JP2003257445A - Separator for fuel cell and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator being light in weight and having excellent mechanical strength and excellent molding machining property so as to provide a manufacturing method therefor. <P>SOLUTION: A resin component containing phenol resin of 30 to 95 mass % having heat flowability measured by a disc cure method of 100 to 190 mm and a cellulose material of 70 to 5 mass % having a particle diameter of 200 μm or less is molded. The produced molded product is carbonized and baked to obtain the separator for a fuel cell made of amorphous carbon. <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 and a method for manufacturing the same.

[0002]

2. Description of the Related Art Fuel cells are expected as a next-generation power generation device with low pollution and high power generation efficiency. The type of the fuel cell includes alkali type, phosphoric acid type, solid polymer type, molten carbonate type, solid electrolyte type, etc., depending on the type of electrolyte. These fuel cells include a unit cell that generates an electromotive force due to an electrochemical reaction between a hydrogen-containing gas (anode gas) and an oxygen-containing gas (cathode gas), and a fuel cell for a fuel cell interposed between adjacent unit cells that are stacked. A separator (hereinafter, abbreviated as “separator”) is provided.

The separator is in contact with the electrodes of both adjacent unit cells to electrically connect the unit cells together and to separate the reaction gas, and forms a gas flow path on the surface thereof. In order to do so, it is general that groove processing is applied. Fuel cells that operate at relatively low temperatures, such as alkaline type, phosphoric acid type, and solid polymer type, have a groove for flowing cooling water to one side of the separator for the purpose of stabilizing the operating temperature. There is also.

The characteristics required for the separator are that it has electrical conductivity, low gas permeability, heat resistance and corrosion resistance, does not react with anode gas and cathode gas, and has excellent mechanical strength. There are things such as being present. In addition, since the fuel cell uses a plurality of separators due to its structure, it is also important that the fuel cell is lightweight, for example, when it is used for an automobile.

Although the separator made of a metal such as titanium or stainless steel has excellent heat resistance and conductivity,
Cutting is required to form the groove shape as described above. In addition, the molded product after cutting has to have its surface plated with a precious metal or the like in order to improve the corrosion resistance and reduce the contact resistivity, which is not only a factor of high cost but also a heavy weight. There is a problem that becomes large.

On the other hand, a separator made of a carbon material such as graphite or an amorphous carbon material is lightweight, has excellent corrosion resistance, and has good conductivity. However, since a separator made of such a material cannot be subjected to molding processing such as injection molding, after manufacturing a flat plate, one or both surfaces of this flat plate are subjected to cutting processing so that the above-mentioned groove is formed. It is necessary to form the shape, which increases the processing cost. Further, the graphite plate is apt to cause cracks and cracks during cutting, and the amorphous carbon plate has a problem that the cutting itself is more difficult than that of a metal material.

Further, in Japanese Unexamined Patent Publication No. 4-284363, carbon fibers are impregnated with a thermosetting resin liquid and pressure-molded,
A separator obtained by carbonizing this in a non-oxidizing atmosphere is disclosed, but this separator must be impregnated with a thermosetting resin liquid several times in order to improve gas impermeability and fired. However, there is a problem that cracks due to expansion and contraction of the separator increase due to repeated impregnation and firing, and there is a problem that the cost becomes higher.

Further, Japanese Patent Laid-Open No. 10-334927,
JP-A-59-213610, JP-A-60-150
In Japanese Patent No. 559, Japanese Patent Laid-Open No. 2000-21421, Japanese Patent Laid-Open No. 2001-143719, etc., a resin separator in which graphite powder is contained in a thermosetting resin is proposed. Although these separators are lightweight, their mechanical characteristics and electrical performance are inferior to those of a separator made of a carbon material or an amorphous carbon material, and thus further improvement is desired. Further, when a separator is produced using the resin composition, it is necessary to form a groove that is a gas flow path on the surface of the separator as described above, so that it is suitable for mass production such as injection molding and compression molding. Although it is desirable to use a suitable molding method, simply adding graphite powder to the thermoplastic resin will cause an increase in viscosity during melt molding, resulting in poor fluidity during molding, or curing during thermosetting. In many cases, the moldability is inferior because the speed becomes slow, and the yield is poor and the productivity is inferior.

[0009]

Therefore, the present invention solves such problems and is excellent in mechanical strength, lightweight, and
Moreover, it is an object of the present invention to provide a separator excellent in moldability and a manufacturing method thereof.

[0010]

As a result of intensive studies to solve the above problems, the present inventors have found that a phenol resin having specific thermal characteristics and a cellulosic material having a specific particle size are contained. The inventors have found that the above problems can be solved by forming a fuel cell separator from amorphous carbon obtained by carbonizing and firing the resin composition described above, and have reached the present invention.

That is, the present invention contains 30 to 95% by mass of a phenol resin having a heat fluidity of 100 to 190 mm as measured by the disc cure method and 70 to 5% by mass of a cellulosic material having a particle diameter of 200 μm or less. A gist of the present invention is a separator for a fuel cell, which is made of amorphous carbon obtained by molding and carbonizing a resin composition.

Further, a phenol resin 30-95 having a heat fluidity of 100-190 mm as measured by the disc cure method is used.
It is molded by using a resin composition containing 70% by mass and 70% by mass of a cellulosic material having a particle diameter of 200 μm or less, and the molded product obtained is carbonized and fired to obtain amorphous carbon. The gist of the invention is a method of manufacturing a fuel cell separator.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. A separator for a fuel cell has a large number of grooves for forming a flow path for a reaction gas such as an anode gas and a cathode gas on at least one surface, and a groove for the reaction gas on one surface. On the other side, there is one in which a groove for flowing a heat medium such as cooling water is formed in order to stabilize the operating temperature of the fuel cell. Alternatively, in addition to the groove form, there is a form in which a concave flow path is formed oppositely by having a large number of protrusions protruding from the surface of the separator.

In the present invention, in order to obtain a fuel cell separator having such a complicated groove shape, a phenol resin having specific thermal characteristics and a cellulosic material having a specific particle size are mixed in a specific ratio. It is necessary to perform molding processing using the resin composition contained. By using a phenolic resin, which is a thermosetting resin, as a resin component, the molded processed product that has been cured after molding does not melt due to heat, and carbonizes while maintaining its shape in the subsequent firing step,
The target amorphous carbon fuel cell separator can be obtained. Further, by using a phenol resin having a specific thermal characteristic, the fluidity at the time of melt molding is improved, and in addition, a predetermined amount of a cellulosic material having a role of a filler in the phenol resin and an effect of improving the moldability is provided. By only containing and dispersing uniformly, it is difficult to mold, especially injection molding, only with the phenol resin, but an appropriate melt viscosity can be obtained during melt molding, and the moldability can be further improved. Further, it is possible to accelerate the thermal curing of the resin during the thermal curing, and it is possible to maintain the form of the molded product as a carbon material. By performing a molding process using a resin composition having good moldability and thermosetting property as described above, even a separator having a complicated groove shape or a concave flow path as described above can be easily molded. It can be a processed product.

However, the molded product as it is cannot be used as a separator for a fuel cell because of its high electrical characteristics, especially electrical resistivity, so the molded product obtained by molding is carbonized and fired. It is necessary to make it amorphous carbon. In the state of molded products, it is an insulating material because it is a resin molded product, but it will satisfy the electrical characteristics as a fuel cell separator by carbonizing and firing it into amorphous carbon, and it will also have mechanical strength and gas. A fuel cell separator having excellent impermeability and corrosion resistance can be obtained.

Upon firing, the molded product can be carbonized with a phenol resin while maintaining its shape. In addition, since the cellulosic material, which is a carbonaceous material, is a material that can be carbonized and fired by heating it in an inert atmosphere, the firing obtained by carbonizing and firing the molded product in an inert atmosphere The product has some voids (pores) due to the difference in residual carbon ratio between the cellulosic material and the phenol resin.
Etc. occur. With this void, the bulk density of the separator is lowered, and the weight of the separator can be reduced,
The firing time in the firing process can be shortened. In addition,
This void does not reduce the gas permeability.

The phenol resin in the present invention has a heat fluidity of 100 to 190 mm as measured by the disc cure method.
Must be in the range. If the heat fluidity of the phenolic resin is less than 100 mm, the fluidity at the time of molding is insufficient and it becomes impossible to form a complicated shape. If the heat fluidity exceeds 190 mm, the viscosity at the time of heat melting is low and air bubbles are trapped. However, when it is molded, it flows too much and the moldability deteriorates.

The term "thermofluidity" as used in the present invention refers to the property of being solid at room temperature but exhibiting fluidity when a load is applied in a heated state. Unlike ordinary thermoplastic resins, thermosetting phenolic resins undergo intramolecular and intermolecular condensation to crosslink when heating is continued at a temperature at which they have fluidity for a certain period of time or longer. Then
This has the property of hardening. Therefore, as a measure of the heat fluidity, the flow (diameter extension: mm) of the sample resin disk under a predetermined load at 160 ° C. measured by the JIS standard disc cure method is used.

The cellulosic material in the present invention includes cellulose extracted from mechanically or chemically refined wood pulp, cotton, non-wood pulp, etc., as well as a cellulose component, which is carbonized by firing. It can be, for example, wood flour composed of wood, pulp derived from wood, non-wood pulp or a mixture thereof.

The cellulosic material used in the present invention is often not in the shape of a true sphere but in the shape of an ellipse having a certain length. The particle diameter in the present invention refers to the length of the long side of the elliptical shape.

By the way, in the fired product of the present invention, voids are generated due to the difference in the residual carbon ratio between the phenol resin and the cellulosic material. The voids are preferably spherical in view of mechanical properties. The size of the voids is preferably as small as possible from the viewpoint of mechanical properties. Since the shape and size of the voids are affected by the shape and size of the cellulosic material, the shape of the cellulosic material is preferably close to a sphere, and the particle size thereof is preferably as small as possible. Therefore, in the present invention, the particle size of the cellulosic material needs to be 200 μm or less.

The particle size of the cellulosic material is 200
When it exceeds μm, the dispersibility of the cellulosic material in the resin deteriorates, the fluidity at the time of molding deteriorates, and the moldability decreases, so that it becomes difficult to process into a molded product having a complicated shape. . The lower limit of the particle size is not particularly limited, but the practical range of the particle size is 5 to 50 μm in the case of cellulose and 1 in the case of wood flour or pulp.
A range of 00 to 200 μm is suitable.

The above-mentioned phenol resin and cellulosic material are contained in the resin composition forming the fuel cell separator in an amount of 30 to 95% by mass of the phenol resin and 70 to 5% by mass of the cellulosic material. There is a need. When the content of the phenol resin is less than 30% by weight, the characteristics of the phenol resin are not sufficiently reflected in the mixture, the fluidity is deteriorated and the moldability is deteriorated. Further, since the content of the cellulosic material becomes too large, the proportion of voids due to the cellulosic material in the carbonized and fired product is large, and the bulk density is low, but the mechanical properties such as bending strength and bending elastic modulus are low. Will be inferior in physical characteristics. When the content of the phenolic resin exceeds 95% by mass, the content of the cellulosic material becomes small, the role as a filler becomes insufficient, the effect of promoting thermosetting becomes low, and the moldability deteriorates. Further, although the carbonized and fired product has improved mechanical strength, it has a large bulk density and cannot reduce the weight of the separator.

The resin composition forming the fuel cell separator according to the present invention contains the above-mentioned phenol resin and a cellulosic material as main components, but it is intended to further improve the performance as long as the characteristics are not impaired. As the thermosetting resin, for example, a phenol resin different from those other than the above thermal characteristics, polycarbodiimide resin, furfuryl alcohol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester, aromatic polyimide, copolymers thereof Or a mixture thereof, and a modifier such as a cross-linking agent can be added. Further, it may contain a carbon material such as carbon black, graphite powder, carbon fiber, inorganic fiber, inorganic powder or glassy carbon, or a substance carbonized by firing.

As the molding method of the resin composition having the above-mentioned constitution, a standard molding method such as injection molding method, compression molding method and transfer molding method can be adopted. It is short and can easily handle complex shapes, and the product has good dimensional accuracy.
Injection molding is preferred because it is suitable for continuous production. When performing the molding process by injection molding, it is preferable that the molding material is preliminarily subjected to the injection molding process by using a mold having a size and shape that allows for dimensional shrinkage during firing.

The molded product obtained by the molding process is fired to obtain amorphous carbon, and this carbonization and firing is preferably performed in a vacuum or an inert gas atmosphere. Examples of the inert gas include nitrogen gas, helium gas, argon gas and the like. Firing temperature is 70
It is preferably in the range of 0 to 1600 ° C. If the firing temperature is lower than 700 ° C, the resin composition cannot be carbonized sufficiently, resulting in poor electrical performance and mechanical properties. Further, even if the firing temperature exceeds 1600 ° C, it is possible to obtain the target amorphous carbon separator, but there is little structural change, and the improvement in the performance of the separator obtained with respect to the manufacturing utility cannot be observed, and the energy consumption is reduced. Since this causes a loss, it is appropriate that the upper limit of the firing temperature be 1600 ° C. Therefore, the firing temperature is 900 to 12
The range of 00 ° C. is more preferable from the viewpoint of effectively utilizing energy during production.

The bending strength of the separator of the present invention produced as described above is preferably 60 MPa or more. If the bending strength is less than 60 MPa, it may not be suitable for practical use as separator strength. The bending elastic modulus of the separator is preferably 30 GPa or less, more preferably 25 GPa or less. If the flexural modulus is higher than 30 GPa, the rigidity becomes too high and cracks occur more often, which is not suitable for practical use. further,
The bulk density of the separator is preferably 1.5 g / cm ³ or less, more preferably 1.2 g / cm ³ or less. When the bulk density exceeds 1.5 g / cm ³ , the weight reduction is impaired in the fuel cell stack using a plurality of separators.

By using the molded product thus molded and processed as a separator made of carbonized and baked amorphous carbon, a structure having a shape suitable for a fuel cell separator can be manufactured continuously and uniformly. Since the post-processing such as the cutting step is not necessary or can be reduced, the fuel cell separator made of amorphous carbon can be obtained with good mass productivity. Therefore,
When these separators are stacked and used in a fuel cell, a fuel cell having a long life, high reliability and light weight can be obtained.

The size of the separator used in the present invention is not particularly limited, and the design can be changed according to the purpose, and the plane shape and groove shape can be changed variously according to the purpose. Is.

[0030]

EXAMPLES Next, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. The measurement of various physical properties in Examples and Comparative Examples was carried out by the following methods. (1) Thermal fluidity (mm): JIS-K-6911 19
95 5.3.2 Based on the method described in [Molding material (disc type)], 2 g of a sample is hot pressed at a temperature of 160 ° C. for 1 minute with a load of 1145 kg, and the diameter of the disc formed (the longest diameter and the shortest diameter). The average value of). (2) Moldability: The resin composition was judged to be “good” when the resin composition had good fluidity during molding and was able to be well filled in the mold and an appropriate curing rate was obtained. Further, when the resin composition was inferior in fluidity and could not be filled in the mold well, or when air bubbles or the like were mixed in or a uniform product could not be manufactured in the molding process, it was judged as "poor". In addition, when the curing speed was too slow and the product could not be molded into a desired product shape, it was indicated as "unmoldable". (3) State of fired product: The appearance of the obtained molded product is visually observed, and if there is no crack or crack, "no problem"
The case where there were 5 or more bubbles having a size of 1 mm or more was defined as "there are many bubbles", and the case where the surface of the fired product was uneven due to bubbles or the like was defined as "surface roughness". (4) Flexural strength (MPa) and flexural modulus (GPa):
According to the 4-point bending test method described in JIS R1601, an autograph AGS-100G (manufactured by Shimadzu Corporation) was used, and a ceramic bending test jig (AGS-5KN) was used as a jig.
Shape) was used to measure a bending speed of 0.5 mm / min, a distance between upper fulcrums of 10 mm and a distance between lower fulcrums of 30 mm, and the obtained values were analyzed by TRAPEZIUM to obtain bending strength and bending elastic modulus. . (5) Bulk density (g / cm ³ ): The value obtained by dividing the weight of the measurement object by the volume obtained from the width, length, and thickness of the measurement object was defined as the bulk density. Example 1 70% by mass of a phenol resin (Univex N type manufactured by Unitika Ltd.) having a heat fluidity of 150 mm and a particle diameter of 24
A resin composition containing 30% by mass of cellulose powder (KC Flock W-400G manufactured by Nippon Paper Industries Co., Ltd.) having a diameter of μm is injection-molded by using a mold in which firing shrinkage is expected in advance, 125 mm in length × 125 mm in width, With a thickness of 2.5 mm,
1.0mm deep and 1.2mm wide to be gas passages on both sides
A molded body having a groove of mm was obtained. This molded body is carbonized and baked at 1000 ° C. in a nitrogen gas atmosphere using a high-performance baking furnace, and has a length of 100 mm × width of 100 mm and a thickness of 2.0 mm. 1.0 m
A fuel cell separator made of amorphous carbon having a groove of m was obtained.

Table 1 shows the composition and moldability of the obtained fuel cell separator.

[0032]

[Table 1] Examples 2 to 6 Instead of the above Example 1, a resin material was used in which various conditions were changed as shown in Table 1. Other than that, injection molding was performed in the same manner as in Example 1 to obtain a fuel cell separator.

Table 1 shows the composition and moldability of the obtained fuel cell separator. Example 7 Wood flour having a particle diameter of 100 μm was used instead of cellulose. Other than that, injection molding was performed in the same manner as in Example 1 to obtain a fuel cell separator.

Table 1 shows the composition and moldability of the obtained fuel cell separator. In Examples 1 to 7, as the resin composition forming the fuel cell separator, the phenol resin having the heat fluidity of the present invention and the cellulosic material having the particle diameter of the present invention were contained within the scope of the present invention. Since the resin composition was used, the resin composition is excellent in fluidity at the time of melting or in the mold, and even a molded product having a complicated groove shape suitable for a fuel cell separator, Good molding process was possible by injection molding. Further, the obtained molded product did not contain air bubbles, and a fuel cell separator made of amorphous carbon could be obtained by carbonizing and baking the molded product. Furthermore, the separator is excellent in mechanical properties such as bending strength and bending elastic modulus,
It had a low bulk density and was lightweight. Comparative Example 1 A phenol resin having a thermal fluidity of 80 mm, which is lower than the range of the present invention, was used. And otherwise, Example 1
A fuel cell separator was prepared in the same manner as in (1).

Table 1 shows the composition and physical properties of the obtained fuel cell separator. Comparative Example 2 A phenol resin having a heat fluidity of 250 mm, which is higher than the range of the present invention, was used. A fuel cell separator was produced in the same manner as in Example 1 except for the above, but the flowability during melting was too high and the melt viscosity was too low to obtain a molded product. Comparative Example 3 Cellulose (KC Flock W-50S) manufactured by Nippon Paper Industries Co., Ltd.
Was classified and used with a particle diameter of 250 μm. A fuel cell separator was produced in the same manner as in Example 1 except for the above.

Table 1 shows the composition and moldability of the obtained fuel cell separator. Comparative Example 4 The compounding ratio of the phenol resin was 20% by mass, which was less than the range of the present invention, and the compounding ratio of cellulose powder was 80% by mass, which was more than the range of the present invention. Other than that, an attempt was made to produce a fuel cell separator in the same manner as in Example 1, but the fluidity of the mixture was so low that it could not be filled in a mold, and a molded product could be obtained. There wasn't. Comparative Example 5 The blending ratio of the phenol resin was higher than the range of the present invention 9
The content of cellulose powder was set to 8% by mass, which was less than the range of the present invention and was set to 2% by mass. Other than that, an attempt was made to produce a fuel cell separator in the same manner as in Example 1, but since the mixture had high fluidity, air bubbles were entrained, and the curing speed in the mold was slow, the desired molding was performed. Since it was impossible to process into a product shape, a molded product could not be obtained.

In Comparative Example 1, the heat fluidity of the phenol resin was too low, so that the resin could not be sufficiently filled in the mold, resulting in poor moldability. Moreover, since many bubbles were generated in the obtained molded product, many bubbles were also generated in the fired product, and it was not applicable as a separator.

In Comparative Example 2, a molded product could not be obtained because the heat fluidity of the phenol resin was too high.
In Comparative Example 3, since the particle size of cellulose was beyond the range of the present invention, the fluidity of the resin composition was non-uniform and the moldability was poor. Further, the obtained fired product, the portion where the cellulose portion was exposed causes surface roughness, and also large pores are generated by carbonization even in the portion of the cellulose contained inside, which is applicable as a separator. There wasn't.

In Comparative Example 4, since the content of cellulose exceeded the range of the present invention, the fluidity was not exhibited, and in Comparative Example 5, since the content of cellulose was less than the range of the present invention, the filler was used. No effect was exhibited, and a molded product could not be obtained in any case.

[0040]

As described above, according to the fuel cell separator of the present invention, by using a resin composition containing a phenol resin having a specific thermal characteristic and a specific cellulosic material in a specific ratio, fluidity is improved. With this, the acceleration property at the time of heat curing is improved, the moldability is improved, and a molded product with good dimensional accuracy can be continuously and uniformly manufactured by a molding process capable of mass production such as injection molding. Further, by carbonizing and firing this molded product into amorphous carbon, it is possible to obtain a separator having high strength, excellent heat resistance and corrosion resistance, gas impermeability and conductivity, and due to the cellulosic material. The weight of the separator can be reduced due to the voids. Therefore, the fuel cell provided with this separator is lightweight, has a long life, and is highly reliable.

Further, according to the method for producing a fuel cell separator of the present invention, the fuel cell separator of the present invention can be produced with high productivity.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Terumasa Yoshinaga             23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd.             Shikisha Central Research Institute F-term (reference) 5H026 AA03 AA04 AA06 BB00 BB01                       BB02 CC03 EE05 HH00 HH01                       HH05 HH08

Claims (5)

[Claims] 1. A phenolic resin having a thermal fluidity of 100 to 190 mm, measured by a disc cure method, of 30 to 95% by mass, and a cellulosic material 70 having a particle diameter of 200 μm or less.
A separator for a fuel cell, which is made of amorphous carbon obtained by molding and carbonizing a resin composition containing 5% by mass to 5% by mass. 2. A flexural strength of 60 MPa or more, a flexural modulus of 30 GPa or less, and a bulk density of 1.5 g / c.
The fuel cell separator according to claim 1, wherein the separator is m ³ or less. 3. A phenolic resin having a thermal fluidity of 100 to 190 mm, measured by a disc cure method, of 30 to 95% by mass, and a cellulosic material 70 having a particle diameter of 200 μm or less.
A method for producing a separator for a fuel cell, characterized by molding using a resin composition containing 5% by mass to 5% by mass, and carbonizing and baking the obtained molded product to obtain amorphous carbon. 4. The method for producing a fuel cell separator according to claim 3, wherein a molded product is obtained by injection molding. 5. The method for producing a fuel cell separator according to claim 3, wherein carbonization firing is performed at 700 to 1600 ° C.