JP4458877B2 - Manufacturing method of fuel cell separator - Google Patents

Description

  The present invention relates to a method for manufacturing a separator for a fuel cell, and more specifically, a fuel cell configured by stacking a plurality of single cells, provided between adjacent single cells, and a fuel gas channel and an oxidizing gas channel between electrodes. It is related with the manufacturing method of the separator for fuel cells which forms fuel cell, and separates fuel gas and oxidizing gas, and was excellent in corrosion resistance and conductivity especially after fabrication.

A separator constituting a fuel cell, particularly a polymer electrolyte fuel cell, is disposed in contact with each electrode sandwiching a solid electrolyte membrane from both sides, and a supply gas such as a fuel gas or an oxidant gas is provided between the electrodes. It is necessary to form a passage and to be excellent in current collecting performance for deriving current in contact with an electrode.
In general, a separator for a fuel cell is composed of a dense carbon graphite having excellent strength and conductivity as a base material, or a metal material such as stainless steel (SUS), titanium, or aluminum.

Usually, a large number of protrusions, grooves, and the like are formed on the surface of the separator that faces the electrodes.
Therefore, the separator composed of the above-mentioned dense carbon graphite has high electrical conductivity and high current collecting performance is maintained even after long-term use. 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 processing cost increases and mass production is difficult.

On the other hand, the separator made of the above metal material has excellent strength and ductility compared to dense carbon graphite, so the formation of a large number of protrusions and grooves for forming a gas flow path is a press process. There is an advantage that 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 is increased, thereby reducing the current collecting performance of the separator. is there.
Therefore, a material in which a surface of a metal material excellent in workability is coated with a noble metal material such as gold excellent in corrosion resistance as a constituent material of the separator has been studied. However, since such a material is extremely expensive, there is a problem that it lacks versatility.

  Therefore, a fuel cell separator in which at least one surface of a metal substrate is coated with a resin layer in which conductive particles are mixed has been proposed. However, in order to maintain high conductivity, it is necessary to highly fill the resin layer with a conductive agent. As a result, the resin layer becomes brittle, and a large number of protrusions, grooves, etc. for forming a gas flow path by pressing When the metal layer is formed, pinholes, voids, and microcracks are generated in the resin layer, and when used as a fuel cell separator for a long time, the metal substrate rusts and the resistance value increases.

JP 2002-15750 A JP 2002-343375 A

  An object of the present invention is a method of manufacturing a separator for a fuel cell mainly composed of a metal substrate that has excellent corrosion resistance and can be produced at a relatively low cost, and further includes a number of protrusions for forming a gas flow path by pressing. Even if pinholes, voids, microcracks, etc. are generated in the resin layer by forming a portion, a groove, etc., a fuel cell separator is provided that can restore these and extract the inherent corrosion resistance of the resin It is in.

The present invention has found a method for producing a fuel cell separator capable of solving the above-mentioned problems, and the gist thereof is as follows:
In a fuel cell separator in which a thermoplastic resin layer mixed with a conductive filler is laminated on at least one surface of a metal substrate and then a fuel gas channel is formed by pressing, after the fuel gas channel is formed by pressing In the method for producing a fuel cell separator, the heat treatment is performed at a temperature not lower than the melting point of the resin and not higher than (melting point temperature + 80 ° C.).
Furthermore, the thermoplastic resin layer is selected from a fluororesin and a fluorine-based elastomer, a polyolefin resin and a polyolefin elastomer, and the metal substrate is selected from stainless steel, titanium, aluminum, copper, nickel, and steel. In addition, it is included that the conductive filler is selected from carbon, carbon nanofiber, metal carbide, metal oxide, metal nitride, metal fiber, and metal powder.
As another gist, a thermoplastic resin layer mixed with a conductive filler in a mixing ratio of 15% to 40% by volume is laminated on at least one surface of a metal substrate, and then a fuel gas flow path is formed by pressing. In the manufacturing method of a separator for a fuel cell, a pinhole generated in a resin layer by forming a fuel gas flow path by pressing and then heat-treating the resin at a melting point or higher and (melting point + 80 ° C.) or lower. This is a fuel cell incorporating a separator obtained by a method for producing a fuel cell separator characterized by repairing voids, voids, and microcracks.

  According to the present invention, a fuel cell separator mainly composed of a metal substrate that has high electrical conductivity, excellent corrosion resistance, and can be produced at a relatively low cost is obtained, and further, a gas flow path is formed by pressing. Even if a large number of protrusions, grooves, etc. are formed, the resin layer will not be cut or cracked, and a fuel cell separator coated with a resin layer mixed with a conductive filler on a metal substrate can be obtained. A fuel cell that can be operated for a long time can be provided.

The present invention will be described in detail below.
As the metal substrate used in the separator of the present invention, stainless steel, titanium, aluminum, copper, nickel, steel, etc. made into a sheet shape and a coil shape, a foil shape, and surface treatment are applied to them. And the like. The thickness of the metal plate is not particularly limited, but is preferably in the range of 0.05 to 0.5 mm in order to satisfy both formability and weight reduction in a balanced manner.
In addition, the metal plate has various metal platings, for example, tin plating, nickel plating, galvanization, etc., multi-layered plating, alloying plating, etc., in terms of corrosion resistance, press workability, and adhesion to the resin. Or you may provide an etching layer and a grinding | polishing layer in order to improve adhesiveness with a resin layer, such as a phosphate process.

As the resin layer, a fluororesin and a fluoroelastomer, a polyolefin resin and a polyolefin elastomer can be used because of corrosion resistance. In the case of fluororesin and fluoroelastomer, specifically, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) , EPE (tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE (polychlorotrifluoroethylene), ECTFE (chlorotrifluoroethylene-ethylene copolymer) Polymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), THV (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer), VDF- FP (vinylidene fluoride-hexafluoropropylene copolymer), TFE-P (vinylidene fluoride-propylene copolymer), fluorine-containing silicone rubber, fluorine-containing vinyl ether rubber, fluorine-containing phosphazene rubber, fluorine-containing thermoplastic At least one fluororesin and fluororubber made of elastomer can be used.
Among the resins exemplified above, PVDF, THV, VDF-HFP and TFE-P containing vinylidene fluoride are particularly preferable from the viewpoint of moldability.

In the case of polyolefin resin and polyolefin elastomer, specifically, at least one kind of polyolefin and polyolefin elastomer composed of polyethylene, polypropylene, polybutene, poly-4-methyl 1-pentene, polyhexene, polyoctene can be used.
Among the resins exemplified above, an elastomer containing polypropylene is particularly preferable from the viewpoint of heat resistance and moldability.

It is necessary to mix a conductive filler into the resin layer, and carbon, carbon nanofiber, metal carbide, metal oxide, metal nitride, metal fiber, and metal powder can be suitably used as the conductive particles.
Graphite, carbon black, expanded graphite, carbon fiber, etc. are used as carbon, and carbon nanofiber is a single carbon tube structure generated from arc discharge method, vapor phase growth method, laser deposition method, organic solvent combustion method, etc. Single-tube type, double-type double-tube type, multi-type multi-type structure including more than triple, and nanohorn type with at least one end of the tube closed, carbon network with cup shape without bottom A cup shape or the like in which many layers are stacked is also included.
Metal carbides include tungsten carbide, silicon carbide, calcium carbide, zirconium carbide, tantalum carbide, titanium carbide, niobium carbide, molybdenum carbide, and vanadium carbide. Metal oxides include titanium oxide, ruthenium oxide, and indium oxide. Metal nitride includes chromium nitride, aluminum nitride, molybdenum nitride, zirconium nitride, tantalum nitride, titanium nitride, gallium nitride, niobium nitride, vanadium nitride, boron nitride, etc. Metal fibers include iron fiber, copper fiber, stainless steel fiber Examples of the metal powder include tan powder, nickel powder, tin powder, tantalum powder, and niobium powder.
Among the above conductive fillers, carbon-based fillers and carbon nanofibers are preferable from the viewpoint of excellent conductivity and corrosion resistance.

  The mixing ratio of the conductive filler in the resin layer may be appropriately determined so that the volume resistivity of the resin layer is 1.0 Ω · cm or less at 5% to 40% by volume, and the volume is less than 5% by volume. When the resistivity exceeds 1.0 Ω · cm, the conductivity is inferior, and when it exceeds 40% by volume, molding tends to be difficult.

Moreover, in order to reduce the sheet resistance value after laminating the resin layer mixed with the metal substrate and the conductive filler, the low electrical resistance layer 1 is provided on the outermost layer on the metal substrate side of the resin layer mixed with the conductive filler. It is preferable.
The mixing ratio of the conductive filler in the low electrical resistance layer 1 is preferably in the range of 15% by volume to 40% by volume. When the mixing ratio is less than 15% by volume, the contact resistance between the metal plate and the resin layer in which the conductive filler is mixed. The area resistance value after laminating a resin layer in which a metal substrate and a conductive filler are mixed is likely to be large, and if the mixing ratio exceeds 40% by volume, not only molding is likely to be difficult, but also the metal substrate and The problem of difficult bonding is likely to occur.

Furthermore, in order to reduce the sheet resistance value after laminating the resin layer mixed with the metal substrate and the conductive filler, the low electrical resistance layer is formed on the outermost layer on the opposite side of the metal substrate of the resin layer mixed with the conductive filler. 2 is preferably provided.
The mixing ratio of the conductive filler in the low electrical resistance layer 2 is preferably in the range of 15% by volume to 40% by volume. When the mixing ratio is less than 15% by volume, the resin layer mixed with the conductive filler is in contact with the gas diffusion electrode. The resistance is large, and the area resistance value after laminating the resin layer mixed with the metal substrate and the conductive filler tends to increase. If the mixing ratio exceeds 40% by volume, not only the molding becomes difficult, but also after the press molding. In addition, pinholes, voids, microcracks and the like are likely to occur in the low electrical resistance layer 2, and it is difficult to repair even if heat treatment is performed at a temperature higher than the melting point of the resin.

Adhesives that improve the adhesion to the metal plate, adhesion aids such as silane coupling agents, titanium coupling agents, additives that improve corrosion resistance, etc. are appropriately added to the resin layer mixed with the conductive filler. , May be added.
The thickness of the resin layer is preferably in the range of 10 to 200 [mu] m, and if it is less than 10 [mu] m, the corrosion resistance to the metal substrate is small, and if it exceeds 200 [mu] m, the separator becomes thick and the stacked fuel cell tends to be large.

The method for producing the separator of the present invention is not particularly limited, but a conductive resin sheet having the above-described composition formed in advance is placed on one or both sides of a metal substrate, and laminated and integrated by a hot press method or a pressure roll method. There is a way to make it. For example, after the metal substrate and the conductive resin sheet are overlaid, a hot press method of pressing at a temperature equal to or higher than the melting point of the conductive resin sheet, or after heating the metal substrate to a temperature equal to or higher than the melting point of the conductive resin sheet, There is a method of laminating and integrating by a pressure roll method in which a plurality of rolls are pressure-bonded.
After lamination, it is necessary to form protrusions and grooves by cold press molding, and then heat-treat at a temperature equal to or higher than the melting point of the resin. Here, the melting point is a thermogram when the temperature is raised at a heating rate of 10 ° C./min using a differential operation calorimeter (DSC-7 manufactured by PerkinElmer) according to JIS K 7121. To tell.
The heat treatment temperature is in the range from the melting point of the resin to (melting point + 80 ° C.) or less, preferably (melting point + 50 ° C.) or less, and below the melting point of the resin, it occurs in the press working to form the gas flow path, Pinholes, voids, microcracks, etc. in the resin layer are difficult to repair, and at temperatures exceeding (melting point + 80 ° C.), the resin component may cause thermal decomposition.
In addition, the heat treatment time varies depending on the heat treatment temperature, but it is preferably in the range of 1 minute to 30 minutes, and in less than 1 minute, the resin may not reach the melting point or more. If microcracks or the like are not repaired and the time exceeds 30 minutes, the resin may be thermally oxidized and deteriorated, which is not preferable.

Hereinafter, although an example is described, the present invention is not limited to this.
[Evaluation methods]
Volume resistance value measurement The volume resistance value of the resin layer mixed with the conductive filler was measured in accordance with JIS K 7194 as follows.
Measuring device Loresta HP (Mitsubishi Chemical Corporation)
Measuring method Four-terminal four-probe method (ASP type probe)
Measurement applied current 100mA
(2) Area resistance measurement The area resistance of the conductive resin / metal composite plate obtained by laminating a resin layer in which a metal substrate and a conductive filler are mixed was performed as follows.
Measuring device Resistance meter: YMR-3 type (manufactured by Yamazaki Seiki Laboratories)
Load device: YSR-8 type (manufactured by Yamazaki Seiki Laboratory Co., Ltd.)
Electrodes: 2 brass flat plates (area 1 square inch, mirror finish)
Measurement conditions Method: 4-terminal method Applied current: 10 mA (AC, 287 Hz)
Open terminal voltage: 20 mV peak or less Load load: 18 × 10 ⁵ Pa
Carbon paper: TGP-H-090 (thickness 0.28 mm) manufactured by Toray Industries, Inc.
3. Measurement method Measurement was performed using the measurement apparatus shown in FIG.

(3) Press-molding conductive resin / metal composite plate, the shape of the gas flow path after pressing is corrugated, the pitch of the gas flow path is 3 mm, and the height difference between the corrugated convex part and concave part is 0.5 mm. Using a mold that can be used, a molding test is performed at room temperature with a press molding machine ("Torque Pack Press" manufactured by Amada Co., Ltd., press speed of 45 spm (shot per minute)). Observation was performed at a magnification of 50 with a “Digital HD microscope VH-7000” manufactured by Keyence.
The case where there was no abnormality on the appearance was evaluated as ◯, and the case where the cracks were clearly abnormal was evaluated as x.

(4) Fluororesin (Sumitomo 3M "THV220G" specific gravity 2, melting point = 130 ° C) is dissolved in acetone at the end of the corrosion-resistant press-molded conductive resin / metal composite plate (size 30mm x 30mm) The solution was immersed in a solid solution (solid content concentration: 15% by weight) and sealed. 30 ml of 0.005 mol sulfuric acid aqueous solution and the above-mentioned sealed sample were immersed in a high pressure reaction decomposition vessel (“HU-50” manufactured by Sanai Kagaku Co., Ltd.), put in an oven at 80 ° C., and sampled after 10 days The rusting state was observed.
The case where corrosion occurred on the surface of the metal plate ×, the case where there was a slight corrosion mark Δ, and the case where there was no corrosion mark ○.

Example 1
Carbon black (“Ketjen Black EC600JD” manufactured by Lion Corporation, specific gravity 1.5) 12 volume% at a extrusion temperature of 240 ° C. by a film forming apparatus in which a feed block and a die are attached to two twin-screw extruders. Containing fluorine resin (“THV220G” manufactured by Sumitomo 3M Co., specific gravity 2, melting point = 130 ° C.) Carbon nanofibers on both sides of a thickness of 80 μm (“Gas phase carbon fiber VGCF” manufactured by Showa Denko Co., Ltd., specific gravity 2) 20 A two-type, three-layer conductive resin sheet having a thickness of 10 μm and containing 100% by volume of fluororesin (“THV220G” manufactured by Sumitomo 3M Limited, specific gravity 2, melting point = 130 ° C.) containing 10% by volume was formed.
The volume resistance value of the obtained conductive resin sheet was 0.5 Ωcm.
A silane coupling agent (“TSL8331” manufactured by GE Toshiba Silicones Co., Ltd.) 3% ethanol is applied to SUS304 (thickness 0.3 mm) in which a 0.1 μm surface polishing layer is formed by blast polishing. After applying the solution to both surfaces of SUS304 surface-polished with a # 10 bar coater, it was dried at 150 ° C. for 20 minutes, placed in the order of conductive resin sheet / SUS304 / conductive resin sheet, and laminated integrally by hot pressing Turned into. The hot pressing conditions were a temperature of 180 ° C., 10 minutes, and a pressure of 3.5 × 10 ⁶ Pa (36 kgf / cm ² ).
The load resistance of the obtained conductive resin / metal composite plate: The area resistance value at 18 × 10 ⁵ Pa was 20 mΩcm ² .

  After the obtained conductive resin / metal composite plate was press-molded, it was heat-treated at 150 ° C., which is equal to or higher than the melting point of the resin, for 10 minutes, and the appearance and corrosion resistance test were performed. The obtained results are shown in Table 1.

(Example 2)
Evaluation was performed in the same manner as in Example 1 except that the heat treatment temperature was 200 ° C. which is higher than the melting point of the resin.
The obtained results are shown in Table 1.

(Comparative Example 1)
Evaluation was performed in the same manner as in Example 1 except that no heat treatment was performed.
The obtained results are shown in Table 1.

(Comparative Example 2)
Evaluation was performed in the same manner as in Example 1 except that the heat treatment temperature was 100 ° C. which is lower than the melting point of the resin.
The obtained results are shown in Table 1.

(Comparative Example 3)
Evaluation was performed in the same manner as in Example 1 except that the heat treatment temperature was 120 ° C., which was lower than the melting point of the resin.
The obtained results are shown in Table 1.

(Comparative Example 4)
Evaluation was performed in the same manner as in Example 1 except that the heat treatment temperature was set to 400 ° C. which is equal to or higher than (melting point + 80 ° C.) of the resin.
The obtained results are shown in Table 1.

  As shown in Table 1, after attaching a gas flow path as a fuel by press working, heat treatment was performed without heat treatment or less than the melting point temperature of the conductive resin. Comparative Example 4 that is too low is inferior in corrosion resistance, but Examples 1 and 2 that were heat-treated at a temperature equal to or higher than the melting point temperature of the conductive resin can exhibit the inherent corrosion resistance of the resin and are excellent in corrosion resistance.

The schematic of the apparatus which shows the measuring method of sheet resistance.

Explanation of symbols

1: Brass electrode 2: Carbon paper 3: Separator

Claims (5)

In a method of manufacturing a fuel cell separator in which a thermoplastic resin layer mixed with a conductive filler is laminated on at least one surface of a metal substrate, and then a fuel gas channel is formed by pressing, the fuel gas channel is formed by pressing. A method for producing a fuel cell separator, characterized in that after the formation, a heat treatment is performed at a temperature not lower than the melting point of the resin and not higher than (melting point + 80 ° C.). 2. The method for producing a fuel cell separator according to claim 1, wherein the thermoplastic resin layer is selected from a fluororesin, a fluoroelastomer, a polyolefin resin, and a polyolefin elastomer. 3. The method for manufacturing a fuel cell separator according to claim 1, wherein the metal substrate is selected from stainless steel, titanium, aluminum, copper, nickel, and steel. 4. The conductive filler according to claim 1, wherein the conductive filler is selected from carbon, carbon nanofiber, metal carbide, metal oxide, metal nitride, metal fiber, and metal powder. A method for producing a separator for a fuel cell. A method for producing a fuel cell separator, wherein a thermoplastic resin layer mixed with a conductive filler at a mixing ratio of 15% by volume to 40% by volume is laminated on at least one surface of a metal substrate, and then a fuel gas flow path is formed by pressing. , After forming the fuel gas flow path by pressing, heat treatment is performed at a temperature not lower than the melting point of the resin and not higher than (melting point + 80 ° C.), thereby repairing pinholes, voids and microcracks generated in the resin layer. A fuel cell in which a separator obtained by the method for producing a fuel cell separator is incorporated.

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