JP2005235699A - Fuel cell separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell separator capable of adjusting the electrical conductivity in the thickness direction within an appropriate range while maintaining mechanical characteristics.
SOLUTION: Concave and convex portions 5 are arranged on the front and back surfaces by a molding material 1, and the molding material 1 is prepared by at least a resin 2 and a large number of conductive fillers 3, and most of the conductive fillers 3 are electrically conductive. The filler 3 is oriented in a direction intersecting with the arrangement direction of the uneven portions 5. Then, the arrangement pitch of the uneven portions 5 on the front surface and the uneven portions 5 on the back surface is shifted by 1 pitch. Since the XY plane of most of the conductive fillers 3 is forcibly oriented in the direction intersecting with the arrangement direction of the concavo-convex portions 5, the number of contacts in the thickness direction of the conductive fillers 3 in the resin is reduced. And volume resistivity can be increased or decreased.
[Selection] Figure 1

Description

  The present invention relates to a polymer electrolyte fuel cell separator constituting a fuel cell.

  As shown in FIG. 7, a conventional fuel cell separator is pressed or injection-molded into a plate shape with a predetermined molding material, and uneven portions 5 forming flow paths on both front and back surfaces are arranged at the same pitch. A fuel cell is formed by stacking sheets (see Patent Documents 1 and 2). The predetermined molding material is prepared, for example, by mixing a phenol resin and graphite.

By the way, the separator for fuel cells generally has a value in which the conductivity in the thickness direction (also referred to as the layer direction) and the surface direction are greatly different, and there is a tendency that the conductivity in the thickness direction cannot be sufficiently secured.
In view of this point, conventionally, methods have been proposed for increasing the amount of graphite in the molding material, increasing the graphite, or changing the aspect ratio of the graphite (Patent Document). 3 and 4).
JP-A-10-334927 JP 2003-282026 A JP 2002-100378 A JP 2001-143719 A

The conventional fuel cell separator is configured as described above, and in order to ensure conductivity in the thickness direction, the amount of graphite is increased, the graphite is increased, or the aspect ratio of graphite is changed. Yes.
However, when such a method is adopted, although the conductivity in the thickness direction can be ensured to some extent, the mechanical properties are deteriorated, such as the bending strength is reduced or the strain amount when cracking is reduced. A big problem will arise.

  The present invention has been made in view of the above, and an object thereof is to provide a fuel cell separator capable of adjusting the electrical conductivity in the thickness direction to an appropriate range while maintaining mechanical characteristics.

In the present invention, in order to solve the above-mentioned problem, it is molded with a molding material, and uneven portions are arranged on the front and back surfaces,
The molding material is prepared with at least a resin and a plurality of conductive fillers, and among the plurality of conductive fillers, at least a part of the conductive filler is oriented in a direction crossing the arrangement direction of the concavo-convex parts, The feature is that the arrangement pitch of the uneven portions is shifted.
Note that the resin of the molding material can be a curable resin, the conductive filler can be graphite, and the XY plane can be oriented in a direction crossing the arrangement direction of the concavo-convex portions.

  Here, the molding material in the claims may be blended at least from a resin and a plurality of conductive fillers, and the resin and the plurality of conductive fillers may be blended without being kneaded. preferable. This molding material may contain other materials including a fluororesin, a fluorine-based compound, a coupling agent, a modifier, a filler, and the like.

  The resin includes any of thermoplastic resins, curable resins, and natural / synthetic rubbers, and may or may not be coated with a conductive filler. The conductive filler is preferably formed in a substantially piece-like shape that can be displayed by the XYZ display method, and the XY aspect ratio is preferably in the range of 2 to 100.

  The plurality of conductive fillers only need to be directed in a direction in which at least a part thereof intersects the arrangement direction of the concavo-convex portions, or may be directed to all or most of the conductive fillers. Some of the conductive fillers are preferably oriented so as to intersect with the arrangement direction of the uneven portions at an angle of 30 ° or more.

  The shift in the arrangement pitch may be one pitch, half pitch, or the like. Furthermore, the fuel cell separator according to the present invention can be formed into a rectangular shape, a square shape, a polygonal shape or the like in a plan view, and may be partially thinned or thickened.

According to the present invention, since at least a part of the conductive filler is not directed in the arrangement direction of the concavo-convex portions, but is directed in a direction intersecting with the arrangement direction of the concavo-convex portions, the plurality of conductive fillers forming the conductive path in the thickness direction The number, the number of contacts, and the site can be reduced.
In addition, since the arrangement pitch of the concavo-convex portions on the surface of the fuel cell separator and the concavo-convex portions on the back surface is shifted, the flow of the conductive filler during molding is adjusted, thereby improving the degree of orientation and improving the conductivity in the thickness direction. be able to.

  According to the present invention, it is possible to maintain the mechanical characteristics and adjust the conductivity in the thickness direction within an appropriate range.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In the fuel cell separator according to the present embodiment, as shown in FIGS. The sheet material is formed in a substantially sheet pile shape, and the molding material 1 is prepared by at least the resin 2 and a large number of conductive fillers 3, and the majority of the conductive fillers 3 among the large number of conductive fillers 3 are prepared. It is oriented in a direction intersecting with the arrangement direction of the concavo-convex portions 5, and the arrangement pitch of the concavo-convex portions 5 on the front surface and the concavo-convex portions 5 on the back surface is shifted.

  The molding material 1 is prepared from at least a resin 2 and a large number of conductive fillers 3, and these are used by mixing with a mixer or the like. The molding material 1 includes calcium carbonate, talc, kaolin, diatomaceous earth, silica, bentonite, zeolite, mica, aluminum hydroxide, titanium oxide, activated carbon, charcoal, glass fiber, aramid fiber, etc., as long as the characteristics are not lost. Add as appropriate.

  The blending of the resin 2 and the many conductive fillers 3 is 100 to 2,000 parts by weight of the conductive filler with respect to 100 parts by weight of the resin, preferably 200 to 1,500 parts by weight of the conductive filler with respect to 100 parts by weight of the resin. Is preferably 300 to 1,000 parts by mass of the conductive filler with respect to 100 parts by mass of the resin. This is because if the amount of the conductive filler is less than 100 parts by mass with respect to 100 parts by mass of the resin, the electrical characteristics of the fuel cell separator are hindered. On the contrary, when the amount exceeds 2,000 parts by mass of the conductive filler, it is difficult for the airtightness (gas permeability) and mechanical characteristics of the fuel cell separator.

  As the resin 2, for example, a thermoplastic resin made of PPS or PP, a curable resin made of powdered phenol resin or epoxy resin, or a synthetic rubber made of EPDM, chloroprene, or the like is selectively used. Among these, powder phenolic resin that is easy to adjust the contact angle with water, water resistance, dimensional stability, and mechanical strength is suitable, and more preferably a phenol / formaldehyde resin with a slow curing reaction. Is good.

  The phenol resin used for the resin 2 has 10 or less, preferably 5 or less methylol groups in one molecule. This is because when the number of methylol groups exceeds 10 in one molecule, the water generated during curing tends to cause voids and blisters in the fuel cell separator, which adversely affects mechanical properties and dimensional accuracy. Because.

  The particles of the resin 2 are preferably finer in view of dispersion. Specifically, the average particle size is 1 to 35 μm, preferably 3 to 20 μm. The average molecular weight of the resin 2 is in the range of 3,000 to 20,000, preferably 4,000 to 15,000, more preferably 5,000 to 10,000. This is because when the average molecular weight of the resin 2 is less than 3,000, high filling of the conductive filler 3 becomes difficult, and the surface coating of the conductive filler 3 increases as the melting temperature decreases, and the fuel cell This is based on the reason that the electrical properties of the separator for use deteriorate.

  A large number of conductive fillers 3 are made of, for example, graphite, metal fibers, carbon fibers, and the like, and most of them are in point contact with each other to form a conductive path in the thickness direction. As the conductive filler 3, scaly graphite can be used from the viewpoint of easily adjusting the contact angle with water, reducing the resistance value by contacting each other, and preventing the mechanical strength from decreasing. Preferred (see FIG. 3). This is based on the reason that, for example, if spherical graphite is used, the blending amount must be increased in order to bring the graphites into contact with each other, and the physical properties of the fuel cell separator that is a molded product are reduced.

  As shown in FIG. 3, the conductive filler 3 is formed in a scale-like shape that can be displayed by the XYZ display method, and the aspect ratio of XY is preferably set in the range of 2 to 100, more preferably in the range of 10 to 50. The XY plane 4 displayed by XY is oriented in a direction intersecting with the arrangement direction of the concavo-convex portions 5 (see FIGS. 1 and 2). The reason for the aspect ratio is that when the aspect ratio is less than 2, it is difficult to obtain a sufficient alignment effect. Conversely, when the aspect ratio exceeds 100, it is difficult to obtain a sufficient blend with the resin 2.

  The scale-like graphite as the conductive filler 3 has an average particle size of 5 to 150 μm, preferably 10 to 100 μm. This is because if the average particle size is less than 5 μm, it rises when blended with the resin 2 and the working environment is deteriorated or the electrical characteristics are deteriorated. Conversely, when the average particle size exceeds 150 μm, the mechanical characteristics of the fuel cell separator deteriorate.

Although it does not specifically limit about the bulk density of scale-like graphite, The range of 0.1-1.0 g / cm < ³ > is suitable. This is based on the reason that when the bulk density of graphite is too small, the sealing characteristics of the fuel cell separator deteriorate. Conversely, when the bulk density of graphite is too large, it is based on the reason that the mechanical strength and conductivity of the fuel cell separator are lowered.

As shown in FIG. 1, the fuel cell separator has an uneven surface portion 5 serving as a flow path for gas and cooling water on both the front and back surfaces, which are exposed surfaces, and a density (specific gravity) of 1.9 g / cm ³ or more. The fuel cell is formed by stacking a plurality of layers via an electrolyte membrane, a fuel electrode, an air electrode, and the like.

  The uneven portion 5 on the front surface and the uneven portion 5 on the back surface of the fuel cell separator are arranged side by side in the arrangement direction so that the centers are shifted from each other. The concavo-convex portion 5 includes a concave portion 6 having a substantially inverted trapezoidal cross section that is recessed in the thickness direction and allows hydrogen gas, oxygen gas, and cooling water to flow therethrough, and a convex portion 7 having a substantially trapezoidal cross section adjacent to the concave portion 6. 6 and the convex part 7 are arranged in multiple numbers by turns.

The density of the fuel cell separator is generally set to 1.9 g / cm ³ or more, preferably 1.95 g / cm ³ or more, although it depends on the blending ratio of the resin 2 and the conductive filler 3 (graphite). This is because if the density is 1.9 g / cm ³ or more, sufficient gas impermeability and water repellent effect can be obtained.

  In the above, when manufacturing a separator for a fuel cell, first, at least the resin 2 and a large number of conductive fillers 3 are mixed without kneading to prepare a molding material 1, and this molding material 1 is shown in FIG. The preform 10 is filled and the intermediate is compression molded. At this time, the resin 2 made of a phenol resin flows to fill the gaps between the conductive fillers 3, and most of the conductive fillers 3 made of scaly graphite are in a direction orthogonal to the compression direction along with compression during compression molding, That is, it is oriented substantially parallel to the compression surface.

  When the intermediate body is compression-molded in this way, this intermediate body is set in a main molding die 11 shown in FIG. 5 and subjected to hot press molding, and a shearing force is applied to the intermediate body so that most of the conductive filler 3 is moved in the thickness direction. A fuel cell separator can be manufactured by aligning and arranging the concavo-convex portions 5 on both the front and back surfaces of the fuel cell separator.

  According to the above configuration, the XY surface 4 of most of the conductive fillers 3 is not oriented naturally in the direction intersecting with the arrangement direction (surface direction) of the concavo-convex portions 5, but is consciously and forcibly oriented in the resin 2. The number of contacts in the thickness direction of the conductive filler 3 is reduced, so that the conductivity and volume resistance in the thickness direction can be increased without increasing the graphite filling amount, increasing the graphite size, or changing the aspect ratio of the graphite. The rate can be increased or decreased. Therefore, it becomes easy to adjust the electrical conductivity and volume resistivity in the thickness direction within a predetermined range.

  In addition, since it is possible to easily improve the conductivity in the thickness direction and decrease the volume resistivity, the conductivity can be improved by appropriately changing the composition of the resin 2 and the many conductive fillers 3 so as not to impair the practicality. In addition to securing the properties, it is possible to maintain and improve the bending strength and the amount of strain when cracking. That is, it is possible to achieve both conductivity and strength.

  In addition, the fuel cell separator has a substantially sheet-like shape, and the arrangement pitch of the uneven portion 5 on the front surface and the uneven portion 5 on the back surface is shifted by 1 pitch in the arrangement direction, thereby suppressing irregular flows such as backflow of the conductive filler 3 during molding. In addition, the conductivity in the thickness direction can be significantly improved through the improvement of the degree of orientation. Furthermore, since the change in the cross-sectional shape (between the concave portion 6 and the convex portion 7) can be reduced as compared with the conventional fuel cell separator shown in FIG. 7, the molding operation can be facilitated or an unnecessary skin layer is generated. Therefore, it is possible to significantly reduce the variation in micro characteristics.

Examples of the fuel cell separator according to the present invention will be described below together with comparative examples.
Example First, a molding material having a mass ratio of the powdery phenol resin 10 to the scaly graphite particles 50 was prepared. The graphite particles have an average particle size of 50 μm and an aspect ratio of 20-30. Further, the phenol resin is composed of a phenol / formaldehyde powder described in Japanese Patent Publication No. 62-30211, and has an average particle size of 30 μm, a melting temperature of 100 ° C., a viscosity of 16000 Pa · s, and a viscosity of 2000 Pa · s at 120 ° C. .

Next, 90 g of the adjusted molding material was filled in the preforming mold shown in FIG. 4, and the intermediate was compression molded under the conditions of 120 ° C. and 100 kg / cm ² . During molding, the phenol resin flowed to fill the gaps between the graphite particles, and the graphite particles were oriented in parallel with the compression surface as the compression was performed during compression molding.

After the intermediate body is compression molded in this way, the intermediate body is set in the main mold shown in FIG. 5 and subjected to hot press molding at 190 ° C. and 150 kg / cm ² for 5 minutes. A sheet pile separator for a fuel cell was manufactured (see FIG. 5).
The fuel cell separator was 150 mm × 150 mm × 2 mm in size. The recesses of the fuel cell separator had a groove pitch of 2 mm, a groove width of 1 mm, a drop gradient of 10 °, and a groove depth of 0.7 mm.

Comparative Example 90 g of the same molding material as in the example was filled in a preforming mold, and the intermediate was compression molded under the conditions of 120 ° C. and 100 kg / cm ² . Once the intermediate is compression-molded, this intermediate is set in a main mold and subjected to hot press molding at 190 ° C. and 150 kg / cm ² for 5 minutes. A separator was manufactured (see FIG. 7).
The dimensions of the fuel cell separator and its recess were the same as in the example.

Evaluation of Fuel Cell Separator After manufacturing fuel cell separators in Examples and Comparative Examples, 50 mm × 50 mm was cut out from the groove forming portion, and the conductivity in the surface direction of each fuel cell separator was determined in accordance with JIS-K7194. The resistivity was measured using a resistivity meter [Loresta GP manufactured by Diains, Inc., MCP-T600 type, the probe was a series 4 probe (ASP)].
When measuring in the thickness direction, a fuel cell separator was sandwiched between a pair of gold-plated copper electrodes shown in FIG. 6 and pressurized under the conditions of 10 kg / cm ^2. The results are summarized in Table 1.

  Unlike the comparative example, the separator for the fuel cell of the example can adjust the conductivity in the thickness direction and the volume resistivity within a predetermined range, and can achieve the balance between the conductivity and the strength in the thickness direction. It was confirmed that the conductivity could be improved.

It is a partial cross section explanatory view showing an embodiment of a separator for fuel cells concerning the present invention. It is a principal part enlarged explanatory view which expands and shows the II section of FIG. It is a model perspective view showing the conductive filler in the embodiment of the separator for fuel cells concerning the present invention. It is explanatory drawing which shows the preforming die in embodiment of the separator for fuel cells which concerns on this invention. It is explanatory drawing which shows the main mold and intermediate body in embodiment of the separator for fuel cells which concerns on this invention. It is explanatory drawing which shows the evaluation state of the separator for fuel cells in the Example of the separator for fuel cells which concerns on this invention. It is explanatory drawing which shows the conventional separator for fuel cells.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molding material 2 Resin 3 Conductive filler 4 XY surface 5 Concave part 6 Concave part 7 Convex part

Claims (2)

A fuel cell separator that is molded from a molding material and has uneven portions arranged on the front and back surfaces,
The molding material is prepared with at least a resin and a plurality of conductive fillers, and among the plurality of conductive fillers, at least a part of the conductive filler is oriented in a direction crossing the arrangement direction of the concavo-convex parts, A separator for a fuel cell, wherein the arrangement pitch of the uneven portions is shifted. The fuel cell separator according to claim 1, wherein the molding material resin is a curable resin, the conductive filler is graphite, and the XY plane is oriented in a direction crossing the arrangement direction of the concavo-convex portions.

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