JP2000348739A - Resin composition for fuel cell separator - Google Patents

Abstract

(57) [Problem] To provide a resin composition for a separator of a fuel cell having high conductivity and toughness and excellent productivity. SOLUTION: (a) low melting point metal, (b) metal powder,
It comprises a mixture of (c) a thermoplastic and (d) a thermoplastic elastomer, wherein the metal component combining (a) and (b) is 20 to 70% by volume of the total composition, and (b) ) 10 to 30% by volume of the component,
A resin composition for a fuel cell separator, wherein the proportion of (d) in the resin component obtained by combining (c) and (d) is in the range of 10 to 100% by volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell which is in contact with a pair of electrodes sandwiching an electrolyte membrane, is used for current collection from the electrodes, and has a gas flow path for gas supply at least on the electrode side. And a resin composition for a separator.

[0002]

2. Description of the Related Art The above-mentioned separator of a fuel cell (hereinafter simply referred to as a separator) needs to have a high degree of conductivity in order to collect current from an electrode. Further, gas impermeability, corrosion resistance, mechanical strength, and the like are required. Then, a gas flow path and a cooling groove for supplying gas to the electrode are formed in the separator, and the formation method is conventionally, an end mill, a conductive material such as a metal plate or a carbon plate.
It was formed by performing cutting such as milling.

[0003]

It is known that the separator is made of a metal material such as pure copper or stainless steel as a separator material. However, these metal materials become heavy and are used as fuel gas. Due to long-term contact with hydrogen gas, hydrogen embrittlement occurs and material deterioration occurs.In addition, cutting and etching processes for forming grooves are required, so that an increase in man-hours and an accompanying cost are inevitable. . In addition to metal-based materials, there is an example in which a dense carbon plate material is used and a gas passage is formed in this plate material to form a gas flow path, which is used as a separator. There is a problem that it takes time and productivity is low. Further, as in the case of using a metal plate, it is necessary to cut the slice by using a diamond cutter for forming the plate material together with the processing of the flow path, so that an increase in man-hours and an accompanying increase in cost are inevitable.

An object of the present invention is to solve the problems of the conventional separator and to provide a separator having a high level of conductivity with extremely excellent current collecting properties and high productivity.

[0005]

SUMMARY OF THE INVENTION The present invention has found a composition for a fuel cell separator which can solve the above-mentioned problems. The gist of the present invention is to provide a pair of electrodes sandwiching an electrolyte membrane. A fuel cell separator having a gas flow path for gas supply on the electrode side and a cooling water channel on the opposite electrode side, wherein the separator has a low melting point; Metal, (b) metal powder, (c)
A fuel cell separator comprising a mixture of a thermoplastic resin and (d) a thermoplastic elastomer, wherein the above components are contained in a specific range.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is a schematic sectional view showing the structure of a polymer electrolyte fuel cell. As shown in FIG. 1, the fuel cell 1
No. 0 includes an electrolyte membrane 12, a pair of electrodes 11 having a sandwich structure sandwiching the electrolyte membrane 12 from both sides, and a separator 20 contacting the electrodes while sandwiching the sandwich structure from both sides. The separator 20 has a gas channel 21 for gas supply on the electrode side, and a cooling water channel 22 on the opposite side of the electrode. This cooling water passage 22 can be provided as needed. The total thickness of the separator 20 is usually
It is in the range of 1.0 mm to 3.0 mm.

[0007] In the fuel cell separator of the present invention,
It is characterized in that the material of the separator comprises a mixture of (a) a low melting point metal, (b) a metal powder, (c) a thermoplastic plastic, and (d) a thermoplastic elastomer (hereinafter, referred to as “mixture”). In the mixed material, it is necessary that the metal component including (a) the low melting point metal and (b) the metal powder is contained in the range of 20 to 70% by volume, preferably 45 to 65% by volume of the whole composition, Further, the proportion of the component (b) in the metal component must be in the range of 10 to 30% by volume. If the metal component is less than 20% by volume, it is difficult to exhibit conductivity, and if it exceeds 70% by volume, there is a problem that fluidity is reduced and moldability is poor. Further, the metal powder (b) acts as a dispersing aid for the low-melting point metal. When the proportion of (b) in the metal component is 10% by volume or less, the dispersion state deteriorates. With the decrease in the temperature, there is a problem that the material is apt to become brittle and the conductivity is also reduced.

As the low-melting point metal of the component (a), various kinds can be used. Usually, metals having a melting point of 300 ° C. or less, such as Pb / Sn, Pb / Sn / Bi, and Pb / Sn / A
g, Pb / Ag, Sn / Ag, Sn / Bi, Sn / C
A u, Sn / Zn-based solder alloy can be suitably used. The metal powder of the component (b) serves as a dispersing aid for the low melting point metal, and Cu, Ni, Al, Cr and alloy powders thereof can be suitably used, and the average particle size is 1 to 50.
The range of μm is preferred. The average particle diameter is a number average particle diameter obtained by photographing a sample with a transmission electron microscope and obtaining the photograph. When the average particle size is less than 1 μm, handling during mixing is difficult, and when the average particle size exceeds 50 μm, the dispersibility tends to decrease.

The thermoplastic resin of the component (c) used in the mixture may be any thermoplastic that can withstand the environment in which the separator is used. From the viewpoint of heat resistance, water resistance and chemical resistance, polypropylene (PP) ), An ABS resin, a PC resin, a modified PPO resin, a polyacetal resin, a PPS resin, and a liquid crystal polymer resin. The thermoplastic elastomer of the component (d) may be any one having good kneadability with the thermoplastic of the component (c) to be used. Ester-based elastomers and amide-based elastomers are preferably used. For example, when the thermoplastic resin of the component (c) is PP, an olefin-based elastomer excellent in kneading properties is suitable as the thermoplastic elastomer (d). The function of (d) in the mixed material is to reduce the brittleness of the entire mixed agent and impart toughness, and the proportion of the resin component combining (c) and (d) is 10 to 100% by volume, preferably 10-30
It is mixed in the range of volume%. If it is less than 10% by volume, it does not contribute to the reduction of the brittleness of the mixture, and if it is higher than 100% by volume, the mixture becomes too soft, making it difficult to maintain its shape as a separator.

The durometer D hardness of the thermoplastic elastomer (d) used is 55 (JI
The following resins are suitable. If the hardness is higher, the resin is too hard to perform the function of improving the brittleness. As the above-mentioned mixed material, it is preferable to use a method in which a mixture obtained by physically mixing powders is kneaded at a predetermined temperature by a kneader such as a kneader or a twin-screw extruder and then granulated. In kneading, the temperature at which the low-melting-point metal of the component (a) is in a semi-molten state is preferable. An appropriate metal composition is selected according to the melting temperature of the resin component serving as a matrix, and the low-melting-point metal and copper as a dispersing aid are selected. It is necessary to appropriately select the addition ratio of metal powder such as powder and nickel powder.

The granulated mixture obtained by the above method can be shaped by performing injection molding, transfer molding, press molding or the like using a mold having a separator shape. In view of productivity, injection molding is effective. Although the obtained molded article functions as a separator as it is, it is preferable to apply a metal plating of gold, silver or the like or sputtering to the surface in consideration of the durability of the electrode side. Electroplating of metal components in the separator can be prevented by plating or sputtering of these metals.

As described above, the separator of the fuel cell unit of the present invention exhibits high conductivity and maintains a certain degree of toughness because the thermoplastic contains the low melting point metal and the thermoplastic elastomer. it can. In addition, since a molding method similar to that of a normal thermoplastic resin can be used, a cutting process is not required for forming a shape having a flow path. Therefore, the separator of the fuel cell unit according to the present invention has high conductivity and toughness required as a separator, and has high productivity.

[0013]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. (Example 1) Pb / Sn based solder (P
b 70%, Sn 30%), average particle size 10 as metal powder
μm copper powder and PP resin as thermoplastic resin (“P
N640 "(manufactured by Tokuyama Corporation) and Santoprene (" 121-50M "manufactured by AES Japan) as a thermoplastic elastomer. Physical mixing of each raw material powder in advance (low melting point metal 45% by volume, metal powder 5% by volume, thermoplastic resin 25% by volume, thermoplastic elastomer 25% by volume)
Using a twin-screw extruder ("2D25-S" manufactured by Toyo Seiki Co., Ltd.), the mixture was melt-kneaded and then pelletized to prepare solder-containing resin pellets. Extrusion conditions are as follows.

Cylinder temperature: 220 ° C. Screw rotation speed: 20 r. p. m. Thereafter, the solder-containing resin pellets prepared above were injection-molded in a molding die for injection molding in which the female mold and the male mold were opposed to each other under the following conditions. Mold temperature: 40 ° C Cylinder temperature: 220 ° C Screw rotation speed: 50r. p. m. Injection rate: 60 cm ³ / sec Injection pressure: 80 MPa Back pressure: 2 MPa Holding pressure (cooling) time: 40 sec After cooling, the mold was removed to obtain the intended separator.

The characteristics of this separator were as follows. Volume resistivity: 4.5 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (vs. helium gas) Deflection at break in bending test (index of brittleness): 2.5 m
m (according to JIS K7111: test specimen width 10 mm, fulcrum distance 20 mm, test speed 0.5 mm / min)

(Comparative Example 1) All the resin components of Example 1 were evaluated as thermoplastic resins (without thermoplastic elastomer), and the other components were evaluated under the same conditions. The characteristics of this separator were as follows. Volume resistivity: 5.2 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (vs. helium gas) Deflection at break in bending test (index of brittleness): 0.61
mm (according to JIS K7111: specimen width 10 mm, fulcrum distance 20 mm, test speed 0.5 mm / min)

Example 2 Lead-free solder (Sn-4Cu-2Ni) was used as the low melting point metal, copper powder having an average particle diameter of 10 μm was used as the metal powder, and PP was used as the thermoplastic resin.
("PN640" manufactured by Tokuyama Corporation) Santoprene ("121-50M" A) as a thermoplastic elastomer
ES Japan). Each raw material powder is physically mixed in advance (low melting point metal 45% by volume, metal powder 5% by volume, thermoplastic resin 25% by volume, thermoplastic elastomer 2
After melt-kneading using a twin-screw extruder (“2D25-S” manufactured by Toyo Seiki Co., Ltd.), the mixture was pelletized to prepare solder-containing resin pellets. Extrusion conditions are as follows.

Cylinder temperature: 220 ° C. Screw rotation speed: 20 r. p. m. Thereafter, the solder-containing resin pellets prepared above were injection-molded in a molding die for injection molding in which the female mold and the male mold were opposed to each other under the following conditions. Mold temperature: 40 ° C Cylinder temperature: 220 ° C Screw rotation speed: 50r. p. m. Injection rate: 60 cm ³ / sec Injection pressure: 80 MPa Back pressure: 2 MPa Holding pressure (cooling) time: 40 sec After cooling, the mold was removed to obtain the intended separator.

The characteristics of this separator were as follows. Specific volume resistance value: 8.2 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (vs. helium gas) Deflection at break in bending test (index of brittleness): 2.8 m
m (according to JIS K7111: test specimen width 10 mm, fulcrum distance 20 mm, test speed 0.5 mm / min)

(Comparative Example 2) All the resin components of Example 2 were evaluated as thermoplastic resins (without thermoplastic elastomer), and the other components were evaluated under the same conditions. The characteristics of this separator were as follows. Volume resistivity: 6.7 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (vs. helium gas) Flexure at break in bending test (index of brittleness): 0.68
mm (according to JIS K7111: specimen width 10 mm, fulcrum distance 20 mm, test speed 0.5 mm / min)

[0021]

As described above, the fuel cell separator of the present invention exhibits high conductivity because the resin contains a low melting point metal. In addition, since a molding method similar to that of a normal thermoplastic resin can be used, a cutting process is not required for forming a shape having a flow path. Further, since an elastomer is used as the resin component, brittleness can be suppressed. As a result, the separator of the fuel cell unit of the present invention has the advantages of having high conductivity and toughness required as a separator and being excellent in productivity.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a fuel cell unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Fuel cell 11 ... Electrode 12 ... Electrolyte membrane 20 ... Separator 21 ... Gas flow path 22 ... Cooling water channel

Claims (5)

[Claims] (1) a low melting point metal, (b) a metal powder,
It comprises a mixture of (c) a thermoplastic and (d) a thermoplastic elastomer, wherein the metal component combining (a) and (b) is 20 to 70% by volume of the total composition, and (b) ) 10 to 30% by volume of the component,
A resin composition for a fuel cell separator, wherein the proportion of (d) in the resin component obtained by combining (c) and (d) is in the range of 10 to 100% by volume. 2. The low melting point metal of component (a) is Pb / Sn,
Pb / Sn / Bi, Pb / Sn / Ag, Pb / Ag, S
2. A solder alloy selected from the group consisting of n / Ag, Sn / Bi, Sn / Cu, and Sn / Zn.
The resin composition for a separator of the fuel cell according to the above. 3. The metal powder of component (b) is Cu, Ni, A
2. The powder of claim 1, wherein said powder is made of l, Cr or an alloy powder thereof, and has an average particle diameter in the range of 1 to 50 μm.
3. The resin composition for a separator of a fuel cell according to any one of claims 1 to 2. 4. The thermoplastic resin of component (c) is a polyolefin resin, ABS resin, PC resin, modified PPO
The resin composition for a fuel cell separator according to any one of claims 1 to 3, wherein the resin composition is selected from a resin, a polyacetal resin, a PPS resin, and a liquid crystal polymer resin. 5. The thermoplastic elastomer of component (d) is selected from olefin elastomers, styrene elastomers, vinyl chloride elastomers, urethane elastomers, ester elastomers and amide elastomers. A resin composition for a fuel cell separator according to any one of claims 1 to 4.