JP5968857B2 - Method for producing titanium fuel cell separator - Google Patents

Description

  The present invention relates to a method for producing a titanium fuel cell separator used in a fuel cell.

  Unlike primary batteries such as dry batteries and secondary batteries such as lead-acid batteries, fuel cells that can continuously extract power by continuing to supply fuel such as hydrogen and oxidants such as oxygen have high power generation efficiency. It is not significantly affected by the size of the system, and there is little noise and vibration. Therefore, the fuel cell is expected as an energy source covering various uses and scales. Specifically, the fuel cell includes a polymer electrolyte fuel cell (PEFC), an alkaline electrolyte fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), and a solid oxide. It has been developed as a type fuel cell (SOFC) and biofuel cell. In particular, solid polymer fuel cells are being developed for use in fuel cell vehicles, home cogeneration systems, mobile devices such as mobile phones and personal computers.

  A polymer electrolyte fuel cell (hereinafter referred to as a fuel cell) is a single cell in which a polymer electrolyte membrane is sandwiched between an anode and a cathode, and a groove serving as a gas (hydrogen, oxygen, etc.) channel is formed. A plurality of the single cells are overlapped via a separator (also called a bipolar plate).

  Since the separator is also a part for taking out the current generated in the fuel cell to the outside, a material having a low contact resistance (which means that a voltage drop occurs due to an interface phenomenon between the electrode and the separator surface). Applied. In addition, the separator is required to have high corrosion resistance because the inside of the fuel cell is an acidic atmosphere having a pH of about 2 to 4, and the low contact resistance (conductivity) is maintained for a long time during use in this acidic atmosphere. The characteristic that

  In order to satisfy these requirements, a separator using a metal material as a base material is directed and the following proposals have been made.

For example, a metal material such as aluminum alloy, stainless steel, nickel alloy, titanium alloy, etc. that can be thinned and has excellent workability and high strength is used as a base material, and Au, Pt, etc. that have both corrosion resistance and conductivity. A separator that has been coated with a noble metal to impart corrosion resistance and conductivity has been proposed.
However, these noble metal materials are very expensive and therefore expensive.

  Here, carbon is attracting attention as a material that satisfies the requirements of conductivity, durability, and low cost, and application of carbon to a separator is being studied. Specifically, a method of forming an intermediate layer and a carbon thin film on the surface of the oxide film of the substrate itself by a vapor deposition method (Patent Document 1), a portion made of a metalloid element and carbon on the substrate surface (Patent Document 2), a separator in which carbon particles are attached to a base material made of a metal material such as titanium or stainless steel (Patent Document 2) For example, Patent Documents 3 to 6) have been studied.

Japanese Patent No. 4147925 Japanese Patent Laid-Open No. 2004-14208 Japanese Patent No. 3904690 Japanese Patent No. 3904696 Japanese Patent No. 4886885 Japanese Patent No. 5108986

The techniques disclosed in Patent Documents 1 and 2 form a conductive thin film on a metal substrate by vapor deposition, but press forming for forming a gas flow path on the substrate after the thin film is formed. When performing, there is a high possibility that the thin film will peel off from the substrate. Therefore, it is necessary to form the conductive thin film one by one under a vacuum after press molding, and there is a disadvantage that productivity is poor.
On the other hand, the techniques disclosed in Patent Documents 3 to 6 have the possibility that the carbon particles and the carbon layer can withstand the press molding, but the carbon particles fall off during handling after the press molding (such as the operation of incorporating the separator into the cell). Or the carbon layer may peel off. As a result, the base material may be locally exposed and the conductivity may be lowered.

  This invention is made | formed in view of the said problem, The subject is the handling after press molding, when a carbon-type conductive layer (a carbon layer, a conductive resin layer) coat | covers the base-material surface favorably. A method for producing a titanium fuel cell separator capable of maintaining high conductivity for a long time even in a high temperature / acid atmosphere inside the cell while suppressing the possibility of peeling of the carbon-based conductive layer during the operation of incorporating the separator into the cell, etc. Is to provide.

  As a result of intensive studies, the inventors performed a press molding step after the carbon layer forming step and the conductive resin layer forming step, or formed a conductive resin layer after the carbon layer forming step and the press molding step. By performing the process, the possibility of peeling of the carbon-based conductive layer (carbon layer, conductive resin layer) during handling after press molding can be reduced, and high conductivity can be maintained for a long time. The headline and the present invention were created.

  In order to solve the above-described problems, a method for manufacturing a titanium fuel cell separator according to the present invention includes a carbon layer forming step of forming a carbon layer containing graphite on a substrate surface made of pure titanium or a titanium alloy, and the carbon layer. After the forming step, a conductive resin layer forming step of forming a conductive resin layer containing carbon powder and resin on the base material on which the carbon layer has been formed; and after the conductive resin layer forming step, the carbon Press forming the base material on which the layer and the conductive resin layer are formed to form a gas flow path.

  Thus, since the manufacturing method of the titanium fuel cell separator according to the present invention performs the press molding step after the carbon layer forming step and the conductive resin layer forming step, the conductive resin layer is protected during the press molding. Since it plays the role of a layer, it is possible to avoid peeling and dropping of the carbon layer during press molding. The two layers of the carbon layer and the conductive resin layer formed on the base material improve conductivity and durability (conductivity durability: property of maintaining conductivity for a long time), and the conductive resin layer The possibility of peeling of the carbon-based conductive layer (carbon layer, conductive resin layer) during handling after press molding is reduced.

  It is preferable that the manufacturing method of the titanium fuel cell separator according to the present invention includes a heat treatment step of heat-treating the base material after the press molding step.

  Thus, since the manufacturing method of the titanium fuel cell separator according to the present invention performs the heat treatment step after the press molding step, the resin on the outermost surface of the conductive resin layer can be partially decomposed and removed. The increase in contact resistance due to the high resin ratio of the conductive resin layer can be suppressed. As a result, a titanium fuel cell separator with a further reduced contact resistance can be produced.

  The method for manufacturing a titanium fuel cell separator according to the present invention preferably includes a heat treatment step of heat-treating the substrate in a non-oxidizing atmosphere between the carbon layer forming step and the conductive resin layer forming step. .

  Thus, since the manufacturing method of the titanium fuel cell separator according to the present invention includes the heat treatment step between the carbon layer forming step and the conductive resin layer forming step, titanium is interposed between the base material and the carbon layer. An intermediate layer containing carbide can be formed. As a result, it is possible to manufacture a titanium fuel cell separator in which the adhesion between the base material and the carbon layer is improved and the possibility of peeling of the carbon layer and the conductive resin layer is reduced.

  Further, the method for producing a titanium fuel cell separator according to the present invention includes a carbon layer forming step of forming a carbon layer containing graphite on a substrate surface made of pure titanium or a titanium alloy, and after the carbon layer forming step, Press forming the base material on which the carbon layer is formed to form a gas flow path, and after the press forming step, carbon powder and resin are formed on the base material on which the carbon layer is formed and press formed. And a conductive resin layer forming step of forming a conductive resin layer including:

  As described above, in the method for manufacturing a titanium fuel cell separator according to the present invention, the conductive resin layer forming step is performed after the press molding step, and the carbon layer follows the deformation of the base material during the press molding. Even if the carbon layer is broken, it can be protected by covering the cracked portion of the carbon layer by forming a conductive resin layer so as to be laminated thereafter. The two layers of the carbon layer and the conductive resin layer formed on the base material improve conductivity and durability (conductivity durability: property of maintaining conductivity for a long time), and the conductive resin layer The possibility of peeling of the carbon-based conductive layer (carbon layer, conductive resin layer) during handling after press molding is reduced.

  The titanium fuel cell separator manufacturing method according to the present invention preferably includes a heat treatment step of heat-treating the substrate after the conductive resin layer forming step.

  Thus, since the manufacturing method of the titanium fuel cell separator according to the present invention includes the heat treatment step after the conductive resin layer forming step, the resin on the outermost surface of the conductive resin layer can be partially decomposed and removed. Therefore, an increase in contact resistance due to a high resin ratio of the conductive resin layer can be suppressed. As a result, a titanium fuel cell separator with a further reduced contact resistance can be produced.

  The method for producing a titanium fuel cell separator according to the present invention preferably includes a heat treatment step of heat-treating the base material in a non-oxidizing atmosphere between the carbon layer forming step and the press forming step.

  Thus, since the manufacturing method of the titanium fuel cell separator according to the present invention includes the heat treatment step between the carbon layer forming step and the press molding step, the titanium carbide is included between the base material and the carbon layer. An intermediate layer can be formed. As a result, it is possible to manufacture a titanium fuel cell separator in which the adhesion between the base material and the carbon layer is improved and the possibility of peeling of the carbon layer and the conductive resin layer is reduced.

In the method for manufacturing a titanium fuel cell separator according to the present invention, since the carbon forming step, the conductive resin layer forming step, and the press molding step are performed in a predetermined order, the carbon layer and the conductive resin layer are separated. -A titanium fuel cell separator formed on the surface of the substrate without dropping off can be produced.
Therefore, according to the manufacturing method of the titanium fuel cell separator according to the present invention, the carbon-based conductive layer (carbon layer, conductive resin layer) can be peeled off during handling after press molding (operation for incorporating the separator into the cell). Possibility is suppressed, and a titanium fuel cell separator capable of maintaining high conductivity for a long time even in a high temperature / acid atmosphere inside the cell can be manufactured.

  In addition, when a separator is used for a motor vehicle use, there is a high possibility of being subjected to friction from a carbon cloth or carbon paper with which the separator surface comes into contact due to vibration during traveling. However, according to the method for manufacturing a titanium fuel cell separator according to the present invention, two layers of a carbon layer and a conductive resin layer are formed on the base material. Possibility of peeling of the system conductive layer (carbon layer, conductive resin layer) can also be suppressed.

(A) And (b) is a flowchart of the manufacturing method of the titanium fuel cell separator which concerns on embodiment of this invention. (A) is typical sectional drawing of the titanium fuel cell separator which concerns on embodiment of this invention, (b) is typical sectional drawing of the titanium fuel cell separator in X part of (a). is there. It is typical sectional drawing of the fuel cell separator which concerns on the Example of this invention. It is the schematic of the contact resistance measuring apparatus used in the evaluation of the electroconductivity, durability, and abrasion resistance in an Example.

  Hereinafter, the form for implementing the titanium fuel cell separator (henceforth a separator suitably) and the manufacturing method of a separator concerning the present invention are explained in detail.

≪Titanium fuel cell separator≫
As shown in FIG. 2A, the separator 10 according to the present embodiment has an uneven shape in a cross-sectional view because the gas flow path 13 is formed on the surface. The separator 10 is provided between the cell 14 and the cell 14 configured by stacking the gas diffusion layers 11 and 11 and the electrolyte membrane 12.
Specifically, as shown in FIG. 2B, the separator 10 according to the present embodiment includes a base material 1 made of pure titanium or a titanium alloy, and carbon formed on the surface (one side or both sides) of the base material 1. And an intermediate layer 3 between the substrate 1 and the carbon-based conductive layer 2.
2B shows the separator 10 in which the carbon-based conductive layer 2 and the intermediate layer 3 are formed only on one side of the substrate 1, the carbon-based conductive layer 2 and the both sides of the substrate 1 are shown. An intermediate layer 3 may be formed.
Hereinafter, the substrate 1, the carbon-based conductive layer 2, and the intermediate layer 3 of the separator 10 will be described.

<Base material>
The base material of the separator according to this embodiment is obtained by molding a plate material into the shape of a fuel cell separator. It is preferable to use a metal base material from the viewpoint of workability required for forming a groove to be a gas flow path, gas barrier property, conductivity and thermal conductivity, particularly pure titanium or titanium. An alloy is very preferable because it is lightweight, excellent in corrosion resistance, and excellent in strength and toughness.

  The substrate may be prepared by a conventionally known method, for example, a method of melting and casting pure titanium or a titanium alloy to form an ingot, hot rolling, and then cold rolling. Further, the base material is preferably annealed, but the finished state is not limited, and for example, in any finished state such as “annealing + pickling finish”, “vacuum heat treatment finish”, “bright annealing finish”, etc. It does not matter.

  The base material is not limited to pure titanium or titanium alloy having a specific composition, but when a base material made of pure titanium or titanium alloy is used, cold rolling of the titanium material (base material) is performed. From the viewpoint of ease (cold rolling with a total rolling reduction of 35% or more can be performed without intermediate annealing) and securing the press formability after that, for example, 1-4 kinds of pure titanium specified in JIS H 4600, Ti alloys such as Ti-Al, Ti-Ta, Ti-6Al-4V, Ti-Pd can be applied. Among these, pure titanium that is particularly suitable for thinning is preferable. Specifically, O: 1500 ppm or less (more preferably 1000 ppm or less), Fe: 1500 ppm or less (more preferably 1000 ppm or less), C: 800 ppm or less, N: 300 ppm or less, H: 130 ppm or less, with the balance being Ti and What consists of an unavoidable impurity is preferable and a JIS 1 type cold-rolled board can be used. In addition, by using a titanium base material, the strength and toughness of the separator are improved, and since it is lightweight, it is particularly easy to use as an automobile.

  The plate thickness of the substrate is preferably 0.05 to 1.0 mm. If the plate thickness is less than 0.05 mm, the strength required for the substrate cannot be ensured. On the other hand, if it exceeds 1.0 mm, it becomes difficult to perform fine processing of the gas flow path through which hydrogen or air passes. It is.

<Carbon-based conductive layer>
The carbon-based conductive layer has a two-layer structure. And as shown in FIG.2 (b), the carbon-type conductive layer 2 has the carbon layer 21 formed in the side near the base material 1, and the conductive resin layer 22 formed in the side far from the base material 2. Consists of

(Carbon layer)
The carbon layer includes graphite and is provided so as to cover the base material. And since graphite contained in the carbon layer has high crystallinity and excellent conductivity, it imparts conductivity to the separator and also provides durability to maintain conductivity even in the fuel cell internal environment (high temperature, acidic atmosphere). To do.
The graphite contained in the carbon layer is preferably configured to include at least one of scaly graphite powder, scaly graphite powder, expanded graphite powder, and pyrolytic graphite powder.

  And a carbon layer does not contain resin (binder resin) substantially unlike the conductive resin layer mentioned later. Here, “substantially free of resin” means that, in the carbon layer, the mass ratio of the solid component of the resin and graphite (the mass of resin solids in the carbon layer / the mass of carbon powder in the carbon layer) is 0.1 or less. Indicates that

  The carbon layer is preferably coated on the entire surface of the base material, but the entire surface does not necessarily have to be coated, and is coated on at least 40% of the surface in order to ensure conductivity and corrosion resistance. Just do it. If the coverage is less than 40%, the conductivity is insufficient and the required characteristics as a separator are not satisfied. A preferable range of the coverage is 45% or more, and more preferably 50% or more.

Although the adhesion amount of a carbon layer is not specifically limited, It is preferable that it is 2-1000 microgram / cm < ² >. If the amount is less than 2 μg / cm ² , the amount of adhesion is small and the conductivity and corrosion resistance cannot be ensured. If the amount exceeds 1000 μg / cm ² , the effects of conductivity and corrosion resistance are saturated and workability is reduced. Because. And the adhesion amount of a carbon layer becomes like this. More preferably, it is 5 microgram / cm < ² > or more, More preferably, it is 10 microgram / cm < ² > or more.
In addition, the coverage and adhesion amount of the carbon layer can be controlled by the amount of graphite powder applied to the substrate in the graphite powder application step described later.

(Conductive resin layer)
The conductive resin layer includes carbon powder and resin, and functions as a protective film having both conductivity and wear resistance.
The carbon powder contained in the conductive resin layer is preferably carbon black powder, acetylene black powder, graphite powder or a mixed powder thereof. These powders are excellent in conductivity and corrosion resistance, and are inexpensive because they are inexpensive materials.

  The resin (binder resin) for forming the conductive resin layer is one or more resins selected from acrylic resin, polyester resin, alkyd resin, urethane resin, silicone resin, phenol resin, epoxy resin, and fluororesin. . When two or more resins are included, the resins may react with each other or may simply be mixed. However, this resin is preferably a resin that can be made into a paint. Furthermore, it is more preferable to select from a urethane resin, a silicone resin, a phenol resin, an epoxy resin, or a fluororesin that is stable even in a high temperature (80 to 100 ° C.) and acidic (pH 2 to 4) atmosphere in the fuel cell.

  The conductive resin layer is formed by applying a conductive resin paint prepared by mixing a resin and carbon powder, but the mass ratio of the solid component of the resin and the carbon powder in the paint (resin solids in the paint). The partial mass / mass of carbon powder in the paint is preferably 0.5-10. If the mass ratio is less than 0.5, the ratio of the resin component when the conductive resin layer is formed becomes small, so that the strength as the layer is insufficient and the intended wear resistance cannot be obtained. On the other hand, if this mass ratio exceeds 10, the ratio of the carbon powder when it becomes a conductive resin layer becomes small and the electrical resistance as a layer increases, which is not preferable in terms of the characteristics of the separator material. A more preferable range of the mass ratio is 0.8 to 8.

  The thickness of the conductive resin layer is preferably 0.1 to 20 μm. If the thickness of the conductive resin layer is less than 0.1 μm, the conductive resin layer is broken by slight friction, resulting in insufficient wear resistance. On the other hand, if the thickness of the conductive resin layer exceeds 20 μm, the electrical resistance as the layer increases, which is not preferable in terms of the separator characteristics. A more preferable thickness of the conductive resin layer is 0.3 to 19 μm.

(Relationship between carbon layer and conductive resin layer)
When the conductive resin layer is formed on the carbon layer, if the graphite powder added to the conductive resin layer protrudes slightly from the layer, that portion becomes a good conductive path, and the electrical conductivity of the conductive resin layer This is very preferable because the resistance is reduced.
And as above-mentioned, the coverage of a carbon layer does not necessarily need to be 100%, and should just be 40% or more. Here, when the coverage of the carbon layer is smaller than 100%, a part of the surface of the carbon layer has a portion where the surface of the titanium or titanium alloy is exposed. It will be in the state where the conductive resin layer is formed. In other words, a portion in which two carbon-based conductive layers are formed on the substrate and a portion in which only one conductive resin layer is formed are mixed. Conductivity can be obtained even with a single conductive resin layer, but the conductivity is particularly good at the portion where the two carbon-based conductive layers are formed, and this portion becomes a good conductive path. That is, in the present invention, the carbon-based conductive layer has a two-layer structure, so that sufficient conductivity and durability can be obtained macroscopically.
The coverage of the conductive resin layer is preferably 100%, but may be 70% or more in order to ensure wear resistance and conductivity.

<Intermediate layer>
As shown in FIG. 2B, the intermediate layer 3 of the separator 10 according to this embodiment is preferably formed at the interface between the base material 1 and the carbon layer 21. The intermediate layer includes titanium carbide (titanium carbide, TiC) generated by reaction between C and Ti diffusing at the interface between the base material and the carbon layer, and further includes carbon solid solution titanium (C solid solution Ti). ) May be included.
And since titanium carbide has electroconductivity, the electrical resistance in the interface of a base material and a carbon layer becomes small. Therefore, the conductivity of the separator is further improved by providing an intermediate layer containing titanium carbide. In addition, since the intermediate layer containing titanium carbide is formed by the reaction between the base material and the carbon layer, the adhesion between the base material and the carbon layer is improved.

≪Method for manufacturing titanium fuel cell separator≫
Next, a method for manufacturing a titanium fuel cell separator according to the present invention will be described.
As shown in FIG. 1, the separator manufacturing method according to the present invention includes a carbon layer forming step S1, a conductive resin layer forming step S3, and a press molding step S4.
The separator manufacturing method according to the present invention preferably includes a heat treatment step S2 after the carbon layer formation step S1, and after the press molding step S4 (or conductive resin layer formation step S3), the heat treatment step S5. It is preferable to contain. Moreover, the base-material manufacturing process may be included before carbon layer formation process S1.
Hereinafter, after explaining each process in detail, the order of each process is explained.

<Base material manufacturing process>
The base material production process refers to casting or hot rolling the above pure titanium or titanium alloy by a known method, performing annealing / pickling treatment, etc. as needed, and cold rolling to a desired thickness. It is a process of rolling a sheet to produce a plate (strip) material. In addition, although the presence or absence of the annealing finish after cold rolling is not ask | required, in order to ensure the workability required at the time of press molding, it is preferable to anneal after cold rolling. In addition, the presence or absence of the pickling after cold rolling (+ after annealing) does not matter.

<Carbon layer formation process>
The carbon layer forming step S1 is a step of forming a carbon layer containing graphite on the substrate surface.
In the carbon layer forming step S1, first, graphite powder is applied to the surface (one side or both sides) of the base material (graphite powder applying step). The application method is not particularly limited, but a slurry in which graphite powder is directly adhered to a base material in a powder form or graphite powder is dispersed in a paint containing an aqueous solution such as methylcellulose or a binder such as a resin is used. It may be applied to the surface of the material.

  About the graphite powder apply | coated to the surface of a base material, it is preferable to use a thing with a diameter of 0.5-100.0 micrometers. When the diameter is less than 0.5 μm, the force with which the powder is pressed against the base material during the rolling process described later becomes small and it is difficult to adhere to the base material. On the other hand, when the diameter exceeds 100.0 μm, it becomes difficult to adhere to the surface of the base material in the graphite powder coating step and the rolling step described later.

The method of applying the slurry in which the graphite powder is dispersed to the substrate is not particularly limited, but the slurry may be applied to the substrate using a bar coater, roll coater, gravure coater, dip coater, spray coater or the like. That's fine.
The method for adhering the graphite powder on the substrate is not limited to the above method, and the following method is also used. For example, a method of sticking a graphite powder-containing film prepared by kneading graphite powder and a resin onto a substrate, a method of driving graphite powder onto the substrate surface by shot blasting, and supporting it on the substrate surface are conceivable. .

  And in carbon layer formation process S1, after apply | coating graphite powder, the graphite powder is crimped | bonded to the base-material surface by performing cold rolling (crimping process). By passing through the pressure bonding step, the graphite powder is pressure bonded to the substrate surface as a carbon layer. In addition, since the carbon powder adhering to the substrate surface also serves as a lubricant, the lubricant does not have to be used when performing cold rolling. After rolling, the graphite powder is not granular, and is attached in a thin layer on the substrate to cover the substrate surface.

In this crimping step, in order for the carbon layer to be crimped to the substrate with good adhesion, it is preferable to perform rolling at a total rolling reduction of 0.1% or more.
The rolling reduction is a value calculated from the change in material thickness including the carbon layer before and after cold rolling, and “rolling reduction = (t0−t1) / t0 × 100” (t0: after the graphite powder coating step) , Initial material thickness, t1: material thickness after rolling).

<Heat treatment process>
The heat treatment step S2 is a step of heat-treating the base material on which the carbon layer is formed in a non-oxidizing atmosphere. Specifically, in the heat treatment step S2, the intermediate layer containing titanium carbide formed by the reaction between the base material and the carbon layer is formed at the interface between the base material and the carbon layer. This is a step of performing heat treatment in a non-oxidizing atmosphere after the crimping step. In addition, a base material is annealed by heat processing process S2, and the workability at the time of press molding is also securable.

It is preferable that the range of the heat processing temperature in heat processing process S2 is 300-850 degreeC. When the heat treatment temperature is less than 300 ° C., the reaction between graphite (carbon layer) and the substrate hardly occurs, and the adhesion is difficult to improve. On the other hand, if the heat treatment temperature exceeds 850 ° C., phase transformation of the base material (titanium) may occur, and mechanical properties may be deteriorated.
The range of the heat treatment temperature in the heat treatment step S2 is more preferably 400 to 800 ° C, and further preferably 450 to 780 ° C.

Moreover, it is preferable that the time of the heat processing in heat processing process S2 is 0.5 minute-10 hours. Then, it is preferable to appropriately adjust the time depending on the temperature, such as a long-time treatment when the temperature is low and a short-time treatment when the temperature is high. Further, the heat treatment temperature and time can be appropriately adjusted depending on the state of the material, such as heat treatment in a roll-to-roll or sheet shape, or heat treatment in a coiled state.
The resin component (binder resin component) and solvent contained in the slurry in which the graphite powder is dispersed are carbonized by this heat treatment to become almost inorganic, so that the resin component is substantially contained in this carbon layer. And good conductivity can be obtained.

  The heat treatment step S2 is performed in a non-oxidizing atmosphere such as a vacuum or an Ar gas atmosphere. The non-oxidizing atmosphere in the heat treatment step S2 is an atmosphere having a low oxygen partial pressure, and preferably an atmosphere having an oxygen partial pressure of 10 Pa or less. If it exceeds 10 Pa, graphite reacts with oxygen in the atmosphere to become carbon dioxide (causes a combustion reaction), and the base material is oxidized to deteriorate the conductivity. is there.

<Conductive resin layer forming step>
The conductive resin layer forming step S3 is a step of forming a conductive resin layer containing carbon powder and resin on the base material on which the carbon layer is formed. In this conductive resin layer forming step S3, specifically, a conductive resin coating is laminated and applied to the surface of the carbon layer formed on the substrate.
This conductive resin paint is prepared by using the above-described carbon powder in a paint containing the above-described resin (binder resin) by dispersing it so that the mass ratio of the resin solid content to the carbon powder falls within the above range. Good.
In addition, it does not specifically limit about the solvent of a conductive resin coating material, What is necessary is just to use a well-known organic solvent.

  The method of applying the conductive resin paint in which the carbon powder is dispersed to the base material is not particularly limited, but it is conductive on the carbon layer using a bar coater, roll coater, gravure coater, dip coater, spray coater or the like. What is necessary is just to apply a functional resin paint.

<Press molding process>
The press forming step S4 is a step of forming a gas channel by forming a base material.
The base material in the press molding step S4 may be molded by a known press molding apparatus using a molding die. In addition, the presence or absence of the use of the lubricant during press molding may be appropriately determined according to the complexity of the target shape, etc., and when performing press molding using the lubricant, a process for removing the lubricant, What is necessary is just to carry out as a part of press molding process.

<Heat treatment process>
The heat treatment step S5 is a step of heat-treating the base material on which the carbon layer and the conductive resin layer (and the intermediate layer) are formed at a predetermined temperature.
In the heat treatment step S5, heat treatment is performed in the range of 200 to 550 ° C. in order to further reduce the contact resistance of the conductive resin layer. When the resin component ratio in the conductive resin layer is high, the contact resistance may be slightly high. In such a case, the outermost surface of the conductive resin layer is reduced by performing heat treatment in the range of 200 to 550 ° C. A part of the covering resin film is decomposed and removed, so that the added carbon powder is exposed, and the conductivity in this part is increased.

If the heat treatment temperature is lower than 200 ° C., the effect of reducing contact resistance is weak, so it takes a long time to reduce the target contact resistance. On the other hand, if the temperature exceeds 550 ° C., the effect of reducing the contact resistance is saturated, and further, the decomposition of the conductive resin layer may proceed excessively, and the target wear resistance may not be obtained.
The range of the heat treatment temperature in the heat treatment step S4 is preferably in the range of 250 to 500, more preferably in the range of 270 to 450 ° C.
And the heat treatment atmosphere of heat treatment process S4 can be implemented in the atmosphere containing oxygen like air atmosphere, for example.

≪Order of each process≫
The order of each process described above in the method for producing a titanium fuel cell separator according to the present invention will be described in detail.

  In the separator manufacturing method according to the present invention, after the carbon layer forming step S1 (and the heat treatment step S2), as shown in FIG. 1A, the conductive resin layer forming step S3 → the press molding step S4 → the heat treatment step S5. In this order, as shown in FIG. 1B, there are a press molding step S4, a conductive resin layer forming step S3, and a heat treatment step S5.

In the case of the order shown in FIG. 1A, since the conductive resin layer forming step S3 is performed before the press molding step S4, the conductive resin layer is formed at the time of press molding when the base material is subjected to press molding. Since it plays the role of a protective layer, it is possible to avoid peeling and dropping of the carbon layer during press molding.
In addition, although it is anticipated that a crack will generate | occur | produce in a conductive resin layer depending on the grade of press molding process S4, in such a case, conductive resin layer formation process S3 is performed again after press molding process S4. Also good.

  In the order shown in FIG. 1B, the conductive resin layer forming step S3 is performed after the press forming step S4. However, the carbon layer cannot follow the deformation of the base material at the time of press forming, and should be carbon. Even if the layer is broken, the conductive resin layer is formed so as to be laminated thereafter, so that the layer covers and protects the cracked portion of the carbon layer. As a result, the possibility of peeling and dropping of the carbon layer from the substrate can be reduced.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the design can be appropriately changed without departing from the gist of the present invention described in the claims.

  Next, the titanium fuel cell separator according to the present invention will be specifically described by comparing an example satisfying the requirements of the present invention with a comparative example not satisfying the requirements of the present invention.

≪Preparation of test specimen≫
[Base material]
As the substrate, a JIS type 1 titanium substrate was used.
The chemical composition of the titanium substrate (cold rolling finish) is O: 450 ppm, Fe: 250 ppm, N: 40 ppm, the balance being Ti and inevitable impurities. And the plate | board thickness of the titanium base material was 0.1 mm, and the size was 80x160 mm. The titanium substrate is obtained by subjecting a titanium raw material to a conventionally known melting step, casting step, hot rolling step, and cold rolling step.

[Carbon layer]
As the graphite powder, expanded graphite powder (manufactured by SEC Carbon, SNE-6G, average particle diameter 7 μm, purity 99.9%) is used, and the graphite powder is 7 wt% in a 0.7 wt% carboxymethyl cellulose aqueous solution. A slurry was prepared by dispersing. And the slurry was apply | coated to both surfaces of the titanium base material using the 5th count bar coater, and the graphite powder coating material was produced.
Then, using a two-stage rolling mill with a work roll diameter of 200 mm, roll pressing was performed with a load of 2.5 tons, and the graphite powder was crushed and adhered onto the substrate. The work roll is not coated with lubricating oil.
The material forming the carbon layer was subjected to a heat treatment at a temperature of 650 ° C. for 5 minutes in a vacuum atmosphere of 6.7 × 10 ⁻³ Pa.
In addition, the coverage of the carbon layer of the test body obtained by this method was approximately 60%.

[Conductive resin layer-1]
The conductive resin paints are phenol resin (Arakawa Chemical Industries, Tamanol 2800), acrylic resin (Toray Fine Chemical, Cotax LH681), epoxy resin (Cemedine, EP106), polyester resin (Arakawa Chemical Industries). Made of 7005N) and silicone resin (manufactured by Shin-Etsu Silicone Co., Ltd., KR251), and carbon powder was dispersed in each paint. As carbon powder, carbon black powder (manufactured by Cabot, Vulcan XC72, average particle size 40 nm, purity 99.2%), graphite powder (manufactured by Ito Graphite Co., Ltd., Z-5F, average particle size 4 μm, purity 98.9%) ) Was used.
Using an organic solvent suitable for each resin-based paint, the concentration of solid content (resin component + carbon powder) in the paint (= ((resin component mass + carbon powder mass) × 100) / paint mass) is Carbon black so that the mass concentration of carbon powder in the solid content (= (carbon powder mass × 100) / (resin component mass + carbon powder mass)) is approximately 25% by mass so that it is approximately 18% by mass. The concentration was adjusted so that the ratio of the powder to the graphite powder was 10: 1, and the paint was applied onto the material on which the carbon layer was formed using a bar coater and dried. Thus, the conductive resin layer was formed on both surfaces of the substrate. The test body which changed the thickness of the conductive resin layer by changing the count of the bar coater used at this time was produced.

[Press molding]
A substrate having a carbon layer and a conductive resin layer formed on the surface was cut out to 50 mm × 50 mm, and then press-molded with a mold to obtain a shape as shown in FIG.

[Heat treatment after forming conductive resin layer]
Some of the specimens obtained by press molding after forming the conductive resin layer were subjected to heat treatment. And heat processing was implemented by adjusting process time suitably on the conditions of 300-400 degreeC in air | atmosphere atmosphere.

≪Evaluation of specimens≫
[Measurement of carbon layer coverage]
Using a scanning electron microscope, the surface of the test body on which the carbon layer was formed was observed in a range of 550 × 400 μm at an observation magnification of 200 times, and the reflected electron image was taken. The reflected electron image is binarized into a portion where the carbon layer is covered by image processing and a portion where the base material is exposed without being covered by the carbon layer, and the area ratio occupied by the carbon layer is calculated and the coverage ratio is calculated. Asked. Observation was performed for 3 fields per specimen, and the average value of 3 fields was calculated.

[Measurement of conductive resin layer thickness]
The material thickness before and after forming the conductive resin layer on the test body on which the carbon layer was formed was measured using a micrometer, and the thickness of the conductive resin layer was calculated from the difference in thickness before and after. The thickness was measured at three locations per specimen and the average value at three locations was calculated.

[Contact resistance measurement]
About each obtained test body, contact resistance was measured using the contact resistance measuring apparatus shown in FIG. Specifically, both sides of the test body are sandwiched between two carbon papers, and the outside is sandwiched between two copper electrodes with a contact area of 4 cm ² and pressurized with a load of 40 kgf, and 7.4 mA is applied using a direct current power source. A current was applied, and a voltage applied between the carbon papers was measured with a voltmeter, and a contact resistance (initial contact resistance) was obtained assuming that the contact area was 2/5 of a flat plate.
The conductivity was good when the initial contact resistance was 12 mΩ · cm ² or less, and the conductivity was poor when the initial contact resistance exceeded 12 mΩ · cm ² .

[Durability evaluation]
In addition, durability evaluation (durability test) was performed on the test body in which the initial contact resistance was determined to be acceptable. That is, after the specimen was immersed in an 80 ° C. sulfuric acid aqueous solution (pH 2) having a specific liquid volume of 10 ml / cm ² for 500 hours, the specimen was taken out from the sulfuric acid aqueous solution, washed and dried, and The contact resistance was measured by the same method.
When the contact resistance after the durability test was 15 mΩ · cm ² or less, the durability passed, and when the contact resistance exceeded 15 mΩ · cm ² , the durability was rejected.

[Evaluation of wear resistance]
The wear resistance of the carbon-based conductive layer was evaluated using the contact resistance measuring device (see FIG. 4) used for measuring the contact resistance. The prepared specimen is sandwiched between two carbon cloths from both sides, and the outside is pressurized to a contact load of 40 kgf with a copper electrode having a contact area of 4 cm ² , and the specimen is held while being pressed from both sides. Drawing was performed in a direction parallel to the direction of the groove (pull-out test). After the pull-out test, the sliding region on the surface of the test body was observed with an optical microscope, and the remaining state of the carbon-based conductive layer, that is, the degree of exposure of the base material was evaluated.
Judgment criteria for abrasion resistance is ◎, where no exposure of the base material is seen on the surface of the convex region of the groove of the test specimen (planar portion 4 on the outer surface of the gas flow path) and no exposure is seen in the R section. No exposure of the substrate is seen on the surface of the groove convex area, but a slight exposure of the base material is seen in the R part, ○, the ratio of the exposed area of the base material on the surface of the specimen groove convex area When the ratio is less than 50%, Δ, and when the ratio of the exposed area of the base material is 50% or more, ×, and ◯ or more is determined as acceptable.

  Table 1 shows the resin type and thickness of the conductive resin layer, the heat treatment conditions after the formation of the conductive resin layer, the contact resistance and the abrasion resistance evaluation results after the initial and durability tests.

Specimen No. 1 is only a carbon layer, and the initial conductivity is excellent, but the durability is within the acceptable range, but the contact resistance value is significantly increased, and the wear resistance is insufficient. became.
On the other hand, the specimen No. Nos. 2 to 9 were produced by the method defined in the present invention, and all of conductivity, durability and wear resistance were acceptable after press molding. In particular, the specimen No. 1 was heat-treated after forming the conductive resin layer. 3, 4, 7, and 9 are preferable because they have low contact resistance and good durability.

≪Preparation of test specimen≫
A carbon layer having a coverage of about 60% is formed on a pure titanium substrate by the same method and material as in Example 1, heat-treated, press-molded on the material, and then conductive on both sides by the following method. A functional resin layer was formed.

[Conductive resin layer-2]
The conductive resin paints are phenol resin (Arakawa Chemical Industries, Tamanol 2800), acrylic resin (Toray Fine Chemical, Cotax LH681), epoxy resin (Cemedine, EP106), polyester resin (Arakawa Chemical Industries). Made of 7005N) and silicone resin (manufactured by Shin-Etsu Silicone Co., Ltd., KR251), and carbon powder was dispersed in each paint. As carbon powder, carbon black powder (manufactured by Cabot, Vulcan XC72, average particle size 40 nm, purity 99.2%), graphite powder (manufactured by Ito Graphite Co., Ltd., Z-5F, average particle size 4 μm, purity 98.9%) ) Was used.
Using an organic solvent suitable for each resin-based paint, the concentration of solid content (resin component + carbon powder) in the paint (= ((resin component mass + carbon powder mass) × 100) / paint mass) is Carbon black so that the mass concentration of carbon powder in the solid content (= (carbon powder mass × 100) / (resin component mass + carbon powder mass)) is approximately 40 mass% so as to be approximately 18 mass%. The concentration was adjusted so that the ratio of the powder to the graphite powder was 4: 1, and the paint was spray-coated on the material after press molding and dried. Thus, various test bodies were produced by forming conductive layers on both sides of the material after press molding.

[Heat treatment after forming conductive resin layer]
Some of the specimens obtained by forming the conductive resin layer after press molding were subjected to heat treatment. An atmospheric heat treatment was used and the treatment time was appropriately adjusted under the condition of 400 ° C.

≪Evaluation of specimens≫
Evaluation of initial contact resistance, durability, and abrasion resistance was carried out in the same manner as in Example 1.
In addition, the thickness of the conductive resin layer after applying the conductive resin paint spray is the place that seems to be average in the field of view by performing cross-sectional processing after filling a part of the material with resin and performing SEM observation from the cross-section. The resin layer thickness at was measured. Cross-sectional observation was performed for 3 fields per specimen, and the average value of 3 fields was calculated.

  Table 2 shows the resin type and thickness of the conductive resin layer, the heat treatment conditions after the formation of the conductive resin layer, the contact resistance after the initial test and the durability test, and the abrasion resistance evaluation results.

  Specimen No. 10-16 were produced by the method prescribed | regulated to this invention, and after press molding, all of electroconductivity, durability, and abrasion resistance were the acceptable ranges. In addition, the thing which formed the conductive resin layer after press molding obtained the very favorable result about abrasion resistance.

DESCRIPTION OF SYMBOLS 1 Base material 2 Carbon type conductive layer 3 Intermediate layer 10 Titanium fuel cell separator (separator)
21 Carbon layer 22 Conductive resin layer S1 Carbon layer forming step S2 Heat treatment step S3 Conductive resin layer forming step S4 Press molding step S5 Heat treatment step

Claims (6)

A carbon layer forming step of forming a carbon layer containing graphite on a substrate surface made of pure titanium or a titanium alloy;
After the carbon layer forming step, a conductive resin layer forming step of forming a conductive resin layer containing carbon powder and resin on the base material on which the carbon layer is formed;
After the conductive resin layer forming step, a press molding step of press-molding the base material on which the carbon layer and the conductive resin layer are formed to form a gas flow path;
The manufacturing method of the fuel cell separator made from titanium characterized by including.   The method for producing a titanium fuel cell separator according to claim 1, further comprising a heat treatment step of heat-treating the base material after the press molding step.   The titanium-made product according to claim 1 or 2, further comprising a heat treatment step of heat-treating the base material in a non-oxidizing atmosphere between the carbon layer forming step and the conductive resin layer forming step. Manufacturing method of fuel cell separator. A carbon layer forming step of forming a carbon layer containing graphite on a substrate surface made of pure titanium or a titanium alloy;
After the carbon layer forming step, a press forming step of press forming the base material on which the carbon layer is formed to form a gas flow path;
After the press molding step, a conductive resin layer forming step in which the carbon layer is formed and a conductive resin layer containing carbon powder and a resin is formed on the press-molded base material;
The manufacturing method of the fuel cell separator made from titanium characterized by including.   The method for producing a titanium fuel cell separator according to claim 4, further comprising a heat treatment step of heat-treating the substrate after the conductive resin layer forming step.   The titanium fuel cell separator according to claim 4 or 5, further comprising a heat treatment step of heat-treating the base material in a non-oxidizing atmosphere between the carbon layer forming step and the press molding step. Manufacturing method.

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