JP2021125323A - Fuel cell separator material and fuel cell separator - Google Patents

Abstract

To provide a fuel cell separator material capable of achieving both desired good electrical characteristics and mechanical strength without controlling the blending amount of graphite powder and a phenol resin.SOLUTION: A fuel cell separator material includes graphite particles whose surface is coated with a binder resin, and carbon fibers, and the degree of graphitization of carbon fibers is 0.20 to 0.74.SELECTED DRAWING: Figure 1

Description

The present invention relates to a separator material for a fuel cell.

In recent years, a separator for a fuel cell (hereinafter, may be simply referred to as a "separator") has been developed, which is composed of a composite material in which a thermosetting resin such as a phenol resin is used as a binder in graphite powder. Since graphite has low electrical resistance and excellent corrosion resistance, the composite material is attracting attention as a material that can replace the metal plate that has been studied from the viewpoint of improving the mechanical strength of the separator.

The higher the content of the binder resin in the separator, the better the mechanical strength and gas permeability, but instead, the electrical properties such as volume resistance are lowered. From this point of view, a separator for a fuel cell has been proposed in which a surface is coated with a phenol resin and a graphite powder having a predetermined particle size is used and pressure-molded under various molding conditions (for example, a patent). Reference 1).

Japanese Unexamined Patent Publication No. 2002-198066

However, in the above-mentioned conventional separator for a fuel cell, it is necessary to control the electrical characteristics and the mechanical strength by the blending amount of the graphite powder and the phenol resin, so that the desired good electrical characteristics and the mechanical strength are compatible with each other. Was difficult.

Therefore, the present invention has been made in view of the above-mentioned problems, and is a fuel capable of achieving both desired good electrical characteristics and mechanical strength without controlling the blending amount of the graphite powder and the phenol resin. Battery Separator Material "Hereinafter, it may be simply referred to as" separator material ". The purpose is to provide.

In order to achieve the above object, the fuel cell separator material of the present invention is a fuel cell separator material containing graphite particles whose surface is coated with a binder resin and carbon fibers, and the carbon fibers are graphitized. The degree is 0.25 to 0.74.

According to the present invention, it is possible to provide a fuel cell separator material having desired good electrical properties and mechanical strength.

It is a scanning electron microscope (SEM) photograph of the sample plate prepared in Example 1. FIG.

The separator material for a fuel cell of the present invention contains graphite particles whose surface is coated with a binder resin (hereinafter, may be referred to as “resin-coated particles”) and carbon fibers. Further, the fuel cell separator of the present invention is, for example, a polymer electrolyte fuel composed by forming a single cell together with an anode electrode and a cathode electrode arranged via a solid polymer membrane and stacking a plurality of the single cells. It is used for a battery and is formed of the separator material for a fuel cell of the present invention.

<Graphite particles>
The graphite particles contained in the resin-coated particles are themselves composed of particles or powder. The shape of the graphite particles is not particularly limited, and those having any shape can be used.

The graphite particles are composed of, for example, natural graphite (eg, scaly graphite, massive graphite, earthy graphite), artificial graphite, expanded graphite, expanded graphite, carbon black, and kiss graphite, and a combination thereof. .. Of these, it is preferable that it is composed of natural graphite or artificial graphite. The average particle size of the graphite particles is preferably 5 μm to 500 μm, more preferably 10 μm to 300 μm.

<Binder resin>
The binder resin contained in the resin-coated particles is a resin that coats the entire surface or a part of the outer surface of the graphite particles.

This binder resin is a thermosetting resin or a thermoplastic resin, and the thermosetting resin constituting the binder resin has, for example, a curing temperature of 30 ° C. to 400 ° C., preferably 50 ° C. to 250 ° C. Can be mentioned.

Examples of the thermosetting resin include phenol resins, epoxy resins, melamine resins, urea resins, alkyd resins, unsaturated polyester resins, diallyl phthalate resins, thermosetting polyimide resins, and organic thermosetting resins such as combinations thereof. Examples thereof include resins and inorganic thermosetting resins such as silicone resins and fluororesins. Organic thermosetting resins are preferable, and phenol resins are particularly preferable, because they are excellent in versatility for separators.

The thermoplastic resin constituting the binder resin is, for example, a resin having a glass transition point, a melting point or a melting temperature of 30 ° C. to 400 ° C., preferably 100 ° C. to 350 ° C.

Thermoplastic resins include, for example, low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), ultra low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), and ultra high density polyethylene. Polyethylene (PE) such as molecular weight polyethylene (UHMW-PE), polypropylene (PP), polymethylpentene (PMP), and olefin resins such as polycyclic olefins, vinyl resins (eg, polyvinyl chloride (PVC) and Polyvinylidene chloride (PVDC)), polystyrene (PS), polyvinyl acetate (PVAc), acrylonitrile-styrene-butadiene resin (ABS), acrylonitrile-styrene resin (AS), acrylic resin (PMMA), polyamide resin (PA) (eg , Nylon 6, Nylon 11, Nylon 12, Nylon 46, Nylon 66, Nylon 6T, Nylon 61, Nylon 9T, Nylon M5T, Nylon MXD, Nylon 610, and Nylon 612), Polyphthalamide resin, Polyacetyl (POM), Polycarbonate (PC), polyester resins (eg polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene naphthalate (PTT)), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and heat. Examples include thermoplastic polyethylene (PI) and combinations thereof. Polypropylene (PP) is preferable because it has good physical properties at the operating temperature and is low in cost.

<Resin coated particles>
The content (adhesion amount) of the binder resin in the resin-coated particles is not necessarily limited, but the content of the binder resin with respect to the entire resin-coated particles is preferably 10% by mass to 80% by mass, preferably 15% by mass to 50% by mass. Is more preferable.

Further, as described above, the binder resin is coated on all or a part of the outer surface of the graphite particles which are the cores of the resin-coated particles, but the thickness of the coating layer is also not particularly limited and is arbitrary. Those set to can be used.

The average particle size of the resin-coated particles is not particularly limited, but is preferably 10 μm to 500 μm, and more preferably 20 μm to 310 μm. If the average particle size of the resin-coated particles is less than 10 μm, voids may occur between the graphite particles and the mechanical strength may decrease. Further, when the average particle size of the resin-coated particles exceeds 500 μm, the gaps between the particles become large when mixed with carbon fibers described later, which affects the deterioration of the mechanical strength and electrical properties of the obtained mixture. May affect.

The method for coating the graphite particles with the binder resin is not particularly limited, and for example, the method described in Patent Document 1 can be used. As such resin-coated particles, for example, those obtained by stirring and mixing liquid phenol and graphite particles with a mixer or the like are commercially available.

Here, in general, in a separator for a fuel cell, from the viewpoint of improving the battery characteristics of the cell stack, the electrical characteristics (conductiveness) are required to have a specific resistance value of 5.2 mΩ · cm or less, and the cell. From the viewpoint of facilitating the assembly of the stack, the mechanical strength is required to be 0.60% or more in bending strain.

However, as described above, in the conventional separator for a fuel cell, it is necessary to control the electrical characteristics and the mechanical strength by the blending amount of the graphite powder and the phenol resin. It was difficult to achieve both bending strain.

Therefore, the present inventors have investigated the above-mentioned problems, and found that by using the above-mentioned resin-coated particles mixed with carbon fibers having a predetermined degree of graphitization, the above-mentioned desired good conductivity and machine can be used. We have found that it is possible to achieve both target strength. Hereinafter, this carbon fiber will be specifically described.

The "inherent resistance value" here means the resistivity measured in accordance with JIS K7194.

Further, the “bending strain” here refers to the nominal change rate of the length of the minute element on the outer peripheral surface at the center between the fulcrums of the test piece, which is measured in accordance with JIS K7171.

<Carbon fiber>
The carbon fiber serves as a conductive path in the separator material, improves the conductivity of the separator after molding, and improves the mechanical strength of the separator after molding by being molded while being entangled with the resin-coated particles.

As the carbon fiber, for example, PAN-based carbon fiber made of acrylic fiber as a raw material, coal or petroleum pitch, or pitch-based carbon fiber made of naphthalene-based pitch can be used.

The separator material of the present invention is characterized in that the degree of graphitization of carbon fibers is 0.20 to 0.74.

This is because when the degree of graphitization is less than 0.20, the mechanical strength is improved, but the conductivity may not be sufficiently improved, and when it is larger than 0.74, the conductivity is improved. However, the mechanical strength may not be sufficiently improved.

That is, by using carbon fibers having a graphitization degree of 0.20 to 0.74, it is possible to achieve both the above-mentioned desired good conductivity and mechanical strength.

The "graphitization degree" here refers to the probability that the reference network surface and the adjacent network surface in the graphite crystal structure are arranged in a graphite manner, which is calculated by using XRD (X-ray diffraction).

Further, it is preferable to use milled fiber (short fiber having a short fiber length) as the carbon fiber, and the average fiber length of the milled fiber is preferably 100 to 680 μm. This is because if the thickness is less than 100 μm, the conductivity is improved, but the carbon fibers are likely to fall off in the separator material, so that the mechanical strength may not be sufficiently improved. Further, when it is longer than 680 μm, the carbon fibers are less likely to fall off in the separator material, so that the mechanical strength is improved, but the conductivity may not be sufficiently improved. Further, 360 to 500 μm is more preferable from the viewpoint of surely achieving both the above-mentioned desired good conductivity and mechanical strength.

The "average fiber length" here means the average length in the fiber length axis direction calculated by dynamic or static image analysis using a particle shape image analysis device. When using a commercially available product, the value described in the catalog can be adopted.

Further, the content of carbon fibers in the entire separator material is preferably 3 to 13% by mass or less. This is because if it is less than 3% by mass, the conductivity is improved, but the mechanical strength may not be sufficiently improved, and if it is more than 13% by mass, the content of the resin coating particles is lowered. This is because the conductivity may not be sufficiently improved.

Hereinafter, the present invention will be described based on examples. The present invention is not limited to these examples, and these examples can be modified or modified based on the gist of the present invention, and they are not excluded from the scope of the invention. No.

(Example 1)
<Preparation of sample plate>
Expanded graphite particles coated with phenolic resin, which is a resin-coated particle (manufactured by Lignite Co., Ltd., trade name: GPS-3076, average particle size of graphite particles: 200 μm, content of phenolic resin in the entire resin-coated particles: 30% by mass) ) 1 g of pitch-based milled fiber (manufactured by Osaka Gas Chemical Co., Ltd., trade name: Donna Carbomilled S-241, graphitization degree: 0.20), which is a carbon fiber, is added to 14 g, and then the temperature is lowered to room temperature. To prepare a separator material for a fuel cell. The content of the milled fiber with respect to the entire separator material for the fuel cell was 6.7% by mass. Further, a milled fiber having an average fiber length of 140 μm was used.

Next, a fuel cell separator material produced was charged into a preforming mold, the temperature is 55 ° C., 30 seconds pressure under the conditions of 100 kg / cm ^3, pressure-molded, then cooled to room temperature As a result, a preformed body having a width of 50 mm, a length of 80 mm, and a thickness of 2 mm was obtained.

Next, install the preform produced in this mold, temperature of 165 ° C., 120 seconds pressure under the conditions of 500 kg / cm ^3, pressure-molded and then cooled to room temperature. Then, the obtained molded product was annealed (165 ° C., 3 hours) using an electric furnace to obtain a sample plate of this example.

A scanning electron microscope (SEM) photograph of the obtained sample plate is shown in FIG. As shown in FIG. 1, it can be seen that the milled fiber is molded while being entangled with the resin coating particles.

<Measurement of intrinsic resistance value>
Using a Lorester measuring instrument (MCP-T600; manufactured by Mitsubishi Chemical Corporation), the intrinsic resistance value [mΩ · cm] was measured at any one point on the prepared sample plate based on JIS-K7194. The above results are shown in Table 1.

<Measurement of bending strain>
Using a precision universal testing machine (AG-20kNI: manufactured by Shimadzu Corporation), the prepared sample plate was processed to a width of 10 mm, a length of 80 mm, and a thickness of 2 mm based on JIS K7171 and bent strain [%]. Was measured. The above results are shown in Table 1.

(Example 2)
From the above-mentioned pitch-based milled fiber to carbon fiber, PAN (polyacrylonitrile) -based milled fiber (manufactured by Nippon Polymer Sangyo Co., Ltd., trade name: CFMP-150X, graphitization degree: 0.20, average fiber length: A sample plate was prepared in the same manner as in Example 1 described above except that it was changed to 100 μm), and the intrinsic resistance value and bending strain were measured. The above results are shown in Table 1.

(Example 3)
Except for changing the carbon fiber from the above-mentioned milled fiber to a pitch-based milled fiber having a graphitization degree of 0.27 (manufactured by Kureha Corporation, trade name: Kureka Chop M201S, average fiber length: 150 μm). , A sample plate was prepared in the same manner as in Example 1 described above, and the intrinsic resistance value and bending strain were measured. The above results are shown in Table 1.

(Example 4)
Except for changing the carbon fiber from the above-mentioned milled fiber to a pitch-based milled fiber having a graphitization degree of 0.64 (manufactured by Mitsubishi Chemical Corporation, trade name: dialead, average fiber length: 200 μm). , A sample plate was prepared in the same manner as in Example 1 described above, and the intrinsic resistance value and bending strain were measured. The above results are shown in Table 1.

(Comparative Example 1)
A sample plate was prepared in the same manner as in Example 1 described above except that no milled fiber was used, and the intrinsic resistance value and bending strain were measured. The above results are shown in Table 1.

(Comparative Example 2)
Except for changing the carbon fiber from the above-mentioned milled fiber to a PAN-based milled fiber having a graphitization degree of 0.19 (manufactured by Teijin Limited, trade name: Tenax HT M800 160MU, average fiber length: 160 μm). Prepared a sample plate in the same manner as in Example 1 described above, and measured the intrinsic resistance value and bending strain. The above results are shown in Table 1.

(Comparative Example 3)
The carbon fiber was changed from the above-mentioned milled fiber to a pitch-based milled fiber having a degree of graphitization of 0.75 (manufactured by Nippon Graphite Fiber Co., Ltd., trade name: XN-100, average fiber length: 150 μm). Except for the above, a sample plate was prepared in the same manner as in Example 1 described above, and the intrinsic resistance value and bending strain were measured. The above results are shown in Table 1.

As shown in Table 1, in Examples 1 to 4 in which the degree of graphitization of the milled fiber is 0.20 to 0.74, the intrinsic resistance value is 5.2 mΩ · cm or less and the bending strain is 0. It is 60% or more, and it can be seen that the desired good conductivity and mechanical strength can be achieved at the same time.

On the other hand, in Comparative Example 1 in which the milled fiber is not used, the intrinsic resistance value is 5.2 mΩ · cm or less, but the bending strain is less than 0.60%, and the desired good mechanical strength is obtained. It turns out that it cannot be done.

Further, in Comparative Example 2 in which the degree of graphitization of the milled fiber is less than 0.20, although the bending strain is 0.60% or more, the intrinsic resistance value is larger than 5.2 mΩ · cm, which is a desired good condition. It can be seen that conductivity cannot be obtained.

Further, in Comparative Example 3 in which the degree of graphitization of the milled fiber is larger than 0.74, although the intrinsic resistance value is 5.2 mΩ · cm or less, the bending strain is the same as in Comparative Example 1 in which the milled fiber is not used. Similarly, it is less than 0.60% (0.57), and it can be seen that the desired good mechanical strength cannot be obtained.

(Example 5)
A sample plate was prepared in the same manner as in Example 1 above, except that the content of milled fiber in the entire fuel cell separator material was changed to 9.7% by mass, and the natural resistance value and bending strain were adjusted. It was measured. The above results are shown in Table 2.

(Example 6)
A sample plate was prepared in the same manner as in Example 1 above, except that the pitch-based milled fiber of Example 1 having an average fiber length of 220 μm was used. Bending strain was measured. The above results are shown in Table 2.

(Example 7)
A sample plate was prepared in the same manner as in Example 1 above, except that the milled fiber of Example 1 described above had an average fiber length of 360 μm, and the specific resistance value and bending strain were set. It was measured. The above results are shown in Table 2.

(Example 8)
A sample plate was prepared in the same manner as in Example 1 above, except that the milled fiber of Example 1 described above had an average fiber length of 500 μm, and the natural resistance value and bending strain were set. It was measured. The above results are shown in Table 2.

(Example 9)
A sample plate was prepared in the same manner as in Example 1 above, except that the milled fiber of Example 1 described above had an average fiber length of 680 μm, and the natural resistance value and bending strain were obtained. Was measured. The above results are shown in Table 2.

As shown in Table 2, in Examples 5 to 9 in which the average fiber length of the milled fiber is 100 to 680 μm, the intrinsic resistance value is 5.2 mΩ · cm or less and the bending strain is 0.60% or more. Therefore, it can be seen that the desired good conductivity and mechanical strength can be achieved at the same time.

In particular, in Example 7 (average fiber length of 360 μm) and Example 8 (average fiber length of 500 μm), the intrinsic resistance value is 5.0 mΩ · cm or less and the bending strain is 0.70% or more. It can be seen that the balance between conductivity and mechanical strength is excellent.

(Example 10)
The above-mentioned milled fiber of Example 1 described above, except that the milled fiber having an average fiber length of 360 μm was used and the content of the milled fiber with respect to the entire separator material for a fuel cell was changed to 3.2% by mass. A sample plate was prepared in the same manner as in Example 1 of the above, and the intrinsic resistance value and the bending strain were measured. The above results are shown in Table 3.

(Example 11)
The above-mentioned milled fiber of Example 1 described above, except that the milled fiber having an average fiber length of 360 μm was used and the content of the milled fiber with respect to the entire separator material for a fuel cell was changed to 6.7% by mass. A sample plate was prepared in the same manner as in Example 1 of the above, and the intrinsic resistance value and the bending strain were measured. The above results are shown in Table 3.

(Example 12)
The above-mentioned milled fiber of Example 1 described above, except that the milled fiber having an average fiber length of 360 μm was used and the content of the milled fiber with respect to the entire separator material for a fuel cell was changed to 12.9% by mass. A sample plate was prepared in the same manner as in Example 1 of the above, and the intrinsic resistance value and the bending strain were measured. The above results are shown in Table 3.

(Example 13)
The above-mentioned milled fiber of Example 1 described above, except that the milled fiber having an average fiber length of 500 μm was used and the content of the milled fiber with respect to the entire separator material for a fuel cell was changed to 3.2% by mass. A sample plate was prepared in the same manner as in Example 1 of the above, and the intrinsic resistance value and the bending strain were measured. The above results are shown in Table 3.

(Example 14)
The above-mentioned milled fiber of Example 1 described above, except that the milled fiber having an average fiber length of 500 μm was used and the content of the milled fiber with respect to the entire separator material for a fuel cell was changed to 12.9% by mass. A sample plate was prepared in the same manner as in Example 1 of the above, and the intrinsic resistance value and the bending strain were measured. The above results are shown in Table 3.

As shown in Table 3, in Examples 7 to 8 and 10 to 14 in which the content of the milled fiber with respect to the entire separator material for the fuel cell is 3 to 13% by mass, the intrinsic resistance value is 5.2 mΩ · cm. It can be seen that the bending strain is 0.60% or more, and the desired good conductivity and mechanical strength can be achieved at the same time.

As described above, the present invention is particularly suitable for a fuel cell separator used in the automobile industry, the housing industry, and the like.

Claims (6)

A fuel cell separator material containing graphite particles whose surface is coated with a binder resin and carbon fibers.
A separator material for a fuel cell, wherein the carbon fiber has a graphitization degree of 0.20 to 0.74. The separator material for a fuel cell according to claim 1, wherein the average fiber length of the carbon fibers is 100 to 680 μm. The fuel cell separator material according to claim 1 or 2, wherein the content of the carbon fibers in the entire fuel cell separator material is 3 to 13% by mass. The separator material for a fuel cell according to any one of claims 1 to 3, wherein the carbon fiber is a milled fiber. The separator material for a fuel cell according to any one of claims 1 to 4, wherein the binder resin is a thermosetting resin. A fuel cell separator made of the fuel cell separator material according to any one of claims 1 to 5.

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