JP2007115619A - Fuel cell separator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell separator in which the wettability of water in wide range of grooves of a passage of a fuel gas is improved and which can maintain hydrophilic performance, even if it is used for a long period and is superior in conductivity, and to provide its manufacturing method. <P>SOLUTION: This relates to a fuel cell separator, in which a hydrophilic resin sheet containing a hydrophilic resin having a powder-like carbon material and caprolactam group is laminated on at least at a part of substrate surface, having as a constituent component a thermoset resin or the thermoset resin and carbon material; furthermore, this relates to a manufacturing method or the like of a fuel cell, in which a sheet-shape forming material for substrate containing a thermoset resin and carbon material is preliminarily hardened and a hydrophilic resin sheet, containing the hydrophilic resin having a powder-like carbon material and caprolactam group, is laminated and formed on at least a part of its one face. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell separator having a hydrophilic conductive layer with improved surface hydrophilicity and a method for producing the same.

BACKGROUND ART A fuel cell is a type of power generation method that receives a supply of fuel to an electrode and directly converts chemical energy of the fuel into electric energy, and has a high energy conversion efficiency. In such a fuel cell, a fuel gas containing hydrogen is supplied to the anode and an oxidizing gas containing oxygen is supplied to the cathode. When an electrochemical reaction proceeds at each electrode, the anode side or Formed water is produced on the cathode 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 forms 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. 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. In order to prevent the conductivity from decreasing due to shortage of water, water is added to the fuel gas supplied to the cathode side to supplement the electrolyte membrane with water.
For this reason, water produced as described above is not generated by the cell reaction at the cathode of the polymer electrolyte fuel cell, but water vapor in the fuel gas supplied to the cathode may condense.

  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 gas flow path is also blocked on the cathode side and the flow of the fuel gas is obstructed, leading to a decrease in battery performance.

  In this case, since the proton generated in the cathode reaction moves to the anode side in a hydrated state as described above, on the anode side, in addition to the generated water, water molecules brought in along with the movement of the proton are also added. Water becomes excessive, and the gas flow path is more likely to be blocked.

In view of this, conventionally, a predetermined member constituting the fuel cell has been subjected to a hydrophilic treatment, thereby improving the discharge of generated water. By subjecting the members constituting the fuel cell to hydrophilic treatment, the generated water does not stay as water droplets but is guided to a predetermined flow path by the hydrophilic member, thereby preventing the generated water from inhibiting gas diffusion. Can do.
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 needs to be performed not only on the gas diffusion electrode but also on the separator.

The separator is usually formed by a gas-impermeable conductive member such as a dense carbon, and a rib structure that forms a gas flow path with the gas diffusion electrode is formed on the surface thereof. ing.
Conventionally, various methods have been proposed for hydrophilic treatment of the separator. That is, a hydrophilic material such as silicon oxide, aluminum oxide, starch acrylic acid copolymer resin, polyacrylate, and polyvinyl alcohol is added and mixed into the raw materials constituting the separator, and the separator material itself There has been proposed a method of hydrophilizing (see, for example, Patent Document 1).
Further, a method of imparting hydrophilicity to a separator surface made of various materials by performing a treatment such as a low-temperature plasma treatment in a hydrophilizing gas (see, for example, Patent Document 2), and a surface of a separator having a flame around 1000 ° C. A method of imparting hydrophilicity by treating with (for example, see Patent Document 3) has been proposed.

  Furthermore, a conductive coating containing a resin binder is formed on the surface of various separators, and pores are retained in the coating, microcracks are generated, and fine irregularities are formed inside to impart hydrophilicity. A method (for example, see Patent Document 4), a method for imparting hydrophilicity by applying a mixture of a hydrophilic phenolic resin and an epoxy resin to the surface of the separator and curing it (for example, see Patent Document 5), -Apply and impregnate a hydrophilic epoxy resin containing a metal oxide on the surface of the metal, or apply and impregnate only a hydrophilic epoxy resin on the surface of the metal oxide and the separator, and then apply the hydrophilic resin by heating. A method of providing a hydrophilic member or forming a hydrophilic film, such as a method of imparting hydrophilicity by curing (see, for example, Patent Document 6 and Patent Document 7) has been proposed.

However, the method of hydrophilizing the separator material itself has a problem that the strength of the entire molded product is lowered and the original shape cannot be maintained when power generation is performed at a high temperature.
In addition, when plasma treatment or the like is performed on the coating film on the separator surface having a rib structure, the thickness of the hydrophilic layer on the surface is as thin as about submicron, and it is difficult to maintain the surface hydrophilic property for a long time. Along with the decrease, the retention of the generated water causes a decrease in electromotive force.
In the method of forming a hydrophilic film, a hydrophilic substance can be easily applied to the convex portions on the surface of the separator having a rib structure, but cannot be applied to the gas flow path of the concave portions that require hydrophilicity. It may not be possible to confer sex. In addition, a hydrophilic film generally swells due to water absorption and easily changes in volume, and has a very high possibility of peeling from the substrate, or even without peeling, the film gradually elutes during use, and the hydrophilicity of the recesses is lost. There is a fear.
When the hydrophilic film does not contain a conductive material, an insulating film is formed on the separator surface, and there is a problem that a treatment for securing conductivity with the gas diffusion electrode is required. Further occurs.
Furthermore, Patent Document 1 proposes a method of laminating a hydrophilic sheet on a non-hydrophilic sheet that does not contain a hydrophilic substance.
However, in this method, although the hydrophilicity of the gas flow path is increased, the strength in the hot water environment cannot be maintained, and the structure of the fuel cell separator may not be maintained.

Japanese Patent Laid-Open No. 10-3931 WO99 / 40642 pamphlet JP 2002-313356 A JP 2000-58083 A JP 2000-251903 A JP 2003-217608 A JP 2003-297385 A

  As described above, in the separator having a rib structure, water generated in the groove portion stays and cannot be discharged smoothly, so there is no decrease in electromotive force, high electrical conductivity can be secured, and stable hydrophilicity can be ensured. There was a need to provide a separator that could be granted.

  In view of such a demand, the present invention improves the wettability of water over a wide area of the groove portion which is a passage of fuel gas, and can maintain the hydrophilicity even when used for a long period of time. It aims at providing the fuel cell separator excellent also in the property, and its manufacturing method.

As a result of studying the above problems, the present inventors have found that when a hydrophilic resin sheet having a powdery carbon material on the surface and containing a hydrophilic resin is laminated on the molding material for the substrate, the hydrophilicity in the gas flow path is improved. As a result of discovering that the conductivity can be maintained for a long period of time, the present invention has been completed.
In the present invention, a hydrophilic resin sheet containing a powdery carbon material and a hydrophilic resin having a caprolactam group is laminated on at least a part of the surface of a substrate containing a thermosetting resin or a thermoplastic resin and a carbon material as constituent components. The present invention relates to a fuel cell separator.

  Further, the present invention preliminarily cures a sheet-like molding material for a substrate containing a thermosetting resin and a carbon material, and contains a powdery carbon material and a hydrophilic resin having a caprolactam group on at least a part of one side thereof. A method of manufacturing a fuel cell separator characterized by laminating and molding a hydrophilic resin sheet, and a sheet-like molding material containing a thermoplastic resin and a carbon material are preliminarily heated, and then on at least a part of one side thereof The present invention also relates to a method of manufacturing a fuel cell separator, characterized by laminating and molding a hydrophilic resin sheet containing a powdery carbon material and a hydrophilic resin having a caprolactam group. Furthermore, the present invention relates to a fuel cell incorporating the fuel cell separator.

  The fuel cell separator of the present invention exhibits high wettability in the groove by having a hydrophilic conductive layer, and even if oxidant gas flows into the groove, the generated water does not stay in the groove. And can be discharged smoothly. As a result, the supply of fuel gas is not hindered by excessive water and the electromotive force is stabilized, so that the fuel cell stack using the separator of the present invention can stably generate power over a long period of time. .

The substrate in the present invention means a portion that becomes a base of a molded article of a fuel cell separator having a thermosetting resin or a thermoplastic resin and a carbon material as constituent components.
Examples of the carbon material constituting the substrate include artificial graphite, flake shaped natural graphite, massive natural graphite, expanded graphite, carbon black, acetylene black, ketjen black, and amorphous carbon. Among these, artificial graphite, flake shaped natural graphite, massive natural graphite, and expanded graphite are preferable in terms of conductivity and cost. These carbon materials can be used singly or in combination. Moreover, it is preferable that the average particle diameter is 100-400 micrometers, and, as for the particle diameter of a carbon material, it is more preferable that an average particle diameter is 200-300 micrometers. The aspect ratio of the carbon material is preferably 1-5. A carbon material having an aspect ratio of 1 to 5 and 200 to 300 μm is particularly preferable. A fiber made of the above carbon material, for example, a carbon fiber having a fiber length of 1 to 15 mm, a mat, a sheet, paper, or the like can also be used.
These carbon materials are preferably 50 to 95% by weight and more preferably 65 to 90% by weight in the substrate.

  Examples of the thermosetting resin constituting the substrate include polycarbodiimide resin, phenol resin, furfuryl alcohol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, vinyl ester resin, bismaleimide triazine resin, polyamino Examples thereof include bismaleimide resins and diallyl phthalate resins, and among these, vinyl ester resins are preferable in terms of corrosion resistance and durability. This thermosetting resin can be used in the form of powder or viscous liquid, and when it is not in these forms, it can be mixed with a solvent such as water, alcohol or ketone, or a liquid reactive diluent such as styrene. Used in liquid form.

  In addition, examples of the thermoplastic resin include polyphenylene sulfide, polyolefin, polyamide, polyimide, polysulfone, polyphenylene oxide, liquid crystal polymer, and polyester. Polyphenylene sulfide is preferable because of excellent heat resistance and acid resistance. The shape of the resin is powder, film, woven fabric, non-woven fabric, mat or the like, but non-woven fabric is particularly preferred from the viewpoint of easy handling.

  In the present invention, in order to stably keep the sheet-form molding material for a substrate made of a thermosetting resin in a certain shape, fine particles that can adsorb the solvent in the resin to the composition containing the thermosetting resin and the carbon material. It is preferable to add substances. When such a particulate material is added and then molded using a prepreg-shaped sheet, a separator having good handleability of the resin sheet and excellent adhesion between the laminated sheets can be obtained. These fine particles absorb a normal organic solvent to become a gel, and the uncured portion in the resin sheet and the thermosetting resin in the substrate are cured, thereby bringing the substrate and the hydrophilic resin sheet into close contact with each other. Can be improved.

Examples of the fine particle substance capable of adsorbing the solvent include fine particles made of acrylic polymer, polystyrene, thermoplastic polyester, and the like. Of these, acrylic polymers and polystyrene are preferred in terms of solvent adsorption characteristics. The average particle diameter of these fine particles is preferably from several hundred nm to several tens of μm in consideration of handling properties and solvent adsorption ability.

  As other raw materials constituting the substrate, monomers having an ethylenically unsaturated double bond such as styrene, divinylbenzene, (meth) acrylic acid, t-butylstyrene, vinylnaphthalene, diacyl peroxide, peroxyester, etc. Examples thereof include a curing initiator, a curing accelerator such as cobalt naphthenate, a curing retarder such as hydroquinone and p-benzoquinone, a plasticizer, a low shrinkage agent, a thixotropic agent, and a surfactant.

The separator of the present invention is formed by laminating a hydrophilic resin sheet described later on at least a part of the substrate surface.
On the surface of the substrate, there is a so-called gas flow path (groove) portion through which fuel gas, oxidant gas, and cooling water circulate. Since hydrophilicity of this portion is required, only this portion is a hydrophilic resin sheet. However, a hydrophilic resin sheet may be laminated on the entire surface of the substrate. “At least part of the substrate surface” means this. When the hydrophilic resin sheet is laminated only on the gas flow path, the hydrophilic resin sheet may be formed after the hydrophilic resin sheet is laminated on the corresponding part of the gas flow path of the molding material for the substrate described later.

Any hydrophilic resin sheet may be used as long as it includes a powdery carbon material and a hydrophilic resin having a caprolactam group.
Examples of the hydrophilic resin sheet containing a powdery carbon material and a hydrophilic resin having a caprolactam group include a hydrophilic resin sheet in which the powdery carbon material is uniformly dispersed, and a hydrophilic resin sheet having a powdery carbon material on the surface. Etc.
Examples of the hydrophilic resin sheet in which the powdered carbon material is uniformly dispersed include, for example, a non-woven sheet formed from a powdered carbon material and hydrophilic thermoplastic resin fibers, a powdered carbon material and powdered hydrophilic thermosetting And a resin sheet obtained by molding a mixture with a functional resin.
As the hydrophilic resin sheet having a powdery carbon material on the surface, for example, a hydrophilic resin sheet in which a powdery carbon material is fixed to a hydrophilic thermoplastic resin sheet such as a nonwoven fabric by heat fusion, or the surface of a thermosetting resin solution. A powdered carbon material is sprayed and then heated to partially cure the thermosetting resin so that the powdered carbon material is fixed and a hydrophilic resin sheet or the like can be used. These resin sheets can be appropriately used according to the characteristics of the resin used.
The hydrophilic resin sheet in which the powdery carbon material is fixed on the hydrophilic resin is particularly preferably one in which the powdery carbon material is exposed on at least a part of the surface portion. When the carbon material is exposed, the carbon material is easily exposed on the surface of the obtained separator, and as a result, the conductivity required for the separator is increased.

  The content of the powdery carbon material of the hydrophilic resin sheet used in the present invention is preferably the same as that of the powdery carbon material constituting the substrate. That is, it is preferable that it is 50 to 95 weight% in a hydrophilic resin sheet, and it is more preferable that it is 65 to 90 weight%.

As the powdery carbon material, those listed as the carbon material in the substrate can be used.
The particle size of the powdery carbon material is preferably 150 to 400 μm, more preferably 200 to 300 μm, as in the case of the powdered carbon material constituting the substrate.

  The area of the carbon material on the surface of the hydrophilic resin sheet having the powdery carbon material is 20 to 80% of the surface of the separator in which the base molding material and the hydrophilic resin sheet are integrated by compression molding. It is preferable that it is 30 to 70%. When the area of the carbon material is in the range of 20 to 80%, not only the conductivity is good, but also the wettability to water is excellent.

  The thickness of the hydrophilic resin sheet needs to be such that the sheet is not torn off due to deformation when compression molded. In addition, if the thickness is too thick, the content of the substrate contained in the separator is reduced, and there is a concern that required properties such as strength cannot be satisfied. Therefore, the thickness of the hydrophilic resin sheet is preferably 0.05 to 5 mm, More preferably, it is 0.05-3 mm.

  By using such a powdery carbon material, conductivity is imparted to the hydrophilic resin sheet. However, if the conductivity is insufficient due to the thickness of the sheet or the content of the powdery carbon material, effective conductivity is obtained. In order to impart, a sheet made of carbon fiber (hereinafter referred to as carbon fiber sheet) is preferably used as the base fabric. By using the carbon fiber sheet, it is possible to improve the strength and heat resistance of the hydrophilic resin sheet.

Unit weight of such carbon fiber sheet, 1~30g / ^{m 2,} more preferably from 5 to 20 g / ^{m 2.} The form of the carbon fiber sheet is preferably a non-woven fabric with less fiber orientation. If the unit weight is increased, the thickness is increased and the resin impregnation property is deteriorated or the groove transfer property of the separator is deteriorated at the time of compression molding. Therefore, the optimum one is selected according to the groove shape.
As carbon fibers to be used, carbon nanofibers and nanotubes having a diameter of 1 μm or less can be used in addition to general carbon fibers having a fiber diameter of 1 to 10 μm, and they are appropriately selected and used.

The hydrophilic resin constituting the hydrophilic resin sheet preferably has water retention but does not swell with water. Furthermore, in the case of a hydrophilic resin sheet having a powdery carbon material on the surface, it is particularly preferable that the powdery carbon material can be fixed because a layer of the powdery carbon material can be formed on the surface of the sheet.
The hydrophilic resin used in the present invention is a resin having a caprolactam group forming a ring containing an amide bond that exhibits hydrophilic performance. Such a resin is obtained by polymerizing a compound having a hydrophilic functional group such as vinyl caprolactam and another vinyl compound such as vinyl acetate, styrene, or a hydrophobic (meth) acrylic acid ester.

  The vinyl caprolactam is preferably 30 to 90% by weight, more preferably 40 to 85% by weight, in the constituent components of the hydrophilic resin. If vinylcaprolactam is in the above range, a separator having excellent hydrophilicity and improved properties such as strength and durability against hot water can be obtained.

  Since caprolactam groups are unlikely to be detached from the main chain constituting the hydrophilic resin, hydrophilic resins containing this functional group are resistant to use when used in fuel cell separators used in high-temperature and high-humidity atmospheres. Excellent hydrolyzability.

  In addition, when polyvinyl caprolactam, which is a polymer of vinyl caprolactam, is used as a hydrophilic resin, the glass transition temperature is around 155 ° C., which is much higher than the operating temperature of the polymer electrolyte fuel cell. Even if it contains water, there is also an effect that the separator is not likely to be deformed.

Such hydrophilic resins include, for example, a method of reacting vinylcaprolactam with a thermosetting resin having a non-hydrophilic ethylenically unsaturated double bond, and reacting vinylcaprolactam with a compound having an ethylenically unsaturated double bond. A method of mixing a non-hydrophilic thermoplastic resin or a thermosetting resin with a long-chain hydrophilic thermoplastic resin obtained by heating, or thermosetting having vinyl caprolactam and the non-hydrophilic ethylenically unsaturated double bond It can be produced by a method of semi-curing a resin or a compound having an ethylenically unsaturated double bond.
In the hydrophilic resin sheet used in the present invention, a non-hydrophilic resin can be used in combination with the hydrophilic resin depending on the strength and purpose as long as the hydrophilicity of the separator is maintained. As these non-hydrophilic resins, the above-mentioned thermosetting resins and thermoplastic resins can be used.

  When the hydrophilic resin of the hydrophilic resin sheet is a thermosetting resin, fine particles capable of adsorbing the solvent in the resin to the composition containing the thermosetting resin and the carbon material, as in the case of the molding material for a substrate. It is preferable to add a substance. As the fine particle substance that adsorbs the solvent, the above-mentioned substances can be used.

Next, a specific method for producing the hydrophilic resin sheet will be described separately for cases where the resin of the hydrophilic resin sheet is a thermosetting resin and a thermoplastic resin.
Two or less typical production methods in the case where the resin of the hydrophilic resin sheet is a thermosetting resin are exemplified below.
The first is a case where the powdery carbon material is uniformly present in the sheet. The raw material, which is a constituent component of the molding material, is kneaded so as to be uniform with a predetermined blending to create a mixture. Next, after kneading, a sheet-like molding material in a gel state can be obtained by adjusting the shape into a sheet shape using two rolls or the like and then maintaining the shape as it is. Moreover, a desired sheet-like molding material can be obtained by preparing a gel-like lump molding material without using two rolls and adjusting the shape into a sheet shape using two rolls or the like.

The second is a case where a hydrophilic resin sheet in which a large amount of powdery carbon material is distributed on the surface is prepared.
A predetermined amount of a resin solution containing a hydrophilic resin and other thermosetting resin is poured into a container corresponding to the size of the plane of the separator or the shape of the electrode portion. When a carbon fiber sheet is used as the base fabric, the resin solution is poured on the carbon fiber sheet previously laid on the bottom of the container. Next, a predetermined amount of carbon powder is spread on the resin solution so as to be uniformly distributed with respect to the bottom surface of the container. Next, the container containing the resin solution is heated for a certain period of time, and the resin component is partially or pre-crosslinked to form a prepreg.
In the resin solution, a polymerization initiator and a polymerization inhibitor can be appropriately blended when making a prepreg state or when completely curing at the time of press molding. Further, it may contain other plasticizers, low shrinkage agents, thixotropic agents, surfactants and the like.

  When the resin of the hydrophilic resin sheet is a thermoplastic resin, the thermoplastic resin is put in a container kept at a temperature higher than the temperature at which the resin melts so that the thickness of the resin is uniform on the bottom surface of the container. On top of that, carbon powder is spread evenly. When a carbon fiber sheet is used as the base fabric, the resin is put on the carbon fiber sheet laid on the bottom of the container as in the case of the thermosetting resin. By such a method, a hydrophilic resin sheet having a structure in which the carbon powder is uniformly distributed and the carbon powder is exposed can be produced.

  When creating a hydrophilic resin sheet, when a carbon fiber sheet is used as the base fabric, the thermosetting resin and the thermoplastic resin can be diluted with a solvent in order to improve the wettability with respect to the carbon fiber. Examples of the diluent include reactive diluents such as styrene, divinylbenzene, (meth) acrylic acid, t-butylstyrene, and vinylnaphthalene, and non-reactive diluents such as toluene, methanol, ethanol, acetone, and methyl ethyl ketone. It is done.

  Next, a method for producing a fuel cell separator by laminating and molding a hydrophilic resin sheet on at least a part of the surface of the substrate molding material of the present invention will be described.

Examples of such methods include the following methods.
(I) In the case where the resin constituting the base molding material and the hydrophilic resin of the hydrophilic resin sheet are made of a thermosetting resin, the base molding material containing the thermosetting resin and the carbon material is precured. A method of laminating a hydrophilic resin sheet containing a powdered carbon material on a part of at least one surface thereof and then molding the resulting laminate is exemplified. Specifically, a prepreg-like hydrophilic resin sheet containing a powdery carbon material is laminated on a base molding material made of a prepreg-like resin and a carbon material in a mold and molded. This method is preferable in that the lamination position of the base molding material and the hydrophilic resin sheet is stabilized and the adhesion between the two is improved.
(Ii) When the resin constituting the molding material for the substrate is made of a thermoplastic resin, and the hydrophilic resin of the hydrophilic resin sheet is made of a thermosetting resin or a thermoplastic resin, the thermoplastic resin and the carbon material are included. There is a method in which the base molding material is heated in advance, a hydrophilic resin sheet containing a powdered carbon material is laminated on at least a part of one side thereof, and then the resulting laminate is molded. Specifically, a mixture of a resin and a carbon material is molded to produce a sheet-like molding material for a substrate, and the molding material is heated to a temperature not lower than the melting point and not lower than the glass transition point of the resin in the molding material, The molding material is placed in a mold, and a hydrophilic resin sheet containing a powdered carbon material prepared in advance is laminated and molded thereon.

The base molding material can be produced by a known and commonly used method.
That is, first, the raw material, which is a component of the molding material for the substrate, is kneaded so as to be uniform with a predetermined blending to create a mixture.
Next, when the resin in the mixture is a thermosetting resin, a sheet-like molding material in a gel state is obtained by adjusting the shape into a sheet shape using a two-roll or the like after kneading and then maintaining the shape as it is be able to. Moreover, a desired sheet-like molding material can be obtained by preparing a gel-like lump molding material without using two rolls and adjusting the shape into a sheet shape using two rolls or the like. Alternatively, a sheet-shaped molding material can be obtained by preparing a nonwoven fabric in which a carbon material is dispersed from a powdered carbon material and fibers and laminating a plurality of the nonwoven fabrics.
In addition, when the resin in the mixture is a thermoplastic resin, if the shape is adjusted to a sheet shape using two rolls after kneading, then the viscosity increases as the temperature of the molding material decreases, and the shape is stable. Thus, a desired sheet-shaped molding material can be obtained.
Using a two-roll method to adjust the shape into a sheet is preferable because the carbon material is not destroyed and the average particle size does not change, and therefore a fuel cell separator that maintains high conductivity can be obtained. It is.
In addition, it is also possible to use a non-hydrophilic resin sheet prepared by changing the hydrophilic resin of the hydrophilic resin sheet to a non-hydrophilic resin and laminating a plurality of such sheets.
The molding material for the substrate containing the thermosetting resin preferably contains a particulate material capable of adsorbing the solvent in the resin. Examples of the particulate material that can adsorb the solvent include fine particles made of acrylic polymer, polystyrene, thermoplastic polyester, and the like. Of these, acrylic polymers and polystyrene are preferred in terms of solvent adsorption characteristics. The average particle diameter of these fine particles is preferably from several hundred nm to several tens of μm in consideration of handling properties and solvent adsorption ability.

  As a method for laminating a hydrophilic resin sheet on the molding material for the substrate and molding it, a publicly known method can be used. As the molding method, press molding and transfer molding are particularly preferable in order to develop the characteristics of the present invention by molding while maintaining the molding material in a predetermined shape.

  When a thermosetting resin is used as the resin constituting the substrate molding material, the heating temperature varies depending on the type of thermosetting resin used, but the molding conditions are usually 100 to 200 ° C. and added. The pressure is suitably 15 to 60 MPa. In this case, the laminate is placed in a mold, compression molding is performed without heating, so-called cold molding, and then the resin is irradiated with energy rays while maintaining the three-dimensional shape unchanged. The method of hardening is also mentioned. Here, the energy ray refers to light having a wavelength shorter than the visible light wavelength, such as ultraviolet rays, infrared rays, electron beams, and radiation. It is appropriate that the pressure in this cold forming is usually 10 to 50 MPa.

  The fuel cell separator usually has a groove for a flow path of fuel gas such as hydrogen gas formed on one side and a groove for a flow path of cooling water formed on the other side, and an oxidant gas such as air on one side. A flow path is formed, and a pair of a cooling water flow path groove formed on the other surface is used as a pair. In some cases, a gas flow channel groove is formed only on one side and a flat plate is formed on the other side.

The fuel cell of the present invention incorporates the fuel cell separator. That is, the electrolyte is sandwiched between electrodes, and further, it is composed of only a single cell, which is a basic structural unit in which the separator is disposed on the outside, or a plurality of such single cells are laminated.

  Here, the fuel cell uses a power generation method in which hydrogen obtained by reforming the fuel is used as a main fuel, and chemical energy when the hydrogen reacts with oxygen is taken out as power. The fuel cell according to the present invention is formed by collecting a single cell for generating power in a stack structure in which a single cell or a plurality of cells are stacked in series and collecting current with current collecting plates provided at both ends of the stack. Examples of such fuel cells include solid polymer fuel cells and phosphoric acid fuel cells.

  The fuel cell of the present invention can be used, for example, as a power source for electric vehicles, portable power sources, emergency power sources, and various mobile power sources such as artificial satellites, airplanes, and space ships.

[Preparation of thermosetting resin]
(Preparation Example 1)
Epilon 850 [bisphenol A type epoxy resin, epoxy equivalent 190, manufactured by Dainippon Ink & Chemicals, Inc.] 910 g, methacrylic acid 398 g, and hydroquinone 0.4 g were added to a 2 L four-necked flask equipped with nitrogen and air introduction tubes. The temperature was raised to 90 ° C. under a gas flow in which nitrogen and air were mixed on a one-to-one basis. 2-methylimidazole 2.0g was put here, and it heated up at 105 degreeC, and made it react for 10 hours. In this way, a vinyl ester resin was obtained. Hereinafter, this vinyl ester resin is referred to as thermosetting resin R-1.

  Next, this vinyl ester resin R-1 was dissolved in 503 g of styrene, 201 g of divinylbenzene (purity 80%) and 0.2 g of toluhydroquinone to obtain a vinyl ester resin liquid having a solid content of 65% by weight. Hereinafter, this is referred to as thermosetting resin V-1.

[Preparation of thermosetting resin molding material used for substrate]
(Preparation Example 2)
In a kneader with a stirring capacity of 2 L, 1235 g of SGS250 (carbon powder with an average particle size of 250 μm, manufactured by ESC Corporation), 315 g of thermosetting resin V-1, 3.2 g of tertiary butyl peroxyisopropyl carbonate as a curing agent, average particles 43.2 g of polymethyl methacrylate fine particles having a diameter of 1 μm were charged and stirred and mixed at room temperature.

  Next, it was taken out into a stainless steel bat and flattened to a thickness of about 10 mm, and then covered with a PET sheet to prevent volatilization. Further, the bat was inserted into a styrene-impermeable multilayer film bag and sealed. The vat was allowed to stand in a 45 ° C. storage for 24 hours and then taken out and allowed to cool at room temperature to obtain a molding material. Hereinafter, this molding material is referred to as a thermosetting resin molding material C-1.

[Preparation of hydrophilic resin sheet]
(Preparation Example 3)
Weigh 35 g of polyvinyl caprolactam (Luviskol Plus; manufactured by BASF), 4.68 g of thermosetting resin V-1 and 0.1 g of tertiary butyl peroxyisopropyl carbonate and 20 g of methyl ethyl ketone as polymerization initiators until uniform. By mixing, a resin solution H-1 for a hydrophilic resin sheet was prepared. A 0.28 g (unit weight 12 g / m ² ) carbon fiber sheet having the same size as the bottom is laid on a glass container having a bottom surface of 16 cm square, and 22.4 g of the resin solution H-1 is placed on the carbon fiber sheet. It was added little by little so as to get evenly wet. Next, 7.0 g of SGS250 was sprayed uniformly from above and adhered. Then, it heated for 30 minutes in a 70 degreeC thermostat. After the container cooled to room temperature, the sheet was peeled off from the container to obtain a hydrophilic resin sheet. Hereinafter, this hydrophilic resin sheet is referred to as hydrophilic resin sheet S-1.

(Preparation Example 4)
35 g of vinylcaprolactam monomer and other components were treated in the same temperature-controlled manner according to the same formulation as in Preparation Example 3 to obtain a hydrophilic resin sheet. Hereinafter, this resin sheet is referred to as a hydrophilic resin sheet S-2.
In this case, the vinyl caprolactam and the thermosetting resin V-1 were subjected to a polymerization reaction in a thermostatic bath, but the reaction was not allowed to proceed completely and became a semi-cured gel state.

(Preparation Example 5)
A four-necked flask similar to Preparation Example 1 was charged with 910 g of epiclone 850, 398 g of methacrylic acid, and 0.4 g of hydroquinone, and the temperature was raised to 90 ° C. under a gas flow in which nitrogen and air were mixed 1: 1. 2-methylimidazole 2.0g was put here, and it heated up at 105 degreeC, and made it react for 10 hours. In this way, a vinyl ester resin was obtained. Next, this vinyl ester resin was dissolved in 503 g of vinyl caprolactam, 201 g of divinylbenzene (purity 80%), and 0.2 g of toluhydroquinone to obtain a vinyl ester resin liquid having a solid content of 65% by weight. Hereinafter, this resin solution is referred to as vinyl ester resin solution V-2. Next, 1235 g of SGS250, 315 g of thermosetting resin V-2, 3.2 g of tertiary butyl peroxyisopropyl carbonate as a curing agent, and 43.2 g of polymethyl methacrylate fine particles having an average particle diameter of 1 μm were added to a kneader having a stirring capacity of 2 L. The mixture was stirred and mixed at room temperature. Next, it was taken out into a stainless steel bat and flattened to a thickness of about 1 mm, and then covered with a PET sheet to prevent volatilization. Further, the bat was inserted into a bag made of a multilayer film impermeable to divinylbenzene and sealed. The vat was allowed to stand for 24 hours in a 45 ° C. storage and then taken out and allowed to cool at room temperature. A hydrophilic resin sheet was obtained by the method described above. Hereinafter, this sheet is referred to as a hydrophilic resin sheet S-3.

(Preparation Example 6)
A hydrophilic resin sheet was obtained in the same manner as in Preparation Example 4 except that SGS-250 was not used. The weight of this sheet was 4.9 g. Similar operations were repeated to obtain a plurality of sheets. Hereinafter, this sheet is referred to as a hydrophilic resin sheet PS-1.

(Preparation Example 7)
77 g of SGS-250, 10.3 g of vinyl ester resin R-1 prepared in Preparation Example 1, 10.3 g of vinyl caprolactam, 0.5 g of tertiary butyl peroxyisopropyl carbonate as a curing agent, and an average particle diameter of 1 μm 2.3 g of polymethyl methacrylate fine particles were charged and stirred and mixed at room temperature. Next, it was taken out into a stainless steel bat and flattened to a thickness of about 1 mm, and then covered with a PET sheet to prevent volatilization. Further, the bat was inserted into a bag made of caprolactam-impermeable multilayer film and sealed. The vat was allowed to stand for 24 hours in a 45 ° C. storage and then taken out and allowed to cool at room temperature. A hydrophilic resin sheet was obtained by the method described above. Hereinafter, this sheet is referred to as a hydrophilic resin sheet S-4.

[Manufacture of fuel cell separator]
Example 1
The thermosetting resin molding material C-1 obtained in Preparation Example 2 was shaped into a sheet using a roll. The weight and thickness necessary for the sheet-shaped molding material were finely adjusted according to the target molded product standard. That is, the sheet was formed so as to have a unit weight of 2700 g / m ² , the shape was determined according to the molded product, cut, and the weight was adjusted. The shape of the gas flow path of the molded product was approximately 14.5 cm square.
Next, the two hydrophilic resin sheets S-12 obtained in Preparation Example 3 were cut according to the shape of the gas flow path. At this time, the combined weight of the two sheets was 12 g. Next, the thermosetting resin molding material sheet was cut into a 14.5 cm square and finely adjusted so that the weight became 69 g. This sheet was sandwiched between two hydrophilic resin sheets S-12 to obtain a sandwich structure sheet. For the outer peripheral part other than the electrode part, only the thermosetting resin molding material sheet was processed into a necessary shape and the weight was adjusted. The total weight of the outer periphery was 90 g. The material was divided into a total of five sheets, one channel portion and four peripheral portions, and charged into a fuel cell separator-shaped mold. Molded with a compression molding machine under conditions of hydraulic output 160t (gauge pressure), upper mold 140 ° C, lower mold 150 ° C, molding time 5 minutes, 23cm square, thickness 2.8mm, flow path depth 0.8mm A battery separator-like molded product was produced. Then, after cutting unnecessary parts etc., the fuel cell separator was obtained. The average thickness of the sheet fixed to the surface of the flow path portion of the separator was 0.1 mm. The separator was evaluated for appearance, water wettability, conductivity, and hot water resistance. The evaluation results are shown in Table-1.

<< Examples 2, 3, and 4 >>
The hydrophilic resin sheet was used in the same manner as in Example 1 except that the sheet S-2 was used in Example 2, the sheet S-3 was used in Example 3, and the sheet S-4 was used in Example 4. And a fuel cell separator was manufactured.

<< Comparative Example 1 >>
Instead of using two sheets of hydrophilic resin sheet S-1, the same operation as in Example 1 was performed except that a sheet obtained by cutting two sheets of hydrophilic conductive sheet PS-1 obtained in Preparation Example 6 was used. Manufactured. The combined weight of the two sheets was 8 g. Further, compression molding and processing were performed in the same manner except that the weight (14.5 cm square) of the molding material C-1 in the flow path was adjusted to 74 g, and a fuel cell separator having the same shape as that of Example 1 was obtained. The average thickness of the sheet fixed to the surface of the flow path portion of the separator was 0.1 mm. This separator was also evaluated for appearance, water wettability, conductivity, and hot water resistance in the same manner as in Example 1. The evaluation results are shown in Table-1.

<< Comparative Example 2 >>
A separator was manufactured in the same manner as in Example 1 except that two hydrophilic resin sheets S-1 were not used. Further, compression molding and processing were performed in the same manner except that the weight (14.5 cm square) of the molding material C-1 in the flow path was adjusted to 82 g, and a fuel cell separator having the same shape as that of Example 1 was obtained. This separator was also evaluated for appearance, water wettability, conductivity, and hot water resistance in the same manner as in Example 1. The evaluation results are shown in Table-1.

  The measurement method and evaluation criteria used in the present invention are described below.

[Appearance evaluation of molded products]
By visually observing the fuel cell separator obtained in the example as a sample, a sample in which grooves (flow channels) on both the front and back surfaces of the fuel cell separator were formed uniformly was defined as “good”. In addition, those in which defects and whitening were observed in the grooves (flow paths) on both the front and back surfaces of the fuel cell separator were defined as “defective”.

[Evaluation of hydrophilicity of molded products]
Using the molded product obtained in the example as a sample, the contact angle of the convex part of the groove is measured using the CA-Z type (contact angle measuring machine by the droplet method using ion exchange water) manufactured by Kyowa Interface Science. did. As a result of the measurement, an average of 8 times was used as a result. The measurement was performed in an atmosphere of 22 ° C. and a humidity of 60%.

[Evaluation of drainage of molded products]
Drainage was evaluated by a simple method using only the molded products obtained in the examples.

The molded product was placed on a horizontal table, and a drop (0.012 g) of ion-exchanged water was dropped from a height of 5 mm above the groove using a syringe and an injection needle into the recess of the groove. The length developed in the groove after 5 seconds was measured. The average value of 6 measurements was taken as the result. The measurement atmosphere was 22 ° C. and humidity 60%.
At this time, when the inside of the groove is hydrophilic and the wettability with water is excellent, the water quickly develops. The standard at that time is 10 mm or more. When the groove part is inferior in wettability with water, the water maintains the state immediately after dropping. The standard at that time is 5 mm or less. That is, when water droplets are rapidly developed in the groove, stable drainage can be expected without clogging the groove. On the other hand, when water droplets do not spread quickly into the groove, the groove is clogged, and the supply of fuel gas and the like and the discharge of water become unstable, and there is a high possibility that the power generation characteristics will be adversely affected.

[Evaluation of conductivity of molded products]
The conductivity of the molded product obtained in the example was evaluated by measuring the contact resistance of the electrode part (groove, flow path part).
Actually, two gold-plated electrodes with the same dimensions (14.5 cm square) as the electrode part of the molded product and carbon paper (thickness 0.4 mm) of the same dimension are prepared, and the electrode part of the molded product is the same carbon. The sheet was sandwiched between paper and an electrode, and an alternating current of 10 mA was applied with a hydraulic press under a pressure of 1 MPa. The voltage drop ΔV (μV) between the electrodes at this time is measured and used as a conductivity index. The average of three measurements was taken as the result. It can be determined that the lower the voltage drop ΔV, the better the conductivity and the lower the contact resistance. A relative comparison can be made by measuring under the same conditions.

[Evaluation of hot water resistance of molded products]
Only the electrode part (groove, flow path part) of the molded product obtained in the example was cut into a size of 25 mm × 50 mm to prepare a sample piece. The sample piece was sealed in a fluororesin container containing ion-exchanged water, and the container was placed in a 95 ° C. drier and boiled for 200 hours. Thereafter, the sample was slowly cooled to room temperature and taken out. The appearance at that time was visually evaluated. The evaluation criteria at that time are shown below.
Both the grooves on the both sides of the molded product are well maintained and the hydrophilicity is also maintained as "good", part of the grooves on both sides of the molded product is collapsed, and the surface sheet is When it peeled off or swollen, it was defined as “bad”.

[Evaluation of heat distortion resistance of molded products]
The separator obtained in the example was placed on a flat hot plate maintained at 80 ° C., and a flat 1Φ terminal at the tip was pressed against the electrode part (groove, flow path part). A load having a surface pressure of 10 kgf / cm ² was applied to the groove. At that time, the heat deformation resistance was evaluated depending on whether or not the groove portion was deformed. A sample in which almost no deformation was observed was defined as “good”, and a sample in which the groove part was deformed was defined as “defective”.

  As shown in the evaluation results in Table 1, the separators produced according to the examples of the present invention are superior in drainage and electrical conductivity, and also in hot water resistance, compared to the separators produced in accordance with the comparative examples.

  In Example 1, the appearance quality is good, a high-quality molded product is obtained, and the groove (flow path) is excellent in wettability with water, and also has good conductivity and hot water resistance, and excellent drainage. A high-performance fuel cell separator can be provided.

In addition, the separator of Example 1 was incorporated into a single cell of a polymer electrolyte fuel cell, the power was generated at a cell temperature of 80 ° C., and the current-voltage characteristics were measured, and 1 (A / cm ² ) or more. The output (voltage) was stable even in the high current density range.

  On the other hand, Comparative Example 1 has improved wettability with water, but has poor appearance quality and low conductivity. Therefore, it cannot be used as a fuel cell separator, and Comparative Example 2 has good appearance quality and excellent conductivity, but poor wettability with water.

In addition, when the separator of Comparative Example 2 was incorporated into a single cell of a polymer electrolyte fuel cell, the power was generated at a cell temperature of 80 ° C., and the current-voltage characteristics were measured. In the range of high current density of not less than / cm ² ), the output (voltage) became unstable and low.

Claims (11)

A fuel cell formed by laminating a hydrophilic resin sheet containing a powdery carbon material and a hydrophilic resin having a caprolactam group on at least a part of a substrate having a thermosetting resin or a thermoplastic resin and a carbon material as constituent components. Separator. The fuel cell separator according to claim 1, wherein the hydrophilic resin having a caprolactam group contains vinylcaprolactam as a constituent component. The fuel cell separator according to claim 1 or 2, wherein the vinyl caprolactam is 30 to 90% by weight in the constituent components of the hydrophilic resin. The fuel cell separator according to any one of claims 1 to 3, wherein a content of the powdery carbon material is 50 to 95% by weight in the hydrophilic resin sheet. The fuel cell separator according to any one of claims 1 to 4, wherein a content of the carbon material is 50 to 95% by weight in the substrate. The fuel cell separator according to any one of claims 1 to 5, wherein the powdery carbon material has an average particle size of 150 to 400 µm. The fuel cell separator according to any one of claims 1 to 6, wherein the hydrophilic resin sheet uses a sheet made of carbon fiber as a base fabric. The fuel cell separator according to any one of claims 1 to 7, wherein the hydrophilic resin sheet has a thickness of 0.05 to 5.0 mm. Preliminarily curing a base molding material containing a thermosetting resin and a carbon material, and laminating a hydrophilic resin sheet containing a powdered carbon material and a hydrophilic resin having a caprolactam group on at least a part of one surface thereof; Next, a method for producing a fuel cell separator, comprising molding the obtained laminate. A base molding material containing a thermoplastic resin and a carbon material is preheated, and then a hydrophilic resin sheet containing a powdery carbon material and a hydrophilic resin having a caprolactam group is laminated on at least a part of one surface thereof, Next, a method for producing a fuel cell separator, comprising molding the obtained laminate. A fuel cell comprising the fuel cell separator according to claim 1.