JP2002015753A - Fuel cell separator and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell separator that is improved in mechanical strength, electrical properties and gas non-infiltration and a fuel cell using this fuel cell separator. SOLUTION: The fuel cell separator comprises a rib section and a flat section and the flat section comprises a layer which contains expanded graphite and resin and has a density of 1.3-1.75 g/cm3, and a fuel cell using this separator is offered. It is also preferable that the rib section of the fuel cell separator is made of a layer which contains expanded graphite and resin and has a density of 1.45-1.75 g/cm3.

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 attracted a great deal of attention from the viewpoint of measures against global warming and energy savings due to fossil fuel consumption, and research and development are being actively carried out at national and university research institutions and major companies. The function of the separator, one of the components of the fuel cell, is to provide a quantitative supply of hydrogen, natural gas, and oxygen, which are the raw materials for the conductivity and generated energy, and to promptly discharge the generated water. It is an important member that influences. Further, since hundreds of separators are used for one battery, downsizing is required, and at present, all companies are struggling to improve the design, to reduce the thickness, to reduce the weight, and to develop an inexpensive separator.

A conventional separator is formed by cutting a graphite plate for a long time using a high-precision cutting machine in which the shape of the flow path is programmed, and further impregnating the obtained separator with a liquid resin or the like in a vacuum and curing the gas. At present, it is trying to make it impervious. However, since the separator obtained by the above method requires time for the cutting step and the impregnation treatment,
The price per separator is very high, and is not suitable as a separator for a fuel cell used in units of several hundreds.

[0004] In addition, as a separator which can form an inexpensive and accurate flow path and does not impair the characteristics of the fuel cell, a molding material using a resin and expanded graphite powder has a separator having ribs (irregular flow paths) and a flat part. In the case where is molded, there is a problem that the material filling amounts of the rib portion and the flat portion are different and the density of the flat portion is lowered. As a result, a flat portion having a low density has lower mechanical strength and electrical characteristics than a rib portion. In addition, there is a problem in that the flat portion having a reduced density has a lower sealing property for the used gas than the rib portion. Further, in the production of the separator, a low-density portion may be generated in a part of the molded product due to a flaw or chip at the time of demolding, a trouble at the time of production, or the like. As in the previous case, the low-density portion had a problem that the mechanical strength, electrical properties, and impermeability of the molded product were reduced.

Further, in a fuel cell separator provided with holes for supplying gas and water in addition to the flat portions and the rib portions, a problem is that the narrow portions around the holes and the corners are easily damaged in the cell assembling process. Had.

[0006]

SUMMARY OF THE INVENTION The present invention provides a mechanical strength,
An object of the present invention is to provide a fuel cell separator having improved electric characteristics or gas impermeability and a fuel cell using the same. The present invention also provides a fuel cell separator reinforced for mechanical strength, electrical characteristics, or prevention of gas leakage, and a fuel cell using the same.

[0007]

The present invention relates to the following. 1. A fuel cell separator having a rib portion and a flat portion, wherein the flat portion has a layer containing expanded graphite and a resin and having a density of 1.3 to 1.75 g / cm ³ . 2. Item 2. The fuel cell separator according to Item 1, wherein the rib portion comprises a layer containing expanded graphite having a density of 1.45 to 1.75 g / cm ³ and a resin. 3. Item 3. The fuel cell separator according to Item 1 or 2, wherein the rib portion and the flat portion are each a layer in which a layer containing expanded graphite and a resin is continuous. 4. Item 4. The fuel cell separator according to any one of Items 1 to 3, wherein the expanded graphite is an expanded graphite powder. 5. Item 5. The fuel cell separator according to Item 4, wherein the expanded graphite powder is an expanded graphite granulated powder. 6. Item 6. The fuel cell separator according to Item 5, wherein the expanded graphite granulated powder is a pulverized powder of expanded graphite sheet. 7. Item 7. The fuel cell separator according to any one of Items 1 to 6, wherein the separator has a hole in addition to the rib portion and the flat portion. 8. Item 8. A fuel cell comprising the separator according to any one of Items 1 to 7. 9. Item 9. The fuel cell according to item 8, which is a solid polymer type.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In a fuel cell separator according to the present invention, a rib portion has conductivity or electrical conductivity, and a gas flow path is formed when the separator is stacked via an electrolyte membrane, a fuel electrode and an air electrode. Is formed. Further, the flat portion forms a grip portion of the separator, and is configured so that gas does not leak when the gas passes through the flow path. In addition, the rib portion is configured so that gas does not leak when gas passes through a flow path formed when the separators are stacked. The flat part is preferably a grip part for fixing the whole when the separators are stacked.

The flat portion contains expanded graphite and a resin, and contains expanded graphite to have a density of 1.3 to 1.75 g / cm ^3.
With this density, sufficient confidentiality can be maintained. In addition, similarly, the rib part
Including expanded graphite and resin, by including expanded graphite,
A density of 1.45 to 1.75 g / cm ³ ,
With this density, sufficient confidentiality can be maintained. Further, the separator may have a hole in addition to the rib portion and the flat portion, and particularly preferably has the hole in the flat portion. The hole is configured to form a long hole in the stacking direction when a large number of separators are stacked, and to form holes for passing hydrogen gas, oxygen gas, and cooling water. Each hole is configured to be connected to a hydrogen gas flow path, an oxygen gas flow path, and a cooling water flow path formed by the rib portion of the separator. Note that the flat portion may have a hole for passing a fixing bolt when the separator is stacked.

It is preferable that each of the rib portion and the flat portion has a layer containing expanded graphite and a resin, and these layers are continuous layers. Thereby, the moldability at the time of molding for obtaining the separator is good, the separator is given light weight, and the separator is given favorable characteristics such as high toughness and low elasticity.

The expanded graphite as a raw material used in the present invention is preferably expanded graphite powder, and the expanded graphite powder is preferably expanded graphite granulated powder obtained by granulating expanded graphite. As the expanded graphite granulated powder, a pulverized powder of an expanded graphite sheet is particularly preferable. Expanded graphite is a process of immersing raw graphite in a solution containing an acidic substance and an oxidizing agent to form a graphite intercalation compound, and heating the graphite intercalation compound to expand the C-axis direction of the graphite crystal and expand graphite. It can be manufactured by the steps of: The expanded graphite becomes a worm-like shape, and has a complicated entangled shape with no directionality. The magnification of the expanded graphite is preferably higher in order to secure the strength and sealing property of the separator, and is not particularly limited, but is preferably 150 to 300 times. The expanded graphite can be made into an expanded graphite powder by pulverizing the expanded graphite. Before the pulverization, it is preferable to apply pressure to the obtained expanded graphite and compression-mold it into a sheet to obtain an expanded graphite sheet. Further, the obtained expanded graphite powder is subjected to a treatment (such as a high-temperature treatment) for reducing acidic roots contained in the pulverized powder, if necessary.

[0012] The raw material graphite is not particularly limited, but graphite having a high degree of crystal development such as natural graphite, quiche graphite and pyrolytic graphite is preferred. 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. These are preferably used in the form of scaly powder.

The acidic substance used in the processing of the raw graphite is as follows:
Generally, a material which can enter an interlayer of graphite such as sulfuric acid and generate an acidic root (anion) having a sufficient expansion ability is used. The amount of the acidic substance to be used is not particularly limited and is determined according to the desired expansion ratio. For example, it is preferable to use 100 to 1000 parts by weight based on 100 parts by weight of graphite.

Examples of the oxidizing agent used together with the acidic substance include peroxides such as hydrogen peroxide, potassium perchlorate, potassium permanganate and potassium dichromate, and acids having an oxidizing action such as nitric acid. Hydrogen peroxide is particularly preferred from the viewpoint that it can be used and it is easy to obtain good expanded graphite. When hydrogen peroxide is used as the oxidizing agent, it is preferably used as an aqueous solution. At this time, the concentration of hydrogen peroxide is not particularly limited, but is preferably 20% by weight to 40% by weight. The amount of use is not particularly limited, but it is preferable to add 5 to 60 parts by weight of hydrogen peroxide solution to 100 parts by weight of graphite. The acidic substance and the optional oxidizing agent are preferably used in the form of an aqueous solution. Sulfuric acid as an acidic substance is used at an appropriate concentration, but preferably has a concentration of 95% by weight or more, and it is particularly preferable to use concentrated sulfuric acid.

In the above, there is no particular limitation on the method for producing the expanded graphite sheet, but it is generally preferable to apply pressure to the expanded graphite obtained above with a press, roll, or the like to form a sheet. There is no particular limitation on the thickness and density of the sheet when the expanded graphite is formed into a sheet.
A range of 5 mm to 1.5 mm and a density of 0.2 g / cm ³ to
Those having a range of 1.2 g / cm ³ are preferable. The magnitude of the density can be adjusted by adjusting the amount of pressure, the roll gap, and the like. Further, the crushing of the expanded graphite sheet is preferably performed by coarse pulverization and fine pulverization, and thereafter, classification is performed as necessary.

In the present invention, the density of the expanded graphite powder as a raw material is not particularly limited, but is 0.1 to 0.4 g.
/ Cm ³ is preferred. If the density of the expanded graphite powder is too low, the uniform mixing property with the resin tends to decrease, and the sealing property of the obtained molded article (fuel cell separator) tends to decrease. There is a tendency that the effect of improving the mechanical strength and conductivity of the molded article (separator for fuel cells) to be used is reduced.

The average particle size of the expanded graphite powder is not particularly limited, but is preferably in the range of 5 μm to 1000 μm in terms of number average particle size in consideration of mixability with resin and moldability.
The range of 5 μm to 500 μm is more preferable. here,
When the pulverized powder having a number average particle diameter of less than 5 μm is used, the pulverized powder formed and oriented in the final molded body, that is, the fuel cell separator, is short, and the mechanical strength tends to decrease.
When a pulverized powder exceeding 000 μm is used, the mixing property with the resin tends to change.

In the present invention, there are no particular restrictions on the properties of the resin used, but safety and shortening of the manufacturing process (low cost)
In consideration of the above, it is preferable to use a thermosetting resin, a high heat-resistant resin or a thermoplastic resin which can be dry-mixed (solvent-free mixing) and has a stable particle size distribution. The form of use of the resin is preferably powdery, granular, or the like.

The chemical structure and type of the resin used are not limited, and examples thereof include an epoxy resin (together with a curing agent), a melamine resin, a curable acrylic resin, a resol type and a novolak type powdered phenol resin, and the like. Thermosetting resin, powdered polyamide resin, powdered polyamideimide resin, phenoxy resin, acrylic resin and other high heat-resistant resins or thermoplastic resins are used. If necessary, a curing agent and a curing accelerator are used in combination with the thermosetting resin. The form of use of the curing agent and the curing accelerator is preferably in the form of powder, granules, or the like. Among these resins, economy, workability,
It is particularly preferable to use a phenol resin, which is a thermosetting resin, because the property balance after curing is excellent.

The phenolic resin has a uniform particle size as a powder characteristic, has a small amount of blocking (aggregation of powder), has a small amount of gas generated during the reaction, is easy to mold, and has a short heat treatment. Phenol resins having such features as above are preferable, and among them, phenol resins containing a dihydrobenzoxanthine ring polymerized by ring-opening polymerization [having the chemical structural units shown in general formulas (A) and (B)] are preferable. .

[0021]

Embedded image (Wherein the hydrogen bonded to the aromatic ring is substituted with an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group or an alkyl group or an alkoxyl group having 1 to 3 carbon atoms, except for one of the ortho positions of the hydroxyl group. May be substituted by a substituted phenyl group or other hydrocarbon group).

[0022]

Embedded image (Wherein, R ¹ is a hydrocarbon group such as an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group or a phenyl group substituted with an alkyl group or an alkoxyl group having 1 to 3 carbon atoms, and an aromatic ring May be substituted with a similar hydrocarbon group).

When a powdery phenol resin is used as the resin, its particle size distribution is not particularly limited. However, considering the dry mixability with the expanded graphite powder, the number average particle diameter is 1 μm to 1 μm.
A range of 1000 μm is preferable, and a range of 5 μm to 500 μm is more preferable. If the number average particle size is less than 1 μm, the particles will aggregate (block), and not only will the workability be poor, but also it will not be possible to expect uniform mixing with the expanded graphite powder. Similarly, uniform mixing with the expanded graphite powder becomes difficult, and the density of the obtained separator tends to vary greatly.

The mixing ratio of the expanded graphite powder and the resin used in the present invention is determined in consideration of the values of various characteristics of the fuel cell separator as the target final molded product. Expanded graphite powder / resin = 95/5 to 30/70 (weight ratio) is preferable, 90/10 to 50/50 (weight ratio) is more preferable, and 80/20 to 60/4.
A range of 0 (weight ratio) is particularly preferred. Here, when the mixing ratio of the expanded graphite powder and the resin exceeds 95/5, the mechanical strength tends to sharply decrease. On the other hand, when the mixing ratio is less than 30/70, the amount of the expanded graphite powder which is a conductive substance is added. Less,
Electrical characteristics tend to decrease.

There is no particular limitation on the method of mixing the resin and the expanded graphite powder, and a dry method using a shaker, a V blender, or the like that does not apply a large shearing force to the expanded graphite powder during mixing in order to prevent the expansion graphite powder from being pulverized. It is preferable to use a mixing method.
When the expanded graphite powder is pulverized during mixing, the mechanical strength of the resulting fuel cell separator tends to decrease.

Although the above mixed powder can be used directly as molding material powder, in the present invention, in order to further improve the mixing property and the workability at the time of molding, the mixed powder is pressed and formed into a sheet. (Hereinafter referred to as “molding sheet”)
To use). Although there is no particular limitation on the method of manufacturing the forming sheet, for example, a mixture charging tank, a gate adjuster for making the material a certain thickness, a slitter for finishing to a certain width, a transfer device for transferring the processing material, a rolling roll for forming a sheet, and the like And an apparatus for manufacturing a sheet for molding composed of the following. When the flat portion has a hole, it is preferable that the hole is formed in the molding sheet. In order to improve the strength of the molding sheet, the curing reaction of the resin contained in the molding sheet can be partially advanced or partially (not completely) heat-fused before being used for separator production it can. Although there is no limitation on the method of curing reaction or heat melting, for example, a method of heating the obtained forming sheet, more specifically, the above-mentioned rolling roll is provided with a heating device, and this rolling roll is passed through the rolling roll. Sometimes, there is a method of heating, a method of passing the obtained molding sheet through a heating oven, and the like.

In the present invention, the density of the rib portion and the flat portion formed on the molded body is set to have the above-mentioned density. The density of the forming sheet used in the present invention, the number of stacked sheets,
The shape and the like are not particularly limited, and are arbitrarily determined by design values of the area and density ratio of the rib portion and the flat portion of the obtained molded body. In the case of molding using a mold capable of forming a desired separator shape, a necessary number of sheets for forming a molding sheet and a necessary number of sheets are formed only partially to obtain a desired density after molding.

There is no particular limitation on the method of forming the sheet for forming the fuel cell separator, but it is preferable to form the sheet by compression molding. The molding is usually performed using a mold for obtaining a predetermined shape. The molding conditions are preferably 5 to 50 MPa (particularly preferably 10 to 50 MPa).
40 MPa), preferably at 150 to 240 ° C (particularly preferably 170 to 220 ° C). A molding time of 0.5 to 15 minutes is sufficient. When the forming sheet is formed normally, the density in the flat portion is more likely to be lower than that in the rib portion. In order to improve this and make the density of the rib portion and the flat portion uniform or to increase the density of the flat portion, it is preferable to form a sheet by overlapping a forming sheet on the flat portion. The fuel cell separator of the present invention has a rib portion and a flat portion, and the flat portion may have a hole portion. In this case, the hole portion should be formed when the forming sheet is manufactured. ,
The hole may be punched or formed after forming the molded body. 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.

The fuel cell using the separator of the present invention can be manufactured by a known method. In the fuel cell, the separator according to the present invention uses the electrolyte layer made of a solid polymer electrolyte membrane and the like, and two gas diffusion layers sandwiching the electrolyte layer (made up of a fuel electrode, an air electrode, and carbon paper).
The required number of cells formed so as to sandwich them are laminated. The separator in the present invention can be used as a fuel cell separator of an alkaline type, a solid polymer type, a phosphoric acid type, a molten carbonate type, a solid acid type, etc. classified according to the type of the electrolyte. The gasket can be overlaid on the flat part between the separators. In order to improve the handleability of the gasket, it is preferable to use a prepreg (using a glass cloth) as the core material. By using the prepreg as the core material, the workability of assembling the separator and the gasket can be improved. The gasket is preferably bonded and attached to the separator in advance in consideration of the workability of assembling the fuel cell.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a plan view showing a molding die (also used as an upper die and a lower die), which is used as a pair and has a projection 1 for forming a rib of a fuel cell separator on one surface. Is formed. 2 and 3 show molding sheets 2 and 3 having different shapes. A notch 4 is formed at the center of the molding sheet 3 shown in FIG. 3 (the portion where the projection 1 of the mold is inserted). FIG. 4 is a perspective view showing a cell structure of an example of the polymer electrolyte fuel cell. The cell 30 is composed of a three-layer film 34 composed of a solid polymer electrolyte membrane 31, a fuel electrode 32 and an air electrode 33, and fuel cell separators 35 and 36 sandwiching the three-layer film 34 from both sides. The cells 30 are stacked in multiple stages as shown in FIG. 4 to obtain a cell stack 37 as an aggregate. In the figure, four cells are stacked, but in actuality, 100 cells may be used if necessary.
You may overlap more than a step.

[0031]

The present invention will be described below with reference to examples. Example 1 (1) Production of expanded graphite powder 800 g of concentrated sulfuric acid was put into a 3 liter glass beaker.
400 g of natural graphite (fixed carbon: 99% by weight or more, # 599 graphite from China) was mixed with the mixture, and the mixture was stirred for 10 minutes by a stirring motor (60 min ^-1 ) equipped with glass stirring blades, and then hydrogen peroxide was added. 32g of water (35% by weight)
And stirred for 15 minutes. After completion of the stirring, the acid-treated graphite and the acid component were separated by filtration under reduced pressure, the obtained acid-treated graphite was transferred to another container, and 5 liters of water was added.
After stirring for 0 minutes, the washing acid-treated graphite and the washing water were separated by vacuum filtration.

The obtained washed acid-treated graphite was transferred to an enamel vat, leveled uniformly, and heat-treated for 1 hour in a vacuum drier heated to 110 ° C. to remove water. This was further placed in a heating furnace heated to 800 ° C. for 5 minutes to obtain expanded graphite. After cooling, the expanded graphite was rolled with a roll to produce a sheet having a density of 1.0 g / cm ³ . The obtained sheet is pulverized by a coarse pulverizer (Rothoplex (trade name) manufactured by Hosokawa Micron Corporation) and then finely pulverized (free pulverizer M-3 (trade name) manufactured by Nara Machinery Co., Ltd.). It was pulverized to obtain an expanded graphite powder having a number average particle size of 150 μm and a bulk density of 0.19 g / cm ³ . A 200 ml glass graduated cylinder was filled up to the full mouth of the expanded graphite powder, and it was determined from the volume and weight after tapping on a table 50 times from a height of about 2 cm so as not to spill out from the mouth. Hereinafter, the bulk density of the expanded graphite powder was determined in the same manner.

(2) Preparation of phenol resin to be used 1.9 kg of phenol, 1.0 kg of formalin (37% by weight aqueous solution) and 4 g of oxalic acid were charged into a 5-liter flask and reacted at a reflux temperature for 6 hours. Continued
The internal pressure was reduced to 6666.1 Pa (50 mmHg) or less to remove unreacted phenol and water, thereby synthesizing a phenol novolak resin. The obtained resin has a softening point of 84 ° C.
(Ring and ball method) The ratio of trinuclear to polynuclear / binuclear was 92/18 (peak area ratio by gel permeation chromatography).

Next, 1.7 kg of the synthesized phenol novolak resin (corresponding to 16 mol of hydroxyl groups) was mixed with 0.93 kg (corresponding to 10 mol) of aniline, and the mixture was stirred at 80 ° C. for 5 hours to obtain a uniform mixed solution. Prepared. Next, 1.62 kg of formalin was charged into a 5-liter flask, heated to 90 ° C., and the above-mentioned mixed solution of novolak / aniline was added little by little over 30 minutes. After the addition,
Maintain the reflux temperature for 30 minutes, then reduce the pressure of water to 6666.1 Pa (50 mmHg) or less at 100 ° C. for 2 hours to remove the condensed water and obtain 71 mol% of the reactive hydroxyl groups.
Was obtained with a dihydrobenzoxazine-containing resin having a dihydrobenzoxazine ring.

The amount of the hydroxyl group that can react in the phenol novolak resin is calculated as follows. That is, 1.7 kg of the phenol novolak resin (corresponding to 16 mol of hydroxyl groups) is reacted with 1.4 aniline (corresponding to 16 mol) and 2.59 kg of formalin, and a dihydrobenzoxazine ring is formed on all of the hydroxyl groups that can react. The introduced resin was synthesized. Excess aniline and formalin were removed during drying, yielding 3.34 kg. From this,
In the phenol novolak resin, the amount of hydroxyl groups capable of reacting was 14 moles, indicating that dihydrobenzoxazine was cyclized. Next, the resin synthesized as described above was pulverized with a pulverizer to obtain a powdery phenol resin having a small particle size of 23 μm and a small amount of gas generated during the reaction.

(3) Production of compact (fuel cell separator) 350 parts by weight of expanded graphite powder obtained in Example 1 (1) and (2)
150 parts by weight of the powdered phenolic resin (pulverized powder of expanded graphite sheet / phenolic resin = 70/30 (weight ratio)) prepared in the above was charged into a V blender and blended for 3 minutes to obtain a mixed powder. And then 130 on a molding sheet molding machine.
Molding was performed at a pressure of kPa to obtain a molding sheet having a density of 0.7 g / cm ³ and a thickness of 3.2 mm (referred to as molding sheet A). Further, using the above mixed powder, a molding sheet having a density of 0.7 g / cm ³ and a thickness of 1.0 mm (this is referred to as molding sheet B) is formed at a pressure of 130 kPa by a molding sheet molding machine. ) Got.

Next, a mold was prepared. The lower mold was a female mold having a flat molding surface (length and width: 200 mm), and the upper mold was a mold having the projections 1 of FIG. However, in the upper mold,
The height of the protrusion is 1.0 mm, the protrusion pitch is 1.0 mm,
The width of the rib was 1.0 mm and the rib taper was 0 degree. In the above lower mold, a molding sheet 2 having a shape shown in FIG.
3), and one sheet of molding sheet 3 (using molding sheet B) having a cutout 4 at the center shown in FIG. 3 is placed thereon, and then placed on top of it. The part having the upper projection 1 is set downward, and then the surface pressure 1
Molding was performed for 10 minutes while applying a pressure of 50 MPa. Next, the obtained molded body was subjected to a heat treatment at 200 ° C. for 30 minutes to obtain a fuel cell separator. The thickness of the flat part and the rib part of the obtained molded body is 2.0 mm, and the depth of the groove of the rib part is 1.0.
mm.

Comparative Example 1 A fuel cell separator was obtained through the same steps as in Example 1 except that the molding sheet 3 shown in FIG. 3 used in Example 1 (3) was not used. The thickness of the flat part and the rib part of the obtained molded body was 2.0 mm, and the depth of the groove of the rib part was 1.0 mm.

Next, the fuel cell separators obtained in Example 1 and Comparative Example 1 were evaluated for appearance, density of rib portions and flat portions, and gas permeability. Table 1 shows the results. In addition, regarding the appearance, the surface swelling of the molded body,
Scratches and uneven molding were visually determined. For the density, cut out a 2 cm square sample from the center and the flat part of the rib,
The volume and weight were calculated and calculated. In the following,
Same as above. Regarding gas permeability, the amount of oxygen permeated through the 50 mmφ separator test piece 41 in the jig was replaced with water using a homemade gas leak test jig shown in FIG. 5, and within 2 minutes after oxygen was injected. The number of air bubbles generated was confirmed. In order to evaluate gas permeability, for the rib portion, a separator test piece was cut out from the separator for a fuel cell obtained by molding, and was used. Is a simulated separator test piece cut out from a separately molded body (using a mold having a flat molding surface as an upper mold) (however, as a molding sheet 3 corresponding to Example 1, Molding sheet B was prepared in the same manner as in Example 1 except that a sheet having no notch at the center portion was used, and the above-mentioned molding sheet having a flat molding surface was used. In FIG. 5, reference numeral 41 denotes a separator test piece, 42 denotes water, 43 denotes oxygen (surface pressure: 19.6 × 10 ⁴ Pa), and 44 denotes a rubber packing. The size of the separator test piece inside the packing was 34 mmφ.

[0040]

[Table 1]

As shown in Table 1, the fuel cell separator of Example 1 according to the present invention has a smaller variation in the density of the rib portion and the flat portion than the fuel cell separator of Comparative Example 1, and It is clear that the gas impermeability is good.

Example 2 (1) Pulverized powder of expanded graphite sheet The same product as produced in (1) of Example 1 was used.

(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), number average particle size: 20 μm).

(3) Production of molding sheet 350 parts by weight of the pulverized powder of expanded graphite sheet of (1) and 150 parts by weight of powdered phenolic resin of (2) (pulverized powder of expanded graphite sheet / resin = 70/30 (weight) Was charged into a V-type blender and mixed for 3 minutes to obtain a mixed molded powder. Subsequently, the sheet was molded at a pressure of 130 kPa by a molding sheet molding machine to obtain a molding sheet having a density of 0.5 g / cm ³ and a thickness of 2.3 mm (this is referred to as molding sheet C).
The other was a molding sheet having a density of 0.50 g / cm ³ and a thickness of 0.8 mm (referred to as molding sheet D) in the same manner as in (3) of Example 1.

(4) Production of Molded Product (Model Fuel Cell Separator) The same mold as in Example 1 was prepared. On the lower mold, two molding sheets 2 (using the molding sheet C) having the shape shown in FIG. 2 are placed, and further thereon, a notch 4 is formed at the center shown in FIG.
After placing one molding sheet (using the molding sheet D) having the above, the portion having the upper mold projection 1 is set downward on the upper part thereof, and then a surface pressure of 150 MPa is applied. Molded for 10 minutes. Next, the obtained molded body was
Heat treatment was performed at 0 ° C. for 30 minutes to obtain a fuel cell separator. The thickness of the flat part and the rib part of the obtained molded body is 2.
0 mm, and the depth of the groove of the rib portion was 1.0 mm.

Comparative Example 2 A fuel cell separator was obtained through the same materials and steps as in Example 2 except that the molding sheet E was not used.
The thickness of the flat part and the rib part of the obtained molded body is 2.0 m
m, the depth of the groove in the rib portion was 1.0 mm.

Next, the appearance, density and gas permeability of the fuel cell separators obtained in Example 2 and Comparative Example 2 were evaluated. Table 2 shows the results. These evaluation methods are as shown in Example 1.

[0048]

[Table 2]

As shown in Table 2, the separators of Example 2 and Comparative Example 2 had good appearances,
In terms of density, the rib portions were almost the same for both the separators of Example 2 and Comparative Example 2, but the flat portions had lower values for the separator of Comparative Example 2 than for the separator of Example 3. Regarding the gas permeability, the separator of Example 2 had good sealing properties with both the rib portion and the flat portion being 0, but the separator of Comparative Example 2 generated bubbles in the flat portion.

[0050]

The fuel cell separator of the present invention is an inexpensive fuel cell separator having no problem in separator characteristics such as electric characteristics, gas impermeability, dimensional accuracy, liquid lubricity, and mechanical strength. .

[Brief description of the drawings]

FIG. 1 is a plan view showing a molding die (also used as an upper die and a lower die).

FIG. 2 is a plan view showing an example of a molding sheet.

FIG. 3 is a plan view showing an example of another molding sheet.

FIG. 4 is a perspective view showing a cell structure of an example of a polymer electrolyte fuel cell.

FIG. 5 is a sectional view of a gas leak test jig for examining gas permeability.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Protrusion part 2 Molding sheet 3 Molding sheet 4 Notch part 30 Cell 31 Solid polymer electrolyte membrane 32 Fuel electrode 33 Air electrode 34 Three-layer film 35, 36 Fuel cell separator 37 Cell stack 41 Separator test piece 42 Water 43 Oxygen 44 packing

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takayuki Suzuki, Inventor 3-3-1 Ayukawacho, Hitachi City, Ibaraki Prefecture, Hitachi Chemical Co., Ltd. Yamazaki Office (72) Inventor Harubun Hasuda, Harufumi Ayukawacho, Hitachi City, Ibaraki Prefecture No. 3-1 Hitachi Chemical Co., Ltd. Yamazaki Plant F-term (reference) 4J002 AA001 CC031 CC101 CC181 CH081 CL001 CM041 DA026 FD206 GQ00 5H026 AA06 CC03 CC08 CX05 EE06 EE19 HH05

Claims (9)

[Claims] 1. A fuel cell separator having a rib portion and a flat portion, wherein the flat portion contains expanded graphite and a resin,
A fuel cell separator having a layer having a density of 1.3 to 1.75 g / cm ³ . 2. The rib portion has a density of 1.45 to 1.75 g / c.
2. A layer comprising a resin containing expanded graphite having a particle size of m ³ and a resin.
The separator for a fuel cell according to the above. 3. A layer in which a layer containing expanded graphite and a resin in each of a rib portion and a flat portion is a continuous layer.
The separator for a fuel cell according to the above. 4. The expanded graphite is an expanded graphite powder.
4. The fuel cell separator according to any one of claims 1 to 3. 5. The fuel cell separator according to claim 4, wherein the expanded graphite powder is an expanded graphite granulated powder. 6. The fuel cell separator according to claim 5, wherein the expanded graphite granulated powder is an expanded graphite sheet pulverized powder. 7. The fuel cell separator according to claim 1, wherein the separator has a hole in addition to the rib and the flat portion. 8. A fuel cell comprising the separator according to claim 1. 9. The fuel cell according to claim 8, which is of a solid polymer type.