JP2002198063A - Manufacturing method of separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a separator for a fuel cell, in which diffusion of graphite powder and a binder is uniform and, therefore, a uniform gas barrier property, conductivity, or the like can be realized with a comparatively small amount of the binder, in manufacturing the separator for the fuel cell by hot pressing the graphite powder and the binder. SOLUTION: In manufacturing the separator for the fuel cell, graphite powder, after being wetted beforehand into an organic solvent, is mixed with a binder, and is pressure molded under heat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a fuel cell separator, and more particularly, to a method for manufacturing a fuel cell separator in which graphite powder and a binder are pressure-formed under heating.

[0002]

2. Description of the Related Art In recent years, fuel cells utilizing the reaction between hydrogen and oxygen have attracted attention as power generation systems that respond to resource problems and environmental problems, and their practical use in various fields is being studied. The basic structure of the fuel cell is that the electrolyte is sandwiched between porous positive and negative electrode plates, and gas barrier properties,
It has a structure in which several tens to several hundreds of cells provided with conductive plate-shaped separators are stacked, and typically, a groove as a reaction gas flow path for hydrogen, air, and the like is formed in each of the positive and negative electrode plates. There are a ribbed electrode system engraved on the surface of the separator and a ribbed separator system engraved on the surface of each separator.These separators are mainly produced by heating graphite powder using phenolic resin as a binder under heating. It is manufactured by pressing.

However, conventional fuel cell separators cannot use a large amount of a binder in terms of gas barrier properties and conductivity as a separator, so that the graphite powder and the binder are not dispersed. There is a problem in that the separator tends to be uniform, and the uniformity of performance as a separator is thereby impaired.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in producing a fuel cell separator by press-molding graphite powder and a binder under heating. Therefore, according to the present invention, in producing a fuel cell separator by press-molding graphite powder and a binder under heating, the dispersion of the graphite powder and the binder is uniform, and therefore, a relatively small amount of It is an object of the present invention to provide a method for producing a fuel cell separator, which can express uniform gas barrier properties, conductivity, and the like with high performance using a binder.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a graphite powder is mixed with a binder and then molded under pressure under heating to produce a separator for a fuel cell. And a method of manufacturing a fuel cell separator.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a fuel cell separator of the present invention, the graphite powder may be, for example, natural graphite such as flaky, granular, massive, earthy, etc., expanded graphite, or expanded graphite.
Using petroleum coke or pitch coke as the main raw material, kneading,
A mass of artificial graphite or the like produced by molding, firing, and graphitizing, and the like is ground as necessary.

[0007] The graphite powder in the present invention preferably has an ash content of 1% or less, particularly preferably 0.5% or less, from the viewpoints of conductivity, battery performance and the like. Further, the content of alkali metal and alkaline earth metal and transition metal is preferably 500 ppm or less, 100 ppm
The following are particularly preferred.

In addition, the surface smoothness of a separator,
In terms of gas barrier properties and battery characteristics, volatile components are 2
% Or less, and particularly preferably 1% or less. Further, it is preferable that the fixed carbon is 98% or more.
Those with 9% or more are particularly preferred.

Further, the graphite powder in the present invention includes:
In terms of separator performance, etc., the maximum particle size is 1,000μ
m, preferably 500 μm, more preferably 300 μm. Further, from the viewpoint of separator moldability, performance, and the like, it is preferable that fine powder is not contained. Therefore, the average particle size is preferably from 1 to 100 μm, more preferably from 3 to 70 μm,
It is particularly preferably from 5 to 50 μm.

In the method for producing a fuel cell separator of the present invention, the binder is not particularly limited, and may be a saturated polyester resin, a styrene-acryl resin, a styrene resin, a polyamide resin, a polycarbonate resin, a polysulfone. Resin, polyvinyl chloride resin, polyolefin resin, polyphenylene ether resin, polyphenylene sulfide resin, polyvinyl butyral resin,
Thermoplastic resins such as acrylic resin, fluororesin, phenoxy resin and urethane resin, and resins such as thermosetting resins such as diallyl phthalate resin, phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, urea resin, and natural Rubber (isoprene rubber) and synthetic rubber such as butadiene rubber, isoprene rubber, chloroprene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, butyl rubber, ethylene propylene rubber, urethane rubber, fluorine rubber, silicon rubber, and styrene Thermoplastic elastomers such as a thermoplastic elastomer, a urethane thermoplastic elastomer, a polyester thermoplastic elastomer, a polyamide thermoplastic elastomer, and a polyolefin thermoplastic elastomer can be used. Inside, novolak resin, resole resin,
And phenolic resins such as modified resins thereof, polyolefin resins, or butadiene rubber, isoprene rubber, styrene butadiene rubber, and rubber such as butyl rubber, styrene-based thermoplastic elastomer, thermoplastic elastomer such as polyolefin-based thermoplastic elastomer, or Mixtures of these resins, rubbers, elastomers and the like are preferred.

Here, novolak resins include, for example, phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol,
o-ethylphenol, m-ethylphenol, p-ethylphenol, propylphenol, n-butylphenol, tert-butylphenol, 1-naphthol, 2-naphthol, 4,4′-biphenyldiol,
Bisphenol A, pyrocatechol, resorcinol,
At least one of phenols such as hydroquinone, pyrogallol, 1,2,4-benzenetriol, phloroglicinol and the like are acid-catalyzed, for example, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde and furfural, or acetone , Methyl ethyl ketone, a resin polycondensed with at least one of ketones such as methyl isobutyl ketone, and the resole resin is the same except that an alkali catalyst is used instead of the acid catalyst in the polycondensation of the novolak resin. It is a polycondensed resin.

The phenol resin as the binder in the present invention is preferably a novolak resin.
It is preferable to use a curing agent to cure at the time of pressure molding under heating of the separator. As the curing agent, for example, typically, hexamethylenetetramine, and a methylol group, an alkoxymethyl group, an acetoxy group as a functional group An amino compound having at least two methyl groups or the like, specifically, a melamine derivative such as methoxymethylated melamine;
Benzoguanamine derivatives, glycoluril derivatives, urea resin derivatives, resole resins and the like can be mentioned.
These curing agents are used in an amount of usually 5 to 15% by weight, preferably 5 to 10% by weight, based on the total amount with the resin.

In the method for producing a fuel cell separator according to the present invention, the graphite powder and the binder are mixed, for example, by mixing both, or further adding a curing agent, a cross-linking agent or the like, to a tumbler blender, a ribbon blender. , V-type blender, Henschel mixer, super mixer, etc., by mixing uniformly, or by mixing and kneading with a kneading machine such as a single or twin screw extruder, roll, Banbury mixer, kneader, Brabender etc. Done.

In the present invention, it is essential that the graphite powder be wetted with an organic solvent before mixing. If the graphite powder is not wetted with an organic solvent beforehand, the object of the present invention cannot be achieved. .

When mixing the graphite powder moistened with an organic solvent with the binder, the moistened graphite powder may be heated or pressed as appropriate, or the binder may be heated to a temperature higher than its glass transition point or melting point. The binder can be mixed by heating or the like, but it is preferable to use the binder as a solution or dispersion of an organic solvent.

The organic solvent used for wetting the graphite powder and for dissolving or dispersing the binder is, for example, alkanes such as butane, pentane, hexane, heptane and octane, cyclopentane and cyclohexane. , Cycloheptane, cycloalkanes such as cyclooctane,
Ethanol, propanol, butanol, amyl alcohol, hexanol, heptanol, octanol, decanol, undecanol, diacetone alcohol, furfuryl alcohol, alcohols such as benzyl alcohol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, etc. Propylene glycols such as cellosolves, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, and dipropylene glycol dimethyl ether Acetone, methyl amyl ketone,
Ketones such as cyclohexanone and acetophenone, ethers such as dioxane and tetrahydrofuran, butyl acetate, amyl acetate, ethyl butyrate, butyl butyrate, diethyl oxalate, ethyl pyruvate, ethyl-2-hydroxybutyrate, ethyl acetoacetate, methyl lactate ,
Esters such as ethyl lactate and methyl 3-methoxypropionate; halogenated hydrocarbons such as chloroform, methylene chloride and tetrachloroethane; benzene, toluene;
Examples thereof include aromatic hydrocarbons such as xylene and cresol, and highly polar solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

As the organic solvent in the binder solution or dispersion, those capable of dissolving the binder are preferable, and those having a solubility index similar to that of the binder are preferable. For example, an alcohol is preferable for a thermosetting resin such as a phenol resin, and an aromatic hydrocarbon is preferable for a thermoplastic resin such as a polyolefin resin and a rubber and a thermoplastic elastomer.

Further, it is preferable that the organic solvent in wetting the graphite powder and the organic solvent in the solution or dispersion of the binder have an azeotropic property,
Those having an approximate solubility index, for example, H. Hi
The difference in solubility index (δ) of ldebrand is more preferably 15% or less, preferably 10% or less, more preferably 8% or less, and particularly preferably the same organic solvent.

The amount of the organic solvent used in wetting the graphite powder with the organic solvent is preferably 1 to 300 parts by weight based on 100 parts by weight of the graphite powder.
The concentration of the binder in the solution or dispersion of the organic solvent is preferably 1 to 90% by weight.

In the case where a curing agent, a cross-linking agent or the like for the binder is used, a method of mixing the curing agent or the cross-linking agent with the binder or an organic solvent solution or dispersion thereof, graphite powder, Any method such as a method of mixing with the organic solvent wet substance, a method of mixing as a solution or dispersion liquid or a wet substance of the organic solvent may be used, but it is preferable to add the graphite powder to the organic solvent wet substance and use it.

In the present invention, the binder is preferably used in an amount of 1 to 60 parts by weight, more preferably 1 to 30 parts by weight, based on 100 parts by weight of the graphite powder. Is particularly preferably 5 to 30 parts by weight,
Further, it is particularly preferable that the content of the thermoplastic resin, rubber, and thermoplastic elastomer is 1 to 30 parts by weight.
Preferably it is 20 parts by weight. When the amount of the binder used is less than the above range, the mechanical strength and the like of the obtained separator tend to be inferior. On the other hand, when the amount exceeds the above range, the performance such as the conductivity of the separator tends to be impaired.

In the above-mentioned mixing, the obtained mixture becomes wet, paste-like or lump-like, and the mixture is heated and dried as appropriate for pressure molding under heating described later.
The heating temperature at this time may be any temperature at which the used organic solvent can be evaporated and the binder is not deteriorated.
The temperature is about 00 ° C. or lower, preferably about 200 ° C. or lower, and the content of the organic solvent in the mixture is preferably 1% by weight.
Dry until:

The mixture after the heating and drying usually forms non-uniform granules or agglomerates. Therefore, the granules or the agglomerates are mixed with a mixer, a jaw crusher, a gyratory crusher, a roll mill, a sample mill, or the like. The material is roughly pulverized by a jet mill, a hammer mill, an impeller breaker, or the like so that the maximum particle size is preferably less than 3 mm.

When this pulverized material is used as a binder with a thermosetting resin by a compression molding machine or the like, or when the thermoplastic resin, rubber, or thermoplastic elastomer is used as a binder and cross-linked, When the binder is cured and crosslinked at a temperature not higher than the temperature at which the binder is not decomposed, or when the thermoplastic resin, rubber, or thermoplastic elastomer is used as the binder without crosslinking, the binder is melted. The temperature is not higher than the temperature and is not decomposed, for example, preferably under heating at a temperature of 50 to 400 ° C, more preferably 100 to 350 ° C, preferably 20 to 400 MPa, more preferably 40 to 300 MPa.
Usually, a desired plate-shaped separator having a length of about 50 to 500 mm and a thickness of about 1 to 10 mm is produced by pressure molding at the pressure of a.

At this time, for example, when a phenol resin is used as a binder, a curing reaction occurs when a curing agent is used in the case of a novolak resin and when a curing agent is not used in the case of a resol resin. , And becomes a cured product. Further, when a thermoplastic resin, rubber or thermoplastic elastomer to which a crosslinking agent is added is used as the binder, a crosslinking reaction occurs to form a crosslinked product.

In the present invention, the term "pressure molding under heating" includes not only compression molding but also transfer molding, injection compression molding, injection molding, and the like. Injection molding is preferred from the viewpoint of (1), but compression molding is preferred from the viewpoint of easy control of molding conditions and physical properties of the separator.

In the pressure molding, a large number of linear ridges or the like are formed in parallel with the surface of the mold, so that the linear separator or the like can be formed on one or both surfaces of the plate-like separator. A groove for a reaction gas flow path corresponding to the ridge can be formed.

According to the present invention, the obtained fuel cell separator has a uniform dispersion of the graphite powder and the binder, so that even with a relatively small amount of the binder, the affinity between the two increases and the bulk density, It has excellent conductivity and the like, and can also improve mechanical properties such as bending strength.

[0029]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

Example 1 3.5 g of hexamethylenetetramine was added to 500 g of natural graphite powder having an average particle size of 20 μm, and ethanol 79 was added.
g, and mixed for 5 minutes to wet the graphite powder. Then, a 50% by weight ethanol solution of a commercially available novolak resin (having a volatile content of free phenol or the like of 1% by weight or less) is 100%.
g was added and mixed and kneaded in a double-arm kneader for 1 hour, taken out of the kneader, kept at room temperature for 2 hours, and then heated and dried at 70 ° C. for 30 minutes. Subsequently,
The obtained kneaded material was pulverized in a mixer for 2 minutes and sieved through a 16-mesh (aperture: 1 mm) sieve so that the total amount became 1 mm or less.
The plate was press-formed at a temperature of 250 ° C. under a pressure of 98 MPa for 5 minutes, cooled to 60 ° C., and then depressurized to produce a plate-shaped fuel cell separator having a length of 100 mm and a width of 100 mm and a thickness of 5 mm.

In the obtained separator, the dispersed state of the graphite powder and the novolak resin was uniform by visual observation and under a microscope, the bulk density was 1.98 g / cm ³ , and the resistance was measured by a four-terminal method (Mitsubishi Chemical Corporation). The surface resistance value measured by “Lauresta MP” manufactured by Nissan Chemical Industries, Ltd. was 7Ω / □.

Example 2 Toluene 8 was added to 500 g of natural graphite powder having an average particle size of 20 μm.
After adding 7 g and mixing for 5 minutes to wet the graphite powder,
10 g of commercially available styrene-butadiene rubber was added to toluene.
2 g was added, and the mixture was mixed and kneaded in a double-arm kneader for 1 hour.
Hold for a time, then heat and dry at 70 ° C. for 30 minutes. Subsequently, the obtained kneaded material was pulverized in a mixer for 2 minutes and sieved through a 16-mesh (1 mm mesh) sieve to thereby reduce the total amount to 1 mm or less. The plate was press-molded at a temperature of 98 MPa for 5 minutes, cooled to 60 ° C., and then depressurized to produce a plate-like fuel cell separator having a length of 100 mm and a width of 5 mm and a thickness of 5 mm.

In the obtained separator, the dispersed state of the graphite powder and the styrene-butadiene rubber was uniform by visual observation and under a microscope, and the bulk density was 1.98 g / cm ^3.
Terminal method resistance tester (Mitsubishi Chemical Corporation "Lauresta MP")
Was 8 Ω / □.

Example 3 Toluene 8 was added to 500 g of natural graphite powder having an average particle size of 13 μm.
After adding 7 g and mixing for 5 minutes to wet the graphite powder,
A solution obtained by dissolving 25 g of a styrene-based thermoplastic elastomer, which is a hydrogenated derivative of a commercially available styrene-butadiene block copolymer (styrene content: about 30% by weight), in 100 g of toluene was added, and mixed for 1 hour in a double-arm kneader.
After kneading, it was taken out of the kneader, heated at 130 ° C. for 5 hours and dried. Subsequently, the obtained kneaded material was pulverized in a mixer for 1 minute to form a 16 mesh (mesh size 1 m).
m), the total amount is 1
mm, and then crushed to a temperature of 180 ° C., 9
Press molding under a pressure of 8 MPa for 5 minutes, cooling to 60 ° C., and then depressurizing, each 100 m in length and width
m, a plate-shaped fuel cell separator having a thickness of 5 mm was produced.

The obtained separator has a uniform dispersion state of the graphite powder and the styrene-based thermoplastic elastomer visually and microscopically, and has a bulk density of 2.08 g / cm ^3. The surface resistance value measured by Mitsubishi Chemical “Lauresta MP”) was 4Ω / □. Also, from the obtained separator, length 100mm,
A test piece having a thickness of 5 mm cut out to a size of 10 mm in width was used, and the distance between supporting points was set to 80 in accordance with JIS K7171.
mm, the test speed was 5 mm / min, the maximum bending stress measured by applying a load by applying an indenter to the plate surface of the separator was 26 MPa, and the deflection at the maximum bending stress was 1.6.
mm.

Comparative Example 1 500 g of natural graphite powder was not wetted with toluene.
Styrene-based thermoplastic elastomer 25g in toluene 1
A fuel cell separator was manufactured in the same manner as in Example 3 except that a solution dissolved in 00 g was added. In the obtained separator, the dispersion state of the graphite powder and the styrene-based thermoplastic elastomer visually and microscopically was slightly inferior in uniformity as compared with Example 3, the bulk density was 2.03 g / cm ³ , and the surface resistance was Was 5Ω / □. The maximum bending stress was 21 MPa, and the deflection at the maximum bending stress was 0.9 mm.

[0037]

According to the present invention, in producing a fuel cell separator by press-molding graphite powder and a binder under heating, the dispersion of the graphite powder and the binder is uniform, Therefore, it is possible to provide a method for manufacturing a fuel cell separator that can exhibit uniform gas barrier properties, conductivity, and the like with high performance with a relatively small amount of binder.

Claims (11)

[Claims] 1. A fuel cell comprising: mixing graphite powder and a binder; and press-molding the mixture under heating to produce a separator for a fuel cell, wherein the graphite powder is wetted in advance with an organic solvent. Manufacturing method of separators for automobiles. 2. The method for producing a fuel cell separator according to claim 1, wherein the amount of the organic solvent used in wetting the graphite powder with the organic solvent is 1 to 300 parts by weight based on 100 parts by weight of the graphite powder. 3. The method for producing a fuel cell separator according to claim 1, wherein the binder is used as a solution or dispersion of an organic solvent. 4. The method for producing a fuel cell separator according to claim 3, wherein the concentration of the binder in the solution or dispersion of the organic solvent is 1 to 90% by weight. 5. An organic solvent for wetting graphite powder and an organic solvent for a binder solution or dispersion,
5. The method for producing a fuel cell separator according to claim 3, wherein the organic solvent has an approximate solubility index. 6. An organic solvent for wetting graphite powder, and an organic solvent in a binder solution or dispersion,
The method for producing a fuel cell separator according to claim 3 or 4, wherein the same organic solvent is used. 7. The method for producing a fuel cell separator according to claim 1, wherein the binder is used in an amount of 1 to 60 parts by weight based on 100 parts by weight of the graphite powder. 8. The method for producing a fuel cell separator according to claim 1, wherein a thermosetting resin and / or a thermoplastic resin is used as the binder. 9. The method for producing a fuel cell separator according to claim 1, wherein a rubber and / or a thermoplastic elastomer is used as the binder. 10. The graphite powder has an average particle size of 1 to 100 μm.
The method for producing a fuel cell separator according to claim 1, wherein: 11. The method for producing a fuel cell separator according to claim 1, wherein a groove for a reaction gas flow path is formed on the surface of the separator during pressure molding under heating.