JP7021869B2 - Method for manufacturing carbon fiber sheet, gas diffusion electrode, membrane-electrode assembly, polymer electrolyte fuel cell, and carbon fiber sheet - Google Patents

Description

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

Conventionally, the carbon fiber sheet has been used as a base material for a gas diffusion electrode for a fuel cell, as an electrode for an electric double layer capacitor, or as an electrode for a lithium ion secondary battery by utilizing its conductivity and porosity. It is being considered for use.

As such a carbon fiber sheet, a fiber web in which carbon fibers and a binder for making is mixed is made, and the fiber web is impregnated with a thermosetting resin such as a phenol resin and cured, and then the temperature is 1000 ° C. or higher. A carbon fiber sheet manufactured by firing in is known. Considering the mass productivity of the carbon fiber sheet, it is desired that the carbon fiber sheet has flexibility that can be rolled into a roll shape. Although the carbon fiber sheet has excellent conductivity, it can be rolled into a roll shape. It was not possible, the flexibility was insufficient, and the handleability was poor.

In addition, the applicant of the present application stated, "Carbon black and polytetrafluoroethylene resin or polyvinylidene fluoride are used on a base material for a gas diffusion electrode made of a glass non-woven fabric having a binder containing an acrylic resin and / or a vinylidene acetate resin attached to glass fibers. We have proposed "a gas diffusion electrode in which a conductive paste containing a vinylidene resin is adhered and fired" (Patent Document 1), but the glass fiber has high rigidity and the conductive paste is adhered and fired. Moreover, since the rigidity was further increased, the flexibility was insufficient and the handleability was poor.

As a carbon fiber sheet that can solve such a problem of flexibility, the applicant of the present application states that "conductivity including a fibrous material having a first conductive material and a second conductive material connecting 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 amount of 1 mm or more. (Patent Document 2) was proposed. This conductive porous body had a certain degree of flexibility, but the flexibility was insufficient and the handling was poor.

Japanese Unexamined Patent Publication No. 2008-20945

Japanese Unexamined Patent Publication No. 2017-59309

The present invention has been made under such circumstances, and is a carbon fiber sheet, a gas diffusion electrode, a membrane-electrode assembly, a polymer electrolyte fuel cell, and a carbon fiber sheet having excellent flexibility and handleability. The purpose 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 the 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 inside the carbon fiber sheet in the thickness direction, large particles or large particle aggregates have a substantially spherical shape, and large particles or large particles are present. The particle agglomerates are present in point contact with the carbon fibers, no film is formed between the large particles or large particle agglomerates and the carbon fibers, and / or the large particles or large particle agglomerates. It is preferable that the aggregate has conductivity.

Further, in the carbon fiber sheet of the present invention, the carbon fiber sheet in which large particles or large particle aggregates have conductivity can be suitably used as a base material for a gas diffusion electrode.

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

The method for producing a carbon fiber sheet of the present invention is a step of spinning a precursor carbon fiber using a spinning liquid containing a carbonizable resin, a step of supplying particles or particle aggregates to the precursor carbon fiber, and a step in the thickness direction. At the stage of forming the precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers, the precursor carbon fibers constituting the precursor carbon fiber sheet are carbonized, and the average of the carbon fibers is averaged between the carbon fibers in the thickness direction. A step of making a carbon fiber sheet containing large particles or large particle aggregates having a diameter larger than the fiber diameter is included.

The step of supplying the particles or the particle aggregates to the precursor carbon fiber is carried out by spraying the dispersion liquid containing the particles or the particle aggregates onto the precursor carbon fibers, particularly the dispersion liquid containing the particles or the particle aggregates. It is preferable to fragment the particles into charged droplets and spray them onto the precursor carbon fibers.

Further, it is preferable that the step of spinning the precursor carbon fiber is carried out by an electrostatic spinning method, and it is preferable that large particles or large particle aggregates have conductivity.

In the present invention, there are few contacts between carbon fibers due to 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. Since the carbon fibers can be curved along the large particles or the large particle aggregates due to the presence of the large particles or the large particle aggregates, it is considered that the carbon fibers are excellent in flexibility and handleability. .. In addition, since large particles or large particle aggregates act like pillars in a house, there is also an effect that they are not easily damaged by pressure in the thickness direction.

The presence of large particles or large particle agglomerates inside the carbon fiber sheet in the thickness direction is superior to flexibility.

When the large particles or the large particle aggregates have a substantially spherical shape, the contact area between the large particles or the large particle aggregates and the carbon fibers is small, and the degree of freedom of the carbon fibers is not so limited, so that the carbon fiber sheet is flexible. Better in sex.

When the large particles or the large particle agglomerates are present in the state of being in point contact with the carbon fibers, the contact area between the large particles or the large particle agglomerates and the carbon fibers is small, and the degree of freedom of the carbon fibers is not so limited. The carbon fiber sheet is superior in flexibility because it is not.

If no film is formed between the large particles or large particle aggregates and the carbon fibers, the carbon fiber sheet is more flexible because the degree of freedom of the carbon fibers is not so limited. In addition, the voids in the carbon fiber sheet can be effectively used. For example, it has excellent gas diffusivity and water permeability.

When the large particles or the large particle aggregates have conductivity, the carbon fiber sheet has excellent conductivity and can be suitably used for applications requiring conductivity.

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

In the gas diffusion electrode, large particles or large particle aggregates have conductivity, and the catalyst is supported on a carbon fiber sheet with excellent conductivity, so that the electrical resistance is low and the solid height capable of exhibiting sufficient power generation performance. Can manufacture molecular fuel cells.

Since the membrane-electrode assembly includes the gas diffusion electrode, it is possible to manufacture a polymer electrolyte fuel cell having low electrical resistance and exhibiting sufficient power generation performance.

Since the polymer electrolyte fuel cell is provided with the gas diffusion electrode, the electric resistance is low and sufficient power generation performance can be exhibited.

In the method for producing a carbon fiber sheet of the present invention, since particles or particle aggregates are supplied to the precursor carbon fibers, the carbon fiber sheet containing large particles or large particle aggregates between the carbon fibers in the thickness direction. Can be manufactured. That is, it is possible to manufacture a carbon fiber sheet having excellent flexibility and excellent handleability.

When the dispersion liquid containing the particles or the 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 the large particle aggregates and the carbon fibers.

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

Further, when the precursor carbon fiber is spun by the electrostatic spinning method, it is possible to spin a continuous precursor carbon fiber having a uniform fiber diameter. Therefore, it is possible to manufacture a carbon fiber sheet which is excellent in conductivity, has a large surface area, and can effectively utilize the carbon fiber surface.

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

Electron micrograph (2500 times) in the thickness direction cross section of the carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Enlarged electron micrograph (20000 times) of carbon particle aggregates of carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Electron micrograph (5000x) on the surface of the carbon continuous fiber nonwoven fabric (carbon fiber sheet) in Example 1 Electron micrograph (2500 times) in the thickness direction cross section of the carbon continuous fiber nonwoven fabric to which Ketjen black was applied in Comparative Example 3 Enlarged electron micrograph (20000x) of carbon particle aggregates of carbon continuous fiber non-woven fabric with Ketjen black in Comparative Example 3 Electron micrograph (5000x) on the surface of the carbon continuous fiber non-woven fabric with Ketjen black in Comparative Example 3

In the carbon fiber sheet of the present invention, the contact points between the carbon fibers are formed by 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. Due to the low degree of freedom of the carbon fibers and the presence of large particles or agglomerates, the carbon fibers can be curved along the large particles or agglomerates of carbon. Since there is a margin to follow the deformation when the fiber sheet is bent, it is considered to be excellent in flexibility and handleability. In addition, since large particles or large particle aggregates act like pillars 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 orthogonal to both surfaces, and "both surfaces" means a surface having the largest area in the carbon fiber sheet and facing the surface. Means a face.

The carbon fiber of the present invention can be, for example, a PAN-based carbon fiber. Also, the carbon fiber can contain a conductive material. When the conductive material is contained in this way, the conductivity and the mechanical strength are more excellent. Such conductive materials include, for example, fullerene, carbon nanotubes, carbon nanohorns, graphite, graphene, vapor-grown carbon fiber, carbon black, metals (eg, 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 suitable because they have excellent conductivity, are easily oriented in the length direction in carbon fibers, and can increase conductivity and mechanical strength.

When the carbon fiber of the present invention is in a state where there are no voids inside the fiber, it is suitable because it is excellent in mechanical strength and conductivity. This "no voids inside the fiber" means that the contour of the cut surface in the thickness direction of the carbon fiber sheet is continuous, and the entire cross section of the carbon fiber having a clear cross section shape can be accommodated in 1 to 3 fibers. It means that the number of carbon fibers in which no voids are observed is 70% or more by observing the carbon fibers in 10 places. It should be noted that the carbon fiber contains the conductive material as described above, and the voids clearly formed by the conductive material falling off when the carbon fiber sheet is cut in the thickness direction are included in the voids. do not have. Further, 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 fibers, so that the carbon fibers contain the conductive material containing voids. Even so, it is considered that there are no voids inside the fiber.

The average fiber diameter of the carbon fibers of the present invention is not particularly limited, but the mechanical strength of the carbon fiber sheet itself is such that the mechanical strength of the carbon fibers themselves is excellent and there are some contact points between the carbon fibers. It is preferably 10 nm to 20 μm, more preferably 50 nm to 10 μm, and even more preferably 100 nm to 5 μm so as to have excellent conductivity.

The "average fiber diameter" in the present invention means the arithmetic mean value of the fiber diameters at 40 points of the carbon fibers, and the "fiber diameter" is the width orthogonal to the length direction when the carbon fibers are observed by micrographs. means.

The carbon fiber is preferably a continuous fiber so as to have excellent conductivity. When the carbon fiber sheet of the present invention is used as a base material for a gas diffusion electrode, there is substantially no fiber end portion of the carbon fiber, and there is also an effect that the solid polymer film is not damaged. The carbon fiber, which is such a continuous fiber, is obtained after spinning the continuous precursor carbon fiber (for example, electrostatic spinning method, spunbond method, etc.) using, for example, a spinning liquid containing a carbonizable organic material. It can be produced by carbonizing an organic material (precursor carbon fiber) that can be carbonized. The term "continuous fiber" refers to an electron micrograph when a carbon fiber sheet is photographed using an electron microscope at a magnification such that one side of the photographed image is about 60 times the average fiber diameter of the carbon fiber. It means that the number of ends of carbon fiber per sheet is 0.3 or less. That is, it means that the number of carbon fiber ends per electron micrograph obtained by dividing the total number of carbon fiber ends in 20 electron micrographs by the number of photographs (20) is 0.3 or less. The photography is performed continuously at different locations in the central portion of the surface of the carbon fiber sheet not including the cut portion. For example, when confirming whether carbon fibers having an average fiber diameter of 1 μm are continuous fibers, photography using an electron microscope is performed at continuously different points in the central portion of the surface of the carbon fiber sheet not including the cut portion. In, 20 sheets (4 rows x 5 columns) were performed at a magnification (2500 times) so that one side of the photographed image was about 60 μm, and the number of carbon fiber edges per electron micrograph was calculated. For example, it can be considered as a continuous fiber.

The carbon fiber sheet of the present invention does not have to be composed of one type of carbon fiber, but may be composed of 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 / absence of a conductive material, the type of the conductive material, the presence / absence of voids inside the carbon fibers, the average fiber diameter, the fiber length, and the like. ..

It is preferable that the carbon fibers constituting the carbon fiber sheet of the present invention are joined so as to have excellent mechanical strength and excellent conductivity. It should be noted that the bonding between the carbon fibers is preferably made by the carbide of the organic material so that the adhesion between the carbon fibers is excellent and the mechanical strength and the 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 a magnified electron micrograph of the carbon particle aggregates 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 agglomerates in addition to the carbon fibers as described above, and large particles or large particle agglomerates having a diameter larger than the average fiber diameter of the carbon fibers. The carbon fibers are contained between the carbon fibers in the thickness direction, the bonding between the carbon fibers is hindered, the number of contacts between the carbon fibers is small, and the presence of large particles or large particle aggregates causes the carbon fibers to form. Since it can be curved along a large particle or a large particle aggregate, it is considered to have excellent flexibility and handleability. That is, there are few contacts between the carbon fibers, the degree of freedom of the carbon fibers is relatively high, and if the carbon fibers are curved, there is a margin to follow the deformation when the carbon fiber sheet is bent. Therefore, the present invention. Carbon fiber is considered to have excellent flexibility.

As described above, if the large particles or the 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 between the carbon fibers is hindered and the flexibility is excellent. Although it is a carbon fiber sheet, the diameter of the large particles or large particle aggregates is preferably 1.5 times or more the average fiber diameter of the carbon fibers so that the bonding between the carbon fibers can be reliably 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 particles or the large particle aggregates is too large, the carbon fibers are hardly bonded to each other, and the mechanical strength, conductivity, etc. of the carbon fiber sheet tend to be significantly deteriorated. The diameter of the particle agglomerates is preferably 60 times or less, more preferably 50 times or less, still more preferably 40 times or less the average fiber diameter of the carbon fibers. The diameter of the large particles or the large particle aggregates may be larger than the average fiber diameter of the carbon fibers and is not particularly limited, but is preferably 0.1 μm to 1000 μm, preferably 0.5 μm to 100 μm. It is more preferably 1 μm to 30 μm, still more preferably 1 μm to 10 μm.

The "diameter" of the large particles or agglomerates of large particles is the diameter of the 50 large particles or agglomerates of large particles shown in the electron micrograph taken by taking an electron micrograph in the thickness direction cross section of the carbon fiber sheet. Arithmetic average value. When the shape of the large particles or large particle aggregates is non-circular on the photograph, the diameter of the circle having the same area as the area of the large particles or large particle aggregates on the photograph is set to the large particles or large particles. Considered as the diameter of the particle agglomerates.

The material constituting the large particles or large particle aggregates of the present invention may be conductive or non-conductive, but when the conductivity of carbon fibers is used, the large conductive particles or It is preferably a large particle agglomerate. The former conductive material means a material having an electrical resistivity of ¹⁰³ Ω · cm or less, and for example, carbon (for example, Ketjen black, acetylene black, carbon black, carbon nanotube, carbon nanofiber, graphene, carbon nanohorn, etc. Graphite, graphene, etc.), metals (silver, aluminum, nickel, gold, palladium, platinum, cadmium, cobalt, copper, iron, zinc, etc.), conductive metal oxides (tin oxide-doped indium oxide, tin oxide, zinc oxide, etc.) ), And carbon is suitable from the viewpoint of chemical resistance, conductivity and the like, 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 103 Ω · cm, for example, a non-conductive metal oxide (for example, silicon oxide, aluminum oxide, iron oxide, manganese dioxide, copper oxide). , Nickel oxide, cobalt oxide, zinc oxide, titanium-containing oxide, zeolite, catalyst-supported ceramics, etc.), organic resin (polyamide resin, polyester resin, polyolefin resin, fluororesin, etc.), activated carbon powder (for example, Steam-activated charcoal, alkali-treated activated charcoal, acid-treated activated charcoal, etc.), ion exchange resin powder, plant seeds, etc. can be mentioned.

The shape of the large particles or large particle aggregates of the present invention is not particularly limited, but is, for example, substantially spherical (substantially spherical or true spherical), fibrous, needle-like (for example, tetrapot-like), or flat plate. , Polyhedral shape, feather-like, amorphous shape. Among these, the substantially spherical shape is a suitable shape because the contact area with the carbon fibers is small and the degree of freedom of the carbon fibers is not easily reduced.

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 1.2 or less. More preferred.

(aspect ratio)
(1) In the electron micrograph on the surface of the carbon fiber sheet, select large particles or large particle aggregates that can clearly observe the entire outline of each individual.
(2) Draw the longest line segment (longest line segment) formed by connecting two points on the outer circumference of the selected large particles or large particle aggregates.
(3) Draw the longest line segment (orthogonal line segment) formed by connecting two points on the outer circumference of the selected large particles or large particle aggregates orthogonal to the longest line segment.
(4) Obtain the ratio of the longest line segment (major diameter) to the orthogonal line segment (minor diameter). 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 particles arbitrarily selected, and the arithmetic mean value of the longest line segment (major diameter) / orthogonal line segment (minor diameter) 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 selected from diameter, material, shape, conductive or non-conductive, and / or hollow or solid. Large particles or agglomerates of large particles may be mixed.

Although the carbon fiber sheet of the present invention contains large particles or large particle aggregates, it is preferable that the carbon fiber sheet is contained so as to be present inside the carbon fiber sheet in the thickness direction. When present inside in this way, even if stress due to bending is applied, large particles or large particle aggregates relieve the stress, so that it is considered to be more excellent in flexibility. Although large particles or large particle aggregates can be present only inside the carbon fiber sheet, they are also present near the surface in addition to the inside of the carbon fiber sheet so as to have excellent flexibility. Is preferable. That is, it is preferable that large particles or large particle aggregates are present throughout the thickness direction of the carbon fiber sheet. The "inside" of this carbon fiber sheet means the central region when a cross-sectional photograph of the carbon fiber sheet in the thickness direction 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 a surface when divided into three equal parts by the straight line.

When large particles or large particle aggregates are contained inside the carbon fiber sheet in the thickness direction, it is not necessary that the large particles or large particle aggregates are uniformly present throughout the inside of the carbon fiber sheet, and the large particles do not need to be present. Alternatively, layers of large particle aggregates and layers of carbon fibers may be present alternately.

Further, when the carbon fiber sheet contains large particles or large particle aggregates only inside, the vicinity of the surface can be composed of only carbon fibers or only large particles or large particle aggregates.

In the carbon fiber sheet of the present invention, large particles or large particle agglomerates may be present in any manner, but the large particles or large particle agglomerates are present in a state of being in point contact with the carbon fibers. Is preferable. When they exist in such a pointed state, the contact area between the large particles or the large particle aggregates and the carbon fibers is small, the degree of freedom of the carbon fibers is not so limited, and the carbon fiber sheet has a carbon fiber sheet. This is because it is more flexible. Such a pointally contacted state is easily achieved when large particles or large particle aggregates having a substantially spherical shape are bonded to carbon fibers without deforming the shape.

Further, in the carbon fiber sheet of the present invention, it is preferable that the large particles or the large particle aggregates exist in a state where a film is not formed between the large particles or the large particle aggregates. This is because 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 more excellent in flexibility. If the film is not formed, the voids of the carbon fiber sheet can be effectively used. That is, if a film is formed between the carbon fibers and large particles or large particle aggregates, the voids of the carbon fiber sheet in the vicinity of the film tend to be unable to be effectively used, but the film must be formed. For example, the voids of the carbon fiber sheet can be effectively used. Such a "non-filming" state is, for example, a state in which large particles or large particle aggregates are adhered to, adhered to, welded, or fixed to carbon fibers in a pointed or linear manner. When large particles or large particle aggregates are adhered to carbon fibers using a liquid adhesive, a film is likely to be formed.

As described above, the carbon fiber sheet of the present invention contains large particles or large particle aggregates between the carbon fibers in the thickness direction, but is not limited to the thickness direction, and the carbon fibers in the surface direction of the carbon fiber sheet. In between, it is preferable to contain large particles or large particle aggregates in whole or in part (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. Even when large particles or agglomerates of large particles are contained in the plane direction, the large particles or agglomerates of large particles are substantially spherical in contact with the carbon fibers in a substantially spherical shape, as in the case of being present between the carbon fibers in the thickness direction. It is preferable that the film is not formed between the state and / or the carbon fiber and is 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 contain 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 carbon fibers. You may be doing it. In the carbon fiber sheet of the present invention, since it is considered that large particles or large particle aggregates have flexibility, it is preferable that there are many large particles or large particle aggregates, and specifically, large particles or large particles. The number of agglomerates in the thickness direction of the carbon fiber sheet is preferably 1 or more, more preferably 25 or more, and further preferably 50 or more. It should be noted that this number is a photographable magnification in which both surfaces of the carbon fiber sheet fit and the cross section of the carbon fiber sheet occupies 80% or more of the photographed image area, and 20 cross-sectional photographs in the thickness direction of the carbon fiber sheet are taken. It means the number of large particles or large particle aggregates per one cross-sectional photograph when a single image is taken. That is, it means the number of large particles or large particle agglomerates per cross-sectional photograph obtained by dividing the total number of large particles or large particle agglomerates in 20 cross-sectional photographs by the number of photographs (20). The photographs are taken at continuously different points in the center of the cross section not including the edges of the 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 occupy 1 mass% or more of the entire carbon fiber sheet so that there are few contacts between the carbon fibers. It is more preferable that it occupies 5 mass% or more, and it is further preferable that it occupies 10 mass% or more. The large particles or large particle aggregates preferably occupy 0.9 mass% or more of the entire carbon fiber sheet, more preferably 4.5 mass% or more, and occupy 9 mass% or more. Is more preferable. On the other hand, if the amount of particles or particle agglomerates is too large, the strength of the carbon fiber sheet tends to be low, and from this point, the handleability tends to be poor. Therefore, the particles or particle agglomerates are 99 mass% of the entire carbon fiber sheet. It preferably occupies the following, more preferably 95 mass% or less, and even more preferably 90 mass% or less. Since it is preferable that the large particles or large particle aggregates of the present invention occupy a large proportion of the entire particles or particle aggregates, the large particles or large particle aggregates occupy 99 mass% or less of the entire carbon fiber sheet. It is more preferable that it occupies 95 mass% or less, and further preferably 90 mass% or less.

As described above, the carbon fiber sheet of the present invention contains large particles or large particle aggregates between the carbon fibers in the thickness direction, has few contacts between the carbon fibers, and is in a porous state, so that the inside of the carbon fiber sheet is in a porous state. The voids can be effectively used. Specifically, it is preferable that the apparent density is 0.40 g / cm ³ or less in a porous state. The smaller the apparent density, the more porous it is and the more effectively the internal voids can be used. Therefore, it is more preferably 0.20 g / cm ³ or less, and further preferably 0.12 g / cm ³ or less. If the apparent density is too small, the morphological stability tends to be inferior, so that it is preferably 0.01 g / cm ³ or more. This "apparent density" is a value calculated by dividing "grain (unit: g / m ² )" by "thickness (unit: μm)", and "grain" is a value obtained by dividing a carbon fiber sheet by 10 cm. The mass of the sample obtained by cutting into corners is measured and converted into a mass of 1 m ² in size. "Thickness" is the thickness gauge manufactured by Mitutoyo Co., Ltd .: Code No. 547-401: A value measured using a measuring force of 3.5 N or less).

Although the carbon sheet of the present invention contains carbon fibers and large particles or large particle aggregates, it may also contain other materials. For example, recycled fibers such as rayon, polynosic, cupra; semi-synthetic fibers such as acetate fibers; nylon fibers, vinylon fibers, fluorofibers, polyvinyl chloride fibers, polyester fibers, acrylic fibers, polyethylene fibers, polyolefin fibers or polyurethane fibers, etc. 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; and the like can also be included.

The form of the carbon fiber sheet of the present invention is not particularly limited, but may be, for example, a non-woven fabric form in which carbon fibers are randomly oriented, a woven fabric or knitted form in which the fibers are regularly oriented. In particular, the non-woven fabric form is suitable because the voids are fine and the porosity is high.

The texture of the carbon fiber sheet of the present invention is not particularly limited, but is preferably 0.5 to 500 g / m ² so as to be excellent in mechanical strength and conductivity, and is preferably 1 to 400 g / m ² . It is more preferably 3 to 300 g / m ² , further 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, still more preferably 5 to 500 μm, still more preferably 10 to 300 μm.

When the carbon fiber sheet of the present invention is used in an application requiring conductivity, the electric resistance is preferably 500 mΩ · cm ² or less, more preferably 100 mΩ · cm ² or less, and 20 mΩ · cm ² or less. The following is more preferable. This "electrical resistance" is a value obtained by the following procedure.
(1) A carbon fiber sheet is cut into 5 cm squares (area: 25 cm ² ) to prepare a sample.
(2) The sample is sandwiched between gold-plated metal plates from both sides, and the voltage (V) is measured in the laminating direction of the metal plates under pressure at 2 MPa and a current (I) of 1 A is applied.
(3) Calculate the resistance (R = V / I).
(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 has excellent handleability, and when large particles or large particle aggregates have conductivity, the conductivity is further excellent, so that the carbon fiber sheet is suitably used as a base material for electrodes. 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 a 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 manufactured.

When the large particles or large particle aggregates of the present invention have conductivity and a carbon fiber sheet having excellent conductivity is used as a base material for a gas diffusion electrode, not only the carbon fibers of the present invention are excellent, but also the carbon fibers of the present invention are used. Since the sheet is porous, if the voids between the carbon fibers are not filled, the base material for the gas diffusion electrode (carbon fiber sheet) has excellent drainage in the thickness direction and the surface direction, and also has excellent drainage property. It has excellent diffusivity of the supplied gas.

If a fluororesin is contained in the voids between the carbon fibers of the base material for the gas diffusion electrode (carbon fiber sheet), the liquid water is easily extruded, so that the drainage property is excellent. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy alkane resin (PFA), and four hoots. Ethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), fluorovinylidene / 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 conductivity, and a catalyst is supported on a carbon fiber sheet having excellent conductivity, so that electric resistance is low and sufficient power generation performance can be exhibited. It is possible to manufacture a polymer electrolyte fuel cell. Further, in the gas diffusion electrode of the present invention, a catalyst is supported on a carbon fiber sheet, for example, a catalyst is supported on the surface of carbon fibers and / or large particles or large particle aggregates, and electron conduction by contact between the catalysts alone is sufficient. There are few catalysts isolated from the electron conduction path because the electron conduction path is also formed by carbon fibers and / or large particles or large particle aggregates. Therefore, the catalyst can be used efficiently and the amount of the catalyst can be reduced.

The gas diffusion electrode of the present invention has exactly 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-lantern alloy, titanium-iron alloy, etc. It can be one or more types of catalysts selected from these.

In addition to the catalyst, it is preferable to contain an electron conductor and a proton conductor, and the electron conductor is preferably made of a conductive material similar to large particles such as carbon black or large particle aggregates. Yes, the catalyst may be carried on this electron conductor. Further, as the proton conductor, an ion exchange resin is suitable.

Such a gas diffusion electrode can be produced, for example, by the following method. First, a catalyst (for example, a carbon powder carrying a catalyst such as platinum) is added to a single or mixed solvent consisting of ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol dimethyl ether, etc. and mixed, and then an ion exchange resin is added. The solution is added and mixed uniformly by ultrasonic dispersion or the like to prepare a catalytic dispersion suspension. Then, the carbon fiber sheet of the present invention can be coated with or sprayed with the catalyst dispersion suspension 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 manufacture a polymer electrolyte fuel cell having low electrical resistance and 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 is provided with the gas diffusion electrode as described above. For example, the solid polymer film may be a perfluorocarbon sulfonic acid-based resin film, a sulfonated aromatic hydrocarbon-based resin film, an alkyl sulfonated aromatic hydrocarbon-based resin film, or the like.

Such a membrane-electrode assembly can be manufactured, for example, by sandwiching a solid polymer membrane between the catalyst-supporting surfaces of a pair of gas diffusion electrodes and heat-pressing them. Further, after the catalyst dispersion suspension as described above is applied to the 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 laminating so as to be in contact with each other and hot pressing.

Since the polymer electrolyte fuel cell of the present invention is provided with the gas diffusion electrode, it has low electrical resistance and can exhibit sufficient power generation performance.

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

The bipolar plate may be any as long as it has high conductivity, does not allow gas to pass through, and has a flow path capable of supplying gas to the gas diffusion electrode, and is not particularly limited, but for example, a carbon molding material. A carbon-resin composite material, a metal material, or the like can be used.

The carbon fiber sheet of the present invention is, 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. At the stage of forming the precursor carbon fiber sheet in which particles or particle aggregates are present between the carbon fibers, the precursor carbon fibers constituting the precursor carbon fiber sheet are carbonized, and the average fibers of the carbon fibers are placed between the carbon fibers in the thickness direction. It can be produced by a method including a step of making a carbon fiber sheet containing large particles or large particle aggregates having a diameter larger than the diameter. In this way, 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 contact points between the carbon fibers in the thickness direction are reduced. Further, since the carbon fibers can be curved along the large particles or the large particle aggregates, it is considered that a carbon fiber sheet having excellent flexibility and excellent handleability can be produced.

More specifically, first, a step of spinning the precursor carbon fiber using a spinning solution containing a carbonizable resin is carried out. The carbonizable resin is not particularly limited, but is, for example, a phenol resin, a urea resin, a melamine resin, an unsaturated polyester resin, an epoxy resin, a xylene resin, a urethane resin, a silicone resin, a thermosetting polyimide resin, and a thermosetting resin. Thermo-curable resins such as sex polyimide resin and thermo-curable polyamide resin; polystyrene resin, polyester resin, polyolefin resin, polyimide resin, polyamide resin, polyamide imide resin, polyvinyl acetate resin, vinyl chloride resin, fluororesin, polyacrylonitrile resin , Acrylic resin, polyether resin, polyvinyl alcohol, polyvinylpyrrolidone, pitch, polyamino acid resin, polybenzoimidazole resin and other thermoplastic resins; cellulose (polysaccharide), tar; Examples thereof include a coalescence (for example, an acrylonitrile / butadiene / styrene copolymer, an acrylonitrile / styrene copolymer, etc.). Among these, it is preferable to use an acrylic resin having a polyacrylonitrile content of 85% or more because it has a high carbonization rate, no voids inside the fiber, and is easy to obtain a carbon fiber having high strength and high elastic modulus.

In addition, a conductive material can be mixed so as to increase the conductivity and mechanical strength of the carbon fiber. The conductive material can be the above-mentioned conductive material, and carbon nanotubes are preferable.

Also, in place of or in addition to conductive materials, silicones such as polydimethylsiloxane and metal alkoxides (methoxides such as silicon, aluminum, titanium, zirconium, boron, tin and zinc, ethoxides, propoxides, butoxides, etc.) can be used. It is also possible to mix a polymer obtained by polymerizing a known inorganic compound such as a polymerized inorganic polymer.

After preparing such a material, a spinning solution containing a carbonizable resin is prepared for spinning the precursor carbon fibers. In some cases, a spinning solution containing a conductive material, silicone, and / or an inorganic polymer is prepared.

The solvent constituting the spinning solution may be any solvent as long as it 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, and these solvents can be a single solvent or a mixed solvent. It is also possible to add a poor solvent as long as there is no problem in spinnability.

The solid content concentration of the carbonizable resin in the spinning liquid 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 if it is less than 1 mass%, the productivity is extremely lowered, and if it is more than 50 mass%, the spinning tends to be unstable.

Then, the precursor carbon fiber is spun using the spinning liquid as described above. As a method for forming the precursor carbon fibers, for example, a dry spinning method, an electrostatic spinning method, and a gas are applied to a spinning liquid discharged from a liquid discharging unit as disclosed in Japanese Patent Application Laid-Open No. 2009-287138. Examples thereof include a method in which the spinning liquid is discharged in parallel and a shearing force is applied to the spinning liquid in a straight line to form fibers. Among these, the electrostatic spinning method or the spinning method disclosed in Japanese Patent Application Laid-Open No. 2009-287138 is suitable because it is easy to spin a precursor carbon fiber having a small fiber diameter of 3 μm or less on average. Further, according to the dry spinning method or the electrostatic spinning method, it is suitable because it is easy to spin the precursor carbon fiber which is a continuous fiber. In particular, according to the electrostatic spinning 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 conductivity, and has a large surface surface, and the carbon fiber surface can be effectively used. It is suitable because it can produce a carbon fiber sheet.

The "precursor carbon fiber" in the present invention means a fiber in a state where the carbonizable resin is not carbonized, and since the carbonizable resin is carbonized to form carbon fiber, it becomes a source of carbon fiber. In the sense of fiber, it is expressed as precursor carbon fiber.

Then, a step of supplying particles or particle aggregates to the precursor carbon fibers is carried out. By supplying the particles or particle aggregates, a precursor carbon fiber sheet containing large particles or large particle aggregates can be produced between the carbon fibers in the thickness direction, and as a result, the flexibility is excellent and the handleability is excellent. It is possible to produce an excellent carbon fiber sheet.

The method of supplying the particles or the particle agglomerates is not particularly limited, but for example, a method of ejecting the particles or the particle agglomerates by the action of a compressed gas, or a dispersion liquid containing the particles or the particle agglomerates is a compressed gas or ultrasonic waves. A method of spraying by the action of the above, a method of fragmenting a dispersion liquid containing particles or particle agglomerates into charged droplets by the action of static electricity, and the like, and the like can be mentioned. Among these supply methods, the method of spraying the dispersion liquid 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 having no film between the precursor carbon fibers. Is. In particular, the method of fragmenting and spraying a dispersion liquid containing particles or particle agglomerates into charged droplets by the action of electrostatic has a substantially spherical shape in the case of large particle agglomerates, and large particles or large particles. It is suitable because the particle agglomerates adhere in a state of being in point contact with the precursor carbon fibers, and it is easy to produce a precursor carbon fiber sheet in which a film is not formed between the large particles or the large particle aggregates and the precursor carbon fibers. Is. That is, since the droplets are electrically repelled and fragmented, it is difficult to form a film containing large particles or large particle aggregates between the precursor carbon fibers. In particular, when a droplet charged with a polarity opposite to the charge of the precursor carbon fiber is sprayed onto the charged precursor carbon fiber as in the case where the precursor carbon fiber is spun by the electrostatic spinning method, the action of the charge causes the charge to act. Droplets containing large particles or large particle aggregates can be reliably attached to the precursor carbon fibers. For example, when a droplet charged with a polarity opposite to the charge of the precursor carbon fiber is sprayed on the flying precursor carbon fiber before the precursor carbon fiber spun by the electrostatic spinning method is accumulated on the collector, the charge is charged. By the action, droplets containing large particles or large particle aggregates can be reliably attached to the precursor carbon fibers. When the charged droplets are sprayed on the uncharged precursor carbon fibers, the polarity of the charged droplets is not particularly limited. For example, even when spun by the electrostatic spinning method, it is related to the polarity when spraying charged droplets on the uncharged precursor carbon fibers that have accumulated on the grounded collector. Droplets containing depletedly charged droplets can be sprayed to attach large particles or droplets containing large particle aggregates to the precursor carbon fibers.

The supply of the particles or particle aggregates to the precursor carbon fibers is, for example, to the precursor carbon fibers in a flying state after spinning, and to the precursor carbon fibers immediately after the precursor carbon fibers are accumulated on the collector. Alternatively, it can be carried out for the precursor carbon fibers after the precursor carbon fibers have accumulated to some extent on the collector. In particular, when particles or particle agglomerates are supplied to the precursor carbon fibers in the flying state after spinning or to the precursor carbon fibers immediately after the precursor carbon fibers are accumulated on the collector, between the precursor carbon fibers. As a result of hindering contact and being able to bend the precursor carbon fiber along the large particles or large particle aggregates, it is considered that it is easy to produce a carbon fiber sheet having better flexibility and better handleability. It is preferable to supply particles or particle aggregates at the above stage.

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

When a dispersion liquid of particles or particle aggregates is used, the solvent in the dispersion liquid is not particularly limited as long as it can disperse the particles or particle aggregates without dissolving them. The concentration of 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%. More preferred.

Further, when a dispersion liquid of conductive particles or particle aggregates is used and the dispersion liquid is fragmented into charged droplets and sprayed, it tends to be difficult to fragment, so a dispersion liquid containing an organic resin is prepared. However, it is preferable that the particles are easily fragmented into charged droplets. Examples of such an organic resin include nylon resin, vinylon resin, fluororesin, polyvinyl chloride resin, polyester resin, polyolefin resin, polyvinyl alcohol, and polyethylene glycol.

When preparing a dispersion liquid containing an organic resin in this way, the solvent in the dispersion liquid can be dispersed without dissolving particles or particle aggregates, and can also dissolve or disperse the organic resin. Anything is fine, and it is not particularly limited. When the dispersion liquid contains an organic resin, the dispersion liquid may be one in which conductive particles or particle aggregates are dispersed in the melt of the organic resin.

Next, a step of forming a precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers in the thickness direction is performed. For example, when the particles or particle aggregates are supplied to 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. It is possible to form a precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers in the thickness direction. Further, 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 are supplied between the precursor carbon fibers in the thickness direction at the same time as the particles or particle aggregates are supplied to the precursor carbon fibers. Can form a precursor carbon fiber sheet in which is present. Further, when particles or particle aggregates are supplied to the sheet-shaped precursor carbon fibers after the precursor carbon fibers have accumulated to some extent on the collector, the sheet-shaped precursor carbon fibers to which the particles or particle aggregates are attached are obtained. It can be laminated to form a multi-layered precursor carbon fiber sheet.

At the stage of forming the precursor carbon fiber sheet, if particles or particle aggregates are supplied so that particles or particle aggregates are present between the precursor carbon fibers in the thickness direction inside the precursor carbon fiber sheet, the thickness is increased. It is possible to produce a carbon fiber sheet in which particles or particle aggregates are present inside in the direction. For example, when the supply of particles or particle aggregates to the precursor carbon fibers is performed on the precursor carbon fibers in a flying state after spinning, or immediately after the precursor carbon fibers are accumulated on the collector, the precursor carbon fibers When the particles or particle aggregates are supplied to the precursor fibers constituting the inside of the precursor carbon fiber sheet, the particles or particles are supplied between the precursor carbon fibers in the thickness direction of the inside. It is possible to form a precursor carbon fiber sheet in which aggregates are present. Further, when particles or particle aggregates are supplied to the sheet-shaped precursor carbon fibers that have accumulated to some extent on the collector, the sheet-shaped precursor carbon fibers to which the particles or particle aggregates are attached constitute the inside. As such, it is possible to form a precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers in the inner thickness direction.

Then, the precursor carbon fibers constituting the precursor carbon fiber sheet are carbonized, and the carbon fiber sheet of the present invention, that is, large particles having a diameter larger than the average fiber diameter of the carbon fibers between the carbon fibers in the thickness direction or A carbon fiber sheet containing a large particle agglomerate can be produced.

This carbonization step is not particularly limited as long as it can carbonize the carbonizable resin constituting the precursor carbon fiber, but is not particularly limited, and is, for example, in an inert gas atmosphere such as nitrogen, helium, or argon at a maximum temperature of 800 to 3000 ° C. It can be carried out by heating. The rate of temperature rise is preferably 5 to 100,000 ° C./min, more preferably 5 to 1000 ° C./min. The holding time at the maximum temperature is preferably 3 hours or less, and more preferably 1 to 120 minutes.

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

The above is an example of the method for producing a carbon fiber sheet of the present invention, but it is possible to impart or improve physical properties suitable for each application 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, polytetrafluoro is used to improve the water repellency, drainage and gas diffusivity of the carbon fiber sheet. A carbon fiber sheet can be immersed in a fluorine-based resin dispersion such as an ethylene dispersion to impart a fluorine-based resin, and then sintered at a temperature of 300 to 350 ° C. When the large particles or large particle aggregates are conductive, the precursor carbon fiber sheet or the carbon fiber sheet is pressed to enhance the adhesion between the precursor carbon fibers or the carbon fibers to enhance the conductivity. You can also do it. However, since the carbon fiber sheet of the present invention is preferably in a porous state having an apparent density of 0.40 g / cm ³ or less, it is preferable to appropriately adjust the pressing force.

A carbon fiber sheet made of carbon fibers having no voids inside can be easily manufactured by using a carbonizable resin having a high carbonization rate. For example, when polyacrylonitrile, epoxy resin, phenol resin, or the like is used, it is easy to produce a carbon fiber sheet made of carbon fibers having no voids inside.

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 locking mill to prepare a spinning solution having a solid content concentration of 15 mass%.

(Preparation of particle aggregate dispersion)
Ketchen Black water dispersion [Lion Co., Ltd., 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 fibers obtained by spinning the spinning solution by the electrostatic spinning method under the following conditions are directly integrated on the stainless steel drum as the counter electrode, and at the same time, the electrostatic spray of the carbon dispersion is performed under the following conditions. Then, it is fragmented into charged droplets and sprayed from the upper part 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 Ket A non-woven fabric of precursor carbon continuous fiber mixed with chain black (mass ratio of precursor carbon continuous fiber and Ketjen black = 70:30) was prepared.

Subsequently, the precursor carbon continuous fiber non-woven fabric is subjected to oxidation treatment in air at a temperature of 220 ° C. for 30 minutes and at a temperature of 260 ° C. for 1 hour to insolubilize the PAN constituting the precursor carbon continuous fiber. A fused precursor carbon continuous fiber non-woven fabric was used.

Then, the infusible precursor carbon continuous fiber non-woven fabric was subjected to carbonization firing treatment (heating rate: 10 ° C./min) at a maximum temperature of 800 ° C. for 1 hour in a nitrogen gas atmosphere using a vacuum substitution type electric furnace. , Carbon continuous fiber non-woven fabric (average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber) was produced.

When the cross section in the thickness direction of this carbon continuous fiber non-woven fabric, the enlargement of the spherical large particle agglomerates, and the electron micrographs on the surface (see FIGS. 1 to 3) were taken and observed, Ketjen Black was found to be the spherical large particle agglomerates. It was contained between the carbon fibers in the thickness direction in the form of (diameter: 4 μm, aspect ratio: 1.2) (number of spherical large particle aggregates: 50). In addition, the large spherical particle aggregates of Ketjen Black were in a state of being in point contact with the carbon fibers and in a state of being adhered without forming a film. Further, while the carbon continuous fibers were bonded to each other in some places, there were also places where the carbon continuous fibers were bonded to each other via the Ketjen black spherical large particle agglomerates. Furthermore, a part of the carbon continuous fiber was in a state of being curved by the Ketjen black spherical large particle agglomerate. Further, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates inside, in the entire thickness direction including the vicinity of the surface, and in the entire surface direction.

Note <Electrostatic spinning conditions>
Electrode: Metal nozzle (inner diameter 0.41 mm) and grounded stainless steel drum Discharge rate: 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 rate: 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 non-woven fabric is the same as in Example 1 except that the spray amount of the carbon dispersion is increased and the mixed mass ratio of the precursor carbon continuous fiber and Ketjen black in the precursor carbon continuous fiber non-woven fabric is 50:50. (Average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber) was manufactured. When the cross section in the thickness direction of this carbon continuous fiber non-woven fabric, the enlargement of the spherical large particle agglomerates, and the electron micrograph on the surface were taken and observed, Ketchen Black showed the spherical large particle agglomerates (diameter: 4 μm, aspect ratio:: In the form of 1.2), it was contained between the carbon fibers in the thickness direction (number of spherical large particle aggregates: 80). In addition, the large spherical particle aggregates of Ketjen Black were in a state of being in point contact with the carbon fibers and in a state of being adhered without forming a film. Further, while the carbon continuous fibers were bonded to each other in some places, there were also places where the carbon continuous fibers were bonded to each other via the Ketjen black spherical large particle agglomerates. Furthermore, a part of the carbon continuous fiber was in a state of being curved by the Ketjen black spherical large particle agglomerate. Further, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates inside, in the entire thickness direction including the vicinity of the surface, and in the entire surface direction.

(Example 3)
The carbon continuous fiber non-woven fabric is the same as in Example 1 except that the spray amount of the carbon dispersion is increased and the mixed mass ratio of the precursor carbon continuous fiber and Ketjen black in the precursor carbon continuous fiber non-woven fabric is set to 20:80. (Average fiber diameter: 350 nm, carbon continuous fiber has no voids inside the fiber) was manufactured. When the cross section in the thickness direction of this carbon continuous fiber non-woven fabric, the enlargement of the spherical large particle agglomerates, and the electron micrograph on the surface were taken and observed, Ketchen Black showed the spherical large particle agglomerates (diameter: 4 μm, aspect ratio:: In the form of 1.2), it was contained between the carbon fibers in the thickness direction (number of spherical large particle aggregates: 150). In addition, the large spherical particle aggregates of Ketjen Black were in a state of being in point contact with the carbon fibers and in a state of being adhered without forming a film. Further, while the carbon continuous fibers were bonded to each other in some places, there were also places where the carbon continuous fibers were bonded to each other via the Ketjen black spherical large particle agglomerates. Furthermore, a part of the carbon continuous fiber was in a state of being curved by the Ketjen black spherical large particle agglomerate. Further, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large particle aggregates inside, in the entire thickness direction including the vicinity of the surface, and in the entire surface direction.

(Comparative Example 1)
Similar to Example 1, it is composed of only PAN-based carbon continuous fibers (average fiber diameter: 350 nm, carbon continuous fibers have no voids inside the fibers) except that the carbon dispersion is not sprayed by electrostatic spray. A carbon continuous fiber non-woven fabric was produced. When an electron micrograph on the surface of this carbon continuous fiber nonwoven fabric was taken and observed, the carbon continuous fibers were in a linear state, and the carbon continuous fibers were in a state of being bonded to each other.

(Comparative Example 2)
The precursor carbon continuous fibers obtained by spinning the spinning solution by the electrostatic spinning method under the same conditions as in Example 1 are directly accumulated on a stainless steel drum as a counter electrode to form a precursor carbon continuous fiber nonwoven fabric, and then the above-mentioned The carbon dispersion was electrostatically sprayed under the same conditions as in Example 1, and the precursor carbon continuous fiber was fragmented into charged droplets and already accumulated from the upper part of the stainless drum to form a non-woven fabric. By spraying toward the non-woven fabric, a precursor carbon continuous fiber non-woven fabric having Ketjen black adhered to the surface (mass ratio of precursor carbon continuous fiber to Ketjen black = 70:30) was prepared.

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

When the cross section in the thickness direction of this carbon continuous fiber non-woven fabric, the enlargement of the spherical large particle aggregate, and the electron micrograph on the surface were taken and observed, Ketchen Black was found to be the spherical large particle aggregate (diameter: 4 μm, aspect ratio:: In the form of 1.2), it was contained between the carbon continuous fibers in the plane direction in a state of being adhered without forming a dot film, but was not contained between the carbon fibers in the thickness direction. .. Furthermore, the carbon continuous fibers are linear, and there are places where the carbon continuous fibers are joined to each other, and there are places where the carbon continuous fibers are joined to each other via the Ketjen black spherical large particle agglomerates. There wasn't. That is, there was no place where the bonding between carbon continuous fibers was hindered by the Ketjen black spherical large particle agglomerates. Further, the carbon continuous fiber nonwoven fabric had Ketjen black spherical large agglomerates on the entire surface only on the surface thereof, and the Ketjen black spherical large particle agglomerates were in a state of being easily dropped off.

(Comparative Example 3)
A carbon continuous fiber non-woven fabric produced in the same manner as in Comparative Example 1 was used in Ketjen Black's water dispersion [Lion Co., Ltd., Lion Paste W-311N, solid content: 16.5 mass%, primary particle size: 40 nm]. After soaking in, the non-woven fabric of carbon continuous fiber having Ketjen black (average fiber diameter: 350 nm, mass ratio of carbon continuous fiber to Ketjen black = 45:55, carbon continuous fiber) is dried at a temperature of 80 ° C. for 1 hour. Has no voids inside the fiber).

When the cross section in the thickness direction of the carbon continuous fiber non-woven fabric having Ketjen Black, the enlargement of Ketjen Black, and the electron micrographs on the surface (see FIGS. 4 to 6) were taken and observed, Ketjen Black was the film. 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. No Ketjen black spherical large particle agglomerates were contained between the carbon fibers in the thickness direction. The carbon continuous fibers are linear, and while the carbon continuous fibers are bonded to each other in some places, the carbon continuous fibers are also bonded to each other in a film containing Ketjen Black.

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

Next, carbon nanotubes (CNTs) synthesized by the CVD method [trade name: VGCF-H (manufactured by Showa Denko KK), fiber diameter: 150 nm, aspect ratio: 40, multi-walled carbon nanotubes] were mixed with the solution. After stirring, DMF was further added and diluted to disperse the carbon nanotubes to obtain a dispersion solution.

Further, a carbonizable resin (EP) containing a cresol novolak epoxy resin as a main agent and a novolak 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. 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 locking mill to prepare a second spinning solution having a concentration of 20 mass%.

Next, the first precursor carbon continuous fiber is spun from the first spinning liquid by the electrostatic spinning method under the following conditions, and the first precursor carbon continuous fiber is directly accumulated on the stainless drum which is the counter electrode, and at the same time, the second spinning liquid is electrostatically spun. According to the method, the second precursor carbon continuous fiber is spun under the following conditions and directly collided with the first precursor carbon continuous fiber aggregate to accumulate, and the first precursor carbon continuous fiber and the second precursor carbon continuous fiber are formed. A mixed precursor carbon continuous fiber non-woven fabric was prepared.

Note (electrostatic spinning conditions)
(1) First spinning liquid Electrode: Metallic nozzle (inner diameter: 0.33 mm) and grounded stainless steel drum Discharge rate: 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 liquid 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: + 15kV
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 carried out for 1 hour in a hot air dryer set at a temperature of 150 ° C. to perform the first precursor. The epoxy resin constituting the carbon continuous fiber was cured to prepare a cured precursor carbon continuous fiber non-woven fabric.

Subsequently, in the same manner as in Example 1, insolubilization and carbonization firing treatment of the cured precursor carbon continuous fiber was carried out, and the carbon continuous fiber non-woven fabric (average fiber diameter: 1.5 μm, the carbon continuous fiber has voids inside). Manufactured.

When an electron micrograph on the surface of this carbon continuous fiber non-woven fabric was taken and observed, the carbon continuous fibers were bonded to each other in a curved state rather than in a linear state.

<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 as shown in Table 1.
(1) A carbon continuous fiber non-woven fabric is cut into 5 cm squares (area: 25 cm ² ) to prepare a sample.
(2) The sample is sandwiched between gold-plated metal plates from both sides, and the voltage (V) is measured in the laminating direction of the metal plates under pressure at 2 MPa and a current (I) of 1 A is applied.
(3) Calculate the resistance (R = V / I).
(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 this sample was folded in half, a load of 1.2 kPa was applied for 5 seconds by sandwiching it between metal plates. After that, the sample was taken out from between the metal plates, and it was confirmed whether the sample was broken, that is, whether the sample was cracked and broken in two. The results are as 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 containing large particles or large particle aggregates between the carbon fibers in the thickness direction. In addition, it was found that the conductivity was also excellent because it contained large conductive particles or large particle aggregates.

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

Claims (5)

The stage of spinning precursor carbon fibers using a spinning solution containing a carbonizable resin,
The step of supplying particles or particle aggregates to the precursor carbon fibers,
The stage of forming a precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers in the thickness direction,
The precursor carbon fibers constituting the precursor carbon fiber sheet are carbonized to obtain a carbon fiber sheet containing 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. step,
It is a manufacturing method of carbon fiber sheet including
A step of supplying the particles or particle aggregates to the precursor carbon fibers and a step of forming a precursor carbon fiber sheet in which particles or particle aggregates are present between the precursor carbon fibers in the thickness direction.
(1) Particles or particle aggregates are supplied to the precursor carbon fibers in a flying state after spinning, and the precursor carbon fibers to which the particles or particle aggregates are attached are accumulated on the collector to form a precursor carbon fiber sheet. how to,
(2) Particles or particle aggregates are supplied to the precursor carbon fibers immediately after the precursor carbon fibers are accumulated on the collector, and the precursor carbon fibers are accumulated on the precursor carbon fibers to which the particles or particle aggregates are attached. , A method of supplying particles or particle aggregates to the precursor carbon fibers immediately after the accumulation to form a precursor carbon fiber sheet.
(3) Particles or particle aggregates are supplied to the sheet-shaped precursor carbon fibers after the precursor carbon fibers have accumulated to some extent on the collector to form sheet-shaped precursor carbon fibers to which the particles or particle aggregates are attached. A method of laminating sheet-shaped precursor carbon fibers to which particles or particle aggregates are attached to form a multi-layered precursor carbon fiber sheet.
A method for manufacturing a carbon fiber sheet, characterized in that it is carried out by a method selected from among . The carbon fiber sheet according to claim 1, wherein the step of supplying the particles or the particle aggregates to the precursor carbon fibers is carried out by spraying the dispersion liquid containing the particles or the particle aggregates onto the precursor carbon fibers. Manufacturing method. The step of supplying the particles or the particle aggregates to the precursor carbon fibers is characterized in that the dispersion liquid containing the particles or the particle aggregates is fragmented into charged droplets and sprayed onto the precursor carbon fibers. The method for producing a carbon fiber sheet according to claim 1 or 2. The method for producing a carbon fiber sheet according to any one of claims 1 to 3, wherein the step of spinning the precursor carbon fiber is carried out by an electrostatic spinning method. The method for producing a carbon fiber sheet according to any one of claims 1 to 4, wherein the large particles or large particle aggregates have conductivity.

Images