JP2003257447A - Separator for fuel cell, manufacturing method therefor, and fuel cell by use of separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell having excellent gas non- penetration property, mechanical strength, and electric resistance and a manufacturing method therefor so as to provide the fuel cell by use of the separator for the fuel cell. <P>SOLUTION: This separator for the fuel cell is made of crystalline epoxy resin and expansion graphite. This manufacturing method for the separator for the fuel cell is constituted by mixing the crystalline epoxy resin with the expansion graphite and then molding by forming the mixture into a sheet. The fuel cell having the separator for the fuel cell or the separator for the fuel cell manufactured by the manufacturing method is provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator, a method for manufacturing the same, 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 viewpoints of measures to prevent global warming due to the consumption of large amounts of fossil fuels, energy conservation measures, etc., and research and development are actively carried out by national and university research institutions and major companies. It is being appreciated.

The function of the separator, which is one of the constituent members of the fuel cell, is to quantitatively supply hydrogen, natural gas and oxygen, which are raw materials for conductivity and generated energy, and to quickly discharge generated water. It is an important member that affects the battery characteristics. In particular, since hundreds of separators are used in one battery, downsizing is demanded, and each company is currently surpassing the development of improved designs, thin plates, lightweight and inexpensive separators.

In the conventional separator, a graphite plate is cut for a long time with a high-precision cutting machine in which the shape of the flow path is programmed, and the obtained separator is vacuum impregnated with a liquid resin or the like to be cured and gas The current situation is to make it impervious. However, since the separator obtained by the above method requires a long time for the cutting process and the impermeability treatment, the price per separator is very high and it is not suitable as a separator for a fuel cell used in units of several hundreds. Is.

Further, when the material is prepared (dry method) at a low cost in consideration of environmental problems and without a solvent, processed into a molding sheet and molded into a mold type separator, the resin used is preferably a powdered resin. , General powder resin (thermosetting type),
Since the molecules having a crystal structure are not included in the molecular unit that constitutes the resin, or even if the molecules have few molecules, the molecular motion that constitutes the resin in the high temperature region becomes unstable,
If the temperature control at the time of molding is not made very strict, defects will occur in the obtained molded body.

For this reason, when molding is carried out by a moving mold, the steps of taking out the mold, filling the material, assembling the mold, pressing set, and the like are repeated, so that the temperature of the mold changes greatly and the material is contained in the filled material. The heat history applied to the resin also greatly changes, and the viscosity of the resin changes greatly until just before gelation. It is considered that this state is maintained until the initial stage of main molding under pressure.

In particular, in the molding of a separator composed of a complicated rib (concave and convex) portion, a flat portion and a hole portion provided as necessary, a stable resin flow (viscosity) produces a stable molded body. It is a very important factor above. When the separator is molded using a material having a resin whose flowability is unstable, a resin-rich portion and a filler-rich portion occur in the same molded body, and the density of the molded body greatly fluctuates. There arises a problem that characteristic values such as gas impermeability, mechanical strength and electric resistance, which are important characteristics, are reduced.

[0008]

SUMMARY OF THE INVENTION The present invention provides a fuel cell separator excellent in gas impermeability, mechanical strength, electrical resistance and the like, and a method for producing the same. Further, the present invention provides a fuel cell using a fuel cell separator excellent in gas impermeability, mechanical strength, electric resistance and the like.

[0009]

The present invention relates to the following. 1. A fuel cell separator composed of crystalline epoxy resin and expanded graphite. 2. The crystalline epoxy resin has a viscosity change of 0.002 Pa.s in the range of 150 ° C to 180 ° C. s ~ 0.008P
a. 2. The fuel cell separator according to item 1, which is in the range of s. 3. Item 3. The fuel cell separator according to Item 1 or 2, wherein the expanded graphite is an expanded graphite sheet pulverized powder. 4. Item 1 in which the separator has a rib portion and a flat portion
3. The fuel cell separator according to any one of 3 above.

5. A method for producing a separator for a fuel cell, which comprises forming a sheet by molding after mixing a crystalline epoxy resin and expanded graphite. 6. The crystalline epoxy resin has a viscosity change of 0.002 Pa.s in the range of 150 ° C to 180 ° C. s ~ 0.008P
a. Item 6. The method for producing a fuel cell separator according to Item 5, wherein the range is s. 7. Item 7. The method for producing a fuel cell separator according to Item 5 or 6, wherein the expanded graphite is a crushed powder of expanded graphite sheet. 8. Item 5 in which the separator has a rib portion and a flat portion
8. The method for producing a fuel cell separator according to any one of 7). 9. Item 5 in which the molding method is a compression molding method
9. The method for producing a fuel cell separator according to any one of 8 to 8.

10. A fuel cell comprising the fuel cell separator according to any one of Items 1 to 4 or the fuel cell separator obtained by the manufacturing method according to any one of Items 5 to 9. 11. Item 11. The fuel cell according to item 10, which is a solid polymer type.

[0012]

In the fuel cell separator according to the present invention, the rib portion has conductivity or conductivity, and when the separators are stacked with the electrolyte membrane, the fuel electrode and the air electrode, the gas flow passage is formed. Is formed. Further, the rib portion is configured so that gas does not leak when the gas passes through the flow path formed when the separators are stacked.

On the other hand, 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 above-mentioned flow path. Further, it is preferable that the flat portion serves as a grip portion for fixing the whole when the separators are stacked.

The flat portion has a density of 1,300 kg / m ³ by containing a crystalline epoxy resin and expanded graphite.
It can be set to ˜1,750 kg / m ^3, and by having this density, sufficient airtightness can be maintained.
Similarly, the rib portion also has a density of 1,450 kg / m ³ to 1,75 by including a crystalline epoxy resin and expanded graphite.
It can be set to 0 kg / m3, and by having this density, sufficient airtightness can be maintained.

The separator may have holes other than the rib and the flat portion, and it is particularly preferable that the separator has the holes. The hole portion is configured to form a long hole in the stacking direction when a large number of separators are stacked, and a hole for passing hydrogen gas, oxygen gas, and cooling water is formed. Each hole is configured to be connected to the hydrogen gas passage, the oxygen gas passage, and the cooling water passage formed by the rib portion of the separator. Note that the flat portion may have a hole for passing a fixing bolt when the separators are stacked.

It is preferable that the rib portion and the flat portion each have a layer containing a crystalline epoxy resin and expanded graphite, and these layers are continuous. As a result, the moldability at the time of molding for obtaining the separator is good, and the separator is lightweight, and at the same time, the separator is provided with favorable properties such as high toughness and low elasticity.

If the thickness of the separator is as thin as 1 mm or less, the flat portion may be flattened to improve its strength, if necessary.
A reinforcing material may be used for at least a part of the portion. The method of using the reinforcing material and the material to be used are not particularly limited, but in view of cost, a method of laminating the glass cloth on the molding sheet portion where the flat portion is formed and molding is preferable. By using the reinforcing material, the density of the flat portion can be improved and the density difference with the rib portion can be reduced.

The expanded graphite used in the present invention is obtained by immersing raw graphite into a solution containing an acidic substance and an oxidizing agent to form a graphite intercalation compound, and heating the graphite intercalation compound to obtain C of graphite crystal. It can be manufactured by a process of expanding in the axial direction to obtain expanded graphite. As a result, the expanded graphite becomes a bug-like shape and has a entangled complex shape with no directivity.

The expansive graphite preferably has a high magnification to secure the strength and gas impermeability of the separator, and is not particularly limited, but is preferably 150 times or more, and more preferably 150 times to 300 times. preferable.

Expanded graphite can be made into expanded graphite powder by crushing the expanded graphite, but it is preferable to apply pressure to the obtained expanded graphite before crushing and compression-mold it into a sheet to obtain an expanded graphite sheet. A crushed powder of the expanded graphite sheet can be obtained by crushing the obtained expanded graphite sheet. Further, the obtained expanded graphite sheet pulverized powder is subjected to a treatment (high temperature treatment or the like) for reducing the acidic roots contained in the pulverized powder, if necessary.

The above-mentioned raw material graphite is not particularly limited, but highly crystallized graphite such as natural graphite, Kissuille graphite and pyrolytic graphite is preferable. Natural graphite is preferable in consideration of the balance between the obtained properties 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 scale-like powder.

The acidic substance used to treat the raw graphite is
Generally, a material that can penetrate between layers of graphite such as sulfuric acid to generate an acidic root (anion) having a sufficient expansion ability is used. The amount of the acidic substance used is not particularly limited and is determined by the desired expansion ratio. For example, graphite 1
It is preferable to use 100 to 1000 parts by weight with respect to 00 parts by weight.

As the oxidizing agent used together with the acidic substance, peroxides such as hydrogen peroxide, potassium perchlorate, potassium permanganate, potassium dichromate, etc., and acids having an oxidizing action such as nitric acid are used. Hydrogen peroxide is particularly preferable from the viewpoint that it is possible to obtain good expanded graphite easily. 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 used is also not particularly limited, but it is preferable to add 5 parts by weight to 60 parts by weight as hydrogen peroxide solution to 100 parts by weight of graphite.

The acidic substance and the 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 a concentration of 95% by weight or more is preferable, and concentrated sulfuric acid is particularly preferable.

In the above, the method for producing the expanded graphite sheet is described.
Although there is no particular limitation, generally, the expanded black obtained above
Sheets of lead can be formed by applying pressure with a press, roll, etc.
And are preferred. Of the expanded graphite sheet
The thickness and density are not particularly limited, but the thickness is 0.
Range of 5mm-1.5mm and density is 200kg / m
^Three~ 1,700kg / m^ThreeThe range of is preferable. Thickness
If the size is less than 0.5 mm, the obtained molded product becomes brittle.
There is a tendency, and if it exceeds 1.5 mm, the moldability deteriorates.
Tend. The density is 200 kg / m^ThreeTo be less than
Electric resistance tends to deteriorate, 1,700 kg / m^Three
If it exceeds, mechanical strength tends to decrease. High density
Is adjusted by adjusting the amount of pressurization, roll gap, etc.
can do. In addition, crushing the expanded graphite sheet
It is preferable to carry out pulverization and fine pulverization.
Classify if necessary.

In the present invention, the density of expanded graphite as a raw material is not particularly limited, but it is 100 kg / m ³ to
A range of 400 kg / m ³ is preferred. If the density of the expanded graphite is too low, the homogeneity of mixing with the resin will decrease, and the gas impermeability of the resulting molded product (separator for fuel cell) will tend to decrease. The effect of improving the mechanical strength and conductivity of the molded body (fuel cell separator) is likely to decrease.

The average particle size of the crushed powder of the expanded graphite sheet is not particularly limited, but considering the mixing property with the resin and the moldability, the number average particle size is preferably in the range of 5 μm to 1000 μm, and in the range of 25 μm to 500 μm. Is more preferable,
The range of 50 μm to 400 μm is more preferable. If the number average particle size is less than 5 μm, the length of the crushed powder of the expanded graphite sheet formed and oriented in the final molded product, that is, the fuel cell separator, tends to be short, and the mechanical strength tends to decrease.
If it exceeds 00 μm, the mixing property with the resin tends to change.

The resin used in the present invention is a crystalline epoxy resin which can be dry-mixed (solvent-free mixture) and has a stable particle size distribution in consideration of safety, shortening of manufacturing process (low cost) and the like. Is required to be used.
The crystalline epoxy resin is preferably used in the form of powder or particles.

The crystalline resin refers to a resin that includes, in the molecule that determines the resin structure, molecules that are symmetrically and regularly arranged periodically, and is characterized by being stable at a relatively high temperature and having a melting point or higher. It shows high fluidity at the temperature of. Therefore, the filler can be highly filled, and the obtained cured product exhibits physical properties with little variation, and is expected to have low water absorption due to the hydrophobic group effect.

The crystalline epoxy resin to be used may be crystalline, and there is no limitation on the crystallinity (ratio of the mass of the crystalline part to the total mass) and the chemical structure. A thermosetting epoxy resin in which the number of crystal structure molecules contained in one unit of the molecular structure constituting the above is 70% or more of the total number of molecules is preferable. When the content of the crystal structure molecule is less than 70%, it tends to be stable at a high temperature and to lower the fluidization at a melting point or higher. The crystalline epoxy resin is used in combination with a curing agent and, if necessary, a curing accelerator.

The crystalline epoxy resin used in the present invention is
Considering the reduction of the defective rate of the obtained molded product and the improvement of the molding cycle, the crystalline epoxy resin has a temperature of 150 ° C to 180 ° C.
The viscosity change in the range of 0.002 Pa is 0.002 Pa.s. s to 0.00
8 Pa. It is preferably in the range of s, 0.003P
a. s-0.007 Pa.s. More preferably, it is in the range of s. It is difficult to uniformly impregnate the expanded graphite sheet pulverized powder to be mixed when the viscosity change is larger than the above range,
The obtained molded product has a structure in which the resin and the crushed powder of the expanded graphite sheet are not uniform, and tends to be a molded product with low initial properties such as mechanical strength and electrical properties, while the viscosity change is smaller than the above range. The separation of the crushed powder and the expanded graphite sheet becomes clear, and the resin component flows out from the degassing part of the molding die at the time of molding, and the phenomenon that the amount of resin increases in the outer peripheral part of the resulting molded product becomes prominent. Also, the obtained molded product tends to have low initial properties as described above.

The crystal structure contained in the crystalline epoxy resin is not particularly limited, but in consideration of the physical properties and moldability of the obtained molded product, the resin containing the chemical structural unit represented by the general formula (A) as the main component is used. preferable. Further, the gelling time of the resin, which is an important factor in producing an optimum molded body, is arbitrarily determined by the type and amount of the curing agent and, if necessary, the curing accelerator used.

[0033]

[Chemical 1]

The curing agent used in combination with the crystalline epoxy resin is not particularly limited, and aromatic amine, acid anhydride, phenol novolac resin and the like are used. It is preferable to use a phenol novolac resin in consideration of the characteristics of the molded product obtained from these curing agents, the cost, and the like.

There is no particular limitation on the kind of the curing accelerator used if necessary, and triphenylphosphine (TP) is taken into consideration in consideration of the physical properties and cost of the obtained molded product.
P) is preferred.

There are no particular restrictions on the method for adjusting the above-mentioned materials, and examples thereof include a dry mixing method, a wet mixing adjusting method using an organic solvent, and a method of mixing and adjusting the material by melting. In consideration of uniform mixing, safety, cost, etc., a melt blending method in which materials are melted and mixed using a kneader or a roll is preferable.

The melt blending method involves heating a material to give a resin,
It is necessary to pay attention to gelation and hardening due to the reaction of the materials during mixing in order to mix the hardening agent and the hardening accelerator to be used if necessary. The magnitude of the shearing force and cooling during the mixing of the equipment used It is necessary to confirm the presence or absence of equipment. In general, it is preferable to raise the temperature of the mixing section of the apparatus above the melting point of the resin to be blended and to charge the materials last so that the reaction can be greatly accelerated.

The resin mixture obtained by the above-mentioned method is cooled, pulverized and classified to obtain the resin material used in the present invention. The method of pulverizing the obtained resin mixture is not particularly limited, but a method of coarsely pulverizing and then finely pulverizing is preferable because the average particle size of the obtained resin mixture is stable. The method for classifying the obtained pulverized powder is also not particularly limited, but it is preferable to use an automatic sieving machine having a classifying mesh according to the target particle size in terms of cost and classification accuracy.

There is no particular limitation on the particle size distribution of the resin mixture, but in consideration of the dry mixing property with the expanded graphite sheet pulverized powder, the number average particle size is preferably in the range of 1 μm to 1000 μm, and more preferably in the range of 5 μm to 500 μm. More preferable. If the number average particle size is less than 1 μm, the particles may agglomerate (broking), resulting in poor workability and a tendency that uniform mixing with the expanded graphite sheet pulverized powder may not be expected.
On the other hand, when it exceeds 1000 μm, it becomes difficult to uniformly mix it with the crushed powder of the expanded graphite sheet as described above, and the density of the obtained separator tends to vary greatly.

The mixing ratio of the expanded graphite and the resin mixture used in the present invention is determined in consideration of the values of various characteristics of the fuel cell separator which is the final molded product to be the target. Expanded graphite / resin mixture = 95 / 5-30 /
The range of 70 (weight ratio) is preferable, and 90/10 to 50 /
The range of 50 (weight ratio) is more preferable, and 80/20 to 6
The range of 0/40 (weight ratio) is more preferable. Here, if the mixing ratio of the expanded graphite and the resin mixture exceeds 95/5, the mechanical strength tends to decrease sharply, while on the other hand, 30/7
If it is less than 0, the amount of expanded graphite that is a conductive substance added is small, and the electrical characteristics tend to deteriorate.

There is no particular limitation on the method of mixing the expanded graphite and the resin mixture, and dry mixing using a shaker, a V blender or the like that does not apply a large shearing force to the expanded graphite at the time of mixing in order to prevent the expanded graphite from being pulverized. The method is preferred. If the expanded graphite is pulverized during mixing, the mechanical strength of the resulting fuel cell separator tends to decrease.

The above-mentioned mixed powder can be directly used as a molding material powder, but in the present invention, in order to further improve the mixing property and workability at the time of molding, the mixed powder is pressure-molded to form a sheet. The sheet (hereinafter referred to as the forming sheet) that has been used is used. There is no particular limitation on the method for producing the forming sheet, but for example, a mixture charging tank, a gate adjusting machine for adjusting the material to a constant thickness, a slitter for finishing to a constant width, a transfer device for transferring the processing material, a rolling roll for sheeting, etc. It is possible to use a molding sheet manufacturing apparatus or the like. When the flat portion has a hole, it is preferable that the sheet is formed with the hole.

In order to improve the strength of the molding sheet, the curing reaction of the resin contained in the molding sheet is partially promoted, or the molding sheet is partially (not completely) heat-melted before manufacturing the separator. Can be offered. There is no limitation on the curing reaction or the method of heat-melting, for example, a method of heating the obtained forming sheet, more specifically, the above-mentioned rolling roll shall be equipped with a heating device and passed through this rolling roll. There are a method of occasionally heating and a method of passing the obtained molding sheet through a heating oven.

There is no particular limitation on the density, the number of layers, the shape, etc. of the molding sheet used in the present invention, and it is arbitrarily determined by the design value 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, after forming the forming sheets, the necessary number of sheets is overlapped to obtain a desired density, or only a part of the required number of sheets is overlapped and formed. The molding method for obtaining the above molded body (fuel cell separator) is not particularly limited, but compression molding is preferable.

In order to improve the mechanical strength and electrical characteristics of the flat portion, adjust the density, etc., a conductive sheet, a gas impermeable sheet or a material having an insulating property is laminated on the molding sheet as a reinforcing sheet, It can be molded and integrated.
These reinforcing sheets may be laminated with the forming sheet only in the portion corresponding to the reinforcing layer in forming, and may be arbitrarily laminated with the forming sheet in other portions where the density or the like is desired to be improved.

As the electrically conductive sheet or the gas impermeable sheet, it is preferable to use an expanded graphite sheet (a sheet which is a base of crushed powder of expanded graphite sheet which is preferably used as a molding material). There is no limitation on the thickness of the expanded graphite sheet, but 0.5 mm-
It is preferably in the range of 1.2 mm. The density of the expanded graphite sheet is not particularly limited, and is selected in consideration of the density of the molding sheet to be integrally used.
Range of 0kg ^{/ m 3} ~1,200kg ^/ m 3 is preferred.

As the electrically conductive sheet, other than the expanded graphite sheet, any electrically conductive sheet that can be processed into a sheet can be used. There is no limit to the material. In the present invention, sheets having different densities can be used in combination as required.

As the gas-impermeable sheet, for example, a glass cloth (glass woven cloth or glass non-woven cloth), a fiber woven cloth or non-woven cloth such as carbon fiber impregnated with a resin, and a prepreg which is easily handled can be used. A glass cloth is particularly preferable among the fiber woven cloth and the non-woven cloth. As the material having an insulating property, it is preferable to use a prepreg (curing degree of resin is B stage) obtained by impregnating glass cloth (glass woven cloth or glass nonwoven cloth) with resin and drying.

The glass composition of the glass cloth is not particularly limited, but C glass or E glass can be used. The glass fiber diameter is preferably in the range of 3 μm to 18 μm. Glass cloth or glass fiber of its raw material,
A silane-based surface treatment is preferable in order to secure adhesiveness with the resin, and the plate thickness is 0.15 mm to 0.33 mm.
It is preferable that the glass woven fabric is mainly a plain weave.

The resin for the prepreg is not particularly limited, but a resin having the same melting point and gelling time as that of the resin used for the molded body is preferable, and the resin mixture (crystalline epoxy resin / curing agent / curing agent / The same as the curing accelerator mixture) is preferable.

In the above prepreg, the resin can be impregnated by applying a resin varnish to a fiber woven fabric or a fiber nonwoven fabric. The resin amount (solid content) applied to the fiber woven fabric or fiber nonwoven fabric is preferably 30% by weight to 60% by weight, and 40% by weight to 50% by weight with respect to the glass cloth.
Is more preferable. If the amount of the resin is less than 30% by weight, the gas impermeability level tends to decrease, and if it exceeds 60% by weight, the fiber ratio tends to be small and the strength reinforcing effect tends to decrease. The resin is preferably semi-cured to the B stage state.

There are no particular restrictions on the form of use of the reinforcing sheet, but by using a reinforcing sheet that has been processed into the shape of the portion to be reinforced, it is possible to shorten the molding processing time and improve the dimensional accuracy of the resulting molded body. It has a great influence and is effective. When a reinforcing sheet having no resin on the surface is used, the surface may be coated with a resin in order to improve the adhesiveness between the molding sheet and the reinforcing sheets during molding.

The forming method of the forming sheet for obtaining the fuel cell separator or the forming method of forming the forming sheet and the reinforcing sheet is not particularly limited, but the compression forming method is preferable. Molding is usually performed using a mold for obtaining a predetermined shape. The molding conditions are preferably 5 MPa to 50 MPa (particularly preferably 10 MPa to 40 MPa), preferably 150 ° C.
It is preferable to carry out at 240 ° C (particularly preferably 170 ° C to 220 ° C). A molding time of 0.5 to 15 minutes is sufficient.

When the molding sheet is molded normally, the density at the flat portion is likely to be lower than that at the rib portion. In order to improve this and to make the density of the rib and the flat part uniform or to increase the density of the flat part, a forming sheet is laid on the flat part, or a reinforcing sheet is laid on the forming sheet. It is preferable.

When the forming sheet and the reinforcing sheet are integrated, the required number of forming sheets and reinforcing sheets are laminated in an arbitrary order, and the laminate is formed in the mold once.
There is a method of forming a forming sheet or a reinforcing sheet, laminating the forming sheet or the reinforcing sheet on the obtained formed product, and repeating the forming operation as many times as necessary to obtain a final formed body.

The fuel cell separator of the present invention has ribs and flat portions, and the flat portions may have holes. In this case, the holes are formed when the molding sheet is produced. Alternatively, the holes may be punched after forming the molded body.
The size of the fuel cell separator according to the present invention is not particularly limited, and is appropriately selected according to the size of the fuel cell.

When the reinforcing sheet is used and the forming sheet is used alone (one piece), the forming sheet is set in a flat portion before or after being inserted into the mold. It is preferable to be integrated with the molding sheet during molding.

The fuel cell using the separator of the present invention can be manufactured by a known method. The fuel cell has a structure in which an electrolyte layer made of a solid polymer electrolyte or the like and a required number of cells formed so as to sandwich the electrolyte layer are laminated by the separator of the present invention. The separator of the present invention can be used as a separator for fuel cells of alkaline type, solid polymer type, phosphoric acid type, molten carbonate type, solid acid type, etc., which are classified according to the type of electrolyte.

Embodiments of the present invention will be described below.
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 set of two and has a protrusion 1 for forming a rib portion of a fuel cell separator on one surface. Has been formed. 2 and 3 are 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 part into which the protrusion 1 of the mold is inserted).

FIG. 4 shows a sectional view of a fuel cell separator (one example). The fuel cell separator 11 is formed by stacking a molding sheet 12, a conductive sheet 13, and a molding sheet 12 in this order. The fuel cell separator 11 is
The rib portion 14 and the flat portion 15. FIG. 5 is a plan view of a fuel cell separator (one example) according to an embodiment of the present invention, and FIG. 6 is a cross-sectional view taken along the line AA of FIG. 5, and 21 is a rib for securing a supply passage for gas and cooling water. Rib portion having (groove), 22
Is a hole for supplying gas and cooling water, and 23 is a hole 22
A gasket for sealing the periphery, 24 is a reinforcing sheet for reinforcing the separator, and 25 is a flat portion.

FIG. 7 is a perspective view showing the cell structure of an example of the polymer electrolyte fuel cell. The cell 30 is composed of a three-layer film 34 including 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. This cell 3
0s are stacked in multiple stages as shown in FIG. 7 to obtain a cell stack 37 as an aggregate. Although the cells are stacked in four layers in the figure, in actuality, they may be stacked in 100 layers or more if necessary.

[0062]

EXAMPLES The present invention will be described below with reference to examples. Example 1 (1) Manufacture of crushed powder of expanded graphite sheet 800 g of concentrated sulfuric acid was put into a 3 liter glass beaker.
400 g of natural graphite (fixed carbon number 99% by weight or more, Chinese # 599 graphite) was added to this, and the mixture was stirred for 10 minutes by a stirring motor (60 min ⁻¹ ) equipped with a glass stirring blade, and then peroxide was added. Hydrogen water (concentration 35% by weight) 3
2 g was blended and stirred for 15 minutes. After completion of stirring, acid-treated graphite and acid components are separated by vacuum filtration, the obtained acid-treated graphite is transferred to another container, 5 liters of water is added, stirred for 10 minutes with a large stirring blade, and washed by vacuum filtration. Acid-treated graphite and washing water were separated.

The thus-obtained washed acid-treated graphite was transferred to a enamel vat and uniformly leveled, and heat-treated for 1 hour in a vacuum dryer heated to 110 ° C. to remove water. This was placed in a heating furnace further heated to 800 ° C. for 5 minutes to obtain expanded graphite. After cooling, this expanded graphite was rolled with a roll to prepare a sheet having a density of 1,000 kg / m ³ . The obtained sheet was crushed with a coarse crusher (Hosokawa Micron Co., Ltd., Rotoplex (trade name)), and then with a fine crusher (Nara Machinery Co., Ltd., free crusher M-3 (trade name)). Pulverized to have a number average particle size of 150 μm and a bulk density of 190 kg / m
^A crushed powder of expanded graphite sheet No. ³ was obtained.

The bulk density is the volume after placing the crushed powder of the expanded graphite sheet into the upper graduated scale in a glass graduated cylinder of 200 ml and tapping on the table 50 times from a height of about 2 cm so as not to spill from the mouth. And calculated from the weight.

(2) Production of crystalline epoxy resin mixed powder to be used As a crystalline epoxy resin, a crystalline epoxy resin containing the chemical structural unit represented by the general formula (A) as a main component and having a crystallization rate of 98%. (YDC-1312 manufactured by Tohto Kasei Co., Ltd.
(Trade name)), the curing agent is a phenol novolac type (home-made, softening point 86 ° C.) having the chemical structure represented by the general formula (B), and the curing agent is triphenylphosphine (TPP). , (Wako Pure Chemical Industries, Ltd. reagent)
It was used. The basic compounding ratio of the above materials is crystalline epoxy resin / phenol novolac resin (equivalent compounding)
And TPP is 1.5 phr (1.
5% by weight).

[0066]

[Chemical 2]

The method for producing the crystalline epoxy resin mixed powder will be described below. A pot having a mixing blade of a table-top kneader with a cooling device (PBV type, manufactured by Irie Shosha Co., Ltd., capacity 300 ml) was heated to 120 ° C., while 130 g of the above crystalline epoxy resin, The phenol novolac resin (120 g) and the triphenylphosphine (1.9 g) were placed in a vinyl bag, air was introduced into the bag, and the mixture was shaken well to carry out dry mixing.

The mixed material was put in the pot for 20 seconds while rotating the mixing blade of the kneader, and then kneaded for 3 minutes. During this time, the amount of cooling water was adjusted so that the temperature inside the pot would not exceed 120 ° C. After the kneading was completed, the mixed material was immediately taken out from the pot and left at room temperature.

Next, the mixture obtained above was placed in a double-layered vinyl bag, lightly hit with a hammer, coarsely crushed, and then finely crushed with a universal mixer equipped with a cooling device. The fine powder of the obtained mixture was sieved with a sieve of 100 μm, and the powder having a diameter of more than 100 μm was further pulverized to obtain a crystalline epoxy resin mixed powder having an average particle diameter of 30 μm.

(3) Manufacture of molded body (separator for fuel cell) 350 parts by weight of crushed powder of expanded graphite sheet obtained in Example 1 (1) and crystalline epoxy resin mixed powder 15 produced in (2)
0 part by weight (expanded graphite sheet pulverized powder / crystalline epoxy resin mixed powder = 70/30 (weight ratio)) was put into a tabletop V blender and blended for 3 minutes to obtain a mixed powder.

Next, 130 KP is applied with a sheet forming machine for molding.
Molding was performed under a pressure of a to obtain a molding sheet having a density of 600 kg / m ³ and a thickness of 3.2 mm (this is referred to as molding sheet A). Further, using the above-mentioned mixed powder, it was molded at a pressure of 130 KPa by a molding sheet molding machine to obtain a density of 600.
A molding sheet having a Kg / m3 and a thickness of 1.0 mm (this is referred to as molding sheet B) was obtained.

Next, a mold was prepared. The lower mold was a female mold having a flat molding surface (vertical, horizontal 200 mm), and the upper mold was a mold having the protrusion 1 of FIG. However, in the upper mold,
The height of the protrusions was 1.0 mm, the protrusion pitch was 1.0 mm, the rib width was 1.0 mm, and the rib taper was 0 degree.

One molding sheet 2 (using the molding sheet A) having the shape shown in FIG. 2 is placed on the lower mold, and a cutout portion 4 at the central portion shown in FIG. 3 is further provided thereon. After placing one molding sheet 3 (using the molding sheet B), the part having the upper mold protrusion 1 is set downward on the upper part thereof, and then at a surface pressure of 15 MPa and a temperature of 160 ° C. Molded for 10 minutes. Then, the obtained molded body was heat-treated at 180 ° C. for 30 minutes to obtain a fuel cell separator.
The thickness of the flat portion and rib portion of the obtained fuel cell separator was 2.0 mm, and the groove depth of the rib portion was 1.0 mm.

Comparative Example 1 (1) Production of crushed powder of expanded graphite sheet The same one as produced in Example 1 (1) was used. (2) Production of epoxy resin mixed powder to be used Without using the crystalline epoxy resin mixed powder of Example 1 (2), as an epoxy resin (Toto Kasei Co., Ltd., cresol novolac type, YDCN-701 (trade name) )) 1
30 g, as curing agent, phenol novolac resin (home-made) 110 g (equal amount), triphenylphosphine (TPP) (Wako Pure Chemical Industries, Ltd., reagent) 2.4 g
An epoxy resin mixed powder was obtained through the same steps as in Example 1 (2) except that was used.

(3) Manufacture of Molded Article (Fuel Cell Separator) A fuel cell separator was obtained through the same steps as in Example 1 (3). The thickness of the flat portion and the rib portion of the obtained fuel cell separator was 2.0 mm, and the groove depth of the rib portion was 1.0 m.
It was m.

Next, regarding the resins used in Example 1 and Comparative Example 1, 150 ° C., 160 ° C., 170 ° C. and 180 ° C.
The viscosity at the temperature of ° C was measured. The results are shown in Table 1. Further, the fuel cell separators obtained in Example 1 and Comparative Example 1 were evaluated for the amount of burrs attached to the mold, the density of ribs and flat portions, gas impermeability, and the appearance of the molded body. The results are shown in Table 1.

The amount of burrs attached to the mold and the appearance of the molded product (surface swelling, scratches, uneven molding) were visually evaluated. The density is 2 from the center and the flat part of the rib.
A cm square sample was cut out, and their volume and weight were measured and calculated.

For gas impermeability, a homemade gas leak test jig shown in FIG.
The amount of oxygen passing through the separator test piece 41 having a size of (Φ) was replaced in water, and the number of bubbles generated within 2 minutes after the injection of oxygen was confirmed. Further, in order to evaluate the gas impermeability, for the rib portion, a separator test piece was used by cutting from the fuel cell separator obtained by molding,
In the flat part, all surfaces are flat without forming ribs (using a mold with a flat molding surface as the upper mold)
A simulated separator test piece cut out from a separately molded molded body (however, as the one corresponding to Example 1, a molding sheet B having no notch in the center portion was used as the molding sheet 3 and the above-mentioned mold was used as the upper mold. (Prepared in the same manner as in Example 1 except that the molding surface was flat) was used.

In FIG. 8, 41 is a separator test piece, 4
2 is water, 43 is oxygen (surface pressure: 19.6 × 10 ⁴ Pa), and 44 is a rubber packing. The size of the inside of the packing of the separator test piece was 34 mm.

[0080]

[Table 1]

[0081]

[Table 2]

As shown in Table 1, the crystalline epoxy resin used in Example 1 according to the present invention has a lower melt viscosity than the epoxy resin used in Comparative Example 1 and the viscosity due to the difference in measurement temperature. It is clear that the change is small.
In addition, as shown in Table 2, the fuel cell separator obtained in Example 1 according to the present invention has a higher density of rib portions and flat portions than the fuel cell separator of Comparative Example 1,
It is clear that the amount of burr generated is small, gas impermeability and appearance are good.

[0083]

The fuel cell separator of the present invention is a fuel cell separator excellent in gas impermeability, mechanical strength, electric resistance and the like. Further, according to the production method of the present invention, a fuel cell separator having excellent gas impermeability, mechanical strength, electrical resistance and the like can be obtained. Furthermore, the fuel cell of the present invention is a high-performance fuel cell having a fuel cell separator excellent in gas impermeability, mechanical strength, electric resistance and the like.

[Brief description of drawings]

FIG. 1 is a plan view showing a molding die (also serving 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 cross-sectional view showing a model fuel cell separator with one rib.

FIG. 5 is a plan view of a ribbed fuel cell separator according to an embodiment of the present invention.

6 is a cross-sectional view taken along the line AA of FIG.

FIG. 7 is a perspective view showing a cell structure of an example of a polymer electrolyte fuel cell.

FIG. 8 is a cross-sectional view of a gas leak test jig for examining gas permeability.

[Explanation of symbols]

1 Protrusion 2 Forming Sheet 3 Forming Sheet 4 Notch 11 Model Ribbon Fuel Cell Separator 12 Forming Sheet 13 Conductive Sheet 14 Rib 15 Flat 21 Rib 22 Hole 23 Gasket 24 Reinforcing Sheet 25 Flat part 30 Cell 31 Solid polymer electrolyte membrane 32 Fuel electrode 33 Air electrode 34 Three-layer membrane 35, 36 Fuel cell separator 37 Cell stack 41 Separator test piece 42 Water 43 Oxygen 44 Packing

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Claims (11)

[Claims] 1. A fuel cell separator comprising a crystalline epoxy resin and expanded graphite. 2. The crystalline epoxy resin is 150 ° C. to 18 ° C.
The viscosity change in the range of 0 ° C. is 0.002 Pa.s. s ~ 0.0
08 Pa. The fuel cell separator according to claim 1, wherein the range is s. 3. The fuel cell separator according to claim 1, wherein the expanded graphite is a crushed powder of expanded graphite sheet. 4. The fuel cell separator according to claim 1, wherein the separator has a rib portion and a flat portion. 5. A method for producing a fuel cell separator, which comprises mixing a crystalline epoxy resin and expanded graphite, and then forming the sheet into a sheet. 6. The crystalline epoxy resin is 150 ° C. to 18 ° C.
The viscosity change in the range of 0 ° C. is 0.002 Pa.s. s ~ 0.0
08 Pa. The method for producing a fuel cell separator according to claim 5, wherein the range is s. 7. The method for producing a fuel cell separator according to claim 5, wherein the expanded graphite is a crushed powder of expanded graphite sheet. 8. The method for producing a fuel cell separator according to claim 5, wherein the separator has a rib portion and a flat portion. 9. The method for producing a fuel cell separator according to claim 5, wherein the molding method is a compression molding method. 10. A fuel cell comprising the fuel cell separator according to any one of claims 1 to 4 or the fuel cell separator obtained by the manufacturing method according to any one of claims 5 to 9. 11. The fuel cell according to claim 10, which is a solid polymer type.