JP4066095B2 - Manufacturing method of fuel cell separator and fuel cell - Google Patents

Description

The present invention relates to a method for producing a fuel cell separator with improved surface hydrophilicity. In particular, the present invention relates to a method for manufacturing a fuel cell separator in which the hydrophilicity of a groove portion of a gas channel is improved, and a fuel cell having a stable output.

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 high energy conversion efficiency. In such a fuel cell, a fuel gas containing hydrogen is supplied to the cathode and an oxidizing gas containing oxygen is supplied to the anode through the gas flow path formed in the separator. As the electrochemical reaction proceeds, product water is produced on 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 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.

  It is desirable that the fuel cell separator quickly discharges generated water generated during power generation and does not block the gas flow path. At that time, it is desirable that the separator surface, in particular the gas flow path part, be hydrophilic, and if the gas flow path part is highly hydrophobic, the gas flow path is likely to be clogged by humidified water and generated water, and power generation performance is improved. It will lead to a decline.

  Therefore, conventionally, hydrophilic treatment has been applied to a predetermined portion of a member such as a fuel cell separator, thereby improving the discharge of produced water. In particular, by hydrophilic treatment of the gas flow path portion, the generated water does not stay as water droplets, and the generated water can be prevented from inhibiting gas diffusion.

The following method has been proposed as a conventional method for hydrophilic treatment of this separator.
That is, a porous carbon member having a water absorption rate of 30 to 80% is provided at the inlet or outlet of the fuel channel, or polyacrylamide is also provided on the surface of the fuel gas channel and preferably on the surface of the oxidizing gas channel. A method of forming a hydrophilic coating such as the above has been proposed (for example, see Patent Document 1).
In addition, a method of imparting hydrophilicity to the surface of a conductive separator made of various materials by performing a hydrophilic treatment such as a low-temperature plasma treatment in a hydrophilic gas (see, for example, Patent Document 2), and a resin binder are included. There has been proposed a method for imparting hydrophilicity by treating the surface of the separator with a flame of about 1000 ° C. (see, for example, Patent Document 3).
Furthermore, a method for imparting hydrophilicity by applying a mixture of a hydrophilic phenolic resin and an epoxy resin to the surface of a separator containing a resin binder and curing it has been proposed (for example, see Patent Document 4).

  Furthermore, after forming a gel film mainly composed of silicon oxide by a sol-gel method on the surface of a separator using a glassy carbon material, a method of forming a hydrophilic film leaving a hydroxyl group by irradiation with vacuum ultraviolet light (for example, Patent Document 5) has been proposed.

However, a hydrophilic coating film obtained by a method of applying a hydrophilic paint or resin to the separator surface is generally swollen by water absorption and easily changes in volume, and has a very high possibility of peeling from the substrate. Or, it is likely to elute gradually during use and the hydrophilicity is lost, and this method is not practical. In addition, this eluting substance may adversely affect power generation characteristics.
In addition, when plasma treatment or the like is performed on the surface of the separator surface having a rib structure, the hydrophilic layer on the surface is as thin as about submicron, making it difficult to maintain surface hydrophilicity for a long period of time. At the same time, the electromotive force becomes unstable due to the retention of the generated water, and eventually the electromotive force is lowered.
In addition, when a hydrophilic material that does not contain conductive materials such as epoxy resin and silicon oxide is applied to the separator surface, an insulating film is formed on the separator surface, and the conductivity between the gas diffusion electrode and the separator is reduced. However, there is a problem that the process is lowered or a process for ensuring conductivity is required.

Japanese Patent Laid-Open No. 8-138692 WO99 / 40642 pamphlet JP 2002-313356 A JP 2000-251903 A JP 2004-103271 A

As described above, in the separator having a rib structure, the water generated in the gas flow path needs to solve the problem that the electromotive force is lowered due to the fact that the water cannot be discharged smoothly. There has been a demand for providing a separator that can ensure conductivity and can provide stable hydrophilicity.
In view of such demands, the present invention provides a fuel cell separator with improved hydrophilicity, improved wettability of water over a wide area of a groove that is a fuel gas flow path, and excellent conductivity. It aims to provide a method.

  As a result of intensive studies on the above problems, the present inventor applied a radical polymerizable monomer liquid having a hydrophilic group to the groove on the surface of the preform, and irradiated the radiation to cause graft polymerization. As a result of finding out that a fuel cell separator having a polymer layer formed, good wettability and excellent conductivity is obtained, the present invention has been completed.

That is, the present invention is a method for producing a separator for a fuel cell in which hydrophilicity is imparted to at least a part of a preform formed from a thermosetting resin or a thermoplastic resin and a carbon material, and includes at least a step. 1. A method for producing a fuel cell separator, comprising sequentially performing step 1, step 3, step 3 and step 4, or step 1, step 3, step 2 and step 4.
(1) Step 1 for performing a treatment for increasing affinity with the radical polymerizable monomer liquid having a hydrophilic group and / or a functional group that can be converted into a hydrophilic group on the preform, (2) on the treated surface Step 2 for applying a radical polymerizable monomer liquid having a hydrophilic group and / or a functional group that can be converted to a hydrophilic group, (3) Step 3 for irradiating the treated surface with radiation, (4) Step 1 Step 4 for cleaning the separator for a fuel cell obtained through Step 2 and Step 3
Is to provide.
The present invention also provides a fuel cell comprising a solid polymer electrolyte membrane, a gas diffusion electrode, and a fuel cell separator obtained by the above method.

  The fuel cell separator obtained by the present invention is excellent in water discharge performance because the surface is made hydrophilic without impairing material properties such as mechanical strength and conductivity. Further, since hydrophilicity can be imparted only by graft polymerization to a site that requires hydrophilicity, a desirable product can be provided. That is, it has high wettability with water generated inside the groove by applying a radically polymerizable monomer having a hydrophilic group only inside the groove and irradiating with radiation. The water can flow and be discharged without stagnation. As a result, in such a separator, the supply of fuel gas is not hindered by excess water, so the fuel cell stack incorporating this separator has a stable electromotive force and can generate stable power over a long period of time. It becomes.

Hereinafter, the present invention will be described in detail.
The present invention applies a radically polymerizable monomer liquid having a hydrophilic group to at least a part of a preform composed of a thermosetting resin or a thermoplastic resin and a carbon material, and irradiates with radiation. It is a manufacturing method of the separator for fuel cells to which the property was provided.
First, a preform formed from a thermosetting resin or thermoplastic resin and a carbon material is prepared.
The preform here refers to a molding material containing a thermosetting resin and a carbon material cured by heating or the like and molded into a predetermined shape, or a molding material containing a thermoplastic resin and a carbon material. It means a product that has been melted by the method described above, etc., made into a predetermined shape, and then solidified by cooling and molding. When a thermosetting resin is used, the preform has a three-dimensional crosslinked structure.
Examples of such a carbon material include artificial graphite, flake shaped natural graphite, massive natural graphite, expanded graphite, carbon black, acetylene black, ketjen black, and amorphous carbon. One kind of these or a mixture of two or more kinds can be used. Particularly when used as a fuel cell separator, graphite having an average particle diameter of 100 to 400 μm is preferable, and graphite having an aspect ratio of 1 to 5 and an average particle diameter of 200 to 300 μm is more preferable. Further, as the carbon material, fibers made of the above carbon raw materials, for example, carbon fibers having a fiber length of 1 to 15 mm, mats, sheets, papers, and the like can be used.

Further, the thermosetting resin is not particularly limited. For example, polycarbodiimide resin, phenol resin, furfuryl alcohol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, vinyl ester resin, bismaleimide triazine resin, Examples thereof include polyamino bismaleimide resin and diallyl phthalate resin. Of these, vinyl ester resins are preferred. This thermosetting resin is used in the form of a powder or used as a viscous liquid, or mixed with a liquid reactive diluent such as styrene and used in a liquid state.
Examples of the thermoplastic resin include polyphenylene sulfide, polyolefin, polyamide, polyimide, polysulfone, polyphenylene oxide, liquid crystal polymer, and polyester. Of these, polyphenylene sulfide is particularly preferred because of its excellent heat resistance and acid resistance.
These thermosetting resins and thermoplastic resins are appropriately selected according to the intended use and required performance.

  Various compounding agents suitable for the resin can be added to the molding material of the preform. For example, in the case of a vinyl ester resin, a polymerization initiator such as an organic peroxide, a thickening agent that imparts a preferable viscosity during compression molding, a low shrinkage agent that relieves shrinkage stress during the curing reaction, and a mold release agent as necessary It is preferable to use a polymerization regulator or the like. When polyphenylene sulfide is used, it is preferable to use a mold release agent, an antioxidant or the like in order to improve moldability and prevent thermal deterioration.

  The resulting molding material can be molded into a preform using various molding methods such as compression molding and injection molding using a mold having a desired shape.

When a thermosetting resin is used as a material constituting the preform, an uncured molded body composed of the resin and a carbon material is molded, and then the molded body is placed in a separator-shaped molding die and heated and compressed. Then, a preform can be produced by molding. The heating temperature at this time varies depending on the type of thermosetting resin to be used, but is usually 100 to 200 ° C., and the pressure is usually 15 to 60 MPa.
When a thermoplastic resin is used as a material constituting the preform, a sheet made of the resin and a carbon material is formed, the sheet is heated to a temperature not lower than the melting point but not lower than the glass transition point of the resin, and then a separator shape. A preform can be produced by placing a heated sheet in a molding die, heating to a temperature equal to or higher than the melting point, compression molding, and then cooling. In this case, the pressure is usually 10 to 50 MPa.

In the present invention, the preform obtained above is subjected to 1) pretreatment (step 1), 2) a radical polymerizable monomer solution having a hydrophilic group (hereinafter referred to as grafting treatment solution) is applied (step 2), 3) A fuel cell separator is obtained by irradiating with radiation (step 3) and 4) washing (step 4).
Next, step 1, step 2, step 3 and step 4 will be described sequentially.
(Process 1)
This is a step of pre-treating the preform in advance in order to improve the affinity with the graft processing solution. Specific examples of the pretreatment include blast treatment, ultraviolet irradiation treatment, ultraviolet ozone treatment, plasma treatment, corona treatment, acid treatment, alkali treatment, and the like, and a method suitable for the purpose can be appropriately selected. The blast treatment and the ultraviolet irradiation treatment are preferred. Either or both of blast treatment and ultraviolet irradiation treatment may be performed. At this time, it is desirable to sufficiently remove the external mold release agent used at the time of molding.
Blasting is a process in which, for example, glass fine particles are sprayed onto a preform, and the surface is thinned to form minute irregularities.
Ultraviolet irradiation treatment, ultraviolet ozone treatment, plasma treatment, corona treatment, and the like form a hydroxyl group, a carboxyl group, and the like as polar groups on the surface by respective chemical treatments.
In the acid treatment, for example, a preform is immersed in concentrated sulfuric acid and treated under heating to remove surface impurities such as a release agent. In the alkali treatment, for example, a preform is immersed in a sodium hydroxide solution and treated under heating to remove surface impurities such as a release agent.
Since the affinity between the grafting treatment liquid and the substrate is enhanced by performing Step 1, the separator is efficiently grafted by the electron beam irradiation in Step 2 and has excellent hydrophilic performance and long-term durability.
If this step 1 is not performed, grafting is not sufficiently performed in step 2, so that hydrophilic components are removed by washing in step 3, and good hydrophilicity cannot be obtained. Further, the hydrophilicity is lowered during the operation of the fuel cell, which may adversely affect the power generation characteristics.

(Process 2)
In this step, a radically polymerizable monomer liquid having a hydrophilic group and / or a functional group that can be converted into a hydrophilic group is applied to at least a part of the surface of the preform. The “part” of “at least part of the surface of the preform” refers to a gas flow path of the preform.
Such a radical polymerizable monomer having a hydrophilic group and / or a functional group that can be converted into a hydrophilic group has a functional group that reacts with a radical generated by irradiation with radiation, and has a hydrophilic group that forms a polymer. It is a compound having a functional group.

Examples of such a hydrophilic group and / or a functional group that can be converted into a hydrophilic group include a carboxyl group, a lactam ring, a sulfonic acid group, a hydroxyl group, a silyl group, an epoxy group, a phosphoric acid group, an N, N-dialkylamino group, N -Functional groups such as alkylamide groups.
Of these functional groups, a lactam ring, a hydroxyl group, a silyl group, and an epoxy group are desirable from the viewpoint of the stability of the hydrophilic effect.
Representative examples of compounds having these functional groups include monomers having a carboxyl group such as (meth) acrylic acid, fumaric acid, maleic acid, itaconic acid and salts thereof, N-vinylpyrrolidone, and N-vinyl. Monomers having a lactam ring such as caprolactam, monomers having a sulfonic acid group such as sulfobutyl methacrylate, acrylamide propane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, hydroxyl group-containing (meth) acrylic acid ester, glycerin mono Monomers having a hydroxyl group such as methacrylate, hydroxyethyl (meth) acrylate, N-hydroxyethyl (meth) acrylamide, monomers having a silyl group such as vinyltriethoxysilane, triethoxypropyl methacrylate, glycidyl methacrylate, etc. A monomer having an epoxy group such as an epoxy group-containing (meth) acrylate ester, a monomer having a phosphate group such as a phosphate group-containing (meth) acrylate ester such as methacryloyloxyethyl acid phosphate, N, Examples thereof include a monomer having an N, N-dialkylamino group such as N-dimethylaminopropyl (meth) acrylamide, and a monomer having an N-alkylamide group such as N-isopropyl (meth) acrylamide. Examples of other radically polymerizable monomers having a hydrophilic group include vinyl benzoic acid and salts thereof, and other (meth) acrylic acid polyoxyalkylene ester compounds.
Further, it may be a radical polymerizable monomer having a functional group that can be converted into a hydrophilic group such as a carboxylic acid group, a sulfonic acid group, a hydroxyl group, or a silanol group by hydrolysis after contact with water.
At this time, a material having a small adverse effect on the fuel cell characteristics is appropriately selected and used.

Among these radically polymerizable monomers, hydroxyl group-containing (meth) acrylic acid ester, glycidyl group-containing (meth) acrylic acid ester, vinyltriethoxysilane are particularly preferred from the viewpoints of expression of hydrophilic effect and hydrolysis resistance. N-vinylcaprolactam is preferred. Of these, N-vinylcaprolactam is particularly desirable. Poly-N-vinylcaprolactam obtained by polymerizing this N-vinylcaprolactam can achieve both hydrophilicity and hot water resistance, which has been extremely difficult in the past, and hardly decomposes under hot water at 100 ° C. or less. .
These radically polymerizable monomers can be used alone or in admixture of two or more. Other monomers may be mixed and copolymerized. Further, a hydrophobic (meth) acrylic monomer or the like may be used in combination as long as the hydrophilic performance is not impaired. The kind of monomer is appropriately selected and used in consideration of the balance between surface hydrophilicity and water resistance.

  The grafting solution used in the present invention is preferably used after diluting the radical polymerizable monomer in a solvent such as water or a water-soluble organic solvent. Examples of such a solvent include a mixed solvent of water and methanol, and a lower alcohol such as ethanol. By diluting with these solvents, the wettability of the preform to the grafting solution is improved, the efficiency of grafting by radiation is increased, and good hydrophilicity can be imparted to the surface of the preform. Further, by using a diluting solvent, gelation of the homopolymer component coexisting with the unreacted radical polymerizable monomer after the electron beam irradiation in step 3 described later can be reduced, or cleaning in step 4 described later can be easily performed. The effect to make is recognized.

The dilution concentration of the radically polymerizable monomer is 10 to 80% by weight, preferably 20 to 60% by weight, although it varies depending on the monomer used, the composition of the diluent solvent and the surface state of the molded product. .
About a solvent composition, it changes with monomers and a molded article surface state to be used similarly. Preferably, water / water-soluble organic solvent = 0/100 to 80/20 (% by weight), and only the water-soluble organic solvent may be used.
In addition, a polymerization regulator such as copper chloride and hydroquinone can be added to the grafting solution as necessary. If there is no problem in performance, an additive such as a surfactant may be used.

The grafting solution is preferably preliminarily reduced in dissolved oxygen by passing an inert gas such as nitrogen immediately before use. Furthermore, it is preferable that the grafting treatment liquid is applied in an inert gas atmosphere. Thereby, dissolved oxygen can be further reduced and the effect of grafting by radiation irradiation can be further enhanced.
On the surface of the preform, there is a so-called gas channel (groove) part through which fuel gas, oxidant gas and cooling water circulate, and the hydrophilicity of this part is required. However, it may be applied to the entire surface of the preform. This means at least part of the surface of the preform.

The method for applying the graft treatment liquid is not particularly limited, and examples thereof include a method using a brush, a spray, a curtain coater, or the like. You may apply | coat to the whole separator or only an electrode part.
The thickness of the coating layer is usually about 0.01 to 0.5 mm, although it depends on the composition of the graft treatment liquid and the concentration of the radical polymerizable monomer. In particular, in the electrode groove portion, grafting is performed as long as the electron beam can sufficiently reach the bottom portion of the groove even when it is filled with the grafting solution and has a thickness of 0.5 mm or more.

  In addition, after applying the graft treatment liquid, it may be immediately subjected to radiation treatment of the next step, but in order to increase the penetration of the graft treatment liquid into the preformed body surface, after application, after standing at room temperature, It is desirable to perform radiation irradiation treatment. This standing time is about 1 minute to 5 days, although it depends on the preform and the grafting solution used. When the standing time is long, it is desirable to store the container in a sealed container or bag that is purged with nitrogen in order to prevent volatilization and alteration of the grafting solution.

(Process 3)
In the present invention, the surface to which the grafting solution is applied is then irradiated with radiation.
As radiation, alpha rays, beta rays (electron rays), gamma rays, etc. can be used. Among these, the use of an electron beam is desirable from the viewpoint of productivity and device handling.
For example, as graft polymerization with an electron beam, only a preform is irradiated with an electron beam, and then a pre-irradiation method in which the preform is contacted with a monomer, and a simultaneous irradiation method in which an electron beam is irradiated in the presence of the preform and the monomer There is.
The pre-irradiation method is to apply the graft treatment liquid in step 2 after irradiating with electron beam irradiation. In this case, in order to further accelerate the polymerization, it is preferable to perform a heating treatment at 40 to 100 ° C. for about 1 to 4 hours. This pre-irradiation method is a method in which step 2 is performed after step 3 is performed.
In the simultaneous irradiation method, after performing step 2, the electron beam irradiation in step 3 is performed. Since electron beam irradiation is performed in the presence of monomers, grafting efficiency is higher and productivity is higher than in the pre-irradiation method. Therefore, in this invention, the simultaneous irradiation method is more preferable from the point of the hydrophilic effect expression and the point of productivity.

Electron beam irradiation is usually performed using an electron beam irradiation apparatus.
In the electron beam irradiation apparatus, since the acceleration voltage is proportional to the transmission power of the electron beam, it is determined appropriately depending on the electron beam arrival depth that is usually estimated from the density of the preform and the target hydrophilization depth. However, in actual operation, the hydration effect may not be obtained by the acceleration voltage, so that the acceleration voltage can be calculated from the measured values of contact angle, water wettability, etc. so that the targeted hydrophilic effect can be obtained. Is determined.
The acceleration voltage is preferably 100 to 5000 kilovolts (hereinafter referred to as “kV”). More preferably, it is 200-1000 kV. If it exists in this range, the surface of this preforming body which consists of resin and a carbon material can be grafted uniformly.

The irradiation dose of radiation is appropriately determined in consideration of the intended hydrophilic performance and physical property degradation of the substrate caused by irradiation. Usually about 20 to 1000 kilo gray (hereinafter referred to as “kGy”) is appropriate. Preferably it is 100-800 kGy. If the irradiation dose is less than 20 kGy, sufficient graft polymerization may not occur depending on the type of monomer used. On the other hand, if it exceeds 1000 kGy, the physical properties of the substrate deteriorate.
The radiation irradiation may be performed by irradiating a predetermined dose at a time or by dividing into two or more. Whether the irradiation is performed at once or divided into two or more times, the single dose is preferably 20 to 400 kGy. If the irradiation dose at one time is too high, the preform and the graft processing liquid become high temperature and there is a risk of thermal deterioration. The atmosphere at the time of irradiation with radiation may be either air or an inert gas atmosphere such as nitrogen, but it is desirable to perform the treatment in a nitrogen atmosphere.
In the fuel cell separator, when both the gas flow paths on both sides of the front and back are grafted, radiation is usually performed one side at a time, but if the radiation reaches the back side and the desired hydrophilicity is obtained on both sides, Irradiation from only one side is also acceptable.

  Moreover, after irradiating with radiation, heat treatment may be performed in order to further promote the grafting treatment and increase hydrophilicity. As this heating condition, it is desirable that it is 1 to 120 minutes at 40 to 120 ° C. When using a preform that is difficult to graft or a monomer that is slow to polymerize, it is preferable to increase the heating temperature and set the time longer. It does not specifically limit as a heating method, The method suitable for a process and an installation is selected suitably.

Furthermore, a chemical treatment can also be performed on the preform after the grafting treatment. This treatment can further increase the hydrophilicity. Examples of such chemical treatment include acid treatment such as sulfuric acid and alkali treatment such as sodium hydrogen carbonate water.
Moreover, you may repeat the process 2 and the process 3 of the said grafting process in multiple times as needed.

(Process 4)
The fuel cell separator obtained by irradiation with radiation in the above-described Step 2 and Step 3 is washed with water or a solvent. Cleaning is performed by appropriately selecting a method suitable for the separator material and the type of graft polymer.
For example, first, washing is performed with ion-exchanged water or the like in order to remove excess grafting solution and adsorbed polymer. The conditions in this case are, for example, about 30 to 60 ° C. for about 5 to 30 minutes, and if necessary, washing is performed a plurality of times under these conditions. Further, in order to completely remove the adsorbed polymer and the like, it is preferable to perform washing with warm water. The conditions in this case are, for example, about 60 to 100 ° C. for about 30 to 120 minutes, and if necessary, multiple times are performed under these conditions.
Step 4 prevents unreacted radically polymerizable monomer, diluent solvent, adsorbed polymer and the like from eluting during operation of the fuel cell, and does not adversely affect the power generation characteristics of the fuel cell.
The cleaning process in step 4 is an essential step in order to maintain the quality required for the fuel cell separator.
Thereafter, by drying, a fuel cell separator molded product having a hydrophilic surface can be obtained. Examples of the drying method include a method of drying using instruments such as a hot air dryer, a vacuum dryer, and an infrared dryer. When complete drying is not necessary, the film is dried at room temperature. As drying conditions, it is about 30 to 120 minutes, for example at 20-100 degreeC. Although it is usually once, if necessary, drying may be performed a plurality of times. In this case, it is desirable to dry after removing water droplets by air blow or the like.

The fuel cell separator used for this invention is obtained by implementing the said process 1, the process 2, the process 3, and the process 4.
In such a fuel cell separator, a hydrophilic polymer layer graft-polymerized by radiation irradiation is formed on the surface, particularly in the groove. This polymer layer is chemically bonded to the separator, and the hydrophilicity hardly changes under storage at room temperature. In addition, it is confirmed that the performance is maintained for a long period of time in evaluation such as a boiling test, and it is not a coating film by simple adsorption or the like. Furthermore, the hydrophilicity is not changed before and after the actual operation of the fuel cell, and excellent durability is maintained. In addition, the high conductivity essential for the separator is also maintained.

  The fuel cell separator having a hydrophilic surface according to the present invention is used in a fuel cell stack by combining a plurality of single cells joined through a gas diffusion membrane (GDL). Examples of such fuel cells include solid polymer fuel cells and phosphoric acid fuel cells.

  Next, preparation examples, examples and comparative examples will be shown to specifically explain the present invention. Parts and% in these examples represent parts by weight and% by weight.

[Preparation of <thermosetting resin molding material> to be a substrate used in the present invention]
(Preparation Example 1) (Preparation of thermosetting conductive molding material)
To a kneader with a stirring capacity of 2 L, carbon powder (average particle size 250 microns) 1235 g, bisphenol A type vinyl ester resin 315 g, t-butylperoxyisopropyl carbonate 3.2 g, polyethylene powder (low shrinkage agent) 4.8 g, polymethacryl 43.2 g of methyl acid powder (thickener) was charged and stirred and mixed at room temperature.
Then, it took out to the bag made from a gas barrier multilayer film, and sealed it. The bag was allowed to stand for 24 hours in a 45 ° C. storage, then taken out and allowed to cool at room temperature. Let the obtained molding material be the thermosetting resin molding material C-1.

(Preparation Example 2) <Manufacture of separator shaped molded article for fuel cell> of substrate used in the present invention
The thermosetting resin molding material C-1 obtained in Preparation Example 1 was shaped, cut, weight-adjusted according to the molded product, and charged into a fuel cell separator-shaped mold. Molded with a compression molding machine under conditions of a surface pressure of 33 MPa, an upper mold of 140 ° C., a lower mold of 150 ° C. and a molding time of 5 minutes, a 23 cm square, a thickness of 2.8 mm, an electrode part channel groove width of 1 mm, and a depth of 0.8 mm. A separator-like molded product for a fuel cell was manufactured. Thereafter, unnecessary portions were cut and processed. This is designated as a molded product F-1.

(Preparation Example 4) <Production of Graft Treatment Solution> Used in the Present Invention
40 g of N-vinylcaprolactam (trade name V-CAP / RC, manufactured by ISP Japan) and 60 g of ethanol were stirred and mixed at room temperature to obtain a pale yellow solution. The monomer concentration was 40%. This is designated grafting solution G-1.

(Preparation Example 5) <Production of Graft Treatment Solution> Used in the Present Invention
Glycerol monomethacrylate (manufactured by Nippon Oil & Fats, trade name Blemmer GLM) 40 g and ethanol 60 g were stirred and mixed at room temperature to obtain a pale yellow solution. The monomer concentration was 40%. This is designated grafting solution G-2.

Example 1
The molded product F-1 obtained in Preparation Example 2 was pretreated by blasting the electrode part (groove part) with a blasting apparatus. To this molded article, a nitrogen gas blow treatment grafting solution G-1 was uniformly applied to the electrode channel grooves in the atmosphere and dried at room temperature for about 10 minutes. Thereafter, an electron beam was irradiated at room temperature in an acceleration voltage of 300 kV, an irradiation dose of 200 kGy, and a nitrogen atmosphere. In order to remove unreacted components, after washing twice with room temperature ion exchanged water, washing with warm water with 95 degreeC ion exchanged water was further performed for 3 hours. Finally, it was washed with ion-exchanged water at room temperature and then dried at room temperature for 24 hours. In this way, a fuel cell separator H-1 was obtained. The separator was evaluated for water wettability, conductivity, hot water resistance, and fuel cell operating characteristics of the electrode channel. The evaluation results are shown in Table-1.

Example 2
The same operation as in Example 1 was performed except that the graft treatment liquid G-2 was used instead of the graft treatment liquid G-1. In this way, a fuel cell separator H-2 was obtained. With respect to this separator as well as in Example 1, water wettability, conductivity, hot water resistance and fuel cell operating characteristics of the electrode channel grooves were evaluated. The evaluation results are shown in Table-1.

Example 3
Instead of the blast treatment, the same operation as in Example 1 was performed except that the surface treatment was performed for 30 minutes with a UV ozone treatment apparatus. Thus, a fuel cell separator H-3 was obtained. With respect to this separator as well as in Example 1, water wettability, conductivity, hot water resistance and fuel cell operating characteristics of the electrode channel grooves were evaluated. The evaluation results are shown in Table-1.

<< Comparative Example 1 >>
The molded product F-1 obtained in Preparation Example 3 was pretreated by blasting the electrode part (groove part) with a blasting apparatus. Thereafter, grafting was not performed, and the same operation as in Example 1 was performed. Thus, a fuel cell separator S-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.

<< Comparative Example 2 >>
The molded product F-1 obtained in Preparation Example 3 was pretreated by blasting the electrode part (groove part) with a blasting apparatus. Thereafter, the surface modification treatment was performed for 30 minutes using a UV ozone treatment apparatus without performing the graft treatment. Thereafter, washing and drying were performed in the same manner as in Example 1. Thus, a fuel cell separator S-2 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.

<< Comparative Example 3 >>
The same operation as in Example 1 was performed except that blasting was not performed in Example 1. Thus, a fuel cell separator S-3 was obtained. With respect to this separator as well as in Example 1, water wettability, conductivity, hot water resistance and fuel cell operating characteristics of the electrode channel grooves were evaluated. The evaluation results are shown in Table-1.

<< Comparative Example 4 >>
The same operation as in Example 1 was performed except that cleaning with ion-exchanged water in Example 1 was not performed.
After irradiation with the electron beam, it was dried at 80 ° C. for 1 hour to obtain a fuel cell separator S-4. With respect to this separator as well as in Example 1, water wettability, conductivity, hot water resistance and fuel cell operating characteristics of the electrode channel grooves were evaluated. The evaluation results are shown in Table-1.

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

[Evaluation of hydrophilicity of molded products]
Using the molded product obtained in the above example as a sample, the contact angle of the convex portion of the groove of the molded product was measured by a droplet method using ion-exchanged water using a CA-Z type manufactured by Kyowa Interface Science. . As the measurement value, an average value of values obtained by eight measurements was used. The measurement atmosphere was 22 ° C. and humidity 60%.
In addition, as a value of a contact angle, it is desirable on performance that it is 50 degrees or less.

[Evaluation of drainage of molded products]
The molded product obtained in the above example was used as a sample, and drainage was evaluated by a simple method using only this sample.
A sample is placed on a horizontal base, and one drop (0.025 g) of ion-exchanged water is dropped from a height of 5 mm above the groove using a syringe and an injection needle into the electrode channel groove. As the measurement value, the length developed in the groove after 10 seconds was measured, and the average value of the values obtained by six measurements was used. 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 of the drainage at that time is determined to be excellent in wettability if it is 20 mm or more. Moreover, if it is 10 mm or less, it will be judged that a groove part is inferior in wettability with water. In this case, water maintains the state as it is immediately after dropping.
In the case where 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, which increases the possibility of adversely affecting power generation characteristics.

[Evaluation of conductivity of molded products]
The conductivity was evaluated by measuring the contact resistance of the electrode part (groove, flow path part) using the molded product obtained in the above example as a sample.
Specifically, two gold-plated electrodes with the same dimensions (14.5 cm square) as the electrode part of the sample and carbon paper (thickness 0.4 mm) with the same dimensions are prepared, and the electrode part of the molded product is the same carbon. The sheet is sandwiched between paper and an electrode, and a 10 mA alternating current is applied under a pressure of 1 MPa with a hydraulic press. The voltage drop ΔV (μV) between the electrodes at this time is measured and used as a conductivity index. The average value of three measurements was used as the measurement value. 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.
This value is desirably equal to the ΔV value of the molded product of Comparative Example 1 without grafting.

[Evaluation of hot water resistance of molded products]
Using the molded article obtained in the above example as a sample, only the electrode part (groove, flow path part) of the sample was cut into a size of 25 mm × 50 mm to prepare a specimen. This sample was sealed in a fluororesin container containing ion-exchanged water, and the container was placed in a 95 ° C. drier and boiled for 500 hours. Thereafter, the sample was slowly cooled to room temperature and the specimen was taken out. The appearance at that time is visually evaluated. The evaluation criteria at that time are shown below.
Good: The shape is well maintained on the grooves on both sides of the molded product.
Defect: A part of the groove on the surface of the molded product is collapsed.

[Evaluation of drainage of molded products after heat-resistant water test]
About the test piece after the said hot water resistance test, the said drainage evaluation was performed. The specimen was taken out and allowed to stand at room temperature for 24 hours and dried.

[Production and power generation performance test of polymer electrolyte fuel cell]
A solid polymer electrolyte membrane and a gas diffusion electrode were combined with the separators obtained in Examples and Comparative Examples to constitute a single cell solid polymer fuel cell. Electric power was generated at a cell temperature of 80 ° C., a dew point of humidified gas of 80 ° C., a hydrogen gas utilization rate of 40%, an air utilization rate of 70%, and a current density of 0.2 A / cm ² . After 24 hours, the voltage was measured for 1 hour thereafter, and the average voltage and the standard deviation of the voltage value fluctuation were calculated.
It is desirable that the voltage is high and stable. Note that the blockage of the electrode flow path causes fluctuations and decreases in the voltage value.

As is apparent from the results shown in Table 1, the fuel cell separator obtained in Example 1 has good conductivity and high quality, and the groove (flow path) is wettable with water. In addition, the hot water resistance is also good. A high-performance fuel cell separator having excellent drainage can be provided.
Further, even in a power generation test using a single cell of a polymer electrolyte fuel cell, there was little voltage fluctuation and the output (voltage) was stable.
The fuel cell separators obtained in Examples 2 and 3 also have good conductivity and high quality, and the groove (flow path) portion has excellent wettability with water, and also has good hot water resistance. A high-performance fuel cell separator with excellent drainage can be provided. Similarly, in a power generation test using a single cell of a polymer electrolyte fuel cell, the output (voltage) was stable with little voltage fluctuation.
On the other hand, since the fuel cell separator obtained in Comparative Example 1 does not undergo grafting, it has excellent conductivity but poor wettability with water. Therefore, when this separator was incorporated into a single cell of a polymer electrolyte fuel cell and power was generated under the same conditions, the voltage swing was large and the output (voltage) was unstable.
The fuel cell separator obtained in Comparative Example 2 has excellent conductivity and good wettability with water. However, when power was generated under the same conditions, the output (voltage) was unstable. When the drainage of this separator was evaluated after disassembling the fuel cell, the distance at which the water was developed was reduced to 10 mm. It was found that the hydrophilicity does not last.
The fuel cell separator obtained in Comparative Example 3 had slightly poor wettability with water, and the output (voltage) was unstable when power was generated under the same conditions.
The fuel cell separator obtained in Comparative Example 4 has good wettability with water, but when power is generated under the same conditions, the output (voltage) gradually decreases from 0.7 V to 0.58 V, and the output Was also unstable.

Claims (7)

A method for producing a separator for a fuel cell in which hydrophilicity is imparted to at least a part of a preform formed from a thermosetting resin or a thermoplastic resin and a carbon material, and includes at least step 1, step 2, and step 3. A method for manufacturing a separator for a fuel cell, comprising sequentially performing Step 3 and Step 4, or Step 1, Step 3, Step 2, and Step 4.
(1) Step 1 for performing a treatment for increasing affinity with the radical polymerizable monomer liquid having a hydrophilic group and / or a functional group that can be converted into a hydrophilic group on the preform, (2) on the treated surface Step 2 for applying a radical polymerizable monomer liquid having a hydrophilic group and / or a functional group that can be converted to a hydrophilic group, (3) Step 3 for irradiating the treated surface with radiation, (4) Step 1 Step 4 for cleaning the separator for a fuel cell obtained through Step 2 and Step 3 The manufacturing method of the separator for fuel cells of Claim 1 which implements the said process 1, the process 2, the process 3, and the process 4 sequentially. The hydrophilic group or a functional group that can be converted into a hydrophilic group is a carboxyl group, a lactam ring, a sulfonic acid group, a hydroxyl group, a silyl group, an epoxy group, a phosphoric acid group, an N, N-dialkylamino group, or an N-alkylamide. The method for producing a fuel cell separator according to claim 1, which is at least one functional group selected from the group consisting of groups. 2. The fuel cell separator according to claim 1, wherein the hydrophilic group or the functional group that can be converted into the hydrophilic group is at least one functional group selected from the group consisting of a hydroxyl group, a lactam ring, a silyl group, and an epoxy group. Method. The method for producing a fuel cell separator according to claim 1, wherein the treatment for increasing affinity in step 1 is blast treatment and / or ultraviolet irradiation treatment. The method for manufacturing a fuel cell separator according to claim 1, wherein the step 4 includes a step of washing with warm water. A polymer electrolyte fuel cell comprising a polymer electrolyte membrane, a gas diffusion electrode, and a fuel cell separator obtained by the production method according to claim 1.