Carbon sheet and method for manufacturing the same, gas diffusion electrode, and fuel cell

Abstract

The present application provides a carbon sheet suitable for a gas diffusion electrode capable of preventing collapse of a gas flow path provided on a separator film and not deteriorating the electric resistance in a direction perpendicular to the plane. The carbon sheet of the present application for achieving the above object has a first surface and a second surface on the opposite side of the first surface, and when a specific interval is 20-fold divided in the thickness direction to be 20 layers, the fiber orientation degree of the surface layer on the first surface side is 1.20 or more and 3.00 or less, the region formed by the continuous layers among the aforementioned layers satisfying a specific condition is referred to as a first surface side region, and the region formed by the layers among the aforementioned layers not included in the first surface side region is referred to as a second surface side region, the thickness of the aforementioned first surface side region is 40% or less of the thickness of the entire carbon sheet, and the difference between the average fiber orientation degree of the aforementioned second surface side region and the fiber orientation degree of the surface layer on the aforementioned first surface side is greater than 0.10.

Description

TECHNICAL FIELD

[0001] The present application relates to a carbon sheet and a method for manufacturing the same, a gas diffusion electrode, and a fuel cell. BACKGROUND

[0002] A solid polymer fuel cell obtains electromotive force by an electrochemical reaction occurring at both electrodes by supplying a fuel gas containing hydrogen to an anode and an oxidizing gas containing oxygen to a cathode. The solid polymer fuel cell is generally configured by sequentially stacking a separator, a gas diffusion electrode, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion electrode, and a separator. For the gas diffusion electrode, high gas diffusivity for diffusing the gas supplied from the separator to the catalyst layer, high water dischargeability for discharging water generated along with the electrochemical reaction to the separator, and high electric conductivity for extracting the generated current are required. Therefore, a gas diffusion electrode using an electrically conductive porous substrate containing carbon fibers and a microporous layer formed on the surface thereof is widely used.

[0003] In order to efficiently supply the fuel gas (anode side: hydrogen, cathode side: atmosphere, oxygen) from the gas diffusion electrode to the catalyst layer with high efficiency, it is necessary to transfer the fuel gas to the entire surface by a gas flow path provided on the separator adjacent to the gas diffusion electrode. In addition, in order to efficiently diffuse the fuel gas reaching the gas diffusion electrode from the separator within the gas diffusion electrode, various proposals have been made for the structure of the gas diffusion electrode.

[0004] For example, a gas diffusion electrode in which the carbon sheet constituting the gas diffusion electrode has a fiber orientation is proposed (Patent Literature 1).

[0005] In addition, a gas diffusion electrode in which 2 to 8 sheets of carbon sheets having a fiber orientation are stacked is proposed (Patent Literature 2).

[0006] In addition, a gas diffusion electrode in which a carbon sheet having a strong fiber orientation and a carbon sheet having a weak fiber orientation are stacked is proposed (Patent Literature 3).

[0007] In addition, a gas diffusion electrode having a gradient of fiber orientation in the thickness direction of a single layer is proposed (Patent Literature 4).

[0008] PRIOR ART DOCUMENTS

[0009] PATENT LITERATURE

[0010] Patent Literature 1: Japanese Patent Application Publication No. 2006-222024

[0011] Patent Literature 2: U.S. Patent Application Publication No. 2017 / 0301923

[0012] Patent Literature 3: Japanese Patent Application Publication No. 2013-191435

[0013] Patent Document 4: Korean Patent Publication No. 2016-0120060 SUMMARY

[0014] PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] However, in the invention described in Patent Document 1, the carbon sheet has strong fiber orientation in the entire carbon sheet, and has strong strength in the orientation direction, but weak strength in the direction orthogonal to the orientation direction of the fiber, and there is a problem that breakage and tearing easily occur at the time of transportation and at the time of processing. In addition, in the case where the entire carbon sheet has strong fiber orientation, the bending stiffness in the orientation direction of the fiber becomes strong, and the carbon sheet is arranged in a manner that the fiber orientation is substantially perpendicular to the gas flow path provided on the surface of the separator, and thus it is possible to suppress the collapse of the carbon sheet into the gas flow path, and it is expected to have an effect of suppressing the pressure loss at the time of supplying fuel gas, but on the other hand, the distribution of the resin carbon compound in the carbon sheet is biased to the fiber direction, and thus there is a problem that the resistance in the thickness direction (direction perpendicular to the surface) of the carbon sheet deteriorates.

[0016] In the inventions described in Patent Document 2 and Patent Document 3, the carbon sheet is laminated in two or more layers, and thus there is a problem that delamination between the layers occurs at the time of power generation, and the resistance deteriorates due to the destruction of the contact point, and the power generation performance deteriorates due to overflow at the delamination site. In addition, since the carbon sheets are laminated after a plurality of carbon sheets are manufactured, the increase in the number of processing steps becomes a problem in terms of productivity.

[0017] In the invention described in Patent Document 4, the gradient of the fiber orientation in the thickness direction (direction perpendicular to the surface) is present within a single layer, but the thickness is not present in the region where the fiber is strongly oriented, and thus there is a problem that the suppression of the collapse of the carbon sheet into the gas flow path cannot be sufficiently performed.

[0018] The object of the present application is to provide a carbon sheet in which the resistance in the direction perpendicular to the surface does not deteriorate at the time of manufacturing a gas diffusion electrode, and in which the collapse into the gas flow path applied to the separator is prevented, and to provide a gas diffusion electrode including the carbon sheet, and a fuel cell including the gas diffusion electrode, in view of the problems in the related art.

[0019] MEANS FOR SOLVING THE PROBLEMS

[0020] In order to solve the above problems, the present application has the following configuration. That is,

[0021] The carbon sheet of the present invention has a first surface and a second surface located on the opposite side of the first surface. When the interval from the surface with a 50% fill rate closest to the first surface to the surface with a 50% fill rate closest to the second surface is divided into 20 equal parts in the thickness direction and defined as 20 layers, the fiber orientation degree of the outermost layer on the first surface side is 1.20 or more and 3.00 or less. When the region formed by the continuous layer having a fiber orientation degree within ±0.10 of the fiber orientation degree of the outermost layer on the first surface side is designated as the first surface side region, and the region formed by the layer not included in the first surface side region is designated as the second surface side region, the thickness of the first surface side region is 40% or less of the overall thickness of the carbon sheet, and the difference between the average fiber orientation degree of the second surface side region and the fiber orientation degree of the outermost layer on the first surface side is greater than 0.10.

[0022] (Here, the fill rate of the surface is measured from one surface of the carbon sheet to another at 3.9 μm intervals. The average fill rate of the resulting surfaces is then calculated. A 50% fill rate is 50% of this average. Furthermore, the fill rate of the layer is the average value obtained using the fill rates of the surfaces forming the layer.)

[0023] Invention Effects

[0024] According to the present invention, a carbon sheet suitable for a gas diffusion electrode can be provided, which can prevent the resistance in the direction perpendicular to the surface from deteriorating and can prevent collapse of the gas flow path disposed on the isolation membrane, which was difficult in the past. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a fuel cell including the gas diffusion electrode of the present invention.

[0026] Figure 2 This is a schematic diagram of the collapse evaluation method for the gas diffusion electrode of the present invention.

[0027] Figure 3 This is a schematic diagram showing the fill rate distribution relative to the thickness direction when measuring the fiber orientation degree in the thickness direction of the carbon sheet of the present invention.

[0028] Figure 4 This is a schematic diagram illustrating the fiber orientation distribution of the carbon sheet of the present invention.

[0029] Figure 5 This is a schematic diagram showing the filling rate distribution of the carbon sheet of the present invention divided into multilayer body X and multilayer body Y.

[0030] Figure 6 This is a schematic diagram of an example of a paper machine capable of controlling the fiber orientation of carbon fiber paper. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present application will be described, but the present application is not limited to these embodiments. Further, in order for the reader to understand, sometimes the symbols of the drawings are marked in the sentences in the specification, but the drawings are examples, and the present application is not limited to the embodiments of the drawings.

[0032] [Carbon sheet]

[0033] The carbon sheet 1 of the present application has a first surface 11 and a second surface 12 located on the opposite side of the first surface, and when the interval from the surface 13 having a 50% packing rate 15 closest to the first surface to the surface 14 having a 50% packing rate closest to the second surface is divided into 20 equal parts in the thickness direction to provide 20 layers 17, the fiber orientation degree of the surface layer on the first surface side is 1.20 or more and 3.00 or less, the region formed by the continuous layers having a fiber orientation degree within ±0.10 of the fiber orientation degree of the surface layer on the first surface side among the layers is referred to as a first surface side region 1-1, and the region formed by the layers not included in the first surface side region among the layers is referred to as a second surface side region 1-2, the thickness of the first surface side region is 40% or less of the overall thickness of the carbon sheet, and the difference between the average fiber orientation degree of the second surface side region and the fiber orientation degree of the surface layer on the first surface side is greater than 0.10. In the present application, "divided into 20 equal parts in the thickness direction to provide 20 layers" means that the interval from the surface having a 50% packing rate closest to the first surface to the surface having a 50% packing rate closest to the second surface is divided into 20 equal parts in the thickness direction of the carbon sheet. Figure 3 In this way, in the interval from the surface having a 50% packing rate closest to the first surface to the surface having a 50% packing rate closest to the second surface of the carbon sheet, the thickness of the overall carbon sheet obtained by dividing the carbon sheet in the thickness direction 10 into 20 equal parts is referred to as the thickness of the above interval.

[0034] The carbon sheet of the present application is preferably porous. The carbon sheet is porous, whereby excellent gas diffusivity for diffusing the gas supplied from the separator to the catalyst and high water drainage for draining the water generated by the electrochemical reaction to the separator can be both achieved. Further, in order to have high conductivity for extracting the generated electric current, it is preferable to use a porous body having conductivity. As the above porous body, a porous body containing carbon fibers such as a carbon fiber paper body, a carbon fiber fabric, and a felt-type carbon fiber nonwoven fabric is preferably used. Among them, a carbon fiber paper body, which is excellent in the property of absorbing dimensional changes in the direction perpendicular to the surface of the electrolyte membrane, i.e., "elasticity", can make the thickness of the porous body thin, and easily control the fiber orientation state in the thickness direction, is preferably used as the porous body. Further, the carbon sheet of the present application is preferably in a form in which a binder material is given to the porous body, and more preferably contains a carbon fiber paper body and a binder material. Thereby, the rigidity of the carbon sheet is improved, and the binder material functions as a conductive path, whereby the conductivity can be improved.

[0035] In the present application, the packing rate refers to the proportion of the constituent components of the carbon sheet occupying the area of the plane obtained by slicing the carbon sheet with a plane perpendicular to the thickness direction, with respect to the total area. That is, the area occupancy rate of the portion excluding the voids inside the carbon sheet. Details of the packing rate measurement method are described later. The packing rate of the plane is measured at every certain thickness from one surface to the other surface of the carbon sheet, and then the average value of the packing rates of the obtained planes is calculated, and the 50% packing rate is the value of 50% of the average value. Further, the packing rate of the layer is the average value obtained using the packing rates of the planes forming the layer.

[0036] In the present application, the packing rate refers to the proportion of the constituent components of the carbon sheet occupying the area of the plane obtained by slicing the carbon sheet with a plane perpendicular to the thickness direction, with respect to the total area. That is, the area occupancy rate of the portion excluding the voids inside the carbon sheet. Details of the packing rate measurement method are described later. The packing rate of the plane is measured at every certain thickness from one surface to the other surface of the carbon sheet, and then the average value of the packing rates of the obtained planes is calculated, and the 50% packing rate is the value of 50% of the average value. Further, the packing rate of the layer is the average value obtained using the packing rates of the planes forming the layer.

[0037] In the present application, the packing rate refers to the proportion of the constituent components of the carbon sheet occupying the area of the plane obtained by slicing the carbon sheet with a plane perpendicular to the thickness direction, with respect to the total area. That is, the area occupancy rate of the portion excluding the voids inside the carbon sheet. Details of the packing rate measurement method are described later. The packing rate of the plane is measured at every certain thickness from one surface to the other surface of the carbon sheet, and then the average value of the packing rates of the obtained planes is calculated, and the 50% packing rate is the value of 50% of the average value. Further, the packing rate of the layer is the average value obtained using the packing rates of the planes forming the layer.

[0038] In the present application, the packing rate refers to the proportion of the constituent components of the carbon sheet occupying the area of the plane obtained by slicing the carbon sheet with a plane perpendicular to the thickness direction, with respect to the total area. That is, the area occupancy rate of the portion excluding the voids inside the carbon sheet. Details of the packing rate measurement method are described later. The packing rate of the plane is measured at every certain thickness from one surface to the other surface of the carbon sheet, and then the average value of the packing rates of the obtained planes is calculated, and the 50% packing rate is the value of 50% of the average value. Further, the packing rate of the layer is the average value obtained using the packing rates of the planes forming the layer.

[0039] The difference between the fiber orientation degree of the surface layer on the side of the second surface and the fiber orientation degree of each layer belonging to the region on the side of the second surface is preferably within ±0.10. If the difference is within ±0.10, the deterioration of the electric resistance can be prevented by the uniform mesh structure.

[0040] In the carbon sheet of the present application, the average orientation degree of the region on the side of the second surface is preferably 1.20 or less. By making the average orientation degree of the region on the side of the second surface within the above range, the intersection of the fibers with each other is ensured, and the deterioration of the electric resistance can be suppressed by increasing the electrically conductive path.

[0041] In the carbon sheet of the present application, the difference between the fiber orientation angle of the surface layer on the side of the first surface and the fiber orientation angle of the surface layer on the side of the second surface is preferably within 45°, more preferably within 30°. If the difference between the fiber orientation angles of the two surfaces is within 45°, the fibers of the two surfaces almost face in the same direction, and thus further effects are obtained in the collapse suppression.

[0042] In the present specification, the "fiber orientation degree" is defined by the intensity of the fiber orientation angle of the most frequent fiber in the two-dimensional plane of the carbon sheet. In the present application, the fiber orientation degree and the fiber orientation angle are measured by a fiber orientation measuring software (FiberOri, ver 8.03, made by Professor Satsuki Enomae, Institute of Environmental and Genome Sciences, The University of Tokyo, HP: http: / / www.enomae.com / FiberOri / index.htm). The closer the fiber orientation degree is to 1.00 (lower limit value) in the fiber orientation measuring software, the more the fiber is non-oriented, and the larger the value, the stronger the fiber orientation. In addition, the fiber orientation angle is 90° in the case where the majority of the fibers in the image face the upward direction of the screen, 0° in the case where the fibers face the right side of the screen, and 180° in the case where the fibers face the left side of the screen. Therefore, the orientation of the image mapped on the screen and the orientation of the actual sheet need to be determined in advance.

[0043] [Procedure for measuring fiber orientation and filling rate]

[0044] On a three-dimensional measurement X-ray CT (Yamato Science, product name TDM1000H-CF), a carbon sheet (size: 10 mm in length x 5 mm in width) was installed, and 360° scanning was performed with the longitudinal axis as the rotation axis to produce a 3D image of "4 mm x 4 mm x sheet thickness [mm]". In the examples described later, the photographing was performed at a tube voltage of 60 kV and a tube current of 60 μA. At this time, each slice image constituting the 3D image was set to a thickness of 3.9 μm. Next, using the image analysis software attached to the X-ray CT, the 3D image was divided into 20 equal parts in the thickness direction to produce 20 layers. At this time, the interval into which the 20 layers were divided needed to be determined. First, all the slice images constituting the 3D image were output from the image analysis software attached to the X-ray CT. Next, in each of the obtained slice images, the background portion in which the carbon sheet was not present was distinguished from the carbon sheet by binary processing. For example, using the image processing program "ImageJ (ver 1.53a, HP: https: / / imagej.nih.gov / ij / )", each of the obtained slice images was distinguished in brightness in 1 to 255 stages, the point at which the separation of the two peaks obtained when the brightness histogram was plotted was noted as the threshold value of the brightness, and binary processing was performed (Otsu's binary processing). That is, the distinction was made between the dark side of the brightness (background) and the bright side of the brightness (constituent of the carbon sheet). The proportion of the area of the bright side of the binary processing to the total area of each slice image was noted as the filling rate [%]. Next, the filling rates of each of the slice images were plotted from one surface of the carbon sheet toward the other surface, and the distribution of the filling rates was confirmed 16. In the distribution of the filling rates thus obtained, the average value of the area in which the filling rate was greater than 0% was calculated, and the value at 50% of the average value was noted as the 50% filling rate. After the surface 13 closest to the first surface and the surface 14 closest to the second surface of the carbon sheet having the 50% filling rate were determined, the interval sandwiched by the two surfaces having the 50% filling rate was divided into 20 equal parts, and the 20 layers were set. The 20 layers were observed in the direction perpendicular to the surface to produce a plan view, and the plan view was input into the above-described fiber orientation measurement software to calculate the fiber orientation degree and the fiber orientation angle.

[0045] Note that, in order to evaluate the filling rate and the fiber orientation degree of the carbon sheet, multiple measurements were performed to calculate the average value. In the examples described later, sampling and measurement were performed at 30 sites in different parts of the carbon sheet, and the average value was calculated.

[0046] In the above-described analysis method, as Figure 4 thus, the thickness [%] of the first surface side region, the thickness [%] of the second surface side region, and the fiber orientation degree of each layer can be determined.

[0047] In the carbon sheet of the present application, preferably, in the interval from the surface having the 50% filling rate closest to the first surface to the surface having the 50% filling rate closest to the second surface,Figure 5 In this case, when the aforementioned interval is divided into two in the thickness direction to provide two multilayers, and the multilayer on the first surface side is denoted as multilayer X19 and the multilayer on the second surface side is denoted as multilayer Y20, the filling rate of the multilayer Y is lower than the filling rate of the multilayer X.

[0048] Here, the filling rate of each multilayer refers to the average of the filling rates of the layers included in each multilayer. In addition, the multilayer X includes the first to tenth layers from the first surface side of the present application, and the multilayer Y includes the eleventh to twentieth layers.

[0049] By making the filling rate of the multilayer X higher than the filling rate of the multilayer Y, as described in the [resin impregnation step] described later, the adhesive material on the multilayer X side increases to form a rigid plane. Therefore, when the carbon sheet of the present application is used for a gas diffusion electrode of a fuel cell, by arranging the multilayer X side on the separator membrane side, collapse into the gas flow path provided on the separator membrane can be suppressed.

[0050] Further, when the aforementioned interval from the surface closest to the first surface having a 50% filling rate to the surface closest to the second surface having a 50% filling rate is divided into three in the thickness direction, and for the resulting multilayers, the multilayer on the first surface side is denoted as multilayer X', the multilayer on the second surface side is denoted as multilayer Y', and the multilayer between the multilayer X' and the multilayer Y' is denoted as multilayer Z', it is more preferable to decrease in the order of multilayer X', multilayer Y', and multilayer Z'. Here, the multilayer X' includes the first to seventh layers from the first surface side of the present application, the multilayer Y' includes the fourteenth to twentieth layers, and the multilayer Z' includes the eighth to thirteenth layers. If the filling rate of the multilayer Z is lower than the other two multilayers, the diameter of the fine pores present in the multilayer Z' becomes larger, the gas diffusion property improves, and further, the filling rate of the multilayer X' is higher than that of the multilayer Z', so collapse is more difficult when the separator membrane is pressed, and a gas diffusion electrode that balances power generation properties and mechanical properties can be obtained. In addition, the multilayer X or the multilayer X' having a high filling rate is the first surface side having a high degree of fiber orientation, so collapse can be prevented more strongly.

[0051] Note that in the present application, the "thickness" when measuring the filling rate and the degree of fiber orientation is the unpressurized thickness measured when X-ray CT analysis is performed, i.e., without pressurization, and is different from the "thickness under pressurization" obtained in the 0.15 MPa pressurization measurement described later.

[0052] Note that the carbon sheet can be separated from the gas diffusion electrode, and the degree of fiber orientation and the filling rate of the carbon sheet can be measured. For example, the gas diffusion electrode is heated at 500°C for 60 minutes in the atmosphere, the resin composition included in the microporous layer of the gas diffusion electrode is oxidatively decomposed, and then ultrasonic treatment is performed in ethanol, and dried, thereby removing the residue of the microporous layer, and the carbon sheet can be extracted.

[0053] Further, the density of the carbon sheet of the present application is preferably in the range of 0.20 to 0.40 g / cm3, more preferably in the range of 0.22 to 0.35 g / cm3, and further preferably in the range of 0.24 to 0.31 g / cm3. If the density is 0.20 g / cm3or more, the water vapor diffusivity is small, and the dry-out can be suppressed. Further, the mechanical strength of the carbon sheet is improved, and when used as a gas diffusion electrode for a fuel cell, the electrolyte membrane and the catalyst layer can be sufficiently supported. In addition to this, the electrical conductivity is high, and the power generation performance is improved. On the other hand, if the density is 0.40 g / cm3or less, the water drainage is improved, and the flooding can be suppressed. 3 3 3 3 3

[0054] The carbon sheet having such a density is obtained by controlling the unit area weight of the carbon fiber, the blending amount of the resin component with respect to the carbon fiber, and the thickness of the carbon sheet by the method described in the [Manufacturing method of carbon sheet] described later. Here, the density of the carbon sheet can be calculated by dividing the unit area weight (mass per unit area) of the carbon sheet weighed using an electronic balance by the thickness of the carbon sheet at the time of pressing at a surface pressure of 0.15 MPa.

[0055] The thickness of the carbon sheet of the present application at the time of pressing is preferably in the range of 50 to 230 μm, more preferably in the range of 70 to 210 μm, and further preferably in the range of 90 to 190 μm. The thickness of the carbon sheet at the time of pressing is 230 μm or less, whereby the diffusivity of the gas becomes large, and further the generated water is easily drained. Further, as the entire fuel cell, the size also easily becomes small. On the other hand, the thickness of the carbon sheet at the time of pressing is 50 μm or more, whereby the gas diffusivity in the in-plane direction inside the carbon sheet is improved, and the power generation performance is improved.

[0056] Note that the thickness of the carbon sheet of the present application at the time of pressing is calculated by the following method. That is, the carbon sheet is placed on a smooth platform, and the difference in height between the case where a pressure of 0.15 MPa is applied and the case where there is no object (zero point) is measured. The difference in height is measured at 10 different sites, and the measured values are averaged, and this is recorded as the thickness at the time of pressing.

[0057] As the carbon fiber used in the carbon sheet of the present application, polyacrylonitrile (PAN)-based, pitch-based, and rayon-based carbon fibers, and the like can be given. Among these, PAN-based carbon fibers and pitch-based carbon fibers are preferably used in the present application because of their excellent mechanical strength. Further, a refractory yarn made into a carbon fiber by a carbonization step can also be used. Further, a rayon fiber, an acrylic fiber, a cellulose fiber, and the like, a natural fiber and a synthetic fiber conventionally known can be mixed. ​​​​​

[0058] The average diameter of the single fibers of the carbon fiber used in the present application is preferably in the range of 3 to 20 μm, and more preferably in the range of 5 to 10 μm. If the average diameter of the single fibers is 3 μm or more, the diameter of the fine pores becomes large, the water drainage property is improved, and overflow can be suppressed. On the other hand, if the average diameter of the single fibers is 20 μm or less, it is easy to control the thickness of the carbon sheet, gas diffusion electrode, which is preferable.

[0059] In the case where the carbon fiber paper body preferably used in the present application is used for a carbon sheet, the average length of the single fibers of the carbon fiber is preferably in the range of 3 to 20 mm, and more preferably in the range of 5 to 15 mm. If the average length of the single fibers is 3 mm or more, the mechanical strength, the electrical conductivity, and the thermal conductivity of the carbon sheet, gas diffusion electrode are excellent. On the other hand, if the average length of the single fibers is 20 mm or less, a homogeneous carbon sheet, gas diffusion electrode is obtained.

[0060] [Method for manufacturing carbon sheet]

[0061] The method for manufacturing the carbon sheet of the present application preferably includes a dispersion step of uniformly dispersing a carbon fiber bundle in a liquid to obtain a slurry, and a papermaking step of papermaking the slurry containing the carbon fiber using a papermaking machine having at least a mechanism capable of controlling the orientation in the thickness direction while continuously laminating the carbon fibers.

[0062] Hereinafter, as a preferable mode, examples of the manufacturing method are described, but the present application is not limited to the description below.

[0063] [Dispersion step and papermaking step]

[0064] As an example of the method of manufacturing the carbon sheet of the present application, a manufacturing method of a carbon fiber paper body in which a slurry obtained by dispersing a carbon fiber bundle in an aqueous solution is produced, and the produced slurry is sheeted by a wet papermaking method will be described. As the aqueous solution in which the carbon fiber is dispersed, a defoaming agent, a surfactant, a thickening agent are preferably contained. The defoaming agent suppresses foaming at the time of stirring, and is not particularly limited, and is preferably a urethane-based, a polyoxyalkylene-based, a silicone-based. The surfactant is effective for defibrating the carbon fiber bundle, and is not particularly limited, and is preferably a polyethylene glycol-based, a polyethylene oxide-based. The thickening agent is effective for thickening the aqueous solution and suppressing physical contact of the carbon fiber, and is not particularly limited, and is preferably a polyethylene oxide-based, a polyacrylic acid-based. The viscosity of the aqueous solution in which the carbon fiber is dispersed is preferably 5 to 50 mPa-s, and particularly preferably 8 to 20 mPa-s, in consideration of the dispersibility of the carbon fiber and the drainage property at the time of papermaking. In the case of less than 5 mPa-s, the viscosity is low, and sometimes re-agglomeration of the carbon fibers with each other occurs, and furthermore, if it is more than 50 mPa-s, re-agglomeration of the carbon fibers with each other can be suppressed, but in addition to the fact that the speed of loosening the carbon fiber bundle becomes slow, the drainage property at the time of papermaking also deteriorates and the moisture becomes excessive, and sometimes causes breakage at the time of conveyance, and poor adhesion of the binder resin. The slurry is obtained by dispersing the carbon fiber bundle in the above-described aqueous solution.

[0065] As the method of obtaining a wet body which becomes the base material of the carbon fiber paper body from the above-described slurry, a wet papermaking method in which the carbon fiber and the aqueous solution in the slurry are separated by a papermaking machine such as a long net type papermaking machine, a cylinder type papermaking machine, an inclined type papermaking machine, and the carbon fiber is sheeted, and particularly preferably an inclined type papermaking machine which easily controls the fiber orientation and can suppress re-agglomeration by lowering the concentration of the carbon fiber in the slurry is used. In the wet papermaking method, in order to adjust the weight per unit area and the thickness of the carbon fiber paper body, the concentration of the slurry, the flow rate of the slurry, and the speed of the papermaking net which are sent to the papermaking machine are adjusted, and thereby the weight per unit area and the thickness which can be targeted can be set. In the wet papermaking method, there are single layer papermaking in which one layer is formed, and multi-layer papermaking in which two or more layers of the wet body are laminated, and in consideration of the production stability and the production cost, the single layer papermaking is preferable.

[0066] In the wet papermaking method, the fiber orientation is controlled by the fiber orientation control method described later, and thereby the carbon fiber paper body can be given the fiber orientation.

[0067] An example of the method of controlling the fiber orientation will be described. The fiber orientation of the carbon fiber paper body is determined by the flow speed of the fiber slurry (slurry flow rate) in the papermaking machine, and the speed of the papermaking net 23 in which the fiber is laminated to form the wet body 24. By controlling these speeds, the fiber orientation can be controlled, and in the papermaking step, the ratio of the flow rate of the slurry to the speed of the papermaking net, that is, the "slurry-net speed ratio" is used to set the control conditions.

[0068] Pulp-to-wire speed ratio = Pulp flow rate [m / min] ÷ Paper wire speed [m / min] (Equation 1)

[0069] Generally, the closer the wire speed ratio is to 1, the weaker the fiber orientation; if it is far from 1, the fiber orientation becomes stronger. To increase fiber orientation, there are methods to make the wire speed ratio greater than 1 and methods to make it less than 1. However, from the viewpoint of miniaturizing pumps and other liquid delivery equipment, a wire speed ratio less than 1 is preferred.

[0070] As a method for adjusting the fiber orientation distribution 18 in the thickness direction of the carbon fiber paper body, one method is to stack fibers on a paper wire to change the wire speed ratio at each stage. For example, in the section of the paper machine where the pulp is fed, multiple pulp nozzles 21 are arranged in the height direction, and the flow rate of the pulp fed from each nozzle is adjusted accordingly. A schematic diagram is shown below. Figure 6 By setting it to Figure 6 Such a design allows for fine adjustment of the wire speed ratio along the thickness direction of the carbon fiber paper body, enabling control over the fiber orientation and distribution along this direction. For example, to enhance the fiber orientation on one side of the carbon fiber paper body, adjusting the pulp flow rate at the pulp nozzles located at the top or bottom of the paper machine to make the wire speed ratio less than 1 can enhance fiber orientation. Therefore, as one method to ensure that the fiber orientation angles of the outermost layer on the first surface side and the outermost layer on the second surface side are less than 45°, thus orienting the fibers in the same direction, orientation can be achieved by adjusting the pulp flow rates at the top and bottom of the paper machine.

[0071] Furthermore, before the slurry is fed into each slurry nozzle, it is diluted with a dispersion aqueous solution to adjust the concentration and feed rate. This allows for consistent weight per unit area even if the slurry-to-mesh ratio changes. Additionally, as... Figure 6 In this way, by stretching the partition plate 22 to distinguish adjacent slurry outlets, the flow of slurry leaving each slurry outlet is less likely to interfere with each other, and the fiber orientation and distribution can be controlled with higher precision.

[0072] In the thickness direction, in order to finely adjust the fiber orientation and distribution, the number of slurry nozzles is preferably 3 to 15, more preferably 5 to 10. When there are fewer than 3 slurry nozzles, it is sometimes difficult to perform fine orientation control in the thickness direction. In addition, if there are more than 15 nozzles, the equipment becomes larger and the operation becomes more complicated.

[0073] In addition to the control methods exemplified above, fiber orientation can also be controlled by controlling the liquid level height of the pulp flowing in the paper machine and the liquid viscosity of the pulp.

[0074] To the wet body obtained by papermaking, in general, a binder resin is imparted in order to maintain the shape as a carbon fiber papermaking body. For this imparting, a method such as coating of a binder resin on the wet body is adopted, in which case, various coating devices commercially available can be used. As the coating method, a method such as a spray coater, a curtain coater, a die coater, or the like can be used. The above-mentioned exemplified coating method is merely an example, and is not necessarily limited to these.

[0075] The wet body to which the binder resin is imparted is preferably dried at a temperature of 100 to 180°C. As the drying method, a drying method such as a drum dryer, a Yankee dryer, a hot air dryer, or the like generally used can be used. The above-mentioned exemplified drying method is merely an example, and is not necessarily limited to these. Further, it is preferable to transport while being supported with a heat-resistant belt, a heat-resistant net, a heat-resistant felt, or the like, and to perform hot air drying.

[0076] In the present application, the unit area weight of the carbon fiber in the carbon fiber papermaking body is preferably in the range of 10 to 50 g / m 2 , more preferably in the range of 15 to 35 g / m 2 , and further preferably in the range of 20 to 30 g / m 2 . If the unit area weight of the carbon fiber in the carbon fiber papermaking body is 10 g / m 2 or more, the mechanical strength of the carbon sheet is excellent. Further, if the unit area weight of the carbon fiber is 50 g / m 2 or less, the gas diffusivity and the water drainage in the in-plane direction of the carbon sheet are excellent.

[0077] Here, the unit area weight of the carbon fiber in the carbon fiber papermaking body can be obtained by dividing the mass of the residue obtained by removing the organic matter by keeping a carbon fiber papermaking body cut to 10 cm square in an electric furnace under a nitrogen atmosphere at a temperature of 450°C for 15 minutes by the area (0.01 m 2 ) of the carbon fiber papermaking body.

[0078] The manufacturing method of the carbon sheet of the present application preferably includes a resin impregnation step of imparting a resin to the carbon sheet obtained in the above-mentioned dispersion step and papermaking step, i.e., a carbon fiber papermaking body, a heating and pressurizing step of adjusting the thickness by heating and pressurizing, and a calcination step of carbonizing the carbon sheet to which the resin is imparted. Hereinafter, each step will be described.

[0079] [Resin impregnation step]

[0080] As the method of manufacturing the carbon sheet of the present application, it is preferable to impregnate a resin composition as a binder material in a porous body containing carbon fibers.

[0081] In the present application, the binder material in the carbon sheet refers to a component in the carbon sheet other than the carbon fiber, and mainly functions to bond the carbon fibers to each other. As the binder material, a resin composition impregnated in a porous body containing carbon fibers or a carbonized product thereof can be given. Note that in the present application, the substance in which the resin composition as the binder material is impregnated in the porous body containing carbon fibers is sometimes referred to as a "pre-impregnated body".

[0082] In the present application, the resin composition used when the pre-impregnated body is produced contains a resin component and a solvent, etc. as needed. Here, the resin component refers to a substance containing a thermosetting resin, a thermoplastic resin, etc., and further contains additives such as carbon powder, a surfactant, etc. as needed.

[0083] The carbonization yield of the resin component contained in the above resin composition is preferably 40% by mass or more. Carbonization refers to a state in which a carbon component remains when a substance is burned in an oxygen-occluded state. The carbonization yield is expressed by the proportion of the mass of the carbon component remaining with respect to the mass of the original resin component. If the carbonization yield is 40% by mass or more, the carbon sheet easily becomes a carbon sheet excellent in mechanical properties, electrical conductivity, and thermal conductivity. The carbonization yield of the resin component contained in the resin composition is not particularly limited, and is usually around 60% by mass.

[0084] As the resin constituting the resin component in the above resin composition, a thermosetting resin such as a phenol resin, an epoxy resin, a melamine resin, and a furan resin, etc. is preferable. Among them, a phenol resin is particularly preferable from the viewpoint of high carbonization yield.

[0085] Further, as the resin component in the above resin composition, as an additive added as needed, in order to improve the mechanical properties, electrical conductivity, and thermal conductivity of the carbon sheet, carbon powder can be given. Here, as the carbon powder, furnace black, acetylene black, lamp black, and thermal black, etc. can be used, and graphite such as flaky graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, and flaky graphite, carbon nanotubes, carbon nanofibers, and ground fibers of carbon fibers, etc. can be used.

[0086] The above resin composition can directly use the above resin component, and as needed, various solvents can be contained from the viewpoint of improving the impregnability to the porous body such as a carbon fiber paper body. Here, as the solvent, methanol, ethanol, and isopropanol, etc. can be used.

[0087] The above resin composition is preferably in a liquid state at 25°C under 0.1 MPa. If the resin composition is in a liquid state, the impregnability to the porous body such as a carbon fiber paper body is excellent, and the mechanical properties, electrical conductivity, and thermal conductivity of the obtained carbon sheet are excellent.

[0088] In the impregnation, the resin component is preferably impregnated in an amount of 30 to 400 parts by mass, more preferably 50 to 300 parts by mass, relative to 100 parts by mass of the carbon fibers in the pre-impregnated body. If the amount of the resin component impregnated is 30 parts by mass or more relative to 100 parts by mass of the carbon fibers in the pre-impregnated body, the mechanical properties, electrical conductivity, and thermal conductivity of the carbon sheet are excellent. On the other hand, if the amount of the resin component impregnated is 400 parts by mass or less relative to 100 parts by mass of the carbon fibers in the pre-impregnated body, the gas diffusivity in the in-plane direction and the gas diffusivity in the direction perpendicular to the plane of the carbon sheet are excellent.

[0089] In the present application, as a method of impregnating a resin composition in a porous body containing carbon fibers, a method of impregnating a porous body containing carbon fibers in a resin composition containing a solvent, a method of applying a resin composition containing a solvent on a porous body containing carbon fibers, and a method of forming a layer of a resin composition on a release film and transferring the layer of the resin composition to a porous body containing carbon fibers, and the like are used. Among them, from the viewpoint of excellent productivity, a method of impregnating a porous body containing carbon fibers in a resin composition to which a solvent is added is particularly preferred. By attaching a resin composition to the entire pre-impregnated body, it is possible to attach a binder material to the entire obtained carbon sheet, and thus it is possible to further improve the strength of the carbon sheet.

[0090] The carbon sheet of the present application is preferably such that the packing rate of the multilayer body Y is lower than the packing rate of the multilayer body X, as described above. Such a carbon sheet can be obtained, for example, by impregnating a resin composition in a porous body containing carbon fibers so that the amount of the resin composition impregnated in the multilayer body Y is less than the amount of the resin composition impregnated in the multilayer body X. Thus, after the resin composition that becomes a binder material is uniformly impregnated throughout the porous body containing carbon fibers by impregnation or the like, the excess resin composition attached to one surface is removed before drying, whereby the amount of the resin composition in the direction perpendicular to the plane of the carbon sheet is distributed so as to be controlled, and thus it is possible to control the packing rate of each multilayer body.

[0091] For example, after a porous body containing carbon fibers is impregnated in a solution containing a resin composition to obtain a pre-impregnated body, the solution containing the resin composition is sucked from one surface before drying, or the pre-impregnated body is pressed using rollers having different surface structures, whereby it is possible to attach a binder material throughout the entire body while changing the amount of the resin composition attached to the vicinity of one surface relative to the amount of the resin composition attached to the vicinity of the other surface.

[0092] Further, as another example, after a porous body containing carbon fibers is impregnated with a solution containing a resin composition to obtain a pre-impregnated body, the resin composition is additionally applied to only one surface of the pre-impregnated body using a spray, a gravure roll, or the like, or the pre-impregnated body is dried from one side during drying after impregnation with the resin, whereby the filling rate of one surface and the other surface of the carbon sheet can also be controlled to different values.

[0093] [heating and pressurizing step]

[0094] In the present application, the pre-impregnated body is preferably subjected to heating and pressurization. By heating and pressurization, the resin composition in the pre-impregnated body is thickened and partially crosslinked, and the carbon sheet can be adjusted to a target thickness and density. As a method of heating and pressurization, a method of pressurizing using a heated hot plate, a roll, or a belt can be used. A roll-out and take-up device can also be provided before and after the heating and pressurization device. By providing the device, the pre-impregnated body can be continuously subjected to heating and pressurization. Thickening and crosslinking of the resin composition in the pre-impregnated body can be promoted, and thus additional heating treatment using hot air or the like can also be applied.

[0095] [calcination step]

[0096] In the present application, after a resin composition is impregnated in a porous body containing carbon fibers to produce a pre-impregnated body, in order to carbonize the resin composition, calcination is preferably performed in an inert atmosphere. The calcination can also use a batch-type heating furnace, or a continuous-type heating furnace can be used.

[0097] The maximum temperature of the calcination is preferably in the range of 1300 to 3000°C. If the maximum temperature is 1300°C or higher, the resin component in the pre-impregnated body is carbonized, and the carbon sheet is excellent in conductivity and thermal conductivity. On the other hand, if the maximum temperature is 3000°C or lower, the operating cost of the heating furnace becomes low.

[0098] In the present application, the substance obtained by carbonizing the pre-impregnated body is sometimes referred to as a "carbon fiber calcination body". That is, the carbon fiber calcination body corresponds to a carbon sheet. Both the carbon fiber calcination body before water repellent processing and the carbon fiber calcination body after water repellent processing belong to the carbon sheet.

[0099] [water repellent processing]

[0100] In the present application, in order to improve the drainage property, water repellent processing is preferably performed on the carbon fiber calcination body. The water repellent processing can be performed by applying a water repellent material to the carbon fiber calcination body and performing heat treatment. Note that by performing the water repellent processing, a carbon sheet containing the water repellent material as a binder material can be produced.

[0101] As the water repellent material, from the viewpoint of excellent corrosion resistance, a fluorine-based polymer is preferably used. As the fluorine-based polymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and the like can be given.

[0102] [Gas diffusion electrode]

[0103] Next, the gas diffusion electrode of the present application is described.

[0104] The gas diffusion electrode of the present application has a microporous layer 2 on the side of the second surface of the carbon sheet of the present application. The surface having the microporous layer is referred to as the second surface of the gas diffusion electrode, and the surface not having the microporous layer is referred to as the first surface.

[0105] The microporous layer can be formed by applying a coating liquid on the second surface of the carbon sheet. The coating liquid has an electrically conductive filler dispersed in a dispersion medium such as water or an organic solvent. The coating liquid can also contain a dispersing aid such as a surfactant. As the dispersion medium, water is preferable, and a non-ionic surfactant is preferably used as the dispersing aid. In addition, a water repellent material can also be contained.

[0106] Further, in the present application, the microporous layer also preferably contains an electrically conductive filler, and as the electrically conductive filler, from the viewpoint of physical and chemical stability, a carbon powder is preferable.

[0107] The application of the coating liquid on the carbon sheet can be performed using various commercially available coating devices, and it is also preferable to dry the coating liquid by a drying device after the application.

[0108] The upper limit of the weight per unit area of the microporous layer is not particularly limited, and is preferably 50 g / m 2 More preferably, it is 30 g / m 2 Further preferably, it is 25 g / m 2 Further, as the lower limit, it is preferably 10 g / m 2 More preferably, it is 14 g / m 2 Further preferably, it is 16 g / m 2 or more.

[0109] If the weight per unit area of the microporous layer is 10 g / m 2 or more, the second surface of the carbon sheet can be entirely covered with the microporous layer, further promoting the reverse diffusion of the generated water, and further suppressing the dryout. Further, if the weight per unit area of the microporous layer is 50 g / m 2 or more, the water drainage property is further improved, and the overflow can be further suppressed.

[0110] [Membrane electrode assembly]

[0111] In the present application, by joining the above gas diffusion electrode to at least one side of a solid polymer electrolyte membrane having a catalyst layer on both sides, a membrane electrode assembly can be formed. At this time, by arranging the second surface side of the gas diffusion electrode on the catalyst layer side, in addition to further easily causing the back diffusion of generated water, the contact area of the catalyst layer with the gas diffusion electrode is also increased, the contact resistance can be reduced, and this is preferred. The above catalyst layer is formed from a layer containing a solid polymer electrolyte and a catalyst-supported carbon. As the catalyst, platinum is generally used. Figure 1 The membrane electrode assembly shown, which is composed of the gas diffusion electrode 3 and the electrolyte membrane 4 with a catalyst, is an example in which the gas diffusion electrode of the present application is arranged on both sides, but it is also possible to use the gas diffusion electrode of the present application on only one side and a conventional gas diffusion electrode on the other side.

[0112] [Fuel cell]

[0113] The fuel cell of the present application contains the gas diffusion electrode of the present application as a constituent element, and is a fuel cell in which a separator membrane, a gas diffusion electrode, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion electrode, and a separator membrane are sequentially stacked. That is, as shown in Figure 1 In this way, a fuel cell is constituted by arranging the separator membrane 5 on both sides of the above membrane electrode assembly. The separator membrane is a plate-like member of a good conductor of electricity such as metal or graphite, grooves are formed on the surface in contact with the membrane electrode assembly, and the function of electrically connecting the gas diffusion electrode with the external circuit and being able to supply fuel gas or oxidizing gas and drain generated water is assumed. In order to distribute the fuel gas on the entire surface of the gas diffusion electrode, a separator membrane in which a plurality of straight grooves that become gas flow paths are arranged in parallel on the surface is used, and as the structure of the gas flow path, the parallel groove type, the meandering groove type (snake type) can be cited.

[0114] The fuel cell of the present application is preferably arranged in such a way that the fiber orientation direction of the first surface of the carbon sheet and the direction of the gas flow path provided on the above separator membrane when arranged on the above separator membrane side are approximately perpendicular. Here, in the case where the gas flow path of the separator membrane has a plurality of different directions, the direction of the gas flow path having the highest occupancy ratio is set as the direction of the gas flow path of the separator membrane. By being arranged like this, the gas diffusion electrode is less likely to collapse into the gas flow path provided on the separator membrane, the pressure loss of the fuel gas flowing in the separator membrane can be prevented, and at the same time, the fuel gas can be efficiently supplied to the entire surface of the gas diffusion electrode. Generally, a plurality of objects sandwiched by separator membranes are stacked on both sides of such a membrane electrode assembly via a gasket, thereby constituting a solid polymer type fuel cell.

[0115] Example

[0116] Next, the present application is specifically described by Examples. The materials, carbon sheet (carbon fiber paper body, carbon fiber calcined body) and the method for producing a gas diffusion electrode used in the Examples are shown below.

[0117] <Production of carbon fiber paper body>

[0118] To 100 parts by mass of ion exchange water, 0.01 parts by mass of an antifoaming agent KM-73 (manufactured by Shin-Etsu Chemical Co., Ltd.), 0.01 parts by mass of a thickening agent "NopcoTex (registered trademark) " E-R060 (manufactured by San Nopco Ltd.), and 0.01 parts by mass of a surfactant "Alkox (registered trademark) " CP-B1 (manufactured by Meisei Chemical Works, Ltd.) were added, and the mixture was stirred with a disperser for 10 minutes to prepare an aqueous dispersion solution.

[0119] Next, PAN-based carbon fibers "Torayca (registered trademark) " T300 (manufactured by Toray Industries, Inc.) (average single fiber diameter: 7 μm) cut to 6 mm in length were added to 0.15 parts by mass with respect to 100 parts by mass of the aqueous dispersion solution, and the mixture was stirred with a disperser for 5 minutes to prepare a slurry. Next, using the obtained slurry, papermaking was performed with a papermaking machine in which 10 slurry discharge ports were arranged in the vertical direction as shown in Fig. 1. Figure 6 When the obtained slurry was fed from the disperser to each slurry discharge port, the slurry concentration was adjusted in each pipe by dilution with the aqueous dispersion solution at a different slurry web speed ratio for each pipe as described below, so that the same degree of weight per unit area was obtained. Next, the slurry flow rate was adjusted to the slurry web speed ratio for obtaining the target with each slurry discharge port, and the diluted slurry was fed from each slurry discharge port to the inclined papermaking machine while continuously performing papermaking. At this time, the separation of the fibers in the slurry was promoted by a dewatering mechanism provided at the lower part of the papermaking wire. It should be noted that the slurry discharge port arranged at the upper part of the papermaking machine is referred to as No. 1 slurry discharge port, and the slurry discharge port at the bottom of the papermaking machine is referred to as No. 10 slurry discharge port. Further, as the binder resin, a 10 mass% aqueous solution of polyvinyl alcohol was applied to the wet body exiting from the papermaking machine, and dried at 180°C for 2 minutes to produce a long carbon fiber paper body. The application amount of the polyvinyl alcohol was 22 parts by mass with respect to 100 parts by mass of the carbon fiber paper body.

[0120] <Production of water repellent-processed carbon fiber calcined body>

[0121] A resin mixture obtained by mixing thermosetting resin (resin mixture obtained by mixing KP-743K (manufactured by Arakawa Chemical Industries, Ltd.), a resol type phenol-aldehyde resin "TANOMAL (registered trademark) "759 (manufactured by Arakawa Chemical Industries, Ltd.) at a mass ratio of 1 : 1), flaky graphite BF-5A (average particle diameter 5 μm, aspect ratio 1 : 5) manufactured by Nikkato Graphite Co., Ltd. 5 parts by mass, and solvent (methanol) 85 parts by mass was mixed, and stirred for 1 minute using an ultrasonic dispersing device to obtain a uniformly dispersed resin composition.

[0122] Next, the long carbon fiber paper body was continuously immersed in the impregnation liquid of the resin composition filled in the tank, and the amount of resin adhesion was adjusted by being sandwiched by two rollers. At this time, the two rollers were spaced apart by a certain gap to pass the pre-impregnated body, whereby the amount of adhesion of the entire resin composition was adjusted. Further, one of the two rollers was provided as a smooth metal roller, and the other roller was provided as a gravure roller having a concave-convex structure. The metal roller was arranged on one surface side of the pre-impregnated body, and the gravure roller was arranged on the other surface side, and the pre-impregnated body was passed so that the amount of adhesion of the resin composition on one surface and the other surface of the pre-impregnated body was different. Thereafter, drying was performed by heating at a temperature of 100°C for 5 minutes, and a pre-impregnated body was produced. Next, while being transported in stages, the pre-impregnated body was continuously subjected to heating and pressurization treatment at a temperature of 180°C for a total of 5 minutes by being pressed and heated with hot plates arranged in parallel to each other.

[0123] The pre-impregnated body subjected to the heating and pressurization treatment was introduced into a heating furnace maintained at a maximum temperature of 2400°C in a nitrogen atmosphere, and a carbon fiber calcined body was obtained.

[0124] The carbon sheet (carbon fiber calcined body) produced as described above was cut to 15 cm x 12.5 cm, and immersed in an aqueous dispersion of a polytetrafluoroethylene resin (aqueous dispersion of "POLYFLON (registered trademark) " PTFE dispersion D-201C (manufactured by Daikin Industries, Ltd.) to impregnate the water repellent material in the carbon fiber calcined body. Thereafter, the water repellent-processed carbon fiber calcined body was produced in such a manner that the water repellent material was uniformly adhered by heating and drying in a drier furnace at a temperature of 100°C for 5 minutes, and a carbon sheet used in the following "Production of gas diffusion electrode" was produced.

[0125] <Production of gas diffusion electrode>

[0126] To 100 parts by weight of ion-exchanged water, 9.2 parts by weight of carbon powder "Denka Black" (manufactured by Denka Kogyo Co., Ltd.), 5.5 parts by weight of water-repellent agent "Polyfluon" PTFE dispersion D-1E (an aqueous dispersion containing 60 parts by weight of PTFE resin, manufactured by Daikin Kogyo Co., Ltd.), and 18.5 parts by weight of surfactant "TRITON" X-100 (manufactured by Nakalaitest Co., Ltd.) were added and mixed using a disperser to form a filler-containing coating solution. This filler-containing coating solution was then applied to the entire second surface of the water-repellent carbon sheet using a slit mold coater, and heated at 120°C for 10 minutes, followed by heating at 380°C for 10 minutes. In this way, a microporous layer was formed on the second surface side of the water-repellent carbon sheet, thus creating a gas diffusion electrode.

[0127] <Determination of the weight per unit area of ​​carbon sheet and gas diffusion electrode>

[0128] The carbon sheet or gas diffusion electrode to be measured was cut into 10cm square pieces to prepare samples. The mass [g] of each sample was divided by its area (0.01m²). 2 And find it.

[0129] <Determination of the thickness of carbon sheet and gas diffusion electrode under pressure>

[0130] Using a constant pressure thickness gauge, the carbon sheet or gas diffusion electrode to be measured is placed on a smooth platform. The height difference between the present and absent samples of the sample (carbon sheet or gas diffusion electrode) under an applied pressure of 0.15 MPa is measured. Samples are taken at 10 different locations, and the measured height differences are averaged and recorded as the thickness under pressure.

[0131] <Determination of the average diameter of a single carbon fiber>

[0132] The average diameter of a single carbon fiber was determined using a microscope such as a scanning electron microscope. A photograph of the carbon fibers on one surface of a carbon sheet was taken at 1000x magnification. Thirty different single fibers were randomly selected, and their diameters were measured to calculate the average value. The average diameter of the single fibers on the other surface of the carbon sheet was also calculated. A Hitachi S-4800 scanning electron microscope was used.

[0133] <Determination of Fiber Orientation and Filler Content>

[0134] Measure the fiber orientation degree, fiber orientation angle and filling rate according to the procedure described in the above [Determination Procedure of Fiber Orientation and Filling Rate].

[0135] <Determination of the resistance of a gas diffusion electrode>

[0136] The resistance under pressure was measured using the resistance test mode of "AUTOGRAPH (registered trademark) AGS-X" manufactured by Shimadzu Corporation. A sample of the gas diffusion electrode cut to 22.4 mm square was set on the upper and lower two resistance measuring jigs installed at intervals of 20.0 cm with the microporous layer facing upward. The upper resistance measuring jig was lowered and a load of 1.0 MPa was applied. After the prescribed load was reached, a current of 1.0 ampere was applied using a direct current power supply device connected to the resistance measuring jig. After the current was applied, the voltage value of a digital multimeter was read over a period of 20 seconds, and the value of the resistance was calculated from the measured value and the measurement area.

[0137] In the present application, the resistance value is taken as 7 mΩ-cm 2 and the performance is evaluated as a reference value.

[0138] Measurement of collapse of gas diffusion electrode

[0139] As Figure 2 shown in FIG. 1, a gas diffusion electrode (3 cm square) was disposed on a grooved surface of a grooved block 6 (3 cm square) having 15 grooves with a ridge width of 1 mm, a groove width of 1 mm, and a depth of 1 mm on one surface, with the surface on which the microporous layer was formed facing upward, and a flat block 7 (3 cm square) was further placed on the gas diffusion electrode, thereby preparing a compression unit 8 for sandwiching the gas diffusion electrode with the two blocks. The compression unit was installed between the flat jigs of a universal testing machine (AGX-5 kN manufactured by Shimadzu Corporation) having the flat jigs installed above and below, and the gas diffusion electrode was compressed under a load of 1 MPa, which is the average surface pressure applied to the gas diffusion electrode. The gas diffusion electrode was photographed from the side of the compression unit at a magnification of 1.5 to 2.0 mm in width field using a digital microscope. The length of the perpendicular line from the ridge surface, which is the reference, to the largest portion collapsed into the groove portion was measured as the collapse amount 9 [μm] on the analysis screen of the digital microscope. The collapse amount was measured at three sites among the 15 grooves for one gas diffusion electrode, and the same test was performed on six gas diffusion electrodes, and the collapse amounts of a total of 18 points were measured, and the average value thereof was used for evaluation.

[0140] In the present application, the average collapse amount is taken as 50 μm as a reference, and the performance of the gas diffusion electrode is evaluated.

[0141] (Example 1)

[0142] The wire screen of the inclined papermaking machine was driven at a papermaking speed of 5 m / min, and the slurry obtained by appropriately diluting the original slurry was fed at 0.07 m 3 / min from the No. 1 slurry discharge port, and the slurry obtained by appropriately diluting the original slurry was fed at 0.10 m 3 / min from the No. 2 to 9 slurry discharge ports, and a gas diffusion electrode having a weight per unit area of 30 g / m2 , a carbon fiber paper body having a thickness of 250 μm under pressure. The obtained carbon fiber paper body was treated in the same manner as described in the above <Manufacture of carbon fiber paper body> to obtain a carbon sheet having a weight per unit area of 45 g / m 2 , a carbon sheet having a thickness of 150 μm under pressure. At this time, the fiber orientation degree, the packing degree and their distribution of the obtained carbon sheet were as described in Table 1. Further, using the obtained carbon sheet, a gas diffusion electrode was obtained in the same manner as described in the above <Manufacture of gas diffusion electrode> to obtain a gas diffusion electrode having a weight per unit area of 62 g / m 2 , a gas diffusion electrode having a thickness of 160 μm under pressure. The obtained gas diffusion electrode was measured in the same manner as described in the above <Measurement of resistance of gas diffusion electrode> <Measurement of collapse of gas diffusion electrode>. The resistance of the gas diffusion electrode was 6.0 mΩ-cm 2 , the collapse amount was 42 μm, and all were good.

[0143] (Examples 2 to 4)

[0144] In the above <Manufacture of carbon fiber paper body>, the slurry concentration and the slurry feed amount were appropriately adjusted, the ratio of the thickness of the first surface side region and the second surface side region to the thickness of the entire carbon sheet was changed, and otherwise, a gas diffusion electrode was manufactured in the same manner as in Example 1. In any of the examples, the resistance of the gas diffusion electrode was 7 mΩ-cm 2 The collapse amount was 50 μm or less, and all were good.

[0145] (Examples 5 to 7)

[0146] In the above <Manufacture of carbon fiber paper body>, the slurry concentration and the slurry feed amount were appropriately adjusted, the fiber orientation degree of the surface layer on the first surface side was changed, and otherwise, a gas diffusion electrode was manufactured in the same manner as in Example 1. In any of the examples, the resistance of the gas diffusion electrode was 7 mΩ-cm 2 The collapse amount was 50 μm or less, and all were good.

[0147] (Examples 8, 9)

[0148] In the above <Manufacture of carbon fiber paper body>, the slurry concentration and the slurry feed amount were appropriately adjusted, the average of the fiber orientation degree of the surface layer on the first surface side and the fiber orientation degree of the second surface side region was changed, and otherwise, a gas diffusion electrode was manufactured in the same manner as in Example 1. In any of the examples, the resistance of the gas diffusion electrode was 7 mΩ-cm 2 The collapse amount was 50 μm or less, and all were good.

[0149] (Example 10)

[0150] The gas diffusion electrode was produced in the same manner as in Example 8, except that the thickness of the first surface side region and the second surface side region with respect to the thickness of the entire carbon sheet was changed, and the average value of the degree of fiber orientation of the second surface side region was changed. The resistance of the gas diffusion electrode was 6.6 mΩ-cm 2 , and the collapse amount was 37 μm, both of which were good.

[0151] (Example 11)

[0152] The gas diffusion electrode was produced in the same manner as in Example 9, except that the thickness of the first surface side region and the second surface side region with respect to the thickness of the entire carbon sheet was changed, and the average value of the degree of fiber orientation of the second surface side region was changed. The resistance of the gas diffusion electrode was 6.7 mΩ-cm 2 , and the collapse amount was 35 μm, both of which were good.

[0153] (Example 12)

[0154] The gas diffusion electrode was produced in the same manner as in Example 1, except that the resin impregnation was performed using two metal rollers, and the filling rate of the adhesive material of the first surface side and the second surface side was made the same. The resistance of the gas diffusion electrode was 6.0 mΩ-cm 2 , and the collapse amount was 44 μm, both of which were good.

[0155] (Example 13)

[0156] The gas diffusion electrode was produced in the same manner as in Example 1, except that the gap of the two rollers was adjusted, and the difference in the filling rate of the adhesive material of the multilayer body X and the multilayer body Y was increased. The resistance of the gas diffusion electrode was 6.1 mΩ-cm 2 , and the collapse amount was 39 μm, both of which were good.

[0157] (Example 14)

[0158] The gas diffusion electrode was produced in the same manner as in Example 1, except that the positions of the two rollers were exchanged, and the size relationship of the filling rate of the multilayer body X and the multilayer body Y was reversed. The resistance of the gas diffusion electrode was 6.2 mΩ-cm 2 , and the collapse amount was 44 μm, both of which were good.

[0159] (Comparative Example 1)

[0160] The gas diffusion electrode was produced in the same manner as in Example 1, except that the fiber orientation degree of the surface layer on the first surface side was changed. The resistance of the gas diffusion electrode was 5.1 mΩ-cm 2 was good, but the collapse amount was 54 μm, and the performance was insufficient. In addition, the fiber orientation degree was low, and thus the strength was weak, and there was a problem in that breakage due to tension during processing occurred.

[0161] (Comparative Example 2)

[0162] The gas diffusion electrode was produced in the same manner as in Example 1, except that the fiber orientation degree of the surface layer on the first surface side, the fiber orientation degree of the surface layer on the second surface side, and the average orientation degree of the region on the second surface side were changed. The resistance of the gas diffusion electrode was 5.3 mΩ-cm 2 was good, but the collapse amount was 52 μm, and the performance was insufficient. As in Comparative Example 1, the fiber orientation degree was low, and thus the strength was weak, and there was a problem in that breakage due to tension during processing occurred.

[0163] (Comparative Example 3)

[0164] The gas diffusion electrode was produced in the same manner as in Example 1, except that the fiber orientation degree of the surface layer on the first surface side and the average orientation degree of the region on the second surface side were changed. The collapse amount of the gas diffusion electrode was 31 μm, and was extremely good, but the resistance was 8.0 mΩ-cm 2 and the performance was insufficient. In addition, the fiber orientation degree of the region on the first surface side of the carbon sheet was high, and thus the sheet was slightly easy to roll in a direction perpendicular to the orientation direction, and the operability during processing was slightly difficult.

[0165] (Comparative Example 4)

[0166] The gas diffusion electrode was produced in the same manner as in Example 1, except that the fiber orientation degree of the entire sheet was set to be constant at 1.10, by appropriately adjusting the slurry concentration and the slurry feed amount. The resistance of the gas diffusion electrode was 5.0 mΩ-cm 2 was good, but the collapse amount was 55 μm, and the performance was insufficient. As in Comparative Example 1, the fiber orientation degree was low, and thus the strength was weak, and there was a problem in that breakage due to tension during processing occurred frequently.

[0167] (Comparative Example 5)

[0168] In the above-described fabrication of carbon fiber paper, the slurry concentration and slurry feed rate were appropriately adjusted to maintain a constant fiber orientation of 3.10 for the entire sheet. Otherwise, a gas diffusion electrode was fabricated in the same manner as in Example 1. This gas diffusion electrode exhibited an excellent collapse of 28 μm, but its resistance was 9.5 mΩ·cm. 2 The carbon sheet exhibits severe degradation and inadequate performance. Furthermore, its high overall fiber orientation makes it extremely prone to curling in the direction perpendicular to the orientation, resulting in significant processing difficulties.

[0169] (Comparative Example 6)

[0170] In the above-described fabrication of carbon fiber paper, the appropriate slurry concentration and slurry delivery rate were adjusted, and the thickness ratio of the first and second surface-side regions to the overall thickness of the carbon sheet was changed. Otherwise, the gas diffusion electrode was fabricated in the same manner as in Example 1. The gas diffusion electrode had a collapse of 37 μm, which is slightly good, but its resistance was 7.5 mΩ·cm. 2 The resistance deteriorated slightly, resulting in insufficient performance. It is speculated that the increased proportion of the first surface side region relative to the overall thickness of the carbon sheet led to the deterioration of the resistance.

[0171] (Comparative Example 7)

[0172] In the above-described fabrication of carbon fiber paper, the appropriate slurry concentration and slurry delivery rate were adjusted, and the thickness ratio of the first and second surface-side regions to the overall thickness of the carbon sheet was changed. Otherwise, the gas diffusion electrode was fabricated in the same manner as in Example 1. The collapse of this gas diffusion electrode was 33 μm, which is good, but the resistance was 8.3 mΩ·cm. 2 Furthermore, the performance deteriorated, resulting in inadequate resistance. It is speculated that the proportion of the first surface side region relative to the overall thickness of the carbon sheet further increased compared to Comparative Example 6, leading to further deterioration in electrical resistance.

[0173] [Table 1]

[0174]

[0175] [Table 2]

[0176]

[0177] Industrial applicability

[0178] The carbon sheet of the present invention is suitable for use in fuel cells, especially solid polymer fuel cells.

[0179] Explanation of reference numerals in the attached figures

[0180] 1: Carbon sheet

[0181] 1-1: First surface side region

[0182] 1-2: 2nd surface side region

[0183] 2: microporous layer

[0184] 3: gas diffusion electrode

[0185] 4: electrolyte membrane with catalyst

[0186] 5: separator

[0187] 6: grooved block

[0188] 7: flat block

[0189] 8: compression unit

[0190] 9: collapse amount

[0191] 10: thickness direction of carbon sheet

[0192] 11: 1st surface side

[0193] 12: 2nd surface side

[0194] 13: surface with 50% packing rate closest to 1st surface

[0195] 14: surface with 50% packing rate closest to 2nd surface

[0196] 15: 50% packing rate

[0197] 16: distribution of packing rate

[0198] 17: 20 layers

[0199] 18: fiber orientation degree distribution

[0200] 19: multilayer body X

[0201] 20: multilayer body Y

[0202] 21: slurry discharge port

[0203] 22: partition plate

[0204] 23: papermaking wire

[0205] 24: wet body

Claims

1. A carbon sheet having a first surface and a second surface on the opposite side of the first surface, wherein, in a range from a surface having a 50% packing rate closest to the first surface to a surface having a 50% packing rate closest to the second surface, when the aforementioned range is divided into 20 layers in the thickness direction, the fiber orientation degree of the surface layer on the first surface side is 1.20 or greater and 3.00 or less, the region formed by the continuous layers among the aforementioned layers having a fiber orientation degree that differs from the fiber orientation degree of the surface layer on the first surface side by ±0.10 or less is referred to as a first surface side region, the region formed by the layers among the aforementioned layers that are not included in the first surface side region is referred to as a second surface side region, the thickness of the first surface side region is 40% or less of the overall thickness of the carbon sheet, and the difference between the average fiber orientation degree of the second surface side region and the fiber orientation degree of the surface layer on the first surface side is greater than 0.

10. Here, the packing rate of a surface is measured every 3.9 μm from one surface to the other surface of the carbon sheet, and then the average of the packing rates of the resulting surfaces is calculated, and the 50% packing rate is the value that is 50% of the average; further, the packing rate of a layer is the average value obtained using the packing rates of the surfaces that form the layer.

2. The carbon sheet of claim 1, wherein, The difference between the fiber orientation angle of the surface layer on the first surface side and the fiber orientation angle of the surface layer on the second surface side is within 45°.

3. The carbon sheet according to claim 1 or 2, wherein, when the aforementioned range is divided into 2 multilayer bodies in the thickness direction, the multilayer body on the first surface side is referred to as multilayer body X, and the multilayer body on the second surface side is referred to as multilayer body Y, the packing rate of multilayer body Y is lower than the packing rate of multilayer body X.

4. The carbon sheet according to claim 1 or 2, which comprises a carbon fiber paper body and a binder material.

5. The carbon sheet of claim 1 or 2, wherein, The average orientation degree of the second surface side region is 1.20 or less.

6. A gas diffusion electrode having a microporous layer on the second surface side of the carbon sheet according to any one of claims 1 to 5.

7. A fuel cell comprising the gas diffusion electrode according to claim 6 as a constituent element, in which a separator film, a gas diffusion electrode, a catalyst layer, an electrolyte film, a catalyst layer, a gas diffusion electrode, and a separator film are sequentially stacked.

8. The fuel cell of claim 7, wherein, The carbon sheet is obtained by arranging the fiber orientation direction of the first surface of the carbon sheet approximately perpendicular to the direction of a gas flow path provided in the separator film when the separator film is arranged on the first surface.

9. The method of manufacturing a carbon sheet according to any one of claims 1 to 8, comprising: a dispersion step of uniformly dispersing a carbon fiber bundle in a liquid to obtain a slurry; and a papermaking step of papermaking the slurry containing the carbon fiber using a papermaking machine having at least a mechanism capable of controlling orientation in the thickness direction while continuously stacking the carbon fibers.

10. A method of manufacturing a carbon sheet comprising: a resin impregnation step of impregnating a resin into the carbon sheet obtained by the manufacturing method of the carbon sheet according to claim 9; a heating and pressurizing step of adjusting the thickness by heating and pressurizing; and a calcination step of carbonizing the carbon sheet to which the resin is impregnated.

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