WO2016063983A1 - Fuel-cell porous separator, fuel cell, and method for manufacturing fuel-cell porous separator - Google Patents

Abstract

A fuel-cell porous separator according to the present invention is formed of a composition including a resin material and a carbonaceous material, wherein the content of the carbonaceous material accounts for 80-95 mass% of the total mass of the carbonaceous material and the resin material, and fine pores with a fine-pore diameter of 1.5-4.0 μm account for 90 vol% or more in a fine-pore distribution of the fuel-cell porous separator as measured by the mercury intrusion method.

Description

Porous separator for fuel cell, fuel cell, and method for producing porous separator for fuel cell

The present invention relates to a porous separator for a fuel cell, a fuel cell, and a method for producing a porous separator for a fuel cell.
This application claims priority based on Japanese Patent Application No. 2014-216178 filed in Japan on October 23, 2014, the contents of which are incorporated herein by reference.

A fuel cell is a clean power generation device that uses hydrogen and oxygen to generate power through the reverse reaction of water electrolysis, and does not emit any other substances than water. Therefore, it is attracting attention from the viewpoint of environmental issues and energy issues. Fuel cells are classified into several types depending on the type of electrolyte used. Among fuel cells, a polymer electrolyte fuel cell that operates at a low temperature is considered most promising for automobiles and consumer use. This fuel cell is usually a membrane electrode assembly (MEA :) formed by integrating a solid polymer membrane acting as a solid polymer electrolyte and a gas diffusion electrode carrying a pair of catalysts sandwiching the solid polymer membrane. The basic unit is a single cell having a Membrane-Electrode Assembly) and a separator that is sandwiched from the outside of the MEA and separates fuel gas and oxidant gas. Then, by stacking a large number of single cells, high power generation can be achieved in the fuel cell.

In a fuel cell having such a structure, a fuel gas (hydrogen, etc.) and an oxidant gas (oxygen, etc.) are usually supplied to a separator for partitioning a single cell, and product gas and surplus gas are carried away. Gas flow paths (grooves) are provided. Therefore, the separator is required to have high gas impermeability capable of completely separating these gases and high conductivity in order to reduce the internal resistance. Furthermore, the separator is required to have excellent thermal conductivity, durability, strength, and the like.

In order to achieve these requirements, both fuel cell separators using metallic materials and carbonaceous materials have been studied. Among these materials, a fuel cell separator using a metal material has a problem in terms of corrosion resistance. In order to solve the problem, attempts have been made to coat the surface with a noble metal or carbon. However, sufficient durability cannot be obtained, and the cost of coating becomes a problem.

In contrast, fuel cell separators using carbonaceous materials are lighter and have the advantage of not corroding, and are being studied. Fuel cell separators using such carbonaceous materials include solid separators and porous separators. The solid separator is formed by completely sealing a carbonaceous material having conductivity with a resin material, and neither gas nor water permeates. Therefore, the solid separator is mainly used for an external humidification type fuel cell. On the other hand, the porous separator is formed by connecting carbonaceous materials with a small amount of resin binder and having micro pores therein, and is therefore mainly used for an internal humidification type fuel cell.

In external humidification type fuel cells using solid separators, it is necessary to humidify the reaction gas using a humidifier in order to swell the solid polymer membrane and impart proton conductivity. In the internal humidification type fuel cell, the cooling water can be permeated into the power generation unit via the separator and humidified. In addition, since the pores inside the porous separator are filled with cooling water, gas barrier properties against fuel gas, oxidant gas, generated gas and the like are also exhibited. Therefore, it is not necessary to install a humidifier, and research on an internal humidification type fuel cell is underway.
However, since the porous separator maintains its shape by joining carbonaceous materials with a resin binder, it is difficult to obtain sufficient strength. Further, when the amount of the resin binder is increased in order to obtain strength, there is a problem that high water permeability cannot be obtained. Therefore, there is a demand for a porous separator for a fuel cell that has both conductivity and strength and is highly uniform.

For example, Patent Document 1 describes a porous separator for a fuel cell that includes a resin material containing an epoxy resin having a predetermined porosity and a carbon material powder. However, although the porosity with respect to the whole is described, the distribution of the pore diameter is not described, and it cannot be said that the uniformity is high.
Patent Document 2 describes a hydrophilic porous material having a specific pore radius and porosity.
Furthermore, Patent Document 3 describes a water moving plate having pores having a size equal to or smaller than a predetermined pore diameter.

JP2013-0669605A JP 2006-004920 A Special table 2002-518815 gazette

However, conventional porous separators for fuel cells have failed to realize a porous separator for fuel cells that achieves both conductivity and strength and is highly uniform.

As a result of the intensive studies by the inventors, it has been found that the porous separator for a fuel cell has a large variation in pore diameter distribution within the surface of one molded body. This is presumably because the porous separator needs to be press-molded at a pressure lower than the pressure for forming the solid separator in order to maintain the porous structure. With this in-plane variation, there is a problem that the conductivity and strength are reduced.
In addition, if the pore diameter distribution varies in the plane, gas leakage occurs from the location where the pore diameter is large, so that the gas seal pressure decreases. In addition, water absorption is good where the pore diameter is large, and water absorption is poor where the pore diameter is small, resulting in variations in water absorption within the surface, which reduces power generation performance when used as a fuel cell. Connected.

The present invention is intended to solve the above-described problems, and an object of the present invention is to provide a porous separator for a fuel cell that has both conductivity and strength and is highly uniform.

The inventors of the present invention have made extensive studies to solve the above problems.
As a result, it is possible to provide a porous separator for a fuel cell that achieves both conductivity and strength and has high uniformity by keeping the pore density within a predetermined range and keeping the volume fraction of the carbonaceous material constant. As a result, the inventors have found that the present invention can be accomplished.

(1) A porous separator for a fuel cell according to one aspect of the present invention is a porous separator for a fuel cell formed by using a composition containing a resin material and a carbonaceous material, and the carbonaceous material In addition, the content of the carbonaceous material in the total mass of the resin material is 80 to 95% by mass, and among all the pores in the pore distribution determined by the mercury intrusion method, the pore diameter is 1.5 to 4. The pore which is 0 μm is 90 vol% or more.

(2) In the porous separator for a fuel cell according to (1), the resin material is poly (1,2-butadiene), epoxy-modified polybutadiene, hydroxyl-modified polybutadiene, maleic acid-modified polybutadiene, acrylic-modified polybutadiene, amine One kind selected from the group consisting of modified polybutadiene and hydrogen-modified polybutadiene may be included.

(3) A fuel cell according to an aspect of the present invention includes the porous separator for a fuel cell according to the above (1) or (2).

(4) A method for producing a porous separator for a fuel cell according to one aspect of the present invention includes a curable resin composition in which at least a resin material and a carbonaceous material are mixed, and the content of the carbonaceous material is 80 to 95% by mass. A mixing step for preparing a product, a sheeting step for converting the composition obtained by mixing into a green sheet having an in-plane variation of the sheet thickness within 10% of the average thickness of the sheet thickness, and sheeting And a pressing step of forming the green sheet obtained in the step.

(5) In the method for producing a porous separator for a fuel cell according to (4) above, even if the thickness of the green sheet is 1.1 times or more and 2 times or less with respect to the mold thickness during the pressing step. Good.

(6) In the method for producing a porous separator for a fuel cell according to any one of (4) and (5), in the sheet forming step, the temperature of the green sheet is equal to or higher than a temperature at which condensation does not occur and the resin is cured. It is good also as below the temperature which does not.

(7) In the method for producing a porous separator for a fuel cell according to any one of (4) to (6), the green sheet is heated at a temperature of 150 to 240 ° C. in the pressing step. Also good.

(8) In the method for producing a porous separator for a fuel cell according to any one of (4) to (7), the green sheet may be pressurized at a pressure of 2 to 25 MPa in the pressing step. Good.

The porous separator for a fuel cell according to one embodiment of the present invention has a carbonaceous material content of 80 to 95% by mass in the total mass of the carbonaceous material and the resin material, and is obtained by a mercury intrusion method. In the pore distribution of the fuel cell porous separator, the pores having a pore diameter of 1.5 to 4.0 μm are 90 vol% or more. Since the ratio of the carbonaceous material in the fuel cell porous separator is large, high conductivity can be maintained.
Also, the pore diameters are uniform and in-plane with little variation. Therefore, there are few defects in the interior during molding, and high strength can be realized. Furthermore, since there is little variation in pore diameter, there is little variation in air permeability. When used as a separator for a fuel cell, problems such as a decrease in gas seal pressure and deterioration in water absorption can be suppressed.

Since the fuel cell according to an embodiment of the present invention uses a porous separator for a fuel cell that has both conductivity and strength and high uniformity, a fuel cell having high power generation performance can be realized.

A method for producing a porous separator for a fuel cell according to an embodiment of the present invention includes a curable resin composition in which at least a resin material and a carbonaceous material are mixed, and the content of the carbonaceous material is 80 to 95% by mass. A mixing step of preparing, and a sheeting step of forming the composition obtained by mixing into a green sheet having an in-plane variation of the sheet thickness within 10% of the average thickness of the sheet. Therefore, the pore diameter of the porous separator for a fuel cell can be set within a predetermined range, and both the conductivity and strength of the obtained porous separator for a fuel cell are compatible, and the porous separator for a fuel cell has higher uniformity. Can be produced.

It is a cross-sectional schematic diagram of the fuel cell concerning one Embodiment of this invention. 1 is a porous separator for a fuel cell according to an embodiment of the present invention, (a) is a schematic diagram of a configuration of a porous separator for a fuel cell, and (b) is a surface SEM (scanning) of the porous separator for a fuel cell. Type electron microscope) image (× 250 times). The in-plane variation of the air permeability of the porous separator for fuel cells of Example 1 and Comparative Example 1 is shown. The in-plane bending strength and specific resistivity of the porous separator for a fuel cell of Example 1 and Comparative Example 1 are shown. The result of having measured the pore distribution of the porous separator for fuel cells concerning one Embodiment of this invention using the mercury intrusion method is shown. It is the cross-sectional schematic diagram which showed the measuring method of the gas seal pressure typically. The result of the air permeability variation with respect to the green sheet thickness variation in the pressing process is shown. The result of the average pore diameter of the porous separator for fuel cells obtained with respect to the green sheet thickness is shown. The result of the porosity of the porous separator for fuel cells obtained with respect to the green sheet thickness is shown. The result of the air permeability of the porous separator for fuel cells obtained with respect to the green sheet thickness is shown. It is the cross-sectional schematic diagram which showed typically the measuring method of water permeability.

Hereinafter, embodiments of the present invention will be described in detail. In addition, this invention is not limited only to the example shown below.

"Fuel cell"
FIG. 1 is a schematic cross-sectional view of a fuel cell 100 according to an embodiment of the present invention. The fuel cell 100 includes a power generation unit 20, a gas diffusion layer 30 disposed so as to sandwich the power generation unit 20, and a fuel cell porous separator (separator) 10 disposed so as to sandwich the gas diffusion layer 30. .
The fuel cell porous separator 10 can supply the water supplied from the cooling water 40 to the gas diffusion layer 30 to humidify the power generation unit 20. Further, since the porous separator 10 for a fuel cell has high in-plane uniformity of the pore diameter, there is no possibility that gas leaks from a specific location within the surface or only a specific location has high water absorption. Therefore, hydrogen gas and air supplied to the power generation unit 20 can be kept inside the fuel cell 100, and humidification of the power generation unit 20 can be made uniform.
That is, since the highly uniform porous separator 10 for fuel cells is used, the fuel cell 100 having high power generation performance can be realized.

The gas diffusion layer 30 has functions such as supplying hydrogen or air as a fuel to an electrode (catalyst), collecting electrons generated by a chemical reaction at the electrode, moisturizing the electrolyte membrane, and discharging generated water. The gas diffusion layer 30 is not particularly limited, and commonly used members can be used, and carbon paper, carbon cloth, and the like are preferably used.

Further, the power generation unit 20 is not particularly limited, and a structure generally used as a fuel cell can be used. Specifically, a structure in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an air electrode can be used. Moreover, what is generally used can be used suitably for a solid polymer electrolyte membrane, a fuel electrode, and an air electrode.

"Porous separator for fuel cells"
FIG. 2 (a) is a schematic view of the porous separator for fuel cells of the present invention, and FIG. 2 (b) is a surface SEM image (× 250 times) of the porous separator for fuel cells of the present invention.
As shown in FIG. 2A, the fuel cell porous separator 10 is formed by molding a composition including a resin material (resin component) 1 and a carbonaceous material 2. The carbonaceous materials 2 are bonded together by the resin material 1, and water can pass through these gaps (dotted line arrows). These gaps can also be confirmed from the surface SEM photograph of FIG. In the pore distribution of the fuel cell porous separator 10 obtained by the mercury intrusion method, the content of the carbonaceous material in the total mass of the carbonaceous material and the resin material is 80 to 95% by mass. The pores having a diameter of 1.5 to 4.0 μm are 90 vol% or more. Therefore, it is possible to realize the fuel cell porous separator 10 having both conductivity and strength and high uniformity. The content of the carbonaceous material can be calculated from the composition ratio of the carbonaceous material and the resin material and the respective densities.

The porous separator 10 for a fuel cell has a pore distribution obtained by mercury porosimetry of 90 vol% or more with a pore diameter of 1.5 to 4.0 μm. The pores having a diameter of 2.0 to 4.0 μm are preferably 90 vol% or more, and the pores having a diameter of 2.5 to 4.0 μm are more preferably 90 vol% or more.
In general, when the content of the carbonaceous material is increased in order to increase the conductivity, the strength of the porous separator for a fuel cell is decreased. However, in the pore distribution obtained by the mercury intrusion method of the fuel cell porous separator 10, if the pores having a pore diameter of 1.5 to 4.0 μm are 90 vol% or more, the whole is uniform, High strength can be obtained.
Furthermore, since there is little variation in the pore diameter, the air permeability is also less variation in the surface, and when used as a fuel cell separator, problems such as a decrease in gas seal pressure and deterioration in water absorption can be suppressed. In the pore distribution obtained by the mercury intrusion method, if the pores having a pore diameter of 1.5 to 4.0 μm are 90 vol% or more, gas leakage occurs from the large pore diameter in the plane. And good gas barrier properties can be secured. Moreover, if the variation in the pore diameter is large, the water absorption variation occurs in the surface, and the humidification of the fuel cell power generation unit varies, resulting in a decrease in power generation performance. However, when the pore distribution is in the above range, there is little variation in water absorption, and power generation performance can be maintained well.
The mercury intrusion method uses the high surface tension of mercury to apply pressure to inject mercury into the fine pores of the powder and determine the specific surface area and pore distribution from the pressure and the amount of mercury intruded. It is.

In the fuel cell porous separator 10, the volume ratio of all pores is preferably 12 to 25 vol%, more preferably 15 to 21 vol%, and further preferably 17 to 20 vol%. When the volume ratio is 12 vol% or more, sufficient water permeability can be secured. When the volume ratio is 25 vol% or less, the gas barrier property is good. In addition, the strength of the fuel cell porous separator 10 is sufficiently maintained.

The air permeability of the fuel cell porous separator 10 is such that 100 ml of air passes from the front surface to the back surface of the sample in the area of 6.4 cm ² (diameter 28.6 mm) of the fuel cell porous separator 10. It is obtained by measuring the time required. This measurement can be performed using a Gurley measuring device. The Gurley measuring instrument is mainly composed of a piston member that pushes air into a sample and a device that measures the time for which the pushed air passes through the sample. The air pressure at this time is 1.22 kPaG. In the examples described later, a Gurley type densometer manufactured by Toyo Seiki Seisakusho is used as the Gurley measuring instrument.
The air permeability when the thickness of the fuel cell porous separator 10 is 2 mm is preferably in the range of 150 to 600 s / 100 ml, more preferably in the range of 200 to 500 s / 100 ml, and 200 to 300 s / 100 ml. More preferably, it is in the range of 100 ml.
If the air permeability is in the range of 150 to 600 s / 100 ml, it means that there are so many pores and high water permeability can be obtained. When the water permeability is high, the pores in the fuel cell porous separator are filled with moisture, so that the gas barrier property is improved.

The variation in the air permeability of the fuel cell porous separator 10 is preferably within a range of ± 150 s / 100 ml, more preferably within a range of ± 100 s / 100 ml, and within a range of ± 50 s / 100 ml. Further preferred. If the variation in air permeability of the fuel cell porous separator 10 is in the range of ± 150 s / 100 ml, the in-plane variation of the fuel cell porous separator 10 is sufficiently small. If the variation in the in-plane air permeability is small, the in-plane pore distribution approaches a constant value, so that a homogeneous porous separator 10 for a fuel cell can be obtained. The variation in the air permeability depends on the area of the fuel cell porous separator 10, but when there is an area of 200 cm ² or more, for example, the result of each air permeability measured at any nine points in the plane. It can be expressed by the difference between the maximum value and the minimum value.

The resistivity in the thickness direction of the fuel cell porous separator 10 is preferably 30 mΩ · cm or less, more preferably 25 mΩ · cm or less, and further preferably 20 mΩ · cm or less. If the resistivity of the fuel cell porous separator is 30 mΩ · cm or less, sufficient conductivity can be ensured.

The bending strength of the fuel cell porous separator 10 is preferably 15 MPa or more, more preferably 20 MPa or more, and further preferably 25 MPa or more. When the bending strength is 15 MPa or more, the porous separator for fuel cells is not easily destroyed and exhibits high strength.

The bulk density of the fuel cell the porous separator 10 is preferably 1.4 ~ 1.8g / cm ^3, more preferably 1.55 ~ 1.75g / cm ^3. If the density of the fuel cell porous separator is within the above range, the optimum air permeability can be exhibited. Therefore, both water permeability and gas barrier properties are good.

The fuel cell porous separator 10 is preferably hydrophilized. More preferably, the inside of the fuel cell porous separator 10 is made hydrophilic. If the absorption performance when 5 μl of water is absorbed in the fuel cell porous separator 10 having a size of 100 mm × 200 mm is 0.1 to 15 seconds, it can be considered that it has been sufficiently hydrophilized. If the water absorption of the porous separator 10 for fuel cells is within the above range, the water absorption is sufficiently high, and the gas seal pressure in the water absorption state is also high. That is, both water permeability and gas barrier properties are good.

In addition, the fact that the inside of the fuel cell porous separator 10 has been hydrophilized means that the fluorine element in the depth direction from the surface of the fuel cell porous separator 10 using X-ray photoelectron spectroscopy (XPS). And it can confirm by measuring the content rate of an oxygen element. Content ratio of fluorine element and oxygen element on the surface of the communication hole in the central portion in the thickness direction of the porous separator for fuel cell 10 when the porous separator 10 for fuel cell is measured by X-ray photoelectron spectroscopy (XPS) Is preferably 10 at% or more. Moreover, it is more preferable that each of the fluorine element content ratio and the oxygen element content ratio is 5 at% or more. If the total content ratio of fluorine element and oxygen element on the surface of the communication hole in the central portion in the thickness direction of the fuel cell porous separator 10 is 10 at% or more, the fuel cell porous separator 10 is sufficiently hydrophilized. High water absorption and water permeability can be obtained.

Further, the method of hydrophilizing the inside of the fuel cell porous separator 10 is preferably exposed to a fluorine gas and oxygen gas-containing gas atmosphere, and the fuel cell porous separator obtained by the method has its inside. Any of a COF group, a CF group, and a COOH group is formed in the resin material existing on the surface of the pores. More specifically, by exposing to a gas containing fluorine gas and oxygen gas, the gas is introduced into the pores, and a part of the resin material that forms the pore surface is composed of COF groups, CF groups, Substituted by any group of COOH groups. Hydrophilization is realized by these groups, and the amount of fluorine element and the amount of oxygen element derived therefrom can be detected by X-ray photoelectron spectroscopy (XPS).
The COF group and the CF group are intermediate products that reach the COOH group, and these groups also contribute to the hydrophilization. As a form of use as a porous separator for a fuel cell, since these pores are filled with water, most of the COF groups and CF groups are hydrolyzed and converted to COOH groups during use. In order to confirm the hydrophilization performance before mounting on the fuel cell, the porous separator for the fuel cell is immersed in water, and many COF groups and CF groups are hydrolyzed in advance and replaced with COOH groups. It is preferable to keep it. The CF group means a state in which the H atom of the —C—H bond of the resin material is replaced with an F atom. It may be —CFH ₂ , —CF ₂ H, —CF ₃ or the like.
The bonding of these groups can be confirmed by determining the binding energy from X-ray photoelectron spectroscopy (XPS).

The porous separator 10 for fuel cells has various impurities such as metal elements, conductive ions, oils and fats as impurities inside. When the fuel cell porous separator 10 is used as a fuel cell separator, these various impurities may elute and adversely affect the power generation characteristics of the fuel cell. Therefore, it is preferable to suppress as much as possible the elution of impurities from the porous separator for fuel cells into water.

"Carbonaceous materials"
The content of the carbonaceous material 2 with respect to the total mass of the carbonaceous material 2 and the resin material 1 is in the range of 80 to 95% by mass. When the carbonaceous material 2 is 80% by mass or more, sufficient conductivity can be secured. Moreover, if it is less than 95% by mass, the fluidity of the green sheet, which is the workpiece in the press working described later, is good, and the plate thickness deviation of the molded fuel cell porous separator can be made sufficiently small. Moreover, since the thickness deviation of the green sheet formed in the sheet forming step described later can be sufficiently reduced, the pore diameter of the formed fuel cell porous separator can be made uniform in the plane. . In addition, in order to obtain a molded body with good thickness accuracy from a composition including the carbonaceous material 2 and the resin material 1, the green sheet is a predetermined temperature at a temperature at which curing does not start using an extruder, a roll, a calendar, or the like. It means a sheet-like molded product formed into a thickness and a width.

The size of the carbonaceous material 2 is preferably 3 μm to 150 μm, more preferably 5 μm to 100 μm, and even more preferably 10 μm to 80 μm. When the size of the carbonaceous material 2 is changed, the pore shape and the like of the porous separator for a fuel cell can be changed. When the average particle size (d50) of the carbonaceous material is 3 μm to 150 μm, the pore diameter distribution of the fuel cell porous separator obtained by the mercury intrusion method can be 1.0 to 5.0 μm. . When a porous separator for a fuel cell having the pore diameter is used for a fuel cell, high performance can be obtained.

Carbonaceous materials 2 include carbonaceous materials such as carbon black, carbon fibers (pitch-based, PAN-based), amorphous carbon, expanded graphite, quiche graphite, artificial graphite, natural graphite, vapor grown carbon fiber, carbon nanotube, fullerene, etc. 1 type, or 2 or more types of mixtures chosen from among these are mentioned. Among these, since carbon black has lower conductivity and filling properties than other materials, carbon fiber (pitch-based, PAN-based), amorphous carbon, expanded graphite, quiche graphite, artificial graphite, natural graphite, gas phase method One or a mixture of two or more selected from carbon fibers, carbon nanotubes, and fullerenes is preferred. In addition, when the carbonaceous material contains boron, a material having high conductivity is obtained, and among them, the artificial graphite containing boron can reduce impurities.

(Carbon black)
As carbon black which is an example of carbonaceous material, incomplete combustion of natural gas, etc., ketjen black obtained by thermal decomposition of acetylene, acetylene black, furnace carbon obtained by incomplete combustion of hydrocarbon oil or natural gas, Examples thereof include thermal carbon obtained by thermal decomposition of natural gas.

(Carbon fiber)
Examples of carbon fibers (pitch-based, PAN-based) that are examples of carbonaceous materials include pitch-based made from heavy oil, by-product oil, coal tar, and the like, and PAN-based made from polyacrylonitrile.
The average fiber length of the carbon fibers is obtained by measuring the number average fiber length by image analysis of 100 fiber lengths observed using SEM (manufactured by JEOL Ltd., JSM-5510). The carbon fiber referred to here is one having a ratio of (major axis length / minor axis length) of 10 or more.

(Amorphous carbon)
Amorphous carbon, which is an example of a carbonaceous material, is a method in which a phenol resin is cured and baked and pulverized to form a powder, or a method in which a phenol resin is cured in a spherical, indeterminate shape and baked. The thing obtained by etc. is mentioned. In order to obtain highly conductive amorphous carbon, it is preferable to perform a heat treatment at 2000 ° C. or higher.

(Expanded graphite)
As expanded graphite, which is an example of a carbonaceous material, for example, graphite having a highly crystalline structure such as natural graphite and pyrolytic graphite is mixed with a mixture of concentrated sulfuric acid and nitric acid, or concentrated sulfuric acid and hydrogen peroxide water. Immersion treatment in a strong oxidative solution such as a mixed solution to form a graphite intercalation compound, which is washed with water and then rapidly heated to expand the C-axis direction of the graphite crystal, and once the sheet Examples thereof include powder obtained by pulverizing a product rolled into a shape.

(Quiche graphite)
Examples of the quiche graphite that is an example of the carbonaceous material include planarly crystallized carbon, etc., in which molten pig iron is precipitated as the temperature is lowered by hot metal pretreatment or the like. Since this quiche graphite is generated as a mixture with slag and iron oxide, powder with high purity quiche graphite separated from slag and iron oxide by beneficiation, recovered and further pulverized to a size suitable for the application is preferable. Used.

(Artificial graphite)
As the artificial graphite which is an example of the carbonaceous material, for example, graphitized powder obtained by the following method is used. Usually, in order to obtain artificial graphite, coke is produced. Petroleum pitch or coal pitch is used as a raw material for coke. These raw materials are carbonized into coke. In order to obtain graphitized powder from coke, generally, a method of pulverizing coke and then graphitizing, a method of pulverizing coke itself and then pulverizing, or a calcined product formed by adding binder to coke and calcined (coke) In addition, there is a method in which the calcined product is co-graphitized and then pulverized into powder. Since it is better for the raw material coke or the like to have as little crystals as possible, a heat-treated material at 2000 ° C. or lower, preferably 1200 ° C. or lower is suitable. As a method for graphitizing, a method using an Atchison furnace in which powder is placed in a graphite crucible and directly energized, a method of heating powder with a graphite heating element, or the like can be used.

(Gas-phase carbon fiber, carbon nanotube)
The carbonaceous material preferably contains 0.1 to 50% by mass of vapor grown carbon fiber and / or carbon nanotube. More preferably, the content is 0.1 to 45% by mass, and still more preferably 0.2 to 40% by mass.

(Vapor grown carbon fiber)
As vapor grown carbon fiber, for example, an organic compound such as benzene, toluene, natural gas, or hydrocarbon gas is used as a raw material, and pyrolysis is performed at 800 to 1300 ° C. together with hydrogen gas in the presence of a transition metal catalyst such as ferrocene. Examples thereof include carbon fibers obtained by reacting and having a fiber length of about 0.5 to 10 μm and a fiber diameter of 200 nm or less. A more preferable size of the fiber diameter is 160 nm or less, and further preferably 120 nm or less. If the fiber diameter is larger than 200 nm, the effect of obtaining high conductivity is reduced, which is not preferable. Further, the carbon fiber obtained by the above method is preferably graphitized at about 2300 to 3200 ° C.
In addition, it is more preferable that the graphitization process here is performed in inert gas atmosphere with graphitization catalysts, such as boron, boron carbide, beryllium, aluminum, and silicon.

(carbon nanotube)
In recent years, not only the mechanical strength of carbon nanotubes but also the field emission function and the hydrogen storage function have attracted industrial attention, and the magnetic function has begun to pay attention. This type of carbon nanotube is also called graphite whisker, filamentous carbon, graphite fiber, ultrafine carbon tube, carbon tube, carbon fibril, carbon microtube, carbon nanofiber, etc., and the fiber diameter is about 0.5-100 nm belongs to. Carbon nanotubes include single-walled carbon nanotubes having a single graphite film forming a tube and multi-walled carbon nanotubes having multiple layers. In the present invention, both single-walled and multi-walled carbon nanotubes can be used. However, it is preferable to use single-walled carbon nanotubes because a composition having higher conductivity and mechanical strength tends to be obtained.
Carbon nanotubes are produced, for example, by the arc discharge method, laser evaporation method, thermal decomposition method, etc. described in “Fundamentals of Carbon Nanotubes” by Saito and Itou (page 23-57, published by Corona, 1998). In order to increase the purity, it is obtained by purification by a hydrothermal method, a centrifugal separation method, an ultrafiltration method, an oxidation method or the like. More preferably, high temperature treatment is performed in an inert gas atmosphere at about 2300 to 3200 ° C. to remove impurities. More preferably, high temperature treatment is performed at about 2300 to 3200 ° C. in an inert gas atmosphere together with a graphitization catalyst such as boron, boron carbide, beryllium, aluminum and silicon.

(Carbonaceous material containing boron)
Boron is preferably contained in the carbonaceous material 2 in an amount of 0.05 to 5% by mass, more preferably 0.06 to 4% by mass, and even more preferably 0.06 to 3% by mass. When the boron content is less than 0.05% by mass, the intended highly conductive carbonaceous material tends to be difficult to obtain. Further, even if the boron content exceeds 5 mass%, it tends to be difficult to contribute to the improvement of the conductivity of the carbonaceous material, the amount of impurities increases, and other physical properties are deteriorated. A tendency tends to occur. There is no restriction | limiting in particular as a measuring method of the total amount of boron contained in the carbonaceous material 2. FIG. For example, a value measured by inductive plasma emission spectrometry (hereinafter abbreviated as “ICP”) or induction plasma emission spectroscopic mass spectrometry (hereinafter abbreviated as “ICP-Ms”) can be used. . Specifically, sulfuric acid and nitric acid are added to a carbonaceous material containing boron as a sample, and it is decomposed by heating to 230 ° C. with microwaves (digester method), and further, perchloric acid (HClO ₄ ) is added. A method of diluting the decomposed product with water and applying it to an ICP emission spectrometer and measuring the amount of boron is exemplified.

Examples of the method of incorporating boron into the carbonaceous material 2 include carbon such as carbon black, carbon fiber, amorphous carbon, expanded graphite, quiche graphite, artificial graphite, natural graphite, vapor grown carbon fiber, carbon nanotube, and fullerene. A mixture of one or two or more selected from the material 2 and a boron source such as B alone, B ₄ C, BN, B ₂ O ₃ , H ₃ BO _3, etc. Examples thereof include a method of graphitizing at 3200 ° C. When the mixing of the carbonaceous material 2 and the boron source is uneven, the carbonaceous material 2 containing boron not only becomes uneven, but also increases the possibility of sintering during graphitization. . In order to uniformly mix the carbonaceous material and the boron source, the boron source is made into a powder having a particle size of about 50 μm or less, preferably about 20 μm or less, and then mixed with the powder of the carbonaceous material. It is preferable.

The form of boron contained in the carbonaceous material 2 containing boron is not particularly limited as long as boron and / or boron compounds are mixed in the carbonaceous material 2. When the carbonaceous material has a graphite crystal, it is more preferable that boron and / or a boron compound exist between the layers of the graphite crystal, or that a part of carbon atoms forming the graphite crystal is substituted with a boron atom. preferable. When a part of the carbon atom is substituted with a boron atom, the bond between the boron atom and the carbon atom may be any bonding mode such as a covalent bond or an ionic bond.

(Crushing of coke, etc.)
For pulverization of coke used for the production of carbonaceous material 2 and artificial graphite and natural graphite used as carbonaceous material 2, high-speed rotary pulverizer (hammer mill, pin mill, cage mill) and various ball mills (rolling mill, A crusher such as a vibration mill, a planetary mill) or a stirring mill (bead mill, attritor, distribution pipe mill, annular mill) can be used. Further, a screen mill, a turbo mill, a super micro simil, a jet mill, etc., which are fine pulverizers, can be used by selecting the conditions. Coke, natural graphite, and the like are preferably pulverized using these pulverizers, and the pulverization conditions are selected at that time, and the powder is classified as necessary, and the average particle size and particle size distribution are controlled and used.

(Classification of coke etc.)
As a method for classifying coke powder, artificial graphite powder, natural graphite powder, etc., any method can be used as long as separation is possible. For example, a sieving method or a forced vortex type centrifugal classifier (micron separator, turboplex, turboclassic) Airflow classifiers such as fire, super separator) and inertia classifiers (improved virtual impactor, elbow jet) can be used. Further, a wet sedimentation method or a centrifugal classification method can be used.

"Resin material"
Examples of the resin material 1 include a thermosetting resin. If it is a thermosetting resin, a molding cycle can be shortened.
Examples of the resin material 1 include poly (1,2-butadiene), epoxidized modified polybutadiene, hydroxyl group modified polybutadiene, maleic acid modified polybutadiene, acrylic modified polybutadiene, amine modified polybutadiene, hydrogen modified polybutadiene, poly (3,4-isoprene). ), One or more components selected from a novolac-type epoxy resin and a novolac-type phenol resin can be used. These resin materials are preferable because they improve the hot water resistance when the fuel cell porous separator is used as a fuel cell separator.
Moreover, it is more preferable that the resin material 1 has polarity. Examples of the resin material having polarity include modified polybutadiene such as epoxy-modified polybutadiene, hydroxyl group-modified polybutadiene, maleic acid-modified polybutadiene, acrylic-modified polybutadiene, amine-modified polybutadiene, and hydrogen-modified polybutadiene. When such a resin material has a polarity, the carbonaceous material causes electrostatic induction due to this polarity, and the adhesive force with the carbonaceous material 2 becomes stronger due to the electric attractive force. That is, by using a resin material having polarity, it is possible to improve the strength of the porous separator for fuel cells while maintaining the molding cycle, releasability and storage stability.

The content of the resin material 1 in the total mass of the carbonaceous material 2 and the resin material 1 is preferably in the range of 5 to 20% by mass. When the resin material is 5% by mass or more, the strength of the separator can be sufficiently secured when the fuel cell porous separator is used as a fuel cell separator. Further, when the resin material is 20% by mass or less, a sufficient total pore specific surface area is obtained, and the water permeability is improved. Further, from the viewpoint of durability when used as a fuel cell separator, it is preferable to use a resin having a melting point or glass transition temperature of 120 ° C. or higher of a molded article after heat molding.

"Other additives"
When the fuel cell porous separator 10 is used as a fuel cell separator, in addition to the carbonaceous material as a filler and the resin material, if necessary, a monomer, a reaction initiator, a curing retarder, an elastomer, And a resin modifier etc. can be contained. Furthermore, in order to improve hardness, strength, conductivity, moldability, durability, weather resistance, water resistance, etc., glass fiber, whisker, organic fiber, UV stabilizer, antioxidant, mold release agent, lubricant, increase Additives such as a sticking agent, a low shrinkage agent, and a hydrophilicity imparting agent can be contained as necessary.

"Production method of porous separator for fuel cell"
The manufacturing method of the porous separator 10 for fuel cells of this embodiment is obtained by the mixing process which mixes at least the resin material 1 and the carbonaceous material 2, the sheet forming process which makes the mixed mixture into a sheet, and a sheet forming process. And a pressing process for forming the green sheet.

"Mixing process"
(Mixing method)
First, resin material 1 and carbonaceous material 2 and other additives as necessary are mixed to prepare a resin composition having a carbonaceous material content of 80 to 95% by mass.
In the mixing step, a generally used mixer or kneader is used and mixed as uniformly as possible while keeping constant at a temperature at which curing does not start. Examples of the mixer or kneader include a roll, an extruder, a kneader, a Banbury mixer, a Henschel mixer, and a planetary mixer.
In addition, when adding a curing initiator among other additives, it is preferable to mix all other components uniformly and then add and mix the curing initiator at the end. In addition, when adding a resin material having a high melting point and solid at room temperature, all components can be uniformly mixed by adding other components after first adding them to the mixer and melting them. .

(Crushing method)
After obtaining the composition which is a mixture in the mixing step, a green sheet is produced for the purpose of uniform material supply to the molding machine. In order to make the thickness and specific gravity of the green sheet uniform, the composition needs to be pulverized in advance. For pulverization, a homogenizer, a Willet pulverizer, a high-speed rotary pulverizer (hammer mill, pin mill, cage mill, blender) or the like can be used, and it is preferable to pulverize while cooling in order to prevent aggregation of materials.

"Sheet making process"
In order to obtain a molded body with good thickness accuracy from the above pulverized composition, a green sheet having a predetermined thickness and width is once molded at a temperature at which curing does not start using an extruder, a roll, a calendar, or the like. In order to form the thickness more accurately, it is preferable to roll with a roll or a calender after forming with an extruder. In order to eliminate unnecessary voids and air in the green sheet, it is preferable to perform extrusion molding in a vacuum state. In addition, when a sheet is formed using a roll, the thickness of the sheet tends to gradually increase from the start to the end of sheet forming. In that case, in order to produce a uniform green sheet, by changing the direction of feeding the green sheet to the roll, and repeating the operation of feeding the roll from the portion where the thickness of the sheet is large, the green sheet having a uniform thickness Can be produced. In some cases, the roll is heated to obtain a green sheet. When heated, a green sheet having a smaller thickness and a uniform thickness can be obtained.

In the present invention, a green sheet having a thickness variation within 10% of the average thickness of the green sheet is used. If the variation in the thickness of the green sheet is larger than 10% of the average thickness of the green sheet, it cannot be uniformly pressurized in the pressing process described later, and the pore distribution in the plane of the fuel cell porous separator Variation may occur. Preferably, it is within 7%, more preferably within 5%, still more preferably within 3%.

In the sheet forming step, the temperature of the green sheet is preferably set to a temperature that is not less than the temperature at which condensation does not occur and the resin does not cure. For example, when epoxidized polybutadiene is used as the resin material 1, the temperature is preferably 10 ° C. to 100 ° C., more preferably 20 ° C. to 40 ° C. When the sheet forming process is performed at a temperature at which condensation occurs, there is a problem that the green sheet becomes brittle due to moisture. Further, when sheeting is performed at a temperature at which curing occurs, a curing reaction that should originally occur in the press process described later also occurs in the sheeting process, and a uniform green sheet cannot be obtained.

In the sheet forming step, when a green sheet is formed using a roll, the number of rotations is preferably 1 rpm to 5 rpm, depending on the size of the roll. If the rotation speed of the roll is 1 rpm or more, it is preferable from the viewpoint of productivity. Moreover, the uniformity of the thickness of a green sheet is easy to ensure that the rotation speed of a roll is 5 rpm or less.

In the sheet forming step, when a green sheet is formed using a roll, the gap between the rolls is preferably in the range of 0.5 mm to 2.5 mm. When the gap between rolls is 0.5 mm or more, the pore diameter of the porous separator for a fuel cell to be finally formed is appropriately controlled without excessively dense green sheets in the sheeting process, It can maintain its temperament and water permeability. When the gap between the rolls is 2.5 mm or less, it is easy to control the thickness of the finally formed porous separator for a fuel cell.

In the sheet forming step, rolling using a roll, a calendar, etc. is preferably repeated a plurality of times. For example, when rolling between the rolls only once, the thickness may vary at the beginning and end of introducing the workpiece into the roll. Therefore, by repeating the rolling a plurality of times, thickness variations at the beginning and end of introducing the green sheet into the roll can be further suppressed. Moreover, when performing it multiple times, it is more preferable to carry out, changing the direction of the start and end of the green sheet introduced into a roll.

"Pressing process"
The obtained green sheet is cut or punched to a desired size, and the sheets are placed in a mold in one or two or more in parallel, or inserted in layers, and heated and pressed with a compression molding machine. A porous separator for a fuel cell is obtained.

The pressing step is preferably performed while heating the green sheet at 150 to 240 ° C. When the pressing process is performed at 150 ° C. or higher, the curing rate can be sufficiently fast to maintain productivity. Specifically, a time of 0.5 minutes or more is required to obtain a molded product having sufficient strength in the pressing process. Moreover, if it heats at 240 degrees C or less, the oxidation deterioration of the resin material can be prevented and the intensity | strength of a molded article can be maintained.
The pressurization time is preferably 0.5 minutes to 30 minutes. In the case of a pressurization time shorter than 0.5 minutes or more, curing is sufficiently advanced and good strength can be obtained. Moreover, productivity can be maintained by the pressurization time of 30 minutes or less.
Further, in the pressing step, it is preferable to pressurize the green sheet under conditions of 2 MPa to 25 MPa. Under a pressure condition of 2 MPa or more, the porosity of the molded body can be appropriately controlled, and the strength of the fuel cell porous separator can be maintained. Further, under a pressure condition of 25 MPa or less, a sufficient porosity can be secured and water absorption can be maintained.

The green sheet is preferably the same as the porous separator for a fuel cell and slightly smaller in length and width. After molding, complete curing may be performed by performing after-curing for 10 minutes to 600 minutes in a temperature range of 150 ° C. to 200 ° C. After-curing makes it easy to suppress warping of the product by applying pressure to 0.3 MPa or higher. Further, when molding is performed by applying a pressure of 15 MPa or less, a sufficient porosity of the fuel cell porous separator can be secured.

Moreover, it is preferable that the thickness of the green sheet introduced into the mold is 1.1 times or more and 2 times or less with respect to the mold thickness in the pressing step. By setting it as the said range, the air permeability of the porous separator for fuel cells obtained can be 600 s / 100 ml or less.
In producing a porous separator for a fuel cell, in order to obtain a good product having no defects, it is preferable to evacuate the cavity during molding.

The porous separator for a fuel cell obtained by such a method has a high pore distribution with a pore diameter of 1.5 to 4.0 μm of 90 vol% or more in the pore distribution obtained by the mercury intrusion method. A strong and uniform porous separator for fuel cells can be obtained. In a method of forming pores by firing a mixed molded body of a resin material and a carbonaceous material and removing the resin material, which has been conventionally used as a method for manufacturing a porous separator for a fuel cell, Pore distribution cannot be obtained.

"Hydrophilization process"
The obtained porous separator for a fuel cell is preferably subjected to a hydrophilic treatment. In addition, hydrophilization means making the way of getting wet with water better than the present condition, or making a contact angle small. On the other hand, making water wet worse than the current situation and increasing the contact angle are called water repellency.
In the hydrophilization treatment, it is effective to change the surface to an electrically polarized molecular structure. To that end, functional groups such as a highly polar carboxyl group, carbonyl group, hydroxy group, amino group, sulfo group, cyano group, etc. In addition, it is preferable to introduce elements having high electronegativity in a balanced manner. As a method thereof, a method of performing high energy treatment such as plasma treatment, corona treatment, ozone treatment and UV treatment in a predetermined atmosphere, a method of contacting with a reactive gas, and immersion in a chemical such as a strong acid. There are methods. Other methods include surface coating with a hydrophilic coating agent and surface modification by sputtering.
Further, in the case of a material that originally has a polar group or a material having a static contact angle of 80 ° or less on the surface, the surface may be hydrophilized only by roughening the surface by blasting or the like.
Moreover, it is more preferable that the hydrophilic treatment is performed to the surface and the inside of the fuel cell porous separator. Specifically, it is preferable that the porous separator for a fuel cell is exposed to an atmosphere containing fluorine gas and oxygen gas to make the surface and the inside of the pores hydrophilic. It absorbs water more quickly when both the surface and inside are hydrophilized than when only the surface is hydrophilized. Moreover, it can suppress that the hydrophilization performance deteriorates with time.

Whether the porous separator for fuel cells is sufficiently hydrophilic can be evaluated by dropping a small amount of pure water as described above. Further, it can be confirmed by X-ray photoelectron spectroscopy (XPS) that the hydrophilic treatment has been applied to the inside as described above.

"Washing process"
The porous separator for a fuel cell that has been subjected to the hydrophilization treatment step is preferably washed. If the porous separator for a fuel cell after the hydrophilization treatment is incorporated into the fuel cell as it is and the power is generated, the output may decrease over time due to the influence of impurities. Therefore, it is necessary to wash water-soluble impurities such as hydrogen fluoride provided by the hydrophilization treatment and metal components contained in the raw material. At this time, it is washed with pure water, but if heated, it can be washed efficiently. Further, by performing the washing step, many COF groups and CF groups can be hydrolyzed in advance and replaced with COOH groups before mounting on the fuel cell. By completing substitution of these groups in advance before mounting, performance inspection and the like can be performed before mounting on the fuel cell, which is preferable in terms of production management.

The porous separator for a fuel cell after the washing step preferably has an elution amount of various metal ions of 10 ppm or less when 30 g of the porous separator for a fuel cell is immersed in warm water at 80 ° C. for 4 days. More preferably, it is more preferably 1 ppm or less.

Hereinafter, examples of the present invention will be described. In addition, this invention is not limited only to a following example.

(Example 1)
Spherical artificial graphite SCMG (registered trademark: Showa Denko KK) boron-doped product: SCMG IV was graphitized at 2900 ° C. and used as a carbonaceous material. The cumulative distribution diameter (mass basis) of the carbonaceous material at this time was D10 = 7 μm, D50 = 26 μm, and D90 = 49 μm. As a resin material, epoxidized polybutadiene (JP200 epoxy equivalent: 210-240 g / eq number average molecular weight 2000-3000, manufactured by Nippon Soda Co., Ltd.) obtained by modifying an epoxy group into poly (1,2-butadiene) was used. A carbonaceous material 13.5 kg (90% by mass) and a resin material 1.5 kg (10% by mass) were introduced into a pressure kneader (TD10-20MDX manufactured by Toshin) and mixed to obtain a uniform mixture. .

The obtained mixture was pulverized once using a Willet pulverizer (WM type manufactured by Yoshida Seisakusho Co., Ltd.) and then rolled using a roll to obtain a green sheet. At this time, the conditions for rolling with a roll were a temperature of 25 ° C., a rotational speed of 1.5 rpm, and a gap between rolls of 1.2 mm. In addition, the number of times of rolling by the roll was 6 times.
Finally, the obtained green sheet was cut into a size of 123 mm in length × 180 mm in width, and inserted into a mold having a size of 123 mm in length × 180 mm in width × 2.2 mm in thickness with a thickness of 2.7 mm. This green sheet was press-molded under the conditions of a temperature of 186 ° C., a pressure of 5 to 9 MPa, and a time of 20 minutes to obtain a porous separator for a fuel cell. Further, the obtained porous separator for a fuel cell was subjected to after-curing for 30 minutes at 180 ° C. and 0.5 MPa. Furthermore, the hydrophilic treatment was performed using a mixed gas of 4 vol% fluorine gas, 20 vol% oxygen gas, and 76 vol% nitrogen gas, and the porous separator for a fuel cell after the hydrophilic treatment was washed.
Washing was performed as follows. First, in a PP container (178 × 251 × t91 mm), 1800 ml of purified water and 200 ml of a neutral detergent (Clean Ace (product name): ASONE (manufacturer name)) were placed. Subsequently, three separators (123 × 180 × t2.2 mm) were placed in the container. And the container was put into a 45 degreeC thermostat for 24 hours. Thereafter, the container was taken out, the cleaning liquid contained therein was discarded, 2000 ml of purified water was added, and the container was placed in a 45 ° C. constant temperature bath for 24 hours. The process from taking out the container to storing in a thermostatic chamber was repeated once more. Finally, the container was taken out from the thermostatic bath, and the cleaning liquid contained therein was discarded. The separator was dried at 80 ° C. for 4 hours.
The resistivity of the porous separator for a fuel cell obtained at this time was 17 mΩ · cm, and the bending strength was 25 MPa. Each measured value was shown as an average value of nine values measured by the method described later.

(Comparative Example 1)
The mixture was directly pressed without rolling with a roll, that is, without forming a green sheet. Other conditions were the same as in Example 1.

FIG. 3 shows the in-plane variation in the air permeability of the porous separator for a fuel cell of Example 1 and Comparative Example 1. In Example 1, the air permeability was measured at a total of nine locations near the center of the porous separator for fuel cells having a size of 123 mm long × 180 mm wide, near each vertex, and near the middle point between each vertex. In Comparative Example 1, the air permeability was measured at four locations near each vertex. As a result, it can be seen that in Example 1 in which the sheet forming process was performed, the variation in air permeability was very small.

FIG. 4 shows the bending strength and specific resistivity with respect to the air permeability measured at 9 points of the porous separator for fuel cells of Example 1, and the air permeability measured at 4 points of the porous separator for fuel cells of Comparative Example 1. The bending strength and the specific resistivity with respect to the degree are shown. It can be seen that the porous separator for a fuel cell of Example 1 has a constant bending strength in the plane and high strength as a whole. It can also be seen that the specific resistivity is constant in the plane and the conductivity is uniform.

The bending strength was measured according to JIS K6911. Specifically, a non-measured object was cut to a width of 10 mm using a cutting machine (model RC-150 manufactured by Ritoku) and measured using a tabletop electric tester (model LSC-1 / 30 manufactured by JT Toshi). did. At this time, cutting was performed so that the center portion of each air permeability measurement range becomes a load point in the bending strength measurement so that the correspondence between the air permeability and the bending strength can be understood.
The specific resistivity was measured by a four-probe method according to JIS K7194. Specifically, using a low resistivity meter (Mitsubishi Chemical Analytech Loresta (registered trademark) FP), the vicinity of the center of the porous separator for fuel cells of size 123 mm x 180 mm, each apex, each apex Measurements were made at a total of nine locations near the midpoint, and the average value was measured.

(Comparative Example 2)
A porous separator for a fuel cell was formed in the same manner as in Example 1 except that the number of rolls was one. The resistivity of the porous separator for a fuel cell obtained at this time was 80 mΩ · cm, and the bending strength was 11 MPa.

(Comparative Example 3)
A porous separator for a fuel cell was formed in the same manner as in Example 1 except that the number of rolling of the roll was set to 2. The resistivity of the porous separator for a fuel cell obtained at this time was 60 mΩ · cm, and the bending strength was 13 MPa.

In FIG. 5, the result of having measured the pore distribution of Example 1, Comparative Example 2, and Comparative Example 3 by the mercury intrusion method is shown. The measurement conditions of the mercury intrusion method were as follows.
Measuring instrument: AutoPoreIV 9500 (Company name: micromeritics-shimadzu)
Mercury constant: contact angle 130 °, surface tension 485 dyne / cm, density 13.5 g / ml
Deaeration: maintained at 50 μmHg or less for 5 minutes Mercury encapsulation: 1.33 psi
Pressure range: 1.5-33000 psi
Pressure equilibration: Hold for 10 seconds Stem volume: 0.4120 ml
Sample: about 1cm square Stem usage: about 5-16%

As a result, the fuel cell porous separator of Example 1 showed a sharp peak in the pore distribution as compared with the fuel cell porous separators of Comparative Example 2 and Comparative Example 3. That is, it can be seen that the in-plane pore distribution is uniform.

Table 1 shows the variation in the thickness of the green sheets obtained in Example 1 and Comparative Examples 2 and 3, and the performance of the porous separator for a fuel cell formed using these green sheets.
When the air permeability was set to a sample thickness of 2 mm and a gas permeation area of 6.4 cm ² (area of 28.6 mm in diameter), the time required for 100 ml of gas to pass through the sample was measured. The pressure at this time was 1.22 kPaG.
The gas seal pressure was evaluated as follows using the evaluation apparatus 50 shown in FIG. The evaluation device 50 mainly includes a water W accommodating portion 51 a, a sample 10 accommodating portion, a structure 51 having a hollow portion, and a means 52 for applying pressure to the sample 10. The container 51a for water W is provided on one side (the upper side in FIG. 7) sandwiching the separator of the container for the sample 10. The hollow portion is provided on the other side (the lower side of FIG. 7) of the accommodating portion of the sample 10. The means 52 for applying pressure is connected to the cavity and is configured to apply pressure to the sample 10 through this cavity.
First, normal temperature purified water was sprinkled on the bat, and a separator was attached as a sample 10 for 1 hour. Next, as shown in FIG. 6, the sample 10 was set at a predetermined position of the evaluation device 50. Sample 10 was 123 mm × 180 mm × 2.2 mm. Next, water was applied on the sample 10. Next, compressed air was supplied from the means 52 for applying pressure via the cavity, and pressure was applied to the sample 10 from the bottom 10a side. The applied pressure gradually increased from 0, and the pressure when the bubble B started to be generated from the sample 10 was evaluated as the gas seal pressure.
The water permeability was evaluated as follows using the evaluation apparatus 60 shown in FIG. The evaluation device 60 mainly includes a structure 61 having a water W accommodating portion 61 a and a sample 10 accommodating portion, and means 62 for applying pressure to the sample 10. The accommodation part 61a for water W is provided on one side (the upper side in FIG. 8) sandwiching the separator of the accommodation part for the sample 10. The means 62 for applying pressure is connected to the water W accommodating portion 61a, and is configured to apply pressure to the sample 10 through the accommodating portion 61a.
First, normal temperature purified water was sprinkled on the bat, and a separator was attached as a sample 10 for 1 hour. Next, as shown in FIG. 11, the sample 10 was set at a predetermined position of the evaluation device 60. Sample 10 was 123 mm × 180 mm × 2.2 mm. Next, water was applied on the sample 10. Next, compressed air was supplied into the accommodating part 61a from the means 62 for applying pressure, and pressure was applied to the sample 10 from the upper part 10b side through the water in the accommodating part 61a. It adjusted using the regulator so that the applied pressure might be set to 14 kPa. The weight of the water W2 that permeated the sample 10 was measured with an electronic balance between 60 seconds after reaching the steady state and 120 seconds after.
For water absorption, 5 μl of ion-exchanged water was dropped using a microsyringe in the center of a 100 mm × 200 mm × 2 mm sample, and the time until the droplet was completely absorbed was measured.
The volume ratio of pores having a pore diameter of 1.5 to 4.0 μm to all pores was calculated from the pore distribution measured by the mercury intrusion method shown below. Six 10 mm × 10 mm × 2 mm sized samples were cut out from 100 mm × 200 mm × 2 mm sized samples, and a graph of the relationship between the pore diameter and the occupied volume at the pore diameter was obtained by mercury porosimetry. From the graph, the volume ratio of the pores having a pore diameter of 1.5 to 4.0 μm with respect to all the pores was obtained, and the average value of the six data was taken as the sample volume ratio. The volume ratio was obtained from the area between 1.5 μm and 4.0 μm from FIG.

　　　　　　　　　　　　　　　　　　

At this time, the variation in the thickness of the green sheet and the variation in the air permeability were obtained as a difference between the maximum value and the minimum value by measuring nine samples of 123 mm × 180 mm. The in-plane variation of the green sheet thickness with respect to the average value of the green sheet thickness was 1% in Example 1, 23% in Comparative Example 2, and 12% in Comparative Example 3. FIG. 7 shows the result of the air permeability variation with respect to the green sheet thickness variation.
As a result, it can be seen that when the variation in the thickness of the green sheet is small, the variation in the air permeability is small. That is, the gas leak pressure can be increased, and a fuel cell porous separator with high gas shielding properties can be obtained.

(Examples 2 to 6)
Next, the relationship between the green sheet thickness and the air permeability when the green sheet was pressed was examined. The obtained green sheet was cut into a size of 123 mm long × 180 mm wide, and the green sheet thickness was 2.30 mm, 2.50 mm, 2.68 mm, 2.76 mm, and 2.76 mm with respect to a mold having a thickness of 2.2 mm. A porous separator for a fuel cell was formed to be 88 mm. Other conditions were the same as in Example 1. The results are shown in Table 2. The in-plane variation of the green sheet thickness with respect to the average value of the green sheet thickness is 3% in Example 2, 2% in Example 3, 1% in Example 4, 2% in Example 5, and 2% in Example 6. Met.

　　　　　　　　　　　　　　　　　　

FIG. 8 shows a graph of average pore diameter versus green sheet thickness. The average pore diameter was the peak value of pore distribution measured by mercury porosimetry. The porosity was calculated from the pore distribution measured by the mercury intrusion method. FIG. 9 shows a graph of porosity versus green sheet thickness. FIG. 10 shows a graph of the air permeability with respect to the green sheet thickness.
As a result, it can be seen that when the thickness of the green sheet to be pressed is increased, the air permeability increases. This is presumably because if the amount of material to be pressed is large, the porous separator for fuel cells after press molding becomes dense. Particularly in Examples 2 to 5, the air permeability is preferably 600 s / 100 ml or less.

By using the porous separator for fuel cells of the present invention as a separator for fuel cells, a fuel cell having high power generation performance is realized because the porous separator for fuel cells having high strength, conductivity, water permeability and gas barrier properties is used. can do.

DESCRIPTION OF SYMBOLS 1 ... Resin material, 2 ... Carbonaceous material, 10 ... Porous separator for fuel cells,
DESCRIPTION OF SYMBOLS 10a ... Bottom part, 10b ... Upper part, 20 ... Power generation part, 30 ... Gas diffusion layer, 40 ... Cooling water, 50 ... Evaluation apparatus, 51 ... Structure, 51a ... Water accommodating part, 52 ... Means to apply pressure, 60 ... Evaluation device, 61 ... Structure, 61a ... Water container, 62 ... Means for applying pressure, B ... Bubble, W ... Water, W2 ... Water, 100 ... Fuel cell

Claims (8)

1. A porous separator for a fuel cell formed by using a composition containing a resin material and a carbonaceous material,
   The content of the carbonaceous material in the total mass of the carbonaceous material and the resin material is 80 to 95% by mass,
   A porous separator for a fuel cell, wherein a pore having a pore diameter of 1.5 to 4.0 μm among all pores in a pore distribution determined by a mercury intrusion method is 90 vol% or more.
2. The resin material includes one selected from the group consisting of poly (1,2-butadiene), epoxy-modified polybutadiene, hydroxyl group-modified polybutadiene, maleic acid-modified polybutadiene, acrylic-modified polybutadiene, amine-modified polybutadiene, and hydrogen-modified polybutadiene. 2. A porous separator for a fuel cell according to 1.
3. A fuel cell comprising the porous separator for a fuel cell according to claim 1 or 2.
4. A mixing step of mixing at least a resin material and a carbonaceous material to prepare a curable resin composition having a carbonaceous material content of 80 to 95% by mass;
   A sheeting step of forming the composition obtained by mixing into a green sheet having an in-plane variation of the sheet thickness within 10% of the average thickness of the sheet,
   And a pressing step for forming the green sheet obtained in the sheet forming step.
5. The method for producing a porous separator for a fuel cell according to claim 4, wherein the thickness of the green sheet is 1.1 times or more and 2 times or less with respect to the mold thickness at the time of the pressing step.
6. 6. The fuel cell porous separator according to claim 4, wherein, in the sheet forming step, the temperature of the green sheet is not less than a temperature at which condensation does not occur and not more than a temperature at which the resin does not cure. Production method.
7. The method for producing a porous separator for a fuel cell according to any one of claims 4 to 6, wherein in the pressing step, the green sheet is heated at a temperature of 150 to 240 ° C.
8. The method for producing a porous separator for a fuel cell according to any one of claims 4 to 7, wherein the green sheet is pressurized at a pressure of 2 to 25 MPa in the pressing step.

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