JP6932447B2 - Paste composition for forming microporous layer and gas diffusion layer for fuel cell - Google Patents

Description

According to the present invention, a micro is applied to the surface of a conductive porous base material such as carbon paper constituting a gas diffusion layer (GDL) for a fuel cell to form a microporous layer (MPL). It relates to a paste composition for forming a porous layer and a gas diffusion layer using the same, and particularly to a paste composition for forming a microporous layer capable of forming a microporous layer at low cost and a gas diffusion layer for a fuel cell using the same. It is a thing.

In recent years, fuel cells, especially polymer electrolyte fuel cells (PEFCs), have attracted a great deal of attention because of their applicability to a wide range of applications such as automobiles, household power supplies, and home appliances.
The polymer electrolyte fuel cell uses an ionic conductive polymer film as an electrolyte, and a negative electrode and a positive electrode are bonded to this to form one single cell, and a plurality of single cells are formed via a separator. It has a configuration (stack) that obtains a high voltage by stacking.

Generally, one single cell constituting a solid polymer electrolyte fuel cell has platinum on both sides of a polymer electrolyte membrane (ion conductive solid polymer electrolyte membrane) that selectively permeates specific ions. A cathode (+) side electrode composed of an electrode catalyst layer made of a conductive material such as carbon and an ion exchange resin carrying a catalyst such as, and a porous gas diffusion layer (GDL) arranged outside the electrode catalyst layer. And the electrode on the anode (−) side is arranged to form a membrane / electrode assembly (MEGA; Membrane-Electrode-Gas Diffusion Layer Assembly).
Then, in the polymer electrolyte fuel cell, fuel gas (anode gas) or oxidation gas (cathode gas) is supplied or generated gas and excess gas are discharged to the outside of the gas diffusion layer constituting this membrane / electrode assembly. A separator forming a gas flow path is arranged, a membrane / electrode assembly is sandwiched between the separators, and a configuration (stack) in which a plurality of single cells are stacked enhances power generation.

Since the polymer electrolyte fuel cell having such a configuration can obtain energy with high efficiency and has a low environmental load, it is being used as a power source (drive source) for automobiles, and is used as a fuel for automobiles. It is desired to reduce the cost of each member constituting the fuel cell for the further spread of the battery.

By the way, in such a polymer electrolyte fuel cell, as described above, in order to efficiently react the fuel gas (anodic gas) and the oxide gas (cathode gas), gas is applied to the catalyst layer carrying a catalyst such as platinum. A leading gas diffusion layer is used. That is, the gas diffusion layer plays a role of diffusing the fuel gas or oxidation gas supplied from the gas flow path of the separator to the catalyst layer adjacent to the gas diffusion layer (gas diffusivity), and efficiently moves electrons. It has a conductive function and a current collecting function. Further, in the gas diffusion layer, hydrogen and oxygen during power generation are used in order to suppress a flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer are blocked by water), secure a gas passage, and maintain stable power generation performance. Water repellency (moisture permeability) that discharges excess reaction-generated water and condensed water generated by the electrochemical reaction of the above is also required.

Conventionally, such a gas diffusion layer is a microporous layer containing carbon and a water-repellent resin as main components on a carbon base material (conductive porous base material) such as carbon cloth made of carbon fiber and carbon paper. (Micro Porous Layer; hereinafter, sometimes abbreviated as "MPL") has been developed. The gas diffusion layer made of this carbon base material and MPL is made of carbon and water repellency with respect to a carbon base material such as carbon paper obtained by binding carbon fibers with a phenol resin and carbonizing the phenol resin, for example. It is known that it can be formed by applying a paste-like mixture for forming MPL containing a resin, drying and firing.

And, as a known technique of this kind, there are, for example, Patent Document 1 and Patent Document 2. Patent Document 1 describes a gas obtained by applying a water-repellent paste obtained by mixing a conductive filler, a fluororesin, a fibrous filler, and pore-forming agent particles that are thermally decomposed by firing to a base material, drying and firing. The technology for obtaining a diffusion layer is disclosed.
Patent Document 2 also discloses a paste composition for forming a conductive porous layer containing conductive carbon particles, conductive carbon fibers, a water-repellent resin, and a dispersant.

Here, as described in Patent Documents 1 and 2, it is conventionally stated that the addition of fibrous fillers and conductive carbon fibers can prevent cracks from occurring during drying and firing after coating. As measures to prevent cracks on the surface of MPL, carbon nanotubes (hereinafter abbreviated as "CNT") and vapor-grown carbon fiber (hereinafter abbreviated as "VGCF") may be abbreviated. There is), the use of vapor-grown nanocarbon fiber (Vapor Grown Nanocarbon Fiber; hereinafter, sometimes abbreviated as "VGNF") is known.

JP 2006-294559 JP-A-2014-241290

However, materials such as carbon nanotubes (CNT), vapor-grown carbon fibers (VGCF), and vapor-grown nanocarbon fibers (VGNF) that have been conventionally used for crack suppression are expensive, and Patent Document 1 and Patents The technique of Document 2 has a problem of high cost.
However, if materials such as carbon nanotubes (CNT), vapor-grown carbon fibers (VGCF), and vapor-grown nanocarbon fibers (VGNF) are omitted, the shrinkage stress during film formation of MPL becomes large. As a result, cracks are likely to occur in the MPL. In particular, if there are cracks in the MPL, the durability is lowered and not only the characteristics of the MPL cannot be fully exhibited, but also water tends to accumulate in the cracks, so that the cracks are accumulated at the interface between the cracks generated in the MPL and the catalyst layer. There is a problem that the water is frozen when the temperature is below freezing, and the MPL and the catalyst layer are separated or a part of them is missing. Therefore, the performance of the fuel cell is adversely affected, and the life of the fuel cell is shortened.

The applicant has previously filed a patent application for an invention relating to an MPL forming paste as Japanese Patent Application No. 2017-022945. In this prior application, by combining graphite with a low specific surface area and acetylene black with a high specific surface area, it is possible to improve both the conductivity and gas permeability of MPL, and further provide a technology that enables cost reduction. However, no disclosure or suggestion has been made regarding a technique for suppressing MPL cracks at low cost.

Therefore, an object of the present invention is to provide a paste composition for forming a microporous layer capable of suppressing the occurrence of cracks in the microporous layer by using an inexpensive material, and a gas diffusion layer for a fuel cell using the same. be.

The paste composition for forming a microporous layer according to the invention of claim 1 contains carbon black, a water-repellent resin, a dispersant, and a solvent, and the carbon black has a DBP absorption amount of 210 ml / 100 g to 262 ml /. The first carbon black, which is in the range of 100 g and has an iodine adsorption amount in the range of 85 mg / g to 97 mg / g, and the DBP absorption amount is in the range of 32 ml / 100 g to 48 ml / 100 g, and the iodine adsorption amount is in the range of 32 ml / 100 g to 48 ml / 100 g. It is used in combination with a second carbon black in the range of 15 mg / g to 20 mg / g, and is applied to the surface of a conductive porous base material such as carbon paper, dried and fired to form a microporous layer. Is what forms.

The first carbon black has a DBP absorption amount of 210 ml / 100 g or more and 262 ml / 100 g or less. For example, acetylene black and furnace black can be mentioned. In particular, acetylene black is preferable because it can secure high gas diffusivity, high strength, high conductivity, etc. in the microporous layer and can exhibit good battery performance.
The second carbon black has a DBP absorption amount of 32 ml / 100 g or more and 48 ml / 100 g or less. For example, thermal black and furnace black can be mentioned. In particular, thermal black is preferable because it contains few impurities, can secure high conductivity and the like, and can exhibit good battery performance.

Here, the amount of DBP absorbed is measured in accordance with JIS K6217-4. The amount of DBP absorbed is an index showing the size of the structure, and by utilizing the fact that the porosity between carbon black aggregates has a positive correlation with the structure, DBP (Dibutyl Phthalate) is absorbed in the space and the amount of DBP absorbed. The structure is indirectly quantified by. The larger (higher) this number is, the more developed the carbon black structure is, and the higher the structure is. It shows that there is. The structure indicates the degree of development of a chain of aggregates (aggregates) composed of several to several tens of carbon black, that is, the degree of development of the connection of carbon black particles. If the number of carbon particles constituting the aggregate is large or the shape is complicated, the amount of DBP absorbed becomes high.

That is, the carbon black is a combination of a first carbon black having a high structure and a second carbon black having a low structure.
Here, in comparison between the first carbon black and the second carbon black, the size of the structure with developed aggregates (chain structure) is relatively high, and the structure with less developed aggregates. The size of (chain structure) is expressed as low structure.

The first carbon black has an iodine adsorption amount of 85 mg / g or more and 97 mg / g or less, and the second carbon black has an iodine adsorption amount of 15 mg / g or more and 20 mg / g or less.

Here, the amount of iodine adsorbed is an index showing the specific surface area of carbon black, which has a correlation with the surface area of carbon black, and is measured in accordance with JIS K6217-1. The larger the value, the larger the specific surface area of carbon black, and the smaller the value, the smaller the specific surface area. In general, the smaller the particle size, the larger the specific surface area. Therefore, the larger the index, the smaller the particle size, and the smaller the index, the larger the particle size.

That is, since the amount of iodine adsorbed by the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodine adsorbed by the second carbon black is in the range of 15 mg / g to 20 mg / g, the first carbon Black has a larger specific surface area than the second carbon black, and the second carbon black has a smaller specific surface area than the first carbon black.

In the paste composition for forming a microporous layer of the invention of claim 1, the blending ratio of the first carbon black / the second carbon black is the first carbon black / the second carbon black = 20/80 to 80 /. It is within the range of 20.

Of the first carbon black and the second carbon black showing the above compounding ratio, the former means the mass% of the first carbon black with respect to the total mass of the first carbon black and the second carbon black, and the latter. Means the mass% of the second carbon black with respect to the total mass of the first carbon black and the second carbon black. That is, in the first carbon black and the second carbon black, the blending amount of the first carbon black is 20% by mass or more and 80% by mass or less with respect to the total amount of the first carbon black and the second carbon black. Yes, the blending amount of the second carbon black is 20% by mass or more and 80% by mass or less, and the blending ratio thereof is within the range of 20/80 ≦ the first carbon black / the second carbon black ≦ 80/20. Is what.

The gas diffusion layer for a fuel cell according to the invention of claim 2 has a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and an iodine adsorption amount of 85 mg / g to 97 mg with respect to the conductive porous base material. The first carbon black in the range of / g and the second carbon black in the DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g and the iodine adsorption amount in the range of 15 mg / g to 20 mg / g. A microporous layer-forming paste composition containing a water-repellent resin, a dispersant, and a solvent is applied, dried, and fired to form a microporous layer on the conductive porous substrate. It is made up of.

The first carbon black has a DBP absorption amount of 210 ml / 100 g or more and 262 ml / 100 g or less. For example, acetylene black and furnace black can be mentioned. In particular, acetylene black is preferable because it can secure high gas diffusivity, high strength, high conductivity, etc. in the microporous layer and can exhibit good battery performance.
The second carbon black has a DBP absorption amount of 32 ml / 100 g or more and 48 ml / 100 g or less. For example, thermal black and furnace black can be mentioned. Thermal black is preferable because it contains few impurities, can secure high conductivity and the like, and can exhibit good battery performance.

Here, the amount of DBP absorbed is measured in accordance with JIS K6217-4. The amount of DBP absorbed is an index showing the size of the structure, and by utilizing the fact that the porosity between carbon black aggregates has a positive correlation with the structure, DBP (Dibutyl Phthalate) is absorbed in the space and the amount of DBP absorbed. The structure is indirectly quantified by. The larger (higher) this number is, the more developed the carbon black structure is, and the higher the structure is. It shows that there is. The structure indicates the degree of development of a chain of aggregates (aggregates) composed of several to several tens of carbon black, that is, the degree of development of the connection of carbon black particles. If the number of carbon particles constituting the aggregate is large or the shape is complicated, the amount of DBP absorbed becomes high.

That is, the carbon black is a combination of a first carbon black having a high structure and a second carbon black having a low structure.
Here, in comparison between the first carbon black and the second carbon black, the size of the structure with developed aggregates (chain structure) is relatively high, and the structure with less developed aggregates. The size of (chain structure) is expressed as low structure.

The first carbon black has an iodine adsorption amount of 85 mg / g or more and 97 mg / g or less, and the second carbon black has an iodine adsorption amount of 15 mg / g or more and 20 mg / g or less.

Here, the amount of iodine adsorbed is an index showing the specific surface area of carbon black, which has a correlation with the surface area of carbon black, and is measured in accordance with JIS K6217-1. The larger the value, the larger the specific surface area of carbon black, and the smaller the value, the smaller the specific surface area. In general, the smaller the particle size, the larger the specific surface area. Therefore, the larger the index, the smaller the particle size, and the smaller the index, the larger the particle size.

That is, since the amount of iodine adsorbed by the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodine adsorbed by the second carbon black is in the range of 15 mg / g to 20 mg / g, the first carbon Black has a larger specific surface area than the second carbon black, and the second carbon black has a smaller specific surface area than the first carbon black.

The gas diffusion layer for a fuel cell according to the second aspect of the present invention has a blending ratio of the first carbon black / the second carbon black of the first carbon black / the second carbon black = 20/80 to 80/20. It is within the range.

Of the first carbon black and the second carbon black showing the above compounding ratio, the former means the mass% of the first carbon black with respect to the total mass of the first carbon black and the second carbon black, and the latter. Means the mass% of the second carbon black with respect to the total mass of the first carbon black and the second carbon black. That is, in the first carbon black and the second carbon black, the blending amount of the first carbon black is 20% by mass or more and 80% by mass or less with respect to the total amount of the first carbon black and the second carbon black. Yes, the blending amount of the second carbon black is 20% by mass or more and 80% by mass or less, and the blending ratio thereof is within the range of 20/80 ≦ the first carbon black / the second carbon black ≦ 80/20. Is what.

According to the paste composition for forming a microporous layer according to the invention of claim 1, it contains carbon black, a water-repellent resin, a dispersant, and a solvent, and the amount of DBP absorbed as the carbon black is 210 ml / 100 g or more. The first carbon black, which is in the range of 262 ml / 100 g and the amount of iodine adsorbed is in the range of 85 mg / g to 97 mg / g, and the DBP absorption amount is in the range of 32 ml / 100 g to 48 ml / 100 g, and the amount of iodine adsorbed. It is used in combination with a second carbon black whose amount is in the range of 15 mg / g to 20 mg / g.

The present inventors have been diligently conducting experimental research on a technology capable of suppressing cracks in MPL, focusing on carbon black, which has extremely diverse physical property values and characteristics depending on manufacturing conditions and is available at low cost, and the degree of structural development. It has been found that cracks in MPL can be suppressed by controlling the chain structure and three-dimensional structure of carbon particles by combining carbon black having a specific difference in the above, and the present invention has been completed based on these findings.

That is, as carbon black, a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination. Then, the shrinkage stress at the time of film formation forming the MPL (the shrinkage stress generated at the time of drying and firing after applying the paste composition for forming a microporous layer to the conductive porous base material) can be relaxed, and cracks in the MPL can be relaxed. Was able to be suppressed.

Here, if the DBP absorption amount of the first carbon black is too small, the development of the structure of the first carbon black is low, and the formation of a strong three-dimensional structure by the chain of carbon black particles is reduced. Cracks are likely to occur in the MPL. Further, during coating, strike-through of the paste component (a phenomenon in which carbon black of the paste component escapes to the back surface side of the conductive porous base material on the opposite side to the coated surface) occurs, and the coatability is deteriorated. If the paste component strikes through, the water repellency, gas diffusivity, etc. of the gas diffusion layer deteriorate, which leads to a decrease in the power generation performance of the fuel cell.
On the other hand, if the DBP absorption amount of the first carbon black is too large, the structure is highly developed, so that the viscosity at the time of coating is high and the coatability is lowered, and the surface smoothness of MPL is also lowered. It should be noted that the decrease in the surface smoothness of the MPL reduces the bondability with the catalyst layer and causes stress due to the bite into the catalyst layer, which leads to a decrease in the battery performance and durability of the fuel cell.

Further, even if the DBP absorption amount of the second carbon black is too small, the chain structure of the carbon black particles is weak due to the low development of the structure of the second carbon black, and cracks are likely to occur in the MPL. Further, the paste component is likely to strike through during coating, and the coatability is also lowered.
On the other hand, if the amount of DBP absorbed by the second carbon black is too large, the structure is highly developed, so that the crack suppressing effect of MPL cannot be obtained.

If the first carbon black is in the range of DBP absorption amount of 210 ml / 100 g to 262 ml / 100 g and the second carbon black is in the range of DBP absorption amount of 32 ml / 100 g to 48 ml / 100 g, the coating is applied. Cracks in MPL can be effectively suppressed without deteriorating the properties and surface smoothness of MPL.

By the way, conventionally, in the production of MPL forming paste, carbon, water-repellent resin and the like are dispersed in a solvent by using a dispersant such as a surfactant and a thickener in order to secure coatability and film forming property. Is commonly done. However, if the dispersant blended in the MPL forming paste remains in the MPL, the water repellency of the MPL is impaired. This is because the hydrophilic groups of the dispersant trap water. Therefore, in order to develop sufficient water repellency, it is necessary to apply the MPL forming paste to the conductive porous substrate and then sufficiently decompose and remove the dispersant contained in the MPL forming paste by heating. was there.
Therefore, in the drying / baking step after applying the MPL forming paste, it takes a lot of time to thermally decompose and volatilize the dispersant, or it is necessary to treat the dispersant at a high temperature, and the dispersant is decomposed and removed. The reality is that the burden of this is increasing. Therefore, considering the widespread use of fuel cells, it is also desired to reduce the burden of decomposing and removing the dispersant during the drying / firing process from the viewpoint of improving productivity and reducing costs.

Therefore, as a result of diligent studies and pursuit of a technique capable of further reducing the load during drying and firing, the present inventors have specified the amount of iodine adsorbed on the first carbon black and the amount of iodine adsorbed on the second carbon black. It was found that the load during drying and firing can be reduced by controlling the amount in the above range, and based on these findings, the amounts of iodine adsorbed on the first carbon black and the second carbon black were defined.

That is, when the iodine adsorption amount of the first carbon black is in the range of 85 mg / g to 97 mg / g and the iodine adsorption amount of the second carbon black is in the range of 15 mg / g to 20 mg / g, the entire carbon black Since the specific surface area is suppressed, the carbon black can be sufficiently dispersed even with a small amount of the dispersant, and the viscosity characteristics suitable for coating can be obtained. In this way, since the amount of the dispersant required for dispersion can be suppressed, the heating time during the drying / firing step of thermally decomposing / volatilizing the dispersant can be shortened, and the load of the drying / firing step can be reduced. ..

Here, if the amount of iodine adsorbed by the first carbon black is too small, the chain of the three-dimensional structure of the carbon black particles is weak, and cracks are likely to occur in the MPL.
On the other hand, if the amount of iodine adsorbed by the first carbon black is too large, the viscosity at the time of coating is high and the coatability is lowered, and the surface smoothness of MPL is lowered. Further, since the specific surface area is large, a large amount of dispersant required for dispersing carbon black is required, and the effect of reducing the load in the drying / firing step cannot be obtained.

If the amount of iodine adsorbed on the second carbon black is too small, the surface area of the MPL is uneven because the specific surface area is small and the particle size is large. If the MPL has irregularities, the bondability with the catalyst layer is lowered, and stress is applied by biting into the catalyst layer, which leads to deterioration of the battery performance and durability of the fuel cell. In addition, the chain structure of carbon black particles is weak, and cracks are likely to occur in the MPL.
On the other hand, if the amount of iodine adsorbed on the second carbon black is too large, a large amount of dispersant required for dispersing the carbon black is required because the specific surface area is large, and the effect of reducing the load in the drying / firing step cannot be obtained.

If the amount of iodine adsorbed by the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodine adsorbed by the second carbon black is in the range of 15 mg / g to 20 mg / g, the coatability and MPL The heating time for decomposing and removing the dispersant during the drying / firing step can be shortened without lowering the surface smoothness of the surface, and the load on the drying / firing step can be effectively reduced. Then, by reducing the load in the drying / firing process, it is possible to reduce the manufacturing cost and improve the productivity.

Using carbon black that can be obtained inexpensively in this way, the first carbon having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and an iodine adsorption amount in the range of 85 mg / g to 97 mg / g. By using black in combination with a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g and an iodine adsorption amount in the range of 15 mg / g to 20 mg / g, coatability is achieved. Microporous, which can effectively suppress cracks in MPL at low cost without lowering the surface smoothness of MPL, and can reduce the load in the drying / baking process, resulting in cost reduction and improvement in productivity. It becomes a layer-forming paste composition.

According to the paste composition for forming a microporous layer of the invention of claim 1 , the blending ratio of the first carbon black / the second carbon black is such that the first carbon black / the second carbon black = 20/80 to It is within the range of 80/20.

If the blending ratio of the second carbon black to the first carbon black is too large, the carbon black, which is a component of the paste composition, may strike through and the coatability may be lowered, which may affect the battery performance. There is. On the other hand, if the blending ratio of the second carbon black to the first carbon black is too small, the effect of suppressing cracks in MPL is low, and it is not suitable for practical use.

When the blending ratio of the first carbon black / the second carbon black is preferably 20/80 or more and 80/20 or less, cracks in the MPL are effectively suppressed without deteriorating the coatability. be able to. More preferably, the blending ratio of the first carbon black / the second carbon black is 20/80 or more and 50/50 or less, and more preferably 20/80 or more and 30/70 or less.

According to the gas diffusion layer for a fuel cell of the invention of claim 2 , the DBP absorption amount is in the range of 210 ml / 100 g to 262 ml / 100 g, and the iodine adsorption amount is in the range of 85 mg / g to 97 mg / g. Dispersion of 1 carbon black, a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g, and an iodine adsorption amount in the range of 15 mg / g to 20 mg / g, and a water-repellent resin. A paste composition for forming a microporous layer containing an agent and a solvent was applied to a conductive porous base material, dried and fired to form the conductive porous base material and its surface. It consists of a microporous layer.

The present inventors have been diligently conducting experimental research on a technology capable of suppressing cracks in MPL, focusing on carbon black, which has extremely diverse physical property values and characteristics depending on manufacturing conditions and is available at low cost, and the degree of structural development. It has been found that cracks in MPL can be suppressed by controlling the chain structure and three-dimensional structure of carbon particles by combining carbon black having a specific difference in the above, and the present invention has been completed based on these findings.

That is, as carbon black, a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination. Then, the shrinkage stress at the time of film formation forming the MPL (the shrinkage stress generated at the time of drying and firing after applying the paste composition for forming a microporous layer to the conductive porous base material) can be relaxed, and cracks in the MPL can be relaxed. Was able to be suppressed.

Here, if the amount of DBP absorbed by the first carbon black is too small, the development of the structure of the first carbon black is low, and the formation of a strong three-dimensional structure by the chain of carbon black particles is reduced. Cracks are likely to occur in the MPL. Further, during coating, strike-through of the paste component (a phenomenon in which carbon black of the paste component escapes to the back surface side of the conductive porous base material on the opposite side to the coated surface) occurs, and the coatability is deteriorated. If the paste component strikes through, the water repellency of the gas diffusion layer decreases, which leads to a decrease in the power generation performance of the fuel cell.
On the other hand, if the DBP absorption amount of the first carbon black is too large, the structure is highly developed, so that the viscosity at the time of coating is high and the coatability is lowered, and the surface smoothness of MPL is also lowered. It should be noted that the decrease in the surface smoothness of the MPL reduces the bondability with the catalyst layer and causes stress due to the bite into the catalyst layer, which leads to a decrease in the battery performance and durability of the fuel cell.

Further, even if the DBP absorption amount of the second carbon black is too small, the chain structure of the carbon black particles is weak due to the low development of the structure of the second carbon black, and cracks are likely to occur in the MPL. Further, the paste component is likely to strike through during coating, and the coatability is also lowered.
On the other hand, if the amount of DBP absorbed by the second carbon black is too large, the structure is highly developed, so that the crack suppressing effect of MPL cannot be obtained.

If the first carbon black is in the range of DBP absorption amount of 210 ml / 100 g to 262 ml / 100 g and the second carbon black is in the range of DBP absorption amount of 32 ml / 100 g to 48 ml / 100 g, the coating is applied. Cracks in MPL can be effectively suppressed without deteriorating the properties and surface smoothness of MPL.

By the way, conventionally, in the production of MPL forming paste, carbon, water-repellent resin and the like are dispersed in a solvent by using a dispersant such as a surfactant and a thickener in order to secure coatability and film forming property. Is commonly done. However, if the dispersant blended in the paste remains in the MPL, the water repellency of the MPL is impaired. This is because the hydrophilic groups of the dispersant trap water. Therefore, in order to develop sufficient water repellency, it is necessary to sufficiently decompose and remove the dispersant contained in the paste by heating after applying the paste to the conductive porous substrate.
Therefore, in the drying / baking process after applying the paste, it takes a lot of time to thermally decompose and volatilize the dispersant, or it is necessary to treat the dispersant at a high temperature, which is a burden for decomposing and removing the dispersant. Is getting bigger. Therefore, considering the widespread use of fuel cells, it is also desired to reduce the burden of decomposing and removing the dispersant during the drying and firing steps from the viewpoint of improving productivity and reducing costs.

Therefore, as a result of diligent studies and pursuit of a technique capable of further reducing the load during drying and firing, the present inventors have specified the amount of iodine adsorbed on the first carbon black and the amount of iodine adsorbed on the second carbon black. It was found that the load during drying and firing can be reduced by controlling the amount in the above range, and based on these findings, the amounts of iodine adsorbed on the first carbon black and the second carbon black were defined.

That is, when the amount of iodide adsorbed on the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodide adsorbed on the second carbon black is in the range of 15 mg / g to 20 mg / g, the entire carbon black Since the specific surface area is suppressed, the carbon black can be sufficiently dispersed even with a small amount of the dispersant, and the viscosity characteristics suitable for coating can be obtained. In this way, since the amount of the dispersant required for dispersion can be suppressed, the heating time during the drying / firing step of thermally decomposing / volatilizing the dispersant can be shortened, and the load of the drying / firing step can be reduced. ..

Here, if the amount of iodine adsorbed by the first carbon black is too small, the chain of the three-dimensional structure of the carbon black particles is weak, and cracks are likely to occur in the MPL.
On the other hand, if the amount of iodine adsorbed by the first carbon black is too large, the viscosity at the time of coating is high and the coatability is lowered, and the surface smoothness of MPL is lowered. Further, since the specific surface area is large, a large amount of dispersant required for dispersing carbon black is required, and the effect of reducing the load in the drying / firing step cannot be obtained.

If the amount of iodine adsorbed on the second carbon black is too small, the surface area of the MPL is uneven because the specific surface area is small and the particle size is large. If the MPL has irregularities, the bondability with the catalyst layer is lowered, and stress is applied by biting into the catalyst layer, which leads to deterioration of the battery performance and durability of the fuel cell. In addition, the chain structure of carbon black particles is weak, and cracks are likely to occur in the MPL.
On the other hand, if the amount of iodine adsorbed on the second carbon black is too large, a large amount of dispersant required for dispersing the carbon black is required because the specific surface area is large, and the effect of reducing the load in the drying / firing step cannot be obtained.

If the amount of iodine adsorbed by the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodine adsorbed by the second carbon black is in the range of 15 mg / g to 20 mg / g, the coatability and MPL The heating time for decomposing and removing the dispersant during the drying / firing step can be shortened without lowering the surface smoothness of the surface, and the load on the drying / firing step can be effectively reduced. Then, by reducing the load in the drying / firing process, it is possible to reduce the manufacturing cost and improve the productivity.

In this way, carbon black, which is inexpensively available in the composition for forming a microporous layer, is used, the amount of DBP absorbed is in the range of 210 ml / 100 g to 262 ml / 100 g, and the amount of iodine adsorbed is 85 mg / g to 97 mg / g. The first carbon black in the range of 32 ml / 100 g to 48 ml / 100 g, and the second carbon black having an iodine adsorption amount in the range of 15 mg / g to 20 mg / g. When used in combination, cracks in MPL are effectively suppressed at low cost without deteriorating coatability and surface smoothness of MPL, and the load on the drying / baking process is reduced, resulting in cost reduction and production. A gas diffusion layer for a fuel cell with improved properties can be formed.

According to the gas diffusion layer for a fuel cell according to the invention of claim 2 , the compounding ratio of the first carbon black / the second carbon black is the first carbon black / the second carbon black = 20/80 to 80. It is within the range of / 20.

If the blending ratio of the second carbon black to the first carbon black is too large, the carbon black, which is a component of the paste composition, may strike through and the coatability may be lowered, which may affect the battery performance. There is. On the other hand, if the blending ratio of the second carbon black to the first carbon black is too small, the effect of suppressing cracks in MPL is low, and it is not suitable for practical use.

Compounding ratio of the first carbon black / the second carbon black is preferably 20/80 or more, as long as 80/20 or less, good coating properties of the coating film M PL, effectively MPL Cracks are suppressed. More preferably, the blending ratio of the first carbon black / the second carbon black is 20/80 or more and 50/50 or less, and more preferably 20/80 or more and 30/70 or less.

FIG. 1 is a schematic diagram showing a schematic configuration of a polymer electrolyte fuel cell using a gas diffusion layer formed by applying the paste composition for forming a microporous layer according to the embodiment of the present invention to a conductive porous base material. It is a figure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Since the same symbol and the same reference numeral mean the same or corresponding functional parts in the embodiment, duplicate detailed description will be omitted here.

First, with respect to the structure of the polymer electrolyte fuel cell (single cell) in which the gas diffusion layer for the fuel cell using the paste composition for forming the microporous layer according to the present embodiment is incorporated, refer to the schematic configuration diagram of FIG. I will explain while. In the figure, the anode side is A and the cathode side is K.

As shown in the figure, the gas diffusion layer 14 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A) is composed of a catalyst-supported carbon in which a noble metal catalyst such as platinum, gold, or palladium is supported by carbon, and an ion exchange resin, and is oxidized. It is joined to the catalyst layer 13 (cathode side catalyst layer 13K, anode side catalyst layer 13A) on which gas or fuel gas reacts, and integrally constitutes an electrode 12 (cathode electrode 12K, anode electrode 12A). Then, it is disposed together with the catalyst layer 13 on both sides of the polymer electrolyte membrane 11 (core of a single cell) that selectively permeates specific ions to form a membrane / electrode assembly (MEGA) 10.
The film / electrode joint 10 is provided with a cathode side separator 20K provided with an oxidation gas flow path 21K for supplying an oxidation gas serving as an oxidizing agent outside the cathode side gas diffusion layer 14K, and outside the anode side gas diffusion layer 14A. It is sandwiched between the anode side separator 20A provided with the fuel gas flow path 21A for supplying the fuel gas in the above, and forms a single cell of the fuel cell 1.

That is, in the fuel cell 1 in which the gas diffusion layer 14 to which the paste composition for forming the microporous layer according to the present embodiment is applied, an oxidation gas such as oxygen gas reacts on one surface of the polymer electrolyte film 11. A cathode electrode 12K composed of a cathode side catalyst layer 13K and a cathode side gas diffusion layer 14K is arranged, and an anode side catalyst layer 13A and an anode side gas diffusion layer 14A on which a fuel gas such as hydrogen gas reacts are arranged on the other surface. The membrane / electrode joint 10 that constitutes the power generation unit by arranging the anode electrode 12A composed of the above, and the cathode side separator 20K and the membrane / electrode joint that are arranged on the surface of the cathode electrode 12K of the membrane / electrode joint 10. It is composed of an anode side separator 20A arranged on the surface of the anode electrode 12A of the body 10.

Here, the gas diffusion layer 14 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A) according to the present embodiment is a paste composition for forming a microporous layer, which will be described later, on the surface of the conductive porous base material 16. The microporous layer (microporous layer) 15 (cathode side microporous layer 15K, anode side microporous layer 15A) becomes a conductive porous base material 16 (cathode side conductive porous layer). It is formed on one side of a quality base material 16K and an anode-side conductive porous base material 16A).
The gas diffusion layer 14 composed of the conductive porous base material 16 and the microporous layer 15 is arranged with the microporous layer 15 side on the catalyst layer 13 side and the conductive porous base material 16 side on the separator 20 side. It is incorporated so as to be arranged in the fuel cell 1 to form a fuel cell 1.

With such a configuration, when the oxidation gas is supplied from the outside to the oxidation gas flow path 21K of the cathode side separator 20K, a part of the oxidation gas flowing along the oxidation gas flow path 21K is the cathode side gas diffusion layer 14K. Infiltrates into the inside from the surface on the 16K side of the conductive porous base material of. The other unreacted oxidizing gas flows along the oxidizing gas flow path 21K and is discharged to the outside of the fuel cell 1.
Similarly, when fuel gas is supplied from the outside to the fuel gas flow path 21A of the anode side separator 20A, a part of the fuel gas flowing along the fuel gas flow path 21A is conductive in the anode side gas diffusion layer 14A. It penetrates into the inside from the surface on the porous base material 16A side. The other unreacted fuel gas flows as it is along the fuel gas flow path 21A and is discharged to the outside of the fuel cell 1.
Then, when the oxidation gas and the fuel gas react with each other, electric power is taken out between the cathode side separator 20K and the anode side separator 20A.
The microporous layer 15 may be formed on both the front and back surfaces of the conductive porous base material 16.

Next, the microphone porous layer 15 applied to the fuel cell gas diffusion layer 14 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A) incorporated in the fuel cell 1 having such a configuration is formed. The paste composition for forming a microporous layer for this purpose will be described.

The paste composition for forming a microporous layer of the present embodiment (hereinafter, may be abbreviated as “MPL paste composition”) is the conductivity of the microporous layer 15 (hereinafter, may be abbreviated as “MPL15”). Contains carbon black as a conductive material for ensuring properties, a water-repellent resin for ensuring the water repellency of MPL15, a solvent, and a dispersant for dispersing carbon black or the water-repellent resin in the solvent. Is what you do.

Carbon black is selected as the conductive material for imparting conductivity to MPL15. In carbon black, a plurality of primary particles are fused to form a three-dimensional structure called a structure.

The carbon black blended in the MPL paste composition of the present embodiment includes a first carbon black such as high-structured acetylene black having a well-developed structure and a low-structured thermal black having a low carbon structure. It is used in combination with the second carbon black.

Specifically, a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination. do. Preferably, the amount of DBP absorbed by the second carbon black is within the range of 0.1 to 0.2 times, more preferably within the range of 0.12 to 0.19 times, the amount of DBP absorbed by the first carbon black. Is.
As described above, as carbon black, the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and the second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used. When used in combination, the chain structure of carbon black is balanced in the coating film made of the MPL paste composition, and the shrinkage stress generated during film formation can be relaxed, so that the occurrence of cracks in MPL15 is suppressed. Since carbon black is a material that can be obtained at a lower cost than CNT, VGCF, etc., cost reduction can be achieved.

In particular, if the DBP absorption amount of the first carbon black is in the range of 210 ml / 100 g to 262 ml / 100 g and the DBP absorption amount of the second carbon black is in the range of 32 ml / 100 g to 48 ml / 100 g, the coatability And, while ensuring the surface smoothness of MPL15, cracks in MPL15 can be effectively suppressed.

That is, if the DBP absorption amount of the first carbon black is too small, the occurrence of cracks cannot be prevented. This is because if the structure of the first carbon black is low, the formation of a strong three-dimensional structure due to the chain of carbon black particles is reduced.
On the other hand, if the DBP absorption amount of the first carbon black is too large, the coatability and the smoothness of the coating film of MPL15 are also lowered. This is because if the structure is developed too high, the viscosity of the MPL paste composition increases, and when the MPL paste composition is applied to the conductive porous base material 16, coating streaks occur, resulting in uniform coating. This is because the sex cannot be secured. If the coating film of the MPL 15 has many irregularities, the bondability with the catalyst layer 13 may be deteriorated, or the catalyst layer 13 may be stressed by the convex portions, which may reduce the output and the life of the fuel cell 1. ..

Even if the amount of DBP absorbed by the second carbon black is too small, cracks occur because the structure of the second carbon black is less developed and the formation of a strong three-dimensional structure by the chain of carbon black particles is reduced. Cheap. Further, the viscosity of the MPL paste composition is low, the coatability is lowered, and the paste component strikes through (the phenomenon that the carbon black of the paste component escapes to the back surface side of the conductive porous base material 16 on the opposite side to the coated surface. ) Occurs. If the paste component strikes through, it may affect the battery performance.
On the other hand, if the amount of DBP absorbed by the second carbon black is too large, the crack suppressing effect of MPL15 cannot be obtained because the structure is highly developed.

Therefore, if the DBP absorption amount of the first carbon black is in the range of 210 ml / 100 g to 262 ml / 100 g and the DBP absorption amount of the second carbon black is in the range of 32 ml / 100 g to 48 ml / 100 g, the first carbon The structure of black and the second carbon black is well-balanced, and the shrinkage stress generated during film formation is alleviated by the appropriate three-dimensional chain structure of carbon black particles, while maintaining coatability and surface smoothness of MPL15. It is possible to stably suppress cracks in MPL15 with an inexpensive material. More preferably, the DBP absorption amount of the first carbon black is in the range of 210 ml / 100 g to 250 ml / 100 g, and the DBP absorption amount of the second carbon black is in the range of 32 ml / 100 g to 48 ml / 100 g. Within this range, it is easy to control the characteristics of MPL15 by adjusting the blending ratio of the first carbon black and the second carbon black.

Further, for the first carbon black, the iodine adsorption amount is preferably in the range of 85 mg / g to 97 mg / g. The amount of iodine adsorbed on the second carbon black is preferably in the range of 15 mg / g to 20 mg / g.
Within this range, the specific surface area of the entire carbon black is low, so that the amount of the dispersant required for dispersing the carbon black can be reduced. Therefore, it is possible to shorten the drying / firing time required for decomposing / eliminating the dispersant in the drying / firing step to develop sufficient water repellency. Alternatively, it is possible to reduce the heating temperature during drying and firing. Further, since a strong shear stress is not required for high dispersion, the three-dimensional structure of carbon black is maintained, and the strength and durability of MPL15 can be ensured. Further, energy consumption and manufacturing cost in the mixing and dispersing step and the drying and firing step can be suppressed.

Preferably, the amount of iodine adsorbed on the second carbon black is in the range of 0.1 to 0.2 times, more preferably 0.15 to 0.2 times, the amount of iodine adsorbed on the first carbon black. It is within the range.

Here, if the amount of iodine adsorbed by the first carbon black is too small, cracks are likely to occur in the MPL. This is because the formation of a strong three-dimensional structure due to the chain of carbon black particles is reduced.
On the other hand, if the amount of iodine adsorbed by the first carbon black is too large, the coatability is lowered due to the increase in viscosity of the MPL paste composition, and the surface smoothness of MPL15 is also lowered. Further, since the specific surface area is large, a large amount of dispersant required for dispersing carbon black is required, and the effect of reducing the load in the drying / firing step cannot be obtained.

Further, when the amount of iodine adsorbed on the second carbon black is too small, the MPL15 is likely to have irregularities due to its small specific surface area and large particle size, and the surface smoothness of the MPL15 is lowered. In particular, if the MPL 15 has a convex portion, structural stress is given to the MPL 15 by biting into the catalyst layer 13 when forming the fuel cell 1. Further, the bondability with the catalyst layer 13 may be deteriorated, or the electric charge may be concentrated around the convex portion. Therefore, the output and life of the fuel cell 1 may decrease. Further, the chain structure of carbon black particles is weak, and cracks are likely to occur in MPL15.
On the other hand, if the amount of iodine adsorbed on the second carbon black is too large, a large amount of dispersant required for dispersing the carbon black is required because the specific surface area is large, and the effect of reducing the load in the drying / firing step cannot be obtained.

Therefore, if the amount of iodine adsorbed by the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodine adsorbed by the second carbon black is in the range of 15 mg / g to 20 mg / g, the coatability And while maintaining the surface smoothness of MPL15, the occurrence of cracks can be suppressed, and the heating time for decomposing and removing the dispersant during the drying and firing steps can be significantly shortened, reducing the load on the drying and firing steps. can. Then, by shortening the drying / firing time, the electric power required for drying / firing can be reduced, and the production efficiency can be improved. In addition, by reducing the amount of electricity, it is possible to reduce the amount of carbon dioxide emitted, and the load on the natural environment can be reduced.

Such a combination of the first carbon black and the second carbon black is preferably 20/80 ≦ first carbon black / second carbon black ≦ 80/20.
If the blending ratio of the second carbon black is too large as compared with the first carbon black, the viscosity characteristics of the MPL paste composition are lowered and the paste components are strike-through, which may lower the battery performance. On the other hand, if the compounding ratio of the second carbon black is too small as compared with the first carbon black, the effect of relaxing the shrinkage stress at the time of film formation cannot be obtained, and the occurrence of cracks cannot be suppressed.

Therefore, preferably, the coating property is maintained by setting the blending ratio of the first carbon black and the second carbon black within the range of the first carbon black / the second carbon black = 20/80 to 80/20. At the same time, the occurrence of cracks in the MPL 15 can be stably suppressed, and the battery performance of the fuel cell 1 can be improved.

Examples of the water-repellent resin to be blended in the MPL paste composition of the present embodiment include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and perfluoroalkoxy alkanes resin. Fluorescent resins such as (PFA), polychlorotrifluoroethylene (PCTFE), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyfluorinated vinylidene (PVdF) , Silicone resin, etc. can be used. These can be used individually by 1 type or in combination of 2 or more types as appropriate. Normally, a water-repellent resin such as a fluororesin does not disperse in water as it is, so a water-repellent resin such as a fluororesin dispersed in water with an appropriate surfactant (dispersant) is emulsified. The emulsion is added in the form of a dispersion in which a water-repellent resin such as a fluororesin is dispersed.

By the way, an emulsion (emulsion; also referred to as an "emulsion") is also called an emulsion, and in the original sense, a liquid particle in the liquid forms a milky state as colloidal particles or coarser particles (dispersion system). Although there is (Saburo Nagakura et al., "Iwanami Physics and Chemistry Dictionary (5th Edition)", p. 152, published by Iwanami Shoten Co., Ltd. on February 20, 1998), it is generally used in a broader sense in this specification. The term "emulsion" is used here as "a liquid in which solid or liquid particles are dispersed".

Among these, a fluorine-based polymer material having excellent water repellency and corrosion resistance during an electrode reaction is preferable, and a PTFE emulsion capable of obtaining high water repellency is particularly preferable. The PTFE as the water-repellent resin may be a homopolymer of tetrafluoroethylene, a halogenated olefin such as chlorotrifluoroethylene or hexafluoropropylene, or another fluorine-based monomer such as perfluoro (alkyl vinyl ether). It may be a modified PTFE containing a unit derived from.

The average molecular weight of the water-repellent resin is preferably in the range of 50,000 to 1,000,000. If the average molecular weight is too low, the binding property as a binder for binding carbon black particles is small, while if the average molecular weight is too large, the paste tends to become fibrous during mixing and become poorly dispersed, resulting in paste stability. However, it becomes fibrous and hardens due to shearing force in the manufacturing process such as coating, which causes a change in concentration, clogging of pipes and pumps, and poor coating. Incidentally, when the water-repellent resin is a fluorine-based polymer, it is difficult to measure the average molecular weight by the melt viscosity because the fluorine-based polymer is difficult to dissolve in a solvent. Therefore, the specific gravity method for obtaining the average molecular weight from the relationship between the specific gravity and the number average molecular weight is applied.
Further, if the content of the water-repellent resin is too small, the water repellency is insufficient, or the binder effect is small and high coating film strength and bonding strength cannot be obtained. On the other hand, if the content is too large, the pores of MPL15 are reduced and the gas permeability is lowered. Therefore, it is desirable that the water-repellent resin has a content in the range of 5 to 50% by mass in terms of solid content in the total solid content of the MPL paste composition.

Further, in the MPL paste composition of the present embodiment, a dispersant is added to disperse and stabilize carbon black or a water-repellent resin in a solvent, or to adjust the viscosity.
Examples of such dispersants include polyoxyethylene tridecyl ether, polyoxyethylene alkyl phenyl ether (Triton X-100, etc.), polyoxyethylene lauryl ether, polyoxyethylene distyrene phenyl ether, and polyoxyethylene alkylene. Nonionic (nonionic) surfactants such as alkyl ethers and polyethylene glycol alkyl ethers, cationic surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium chlorides and alkylpyridium chlorides, polyoxyethylene fatty acid esters, acidic groups Surface active agents such as anionic surfactants such as structurally modified polyacrylates, polyethylene oxide, methyl cellulose, hydroxyethyl cellulose, polyethylene glycol (for example, ethers of alkylphenol and polyethylene glycol, higher aliphatic alcohols and polyethylene glycol). (Ethers, etc.), polyvinyl alcohol-based thickeners, etc. are used.

Among these, nonionic (nonionic) surfactants are preferable because they have a low content of metal ions and are less likely to cause deterioration of battery performance due to short circuits, etc., and are particularly preferable as carbon black and water repellent resins. When using the PTFE emulsion of the above, in order to improve the wettability and dispersibility of these carbon blacks and polyethylene particles, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene alkyl phenyl ether ( Triton X-100) and the like are preferably used. As described above, an emulsion of a water-repellent resin or the like may be mixed in a state containing a dispersant.

By blending such a dispersant, the dispersibility of carbon black and the water-repellent resin is improved, the stability of the paste is enhanced, and the coatability and storability are improved. In addition, it is possible to prevent a change in concentration and clogging of pipes, pumps, etc. at the time of coating, and good film forming property can be obtained. Further, the MPL 15 which is homogeneous and has less surface undulation can be formed, the contact resistance with the catalyst layer 13 becomes small, characteristics such as good gas diffusivity can be obtained, and a stable output can be obtained in the fuel cell 1. The type of dispersant such as a surfactant or a thickener is selected according to the properties required for MPL15 and the compounding material, and the dispersant may have two functions of a surfactant and a thickener.

The dispersant is blended in an amount necessary to disperse carbon black or a water-repellent resin in a solvent by adding the dispersant to ensure coatability suitable for coating. And because it causes deterioration of battery performance, it is adjusted within the range where such a problem does not occur.

In particular, when the iodine adsorption amount of the first carbon black is in the range of 85 mg / g to 97 mg / g and the iodine adsorption amount of the second carbon black is in the range of 15 mg / g to 20 mg / g,
The specific surface area of the entire carbon black is low, and the amount of dispersant (surfactant, etc.) required for dispersion in a solvent can be reduced.

As described above, the first carbon black such as acetylene black having a predetermined range of DBP absorption amount and iodine adsorption amount, and the thermal black having a smaller DBP absorption amount and less iodine adsorption amount than the first carbon black, etc. In order to apply the MPL paste composition containing the second carbon black, a water-repellent resin such as PTFE, and a dispersant such as a surfactant to the gas diffusion layer 14 for the fuel cell 1, the gas diffusion layer 14 is provided. When applied to the surface of the constituent conductive porous base material 16, the above-mentioned compounding material is mixed and dispersed in a solvent such as ion-exchanged water to prepare a paste.

As the solvent (dispersion medium) at this time, each compounding material of carbon black, water-repellent resin, and dispersant can be mixed and dispersed to ensure coatability, and the solvent is dried after being applied to the surface of the conductive porous base material 16. -It may be any one that disappears (volatilizes) in the firing step, and an aqueous solvent such as ion-exchanged water is preferably used. If it is an aqueous solvent such as ion-exchanged water, the dispersibility of the water-repellent resin such as PTFE emulsion is better than that when an organic solvent is used, the water-repellent resin does not separate, and the film forming property is good. Is obtained. In addition, workability during coating and firing is good, and there is no risk of ignition. Furthermore, it does not impose an environmental load and is low in cost.

Further, in the process of adding each compounding material to an arbitrary container and mixing and dispersing them, stirring using a general mixer such as a dispenser or planetary or a bead mill or the like is also possible, but a stirring blade or the like can be used. It is desirable to disperse by utilizing the collision energy generated by the contact (collision) between the materials and the contact (collision) of the material with the inner wall of the stirring container without using the shearing force of the material. For example, it is preferable to mix and disperse using a planetary stirring / defoaming device or the like that can set the revolution / rotation to a specific value. As a result, carbon black can be dispersed while maintaining the three-dimensional structure of carbon black without causing destruction of the three-dimensional structure of carbon particles of carbon black, so that a strong three-dimensional bond between the water-repellent resin and carbon black can be achieved. It is possible to obtain the strength of the coating film which is hard to be broken and prevent the occurrence of cracks. In addition, when high shear stress is applied during mixing and dispersion, carbon black particles and water-repellent resin particles tend to agglomerate, and a large amount of agglomerates occur, causing clogging of the filter and chipping of the coating film during coating. By using a planetary stirring / defoaming device, agglomeration of particles is prevented, and clogging of the filter and loss of the coating film during coating are prevented. Further, by using a planetary stirring / defoaming device, since the device does not have a stirring blade or the like, cleaning is not troublesome and the yield is improved, so that the cost can be reduced. .. In addition, when carrying out this invention, it is possible to add other additives as needed.

The MPL paste composition thus prepared in the form of a paste is applied to the surface of the conductive porous base material 16 constituting the gas diffusion layer 14 for the fuel cell 1, and then dried and fired. , MPL15 coating film. Then, as shown in FIG. 1, the gas diffusion layer 14 is formed by the conductive porous base material 16 and the coating film of MPL15 formed on one side thereof.

Here, the conductive porous base material 16 to which the MPL paste composition is applied is generally used in the gas diffusion layer 14 of the conventional fuel cell 1 (particularly, the polymer electrolyte fuel cell 1). That is, a porous substrate having gas permeability and conductivity is used. For example, carbon materials such as graphite (including nanocarbon materials) are composed of fibrous, particulate, woven fabric, non-woven fabric, mesh, lattice, punched materials, foams and other porous materials. Can be used. In particular, carbon fiber is preferable from the viewpoint of gas permeability and the like, and more specifically, a carbon base material such as carbon paper, carbon cloth, and carbon felt (carbon non-woven fabric) is preferably used. These are selected in consideration of the usage status of the fuel cell 1, operating conditions, and the like.

If necessary, the conductive porous base material 16 such as carbon paper and carbon cloth is subjected to a water repellent treatment in order to improve the water repellency of the gas diffusion layer 14. As the water repellent used for this water repellent treatment, the same water repellent resin that can be used in the above-mentioned MPL paste composition is used.

The thickness of the conductive porous base material 16 constituting the gas diffusion layer 14 for the fuel cell 1 is set in consideration of the operating conditions and the required performance of the fuel cell 1, but the conductive porous base material If 16 is too thin, the strength will be insufficient and the performance of the gas diffusion layer 14 such as stable gas diffusivity, drainage, and conductivity will not be obtained, or the handling will be poor and the position will be misaligned with the catalyst layer 13. It may occur and cause a decrease in battery performance. Further, if the conductive porous base material 16 is too thick, the gas diffusivity is lowered and the internal resistance value is increased, so that high battery performance cannot be obtained. Therefore, for example, it is used with a thickness in the range of 2 μm to 500 μm.

The MPL paste composition is applied to the conductive porous substrate 16 by brush coating, brush coating, roll coater method, bar coater method, die coater method, blade method, knife coater method, spin coater method, screen printing, rotary screen printing. , Curtain coating method, dip coater method, spray coater method, gravure coater method, applicator, spray spray and the like. In particular, the die coater method is suitable because the amount of coating can be quantified regardless of the surface roughness of the conductive porous base material 16, but is not necessarily limited to this.

The coating film thickness of the MPL paste composition is set in consideration of the operating conditions of the fuel cell 1 and the performance required for the MPL 15. For example, the dry film thickness (thickness of MPL15) of the coating film after drying and firing is set to be in the range of 1 μm to 300 μm, preferably in the range of 10 to 100 μm.
If the dry film thickness is too thin, the effect of absorbing the unevenness of the conductive porous base material 16 and preventing the fibers of the conductive porous base material 16 from sticking into the electrolyte membrane 11 cannot be obtained. On the other hand, if the coating film thickness is too thick, the surface smoothness tends to decrease due to shrinkage due to drying and firing, and the contact resistance with the catalyst layer 13 increases. Further, when the dry film thickness is thick, the electric resistance in the thickness direction becomes high.
When the dry film thickness is in the range of 1 μm to 300 μm, MPL15 having high surface smoothness can be obtained, and good gas permeability and electrical resistance can be ensured. Further, it is desirable that the thickness of the MPL 15 is 50% or less with respect to the thickness of the conductive porous base material 16. When the difference in thickness is within an appropriate range, the shrinkage stress between the conductive porous base material 16 and the MPL 15 due to drying and firing is small, and high bonding strength can be obtained. Further, the smoothness of the entire gas diffusion layer 14 is increased, and the contact resistance with the catalyst layer 13 is reduced.

The MPL paste composition applied to the conductive porous base material 16 in this manner is dried and fired to form a coating film made of MPL15 having conductivity, water repellency and gas diffusivity. That is, by drying and firing, the dispersant and solvent (moisture) in the MPL paste composition are removed to ensure water repellency by the water-repellent resin, and pores (voids) are formed to ensure gas diffusivity. Then, it is possible to obtain MPL15 in which conductivity is ensured by carbon black. Further, a part of the water-repellent resin is melted and a conductive material (a conductive substance such as carbon particles or carbon fibers of the conductive porous base material 16) is bound to form MPL15 to be strong. do.

At this time, if the dispersant is not sufficiently removed by heat treatment in the drying / firing step, water is trapped by the remaining hydrophilic groups of the dispersant, so that sufficient water repellency can be exhibited in MPL15. However, when applied to the fuel cell 1, practical water repellency cannot be obtained. Therefore, in the drying / firing treatment, a sufficient time and temperature are required to remove the dispersant.

In particular, in the present embodiment, the iodine adsorption amount of the first carbon black is in the range of 85 mg / g to 97 mg / g, and the iodine adsorption amount of the second carbon black is in the range of 15 mg / g to 20 mg / g. If there is, the specific surface area of the entire carbon black can be suppressed, and the amount of the dispersant (surfactant or the like) required for dispersion in the solvent can be reduced. Further, the increase in viscosity of the MPL paste composition is suppressed, and the viscosity characteristics suitable for coating can be obtained with a small amount of solvent. Therefore, the firing / drying time required for thermally decomposing / volatilizing the dispersant and the solvent (moisture) can be shortened, and the dispersant and the solvent (moisture) can be sufficiently removed in a short drying / firing time. That is, the drying / firing time required to sufficiently remove the dispersant and the solvent (moisture) to develop water repellency can be shortened.

When the drying / firing time is short in this way, the electric power required for drying / firing can be reduced, and the length of the drying / firing furnace can be shortened, so that the load required for the drying / firing process can be reduced, and the manufacturing cost can be reduced. Can be reduced. As a result, it is possible to reduce the cost of the gas diffusion layer 14, and thus the fuel cell 1. Moreover, since the amount of carbon dioxide emitted can be reduced by reducing the amount of electricity, the load on the natural environment can be reduced. In addition, the production efficiency can be improved by shortening the drying / firing time.

The drying / firing temperature at this time is set to a temperature at which the dispersant can be thermally decomposed / volatilized and removed. For example, the dispersants are polyoxyethylene tridecyl ether and polyoxyethylene alkyl phenyl ether (Triton X-100). ) Etc., the temperature is set in the range of 250 to 350 ° C.
If the drying / firing temperature is too low, the dispersant cannot be sufficiently thermally decomposed / volatilized to be removed even if the drying / firing time is lengthened, and the dispersant remains and moisture is caused by those hydrophilic groups. Is trapped, so that sufficient water repellency cannot be exhibited in the gas diffusion layer 14 to be formed.
On the other hand, if the drying / firing temperature is too high, the coating film components such as the water-repellent resin are thermally decomposed and the components of MPL15 are deteriorated, or the deformation of MPL15 is increased due to a high temperature change and the smoothness is lowered. , Cracks occur, and it becomes difficult to form MPL15 that satisfies the desired required performance. Furthermore, the load in the drying / firing process and the load on the natural environment increase, and the manufacturing cost also increases.

If the dispersant is, for example, polyoxyethylene alkyl phenyl ether (Triton X-100) or polyoxyethylene tridecyl ether, the drying / firing temperature can be set within the range of 250 ° C to 350 ° C to spread the dispersant. Is completely decomposed and volatilized and does not remain, so that water repellency, which is an important characteristic of the gas diffusion layer 14, which greatly affects power generation efficiency, can be secured, MPL15 having desired characteristics can be formed, and a conductive porous base material can be formed. Good bonding with 16 can be ensured.

As described above, the iodine adsorption amount of the first carbon black is in the range of 85 mg / g to 97 mg / g, and the iodine adsorption amount of the second carbon black is in the range of 15 mg / g to 20 mg / g. Since the amount of dispersant (surfactant, etc.) required for dispersion in the solvent is small and the viscosity characteristics are suitable for coating with a small amount of solvent, it can be dispersed even at low drying and firing temperatures. The drying / firing time required for removing the agent and the solvent (moisture) does not become significantly long, and it is possible to develop water repellency by drying / firing for a short time. That is, even when drying / firing at a lower temperature, the drying / firing time required for removing the dispersant and the solvent (moisture) can be shortened, and the drying / firing temperature can be reduced. Further, by reducing the drying / firing temperature, it is possible to suppress the electric power required for drying / firing to reduce the load applied to drying / firing, and it is possible to reduce the manufacturing cost. Further, the load applied to the natural environment can be reduced, and further, deterioration of the coating film component due to high temperature heating, generation of cracks, deterioration of the fixing force to the conductive porous base material 16, and the like can be prevented.

In the drying / firing step involving heat treatment, the order of drying and firing is not particularly limited, and drying and firing may be performed at the same time. It is also possible to change the temperature and time conditions between the heat treatment mainly for decomposing and removing the dispersant and the heat treatment mainly for binding by melting the water-repellent resin, and each heat treatment can be performed separately. be.

In this way, the MPL paste composition is applied to the surface of the conductive porous base material 16, dried and fired to form MPL 15 on the conductive porous base material 16, and the conductive porous material 16 is formed. A fuel cell gas diffusion layer 14 composed of the base material 16 and the MPL 15 can be obtained. In the fuel cell 1 in which the fuel cell diffusion layer 14 made of the conductive porous base material 16 and the MPL 15 is incorporated, the MPL 15 The presence improves gas diffusivity and water management and stabilizes power generation performance. Further, by adjusting the components of MPL15, it is possible to obtain controllability of performance according to the battery usage environment, operating conditions, etc., which is difficult only with the conductive porous base material 16. Further, the MPL 15 absorbs the undulations of the conductive porous base material 16 to obtain a smooth surface. That is, the MPL 15 can avoid the occurrence of a short circuit due to fraying or fluffing of the carbon fibers of the conductive porous base material 16 piercing or contacting the catalyst layer 13 or the polymer electrolyte membrane 11.

Then, in the gas diffusion layer 14 produced by using the MPL paste composition of the present embodiment, the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g in the MPL paste composition is used. By using the second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g in combination, the shrinkage stress generated in the coating film when heated in the drying / firing step is alleviated. The generation of cracks on the surface of MPL15 is suppressed. Then, since the durability of the gas diffusion layer 14 is improved and the characteristics of the gas diffusion layer 14 are stabilized by reducing the cracks of the MPL 15, the durability and the output characteristics of the fuel cell 1 can be improved.

In particular, the DBP absorption amount of the first carbon black in the MPL paste composition is in the range of 210 ml / 100 g to 262 ml / 100 g, and the DBP absorption amount of the second carbon black is in the range of 32 ml / 100 g to 48 ml / 100 g. If there is, it is possible to secure the coatability without causing strike-through of the paste due to the decrease in viscosity or the occurrence of coating streaks due to the increase in viscosity, and further, the surface of MPL15 has less unevenness and undulations on the surface. Excellent smoothness. Since the MPL 15 having a smooth surface can be formed, the contact with the catalyst layer 13 is good even when the fuel cell 1 is incorporated, and the catalyst layer 13 is not mechanically stressed. It is possible to improve the durability and stable output characteristics. Moreover, since carbon black is remarkably low in price as compared with VGCF and CNT, the cost can be reduced.

In this way, the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and the second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination at low cost. By using carbon black, which is a suitable material, the occurrence of cracks on the surface of MPL15 can be suppressed. Since the occurrence of cracks on the surface of the MPL15 can be suppressed, the situation where water accumulates in the cracks on the surface of the MPL15 can be prevented. It is possible to prevent peeling and destruction of 13 and MPL15. Further, when cracks are suppressed, the gas diffusibility becomes uniform, and a uniform gas supply can be performed. Therefore, it is possible to cope with changes in the ambient environment conditions of the fuel cell 1 and to enable a stable output of the fuel cell 1 with high durability.

As described above, the high-structured first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and the low-structured first carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g. Since 2 carbon black is used in combination, the pore size and porosity of MPL are controlled by adjusting the composition of the high-structured first carbon black and the low-structured second carbon black, that is, the characteristics such as gas diffusivity and conductivity are controlled. Is easily possible.

Further, since carbon black generally has an aggregated structure of carbon particles having a diameter (primary particle diameter) of about 3 to 500 nm, MPL15 having a smooth surface and excellent surface smoothness can be obtained. Therefore, the adhesion to the catalyst layer 13 can be increased, the contact resistance on the contact surface can be reduced, and the power generation efficiency can be improved. Further, biting into the catalyst layer 13 is prevented, and stress can be reduced. Therefore, the output and durability of the fuel cell 1 can be improved.
That is, since cracks on the surface of MPL15 are suppressed and the surface smoothness is excellent, the bonding strength with the catalyst layer 13 is higher, the effect of preventing peeling between MPL15 and the catalyst layer 13 is also high, and the length of the fuel cell 1 is high. The life can be extended. Further, since the crack of the MPL 15 is suppressed and the contact resistance with the catalyst layer 13 is small, it is possible to improve the battery performance by improving the conductivity.

Further, when the amount of iodide adsorbed on the first carbon black is in the range of 85 mg / g to 97 mg / g and the amount of iodide adsorbed on the second carbon black is in the range of 15 mg / g to 20 mg / g, it is added to the solvent. The amount of dispersant (surfactant, etc.) required for dispersion can be reduced. In addition, the increase in viscosity is suppressed, and the viscosity characteristics suitable for coating can be obtained with a small amount of solvent. Therefore, the firing / drying time required for thermally decomposing / volatilizing the dispersant and the solvent (moisture) can be shortened, the production time of the gas diffusion layer 14 can be shortened, and the productivity can be improved. Further, since the amount of energy used and the cost can be reduced by shortening the firing / drying time, the manufacturing cost can be reduced.

Therefore, the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and an iodine adsorption amount in the range of 85 mg / g to 97 mg / g, and a DBP absorption amount of 32 ml / 100 g to The occurrence of cracks in MPL15 is caused by the combined use of a predetermined carbon black, which is an inexpensive material, with the second carbon black, which is in the range of 48 ml / 100 g and has an iodine adsorption amount in the range of 15 mg / g to 20 mg / g. In addition to being able to be suppressed, the load on the firing / drying step can be reduced by shortening the firing / drying time, and the gas diffusion layer 14 can be manufactured at low cost.

That is, the first carbon black is in the range of DBP absorption amount of 210 ml / 100 g to 262 ml / 100 g, and the iodine adsorption amount is in the range of 85 mg / g to 97 mg / g, and the second carbon black is in the range of DBP absorption amount of 32 ml / 100 g. When the amount is within the range of ~ 48 ml / 100 g and the amount of iodine adsorbed is within the range of 15 mg / g to 20 mg / g, the specific surface area and the structure of the first carbon black are balanced, and the specific surface area of the second carbon black Since the structure is balanced, it is possible to suppress cracks on the surface of MPL15 while maintaining good coatability and surface smoothness of MPL15, and it is possible to shorten the heat treatment time required for removing the dispersant, which is an inexpensive material. It is possible to reduce the cost by using carbon black and shortening the heat treatment time.

Further, the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and an iodine adsorption amount in the range of 85 mg / g to 97 mg / g, and a DBP absorption amount of 32 ml / 100 g to 48 ml / g. Since it is used in combination with the second carbon black, which is in the range of 100 g and has an iodine adsorption amount in the range of 15 mg / g to 20 mg / g, it does not pierce the polymer electrolyte membrane 11 like fibers. In addition, since these carbon blacks have a small particle size, the surface of the coating film of MPL15 has less unevenness. Therefore, even when the fuel cell 1 is incorporated, the polymer electrolyte membrane 11 and the catalyst layer 13 are less likely to be deteriorated, and the durability of the fuel cell 1 can be improved.

Next, the compounding composition of the paste composition for forming a microporous layer according to the embodiment of the present invention is specifically shown, and the paste composition for forming a microporous layer and the gas diffusion layer for a fuel cell produced using the same are shown. 14 examples will be described.

First, MPL paste compositions containing the formulations of Examples 1 to 6 were prepared with the formulation contents shown in Table 1 as the formulation composition of the MPL paste composition according to the present embodiment. In addition, for comparison, MPL paste compositions according to Comparative Examples 1 to 5 were also prepared. The compounding contents of each example are shown in the upper part of Table 1, and the compounding contents of each comparative example are shown in the upper part of Table 2.

In the MPL paste compositions according to Examples and Comparative Examples, acetylene black (for example, "Denka Black (registered trademark)" manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as the first carbon black, and thermal black was used as the second carbon black. (For example, "Thermax (registered trademark)" manufactured by Cancarb and "Asahi Thermal" manufactured by Asahi Carbon Co., Ltd.) were used.
Further, a PTFE emulsion (manufactured by Daikin Industries, Ltd .: POLYFLON PTFE D-210C [solid content (resin content) 61%]) was used as the water-repellent resin, and the surfactant Triton X-100 was used as the dispersant. Ion-exchanged water was used as the solvent. The PTFE emulsion also contains a nonionic surfactant (dispersant) for stabilizing PTFE fine particles as a water-repellent resin.

The DBP absorption amount and iodine adsorption amount of acetylene black as the first carbon black and thermal black as the second carbon black are as shown in Tables 1 and 2.
Here, the DBP absorption amount (ml / 100 g) conforms to JIS K 6217-4, and the viscosity characteristics when DBP is added to carbon black using an S-500 absorption amount measuring device (manufactured by Asahi Soken Co., Ltd.). The torque generated by the change in the above torque was detected, and the amount of DBP added at 70% of the maximum torque was obtained by converting it per 100 g of the sample.
The amount of iodine adsorbed (mg / g) is in accordance with JIS K 6217-1, and the dried carb black is weighed, mixed with a standard iodine solution (0.0473N), and the supernatant is centrifuged to thiosulfate. It was titrated with a sodium solution and calculated from the titrated value and the mass of the sample.

The blending amount (part by weight) of each material is as shown in Tables 1 and 2. In all of Examples and Comparative Examples, the blending amount and blending ratio of each material are adjusted so that the total amount of the MPL paste composition is 400 g.
In Example 1, 15.5 parts by weight of acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g as the first carbon black, and a DBP absorption amount of 40 ml / 100 g as the second carbon black, iodine adsorption. 3.9 parts by weight of thermal black with an amount of 17 mg / g, 4.3 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.6 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 1 was prepared by blending 1.6 parts by weight of -100 and 74.7 parts by weight of ion-exchanged water.

In the blending of Example 1, the blending ratio of the first carbon black / the second carbon black is 80/20, and the blending amount of the second carbon black is 25 with respect to 100 parts by weight of the blending amount of the first carbon black. It is a part by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the blending amount of the first carbon black is 65.7 parts by weight, the blending amount of the second carbon black is 16.5 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 82.2 parts by weight.

In Example 2, DBP absorption amount of 230 ml / 100 g as the first carbon black, 10.6 parts by weight of acetylene black having an iodine adsorption amount of 92 mg / g, DBP absorption amount of 40 ml / 100 g as the second carbon black, and iodine adsorption. 10.6 parts by weight of thermal black with an amount of 17 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 2 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

In the blending of Example 2, the blending ratio of the first carbon black / the second carbon black is 50/50, and the blending amount of the second carbon black is 100 with respect to 100 parts by weight of the blending amount of the first carbon black. It is a part by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the blending amount of the first carbon black is 41.9 parts by weight, the blending amount of the second carbon black is 41.9 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 83.8 parts by weight. In Example 2, the total amount of carbon black blended was increased as compared with Example 1, but since the blending ratio of the second carbon black was increased, a small amount of the dispersant used was sufficient for carbon. I was able to disperse the black.

In Example 3, the DBP absorption amount of 230 ml / 100 g as the first carbon black, 4.6 parts by weight of acetylene black having an iodine adsorption amount of 92 mg / g, and the DBP absorption amount of 40 ml / 100 g as the second carbon black, iodine adsorption 18.3 parts by weight of thermal black with an amount of 17 mg / g, 5.1 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 3.1 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 3 was prepared by blending -100 by 0.6 parts by weight and ion-exchanged water by 71.4 parts by weight.

In the compounding of Example 3, the compounding ratio of the first carbon black / the second carbon black is 20/80, and the compounding amount of the second carbon black is 400 with respect to 100 parts by weight of the compounding amount of the first carbon black. It is a part by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the amount of the first carbon black compounded is 17.2 parts by weight, the amount of the second carbon black compounded is 68.8 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 86 parts by weight. In Example 3, the total amount of carbon black blended was increased as compared with Examples 1 and 2, but since the blending ratio of the second carbon black was increased, a smaller amount of dispersant was used. The amount was sufficient to disperse the carbon black.

In Example 4, a DBP absorption amount of 210 ml / 100 g as the first carbon black, an acetylene black having an iodine adsorption amount of 85 mg / g was 10.6 parts by weight, and a DBP absorption amount of 32 ml / 100 g as the second carbon black, iodine adsorption. 10.6 parts by weight of thermal black with an amount of 15 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 4 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

In the compounding of Example 4, the compounding ratio of the first carbon black / the second carbon black is 50/50, and the compounding amount of the second carbon black is 100 with respect to 100 parts by weight of the compounding amount of the first carbon black. It is a part by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the blending amount of the first carbon black is 41.9 parts by weight, the blending amount of the second carbon black is 41.9 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 83.8 parts by weight.

In Example 5, DBP absorption amount of 250 ml / 100 g as the first carbon black, 10.6 parts by weight of acetylene black having an iodine adsorption amount of 95 mg / g, DBP absorption amount of 48 ml / 100 g as the second carbon black, and iodine adsorption. 10.6 parts by weight of thermal black with an amount of 20 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 5 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

Even in the compounding of Example 5, the compounding ratio of the first carbon black / the second carbon black is 50/50, and the compounding amount of the second carbon black is 100 with respect to 100 parts by weight of the compounding amount of the first carbon black. It is a part by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the blending amount of the first carbon black is 41.9 parts by weight, the blending amount of the second carbon black is 41.9 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 83.8 parts by weight.

In Example 6, acetylene black having a DBP absorption amount of 262 ml / 100 g and an iodine adsorption amount of 97 mg / g as the first carbon black was 6.7 parts by weight, and DBP absorption amount was 32 ml / 100 g as the second carbon black and iodine adsorption. 15.8 parts by weight of thermal black with an amount of 15 mg / g, 4.8 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Example 6 was prepared by blending 0.8 parts by weight of -100 and 71.9 parts by weight of ion-exchanged water.

In the compounding of Example 6, the compounding ratio of the first carbon black / the second carbon black is 30/70, and the compounding amount of the second carbon black is 235 with respect to 100 parts by weight of the compounding amount of the first carbon black. 0.8 parts by weight. Further, with respect to 100 parts by weight of the total solid content of the paste composition, the blending amount of the first carbon black is 25.6 parts by weight, the blending amount of the second carbon black is 60.3 parts by weight, and the first. The total amount of carbon black and second carbon black blended is 85.9 parts by weight.

On the other hand, Comparative Examples 1 to 4 use carbon black, which is different from Examples 1 to 6 in the amount of DBP absorbed and the amount of iodine adsorbed.
In Comparative Example 1, 10.6 parts by weight of acetylene black having a DBP absorption amount of 185 ml / 100 g and an iodine adsorption amount of 81 mg / g as the first carbon black, and a DBP absorption amount of 40 ml / 100 g as the second carbon black, iodine adsorption. 10.6 parts by weight of thermal black with an amount of 17 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Comparative Example 1 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

In Comparative Example 2, 10.6 parts by weight of acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g as the first carbon black, and a DBP absorption amount of 51 ml / 100 g as the second carbon black, iodine adsorption. 10.6 parts by weight of thermal black with an amount of 26 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Comparative Example 2 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

In Comparative Example 3, 10.6 parts by weight of acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g as the first carbon black, and 26 ml / 100 g of DBP absorption amount as the second carbon black, iodine adsorption. 10.6 parts by weight of thermal black with an amount of 11 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Comparative Example 3 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

In Comparative Example 4, 10.6 parts by weight of acetylene black having a DBP absorption amount of 270 ml / 100 g and an iodine adsorption amount of 100 mg / g as the first carbon black, and 32 ml / 100 g of DBP absorption amount as the second carbon black, iodine adsorption. 10.6 parts by weight of thermal black with an amount of 15 mg / g, 4.7 parts by weight of PTFE emulsion as a water-repellent resin (of which solid content (resin content); 2.9 parts by weight), Triton X as a dispersant The MPL paste composition according to Comparative Example 4 was prepared by blending -100 by 1.2 parts by weight and ion-exchanged water by 72.9 parts by weight.

Further, in Comparative Example 5, only the first carbon black is blended as the carbon black without using the first carbon black and the second carbon black having a predetermined DBP absorption amount and iodine adsorption amount in combination.
That is, in Comparative Example 5, 17.6 parts by weight of acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g as the first carbon black, and 3.9 parts by weight of the PTFE emulsion as a water-repellent resin. (Of which, solid content (resin content); 2.4 parts by weight), 1.8 parts by weight of Triton X-100 as a dispersant, and 76.7 parts by weight of ion-exchanged water were added to the MPL paste according to Comparative Example 5. It was made into a composition.

In the production of the MPL paste composition according to each of these Examples and Comparative Examples, first, ion-exchanged water as a solvent and Triton X-100 as a dispersant were placed in a container (Kinki Container Co., Ltd.'s "Nanko Container No. 60 ”) and stir to dissolve Triton X-100. Further, a predetermined carbon black and PTFE emulsion as a water-repellent resin are put therein. Then, using a planetary stirring / defoaming device (“Rotating / Revolving Mixer AR500” manufactured by Shinky Co., Ltd.), the stirring mode is defoamed in order at a rotation speed of 500 rpm for 1 minute and in a stirring mode at a rotation speed of 2000 rpm for 3 minutes. Mix and disperse and defoam for 2 minutes at a rotation speed of 2000 rpm in the foam mode. In this way, MPL paste compositions according to Examples and Comparative Examples were produced.

Further, a gas diffusion layer 14 for a fuel cell was produced using the MPL paste composition according to Examples and Comparative Examples produced in this manner. Specifically, while pulling carbon paper (manufactured by Toray Industries, Inc .; TGP-060, average penetrating pore diameter 30 μm; measured by a palm paste meter) as the conductive porous base material 16 at a speed of 1 m / min, the carbon paper is pulled. The MPL paste composition according to each Example and each Comparative Example was applied to one side using a thin film coating tool (die head). ^{The coating amount at this time is 30 g / m 2 in} terms of the weight of the dry coating film (the weight of the coating film after drying and firing to form the microporous layer 15) from the thin film coating tool (die head) to the MPL paste composition. A predetermined amount of the substance was discharged. Then, the gas diffusion layer 14 made of the conductive porous base material 16 (carbon paper) and MPL 15 was produced by drying and firing (heat treatment) at 350 ° C. in an air atmosphere.

Here, drying and firing (heat treatment) at 350 ° C. was carried out for a predetermined time until the water repellency of MPL15 was developed. Specifically, a coating film of an MPL paste composition (a coating film of an MPL paste composition) which is dried and fired (heated) for a predetermined time, the obtained gas diffusion layer 14 is erected vertically, and is applied to a conductive porous base material 16 made of carbon paper. The surface of MPL15) was sprayed with ion-exchanged water (about 3 g of ion-exchanged water was sprayed in 5 portions), and the water-repellent state of whether or not water droplets adhered was confirmed. At this time, when the water droplets fell without adhering, it was judged that sufficient water repellency was exhibited. On the other hand, it was judged that the water repellency was insufficient for those with water droplets still attached, and the drying / firing time was extended again with a new test product to dry / fire. After that, the above water repellency confirmation test was performed again. For those whose water repellency was not confirmed, the drying and firing time was extended again with a new test product, and drying and firing were carried out until the water repellency of MPL15 was confirmed in the above water repellency confirmation test.

In this way, drying and firing (heat treatment) was performed until sufficient water repellency of MPL15 was confirmed, and the time required for drying and firing (heat treatment) until sufficient water repellency was exhibited in MPL15 was determined. The drying / firing time (heat treatment time) required for confirming sufficient expression of water repellency in MPL15 in each Example and each Comparative Example is as shown in the lower part of Tables 1 and 2.

Then, various characteristics of the MPL paste composition thus produced and the gas diffusion layer 14 using the MPL paste composition were evaluated. Specifically, as shown in the lower part of Tables 1 and 2, the coatability, the drying / firing time at 350 ° C., the presence or absence of cracks in MPL15, and the surface smoothness of MPL15 were evaluated.

Regarding the coatability, when the MPL paste composition is applied to the conductive porous base material 16 made of carbon paper, the carbon paper (the surface opposite to the coated surface (MPL15 forming surface) of the MPL paste composition) ( It was visually confirmed (determined by the black color of carbon black) whether or not carbon black, which is a component of the MPL paste composition, was missing from the back surface side of the conductive porous base material 16). That is, looking at the back surface of the conductive porous base material 16 on the side opposite to the coated surface of the MPL paste composition, the carbon black of the MPL paste composition coated on the surface of the conductive porous base material 16 is conductive. It was visually observed whether or not the material had penetrated through the pores of the porous porous substrate 16 to the surface opposite to the coated surface.

Further, when the MPL paste composition was applied to the conductive porous base material 16 made of carbon paper, it was visually confirmed whether or not coating streaks and scratches (rubbing) were formed on the coating film.

Regarding the coatability, the presence of carbon black, which is a paste component, was not confirmed on the back surface side of the conductive porous base material 16 on the side opposite to the coated surface of the MPL paste composition (paste component). (No strike-through) and no coating streaks or faintness were confirmed on the coating film of the MPL paste composition, which was evaluated as ◯. On the other hand, the presence of carbon black, which is a paste component, was confirmed on the back surface side of the conductive porous base material 16, that is, the paste component permeated (penetrated) into the conductive porous base material 16 and the back surface thereof. If it comes off to the side, the water repellency and gas permeability of the gas diffusion layer 14 will decrease, and the moisture generated in the electrodes of the fuel cell 1 will not be removed smoothly, which may adversely affect the battery performance. Therefore, it was judged that it was not suitable for practical use, and it was evaluated as x. Further, those in which coating streaks and faintness of the coating film were confirmed were also judged to be unsuitable for practical use because the function of MPL15 deteriorated, and were evaluated as x.

Regarding the drying / firing time (heat treatment time) at 350 ° C., the appearance of water repellency was confirmed by the presence or absence of adhesion when water was sprayed on the coating film (MPL15) of the MPL paste composition, and water droplets did not adhere. The time required for drying and firing until the state was reached was evaluated. If the drying / firing time until sufficient water repellency is confirmed, that is, the drying / firing time required for the dispersant to be sufficiently eliminated / removed and water repellency is developed, carbon black is used. As a result, the drying / firing time (7.5 minutes) of Comparative Example 5, which corresponds to the conventional example in which only acetylene black is blended, can be significantly shortened, the load of the drying / firing process is reduced, and the manufacturing cost is reduced. Judging that it could be done, it was evaluated as ○. The drying / firing time required for MPL15 to develop water repellency of 7 minutes or more was evaluated as x because the load of the drying / firing step was the same as the conventional one.

Regarding cracks in MPL15, the surface of MPL15 in the gas diffusion layer 14 was observed at room temperature (20 to 25 ° C.), and cracks having a width of 30 μm or more and a length of 200 μm or more were found in a range of 3 mm × 2.5 mm on the surface. If the number is less than 5, it is judged that the occurrence of cracks is suppressed to be equal to or higher than that of MPL15 using the conventional VGCF, CNT, etc., and the effect of reducing cracks is obtained, and the value is evaluated as ◯. Those having 5 or more cracks were evaluated as x because the durability of MPL15 was judged to be low.

Regarding the surface smoothness, when the surface (about 15 cm in length) of the MPL15 of the gas diffusion layer 14 is observed with a laser microscope at room temperature (20 to 25 ° C.), there should be no convex portion having a height of more than 10 μm on the surface. For example (if the convex portion is 10 μm or less), it is judged that the convex portion does not bite into the catalyst layer 13 and gives stress even when it is incorporated in the fuel cell 1, and the adhesiveness with the catalyst layer 13 is good. It was evaluated as ○. When the fuel cell 1 has a convex portion having a height of more than 10 μm, the fuel may bite into the catalyst layer 13 to reduce its durability or the adhesiveness to the catalyst layer 13 may be lowered. It was judged that the battery performance of the battery 1 might deteriorate, and the value was evaluated as x.

These evaluation results are as shown in the lower part of Tables 1 and 2.
As shown in Table 1, in each of Examples 1 to 6, the strike-through of the carbon black which is the paste component (as described above, the carbon black of the paste component is the pores of the conductive porous base material 16). The phenomenon of penetrating to the back surface side of the conductive porous base material 16) was not confirmed, and there were no coating streaks or rubbing on the coating film of the MPL paste composition, and the coating property was evaluated as ◯. rice field.
Furthermore, the drying / firing time at 350 ° C. required for the development of water repellency was 5 minutes or less, which was significantly shorter than before, and was evaluated as ◯.
Furthermore, in MPL15, the occurrence of predetermined cracks was less than 5, and the occurrence of cracks was effectively suppressed, which was evaluated as ◯.
As for the surface smoothness of MPL15, the presence of a convex portion exceeding 10 μm was not confirmed on the surface of MPL15, and the evaluation was ◯.

In particular, from the evaluation results of Example 1 and Examples 2 to 6, the blending ratio of carbon black as the first carbon black and thermal black as the second carbon black is 50/50 ≦ acetylene black / thermal black. When ≤20 / 80, the drying / firing time at 350 ° C. required for water repellency to be developed is 3 minutes or less, the load on the drying / firing step is greatly reduced, and the effect of reducing the manufacturing cost is enhanced. .. That is, by blending the thermal black as the second carbon in the same amount or more as the carbon black as the first carbon, the carbon black can be produced with a small amount of the dispersant and the amount of the solvent (the amount of ion-exchanged water used). Since it can be dispersed in a solvent (ion-exchanged water), the drying / firing time required for decomposition / volatilization of the dispersant and the solvent can be significantly shortened.

As described above, in Examples 1 to 6, all the evaluation items were evaluated as ◯.
On the other hand, in Comparative Example 1, the DBP absorption amount and the iodine adsorption amount of acetylene black were smaller than those in Examples 1 to 6, the DBP absorption amount was 185 ml / 100 g, and the iodine adsorption amount was 81 mg / g. It uses acetylene black from.
In Comparative Example 1, the drying / firing time required for water repellency to be exhibited and the surface smoothness of MPL15 were evaluated as ◯, but the coatability was evaluated on the side opposite to the paste-coated surface of carbon paper. On the back surface side, the presence of carbon black was confirmed, and strike-through of the paste component occurred, which was evaluated as x. In addition, many cracks were generated in MPL15, and the evaluation was x.

That is, in Comparative Example 1, the acetylene black used in combination with the thermal black having a DBP absorption amount of 40 ml / 100 g and an iodine adsorption amount of 17 mg / g has a DBP absorption amount of 185 ml / 100 g and an iodine adsorption amount of 81 mg / g, and the acetylene black. Since the structure is low and its specific surface area is small, cracks are likely to occur. Furthermore, due to the low development of the structural structure of acetylene black, the viscosity was low, and it was not possible to secure the viscosity characteristics suitable for coating.

Therefore, the acetylene black as the first carbon black preferably has a DBP absorption amount of 210 ml / 100 g or more and an iodine adsorption amount of 85 mg / g or more from Examples 1 to 6. When the DBP absorption amount of acetylene black is 210 ml / 100 g or more and the iodine adsorption amount is 85 mg / g or more, the flow characteristics and the viscosity characteristics suitable for coating without strike-through of the paste component can be secured, and a predetermined value is obtained. Cracks can be reduced when used in combination with thermal black.

Further, in Comparative Example 2, the DBP absorption amount and the iodine adsorption amount of the thermal black were larger than those in Examples 1 to 6, and the DBP absorption amount was 51 ml / 100 g and the iodine adsorption amount was 26 mg / g. It uses black.
In Comparative Example 2, the coatability, the drying / firing time required to develop water repellency, and the surface smoothness of MPL15 were evaluated as ◯, but the MPL15 was inferior in the effect of suppressing crack generation. It was evaluated as x.

That is, in Comparative Example 2, the thermal black used in combination with acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g was different from the thermal black having a DBP absorption amount of 51 ml / 100 g and an iodine adsorption amount of 26 mg / g. Since the structure is too high, the effect of relaxing the shrinkage stress at the time of film formation of MPL15 is small, and the generation of cracks cannot be effectively suppressed.

Therefore, the thermal black as the second carbon black preferably has a DBP absorption amount of 48 ml / 100 g or less from Examples 1 to 6. When the DBP absorption amount of thermal black is 48 ml / 100 g or less, crack generation of MPL15 can be effectively suppressed.
Further, according to the experimental research by the present inventors, if the amount of iodine adsorbed by the thermal black as the second carbon black is too large, the amount of the dispersant required to disperse it increases, so that it is dried. It has been confirmed that the firing load cannot be reduced.
Therefore, from Examples 1 to 6, if the DBP absorption amount of thermal black is 48 ml / 100 g or less and the iodine adsorption amount is 20 mg / g or less, crack generation of MPL15 can be effectively suppressed and drying. The firing time can be significantly shortened, and the load during drying and firing can be reduced.

In Comparative Example 3, the DBP absorption amount and the iodine adsorption amount of the thermal black were smaller than those of Examples 1 to 6, and the thermal black having a DBP absorption amount of 26 ml / 100 g and an iodine adsorption amount of 11 mg / g was produced. It was used.
In Comparative Example 3, the drying / firing time required to develop water repellency was evaluated as ◯, but the coatability was carbon black on the back surface opposite to the paste-coated surface of carbon paper. Was confirmed, and the paste component was strike-through, and the evaluation was x. In addition, many cracks were generated in MPL15, and the evaluation was x. Further, the surface smoothness of MPL15 was inferior, and the evaluation was x.

That is, in Comparative Example 3, the thermal black used in combination with acetylene black having a DBP absorption amount of 230 ml / 100 g and an iodine adsorption amount of 92 mg / g has a DBP absorption amount of 26 ml / 100 g and an iodine adsorption amount of 11 mg / g, and is a thermal black. Due to its low structure and small specific surface area, even when combined with acetylene black, its viscosity is low and it is not possible to secure viscosity characteristics suitable for coating, and because of its large particle size, the surface of MPL15 is smooth. I couldn't secure the sex. Further, the MPL15 lacked the strength and cracks were likely to occur.

Therefore, the thermal black as the second carbon black preferably has a DBP absorption amount of 32 ml / 100 g or more and an iodine adsorption amount of 15 g / g or more from Examples 1 to 6. When the DBP absorption amount of thermal black is 32 ml / 100 g or more and the iodine adsorption amount is 15 mg / g or more, the flow characteristics and the viscosity characteristics suitable for coating without strike-through of the paste component can be secured, and the MPL15 Cracks in MPL15 can be reduced without reducing surface smoothness.

In Comparative Example 4, the DBP absorption amount and the iodine adsorption amount of acetylene black were larger than those of Examples 1 to 6, and the acetylene black having a DBP absorption amount of 270 ml / 100 g and an iodine adsorption amount of 100 mg / g was produced. It was used.
In Comparative Example 4, the drying / firing time required to develop water repellency and the cracks in MPL15 were evaluated as ◯, but in terms of coatability, coating streaks were confirmed on the coating film of MPL15. It was an evaluation of. Further, the surface smoothness of MPL15 was also inferior, and the evaluation was x.

That is, in Comparative Example 4, the acetylene black used in combination with the thermal black having a DBP absorption amount of 32 ml / 100 g and an iodine adsorption amount of 15 mg / g is an acetylene black having a DBP absorption amount of 270 ml / 100 g and an iodine adsorption amount of 100 mg / g. , The structure structure of acetylene black was developed, the viscosity of the MPL paste composition was increased and became hard, streaks were formed in the coating film of the MPL paste composition, and the surface smoothness of MPL15 was also inferior.

Therefore, the acetylene black as the first carbon black preferably has a DBP absorption amount of 262 ml / 100 g or less from Examples 1 to 6. When the DBP absorption amount of acetylene black is 262 ml / 100 g or less, the flow characteristics and the viscosity characteristics suitable for coating can be secured, and the occurrence of cracks can be suppressed without lowering the surface smoothness of MPL15.
Further, according to the experimental research by the present inventors, if the amount of acetylene black adsorbed on iodine as the first carbon black is too large, the amount of the dispersant required to disperse the amount of acetylene black is too large. It has been confirmed that the firing load cannot be reduced.
Therefore, from Examples 1 to 6, if the DBP absorption amount of acetylene black is 262 ml / 100 g or less and the iodine adsorption amount is 97 mg / g or less, the flow characteristics and viscosity characteristics suitable for coating and the surface smoothness of MPL15 are smoothed. While ensuring the properties, the occurrence of cracks can be suppressed, the drying / firing time can be significantly shortened, and the load during drying / firing can be reduced.

Further, Comparative Example 5 is a composition in which thermal black is omitted and only acetylene black is used.
In Comparative Example 5, since the predetermined thermal black was not used, the crack of MPL15 was not suppressed, and the evaluation was x. The drying / firing time required for water repellency to develop is also long, and the evaluation is x.

Further, according to the experiments of the present inventors, in the composition in which acetylene black is omitted and only thermal black is used as carbon black, the carbon black which is a component of the MPL paste composition strikes through, and moreover, there are many cracks and it is strong. It has been confirmed that MPL15 cannot be obtained and the function as MPL15 cannot be fulfilled.

According to the experimental research of the present inventors, the MPL 15 and the MPL 15 obtained by applying the MPL paste composition according to Examples 1 to 6 to the surface of the conductive porous base material 16 and drying and firing it. With respect to the gas diffusion layer 14 made of the conductive porous base material 16, gas diffusion sufficient to diffuse the fuel gas or oxidation gas supplied from the gas flow path of the separator 21 into the catalyst layer 13 adjacent to the gas diffusion layer 14. It has been confirmed that it has the property and that the water discharge property to prevent water clogging (flooding) is ensured. That is, the gas supply and drainage properties are good, and the reaction efficiency when incorporated into the fuel cell 1 is also good. Furthermore, since cracks on the surface of MPL15 are suppressed, it has been confirmed that the conductivity for efficiently moving electrons is also high. In particular, it is suitable for forming the gas diffusion layer 14A on the anode side.

As described above, according to the MPL paste composition according to Examples 1 to 6 in which a predetermined DBP absorption amount of acetylene black and thermal black are used in combination, Comparative Example 5 in which only acetylene black corresponding to the conventional example is used. Compared with, the occurrence of cracks is suppressed. This is because the combined use of acetylene black and thermal black with a predetermined amount of DBP absorption reduces the gaps between the particles and increases the density, and the three-dimensional chain structure of the carbon black particles is moderately relaxed and balanced. This is because the shrinkage stress during film formation is reduced.

Since the cracks on the surface of the MPL15 are suppressed, the water generated by the battery reaction between the catalyst layer 13 and the MPL15 is unlikely to accumulate. It is possible to prevent peeling and breakage. Further, it is possible to prevent vacancies and clogging of the gas flow path 21 due to a part of the catalyst layer 13 and the MPL 15 being missing or particles falling off. Therefore, the life of the fuel cell 1 can be extended, and stable battery performance and battery output can be ensured.
Further, since the crack of the MPL 15 is suppressed in this way, the MPL 15 is not easily broken even when the cells are strongly fastened by the pressure of the separator at the time of stacking when the fuel cell 1 is incorporated.

Further, in the MPL paste compositions according to each of the above Examples 1 to 6, the iodine adsorption amount of thermal black is in the range of 0.15 to 0.21 times the iodine adsorption amount of acetylene black, which is conventional. Compared with Comparative Example 5 in which only acetylene black corresponding to the example was used, the amount of Triton X-100 used as a dispersant was 0.3 to 0.8 times. That is, when the total amount of carbon black is 100 parts by weight, the amount of the dispersant in Comparative Example 5 is 10.2 parts by weight, whereas in the MPL paste compositions of Examples 1 to 6, the amount is 10.2 parts by weight. , The amount of the dispersant is in the range of 2.6 to 8.2 parts by weight, the amount of Triton X-100 used can be reduced by 20% to 75%, and carbon black can be dispersed with a small amount of dispersant. Is. Further, in Examples 1 to 6, the viscosity characteristics suitable for coating are secured even if the amount of ion-exchanged water as a solvent is smaller than that in Comparative Example 5.

Since the amount of the dispersant and the ion-exchanged water used is small, the drying and firing time required to remove and eliminate the dispersant and the ion-exchanged water to develop water repellency is short. That is, in Examples 1 to 6 above, the drying / firing time required to develop water repellency is 0.2 to 0.67 times that of Comparative Example 5, and the drying / firing time is 0.2 to 0.67 times. It takes about 1/5 to 7/10 of the conventional time. Therefore, the energy consumption is small and the manufacturing cost can be reduced.

As described above, the paste composition for forming a microporous layer according to Examples 1 to 6 includes carbon black, PTFE resin as a water-repellent resin, Triton X-100 as a dispersant, and ions as a solvent. A paste composition for forming a microporous layer containing exchanged water, which comprises acetylene black as a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and DBP absorption as carbon black. Thermal black as a second carbon black whose amount is in the range of 32 ml / 100 g to 48 ml / 100 g is used in combination.

Further, the gas diffusion layer 14 according to Examples 1 to 6 has an acetylene black as the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a DBP absorption amount of 32 ml / 100 g. Micro containing thermal black as a second carbon black in the range of 100 g to 48 ml / 100 g, PTFE resin as a water-repellent resin, Triton X-100 as a dispersant, and ion-exchanged water as a solvent. A paste composition for forming a porous layer is applied to a conductive porous base material 16, dried and fired, and the paste composition for forming a microporous layer is applied to the surface of the conductive porous base material 16. MPL15 as a coating layer obtained from the above is formed.

According to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the same, the DBP absorption amount is 210 ml / 100 g to 262 ml / 100 g as inexpensively available carbon black. By using acetylene black as the first carbon black within the range and thermal black as the second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g in combination, the structure of the carbon black The three-dimensional structure in which certain carbon particles are chained is well-balanced, the shrinkage stress during film formation is relaxed, and the occurrence of cracks in MPL15 is suppressed. Therefore, the durability of the MPL15 can be improved, and in particular, it is possible to prevent a situation in which water accumulates in the cracks and freezes at a temperature below the freezing point, causing peeling at the interface between the MPL15 and the catalyst layer 13 or destroying the MPL15. The durability and output characteristics of the fuel cell 1 can be improved.

According to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the same, the DBP absorption amount of acetylene black as the first carbon black is 210 ml / 100 g or more. Good coatability can be ensured without the paste component strike-through when applied, and cracks are less likely to occur in MPL15. When the DBP absorption amount of acetylene black as the first carbon black is 260 ml / 100 g or less, the coatability can be ensured without forming coating streaks on the coating film, and the surface of MPL15 has less unevenness and surface smoothness. Can be secured.
Further, when the DBP absorption amount of the thermal black as the second carbon black is 32 ml / 100 g or more, the paste does not show through due to the decrease in viscosity characteristics, the coatability is good, and the MPL15 is less likely to crack. .. When the DBP absorption amount of the thermal black as the second carbon black is 48 ml / 100 g or less, the occurrence of cracks in the MPL can be effectively suppressed.

Therefore, according to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the same, the amount of DBP absorbed by acetylene black as the first carbon black is 210 ml / 100 g to 262 ml / 100 g. If the amount of DBP absorbed by the thermal black as the second carbon black is within the range of 32 ml / 100 g to 48 ml / 100 g, the occurrence of cracks in the MPL can be effectively suppressed, and the viscosity is reduced. Good coatability without strike-through of the paste or coating streaks due to increased viscosity. Further, the MPL15 has few irregularities and is excellent in surface smoothness. Therefore, even when the fuel cell 1 is incorporated, the contact with the catalyst layer 13 is good and no mechanical stress is applied to the catalyst layer 13, so that the durability of the fuel cell 1 is improved and stable output characteristics are achieved. Can be improved.

Thus, according to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the MPL paste composition, a specific carbon black which is an inexpensive material and has excellent surface smoothness of MPL15 is used in combination. As a result, the occurrence of cracks in the MPL15 can be suppressed, so that the MPL15 capable of exhibiting characteristics such as stable gas diffusivity and conductivity can be formed, and the durability of the MPL15 can be improved. Further, even when it is incorporated in the fuel cell 1, it has good contact with the catalyst layer 13 and does not give mechanical stress to the catalyst layer 13. Therefore, the durability and output stability of the fuel cell 1 can be improved.

In particular, according to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the same, the first carbon black is acetylene black and the second carbon black is thermal black. It is a combination of acetylene black and thermal black, which are significantly cheaper than VGCF and CNT, and the cost is extremely low. Further, both acetylene black and thermal black are manufactured by a thermal decomposition method, have good compatibility, and can effectively relieve shrinkage stress during film formation. Further, both acetylene black and thermal black have high purity, and in particular, acetylene black has extremely few impurities, so that the output characteristics of the fuel cell 1 can be improved without causing deterioration of battery performance due to a short circuit or the like. ..

According to the MPL paste composition according to Examples 1 to 6 and the gas diffusion layer 14 using the MPL paste composition, the amount of acetylene black as the first carbon black adsorbed on iodine is 85 mg / g to 97 mg / g. Since the amount of iodine adsorbed by the thermal black as the second carbon black is within the range of 15 mg / g to 20 mg / g, the amount of the dispersant (surfactant, etc.) required for dispersion in the solvent is used. Is less. In addition, the increase in viscosity is suppressed, and the viscosity characteristics suitable for coating can be obtained with a small amount of solvent. Therefore, the firing / drying time required for thermally decomposing / volatilizing the dispersant and the solvent (moisture) can be shortened, the production time of the gas diffusion layer 14 can be shortened, and the productivity can be improved. Further, since the amount of energy used and the cost can be reduced by shortening the firing / drying time, the manufacturing cost can be reduced.

In particular, when the amount of iodine adsorbed by acetylene black as the first carbon black is 85 mg / g or more, cracks are unlikely to occur in MPL15. Further, when the iodine adsorption amount of acetylene black as the first carbon black is 97 mg / g or less, the coating film is not formed with coating streaks and the coating property is good, and the surface smoothness of MPL15 is also improved. Excellent. Therefore, even when the fuel cell 1 is incorporated, the contact with the catalyst layer 13 is good and no mechanical stress is applied to the catalyst layer 13, so that the durability of the fuel cell 1 is improved and stable output characteristics are achieved. Can be improved.
Further, when the iodine adsorption amount of the thermal black as the second carbon black is 15 mg / g or more, the surface of the MPL15 has less unevenness and the surface smoothness of the MPL15 can be ensured. In addition, cracks are unlikely to occur in MPL15. In addition, when the amount of iodine adsorbed by the thermal black as the second carbon black is 20 mg / g or less, the amount of the dispersant required for dispersion can be effectively suppressed, and the firing / drying time can be significantly shortened. ..

Therefore, the amount of iodine adsorbed by acetylene black as the first carbon black is in the range of 85 mg / g to 97 mg / g, and the amount of iodine adsorbed by thermal black as the second carbon black is in the range of 15 mg / g to 20 mg / g. If it is inside, the coatability is good, the surface smoothness of MPL15 is excellent, cracks can be prevented, and the amount of dispersant required for dispersion is effectively suppressed, and the firing / drying time is long. Can be significantly shortened. Therefore, the cost of the MPL 15 can be reduced and the productivity can be improved, and the durability of the fuel cell 1 can be improved and the stable output characteristics can be further improved.

Thus, acetylene black as the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and an iodine adsorption amount in the range of 85 mg / g to 97 mg / g, and a DBP absorption amount of 32 ml. The coatability and surface smoothness of MPL15 are improved by the combined use with thermal black as the second carbon black, which is in the range of / 100 g to 48 ml / 100 g and the amount of iodine adsorbed is in the range of 15 mg / g to 20 mg / g. It is possible to effectively suppress cracks in MPL15 at low cost and reduce the load in the drying / baking process without reducing the cost, and it is possible to reduce the cost and improve the productivity.

In particular, the average primary particle diameter (medium diameter) of acetylene black as the first carbon black in which the amount of these iodine adsorbed is in the range of 85 mg / g to 97 mg / g is in the range of 20 nm to 45 nm. The average primary particle size (medium diameter) of the thermal black as the second carbon black is 200 nm to 350 nm in the thermal black as the second carbon black in which the amount of iodine adsorbed by the thermal black as the second carbon black is in the range of 15 mg / g to 20 mg / g. In all of these carbon blacks, the average primary particle diameter (medium diameter) of carbon black is not more than 1 μm as in graphite powder, but the average primary particle diameter (medium diameter) of carbon black. Is 350 nm or less, so MPL15 having a smooth surface and excellent surface smoothness can be obtained. When the surface unevenness of the MPL 15 is extremely small, the adhesion to the catalyst layer 13 is increased, the contact resistance on the contact surface is also small, and the power generation efficiency can be increased. In addition, there is little biting into the catalyst layer 13 and no mechanical stress is given. Therefore, the stable output of the fuel cell 1 can be ensured, and the life of the fuel cell 1 can be extended.

According to the definition of terms in the text and explanation of JIS Z 8901 "Test powder and test particles", the medium diameter is the number (or mass) larger than a certain particle size in the particle size distribution of the powder. ) Is the particle size (diameter) when occupying 50% of that of the total powder, that is, the particle size of oversize 50%, and is usually referred to as the median size or 50% particle size and is expressed as D50. By definition, the size of the particle group is expressed by the average particle diameter and the medium diameter, but here, it is a value measured by the display of the product description and the laser diffraction / scattering method. The "medium diameter measured by the laser diffraction / scattering method" is a particle whose integrated weight part is 50% in the particle size distribution obtained by the laser diffraction / scattering method using a laser diffraction type particle size distribution measuring device. Refers to the diameter (D50). The numerical value of the particle size is not strict but is approximate, and of course, it is a rough value including an error due to measurement or the like, and an error of several percent cannot be denied. From the viewpoint of this error, the difference from the average particle size is smaller as it is closer to the normal distribution, and the average particle size ≒ median diameter, and it can be considered that the average particle size = median diameter.

Furthermore, according to the experimental studies of the present inventors, the amount of DBP absorbed by acetylene black as the first carbon black used in Example 1 is in the range of 210 ml / 100 g to 262 ml / 100 g, and the amount of iodine adsorbed is high. The amount of DBP absorbed by thermal black as the second carbon black is in the range of 32 ml / 100 g to 48 ml / 100 g, and the amount of iodine adsorbed is in the range of 15 mg / g to 20 mg / g. When the compounding ratio of acetylene black as the first carbon black and thermal black as the second carbon black is acetylene black / thermal black = 10/90 under the condition of being within the range of, the effect of suppressing cracks is effectively obtained. It has been confirmed that when acetylene black / thermal black = 90/10, strike-through of the paste component is likely to occur.
Therefore, preferably, when the blending ratio of acetylene black and thermal black is within the range of acetylene black / thermal black = 20/80 to 80/20, the amount of DBP absorbed is predetermined without deteriorating the coatability. The combined use of acetylene black and thermal black can effectively suppress cracks in MPL15. Then, it is easy to realize the desired characteristics of MPL15.

By the way, in the above examples, the amount of DBP absorbed is in the range of 210 ml / 100 g to 262 ml / 100 g, and the amount of iodine adsorbed is in the range of 85 mg / g to 97 mg / g. Thermal black as a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g and an iodine adsorption amount in the range of 15 mg / g to 20 mg / g, and PTFE resin as a water-repellent resin. It can also be regarded as an invention of a method for producing a paste composition for forming a microporous layer in which Triton X-100 as a dispersant and ion-exchanged water as a solvent are mixed and dispersed by a planetary stirring / defoaming device.

Further, in the above-mentioned examples, the amount of DBP absorbed is in the range of 210 ml / 100 g to 262 ml / 100 g, and the amount of iodine adsorbed is in the range of 85 mg / g to 97 mg / g. Thermal black as a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g and an iodine adsorption amount in the range of 15 mg / g to 20 mg / g, and PTFE resin as a water-repellent resin. A paste composition for forming a microporous layer prepared by mixing and dispersing Triton X-100 as a dispersant and ion-exchanged water as a solvent with a planetary stirring / defoaming device is used as a conductive porous base material. It can also be regarded as an invention of a method for manufacturing the gas diffusion layer 14 for a fuel cell, which is applied to 16 and dried / fired.

According to the method for producing the paste composition for forming a microporous layer and the method for producing the gas diffusion layer 14 for a fuel cell, the mixture can be dispersed at low cost by a planetary stirring / defoaming device, and the first carbon black is used. The three-dimensional structure of the carbon particles of the second carbon black is maintained, and the acetylene black as the first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and the DBP absorption amount of 32 ml / When used in combination with thermal black as the second carbon black in the range of 100 g to 48 ml / 100 g, the shrinkage stress during film formation of MPL15 is relaxed, and the occurrence of cracks on the surface of MPL15 is suppressed. Therefore, the occurrence of cracks on the surface of MPL15 can be suppressed at low cost.

The paste composition for forming a microporous layer of the present embodiment and the gas diffusion layer 14 for a fuel cell produced using the same are not limited to the polymer electrolyte fuel cell 1, and for example, a direct methanol fuel cell or the like. It can also be applied to other fuel cells.

Further, in carrying out the present invention, the composition, components, blending amount, material, and other manufacturing processes of the paste composition for forming the microporous layer and the other parts of the diffusion layer 14 for the fuel cell are described in the present embodiment. It is not limited.
Further, since the numerical values given in the embodiment of the present invention do not indicate a critical value but an appropriate value suitable for implementation, even if the above numerical value is slightly changed, the implementation is denied. is not it.

In the paste composition for forming a microporous layer of the above embodiment, the first carbon black is acetylene black and the second carbon black is thermal black.
There are two methods for producing carbon black, one is by incomplete combustion of hydrocarbons and the other is by thermal decomposition. Both acetylene black and thermal black are produced by thermal decomposition.

In the fuel cell gas diffusion layer of the above embodiment, the first carbon black is acetylene black and the second carbon black is thermal black.
There are two methods for producing carbon black, one is by incomplete combustion of hydrocarbons and the other is by thermal decomposition. Both acetylene black and thermal black are produced by thermal decomposition.

According to the paste composition for forming a microporous layer of the above embodiment, the first carbon black is acetylene black and the second carbon black is thermal black. When the first carbon black is acetylene black, it can be obtained at a low price and has good compatibility with carbon paper or the like which is a conductive porous base material to be coated. Furthermore, it is conductive due to the chain structure of carbon particles and graphitization. Excellent for. Further, when the second carbon black is thermal black, it can be obtained at a lower cost than acetylene black, and the purity is extremely high and impurities that interfere with the function of the fuel cell are extremely small, so that the stable output of the fuel cell can be improved. Is. Therefore, it is suitable as a material for forming an MPL used for an electrode of a fuel cell at low cost, and an MPL having excellent performance such as conductivity can be formed, and a stable output of the fuel cell can be improved.

According to the fuel cell gas diffusion layer of the above embodiment, the first carbon black is acetylene black and the second carbon black is thermal black.
When the first carbon black is acetylene black, it can be obtained at a low price and has good compatibility with carbon paper or the like which is a conductive porous base material to be coated. Furthermore, it is conductive due to the chain structure of carbon particles and graphitization. Excellent for. Further, when the second carbon black is thermal black, it can be obtained at a lower cost than acetylene black, and the purity is extremely high and impurities that interfere with the function of the fuel cell are extremely small, so that the stable output of the fuel cell can be improved. Is. Therefore, it is suitable as a material for forming MPL used for an electrode of a fuel cell at low cost, MPL having excellent performance is formed, and stable output of the fuel cell can be improved.

1 Fuel cell 14 Gas diffusion layer 15 Microporous layer 16 Conductive porous substrate

Claims (2)

A paste composition for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent.
As the carbon black, a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination. death,
Moreover, the iodine adsorption amount of the first carbon black is in the range of 85mg / g~97mg / g, iodine adsorption amount of the second carbon black is Ri range der of 15mg / g~20mg / g,
The blending ratio of the first carbon black / the second carbon black is in the range of the first carbon black / the second carbon black = 20/80 to 80/20.
The paste composition for forming a microporous layer is characterized in that the water-repellent resin has a content in the range of 5 to 50% by mass in terms of solid content in the total solid content of the paste composition. A paste composition for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent is applied to the surface of a conductive porous base material, and dried and fired to diffuse gas for a fuel cell. It ’s a layer,
As the carbon black, a first carbon black having a DBP absorption amount in the range of 210 ml / 100 g to 262 ml / 100 g and a second carbon black having a DBP absorption amount in the range of 32 ml / 100 g to 48 ml / 100 g are used in combination. death,
Moreover, the iodine adsorption amount of the first carbon black is in the range of 85mg / g~97mg / g, iodine adsorption amount of the second carbon black is Ri range der of 15mg / g~20mg / g,
The blending ratio of the first carbon black / the second carbon black is in the range of the first carbon black / the second carbon black = 20/80 to 80/20.
The gas diffusion layer for a fuel cell , wherein the water-repellent resin has a content in the range of 5 to 50% by mass in terms of solid content in the total solid content of the paste composition.

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