JP2003203643A - Molding material for fuel cell separator and its manufacturing method and fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding material for a fuel cell separator that is superior in molding and conductivity and a method of manufacturing this without using a complicated process, and a fuel cell separator made by molding the above forming material. <P>SOLUTION: This is a molding material for a fuel cell separator which contains as an essential content a thermosetting resin and a carbon-group base material having conductivity and in which carbon-group base material having conductivity in the material at the stage of molding material has an average particle size of 50 μm or more and 100 μm or less, and 85% or more of all particles has a particle size of 10 μm or more and 200 μm or less. It is desirable that the carbon-group base material having conductivity has a particle size of 50 μm or more and 200 μm or less for 30-50% of all particles, and a particle size of 10 μm or more and less than 50 μm for 35-55% of the all particles. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a molding material for a fuel cell separator, a method for producing the same, and a fuel cell separator.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is a kind of power generation device that takes out electricity generated by an electrochemical reaction between a fuel gas and an oxidizing gas. The separator is a separation plate that forms a flow path for fuel gas and oxidizing gas between the electrodes and separates the two gases. It also plays the role of a current collector that collects the electricity generated. Therefore, the separator is required to have high conductivity and gas impermeability.

As a method for producing a polymer electrolyte fuel cell separator, there is known a method in which carbon powder is used as a raw material, a phenol resin is added as a binder to the carbon powder, and the mixture is kneaded, molded, and then carbonized and graphitized (see, for example, Japanese Patent Application Laid-Open No. Hei 10 (1999) -135242). 8
-222241 publication etc.). However, in this case 100
There is a problem in that the time and cost required for production are increased because it includes the step of firing at a high temperature of 0 to 3000 ° C. for a long time and the step of cutting the gas channel in the fired carbon plate. It was Alternatively, a method of using a metal resin composite as a material, such as pressing a groove on a metal plate or the like and then performing resin coating (for example, JP-A-11-
No. 345618 gazette, New Energy Industrial Technology Development Organization, 2000, Polymer Electrolyte Fuel Cell R & D Results Report Summary, P70)
In the environment in which it is used, there is no solution to the problems of layer peeling and metal plate corrosion at the interface layer between metal and resin, and there is no prospect of supplying an appropriate separator in terms of quality and price.

For this reason, various attempts have been made further, and a mold in which a conductive carbon-based material such as graphite or carbon black is bound with a resin to form a molding material, and this is heat-molded to give a groove shape. Molding is considered to be a promising method for achieving both cost and characteristics. In this method, in order to obtain high conductivity as a separator, it is necessary to increase the blending amount of the carbon-based base material in the molding material. But,
When such a large amount of carbon-based material is blended, problems such as insufficient filling due to insufficient fluidity of the material and permeation of fuel gas and oxidizing gas occur. Therefore, a technique for achieving both moldability and conductivity is required, and the optimization of the particle shape of the carbon-based substrate is an important point for this. For this reason, it has been attempted to reduce the aspect ratio of graphite particles used as a carbon-based base material to obtain a molded product having excellent moldability and high conductivity (for example, JP-B-64). -34
No. 0). However, this method has a drawback that the crushing and grinding of the graphite particles and the classification step are required and the production cost becomes high. Moreover, in order to maintain the particle size of the graphite particles optimized by particle size adjustment and leave them in the molded body, the resin and graphite are mixed, and a large amount of the solvent is used to form a slurry and granulate. According to the method (Japanese Patent Laid-Open No. 11-204120), the material has to be made into a material, and there is a problem that the process becomes long.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a molding material for a fuel cell separator having excellent moldability and conductivity, a method for producing the same without complicated steps, and molding the molding material. The present invention provides a separator for a fuel cell.

[0006]

Such objects are achieved by the present inventions (1) to (6) described below. (1) The carbonaceous base material containing a thermosetting resin and a carbonaceous base material having conductivity as essential components, and having conductivity in the molding material at the stage of being formed into a molding material has an average particle size. Is 5
A molding material for a fuel cell separator, which is in the range of 0 μm or more and 100 μm or less, and 85% or more of all particles are in the range of 10 μm or more and 200 μm or less. (2) The conductive carbon-based base material in the molding material at the stage of forming the molding material has 30 to 50% of all particles within a particle size range of 50 μm or more and 200 μm or less, and
The molding material for a fuel cell separator according to (1) above, wherein 35 to 55% of all the particles have a particle size of 10 μm or more and less than 50 μm. (3) The molding material for a fuel cell separator according to the above (1) or (2), wherein the content of the conductive carbon-based substrate is 300 to 900 parts by weight with respect to 100 parts by weight of the thermosetting resin. . (4) A fuel cell separator obtained by molding the molding material for a fuel cell separator according to any one of (1) to (3) above. (5) A method for producing the molding material for a fuel cell separator according to any one of (1) to (3) above,
A method for producing a molding material for a fuel cell separator, which comprises kneading a raw material mixture containing a thermosetting resin and a conductive carbon-based substrate as essential components using a melt-kneading device. (6) A fuel cell separator obtained by molding the molding material obtained by the method for producing a molding material for a fuel cell separator according to (5) above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The molding material for a fuel cell separator of the present invention (hereinafter, simply referred to as “molding material”) contains a thermosetting resin and a conductive carbon-based substrate as essential components, The conductive carbon-based base material in the molding material has an average particle size of 50 to 100 μm, and
It is characterized in that 85% or more of all particles are in the range of 10 μm or more and 200 μm or less in particle diameter. Further, the method for producing a molding material of the present invention, a raw material mixture containing a thermosetting resin and a carbon-based substrate having conductivity as an essential component,
It is characterized in that kneading is performed using a melt kneading device. And the fuel cell separator of the present invention, the molding material,
Alternatively, it is characterized in that the molding material obtained by the above-mentioned manufacturing method is molded. First, the molding material of the present invention will be described.

The thermosetting resin used in the molding material of the present invention is not particularly limited, but examples thereof include phenol resin, epoxy resin, polyester resin, diallyl phthalate resin, and silicone resin. Among these, when a phenol resin or an epoxy resin is used,
Excellent in heat resistance, mechanical strength, electrical stability and price. In addition, since the base resin can be selected from those having a low molecular weight, even in the molding material of the present invention in which the conductive carbon-based material has a high compounding ratio, the material viscosity at the time of manufacturing the molding material can be adjusted. It is preferable because it is easy and fluidity is easily imparted during molding.

The molding material of the present invention contains a conductive carbon-based substrate (hereinafter, simply referred to as "carbon-based substrate") in order to impart conductivity to the molded product. The carbon-based substrate is not particularly limited, and examples thereof include carbon materials such as graphite, carbon fiber, and carbon black. Among these carbon materials, those having excellent conductivity are preferably used, specifically, those having a grown graphite structure, and natural or artificial graphite corresponds to this. There are scaly graphite called natural graphite and soil graphite as the graphite that is calculated naturally, and among them, natural graphite is excellent in conductivity. In addition, regarding artificial graphite, there are heat treated coal-based coke and heat-treated petroleum-based coke,
The shape includes scales, needles, lumps, spheres, aggregates, etc., and all of them have a c-axis (002) inter-layer surface distance (d ₀₀₂ ) of 0.3 obtained by a lattice constant precision method by X-ray analysis.
It has a true specific gravity of 2.0 in the range of 35 to 0.460 nm.
It is preferably in the range of 4 to 2.34. It should be noted that natural graphite and artificial graphite, which are spherically shaped by post-processing, are also preferable because they can impart fluidity during molding. Graphite is mainly preferably used for the carbon-based substrate, but carbon black or carbon fiber may be used in combination if necessary. Carbon black is dispersed in the resin phase to act as a conductive auxiliary agent, and carbon fiber has an effect of improving mechanical properties such as bending and toughness as an effect of its shape.

The carbon-based base material of the present invention has an average particle size in the range of 50 μm or more and 100 μm or less at the stage of forming a molding material, and 85% or more of all particles have a particle size of 10 μm.
As described above, it is characterized by being in the range of 200 μm or less. This makes it possible to improve the moldability when molding the molding material into the fuel cell separator and the conductivity of the molded product. If the average particle size exceeds the upper limit or the number of particles exceeds 200 μm, there will be a large carbon-based base material that is easily broken between the cured thermosetting resins, so that a molded product is obtained. Mechanical strength is reduced. Further, since the large space between the carbonaceous base materials cannot be completely filled with the thermosetting resin, the gas impermeability of the molded product also decreases. Further, a carbonaceous base material having a large particle size appears on the surface, and the surface smoothness of the molded product is impaired, so that the adhesion with the gasket decreases. On the other hand, the fuel cell separator is required to have a high plate thickness accuracy, but if the average particle size is less than the lower limit value or the number of particles having a particle size of less than 10 μ is large, the fluidity at the time of molding becomes small, so Properties deteriorate, and sufficient thickness accuracy cannot be obtained. Further, since the carbon-based base materials are in large contact with each other via the thermosetting resin in the molded product, the conductivity is lowered.

The carbonaceous substrate of the present invention is not particularly limited, but 30 to 50% of all particles are formed at the stage of forming a molding material.
Has a particle size of 50 μm or more and 200 μm or less,
In addition, 35 to 55% of all particles have a particle size of 10 μm or more, 50
It is preferably in the range of less than μm. In a molded product obtained by molding a molding material containing a carbon-based substrate having such a particle size distribution, the carbon-based substrate has a particle size of 50 μm or more and 200
Basically, a structure in which particles with a size of less than μm are arranged in a relatively regular manner is used.
Those having a size of m or more and less than 50 μm are arranged so as to fill the gap. With such a structure, a large gap is unlikely to remain between the carbon-based base materials, so that when the thermosetting resin is filled, even if the amount of the thermosetting resin to the carbon-based base material is small, no unfilled material is left. It is less likely to occur, which results in moldability,
The gas impermeability can be improved.

In the molding material of the present invention, the mixing ratio of the thermosetting resin and the carbon-based base material is not particularly limited, but the carbon-based base material 30 relative to 100 parts by weight of the thermosetting resin.
It is preferably from 0 to 900 parts by weight. More preferably, the carbon-based base material 50 is added to 100 parts by weight of the thermosetting resin.
0 to 800 parts by weight. By blending the carbon-based base material in such a range, it is possible to impart sufficient fluidity when molding the molding material and good conductivity to the fuel cell separator that is a molded article. When the blending amount of the carbon-based base material exceeds the upper limit value, the fluidity at the time of molding becomes insufficient, and it may be difficult to mold a precise shape. On the other hand, when the amount is below the lower limit, the conductivity required for the fuel cell separator may be insufficient. This is because the volume occupied by the thermosetting resin in the molded product increases,
It is considered that there is a high probability that a large amount of resin, which is an insulating layer, exists between the carbon-based base particles, and as a result, the number of insulating portions increases and conductivity decreases.

The molding material of the present invention may be used as a molding material for a fuel cell separator, in addition to the thermosetting resin and the carbon-based base material described above, within a range not deviating from the object and effect of the present invention. Generally used lubricants, release agents, colorants, curing accelerators, flame retardants and the like can be used.

Next, a method for producing the molding material of the present invention (hereinafter simply referred to as "production method") will be described. The production method of the present invention is not particularly limited, and examples thereof include a method of kneading a raw material mixture containing a thermosetting resin and a carbon-based substrate as essential components using a melt-kneading device. The melt-kneading device is not particularly limited, but a known device such as a twin-screw kneader, a twin-screw extruder, a single-screw extruder, or a roll kneader can be used. The kneading conditions are also not particularly limited, and the particle size distribution / property of the raw material carbon-based base material to be used, the type of the melt-kneading device, the composition / property of the molding material, and the particle-size distribution of the carbon-based base material in the target molding material, etc. In consideration of the above, the optimum kneading conditions can be selected and used. This method, compared with a method of mixing a thermosetting resin and a carbon-based substrate and granulating in a slurry using a large amount of a solvent, the process can be simplified and it is necessary to treat the solvent. It is not preferable. In addition, many commercially available carbon-based substrates such as graphite have a relatively sharp particle size distribution. Even when such a carbon-based base material is used, it can be used by kneading with a melt-kneading device without requiring treatment such as classification or combination in advance. For example, using as a raw material a carbon-based substrate having an average particle size larger than the average particle size at the stage of forming a molding material,
By blending a thermosetting resin and the like and kneading with a melt-kneading device, the average particle size is reduced to a small particle size and the distribution is broadened. In this way, the carbon-based base material in the molding material can have a particle size distribution having the effect of the present invention. After being kneaded by using the melt-kneading apparatus in this way, it is cooled and pulverized, or granulated by a pelletizer or the like immediately after the melt-kneading to obtain a molding material.

In addition to the method using the melt-kneading apparatus, when a carbon-based material having a particle size distribution close to that of the target carbon-based material in the molding material is used as a raw material, It is preferable to use a method of forming a molding material without giving a large kneading energy during manufacturing. Such a production method is not particularly limited, but for example, a raw material mixture containing a thermosetting resin, a carbon-based substrate, and other raw materials to be blended as necessary may be used as a Henschel mixer, a ribbon blender, or a universal mixer. Examples of the method include mixing using a stirrer and performing treatment while heating as needed to granulate while mixing to obtain a molding material. When this method is used, it is preferable to preliminarily pulverize raw materials other than the carbon-based base material and perform preliminary mixing. As a result, the mixing accuracy with the carbon-based base material can be made sufficient without giving a large amount of kneading energy, and the carbon-based base material in the molding material can be easily adjusted to the target particle size distribution. be able to.

Next, the fuel cell separator of the present invention will be described. The fuel cell separator of the present invention is formed by molding the molding material or the molding material obtained by the manufacturing method. The method for molding the fuel cell separator of the present invention is not particularly limited, but usually,
Compression molding or transfer molding is used. In the case of using compression molding, it is possible to assist the moldability by molding a preformed product according to the shape of the molded product and molding the preformed product. As an example of compression molding, the pressure is 50 to 400.
kg / cm ^2, temperature of 20 to 70 ° C., molding the preform in time 0.1-2 min, further pressure this 200 to 1500
A molded article for a fuel cell separator can be obtained by molding at a temperature of 150 to 200 ° C. for 1 to 30 minutes in kg / cm ² .

[0017]

EXAMPLES The present invention will be described below with reference to examples. 1. Manufacture of molding material The raw material mixture was mixed at the raw material mixture ratio shown in Table 1 using a Henschel mixer (FM20B manufactured by Mitsui Mining Co., Ltd.) at room temperature.
After mixing at 350 rpm for min., Subsequently, kneading at 80 ° C. using a twin-screw extruder (TEM-50 manufactured by Toshiba Machine),
Granulated. In Table 1, "specific energy during kneading" means the amount of electric power (kW) required to drive the twin-screw kneader.
Was divided by the discharge amount (kg) of the material and used as an index of the kneading degree.

2. Measurement of particle size distribution of carbon-based substrate at the stage of forming a molding material About 1 g of the molding material obtained in Examples and Comparative Examples was sampled, and the resin content contained in this was washed off with acetone using a filter paper to remove carbon. Only the system base material was taken out. After sufficiently drying this, measurement was performed using a laser diffraction particle size distribution analyzer (LA920, manufactured by Horiba, Ltd.).

3. Evaluation of various properties as a material for a fuel cell separator (1) Measurement of resistivity in the penetrating direction It was carried out by the method shown in FIG. Using the molding materials obtained in the examples and comparative examples, the mold temperature was 170 ° C. and the molding pressure was 30.
80 kg / cm ² , compression molding at a molding time of 3 minutes, 80 ×
80 × 15 mm sample 3 and 80 × 80 × 5 mm sample 4 were obtained. The resistance in the penetrating direction was measured using these samples. That is, two samples 3 and 4 having different thicknesses are combined and set on the electrode 1 via the carbon paper 2, and the specific resistance in the penetrating direction is obtained from the resistance value in the state where the thickness of the molded body is different. It was

4. Evaluation of various properties as raw material for fuel cell separator Using the molding materials obtained in Examples or Comparative Examples, mold temperature 170 ° C., molding pressure 400 kg / cm ² , molding time 3
It was compression molded in minutes to obtain a molded product having a size of 300 × 300 × 2 mm. From this, a test piece was cut out, created and evaluated. (1) Flexural modulus and flexural strength: Measured according to JIS K7203. (2) Gas permeability: Using nitrogen gas, JISK7126
It was measured by Method A. (3) Monohole fluidity: measured according to JIS K6911. (4) Thickness accuracy: Using a molded product with a size of 300 x 300 x 2 mm, a thickness of 16 places is measured at equal intervals using a three-dimensional measuring instrument manufactured by Mitutoyo, and the difference between the maximum value and the minimum value is measured. Thickness accuracy was used.

Table 1 shows the blending of the raw materials, the molding materials and the evaluation results of the molded products in Examples and Comparative Examples.

[Table 1] (Note in the table) (1) Phenol resin: The one produced by the following method was used. Formaldehyde (F) and phenol (P) in a 2 liter flask in molar ratio (F / P) = 1.7.
Then, the pH is adjusted to 5.5 by using zinc naphthenate and oxalic acid.
And the reaction was carried out for 4 hours while stirring at 120 rpm. Next, after dehydration temperature was raised to 120 ° C. under normal pressure, the temperature was raised to 160 ° C. while dehydrating under reduced pressure, and then taken out from the flask to obtain a phenol resin (excluding average molecular weight of free phenol = 864). (2) Epoxy resin: manufactured by Japan Epoxy Resin Co., Ltd., Epicoat 1001 (bisphenol A type epoxy resin,
Number average molecular weight 900) (3) Curing agent: Shikoku Kasei Co., Ltd., 2MZ (4) Fatty acid: Toa Kasei carnauba wax (average carbon number 26, melting point 83 ° C.) (5) Artificial graphite 1: Nippon Graphite Industry Co., Ltd. Made by PAG-60
(Average particle size 580 μm) (6) Artificial graphite 2: PAG-80 manufactured by Nippon Graphite Industry Co., Ltd.
(Average particle size 400 μm) (7) Artificial graphite 3: PAG-120 manufactured by Nippon Graphite Industry Co., Ltd.
(Average particle size 120 μm)

In Examples 1, 2, and 3, a raw material mixture prepared by mixing a thermosetting resin, a carbon-based base material, a fatty acid, and the like in predetermined amounts was used.
It was made into a molding material using a twin-screw extruder. Although the average particle size of the carbon-based base materials used as raw materials differs greatly,
By kneading with a melt-kneading device, the carbon-based base material was made into small-sized particles, and the particle size distribution of the carbon-based base material at the stage of forming a molding material could be set within a preferable range. Then, the molded products using these became excellent in conductivity, mechanical strength, gas impermeability, and thickness accuracy. Particularly, in Examples 1 and 2, the particle size distribution of the carbon-based base material at the stage of forming the molding material was the most preferable, so that the thickness accuracy could be further improved. On the other hand, Comparative Example 1
Is a material obtained by using the same carbon-based material as that used in Example 3 as a raw material and kneading at a low kneading degree. The average particle size was large in the particle size distribution of the carbon-based substrate in. As a result, the molded product using this resulted in poor gas impermeability. In Comparative Example 2, the same carbon-based material as that used in Example 1 was used as a raw material and kneaded at a high kneading degree. The average particle size was small in the particle size distribution of the carbon-based substrate at this stage. As a result,
A molded product using this has reduced conductivity and thickness accuracy.

[0023]

INDUSTRIAL APPLICABILITY The present invention contains a thermosetting resin and a carbonaceous base material having conductivity as essential components, and has a conductive carbonaceous group in the molding material at the stage of forming a molding material. Material having an average particle size of 50 μm or more and 100 μm or less, and 85% or more of all particles having a particle size of 10 μm or more and 200 μm or less. Is. A molded product using the molding material of the present invention has excellent conductivity and moldability, and can be suitably used for a fuel cell separator.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method for measuring a through-direction resistivity.

[Explanation of symbols]

1 electrode 2 carbon paper 3 Molded product of resin composition of the present invention (thickness: 15 mm) 4 Molded product of resin composition of the present invention (thickness: 5 mm) 5 constant current device 6 Voltmeter

Claims (6)

[Claims] 1. A carbon-based base material having conductivity, which contains a thermosetting resin and a carbon-based base material having conductivity as essential components, and is contained in the molding material at the stage of forming a molding material. The particle size is in the range of 50 μm or more and 100 μm or less,
Moreover, 85% or more of all particles have a particle size of 10 μm or more, 200
A molding material for a fuel cell separator, which is in the range of μm or less. 2. The conductive carbonaceous base material in the molding material at the stage of forming the molding material is 30 to 50 of all particles.
% Within a range of 50 μm or more and 200 μm or less, and 35 to 55% of all particles have a particle size of 10 μm or more,
The molding material for a fuel cell separator according to claim 1, which is in a range of less than 50 μm. 3. The content of the carbon-based base material having conductivity is
The molding material for a fuel cell separator according to claim 1, which is 300 to 900 parts by weight with respect to 100 parts by weight of the thermosetting resin. 4. A fuel cell separator obtained by molding the molding material for a fuel cell separator according to claim 1. 5. A method for producing the molding material for a fuel cell separator according to claim 1, which comprises a thermosetting resin and a carbonaceous base material having conductivity as essential components. A method for producing a molding material for a fuel cell separator, which comprises kneading a raw material mixture using a melt-kneading device. 6. A fuel cell separator obtained by molding the molding material obtained by the method for producing a molding material for a fuel cell separator according to claim 5.