JP2006032187A - Fuel cell separator and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell and especially the separator for a solid polymer fuel cell, which is superior in characteristics such as conductivity, fuel gas impermeability, heat resistance, acid resistance, hydrolysis resistance, and mechanical strength by using resin fine powders in which it is unnecessary to carry out frozen-pulverization which causes elevation in cost. <P>SOLUTION: This is the separator for the fuel cell having a carbon layer in which a composition containing conductive carbon powders and polyphenylene ether resin fine powders is molded in both sides of a metallic base material, and the separator for the fuel cell in which the weight average particle diameter of the polyphenylene ether resin fine powders is 30 μm or less and not more than the weight average particle diameter of the conductive carbon powders. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a separator for a fuel cell, particularly a polymer electrolyte fuel cell, and a method for producing the same.

  2. Description of the Related Art A fuel cell, for example, a solid polymer type fuel cell, is formed by connecting single cells each having a solid polymer membrane sandwiched between an air electrode and a fuel electrode via a separator having a gas channel groove on the surface. .

  Such a separator for a fuel cell needs to have high conductivity, fuel gas impermeability, and heat resistance, acid resistance, and hydrolysis resistance against a hydrogen / oxygen oxidation-reduction reaction. Further, when connecting via a separator, since it is usually necessary to fasten with a pressure of several MPa, the separator needs to have high mechanical strength such as bending strength.

  For these reasons, conventional separators can be obtained by carbonizing or graphitizing a resin alone such as a phenol resin, or by molding a kneaded product with carbon powder into a flat plate and then carbonizing or graphitizing it in a non-oxidizing atmosphere. It is manufactured by forming a graphite flat plate and further forming grooves serving as gas passages on the surface by cutting or the like. However, this separator requires a heat treatment of 2000 ° C. or higher, and further has a problem that the manufacturing cost is high because the gas flow path is formed by cutting.

  Therefore, Patent Documents 1 to 4 disclose a method for producing a fuel cell separator that forms a mixture of graphite powder and thermoplastic resin powder as a method for producing a fuel cell separator without undergoing a carbonization step and a cutting step. Has been.

  In the production methods of Patent Documents 1 to 4, the thermoplastic resin powder is uniformly and sufficiently dispersed in the graphite powder, and the particle diameter of the thermoplastic resin powder is adjusted in order to function effectively as a binder for the graphite powder. There is a need to. In Patent Documents 1 to 4, a resin mainly composed of a polyphenylene sulfide resin is used as a thermoplastic resin mainly from the viewpoint of heat resistance, but generally the polyphenylene sulfide resin functions effectively as a binder for graphite powder. In order to pulverize to such a fine powder, the freeze pulverization must be repeated many times, which increases the cost. Further, in recent years, from the viewpoint of energy efficiency, a high temperature of 100 ° C. or higher is required as the operating temperature of the polymer electrolyte fuel cell. Accordingly, an electrolyte membrane having a high glass transition temperature is required, and at the same time, A member having a high glass transition temperature is also required, but the polyphenylene sulfide resin also has a problem that the glass transition temperature is low and the heat resistance is not sufficient.

JP 2001-122777 A JP 2001-126744 A JP 2003-36861 A JP 2003-168444 A

  The present invention has been made in view of the above-described conventional problems, and uses resin fine powder that does not require freezing and pulverization, which causes high costs, and has conductivity, fuel gas impermeability, heat resistance, and acid resistance. It aims at providing the separator for fuel cells which is excellent in various characteristics, such as property, hydrolysis resistance, and mechanical strength, especially the separator for solid polymer fuel cells.

  In order to form a carbon layer that functions effectively as a binder for conductive carbon powder and has excellent adhesion to a metal substrate, the present inventor has determined the weight average particle size of the polyphenylene ether resin fine powder. The polyphenylene ether resin having excellent heat resistance, acid resistance and hydrolysis resistance is required to be 30 μm or less and not more than the weight average particle diameter of the conductive carbon powder. The inventors have found that it is easy to make a fine powder and that the particle size can be easily controlled, and that a fine powder satisfying the above requirements can be easily obtained, and the present invention has been completed.

  That is, the fuel cell separator of the present invention is a fuel cell separator having carbon layers formed by molding a composition containing conductive carbon powder and polyphenylene ether resin fine powder on both sides of a metal substrate. The polyphenylene ether resin fine powder has a weight average particle size of 30 μm or less and a conductive carbon powder of the weight average particle size or less.

  The fuel cell separator of the present invention includes “having a gas channel groove on the surface of the carbon layer” as a preferred embodiment.

  The method for producing a separator for a fuel cell of the present invention comprises a conductive carbon powder and a polyphenylene ether resin fine powder, wherein the polyphenylene ether resin fine powder has a weight average particle size of 30 μm or less, and the conductive carbon. A mold in which a composition having a weight average particle size of powder or less, or a sheet formed by molding the composition, is disposed on both sides of a metal substrate and heated to a temperature equal to or higher than the glass transition temperature of the polyphenylene ether resin. It is characterized by pressurizing it in between.

  The method for producing a fuel cell separator of the present invention is as follows: "The polyphenylene ether resin fine powder is pulverized by applying an impact to the polyphenylene ether resin at room temperature", "The mold is a grooved mold. As a preferred embodiment.

  Since the separator for fuel cells of the present invention uses a polyphenylene ether resin for the carbon layer, it is excellent in heat resistance, acid resistance, and hydrolysis resistance. Moreover, by making the weight average particle size of the polyphenylene ether resin fine powder 30 μm or less and the weight average particle size of the conductive carbon powder or less, the polyphenylene ether resin fine powder effectively functions as a binder for the conductive carbon powder. In addition, since the adhesion between the carbon layer and the metal substrate is excellent, the conductivity, fuel gas impermeability, and mechanical strength are also excellent.

  Further, the method for producing a separator for a fuel cell according to the present invention uses a polyphenylene ether resin that is very easy to be finely powdered and easy to control the particle size, so that the particles effectively function as a binder for the conductive carbon powder. Fine powder with a small diameter can be obtained at low cost, and as a result, fuel cell separators with excellent properties such as conductivity, fuel gas impermeability, heat resistance, acid resistance, hydrolysis resistance, and mechanical strength can be manufactured at low cost. can do.

  The separator for fuel cells of the present invention has carbon layers formed by molding a composition containing conductive carbon powder and polyphenylene ether resin fine powder on both sides of a metal substrate.

  Examples of the conductive carbon powder include graphite particles, conductive carbon black (furnace black, acetylene black, ketjen black, etc.), colloidal graphite and the like, and these can be used alone or in combination of two or more.

  As the graphite particles, spherical graphite particles (for example, graphitized mesocarbon microbeads, spheroidized natural and artificial graphite, flute coke, gilsonite coke, etc.), graphite powder having an aspect ratio of 2.0 or less ( For example, natural and artificial graphite powder having an aspect ratio of about 1 to 2.0).

  Mesocarbon microbeads (hereinafter referred to as MCMB) are spherical bodies (mesophase microspheres) having highly oriented crystals and a graphite-like structure. The average particle size of the spherical MCMB is usually about 5 to 50 μm (for example, 5 to 25 μm), preferably 10 to 40 μm (for example, 10 to 25 μm), and particularly about 10 to 30 μm. MCMB is produced by heating bituminous materials such as coal tar, coal tar pitch, heavy oil at about 300 to 500 ° C. The MCMB graphitized product is obtained by graphitizing MCMB by an ordinary method.

  The average particle size of the graphite powder is, for example, about 2 to 35 μm, preferably about 5 to 30 μm. Artificial graphite powder is obtained by using petroleum coke or the like as a raw material, molding and firing, and further graphitizing at a high temperature of 2000 ° C. or higher.

  The polyphenylene ether used in the present invention may be either a polyphenylene ether homopolymer or a polyphenylene ether copolymer mainly composed of a polyphenylene ether structure, but is preferably a polyphenylene ether homopolymer because it is easily pulverized. In addition, as a method for producing poniphenylene ether, many synthetic methods using a phenolic compound typified by 2,6-dimethylphenol as a monomer are known, but they are produced by any known monomer and polymerization method. Polyphenylene ether can also be used.

  Examples of polyphenylene ether homopolymers include poly (2,6-dimethyl-1,4-phenylene) ether, poly (2-methyl-6-ethyl 1,4 phenylene) ether, poly (2,6-diethyl- 1,4-phenylene) ether, poly (2-methyl-6-n-propyl-1,4-phenylene) ether, poly (2-ethyl-6-n-propyl-1,4-phenylene) ether, poly ( 2,6-di-n-propyl-1,4-phenylene) ether, poly (2-methyl-6-i-propyl-1,4-phenylene) ether, poly (2-ethyl-6-i-propyl)- 1,4-phenylene) ether, poly (2,6-di-i-propyl-1,4-phenylene) ether, poly (2-methyl-6-phenyl-1,4-phenylene) ether, poly ( , 6-diphenyl-1,4-phenylene) ether, poly (2-methyl-6-chloro-1,4-phenylene) ether, poly (2-methyl-6-hydroxyethyl-1,4-phenylene) ether, Poly (2-methyl-6-chloroethyl-1,4-phenylene) ether, poly (2-methyl-6-methoxy-1,4-phenylene) ether, poly (2-methyl-1,4-phenylene) ether, poly Mention may be made of homopolymers such as (-1,4-phenylene) ether and poly (2,6-di (p-fluorophenyl) -1,4-phenylene) ether.

  Examples of the polyphenylene ether copolymer include a copolymer of 2,6-dimethylphenol and o-cresol, a copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol, and the like. .

  In addition, the polyphenylene ether used in the present invention can contain other various phenylene ether units that have been proposed to exist in the polyphenylene ether. For example, the following heterostructures can be cited as examples of polyphenylene ether derived from a monomer mainly composed of 2,6-dimethylphenol.

  First, examples of the polyphenylene ether having a different structure at the terminal include an aminoalkyl-substituted terminal group as shown in Chemical Formula 1 and a polyphenylene ether having a 4-hydroxybiphenyl terminal group as shown in Chemical Formula 2.

（式中、Ｒ₃，Ｒ₄は各々独立に炭素数１〜２０の炭化水素基を示す）

(Wherein R ₃ and R ₄ each independently represents a hydrocarbon group having 1 to 20 carbon atoms)

  Examples of the polyphenylene ether having a heterogeneous structure in the polymer chain include 2- (dialkylaminomethyl) -6-methylphenylene ether unit as shown in Chemical Formula 3 and 2- (N-alkyl-N as shown in Chemical Formula 4). Mention may be made of polyphenylene ethers having -phenyl-aminomethyl) -6-methylphenylene ether units.

（式中、Ｒ₃，Ｒ₄は各々独立に炭素数１〜２０の炭化水素基を示す）

(Wherein R ₃ and R ₄ each independently represents a hydrocarbon group having 1 to 20 carbon atoms)

（式中、Ｒ₅は炭素数１〜２０のアルキル基、アルカノール基を示し、Ｒ₆は水素、炭素数１〜１０の置換あるいは非置換アルキル基を示し、ｍは該フェニル基の置換基の数で１から５の整数である）

(In the formula, R ₅ represents an alkyl group having 1 to 20 carbon atoms and an alkanol group, R ₆ represents hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and m represents a substituent of the phenyl group. Number is an integer from 1 to 5)

  Furthermore, examples of the polyphenylene ether having a special structure include quinone-bonded polyphenylene ether as shown in Chemical formula 5 and bifunctional polyphenylene ether as shown in Chemical formula 6.

（式中、ｐ，ｑは連鎖の数で１以上の整数である）

(In the formula, p and q are the number of chains and an integer of 1 or more)

（式中、ｘ，ｙは連鎖の数で０または１以上の整数であるが同時に０ではない）

(In the formula, x and y are 0 or an integer of 1 or more, but not 0 at the same time)

  The polyphenylene ether used in the present invention may be modified with, for example, maleic acid, maleic anhydride, maleic imide, vinyl methoxysilane, γ-aminopropyl methoxysilane, citric acid, malic acid and the like.

  Polyphenylene ether is used as a fine powder having a weight average particle size of 30 μm or less. The fine pulverization of polyphenylene ether can be done easily and efficiently by conveying the polyphenylene ether, which is essentially in the form of powder, by airflow, blowing it to a hard barrier such as metal, and classifying it as necessary. it can. In particular, since polyphenylene ether has the property of being easily pulverized, it can be made into a fine powder having a weight average particle diameter of 30 μm or less without freeze pulverization like other thermoplastic resins.

  The polyphenylene ether resin fine powder needs to have a weight average particle diameter of 30 μm or less, and preferably 20 μm or less. If the particle size of the fine powder is too large, it becomes difficult to disperse uniformly when this fine powder is mixed with the conductive carbon powder, and the polyphenylene ether has a high melt viscosity. Since it is difficult, it becomes difficult to function effectively as a binder for the conductive carbon powder, and the adhesion between the metal substrate and the carbon layer decreases.

  Furthermore, the weight average particle diameter of the polyphenylene ether resin fine powder needs to be not more than the weight average particle diameter of the conductive carbon powder. If the weight average particle size of the fine powder exceeds the weight average particle size of the conductive carbon powder, it is difficult to uniformly disperse the fine powder with the conductive carbon powder, and the polyphenylene ether has a melt viscosity. Since it is difficult to spread even by subsequent heating and pressing, it becomes difficult to function effectively as a binder for the conductive carbon powder, and the adhesion between the metal substrate and the carbon layer is reduced.

  The ratio of the weight average particle diameter of the polyphenylene ether resin fine powder to the weight average particle diameter of the conductive carbon powder (weight average particle diameter of the polyphenylene ether resin fine powder / weight average particle diameter of the conductive carbon powder) is not particularly limited. 1/20 to 1/1 is preferable, and 1/10 to 7/10 is more preferable.

  The mixing ratio of the polyphenylene ether resin fine powder may be appropriately determined in consideration of required conductivity and strength, but is preferably 10 to 60 parts by weight with respect to 100 parts by weight of the conductive carbon powder. More preferably, it is -40 weight part. If the polyphenylene ether resin fine powder is less than 10 parts by weight, the fuel gas impermeability and mechanical strength may be insufficient, and if it exceeds 60 parts by weight, the conductivity may be insufficient.

  The composition used in the present invention may further contain carbon fibers. The type of carbon fiber is not limited, and petroleum-based or coal-based pitch-based carbon fiber, PAN (polyacrylonitrile) -based carbon fiber, rayon-based carbon fiber, phenol resin-based carbon fiber, or the like can be used. The average fiber diameter of carbon fiber can be selected from the range of 0.5-50 micrometers, for example, Preferably 1-30 micrometers, More preferably, it is 5-20 micrometers. The average fiber length of the carbon fibers can be appropriately selected, and is, for example, about 10 μm to 5 mm, preferably about 20 μm to 3 mm. The amount of carbon fiber used can be selected from a range of about 1 to 10% by weight of the entire composition. If the carbon fiber content exceeds 10% by weight, the gas tightness may be lowered, and the gas permeability may be increased.

  Coupling agents, mold release agents, lubricants, plasticizers, stabilizers, etc. are appropriately blended in the composition composed of thermoplastic resin fine powder, conductive carbon powder and, if necessary, carbon fiber. May be.

  The thickness of the carbon layer formed by molding the above composition is not particularly limited, but is preferably 0.3 mm to 3 mm, more preferably 0.5 mm to 2 mm, from the viewpoint of forming a hydrogen or air flow path.

  Although it does not specifically limit as a metal base material, Ferritic stainless steel, a copper plate, etc. are preferable from an acid-resistant viewpoint. In addition, the thickness of the metal substrate is preferably 0.05 mm to 1 mm, more preferably 0.1 mm to 0.5 mm, from the viewpoints of fuel gas impermeability, mechanical strength, and conductivity.

  The separator for a fuel cell of the present invention can be obtained by arranging the above composition on both sides of a metal substrate, heating and pressurizing, and molding the composition into a predetermined shape. Alternatively, the above composition may be preliminarily heated and pressed to form a sheet, and the sheet may be placed on both sides of a metal substrate, heated and pressed, and formed into a predetermined shape.

  When the sheet is formed in advance or when the separator is formed, the composition or sheet is disposed between the molds heated on the glass transition temperature of polyphenylene ether or higher on both sides of the metal substrate. It can be done by sandwiching. When the composition is heated and pressurized, it is preferable that the composition is pressurized in a powder form and then heated to a temperature equal to or higher than the glass transition temperature because the polyphenylene ether resin can easily flow and can be uniformly pressed. Moreover, the groove | channel for gas channels can be formed in the surface by using a metal mold | die with a groove | channel.

  As a method of heating the mold, a conventionally known method such as high frequency induction heating can be used. Moreover, it is preferable that a press pressure is 10-50 Mpa. If the pressing pressure is too low, the mechanical strength and conductivity may be insufficient. Moreover, even if the press pressure is increased excessively, the mechanical strength and conductivity cannot be greatly improved, but the equipment burden increases.

  Hereinafter, the present invention will be further described by examples and comparative examples.

In addition, the evaluation method in an Example is as follows.
(1) Bending strength Measured according to ASTM D790. The created separator was cut out with a width of about 15 mm and measured at a span interval of 50.8 mm and a crosshead speed of 2 mm / min.

(2) Volume resistance Volume resistance was measured using a low resistivity meter “Lorester EP” (manufactured by Dia Instruments Co., Ltd.).

(3) Hydrogen Permeation Coefficient The hydrogen permeation coefficient was measured under an environment of 40 ° C. by ASTM D1434 gas permeability test (differential pressure method).

<Example 1>
20 wt% of polyphenylene ether resin powder (weight average diameter 10 μm, manufactured by Asahi Kasei Chemicals Corporation) ground at room temperature with a jet mill and conductive carbon powder (weight average diameter 50 μm, manufactured by Oriental Sangyo Co., Ltd. “OS Carbon Powder AT-NO” .5S ") 80 wt% was dry mixed with a jet mill, placed on both sides of a 0.2 mm thick stainless steel SUS304 plate, heated and pressed at 240 ° C and 25 MPa, cooled, 100 mm x 100 mm x thickness 2 A separator having a thickness of 2 mm (carbon layer thickness: 1 mm each) was prepared.

When the bending strength of this separator was measured, the carbon layer was destroyed at 50 MPa, but it was not peeled off from the metal substrate. The volume resistance was 3 mΩ · cm, and the hydrogen permeability coefficient was 1 × 10 ⁻¹⁶ mol · m / m ² · s · Pa or less.

<Example 2>
A separator was prepared in the same manner as in Example 1 except that “OS carbon powder AT-NO.15S” (weight average diameter 10.5 μm) manufactured by Oriental Sangyo Co., Ltd. was used as the conductive carbon powder.

When the bending strength of this separator was measured, the carbon layer was destroyed at 50 MPa, but it was not peeled off from the metal substrate. The volume resistance was 3 mΩ · cm, and the hydrogen permeability coefficient was 1 × 10 ⁻¹⁶ mol · m / m ² · s · Pa or less.

<Comparative Example 1>
A separator having a size of 100 mm × 100 mm × thickness 2 mm was prepared in the same manner as in Example 1 except that the metal substrate was not sandwiched.

When the bending strength of this separator was measured, it was broken at 50 MPa. The volume resistance was 8 mΩ · cm, and the hydrogen permeability coefficient was 2 × 10 ⁻¹³ mol · m / m ² · s · Pa.

<Comparative example 2>
A separator was prepared in the same manner as in Example 1 except that “OS carbon powder AT-NO.40S” (weight average diameter 6 μm) manufactured by Oriental Sangyo Co., Ltd. was used as the conductive carbon powder. The physical properties were not evaluated because the bonding due to was not sufficient and the shape of the carbon layer was not maintained.

<Comparative Example 3>
A separator was prepared in the same manner as in Example 1 except that polyphenylene sulfide resin powder (weight average diameter 20 μm, manufactured by Dainippon Ink & Chemicals, Inc.) was used in place of the polyphenylene ether resin powder.

When the bending strength of the separator was measured, the carbon layer was broken at 30 MPa and peeled off from the metal substrate. The volume resistance was 3 mΩ · cm, and the hydrogen permeability coefficient was 1 × 10 ⁻¹⁶ mol · m / m ² · s · Pa or less.

Claims (5)

  A separator for a fuel cell having a carbon layer formed by molding a composition containing conductive carbon powder and polyphenylene ether resin fine powder on both sides of a metal substrate, the weight average of the polyphenylene ether resin fine powder A fuel cell separator having a particle size of 30 µm or less and a weight average particle size of the conductive carbon powder.   2. The fuel cell separator according to claim 1, further comprising a gas channel groove on a surface of the carbon layer.   A composition comprising conductive carbon powder and polyphenylene ether resin fine powder, wherein the polyphenylene ether resin fine powder has a weight average particle size of 30 μm or less and a weight average particle size of the conductive carbon powder or less, or A sheet formed by molding the composition is disposed on both sides of a metal substrate, and is pressed between molds heated to a temperature equal to or higher than the glass transition temperature of the polyphenylene ether resin. Separator manufacturing method.   4. The method for producing a separator for a fuel cell according to claim 3, wherein the fine powder of the polyphenylene ether resin is produced by pulverizing the polyphenylene ether resin by applying an impact to the polyphenylene ether resin at room temperature.   The method for manufacturing a fuel cell separator according to claim 3 or 4, wherein the mold is a grooved mold.