JP6637867B2 - Method for producing carbon coated separator material for fuel cell - Google Patents

Description

  The present invention relates to a method for producing a carbon coat separator material for a fuel cell obtained by applying a carbon black dispersion paint on a substrate made of pure titanium or a titanium alloy, and more particularly to an improvement of the carbon black dispersion paint. About.

  A fuel cell is a single cell in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and has a separator (also referred to as a bipolar plate) in which a groove serving as a gas (hydrogen, oxygen, etc.) flow path is formed. Through a plurality of the single cells. The output of the fuel cell can be increased by increasing the number of cells per stack.

Since the separator for a fuel cell also plays a role in passing the generated current to an adjacent cell, the separator material constituting the separator has high conductivity and high conductivity at high temperatures and acidity inside the cell of the fuel cell. Conductive durability that can be maintained for a long time even in an atmosphere is required. Here, high conductivity and high conductivity durability mean that the contact resistance is low. The contact resistance means that a voltage drop occurs between the electrode and the separator surface due to an interface phenomenon.
Separator materials developed to satisfy the above-mentioned requirements are proposed in, for example, Patent Documents 1 to 4.

  Patent Document 1 discloses a separator for a polymer electrolyte fuel cell, a metal substrate having an oxide film of the substrate itself on the surface, and a conductive thin film formed on the surface of the oxide film of the substrate. And an intermediate layer that enhances adhesion between the oxide film of the base material itself and the conductive thin film, wherein the conductive thin film is formed from carbon (C) formed at an atomic level. Wherein the intermediate layer is formed of at least one element selected from the group consisting of metals such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W and metalloid elements such as Si and B. Containing (Me), carbon (C) formed on the (Me) layer, and an element (Me) of a metal or metalloid element, and blending carbon (C) with increasing distance from the base material At least one of a (Carbon-Me) gradient layer and a proportion increasing Ranaru fuel cell separator is described.

  In this fuel cell separator, an intermediate layer is formed between the base material and the conductive thin film to enhance the adhesion therebetween. However, since the conductive thin film and the intermediate layer are stacked by vapor deposition, there is a possibility that adhesion at the interface between the intermediate layer and the conductive thin film is weak. Therefore, when used in a fuel cell, the intermediate layer and the conductive thin film may peel off or the like, and the conductivity may be reduced.

  Further, Patent Document 2 discloses a fuel cell separator having a base material made of a metal and a surface treatment layer formed on the surface of the base material, wherein the surface treatment layer is made of a metal or metalloid element (Me ) Or a metal or metalloid metal carbide (MeC), and a base material side portion composed of carbon (C) formed at an atomic level, or a metal or metalloid element (Me) or a metal formed on carbon. Alternatively, there is described a fuel cell separator having a base material and an opposite portion made of (C + Me or MeC) in which a metalloid metal carbide (MeC) is compounded at an atomic level.

  However, in the fuel cell separator, since the substrate-side portion and the opposite side portion of the surface treatment layer are laminated by vapor phase film formation, there is a possibility that adhesion at these interfaces is weak. . Therefore, when used in a fuel cell, there is a possibility that the conductivity may be reduced due to separation of the substrate side portion and the opposite side portion.

In Patent Document 3, a conductive carbon film is coated on the surface of a metal plate, and the conductive carbon film is formed at a film forming temperature of 400 to 600 ° C. by a chemical vapor synthesis method or a sputtering method. The unpaired electron density in the conductive carbon film is 1020 / cm ³ or more, the G / D ratio by Raman spectroscopy is 0.5 or less, and the resistivity is 10 Ωcm or less. A fuel cell separator is described.

  In this fuel cell separator, a conductive carbon film is directly formed on a substrate surface by a chemical vapor synthesis method or a sputtering method. Therefore, the adhesion between the substrate and the conductive carbon film may be weak. Therefore, when used in a fuel cell, the base material and the conductive carbon film may be separated, and the conductivity may be reduced.

  Patent Literature 4 describes a fuel cell separator having a coating layer on a metal substrate, wherein the coating layer has an amorphous carbon layer and a conductive portion. ing.

  However, in this fuel cell separator, since the carbon layer is formed directly on the substrate, the adhesion between them may be weak. Therefore, when used in a fuel cell, the substrate and the carbon layer may be peeled off and the conductivity may be reduced.

  From such a background, the present applicant discloses in Japanese Patent Application No. 2015-104578 that a carbon black-dispersed coating material is applied on a substrate made of pure titanium or a titanium alloy, and then heat-treated under a low oxygen partial pressure. A carbon-coated separator material for a fuel cell having a mixed layer in which titanium (rutile) and carbon black are mixed and dispersed has been proposed.

Japanese Patent No. 4147925 JP 2004-14208 A JP 2007-207718 A JP 2008-204876 A

  Although the above-mentioned carbon-coated separator material for fuel cells by the present applicant can achieve both conductivity and durability by a mixed layer of titanium oxide and carbon black, there is a concern that the carbon black coating film may peel off during handling in the manufacturing process. There is room for improvement in process stability.

  Accordingly, the present invention relates to a method for producing a carbon-coated separator material for a fuel cell in which a mixed layer of titanium oxide and carbon black is formed. It is an object of the present invention to improve the peeling and abrasion of the film and to form a good mixed layer on the titanium base material during the subsequent heat treatment so that the high conductivity can be maintained for a long time.

  The method of manufacturing a carbon-coated separator material for a fuel cell according to the present invention, which has solved the above-mentioned problem, comprises applying a carbon black-dispersed coating material to a titanium base material having a carbon concentration of 10 atomic% or less at a depth of 10 nm from the outermost surface. A method for producing a carbon coated separator material for a fuel cell, comprising: a coating step of coating, and a heat treatment step of performing a heat treatment at a temperature range of 500 to 800 ° C. under a low oxygen partial pressure having an oxygen partial pressure of 25 Pa or less after the coating step. The carbon black-dispersed coating material used in the application step contains carbon black and a binder resin made of a resin that decomposes without heating when heated to 500 ° C. or lower.

  The carbon coated separator material for a fuel cell obtained by the above manufacturing method is such that titanium oxide from the base material is diffused into the coating film made of the carbon black dispersion paint on the titanium base material, and the titanium oxide and the carbon black are mixed. A mixed layer is formed. In this mixed layer, carbon black forms a conductive path, and high conductivity is obtained. In addition, carbon black and titanium oxide are stable without oxidation even in a high-temperature acidic atmosphere (for example, 80 ° C., pH 2) in a fuel cell. Therefore, the carbon-coated separator material for a fuel cell has both high conductivity and corrosion resistance.

  Furthermore, since the carbon black dispersion coating contains a binder resin that decomposes without residue when heated at 500 ° C. or less, the adhesion between the coating film and the substrate after the carbon black dispersion coating is applied and the abrasion resistance of the coating film are good. In addition, since no resin-derived residue remains after the heat treatment, a mixed layer is favorably formed, and good conductivity is obtained. Such a binder resin is preferably at least one of an acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, and polyurethane. Further, it is preferable that the binder resin and the carbon black have a solid content mass ratio of (binder resin solid content / carbon black solid content) = 0.3 to 2.5.

  According to the present invention, a carbon-coated separator material for a fuel cell in which a mixed layer of titanium oxide and carbon black is formed on a titanium base material is obtained. Includes a binder resin to improve the handling resistance (coating peeling and abrasion) of the coating when the carbon black dispersion coating is applied to the substrate, and to provide a good coating on the titanium substrate during the subsequent heat treatment. A mixed layer is formed.

FIG. 2 is a schematic sectional view showing a carbon-coated separator material for a fuel cell obtained by the production method of the present invention. 4 is a flowchart illustrating the content of a method for producing a carbon coated separator material for a fuel cell according to the present invention. FIG. 4 is a schematic explanatory view showing a state in which a carbon black dispersion paint is applied to the surface of a substrate 2 in an application step S2. FIG. 4 is a schematic explanatory view showing a state where a mixed layer 3 in which titanium oxide 4 in which part or all of titanium atoms diffused outward from a base material 2 are oxidized in a heat treatment step S3 and carbon black 5 are mixed is formed. It is a schematic diagram explaining a situation that a contact resistance value of a test object is measured. 4 is a graph showing the relationship between the ratio (solid content of acrylic resin / solid content of carbon black) and the contact resistance obtained in the examples.

  Hereinafter, an embodiment of a method for manufacturing a carbon-coated separator material for a fuel cell according to the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the carbon-coated separator material for a fuel cell is referred to as “carbon-coated separator material”.

(Carbon coated separator material)
First, the carbon-coated separator material obtained by the method of the present invention will be described. FIG. 1 is a schematic sectional view illustrating the configuration.
As shown in FIG. 1, a carbon-coated separator material 1 has a titanium oxide 4 (see FIG. 4) and a carbon black 5 (see FIG. 4) on a substrate (hereinafter simply referred to as a substrate) 2 made of pure titanium or a titanium alloy. ) Is formed.

  Here, examples of the pure titanium include, for example, 1 to 4 types specified in JIS H 4600. Examples of the titanium alloy include Ti-Al, Ti-Nb, Ti-Ta, Ti-6Al-4V, and Ti-Pd. However, in any case, it is not limited to the above example. When the substrate is made of pure titanium or a titanium alloy, it can be made light and excellent in corrosion resistance. Further, even if there is a portion or an end face portion which is exposed without being covered with the mixed layer described later on the surface of the base material, the titanium or titanium alloy may be used in a high temperature acidic atmosphere (for example, 80 ° C., pH 2) in the fuel cell. Are not eluted and there is no risk of deteriorating the solid polymer membrane.

  The substrate 2 is preferably a cold plate material having a thickness of 0.05 to 1 mm, for example. When the thickness is in this range, the requirements for weight reduction and thickness reduction of the separator are satisfied, the strength and handling properties as a separator material are provided, and it is relatively easy to press-process the separator into a shape. The substrate may be in the form of a long strip wound in a coil shape, or may be in the form of a sheet cut into a predetermined size.

The titanium oxide in the mixed layer 3 includes a crystalline rutile structure, and this portion has excellent conductive corrosion resistance. On the other hand, in the carbon black 5 in the mixed layer 3, 70% or more of the carbon detected when the bonding state of the carbon in the mixed layer was analyzed by X-ray photoelectron spectroscopy, that is, a C—C bond, that is, It exists as a single carbon black 5 having a bond between carbon and carbon, and is distributed from the outermost surface of the carbon-coated separator material 1 to the substrate 2 (see FIG. 4). That is, the carbon black 4 (see FIG. 4) serves as a conductive path for passing a current, and the carbon black is stable against oxidation, so that the conductivity is stably maintained. By forming such a mixed layer 3, the carbon coat separator material 1 can achieve both high conductivity and conductive corrosion resistance.
On the other hand, when carbon reacts with titanium to form titanium carbide, the bond of carbon becomes a bond of Ti—C. However, this titanium carbide has conductivity but is easily oxidized. In such a case, the conductive corrosion resistance becomes insufficient.

  When the cross section of the mixed layer 3 is observed, the carbon black 5 has a granular form, and the granular carbon black 5 is buried in the matrix of the mixed layer 3 (the matrix of titanium oxide 4). It has become. The above-described cross section may be obtained in a direction parallel to the thickness direction, or may be obtained in a direction perpendicular to the thickness direction, and may be obtained in a direction oblique to the thickness direction. It may be obtained. It can be confirmed that the carbon black 5 has a granular form in any of the cross sections.

  The carbon black 5 has a portion protruding from the outermost surface of the mixed layer 3 when one or a plurality of particles are connected to each other, and exists as a conductive path through which an electric current flows while being dispersed to the interface between the mixed layer 3 and the base material 2. It is desirable to do.

  The range of the thickness of the mixed layer 3 is preferably from 10 to 500 nm. When the thickness of the mixed layer 3 is in this range, high conductivity and conductive corrosion resistance can be provided. If the thickness of the mixed layer 3 is less than 10 nm, the conductive corrosion resistance becomes insufficient, and oxidation may proceed in the fuel cell, and the conductivity may be deteriorated. On the other hand, when the thickness of the mixed layer 3 exceeds 500 nm, there is a possibility that the base material 2 may be separated and fall off due to deformation of the base material 2 during press working for forming a gas flow path in the carbon-coated separator material 1.

  Note that a layer (not shown) of amorphous or crystalline carbon black may be further stacked on the mixed layer 3. This carbon black layer is a layer in which the carbon black used when the method of manufacturing the carbon coated separator material 1 according to the present embodiment is performed is left. Further, the mixed layer 3 can be formed only on one side of the substrate 2, but can also be formed on both sides.

(Production method of carbon coated separator material)
Next, a method for manufacturing the carbon-coated separator material 1 according to the present embodiment will be described with reference to FIG.
FIG. 2 is a flowchart illustrating the content of the method for manufacturing a carbon-coated separator material according to the present embodiment. As shown in FIG. 2, the method for manufacturing a carbon-coated separator material according to the present embodiment includes a coating step S2 and a heat treatment step S3, and these steps are performed in this order. By performing the method for manufacturing a carbon-coated separator material according to the present embodiment, the carbon-coated separator material 1 shown in FIG. 1 can be manufactured.

(Coating process)
The coating step S2 is performed on the surface of the base material 2 having a carbon concentration of 10 atomic% or less at a depth of 10 nm from the outermost surface by using a powder of carbon black 5 and a resin which decomposes without heating by heating at 500 ° C. or less. This is a step of applying a carbon black dispersion paint containing a binder resin (see FIG. 3). If the carbon concentration at a depth of 10 nm from the outermost surface is 10 atomic% or less, the average carbon concentration at a depth of 5 to 50 nm from the outermost surface is also 10 atomic% or less. Can be paraphrased.

  Here, the carbon concentration at a depth of 10 nm from the outermost surface will be described. The carbon concentration at a position at a depth of 10 nm from the outermost surface of the substrate 2 is measured, for example, by performing a composition analysis in the depth direction using an X-ray photoelectron spectroscopy (X-ray Photoelectron Spectroscopy; XPS). can do. Normally, carbon resulting from adsorption of organic substances and the like present in the atmosphere is detected from the surface layer of the base material 2. In the present invention, the portion excluding the surface layer portion (contamination layer) of the base material 2 on which organic substances are adsorbed is defined as the “outermost surface”, and the carbon concentration at a depth of 10 nm from the outermost surface is specified to be 10 atomic% or less. are doing. The fact that the carbon concentration at this position exceeds 10 atomic% means that processing oil and organic substances existing in the atmosphere infiltrate into the surface layer of the base material 2 during a process such as rolling for manufacturing the base material 2. Or it is very likely that they have reacted with titanium to form titanium carbide. If the surface layer of the base material 2 is contaminated with processing oil or organic matter, or if titanium carbide is formed, the carbon black 5 is bonded to the surface of the base material 2 when heat treatment is performed in a heat treatment step S3 described below. It becomes difficult to do. Therefore, as a result of the difficulty in forming the mixed layer 3, there is a possibility that high conductivity and high conductivity durability cannot be obtained.

Therefore, when the carbon concentration at a depth of 10 nm from the outermost surface of the base material 2 exceeds 10 atomic%, it is preferable to perform a carbon concentration reduction treatment step S1 described later before performing the coating step S2. On the other hand, when the carbon concentration at the position described above is 10 atom% or less, the coating step S2 can be performed without performing the carbon concentration reduction processing step S1. The carbon concentration at a position 10 nm deep from the outermost surface of the substrate 2 can be suppressed by adjusting the rolling process such as reducing the rolling reduction per pass of the cold rolling to 10% or less. , And 10 atomic% or less. It is preferable that the carbon concentration at a position at a depth of 10 nm from the outermost surface of the substrate 2 is lower. The carbon concentration at the position is, for example, preferably 9 atomic% or less, and more preferably 8 atomic% or less.
In order to more reliably obtain high conductivity and conductive durability, it is preferable to always perform the carbon concentration reduction processing step S1 described later.

  In order to form the mixed layer 3 on the surface of the substrate 2, an aqueous or oily liquid (dispersion paint) containing the powder of the carbon black 5 and the binder resin is applied. As the aqueous liquid, for example, water can be used as a solvent. As the oily liquid, for example, ethanol, toluene, cyclohexanone and the like can be used.

  The particle size of the powder of the carbon black 5 is preferably 20 to 200 nm. The powder of carbon black 5 tends to form aggregates in the paint, but in the present production method, it is preferable to use a paint devised so as not to form aggregates. For example, it is preferable to use a coating prepared using carbon black powder having a dispersibility enhanced by chemically bonding a functional group such as a carboxyl group to the surface of the carbon black 5 so as to repel each other.

  As the binder resin, a resin that decomposes without residue when heated at 500 ° C. or lower is used. As such a binder resin, an acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, or polyurethane is preferable, and each may be used alone, or two or more kinds may be used in combination. Among these, an acrylic resin is more preferable because it is considered that the lower the temperature at which the decomposition is completed, the lower the temperature at which the formation of the mixed layer 3 is affected in the heat treatment step S3.

  In addition, as a resin in which a residue remains at the same temperature, a phenol resin, a fluorine resin, a silicone resin, and the like can be given. If there is a residue in the mixed layer 3 or on the surface or at the interface with the base material, the conductive path of the carbon black 5 is cut off to lower the conductivity.

  The compounding ratio of the carbon black 5 and the binder resin in the carbon black-dispersed coating material is preferably a solid content mass ratio of (binder resin solid content / carbon black solid content) = 0.3 to 2.5. This shows that the larger the ratio is, the smaller the amount of the carbon black 5 is. As a result, the conductivity is lowered. If the ratio exceeds 2.5, the desired conductivity cannot be obtained. On the other hand, it is shown that the smaller the ratio is, the smaller the amount of the binder resin is. As a result, the adhesion between the base material 2 and the coating film is reduced. Can not be obtained. In consideration of the adhesion between the watching material 1 and the mixed layer 3, it is more preferable to set the ratio to 0.4 or more. Further, in consideration of conductivity, it is more preferable to set this ratio to 2.3 or less.

  In addition, a viscosity modifier, a surfactant, and the like may be added to the carbon black dispersion paint in a range that does not affect the conductivity and the adhesion.

The coating amount of the carbon black-dispersed coating material on the substrate 2 is preferably 5 to 100 μg / cm ² in terms of the total solid content of the carbon black 5 and the binder resin. If the total solid content in the coating amount is less than 5 μg / cm ² , the respective amounts of the carbon black 5 and the binder resin are too small, and the desired conductivity and adhesion cannot be obtained. More preferably, it is 7 μg / cm ² or more. On the other hand, if the total solid content exceeds 100 μg / cm ² in the coating amount, the effect of improving conductivity and adhesion is saturated, but the cost is increased. More preferably, the concentration is 80 μg / cm ² or less.

  Examples of a method of applying the carbon black dispersion paint to the base material 2 include brush coating and using a bar coater, a roll coater, a gravure coater, a die coater, a dip coater, a spray coater, and the like. It is not limited.

(Heat treatment process)
The heat treatment step S3 is a step of heat-treating the substrate 2 that has been subjected to the application step S2 under a low oxygen partial pressure having an oxygen partial pressure of 25 Pa or less. By the heat treatment step S3, as shown in FIG. 4, on the surface of the heat-treated base material 2, titanium oxide 4 in which some or all of the titanium atoms diffused outward from the base material 2 are oxidized, and carbon black 5 A mixed layer 3 is formed. By forming this mixed layer 3, high conductivity and high conductivity durability can be imparted to the fuel cell separator material 1.

  If the oxygen partial pressure in the heat treatment step S3 exceeds 25 Pa, the reaction between carbon and oxygen may result in carbon dioxide (combustion). That is, the oxidative decomposition of the carbon black 5 occurs, and the titanium on the surface of the base material 2 is oxidized at the exposed portion where the surface of the base material 2 is exposed, so that a large amount of titanium oxide 4 is generated (the layer of the titanium oxide 4 becomes too thick ). Further, in addition to this, the mixed layer 3 in which the titanium oxide 4 in which some or all of the titanium atoms diffused outward from the substrate 2 are oxidized and the carbon black 5 are not mixed is not formed, so that high conductivity and high conductivity durability are obtained. I can not get sex. Therefore, the heat treatment needs to be performed under reduced pressure or using an inert gas such as an Ar gas or a nitrogen gas or a mixed gas of such an inert gas and oxygen as described above to reduce the oxygen partial pressure to 25 Pa or less. .

The oxygen partial pressure is preferably, for example, in the range of 0.2 to 21 Pa. Further, the temperature of the heat treatment is preferably, for example, in a temperature range of 500 to 800 ° C. When the oxygen partial pressure and the temperature of the heat treatment are respectively in the above-mentioned ranges, part or all of the titanium atoms diffused outward from the base material 2 react with a small amount of oxygen in the atmosphere to form titanium oxide 4, and titanium oxide 4 Layer 3 in which carbon black 5 and carbon black 5 are mixed can be reliably formed.
On the other hand, when heat treatment is performed in an atmosphere having an extremely low oxygen partial pressure, the reaction in which titanium and carbon black 5 combine to form TiC becomes dominant. Although TiC has a low contact resistance, it is not preferable in a high-temperature acidic atmosphere (for example, 80 ° C., pH 2) in a fuel cell because oxidation proceeds to increase the resistance. On the other hand, the titanium oxide 4 and the carbon black 5 contained in the mixed layer 3 are not oxidized and stable even in a high-temperature acidic atmosphere (for example, 80 ° C., pH 2) in the fuel cell. Therefore, according to the manufacturing method according to the present invention, the carbon-coated separator material 1 having high conductivity and conductive durability can be manufactured.
That is, in order to form the mixed layer 3 in which the titanium oxide 4 and the carbon black 5 are mixed on the base material 2, a specific amount of oxygen needs to be present in the heat treatment atmosphere, and the upper limit of the oxygen partial pressure is For example, the pressure can be set to 20 Pa, and the lower limit of the oxygen partial pressure can be set to, for example, 0.05 Pa. The lower limit of the heat treatment temperature can be, for example, 600 ° C., and the upper limit of the heat treatment temperature can be, for example, 750 ° C. Even if the upper and lower limits of the oxygen partial pressure and the lower and upper limits of the heat treatment temperature are set as described above, the carbon-coated separator material 1 can be manufactured.

  The time of the heat treatment can be, for example, 30 minutes when the temperature of the heat treatment is 500 ° C., and 1 to 2 minutes when the temperature of the heat treatment is 700 ° C. The time of the heat treatment is not limited to the example described above, and can be appropriately set depending on the temperature of the heat treatment.

  When the heat treatment is performed in an atmosphere having a low oxygen partial pressure close to 0.2 Pa in a low-temperature condition of about 400 ° C., the formation of titanium oxide 4 is slightly insufficient, and although the conductivity is high, the durability is slightly insufficient. Might be. In such a case, after the heat treatment under the low oxygen partial pressure, heat treatment is performed in an air atmosphere to promote the formation of the titanium oxide 4 and improve the durability. The heat treatment in the air atmosphere may be performed under such a condition that the carbon black 5 hardly burns and the titanium oxide 4 is formed. Such conditions include, for example, a low temperature side (for example, 200 ° C. or more and less than 350 ° C.) in a temperature range of 200 to 500 ° C. for 30 to 60 minutes, and a high temperature side (for example, 350 ° C. or more and 500 ° C. or less). If so, the conditions may be appropriately adjusted, such as 0.5 to 5 minutes.

  When the amount of the binder resin composed of a resin which decomposes without residue by heating at 500 ° C. or less contained in the carbon black dispersion paint is large, the binder resin is generated when the binder resin is thermally decomposed before the heat treatment under the low oxygen partial pressure. A "degassing" heat treatment for removing the gas to be removed is preferred. This degassing treatment is preferably performed in a temperature range of 400 to 600 ° C. under vacuum, and the mixed layer and the base material are subjected to a heat treatment under a low oxygen partial pressure after removing the impurity gas by the degassing treatment. An effect of improving adhesion is also expected.

  As described above, according to the method for producing a carbon-coated separator material of the present invention, in the coating step S2, the base material 2 having a carbon concentration of 10 atomic% or less at a depth of 10 nm from the outermost surface. Is coated with a carbon black-dispersed coating material containing carbon black 5 and a binder resin made of a resin that decomposes without heating when heated to 500 ° C. or lower. Next, in the heat treatment step S3, the substrate 2 is heat-treated under a low oxygen partial pressure where the oxygen partial pressure is 25 Pa or less. Therefore, as shown in FIG. 4, the surface of the heat-treated base material 2 is mixed with titanium oxide 4 in which some or all of the titanium atoms diffused outward from the base material 2 are oxidized and carbon black 5. Layer 3 is formed. By forming this mixed layer 3, high conductivity and high conductivity durability can be imparted to the carbon-coated separator material 1. In addition, it improves the handling resistance (coating peeling and abrasion) of the coating when the carbon black dispersion coating is applied to the substrate with the binder resin, and mixes well with the titanium substrate during the subsequent heat treatment. A layer is formed. Therefore, when a separator (not shown) is formed by using the carbon-coated separator material 1 manufactured by the present manufacturing method and used for a fuel cell (not shown), a low contact resistance can be maintained for a long time inside the fuel cell. Can be maintained (high conductive durability). Further, since the substrate 2 is made of titanium or a titanium alloy, there is no danger of titanium being eluted inside the cell of the fuel cell, and the performance of a solid polymer membrane (not shown) is not deteriorated.

  The method of manufacturing the carbon-coated separator material according to the present embodiment is as described above. However, as described above, when the carbon concentration at a position at a depth of 10 nm from the outermost surface of the base material 2 exceeds 10 atomic%. Even if the heat treatment is performed in the heat treatment step S3, outward diffusion of titanium atoms from the base material 2 to the carbon black 5 is hindered, and the mixed layer 3 is hardly formed. Therefore, in such a case, as shown in FIG. 2, the carbon concentration reduction processing step S1 is performed before the coating step S2.

(Carbon concentration reduction process)
The carbon concentration reduction treatment step S1 is a step of treating the surface of the base material 2 before the coating step S2 to reduce the carbon concentration at a position at a depth of 10 nm from the outermost surface to 10 atomic% or less. That is, the carbon concentration reduction treatment step S1 is a step of forming a natural oxide film by removing a region contaminated with organic substances and the like on the outermost surface of the base material 2 and a region where titanium carbide is formed.

When the carbon concentration at a depth of 10 nm from the outermost surface of the base material 2 exceeds 10 atomic%, the carbon concentration can be reduced to 10 atomic% or less by, for example, using an acidic aqueous solution containing hydrofluoric acid. It is preferable to perform pickling treatment for pickling 2. Further, the acidic aqueous solution containing hydrofluoric acid may contain nitric acid, sulfuric acid, hydrogen peroxide, etc., alone or in combination. For example, in the case of a mixed aqueous solution of hydrofluoric acid and nitric acid, the concentration of hydrofluoric acid is preferably 0.1 to 5% by mass, and more preferably 1% by mass. On the other hand, the nitric acid concentration is preferably 1 to 20% by mass, and more preferably 5% by mass or the like. For example, in the case of a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide, the concentration of hydrofluoric acid is preferably 0.1 to 5% by mass, more preferably 1% by mass. On the other hand, the concentration of hydrogen peroxide is preferably 1 to 20% by mass, more preferably 5% by mass or the like.
Examples of the composition and concentration of the aqueous solution used for the pickling treatment have been given, but the present invention is not limited thereto. For example, a hydrofluoric acid aqueous solution having the above-mentioned concentration can be used alone instead of the above-mentioned mixed aqueous solution containing hydrofluoric acid.

  As described above, by performing the carbon concentration reduction processing step S1, even when the carbon concentration at the position described above exceeds 10 atomic%, the carbon concentration at the position is reliably reduced to 10 atomic% or less. can do. Therefore, it is possible to reliably manufacture the carbon-coated separator material 1 having high conductivity and conductive durability. Here, as described above, the carbon concentration of the outermost surface of the substrate 2 pickled by the pickling treatment is preferably, for example, 9 at%, and more preferably 8 at%.

  The temperature of the mixed aqueous solution in the pickling treatment can be, for example, room temperature, but can be adjusted in the range of 10 to 90 ° C. in consideration of the treatment speed and the like. The immersion time can be adjusted within a range of, for example, several minutes to several tens of minutes, and can be, for example, 5 to 7 minutes. These conditions can be appropriately set according to the carbon concentration at a position at a depth of 10 nm from the outermost surface of the substrate 2.

In addition, the processing method for reducing the carbon concentration at a position at a depth of 10 nm from the outermost surface of the base material 2 to 10 atomic% or less in the carbon concentration reduction processing step S1 is not limited to the above-described pickling treatment. For example, heat treatment is performed at a temperature of 650 ° C. or more in a vacuum (1.3 × 10 ⁻³ Pa or less) to diffuse carbon into the base material 2, or a layer having a high carbon concentration is formed by shot blasting or polishing. It is also possible to apply the removal.

The method for producing a carbon-coated separator material according to the present embodiment can include any step other than the steps described above.
For example, before the carbon concentration reduction processing step S1, a rolling / winding step of rolling the material to a target thickness and winding the coil, and a degreasing step of removing rolling oil (not shown in FIG. 2) are included. You may go out.
Further, a cleaning / drying step (not shown in FIG. 2) for cleaning and drying the substrate may be included between the carbon concentration reduction processing step S1 and the coating step S2.
A drying step (not shown in FIG. 2) for drying the coated surface may be included between the coating step S2 and the heat treatment step S3.
Further, after the heat treatment step S3, a correction step (leveling step) (not shown in FIG. 2) for correcting the warpage of the base material 2 in the length direction caused by the heat treatment and flattening the same may be included.
The correction can be performed by using a tension leveler, a roller leveler, a stretcher, or the like. Further, a cutting step of cutting the carbon-coated separator material 1 having been subjected to the heat treatment step S3 or the straightening step to a predetermined size may be included.
All of these steps are optional steps and can be performed as needed.

(One Embodiment of Production of Fuel Cell Separator)
In order to produce a fuel cell separator (not shown) using the carbon-coated separator material 1 produced by the production method according to the present embodiment, a gas flow path through which a gas flows through the produced carbon-coated separator material 1 It is preferable to perform a press molding step (not shown) for forming a gas inlet for introducing a gas into the gas flow path.

  The molding of the carbon-coated separator material 1 by the press molding process is performed by attaching a molding die (for example, a molding die for forming a gas flow passage and a gas inlet) to a known press molding device to form a desired shape. It can be performed by pressing. When a lubricant needs to be used during molding, it can be used as appropriate. When press-molding using a lubricant, it is preferable to perform the step for removing the lubricant after the press-forming step.

When the carbon coating separator material 1 is press-formed, the mixed layer 3 of the titanium oxide 4 and the carbon black 5 on the surface cannot completely follow the deformation of the base material 2 and the newly formed surface of the base material 2 partially May be exposed. Although a natural oxide film is formed on the exposed portion, if the corrosion resistance is insufficient, a heat treatment in the air after the press molding step can enhance the corrosion resistance of the exposed new surface.
The heat treatment in the air atmosphere may be performed under such a condition that the carbon black 5 hardly burns and the titanium oxide 4 is formed. Such conditions include, for example, a low temperature side (for example, 200 ° C. or more and less than 350 ° C.) in a temperature range of 200 to 500 ° C. for 30 to 60 minutes, and a high temperature side (for example, 350 ° C. or more and 500 ° C. or less). If so, the conditions may be appropriately adjusted such as 0.5 to 5 minutes.

(Other Embodiment of Production of Fuel Cell Separator)
The manufacturing method according to the present invention may be a method of manufacturing a fuel cell separator in which a gas flow path and a gas inlet are formed. In this case, a press forming step (not shown) for forming a gas flow path and a gas inlet may be performed before the above-mentioned coating step S2.
Specifically, for example, after rolling and annealing pure titanium or a titanium alloy to produce the base material 2, the above-described press forming step is performed, and then, if necessary, the carbon concentration reduction processing step S1 is performed. It is preferable to perform the heat treatment step S3 after performing the step S2. In this case, between the press molding step and the carbon concentration reduction processing step S1, a degreasing treatment for removing oil adhering to the surface of the substrate 2 can be performed.
In addition, for example, after rolling and annealing pure titanium or a titanium alloy to produce the base material 2, if necessary, a carbon concentration reduction treatment step S1 is performed, then a press molding step is performed, and a coating step S2 is performed. After that, a heat treatment step S3 is preferably performed. In this case, a degreasing treatment for removing oil adhering to the surface of the base material 2 can be performed between the press molding step and the coating step S2.

  Next, the contents of the present invention will be specifically described with reference to examples.

(1) Preparation of test specimen [base material]
A cold rolled material of pure titanium (one type specified in JIS H 4600) having a thickness of 0.1 mm was used as a base material, and cut into a size of 50 × 150 mm.
As a result of measuring the carbon concentration at a position at a depth of 10 nm from the outermost surface of the substrate by XPS analysis, the used base material was 18 atom% (average carbon concentration between 5 and 50 nm deep from the outermost surface). Was 18 atomic%), so that the following pickling treatment was performed, and further, the following steps were performed to prepare a test body.

[Pickling treatment]
A mixed aqueous solution containing 5% by mass of nitric acid and 0.5% by mass of hydrofluoric acid (an acidic aqueous solution containing hydrofluoric acid) was prepared as a pickling treatment solution. Then, the base material cut into the size of 50 × 150 mm is immersed in the mixed aqueous solution at a room temperature for 5 to 7 minutes to remove a region having a high carbon concentration on the outermost surface of the base material, and then washed with water and super-cooled. It was sonicated and dried.
As a result of measuring the carbon concentration at a position at a depth of 10 nm from the outermost surface of the base material thus treated by XPS analysis, it was found to be 5 atom% or less (average carbon concentration of 5 to 50 nm from the outermost surface). The concentration was also 5 atomic%).

[Application of carbon black dispersion paint]
A commercially available carbon black-containing paint (Aqua Black-162 manufactured by Tokai Carbon Co., Ltd.) was used, and the paint was appropriately diluted with distilled water and ethanol, and an acrylic resin was added to prepare a carbon black dispersion paint. The ratio (solid content of acrylic resin / solid content of carbon black) was changed in the range of 0 to 3.5 depending on the amount of the acrylic resin added. Then, the carbon black dispersion paint was applied on a substrate by brush coating. The coating amount was in the range of 30 to 40 μg / cm ² in terms of the total solid content of carbon black and acrylic resin.

[Heat treatment]
After applying the carbon black dispersion coating, a test piece of 20 × 50 mm was cut out, and the test piece was subjected to a heat treatment at an oxygen partial pressure of 1.2 Pa, a heating temperature of 650 to 700 ° C., and a processing time of 10 to 60 seconds to obtain a test piece. Manufactured. This heat treatment was performed using a vacuum heat treatment furnace, and the adjustment of the oxygen partial pressure was performed by adjusting the degree of vacuum.

  Then, the contact resistance value of the test piece immediately after the production was measured as described below.

[Measurement of contact resistance value]
The contact resistance of each specimen was measured using the contact resistance measuring device 10 shown in FIG. More specifically, both surfaces of the test body 11 are sandwiched between carbon cloths 12 (manufactured by Fuel Cell Earth, CC6 Plain, thickness 26 mils (about 660 μm)), and the outside is further sandwiched by two copper electrodes 13 having a contact area of 1 cm ^2. It was pinched and pressed with a load of 98 N (10 kgf). Then, a current of 7.4 mA was applied by using the DC current power supply 14, and the voltage applied between the carbon cloths 12 was measured by the voltmeter 15 to determine the contact resistance value. When the contact resistance value was less than 8 mΩ · cm ² , the conductivity was judged to be good (pass).

  In addition, the test piece immediately after the preparation was evaluated for adhesion as follows.

(Evaluation of adhesion)
For each specimen, a cellophane tape was applied to the coating film after the carbon black dispersion coating was applied to the substrate, and a 90 ° peeling test was performed. Passed.

In addition, after forming each coating film in which the (acrylic resin solid content / carbon black solid content) ratio was changed, a heat treatment was performed to form a mixed layer (titanium oxide + carbon black). And the contact resistance value of the test body which formed this mixed layer was measured. FIG. 6 is a graph showing the relationship between the ratio (solid content of acrylic resin / solid content of carbon black) and the contact resistance value. As shown in the figure, the contact resistance increases as the (acrylic resin solid content / carbon black solid content) ratio increases, and the (acrylic resin solid content / carbon black solid content) ratio falls within a range of 2.5 or less. The contact resistance was less than 8 mΩ · cm ^2, indicating that the conductivity was good.

  However, in the evaluation of coating film adhesion, when the (acrylic resin solid content / carbon black solid content) ratio was less than 0.3, the coating film was peeled and the substrate was exposed, and the adhesion was unacceptable. Was.

  As described above, when the (acrylic resin solid content / carbon black solid content) ratio is in the range of 0.3 to 2.5, both conductivity and coating film adhesion can be favorably achieved.

DESCRIPTION OF SYMBOLS 1 Separator material for fuel cells 2 Substrate 3 Mixed layer 4 Titanium oxide 5 Carbon black S1 Carbon concentration reduction process S2 Coating process S3 Heat treatment process

Claims (3)

An application step of applying a carbon black dispersion paint to a titanium base material having a carbon concentration of 10 atomic% or less at a depth of 10 nm from the outermost surface;
A heat treatment step of performing a heat treatment at a temperature range of 500 to 800 ° C. under a low oxygen partial pressure having an oxygen partial pressure of 25 Pa or less after the applying step, a method of producing a carbon coat separator material for a fuel cell,
The method for producing a carbon-coated separator material for a fuel cell, wherein the carbon black-dispersed coating material used in the coating step contains carbon black and a binder resin composed of a resin that decomposes without heating when heated to 500 ° C. or less. .   The method according to claim 1, wherein the binder resin is at least one of acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, and polyurethane.   The binder resin and the carbon black in the carbon black-dispersed coating material have a solid content ratio of (binder resin solid content / carbon black solid content) = 0.3 to 2.5. Item 3. The method for producing a carbon-coated separator material for a fuel cell according to Item 1 or 2.

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