JP2007035615A - Separator for fuel cell, manufacturing method thereof, and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a fuel cell with improved water wettability in a groove and a method for producing the same.
SOLUTION: A fuel cell separator including a resin and a conductive material as constituents and having a sulfonic acid group added to at least a part of a gas channel surface by sulfuric acid gas treatment, the gas channel of the separator The resin existing on the surface and the sulfonic acid group are bonded to each other, and the ratio of the sulfur atom in the sulfonic acid group on the gas flow path surface is 0.1 to 4 as a value measured by energy dispersive X-ray spectroscopy. The present invention relates to a separator for a fuel cell, a method for manufacturing the same, and a fuel cell.
[Selection figure] None

Description

  The present invention relates to a fuel cell separator having excellent surface hydrophilicity, a method for producing the same, and a fuel cell using the separator.

  A fuel cell refers to a device for taking out electricity and thermal energy by utilizing an electrochemical reaction between a fuel and an oxidant, and generally has two electrodes provided on both sides thereof via an electrolyte. The basic structure is a single cell sandwiched between two separators provided with a supply path for supplying a fuel such as hydrogen gas or an oxidant such as oxygen gas or air. When high output is required, a stack structure in which a plurality of single cells are stacked in series is used, and current is collected by current collecting plates provided at both ends of the stack.

  There are various types of fuel cells depending on the type of electrolyte, fuel, oxidant, etc. Among them, solid polymer electrolyte membranes that use electrolyte as solid polymer electrolyte membrane, hydrogen gas as fuel, air as oxidant, and fuel A methanol direct type fuel cell that directly extracts hydrogen from methanol inside the battery and uses it as fuel can efficiently generate power at a relatively low operating temperature of 100 ° C. or lower during power generation.

The separators constituting these fuel cells are usually formed by a gas-impermeable conductive member made of a molded plate using a mixture of a conductive material such as graphite and a resin, and gas diffusion is formed on the surface thereof. A rib structure that forms a gas flow path with the electrode is formed. As such a separator, the supply path of the reaction gas flowing into the fuel battery cell is secured by the gas flow path, and the role of transmitting electricity generated by the fuel battery cell to the outside is assumed. In order to perform sufficiently, it is required not only to be made of a material having high conductivity in the surface direction and the thickness direction, but also to reduce the resistance of the surface in contact with the electrode portion.
In response to this demand, a separator having a reduced contact resistance with an electrode portion and a manufacturing method thereof have been proposed (see, for example, Patent Document 1 and Patent Document 2). This separator is formed by molding a mixture of a conductive material and a thermoplastic resin or a thermosetting resin, and then machining the surface of the separator to a specific surface roughness by polishing the surface to make contact with the surface. The resistance is reduced.
However, the above-mentioned separator improves the contact resistance with the electrode part to some extent, but is not sufficient, and the hydrophilicity is rough, and the surface becomes rough. There are things to do.

The fuel cell incorporating the fuel cell separator is supplied with a fuel gas containing hydrogen at the cathode and supplied with an oxidizing gas containing oxygen at the anode, but the electrochemical reaction proceeds at each electrode. At this time, generated water is generated on the cathode side or the anode side.
Usually, the produced water is vaporized in the oxidizing gas supplied to the anode side, and is discharged out of the fuel cell together with the oxidizing gas. However, when the amount of generated water increases, the generated water cannot be exhausted only by vaporizing it in the oxidizing gas. In this way, if the generated water that remains without being vaporized in the oxidizing gas becomes water droplets around the anode, the gas flow path is blocked and the flow of the oxidizing gas around the anode is hindered, leading to a decrease in battery performance. End up.

Such blockage of the gas flow path can occur not only in the anode but also in the cathode. At the cathode of the fuel cell, the generated water as described above is not generated by the cell reaction, but the water vapor in the fuel gas supplied to the cathode may condense. Normally, when an electrochemical reaction proceeds, protons generated in the cathode reaction on the cathode side move to the anode side in a state of being hydrated with a predetermined number of water molecules. However, in order to prevent this, the fuel gas supplied to the anode side is humidified to supplement the electrolyte membrane with water.
Thus, the water vapor added to the fuel gas may condense in the gas flow path when the fuel cell is started or when the operating temperature of the fuel cell is lowered and the saturated vapor pressure is lowered. In this case, the flow path of the gas is also blocked on the anode side and the flow of the fuel gas is hindered, leading to a decrease in battery performance.
As described above, protons generated in the cathode reaction move to the anode side in a hydrated state. Therefore, on the anode side, in addition to the generated water described above, water molecules brought in along with the movement of protons are added, and water is further added. It becomes an excessive state, and the gas flow path is easily blocked. Such a clogging phenomenon is a phenomenon that is noticeable in a fuel cell separator made of a conductive material and a resin.

Therefore, conventionally, the entire surface of the fuel cell separator made of a conductive material and a resin or the surface of the gas flow path has been subjected to a hydrophilic treatment, thereby improving the discharge of generated water. By subjecting the members of the fuel cell separator made of a conductive material and a resin to hydrophilic treatment, the generated water can be guided to a predetermined flow path without staying as water droplets. Can be prevented.
The previously described solid polymer fuel cell uses a solid polymer membrane as an electrolyte layer, a pair of gas diffusion electrodes sandwiching the solid polymer membrane, and a gas diffusion electrode from the outside to oxidize the fuel gas A single cell having a separator for separating gas is used as a basic unit, and a plurality of single cells are stacked. In such a polymer electrolyte fuel cell, the hydrophilic treatment as described above is performed on the separator, but is also performed on other gas diffusion electrodes.

Examples of a method for hydrophilic treatment of such a separator for a fuel cell made of a conductive material and a resin include the following methods.
First, a method has been proposed in which a porous carbon member having a water absorption rate of 30 to 80% is provided at the entrance or exit of a gas flow path (see, for example, Patent Document 3). However, the separator obtained by this method has a problem that the hydrophilic performance is lowered with the passage of time, and it is necessary to go through a complicated process of disposing a water absorbing member at the time of molding or after molding. There was also.
Further, as a hydrophilic treatment method, a method of forming a coating or a coating film on the surface of the fuel gas channel and preferably on the surface of the oxidizing gas channel with various hydrophilic resins, hydrophilic organic compounds and inorganic compounds (for example, patent documents) 4 and Patent Document 5) have been proposed. However, since the separator obtained by these methods forms an insulating film on the surface, the conductivity is remarkably reduced, or the elution from the film causes a decrease in the durability of the fuel cell. It was.

Furthermore, as another method of hydrophilic treatment, silicon oxide, aluminum oxide, starch, acrylic acid copolymer resin, polyacrylic acid salt, polyvinyl alcohol in the raw material constituting the conductive separator containing the resin binder A method of hydrophilizing the separator material itself by adding and mixing a hydrophilic substance such as water and a water-absorbing resin has been proposed (for example, see Patent Document 6). Since water absorbs water and various impurities from the hydrophilic and water-absorbing substances are eluted in the water, there is a problem that the characteristics of the fuel cell in which these separators are incorporated are significantly hindered.
Further, as a hydrophilic treatment method, a surface of a conductive separator made of various materials is imparted with hydrophilicity by performing treatments such as low-temperature plasma treatment, corona treatment, and ultraviolet irradiation in a hydrophilization gas (for example, Patent Document 7). Have been proposed). However, the hydrophilization by these methods has a property that the effect decreases with time, and there are cases where the hydrophilization treatment must be performed in a vacuum, which causes a problem in the process.
Further, there has been proposed a method for hydrophilizing the surface by performing atmospheric pressure discharge plasma treatment using a sulfur element-containing compound or the like as a treatment gas (see, for example, Patent Document 8). However, in this proposal, the graphite fuel cell separator is plasma-treated under strong conditions, so the graphite on the separator surface oxidizes and ashes, causing a decrease in conductivity and damage to the shape of the molded product. There is a problem of being unable to endure.
JP 2002-270203 A Japanese Patent Laid-Open No. 11-297338 Japanese Patent Laid-Open No. 8-138692 JP 2003-217608 A JP 2003-297385 A Japanese Patent Laid-Open No. 10-3931 WO99 / 40642 pamphlet JP 2002-25570 A

As described above, in the separator having the rib structure, in order to solve the problem that the electromotive force of the fuel cell is reduced because the water generated and retained in the groove portion cannot be smoothly discharged to the outside. At present, the optimal method has not been found yet.
An object of the present invention is to provide a fuel cell separator having improved water wettability in a groove and a method for producing the same.

The present inventors have found that a separator having a stable hydrophilic property can be obtained by applying a specific amount of a sulfonic acid group to the resin present on the surface by treating the surface of the separator with sulfuric acid gas. The present invention has been completed.
That is, the present invention is a fuel cell separator comprising a resin and a conductive material as constituent components, and having a sulfonic acid group added to at least a part of a gas flow path surface by sulfuric acid gas treatment, A resin and a sulfonic acid group existing on the flow path surface are bonded to each other, and a ratio of sulfur atoms in the sulfonic acid group on the gas flow path surface is 0.1 as a value measured by energy dispersive X-ray spectroscopy. The present invention provides a separator for a fuel cell, characterized by being -4.0 atomic%. The present invention also relates to a method for producing a fuel cell separator in which the ratio of sulfur atoms on the gas flow path surface is 0.1 to 4.0 atomic% as measured by energy dispersive X-ray spectroscopy, Provided is a method for producing a fuel cell separator, characterized in that a sulfuric acid-containing gas is brought into contact with a gas channel surface of a fuel cell separator material obtained by molding a conductive composition containing a resin and a conductive material. To do. Furthermore, the present invention provides a fuel cell in which the fuel cell separator is incorporated.

  The separator for a fuel cell according to the present invention improves the wettability of water by adding a sulfonic acid group to a resin present on the surface of the separator gas flow path in a sulfuric acid-containing gas. The battery has no stagnation of water due to the inflow of fuel gas, and is excellent in discharging water to the outside. For this reason, the fuel cell of the present invention does not hinder the supply of fuel gas due to excessive water, the electromotive force is stable, there is little influence of impurities such as elution, and stable power generation is possible over a long period of time. It becomes possible.

The fuel cell separator of the present invention is made hydrophilic by imparting sulfonic acid groups to at least a part of the gas flow path surface of the fuel cell separator material by sulfuric acid gas treatment, thereby improving the wettability of water.
The degree of hydrophilization is based on the content of sulfur atoms in the sulfonic acid group present on the separator channel surface.
The amount of sulfur atoms in the sulfonic acid group is 0.1 to 4.0 atomic% as measured by the energy dispersive X-ray analysis, with the abundance ratio on the gas flow path surface being 2. 0 to 4.0 atomic% is preferable. If the amount of sulfur atoms is 0.1 to 4.0 atomic percent, the hydrophilicity is excellent and the effect can be maintained over a long period of time. On the other hand, if the amount of sulfur atoms exceeds 4.0% by number on the surface, the treatment conditions inevitably become stronger, which increases the roughness of the surface of the molded product and increases the water absorption rate. The physical properties as a separator are remarkably reduced, such as an increase or a decrease in strength.
The part of the gas channel surface mainly refers to a groove on the gas channel surface, and may include other parts.

The sulfuric acid gas treatment of the present invention means that a sulfonic acid group is imparted to the substrate surface by bringing the sulfuric acid-containing gas into contact with the substrate. As a method for imparting a sulfonic acid group using a sulfuric acid-containing gas, a known method is used. For example, a method in which the separator material is brought into contact in a gas of anhydrous sulfuric acid gas or fuming sulfuric acid gas. Among these, the method of contacting in a gas of anhydrous sulfuric acid gas is preferable because of its high reactivity with the substrate.
The sulfonic acid group is imparted to the separator by bonding with a resin present on the surface of the gas flow path.
Examples of the bonding form between the sulfonic acid group and the resin include a covalent bond, a coordination bond, an ionic bond, a hydrogen bond, and a van der Waals bond. Among these, a state in which the sulfonic acid group is bonded by a covalent bond is preferable because it is not easily dissociated or easily detached.

Examples of the anhydrous sulfuric acid-containing gas that can be used for the production of the fuel cell separator of the present invention include gaseous anhydrous sulfuric acid and gaseous anhydrous sulfuric acid diluted with an inert gas.
The anhydrous sulfuric acid-containing gas is preferably gaseous anhydrous sulfuric acid diluted with an inert gas because the ratio of anhydrous sulfuric acid to the separator material can be strictly controlled.
The abundance ratio of sulfur atoms in the sulfonic acid group on the gas flow path surface is a value measured by an energy dispersive X-ray analysis method, specifically, a value measured using an energy dispersive X-ray analyzer. Is based.
This energy dispersive X-ray analyzer performs spectroscopic analysis of X-rays generated from elements using an energy dispersive semiconductor detector.
As a specific measurement method, by using an energy dispersive X-ray analyzer and analyzing the separator surface at a magnification of 100 times, characteristic X-rays specific to elements generated by electron beam irradiation are detected and obtained. The element is qualitatively and quantitatively determined from the peak position and intensity of the spectrum.
Examples of the energy dispersive X-ray analyzer include JSM-5900LV (manufactured by JEOL Ltd.).
The sulfonic acid group on the separator surface can be detected using an X-ray photoelectron spectrometer (ESCA).

Examples of the inert gas include a gas that does not substantially react with any of sulfuric anhydride and the material constituting the separator material, and has a dry water content as low as possible. Specifically, air, Mention may be made of carbon dioxide, helium, dry nitrogen, and dry argon, and mixtures thereof.
The anhydrous sulfuric acid diluted with an inert gas is obtained by diluting sulfuric acid (boiling point 44.8 ° C.) gasified with an inert gas such as air, carbon dioxide, nitrogen, helium, or argon. The concentration of anhydrous sulfuric acid gas in anhydrous sulfuric acid diluted with an inert gas is not particularly limited, but is preferably 0.1 to 80% by volume.
Other examples of the sulfuric anhydride-containing gas include a mixture of a gaseous Lewis base and anhydrous sulfuric acid, a mixture of a gaseous Lewis base, anhydrous sulfuric acid, and the inert gas.
The molar ratio of sulfuric anhydride to Lewis base in the sulfuric anhydride-containing gas can usually be freely selected depending on the material or purpose.

As a method for bringing the fuel cell separator into contact with the anhydrous sulfuric acid-containing gas and imparting a sulfonic acid group to the gas flow path surface, for example, the fuel cell separator is housed in an acid-resistant sealed container in which the anhydrous sulfuric acid-containing gas flows, Examples thereof include a batch method in which the separator is brought into contact and a continuous method in which a separator is continuously passed through a chamber through which an anhydrous sulfuric acid-containing gas flows.
Specifically, this can be achieved by determining the contact time between the separator and the anhydrous sulfuric acid-containing gas, the gas temperature, the temperature of the sealed container, and the anhydrous sulfuric acid gas flow rate. The contact time is usually in the range of 0.1 seconds to 120 minutes, and preferably in the range of 1 to 60 minutes. If it is in the range of 0.1 second to 120 minutes, it can be uniformly processed and a corresponding effect can be expected. The temperature of the sealed container is usually preferably in the range of 0 ° C to 100 ° C, more preferably in the range of 10 ° C to 90 ° C, and particularly preferably in the range of 20 ° C to 80 ° C.

The flow rate and treatment time of sulfuric anhydride-containing gas can be obtained even if the entire separator is placed in a closed container and the gas flow rate is increased and the time is increased. Can supply a predetermined amount of the sulfonic acid group to the surface in a small amount and in a short time. When the whole separator is put in a closed container, the flow rate is usually 0.01 to 10,000 ml / min in terms of 100% sulfuric anhydride gas. With this flow rate, the processing time is moderate and efficient. This flow rate depends on the size of the sealed container and is preferably in the range of 0.5 to 5 times the volume of the sealed container per minute.
In addition, in the application of the sulfonic acid group, it is preferable that the fuel cell separator material is pretreated and then brought into contact with sulfuric anhydride-containing gas. By performing the pretreatment, the sulfonic acid group can be imparted in a shorter time than in the case where the pretreatment is not performed.
Examples of the pretreatment method include drying. This is because anhydrous sulfuric acid in the anhydrous sulfuric acid-containing gas may be changed to concentrated sulfuric acid if any moisture is present in the system.
As a drying method, a method of standing in a desiccator containing a desiccant such as silica gel, a method of standing in a dryer at a temperature higher than room temperature such as 50 ° C., and moisture using a vacuum dryer. The method of removing etc. are mentioned.
Examples of the pretreatment method include drying, heat treatment, flame treatment, corona treatment, ultraviolet irradiation treatment, plasma treatment and the like.

Furthermore, in the present invention, it is preferable that after the sulfonic acid group is added to the separator, it is immediately post-treated to remove sulfuric acid remaining on the surface of the separator. Examples of the post-treatment method include washing with water, treatment with an aqueous solution of sodium bicarbonate and lime water, and the like. It is preferable to wash with ion exchange water at 10 ° C. or higher after washing with an alkaline solution.
In the separator of the present invention, the wettability of the gas channel surface is improved by adding a sulfonic acid group to the gas channel surface.
The wettability can be evaluated based on the contact angle with water when used as a fuel cell separator. The contact angle value is 80 degrees or less, preferably 70 degrees or less. Thus, when the contact angle with water is 80 degrees or less, the generated water generated during operation as a fuel cell separator is drained without staying in the separator groove flow path, so that a stable voltage is maintained. Can do.

Moreover, the separator for fuel cells after imparting the sulfonic acid group needs to maintain the elution property before imparting. Thus, if elution property does not fall, the separator for fuel cells which was excellent in long-term stability and excellent in drainage property can be obtained.
In this case, as the elution property, when the electric conductivity of the ion-exchanged water was measured after being left in the ion-exchanged water at 95 ° C. for 60 hours twice, it was twice the value before the addition of the sulfonic acid group. The following is preferable.

The fuel cell separator used in the present invention is formed by molding a conductive composition containing a resin and a conductive material.
Examples of conductive materials include metal powders, metal fibers, tin oxide, and other metals or conductive inorganic oxides, artificial graphite, flake-like natural graphite, massive natural graphite, expanded graphite, carbon nanotubes, PAN-based or pitch Graphite-based fibers, PAN-based or pitch-based carbon fibers, graphite powder obtained from spherulite (mesoface) pitch, carbon black, acetylene black, ketjen black, or amorphous carbon. One kind of these or a mixture of two or more kinds can be used. Of these, graphite is preferable in that the separator has good conductivity. Moreover, as an average particle diameter, it is preferable that it is 100-400 micrometers, and it is especially preferable that an aspect ratio is 1-5 and an average particle diameter is 200-300 micrometers. As the conductive material, milled fiber, chopped fiber, non-woven fabric, mat, sheet, paper, film or the like obtained from the above fibrous conductive material can be used.
The amount of the conductive material used is preferably 50 to 90% by weight in the conductive composition, and among these, 60 to 85% by weight is particularly preferable.

The resin used in the present invention may be either a thermosetting resin or a thermoplastic resin, or a mixture of two or more selected from these resins may be used.
Examples of the thermosetting resin include polycarbodiimide, phenol resin, furfuryl alcohol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, vinyl ester resin, bismaleimide triazine resin, polyamino bismaleimide resin. And diallyl phthalate resin. Of these thermosetting resins, phenol resins and vinyl ester resins are preferred from the viewpoint of acid resistance. These thermosetting resins are used in the form of powder or liquid as they are, or dissolved in a solvent such as water, alcohol or ketone, or a reactive diluent such as styrene.

Examples of the thermoplastic resin include polyarylene sulfide, polyolefin, polyamide, polyimide, polysulfone, polyphenylene oxide, liquid crystal polyester, and polyester. Of these thermoplastic resins, polyarylene sulfide is preferable from the viewpoint of heat resistance, and polyolefin is preferable from the viewpoint that a sulfur atom-containing group is easily attached.
Examples of the shape of the thermoplastic resin include powders, granules, films, woven fabrics, non-woven fabrics, mats, sheets, and the like, but non-woven fabrics and films are particularly preferable because of easy handling.

When using a thermosetting resin as the resin, in the conductive composition, thickener, low shrinkage agent, radical polymerization initiator, polymerization inhibitor, internal mold release agent, compatibilizing agent, other fillers , Colorants and the like.
The amount of these additives used can be freely selected depending on the type of thermosetting resin and the purpose of use of the molded body.

As such a thickener, an isocyanate compound, a powder acrylic resin, a metal oxide, or the like is used.
Examples of the low shrinkage agent include thermoplastic resins. Examples of such thermoplastic resins include polystyrene, styrene copolymers such as styrene and (meth) acrylic acid ester copolymers, styrene-conjugated diene block copolymers, and styrene-hydrogenated conjugated diene block copolymers. , (Meth) acrylic acid ester polymers not containing styrene such as polymethyl methacrylate and polyacrylic acid n-butyl ester, polyvinyl chloride, polyethylene, polyphenylene ether, polyvinyl carbazole and the like. Of these thermoplastic resins, polystyrene and polyphenylene ether are preferable from the viewpoint of water resistance.

  Examples of the radical polymerization initiator include a thermal polymerization initiator, an ultraviolet polymerization initiator, and an electron beam polymerization initiator. The amount of the radical polymerization initiator used is preferably 0.1 to 10 parts by weight, particularly preferably 1 to 5 parts by weight with respect to 100 parts by weight of the resin component. Examples of the thermal polymerization initiator include organic peroxides such as diacyl peroxide, peroxy ester, hydroperoxide, ketone peroxide, alkyl perester, and carbonate. These are suitably selected according to the molding conditions. Examples of the ultraviolet polymerization initiator include photosensitizers such as acylphosphine oxide, benzoin ether, benzophenone, acetophenone, and thioxanthone. These can be used by appropriately selecting preferred ones according to molding conditions. Examples of the electron beam polymerization initiator include halogenated alkylbenzene and disulfide.

A conventionally known polymerization inhibitor can be used as the polymerization inhibitor. Specific examples include hydroquinone, pt-butylcatechol, t-butylhydroquinone, toluhydroquinone, p-benzoquinone, naphthoquinone, hydroquinone monomethyl ether, phenothiazine, copper naphthenate, copper chloride and the like. These polymerization inhibitors may be used alone or in a combination of two or more.
Examples of the internal release agent include paraffinic compounds such as carnauba wax, higher fatty acids such as stearic acid and montanic acid, higher fatty acid salts such as zinc stearate, or fatty acid ester compounds, alkyl phosphate esters, modified silicone oils, modified Fluorine compounds are exemplified. These can be used by appropriately selecting preferred ones according to molding conditions and various uses.

The compatibilizing agent has an effect of preventing the time-dependent separation due to the addition of the low shrinkage agent such as polystyrene and finely dispersing the low shrinkage agent. Examples of the compatibilizer include vinyl group-containing compounds such as vinyl group-containing polystyrene, vinyl group-containing styrene copolymers, vinyl group-containing acrylic ester copolymers, and the like.
As other fillers, in order to accelerate the curing, a radical polymerization accelerator, that is, a curing accelerator can be used in combination with the radical polymerization initiator. Examples of the curing accelerator include metal salts such as cobalt naphthenate and cobalt octenoate, and tertiary amines such as N, N-dimethylaniline, N, N-di (hydroxyethyl) paratoluidine, and dimethylacetoacetamide. Etc. These can be appropriately selected and used as necessary.

Moreover, it is preferable to add a rubber-based resin as a filler in order to improve toughness, impact resistance and the like. Examples of the rubber resin include acrylonitrile butanediene resin and crosslinkable rubber fine particles.
When using a thermosetting resin, if necessary, a heat stabilizer, a diluent, a reactive diluent, a conductive filler, an antioxidant, a release agent, a lubricant, an antistatic agent, a light stabilizer, Various additives such as ultraviolet absorbers and flame retardants can be added.
The amount of these additives used can be freely selected according to the type of resin and the purpose of use of the molded body.

  When a thermoplastic resin is included as the resin, a thermoplastic elastic body can be added to the thermoplastic resin as an impact resistance improver. Examples of the thermoplastic elastic body include an olefin resin having an organic functional group in the molecule, an acrylic rubber having an organic functional group, a styrene elastic body having an organic functional group, and a nitrile elastic body having an organic functional group. It is done.

In order to obtain the fuel cell separator material from the conductive composition used in the present invention, it can be produced, for example, by the production method described below.
First, when a thermosetting resin is used as a material constituting the conductive composition, an uncured preform composed of the resin and a conductive material is formed, and then the preform is applied to a separator mold. It can be manufactured by putting the mold and heating and compressing it. The heating temperature at this time varies depending on the thermosetting resin to be used, but is usually 100 to 200 ° C., and the pressure is usually 5 to 60 MPa.
Moreover, when using a thermoplastic resin as resin, a separator material can be manufactured by using a well-known method. Known methods include 1) a method including a step of melt-kneading materials, and 2) a method not including a step of melt-kneading.
1) As a method including a step of melt-kneading materials, specifically, a thermoplastic resin and a conductive material are melt-kneaded in advance with an extruder or the like to form pellets, irregular particles, powders, After extruding into a sheet or film, drying the extrudate and then molding it with an injection molding machine, injection compressor, etc., stamping the dried sheet or film with a press molding machine, etc. The method of shape | molding by the method is mentioned.

Moreover, 2) As a method not including the step of melt-kneading, a method of molding a sheet-shaped molding material prepared by another method, a method of molding a graphite powder or a mixture of a graphite powder and a thermoplastic resin powder is molded. Methods and the like.
Examples of the method for producing the sheet-shaped molding material of 2) include: a) a method of attaching a particulate conductive material (hereinafter referred to as conductive material particles) to a resin sheet such as a nonwoven fabric without using an adhesive; b) a nonwoven fabric For example, a method of adhering conductive material particles to a resin sheet such as an adhesive via an adhesive may be used. Among these, the method a) is preferable in that the content of the conductive material particles in the molding material can be increased. Specifically, the method a) is performed by sequentially performing the following steps (a1) and (a2).
Step (a1) is a step of uniformly dispersing the conductive material particles on the surface of the resin sheet.
It is preferable to spread the conductive material particles so as to cover the entire surface of the resin sheet, and to spread the contact area between the conductive material particles and the resin sheet as much as possible.

There are no particular restrictions on the method of spraying the conductive material particles. For example, a) a method of spraying the required amount of conductive material particles evenly on a resin sheet with a spraying device having a large number of nozzles; Examples thereof include a method in which conductive material particles are placed on one end of the resin sheet surface and spread uniformly over the entire surface of the resin sheet with a squeegee plate. The method (b) is preferred in that a more uniform and uneven conductive material particle layer can be obtained. In this case, the amount of the conductive material particles is preferably twice or more the amount that is expected to adhere.
Step (a2) is a step of attaching a part of the conductive material particles to the resin sheet.
As a method of attaching the conductive material particles to the resin sheet, (a2-1) After the conductive material particles are dispersed on the surface of the resin sheet, the conductive material particles are attached to the resin sheet using a pressure roll or a press. -A method of pressing the conductive material particles into the resin sheet, and (a2-2) When the resin sheet is composed of non-woven fabric or other fibers, the conductive material particles are pressed against the resin sheet. (A2-3) When the resin sheet is softened or melted by heating, heat is applied to the resin sheet and / or the conductive material particles to heat the resin sheet and fiber. -A method in which all or part of the sheet is melted and then the conductive material particles are thermally fused to the resin sheet. These methods (a2-1), (a2-2), and (a2-3) may be combined.

Examples of the heat fusion method in the method (a2-3) include a calender roll, a hot air heater, a far infrared heater, and a heating method using water vapor. From the viewpoint of preventing scattering, heating with a calender roll or a far infrared heater is preferred. In the case of a crystalline thermoplastic resin that is crystallized above the glass transition temperature if the thermoplastic resin is amorphous, or above the glass transition temperature if it is crystalline but not crystallized, and at a temperature at which crystallization does not start Is preferably heat-sealed by adjusting the temperature to 10 ° C. or lower than the melting point.
2) Among methods not including the step of melt-kneading, when molding a graphite powder or a graphite granule mixed with a thermoplastic resin powder, the graphite and the resin are easily separated, so that this separation is prevented. It is preferable to uniformly disperse the resin by heat fusing the resin to graphite, fixing the graphite using the resin as an adhesive, or mixing the slurryed resin and graphite.

The separator for a fuel cell used in the present invention is a molding set at a temperature higher than the glass transition temperature when the thermoplastic resin in the conductive composition is an amorphous resin, and higher than the melting point when the resin is a crystalline resin. It can be obtained by putting in a mold, pressurizing, cooling in a pressurized state, and compression molding. The cooling rate at this time can be selected arbitrarily. The pressure is usually 5 to 100 MPa. Further, it can be obtained by stampable molding using a thermoplastic resin sheet or a powder material previously blocked.
The separator material for a fuel cell used in the present invention usually has a groove of a flow path of fuel gas, for example, hydrogen gas formed on one side and a groove of a flow path of cooling water formed on the other side, A pair of grooves having a channel for an oxidant gas, for example air, formed on the other surface and channels for a cooling water formed on the other surface is used as a pair. Alternatively, a pair of separators in which a gas channel groove is formed only on one surface and the other surface is a flat plate may be used.
Thus, the fuel cell separator of the present invention is directly bonded to both sides of the electrolyte membrane / electrode assembly (MEA), or a plurality of single cells bonded through the gas diffusion membrane (GDL) are combined. The fuel cell includes a polymer electrolyte fuel cell and the like.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the following, all parts and percentages are by weight unless otherwise specified.
The measurement method and evaluation criteria regarding electrical resistance, wettability, elution characteristics, and drainage are described for the fuel cell separator and fuel cell of the present invention.

[Sample preparation]
A predetermined amount of a conductive composition containing a thermosetting resin used in the examples described later is taken out, filled in a flat plate mold, and pressure is 140 kgf / cm ² (gauge pressure), an upper mold is 150 ° C., Molding was performed under the conditions of a lower mold of 145 ° C. and a molding time of 5 minutes to produce a flat molded product having a width of 130 mm, a length of 200 mm, and a thickness of 3 mm. This flat molded product was cut into a predetermined size shown below, and electrical resistance, wettability evaluation, and dissolution property evaluation were performed.
In addition, a fuel cell separator having the same dimensions as the experimental fuel cell separator (width 80 mm × length 80 mm) proposed by the Japan Automobile Research Institute (JARI) was formed. A fuel cell single cell stack was assembled using this separator.
<Separator for fuel cell>

[Measurement method of electrical resistance]
Evaluation was made by measuring the electrical resistance in the thickness direction using a test piece that was obtained by cutting the flat molded product into a size of 50 mm long, 50 mm wide and 3 mm thick.
Actually, a test piece was sandwiched between two gold-plated electrodes on a copper plate having the same dimensions as the test piece, and an alternating current of 10 mA was applied with a hydraulic press under a pressure of 1 MPa. The electrical resistance in the thickness direction was measured from the voltage drop ΔV (μV) between the electrodes at this time. The average of three measurements was taken as the result.

(Wettability evaluation)
Using a test piece having the same shape as the test piece for measuring electrical resistance, the contact angle on the surface of the molded product was measured by a droplet method using ion-exchanged water. The machine used is a CA-Z type manufactured by Kyowa Interface Science. The average value of 8 measurements is taken as the result. The measurement atmosphere is 22 ° C. and humidity 60%. In general, the better the wettability, the smaller the contact angle.

[Elution characteristics]
The molded product was cut into a size of 25 mm × 70 mm to prepare a sample piece. Four sample pieces are put in a fluororesin container containing 400 g of ion exchange water, and the container is put in a 95 ° C. drier and boiled for 60 hours. Thereafter, the sample was slowly cooled to room temperature and taken out. Thereafter, ion-exchanged water was replaced with a new solution, and boiling was performed again under the same conditions. The evaluation of the dissolution property was carried out by measuring the electric conductivity of the remaining ion-exchanged water from which the second sample piece (hereinafter referred to as sample piece 1) was taken out using ES-51 (Horiba Seisakusho). It is assumed that In general, the smaller the amount of electrolyte elution, the smaller the electrical conductivity.

[Measurement of sulfur content]
The surface of the sample piece 1 was subjected to elemental analysis at a magnification of 100 times using an energy dispersive X-ray analyzer (JED-2200, manufactured by JEOL Ltd.), and the atomic percentage of sulfur atoms was measured.

(Identification of sulfonic acid group)
The surface of the sample piece 1 was identified using a high performance X-ray photoelectron spectrometer (AXIS-HS, manufactured by Kratos) under the conditions of Mg-kα rays, 15 kV, 10 mA. From the analysis of the S2p narrow scan photoelectron spectrum, a binding energy peak derived from a sulfonic acid group was confirmed at 169 eV.

<Fuel cell>
[Drainage evaluation]
The utilization rate of the fuel cell obtained above was changed every 10% from a current density of 0.2 A / cm ² , a separator temperature of 80 ° C., a humidifying water temperature of 70 ° C., and a utilization rate of 30 to 80%. A power generation test was conducted for 10 minutes, and the value of the utilization rate at which the voltage started to fluctuate greatly (ΔV = maximum value−minimum value ≧ 0.01) was measured. It can be said that the better the drainage of the generated water, the higher the utilization rate that voltage fluctuation occurs, and the stable power generation characteristics are maintained.

Examples 1 and 2
The following raw materials and composition blends were uniformly mixed, sealed in a styrene monomer-impermeable multilayer film, and allowed to stand at room temperature for 24 hours to prepare a conductive composition.
1) Vinyl ester resin (bisphenol A type, number average molecular weight = 633 (GPC measurement value)) 18.8%
2) Tertiary butyl peroxyisopropyl carbonate (curing agent) 0.2%
3) Powdered acrylic resin 3.0%
4) Graphite powder (average particle size is 300 μm) 78%
This conductive composition was molded under the conditions described above to obtain a molded plate for evaluation. This molded plate was imparted with sulfonic acid groups (hereinafter referred to as sulfonation treatment) under the following conditions.
First, the molded plate was dried at 100 ° C./3 hrs, and then the molded plate was housed in an acid-resistant 5 L sealed container in which anhydrous sulfuric acid diluted 10-fold with nitrogen gas circulated at a flow rate of 5000 ml / min. The molded plate accommodated in the container was allowed to stand at a temperature of 60 ° C. for 5 and 10 minutes to sulfonate the molded plate. Subsequently, it was washed with an aqueous sodium bicarbonate solution, further washed with ion-exchanged water, dried to obtain a sulfonated molded plate.
This molded plate was cut into a predetermined size, and the sulfur atom content, electrical resistance, wetting characteristics, and dissolution properties were evaluated. The results are shown in Table-1. Further, a binding energy peak derived from a sulfonic acid group was confirmed at 169 eV from a spectrum obtained using the high performance X-ray photoelectron spectrometer.

Comparative Example 1
In Example 1, each physical property was evaluated in the same manner as in Example, using a molded plate whose surface was blasted so as to have an average roughness Ra = 1.1 μm instead of not sulfonating. The results are shown in Table-1.
Comparative Example 2
As a hydrophilic resin coating resin, the following composition was used. In Example 1, a molded plate having a surface blasted to have an average roughness Ra = 1.1 μm was used instead of the sulfonation treatment. It apply | coated to the molded board so that it might become about 12 micrometers using a hand coater.
1) DECONAL EXB614B (hydrophilic epoxy resin, manufactured by Nagase Chemtech) 90%
2) Aminoethylethanolamine (curing agent) 10%
The applied molded plate was heated at 60 ° C./10 minutes and then at 180 ° C./60 minutes to form a cured film. The thickness of the cured coating was about 10 μm.
Each physical property of the molded article formed with a coating with the hydrophilic resin was evaluated in the same manner as in Example 1. The results are shown in Table-1.
Comparative Example 3
A graphite plate (IG-11 manufactured by Toyo Tanso Co., Ltd.) was cut into the above size and sulfonated in the same manner as in Example 1. Each physical property of this sulfonated graphite plate was evaluated in the same manner as in Example 1. The results are shown in Table-1. Further, a binding energy peak derived from a sulfonic acid group was not confirmed at 169 eV from the spectrum obtained using the high performance X-ray photoelectron spectrometer.

本発明の製造方法により得た成形品は、濡れ性に優れ、かつ水に対する溶出物の発生が抑えられ、導電性に優れていることがわかる。これに対し、ブラスト処理をした比較例１は、水に対する濡れ性が著しく劣る。比較例２の親水性エポキシ樹脂の被膜を形成させた成形品は濡れ性が良くなるが、導電性が低下し、かつ水に対する溶出性が大きい。比較例３のスルホン化黒鉛板はスルホン化処理しても親水性が付与されず、接触角が高い。

It can be seen that the molded product obtained by the production method of the present invention is excellent in wettability, is less likely to be eluted with water, and is excellent in conductivity. On the other hand, the comparative example 1 which performed the blast process is remarkably inferior in the wettability with respect to water. The molded article formed with the hydrophilic epoxy resin film of Comparative Example 2 has good wettability, but has a low conductivity and a high elution property with respect to water. Even if the sulfonated graphite plate of Comparative Example 3 is sulfonated, no hydrophilicity is imparted and the contact angle is high.

Example 3 and Comparative Example 4
On a PPS fiber nonwoven fabric having a size of 150 mm × 150 mm (weight is 15 g / m ² , thickness is 60 μm, average void size is 38 μm, porosity is 85%, melting point is 285 ° C.), artificial graphite particles ( (Amorphous, average particle diameter is 88 μm) 5 g is sprayed, and then a spacer having a height of 0.8 mm is placed on both ends of the non-woven fabric, and the spacer is scanned from one side of the spacer along the other side. The plate was moved and spread so that the artificial graphite particles were placed on the entire surface of the nonwoven fabric.
Next, the calender roll previously heated to 285 ° C. was moved from one side to the other side while being pressed against the graphite side of the nonwoven fabric. Next, after natural cooling, the non-fused graphite is removed by air-blowing (5 kgf / cm ² ), so that the apparent thickness is 0.15 mm, the basis weight is 75 g / m ² , the gap A sheet-shaped molding material having a rate of about 73% was obtained.
This sheet was molded by a stampable molding method. That is, a stack of 70 sheets of the sheet-shaped molding material was heated to 340 ° C. with a far-infrared heater to melt the PPS fiber, and immediately put into a mold heated to 150 ° C. mounted on a press molding machine. The resulting molded plate was shaped by cooling and solidifying by pressurizing at 40 MPa, and the same molded plate as in Example 1 was formed.
This separator was sulfonated in the same manner as in Example 2. About this separator, the binding energy peak derived from a sulfonic acid group was confirmed at 169 eV from the spectrum obtained using the high performance X-ray photoelectron spectrometer.
As Comparative Example 3, a molded plate not subjected to sulfonation treatment was blasted so as to have an average roughness Ra = 1.1 μm, and an evaluation sample was prepared.
Using these separators, the electrical resistance, wettability, and elution properties were tested in the same manner as in Example 1. The results are shown in Table-2.

＊ＰＰＳの硫黄原子含有量はスルホン化処理後の硫黄原子含有量からスルホン化前の硫黄原子含有量を引いた値である。

* The sulfur atom content of PPS is a value obtained by subtracting the sulfur atom content before sulfonation from the sulfur atom content after sulfonation.

Example 4 and Comparative Example 5
The separator obtained in “Preparation of Sample” was subjected to sulfonation treatment under the same conditions as in Example 2. Using this separator, drainage evaluation was performed.
As Comparative Example 5, the power generation characteristics as a fuel cell were evaluated in the same manner as in Example 3 by using a separator that was not sulfonated and the surface was blasted so as to have an average roughness Ra = 1.1 μm.
As a result, the voltage fluctuation started from a utilization factor of 70% in Example 4, whereas it started from a utilization factor of 50% in Comparative Example 5. In Example 4, a binding energy peak derived from a sulfonic acid group was confirmed at 169 eV from the spectrum obtained using the high performance X-ray photoelectron spectrometer.
Since the fuel cell using the separator of the present invention has good drainage of generated water, it exhibits stable power generation characteristics at a higher utilization rate than the comparative example.

Claims (6)

A separator for a fuel cell comprising a resin and a conductive material as constituents, and having a sulfonic acid group added to at least a part of a gas flow path surface by sulfuric acid gas treatment, and is present on the gas flow path surface of the separator The resin and the sulfonic acid group are bonded, and the ratio of the sulfur atom in the sulfonic acid group on the surface of the gas channel is 0.1 to 4.0 atomic number as measured by energy dispersive X-ray spectroscopy. % Is a separator for a fuel cell. The fuel cell separator according to claim 1, wherein the sulfuric acid gas is anhydrous sulfuric acid gas. A method for producing a separator for a fuel cell, wherein the ratio of sulfur atoms on the gas flow path surface is 0.1 to 4.0 atomic% as measured by energy dispersive X-ray spectroscopy, comprising: resin and conductive A method for producing a fuel cell separator, comprising bringing a gas containing sulfuric acid into contact with a gas channel surface of a fuel cell separator material obtained by molding a conductive composition containing a conductive material. The method for producing a fuel cell separator according to claim 3, wherein the sulfuric acid is anhydrous sulfuric acid. The method for producing a fuel cell separator according to claim 3, wherein after the fuel cell separator material is pretreated, a sulfuric acid-containing gas is brought into contact therewith. A fuel electric field comprising the fuel cell separator according to claim 1 or 2.