individual contours are selected.
(2) Draw the longest line segment (longest line segment) formed by connecting two points on the outer periphery of the selected large particle or large particle aggregate.
(3) Draw the longest line segment (orthogonal line segment) that is orthogonal to the longest line segment and connects two points on the outer periphery of the selected large particle or large particle aggregate.
(4) The ratio of the longest line segment (major axis) and the orthogonal line segment (minor axis) is obtained. That is, the value of the longest line segment (major axis) / orthogonal line segment (minor axis) is obtained.
(5) The above operations (1) to (4) are performed on 50 arbitrarily selected particles, and the arithmetic average value of the longest line segment (major axis) / orthogonal line segment (minor axis) is calculated as the aspect ratio. And

  The large particles or large particle aggregates may be hollow or solid.

  In the carbon fiber sheet of the present invention, the large particles or large particle aggregates differ in at least one point selected from diameter, material, shape, conductive or non-conductive, and / or hollow or solid. Large particles or large particle aggregates may be mixed.

  The carbon fiber sheet of the present invention contains large particles or large particle aggregates, but is preferably included so as to be present in the thickness direction of the carbon fiber sheet. Thus, when it exists in the inside, even if the stress by bending is added, since a large particle or a large particle aggregate relieve | moderates the stress, it is thought that it is excellent by a softness | flexibility. In addition, large particles or large particle aggregates can be present only inside the carbon fiber sheet, but are also present in the vicinity of the surface in addition to the inside of the carbon fiber sheet so as to be excellent in flexibility. Is preferred. That is, it is preferable that large particles or large particle aggregates exist throughout the thickness direction of the carbon fiber sheet. The “inside” of the carbon fiber sheet means a middle region when a cross-sectional photograph in the thickness direction of the carbon fiber sheet is taken and the two surfaces are divided into three equal parts by a straight line parallel to the surface. “Nearby” means a region including the surface when divided into three equal parts by the straight line.

  In addition, when large particles or large particle aggregates are included in the thickness direction of the carbon fiber sheet, the large particles or large particle aggregates need not be uniformly present throughout the carbon fiber sheet. Or the layer of a large particle aggregate and the layer of carbon fiber may exist alternately.

  Moreover, when a carbon fiber sheet contains a large particle or a large particle aggregate only in an inside, the surface vicinity can be comprised only from a carbon fiber or a large particle or a large particle aggregate.

  In the carbon fiber sheet of the present invention, the large particles or large particle aggregates may be present in any way, but the large particles or large particle aggregates are present in a state of being in point contact with the carbon fibers. Is preferred. When present in such a point contact state, the contact area between the large particle or large particle aggregate and the carbon fiber is small, the degree of freedom of the carbon fiber is not so limited, the carbon fiber sheet is This is because it is more flexible. Such a point contact state is easy to achieve when large particles or large particle aggregates having a substantially spherical shape are bonded to carbon fibers without deforming the shape.

  Moreover, in the carbon fiber sheet in the present invention, it is preferable that the large particles or large particle aggregates exist in a state where no film is formed between the carbon fibers and the carbon fibers. If the film is not formed in this way, the degree of freedom of the carbon fiber is not so limited, and the carbon fiber sheet is superior in flexibility. In addition, when the membrane | film | coat is not formed, there also exists an effect that the space | gap of a carbon fiber sheet can be utilized effectively. In other words, when a film is formed between carbon fibers and large particles or large particle aggregates, there is a tendency that voids in the carbon fiber sheet in the vicinity of the film cannot be effectively used, but the film must be formed. For example, the voids of the carbon fiber sheet can be used effectively. Such a “not forming film” state is, for example, a state in which large particles or large particle aggregates are bonded, adhered, welded, or fixed to carbon fibers in a dotted or linear manner. In addition, a film | membrane is easy to be formed when large particles or a large particle aggregate is adhere | attached on carbon fiber using a liquid adhesive agent.

  As described above, the carbon fiber sheet of the present invention includes large particles or large particle aggregates between carbon fibers in the thickness direction, but is not limited to the thickness direction, and the carbon fibers in the plane direction of the carbon fiber sheet. In the meantime, it is preferable that large particles or large particle aggregates are contained entirely or partially (staggered, square arrangement, random, etc.). In particular, it is preferable to include large particles or large particle aggregates between the entire carbon fibers in the thickness direction and the plane direction of the carbon fiber sheet. In the case where large particles or large particle aggregates are included in the plane direction, the large particles or large particle aggregates are substantially spherical and contacted with the carbon fibers in the same manner as in the case where they exist between the carbon fibers in the thickness direction. A film is not formed between the state and / or the carbon fiber, and it is preferably present so as not to impair the flexibility of the carbon fiber sheet.

  Further, the carbon fiber sheet of the present invention does not need to have only large particles or large particle aggregates, and there are also small particles or small particle aggregates having a diameter equal to or smaller than the average fiber diameter of the carbon fibers. You may do it. In the carbon fiber sheet of the present invention, since it is considered that the large particles or large particle aggregates have flexibility, it is preferable that there are many large particles or large particle aggregates, specifically, large particles or large particles. The number of the aggregates in the thickness direction of the carbon fiber sheet is preferably 1 or more, more preferably 25 or more, and even more preferably 50 or more. In addition, this number is a photographable magnification in which both surfaces of the carbon fiber sheet are accommodated and the cross section of the carbon fiber sheet occupies 80% or more of the photographed image area. It means the number of large particles or large particle aggregates per cross-sectional photograph when one image is taken. That is, it means the number of large particles or large particle aggregates per cross-sectional photograph obtained by dividing the total number of large particles or large particle aggregates in 20 cross-sectional photographs by the number of photographs (20). In addition, photography is performed in the location which is continuously different in the center of the cross section which does not include the edge part of a carbon fiber sheet.

  The carbon fiber sheet of the present invention contains carbon fibers and particles or particle aggregates, but the particles or particle aggregates account for 1 mass% or more of the entire carbon fiber sheet so that there are few contacts between the carbon fibers. It is preferable that it occupies 5 mass% or more, and more preferably 10 mass% or more. The large particles or large particle aggregates preferably account for 0.9 mass% or more of the entire carbon fiber sheet, more preferably 4.5 mass% or more, and 9 mass% or more. Is more preferable. On the other hand, if the amount of particles or particle aggregates is too large, the strength of the carbon fiber sheet is lowered, and the handleability tends to deteriorate from this point, so the particles or particle aggregates are 99 mass% of the total carbon fiber sheet. It is preferable to occupy the following, more preferably 95 mass% or less, and even more preferably 90 mass% or less. Since it is preferable that the ratio of the large particles or large particle aggregates in the present invention to the entire particles or particle aggregates is high, the large particles or large particle aggregates account for 99 mass% or less of the entire carbon fiber sheet. Preferably, it occupies 95 mass% or less, and more preferably occupies 90 mass% or less.

As described above, the carbon fiber sheet of the present invention includes large particles or large particle aggregates between the carbon fibers in the thickness direction, and has a small number of contacts between the carbon fibers. These voids can be used effectively. Specifically, it is preferable that the apparent density is in a porous state of 0.40 g / cm ³ or less. The smaller the apparent density, the more porous and its internal voids can be used effectively, so 0.20 g / cm ³ or less is more preferred, and 0.12 g / cm ³ or less is even more preferred. If the apparent density is too small, the shape stability tends to be inferior, and therefore it is preferably 0.01 g / cm ³ or more. This “apparent density” is a value calculated by dividing “weight (unit: g / m ² )” by “thickness (unit: μm)”, and “weight” is 10 cm for a carbon fiber sheet. The mass of a sample obtained by cutting into corners is measured, and the value converted to a mass of 1 m ² is referred to. “Thickness” is a thickness gauge (manufactured by Mitutoyo Corporation: Code No. 547-401: A value measured using a measuring force of 3.5 N or less).

  In addition, although the carbon sheet of this invention contains carbon fiber and a large particle or a large particle aggregate, it can also contain another material. For example, recycled fibers such as rayon, 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 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;

  Although the form of the carbon fiber sheet of the present invention is not particularly limited, it can be, for example, a nonwoven fabric form in which carbon fibers are randomly oriented, or a woven or knitted form in which fibers are regularly oriented. In particular, the non-woven fabric is preferable because the voids are fine and have a high porosity.

Basis weight of the carbon fiber sheet of the present invention is not particularly limited, as excellent mechanical strength, the electrical conductivity is preferably from ^{0.5~500g / m 2, 1~400g / m} 2 It is more preferable that it is 3-300 g / m < ² >, and it is still more preferable that it is 5-200 g / m < ² >. Moreover, although thickness is not specifically limited, It is preferable that it is 1-2000 micrometers, It is more preferable that it is 3-1000 micrometers, It is further more preferable that it is 5-500 micrometers, 10-300 micrometers is still more preferable.

The carbon fiber sheet of the present invention, when used in applications requiring electrical conductivity, it is preferable electric resistance of 500mΩ · cm ² or less, more preferably at 100 m [Omega · cm ² or less, 20 m [Omega · cm ² More preferably, it is as follows. This “electric resistance” is a value obtained by the following procedure.
(1) A carbon fiber sheet is cut into 5 cm square (area: 25 cm ² ) to prepare a sample.
(2) The sample is sandwiched between metal plates plated with gold from both sides, and the voltage (V) is measured in a state where a current (I) of 1 A is applied under pressure of 2 MPa in the stacking direction of the metal plates.
(3) The resistance (R = V / I) is calculated.
(4) The electrical resistance is calculated by multiplying the resistance (R) by the area of the sample (25 cm ² ).

  The carbon fiber sheet of the present invention is flexible and excellent in handleability, and when large particles or large particle aggregates have conductivity, the conductivity is further excellent, and therefore it is suitably used as a substrate for an electrode. be able to. 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 produced. Further, when used as a base material for a gas diffusion electrode of a polymer electrolyte fuel cell, a polymer electrolyte fuel cell that can exhibit excellent power generation performance can be produced.

  When the large particle or large particle aggregate of the present invention has conductivity and a carbon fiber sheet having excellent conductivity is used as a base material for a gas diffusion electrode, the carbon fiber of the present invention is not only excellent in conductivity. Since the sheet is porous, if nothing is filled in the gaps between the carbon fibers, the gas diffusion electrode substrate (carbon fiber sheet) is excellent in drainage in the thickness direction and the surface direction, Excellent diffusibility of supplied gas.

  In addition, since the liquid water is easy to be extruded when the fluorine-type resin is contained in the space | gap between carbon fibers of the base material for carbon diffusion electrodes (carbon fiber sheet), it is excellent in drainage. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene. 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.

  In the gas diffusion electrode of the present invention, large particles or large particle aggregates have electrical conductivity, and a catalyst is supported on a carbon fiber sheet having excellent electrical conductivity, so that electric resistance is low and sufficient power generation performance can be exhibited. A polymer electrolyte fuel cell can be manufactured. In the gas diffusion electrode of the present invention, the catalyst is supported on the carbon fiber sheet. For example, the catalyst is supported on the surface of the carbon fiber and / or the large particle or the large particle aggregate. In addition, since an electron conduction path is formed by carbon fibers and / or large particles or large particle aggregates, there are few catalysts isolated from the electron conduction path. As a result, the catalyst can be used efficiently and the amount of catalyst can be reduced.

  The gas diffusion electrode of the present invention has the same structure as the conventional gas diffusion electrode except that the catalyst is supported on the carbon fiber sheet of the present invention as described above. For example, the catalyst may be platinum, platinum alloy, palladium, palladium alloy, titanium, manganese, magnesium, lanthanum, vanadium, zirconium, iridium, rhodium, ruthenium, gold, nickel-lanthanum alloy, titanium-iron alloy, or the like. And can be one or more catalysts selected from these.

  In addition to the catalyst, an electron conductor and a proton conductor are preferably included, and the electron conductor is preferably made of a conductive material similar to that of large particles or large particle aggregates such as carbon black. Yes, the catalyst may be supported on this electron conductor. Moreover, an ion exchange resin is suitable as the proton conductor.

  Such a gas diffusion electrode can be manufactured by the following method, for example. First, a catalyst (for example, carbon powder carrying a catalyst such as platinum) is added and mixed in a single or mixed solvent composed of ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol dimethyl ether, etc., and this is mixed with an ion exchange resin. The solution is added and mixed uniformly by ultrasonic dispersion or the like to obtain a catalyst dispersion suspension. Then, the catalyst dispersion suspension can be coated or sprayed on the carbon fiber sheet of the present invention and dried to produce a gas diffusion electrode.

  Since the membrane-electrode assembly of the present invention is provided with the gas diffusion electrode having excellent conductivity as described above, it is possible to produce a polymer electrolyte fuel cell having low electric resistance and capable of exhibiting sufficient power generation performance. .

  The membrane-electrode assembly of the present invention can be exactly the same as the conventional membrane-electrode assembly except that it includes the gas diffusion electrode as described above. For example, the solid polymer film may be a perfluorocarbon sulfonic acid resin film, a sulfonated aromatic hydrocarbon resin film, an alkylsulfonated aromatic hydrocarbon resin film, or the like.

  Such a membrane-electrode assembly can be manufactured, for example, by sandwiching a solid polymer membrane between the catalyst support surfaces of a pair of gas diffusion electrodes and hot pressing. Further, after applying the catalyst dispersion suspension as described above to a support to form a catalyst layer, the catalyst layer is transferred to a solid polymer membrane, and then the carbon fiber sheet of the present invention is applied to the catalyst layer. It can also be manufactured by a method of laminating so as to be in contact with each other and hot pressing.

  Since the polymer electrolyte fuel cell of the present invention includes the gas diffusion electrode, it has a low electric resistance and can exhibit sufficient power generation performance.

  The fuel cell of the present invention can be exactly the same as a conventional fuel cell except that it includes the gas diffusion electrode as described above. For example, it has a structure in which a plurality of cell units sandwiching a membrane-electrode assembly as described above between a pair of bipolar plates are stacked. For example, a plurality of cell units can be stacked and fixed.

  The bipolar plate is not particularly limited as long as the bipolar plate has high conductivity, does not transmit gas, and has a flow path capable of supplying gas to the gas diffusion electrode. A carbon-resin composite material, a metal material, or the like can be used.

  The carbon fiber sheet of the present invention includes, for example, a step of spinning a precursor carbon fiber using a spinning solution containing a carbonizable resin, a step of supplying particles or particle aggregates to the precursor carbon fiber, and a precursor in the thickness direction. A step of forming a precursor carbon fiber sheet in which particles or particle aggregates exist between the carbon fibers, carbonizing the precursor carbon fibers constituting the precursor carbon fiber sheet, and an average fiber of the carbon fibers between the carbon fibers in the thickness direction A carbon fiber sheet containing large particles or large particle aggregates having a diameter larger than the diameter. Thus, by interposing large particles or large particle aggregates having a diameter larger than the average fiber diameter of the carbon fibers between the carbon fibers in the thickness direction, the number of contacts between the carbon fibers in the thickness direction is reduced, Moreover, since carbon fiber can be curved along a large particle or a large particle aggregate, it is considered that a carbon fiber sheet having excellent flexibility and excellent handleability can be produced.

  More specifically, first, the step of spinning the precursor carbon fiber using a spinning solution containing a carbonizable resin is performed. The carbonizable resin is not particularly limited. For example, phenol resin, urea resin, melamine resin, unsaturated polyester resin, epoxy resin, xylene resin, urethane resin, silicone resin, thermosetting polyimide resin, thermosetting Thermosetting resins such as curable polyimide resins and thermosetting polyamide resins; polystyrene resins, polyester resins, polyolefin resins, polyimide resins, polyamide resins, polyamideimide resins, polyvinyl acetate resins, vinyl chloride resins, fluorine resins, polyacrylonitrile resins , Acrylic resin, polyether resin, polyvinyl alcohol, polyvinyl pyrrolidone, pitch, polyamino acid resin, polybenzimidazole resin and other thermoplastic resins; cellulose (polysaccharide), tar; or monomers of these resins as components Polymers (e.g., acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer) and the like. Among these, it is preferable to use an acrylic resin, particularly polyacrylonitrile having a content of 85% or more, because the carbonization rate is high, there are no voids inside the fiber, and it is easy to obtain a carbon fiber having high strength and high elastic modulus.

  In addition, an electroconductive material can also be mixed so that the electroconductivity and mechanical strength of carbon fiber can be improved. The conductive material can be a conductive material as described above, and is preferably a carbon nanotube.

  In addition to or in addition to conductive materials, silicones such as polydimethylsiloxane and metal alkoxides (methoxides such as silicon, aluminum, titanium, zirconium, boron, tin, and zinc, ethoxide, propoxide, butoxide, etc.) A polymer obtained by polymerizing a known inorganic compound such as a polymerized inorganic polymer can also be mixed.

  After preparing such a material, in order to spin the precursor carbon fiber, a spinning solution containing a carbonizable resin is prepared. In some cases, a spinning solution containing a conductive material, silicone, and / or inorganic polymer is prepared.

  The solvent constituting the spinning solution may be any solvent that can dissolve the carbonizable resin, and is not particularly limited. For example, acetone, methanol, ethanol, propanol, isopropanol, tetrahydrofuran, dimethyl sulfoxide, 1,4- Dioxane, pyridine, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, formic acid, toluene, benzene, cyclohexane, cyclohexanone, carbon tetrachloride, methylene chloride, chloroform, trichloroethane, ethylene Examples thereof include carbonate, diethyl carbonate, propylene carbonate, water, and the like. These solvents can be a single solvent or a mixed solvent. In addition, a poor solvent can be added as long as there is no problem in spinnability.

  The solid content concentration of the carbonizable resin in the spinning solution is not particularly limited as long as it can form carbon fibers, but is preferably 1 to 50 mass%, more preferably 5 to 30 mass%. . This is because when the content is less than 1 mass%, the productivity is extremely lowered, and when the content exceeds 50 mass%, the spinning tends to become unstable.

  Next, the precursor carbon fiber is spun using the spinning solution as described above. As a method of forming this precursor carbon fiber, for example, a dry spinning method, an electrostatic spinning method, a gas is applied to the spinning solution discharged from the liquid discharging unit as disclosed in JP2009-287138A. Examples thereof include a method of discharging fibers in parallel and applying a shearing force to the spinning solution in a straight line to form fibers. Among these, the electrospinning method or the spinning method disclosed in Japanese Patent Application Laid-Open No. 2009-287138 is preferable because a precursor carbon fiber having an average fiber diameter of 3 μm or less and having a small fiber diameter can be easily spun. Further, the dry spinning method or the electrostatic spinning method is preferable because it is easy to spin the precursor carbon fiber that is a continuous fiber. In particular, according to the electrospinning method, it is possible to spin a precursor carbon fiber, which is a continuous fiber having a small fiber diameter and a uniform fiber diameter, has excellent electrical conductivity, has a large surface area, and can effectively use the carbon fiber surface. This is preferable because a carbon fiber sheet can be produced.

  In addition, the “precursor carbon fiber” in the present invention means a fiber in a state where the carbonizable resin is not carbonized, and the carbonizable resin is carbonized to form the carbon fiber. In the sense of fiber, it is expressed as precursor carbon fiber.

  Next, a step of supplying particles or particle aggregates to the precursor carbon fibers is performed. By supplying particles or particle aggregates, it is possible to produce a precursor carbon fiber sheet containing large particles or large particle aggregates between carbon fibers in the thickness direction, and as a result, excellent flexibility and handleability. Can produce a carbon fiber sheet excellent in.

  The method of supplying the particles or particle aggregates is not particularly limited. For example, the method of ejecting the particles or particle aggregates by the action of a compressed gas, or the dispersion containing the particles or particle aggregates may be compressed gas or ultrasonic wave. Examples thereof include a method of spraying by the action of the above, a method of spraying the dispersion liquid containing particles or particle aggregates into droplets having electric charges by the action of static electricity, and the like. Among these supply methods, the method of spraying a dispersion containing particles or particle aggregates by the action of compressed gas or ultrasonic waves is preferable because it is easy to produce a precursor carbon fiber sheet without a film between the precursor carbon fibers. It is. In particular, the method of fragmenting and spraying a dispersion liquid containing particles or particle aggregates into charged droplets by the action of static electricity has a substantially spherical shape in the case of large particle aggregates, and has large particles or large particles. Suitable because the particle aggregate adheres in a state of point contact with the precursor carbon fiber, and it is easy to produce a large particle or a precursor carbon fiber sheet in which a coating is not formed between the large particle aggregate and the precursor carbon fiber. It is. That is, since the droplets are repelled electrically and fragmented, it is difficult to form a film containing large particles or large particle aggregates between the precursor carbon fibers. In particular, as in the case of spinning the precursor carbon fiber by an electrostatic spinning method, when a droplet charged with the opposite polarity to the charge of the precursor carbon fiber is sprayed on the charged precursor carbon fiber, due to the action of the charge, Droplets containing large particles or large particle aggregates can be reliably attached to the precursor carbon fibers. For example, spraying droplets charged with the opposite polarity to the charge of the precursor carbon fiber on the precursor carbon fiber flying before the precursor carbon fiber spun by the electrostatic spinning method is accumulated on the collector is charged. By the action, a droplet containing large particles or large particle aggregates can be reliably attached to the precursor carbon fibers. In addition, when spraying the charged droplet with respect to the precursor carbon fiber which is not charged, the polarity of the charged droplet is not specifically limited. For example, even when spinning by an electrostatic spinning method, when spraying droplets that are accumulated on a grounded collector and are charged against a precursor carbon fiber that has become uncharged, it is related to polarity. The charged droplets can be sprayed to attach the droplets containing large particles or large particle aggregates to the precursor carbon fibers.

  The supply of the particles or particle aggregates to the precursor carbon fiber is, for example, to the precursor carbon fiber in a flying state after spinning, to the precursor carbon fiber immediately after the precursor carbon fiber is accumulated on the collector. Or it can implement with respect to the precursor carbon fiber after a precursor carbon fiber accumulates to some extent on a collector. In particular, when particles or particle aggregates are supplied to the precursor carbon fibers in a flying state after spinning or to the precursor carbon fibers immediately after the precursor carbon fibers are collected on the collector, As a result of being able to prevent contact and curving the precursor carbon fibers along the large particles or large particle aggregates, it is considered that it is easier to produce a carbon fiber sheet with better flexibility and more handleability. It is preferable to supply particles or particle aggregates at the stage.

  As the particles or particle aggregates, the above-mentioned conductive or non-conductive particles or particle aggregates can be used. In particular, it is preferable that particles or particle aggregates have conductivity because a carbon fiber sheet having excellent conductivity can be produced. In order to increase the conductivity, it is preferable to use conductive carbon such as ketjen black or acetylene black as particles or particle aggregates.

  In addition, when using the dispersion liquid of particle | grains or a particle aggregate, the solvent in a dispersion liquid should just be disperse | distributed, without dissolving particle | grains or a particle aggregate, and it does not specifically limit. The concentration of the particles or particle aggregates in the dispersion is not particularly limited, but is preferably 1 to 80 mass%, more preferably 3 to 70 mass%, and 5 to 60 mass%. Further preferred.

  In addition, when using a dispersion of conductive particles or particle aggregates and spraying the dispersion into fragmented droplets having a charge, it tends to be difficult to fragment, so prepare a dispersion containing an organic resin. However, it is preferable to facilitate fragmentation into charged droplets. Examples of such organic resin include nylon resin, vinylon resin, fluororesin, polyvinyl chloride resin, polyester resin, polyolefin resin, polyvinyl alcohol, and polyethylene glycol.

  Thus, when preparing a dispersion liquid containing an organic resin, the solvent in the dispersion liquid can be dispersed without dissolving particles or particle aggregates, and can dissolve or disperse the organic resin. There is no particular limitation as long as it is present. When the dispersion contains an organic resin, the dispersion may be obtained by dispersing conductive particles or particle aggregates in a melt of the organic resin.

  Next, a step of forming a precursor carbon fiber sheet in which particles or particle aggregates exist between the precursor carbon fibers in the thickness direction is performed. For example, when the supply of the particles or particle aggregates to the precursor carbon fibers is performed on the precursor carbon fibers in a flying state after spinning, the precursor carbon fibers to which the particles or particle aggregates are attached are collected on the collector. And a precursor carbon fiber sheet in which particles or particle aggregates exist between the precursor carbon fibers in the thickness direction. In addition, when particles or particle aggregates are supplied to the precursor carbon fibers immediately after the precursor carbon fibers are accumulated on the collector, the precursor carbon fibers are accumulated on the precursor carbon fibers to which the particles or particle aggregates are attached. Since the particles or particle aggregates are supplied to the precursor carbon fibers immediately after the accumulation, the particles or particle aggregates between the precursor carbon fibers in the thickness direction are simultaneously supplied with the particles or particle aggregates to the precursor carbon fibers. Can form a precursor carbon fiber sheet. Further, when the particles or particle aggregates are supplied to the sheet-like precursor carbon fibers after the precursor carbon fibers are accumulated to some extent on the collector, the sheet-like precursor carbon fibers to which the particles or particle aggregates are attached It can be laminated to form a multi-layer precursor carbon fiber sheet.

  In the step of forming the precursor carbon fiber sheet, if the particles or particle aggregates are supplied so that the particles or particle aggregates exist between the precursor carbon fibers in the thickness direction inside the precursor carbon fiber sheet, Carbon fiber sheets in which particles or particle aggregates are present inside in the direction can be produced. For example, when supplying the precursor carbon fibers of particles or particle aggregates to the precursor carbon fibers in a flying state after spinning, the precursor carbon fibers immediately after the precursor carbon fibers are collected on the collector When particles or particle aggregates are supplied to the precursor carbon fiber sheet, if particles or particle aggregates are supplied to the precursor fibers constituting the inside of the precursor carbon fiber sheet, the particles or particles between the precursor carbon fibers in the thickness direction inside A precursor carbon fiber sheet in which aggregates are present can be formed. Further, when supplying particles or particle aggregates to the sheet-like precursor carbon fibers that have been collected to some extent on the collector, the sheet-like precursor carbon fibers to which the particles or particle aggregates are attached constitute the interior. Thus, a precursor carbon fiber sheet in which particles or particle aggregates exist between precursor carbon fibers in the thickness direction inside can be formed.

  And carbonizing the precursor carbon fiber constituting the precursor carbon fiber sheet, the carbon fiber sheet of the present invention, that is, between the carbon fibers in the thickness direction, a large particle having a diameter larger than the average fiber diameter of the carbon fibers or A carbon fiber sheet containing large particle aggregates can be produced.

  This carbonization step is not particularly limited as long as the carbonizable resin constituting the precursor carbon fiber can be carbonized. For example, in an inert gas atmosphere such as nitrogen, helium, and argon, the maximum temperature is 800 to 3000 ° C. It can be carried out by heating. In addition, it is preferable that a temperature increase rate is 5-100,000 degrees C / min, and it is more preferable that it is 5-1000 degrees C / min. Further, the holding time at the maximum temperature is preferably within 3 hours, more preferably from 1 to 120 minutes.

  The carbon fiber sheet of the present invention can be produced by the method as described above. However, when the carbonizable resin constituting the precursor carbon fiber is a polyacrylonitrile resin, the fiber shape can be maintained even after carbonization. Thus, it is preferable to carry out the infusibilization step before the carbonization treatment. This infusibilization can be carried out, for example, by heating at a temperature of 200 to 300 ° C. for 10 to 120 minutes in an oxidizing atmosphere. The infusible heating can be carried out twice or more under different conditions of temperature or time.

The above is an example of the method for producing the carbon fiber sheet of the present invention, but physical properties suitable for each application can be imparted or improved by various post-processing. For example, when the carbon fiber 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 increase the water repellency of the carbon fiber sheet and to enhance drainage and gas diffusion properties, After immersing the carbon fiber sheet in a fluorine resin dispersion such as ethylene dispersion to give the fluorine resin, sintering can be performed at a temperature of 300 to 350 ° C. Moreover, when a large particle or a large particle aggregate is electroconductive, by pressurizing a precursor carbon fiber sheet or a carbon fiber sheet, the adhesiveness of precursor carbon fibers or carbon fibers is improved, and electroconductivity is improved. You can also. However, since the carbon fiber sheet of the present invention is preferably in a porous state with an apparent density of 0.40 g / cm ³ or less, it is preferable to adjust the applied pressure as appropriate.

  In addition, the carbon fiber sheet which consists of carbon fiber without a space | gap inside is easy to manufacture by using carbonizable resin with a high carbonization rate. For example, when polyacrylonitrile, an epoxy resin, a phenol resin, or the like is used, a carbon fiber sheet made of carbon fibers having no voids inside can be easily manufactured.

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

(Preparation of spinning solution)
Polyacrylonitrile (PAN) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to prepare a spinning solution having a solid concentration of 15 mass%.

(Preparation of particle aggregate dispersion)
Ketjen Black water dispersion [Lion Corporation, Lion Paste W-311N, solid content: 16.5 mass%, primary particle size: 40 nm], polyethylene glycol [Wako Pure Chemical Industries, Ltd., molecular weight: 500,000] and pure water were mixed to prepare a carbon dispersion (particle aggregate dispersion) having a ketjen black concentration of 12 mass% and a polyethylene glycol concentration of 0.7 mass%.

Example 1
The precursor carbon continuous fiber obtained by spinning the spinning solution by the electrostatic spinning method under the following conditions is directly accumulated on the stainless drum as the counter electrode, and at the same time, electrostatic spraying of the carbon dispersion liquid is performed under the following conditions. Then, it is fragmented into charged droplets, sprayed from the top of the stainless drum toward the accumulation position of the precursor carbon continuous fiber, and ketjen black is attached to the precursor carbon continuous fiber immediately after the accumulation, and the precursor carbon continuous fiber and the kettle are adhered. A precursor carbon continuous fiber nonwoven fabric mixed with chain black (mass ratio of precursor carbon continuous fiber and ketjen black = 70: 30) was produced.

  Subsequently, the precursor carbon continuous fiber nonwoven fabric is oxidized 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 carbon continuous fiber. It was set as the melted precursor carbon continuous fiber nonwoven fabric.

  Then, the infusible precursor carbon continuous fiber nonwoven fabric is subjected to carbonization baking treatment (temperature increase rate: 10 ° C./min) for 1 hour at a maximum temperature of 800 ° C. in a nitrogen gas atmosphere using a vacuum displacement electric furnace. A carbon continuous fiber nonwoven fabric (average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber) was produced.

  This carbon continuous fiber nonwoven fabric was photographed and observed in a cross section in the thickness direction of the carbon non-woven fabric, enlarged spherical large particle aggregates, and electron micrographs (see FIGS. 1 to 3) on the surface. It was contained between carbon fibers in the thickness direction (diameter: 4 μm, aspect ratio: 1.2) (number of spherical large particle aggregates: 50). In addition, the spherical large particle aggregates of Ketjen Black were in a state where they were adhered without forming a film while being in point contact with the carbon fibers. Furthermore, while the carbon continuous fiber had the location joined with the fiber, the location where the carbon continuous fiber joined via the ketjen black spherical large particle aggregate was also seen. Further, some of the carbon continuous fibers were curved by the ketjen black spherical large particle aggregates. Furthermore, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates throughout the thickness direction including the vicinity of the inside, the vicinity of the surface, and the entire surface direction.

<Electrostatic spinning conditions>
Electrode: Metallic nozzle (inner diameter 0.41 mm) and grounded stainless steel drum Discharge amount: 3.0 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: + 16kV
Temperature / humidity: 25 ° C / 30% RH

<Electrostatic spray conditions>
Electrode: Metallic nozzle (inner diameter 0.41 mm) and grounded stainless steel drum Discharge amount: 2.5 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: + 18kV
Temperature / humidity: 25 ° C / 30% RH

(Example 2)
The carbon continuous fiber nonwoven fabric was increased in the same manner as in Example 1 except that the spray amount of the carbon dispersion was increased and the mass ratio of the precursor carbon continuous fiber and ketjen black in the precursor carbon continuous fiber nonwoven fabric was 50:50. (Average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber). When the cross section in the thickness direction of this carbon continuous fiber nonwoven fabric, the enlargement of spherical large particle aggregates, and an electron micrograph on the surface were taken and observed, Ketjen Black was observed to have spherical large particle aggregates (diameter: 4 μm, aspect ratio: 1.2) and contained between carbon fibers in the thickness direction (number of spherical large particle aggregates: 80). In addition, the spherical large particle aggregates of Ketjen Black were in a state where they were adhered without forming a film while being in point contact with the carbon fibers. Furthermore, while the carbon continuous fiber had the location joined with the fiber, the location where the carbon continuous fiber joined via the ketjen black spherical large particle aggregate was also seen. Further, some of the carbon continuous fibers were curved by the ketjen black spherical large particle aggregates. Furthermore, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates throughout the thickness direction including the vicinity of the inside, the vicinity of the surface, and the entire surface direction.

Example 3
The carbon continuous fiber nonwoven fabric was increased in the same manner as in Example 1 except that the spray amount of the carbon dispersion was increased and the mixed mass ratio of the precursor carbon continuous fiber and ketjen black in the precursor carbon continuous fiber nonwoven fabric was 20:80. (Average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber). When the cross section in the thickness direction of this carbon continuous fiber nonwoven fabric, the enlargement of spherical large particle aggregates, and an electron micrograph on the surface were taken and observed, Ketjen Black was observed to have spherical large particle aggregates (diameter: 4 μm, aspect ratio: 1.2) and included between carbon fibers in the thickness direction (number of spherical large particle aggregates: 150). In addition, the spherical large particle aggregates of Ketjen Black were in a state where they were adhered without forming a film while being in point contact with the carbon fibers. Furthermore, while the carbon continuous fiber had the location joined with the fiber, the location where the carbon continuous fiber joined via the ketjen black spherical large particle aggregate was also seen. Further, some of the carbon continuous fibers were curved by the ketjen black spherical large particle aggregates. Furthermore, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates throughout the thickness direction including the vicinity of the inside, the vicinity of the surface, and the entire surface direction.

(Comparative Example 1)
As in Example 1, except that the carbon dispersion was not sprayed by electrostatic spraying, it consisted only of PAN-based carbon continuous fibers (average fiber diameter: 350 nm, carbon continuous fibers have no voids inside the fibers). A carbon continuous fiber nonwoven fabric was produced. When the electron micrograph in the surface of this carbon continuous fiber nonwoven fabric was image | photographed and observed, the carbon continuous fiber was linear and the carbon continuous fiber was in the state joined by the fibers.

(Comparative Example 2)
After the precursor carbon continuous fibers obtained by spinning the spinning solution by the electrospinning method under the same conditions as in Example 1 are directly accumulated on a stainless drum as a counter electrode to form a precursor carbon continuous fiber nonwoven fabric, The carbon dispersion liquid was electrostatically sprayed with the carbon dispersion liquid under the same conditions as in Example 1 and fragmented into droplets having electric charges, and the precursor carbon continuous fibers already accumulated and formed into a nonwoven fabric form from the upper part of the stainless drum Spraying toward the nonwoven fabric, a precursor carbon continuous fiber nonwoven fabric (mass ratio of precursor carbon continuous fiber and ketjen black = 70: 30) having ketjen black adhered to the surface was produced.

  Subsequently, as in Example 1, the precursor carbon continuous fiber was infusibilized and carbonized and fired to produce a carbon continuous fiber nonwoven fabric (average fiber diameter: 350 nm, the carbon continuous fiber has no voids inside the fiber). did.

  When the cross section in the thickness direction of this carbon continuous fiber nonwoven fabric, the enlargement of spherical large particle aggregates, and an electron micrograph on the surface were taken and observed, Ketjen Black was observed to have spherical large particle aggregates (diameter: 4 μm, aspect ratio: In the form of 1.2), it was included in a state where the carbon continuous fibers in the plane direction were bonded without forming a film in a point manner, but was not included between the carbon fibers in the thickness direction. . Furthermore, the carbon continuous fiber is linear, the carbon continuous fiber has a part where the fibers are joined together, and the part where the carbon continuous fibers are joined via the Ketjen Black spherical large particle aggregate is seen. There wasn't. That is, there was no place where joining of carbon continuous fibers was hindered by Ketjen Black spherical large particle aggregates. Furthermore, the carbon continuous fiber non-woven fabric has ketjen black spherical large-sized aggregates on the entire surface only, and the ketjen black spherical large-sized particle aggregates are in a state where they easily fall off.

(Comparative Example 3)
A carbon continuous fiber nonwoven fabric produced in the same manner as in Comparative Example 1 was used in a ketjen black water dispersion [manufactured by Lion Corporation, Lion Paste W-311N, solid content: 16.5 mass%, primary particle size: 40 nm] The carbon continuous fiber nonwoven fabric (average fiber diameter: 350 nm, mass ratio of carbon continuous fiber to Ketjen black = 45: 55, carbon continuous fiber) Produced no voids inside the fiber).

  The carbon continuous fiber nonwoven fabric having this ketjen black was photographed and observed for a cross section in the thickness direction, an enlargement of the ketjen black, and an electron micrograph on the surface (see FIGS. 4 to 6). In the form, the voids of the carbon fiber sheet were closed in the entire thickness direction and the entire surface direction of the carbon continuous fiber nonwoven fabric. In addition, the Ketjen Black spherical large particle aggregate was not contained between the carbon fibers in the thickness direction. In addition, while the carbon continuous fiber was linear and the carbon continuous fiber had the location joined between the fibers, the location where the carbon continuous fibers were joined with the film | membrane containing ketjen black was also seen.

(Comparative Example 4)
Vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer (THV) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solution having a concentration of 10 mass%.

  Next, 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 mixed in the solution, After stirring, DMF was further added and diluted to disperse the carbon nanotubes, thereby obtaining a dispersion solution.

  Further, a carbonizable resin (EP) containing a cresol novolac epoxy resin as a main component and a novolac type phenol resin as a curing agent is added to the dispersion solution, and the solid content mass ratio of CNT: THV: EP is 40:30:30. Then, a first spinning solution having a solid content concentration of 16 mass% was prepared.

  On the other hand, polyacrylonitrile (PAN) was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to prepare a second spinning solution having a concentration of 20 mass%.

  Next, the first spinning solution is spun on the first precursor carbon continuous fiber by the electrospinning method under the following conditions, and directly accumulated on the stainless drum as the counter electrode, and at the same time, the second spinning solution is electrospun. According to the method, the second precursor carbon continuous fiber is spun under the following conditions, directly collided with the first precursor carbon continuous fiber assembly, and accumulated, and the first precursor carbon continuous fiber and the second precursor carbon continuous fiber are A mixed, precursor carbon continuous fiber nonwoven fabric was prepared.

(Electrostatic spinning conditions)
(1) First spinning solution Electrode: Metallic nozzle (inner diameter: 0.33 mm) and grounded stainless steel drum Discharge amount: 4 g / hour Distance between nozzle tip and stainless steel drum: 8 cm
Applied voltage: + 10kV
Temperature / humidity: 25 ° C / 35% RH

(2) Second spinning solution Electrode: Metallic nozzle (inner diameter: 0.41 mm) and grounded stainless steel drum Discharge amount: 2 g / hour Distance between nozzle tip and stainless steel drum: 12 cm
Applied voltage: +15 kV
Temperature / humidity: 25 ° C / 35% RH

  Next, after adjusting the thickness of the precursor carbon continuous fiber nonwoven fabric using a calender roll (linear pressure 10 N / cm), heat treatment was performed for 1 hour with a hot air dryer set at a temperature of 150 ° C. The epoxy resin which comprises a carbon continuous fiber was hardened, and the hardening precursor carbon continuous fiber nonwoven fabric was prepared.

  Subsequently, as in Example 1, the cured precursor carbon continuous fiber was infusibilized and carbonized and fired, and the carbon continuous fiber nonwoven fabric (average fiber diameter: 1.5 μm, the carbon continuous fiber has voids inside). Manufactured.

  When the electron micrograph in the surface of this carbon continuous fiber nonwoven fabric was image | photographed and observed, the carbon continuous fiber was joined by the fibers in the curved state instead of linear form.

<Measurement of electrical resistance>
The electrical resistance of the carbon continuous fiber nonwoven fabrics of Examples 1 to 3 and Comparative Examples 1 to 4 was measured by the following procedure. The results are shown in Table 1.
(1) A carbon continuous fiber nonwoven fabric is cut into 5 cm square (area: 25 cm ² ) to prepare a sample.
(2) The sample is sandwiched between metal plates plated with gold from both sides, and the voltage (V) is measured in a state where a current (I) of 1 A is applied under pressure of 2 MPa in the stacking direction of the metal plates.
(3) The resistance (R = V / I) is calculated.
(4) The electrical resistance is calculated by multiplying the resistance (R) by the area of the sample (25 cm ² ).

<Evaluation of flexibility>
The carbon continuous fiber nonwoven fabrics of Examples 1 to 3 or Comparative Examples 1 to 4 were cut into 50 mm squares to prepare samples. Next, in a state where the sample was folded in half, a load of 1.2 kPa was applied for 5 seconds by sandwiching the sample with a metal plate. Thereafter, the sample was taken out from between the metal plates, and it was confirmed whether or not the sample was broken, that is, whether the sample was cracked or broken into two. The results are shown in Table 1.

  From the results in Table 1, it was found that the carbon fiber nonwoven fabric has flexibility that does not break even when folded in half by including large particles or large particle aggregates between the carbon fibers in the thickness direction. Moreover, it turned out that it is excellent also in electroconductivity by including the electroconductive large particle or the large particle aggregate.

  The carbon fiber sheet of the present invention is flexible and excellent in handleability. Particularly, when large particles or large particle aggregates have conductivity, they are excellent in conductivity, and therefore suitable as a substrate for electrodes. Can be used. For example, it can be suitably used as a base material for an electrode of a lithium ion secondary battery or an electric double layer capacitor or a gas diffusion electrode of a polymer electrolyte fuel cell.

Claims (15)

A carbon fiber sheet in which particles or particle aggregates exist between carbon fibers, and the particles or particle aggregates are large particles or large particle aggregates having a diameter larger than the average fiber diameter of carbon fibers, in the thickness direction. The carbon fiber sheet characterized by including between the carbon fibers in. 2. The carbon fiber sheet according to claim 1, wherein large particles or large particle aggregates are present in the thickness direction of the carbon fiber sheet. The carbon fiber sheet according to claim 1 or 2, wherein the large particles or large particle aggregates have a substantially spherical shape. The carbon fiber sheet according to any one of claims 1 to 3, wherein the large particles or large particle aggregates are present in a state of being in point contact with the carbon fibers. The carbon fiber sheet according to any one of claims 1 to 4, wherein a film is not formed between the large particles or large particle aggregates and the carbon fibers. The carbon fiber sheet according to any one of claims 1 to 5, wherein the large particle or the large particle aggregate has conductivity. A carbon fiber sheet using the carbon fiber sheet according to claim 6 as a base material for a gas diffusion electrode. A gas diffusion electrode, wherein a catalyst is supported on the carbon fiber sheet according to claim 6. A membrane-electrode assembly comprising the gas diffusion electrode according to claim 8. A solid polymer fuel cell comprising the gas diffusion electrode according to claim 8. Spinning the precursor carbon fiber with a spinning solution containing a carbonizable resin;
Supplying particles or particle aggregates to the precursor carbon fibers;
Forming a precursor carbon fiber sheet in which particles or particle aggregates exist between the precursor carbon fibers in the thickness direction;
The precursor carbon fiber constituting the precursor carbon fiber sheet is carbonized, and the carbon fiber sheet includes large particles or large particle aggregates having a diameter larger than the average fiber diameter of the carbon fibers between the carbon fibers in the thickness direction. Stage,
A method for producing a carbon fiber sheet, comprising: The carbon fiber sheet according to claim 11, wherein the step of supplying particles or particle aggregates to the precursor carbon fibers is performed by spraying the precursor carbon fibers with a dispersion containing the particles or particle aggregates. Manufacturing method. The step of supplying particles or particle aggregates to the precursor carbon fibers is performed by fragmenting a dispersion liquid containing particles or particle aggregates into droplets having electric charges and spraying the droplets on the precursor carbon fibers. The method for producing a carbon fiber sheet according to claim 11 or 12. The method for producing a carbon fiber sheet according to any one of claims 11 to 13, wherein the step of spinning the precursor carbon fiber is performed by an electrostatic spinning method. The method for producing a carbon fiber sheet according to any one of claims 11 to 14, wherein the large particles or large particle aggregates have conductivity.

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