JP2003049049A - Resin composition for fuel battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin composition for a fuel battery separator having excellent resistance to electrical deterioration, and electroconductivity without damaging the moldability to improve a resin composition for the fuel battery separator in which the coexistence of the moldability and the high electroconductivity has been conventionally difficult. SOLUTION: This resin composition for the fuel battery separator consists essentially of (A) 4-24 pts.wt. resol-type phenol resin and (B) 96-76 pts.wt. carbonaceous base material having electroconductivity based on 100 pts.wt. total of the composition. The resol-type phenol resin has phenol nuclear-bound functional groups consisting of methylene group, methylol group and dimethylene ether group, and the proportions of the constituting functional groups are regulated so as to be 20-50 mol%, 10-20 mol% and 40-60 mol%, respectively.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a resin composition for a fuel cell separator.

[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, cutting or polishing. A method that includes a machining step (eg,
Japanese Patent Laid-Open No. 2000-169230), or a method of using a metal resin composite as a material such as forming a groove on a metal plate and then performing resin coating (for example, Japanese Patent Laid-Open No. 11-345618, New Energy Industry). It has been attempted to be created by the Japan Society for Technology Development, 2000 summary report of research and development results of polymer electrolyte fuel cells, P70). However, the method that requires the graphitization process and the machining process cannot reduce the cost because it is difficult to develop to mass production, while the method that uses the grooved metal plate resin composite as the material is used. In the environment, the problem of delamination at the interface layer between metal and resin and the corrosion problem of the metal plate 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 a carbon base material such as graphite or carbon black is used as a binder component with a thermosetting resin such as a general phenol resin, an epoxy resin, or a polyester resin, or a thermosetting resin such as polypropylene. Attempts have been made with molding materials that are highly compounded with plastic resins and the like.

In this method, increasing the graphite compounding ratio in the molding material in order to obtain high conductivity as the separator and increasing the resin compounding ratio in order to improve the moldability are contradictory factors. Therefore, resin selection and design are important points. Among them, thermosetting resins such as phenol resin and epoxy resin are excellent in various points such as heat resistance, mechanical strength, and electrical stability, and the base resin can be selected from low molecular weight, so It has been studied (Japanese Patent Laid-Open No. 11-204120).

When a phenol resin is used, it is difficult to use hexamethylenetetramine-cured novolac-type phenol resin because residual ammonia accompanying the curing becomes a catalyst poison of the platinum-based proton exchange catalyst which is the catalyst of the fuel cell. Resole type phenolic resin will be used.However, in general, in resole type phenolic resin, since the methylol group is retained and the low molecular weight is retained, the activation energy is low and the reactivity as a resin is high, so that the moldability of the resin is high. The width is small. For this reason, it is difficult to develop and adjust a material capable of accurately forming a complicated shape such as a fuel cell separator with a general resol resin.
Further, when an epoxy resin is used, there is a problem of catalyst poison or electrical deterioration due to residual unreacted curing agent or curing accelerator which is an essential component. , A curing accelerator system is being studied,
No effective method has been proposed yet.

[0005]

SUMMARY OF THE INVENTION The present invention has been made for a resin composition for a fuel cell separator in which it is difficult to achieve both the moldability and high conductivity as described above, and its object is The purpose is to provide a resin composition for a fuel cell separator, which is excellent in electrical deterioration resistance and conductivity without impairing moldability.

[0006]

According to the present invention, (1) a phenol nucleus-bonding functional group is composed of a methylene group, a methylol group, and a dimethylene ether group, based on 100 parts by weight of the whole composition. The ratio of 20 to 50
4 to 24 parts by weight of a resole type phenolic resin (A), which is mol%, 10 to 20 mol%, and 40 to 60 mol%;
A resin composition for a fuel cell separator, which contains 96 to 76 parts by weight of a conductive carbon-based base material (B) as an essential component, and (2) a resole-type phenol resin (A) is a free phenol amount. Is 7% by weight or less, the resin composition for a fuel cell separator according to the item (1),
(3) The resin composition for a fuel cell separator according to item (1) or (2), wherein the resol type phenol resin (A) has a number-average molecular weight excluding free phenol of 800 to 1200.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The resol type phenol resin (A) used in the present invention (hereinafter, "resol type phenol resin" is referred to as "resole resin") has a phenol nucleus-bonding functional group of methylene group, methylol group, And a dimethylene ether group, and the ratio of each functional group is 2
It is characterized in that it is 0 to 50 mol%, 10 to 20 mol%, and 40 to 60 mol%. Further, the amount of free phenol is preferably 7% by weight or less, and the number average molecular weight excluding free phenol (hereinafter, abbreviated as Mn) is 800 to 1200.
Is preferred. Such a resole resin is solid at room temperature and can be cured by condensation by heating. A cured product of a general resol resin having a methylol group as a main functional group has a high crosslink density and generally tends to be brittle, but a cured product of the resol resin used in the present invention has a dimethylene ether bond between crosslinking points. The presence of a large number of particles makes it possible to accurately form a flexible, complex, and narrow flow channel structure of the fuel cell separator. The phenol nucleus-bonding functional group in the resol resin can be analyzed by NMR or ICPMS.

The free phenol contained in the resole resin acts as a cross-linking agent when a methylol group is once added to the phenol to condense when the resole resin cures and improves the strength of the molded product. Although effective, if the content exceeds 7% by weight, it will be gasified during curing to form a volatilization path, which may be a factor to increase the gas permeability of the fuel cell separator. Also, Mn is 80
When it is less than 0, sink marks are likely to be generated due to curing shrinkage at the time of molding, and when Mn exceeds 1200, fluidity tends to decrease, and in any case, it may affect the moldability and groove processing accuracy. is there.

As such a resole resin, there is also a so-called liquid resin in the form of a varnish in which the resin is dissolved in an organic solvent such as methyl ethyl ketone or ethyl acetate. When used in the present invention, the solvent is removed in a step. It is preferable to use a solid resin so that it is not necessary. Generally, such a resole resin having many dimethylene ether bonds has a ratio of formaldehyde to phenol (reaction molar ratio) of 1 or more, an addition reaction is performed by a weak acid catalyst, and the dehydration step is performed at a low temperature. It is obtained by solidifying while protecting the methylol group which is a reactive functional group.

The electrically conductive carbon-based substrate (B) used in the present invention means a carbon material such as graphite, carbon fiber or carbon black. Among the carbon materials, those having excellent conductivity have grown graphite structures, and natural or artificial graphite corresponds to this. There are scaly graphite called natural graphite and soil graphite, which are naturally calculated minerals. Among them, natural graphite is excellent in conductivity. Regarding artificial graphite, there are one that heat-treats coal-based coke and one that heat-treats petroleum-based coke, and the shape is scaly,
There are needles, lumps, spheres, aggregates, etc., all of which are c-axis (00
2) Distance between layers (d ₀₀₂ ) is 0.335 to 0.460n
It is sufficient that the true specific gravity is in the range of 2.04 to 2.34 in the range of m.

Amorphous carbon may be contained in the carbon fiber and carbon black which are other carbonaceous base materials having conductivity. Carbon fibers and carbon black disperse in the resin phase and act as a conduction aid, and in the case of carbon fibers, the shape has the effect of improving mechanical properties such as bending and toughness. Blended accordingly.

Next, the compounding amounts of the resol resin (A) and the carbon-based base material (B) will be described. In the present invention,
Resol resin (A) based on 100 parts by weight of the entire composition
Is added in an amount of 4 to 24 parts by weight, and the carbon-based base material (B) having conductivity is added in an amount of 96 to 76 parts by weight.
With such a blending amount, the moldability and the electrical conductivity and mechanical strength of the molded product can be secured. If the compounding amount of the resole resin (A) is less than 4 parts by weight or the compounding amount of the carbon-based base material (B) exceeds 96 parts by weight, sufficient fluidity cannot be secured at the time of molding and a precise shape is formed. Difficult to do. 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, it becomes difficult to secure the strength of the molded body. On the other hand, when the compounding amount of the resole resin (A) exceeds 24 parts by weight or the compounding amount of the carbon-based base material (B) is less than 76 parts by weight, the conductivity is lowered, and a separator suitable for practical use is obtained. Becomes difficult.
It is considered that this is because the increase in the resin volume causes the graphite particles to agglomerate 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.

In the present invention, in addition to the resol resin (A) and the carbon-based base material (B) as described above, a plasticizer or a release agent generally used as a molding material 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 500 to 2000, or a low boiling point organic solvent such as methanol or acetone is used as a volatile solvent. As the release agent, generally used polyvalent organic acids, metal salts or amide compounds are used.

The raw material mixture as described above is formed into a molding material by a method of mixing or kneading, and is molded into a fuel cell separator by compression molding or injection molding. In the case of compression, preforming may be performed in a shape suitable for the molded product to assist the moldability.

The phenol resin used in the present invention uses the resole resin (A) as an essential component. However, as long as the object and effects of the present invention are not impaired, a novolac type phenol resin and other resole type phenol resins are used in combination. However, these cases are also included in the present invention.

[0016]

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

[Synthesis of Phenolic Resin] 1. Phenol resin Formaldehyde (F) and phenol (P) were put into a 2 liter flask at F / P = 1.7, and PH was adjusted to 5.5 using zinc naphthenate and oxalic acid, and stirred at 120 rpm to 4 Reacted for hours. Next, at atmospheric pressure 120
After dehydration temperature rise to ℃, 160 while dehydration under reduced pressure
After the temperature was raised to 0 ° C., it was taken out from the flask to obtain a phenol resin. 2. The pH was adjusted to 6.5 during the phenol resin reaction. A phenol resin was obtained in the same manner as the phenol resin except for the above. 3. The pH was adjusted to 8.5 during the phenol resin reaction. A phenol resin was obtained in the same manner as the phenol resin except for the above. 4. The pH was adjusted to 7.5 during the phenol resin reaction, and the reaction time was 2 hours. A phenol resin was obtained in the same manner as the phenol resin except for the above. 5. Phenol resin PR-51470 (Novolak type phenol resin) manufactured by Sumitomo Bakelite Co., Ltd. was used.

With respect to the above-synthesized phenol resins, the ratio of phenol nucleus-bonded functional groups was determined by NMR, and the amount of free phenol was determined by gas chromatography.
The number average molecular weight was determined by GPC. The characteristics of the obtained phenol resin are shown in Table 1. The phenol resin is a normal novolac type phenol resin.

[0019]

[Table 1]

[Preparation of molding material] (1) Examples 1 to 3 As shown in Table 2, a phenol resin was used as a phenol resin, and carnauba wax was used as a release agent. Black was added 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 Examples 1 to 3, phenolic resin, and
Carnauba wax was used as a release agent, and 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 a material for a 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 Formability] (1) The monohole fluidity was measured according to JIS K6911. (2) Measurement of groove depth accuracy With respect to the molding materials of Examples and Comparative Examples, the width was 1.0 mm, the depth was 0.5 mm, and the length was 160, which corresponds to the fuel cell separator.
A molded product obtained by processing 49 channels of 2.0 mm pitch with 2.0 mm pitch was used. The molded product is a 800 ton press manufactured by Uetaki Co., Ltd. as a molding machine, the mold temperature is 175 ° C., the molding pressure is 800 k
It was molded by compression molding at gf / cm ² and molding time of 2 minutes. The measurement target groove of the molded product is the 4th to 7th pitch (7 pitches in this period) to 46th groove (7 in total). For each groove, measure 3 points in the center in the length direction and 10mm inside from both ends. As points, 7 × 3 = 21 points were measured.
In the measuring method, the difference between the central portion in the width direction of the groove and the central portion of the adjacent flat portion was defined as the groove depth, and the groove depth accuracy was determined by the following formula. The measuring equipment is OLYMPUS STM6-L
M measuring microscope was used. Accuracy of groove depth = (Σ _{i = 1} ^{i = 21} (di−dav) ² ) ^0.5 dav: average value of groove depth at 21 points di: groove depth at i-th position

[0024]

[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, since all of Examples 1 to 3 use the molding material in which the resole resin containing a large amount of dimethylene ether bond and graphite are blended at an appropriate ratio, the electrical characteristics of the molded product are obtained. The mechanical properties, gas permeability, and groove depth accuracy were all good. On the other hand, in Comparative Example 1, when a resin having no dimethylene ether bond was used, the groove depth accuracy was lowered. Further, in Comparative Example 2, since the proportion of dimethylene ether bond group was low, and the molecular weight was slightly small and the amount of free phenol was large,
The groove depth accuracy decreased and the gas permeability also increased slightly. Then, in Comparative Example 3, a part of the resin used in Comparative Example 2 was replaced with a novolac type phenol resin, but the same tendency as in Comparative Example 2 was obtained. In each of Comparative Examples 1 to 3, the electrical characteristics and bending strength were slightly reduced.

[0026]

The present invention is characterized in that 4 to 24 parts by weight of a resole resin having many dimethylene ether bonds and 96 to 76 parts by weight of a carbonaceous base material having conductivity are essential components. Since it is a resin composition for a separator, and a molded article of the composition of the present invention has excellent conductivity and moldability, it 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 in an example of the present invention.

[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 (3)

[Claims] 1. A phenol nucleus-bonding functional group is composed of a methylene group, a methylol group, and a dimethylene ether group, and the ratio of each functional group is 20 to 50 mol%, based on 100 parts by weight of the entire composition. 10 to 20 mol% and 40 to 60 mol% of the resole type phenolic resin (A) 4 to 24 parts by weight and a conductive carbon-based base material (B) 96 to 76 parts by weight are contained as essential components. A resin composition for a fuel cell separator, comprising: 2. The resin composition for a fuel cell separator according to claim 1, wherein the resol type phenol resin (A) has an amount of free phenol of 7% by weight or less. 3. The resin composition for a fuel cell separator according to claim 1, wherein the resol type phenolic resin (A) has a number average molecular weight excluding free phenol of 800 to 1200.