JP2003128872A - Electroconductive phenol resin forming material and fuel cell separator obtained by forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroconductive phenol resin forming material which is excellent in formability, electric characteristics, and mechanical properties, and also to provide a fuel cell separator obtained by forming the material. SOLUTION: The electroconductive phenol resin forming material comprises, as essential components, a dimethylene ether-type resol phenol resin, a carbonaceous base material having conductivity and an amine-base curing agent. The fuel cell separator is obtained by forming the forming material. Preferably, the dimethylene ether-type resol phenol resin is a resin where a phenol nuclear binding functional group is composed of a methylene group, a methylol group and a dimethylene ether group, and each functional group has a molar ratio of 20 to 50%, 10 to 20% and 40 to 60%, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive phenolic resin molding material and a fuel cell separator obtained by molding the same.

[0002]

2. Description of the Related Art Conventionally, a fuel cell separator is formed by molding a mixture of a thermosetting resin and carbonaceous powder, and then firing the molded body to give a required shape by a graphitization process for enhancing conductivity or cutting or polishing. (For example, Japanese Unexamined Patent Publication No. 2000-169230), or a method of using a metal resin composite as a raw material such as forming a groove on a metal plate and then performing resin coating (for example,
The production has been attempted according to JP-A No. 11-345618, New Energy Industrial Technology Development Organization, 2000, Polymer Polymer Fuel Cell Research and Development Results Report Summary, P70). However, the method that requires a graphitization process or a machining process cannot reduce the cost because it is difficult to develop into mass production, while the method that uses a grooved metal plate resin composite as a material is not used. The problem of layer peeling and metal plate corrosion that occurs at the interface layer between metal and resin in a certain environment cannot be solved, 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 it is a molded product of a molding material in which a thermosetting resin such as a phenol resin, an epoxy resin, or a polyester resin is mixed as a binder component with a carbon-based substrate such as graphite or carbon black. Has been attempted.

In this method, it is necessary to increase the compounding ratio of the carbon-based base material in the molding material in order to obtain high conductivity as the separator and to increase the resin compounding ratio in order to improve the moldability. Since these are contradictory factors, resin selection and design are important points. Among them, thermosetting resins such as phenol resins are excellent in various points such as heat resistance, mechanical strength, electrical stability, and cost, and the base resin can be selected from low molecular weight ones. Therefore, various studies have been made (for example, Japanese Patent Laid-Open No.
No. 1-204120).

When a phenol resin is used as a material for the separator, the novolac-type phenol resin cured with hexamethylenetetramine may have residual ammonia as a catalyst poison of a platinum-based proton exchange catalyst which is a catalyst of a fuel cell. Usually, a resol type phenol resin is often used. In general, a resol-type phenol resin has a low molecular weight and a methylol group, and thus has low activation energy and high reactivity as a resin, but since a methylol group is a main functional group, a cured product is Crosslink density is high and it tends to be brittle. Therefore, it is difficult to develop and adjust a material capable of forming a precision molded product having a thin and complicated shape such as a fuel cell separator with a general resol-type phenol resin. On the other hand, when a dimethylene ether type resole phenolic resin is used, the cured product is flexible, due to the large number of dimethylene ether bonds between the cross-linking points, and the flow path structure of the fuel cell separator is complicated and narrow, and the precision is high. Since it can be well molded, it is suitable as a separator for fuel cells, but it has lower reactivity than general resol-type phenolic resins, and it is essential to add a curing aid or the like to enhance the reactivity.

Curing aids generally used for phenolic resin molding materials include alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, and acid-based curing aids typified by boric acid. is there. However, when these curing aids are used in fuel cell separators, alkaline earth metal hydroxides remain in the molded product and cause problems such as catalyst poisoning and electrical deterioration. However, acid-based curing aids are not suitable because they lower the mechanical strength of the molded product. Studies have been conducted on a curing aid and a curing accelerator system which do not cause such a problem, but an effective method has not been proposed yet.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a conductive phenol resin molding material having excellent moldability, electrical characteristics and mechanical characteristics, and a fuel cell separator obtained by molding the same.

[0007]

These objects are achieved by the present invention described in (1) to (8) below. (1) dimethylene ether type resole phenolic resin,
A conductive phenolic resin molding material containing a conductive carbon-based base material and an amine-based curing agent as essential components. (2) The dimethylene ether type resole phenolic resin has a phenol nucleus-bonding functional group composed of a methylene group, a methylol group, and a dimethylene ether group, and the molar ratio of each functional group is 20 to 50% and 10 to 20, respectively. %,
And 40 to 60% of the conductive phenolic resin molding material according to the above (1). (3) The conductive phenol resin molding material as described in (1) or (2) above, wherein the dimethylene ether type resole phenol resin has a free phenol content of 7% by weight or less. (4) The dimethylene ether type resole phenol resin has a number average molecular weight excluding free phenol of 800 to 120.
The electroconductive phenolic resin molding material according to any one of (1) to (3) above, which is 0. (5) The conductive phenolic resin molding material according to any of (1) to (4) above, wherein the conductive carbon-based substrate is graphite. (6) 4 to 22 parts by weight of dimethylene ether type resole phenolic resin, based on 100 parts by weight of the entire molding material,
The conductive phenol resin molding material according to any one of (1) to (5) above, which contains 94 to 76 parts by weight of a conductive carbon-based substrate. (7) Dimethylene ether type resole phenolic resin 1
The conductive phenolic resin molding material according to any one of the above (1) to (6), wherein 0.05 to 2 parts by weight of an amine-based curing agent is mixed with 00 parts by weight. (8) A fuel cell separator obtained by molding the conductive phenolic resin molding material according to any one of (1) to (7) above.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive phenol resin molding material of the present invention (hereinafter referred to as "molding material") and the fuel cell separator using the same will be described in detail below.
The molding material of the present invention contains a dimethylene ether type resole phenolic resin, a conductive carbon-based substrate, and an amine-based curing agent as essential components. The fuel cell separator of the present invention is formed by molding the molding material. First, the molding material of the present invention will be described.

The dimethylene ether type resole phenolic resin (hereinafter referred to as dimethylene ether type resole resin) used in the molding material of the present invention has a phenol nucleus-bonding functional group composed of a methylene group, a methylol group and a dimethylene ether group. It is what is done. The ratio of each of these functional groups is not particularly limited, but is 20
It is preferably -50 mol%, 10-20 mol%, and 40-60 mol%. When the ratio of each functional group is within the above range, the flow channel structure of the fuel cell separator, which is a molded product, can be molded with high precision, and sufficient mechanical strength can be imparted to the molded product. If the ratio of each binding functional group is out of the above range, for example, if the ratio of the methylol group is higher than the upper limit value, the fluidity of the molding material becomes low, and the cured product has a high crosslink density, so that the molded product Becomes brittle, and cracks and chips easily occur.

The amount of free phenol contained in the dimethylene ether type resole resin is not particularly limited, but is preferably 7% by weight or less. Free phenol, when the dimethylene ether type resole resin is cured, acts as a cross-linking agent when a methylol group is once added to the free phenol to condense, and has the effect of improving the strength of the molded product, If the content exceeds the above upper limit value, it will be gasified at the time of curing to form a volatilization path, which may be a factor to increase the gas permeability of the fuel cell separator.

Further, the molecular weight of the dimethylene ether type resole resin is not particularly limited, but the number average molecular weight excluding free phenol is preferably 800 to 1200. By setting the number average molecular weight within this range, good moldability can be obtained when molding the molding material. If the number average molecular weight is less than the lower limit, shrinkage may occur due to curing shrinkage at the time of molding, while if it exceeds the upper limit, the fluidity tends to decrease, and in any case, the moldability and the molded product May affect the machining accuracy of the groove.

The dimethylene ether type resole resin is solid at room temperature and can be cured by condensation by heating. A general resol-type phenol resin has a methylol group as a main functional group, and a cured product thereof has a high cross-linking density, so that the rigidity may be reduced and brittle, but the dimethylene ether-type resol resin used in the present invention is The cured product has many dimethylene ether bonds between the cross-linking points in the resin skeleton, so that it has flexibility, and it is possible to accurately form a complicated and narrow channel structure of the fuel cell separator, Sufficient mechanical strength can be imparted to the molded product. In the present invention, the phenol nucleus-bonding functional group of the dimethylene ether type resole resin can be analyzed by NMR or ICPMS.

The method for producing such a dimethylene ether type resole resin is not particularly limited, but generally, the reaction molar ratio of formaldehyde (F) to phenol (P) (F / P) is 1 or more, and preferably Is 1.0
To 2.0 and the addition reaction is carried out using a divalent metal salt catalyst such as zinc acetate. At this time, the dehydration step is carried out at a low temperature to solidify the methylol group, which is a reactive functional group, while preserving it, whereby the desired dimethylene ether type resole resin is obtained. Such a dimethylene ether type resole resin has a form in which the resin is dissolved in an organic solvent such as methyl ethyl ketone or ethyl acetate, and is not particularly limited to a solid form. As the resin to be added to the molding material of the present invention, the dimethylene ether type resole resin is used as an essential component,
In addition to this, a novolac-type phenol resin and other resol-type phenol resins may be used in combination as long as the objects and effects of the present invention are not impaired, and these cases are also included in the present invention.

A carbon-based substrate having conductivity (hereinafter referred to as "carbon-based substrate") is added to the molding material of the present invention in order to impart conductivity. 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 in graphite as a mineral calculated naturally,
Of these, natural graphite is excellent in conductivity. Regarding artificial graphite, there are those obtained by heat-treating coal-based coke and those obtained by heat-treating petroleum-based coke, and there are scaly, needle-like, lump-like, spherical, agglomerates, etc. as the shape, but any of them is X. The c-axis (002) layer surface distance (d ₀₀₂ ) obtained by the lattice constant precision method by line analysis is 0.335 to 0.4.
In the range of 60 nm, the true specific gravity is 2.04 to 2.34.
It is preferably in the range of.

Further, examples of the carbon-based base material other than graphite include carbon fiber and carbon black, which may contain amorphous carbon. Carbon fibers and carbon black are dispersed in the resin phase to act as a conductive auxiliary agent, and in the case of carbon fibers, the shape has the effect of improving mechanical properties such as bending strength and toughness. Are blended as needed.

Next, the contents of the dimethylene ether type resole resin and the carbonaceous base material will be described. The molding material of the present invention is not particularly limited, but the dimethylene ether type resole resin 4 to 2 is used with 100 parts by weight of the whole molding material.
It is preferable to contain 2 parts by weight and 94 to 76 parts by weight of a conductive carbon-based substrate. More preferably, it is 8 to 20 parts by weight of a dimethylene ether type resole resin, and 90 to 78 parts by weight of a conductive carbon-based substrate. By setting the content within this range, the moldability of the molding material and the electrical characteristics and mechanical strength of the molded product can be secured. If the content of the dimethylene ether type resole resin is less than the lower limit value or the content of the carbon-based base material exceeds the upper limit value, sufficient fluidity cannot be ensured during molding, and a precise shape is molded. Can be difficult. It is considered that this is because the resin does not have the volume necessary to sufficiently fill the spaces between the graphite particles, and as a result, the mechanical strength of the molded product may be affected. On the other hand, when the content of the dimethylene ether type resole resin exceeds the upper limit value or the content of the carbon-based base material falls below the lower limit value, the conductivity of the molded article decreases, and a fuel cell separator suitable for practical use. Can be difficult to obtain. It is considered that this is because the increase in the resin volume causes the graphite particles to aggregate with each other, resulting in the formation of a non-conductive phase portion and a decrease in conductivity. In such a system containing a large amount of resin phase, the combined use of the above-mentioned carbon fiber and carbon black also has a small effect.

As described above, the molding material using the dimethylene ether type resole resin has excellent moldability, and the cured product thereof has flexibility and is suitable for a fuel cell separator. When compared with conventional resol type phenolic resins, the curing reactivity during molding tends to be low. Therefore, an amine-based curing agent is added to the molding material of the present invention as a curing aid to improve the curability. In the present invention, by adding an amine-based curing agent to the molding material, compared with the case of using an alkaline earth metal hydroxide, which is a general curing aid for phenolic resins, the curability can be improved by adding a very small amount. It has been found to be effective in improving. this is,
It is thought that one of the reasons is that the amine-based curing agent is strongly alkaline, and furthermore, the effect can be expressed with the addition of a very small amount, so that the mechanical strength of the molded product is lowered and the catalyst when used as a fuel cell separator. It also has the advantage of having a very small effect on problems such as poison.

The amine-based curing agent to be added to the molding material of the present invention is not particularly limited. For example, ethylenediamine (EDA), diethylenetriamine (DETA),
Triethylenetetramine (TETA), Mensendiamine (MDA), 4,4-Diaminodiphenylmethane (D
DM), metaphenylenediamine (DPDA), diaminodiphenylsulfone (DDS), triethylamine, benzyldimethylamine, 1,8-diazabiscyclo (5,4,0) undecene-1 (DBU), pyrazole, benzotriazole, triazole, etc. Can be mentioned. In addition, 2-methylimidazole, 2-undecylimidazole, 2-ethyl-4-methylimidazole, 2
-Phenyl-4-methylimidazole, 2,4'-diamino-6- [2'-ethyl-4'-methylimidazolyl- (1 ')] ethyl-s-triazine, 2-methylimidazole-isocyanuric acid adduct, An imidazole compound such as a 2-methylimidazole / trimellitic acid adduct can also be used. Among the amine-based curing agents, 1
Among some kinds of compounds, there are those in which two or more kinds of primary, secondary, and tertiary amino groups coexist, and these can be used like other amine-based curing agents. Further, those which form a salt with another compound in order to improve the storage stability can be similarly used. Of these, the use of an imidazole compound is preferable because it has good thermal stability with a dimethylene ether type resole resin and is chemically stable because nitrogen is incorporated into the cyclic skeleton. it is conceivable that.

The amount of the amine-based curing agent to be added is not particularly limited, but is preferably 0.05 to 2 parts by weight, more preferably 0.05 to 0.02 parts by weight based on 100 parts by weight of the dimethylene ether type resole resin. 8 parts by weight. By using an amine-based curing agent in a blending amount within such a range,
It is possible to effectively improve the curability of the molding material without affecting the characteristics of the molded fuel cell separator. If the compounding amount of the amine-based curing agent is less than the lower limit value, the effect of improving the curability becomes small, while if it exceeds the upper limit value, the curability becomes faster and the moldability decreases, and a catalyst poison when used as a separator. Or electrical deterioration may be affected.

In addition to the dimethylene ether type resole resin, the carbon-based base material and the amine-based curing agent as described above, the molding material of the present invention may be used within a range not deviating from the objects and effects of the present invention. As a molding material, a plasticizer or a release agent generally used can be used. In this case, as the plasticizer, a linear compound having a functional group reactive with a phenolic hydroxyl group and having a molecular weight of about 500 to 2000 (for example, epoxidized polyethylene), or a low boiling point organic solvent such as methanol or acetone as a volatile solvent. Etc. can be used. Further, as the release agent, a generally used polyvalent organic acid can be used.

The molding material of the present invention can be manufactured by a conventional method. That is, the raw materials are blended in a predetermined amount, pre-mixed using a ribbon blender or a planetary mixer, and then melt-kneaded using a heating roll or a twin-screw kneader, which is further granulated or crushed after cooling.・
A molding material can be obtained through operations such as classification. Further, the amine-based curing agent and the like can be mixed or kneaded with other raw materials after being diluted or dissolved with a solvent as needed.

Next, the fuel cell separator of the present invention will be described.
And explain. The fuel cell separator of the present invention is
By molding the molding material described in 1.
Is what you get. The molding material of the present invention is used as a fuel cell separator.
When molding into a mortar, compression molding or transfer
Mold by molding. When using compression molding, molded products
Mold the preform according to the shape of and mold this
Therefore, the moldability can be assisted. Use preforms
An example of the compression molding that has been mentioned is a pressure of 50 to 400 kg.
/ Cm ²Preliminary at a temperature of 20-70 ℃ and time of 0.1-2 minutes
A shaped product is molded and the pressure is further increased to 200-1500 kg.
/ Cm²Temperature 150 to 200 ° C, time 1 to 30 minutes
Obtain a fuel cell separator molded product by shaping
be able to.

[0023]

EXAMPLES The present invention will be described below with reference to examples.

[Synthesis of Phenolic Resin] 1. Phenol (P) and formaldehyde (F) were charged at a molar ratio (F / P) = 1.7 into a reaction kettle equipped with a phenol resin reflux condenser stirrer, a heating device, and a vacuum dehydrator, and zinc acetate was added thereto. Was added to 100 parts by weight of phenol. The pH of this reaction system was adjusted to 5.5, and the reflux reaction was carried out for 3 hours. Then, unreacted phenol was removed by performing steam distillation at a vacuum degree of 100 Torr and a temperature of 100 ° C. for 2 hours, and further reacted at a vacuum degree of 100 Torr and a temperature of 115 ° C. for 1 hour to obtain a phenol resin. 2. A phenol resin was obtained by performing the same reaction as in Example 1 except that the pH of the phenol resin reaction system was adjusted to 6.5. 3. A phenol resin was obtained by carrying out the reaction in the same manner as in Example 1 except that the pH of the phenol resin reaction system was adjusted to 8.5.

Phenolic resin synthesized by the above method
For, the ratio of the phenol nucleus-bonded functional group was determined by NMR, the amount of free phenol was determined by gas chromatography, and the number average molecular weight excluding free phenol was determined by GPC. The characteristics of the obtained phenol resin are shown in Table 1.

[0026]

[Table 1]

[Preparation of Molding Material] (1) Examples 1 to 4 As shown in Table 2, a phenol resin, carnauba wax as a release agent, and 2 as an amine-based curing agent were used.
-Methylimidazole was blended, artificial graphite and carbon black were added thereto, and mixed with a Henschel mixer to obtain a raw material mixture. These raw material mixtures were melt-kneaded with a heating kneader at 80 ° C. for 10 minutes and then taken out and pulverized into granules to obtain a molding material. (2) Comparative Example 1 As shown in Table 2, a phenol resin, carnauba wax as a mold release agent, 2-methylimidazole as an amine-based curing agent were mixed, and artificial graphite and carbon black were added thereto, and a Henschel mixer was added. To obtain a raw material mixture. These raw material mixtures were melt-kneaded with a heating kneader at 80 ° C. for 10 minutes and then taken out and pulverized into granules to obtain a molding material. (3) Comparative Examples 2-3 As shown in Table 2, a phenol resin and carnauba wax as a release agent were used, artificial graphite and carbon black were added thereto, and mixed with a Henschel mixer to obtain a raw material mixture. These raw material mixtures were melt-kneaded with a heating kneader at 80 ° C. for 10 minutes and then taken out and pulverized into granules to obtain a molding material.

[Evaluation of Conductivity] The molding material was compression-molded at a mold temperature of 170 ° C., a molding pressure of 200 kg / cm ² , and a molding time of 3 minutes to obtain 80 × 80 × 15 mm samples 3 and 8.
A sample 4 of 0 × 80 × 5 mm was obtained. Using these samples, the resistance in the penetrating direction was measured by the method shown in FIG. 1 to evaluate the conductivity. That is, two samples 3 and 4 having different thicknesses
The combination was set on the electrode 1 via the carbon paper 2, and the specific resistance in the penetrating direction was determined from the resistance values when the molded bodies had different thicknesses. J as comparison data
Volume resistivity was also measured according to IS K 7194.

[Evaluation of various characteristics as material for separator] The molding material was molded at a mold temperature of 170 ° C. and a molding pressure of 200.
300 × 3 by compression molding at kg / cm ² and molding time 3 minutes
A molded product having a size of 00 × 2 mm was obtained. From this, a test piece was cut out, created, and evaluated. (1) Flexural strength and flexural modulus were measured according to JIS K7203. (2) Gas permeability is measured according to JIS K71 using nitrogen gas.
It was measured by the 26A method.

[Evaluation of Moldability] (1) The monohole fluidity was measured according to JIS K6911. (2) Curability: Mold temperature 170 ° C., molding pressure 200 kg
/ Cm ² , 300 × 300 after compression molding with molding time of 3 minutes
A molded product having a size of × 2 mm was obtained. When this was taken out by hand, the one having rigidity that could be taken out was marked with ◯, and the one that could not retain its shape when taken out was marked with x.

Table 2 shows the blending of the molding materials of Examples and Comparative Examples and the evaluation results of molded products. In addition, all the numerical values showing the compounding amount of the molding material represent "parts by weight".

[Table 2] [Note of table] (1) Carnauba wax: Toa Kasei (2) Artificial graphite: Nippon Graphite Co., Ltd., PAG-120 (3) Carbon black: Mitsubishi Chemical, Ketchin black EC

From Tables 1 and 2, Examples 1 to 4 are
It is a molding material in which a phenol resin, which is a dimethylene ether type resole resin, a carbon-based base material, and an amine-based curing agent are mixed in a predetermined ratio, and has good fluidity. The molded product obtained by molding these had good electrical properties, mechanical properties, gas permeability, and curability. On the other hand, in Comparative Example 1, a phenol resin having no dimethylene ether bond was used, but the fluidity was lowered and the mechanical properties and gas permeability were inferior. Further, in Comparative Examples 2 and 3, the phenol resin was used, but the amine-based curing agent was not used, so that the curability was insufficient.

[0033]

INDUSTRIAL APPLICABILITY The present invention is a conductive phenol resin molding material containing a dimethylene ether type resole resin having a predetermined phenol nucleus-bonding functional group, a carbon base material, and an amine curing agent as essential components. The fuel cell separator is excellent in fluidity at the time and exhibits good moldability, and the fuel cell separator obtained by molding the same has excellent electrical characteristics and mechanical characteristics. Therefore, the molding material of the present invention and the fuel cell separator obtained by molding the same are useful as those capable of exhibiting excellent characteristics in the usage environment of the fuel cell.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method for measuring a through-direction resistivity in an example of the present invention.

[Explanation of symbols]

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

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Claims (8)

[Claims] 1. A conductive phenolic resin molding material comprising a dimethylene ether type resole phenolic resin, a conductive carbon-based base material, and an amine-based curing agent as essential components. 2. A dimethylene ether type resole phenolic resin has a phenol nucleus-bonding functional group composed of a methylene group, a methylol group, and a dimethylene ether group, and the molar ratio of each functional group is 20 to 50%, respectively. ~ 2
The conductive phenolic resin molding material according to claim 1, which is 0% or 40 to 60%. 3. The conductive phenolic resin molding material according to claim 1, wherein the dimethylene ether type resole phenolic resin has a free phenol content of 7% by weight or less. 4. The dimethylene ether type resole phenolic resin has a number average molecular weight excluding free phenol of from 800 to 800.
The conductive phenolic resin molding material according to any one of claims 1 to 3, which is 1200. 5. The conductive phenolic resin molding material according to claim 1, wherein the conductive carbon-based substrate is graphite. 6. A total of 100 parts by weight of the molding material, 4 to 22 parts by weight of a dimethylene ether type resole phenolic resin, and 94 to 76 parts by weight of a carbonaceous base material having conductivity. The conductive phenolic resin molding material according to any one of 1. 7. An amine-based curing agent 0.05 per 100 parts by weight of a dimethylene ether type resole phenolic resin.
The conductive phenolic resin molding material according to any one of claims 1 to 6, which is compounded in an amount of 2 to 2 parts by weight. 8. A fuel cell separator obtained by molding the conductive phenolic resin molding material according to claim 1. Description: