JP2002075400A - Separator for fuel cell and fuel cell using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost separator for a fuel cell having superior dimensional precision and no problems in separator characteristics such as gas impermeability, electric characteristics, liquid lubricating ability, and mechanical strength, and to provide a high-performance fuel cell having superior dimensional precision and no problems in separator characteristics such as gas impermeability, electric characteristics, liquid lubricating ability, and mechanical strength and having the low-cost separator for the fuel cell. SOLUTION: This separator for the fuel cell is formed by having a manifold in a compact formed by pressure-forming molding sheets containing expanded graphite and resin, and this fuel cell is formed by having this separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell separator and a fuel cell using the fuel cell separator.

[0002]

2. Description of the Related Art In recent years, fuel cells have received a great deal of attention from the viewpoint of measures to prevent global warming by fossil fuel consumption, energy saving measures, and the like. .

[0003] The function of a separator, which is one of the components of a fuel cell, is to supply hydrogen and oxygen as raw materials for the generated energy quantitatively and to quickly discharge the generated water. Member. In addition, since several hundred separators are used in one battery, compactness is urgently required.Currently, each company is improving the design, reducing the thickness, weight and volume per sheet, and developing an inexpensive separator. I'm shy.

A conventional separator is manufactured by carefully processing a graphite plate over a long period of time with a high-precision cutting machine in which the shape of a flow path is programmed, and then impregnating the obtained separator with a solution resin under vacuum. It was made by curing and gas impermeability. However, the separator obtained above requires a long time for the cutting (formation of a manifold, a flow path, etc.) process and the gas impermeability (impregnation with a liquid resin), so that the price per separator is extremely high. Further, a fuel cell using the separator in units of several hundred sheets is expensive.

On the other hand, the present inventors have developed a new conductive molding material which uses expanded graphite powder and a resin together as a separator which can form an inexpensive and accurate manifold, a flow path and the like and does not impair the characteristics of a fuel cell. Suggested. However, since the separator forms the manifold at the same time as the molding, the thickness of the periphery of the manifold is smaller than that of the other ribs (uneven portions) and flat portions (flat portions) due to burrs generated at the time of molding. It tended to be thinner, which was a major cause of thickness variation. In particular, when the thickness variation of one separator is large, there is a problem that when assembling a stack of many separators, it is difficult to assemble them uniformly due to dimensional errors, and it is difficult to manufacture an optimal fuel cell. Further, when manufacturing a separator having a manifold, a plurality of small manifold forming dies (frames) having poor handling properties are used in the manifold forming portion, so that the efficiency of the molding operation is greatly reduced.

[0006]

The invention according to claims 1 to 5 is excellent in dimensional accuracy, has no problems in separator characteristics such as gas impermeability, electric characteristics, liquid lubrication, mechanical strength, and is inexpensive. A fuel cell separator is provided. The invention according to claims 6 and 7 is excellent in dimensional accuracy, has no problem in separator characteristics such as gas impermeability, electric characteristics, liquid lubricity, and mechanical strength, and has an inexpensive fuel cell separator. The present invention provides a simple fuel cell.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a fuel cell separator comprising a molded body obtained by press-molding a molding sheet containing expanded graphite powder and a resin and provided with a manifold.
Further, the present invention relates to the fuel cell separator, wherein the expanded graphite powder is a pulverized powder of an expanded graphite sheet. In the present invention, the expanded graphite powder has an average particle size of 5 μm to 1000 μm.
And the fuel cell separator described above.

[0008] The present invention also relates to the above fuel cell separator, wherein the resin is a powder, and the average particle size thereof is 1 μm to 1000 μm. Further, the present invention relates to the fuel cell separator, wherein the manifold is provided by a punching method. The present invention also relates to a fuel cell having the above-mentioned separator. Furthermore, the present invention relates to the above fuel cell, which is a solid polymer type.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, there is no limitation on the properties of a molding resin used to obtain a molding sheet.
Considering safety, shortening of manufacturing process (low cost), etc.,
A thermosetting resin and a thermoplastic resin which can be dry-mixed (solvent-free mixing) and have a stable particle size distribution are preferable.

The chemical structure and type of the resin to be used are not limited. For example, powdered epoxy resin (used in combination with a powdered curing agent), powdered melamine resin, powdered acrylic resin, resol-type and novolak-type powdered phenols Resin, powdered polyamide resin, powdered phenoxy resin and the like are used. Among the resins described above, powdered phenol resins are most suitable as the molding resin used in the present invention because of their excellent economic efficiency, workability, and excellent balance of properties after curing.

The powdery phenolic resin used is not particularly limited. The powdery phenolic resin has a uniform particle size as a powdery property, a small amount of blocking (aggregation of the powdery resin), a small amount of gas generated during the reaction, and a low resin flow. It is preferable to use a resin having characteristics such as easy molding and easy completion of heat treatment in a short time. Particularly, a powdered phenol resin having a chemical structural unit represented by the general formulas (A) and (B) is preferably used. It is preferable in terms of controlling volatile gas and heat resistance.

[0012]

Embedded image (Wherein the hydrogen attached to the aromatic ring is substituted with a substituent except for one of the ortho positions of the hydroxyl group).

[0013]

Embedded image (In the formula, R ¹ is a hydrocarbon group, and the hydrogen bonded to the aromatic ring may be substituted with a substituent.)

The average particle size of the powdered phenolic resin is not particularly limited. However, in consideration of dry mixability, the number average particle size is preferably in the range of 1 μm to 1000 μm, and more preferably 10 μm.
The range of -800 µm is more preferable. Number average particle size is 1
When a powdered phenolic resin having a particle diameter of less than μm is used, coagulation of the resin becomes a problem, and there is a tendency that uniform mixing with the expanded graphite powder cannot be expected. Mixing is difficult, and the density of the obtained molded body may partially vary.

As the expanded graphite powder used in the present invention, it is preferable to use an expanded graphite sheet pulverized powder obtained by forming expanded graphite into a sheet, increasing the density and increasing the strength.

The method for producing expanded graphite is not particularly limited. For example, raw graphite is immersed in a solution containing an acidic substance and an oxidizing agent to form a graphite intercalation compound, and then subjected to a high-temperature treatment to be processed in the C-axis direction of the graphite crystal. Can be obtained by swelling.

The raw material graphite is not particularly limited, but is preferably graphite having a high degree of crystal development, such as natural graphite, quiche graphite and pyrolytic graphite. Natural graphite is preferred in consideration of the balance between the obtained characteristics and economy. The natural graphite used is not particularly limited.
Commercial products such as F48C (trade name, manufactured by Nippon Graphite Co., Ltd.) and H-50 (trade name, manufactured by Chuetsu Graphite Co., Ltd.) can be used.

The acidic substance used in the processing of the raw graphite is as follows:
Generally, sulfuric acid or a mixture of sulfuric acid and nitric acid is used. The concentration of the acid is preferably 95% by weight or more. The amount of the acidic substance to be used is not particularly limited, and is determined by a target expansion ratio. For example, 1 to 100 parts by weight of graphite is used.
It is preferable to use from 00 parts by weight to 1000 parts by weight.

Further, as the oxidizing agent used together with the acidic substance, it is preferable to use hydrogen peroxide or hydrochloric acid since a good expanded graphite can be obtained. When hydrogen peroxide is used as the oxidizing agent, the concentration of hydrogen peroxide is not particularly limited, but is preferably 20% by weight to 40% by weight. The amount thereof is not particularly limited, but it is preferable to mix 5 to 60 parts by weight of hydrogen peroxide solution with respect to 100 parts by weight of graphite.

The method for producing the pulverized powder of the expanded graphite sheet used as a preferable material in the present invention is not particularly limited. Generally, the expanded graphite obtained as described above is pressed into a sheet by pressing with a press, a roll or the like. And can be obtained through coarse pulverization, fine pulverization, and a classification step performed as necessary. There is no particular limitation on the thickness and density of the sheet when the expanded graphite is formed into a sheet, but the thickness is 0.5 mm to 1.0 mm.
Those ranges and the density of 5mm is in the range of 0.2g / cm ³ ~1.2g / cm ³ are preferred.

The particle size of the pulverized powder of the expanded graphite sheet is preferably in the range of 5 μm to 1000 μm in terms of number average particle size,
The range of -800 µm is more preferable. Number average particle size is 5
If it is less than μm, the properties of the expanded graphite powder will be weakened, and gas impermeability, electrical properties and mechanical strength will tend to decrease, while if it exceeds 1000 μm, the miscibility with the resin will deteriorate, as described above. Tends to occur.

The mixing ratio of the expanded graphite powder and the resin is arbitrarily determined based on the required required characteristic values of the final molded product.
Usually, the range of expanded graphite powder / resin = 95/5 to 50/50 (weight ratio) is preferable, and the range of 90/10 to 60/40 (weight ratio) is more preferable. When the compounding amount of the expanded graphite powder to be mixed exceeds 95% by weight, gas impermeability and mechanical strength tend to decrease, while when it is less than 50% by weight, the expanded graphite powder which is a conductive substance Is too small and electrical properties tend to deteriorate.

The method of mixing the expanded graphite powder and the resin is not particularly limited. For example, it is preferable to perform dry mixing using a shaker, a V blender or the like which does not apply a large shearing force to the pulverized powder of the expanded graphite sheet. When the pulverized powder of the expanded graphite sheet is broken during mixing, the mechanical strength of the obtained molded body tends to decrease.

The above mixed powder can be used directly as a molding material, but in the present invention, the mixed powder is used as a molding sheet (tablet) in order to further improve the mixing property and the workability. Although there is no particular limitation on the tablet manufacturing method, it is effective to compress the mixed powder into a plate to improve the handling and use.

Although there is no limitation on the method of producing the sheet for molding, it includes, for example, a mixture charging tank, a knife for making the material to have a constant thickness and a constant width, a transfer device for transferring the processing material, a roll for forming a sheet, and the like. For example, a molding sheet manufacturing apparatus to be used can be used.

Further, the molding sheet can be used by adding a part of the resin contained in the molding sheet by heat melting or reacting as needed in order to add strength. There is no limitation on the method of reacting, but there is a method in which a roll to be formed into a sheet is heated and a part of the resin is reacted.

An object of the present invention is to provide a manifold formed on a separator by post-processing after forming, and there is no particular limitation on the density, the number of stacked sheets, the shape, and the like of the forming sheet used in the present invention.

There is no particular limitation on the punching method for post-processing the manifold. For example, the manifold is formed of a cutter blade and cushion material having the same dimensions and the same dimensions and shape as the formed manifold, for example. It is preferable in terms of accuracy and cost to manufacture a manifold by using a wooden mold and a metal mold and applying pressure.

There is no particular limitation on the molding method for obtaining a molded article (separator for a fuel cell), but it is preferable to mold by a compression (pressure) molding method. The dimensions of the fuel cell separator according to the present invention are not particularly limited, and are appropriately selected according to the size of the fuel cell.

[0030]

The present invention will be described below with reference to examples.

Example 1 (1) Production of ground powder of expanded graphite sheet 600 g of sulfuric acid (concentration: 99% by weight) and 200 g of nitric acid (concentration: 99% by weight) were placed in a 3-liter glass flask.
400 g of graphite F48C (fixed carbon: 99% by weight or more, trade name, manufactured by Nippon Graphite Co., Ltd.) was blended with the mixture, and stirred with a stirring motor (120 min ^-1 ) equipped with a glass stirring blade.
And then hydrogen peroxide (concentration 35% by weight) 32
g was blended and stirred for 15 minutes. After completion of the stirring, the acid-treated graphite and the acid component are separated by vacuum filtration, the obtained acid-treated graphite is transferred to another container, 5 liters of water is added, and the mixture is stirred for 10 minutes with a large stirring blade and washed by vacuum filtration. The acid-treated graphite and the wash water were separated.

The obtained washed acid-treated graphite was transferred to an enamel vat, leveled evenly, and dried in a dryer heated to 110 ° C. for 1 hour.
Heat treatment was performed for an hour to remove moisture. 80 more
It was placed in a heating furnace heated to 0 ° C. for 5 minutes to obtain expanded graphite.
After cooling, the expanded graphite was rolled with a roll to a density of 1.0
A sheet having a thickness of 0.8 mm was prepared at g / cm ³ . The obtained sheet is pulverized by a coarse pulverizer (Rosoplex (trade name) manufactured by Hosokawa Micron Corporation) and then finely pulverized (free pulverizer M-3 (trade name) manufactured by Nara Machinery Co., Ltd.). Crush,
An expanded graphite sheet pulverized powder having an average particle size of 150 μm was obtained.

(2) Resin Used As a powdered phenolic resin having a small volatile gas during molding and having a chemical structural unit represented by the general formulas (A) and (B), HR1060 (manufactured by Hitachi Chemical Co., Ltd., (Trade name), average particle size: 20 μm).

(3) Manufacture of forming sheet The pulverized powder of the expanded graphite sheet obtained in (1) (bulk density: 0.2
g / cm ³ ) 350 g of the powdered phenolic resin (2) 150
g (pulverized powder of expanded graphite sheet / resin = 70/30 (weight ratio)) was charged into a V blender and mixed for 3 minutes to obtain a mixed molded powder. Then, the mixed molding powder is subjected to a self-molding sheet manufacturing apparatus composed of a mixture charging tank, a knife, a transfer device (transfer belt) and a compression roll,
1500 g of a molding sheet per 1 m ² were obtained.

(4) Manufacture of molded article with manifold (separator for model fuel cell) Flat plate 1 having the shape (length, width 100 mm, thickness 1 mm) shown in FIG.
Is heated to 180 ° C., one sheet of the molding sheet obtained in (3) is inserted into the mold, and a gauge pressure of 8.82 MPa (90 kgf / cm ^{2) is} applied with a 76-ton press. ) For 10 minutes. During this period, degassing was not performed.

Thereafter, the obtained molded product was heated at 200 ° C. for 30 minutes.
Heat treatment for a further 2 minutes, and further to form a formed body having a manifold (diameter 10 mm) 2 having the shape shown in FIG. 2, placing the formed plate on a punching die having a processed portion (manifold) constituted by a cutter blade, Put this at room temperature 76
The molded body 3 with the manifold was obtained by applying pressure with a ton press under the condition of a gauge pressure of 1.96 MPa (20 kgf / cm ² ). Immediately after the pressurization, the molded article 3 with the manifold was taken out from the mold and cracks near the manifold were confirmed. However, no cracks occurred and there was no problem at all.

Comparative Example 1 Example 1 was repeated, except that a molded article shown in FIG.
A molded article with a manifold was obtained through the same materials and steps as described above.

[Evaluation] Next, the molded bodies with manifolds obtained in Example 1 and Comparative Example 1 are shown in FIG.
The thickness at points E to E was measured with a micrometer.
Table 1 shows the results.

[0039]

[Table 1]

As shown in Table 1, in the molded article with the manifold of Example 1, the thickness of the flat portion around the manifold is almost the same, and the thickness around the manifold is also small. On the other hand, the thickness of the periphery of the manifold of Comparative Example 1 is smaller than that of the flat portion, and the thickness around the manifold has a large variation.

[0041]

The fuel cell separator according to the first to fifth aspects is excellent in dimensional accuracy, has no problem in separator characteristics such as gas impermeability, electric characteristics, liquid lubrication, mechanical strength, and is inexpensive. It is a fuel cell separator. The fuel cells according to claims 6 and 7 are excellent in dimensional accuracy, have no problem in separator characteristics such as gas impermeability, electric characteristics, liquid lubricity, and mechanical strength, and have an inexpensive fuel cell separator. It is a high performance fuel cell.

[Brief description of the drawings]

FIG. 1 is a plan view of a flat plate before a manifold is provided.

FIG. 2 is a plan view of a molded body with a manifold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flat plate 2 Manifold 3 Molded body with manifold

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Takayuki Suzuki, Inventor 3-3-1 Ayukawacho, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Office F-term (reference) 5H026 AA06 BB06 CC08 EE06 EE18 HH01

Claims (7)

[Claims] 1. A fuel cell separator comprising a molded body obtained by press-molding a molding sheet containing expanded graphite powder and a resin, the manifold being provided. 2. The fuel cell separator according to claim 1, wherein the expanded graphite powder is a pulverized powder of an expanded graphite sheet. 3. The expanded graphite powder has an average particle size of 5 μm to 100 μm.
3. The fuel cell separator according to claim 1, wherein the thickness is 0 μm. 4. The resin is a powder having an average particle size of 1
4. The fuel cell separator according to claim 1, wherein the thickness is from μm to 1000 μm. 5. 5. The fuel cell separator according to claim 1, wherein the manifold is provided by a punching method. 6. A fuel cell comprising the separator according to claim 1. 7. The fuel cell according to claim 6, wherein the fuel cell is a solid polymer type.