JP4716649B2 - Conductive molding material, fuel cell separator using the same, and method for producing the same - Google Patents

Description

  The present invention relates to a conductive molding material, a fuel cell separator obtained by using the conductive molding material, and a method for producing the fuel cell separator.

  Fuel cells are highly energy efficient, can reduce environmental pollution, and solid polymer fuel cells that operate at lower temperatures will be widely used in the future as power sources for automobiles, small portable power sources, power sources for stationary power generation, etc. Attention has been paid. As is well known, this polymer electrolyte fuel cell has an electrolyte membrane made of an ion exchange membrane and electrodes on both sides thereof, and is provided with a groove pattern for supplying fuel gas or oxidant gas to each electrode. A stack is formed by laminating a large number of single cells made up of and the like. Furthermore, it has a structure in which current is collected by an outer current collecting plate laminated in multiple layers. The power generation mechanism is such that electric energy is produced by reacting the fuel gas supplied to the anode side electrode with the oxidant gas supplied to the cathode side electrode, and is taken out to the outside by the outer current collecting plate.

  For this reason, the separator has a groove that forms a flow path for supplying fuel gas and oxidant gas, a high gas barrier property that separates the gas mixture, mechanical characteristics to prevent gas leakage due to breakage, and between each fuel cell. Characteristics such as electrical conductivity that can be energized are required. In addition, from the viewpoint of fuel cell installation space, especially for in-vehicle use, it is desired to reduce the size and weight of the fuel cell body, and from this, a separator with a thinner wall thickness is required. .

  Various studies have been conducted to satisfy these characteristics. When a metal having corrosion resistance such as stainless steel or titanium alloy is used as a material for a separator for a fuel cell, the gas barrier property, heat resistance and conductivity are excellent. However, it is said to be one of the materials that are concerned because of the difficulty of ionization and processing by electrolytes and the increased weight. Therefore, in recent years, a fuel cell separator using a carbonaceous material as a main raw material has been studied.

  For example, a technique has been proposed in which expanded graphite having a specific particle diameter is dispersed in a thermoplastic resin or a thermosetting resin to obtain a block-shaped molded body, and then a groove is machined (Patent Document 1). However, this method has a problem that the workability of machining is poor and the cost is high.

  Moreover, after granulating the mixture of graphite powder and a phenol resin, the method of manufacturing a molded object by injection molding is disclosed (patent document 2). This method certainly increases the productivity, but it is necessary to increase the amount of resin as a binder in order to make the raw material fluid, and as a result, there is a problem that the conductivity is lowered. Furthermore, there is a demand for miniaturization of the fuel cell body, such as when used as a fuel cell for automobiles, and it is necessary to reduce the thickness of the separator. However, this method has limitations such as fluidity and resin blending ratio. Therefore, there is a problem that it is difficult to reduce the thickness.

  Furthermore, a method is disclosed in which a carbon powder and a thermoplastic resin are formed into a pellet-like mixture, and then formed into a sheet by extrusion and compression (Patent Document 3). However, this method has a problem that since the graphite material is coated with the binder, the conductive performance tends to be lowered, and when the binder content is reduced, it becomes difficult to form a sheet.

WO97 / 02612 JP 2000-331690 A JP2002-198062

  Accordingly, an object of the present invention is to provide a fuel cell separator having a small thickness and excellent conductivity and strength.

  As a result of intensive studies to achieve the above object, the present inventors have found that a conductive molding material having excellent electrical conductivity and mechanical strength is obtained by blending a carbonaceous substrate and thermoplastic resin fibers at a specific ratio. And it discovered that the separator for fuel cells was obtained, and came to complete this invention.

  That is, the present invention is a conductive molding material containing a carbonaceous substrate (A) and a thermoplastic resin fiber (B) as essential components, and the A / B (mass ratio) is 90/10 to 62 /. The fuel cell separator is characterized in that it is contained in a ratio of 38, and further molded by using the conductive molding material.

  In another aspect of the present invention, the carbonaceous substrate (A) and the thermoplastic resin fiber (B) are suspended in water at a ratio of A / B (mass ratio) of 90/10 to 62/38 and stirred. After mixing, a particle collecting agent is added to obtain a papermaking slurry, the paper is wet-papered to form a sheet, and the sheet is further formed to produce a fuel cell separator. It is a manufacturing method of the separator for fuel cells.

  The conductive molding material of the present invention is excellent in electrical conductivity and mechanical strength, can be suitably used as a fuel cell separator, and can provide a fuel cell separator that is excellent in balance of various performances and highly practical. it can. In addition, by manufacturing a fuel cell separator using a wet papermaking method, a thin separator can be easily manufactured, which contributes to downsizing of the fuel cell main body.

  Examples of the carbonaceous substrate in the present invention include graphite such as natural graphite, artificial graphite, soil graphite, and expanded graphite, carbon black, ketjen black, carbon nanotube, fullerene, mesophase carbon, and the like. It can be used in combination. Here, graphite is preferably used, and in particular, expanded graphite that can maintain mechanical strength even when the molded product is thinned is suitably used. There is no restriction | limiting in particular as expanded graphite, A commercial item can be used, The average particle diameter has a preferable thing of 1-100 micrometers, More preferably, it is 4-50 micrometers.

  The thermoplastic resin fibers in the present invention include polyolefin resins, polyester resins, polycarbonate resins, polystyrene resins, acrylic resins, polyvinyl chloride resins, polyamide resins, polyphenylene ether resins, polyphenylene sulfide resins, polysulfones. Fibers such as vinyl resins, vinyl chloride resins, and polyvinylidene fluoride resins can be used, and these can be used alone or in combination of two or more. Especially, since it is excellent in acid resistance and is comparatively cheap, polyolefin resin fibers, such as a polyethylene resin and a polypropylene resin, are suitable.

  With respect to the thermoplastic resin fibers, those in the form of fine fibers are preferably used from the viewpoint of being uniformly dispersed in the molded product, the average fiber length distribution is 100 μm to 6000 μm, and the fiber diameter is 0.1 to 50 μm. It is preferable. Among them, those having a multi-branched (fibril) shape are preferable, and when a thermoplastic resin fiber having such a shape is used, it becomes easy to supplement the carbonaceous substrate with graphite or the like particularly in a papermaking process. As a particularly preferable thermoplastic resin fiber having such characteristics, for example, SWP manufactured by Mitsui Chemicals, Inc. may be mentioned.

  In the present invention, the blending ratio of these carbonaceous substrate (A) and thermoplastic resin fiber (B) is A / B (mass ratio) of 90/10 to 62/38, preferably 80 / 20-65 / 35. When the carbonaceous substrate is less than this range, it is difficult to obtain sufficient electrical conductivity, and when the number of thermoplastic resin fibers is less than this range, it is difficult to obtain sufficient mechanical strength.

  In the conductive molding material of the present invention, a filler such as carbon fiber, a release agent such as stearic acid, an antioxidant and the like can be used in combination as long as the object and effect of the present invention are not adversely affected. These addition modes can be carried out by mixing in resin fibers, mixing as a slurry with a carbonaceous substrate and resin fibers, and dispersing and mixing in a conductive molding material.

  In the present invention, a fuel cell separator can be obtained by molding using these conductive molding materials. The manufacturing method of the fuel cell separator is not particularly limited, and may be a powder molding method, but it is preferable to use a so-called wet papermaking method from the viewpoint of thinning the separator.

  A method for producing a fuel cell separator by wet papermaking will be described below. First, a carbonaceous base material and a fibrous thermoplastic resin are put into a disaggregation beating machine (for example, a pulper, refiner, Henschel mixer) containing a large amount of water, and then mixed at a high speed to obtain a mixture. Next, after the obtained mixture is transferred into a mixing vessel equipped with a stirring blade, a particle collecting agent is added and mixed at a low speed to obtain a slurry for papermaking having a concentration of 0.01 to 10%. Next, the papermaking slurry is made into a wet sheet having a desired size by using, for example, a continuous or batch type papermaking machine of a long net type or a cylindrical type, and then dehydrated by filtration, decompression, squeezing, etc., and then dried. A sheet type conductive molding material is obtained by drying with a dry dryer, dielectric heating dryer, far-infrared dryer, hot air ventilation dryer).

  Here, the particle collecting agent is not particularly limited, and a particle collecting agent (flocculating agent) generally used in a papermaking process or water treatment unless chlorine ions or ammonium ions that affect the performance of the fuel cell are included. For example, Pyrex RC104, Pyrex RC107 (trade name, manufactured by Meisei Chemical Co., Ltd.), Arafix 502, Arafix 530, Arafix 580 (Brand name, manufactured by Arakawa Chemical Industries), 115CH, 102 ( Cationic particle scavengers such as trade names, manufactured by Mitsui Chemicals, Inc. These may be used alone. For example, Pyrex M (trade name, manufactured by Meisei Chemical Co., Ltd.), Arafloc A-185 (trade name, manufactured by Arakawa Chemical Industry Co., Ltd.), 3100C, 3150B (trade names, Mitsui Chemicals, Inc.) In some cases, it is used in combination with an anionic particle scavenger.

A fuel cell separator is prepared by compression-molding the sheet-like conductive molding material thus obtained. First, a sheet-shaped conductive molding material is filled in a fuel cell separator molding die, and heated and compressed under conditions of a heating temperature of 110 to 300 ° C. and a molding pressure of 30 to 400 kgf / cm ² , and then a temperature of 25 to 25 The target fuel cell separator is obtained by cooling under conditions of 100 ° C. and a molding pressure of about 30 to 400 kgf / cm ² .

  The fuel cell separator obtained in the present invention can be produced in various sizes depending on the purpose, but in particular, a thin one having a thickness of about 0.2 mm to 2 mm can be produced. If the wall thickness is less than 0.2 mm, although it can contribute to the electrical characteristics and the weight reduction of the fuel cell, there is a problem that it is brittle and easily cracked and has poor gas barrier properties. On the other hand, when the wall thickness exceeds 2.0 mm, the volume of the fuel cell separator increases, and there is a problem that the weight and size of the fuel cell itself increase.

  Further, the fuel cell separator obtained in the present invention is excellent in gas barrier properties, high conductivity and mechanical strength, and has an electric resistance of 3 to 50 mΩ · cm and a mechanical strength of 50 to 70 MPa in bending strength. , The bending elastic modulus is 10 to 30 GPa and the bending strain is 0.6 to 1.5%.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples. The performance of the obtained conductive molding material and fuel cell separator was evaluated according to the following method.

(1) Bending strength, bending elastic modulus and bending strain The bending strength and bending elastic modulus were measured according to JIS-K-6911. Further, the bending strain was calculated according to the following equation as the thickness T of the test piece, the distance L between fulcrums (= 16T), and the deflection distance ΔL until the test piece breaks.
Bending strain (%) = 6T × ΔL / L ² × 100

(2) Electric resistance It measured according to JISK7194 using the 4-terminal four-probe method resistivity meter (trade name, Lorester GP, manufactured by Mitsubishi Chemical Corporation).

(3) Dispersibility The specific gravity of a test piece (n = 6) cut into a 30 mm square from a fuel cell separator is measured, and the specific gravity variation is calculated from the maximum value, minimum value, and average value according to the following formula. If it was less than 5%, it was evaluated as ◯ if it was 5% or more.
[Specific gravity variation (%)] = {(maximum value) − (minimum value)} ÷ (average value) × 100

(4) Gas barrier property Applying soapy water to one side of 70mm square of fuel cell separator, flowing 0.02MPa of nitrogen gas from the opposite side, and visually judging the presence or absence of soapy water bubbles, ○ if there are no bubbles, When there was a bubble, it was set as x.

Example 1
In a Henschel mixer, 7 liters of water, expanded graphite powder (trade name Calfite CS-30, manufactured by Marufyo Casting Co., Ltd., average particle size 15 ± 3 μm), polypropylene synthetic fiber (trade name SWP Y600, Mitsui) 20 parts by mass (manufactured by Kagaku Co., Ltd., average fiber length: 1.0 mm, fiber diameter distribution: 5 to 50 μm) were charged and stirred and mixed at high speed to obtain a mixture. Subsequently, after the obtained mixture was transferred into a mixing vessel equipped with a stirring blade, 0.30 parts by mass of a cationic particle collector (trade name Phyrex RC-104, manufactured by Meisei Chemical Co., Ltd.) and 0.2 parts by mass An anionic particle scavenger (trade name Phyrex M, manufactured by Meisei Chemical Industry Co., Ltd.) was added and sufficiently stirred and mixed at a low speed to obtain a papermaking slurry.

Next, the entire amount of the papermaking slurry is injected into a standard square sheet machine (Toyo Seiki's experimental papermaking machine, papermaking mesh 100 mesh, length 250 mm × width 200 mm), filtered and suction-pressed and dehydrated to obtain a wet sheet. After being obtained, it was dried in a hot air circulating dryer at 100 ° C. to complete a sheet-like conductive molding material. This is cut into 10 × 10 cm and filled in a mold heated to 180 ° C., pressed with a compression molding machine at a molding pressure of 200 kgf / cm ² and a molding time of 5 minutes, and then cooled to 100 ° C. under pressure. Then, a separator for a fuel cell having a thickness of 0.5 mm was prepared and performance was evaluated. Similarly, test pieces for physical property tests were prepared and performance was evaluated. The evaluation results are shown in Table 1.

Examples 2-6
As shown in Table 1, except that the blending ratio was changed, a sheet-like conductive molding material was obtained in the same manner as in Example 1, and then a fuel cell separator and a test piece for physical property testing were obtained by compression molding. The performance was evaluated. The results are shown in Table 1. In Example 5, polyethylene synthetic fiber (product name SWP UL410, manufactured by Mitsui Chemicals, Inc., average fiber length 1.0 mm, fiber diameter distribution 2 to 30 μm) is used as the thermoplastic resin fiber in Example 6. Used a polypropylene resin fiber (product name: Pyrene, manufactured by Mitsubishi Rayon Co., Ltd., average fiber length: 6.0 mm, fiber diameter: 30 μm) as a thermoplastic resin fiber.

Example 7
Expanded graphite powder (trade name Calfite CS-30, manufactured by Maruho Castings Manufacturing Co., Ltd., average particle size 15 ± 3 μm) 80 parts by mass, polypropylene synthetic fiber (trade name SWP Y600, manufactured by Mitsui Chemicals, Inc., average fiber length) (0 mm, fiber diameter distribution 5 to 50 μm) 20 parts by mass are mixed with a mixer, 17.0 parts by mass are weighed from the obtained powdered conductive molding material, and heated to 180 ° C. in a 10 × 10 cm mold. Uniform filling. Thereafter, the molding conditions were the same as in Example 1, and a fuel cell separator and a test piece for physical property testing were obtained by compression molding, and the performance was evaluated. The results are shown in Table 1.

Comparative Examples 1 and 2
As shown in Table 1, except that the blending ratio was changed, a sheet-like conductive molding material was obtained in the same manner as in Example 1, and then a fuel cell separator and a test piece for physical property testing were prepared by compression molding. . The results are shown in Table 1.

  As shown in Table 1, the conductive molding materials and fuel cell separators of Examples 1 to 6 are excellent in moldability, dispersibility, and gas barrier properties, and are any of bending strength, bending elastic modulus, bending strain, and electrical resistance. These characteristics are also satisfied. On the other hand, the thing of the comparative example 1 is inferior in bending strength since there is much quantity of a carbonaceous base material (A), and the thing of the comparative example 2 is conductive because there is much quantity of thermoplastic resin fiber (B). The result was inferior to.

  Here, in Example 5, the thermoplastic resin fiber (B) is made of polyethylene fiber, and has characteristics substantially equivalent to those of Example 1.

  The sheet-like conductive molding material of the present invention is excellent in conductivity and mechanical strength and has a possibility of being applicable to electrodes and the like, and can be suitably used particularly as a separator for a fuel cell. A fuel cell separator having a good balance of performance and high practicality can be obtained. In addition, by producing a separator for a fuel cell using a wet papermaking method, not only is production efficiency high and cost is superior, but also a thin separator can be easily produced. This can contribute to the miniaturization of the fuel cell main body.

Claims (6)

A conductive molding material containing, as essential components, a carbonaceous substrate (A) and a thermoplastic resin fiber (B) having an average fiber diameter of 0.1 to 50 μm and an average fiber length of 100 to 6000 μm , A conductive molding material characterized by containing A / B (mass ratio) in a ratio of 90/10 to 62/38.   The conductive molding material according to claim 1, wherein the carbonaceous substrate (A) is graphite.   The conductive molding material according to claim 1 or 2, wherein the thermoplastic resin fiber (B) is a polyolefin resin fiber. The conductive molding material according to claim 1, wherein the thermoplastic resin fiber (B) has a multi-branched shape.   A fuel cell separator formed by using the conductive molding material according to claim 1. A / B (mass ratio) is 90/10 to 62 of carbonaceous substrate (A) and thermoplastic resin fiber (B) having an average fiber diameter of 0.1 to 50 μm and an average fiber length of 100 to 6000 μm. After suspension with water at a ratio of / 38 and stirring and mixing, a particle collecting agent is added to obtain a papermaking slurry, the slurry is wet-papered to form a sheet, and the sheet is further molded to form a fuel cell The manufacturing method of the separator for fuel cells characterized by including the process of manufacturing a separator.