Carbon fiber-resin composite sheet

Abstract

As shown in fig. 1, a carbon fiber-resin composite sheet 10 according to the present invention is composed of a sheet containing a carbon fiber and a resin, and has a first portion 12 and a second portion 14 which are continuous and distinguished in a plane direction, wherein the density of the first portion 12 is greater than the density of the second portion 14, and the first portion 12 and the second portion 14 each number 10 or less.

Description

Carbon fiber-resin composite sheet

[0001] The present invention relates to a carbon fiber-resin composite sheet, and more particularly to a carbon fiber-resin composite sheet used in a fuel cell separator.

[0002] Conventionally, fuel cell separators made of metal materials and carbon materials have been developed. Fuel cell separators made of carbon materials are advantageous in terms of lighter weight and chemical resistance compared to separators primarily made of metal materials. However, such fuel cell separators sometimes lack sufficient strength, and are more susceptible to gas leaks due to cracking than metal separators. Furthermore, increasing the amount of binder components, such as resins, to prevent cracking results in reduced electrical conductivity. Various proposals have been made to address these issues.

[0003] Patent Document 1 discloses a fuel cell separator characterized by having a conductive gas barrier layer (B) on a conductive layer (A) made of conductive fibers bound and solidified with a synthetic resin.

[0004] Patent Document 2 discloses a fuel cell separator comprising a substrate, the substrate including a first conductive layer containing a conductive first carbon material and formed in a resin material, and a second conductive layer containing a conductive second carbon material, formed adjacent to the first conductive layer on at least one side in the thickness direction of the first conductive layer, and bonded to the first conductive layer via the resin material.

[0005] Patent document 3 discloses an electrically conductive article for use as an electrode in a fuel cell, which comprises electrically conductive reinforcement fibers contained in a matrix having a thickness with the fibers mechanically oriented to be parallel to the thickness.

[0006] Patent document 4 discloses a method for manufacturing a fuel cell separator, which includes the steps of: manufacturing a stampable sheet containing a conductive filler and a polymer material; supplying the stampable sheet to a molding machine equipped with a pair of molds engraved with the shape of a fuel cell separator; and thermoforming the stampable sheet supplied to the molding machine into the shape of the separator.

[0007] Patent Document 5 discloses a method for manufacturing a separator for a fuel cell, which includes providing a fiber sheet and a raw material sheet having carbon particles and a resin applied to the fiber sheet, and pressing the raw material sheet to have an uneven shape that forms a flow path for gas flow, thereby obtaining the top portion and the transition portion, and pressing the raw material sheet so that the reduction rate of the top portion is higher than the reduction rate of the transition portion.

[0008] Japanese Patent Application Laid-Open No. 2001-15131 Japanese Patent Application Laid-Open No. 2021-170524 Japanese Patent Application Laid-Open No. 2005-527092 Japanese Patent Application Laid-Open No. 2006-269313 Japanese Patent Application Laid-Open No. 2022-29802

[0009] The present invention provides a novel carbon fiber-resin composite sheet having a portion with good gas impermeability and / or good mechanical strength and a portion with good electrical conductivity.

[0010] After extensive research, the inventors of the present invention found that the above-mentioned problems can be solved by the following means, and thus completed the present invention. That is, the present invention is as follows: <Aspect 1> A carbon fiber-resin composite sheet composed of a sheet containing carbon fiber and a resin, having a first portion and a second portion that are continuous and distinct in the plane direction, the density of the first portion being greater than the density of the second portion, and the number of the first portions and the second portions being 10 or less. <Aspect 2> A carbon fiber-resin composite sheet according to Aspect 1, which satisfies at least one of the following (i), (ii), and (iii): (i) the electrical conductivity in the thickness direction of the first portion is lower than the electrical conductivity in the thickness direction of the second portion, (ii) the gas permeability in the thickness direction of the first portion is lower than the gas permeability in the thickness direction of the second portion, and (iii) the flexural modulus of the first portion is higher than the flexural modulus of the second portion. Aspect 3: The carbon fiber-resin composite sheet according to Aspect 1, wherein there is one each of the first portion and the second portion. Aspect 4: The carbon fiber-resin composite sheet according to any one of Aspects 1 to 3, wherein the first portion is present so as to surround the second portion. Aspect 5: The second portion has a gas permeability in the thickness direction of 6.00 × 10 －５ cm ３ sec －１ cm －２ the volume resistivity in the thickness direction of the second portion is 50 mΩ cm or less; ２ The carbon fiber-resin composite sheet according to any one of Aspects 1 to 4, which is: <Aspect 6> A fuel cell separator, which is constituted by the carbon fiber-resin composite sheet according to any one of Aspects 1 to 5. <Aspect 7> A fuel cell, which has the fuel cell separator according to Aspect 6.

[0011] According to the present invention, it is possible to provide a novel carbon fiber-resin composite sheet having a portion with good gas impermeability and / or good mechanical strength and a portion with good electrical conductivity.

[0012] Fig. 1(a) is a top view of a carbon fiber-resin composite sheet of the present invention. Fig. 1(b) is a side cross-sectional view taken along line Ib-Ib in Fig. 1(a). Fig. 2 is an explanatory diagram of a first embodiment of pressing a precursor structure in the method for producing a carbon fiber-resin composite sheet of the present invention. Fig. 3 is an explanatory diagram of a second embodiment of pressing a precursor structure in the method for producing a carbon fiber-resin composite sheet of the present invention.

[0013] <<Carbon Fiber-Resin Composite Sheet>> As shown in FIG. 1 , a carbon fiber-resin composite sheet 10 of the present invention is composed of a sheet containing carbon fiber and resin, and has a first portion 12 and a second portion 14 that are continuous and distinct in the plane direction, the density of the first portion 12 is greater than the density of the second portion 14, and the number of the first portions 12 and the second portions 14 is 10 or less.

[0014] The first portion having a high density can have good gas impermeability and / or good mechanical strength, such as breaking strength, due to its dense structure. On the other hand, the inventors have unexpectedly found that the second portion having a low density can obtain good electrical conductivity. Without wishing to be bound by theory, this is thought to be because a dense structure makes it easier for the resin to be exposed on the surface of the carbon fiber-resin composite sheet, thereby increasing the resistance, while a moderate density makes it easier for the carbon fibers to be exposed on the surface of the carbon fiber-resin composite sheet, thereby decreasing the resistance.

[0015] The carbon fiber-resin composite sheet of the present invention can be used in a variety of applications, for example, as a separator for a fuel cell.

[0016] In particular, when the carbon fiber-resin composite sheet is used as a fuel cell separator, it is preferable to have one each of the first portion 12 and the second portion 14, as shown in Figures 1(a) and 1(b), from the viewpoint of separating the power supply portion and the sealing portion. In this case, it is particularly preferable that the first portion 12 is present so as to surround the second portion 14.

[0017] The carbon fiber-resin composite sheet of the present invention can satisfy at least one of the following (i), (ii), and (iii): (i) the electrical conductivity in the thickness direction of the first portion is lower than the electrical conductivity in the thickness direction of the second portion; (ii) the gas permeability in the thickness direction of the first portion is lower than the gas permeability in the thickness direction of the second portion; and (iii) the flexural modulus of the first portion is higher than the flexural modulus of the second portion.

[0018] The first and second parts of the carbon fiber-resin composite sheet of the present invention will be described below.

[0019] <First portion> The first portion is a portion whose density is greater than the density of the second portion.

[0020] The number of first portions may be 10 or less, 8 or less, 5 or less, 3 or less, or 1.

[0021] The density of the first portion is not particularly limited as long as it is greater than the density of the second portion, and may be, for example, 1.20 g / cm ３ Above, 1.22g / cm ３ or more, or 1.25 g / cm ３ or more, and may be 1.50 g / cm ３ Below, 1.40g / cm ３ Below, 1.35g / cm ３ or less, or 1.30 g / cm ３ It may be the following:

[0022] In particular, from the viewpoint of electrical conductivity, it is preferable that the ratio of the density of the first portion to the true density of the material is 0.96 or more, or 0.97 or more, and 0.99 or less, or 0.98 or less.

[0023] In the present invention, the "true density of the material" means the weighted average of the true densities of the carbon fiber and resin constituting the carbon fiber-resin composite sheet, weighted by the mass content.

[0024] When the carbon fiber-resin composite sheet of the present invention is used as a fuel cell separator, the first portion can be a seal portion, particularly a peripheral seal portion, of the separator. On the other hand, the first portion does not need to form a flow path for hydrogen and / or oxygen in the fuel cell.

[0025] The gas permeability of the first portion is 1.00×10 －６ cm ３ sec －１ cm －２ This gas permeability can be 7.00×10 or less. －７ cm ３ sec －１ cm －２ Below, 5.00 x 10 －７ cm ３ sec －１ cm －２ Below, 3.00 x 10 －７ cm ３ sec －１ cm －２ Below, 1.00 x 10 －７ cm ３ sec －１ cm －２ Below, 7.00 x 10 －８ cm ３ sec －１ cm －２ Below, 5.00 x 10 －８ cm ３ sec －１ cm －２ Below, 3.00 x 10 －８ cm ３ sec －１ cm －２ Below, 1.00 x 10 －８ cm ３ sec －１ cm －２ Below, 7.00 x 10 －９ cm ３ sec －１ cm －２ Below, 6.00 x 10 －９ cm ３ sec －１ cm －２ or less, or 5.50 x 10 －９ cm ３ sec －１ cm －２or less, and may be 1.00 x 10 －１０ cm ３ sec －１ cm －２ For example, the gas permeability may be 1.00×10 －１０ cm ３ sec －１ cm －２ Above 1.00 x 10 －６ cm ３ sec －１ cm －２ It may be the following:

[0026] In this specification, the gas permeability is measured by a differential pressure method in accordance with JIS K7126-1:2006 for the gas permeability of the produced conductive sheet.

[0027] The ratio of the gas permeability in the thickness direction of the first portion to the gas permeability in the thickness direction of the second portion is 1.00 × 10 －２ This ratio can be 9.00 x 10 －３ Below, 7.00 x 10 －３ Below, 5.00 x 10 －３ Below, 3.00 x 10 －３ Below, 1.00 x 10 －３ Below, 9.00 x 10 －４ Below, 5.00 x 10 －４ Below, 3.00 x 10 －４ or less, or 2.50 x 10 －４ or less, and may be 1.00 x 10 －５ That's it, 3.00 x 10 －５ That's it, 5.00 x 10 －５ That's it, 7.00 x 10 －５ or more, or 9.00 x 10 －５ For example, the ratio may be 1.00×10 －５ Above 1.00 x 10 －２ It may be the following:

[0028] The volume resistivity of the first portion in the thickness direction is 100 mΩ cm ２ The volume resistivity can be 90 mΩ cm or less. ２ Below, 80mΩ・cm ２ Below, 70mΩ・cm ２or less, or 60 mΩ cm ２ can be less than or equal to 20 mΩ cm ２ Above, 25mΩ・cm ２ Above, 30 mΩ・cm ２ Above, 35mΩ・cm ２ Above, 40 mΩ・cm ２ Above, 45 mΩ・cm ２ or more, or 55 mΩ cm ２ For example, the volume resistivity can be 20 mΩ cm or more. ２ 100 mΩ・cm or more ２ It can be:

[0029] In this specification, the volume resistivity was measured by placing carbon paper on both sides of the prepared carbon fiber-resin composite sheet, sandwiching it between gold-plated flat electrodes, applying a pressure of 1 MPa, and then applying a current of 1 A to these flat electrodes to measure the voltage between the electrodes, and subtracting the resistance at the interface between the flat electrode and the carbon paper from the obtained resistance.

[0030] The ratio of the volume resistivity in the thickness direction of the first portion to the volume resistivity in the thickness direction of the second portion may be 3.0 or greater. This ratio may be 3.3 or greater, 3.5 or greater, or 3.7 or greater, and may be 6.0 or less, 5.5 or less, 5.2 or less, 5.0 or less, or 4.7 or less. For example, this ratio may be 3.0 or greater and 6.0 or less.

[0031] <Second portion> The second portion has a density lower than that of the first portion.

[0032] The density of the second portion is not particularly limited as long as it is smaller than the density of the first portion, and may be, for example, 0.90 g / cm ３ Above, 0.95g / cm ３ Above, 1.00g / cm ３ Above, 1.05g / cm ３ or more, or 1.08 g / cm ３ or more, and may be 1.25 g / cm ３ or less, or 1.22 g / cm ３ It may be the following:

[0033] In particular, from the viewpoint of electrical conductivity, it is preferable that the ratio of the density of the second portion to the true density of the material is 0.82 or more, or 0.83 or more, and 0.95 or less, 0.94 or less, or 0.93 or less.

[0034] The number of second portions may be 10 or less, 8 or less, 5 or less, 3 or less, or 1.

[0035] The gas permeability in the thickness direction of the second portion is 6.00×10 －５ cm ３ sec －１ cm －２ This gas permeability can be 5.50×10 or less. －５ cm ３ sec －１ cm －２ Below, 5.20 x 10 －５ cm ３ sec －１ cm －２ Below, 5.00 x 10 －５ cm ３ sec －１ cm －２ or less, or 4.80 x 10 －５ cm ３ sec －１ cm －２ can be less than or equal to 1.00 x 10 －９ cm ３ sec －１ cm －２ That's it, 3.00 x 10 －９ cm ３ sec －１ cm －２ That's it, 5.00 x 10 －９ cm ３ sec －１ cm －２ That's it, 7.00 x 10 －９ cm ３ sec －１ cm －２ That's it, 1.00 x 10 －８ cm ３ sec －１ cm －２ That's it, 3.00 x 10 －８ cm ３ sec －１ cm－２ That's it, 5.00 x 10 －８ cm ３ sec －１ cm －２ That's it, 7.00 x 10 －８ cm ３ sec －１ cm －２ That's it, 1.00 x 10 －７ cm ３ sec －１ cm －２ That's it, 3.00 x 10 －７ cm ３ sec －１ cm －２ That's it, 5.00 x 10 －７ cm ３ sec －１ cm －２ That's it, 7.00 x 10 －７ cm ３ sec －１ cm －２ or more, or 1.00 x 10 －６ cm ３ sec －１ cm －２ This gas permeability may be, for example, 1.00×10 －９ cm ３ sec －１ cm －２ Above 6.00 x 10 －５ cm ３ sec －１ cm －２ It may be the following:

[0036] The volume resistivity of the second portion in the thickness direction is 50 mΩ cm ２ The volume resistivity can be 45 mΩ cm or less. ２ Below, 40mΩ・cm ２ Below, 35 mΩ・cm ２ Below, 30mΩ・cm ２ Below, 25mΩ・cm ２ Below, 20mΩ・cm ２ Below, 18mΩ・cm ２ or less, or 15 mΩ cm ２ can be less than or equal to 1 mΩ cm ２ Above, 3 mΩ・cm ２ Above, 5 mΩ・cm２ Above, 7mΩ・cm ２ or more, or 10 mΩ cm ２ This volume resistivity can be, for example, 1 mΩ cm or more. ２ 50 mΩ・cm or more ２ It may be the following:

[0037] Each material constituting the sheet of the present invention will be described below.

[0038] <Carbon Fiber> Examples of carbon fibers that can be used include milled fibers and chopped fibers, which may be used alone or in combination.

[0039] The average length of the carbon fibers can be, for example, 100 μm or more, 300 μm or more, 500 μm or more, 1.0 mm or more, 1.5 mm or more, 2.0 mm or more, 2.5 mm or more, or 2.8 mm or more, and can be 10.0 mm or less, 8.0 mm or less, 5.0 mm or less, 4.0 mm or less, or 3.5 mm or less.

[0040] The average fiber diameter of the carbon fibers can be 1 μm or more, 3 μm or more, or 5 μm or more, and can be 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0041] The carbon fiber content may be 10% by mass or more, 15% by mass or more, 20% by mass or more, or 23% by mass or more, and 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 27% by mass or less, relative to the mass of the carbon fiber-resin composite sheet.

[0042] <Resin> The resin may be in any form, for example, a resin fiber aggregate.

[0043] The resin preferably has the properties of being resistant to the chemical environment of the fuel cell, not softening or melting at the reaction temperature of the fuel cell, and softening or melting during press molding. Examples of such resins include polypropylene, polyethylene, polyamide, polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polyetherimide (PEI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), liquid crystal polymer (LCP), polyimide (PI), polycarbonate (PC), polyphenylene ether (PPE), polysulfone (PSU), polyethersulfone (PES), polyetheretherketone (PEEK), polyurethane, epoxy resin, silicone resin, urea resin, phenolic resin, thermosetting polyimide, thermosetting isocyanate, and polymers or mixtures of two or more of the above.

[0044] (Resin: Resin Fiber Assembly) The resin fiber assembly can be obtained by melting resin fibers, particularly by partially melting them by hot pressing. The resin constituting the resin fibers may be any of the resins described above.

[0045] <<Fuel Cell Separator>> The fuel cell separator of the present invention is composed of the above-mentioned carbon fiber-resin composite sheet.

[0046] In particular, in the fuel cell separator of the present invention, when the carbon fiber-resin composite sheet has one each of the first and second portions, the first portion can be a sealing portion and the second portion can be a power generation portion. In this embodiment, good electrical conductivity can be obtained in the power generation portion, and gas permeation can be more effectively suppressed in the sealing portion.

[0047] <Fuel Cell> The fuel cell of the present invention has the above-described fuel cell separator.

[0048] The fuel cell may have a general configuration as long as it has the above-mentioned fuel cell separator, and may have, for example, a fuel cell separator, a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer, and a fuel cell separator in this order.

[0049] Any known material used as a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer, or a fuel cell can be used.

[0050] <<Method for producing carbon fiber-resin composite sheet>> The carbon fiber-resin composite sheet of the present invention can be obtained by a method including the following: obtaining a precursor structure having a thermoplastic resin and carbon fibers; pressing the precursor structure; heating the precursor structure while applying pressure from the press to soften or melt the thermoplastic resin and maintaining this state, then cooling the precursor structure to solidify the thermoplastic resin, and then releasing the pressure to obtain a carbon fiber-resin composite sheet.

[0051] Here, any operation can be performed to ensure that the carbon fiber-resin composite sheet has a first portion and a second portion that are continuous and distinct in the plane direction. For example, as shown in Fig. 2(a), a precursor structure 10' of uniform thickness is formed in advance, and the pressing pressure during pressing is set higher in the first portion than in the second portion. Alternatively, as shown in Fig. 2(b), a spacer 30 is placed in the press 20 at a portion 12' corresponding to the first portion of the precursor structure 10' so that the final thickness during pressing is thinner in the first portion than in the second portion. This allows the carbon fiber-resin composite sheet 10 having a first portion 12 and a second portion 14 to be obtained, as shown in Fig. 2(c).

[0052] Also, for example, a precursor structure 10' shown in FIG. 3(a) can be formed in advance so that the thickness of a portion 12' corresponding to the first portion of the precursor structure is thicker than the thickness of a portion 14' corresponding to the second portion of the precursor structure, as shown in FIG. 3(b), and then, as shown in FIG. 3(c), pressing is performed using a press 20 so that the thickness of the resulting carbon fiber-resin composite sheet is uniform, thereby obtaining a carbon fiber-resin composite sheet 10 having a first portion 12 and a second portion 14, as shown in FIG. 3(d).

[0053] <Preparation of Precursor Structure> The precursor structure includes a thermoplastic resin and carbon fibers. In particular, when a thermoplastic resin fiber is used as the thermoplastic resin, the precursor structure may be a precursor fiber structure.

[0054] In particular, the precursor fiber structure can be obtained by a method including: dispersing thermoplastic resin fibers and carbon fibers in water to obtain a precursor fiber water dispersion; and casting the obtained precursor fiber water dispersion into a sheet, followed by dehydration and drying.

[0055] <Pressing of Precursor Structure> When the final thickness of the first portion during pressing is set to be thinner than that of the second portion as described above, for example, the difference in final thickness between the portion that will become the first portion of the carbon fiber-resin composite sheet and the portion that will become the second portion of the carbon fiber-resin composite sheet during pressing may be, for example, 0.35 mm or more, or 0.38 mm or more, and may be 0.50 mm or less, 0.48 mm or less, or 0.46 mm or less. For example, the thickness of the spacer may be 0.35 mm or more and 0.50 mm or less.

[0056] The pressing pressure may be 6 MPa or more, 7 MPa or more, 8 MPa or more, or 9 MPa or more, and may be 15 MPa or less, 14 MPa or less, 13 MPa or less, 12 MPa or less, or 11 MPa or less. For example, the pressing pressure may be 6 MPa or more and 15 MPa or less.

[0057] <Heating and Cooling of Precursor Structure> The precursor structure is heated and cooled by applying pressure from a press to heat the precursor fiber structure to soften or melt the thermoplastic resin and maintain it in this state, then cooling to solidify the thermoplastic resin, and then releasing the pressure.

[0058] The heating temperature is not particularly limited as long as it is higher than the softening temperature or melting point of the thermoplastic resin and lower than the thermal decomposition temperature of the thermoplastic resin, and may be, for example, 150° C. or higher, 170° C. or higher, 200° C. or higher, 220° C. or higher, or 240° C. or higher, and may be 300° C. or lower, 290° C. or lower, 280° C. or lower, 270° C. or lower, or 260° C. For example, the heating temperature may be 150° C. or higher and 300° C. or lower.

[0059] The cooling temperature is not particularly limited as long as it is a temperature that can solidify the thermoplastic resin, and may be, for example, 100° C. or less, 90° C. or less, 80° C. or less, 750° C. or less, 70° C. or less, or 60° C. or less, or may be 15° C. or more, 20° C. or more, or 25° C. or more. For example, the cooling temperature may be 15° C. or more and 100° C. or less.

[0060] The present invention will be specifically explained with reference to examples and comparative examples, but the present invention is not limited to these.

[0061] Example 1: 75 parts by mass of 6-Nylon (registered trademark) as a thermoplastic resin fiber and 25 parts by mass of carbon fiber (average length 3 mm, average fiber diameter 7 μm) as a conductive fiber were dispersed in water to obtain a precursor fiber aqueous dispersion. This was cast onto a wire mesh, dehydrated, and then dried to produce a precursor fiber structure.

[0062] Next, the obtained precursor fiber structure was set in a mold at 70°C or less, and a spacer was placed in the part that would become the first part so that the difference in final thickness during pressing between the part that would become the first part of the carbon fiber-resin composite sheet and the part that would become the second part of the carbon fiber-resin composite sheet would be 0.400 mm.

[0063] Next, this was pressed under a pressure of 10 MPa, and while maintaining the pressure, it was heated to a temperature of 250° C. and held at this temperature for 1 minute.

[0064] Next, the mixture was cooled to 70° C. or less while maintaining the pressure, to prepare the carbon fiber-resin composite sheet of Example 1.

[0065] The first and second portions of the prepared carbon fiber-resin composite sheet were punched out, and the density was calculated from the volume and mass of the punched portions. The true density of the material used was 1.30.

[0066] Examples 2 to 3 Carbon fiber-resin composite sheets of Examples 2 and 3 were produced in the same manner as in Example 1, except that the difference in final thickness during pressing between the portion to become the first portion and the portion to become the second portion was changed as shown in Table 1.

[0067] Comparative Example 1 The separator of Comparative Example 1 was produced in the same manner as Example 1, except that a graphite sheet serving as a conductive gas-blocking sheet was sandwiched between the precursor fiber structures of Example 1, and the separator was pressed at a pressure of 10 MPa so that there was no difference in the final thickness between the first and second parts when pressed.

[0068] Comparative Example 2 A carbon fiber-resin composite sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that no spacer was provided and pressing was performed such that there was no difference in final thickness between the portion that would become the first portion and the portion that would become the second portion during pressing.

[0069] <Evaluation> <Gas permeability> The gas permeability of the second portion of the prepared conductive sheet was measured by a differential pressure method in accordance with JIS K7126-1: 2006. Helium was used as the test gas, and the pressure of the test gas on the high-pressure side was set to 100 kPa.

[0070] <Resistance> Carbon paper was placed on both sides of the prepared carbon fiber-resin composite sheet, which was then sandwiched between gold-plated flat electrodes and a pressure of 1 MPa was applied. Next, a current of 1 A was applied to these flat electrodes, and the voltage between the electrodes was measured. The resistance at the interface between the prepared carbon fiber-resin composite sheet and the carbon paper was measured by subtracting the resistance at the interface between the flat electrode and the carbon paper from the resistance obtained.

[0071] Table 1 shows the configurations and evaluation results of the examples and comparative examples.

[0072]

[0073] In the carbon fiber-resin composite sheets of Examples 1 to 3 in which the density of the first portion is greater than the density of the second portion, the gas permeability of the first portion is 5.09 × 10 －９ cm ３ sec －１ cm －２ The resistance of this first portion is thought to be 57.475 mΩ cm ２ Therefore, it can be seen that the carbon fiber-resin composite sheets of Examples 1 to 3 can have a portion with good gas impermeability and a portion with good electrical conductivity.

[0074] On the other hand, it can be seen that the carbon fiber-resin composite sheet of Comparative Example 2, in which the density of the first portion is the same as the density of the second portion, did not provide a sufficient resistance value. It can also be seen that even when a conductive gas barrier sheet was interposed between two carbon fiber-resin composite sheets as in Comparative Example 1, a sufficient resistance value was still not obtained.

[0075] 10 Carbon fiber-resin composite sheet 12 First part 14 Second part 10' Precursor structure 12' Part corresponding to the first part of the precursor structure 14' Part corresponding to the second part of the precursor structure 20 Press machine 30 Spacer

Claims

1. A carbon fiber-resin composite sheet comprising a sheet containing carbon fiber and resin, the sheet having a first portion and a second portion which are continuous and distinct in the plane direction, the density of the first portion being greater than the density of the second portion, and the number of the first portion and the second portion being 10 or less each.

2. The carbon fiber-resin composite sheet according to claim 1, which satisfies at least one of the following (i), (ii), and (iii): (i) the electrical conductivity in the thickness direction of the first portion is lower than the electrical conductivity in the thickness direction of the second portion, (ii) the gas permeability in the thickness direction of the first portion is lower than the gas permeability in the thickness direction of the second portion, and (iii) the flexural modulus of the first portion is higher than the flexural modulus of the second portion.

3. The carbon fiber-resin composite sheet according to claim 1, wherein the first portion and the second portion are each one piece.

4. A carbon fiber-resin composite sheet according to any one of claims 1 to 3, wherein the first portion is present so as to surround the second portion.

5. The gas permeability in the thickness direction of the second portion is 6.00×10 －５ cm ３ sec －１ cm －２ The volume resistivity in the thickness direction of the second portion is 50 mΩ cm or less. ２ The carbon fiber-resin composite sheet according to any one of claims 1 to 4, wherein:

6. A fuel cell separator comprising the carbon fiber-resin composite sheet according to any one of claims 1 to 5.

7. A fuel cell comprising the fuel cell separator according to claim 6.

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