WO2008133333A1

WO2008133333A1 - Carbonaceous sheet and fuel cell separator using the same

Info

Publication number: WO2008133333A1
Application number: PCT/JP2008/058158
Authority: WO
Inventors: Yutaka Araki; Joichi Takenaka
Original assignee: Jfe Chemical Corporation
Priority date: 2007-04-25
Filing date: 2008-04-21
Publication date: 2008-11-06
Also published as: JP2008270133A

Abstract

Disclosed is a carbonaceous sheet having a weight per unit area of not more than 1000 g/m2. This carbonaceous sheet is composed of a carbon fiber nonwoven fabric having a weight per unit area of 1-30 g/m2 and a resin-coated graphite powder arranged on both sides of the carbon fiber nonwoven fabric and containing 3-20% by mass of a resin. Also disclosed is a fuel cell separator using such a carbonaceous sheet, which is thin and excellent in conductivity and surface smoothness.

Description

Carbonaceous sheet and fuel cell separator using the same

The present invention relates to a carbonaceous material that is thin and excellent in surface smoothness and electrical conductivity, and also relates to a fuel cell separator using the same. Background art

The polymer electrolyte fuel cell has a structure (stack structure) in which about several tens to several hundreds of unit cells are stacked in series. Each unit cell is mainly composed of a solid polymer membrane, a fuel electrode side catalyst, and an air electrode side catalyst opto separator. Among these, the separator is formed with a groove for introducing fuel gas or air on at least one side, and in addition to functioning as a gas flow path, it also functions as a blocking function to prevent mixing of fuel gas and air. . Usually, hydrogen or methanol is used as the fuel gas.

This separator is made of metal or carbon material, but all of them have gas barrier properties against air and fuel gas, conductivity, high mechanical strength, and ions that affect the degradation of high molecular films. Many performances are required such as low elution of ionic impurities. In particular, when the separator is made of a carbon material containing fibers, if there is a defect in surface smoothness such as blistering or fiber exposure, the contact resistance increases and the conductivity decreases. Therefore, excellent surface smoothness such as no swelling or fiber exposure is also required. Also, to reduce the size of the fuel cell, it is necessary to make the separator thinner. Since the separator requires a flow path for fuel gas and air, it is provided with a groove. In order to reduce the thickness of the separator while providing this groove, it is desirable that the cross section be corrugated. For this purpose, a carbon material that is thin and has good workability is desired.

A carbon material for such a separator and a method for producing a separator using the carbon material have been studied. For example, Japanese Patent Application Laid-Open No. 62-166061 proposes forming a separator using a carbon material made of a mixture of black bell powder, a thermosetting resin, and phenol fibers. Yes. This carbon material is excellent in corrosion resistance and has sufficient strength, electrical conductivity, and processability as long as it can be used as a home-use fuel cell separator (thickness: about 2 mm). When molded into a thin shape (thickness: about 0.2 to 0.3 thigh) like an onboard fuel cell, it has the following problems in terms of conductive opacification.

That is, this carbon material is usually formed into a plate shape by injection molding, compression molding or the like to form a separator. However, when the separator is molded by these molding methods, the fiber inhibits the flow of the graphite powder and the thermosetting resin, so that a short shot (hereinafter referred to as “shot”) tends to occur at the edge portion. Therefore, for example, after the carbon material is formed into a sheet shape, it is placed on a mold and subjected to treatments such as heating and compression. However, when the thickness is reduced, the amount of black bells is reduced, so that fibers are easily exposed on the surface, and the smoothness of the surface is impaired.

In addition, in Japanese Patent Laid-Open No. 2 0 0 5-3 3 9 95 3 and Japanese Patent Laid-Open No. 2 0 0 5-2 2 9 9 5 4, the mechanical strength of the fuel cell separator, conductivity, For the purpose of improving moldability, a pre-preda in which a conductive substrate such as carbon fiber or graphite nonwoven fabric is impregnated with a thermosetting resin and graphite particles has been proposed. However, since this pre-preda is completely impregnated with a thermosetting resin and graphite particles in the base material, when the separator is formed by heating, pressurizing, etc., the resin and black particles Does not flow and shots are likely to occur at the edge of the separator. Similarly, there was a problem that fibers were exposed on the surface.

Accordingly, an object of the present invention is to provide a thin carbonaceous sheet excellent in surface smoothness and conductivity and a thin fuel cell separator using the same, and using the same. To do. Disclosure of the invention

That is, the present invention relates to a carbon fiber nonwoven fabric having a weight per unit area of 1 to 30 g / m ² , and a resin containing 3 to 20% by mass of resin on both surfaces of the carbon fiber nonwoven fabric. A carbonaceous sheet having a coated graphite powder and having a weight per unit area of 1000 g / m ² or less.

In this carbonaceous sheet, the carbon fiber nonwoven fabric is a nonwoven fabric of at least one fiber selected from the group consisting of PAN-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, phenol-based carbon fibers, and graphite fibers. Preferably there is.

In any one of the above carbonaceous sheets, the average particle size of the graphite powder constituting the resin-coated graphite powder is preferably 10 to 100 m.

Further, in any one of the above carbonaceous sheets, the resin is at least one selected from the group consisting of a thermoplastic resin, a resole phenol resin, a nopolac phenol resin, an epoxy resin, and an epoxy phenol resin. A seed resin is preferred.

In any one of the above carbonaceous sheets, the resin-coated graphite powder preferably has an average particle size of 15 to L 10 m.

Furthermore, any of the above carbonaceous sheets preferably has a density of 1.7 g / cm ³ or more.

The present invention is also a fuel cell separator using a carbonaceous sheet having a density of 1.7 g / cm ³ or more. .

Furthermore, the present invention is also a fuel cell separator obtained by compression-molding any one of the above carbonaceous sheets.

Further, the present invention is a fuel cell separator molding sheet obtained by adhering resin-coated graphite powder on both surfaces of a carbon-based nonwoven fabric substrate,

The resin-coated graphite powder contains 3 to 20% by mass of resin, the carbon-based nonwoven fabric base material has a basis weight of 1 to 30 g / m ² , and the molding sheet has a basis weight of 10 00 A fuel cell separator molding sheet characterized by having a gZm of ² or less. Brief description of the drawings ''

FIG. 1 is a cross-sectional view of the molded product of the example. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of the embodiment will be described to facilitate understanding of the present invention. The carbonaceous sheet (also referred to as a molding sheet) of the present invention has a carbon fiber non-woven fabric (also referred to as a carbon-based non-woven fabric) as a base material, and a graphite powder having a surface coated with a resin on both sides of the base material. It has resin-coated graphite powder, for example, by adhesion. The fuel cell separator of the present invention is obtained by, for example, compression molding the carbonaceous sheet.

The carbonaceous sheet of the present invention uses a carbon fiber nonwoven fabric composed of discontinuous fibers as the base material. For example, a non-woven fabric (web) in which carbon fibers are dispersed together with a resin by filtering (papermaking) and heating and drying can be exemplified. Alternatively, a non-woven fabric in which a small amount of resin or inorganic binder is sprayed on carbon fibers to bond the carbon fibers together is also equivalent.

On the other hand, when a woven fabric is used as a base material, if it is molded into a separator using this, there is a possibility that the film will not be stretched sufficiently and may break or cause a shot. In addition, because the woven fabric is woven with continuous fiber bundles, it is difficult to reduce the thickness of the place where the fiber bundles overlap, and the volume resistivity differs between the part where the fiber bundles overlap and the part where they do not overlap. There is a possibility that the volume resistivity of the whole separator becomes non-uniform.

On the other hand, since the carbonaceous sheet of the present invention uses a nonwoven fabric as its base material, when the carbonaceous sheet is molded into a separator, the whole can be stretched uniformly, and the corrugated plate shape can be accommodated. it can. Furthermore, since the nonwoven fabric has a structure in which short fibers are laminated, it can be thinned.

In addition, the carbon fiber said by this invention is a high-order concept word also including graphite fiber. Therefore, as the fiber forming the carbon fiber nonwoven fabric, at least one selected from PAN-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, phenol-based carbon fiber and graphite fiber is used. It can also be used. In particular, PAN-based carbon fibers are most preferable because they are readily available and can withstand the shearing force when being molded into a separator. Similarly, the carbonaceous material referred to in the present invention preferably includes not only carbon but also black bells. The average fiber length of the fibers used in the carbon fiber nonwoven fabric is not particularly limited, but is preferably 3 to 50 mm, more preferably 5 to 30 mm. When the average fiber length is 3 mπι or more, sufficient strength is easily obtained when molded as a substrate. On the other hand, when the average fiber length is 50 mm or less, it is easier to form a sheet. Further, the average fiber diameter of the fibers used in the carbon fiber nonwoven fabric is not particularly limited, but is preferably smaller than the particle diameter of the graphite powder from the viewpoint of securing the strength and the contact area between the graphite powder, 50 / m or less, more preferably 3 Ομπι or less, and further preferably 3 to 30 ζπι. -In the present invention, a carbon fiber nonwoven fabric having a weight per unit area (also referred to as basis weight) of 1 to 30 g / m ² is used. More preferably, 1 to 20 g / m ² is used. This is because if the weight per unit area of the carbon fiber nonwoven fabric is less than 1 g / m ² , the effect of improving the strength cannot be obtained, and if it exceeds 30 g / m ² , the black bell powder is used in the separator molding process. This is because it may not enter the carbon fiber nonwoven fabric and may cause delamination of the separator.

For the production of carbon fiber nonwoven fabrics, conventional nonwoven fabric production methods such as the melt-pro method, the water jet method, the dry papermaking method and the wet papermaking method are used. Among them, for example, a wet papermaking method as disclosed in Japanese Patent Application Laid-Open No. 4-232047 is preferable in that a thin and uniform nonwoven fabric can be produced.

When graphite powder is present on both sides of the carbon fiber nonwoven fabric, it has the effect of reducing the volume resistivity of the resulting carbonaceous sheet and improving the conductivity. In the present invention, the graphite powder having a surface coated with a resin is used. The resin coated on the surface of the graphite powder works effectively to improve the uniformity of the composition of the separator obtained using the carbonaceous sheet, heat resistance, mechanical strength, and the like.

In the carbonaceous sheet of the present invention, the carbon fiber nonwoven fabric is not impregnated with resin and graphite powder as in the prior art, but the black bell powder coated with resin is applied to both surfaces of the carbon fiber nonwoven fabric. It exists by adhesion. By doing so, for example, when the carbonaceous sheet is placed in a heated mold and compression-molded to produce a fuel cell separator, the following effects are produced. That is, for resin-coated graphite powder, graphite powder And the resin flow together, not only to the end of the mold, but also to the corners such as the edge of the separator even when the thickness changes in the separator. Thus, no shots are generated in the separator, surface smoothness is improved, and uniform conductivity is ensured. In addition, according to this resin-coated graphite powder, even if the carbonaceous sheet is compressed and the graphite is flown to make it thinner, the resin and graphite flow with a uniform composition, so the amount of resin added is not increased. Strength can be secured while reducing the volume resistivity of the separator. In other words, it is effective to previously coat the resin with graphite powder.

The average particle size of the resin-coated graphite powder is preferably 15 to: L 0 0 zm.

In the resin-coated graphite powder of the present invention, the amount of the resin coated on the surface of the graphite powder is an amount that occupies 3 to 20% by mass of the total amount of the resin and the graphite powder. This is because, if the coating amount of the resin on the black bell powder is less than 3% by mass with respect to the total amount of the resin and the graphite powder, the separator strength is lowered, whereas the mass is 20%. This is because if it exceeds ₀ , the volume resistivity increases and the power generation efficiency deteriorates.

As the resin used for the coating, at least one of a thermoplastic resin and a thermosetting resin can be used. From the viewpoint of heat resistance, durability, dimensional stability, etc., it is preferable to use a thermosetting resin.

Examples of the thermosetting resin include a resol type phenol resin, a novolac type phenol resin, an epoxy resin, and an epoxy monophenol resin. At least one of these resins or a mixed resin can be used. Among these, resol-type phenol resin, epoxy resin, epoxy resin and novolac-type phenol resin are preferred because they have less ion elution, and epoxy resin does not generate gas during curing. It is more preferable.

In addition, the thermosetting resin coated on the surface of the graphite powder has a curing rate of 40% or less, preferably 20% or less, more preferably 10% or less, or an uncured state. Yes. This is because when the curing rate is 40% or less, graphite powders are more likely to adhere to each other in the molding process. In the present invention, the resin-coated graphite powder may contain a coupling agent, a release agent, an inorganic compound that improves fluidity, and various other conventionally disclosed additives. For example, a coupling agent is used for surface modification of graphite powder, and has an effect of improving dispersibility and resin strength. Also, a mold release agent is a mold release property when a separator is molded. There is an effect of improving.

In the present invention, as the graphite powder constituting the resin-coated graphite powder, artificial graphite, natural graphite, and a mixture thereof can be used. The artificial graphite is preferably made from petroleum pitch, coal pitch, or the like, carbonized and calcined, graphitized, and powdered. As the shape of the graphite powder, a flake shape, a needle shape, a spherical shape, or the like can be used. From the viewpoint of moldability, it is preferable to use a spherical shape or a flake shape. ·

The average particle size of the graphite powder is preferably 10 to 100 μπι, more preferably 10 to 85 μπι, and still more preferably 15 to 60 μm. This is because when the black & black average particle size is 10 jm or more, the viscosity at the time of molding is low, so the moldability is excellent. On the other hand, when the average particle size is 100 μm or less, it becomes easier to reduce the thickness. In this effort, the average particle size used was a particle size of 50 wt% when the particle size distribution curve was measured with a particle measuring device (manufactured by Microtrak).

The method for coating the graphite powder with the resin is not particularly limited. For example, a known method such as a mechanochemical method or a thermosetting resin dissolved in an organic solvent, mixed with graphite powder, and dried can be used. Among them, as a method for uniformly coating a small amount of resin, it is preferable to use a method in which the resin is dissolved in a solvent, mixed with graphite powder, and dried. In addition, drying can be carried out by using a conventional method such as agitation while stirring in a fluidized tank, or vacuum drying, but a method including a vacuum drying step is preferably used from the viewpoint of preventing blistering during molding. . Alternatively, a method may be used in which the mixture is uniformly mixed and hardened, then pulverized and adjusted to a predetermined particle size.

In the present invention, a carbonaceous sheet having the above-described resin-coated graphite powder on both surfaces of a carbon fiber nonwoven fabric is prepared by a method such as adhesion. This prevents the fibers that make up the carbon fiber nonwoven fabric from being exposed, provides excellent surface smoothness (no fiber bulging or swelling), and volume resistance. A separator with a low drag rate can be obtained. When the resin-coated graphite powder is attached to only one side of the carbon fiber nonwoven fabric, sufficient mechanical strength cannot be obtained, so that it is difficult to form a separator, and the resin-coated graphite powder is attached. This is not preferable because the carbon-based fibers are exposed on the surface of the separator on the side that is not. The amount of the resin-coated black lead powder adhering to the carbon fiber nonwoven fabric may be the same or different on the front and back surfaces, and may be appropriately selected according to the separator characteristics. Further, in the present invention, the weight per unit area of the obtained carbonaceous sheet is 100 g / m ² or less. More preferably, it is 5 0 to 100 0 g / m ² . The reason is that if the weight per unit area of the carbonaceous sheet is too large, a large amount of the resin-coated graphite powder is adhered to the carbon fiber nonwoven fabric, and a thin separator cannot be formed.

However, it is preferable that the weight per unit area is 50 g / m ² or more because the mechanical strength is high and the manufacture of the carbonaceous sheet facilitates the manufacture of the separator.

The carbonaceous sheet of the present invention preferably has a density of 1.7 g / cm ³ or more. This is because when the density is high, conductivity and gas barrier uniformity are excellent when formed into a fuel cell separator.

Next, an example of the manufacturing method of the carbonaceous sheet of this invention is shown.

First, resin-coated graphite powder is deposited in a mold or the like. Next, a carbon fiber nonwoven fabric is placed thereon, and then a resin-coated graphite powder is further deposited on the carbon fiber nonwoven fabric. After that, the laminate is heated and pressurized to a temperature at which the thermosetting resin softens and melts and does not cure, or higher than the melting point of the thermoplastic resin, and then cooled to produce a carbonaceous sheet. it can.

Next, the manufacturing method of the fuel cell separator of the present invention will be described.

As the method, a conventionally known method can be used. For example, a carbonaceous sheet prepared as described above is placed in a heated mold and compression-molded, or a corrugated plate heated to a temperature range where the thermosetting resin does not sufficiently cure from normal temperature There is a method in which a separator molding sheet (carbonaceous sheet) is placed in the mold, and after the separator is shaped, heat treatment is performed under the condition that the thermosetting resin is cured. Which manufacturing method Even when the method is used, in order to prevent delamination, it is preferable that the resin-coated graphite powder particles penetrate the carbon fiber nonwoven fabric of the formed separator. Example

(Example 1)

Gunei Chemical Industry Co., Ltd. Resol-type phenol resin HKG 100 g was dissolved in 200 g of aseton, mixed with 900 g of natural graphite (spherical, average particle size 60 // m), and then in a vacuum dryer. And dried under reduced pressure at 30 ° C for 12 hours. The graphite powder coated with this phenol resin was placed in a pulverizer and pulverized to adjust the average particle size to 65 μπι.

Next, a PAN-based carbon fiber (manufactured by Toho Tenax, fiber diameter: 7 μιη, length: 13 mm) force ^ a carbon fiber nonwoven fabric having a weight per unit area of 5 gZm ² was prepared by a papermaking method.

Graphite powder coated with the above phenol resin (resin content 10%) is deposited in a 100 mm square flat plate mold at 200 g / m ² , the carbon fiber nonwoven fabric is placed thereon, and the phenol resin is further deposited thereon. There was deposited black 1 powder coated on 200 gZm ² uniform. A carbon fiber nonwoven fabric in which this graphite powder was placed on both sides was pressurized at 80 ° C. and then cooled to produce a carbonaceous sheet (weight per unit area: 405 g / m ² ). Place this carbon sheet on a mold set at 200 ° C, close the mold while applying pressure at 20 OMPa, perform thermosetting molding for 10 minutes, and mold as shown in the cross-sectional view of Fig. 1 I got a product. This molded product is a model of the uneven shape of the fuel cell separator, a: 3 mm in FIG. 1, b: 1 mm. Further, the thickness of the flat part c of the obtained molded product was 220 μηα, and the density was 1.84 g / cm ³ .

The resulting molded product was observed for conductivity (volume resistivity), surface smoothness (exposure of fiber, -swelling) and shots, and the results are shown in Table 1 together with the thickness c of the molded product.

(Example 2)

Nippon Kayaku Co., Ltd. trisphenol type epoxy resin 33 g, curing agent phenol novolak resin 16.5 g, curing catalyst 2-phenylimidazole (2 PZ) 0.5 g dissolved in 200 g of aceton, Natural graphite (spherical, average particle size: 60 μm) 950 g And then dried in a vacuum dryer for 12 hours at a temperature of 30 ° C. under reduced pressure. This epoxy resin or coated graphite powder was put in a powder container and ground to adjust the average particle size to 2 2 τη. -Next, a carbon fiber nonwoven fabric with a weight per unit area of 10 g / m ² was prepared from PAN-based carbon fiber (Toho Tenax diameter 5 / m, length 6 mm) by papermaking. Black bell powder coated with the above epoxy resin (resin content 5%) was deposited in a 100 mm square flat plate mold at a rate of 200 g / m ² , and a carbon fiber nonwoven fabric was placed on top of it. After pressurizing at ° C, it was cooled. Next, 20 g / m ² of graphite powder coated with the epoxy resin is further uniformly deposited on the carbon fiber nonwoven fabric in the mold, repressurized at 80 ° C., and then cooled. Then, a carbonaceous sheet (weight per unit area: 4 10 g / m ² ) was produced. This carbonaceous sheet was placed on a 200 ° C. mold in the same manner as in Example 1, and subjected to thermosetting molding for 10 minutes to obtain a molded product. The resulting molded product was observed for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and shot generation, and the results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 1.95 5 g / cm ³ .

(Example 3)

Nippon Kayaku Co., Ltd. trisphenol type epoxy resin 9 9 g, curing agent phenol nopolac resin 4 9.5 g, curing catalyst 2-phenylimidazole (2 PZ) 1.5 g into caseone 600 0 g After being dissolved and uniformly mixed with natural graphite (spherical, average particle size 20 ^ m) 8 50 g, it was dried under reduced pressure at a temperature of 30 ° C. for 12 hours in a vacuum dryer. This graphite resin covered with epoxy resin 4 was put into a pulverizer and pulverized to adjust the average particle size to 22 μm.

Next, a carbon fiber nonwoven fabric having a weight per unit area of 20 g / m ^{2 from} a PAN-based carbon fiber (Toho Tenax diameter: 7 m, length: 13 mm) force was prepared by a papermaking method. Graphite powder coated with the above epoxy resin (resin content 15%) is deposited in a 100 mm square flat plate mold at 200 gZm ² and a carbon fiber non-woven fabric is placed on it at 80 ° C. Caro. Cooled after pressing. Next, graphite powder 20 g / m ² coated with the above epoxy resin is further uniformly deposited on the carbon fiber nonwoven fabric in the mold, re-pressurized at 80 ° C., cooled, A carbonaceous sheet (weight per unit area: 4 20 g / m ² ) was prepared. This carbonaceous sheet was placed on a 200 ° C. mold in the same manner as in Example 1 and thermosetting molded for 10 minutes to obtain a molded product. The resulting molded product was observed for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and shot generation, and the results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 2.00 g / cm ³ .

(Comparative Example 1)

Instead of the carbon fiber nonwoven fabric, a _{satin weave} fabric made of carbon fiber having a diameter of 7 _μΙη and having a weight per unit area of 30 g / m ² was used as a base material. The graphite powder coated with the epoxy resin used in Example 2 above (resin content 5%) was deposited in a 10 Omm square flat plate mold with 200 gZm ² , and a carbon fiber woven fabric was placed on it. On top of this, graphite powder coated with phenol resin was uniformly deposited at 200 gZm ² . A carbon fiber woven fabric in which this black lead powder was placed on both sides was pressurized at 80 ° C and then cooled to produce a carbonaceous sheet (weight per unit area: 430 gZm ² ). This carbonaceous sheet was placed on a 200 ° C. mold in the same manner as in Example 1, and subjected to thermosetting molding for 10 minutes to obtain a molded product. The resulting molded product was observed for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and shot generation, and the results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 1.43 g / cm ³ .

(Comparative Example 2)

100 g of resol-type phenol resin HKG manufactured by Gunei Chemical Industry Co., Ltd. was dissolved in 400 g of acetone and uniformly mixed with 900 g of natural graphite (spherical, average particle size 60 μm) to prepare a slurry.

Next, a carbon fiber nonwoven fabric with a weight per unit area of 20 gZm ² was prepared from PAN-based carbon fiber (Toho Tenax diameter 7 / iii, length 13 mm) by the papermaking method. After applying the slurry to the obtained carbon fiber nonwoven fabric, it was dried under reduced pressure at a temperature of 30 ° C. for 12 hours in a vacuum dryer (resin content 10%). The weight per unit area of the carbonaceous sheet after drying was 340 g / m ² .

This carbonaceous sheet was molded in the same manner as in Example 1, and the resulting molded product was observed for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and generation of shots. The results are shown in Table 1 together with the thickness c of the molded product. The density of part c is 1. 79 g / cm ³ It was.

(Comparative Example 3.)

A carbonaceous sheet and a molded product were produced in the same manner as in Example 1 except that a carbon fiber nonwoven fabric having a weight per unit area of 40 g / m ² was used as the substrate, and the conductivity (volume resistivity), surface The smoothness (exposure of fibers, swelling) and the occurrence of shots were evaluated. The results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 1.222 g / cm ³ .

(Comparative Example 4)

20 _g of Resol type phenolic resin HKG manufactured by Gunei Chemical Industry Co., Ltd. was dissolved in 200 g of acetone and mixed uniformly with 980 g of natural graphite (spherical, average particle size 60 μιη), then in a vacuum dryer for 12 hours. And dried under reduced pressure at a temperature of 30 ° C. The graphite powder coated with the phenol resin was placed in a powder frame and ground to adjust the average particle size to 63 μπι (resin content 2%).

Next, a carbon fiber nonwoven fabric substrate with a weight per unit area of 10 gZm ² was prepared from PAN-based carbon fiber (Toho Tenax, diameter 7 m, length 13 mm) by the papermaking method.

Except for using these raw materials, carbonaceous sheets and molded products were produced in the same manner as in Example 1 and evaluated for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and occurrence of shots. did. The results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 1.86 g / cm ³ .

(Comparative Example 5)

300 g of resol type phenolic resin HKG made by Gunei Chemical Industry Co., Ltd. was dissolved in 200 g of acetone and mixed uniformly with 70 g of natural graphite (spherical, average particle size 60 m). It was dried under reduced pressure for 30 hours at a temperature of 30 ° C. The graphite powder coated with this phenol resin was placed in a pulverizer and powdered to adjust the average particle size to 65 (resin content 30%).

Next, a carbon fiber nonwoven fabric substrate having a weight per unit area of 10 g / m ² was prepared from PAN-based carbon fibers (made by Toho Tenax, diameter 7 μιη, length 13 mm) by the papermaking method. Except for using these raw materials, carbonaceous sheets and molded products were produced in the same manner as in Example 1 and evaluated for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and occurrence of shots. did. The results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 1.78 g / cm ³ .

(Comparative Example 6)

The graphite powder and carbon fiber nonwoven fabric coated with phenol resin used in Example 1 were used. Black bell powder phenolic resin is coated, 10 Omm angle within the flat die is 750 g / m ² is deposited, thereon Place the 10 g / m ² of carbon fiber nonwoven fabric, phenol resin thereon to further The graphite powder coated with was uniformly deposited at 750 g / m ² . A carbon fiber nonwoven fabric in which this resin-coated black bell powder was placed on both sides was pressed at 80 ° C. and then cooled to prepare a carbonaceous sheet (weight per unit area: 1510 g / m ² ). This carbonaceous sheet was molded in the same manner as in Example 1 to obtain a molded product. The thickness of the flat part c was 750 / m. The obtained molded product was evaluated for conductivity (volume resistivity), surface smoothness (fiber exposure, swelling), and occurrence of shots. The results are shown in Table 1 together with the thickness c of the molded product. The density of part c was 2.01 g / cm ³ .

table 1

Volume resistivity, surface smoothness (expansion and fiber exposure), and occurrence of shots were measured as follows.

(Volume resistivity)

The conductivity of the molded product was evaluated by measuring the volume resistivity by two methods. One was measured with respect to the surface direction of the molded product by using a Loresta HP-550 manufactured by Mitsubishi Chemical Co., Ltd., according to a method (four-probe method) based on JIS K 7 1 94.

In the other, the volume resistivity in the thickness direction of the molded product was measured and evaluated by the following method. In other words, a 5 cm square is cut out from the flat plate part (left side of part a) of the molded product, sandwiched between gold-plated Yin and Yang electrodes, and voltage is applied while applying pressure at 40 MPa (40,8 kgf Z cm ² ) The volume resistivity was measured by applying.

(Surface smoothness)

The surface of the molded product was observed visually, and the presence or absence of S-curvature was observed. The surface was observed with a microscope, and the presence or absence of carbon fiber was observed.

(Occurrence of shot)

The parts a and b of the molded product were cut out, embedded in an epoxy resin and polished, and then observed with an optical microscope to observe the presence or absence of corners on the molded product. As is clear from the results in Table 1, when the carbonaceous sheets of Examples 1 to 3 are used, a thin molded product (fuel cell separator) having a thickness c of around 200 μπα should be easily manufactured. I was able to. Moreover, it was found that the film was excellent in conductivity and surface smoothness, and there was no occurrence of shots. Further, the obtained molded product did not bend even if it was bent lightly, and was sufficient in strength.

On the other hand, in Comparative Example 1, since the woven fabric was used for the base material, the carbon fiber of the base material did not stretch, shots occurred at the corners of part a, and the thickness c was as thick as 300 μm. Low conductivity. Further, in Comparative Example 2, blistering, which was probably caused by the organic solvent impregnated in the carbon fiber nonwoven fabric, and exposure of the fibers and shots at part b were confirmed.

In Comparative Example 3, the weight per unit area of the carbon fiber nonwoven fabric and the carbonaceous sheet is large. Therefore, even when the carbonaceous sheet is pressed, the thickness c is as high as 3600 m. In addition, graphite could not enter the inside of the carbon fiber nonwoven fabric, and voids were generated, and the molded product was peeled off from the upper and lower surfaces.

In Comparative Example 4, since the amount of the phenol resin for coating was small, when the carbonaceous sheet was placed in the mold, the graphite dropped out, and the exposure of carbon fibers was observed on the surface of the molded product. In addition, the strength of the molded product was low, and cracking occurred during handling.

In Comparative Example 5, since the amount of the phenol resin for coating is too large, the volume resistivity values in the surface direction and the thickness direction are large, and the conductivity is low.

In Comparative Example 6, since the laminated graphite powder was too much, the thickness c of the molded product became as thick as 7500 μm, and the thickness could not be reduced. Industrial applicability

According to the present invention employing the above-described configuration, a carbonaceous sheet that can be formed into a thin fuel cell separator that is excellent in conductivity and surface smoothness without causing shots at the edge portion or the like of the separator. Furthermore, a fuel cell separator can be provided. As a result, the fuel cell separator can be reduced in weight and thickness, so that a small polymer electrolyte fuel cell that can be mounted on an automobile or the like can be provided.

Claims

The scope of the claims

1.

A carbon fiber nonwoven fabric having a weight per unit area of 1 to 30 g / m ² ; and a resin-coated black bell powder containing 3 to 20% by mass of a resin on both surfaces of the carbon fiber nonwoven fabric; Carbonaceous sheet with a weight of 1 ΰ 00 g / m ² or less.

2.

2. The carbon according to claim 1, wherein the carbon fiber nonwoven fabric is a nonwoven fabric of at least one fiber selected from the group consisting of PAN-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, phenol-based carbon fibers, and graphite fibers. Quality sheet.

3.

2. The carbonaceous sheet according to claim 1, wherein an average particle diameter of the graphite powder constituting the resin-coated graphite powder is 10 to 100 μm.

Four.

2. The carbonaceous material according to claim 1, wherein the resin is at least one resin selected from the group consisting of a thermoplastic resin, a resol type phenol resin, a nopolac type phenol resin, an epoxy resin, and an epoxy monophenol resin. Sheet.

Five.

The carbonaceous sheet according to claim 1, wherein the resin-coated graphite powder has an average particle size of 15 to 110 µm.

6.

The carbonaceous sheet according to any one of claims 1 to 5, wherein the density of the sheet is 1.7 g / cm ³ or more.

7.

A fuel cell separator using the carbonaceous sheet according to claim 6.

8.

A fuel cell separator obtained by compression-molding the carbonaceous sheet according to claim 1.

9.

A fuel cell separator molding sheet comprising resin-coated graphite powder adhered to both surfaces of a carbon-based nonwoven fabric substrate,

The resin-coated graphite powder contains 3 to 20% by mass of resin, the carbon-based nonwoven fabric base material has a basis weight of 1 to 30 g / m ² , and the molding sheet has a basis weight of 10 00 A fuel cell separator molding sheet characterized by having a gZm of ² or less.