JP2000243409A - Separator member for sold polymer fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator member for a solid polymer fuel cell and a manufacturing method of the same, wherein the separator member is capable of improving and stably maintaining cell performance by solving problems of gas leak of fuel gas or oxidizing gas by restraining breakage and fracture of the separator member in starting, stopping, and normally operating a cell, and further in assembling a cell stack. SOLUTION: This separator member is formed with carbon-resin curable molding containing 40-90 wt.% carbon powder and 60-10 wt.% thermosetting resin, having bending strength >=30 MPa at room temperature, decreasing rate of the bending strength <=30% at room temperature to 100 deg.C, camber <=0.5 mm, Shore hardness <=100, bending elasticity <=20 GPa, and thickness accuracy within ±0.05 mm. The carbon powder and the thermosetting resin are mixed at a predetermined weight ratio, and are crushed and sieved. The crushed powder <=40 mesh are loaded in a die. After pre-loading, the die is opened and gas is discharged and eliminated, and then hot- pressing molding at room temperature to 280 deg.C under 20-400 MPa is provided. After releasing from the die, the molding is held between flat and smooth plates and is heated at 150-280 deg.C for more than five minutes to provide thermosetting process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator member for a fuel cell, for example, a solid polymer type fuel cell used for a small distributed power source such as an automobile or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is composed of an electrolyte membrane composed of a polymer ion exchange membrane such as a fluororesin ion exchange membrane having sulfonic acid groups, and two catalyst electrodes provided on both sides of the electrolyte membrane. A stack is formed by stacking single cells including separators each having a gas supply groove for supplying a fuel gas such as hydrogen or an oxidizing gas such as oxygen or air to each electrode.

A power generation mechanism of a fuel cell is generated by a reaction between a fuel gas (eg, hydrogen gas or hydrogen-containing gas) supplied to an anode side of a cell and an oxidant gas (eg, oxygen-containing gas) supplied to a cathode side. The flow of electrons (e ⁻ ) is taken out to the outside as electric energy. For example, when hydrogen gas is used as the fuel gas and oxygen gas is used as the oxidant gas, the following reaction proceeds. Anode; H ₂ → 2H ⁺ + 2e ⁻ cathode; (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O Total reaction; H ₂ + (1/2) O ₂ → H ₂ O

Therefore, it is necessary to supply the fuel gas and the oxidizing gas to the electrode in a completely separated state, and the separator member is required to have high gas impermeability. Further, when gas leak occurs due to breakage or breakage of the separator member, not only does the above-described electrochemical reaction not smoothly proceed, so that not only does the battery performance deteriorate, but also the fuel gas and the oxidizing gas are mixed, which may cause an explosion. Will occur.

[0005] Breakage or breakage of the separator member is often due to thermal stress due to an uneven temperature distribution state generated during a temperature rise process when the battery is started or a temperature fall process when the battery is stopped. The operating temperature of a polymer electrolyte fuel cell is usually 60 to
Although the temperature is 100 ° C., the temperature may exceed 100 ° C. in the highest temperature portion called a hot spot, and the temperature distribution locally becomes extremely non-uniform, causing a large thermal stress. If the material strength, dimensional accuracy, flatness (warpage), etc. of the separator member are appropriate for such thermal stress, breakage or loss due to thermal stress can be suppressed.

In a polymer electrolyte fuel cell, a battery stack is assembled by stacking the above-described single cells in several tens of layers. In this case, it is important to assemble the cells so that the cells are in close contact with each other. is there. If the adhesion is insufficient, the contact electric resistance increases, the internal resistance of the battery increases, and the temperature distribution becomes more non-uniform, resulting in a decrease in battery performance. Usually, the assembly is performed by bolting the periphery with a tightening force of about 0.05 to 1 MPa. At this time, partial load is generated, and the separator member may be cracked to cause breakage or chipping. Also in this case, if the material strength, dimensional accuracy, flatness (warpage), and the like of the separator member are appropriate, breakage and loss can be suppressed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in a polymer electrolyte fuel cell.
After conducting multilateral studies on factors such as the material strength, shape accuracy, and cell-to-cell adhesion of the separator member, a carbon-resin in which a carbon component and a thermosetting resin component were combined and integrated in a specific range of the amount ratio It has been found that by specifying the strength, shape accuracy, and the like of the cured molded body, breakage and breakage of the separator member can be effectively suppressed.

That is, the present invention has been developed on the basis of the above findings, and its object is to separate the separator at the time of starting and stopping the power generation of the battery, during the normal operation, and at the time of assembling the battery stack. A solid height that suppresses damage and loss of members, eliminates the problem of gas leakage of fuel gas (hydrogen gas or hydrogen-containing gas) or oxidant gas (oxygen-containing gas, etc.), and enables stable maintenance and improvement of battery performance An object of the present invention is to provide a molecular fuel cell separator member and a method of manufacturing the same.

[0009]

According to the present invention, there is provided a separator member for a polymer electrolyte fuel cell according to the present invention, which comprises 40 to 90% by weight of carbon powder and 60 to 90% of a thermosetting resin.
It has a composition of 10% by weight and has a bending strength of 3 at room temperature.
A structural feature is that it is formed from a carbon-resin-cured molded article having a characteristic of not less than 0 MPa and a rate of decrease in bending strength from room temperature to 100 ° C. of not more than 30%.

Further, in the above separator member, the carbon-resin cured molded body has a warpage of 0.5 mm or less, a Shore hardness of 100 or less, a flexural modulus of 20 GPa or less, and a thickness accuracy of ± 0.05 mm or less. You.

Further, the method for producing a separator member for a polymer electrolyte fuel cell according to the present invention is directed to a thermosetting resin having a gelling time of 20 minutes or less and a solid content of 60% or more in 40 to 90% by weight of carbon powder. Is mixed in an amount ratio of 60 to 10% by weight, the mixture is pulverized, and the pulverized particles having a size of 40 mesh or less obtained by sieving are charged into a mold, pre-pressurized, and then the mold is opened once to remove volatile matter. And residual air is removed and then removed from room temperature to 2
It is hot-pressed at a temperature of 80 ° C. and a pressure of 20 to 400 MPa, released from the mold, and sandwiched between flat plates having a smooth surface.
The configuration is characterized in that the thermosetting resin is heated and cured at a temperature of 0 ° C. for 5 minutes or more.

In the above manufacturing method, it is preferable to control the temperature difference in the mold during hot pressing to within 10 ° C., and to perform the heat curing of the thermosetting resin under a pressure of 70 Pa or more. Is desirable.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The separator member for a polymer electrolyte fuel cell according to the present invention is formed from a carbon-resin cured molded body obtained by integrating carbon powder with a thermosetting resin as a binder. For example, artificial graphite, natural graphite, expanded graphite, coke powder, carbon black, and mixtures thereof are used. The thermosetting resin that functions as a binder for carbon powder has heat resistance to withstand a temperature of 80 to 120 ° C., which is a temperature during power generation operation of a polymer electrolyte fuel cell, and a pH of 2 to 3.
There is no particular limitation as long as it has an acid resistance enough to withstand sulfonic acid or sulfuric acid acid. For example, a resin such as a phenol-based resin, a furan-based resin, or an epoxy-based resin is used alone or in combination.

The mixing ratio of the carbon powder and the thermosetting resin is such that the carbon powder is 40 to 90% by weight and the thermosetting resin is 60% by weight.
The amount ratio is set to 10 to 10% by weight. When the carbon powder content is less than 40% by weight and the thermosetting resin content is more than 60% by weight, the electrical conductivity and thermal conductivity are reduced. If there is, the moldability is deteriorated, the gas impermeability and the strength are reduced, and both of them cannot sufficiently function as a separator member.

In the separator member for a polymer electrolyte fuel cell according to the present invention, the cured carbon-resin article has a strength characteristic in which the bending strength at room temperature is 30 MPa or more and the bending strength reduction rate from room temperature to 100 ° C. is 30% or less. It is necessary to be equipped with. As mentioned above, the temperature rise process when the battery starts up, the temperature drop process when the battery stops, and the heat generated by the battery reaction during power generation causes a temperature distribution inside the battery, causing thermal stress and mechanical strain. I do. In particular, the gas supply groove of the separator member has a small thickness and is easily damaged or broken due to the mechanical strain. Therefore, in the present invention, the bending strength at room temperature is 30 MPa or more as the material strength, and the bending strength reduction rate from room temperature to 100 ° C. Is set to 30% or less. The bending strength is a value measured according to JIS K6911.
The values of the bending strength measured at 0 ° C. are A and B, which are values calculated by the formula [(AB) / (A)] × 100 (%).

Although the material strength specified as described above suppresses breakage and chipping, the cured carbon-resin body has a warpage of 0.5 mm or less, a Shore hardness of 100 or less, a flexural modulus of 20 GPa or less, and a thickness of When the material has a material strength and a shape accuracy within ± 0.05 mm in accuracy, breakage and loss can be more effectively suppressed.

In stacking and assembling cells, it is difficult to assemble the cells in close contact with each other if the shape accuracy and the shape of the separator members vary and the planarity is poor. Therefore, in the present invention, the warpage is set to 0.5 mm or less as the flatness, and the thickness accuracy is set to within ± 0.05 mm. Furthermore, Shore hardness is 1
By setting the flexural modulus to not more than 00 and not more than 20 GPa, it is possible to assemble the cell in a state of being in close contact with each other without being damaged or broken at the time of bolting when assembling the cell.

Incidentally, the warpage is set by setting the dial gauge to zero at the reference position with the separator member sample placed on the surface plate.
The amount of warpage is measured at nine points as a whole, and the maximum value is used as the warpage. The thickness accuracy is measured from the average value, the maximum value, and the minimum value by measuring the thickness at nine locations of the separator member sample with a micrometer. Find thickness accuracy and flexural modulus is JISK
It is a value measured according to 6991.

The separator member for a polymer electrolyte fuel cell of the present invention is manufactured by mixing a carbon powder and a thermosetting resin, loading the pulverized particles obtained by pulverizing the mixture into a mold, and performing hot-press molding. A carbon powder such as artificial graphite, natural graphite, expanded graphite, coke powder, and carbon black, and a thermosetting resin such as a phenolic resin, a furan-based resin, and an epoxy-based resin. 60-1
Mix in an amount ratio of 0% by weight. In order to maintain the strength, a thermosetting resin having a gel time of 20 minutes or less and a solid content of 60% or more is used. The gelation time was 15 minutes for the sample.
While stirring at 0 ° C., the time until gelation was measured, and the solid content was measured by placing the sample in an oven maintained at 70 ° C. for 1 hour.
It is a value determined by measuring the percentage of weight residue after standing for 50 minutes and cooling in a desiccator.

The separator member is usually formed into a plate having a thickness of about 1 to 3 mm, and has a depth of about 0.1 mm for supplying a fuel gas or an oxidizing gas to one or both surfaces thereof.
A gas supply groove of 5 to 1 mm is formed. Therefore,
If the carbon powder falls off during these processes and pores are formed, there is a problem that gas impermeability decreases. Therefore, the carbon powder has an average particle size of 50 μm or less and a maximum particle size of 100 μm.
It is desirable to use a powder of μm or less.

The mixing of the carbon powder and the thermosetting resin is carried out by a conventional kneader such as a pressurized kneader or a twin screw kneader. It is preferable to dissolve in an appropriate organic solvent such as ether to lower the viscosity and mix. The mixture is dried if necessary to remove volatile components and the used organic solvent, and then pulverized by a pulverizer and sieved to prepare pulverized particles of 40 mesh or less. The mixture has a wide range of particle size distribution from large particles to small particles, but in particular, the presence of large particles hinders uniform and dense molding at the time of molding. Therefore, pulverized particles of 40 mesh or less are used as molding powder.

The pulverized particles are loaded into a mold provided with a ridge for forming a gas supply groove, pre-pressed at a pressure of about 10 MPa, and then the mold is opened once to remove volatile components and residual air contained therein. Discharge and remove. The structural defects that occur in the molded body due to the removal and removal of this volatile matter and residual air are greatly reduced,
Improvement of gas impermeability and prevention of warpage are achieved.

Next, the mold is closed and hot-pressed at a temperature of room temperature to 280 ° C. and a pressure of 20 to 400 MPa.
After releasing from the mold, the obtained plate-like molded body is sandwiched between flat surfaces of graphite plate and aluminum plate, etc., which have a flat and smooth surface and good thermal conductivity, and are kept at a temperature of 150 to 280 ° C for 5 minutes or more. By performing a heat-curing treatment to advance the curing reaction of the thermosetting resin, it is possible to produce a plate-like molded body having high flatness, little warpage, and excellent corrosion resistance.

Since the temperature distribution in the mold during the hot pressing affects the uniformity of the curing reaction rate of the resin, the temperature distribution in the hot pressing during the hot pressing is made uniform in the structure of the molded body. The temperature difference in the mold, that is, the difference between the temperature of the highest temperature portion and the temperature of the lowest temperature portion is controlled within 10 ° C. If the temperature difference exceeds 10 ° C., the degree of partial change in the cured state during molding is increased, causing thermal distortion, and the molded body is likely to warp.

When the thermosetting resin is subjected to heat treatment at a pressure of 70 Pa or more when the thermosetting resin is sandwiched between flat plates having a flat surface and is subjected to heat curing, a plate-shaped molded product having a flat surface and high flatness is obtained. be able to. In addition, depending on design conditions, a surface smoothing process such as a milling process or a surface process or an outer peripheral processing process is performed.

[0026]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 4, Comparative Examples 1 to 7 A solution prepared by dissolving carbon powder having a true specific gravity of 2.18 and an average particle size of 45 μm, and a phenol resin having a different gelation time and resin solid content in methanol (resin concentration: 20 wt. %) Were mixed in different ratios and mixed using a twin-screw kneader. After vacuum-drying the obtained mixture at room temperature, it is pulverized by a Nara-type pulverizer, and then sieved to adjust pulverized particles having different particle sizes, and a mold provided with a ridge portion for forming a gas supply groove. Was loaded.

The mold has 33 ridges on each side corresponding to a gas supply groove having a width of 1.5 mm and a depth of 1 mm, each having a length of 150 mm, a width of 150 mm and a thickness of 3 mm. It is composed of an upper mold and a lower mold manufactured to obtain a shaped body. The mold is heated and the pressure of 10 MPa is increased to 5
After loading for 2 seconds to pre-press, the mold was opened to discharge and remove volatile gases and residual air. Next, the temperature and pressure were changed and held for 3 minutes to perform hot-press molding. In addition, the temperature difference (difference between the highest temperature and the lowest temperature) in the mold during the hot pressing was adjusted to 8 ° C.

The molded product released from the mold was sandwiched between graphite plates having a smooth surface, and the phenol resin was heat-cured while changing the temperature, pressure and time. The carbon thus produced is
Table 1 shows a comparison of the production conditions of the separator member formed of the cured resin body.

[0030]

[Table 1]

The flexural strength, flexural strength reduction rate, warpage, thickness accuracy, Shore hardness and flexural modulus of these separator members were measured and are shown in Table 2. Further, the measurement of the contact electric resistance and the gas leak test were performed by the following methods, and the results are also shown in Table 2. Measurement of Contact Electric Resistance Ten separator members were laminated and fixed with a tightening force of 1 MPa, and then the laminate was heated to 100 ° C.
A direct current of A was applied to measure the contact electric resistance between the stacked separators. Gas leak test After measuring the contact electric resistance, the laminated separator was dismantled,
A pressure of 1 MPa was applied between each separator with nitrogen gas, and the presence or absence of gas leak was examined.

[0032]

[Table 2]

From the results in Table 1, it can be seen that the separator material manufactured within the scope of the present invention is a product having the characteristics of the present invention. Also, the results in Table 2 show that the separator material having the characteristics of the present invention has a low contact electric resistance and eliminates the occurrence of leakage during battery assembly.
From these results, it is clear that the characteristics selected in the present invention can reduce the contact electric resistance of the members and effectively prevent gas leakage in the battery. Further, the separator material having the above characteristics can be secured by manufacturing it under predetermined conditions.

[0034]

As described above, according to the separator member for a polymer electrolyte fuel cell of the present invention, carbon material having high material strength at room temperature and high temperature and high shape accuracy such as warpage and thickness accuracy can be obtained. Since it is formed from a resin cured molded body, the temperature rise process when the battery starts up, the temperature decrease process when the battery stops,
Alternatively, it is possible to effectively reduce breakage or breakage of the separator member due to thermal stress caused by a non-uniform temperature distribution state generated during normal operation. Further, since the adhesion between cells is improved during battery assembly, an increase in contact electric resistance is prevented, and furthermore, breakage or loss of the separator member due to tightening during battery assembly is also prevented. Therefore, the problem of gas leakage generated due to breakage or breakage of the separator member is also solved, and a polymer electrolyte fuel cell separator member capable of maintaining and improving the cell performance stably can be provided. Further, according to the production method of the present invention, it is possible to produce the polymer electrolyte fuel cell separator member of the present invention having these excellent performances.

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Claims (5)

[Claims] 1. A composition comprising 40 to 90% by weight of carbon powder and 60 to 10% by weight of a thermosetting resin, having a bending strength at room temperature of 30 MPa or more, and a reduction rate of bending strength from room temperature to 100 ° C. of 30% or less. Carbon with the characteristics of
A separator member for a polymer electrolyte fuel cell, wherein the separator member is formed from a cured resin body. 2. The carbon-resin cured molded article has a warpage of 0.5 mm.
Below, Shore hardness is 100 or less, flexural modulus is 20GP
2. The separator member for a polymer electrolyte fuel cell according to claim 1, wherein the thickness accuracy is within ± 0.05 mm. 3. A thermosetting resin having a gelation time of 20 minutes or less and a solid content of 60% or more is mixed with 40 to 90% by weight of carbon powder in an amount ratio of 60 to 10% by weight, and the mixture is pulverized. The crushed granules having a mesh size of 40 mesh or less obtained by sieving were charged into a mold, and after pre-pressing, the mold was once opened to remove volatile matter and residual air, and then the temperature from room temperature to 280 ° C. It is hot-pressed at a pressure of 20 to 400 MPa, and after releasing, it is sandwiched by flat plates having a smooth surface and heated at a temperature of 150 to 280 ° C. for 5 minutes or more to heat and cure the thermosetting resin. Of producing a separator member for a polymer electrolyte fuel cell. 4. The method according to claim 1, wherein the temperature difference in the mold during hot pressing is 1
4. The method for producing a separator for a polymer electrolyte fuel cell according to claim 3, wherein the temperature is controlled within 0 ° C. 5. The heat-curing treatment of a thermosetting resin is performed at 70 Pa.
5. The method according to claim 3, wherein the step is performed under the above pressure.
A method for producing a separator member for a polymer electrolyte fuel cell according to the above.