JP3296801B2 - Carbon composite molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is required to be excellent in mechanical strength and electrical conductivity and gas-impermeable, such as a fuel cell separator used mainly as a battery for electric vehicles. The present invention relates to a carbon composite molded article formed into a predetermined shape from a composite composition obtained by mixing and dispersing a carbon-based conductive filler such as graphite powder in a thermosetting resin such as a phenol resin as a material meeting the requirements.

[0002]

2. Description of the Related Art In addition to the above-mentioned strong mechanical strength, conductivity and gas impermeability, a carbon molded body typified by a fuel cell separator which is also required to have high dimensional accuracy and low cost. It has been conventionally known to use a composite composition formed by bonding graphite powder, which is one of the carbon-based conductive fillers, with a thermosetting resin, commonly known as bond carbon, as a molding material for the above.

However, in a molded article such as a fuel cell separator molded using bond carbon, a volume resistivity indicating the most important mechanical strength, in particular, compressive strength and conductivity, among the above-mentioned required items. Have mutually opposite results. More specifically, in order to obtain the compressive strength required for a molded article such as a separator in a bond carbon obtained by mixing and bonding a graphite powder to a thermosetting resin, a predetermined amount is set using bond carbon having a large proportion of the resin. As shown in the schematic diagram of FIG. 8, in the molded body formed into a shape, the portion without the resin layer 30, that is, the void portion 31 formed in the tissue without sufficiently spreading the resin and the void portion 31 Only the energization path as shown by the arrow x is formed by the graphite particles 32 in contact with the portion 31, and the other portion becomes an insulating portion due to the electric insulation property of the resin, and is required as a whole molded body such as a separator. No favorable results can be obtained in terms of the performance of fuel cells and the like due to the lack of conductivity and an increase in electrical resistance.

On the other hand, in a molded article formed into a predetermined shape using a bond carbon containing a small amount of a resin,
By increasing the molding surface pressure so as to bring the graphite particles 32 into contact with each other, no void portion is formed in the tissue, or
Since the formation of voids is extremely reduced, the number of current paths can be increased and the conductivity of the entire molded body such as a separator can be increased, but the amount of resin that bears the strength of the molded body is small. , Not only the mechanical strength of the molded body, especially the compressive strength is inevitably reduced, but also the elongation of the bond carbon during molding is small and the fluidity is poor,
Moldability is deteriorated, and it is difficult to obtain a molded body having a predetermined shape from the viewpoint of shape as well as dimensional accuracy.

It is also conceivable to use a composite conductive material in which carbon black is mixed and dispersed in a resin as a carbon-based conductive filler instead of graphite powder to form a molded article having a predetermined shape such as a fuel cell separator. In a molded body formed from such a composite conductive material, primary particles formed by collecting thousands of crystallites having a pseudo-graphite structure of carbon black further exist as secondary particles linked in a chain by cohesive force. As a result, a chain-like structure is formed, thereby ensuring the conductivity of the entire molded body.

However, the volume resistivity of the conductive carbon black alone is 2.5 × 10 ⁻¹ Ω · cm, and the volume resistivity (5 ×) in the one-plane direction of highly crystalline graphite represented by natural graphite. 10 ^-5 Ω · cm)
As a molded product such as a separator molded from the above composite conductive material in which only conductive carbon black is mixed and dispersed in a resin, it is not possible to obtain high conductivity required for this type of molded product.

[0007]

As described above, bond carbon obtained by mixing and dispersing graphite powder alone in a resin as a carbon-based conductive filler, or conductive carbon black alone being mixed and dispersed in a resin. Any of the composite conductive materials cannot satisfy both the mechanical strength and conductivity, which are the most strongly required as a molded article such as a fuel cell separator. In particular, in a fuel cell separator used as a battery for an electric vehicle, in order to further improve the cell performance, the compressive strength is 80 MPa or more and the volume resistivity is 5 × 10 ⁻³ Ω · cm.
Although those having the following characteristics are required, a fuel cell separator having such characteristics has not yet been developed.

The present invention has been made in view of the above circumstances, and is intended for a fuel cell which is excellent in moldability, and can exhibit extremely high conductivity while securing necessary and sufficient mechanical strength. An object is to provide a carbon composite molded article such as a separator.

[0009]

In order to achieve the above-mentioned object, a carbon composite molded article according to the present invention comprises a thermosetting resin.
Composite made by mixing and dispersing carbon-based conductive fillers
Carbon composite molding molded into a predetermined shape from the composition
Body, as the carbon-based conductive filler, black
Structure car with lead powder and conductivity index of 60 or more
A combination of carbon, the thermosetting resin in the composite composition
The compounding ratio is 15 to 30% by weight and the structure
-Characterized in that the compounding ratio of carbon is 3 to 10% by weight.

According to the present invention having the above-described structure, by increasing the blending ratio of the thermosetting resin in the composite composition to 15 to 30% by weight, the elongation and fluidity during molding are improved, and uneven molding occurs. Not only excels in dimensional accuracy and shape accuracy, but also maintains high mechanical strength, especially compressive strength.
By index in combination with 60 or more structure carbon, as shown in the schematic view of FIG. 5, the structure carbon emissions present graphite particles 32 each having an order of magnitude lower volume resistivity than the carbon black in the resin layer 30 <br/> The interconnected structure 33 to be formed has succeeded in improving the conductivity of the whole molded body by being connected to each other, and this point will be described in detail below.

That is, as shown in FIG. 6, the crystal plane of graphite has a network plane formed by condensing a large number of conjugated six-membered rings at 3.35.
It overlaps at intervals of angstrom, and the volume resistivity in the direction parallel to this plane (direction of arrow a) is 5 × 10 ⁻⁵ Ω ·
cm, very small, but perpendicular to this (arrow b direction)
Has a large electrical resistivity of 5 × 10 ⁻¹ Ω · cm and has electrical anisotropy. On the other hand, as shown in FIG. 7, the structure carbon has a six-membered ring plane of carbon atoms of 3.4.
Thousands of crystallites 34 having a pseudo-graphite structure formed by stacking three to four layers at an average spacing of ~ 3.6 angstroms form primary particles 35, and the primary particles 35 are further coagulated by 3-100. The carbon particles 33 are present as individual, chain-like secondary particles 36 and form a chain-like carbon structure 33 in the resin layer 30. Thus, the resin layer 30
By contacting and linking the graphite particles 32 with each other by the chain-like carbon structure 33 formed therein, as shown by an arrow y in FIG. 5, a large number of energization paths are formed in the structure of the molded body. The very high conductivity of the entire molded body can be secured by effectively utilizing the low volume resistivity in one direction of the graphite particles 32 filled in the structure of the molded body in a large amount.

The structure carbon used in the present invention has a large specific surface area and a conductivity index of 6
High-structure carbon having a value of 0 or more and having a developed structure is preferable. Typical examples are oil furnace black and acetylene black.

The thermosetting resin used in the present invention is most preferably a phenol resin having excellent wettability with graphite powder, but other than that, an epoxy resin, a urea resin, a melamine resin, and an unsaturated polyester resin. , At least one selected from alkyd resins, polycarbodiimide resins, and furfuryl alcohol resins, which cause a thermosetting reaction when heated, and are stable to the operating temperature and supply gas components of molded articles such as fuel cells. Should be fine.

The graphite powder used in the present invention may be of any type such as natural graphite, artificial graphite, quiche graphite, expanded graphite, etc., and may be arbitrarily selected in consideration of conditions such as cost. Can be.

Further, the mechanical and electrical properties of the molded article formed into a predetermined shape from the composite composition according to the present invention have a volume specific resistance of 5 × 10 ⁻ , particularly when a fuel cell separator is targeted. ^{It is 3} Ω · cm or less, more preferably × 10 ⁻³ Ω · cm or less, and the compressive strength is 80 MPa or more, more preferably 100 MPa or more.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. First, the configuration and operation of a solid polymer electrolyte fuel cell provided with a fuel cell separator as an example of a carbon composite molded article according to the present invention are shown in FIG.
This will be briefly described with reference to FIGS. The solid polymer electrolyte fuel cell 20 is formed of, for example, an electrolyte membrane 1 which is an ion exchange membrane formed of a fluorine-based resin and a carbon cloth, carbon paper or carbon felt woven with carbon fiber yarns. 2 serving as a gas diffusion electrode with a sandwich structure
And a plurality of sets of unit cells 5 each comprising a cathode 3 and separators 4 and 4 sandwiching the sandwich structure from both sides, to form a stack structure in which current collectors (not shown) are arranged at both ends. I have.

As shown in FIG. 2, the two separators 4 have fuel gas holes 6 and 7 containing hydrogen at their peripheral portions.
And oxidizing gas holes 8 and 9 containing oxygen and cooling water holes 10 are formed. When a plurality of sets of the single cells 5 are stacked,
Each hole 6, 7, 8, 9, 10 of each separator 4 penetrates through the inside of the fuel cell 20 in the longitudinal direction, and the fuel gas supply manifold, fuel gas discharge manifold, oxidizing gas supply manifold, oxidizing gas discharge manifold, cooling It is designed to form a channel.

A rib 11 having a predetermined shape is formed on the surface of each of the separators 4.
A fuel gas flow channel 12 is formed between the rib 11 and the surface of the anode 2, and an oxidizing gas flow channel 13 is formed between the rib portion 11 and the surface of the cathode 3.

The solid polymer electrolyte fuel cell 2 having the above structure
At 0, the fuel gas containing hydrogen supplied to the fuel cell 20 from the fuel gas supply device provided outside is supplied to the fuel gas flow channel 12 of each unit cell 5 via the fuel gas supply manifold. The supplied and presents an electrochemical reaction on the anode 2 side of each unit cell 5 on the anode 2 side as follows: H ₂ → 2H ′ + 2e ′ (1), and the fuel gas after the reaction is supplied to the fuel gas passage 12 of each unit cell 5. From the fuel gas exhaust manifold to the outside. At the same time, an oxidizing gas (air) containing oxygen supplied to the fuel cell 20 from an oxidizing gas supply device provided outside is supplied to the oxidizing gas passage 13 of each unit cell 5 via the oxidizing gas supply manifold. At the cathode 3 side of each unit cell 5, an electrochemical reaction of the formula (1/2) O ₂ + 2H ′ + 2e ′ → H ₂ O (2) is obtained, and the oxidizing gas after the reaction is The gas is discharged from the oxidizing gas passage 13 of the single cell 5 to the outside via the oxidizing gas discharge manifold.

Along with the electrochemical reactions of the above formulas (1) and (2), the fuel cell 20 as a whole becomes H ₂ + (１ ／) O ₂ → H ₂ O (3) The chemical reaction progresses, converting the chemical energy of the fuel directly into electrical energy,
A predetermined battery performance is exhibited. The fuel cell 20
Is operated in a temperature range of about 80 to 100 ° C. due to the properties of the electrolyte membrane 1 and thus generates heat. Therefore, the fuel cell 20
During the operation of, cooling water is supplied to the fuel cell 20 from a cooling water supply device provided outside, and the cooling water is circulated through the cooling water passage to suppress a rise in temperature inside the fuel cell 20. I have.

Next, the separator 4 in the solid polymer electrolyte fuel cell 20 having the above configuration and operation is described.
Will be described with reference to FIG. The separator 4, the mixing ratio of the thermosetting resin is 15 to 30 wt%, and is used in combination as the carbon-based conductive filler
Graphite powder and structure with conductivity index of 60 or more
Composition ratio of structural carbon with carbon
Is formed using a composite composition having 3 to 10% by weight and the balance being the blending amount of graphite powder, wherein the graphite powder, thermosetting resin and structural carbon are uniformly mixed and adjusted. Thus, a predetermined compound is created (step S100). Then, this compound is put in mold 1
4 (step S101). In this state, the mold 14 is heated and heated to 150 to 170 ° C., and a press (not shown) is operated to move the mold 14 to 150 to 170 ° C. from the direction of arrow f in FIG.
1500 kgf / cm ² , preferably 300 to 100
By applying a surface pressure in a range of 0 kgf / cm ² (step S102), the separator 4 having a final shape corresponding to the shape of the mold 14 is manufactured (step S103).

The separator 4 manufactured as described above
In the above, the compounding ratio of the thermosetting resin in the composite composition as a constituent material of the separator 4 is 15 to 30% by weight.
Because of this, it has good elongation and fluidity during molding and suppresses the occurrence of molding unevenness, and not only obtains excellent dimensional accuracy and shape accuracy, but also has mechanical strength, especially compressive strength of 80 MPa.
It becomes big as above. Further, since graphite powder and structural carbon are used in combination as the carbon-based conductive filler, as described above based on the schematic diagram of FIG. The structure existing in the resin layer 30
It is possible to increase the conductivity of the entire separator 4 by connecting them with each other by a chain-like structure 33 formed by carbon .

Hereinafter, the present invention will be described in more detail with reference to examples. <Example 1> 70% by weight of natural graphite having a particle diameter of 50μ, 24% by weight of a phenol resin (PR-50273 manufactured by Sumitomo Bakelite Co., Ltd.), and 6% by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) A paste is prepared by preparing a mortar and slidingly mixing the phenol resin and acetylene black together with alcohol until the surface has a mirror-like gloss. This paste is transferred to another vessel and mixed with the above natural graphite particles for 2 to 3 minutes with a mixer to obtain a flake-like mixture. This flaky mixture is
The residual alcohol is dried by spreading to a thickness of 2 to 3 mm on the TFE sheet. After drying, the powder was pulverized with a household mixer to obtain a powder having a size of 150 mesh or less. This powder was filled in a molding die to produce a plate-like molded body having a thickness of 2.5 mm and a size of 100 × 100 mm. <Comparative Example 1> 70% by weight of natural graphite having a particle size of 50μ, phenol resin 30
A bond carbon compound having a compounding ratio of 100% by weight was prepared, and the compound was filled in a mold, and a molding surface pressure of 100 kgf / cm ^{2 was applied} at a molding temperature of 170 ° C. for 10 minutes, and a thickness of 2.5 mm was applied. A plate-shaped molded body having a size of × 100 mm was manufactured. <Comparative Example 2> 50% by weight of conductive carbon black, phenol resin 5
A composite carbon compound having a compounding ratio of 0% by weight was prepared, this compound was filled in a mold, and a molding surface pressure of 100 kgf / cm ^{2 was applied} at a molding temperature of 170 ° C. for 10 minutes to a thickness of 2.5 mm. A plate-shaped molded body having a size of 100 × 100 mm was manufactured. Comparative Example 3 55% by weight of natural graphite having a particle size of 50 μm, 30% by weight of a phenol resin (PR-50273 manufactured by Sumitomo Bakelite Co., Ltd.), and 15% by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) A composite carbon compound was prepared at a ratio of 1: 1 and filled in a mold, and a molding surface pressure of 100 kgf / cm ^{2 was applied} at a molding temperature of 170 ° C. for 10 minutes, and a 100 mm × 1 × 2.5 mm thickness was applied.
A plate-shaped molded body having a size of 00 mm was produced.

When the volume resistivity, flexural strength and compressive strength of each of the plate-like molded bodies manufactured in Example 1 and Comparative Examples 1 to 3 were measured, the results shown in Table 1 were obtained. Was.

[0025]

[Table 1]

As is evident from the results shown in Table 1, the amount of resin was increased as in Example 1 corresponding to the present invention, and graphite powder and a conductive index of 60 were used as conductive fillers.
The molded body manufactured using the above structure carbon in combination has a lower bending resistance and compressive strength than that of the comparative example, while lowering the volume resistivity of the entire molded body, and has a higher conductivity. Can be improved.

By applying the present invention to a separator in a solid polymer electrolyte fuel cell as described in the above embodiment, it is possible to achieve an improvement in cell performance, which is the most effective. However, other than the fuel cell separator, the present invention can be applied to any molded article requiring both mechanical strength and conductivity.

[0028]

As described above, claims 1 to 5 are as described above.
According to the present invention, graphite powder and oil furnace are used as the conductive filler mixed and dispersed in the thermosetting resin.
By using a structural index of 60 or more in combination with a conductive index such as black or acetylene black at an appropriate ratio, graphite powder or conductive carbon black was used alone, as in a conventional bond carbon or composite conductive material. Compared with those, the resin amount is increased to facilitate moldability, not only high dimensional accuracy and shape accuracy are obtained, but also mechanical strength, especially compressive strength, while maintaining large graphite particles in the resin layer. By utilizing the very low volume resistivity of graphite particles that are interconnected by a chain-like structure formed by structural carbon ,
This has the effect that very high conductivity can be ensured as a whole of the molded body, and in particular, the mechanical strength is 80%.
High compressive strength over MPa and volume resistivity 5 × 10 ^-3 Ω
-It is possible to provide a separator for a fuel cell, which is required to have a high conductivity of not more than cm, that has both of these characteristics.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing the configuration of a stack structure of a solid polymer electrolyte fuel cell provided with a fuel cell separator as an example of a carbon composite molded article according to the present invention.

FIG. 2 is an external front view of a separator in the solid polymer electrolyte fuel cell.

FIG. 3 is an enlarged cross-sectional view of a main part showing a configuration of a single cell, which is a structural unit of the solid polymer electrolyte fuel cell;

FIG. 4 is an explanatory view illustrating a manufacturing process and a manufacturing state of the separator.

FIG. 5 is an enlarged schematic sectional view of a main part of the separator.

FIG. 6 is a diagram illustrating a crystal structure of graphite.

FIG. 7 is a diagram illustrating the internal structure of conductive carbon black.

FIG. 8 is an enlarged schematic cross-sectional view of a main part of a molded body formed using conventional bond carbon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Anode 3 Cathode 4 Separator 5 Single cell 14 Die 20 Solid polymer electrolyte fuel cell 30 Resin layer 32 Graphite particle 33 Carbon structure 34 Crystallite of conductive carbon black

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 1/24 H01M 8/02

Claims (5)

(57) [Claims] 1. A carbon-based conductive filler is added to a thermosetting resin.
Into a predetermined shape from a composite composition obtained by mixing and dispersing
A carbon composite formed body is, as the carbon-based conductive filler, graphite powder and a conductive
Combined use of structural carbon with electrical index of 60 or more
And the compounding ratio of the thermosetting resin in the composite composition is 15 to 30% by weight , and the structure carbon
Is 3 to 10% by weight. Wherein said structure carbon is carbon composite formed body of claim 1 which is O-yl furnace black or acetylene black. 3. The thermosetting resin is a phenol resin,
Epoxy resin, urea resin, melamine resin, unsaturated polyester resin, alkyd resin, polycarboimide resin,
The carbon composite molded product according to claim 1, wherein the carbon composite molded product is at least one type selected from a furfuryl alcohol resin. 4. The molded article molded from the composite composition has a volume resistivity of 5 × 10 ⁻³ Ω · cm or less and a compressive strength of 80 MPa or more. Of carbon composite moldings. Fuel cell separator. 5. A molded product of interest is, claims 1 is a separator for a fuel cell-carbon composite formed body according to any of the 4.