JP6170477B2 - Titanium fuel cell separator material and method for producing titanium fuel cell separator material - Google Patents

Description

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

  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
Carbon is attracting attention as a material that satisfies these requirements, and the application of carbon to separators is being studied. Specifically, a carbon separator (for example, Patent Documents 1 to 3) formed from a graphite powder molded body, a graphite and resin mixture molded body, or a metal such as titanium or stainless steel. A separator in which carbon particles are attached to a base material made of a material (for example, Patent Documents 4 to 7) or a carbon film is formed by a chemical vapor deposition (CVD) method or the like has been studied.

Japanese Patent Laid-Open No. 10-3931 Japanese Patent No. 4075343 JP 2005-162550 A Japanese Patent No. 3904690 Japanese Patent No. 3904696 Japanese Patent No. 4886885 Japanese Patent No. 5108986

Fuel cell separators may rub against each other when they are processed into separators or assembled into cells, and the conductive layer (carbon-based conductive layer) formed on the separator surface is scratched at this time. There are concerns about the occurrence. In addition, after the cell is assembled, the separator surface is in contact with the carbon paper that constitutes the gas diffusion layer while being pressurized, but when used in in-vehicle applications, the conductive layer and carbon formed on the separator surface due to vibration associated with running. Friction may occur with the paper. If the conductive layer is easily worn at this time, the electrical resistance between the separator and the carbon paper increases as the usage time becomes longer, and the power generation performance of the fuel cell is lowered.
For this reason, the separator material of the fuel cell separator is required to have wear resistance as well as conductivity and durability (conductivity durability: property of maintaining conductivity for a long period of time).
However, since the techniques disclosed in Patent Documents 1 to 7 are not techniques that take the above-described actual circumstances into account, the techniques relating to wear resistance and the like cannot be sufficiently met, and there is room for improvement.

  The present invention has been made in view of the above-mentioned problems, and the problem is that the titanium fuel cell separator material and the titanium fuel cell separator material are excellent in conductivity and durability and also in wear resistance. It is to provide a method.

  As a result of intensive studies, the inventors formed a carbon-based conductive layer (carbon layer, conductive resin layer) having a two-layer structure on the base material surface of the titanium fuel cell separator material, and the coverage of the carbon layer The present invention has been found by making the resin of the conductive resin layer specified to be a predetermined value and having excellent conductivity and durability as well as excellent wear resistance.

  In order to solve the above problems, a titanium fuel cell separator material according to the present invention is a titanium fuel cell separator material in which a carbon-based conductive layer is formed on a substrate surface made of pure titanium or a titanium alloy, The carbon-based conductive layer has a two-layer structure, and the layer close to the base material in the carbon-based conductive layer is a carbon layer, and the layer far from the base material is a conductive resin layer. The carbon layer contains graphite, the coverage of the carbon layer is 40% or more, the conductive resin layer contains carbon powder and a resin, and the resin is an acrylic resin, It is one or more resins selected from polyester resins, alkyd resins, urethane resins, silicone resins, phenol resins, epoxy resins, and fluororesins.

  Thus, since the titanium fuel cell separator material according to the present invention includes the carbon-based conductive layer having a two-layer structure of the carbon layer and the conductive resin layer, the carbon-based conductive layer is a conductive material of the separator material. And durability can be improved. And since a conductive resin layer functions as a protective film, compared with a separator material provided with only one conductive layer, wear resistance can be improved.

  In the titanium fuel cell separator material according to the present invention, the coverage of the carbon layer is preferably 80% or less.

  As described above, the titanium fuel cell separator material according to the present invention has a carbon layer coverage on the base material of a predetermined value or less, and therefore has been subjected to the press molding process for manufacturing the separator. However, it is possible to suppress the deterioration of wear resistance and adhesion as well as conductivity.

  In the titanium fuel cell separator material according to the present invention, an intermediate layer containing titanium carbide is preferably formed between the base material and the carbon layer.

  Thus, the titanium fuel cell separator material according to the present invention can improve the adhesion between the base material and the carbon layer by forming the intermediate layer between the base material and the carbon layer. . As a result, the possibility of peeling of the carbon-based conductive layer including the carbon layer can be reduced.

  In the titanium fuel cell separator material according to the present invention, the conductive resin layer preferably has a thickness of 0.1 to 20 μm.

  Thus, the titanium fuel cell separator material according to the present invention ensures the effect of improving the wear resistance by defining the thickness of the conductive resin layer within a predetermined range, A significant increase in the electrical resistance value can be prevented, and a suitable aspect can be obtained as a separator material.

  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 the base layer after the carbon layer forming step. A heat treatment step of heat-treating the material in a non-oxidizing atmosphere; and 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 heat treatment step The coverage of the carbon layer is 40% or more, the conductive resin layer contains carbon powder and resin, and the resin is acrylic resin, polyester resin, alkyd resin, urethane resin. And one or more resins selected from silicone resins, phenol resins, epoxy resins, and fluororesins.

Thus, the manufacturing method of the titanium fuel cell separator material according to the present invention includes a carbon layer forming step and a conductive resin layer forming step, thereby forming a two-layer structure of the carbon layer and the conductive resin layer. The present carbon-based conductive layer can be formed on the substrate. As a result, a titanium fuel cell separator material with improved conductivity and durability can be produced by the carbon-based conductive layer. Since the conductive resin layer functions as a protective film, it is possible to manufacture a titanium fuel cell separator material with improved wear resistance compared to a separator material having only one conductive layer.
Furthermore, since the manufacturing method of the titanium fuel cell separator material according to the present invention includes a heat treatment step after the carbon layer forming step, an intermediate layer can be formed between the base material and the carbon layer. And the carbon layer can be improved in adhesion. As a result, it is possible to manufacture a titanium fuel cell separator material in which the possibility of peeling of the carbon-based conductive layer including the carbon layer is reduced.

  In the method for producing a titanium fuel cell separator material according to the present invention, the coverage of the carbon layer is preferably 80% or less.

  As described above, in the method for manufacturing a titanium fuel cell separator material according to the present invention, since the coverage of the carbon layer on the base material is equal to or less than a predetermined value, the press molding process is performed when manufacturing the separator. Even so, it is possible to produce a titanium fuel cell separator material that is naturally conductive, and that suppresses a decrease in wear resistance and adhesion.

  The method for producing a titanium fuel cell separator material according to the present invention preferably includes a heat treatment step of heat-treating the substrate at 200 to 550 ° C. after the conductive resin layer forming step.

  Thus, since the manufacturing method of the titanium fuel cell separator material 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 may 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 material with further reduced contact resistance can be produced.

Since the titanium fuel cell separator material according to the present invention includes a carbon-based conductive layer having a two-layer structure of a carbon layer and a conductive resin layer, the carbon-based conductive layer provides the conductivity and durability of the separator material. Can be improved. And since a conductive resin layer functions as a protective film, compared with a separator material provided with only one conductive layer, wear resistance can be improved.
Therefore, the titanium fuel cell separator material according to the present invention is excellent in conductivity and durability (conductivity durability: property of maintaining conductivity for a long period of time) and also in wear resistance.

The method for producing a titanium fuel cell separator according to the present invention includes a carbon-based conductive material having a two-layer structure of a carbon layer and a conductive resin layer by including a carbon layer forming step and a conductive resin layer forming step. A layer can be formed on a substrate. As a result, a titanium fuel cell separator material with improved conductivity and durability can be produced by the carbon-based conductive layer. Since the conductive resin layer functions as a protective film, it is possible to manufacture a titanium fuel cell separator material with improved wear resistance compared to a separator material having only one conductive layer.
Therefore, according to the method for producing a titanium fuel cell separator material according to the present invention, it is excellent in conductivity and durability (conductivity durability: the property of maintaining conductivity for a long period of time) and also in wear resistance. A fuel cell separator material can be manufactured.

(A) And (b) is typical sectional drawing of the fuel cell separator material made from titanium which concerns on embodiment of this invention. It is a flowchart of the manufacturing method of the titanium fuel ionization separator material which concerns on embodiment 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 manufacturing method of the titanium fuel cell separator material (henceforth a separator material suitably) and a separator material which concern on this invention is demonstrated in detail.

≪Titanium fuel cell separator material≫
As shown to Fig.1 (a), the separator material 10 (10a) which concerns on this embodiment is the base material 1 which consists of pure titanium or a titanium alloy, and the carbon formed in the surface (one side or both sides) of the base material 1 System conductive layer 2. And as shown in FIG.1 (b), the separator material 10 (10b) which concerns on this embodiment may be provided with the intermediate | middle layer 3 between the base material 1 and the carbon-type conductive layer 2. As shown in FIG.
In FIG. 1, the separator material 10 in which the carbon-based conductive layer 2 (and the intermediate layer 3) is formed only on one surface of the base material 1 is illustrated, but the carbon-based conductive layer 2 ( And an intermediate layer 3) may be formed.
Hereinafter, the base material 1, the carbon-based conductive layer 2, and the intermediate layer 3 of the separator material 10 will be described.

<Base material>
The base material of the separator material according to the present embodiment is a metal base material from the viewpoint of workability, gas barrier property, conductivity and thermal conductivity required to form a groove serving as a gas flow path. In particular, pure titanium or a titanium 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 material are improved, and since it is lightweight, it is particularly easy to use as an automotive application.

  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. 1, the carbon-type conductive layer 2 is comprised from the carbon layer 21 formed in the side close | similar to the base material 1, and the electroconductive resin layer 22 formed in the side far from the base material 1. As shown in FIG. The

(Carbon layer)
The carbon layer includes graphite and is provided so as to cover the base material. And since the graphite contained in the carbon layer has high crystallinity and excellent conductivity, it imparts conductivity to the separator material and also has durability to maintain conductivity even in the fuel cell internal environment (high temperature, acidic atmosphere). Give.
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 to graphite (mass of resin solids in the carbon layer / 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 substrate from the viewpoint of conductivity, but it is not always necessary to cover the entire surface, and in order to ensure conductivity and corrosion resistance, 40% of the surface is required. What is necessary is just to coat | cover. If the coverage is less than 40%, the conductivity is insufficient and the required properties as a separator material are not satisfied. A preferable range of the coverage is 45% or more, and more preferably 50% or more.

Here, in manufacturing the separator, assuming that the separator material is press-molded, the material elongation occurs due to the processing. At this time, if the coverage of the carbon layer on the substrate exceeds 80%, the elongation of the carbon layer cannot follow the portion where the elongation of the substrate at the time of processing is large, and separation occurs between the substrate and the carbon layer. In addition, the wear resistance and adhesion of the carbon-based conductive layer (two layers) may be reduced. On the other hand, when the coverage of the carbon layer on the substrate is 80% or less, it is possible to suppress a decrease in wear resistance and adhesion of the carbon-based conductive layer even in a portion where the elongation of the substrate occurs due to processing.
Therefore, considering not only the conductivity but also the compatibility of the wear resistance and adhesion of the carbon-based conductive layer after press molding, the lower limit of the coverage of the carbon layer is preferably 40% or more, more preferably Is 45% or more, particularly preferably 50% or more, and the upper limit is preferably 80% or less, more preferably 75% or less, and particularly preferably 70% or less.
Here, the coverage of the carbon layer can be determined by observing the separator surface on which the carbon layer is formed with an optical microscope or a scanning microscope. For example, the surface of the separator on which the carbon layer is formed is observed using a scanning electron microscope at a magnification of 200 × and a range of 550 × 400 μm, and the reflected electron image is taken. The backscattered electron image is binarized into a portion where the carbon layer is covered by image processing and a portion where the carbon layer is not covered and the base material is exposed, and the area ratio occupied by the carbon layer is calculated and covered. It is a method of obtaining the rate. In addition, when the conductive resin layer is already formed on the carbon layer, the above method may be performed after dissolving and removing the conductive resin layer with an organic solvent or an alkaline solution.

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 characteristics of the separator material. 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.
Here, the coverage of the conductive resin layer can be determined by observing the separator surface on which the conductive resin layer is formed with an optical microscope or a scanning microscope. For example, the surface of the separator on which the conductive resin layer is formed is observed with a scanning electron microscope at a magnification of 200 × at a magnification of 550 × 400 μm, and the reflected electron image is taken. Then, the reflected electron image is binarized into a portion where the conductive resin layer is coated by image processing and a portion where the conductive resin layer is not covered and the base material (or carbon layer) is exposed, and the conductive image is conductive. In this method, the area ratio occupied by the conductive resin layer is calculated to obtain the coverage.

As described above, regarding the coverage of the carbon layer on the substrate, the coverage of the carbon layer on the substrate is 80% or less, in other words, the conductive resin layer is formed in direct contact with the substrate. When the portion is present in an area ratio of 20% or more, a decrease in wear resistance and adhesion of the carbon-based conductive layer can be suppressed even in a portion where the base material has been stretched by press molding.
Therefore, in order to achieve both the conductivity of the separator produced by press-molding the separator material and the wear resistance and adhesion of the carbon-based conductive layer, for the lower limit of the coverage of the carbon layer on the substrate, The upper limit is preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more. The upper limit is preferably 80% or less, more preferably 75% or less, and particularly preferably 70% or less.

<Intermediate layer>
As shown in FIG. 1B, the intermediate layer 3 of the separator material 10 according to this embodiment is 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, by providing the intermediate layer containing titanium carbide, the conductivity of the separator material is further improved. 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 material≫
Next, a method for producing a titanium fuel cell separator material according to the present invention will be described.
As shown in FIG. 2, the method for manufacturing a separator material according to the present invention includes a carbon layer forming step S1, a heat treatment step S2, and a conductive resin layer forming step S3. And it is preferable that the manufacturing method of the separator material which concerns on this invention includes heat processing process S4 after conductive resin layer formation process S3, and also includes a base-material manufacturing process before carbon layer formation process S1. May be.
Hereinafter, each process will be described in detail.

<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. It does not matter if there is an annealing finish after cold rolling, but when performing the press forming process in manufacturing the separator, annealing is performed after cold rolling to ensure the workability required during press forming. Preferably it is done. 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 substrate 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 a press molding process 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.

<Heat treatment process>
The heat treatment step S4 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 S4, 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 ° C, 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.

  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 material 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 50x150 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 size 7 μm, purity 99.9%) is used, and the graphite powder is 8 wt% in a 0.8 wt% carboxymethylcellulose aqueous solution. A slurry was prepared by dispersing. And the slurry was apply | coated to both surfaces of a titanium base material using the 10th, 7th, 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, what was produced using the No. 10 bar coater are specimen Nos. 2 to 4, and what was produced using the No. 7 bar coater are specimen Nos. 5 to 8, and the No. 5 bar. Samples Nos. 9 to 13 were prepared using a coater.

[Conductive resin layer]
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.

[Heat treatment after forming conductive resin layer]
Some of the specimens obtained by forming the conductive resin layer on the carbon layer were subjected to heat treatment. And heat processing was implemented by adjusting process time suitably on the conditions of 200-400 degreeC in air | 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 specimen are sandwiched between two carbon papers, and the outside is sandwiched between two copper electrodes with a contact area of 1 cm ² and pressurized with a load of 10 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 to obtain a contact resistance (initial contact resistance).
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.

[Adhesion evaluation]
After attaching a tape (Sumitomo 3M Mending Tape 12mm width) to the surface of the carbon-based conductive layer of the test specimen, the tape was peeled off in a direction perpendicular to the surface of the test specimen to evaluate the adhesion of the carbon-based conductive layer. It was.
Evaluation criteria for adhesion are ◎ when the adhesive of the tape remains on the surface of the carbon-based conductive layer, ○ when the carbon-based conductive layer is slightly transferred to the tape side, ○ in the carbon-based conductive layer The case where it peeled was set to (triangle | delta), the case where a carbon-type conductive layer peeled from the interface with a base material was set as x, and (circle) or more was set as the pass.

[Evaluation of wear resistance]
The wear resistance of the carbon-based conductive layer was evaluated using the contact resistance measuring device (see FIG. 3) used for measuring the contact resistance. In the contact resistance evaluation, the contact area of the copper electrode was 1 cm ² , but in this evaluation, a copper electrode having a contact area of 4 cm ² was used. The prepared specimen is sandwiched between two carbon cloths from both sides, and the outside is further 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 in the surface direction (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 conductive layer, that is, the degree of exposure of the base material was evaluated.
Judgment criteria for abrasion resistance are ◎ when the substrate surface is not exposed at all on the specimen surface, ◯ when the ratio of the exposed area of the substrate to the specimen surface is less than 30%, ○ specimen surface On the other hand, the case where the ratio of the exposed area of the base material was less than 50% was evaluated as Δ, the case where the ratio of the exposed area of the base material was 50% or more was evaluated as x, and the case where ○ or higher was determined as acceptable.

[Structure of intermediate layer and elemental composition analysis]
After processing the sample on the surface layer of each specimen with an ion beam processing apparatus (Hitachi focused ion beam processing observation apparatus FB-2100), using a transmission electron microscope (TEM: Hitachi field emission analytical electron microscope HF-2200) Cross section is observed at a magnification of 750,000 times, the presence of the intermediate layer is confirmed at the interface between the carbon layer and the titanium base material, and EDX analysis and electron diffraction analysis are performed at any location in the intermediate layer, and titanium carbide is present. It was determined whether or not.

  Carbon layer coverage, presence or absence of titanium carbide in the intermediate layer, resin type and thickness of the conductive resin layer, heat treatment conditions after formation of the conductive resin layer, contact resistance after initial and durability tests, adhesion and resistance The results of wear evaluation are shown in Table 1.

Specimen No. Since No. 1 had no carbon layer and a conductive resin layer was directly formed on a pure titanium base material, the result was that the conductivity was insufficient. In addition, since Specimen No. 2 was formed by forming only one carbon layer as the carbon-based conductive layer, the result was that the adhesion and wear resistance were insufficient, although the conductivity and durability were very excellent. It became.
On the other hand, specimens Nos. 3 to 13 are those in which a conductive resin layer is formed on the carbon layer within the range specified in the present invention, and all of conductivity, durability, adhesion, and wear resistance are obtained. It was an acceptable range. In particular, among the test specimens subjected to heat treatment after the formation of the conductive resin layer, specimen Nos. 7, 8, 10, 12, and 13 have low contact resistance values, and are extremely excellent in conductivity and durability. all right.

  A test piece of 20 × 65 mm was prepared from “test body No. 3” having a carbon layer coverage of 100%, “test body No. 7” having 80%, and “test body No. 10” having 60%. After producing and carrying out the tension process which simulated the material elongation part at the time of a press molding process using this, the abrasion resistance and adhesiveness of the carbon-type conductive layer of an elongation part were evaluated.

[Tensile processing]
Tensile processing was performed using a small tensile testing machine. A line is drawn to a portion 20 mm from both ends of the test piece (distance between lines 25 mm), both ends of the test piece are fixed with a chuck of the tester, and the distance between the lines is 31 mm (average material elongation 25 at a tensile speed of 5 mm / min). %) To obtain a tensile test specimen. Thereafter, the adhesion and wear resistance of the carbon-based conductive layer in the tensile processed part were evaluated in the same manner as in Example 1, and ◎, ○, Δ, and X were determined based on the same criteria. In addition, since this evaluation is stricter evaluation than evaluation of Example 1, it evaluated as more than (triangle | delta) or more as the pass, and the result was shown in Table 2.

As shown in Table 1, the test specimen No. 3, 7, and 10 have good adhesion and wear resistance of the carbon-based conductive layer in a state before tensile processing.
However, when tensile processing assuming a material stretched portion by press molding is performed, the test specimen No. 1 having a carbon layer coverage of 100% is obtained. No. 3 clearly showed a tendency for adhesion and wear resistance to decrease. On the other hand, no. No. 7 shows a slight decrease in adhesion but no significant decrease in wear resistance. No significant decrease in adhesion and wear resistance was observed for No. 10.

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

Claims (7)

A titanium fuel cell separator material in which a carbon-based conductive layer is formed on a substrate surface made of pure titanium or a titanium alloy,
The carbon-based conductive layer has a two-layer structure, and the layer close to the base material in the carbon-based conductive layer is a carbon layer, and the layer far from the base material is a conductive resin layer. And
The carbon layer contains graphite, and the coverage of the carbon layer is 40% or more,
The conductive resin layer includes carbon powder and resin, and the resin is one or more selected from acrylic resin, polyester resin, alkyd resin, urethane resin, silicone resin, phenol resin, epoxy resin, and fluororesin. A titanium fuel cell separator material, characterized in that   The titanium fuel cell separator material according to claim 1, wherein a coverage of the carbon layer is 80% or less.   The titanium fuel cell separator material according to claim 1, wherein an intermediate layer containing titanium carbide is formed between the base material and the carbon layer.   4. The titanium fuel cell separator material according to claim 1, wherein the conductive resin layer has a thickness of 0.1 to 20 μm. 5. 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 heat treatment step of heat treating the base material in a non-oxidizing atmosphere;
After the heat treatment 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,
Including
The coverage of the carbon layer is 40% or more,
Titanium characterized in that the resin of the conductive resin layer is at least one resin selected from acrylic resin, polyester resin, alkyd resin, urethane resin, silicone resin, phenol resin, epoxy resin, and fluororesin Manufacturing method of fuel cell separator material.   6. The method for producing a titanium fuel cell separator material according to claim 5, wherein the coverage of the carbon layer is 80% or less.   The method for producing a titanium fuel cell separator material according to claim 5 or 6, further comprising a heat treatment step of heat-treating the substrate at 200 to 550 ° C after the conductive resin layer forming step.

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