JP2006269313A - Manufacturing method of separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell superior in conductivity, mass-producibility, corrosion resistance, and heat resistance. <P>SOLUTION: A stampable sheet 21 containing a conductive filler and a polymer material is manufactured, the stampable sheet 21 is supplied to a molding machine 33 in which a pair of metal molds 33a in which a fuel cell separator shape is carved in, are added and installed, the stampable sheet 21 supplied to a molding machine is heat-molded in the separator shape, and the separator 31 for the fuel cell is manufactured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell separator, and more particularly to a method of manufacturing a fuel cell separator excellent in conductivity, mass productivity, and corrosion resistance.

A fuel cell configured by stacking a plurality of single cells, particularly a fuel cell separator used in a polymer electrolyte fuel cell, is disposed in contact with each electrode sandwiching a solid electrolyte membrane from both sides, A fuel gas, oxidant gas, and other supply gas passages are formed between the electrodes, and at the same time, in order to establish an electrical connection between the single cells, they have excellent current collecting performance in contact with the electrodes to derive current. Required.

  In general, as a separator for a fuel cell, (1) dense carbon graphite excellent in strength and conductivity, (2) a mixture of conductive carbon material and corrosion-resistant resin, or (3) stainless steel (SUS), titanium, aluminum It is comprised with metal materials, such as.

Usually, a large number of protrusions, grooves, and the like are formed on the surface of the separator that faces the electrodes.
The separator composed of the above (1) dense carbon graphite has high electrical conductivity and high current collecting performance is maintained even after long-term use, but the separator surface is a very brittle material. However, it is not easy to perform machining such as cutting so as to form a large number of protrusions and grooves, and there is a problem that the machining cost is high and mass production is difficult.

  (3) The separator composed of a metal material is superior in strength and ductility as compared with dense carbon graphite, so that a large number of protrusions and grooves are formed to form a gas flow path. There is an advantage that the processing is possible, the processing cost is low, and mass production is easy. However, a metal material has a problem that an oxide film due to corrosion tends to be generated on the surface of the separator in an environment where the separator is used, and the contact resistance between the generated oxide film and the electrode increases, thereby reducing the current collecting performance of the separator. is there.

  Therefore, (2) a separator made of a mixture of a conductive carbon material such as graphite powder and a corrosion-resistant resin (see Patent Document 1 and Patent Document 2) has excellent acid resistance, and a large amount of conductive carbon material relative to the corrosion-resistant resin. By mixing them, the volume resistance of the separator itself can be reduced.

  However, in such a material, since the conductive carbon material is mixed in a large amount, the separator is likely to be brittle, and it is necessary to increase the thickness in order to maintain the strength. There is a problem that it cannot be planned. Furthermore, the corrosion-resistant resin used is a thermosetting resin such as a phenol resin, and it takes a long time to completely cure the resin, so that there is a problem that the productivity is poor.

Japanese Unexamined Patent Publication No. 2000-40517 JP 2000-348740 A

  An object of this invention is to provide the method of manufacturing the separator for fuel cells excellent in electroconductivity, heat resistance, and corrosion resistance with sufficient productivity and mass productivity.

The present invention relates to the following items.
1. A step of manufacturing a stampable sheet containing a conductive filler and a polymer material, a step of supplying the stampable sheet to a molding machine provided with a pair of molds engraved with a fuel cell separator shape, A process for producing a separator for a fuel cell, comprising a step of thermoforming a stampable sheet supplied to a molding machine into a separator shape.
2. The production method according to 1 above, wherein the stampable sheet production step comprises a step of producing a sheet from a suspension containing at least a conductive filler by a paper-making method.
3. The volume ratio of the conductive filler / polymer material in the stampable sheet is in the range of 15/85 to 95/5, and the volume resistance value in the thickness direction at a load of 1.8 MPa is 0.02 to 0.5 Ωcm. 3. The production method according to 1 or 2 above, wherein the production method is a range.
4). The manufacturing method according to any one of the above items 1 to 3, wherein the polymer material is a thermoplastic resin.
5. 5. The production method according to any one of 1 to 4, wherein the conductive filler contains at least one selected from graphite powder, expanded graphite, carbon black, carbon fiber, and carbon nanofiber.
6). 6. The production method according to 5 above, wherein the conductive filler contains at least carbon fiber.

  According to the production method of the present invention, a fuel cell separator excellent in conductivity, heat resistance, and corrosion resistance can be produced with high productivity and mass productivity.

The present invention will be described in detail below.
The stampable sheet formed in the first step of the present invention contains a conductive filler and a polymer material, and has a moldability that can be pressed into a separator shape for a fuel cell by a hot press molding method.
The polymer material used in the present invention is not particularly limited, but a thermoplastic resin that is softened by heating during press molding or preheating thereof is preferably used. For example, polyolefin (PO) resins such as homopolymers or copolymers containing ethylene or polyolefin elastomers, amorphous polyolefin resins (APO) such as cyclic polyolefins, polystyrenes such as polystyrene (PS), ABS, SBS, etc. Resin or hydrogenated styrene elastomer such as SEBS, polyvinyl chloride (PVC) resin, polyvinylidene chloride (PVDC) resin, polymethyl methacrylate (PMMA), acrylic resin such as copolymer acrylic, polyethylene terephthalate (PET) Polyester resin such as nylon 6, nylon 12, polyamide (PA) resin such as copolymer nylon, polyimide (PI) resin, polyetherimide (PEI) resin, polysulfone (PS) resin, polyethersulfone (PES) )resin Polyamideimide (PAI) resin, polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin, polyphenylene ether (PPE), polyoxymethylene (POM) resin, polycarbonate (PC) resin, polyvinyl butyral (PVB) resin, Polyarylate (PAR) resin, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer (THV), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride (PVDF), Fluorine resins or elastomers such as vinyl fluoride (PVF), (meth) acrylate resins, and the like.

  Among the polymer materials exemplified above, those having excellent heat resistance, acid resistance, and softening temperature suitable for thermoforming are preferred, and polyolefin (PO) resin or polyolefin elastomer, non-cyclic polyolefin, etc. Amorphous polyolefin resin (APO), polyimide (PI) resin, polyetherimide (PEI) resin, polysulfone (PS) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyetheretherketone (PEEK) ) Resin, polyphenylene sulfide (PPS) resin, polyphenylene ether (PPE), polyoxymethylene (POM) resin, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer (THV), tetrafluoroethylene-6 Propylene fluoride copolymer (FEP), fluorine Fluoride (PVDF), the use of such fluorine-based resin or elastomer, such as vinyl fluoride (PVF) are preferred.

  For the conductive filler, it is preferable to use particulate carbon-based materials such as graphite powder, expanded graphite and carbon black, and fibrous (including fine fibers) carbon-based materials such as carbon fibers and carbon nanofibers, which are excellent in corrosion resistance. . The graphite powder includes artificial graphite and natural graphite. Expanded graphite is produced by chemically treating graphite powder with an acid or the like, and includes expanded graphite obtained by heat-treating this at a high temperature. Carbon black includes those produced by an oil furnace method (a method for producing liquid hydrocarbons by a partial combustion reaction), a thermal method (a method for producing natural hydrocarbons or liquid hydrocarbons by thermal decomposition), and the like. The carbon fibers include pitch-based carbon fibers and PAN-based carbon fibers, and include both long fibers and short fibers.

  The carbon nanofiber has a fiber diameter of 0.001 to 0.5 μm, preferably 0.003 to 0.2 μm, a fiber length of 1 to 100 μm, preferably 1 to 30 μm, and includes so-called carbon nanotubes. . The carbon nanofiber includes a single type in which the tube structure of the carbon is a single tube, a double type in which the tube structure is a double tube, and a multi-type structure in which the tube structure is triple or more. Nanohorn type with one end closed and the other end open, and cup type with an opening at one end larger than the opening at the other end are also included.

  Among the conductive agents, it is preferable to use graphite powder, carbon fiber, and carbon nanofiber that are excellent in conductivity. These are also preferably used in combination.

  The volume ratio of the conductive filler / polymer material is 15/85 to 95/5, preferably 30/70 to 90/10. When the volume ratio of the conductive filler / polymer material is less than 15/85, Further, it is difficult to develop conductivity, the internal resistance of the fuel cell separator is increased, the contact resistance with the electrode material is also increased, and there is a problem that the performance of the fuel cell is deteriorated. In addition, when the volume ratio of the conductive filler / polymer material is larger than 95/5, the ratio of the conductive filler increases, and the separator tends to become brittle and cannot be thinned.

  The type of the conductive filler, the polymer material, and the volume ratio of the two can be appropriately selected in consideration of the volume resistance value, thickness, strength, and the like necessary for the intended fuel cell separator. In one embodiment of the present invention, the conductive filler is a particulate carbon-based material, and a stampable sheet can be formed by appropriately selecting a volume ratio in combination with a polymer material excellent in moldability.

  In a different embodiment of the present invention, at least a part of the conductive filler is fibrous, particularly carbon fiber. By containing the fibrous conductive filler, the amount of the conductive filler can be increased while maintaining the moldability, so that the degree of freedom such as selection of the polymer material and volume ratio is increased. In this aspect, it is preferable that carbon fiber is contained in an amount of 5% by volume or more, particularly 10 to 100% by volume, particularly 40 to 100% by volume, of the conductive filler.

  The stampable sheet has a volume resistance value in the thickness direction of the sheet at a load of 1.8 MPa in the range of 0.02 to 0.5 Ωcm, preferably 0.03 to 0.3 Ωcm. If the volume resistance value in the thickness direction exceeds 0.5 Ωcm, the internal resistance when used in a fuel cell separator increases, and the problem of poor fuel cell performance tends to occur. Further, in order to make the volume resistance value in the thickness direction less than 0.02 Ωcm, it is necessary to mix a large amount of conductive filler, and there is a problem that the separator tends to become brittle and cannot be thinned. The reason why the load is measured at 1.8 MPa is that the resistance value under conditions close to the actual use of the fuel cell is important. That is, the fuel cell stack is tightened with an appropriate pressure, and if the tightening load is small, the electrolyte membrane, electrode, and separator constituting the fuel cell are likely to be displaced, and the contact resistance of each component increases. On the other hand, if the tightening load is too large, the electrode is destroyed.

Moreover, the thickness of the stampable sheet to be produced is 100 μm to 1,000 μm, preferably 100 μm to 300 μm.
The stampable sheet can be manufactured by various methods. For example, the manufacturing method by the paper-making method from the suspension of a conductive filler, the manufacturing method from the nonwoven fabric mat of a fibrous conductive filler, etc. are mentioned. Here, the manufacturing method by paper-making method is demonstrated.

  In the paper-making method, a conductive filler and a polymer material are mixed and dispersed in a liquid to form a suspension, and this suspension is made using a mesh having a large number of fine pores. A stampable sheet is formed from a web obtained by dehydrating and drying the solid material. Here, the polymeric material may be insoluble or soluble in the suspension. If it is insoluble in the suspending medium, it will exist in the form of powder (including granules) or fiber and will be made together with the conductive filler to form the web, and if it is soluble, the conductive filler will be made. When adhering to the filler, it is taken into the web. Insoluble and soluble polymer materials may be used in combination.

  FIG. 1 shows an example of a stampable sheet manufacturing method by paper sheeting. As shown in the figure, a first hopper 2 and a second hopper 3 are arranged above the dispersion container 1, and the polymer material particles 5 are supplied from the first hopper 2 to the dispersion container 1, and the second The conductive filler 6 is supplied from the hopper 3.

  The polymer material particles 5 and the conductive filler 6 supplied to the dispersion container 1 at a predetermined ratio are mixed and dispersed in the liquid L to become a suspension. One end of a supply line 8 is connected to the dispersion container 1. A first circulation pump 9 is provided in the middle of the supply line 8. The other end of the supply line 8 is connected to the head box 10. Below the head box 10 is disposed a net 12 provided with a number of fine holes that run endlessly by a pair of rollers 11.

  The turbid liquid in the dispersion container 1 is supplied to the head box 10 by the first circulation pump 9. The turbid liquid supplied to the head box 10 is removed from the hole 12 by the endless running net 12 and is made just as paper making and dehydrated. The water dehydrated at this time is collected in the wet box 13. One end of a recovery line 14 is connected to the wet box 13. A second circulation pump 15 is provided in the middle of the recovery line 14, and the other end is opposed to the opened upper surface side of the dispersion container 1. Accordingly, the liquid L in the turbid liquid collected in the wet box 13 is collected in the dispersion container 1.

  The conductive filler and the polymer material which are made in the wet box 13 and remain on the net 12 are turned into a web 16 and supplied to a hot air drying furnace 17 to be dried. On the outlet side of the hot air drying furnace 17, a continuous press 19 formed by arranging a pair of belt conveyors 18 up and down is provided. The web 16 is pressed and solidified by the continuous press 19 to form a conductive resin sheet 21, that is, a stampable sheet.

In the above description, the conductive filler may be either fibrous or particulate. Further, the polymer material may be powdery or fibrous.
Examples of methods other than the paper-making method described above include, for example, supplying a fibrous conductive filler and a fibrous polymer material simultaneously to form a nonwoven fabric or woven fabric in which both fibers are mixed, and then heating and compressing. And a method of forming a stampable sheet. In particular, as a method for forming a thin sheet for a fuel cell separator, paper making is preferred.

In the second step of the present invention, a separator shape is formed by thermoforming from the stampable sheet thus formed.
As shown in FIG. 2, first, the conductive resin sheet 21, that is, the stampable sheet, is supplied to the infrared heating furnace 32 and preheated to a predetermined temperature. Next, the heated conductive resin sheet 21 is supplied to the stamping molding machine 33 and press-molded. At that time, the distance between the pair of molds 33 a of the stamping molding machine 33 is maintained at a clearance corresponding to the thickness of the conductive resin sheet 21. Accordingly, the fuel cell separator material 31 can be obtained by molding the conductive resin sheet 21 into a fuel cell separator shape and then cutting it with the cutter 34. The molding conditions such as the molding temperature and the molding pressure are preferably set according to the material of the stampable sheet. For example, the temperature is 180 to 400 ° C., preferably 200 to 350 ° C., and the pressure is 3 × 10 ⁶ to 5 × 10 ⁸ Pa, preferably 5 × 10 ^{6 to} 5 × 10 ⁷ Pa.

  In the above description, the stamping molding is exemplified as a molding method for obtaining the fuel cell separator material 31 from the conductive resin sheet 21, but a method such as compressed air molding or flow molding may be used instead.

  Further, in the present invention, the stampable sheet may have a multi-layered structure. For example, the stampable sheet is divided into functions that are divided into a layer having a high formability and a layer having a small contact resistance and / or volume resistance. You can also plan.

  The fuel cell separator manufactured by the manufacturing method of the present invention has a volume resistance equivalent to that of the stampable sheet before being molded.

Hereinafter, although an example is described, the present invention is not limited to this.
<Measurement method of volume resistance value>
The volume resistance value in the thickness direction of the fuel cell separator can be evaluated by the following method.

1. Measuring device Resistance meter: YMR-3 type (manufactured by Yamazaki Seiki Laboratory Co., Ltd.)
Load device: YSR-8 type (manufactured by Yamazaki Seiki Laboratory Co., Ltd.)
Electrode: Two brass flat plates (area 6.45 cm2, mirror finish, surface gold plating)

2. Measurement conditions Method: 4-terminal method Applied current: 10 mA (AC, 287 Hz)
Open terminal voltage: 20 mV peak or less Load: 1.8 MPa (18.6 kgf / cm ² )
Carbon paper: TGP-H-090 (thickness 0.28 mm) manufactured by Toray Industries, Inc.

3. Measuring Method With the measuring device shown in FIG. 3, the separator 42 is sandwiched between the flat plate electrodes 41 made of brass from both sides through the carbon paper 43, and a load of 1.8 MPa is applied while applying a predetermined current by the four-terminal method. The voltage was measured.

4). Volume Resistance Calculation Method From the resistance value R (Ω), electrode area (6.45 cm ² ), and sample thickness t (cm) measured by the above method, the volume resistance value in the thickness direction was calculated by the following formula.
Volume resistance value in the thickness direction (Ωcm) = R × (6.45 cm ² / t)

Example 1
PPS (W220A specific gravity 1.35 manufactured by "Polyplastics Co., Ltd.") is used as the polymer material, and carbon short fibers (HTA-0040 specific gravity 1.77 manufactured by "Toho Tenax Co., Ltd.") are used as the conductive filler. The first hopper 2 and the second hopper 3 so that the conductive filler / polymer material volume ratio is 85/15, that is, the conductive filler / polymer material weight ratio is 88.14 / 11.86. Then, the polymer material particles and the conductive filler were supplied to the dispersion container 1 and dispersed in the liquid L to form a suspension. The weight ratio of (conductive filler and polymer material) / liquid L was added so as to be 2% by weight.

The turbid liquid in the dispersion container 1 was supplied to the head box 10 by the circulation pump 9, and was made by the endless traveling net 12 just like paper making and dehydrated. The turbid liquid made in the wet box 13 became a web 16A, was supplied to the hot air drying furnace 17, and was dried at a temperature of 330 ° C. On the outlet side of the hot air drying furnace 17, a continuous press 19 formed by arranging a pair of belt conveyors 18 up and down is provided, and the web 16A is pressed and hardened with a pressure of 1 × 10 ⁶ Pa to obtain a conductive resin. Sheet 21A was formed. The thickness of the obtained conductive resin sheet 21A was 200 μm.

The conductive resin sheet 21A is supplied to the infrared heating furnace 32, heated to 350 ° C. in advance, and then supplied to the stamping molding machine 33 provided with a pair of molds 33A engraved with the shape of the fuel cell separator to obtain 1 × 10 ^7. Press molding was performed at a pressure of Pa. Then, it cut | disconnected with the cutter 34 and obtained 31 A of fuel cell separator materials.

  It was 0.045 Ωcm as a result of measuring the volume resistance value in the thickness direction when the load load of the fuel cell separator material 31A was 1.8 MPa.

  The obtained fuel cell separator had a volume resistivity value in the thickness direction of 0.045 Ω · cm, excellent conductivity, good heat resistance and acid resistance, and had no problems in performance as a fuel cell separator.

  As described above, according to the method for manufacturing a separator for a fuel cell of the present invention, the fuel is particularly excellent in productivity, mass productivity, excellent conductivity, heat resistance, and acid resistance, and can be operated for a long time. The utility as a battery separator is great.

It is a figure explaining the process of forming a stampable sheet in one example of the present invention. It is a figure explaining the process of shape | molding a fuel cell separator material from a stampable sheet. It is a figure which shows the measuring method of a volume resistance value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Dispersion container 2 ... 1st hopper 3 ... 2nd hopper 5 ... Polymer material particle 6 ... Conductive filler 8 supply line 9 ... Circulation pump 10 ... Head box 11 ... Roller 12 ... Net 13 ... Wet box 14 ... Recovery line 15 ... circulation pump 16 ... web 17 ... hot air drying furnace 18 ... belt conveyor 19 ... continuous press 21 ... conductive resin sheet 31 ... fuel cell separator material 32 ... infrared heating furnace 33 ... stamping molding machine 33a ... die 34 ... cutter 41 ... Electrode: 2 flat plates made of brass,
42 ... Fuel cell separator,
43 ... carbon paper

Claims (6)

Producing a stampable sheet containing a conductive filler and a polymer material;
Supplying the stampable sheet to a molding machine provided with a pair of dies engraved with a fuel cell separator shape;
A process for producing a separator for a fuel cell, comprising a step of thermoforming a stampable sheet supplied to a molding machine into a separator shape.   The manufacturing method according to claim 1, wherein the stampable sheet manufacturing step includes a step of manufacturing a sheet by a paper making method from a suspension containing at least a conductive filler.   The volume ratio of the conductive filler / polymer material in the stampable sheet is in the range of 15/85 to 95/5, and the volume resistance value in the thickness direction at a load of 1.8 MPa is 0.02 to 0.5 Ωcm. The manufacturing method according to claim 1, wherein the manufacturing method is a range.   The manufacturing method according to claim 1, wherein the polymer material is a thermoplastic resin.   The manufacturing method according to claim 1, wherein the conductive filler contains at least one selected from graphite powder, expanded graphite, carbon black, carbon fiber, and carbon nanofiber.   The manufacturing method according to claim 5, wherein the conductive filler contains at least carbon fiber.

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