JP2006269090A - Separator for fuel cell, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a solid polyelectrolyte fuel cell in which current collecting performance, molding property, and strength are satisfied, and which is especially superior in corrosion resistance. <P>SOLUTION: In the separator for the fuel cell in which a conductive resin layer mixed with a conductive filler is laminated at least on one face of a metal substrate, the conductive resin layer has at least one resin layer among (a) a first resin layer which has volume resistivity in the range of 1.0 Ωcm or less and has a weight change in the range of 0-0.1% after immersing it for 3 hour into water of 85-95°C, (b) a second resin layer in which the surface of the conductive resin layer is constituted and the volume resistivity is smaller than that of the first resin layer, and a third resin layer which is installed at the interface with the metal substrate and of which the volume resistivity is smaller than that of the first resin layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to 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 forming a fuel gas channel and an oxidizing gas channel between electrodes. In addition, the present invention relates to a fuel cell separator that separates a fuel gas and an oxidizing gas, and particularly to a fuel cell separator that is excellent in corrosion resistance and conductivity after molding.

  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. In order to form the flow channel, a large number of protrusions, grooves, and the like are formed on the surface of the separator that faces the electrode.

  In addition, the electromotive force of the unit cell of the fuel cell is as low as 1 V or less, and usually, a plurality of unit cells are stacked via separators. For this reason, since the separator plays a role of deriving a current in contact with the electrode, a separator having excellent current collecting performance is required.

  Conventionally, fuel cell separators are generally composed of dense carbon graphite having excellent strength and conductivity as a base material, or a metal material such as stainless steel (SUS), titanium, and aluminum.

  However, separators composed of dense carbon graphite have high electrical conductivity and maintain high current collection performance even after long-term use. There is a problem that it is not easy to perform machining such as cutting to form the protrusions and grooves, and that 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 it is possible and mass production is easy. However, even a polymer electrolyte fuel cell that operates at a relatively low temperature is exposed to near-saturated water vapor at a temperature of 70 to 90 ° C. Therefore, a separator using a metal material has an oxide film due to corrosion on its surface. As a result, the contact resistance between the generated oxide film and the electrode increases, and there is a problem that the current collecting performance of the separator is lowered.

  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.

In order to solve these problems, the present applicant has disclosed a separator provided with a resin layer in which a conductive filler is mixed on the surface of a metal substrate (Patent Document 1: JP 2002-15750 A, Patent Document 2). : JP-A-2003-297383, Patent Document 3: JP-A-2004-14272). These separators have high electrical conductivity, excellent current collecting performance, and at the same time, excellent moldability, strength, and corrosion resistance.
JP 2002-15750 A JP 2003-297383 A JP 2004-14272 A

  The present invention has been made to further improve the performance, and an object of the present invention is to provide a solid polymer electrolyte fuel cell separator that satisfies current collecting performance, moldability, and strength, and is particularly excellent in corrosion resistance. .

  The present invention relates to the following items.

1. In a fuel cell separator in which a conductive resin layer mixed with a conductive filler is laminated on at least one surface of a metal substrate,
The conductive resin layer is (a) a volume resistance value is 1.0 Ω · cm or less, and a weight change after being immersed in water at 85 to 95 ° C. for 3 hours is in a range of 0 to 0.1%. A resin layer of
(B) The surface of the conductive resin layer is formed and the volume resistance value is provided at the interface between the second resin layer and the metal substrate, which is smaller than the first resin layer, and the volume resistance value is higher than that of the first resin layer. A separator for a fuel cell having at least one resin layer of the third resin layer having a smaller size.

  2. The first resin layer contains 10-50% by volume of a conductive filler, and the second resin layer and the third resin layer contain 20-90% by volume of a conductive filler, respectively. 2. The fuel cell separator as described in 1 above.

  3. 3. The fuel cell separator according to claim 1 or 2, wherein the conductive fillers of the first to third resin layers contain a carbon-based material.

  4). 4. The fuel according to any one of 1 to 3 above, wherein the conductive filler of the first resin layer is substantially composed of one or more selected from graphitized carbon materials and fine carbon fibers. Battery separator.

5. The fuel cell separator of the 4, wherein the measured from the wide angle X-ray diffraction, grating spacing in the thickness direction of the d ₀₀₂ plane is less than 0.350nm of the graphitized carbon material.

  6). 6. The fuel cell separator according to any one of 1 to 5, wherein the conductive filler contained in each of the second resin layer and the third resin layer contains fine carbon fibers.

  7). 7. The fuel cell separator according to claim 4, wherein the fine carbon fiber has a fiber diameter of 0.001 to 0.5 μm and a fiber length of 1 to 100 μm.

  8). 8. The fuel cell separator as described in any one of 1 to 7 above, wherein the resin is selected from the group consisting of fluororesin, fluororubber, polyolefin resin and polyolefin elastomer.

  9. 9. The fuel cell separator according to any one of claims 1 to 8, wherein the material of the metal substrate is selected from the group consisting of stainless steel, titanium, aluminum, copper, nickel and steel.

  10. Any of 1 to 9 above, wherein the metal substrate has a plating layer made of at least one metal selected from the group consisting of nickel, tin, copper, titanium, gold, platinum, silver and palladium on the surface. A fuel cell separator according to claim 1.

  11. A method for producing the fuel cell separator according to any one of 1 to 10 above, wherein a step of laminating a conductive resin layer in which a resin and a conductive filler are mixed on at least one surface of a metal substrate; The manufacturing method of the separator for fuel cells which has the process of forming the protrusion part and groove part which become a gas flow path by press-processing the board | substrate which laminated | stacked the conductive resin layer.

  12 11. A method for producing a fuel cell separator as described in any one of 1 to 10 above, wherein a step of laminating a conductive resin layer in which a resin and a conductive filler are mixed on at least one surface of a metal substrate; A step of covering the outermost surface of the metal substrate on which the conductive resin layer is laminated with a protective film, a step of forming a protrusion and a groove serving as a gas flow path by pressing the substrate covered with the protective film, And a step of peeling the protective film from the substrate on which the groove is formed.

  As a result of studying the corrosion resistance of the metal substrate, the present inventor has found that there is a strong correlation between the water absorption of the conductive resin layer and the corrosion of the metal substrate. However, the present invention does not simply reduce the water absorption of the entire conductive resin layer, but reduces the water absorption of at least the first resin layer, so that the second resin layer which is the surface layer and the interface layer with the metal substrate The function of the corrosion resistance can be imparted to the entire conductive resin layer without impairing the function of each of the third resin layers.

  That is, the fuel cell separator of the present invention is particularly excellent in corrosion resistance and acid resistance while being mainly composed of a metal substrate that has high electrical conductivity and can be produced at a relatively low cost. Therefore, the fuel cell using the separator of the present invention can be operated for a long time. Moreover, in the production of the fuel cell separator of the present invention, even if a large number of protrusions, grooves, etc. for forming the gas flow path are formed by pressing, the resin layer may be cut or cracked. In this respect, a fuel cell separator having particularly excellent corrosion resistance and acid resistance can be obtained.

  The present invention will be described in detail below.

  FIG. 1 is an enlarged schematic view of the vicinity of a separator of a stacked fuel cell in which a large number of single cells are stacked. The unit cell 1a and the unit cell 1b have solid polymer electrolyte membranes 2a and 2b and electrodes 3a and 3b sandwiching the membrane, respectively, and the unit cell 1a and the unit cell 1b are separated by the separator 10 at the same time. The gas channel 4a is formed on the unit cell 1a side in contact with the electrode 3a, and the gas channel 4b is formed on the unit cell 1b side in contact with the electrode 3b. The separator 10 in this form is provided with the conductive resin layers 12 on both surfaces of the metal substrate 11 and is in contact with both the electrode 3a and the electrode 3b, so that the unit cell 1a and the unit cell 1b are connected in series. ing.

  In this example, the conductive resin layer is provided on both sides of the metal substrate, but in some cases, such as when the separator is used for a terminal cell, the conductive resin layer may be provided only on one side of the metal substrate. In the following drawings, only the layer structure on one side of the metal substrate is shown.

  As described above, the conductive resin layer of the present invention (a) has a volume resistance value of 1.0 Ω · cm or less, and the weight change after being immersed in water at 85 to 95 ° C. for 3 hours is 0 to 0.1%. A first resin layer in the range of (b), and (b) provided at the interface between the metal substrate and the second resin layer constituting the surface of the conductive resin layer and having a volume resistance smaller than that of the first resin layer. And it has at least 1 resin layer among the 3rd resin layers whose volume resistance value is smaller than a 1st resin layer.

  FIG. 2 shows an example of the separator layer structure. In this embodiment, the conductive resin layer 12 provided on the surface of the metal substrate 11 is composed of two layers, a first resin layer 13 and a second resin layer 14. The second resin layer forming the surface layer of the conductive resin layer has a volume resistance value smaller than that of the first resin layer. In this invention, since the 2nd resin layer which comprises a surface layer is excellent in electroconductivity, as shown in FIG. 1, resistance of the contact surface with electrode 3a, 3b can be made small. On the other hand, since the first resin layer provided on the metal substrate side has a volume resistance value of 1.0 Ω · cm or less, the conductivity as high as the second resin layer is not required while maintaining sufficient conductivity. . Therefore, for the first resin layer, for example, by increasing the resin component, the layer can be configured with emphasis on moldability / shape-shaping property, strength, and corrosion resistance. That is, in the present invention, the volume resistance value is changed between the first resin and the second resin, and the function of the conductive resin layer is shared between the first resin layer and the second resin layer, thereby collecting current. Both performance and formability, strength and corrosion resistance in press working can be satisfied.

  FIG. 3 shows an example of a layer structure with different separators. In this example, a third resin layer 15 is further provided between the first resin layer 13 and the metal substrate 11. The third resin layer has a smaller volume resistance value than the first resin layer, and can reduce the contact resistance between the metal substrate and the conductive resin layer. That is, in this embodiment, the third resin layer reduces the contact resistance at the interface between the metal substrate and the conductive resin layer, and the second resin layer reduces the contact resistance with the electrode. By forming a single resin layer with a layer structure that places emphasis on moldability, shapeability, strength, and corrosion resistance, a separator that satisfies both current collecting performance, moldability, strength, and corrosion resistance can be obtained. The volume resistance value of the third resin layer may be equal to or different from the volume resistance value of the second resin layer.

    As another form of the separator, in addition to the first resin layer, a structure in which the third resin layer 15 is provided between the metal substrate, that is, a form in which the second resin layer is not provided in the form of FIG. Can be mentioned. According to this aspect, the contact resistance at the interface between the metal substrate and the conductive resin layer can be reduced by the third resin layer.

  Among the three forms mentioned above, those having both the second resin layer and the third resin layer together with the first resin layer are most preferable from the viewpoint of reducing contact resistance.

  In the present invention, the change in weight when the simple substance of the first resin layer in the conductive resin sheet having such a form is immersed in water at 85 to 95 ° C. for 3 hours is in the range of 0 to 0.1%. If the thickness of the first resin layer is in the range of about 100 μm or less, even if the temperature changes from 85 to 95 ° C., if the immersion time of 3 hours is taken, even if it is immersed for a longer time, the weight changes. Although there is no big difference, the standard temperature is 90 ± 2.5 ° C. Further, as the thickness of the first resin layer increases, it takes time until the weight change is saturated. Therefore, a thickness of 100 μm or less, for example 50 Measured for a thickness of 100 μm (or width). If the weight change of the first resin layer exceeds 0.1% in such a water absorption measurement method, the metal substrate and the plating layer on the surface of the metal substrate are corroded by the moisture impregnated in the first resin layer. The contact resistance between the metal substrate and the conductive resin layer tends to increase. Furthermore, when the metal substrate or the plating layer component on the surface of the metal substrate corrodes, it ionizes, permeates the conductive resin layer, elutes outside the fuel cell separator, and inhibits proton ion conductivity of the solid polymer electrolyte membrane. Problems are likely to occur.

  Thus, in the present invention, by setting the water absorption of the first resin layer within a specific range, the respective functions represented by the conductivity of the second resin layer and the third resin layer are impaired. In addition, a function of corrosion resistance can be imparted to the entire conductive resin layer.

  Next, it demonstrates in detail, showing the material of each layer.

  As the metal substrate used in the separator of the present invention, a thin plate made of stainless steel, titanium, aluminum, copper, nickel, or steel can be suitably used. The thickness is preferably in the range of 0.03 mm to 1.5 mm, particularly preferably in the range of 0.1 to 0.3 mm.

  The surface of the metal substrate may be left as it is, and a surface treatment or a surface layer may be provided for various purposes. For example, in order to improve the adhesion with the conductive resin layer, the metal substrate surface can be primed with a silane coupling agent or the like.

  However, when an increase in contact resistance between the metal substrate and the conductive resin layer becomes a problem due to the primer layer and / or the adhesive layer, the metal substrate and the conductive resin layer are directly provided without providing such a layer. It is also preferable to bond the two.

  It is also preferable that the surface of the metal substrate is rough because the adhesion between the metal substrate and the conductive resin layer is improved. When the metal substrate and the conductive resin layer are directly bonded, the surface is roughened. It is particularly preferable. The degree of roughening is such that the center line average roughness Ra is 0.05 to 5.0 μm, preferably 0.1 to 1.0 μm. If the rough surface is too small, the adhesion with the conductive resin layer becomes insufficient. On the other hand, forming a fine rough surface with a large unevenness takes a long time and is inferior in productivity. An etching method can be used to roughen the surface. For example, it is preferable to determine appropriately according to the type of the metal substrate from mechanical etching using an abrasive, chemical etching using chemicals, electrolytic etching using anodic dissolution using electric energy, and the like.

  In the present invention, it is also preferable to provide a plating layer on the surface of the metal substrate. Depending on the type of metal, an oxide film may be formed on the surface, and the contact resistance may increase. Therefore, by forming a metal plating layer on which the oxide film is difficult to form on the substrate surface, the metal substrate and the conductive resin layer Contact resistance can be reduced. As the metal constituting the plating layer, nickel, tin, copper, titanium, gold, platinum, silver, palladium and the like are preferable. Particularly preferred are nickel, tin, copper and titanium. In addition, examples of the metal substrate material on which such a plating layer is preferably provided include stainless steel, aluminum, titanium, and steel.

  The resin mixed in the conductive resin layer is preferably a fluororesin, fluororubber, polyolefin resin, or polyolefin elastomer because of its chemical resistance. Specific examples of the fluororesin and fluororubber include 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) Coalescence), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), THV (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer), VDF-HFP Vinylidene fluoride-hexafluoropropylene copolymer), TFE-P (vinylidene fluoride-propylene copolymer), fluorine-containing silicone rubber, fluorine-containing vinyl ether rubber, fluorine-containing phosphazene rubber, and fluorine-containing thermoplastic elastomer Can be mentioned. These fluororesins or fluororubbers can be used alone or in admixture of two or more.

  In particular, PVDF, THV, VDF-HFP and TFE-P containing vinylidene fluoride are preferable from the viewpoint of moldability.

  Specific examples of the polyolefin resin and the polyolefin elastomer include polyethylene, polypropylene, polybutene, poly-4-methyl-1-pentene, polyhexene, polyoctene, hydrogenated styrene butadiene rubber, EPDM, EPM, and EBM. Among these, one kind or a mixture of two or more kinds can be used.

  Among these resins, polyethylene, polypropylene, and EPDM are particularly preferable from the viewpoint of heat resistance and moldability.

  Further, the conductive filler is preferably highly conductive and excellent in corrosion resistance, and in particular, a carbon-based material is preferable. Examples of the powdery carbon-based material include graphite (artificial graphite, natural graphite, expanded graphite, etc.) and carbon black, and examples of the fibrous carbon-based material include fine carbon fiber and carbon fiber. The fine carbon fiber has a fiber diameter of 0.001 to 0.5 μm, preferably 0.003 to 0.2 μm, and a fiber length of 1 to 100 μm, preferably 1 to 30 μm from the viewpoint of conductivity. The fine carbon fibers include so-called carbon nanotubes and carbon nanofibers. The carbon nanotube 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. It also includes a nanohorn type in which one end is closed and the other end is open, and a cup type in which the opening at one end is larger than the opening at the other end.

  Only one type of conductive filler may be used, or two or more types may be used in combination. For example, carbon nanotubes and / or carbon nanofibers and carbon black or graphite can be mixed and used.

Here, as the carbon-based material to be contained in the first resin layer, a graphitized carbon material and fine carbon fibers are preferable. The graphitized carbon material is a carbon material having a high graphitization rate, and includes carbon black having an increased graphitization rate in addition to graphite such as artificial graphite, natural graphite, and expanded graphite. In graphite, the hexagonal network structure is sufficiently developed in a layered manner, and the diffraction peak of the (002) plane is observed as a sharp peak at an interlayer distance d ₀₀₂ = 0.335 nm as measured by wide-angle X-ray diffraction of powdered graphite. The graphitized material contained in the first resin layer of the present invention preferably has a peak observed in the range of d ₀₀₂ of 0.350 nm or less (lower limit is 0.335 nm), particularly 0.345 nm or less. Those in which a peak is observed in the range are preferable, and most preferably, the peak is observed in a range of 0.341 nm or less. When such a carbon material having a high graphitization rate or fine carbon fiber is used, the water absorption rate of the resin layer is greatly reduced.

  Carbon black with an increased graphitization rate can be obtained by heat-treating carbon black at a high temperature of 1,500 ° C. or higher.

  Carbon black or ketjen black produced by the oil furnace method, which is generally known as carbon black, has almost no graphitization degree and is not preferable for use in the first resin layer of the present invention.

  The conductive filler contained in the first resin layer may contain a carbon material having a high graphitization rate and / or a conductive material such as carbon black in addition to the fine carbon fiber. The proportion of the high carbon material and / or fine carbon fibers in the conductive filler is preferably 80% by volume or more, more preferably 90% by volume or more, and most preferably consists essentially of them.

  Moreover, as a conductive filler contained in the second and third resin layers, fine carbon fibers are particularly preferable in terms of conductivity and contact resistance.

  The conductive resin layer of the present invention is a mixture of the above-mentioned resin and a conductive filler. At that time, the volume resistance value of the first resin layer in contact with the metal substrate surface is 1.0 Ω · cm or less ( The volume resistance values of the second resin layer and the third resin layer may be appropriately mixed so that the volume low efficiency is smaller than that of the first resin layer. That's fine. The volume resistance values of the second resin layer and the third resin layer are preferably 0.5 Ω · cm or less, particularly 0.3 Ω · cm or less. There is actually an upper limit for making the volume resistance values of the first to third resin layers extremely small, usually 0.0001 Ω · cm or more, for example 0.001 Ω · cm or more, typically 0. .01Ω · cm or more.

  In one embodiment of the present invention, each of the second resin layer and the third resin layer (when present) has a volume content of the conductive filler in each of the layers, and the conductivity in the first resin layer. The layer is configured to be greater than the volume content of the filler. Specifically, the content of the conductive filler in the first resin layer is 10 to 50% by volume (where,% by volume is the volume ratio of the filler to the total volume of the resin layer. The same applies hereinafter. And the content of the conductive filler in the second resin layer and the third resin layer is preferably in the range of 20 to 90% by volume. More preferably, the content in the first resin layer is 15 to 45% by volume, while the content in the second and third resins is 20 to 80% by volume. These contents are preferably selected optimally in consideration of the type of conductive filler and the like, with a volume resistance value of at least 1.0 Ω · cm and in consideration of ease of molding.

  Further, when both the second resin layer and the third resin layer are provided, the type and amount of the conductive filler are appropriately changed so that the second and third resin layers are the same even if they are the same. May be. In a preferred embodiment, the conductive filler contained in the first resin layer is selected from the graphitized carbon material and the fine carbon fibers as described above, and the second resin layer and the third resin layer (respectively present). The conductive filler contained in the case) is a fine carbon fiber. Therefore, in a particularly preferred form, both the second resin layer and the third resin layer exist, and the conductive filler contained in each of them is a fine carbon fiber, and is contained in the first resin layer. This is a case where the conductive filler is a carbon material selected from graphitized carbon materials and fine carbon fibers (particularly graphitized carbon materials are preferred).

  Regarding the thickness of each resin layer, first, the thickness of the first resin layer is usually 5 to 300 μm, preferably 5 to 100 μm, and more preferably 5 to 50 μm. The thicknesses of the second resin layer and the third resin are usually 0.1 to 20 μm, preferably 1 to 10 μm.

  If the thickness of the entire conductive resin layer is too thin, the corrosion resistance to the metal substrate is small, and if it is too thick, the separator becomes thick and the stacked fuel cell becomes large. Thus, it is preferably determined within the normal range of each resin layer. Therefore, it is usually in the range of 5.1 to 340 μm, preferably in the range of 6 to 120 μm, and more preferably in the range of 6 to 70 μm.

Although the manufacturing method of the separator of the present invention is not particularly limited, for example, the first resin layer, the second resin layer, and the third resin layer are each formed in advance as a sheet by ordinary extrusion molding, roll molding method, or the like. In addition, the third resin layer (when present), the first resin layer, and the second resin layer are laminated on one or both surfaces of the metal substrate and integrated by hot pressing. Perform conditions of the heat press method also ordinary pressing conditions, the heating temperature of 120 ° C. to 300 ° C., at a pressure ^{2.9 × 10 6 Pa~9.8 × 10 6} Pa (30kgf / cm 2 ~100kgf / cm 2) approximately That's fine.

  In particular, with respect to the second and third resin layers, a large amount of conductive filler may be contained, and it may be difficult to form a self-holding sheet. It can be laminated by forming a film on the material and thermally transferring it. Examples of the method for forming a film on the transfer substrate include a method in which a solution in which a resin and a conductive filler are dissolved in an appropriate solvent is applied onto the transfer substrate and dried.

  In a fuel cell, it is necessary to form a gas flow path for fuel gas, oxidizing gas, etc. between the separator and the electrode, and the separator surface is provided with a number of protrusions and grooves for forming a gas flow path. Need to be. In order to form the protrusion and the groove, a method of forming a separator having a predetermined shape by forming the protrusion and the groove by pressing after forming a laminate in which a conductive resin layer is provided on a metal substrate is productivity. From the point of view, it is preferable.

  At this time, the resin layer may be cut or cracked depending on conditions during press working. Therefore, in order to prevent this, it is also preferable to press the protective resin film after covering the surface of the conductive resin layer.

  As this protective film, the tensile elongation at break (measured according to JIS K7127) of the film is preferably 150% or more in both the vertical and horizontal directions. If the tensile elongation at break is less than 150%, the elongation as the protective film is small. If a deeper gas flow path is press formed, the resin layer mixed with the conductive filler tends to be cut or cracked.

  Also, the thickness of the protective film is preferably in the range of 5 to 150 μm. If the thickness is less than 5 μm, the film becomes too thin and difficult to handle, and the strength is insufficient, and it tends to break during press molding and hardly function as a protective film. is there. Further, if the thickness exceeds 150 μm, the thickness of the protective film is too thick, and there is a tendency that it is difficult to narrow the intervals between a large number of protrusions and grooves for forming a gas flow path or to form a deep gas flow path. .

  As a material for the protective film, thermoplastic resin, rubber, thermoplastic elastomer, and the like can be used. Specifically, examples of the thermoplastic resin include at least one thermoplastic resin composed of polyolefin, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyurethane, fluororesin, polyamide, polyester, polyamideimide, and the like. .

  Rubbers include natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, butadiene rubber, chloroprene rubber, nitrile rubber, acrylic rubber, epichlorohydrin rubber, chlorinated polyethylene, chlorosulfone. Examples thereof include at least one type of rubber made of fluorinated rubber, silicone rubber, fluorosilicone rubber, fluororubber, polysulfide, urethane rubber and the like.

  Examples of the thermoplastic elastomer include at least one thermoplastic elastomer composed of styrene, olefin, vinyl chloride, urethane, polyester, polyamide, fluorine, conjugated butadiene, silicone, and the like. Among these, polyolefin, ethylene-vinyl acetate copolymer, rubber containing ethylene, and thermoplastic elastomer, which are relatively inexpensive and have a large elongation at break, can be suitably used.

  Here, the method of covering the protective film is not particularly limited, and examples thereof include a pressurizing method and a method using an adhesive.

  Hereinafter, although an example is described, the present invention is not limited to this.

<Measurement of volume resistivity>
The volume resistance value of the conductive film was measured by the following measuring method according to JIS K 7194.
1. Measuring device Loresta HP (Mitsubishi Chemical Corporation)
2. Measurement method Four-terminal four-probe method (ASP type probe)
3. Measurement applied current 100mA

<Method for measuring weight change of first resin layer>
Water is placed in a 1 liter beaker and heated in a water bath to keep the temperature of the water in the beaker between 85-95 ° C.
A sheet of the first resin layer is produced in a thickness range of 50 to 60 μm, cut into 50 × 50 mm, and its weight W1 is weighed.
After the measurement, the first resin layer sheet is immersed in water in a beaker kept at 85 to 95 ° C., and after 3 hours, the sheet is taken out and the water adhering to the surface is sufficiently removed, and then the weight is again measured. Weigh W2.
The weight change of the first resin layer sheet is calculated from the following calculation formula.
(W2-W1) / W1

<Measurement of sheet resistance>
The sheet resistance was evaluated as follows.
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.)
Electrodes: 2 brass flat plates (area 1 square inch, mirror finish)
2. Measurement conditions Method: 4-terminal method Applied current: 10 mA (AC, 287 Hz)
Open terminal voltage: 20 mV peak or less Apparent surface pressure: 18 × 10 ⁵ Pa
Carbon paper: TGP-H-090 (thickness 0.28 mm) manufactured by Toray Industries, Inc.
3. Measurement Method Using the measurement apparatus shown in FIG. 4, the separator 23 is sandwiched by the brass electrode 21 from both sides via the carbon paper 22, and a predetermined load is applied (measurement data in Table 2 is when the load is 1.0 MPa). However, the sheet resistance was obtained by measuring the voltage when a predetermined current was applied by the four-terminal method.

<Corrosion resistance test>
A solution (solid) of fluororesin (“THV220G” manufactured by Sumitomo 3M Limited, specific gravity 2, melting point = 130 ° C.) dissolved in acetone at the end of the press-molded conductive resin / metal composite plate (size 30 mm × 30 mm) And soaked in a concentration of 15% by weight). 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 conductive resin layer was peeled off and the state of rusting 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>
Fluorine resin (THM415G specific gravity 2 manufactured by Sumitomo 3M Co., Ltd.) 60 volume% and graphite (“Showa Denko Co., Ltd. UF-G5 specific gravity 2.2) 40 volume% as a conductive agent are used in a twin screw extruder. Mixed. The interlayer distance _{d 002} plane by wide angle X-ray diffraction of this graphite was 0.336 nm.
The said mixture was shape | molded by extrusion molding (molding temperature 240 degreeC), and the 50-micrometer-thick 1st resin layer 1 was produced. Table 1 shows the volume resistance value and weight change of the obtained first resin layer 1.

  For forming the second resin layer, fluororesin (THV220G specific gravity 2 manufactured by Sumitomo 3M Co., Ltd.) and fine carbon fiber (“Showa Denko (“ Co., Ltd. ”Vapor grown carbon fiber <VGCF> Specific gravity 2) A paint was prepared by mixing at a volume ratio of 30/70. The above-mentioned paint is applied on a base film (polyethylene terephthalate, manufactured by Mitsubishi Chemical Polyester Co., Ltd .: thickness 25 μm) with a bar coater (“Matsuo Sangyo” # 24), the solvent is dried at 80 ° C., and the thickness is 5 μm. Second resin layer 1 was obtained. It was 0.35 ohm-cm when the base film was peeled and the volume resistance value of the 2nd resin layer 1 was measured separately.

On the other hand, a metal substrate having a nickel plating layer of 0.8 μm formed on the surface of SUS304 (thickness 0.3 mm) is used as a metal plate, and a silane coupling agent (TSL8331 manufactured by “GE Toshiba Silicone Co., Ltd.”) is used as a primer. ) A 0.3% ethanol solution was applied to both surfaces of SUS304 on which a plating layer was formed with a # 10 bar coater, and then dried at 100 ° C. for 10 minutes.
On the primer, the above-mentioned paint was applied with a bar coater (“Matsuo Sangyo” # 24), the solvent was dried at 80 ° C., and the third resin layer 1 having a thickness of 5 μm was attached to the metal substrate. .

  In the same manner, the primer layer and the third resin layer 1 were also attached to the back surface of the metal substrate.

  Two sheets of base film / second resin layer 1 and first resin layer 1 are prepared, and base film / second resin layer 1 / first resin layer 1 / third resin layer 1 / primer Layer / metal substrate / primer layer / third resin layer 1 / first resin layer 1 / second resin layer 1 / base film in this order, and laminated and integrated by a hot press method, metal substrate A conductive resin layer in which the second, first, and third resin layers were laminated on both sides was formed.

The hot pressing conditions were a temperature of 200 ° C., 10 minutes, and a pressure of 3.5 × 10 ⁶ Pa (36 kgf / cm ² ). The total thickness of the obtained composite plate 1 was 0.22 mm.

<Example 2>
Fluorine resin (THV415G specific gravity 2 manufactured by Sumitomo 3M Co., Ltd.) 65% by volume and 35% by volume carbon black (“Mitsubishi Chemical Co., Ltd. # 4010 specific gravity 1.75) 35% by volume by a twin screw extruder Mixed. The interlayer distance _{d 002} plane by wide angle X-ray diffraction of the carbon black was 0.341Nm.

  The said mixture was shape | molded by extrusion molding (molding temperature 240 degreeC), and the 50-micrometer-thick 1st resin layer 2 was produced. Table 1 shows the volume resistance value and weight change of the obtained first resin layer 2. Thereafter, the composite plate 2 was produced in the same manner as in Example 1. The total thickness of the composite plate was 0.22 mm.

<Example 3>
Fluorocarbon resin (THV415G specific gravity 2 manufactured by Sumitomo 3M Co., Ltd.) 65% by volume and fine carbon fiber (“Showa Denko Co., Ltd.” gas phase method carbon fiber <VGCF> specific gravity 2) 25% by volume as a conductive agent It mixed with the twin-screw extruder.

  The said mixture was shape | molded by extrusion molding (molding temperature 240 degreeC), and the 50-micrometer-thick 1st resin layer 3 was produced. Table 1 shows the volume resistance value and weight change of the obtained first resin layer 3. Thereafter, a composite plate 3 was produced in the same manner as in Example 1. The total thickness of the composite plate was 0.22 mm.

<Comparative Example 1>
Fluorine resin (THV415G specific gravity 2 manufactured by Sumitomo 3M Co., Ltd.) 88% by volume and carbon black “Lion Co., Ltd.” manufactured by Ketjen Black EC600JD specific gravity 1.5) 12% by volume as a conductive agent using a twin screw extruder. Mixed.

  The said mixture was shape | molded by extrusion molding (molding temperature 240 degreeC), and the 50-micrometer-thick 1st resin layer 4 was produced. Table 1 shows the volume resistance value and weight change of the obtained first resin layer 4. Thereafter, the composite plate 4 was produced in the same manner as in Example 1. The total thickness of the composite plate was 0.22 mm.

  As shown in Table 1, the first resin layer was found to vary greatly in weight change after 3 hours after being immersed in 85-95 ° C. hot water depending on the type of conductive agent contained.

<Results of measuring sheet resistance of Examples 1 to 3 and Comparative Examples 1 and 2>
The measurement results of the sheet resistance values of the composite plates 1 to 4 obtained in Examples 1 to 3 and Comparative Example 1 are shown in Table 2. As Comparative Example 2, resin-impregnated graphite G347B manufactured by Tokai Carbon Co., Ltd. was also evaluated.

  As shown in Table 2, although the sheet resistance of the composite plate 1 is slightly larger than that of the comparative example 2, the sheet resistance values of the composite plates 2, 3 and 4 are small, and the sheet resistance value is almost equivalent to that of the comparative example 2. .

<Acid resistance test results of Examples 1 to 3 and Comparative Example>
An acid resistance test was performed on the composite plates 1 to 4 obtained in Examples 1 to 3 and Comparative Example. The results are shown in Table 3.

  As shown in Table 3, as a result of the acid resistance test, the composite plates 1 to 3 using the first resin layer whose weight change is in the range of 0 to 0.1% are corroded on the surface of the metal substrate (nickel plating layer). Although not confirmed, corrosion was confirmed in the composite plate 4 using the first resin layer having a large weight change.

  As described above, the fuel cell separator of the present invention is particularly excellent in productivity, excellent in conductivity, heat resistance, and acid resistance, and has high utility as a fuel cell separator that can be operated for a long time. .

It is a figure which shows typically the separator vicinity of a fuel cell. It is a figure which shows one example of the layer structure of the separator of this invention. It is a figure which shows one example of the layer structure of the separator of this invention. It is a figure which shows the measuring method of sheet resistance.

Explanation of symbols

1a, 1b Cell 2a, 2b Solid polymer electrolyte membrane 3a, 3b Electrode 4a, 4b Gas flow path 10 Separator 11 Metal substrate 12 Conductive resin layer 13 First resin layer 14 Second resin layer 15 Third resin layer 21 Brass electrode 22 Carbon paper 23 Separator

Claims (12)

In a fuel cell separator in which a conductive resin layer mixed with a conductive filler is laminated on at least one surface of a metal substrate,
The conductive resin layer is (a) a volume resistance value is 1.0 Ω · cm or less, and a weight change after being immersed in water at 85 to 95 ° C. for 3 hours is in a range of 0 to 0.1%. A resin layer of
(B) The surface of the conductive resin layer is formed and the volume resistance value is provided at the interface between the second resin layer and the metal substrate, which is smaller than the first resin layer, and the volume resistance value is higher than that of the first resin layer. A separator for a fuel cell having at least one resin layer of the third resin layer having a smaller size.   The first resin layer contains 10-50% by volume of a conductive filler, and the second resin layer and the third resin layer contain 20-90% by volume of a conductive filler, respectively. The fuel cell separator according to claim 1, wherein:   The fuel cell separator according to claim 1 or 2, wherein the conductive filler of the first to third resin layers contains a carbon-based material.   The conductive filler of the first resin layer is substantially composed of one or more selected from graphitized carbon materials and fine carbon fibers. Fuel cell separator. 5. The fuel cell separator according to claim 4, wherein the interstitial distance in the thickness direction of the d ₀₀₂ plane measured by wide-angle X-ray diffraction of the graphitized carbon material is 0.350 nm or less.   The fuel cell separator according to any one of claims 1 to 5, wherein the conductive filler contained in each of the second resin layer and the third resin layer contains fine carbon fibers. .   The fuel cell separator according to any one of claims 4 to 6, wherein the fine carbon fiber has a fiber diameter of 0.001 to 0.5 µm and a fiber length of 1 to 100 µm.   The fuel cell separator according to any one of claims 1 to 7, wherein the resin is selected from the group consisting of a fluororesin, a fluororubber, a polyolefin resin, and a polyolefin elastomer.   The fuel cell separator according to any one of claims 1 to 8, wherein the material of the metal substrate is selected from the group consisting of stainless steel, titanium, aluminum, copper, nickel, and steel.   The metal substrate has a plating layer made of at least one metal selected from the group consisting of nickel, tin, copper, titanium, gold, platinum, silver and palladium on the surface. The fuel cell separator according to claim 1. A method for producing the fuel cell separator according to any one of claims 1 to 10,
Laminating a conductive resin layer in which a resin and a conductive filler are mixed on at least one surface of a metal substrate;
The manufacturing method of the separator for fuel cells which has the process of forming the protrusion part and groove part which become a gas flow path by press-processing the board | substrate which laminated | stacked the conductive resin layer. A method for producing a separator for a fuel cell according to any one of claims 1 to 10,
Laminating a conductive resin layer in which a resin and a conductive filler are mixed on at least one surface of a metal substrate;
Coating the outermost surface of the metal substrate on which the conductive resin layer is laminated with a protective film;
A step of forming a projection and a groove to be a gas flow path by pressing a substrate covered with a protective film; and
And a step of peeling the protective film from the substrate on which the protrusion and the groove are formed.

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