Separator for fuel cells

Abstract

This separator for fuel cells, which is obtained by molding a resin composition that contains a graphite powder having a cumulative particle diameter distribution d10 of 10-20 μm and a volume porosity of 12-30 cm3 / 100 g as measured by ASTM D6086 at a measurement pressure of 30 MPa, and an epoxy resin component containing a main agent, a curing agent, and a curing accelerator, is excellent in terms of hydrogen gas impermeability, electrical conductivity, and mechanical characteristics even if obtained by compression molding in a short time.

Description

Fuel cell separators

[0001] The present invention relates to a separator for a fuel cell.

[0002] Fuel cell separators provide electrical conductivity to each unit cell, ensure passage for fuel and air (oxygen) to be supplied to the unit cells, and act as a boundary wall separating them. For this reason, separators are required to have various properties, such as high electrical conductivity, high gas impermeability, chemical stability, heat resistance, and hydrophilicity.

[0003] Regarding the improvement of these properties, for example, Patent Document 1 proposes a fuel cell separator that can suppress gas permeability while improving both mechanical strength and electrical conductivity by welding and integrating a plurality of composite sheets and a resin composition. Also, Patent Document 2 proposes a fuel cell separator that suppresses gas permeation by including a plate containing granular or fibrous graphite and granular or fibrous resin as constituent materials and a barrier layer that has better gas barrier properties than the plate.

[0004] However, although the fuel cell separator of Patent Document 1 suppresses gas permeability by welding and integrating multiple composite sheets and a resin composition, the hydrogen gas permeability coefficient at a measurement temperature of 80°C is 1.1 × 10 -13 ~6.8 x 10 -13 mol m / m 2 On the other hand, in Patent Document 2, although the gas impermeability is suppressed by providing a barrier layer with excellent gas barrier properties, the separator requires a long molding time of 1 to 6 minutes, resulting in poor production efficiency.

[0005] JP 2020-145014 A International Publication No. 2023 / 286332

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a fuel cell separator that has excellent hydrogen gas impermeability, electrical conductivity, and mechanical properties even when compression molded in a short period of time.

[0007] As a result of extensive research into achieving the above object, the inventors have discovered that by using a composition containing graphite powder having predetermined physical properties and an epoxy resin component, a fuel cell separator having excellent hydrogen gas impermeability, electrical conductivity, and mechanical properties can be obtained even when compression molded in a short period of time, and have completed the present invention.

[0008] That is, the present invention provides a porous silica particle having a cumulative particle size distribution d10 of 10 to 20 μm and a volume porosity measured by ASTM D6086 of 12 to 30 cm when pressurized with a measurement pressure of 30 MPa. 3 1. A fuel cell separator characterized by being formed by molding a resin composition containing graphite powder having a powder resistivity of less than 3.0 mΩ cm when measured at a pressure of 30 MPa, and an epoxy resin component containing a base resin, a curing agent, and a curing accelerator; 2. A fuel cell separator according to item 1, wherein the graphite powder has a powder resistivity of less than 3.0 mΩ cm when measured at a pressure of 30 MPa; 3. A fuel cell separator according to item 1, wherein the graphite powder has a springback of 13 to 50%; 4. A fuel cell separator according to item 1, wherein the base resin of the epoxy resin is at least one selected from cresol novolac epoxy resins and biphenyl epoxy resins; 5. A fuel cell separator according to item 1, wherein the curing agent of the epoxy resin is a novolac phenolic resin; 6. A fuel cell separator according to item 1, wherein the curing accelerator comprises an imidazole compound having a phenyl group at the 2-position; 7. A fuel cell separator according to item 1, wherein the resin composition comprises 20 to 42 parts by mass of the epoxy resin component per 100 parts by mass of the graphite powder; 8. The hydrogen permeability coefficient at a measurement temperature of 80°C is 1.7 x 10 -16 mol m / m 2 Less than Pa·sec and specific resistance of 23 mΩ·cm 2 8. A fuel cell separator according to any one of 1 to 7, having a bending strength of 44 MPa or more and a bending modulus of elasticity of less than 13 GPa; 9. A fuel cell separator according to any one of 1 to 7, having a cumulative particle size distribution d10 of 10 to 20 μm and a volume void ratio measured by ASTM D6086 of 12 to 30 cm when pressurized with a measurement pressure of 30 MPa. 3The present invention provides a method for producing a separator for a fuel cell, which comprises compression molding a resin composition containing graphite powder (weight: 100g / 100g) and an epoxy resin component containing a base resin, a curing agent, and a curing accelerator, for a compression time of 40 seconds or less.

[0009] The fuel cell separator of the present invention uses a composition containing graphite powder that is easy to compress and has a low volume porosity, and therefore has excellent hydrogen gas impermeability, electrical conductivity, and mechanical properties even when compression-molded for a short time of 40 seconds or less. Furthermore, by using graphite powder with low powder resistivity, the electrical conductivity of the resulting fuel cell separator can be further improved. Furthermore, by using graphite powder with a predetermined springback (elastic recovery), the mechanical properties of the resulting fuel cell separator can be further improved. In particular, a fuel cell separator using graphite powder that combines the three properties of predetermined springback, volume porosity, and powder resistivity has excellent hydrogen gas impermeability, electrical conductivity, and mechanical properties even when compression-molded for a short time of 30 seconds or less.

[0010] FIG. 1 is a schematic side view of a die used in measuring springback of graphite powder.

[0011] The present invention will be described in more detail below. The fuel cell separator according to the present invention has a cumulative particle diameter distribution d10 of 10 to 20 μm and a volume porosity measured by ASTM D6086 of 12 to 30 cm when pressurized at a measurement pressure of 30 MPa. 3 The molded product is characterized by being formed from a resin composition containing graphite powder in an amount of 100 g / 100 g, and an epoxy resin component containing a base resin, a curing agent, and a curing accelerator.

[0012] In the present invention, the cumulative particle size distribution d10 of the graphite powder is 10 to 20 μm, preferably 12 to 16 μm, and more preferably 13 to 15 μm. If the average particle size d10 is less than 10 μm, the epoxy resin tends to cover the surface of the graphite powder, reducing the contact area between the particles and thereby deteriorating the conductivity of the separator itself. On the other hand, if the average particle size d10 exceeds 20 μm, the contact area between the graphite particles and the epoxy resin decreases, potentially resulting in poor gas impermeability of the separator. Note that the average particle size d10 in the present invention is a value measured wet using a particle size distribution analyzer (MT3000, manufactured by Microtrac-Bell Co., Ltd.).

[0013] The volumetric porosity of graphite powder measured by ASTM D6086 is 30 cm when the measurement pressure is 30 MPa. 3 A volume void ratio of 30 cm3 or less is preferable because sufficient gas impermeability can be obtained. 3 If the volume porosity exceeds 12 m / s, a large amount of resin is required to fill the gaps between the particles of graphite powder, which may result in poor conductivity of the separator. 3 If the void volume ratio is less than 100 g / 100 g, the graphite powder will be packed too densely, which may result in a loss of flexibility of the separator. Note that the void volume ratio in the present invention is a value measured at a pressure of 30 MPa using a DVV400 manufactured by Micromeritics Instruments Corporation.

[0014] From the viewpoint of further increasing the electrical conductivity, the powder resistivity of the graphite powder is preferably less than 3.0 mΩ cm when measured at a pressure of 30 MPa. If the powder resistivity is 3.0 mΩ cm or more, the amount of resin added must be reduced to obtain electrical conductivity in the fuel cell separator, which may result in poor gas impermeability of the separator. Note that, although a lower powder resistivity is preferable, the lower limit is usually about 1.0 mΩ cm.

[0015] The springback of the graphite powder is preferably 13 to 50% from the viewpoint of further improving gas impermeability, flexibility, and productivity. If the springback exceeds 50%, the gaps between the graphite powder particles are difficult to collapse during separator molding, which may result in poor gas impermeability of the separator. Furthermore, if the springback value is less than 13%, the flexibility and strength of the separator may be impaired. On the other hand, if the springback of the graphite powder exceeds 50%, it takes time to collapse the gaps between the graphite powder particles, which may result in poor productivity of fuel cell separators. Note that the springback in the present invention refers to the springback of the powder itself, and specifically, as described in detail in the Examples below, it is a value calculated by (Y-X) / X x 100(%), where X is the height of the powder when the powder is placed in a predetermined mold and compressed under a predetermined pressure, and Y is the height of the powder when the pressure is released.

[0016] The graphite powder used in the present invention is not particularly limited in type, as long as it satisfies the volume porosity measured by ASTM D6086. Either natural graphite or artificial graphite may be used. Examples of artificial graphite include artificial graphite obtained by calcining needle coke, artificial graphite obtained by calcining lump coke, spheroidized artificial graphite, and artificial graphite whose surface is treated with a non-graphite layer such as pitch coating. Examples of natural graphite include flake natural graphite, soil graphite, spheroidized natural graphite, and natural graphite whose surface is treated with a non-graphite layer such as pitch coating. In any case, the volume porosity of these graphite powders may be measured, and those falling within the range specified in the present invention may be appropriately selected. These graphite powders may be used alone or in combination of two or more.

[0017] The base resin constituting the epoxy resin component is not particularly limited as long as it has an epoxy group, and examples thereof include o-cresol novolac epoxy resins, phenol novolac epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, biphenyl aralkyl epoxy resins, trisphenol epoxy resins, brominated epoxy resins, dicyclopentadiene epoxy resins, and biphenyl novolac epoxy resins, which can be used alone or in combination of two or more. Among these, o-cresol novolac epoxy resins alone, biphenyl epoxy resins alone, and mixtures thereof are preferred.

[0018] The curing agent constituting the epoxy resin component is not particularly limited as long as it is a phenolic resin, and specific examples thereof include novolac phenolic resins, cresol novolac phenolic resins, resol phenolic resins, aralkyl-modified phenolic resins, biphenyl novolac phenolic resins, trisphenolmethane phenolic resins, etc. These may be used alone or in combination of two or more. Among these, novolac phenolic resins are preferred.

[0019] The curing accelerator constituting the epoxy resin component is not particularly limited as long as it accelerates the reaction between the epoxy group and the curing agent, and examples thereof include phosphine compounds, amine compounds, and imidazole compounds. Among these, in the present invention, it is preferable to use an imidazole compound having an aryl group at the 2-position. Specific examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group, with a phenyl group being preferred. Specific examples of imidazole compounds having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. Note that when an imidazole compound having a short-chain alkyl group such as 2-methylimidazole is used as a curing accelerator, the curing time may be too fast to achieve uniform molding, while when an imidazole compound having a long-chain alkyl group such as 2-undecylimidazole is used, the curing time may be too slow to achieve uniform molding.

[0020] In addition to the above components, the composition used in the present invention may also contain optional components such as an internal mold release agent. The internal mold release agent may be appropriately selected from various internal mold release agents that have conventionally been used in molding separators, and specific examples thereof include stearic acid waxes, amide waxes, montanic acid waxes, carnauba waxes, and polyethylene waxes, which may be used alone or in combination of two or more.

[0021] In the composition used in the present invention, the amount of the epoxy resin components (base, curing agent, and curing accelerator) is not particularly limited, but is preferably 20 to 42 parts by weight, more preferably 27 to 35 parts by weight, and even more preferably 30 to 33 parts by weight, of the epoxy resin component per 100 parts by weight of graphite powder. In this case, the curing agent is preferably blended in an amount of 0.98 to 1.08 equivalents, more preferably 0.99 to 1.05 equivalents, relative to the base component. The amount of the curing accelerator used is also not particularly limited, but is preferably 0.1 to 5.0 parts by weight, more preferably 0.5 to 2.0 parts by weight, relative to 100 parts by weight of the mixture of the base component and curing agent. By using the epoxy resin component in this range, the fluidity of the molding material becomes appropriate, improving moldability, and the resulting fuel cell separator also exhibits improved gas impermeability and electrical conductivity. When an internal mold release agent is used, the amount used is not particularly limited, but is preferably 0.01 to 3.0 parts by mass, more preferably 0.05 to 1.5 parts by mass, per 100 parts by mass of graphite powder.

[0022] The composition used in the present invention may be prepared, for example, by mixing graphite powder, a base agent, a curing agent, and a curing accelerator in predetermined proportions in any order. For this purpose, a mixer such as a planetary mixer, ribbon blender, Loedige mixer, Henschel mixer, rocking mixer, or Nauta mixer can be used. When an internal release agent is used, the order of mixing the ingredients is also arbitrary.

[0023] The fuel cell separator of the present invention is preferably produced by placing the above-described composition in a predetermined mold and compression molding it. Examples of the mold used include a mold for producing fuel cell separators, capable of forming grooves serving as gas flow paths on one or both surfaces of the molded body. The compression molding conditions are not particularly limited, but include a mold temperature of 150 to 190°C and a molding pressure of 30 to 60 MPa, preferably 30 to 50 MPa. The compression molding time is not particularly limited and can be set appropriately from about 3 seconds to 1 hour. However, a short time is preferable from the viewpoint of production efficiency, specifically, 40 seconds or less is preferred, and 30 seconds or less is more preferred. In particular, in the present invention, by using the above-described spring-bag graphite powder, a fuel cell separator with excellent properties can be obtained even when molded for a short time of 30 seconds or less. After compression molding, the product may be further heated at 150 to 200°C for 1 to 600 minutes to promote thermal curing.

[0024] In the present invention, the fuel cell separator (molded body) obtained by the compression molding may be subjected to a surface roughening treatment for the purpose of removing the skin layer, adjusting the surface roughness, etc. The surface roughening method is not particularly limited and may be appropriately selected from various conventionally known surface roughening methods such as blasting and polishing, but air blasting, wet blasting, barrel polishing, and brush polishing are preferred, blasting using abrasive grains is more preferred, and wet blasting is even more preferred.

[0025] In this case, the average particle size (d=50) of the abrasive grains used in the blasting treatment is preferably 3 to 30 μm, more preferably 4 to 25 μm, and even more preferably 5 to 20 μm. The material of the abrasive grains used in the blasting treatment is not particularly limited, and for example, alumina, silicon carbide, zirconia, glass, nylon, stainless steel, etc. can be used, each of which can be used alone or in combination of two or more. The discharge pressure during the wet blasting treatment cannot be generally specified because it varies depending on the particle size of the abrasive grains, etc., but is preferably 0.1 to 1.0 MPa, more preferably 0.15 to 0.5 MPa.

[0026] In the fuel cell separator of the present invention, in order to maintain hydrogen impermeability while reducing the thickness of the fuel cell separator, the hydrogen permeability coefficient at a measurement temperature of 80° C. is set to 1.7×10 -16 mol m / m 2 Pa sec or less is preferable, and 1.5 × 10 -16 mol m / m 2 The smaller the hydrogen permeability coefficient, the better. However, the lower limit is usually 0.1×10 -16 mol m / m 2 .Pa.sec. In order to achieve better power generation performance of the fuel cell, the specific resistance is preferably less than 23 mΩ cm, and more preferably 20 mΩ cm or less. The lower the specific resistance, the better, but the lower limit is usually about 5.0 mΩ cm. Furthermore, the bending strength is preferably 44 MPa or more, and the bending modulus is preferably less than 13 GPa. The upper limit of the bending strength is not particularly limited, but is preferably 100 MPa or less, and the lower limit of the bending modulus is not particularly limited, but is preferably 5.0 GPa or more.

[0027] A fuel cell equipped with the fuel cell separator of the present invention having these properties can maintain stable power generation efficiency over a long period of time. Generally, a solid polymer fuel cell is composed of a large number of unit cells arranged side by side, each unit cell being composed of a pair of electrodes sandwiching a solid polymer membrane and a pair of separators sandwiching the electrodes to form gas supply and discharge channels. The fuel cell separator of the present invention can be used as some or all of these multiple separators.

[0028] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Physical properties in the examples were measured by the following methods.

[0029] [1] Cumulative particle size distribution d10 was measured wet using a particle size distribution measuring device (MT3000 manufactured by Microtrac Bell Co., Ltd.). [2] Void volume ratio The void volume ratio at a pressure of 30 MPa was measured using a DVV400 manufactured by Micromeritics Instruments Corporation. [3] Springback 2 g of graphite powder, the measurement sample, was placed in a mold with an inner diameter of 15 mm as shown in FIG. 1 (A), and the upper surface of the sample was flattened. Then, the upper mold was compressed with a press so that a load of 5.4 t was applied in 5 seconds (see FIG. 1 (B)). The compressed state was maintained for 30 seconds, and the load was released all at once. The height of the upper mold surface in each state was measured using a height gauge, and springback was calculated using the following formula. L0: Height of upper die without sample (mm) L1: Height of upper die under load (mm) L2: Height of upper die without load (mm) Springback (%) = (L2 - L1) / (L1 - L0) x 100 [4] Powder Resistivity Powder resistivity was measured at a pressure of 30 MPa using a powder resistivity measurement system (MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.). [5] Hydrogen Permeability Coefficient Hydrogen permeability was measured at a measurement temperature of 80°C using differential pressure gas chromatography in accordance with JIS K 7126-1 (differential pressure method). [6] Resistivity Measured based on JIS H0602 (Method for measuring resistivity of silicon single crystals and silicon wafers using four probes). [7] Strength Test (Bending Strength, Bending Modulus) A 100 × 20 × 2 mm test piece cut out from the separator was subjected to a three-point bending test with a support distance of 40 mm in accordance with JIS K 6911 "General Test Methods for Thermosetting Plastics" to measure the bending strength and bending modulus.

[0030] Example 1: 100 parts by mass of graphite powder 1 (with the following physical properties), 20.4 parts by mass of epoxy resin 1 (o-cresol novolac type, epoxy equivalent 198 g / eq), 10.8 parts by mass of phenolic resin (novolac type, hydroxyl group equivalent 104 g / eq), and 0.25 parts by mass of 2-phenylimidazole were added to a Henschel mixer and mixed at 800 rpm for 3 minutes to prepare a resin composition for a fuel cell separator. The resulting composition was placed in a mold for producing a fuel cell separator and compression-molded under conditions of a mold temperature of 185°C, a molding pressure of 36.6 MPa, and a molding time of 15 seconds to obtain a dense molded article having gas flow channel grooves and measuring 240 mm x 240 mm x 2 mm. Next, the entire surface of the obtained dense molded body was subjected to a surface roughening treatment by wet blasting using an alumina abrasive (average particle size: d50 = 6 μm) under conditions of a discharge pressure of 0.25 MPa and a conveying speed of 1.5 m / min, thereby obtaining a fuel cell separator.

[0031] Graphite powder 1: artificial graphite, acicular Cumulative particle diameter distribution d10: 13.0 μm Volume void ratio: 17.8 cm 3 / 100g Springback: 30.1% Powder resistance: 2.32mΩ cm

[0032] Example 2 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 2 having the following physical properties, to obtain a fuel cell separator.

[0033] Graphite powder 2: artificial graphite, lumpy Cumulative particle size distribution d10: 14.9 μm Volume void ratio: 13.7 cm 3 / 100g Springback: 36.8% Powder resistance: 2.42mΩ cm

[0034] [Example 3] A composition was prepared in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 3 having the physical properties described below. Further, a fuel cell separator was obtained by compression molding in the same manner as in Example 1, except that the molding time was changed from 15 seconds to 30 seconds.

[0035] Graphite powder 3: artificial graphite, lumpy Cumulative particle size distribution d10: 19.5 μm Volume void ratio: 29.6 cm 3 / 100g Springback: 45.8% Powder resistance: 2.97mΩ cm

[0036] Example 4 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 4 having the following physical properties, to obtain a fuel cell separator.

[0037] Graphite powder 4: artificial graphite, acicular, coated with a non-graphite layer on the surface. Cumulative particle size distribution d10: 11.1 μm. Volume void ratio: 12.5 cm 3 / 100g Springback: 29.9% Powder resistance: 1.80mΩ cm

[0038] Example 5 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 5 having the following physical properties, to obtain a fuel cell separator.

[0039] Graphite powder 5: natural graphite, flake-like Cumulative particle size distribution d10: 11.0 μm Volume void ratio: 13.0 cm 3 / 100g Springback: 15.3% Powder resistance: 2.98mΩ cm

[0040] Example 6 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was replaced with a combination of graphite powder 2 (80 parts by mass) and graphite powder 4 (20 parts by mass), to obtain a fuel cell separator.

[0041] Example 7 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was replaced with a combination of graphite powder 2 (60 parts by mass) and graphite powder 4 (40 parts by mass), to obtain a fuel cell separator.

[0042] Example 8 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was replaced with a combination of graphite powder 3 (80 parts by mass) and graphite powder 5 (20 parts by mass), to obtain a fuel cell separator.

[0043] Example 9 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was replaced with a combination of graphite powder 3 (60 parts by mass) and graphite powder 5 (40 parts by mass), to obtain a fuel cell separator.

[0044] Example 10 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 2 (80 parts by mass) and graphite powder 9 (20 parts by mass) having the physical properties described below, to obtain a fuel cell separator.

[0045] Graphite powder 9: artificial graphite, acicular Cumulative particle diameter distribution d10: 18.5 μm Volume void ratio: 10.2 cm 3 / 100g Springback: 14.1% Powder resistance: 1.53mΩ cm

[0046] Example 11 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 2 (60 parts by mass) and graphite powder 9 (40 parts by mass), to obtain a fuel cell separator.

[0047] Example 12 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 2 (80 parts by mass) and graphite powder 10 (20 parts by mass) having the physical properties described below, to obtain a fuel cell separator.

[0048] Graphite powder 10: natural graphite, spherical, surface coated with a non-graphite layer. Cumulative particle size distribution d10: 10.2 μm. Volume void ratio: 32.6 cm 3 / 100g Springback: 20.0% Powder resistance: 1.64mΩ cm

[0049] Example 13 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 2 (60 parts by mass) and graphite powder 10 (40 parts by mass), to obtain a fuel cell separator.

[0050] Example 14 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 4 (40 parts by mass) and graphite powder 10 (60 parts by mass), to obtain a fuel cell separator.

[0051] Example 15 A composition was prepared in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 11 having the physical properties shown below, and a fuel cell separator was obtained by compression molding in the same manner as in Example 1, except that the molding time was changed from 15 seconds to 31 seconds. Note that a fuel cell separator could not be obtained when the compression molding time was 30 seconds or less.

[0052] Graphite powder 11: artificial graphite, lumpy Cumulative particle size distribution d10: 12.4 μm Volume void ratio: 29.9 cm 3 / 100g Springback: 50.2% Powder resistance: 2.56mΩ cm

[0053] Example 16 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 12 having the following physical properties, to obtain a fuel cell separator.

[0054] Graphite powder 12: natural graphite, flake-like Cumulative particle size distribution d10: 10.4 μm Volume porosity: 12.1 cm 3 / 100g Springback: 13.9% Powder resistance: 3.03mΩ cm

[0055] Comparative Example 1 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 6 having the following physical properties, to obtain a fuel cell separator.

[0056] Graphite powder 6: artificial graphite, acicular Cumulative particle diameter distribution d10: 5.80 μm Volume void ratio: 12.7 cm 3 / 100g Springback: 25.1% Powder resistance: 5.22mΩ cm

[0057] Comparative Example 2 A composition was prepared in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 7 having the following physical properties, and a fuel cell separator was obtained by compression molding in the same manner as in Example 1, except that the molding time was changed from 15 seconds to 70 seconds. Note that a fuel cell separator could not be obtained when the compression molding time was 40 seconds or less.

[0058] Graphite powder 7: artificial graphite, lumpy Cumulative particle size distribution d10: 25.4 μm Volume void ratio: 35.2 cm 3 / 100g Springback: 55.8% Powder resistance: 1.99mΩ cm

[0059] Comparative Example 3 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 8 having the following physical properties, to obtain a fuel cell separator.

[0060] Graphite powder 8: artificial graphite, acicular Cumulative particle diameter distribution d10: 30.6 μm Volume void ratio: 40.2 cm 3 / 100g Springback: 31.2% Powder resistance: 2.01mΩ cm

[0061] Comparative Example 4 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 9 having the following physical properties, to obtain a fuel cell separator.

[0062] Graphite powder 9: artificial graphite, acicular Cumulative particle diameter distribution d10: 18.5 μm Volume void ratio: 10.2 cm 3 / 100g Springback: 14.1% Powder resistance: 1.53mΩ cm

[0063] Comparative Example 5 A composition was prepared and compression molded in the same manner as in Example 1, except that graphite powder 1 was changed to graphite powder 10 having the following physical properties, to obtain a fuel cell separator.

[0064] Graphite powder 10: natural graphite, spherical, surface coated with a non-graphite layer. Cumulative particle size distribution d10: 10.2 μm. Volume void ratio: 32.6 cm 3 / 100g Springback: 20.0% Powder resistance: 1.64mΩ cm

[0065] Comparative Example 6 A composition was prepared and compression-molded in the same manner as in Example 1, except that graphite powder 1 (100 parts by mass) was changed to a combination of graphite powder 4 (40 parts by mass) and graphite powder 6 (60 parts by mass), to obtain a fuel cell separator.

[0066] Example 17 A composition was prepared and compression molded in the same manner as in Example 1, except that the blending amount of epoxy resin 1 in Example 1 was changed from 20.4 parts by mass to 14.4 parts by mass, the blending amount of phenol resin in Example 1 was changed from 10.8 parts by mass to 7.7 parts by mass, and the blending amount of 2-phenylimidazole in Example 1 was changed from 0.25 parts by mass to 0.20 parts by mass, to obtain a fuel cell separator.

[0067] Example 18 A composition was prepared and compression molded in the same manner as in Example 1, except that the blending amount of epoxy resin 1 in Example 1 was changed from 20.4 parts by mass to 26.0 parts by mass, the blending amount of phenol resin in Example 1 was changed from 10.8 parts by mass to 13.9 parts by mass, and the blending amount of 2-phenylimidazole in Example 1 was changed from 0.25 parts by mass to 0.36 parts by mass, to obtain a fuel cell separator.

[0068] Example 19 A composition was prepared and compression molded in the same manner as in Example 1, except that in Example 1, 20.4 parts by mass of Epoxy Resin 1 was changed to 21.0 parts by mass of Epoxy Resin 2, the blending amount of the phenol resin was changed from 10.8 parts by mass to 13.4 parts by mass, and the blending amount of 2-phenylimidazole was changed from 0.25 parts by mass to 0.31 parts by mass, to obtain a fuel cell separator.

[0069] Epoxy resin 2: biphenyl type epoxy resin Epoxy equivalent: 165 g / eq

[0070] Example 20 A composition was prepared and compression-molded in the same manner as in Example 1, to obtain a fuel cell separator, except that in Example 1, 20.4 parts by mass of Epoxy resin 1 was replaced with a combination of 11.0 parts by mass of Epoxy resin 1 and 10.0 parts by mass of Epoxy resin 2, the amount of phenol resin was changed from 10.8 parts by mass to 12.3 parts by mass, and the amount of 2-phenylimidazole was changed from 0.25 parts by mass to 0.30 parts by mass.

[0071] Example 21 A composition was prepared and compression molded in the same manner as in Example 1, except that the blending amount of epoxy resin 1 in Example 1 was changed from 20.4 parts by mass to 13.1 parts by mass, the blending amount of phenol resin from 10.8 parts by mass to 7.0 parts by mass, and the blending amount of 2-phenylimidazole from 0.25 parts by mass to 0.19 parts by mass, to obtain a fuel cell separator.

[0072] Example 22 A composition was prepared and compression molded in the same manner as in Example 1, except that the blending amount of epoxy resin 1 in Example 1 was changed from 20.4 parts by mass to 27.0 parts by mass, the blending amount of phenol resin in Example 1 was changed from 10.8 parts by mass to 14.4 parts by mass, and the blending amount of 2-phenylimidazole in Example 1 was changed from 0.25 parts by mass to 0.37 parts by mass, to obtain a fuel cell separator.

[0073] The hydrogen permeability coefficient, resistivity, flexural strength, and flexural modulus were measured for the fuel cell separators produced in Examples 1 to 22 and Comparative Examples 1 to 6. The results are shown in Tables 1 and 2. Table 1 also shows the physical properties of the graphite powder used, and Table 2 also shows the blending amount of the epoxy resin component.

[0074]

[0075]

[0076] As shown in Tables 1 and 2, the fuel cell separators of Examples 1 to 22 obtained from the fuel cell separator resin compositions within the range specified in the present invention had a hydrogen permeability of 1.7 × 10 at a measurement temperature of 80°C even when the molding time was as short as 40 seconds or less, specifically 15 to 31 seconds. -16 mol m / m 2 It can be seen that the specific resistance is less than 23 mΩ·cm, the bending strength is 44 MPa or more, and the bending modulus is less than 13 GPa, which are suitable values ​​for a fuel cell separator.

Claims

1. The cumulative particle size distribution d10 is 10 to 20 μm, and the volume void ratio measured by ASTM D6086 is 12 to 30 cm when the measurement pressure is 30 MPa. 3 1. A separator for a fuel cell, comprising: a resin composition including graphite powder having a weight of 100 g / 1000 g; and an epoxy resin component including a base agent, a curing agent, and a curing accelerator.

2. A fuel cell separator according to claim 1, wherein the graphite powder has a powder resistivity of less than 3.0 mΩ·cm when measured at a pressure of 30 MPa.

3. The fuel cell separator according to claim 1, wherein the spring back of said graphite powder is 13 to 50%.

4. The fuel cell separator according to claim 1, wherein the base epoxy resin is at least one selected from the group consisting of cresol novolac type epoxy resins and biphenyl type epoxy resins.

5. The fuel cell separator according to claim 1, wherein the hardener for said epoxy resin is a novolac type phenolic resin.

6. The fuel cell separator according to claim 1, wherein the curing accelerator comprises an imidazole compound having a phenyl group at the 2-position.

7. The fuel cell separator according to claim 1, wherein the resin composition contains 20 to 42 parts by mass of the epoxy resin component per 100 parts by mass of the graphite powder.

8. The hydrogen permeability coefficient at a measurement temperature of 80°C is 1.7 x 10 -16 mol m / m 2 Less than Pa·sec and specific resistance of 23 mΩ·cm 2 The fuel cell separator according to any one of claims 1 to 7, wherein the average molecular weight of the fuel cell separator is less than 1000g.

9. The fuel cell separator according to any one of claims 1 to 7, which has a bending strength of 44 MPa or more and a bending modulus of elasticity of less than 13 GPa.

10. The cumulative particle size distribution d10 is 10 to 20 μm, and the volume void ratio measured by ASTM D6086 is 12 to 30 cm when the measurement pressure is 30 MPa. 3 A method for producing a fuel cell separator, comprising compression molding a resin composition containing graphite powder having a mass of 100 g / 100 g and an epoxy resin component containing a base agent, a curing agent, and a curing accelerator for a compression time of 40 seconds or less.

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