JP2011086635A - Separator for fuel cell and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide separators for a fuel cell effective for performance improvement of the fuel cell and superior in gas leakage proofness, and their manufacturing method. <P>SOLUTION: In the separators for a fuel cell of a unit cell to constitute the fuel cell, a surface roughness of sealing parts of the separators for the fuel cell formed of a resin composition containing synthetic resin and a conductive filler in the case of being masked and sealed is made within a range of Ra=0.2 to 0.8 μm at values measured by a surface roughness meter of a probe-tip diameter of 5 μm, Ry of the sealing parts is made within a range of Ry=2 to 9 μm, and RSm of the sealing parts is made within a range of RSm=60 to 150 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell separator and a method for producing the same.

  In recent years, global warming caused by carbon dioxide emitted by burning fossil fuels such as oil and coal has been taken up as an environmental problem. Under such circumstances, an energy saving effect can be expected, and a fuel cell is attracting attention as a clean power generation system, and its practical application is being studied in various fields.

  FIG. 1 is a perspective view schematically illustrating the basic structure of a fuel cell. According to this figure, a fuel electrode (negative electrode) 21 and an air electrode (positive electrode) 22 are sandwiched between electrolytes 3. The fuel cell separator 1 having a plurality of convex portions 4 formed on both side surfaces is disposed on both sides of the electrode 2 to constitute a unit cell A (unit cell).

  The protrusion 4 constitutes a gas supply / discharge groove 5 which is a flow path of hydrogen and oxygen as fuel between adjacent protrusions 4. The gas supply / discharge groove 5 has a function of separating hydrogen, oxygen and cooling water flowing in the fuel cell so as not to be mixed, and transmits electric energy generated by the unit cell A of the fuel cell to the outside. It plays an important role of radiating the heat generated in the cell A to the outside.

  Further, although not shown, the groove 5 and the outer peripheral area of the surface in contact with the electrode 2 are sealed with a mask to prevent gas leakage.

  Then, several tens to several hundreds of the unit cells A are stacked to form a battery body (cell stack). In this unit cell A, hydrogen is supplied to the fuel electrode 21 and oxygen is supplied to the air electrode 22 of the pair of electrodes 2 facing each other through the electrolyte 3, and is directly converted into electric energy by an electrochemical reaction between hydrogen and oxygen. Is done.

  That is, the hydrogen is separated into electrons by the action of the catalyst in the fuel electrode 21, and the hydrogen ions move in the electrolyte 3. Hydrogen ions react with oxygen supplied to the air electrode 22 which is the opposite electrode 2 and electrons returned through an external circuit to become water. Electricity is generated when electrons move through the external circuit.

  The electrolyte 3 includes potassium hydroxide, phosphoric acid, a polymer membrane, and the like, and the fuel cell is classified into an alkaline type, a phosphoric acid type, and a solid polymer type depending on the type.

  Among these, the polymer electrolyte fuel cell, in particular, has an operating temperature as low as about room temperature to about 120 ° C. and can be miniaturized, and therefore is expected to be applied to applications such as home use and automobiles.

  In such a fuel cell, the fuel cell separator 1 includes, for example, a thermosetting resin such as phenol resin or epoxy resin, or a thermoplastic resin such as polypropylene or polyvinylidene fluoride as a binder, and graphite particles or the like as a conductive filler. The resin composition to be contained can be manufactured by compression molding or injection molding so that a plurality of convex portions 4 are formed on both side surfaces thereof as shown in FIG.

  By the way, the fuel cell separator 1 manufactured as described above has a problem that a resin layer called a skin layer is formed on the surface of the separator at the time of molding and the electric resistance becomes high.

In the fuel cell described above, when the resistance of the contact portion between the fuel cell separator 1 and the electrode 2 is large, the output decreases. Therefore, it is desired to reduce the contact resistance. Specifically, the contact resistance between the fuel cell separator 1 and the electrode 2 is required to be less than 10 mΩ · cm ² .

  In the past, various fuel cell separators 1 have been proposed in which the contact surface of the fuel cell separator 1 with the electrode 2 has a predetermined surface roughness in order to reduce the contact resistance (for example, Patent Document 1). ~ 5).

  Conventionally, as a measure to effectively prevent gas leakage (leakage) in the separator for the fuel cell in order to prevent the safety and output efficiency of the fuel cell from being impaired even when sealing with a mask. In addition, it has also been proposed that the surface roughness of the seal portion is predetermined (Patent Documents 6 to 8).

Japanese Patent No. 3504910 JP 2004-6432 A Japanese Patent Laid-Open No. 11-297338 JP 2002-270203 A JP 2003-132913 A JP 2003-132913 A JP 2004-63256 A JP 2003-68317 A

  However, conventionally, the fuel cell separator has been studied for preventing gas leakage, but its effect is still not fully satisfactory, and further improvement of the performance of the fuel cell is desired. The fact is.

  Accordingly, the inventors of the present application have made extensive studies focusing on the surface roughness of the fuel cell separator, and in order to improve the performance of the fuel cell, the surface of the seal portion of the fuel cell separator when sealing with a mask. It was found that gas leakage can be more effectively prevented by adjusting the roughness to a specific range.

  The present invention has been made from the background described above, and it is an object of the present invention to provide a separator for a fuel cell that is effective in improving the performance of the fuel cell and has excellent gas leakage prevention properties, and a method for manufacturing the same.

  The present invention is characterized by the following in order to solve the above-mentioned problems.

  That is, in a separator for a fuel cell of a unit cell constituting a fuel cell, a separator for a fuel cell formed of a resin composition containing a synthetic resin and a conductive filler is used when masked and sealed. Surface roughness measured with a surface roughness meter with a probe tip diameter of 5 μm, Ra = 0.2 to 0.8 μm, Ry of the seal portion measured with a surface roughness meter with a probe tip diameter of 5 μm In the range of Ry = 2 to 9 μm, the RSm of the seal portion is a value measured with a surface roughness meter having a probe tip diameter of 5 μm and RSm = 60 to 150 μm.

  The conductive filler is natural graphite.

  A method of manufacturing a separator for a fuel cell of a unit cell constituting a fuel cell, in which a resin composition containing a synthetic resin and a conductive filler is molded with a mold, masked and sealed The surface roughness of the seal part of the separator for the probe is within the range of Ra = 0.2 to 0.8 μm as measured by a surface roughness meter having a probe tip diameter of 5 μm, and the surface roughness of the seal part is Ry of 5 μm. Adjust so that Ry = 2 to 9 μm in the measured value with the gauge, and RSm of the seal part is in the range of RSm = 60 to 150 μm with the measured value with the surface roughness meter with the probe tip diameter of 5 μm. .

  Further, after forming with a mold, adjustment is performed by blasting.

  And the alumina of the particle size # 500-800 range is used as a blasting abrasive grain.

  According to the present invention, since the surface roughness of the seal portion when sealing by masking is in a specific range of Ra = 0.2 to 0.8 μm, gas leakage at the seal portion is effectively performed. Will be deterred.

  Moreover, the effect of preventing gas leakage is further ensured by setting Ry of the seal portion in a specific range of 2 to 9 μm and RSm of the seal portion in a specific range of 60 to 150 μm.

It is the perspective view which illustrated typically the basic structure (unit cell) of the fuel cell. In an Example, it is the figure which illustrated typically the measuring method of the contact resistance I. FIG. In an Example, it is the figure which illustrated typically the measuring method of contact resistance II.

  The present invention has the above-described features, and the best mode for carrying out the invention will be described below.

  The fuel cell separator 1 of the present invention is formed of a resin composition containing a synthetic resin and a conductive filler in a unit cell A constituting a fuel cell as shown in FIG. The skin layer formed on the surface of the contact portion and the contact portion of the adjacent unit cell A with the fuel cell separator 1 is removed, and the surface roughness meter of the contact portion has a surface roughness of 5 μm. It is preferable that Ra is 0.9 to 1.8 μm as measured by (“Ra” represents arithmetic average roughness (JIS B 0601-2001)).

  Here, since the skin layer formed on the surface is an insulating layer, the contact resistance is reduced by removing the skin layer. Furthermore, contact resistance is reduced by setting the contact portion with the electrode 2 and the contact portion with the fuel cell separator 1 of the adjacent unit cell A to have a predetermined surface roughness as described above.

  That is, these contact portions are formed with irregularities on the surface so as to have a predetermined surface roughness, and the fuel cell separator 1 of the unit cell A between the fuel cell separator 1 and the electrode 2 and adjacent to the fuel cell separator 1. The contact resistance is reduced by increasing the contact portion between them.

  In such a contact portion having a predetermined surface roughness, since the electrode 2 is generally flexible, the contact portion between the fuel cell separator 1 and the electrode 2 tends to increase, and the contact resistance can be greatly reduced. it can. Moreover, between the fuel cell separator 1 and the fuel cell separator 1 of the unit cell A adjacent to each other, the unevenness formed on the surface of each contact portion is effectively meshed, and the contact portion is increased to reduce the contact resistance. .

Specifically, by using the fuel cell separator 1 configured as described above, the contact resistance with the electrode 2 is less than 10 mΩ · cm ² and the contact resistance with the fuel cell separator 1 of the adjacent unit cell A. Is reduced to less than 15 mΩ · cm ² .

  As for the surface roughness of the contact portion, when Ra is less than 0.9 μm, the contact portion is reduced due to the slight warpage and thickness accuracy of the fuel cell separator 1, so the contact resistance cannot be reduced. .

  In the case of exceeding 1.8 μm, the contact portion with the electrode 2 and the contact portion with the fuel cell separator 1 of the adjacent unit cell A are reduced, so that the contact resistance cannot be reduced. In particular, in the contact portion of the adjacent unit cell A with the fuel cell separator 1, the unevenness formed on the surface of the mutual contact portion is not effectively engaged, and the contact portion is reduced.

  Further, in the fuel cell separator 1 of the present invention, in order to further reduce the contact resistance, the average length of the curved elements of the contact portion with the electrode 2 and the contact portion with the fuel cell separator 1 of the adjacent unit cell A is reduced. However, it is preferable that RSm = 110 to 200 μm as measured with a surface roughness meter having a probe tip diameter of 5 μm. ("RSm" represents the average length of curve elements (JIS B 0601-2001).)

  When RSm is less than 110 μm, the slight warpage and thickness accuracy of the fuel cell separator 1 may affect the contact portion, which is not preferable. When RSm exceeds 200 μm, the contact portion between the adjacent unit cell A and the fuel cell separator 1 may decrease, which is not preferable.

  Further, in the present invention, the contact portion with the electrode and the contact portion with the fuel cell separator of the adjacent unit cell are in the range of Ry = 5 to 15 μm. When Ry is in this range, contact during stacking is hardly inhibited.

  When Ry is less than 5 μm, slight warpage of the resin molded product for the separator decreases the contact area, and when Ry exceeds 15 μm, the above-mentioned convex portion is likely to inhibit contact, It is not preferable.

  And in the fuel cell separator of the present invention, from the viewpoint of suppressing gas leakage along with the surface roughness of the contact portion for reducing the contact resistance as described above, as described above, For example, the surface roughness of the seal portion when sealing with a 1 mm-thick stainless steel plate (not particularly limited) masked as a jig can be measured with a similar surface roughness meter with a probe tip diameter of 5 μm. It is extremely effective to set Ra = 0.2 to 0.8 μm in the measured value.

  If Ra in this case exceeds 0.8 μm, the effect of preventing gas leakage is not so great that it is not satisfactory in practice. On the other hand, if the thickness is less than 0.2 μm, the load of the process and means for realizing this will increase, and the effect of preventing gas leakage will not be further increased.

  Moreover, the gas leak effect becomes more reliable by making Ry of a seal part into 2-9 micrometers and RSm = 60-150 micrometers.

  And the separator 1 for fuel cells of this invention is formed from the resin composition containing a synthetic resin and an electroconductive filler as mentioned above.

  Synthetic resins include epoxy resins, phenol resins, polyimide resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins and other thermosetting resins, polyphenylene sulfide resins, polyphenylene ether resins, polysulfone resins, polyamide resins, Examples thereof include thermoplastic resins such as acrylic resins, polystyrene resins, and polycarbonate resins.

  Conductive fillers include graphitized carbonaceous materials such as mesocarbon microbeads, graphitized coal-based coke and petroleum-based coke, processed powders of graphite electrodes and special carbon materials, natural graphite, quiche graphite, Examples thereof include graphite particles such as expanded graphite, and only one kind may be used or a plurality of kinds may be mixed and used. As this average particle diameter, it is generally considered to use a particle having a range of 10 to 200 μm in order to obtain high conductivity.

  For the conductive filler as described above of the present invention, natural graphite is considered particularly suitable. This is due to the fact that natural graphite has high crystallinity, lowers the contact resistance value, has lower hardness than artificial graphite, and the contact area is hardly affected by surface roughness.

  The blending ratio of the synthetic resin and the conductive filler in this resin composition is, for example, 5 to 100 parts by weight of the synthetic resin with respect to 100 parts by weight of the conductive filler in consideration of the strength and conductivity of the fuel cell separator. It is preferable to mix | blend in the range.

  And the resin composition as mentioned above is mix | blended by a suitable method, and is obtained by kneading | mixing as needed. A normal kneader can be used for the kneading, and examples thereof include a kneader, a mixer, and a ball mill.

  Using the resin composition thus obtained, for example, as shown in FIG. 1, the final shape is formed with a plurality of convex portions 4 on both side surfaces thereof, and gas supply / discharge between adjacent convex portions 4 is performed. It molds with a metal mold | die so that it may become the fuel cell separator 1 which comprises the groove 5 for use. The molding method is not particularly limited, and generally used methods such as compression molding, injection molding and transfer molding are considered.

  In any of these methods, it is effective to control the surface roughness of the mold when molding the resin molded product for the separator of the present invention. For example, from the viewpoint of the effect of preventing gas leakage at the seal portion, it is preferably considered that the surface roughness of the mold is Ra = 0.2 to 0.8 μm.

  And after this invention shape | molds with a metal mold | die, while removing the skin layer formed in the surface of the contact part of this molded article and an electrode, and the contact part of the separator for fuel cells of an adjacent unit cell, these More preferably, the average length of the curved elements of the contact portion is such that Ra = 0.9 to 1.8 μm as measured by a surface roughness meter having a probe tip diameter of 5 μm. Then, it is roughened so that RSm = 110 to 200 μm as measured by a surface roughness meter with a probe tip diameter of 5 μm. Thereby, the contact resistance can be reduced, and the fuel cell separator 1 capable of improving the performance of the fuel cell can be easily manufactured.

  The method of removing the skin layer or roughening the contact portion is not particularly limited, and examples thereof include a method using YAG laser irradiation, blasting, etching, and grinding (lapping and polishing). In particular, blasting can be automated, and the skin layer can be removed and the surface roughened simultaneously, and the thickness accuracy of the molded product secured by the mold, that is, the precision of the mold. It can be carried out easily in a short time without impairing the thickness accuracy of the molded product formed high.

  Blasting is performed by spraying abrasive particles such as alumina, glass beads, glass powder, etc. with a gun for shot blast beads, and the type, particle size, combination of particle sizes, discharge pressure, and processing. Blasting conditions such as time are appropriately set according to the purpose.

  In the present invention, it is preferable to use alumina having a specific particle size, that is, in the range of particle size # 500 to 800, during blasting. By using this alumina, it is possible to reliably and efficiently produce the fuel cell separator of the present invention.

Hereinafter, examples will be shown and described in more detail. Of course, the present invention is not limited by the following examples.

<Examples 1-4, Comparative Examples 1-5>
After 15% of isopropyl alcohol was sprayed on the compound having the conditions shown in Table 1 and stirred, the mixture was put into a kneader heated to a predetermined temperature. As a kneader, an S2KRC kneader (manufactured by Kurimoto Iron Works) was used.

  Next, the obtained resin composition was pulverized to a particle size of 500 μm or less with a granulator.

なお、表１において、＊１〜＊７は次のものを表す。
＊１ ＥＯＣＮ−１０２０−７５（日本化薬）
＊２ ＰＳＭ４３５７（群栄化学工業）
＊３ トリフェニルホスフィン（四国化成）
＊４ 天然黒鉛：ＷＲ−５０Ａ（中越黒鉛工業所）平均粒径５０μｍ
＊５ Ａ１８７（日本ユニカー）
＊６ Ｆ１−１００（大日化学工業）
＊７ Ｊ−９００（大日化学工業）
上記で得られた粉砕物を、１７５℃、２０ＭＰａで３分間成形し、２ｍｍ厚の１００ｍｍ□平板とした。その平板より５０ｍｍ□を切り出して、接触抵抗を測定するための試験片とした。次いで、この試験片の表面が表２および表３に示す表面粗度（プローブ先端径５μｍの表面粗さ計での測定値）になるように、研磨剤粒子として（粒度＃８００）を用い、処理時間などの加工条件を設定してブラスト加工により仕上げた（ただし、比較例１の試験片はブラスト加工していない）。

In Table 1, * 1 to * 7 represent the following.
* 1 EOCN-1020-75 (Nippon Kayaku)
* 2 PSM4357 (Gunei Chemical Industry)
* 3 Triphenylphosphine (Shikoku Chemicals)
* 4 Natural graphite: WR-50A (Chuetsu Graphite Industry) Average particle size 50 μm
* 5 A187 (Nihon Unicar)
* 6 F1-100 (Daichi Chemical Industry)
* 7 J-900 (Daichi Chemical Industry)
The pulverized product obtained above was molded at 175 ° C. and 20 MPa for 3 minutes to give a 2 mm thick 100 mm square plate. A 50 mm square was cut out from the flat plate to obtain a test piece for measuring contact resistance. Then, using (particle size # 800) as abrasive particles so that the surface of this test piece has the surface roughness shown in Tables 2 and 3 (measured with a surface roughness meter having a probe tip diameter of 5 μm), Processing conditions such as processing time were set and finished by blasting (however, the test piece of Comparative Example 1 was not blasted).

The contact resistance between the fuel cell separator and the electrode was measured in place of the method shown in FIG. 2 (contact resistance I). As shown in FIG. 2, both sides of one of the test pieces prepared above were sandwiched between carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.), and then the conductive block (the aluminum block was plated with gold). The voltage generated between the carbon papers when a current of 1 A was passed under a pressure of 1 MPa was measured, and the contact resistance I was calculated from the following equation. The results are shown in Tables 2 and 3.
Contact resistance (I, II) = measured voltage / current (1A) × contact area The contact resistance between the fuel cell separator and the fuel cell separator of the adjacent unit cell was measured by the method shown in FIG. Contact resistance II). As shown in FIG. 3, two test pieces prepared as described above are sandwiched between conductive blocks, and the voltage generated between the test pieces when a current of 1 A is applied under a pressure of 1 MPa is measured. Contact resistance II was calculated. The results are shown in Tables 2 and 3.

  Further, the He gas leak (leakage) in the seal portion was also measured. The results are shown in Tables 2 and 3. For He gas leak, pressure is applied to a separator molded product (0.2 mm thin hand plate) assuming a 1.5 MPa stack, and the amount of leak (cc / min) due to pressure drop when gas pressure (30 kPa) is applied. Was calculated.

表２および表３より、シール部でのＨｅガスリークの抑止について、シール部表面粗度をＲａ＝０．２〜０．８μｍ、Ｒｙ＝２〜９μｍ、ＲＳｍ＝６０〜１５０μｍとすることによって優れた効果が得られること（実施例１〜４）が確認された。

From Table 2 and Table 3, the suppression of He gas leakage at the seal portion was excellent by setting the surface roughness of the seal portion to Ra = 0.2 to 0.8 μm, Ry = 2 to 9 μm, and RSm = 60 to 150 μm. It was confirmed that an effect was obtained (Examples 1 to 4).

A Unit cell 1 Fuel cell separator 2 Electrode 21 Fuel electrode 22 Air electrode 3 Electrolyte 4 Protrusion 5 Groove for gas supply / discharge

Claims (5)

  In a separator for a fuel cell of a unit cell constituting a fuel cell, a surface roughness of a seal part when sealing with a mask of a separator for a fuel cell formed of a resin composition containing a synthetic resin and a conductive filler. The measured value with a surface roughness meter with a probe tip diameter of 5 μm is within the range of Ra = 0.2 to 0.8 μm, the Ry of the seal part is within the range of Ry = 2 to 9 μm, and the RSm of the seal part is A separator for a fuel cell, wherein RSm = 60 to 150 μm.   The separator for a fuel cell according to claim 1, wherein the conductive filler is natural graphite.   A method of manufacturing a separator for a fuel cell of a unit cell constituting a fuel cell, wherein the separator for a fuel cell is molded with a resin composition mold containing a synthetic resin and a conductive filler, masked and sealed. The surface roughness of the seal portion measured with a surface roughness meter with a probe tip diameter of 5 μm is in the range of Ra = 0.2 to 0.8 μm, the Ry of the seal portion is in the range of Ry = 2 to 9 μm, the seal The method for producing a separator for a fuel cell is characterized in that the RSm of the part is adjusted so as to be within a range of RSm = 60 to 150 μm.   The manufacturing method of the separator for fuel cells of Claim 3 adjusted by blasting after shaping | molding with a metal mold | die.   The method for producing a fuel cell separator according to claim 4, wherein alumina having a particle size in the range of # 500 to 800 is used as the blast abrasive grain.

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