JP2003142119A - Method of manufacturing metallic separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a sound separator by restraining a conductive inclusion from falling when molding it by press-molding. SOLUTION: A high polymer film 20 of polyvinylidene chloride is sandwiched between a pair of upper and lower dies 1a, 1b and a material plate 10 of a separator to mold them by pressing. A plurality of films 20 may be used and lubricant may be applied to one face or both faces of the film 20. As for the thickness of the film, the total thickness sandwiched between the dies 1a, 1b and the material plate 10 is preferably as much as 0.01-0.5 mm when the lubricant is not used, and it is preferably as much as 0.006-0.2 mm when the lubricant is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metallic separator included in a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art In a polymer electrolyte fuel cell, a laminated body in which separators are laminated on both sides of a flat plate-like electrode structure (MEA: Membrane Electrode Assembly) constitutes one unit.
A plurality of units are stacked to form a fuel cell stack. The electrode structure has a three-layer structure in which an electrolyte membrane made of an ion exchange resin or the like is sandwiched between a pair of gas diffusion electrodes forming a positive electrode (cathode) and a negative electrode (anode). The gas diffusion electrode has a gas diffusion layer formed outside the electrode catalyst layer that is in contact with the electrolyte membrane. Further, the separator is laminated so as to be in contact with the gas diffusion electrode of the electrode structure, and a gas flow path or a refrigerant flow path for allowing gas to flow is formed between the separator and the gas diffusion electrode. According to such a fuel cell, for example, hydrogen gas, which is a fuel, is caused to flow in the gas flow passage facing the gas diffusion electrode on the negative electrode side, and oxygen or air is oxidized in the gas flow passage facing the gas diffusion electrode on the positive electrode side. When a volatile gas is flowed, an electrochemical reaction occurs and electricity is generated.

The separator supplies electrons generated by the catalytic reaction of hydrogen gas on the negative electrode side to an external circuit,
It is necessary to have a function of sending electrons from the external circuit to the positive electrode side. Therefore, a conductive material made of graphite-based material or metal-based material is used for the separator. Particularly, the metal-based material has excellent mechanical strength and can be made lighter and more compact by thinning it. It is said to be advantageous in that The metal separator is, for example, a thin plate made of stainless steel in which conductive inclusions forming a conductive path are dispersed and exposed on the surface, and the material plate is press-molded to form the gas flow path or the refrigerant flow path. The thing formed is mentioned.

[0004]

The above-mentioned press-molding is carried out by sandwiching the material plate of the separator by a mold for press-molding. At this time, the conductive inclusions on the surface of the material are rubbed against the mold. Dropouts were often happening. If you use a separator from which conductive inclusions have fallen,
During operation of the fuel cell, pitting corrosion starting from the drop marks is generated,
The problem that corrosion progresses occurs.

Therefore, an object of the present invention is to provide a method for producing a metallic separator for a fuel cell, which can produce a sound separator by suppressing the dropping of conductive inclusions during press molding.

[0006]

Means for Solving the Problems The present invention relates to the production of a metal separator for a fuel cell having a conductive inclusion in a metal structure by press molding, in which a metal mold for press molding and a separator material plate are provided. It is characterized in that a polymer film is sandwiched between them.

According to the present invention, during pressing, the friction between the material plate and the film is reduced, and the film is stretched to reduce the friction of the material plate with respect to the mold. The falling of sexual inclusions is suppressed. In addition, by sandwiching the film, the space between the die and the blank plate is filled with the film during pressing, eliminating the gap, preventing uneven contact of the blank plate with respect to the mold, and allowing the blank plate to cover the entire blank plate. The press load from can be efficiently applied.

In the present invention, a plurality of films may be used or a lubricant may be attached to one side or both sides of the film. By adopting these measures, the above effect is further enhanced. If the thickness of the film is too thin, the above effect is not exhibited well, and if it is too thick, the molding accuracy is lowered and the desired size and shape are not easily obtained, and molding defects easily occur.
From this, the thickness of the film is 0.01 when the lubricant is not used and the total thickness sandwiched between the mold and the material plate is 0.01.
It is preferably about 0.5 mm, and when a lubricant is used, it is preferably about 0.006 mm to 0.2 mm.

As a material for the polymer film of the present invention, polyvinylidene chloride having a large amount of elongation and an appropriately soft characteristic is preferably used. Examples of the polymer film include Teflon (registered trademark) film and cellophane film, but the former is not a suitable material because it has high hardness and the latter has small elongation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. (I) First Embodiment FIG. 1 shows the processes of the manufacturing method of the separator of the first embodiment in the order of (a) and (b). The material plate 10 of the separator shown in FIG. 1A is an austenitic stainless steel plate having conductive inclusions. This material plate 10
As the components of, the components shown in Table 1 and the balance of Fe and B
And unavoidable impurities, and Cr and B
Satisfies the following expression (1). Cr (wt%) + 3 × Mo (wt%) − 2.5 × B (wt%) ≧ 17 (1) Then, B is M ₂ B and MB type boride, M
₂₃ (C, B) ₆ type boride is deposited on the surface. These borides are conductive inclusions that form a conductive path on the surface of the separator, and are dispersed / exposed on the surface of the material plate 10. The material plate 10 has a thickness of 0.2 mm, for example.

[0011]

[Table 1]

To manufacture a separator, first, referring to FIG.
As shown in (a), a film 2 made of polyvinylidene chloride having a thickness of 0.01 to 0.5 mm is provided on both sides of the material plate 10.
Distribute one 0. Next, as shown in FIG. 1 (b), the material plate 10 is pressed by a predetermined press load by the upper and lower molds 1a and 1b, and press-molded. The material plate 10 is formed into a separator 10A in which concave and convex portions are formed by the upper and lower molds 1a and 1b, and the grooves on the front and back sides are gas passages and refrigerant passages. After molding, the mold is opened and the film 20 is peeled off to obtain the separator 10A as a product.

Thus, the molds 1a and 1b and the material plate 10 are
The film 20 is sandwiched between the base plate 10 and the film 2 during press forming.
0 causes slippage or elongation of the film 20, which causes the material plate 1 for the molds 1a and 1b.
Zero friction is reduced. As a result, the conductive inclusions on the surface of the material plate 10 (separator 10A after molding) are prevented from falling off, and a sound separator can be obtained. Further, by sandwiching the film 20, the molds 1a and 1b are pressed at the time of pressing.
The space between the base material plate 10 and the material plate 10 is filled with the film 20, so that no gap is formed. Therefore, the material plate 1 for the molds 1a and 1b
Uneven contact of 0 is prevented, and the press load from the molds 1a and 1b can be efficiently applied to the entire surface of the material plate 10.

(II) Second Embodiment FIG. 2 shows the process of the separator manufacturing method of the second embodiment in the order of (a) and (b). In the second embodiment, the two stacked films 20, 20 are connected to the mold 1a,
It is sandwiched between 1b and the material plate 10 and press-molded.
In this case, the thickness of the film is 2
It is the total thickness of 0 and 20. By using two films 20 in this way, slippage occurs between the two films 20, 20 and the friction reducing effect is increased.

(III) Third Embodiment FIG. 3 shows the process of the separator manufacturing method of the third embodiment in the order of (a) and (b). In the third embodiment, one film 20 is arranged between the molds 1a and 1b and the material plate 10 as in the first embodiment, but the lubricant 30 is applied to both surfaces of the film 20. ing. The lubricant 30 is liquid or powdery such as lubricating oil. When the lubricant 30 is applied to both sides of the film 20, the film 20 becomes more slippery with respect to the molds 1a and 1b and the material plate 10, and the friction reducing effect is increased. In addition,
Since the effect of this embodiment is exhibited by the presence of the lubricant between the film 20 and the molds 1a and 1b during press molding, the lubricant 30 may be applied to the inner surface of the mold.

(IV) Fourth Embodiment FIG. 4 shows the process of the method for manufacturing a separator of the fourth embodiment in the order of (a) and (b). In the fourth embodiment, two films 20, 2 are used as in the second embodiment.
0 is sandwiched between the molds 1a and 1b and the material plate 10, but a lubricant is sandwiched between the two films 20 and 20. According to this, the two films 20 become more slippery and the friction reducing effect is increased.

[0017]

EXAMPLES Next, examples of the present invention will be described. A. Production of Separator [Example 1] A 0.2 mm-thick austenitic stainless steel sheet containing each component shown in Table 2 and the balance Fe and unavoidable impurities was cut into a square shape of 100 mm x 100 mm to form a separator. I got a blank board. Next, a film made of polyvinylidene chloride having a size to cover the material plate was placed on both sides of the material plate, and the material plate was press-molded with a press load of 50 tons by the method shown in FIG. 1 to obtain a separator. . As shown in Table 3, the thickness of the film was set to 14 types in the range of 0.001 to 0.7 mm, and 14 types of separators having different film thickness were obtained.

[0018]

[Table 2]

[0019]

[Table 3]

[Embodiment 2] The same as Embodiment 1 except that the method shown in FIG. 2, that is, the method of sandwiching two films between a die and a material plate is used. 14 types of separators according to Example 2 were obtained. The thickness of the film in this case is the total thickness of the two stacked films.

[Embodiment 3] A method shown in FIG. 3, that is, a proper amount of a lubricant is applied to both surfaces between a die and a material plate 1
Except for adopting the method of sandwiching a sheet of film,
In the same manner as in Example 1, 14 types of separators according to Example 3 were obtained. The lubricant is lubricating oil (MOLYKOT
ED-321R: manufactured by Dow Corning) was used.

[Embodiment 4] Other than adopting the method shown in FIG. 4, that is, the method of forming by sandwiching two films having the same lubricant as described above between the mold and the material plate. In the same manner as in Example 1, 14 types of separators according to Example 4 were obtained. An appropriate amount of the lubricant was applied to one surface of one film, and the other film was superposed on the surface to which the lubricant was applied.

Comparative Example A separator of a comparative example was obtained in the same manner as in Example 1 except that the film was not directly sandwiched between the mold and the material plate but was directly press-molded.

FIG. 5 shows the overall plane of the separator molded by the above-mentioned examples and comparative examples. Also,
FIG. 6 shows a partial cross section and a design dimension of the concavo-convex shaped portion of the separator.

B. Measurement of drop-out rate of conductive inclusions For each separator manufactured as described above, 10 mm by including a part where the conductive inclusions are likely to drop off by press molding (a part that is bent or stretched by press molding). It was obtained by cutting out a test piece of × 20 mm by a wire cutting method. 20 these test pieces
It was embedded in a cylindrical thermosetting phenolic resin having a diameter of 30 mm by a hydraulic automatic resin embedding machine so that the mm cross section became the observation surface. The observation surface of this test piece was polished in order of roughness # 600 and # 1000 using a water resistant polishing paper. Next, the observation surface of the test piece was buffed by using diamond paste in the order of 3 μm and 0.25 μm to finish it into a mirror surface. The observation surface of this test piece was imaged with an inverted metallurgical microscope at a magnification of 400 times, and from the obtained photograph, the number (a) of conductive inclusions protruding from the base material and the conductive inclusions from the base material. The number of holes (b) formed by falling off was measured. And
The measurement was carried out until a + b reached 1000, and the numerical values of a and b were applied to the following equation (2) to obtain the falling rate of the conductive inclusions. Dropout rate (%) = {b / (a + b)} × 100 (2)

The results of the above measurements are shown in Table 3 together with graphs in FIGS. The dropout rate of the separator of the comparative example was 88%, and the data is shown in FIGS. 7 to 10.

As shown in FIGS. 7 and 8, in Examples 1 and 2, the film thickness (total thickness)
Is 0.01 mm or more, the dropping rate of the conductive inclusions is significantly reduced and stable. However, when the thickness of the film exceeds 0.5 mm, the separator has defective molding. Therefore, in the methods of Example 1 and Example 2, if the polyvinylidene chloride film having a thickness of 0.01 to 0.5 mm is applied, the effect of suppressing the dropping of the conductive inclusions can be remarkably obtained. I understood.

As shown in FIGS. 9 and 10, Example 3 is used.
Further, regarding Example 4, when the film thickness (total thickness) is 0.006 mm or more, the falling rate of the conductive inclusions is remarkably low and stable. However, when the thickness of the film exceeds 0.2 mm, the separator has a defective molding. Therefore, Example 3
And in the method of Example 4, the thickness is 0.006 to 0.2.
It was found that the use of a polyvinylidene chloride film having a thickness of 10 mm can remarkably obtain the effect of suppressing the falling of the conductive inclusions.

[0029]

As described above, according to the present invention,
Since a polymer film that reduces friction is sandwiched between the mold and the material plate of the separator and press-molding is performed, it is possible to prevent the conductive inclusions from falling off and produce a sound separator.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing processes of a manufacturing method according to a first embodiment of the present invention in the order of (a) and (b).

FIG. 2 is a cross-sectional view showing the process of the manufacturing method according to the second embodiment of the present invention in the order of (a) and (b).

FIG. 3 is a sectional view showing a process of the manufacturing method according to the third embodiment of the present invention in the order of (a) and (b).

FIG. 4 is a cross-sectional view showing the process of the manufacturing method according to the fourth embodiment of the present invention in the order of (a) and (b).

FIG. 5 is a photograph showing a plane of a separator manufactured in an example of the present invention.

FIG. 6 is a cross-sectional view of a concavo-convex molded portion of a separator manufactured in an example of the present invention.

FIG. 7 is a diagram showing the relationship between the film thickness and the falling rate of conductive inclusions in Example 1 of the present invention.

FIG. 8 is a graph showing the relationship between the film thickness and the falling rate of conductive inclusions in Example 2 of the present invention.

FIG. 9 is a diagram showing the relationship between the film thickness and the falling rate of conductive inclusions in Example 3 of the present invention.

FIG. 10 is a graph showing the relationship between the film thickness and the falling rate of conductive inclusions in Example 4 of the present invention.

[Explanation of sign]

1a, 1b ... Mold 10 ... Material plate 10A ... separator 20 ... film 30 ... Lubricant

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Makoto Tsuji             1-4-1 Chuo Stock Market, Wako City, Saitama Prefecture             Inside Honda Research Laboratory F-term (reference) 5H026 AA06 BB02 CC03 EE02

Claims (4)

[Claims] 1. When a metal separator for a fuel cell having a conductive inclusion in a metal structure is manufactured by press molding, a polymer film is sandwiched between a press mold and a separator material plate. A method for producing a metal separator for a fuel cell, comprising: 2. The method for producing a metallic separator for a fuel cell according to claim 1, wherein the film is a plurality of sheets. 3. The method for producing a metallic separator for a fuel cell according to claim 1, wherein a lubricant is attached to one side or both sides of the film. 4. The method for producing a metallic separator for a fuel cell according to claim 1, wherein the material of the film is polyvinylidene chloride.