JP2024005571A - Coating paste for forming microporous layer and manufacturing method thereof, and gas diffusion layer for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the performance of a gas diffusion layer by forming a microporous layer with high porosity.

SOLUTION: A coating paste for forming a microporous layer includes a carbon black, a water-repellent resin, a dispersant, and a solvent, and the carbon black with DBP absorption within the range of 300 ml/100 g or more and 500 ml/100 g or less has a secondary aggregation diameter in which the carbon black passes through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less).

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention provides a microporous layer (MPL) by coating the surface of a conductive porous base material (gas diffusion layer electrode base material) constituting a gas diffusion layer (GDL: Gas Diffusion Layer) for fuel cells. The present invention relates to a coating paste for forming a microporous layer that forms a microporous layer, a method for producing the same, and a gas diffusion layer for fuel cells using the same. The present invention relates to an industrial paste, a method for producing the same, and a gas diffusion layer for a fuel cell using the same.

In recent years, fuel cells, particularly polymer electrolyte fuel cells (PEFC), have been attracting a lot of attention because of their applicability to a wide range of applications such as automobiles, household power sources, and home appliances.
Polymer electrolyte fuel cells use an ion-conducting polymer membrane as an electrolyte, bond a negative electrode and a positive electrode to this to form a single cell, and then connect multiple single cells through a separator. It has a structure (stack) that obtains high voltage by laminating layers.

Generally, one single cell that constitutes a 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 supporting a catalyst, and a porous gas diffusion layer (GDL) placed outside the electrode catalyst layer. and an anode (-) side electrode, forming a membrane-electrode-gas diffusion layer assembly (MEGA).
In polymer electrolyte fuel cells, fuel gas (anode gas) or oxidizing gas (cathode gas) is supplied to the outside of the gas diffusion layer that constitutes this membrane/electrode assembly, and generated gas and excess gas are discharged. The membrane/electrode assembly is sandwiched between the separators, and a structure (stack) in which a plurality of single cells are stacked increases power generation performance.

Polymer electrolyte fuel cells with this configuration are being used as power sources (driving sources) for automobiles because they can obtain energy with high efficiency and have a low environmental impact. In order to further popularize fuel cells, it is desired to increase the output of the fuel cell by improving the performance of each component that makes up the fuel cell.

By the way, in the structure of such a polymer electrolyte fuel cell, in order to efficiently react the fuel gas (anode gas) and the oxidizing gas (cathode gas), a catalyst such as platinum is supported and the electrochemical reaction is carried out. A gas diffusion layer that guides the fuel gas or oxidizing gas supplied from the gas flow path of the separator is adjacent to the catalyst layer that performs this process. In other words, the gas diffusion layer constituting the electrode of a single cell battery is formed to increase the diffusivity of the reaction gas, and the gas diffusion layer that constitutes the electrode of a single cell battery is formed to increase the diffusivity of the reaction gas, and is designed to diffuse the fuel gas or oxidizing gas supplied from the gas flow path of the separator to the adjacent catalyst layer. (gas diffusivity, gas permeability). Further, this gas diffusion layer between the separator and the catalyst layer is required to have a conductive function and a current collecting function to efficiently transfer the electrons necessary for the electrochemical reaction. Furthermore, in order to improve power generation performance and stabilize power generation performance, it is necessary to maintain the polymer electrolyte membrane in an optimally moist state from the viewpoint of obtaining high proton conductivity (electroconductivity) at the electrode, and to prevent excess moisture in the catalyst layer. It is important to suppress the flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer are clogged with water) by quickly discharging the water. At the same time, it is necessary to have drainage properties (water repellency, moisture permeability) to discharge excess reaction product water and dew water generated by the electrochemical reaction of hydrogen and oxygen during power generation. It is also required to have a role in taking in and discharging moisture, that is, moisture management through diffusivity.

Therefore, in recent years, in this gas diffusion layer, for example, a conductive porous base material (gas diffusion layer electrode base material) made of carbon paper, carbon cloth, carbon felt, etc., has been replaced with a material such as PTFE. Forming a coating thin film called a microporous layer (MPL) (sometimes called a microporous layer, carbon layer, or sealing layer) whose main components are a water-repellent resin and a conductive material such as carbon black. This suppresses the formation of a liquid film at the interface with the adjacent catalyst layer, promotes water discharge and back-diffusion of produced water, and improves the water management performance (water content control) of polymer electrolyte fuel cells. It has been proposed to improve power generation performance. By forming the microporous layer on the conductive porous base material, the microporous layer can act as a buffer between the catalyst layer and the conductive porous base material, or as a buffer material for the surface of the conductive porous base material. It also functions as a make-up touch-up effect to prevent transfer to the film. In addition, in the case where a microporous layer-forming paste is applied to a conductive porous substrate and then dried and fired to form a microporous layer, fine control of the characteristics of the gas diffusion layer is easily possible by adjusting the paste components. do.

Here, as this type of known technology, there are, for example, Patent Document 1 and Patent Document 2.
Patent Document 1 has a carbon sheet and a microporous layer, the carbon sheet is porous, the DBP oil absorption amount of carbon powder contained in the microporous layer is 70 to 155 ml/100 g, and the microporous layer The penetration index (L/W) calculated from the basis weight (W) of the microporous layer and the thickness (L) of the microporous layer is 1.10 to 8.00, and the thickness of the microporous layer ( Discloses a gas diffusion electrode base material in which L) is 10 to 100 μm.

Further, in Patent Document 2, a first carbon containing carbon black, a water-repellent resin, a dispersant, and a solvent and having a DBP absorption amount within the range of 210 ml/100 g to 262 ml/100 g is used as the carbon black. black and a second carbon black whose DBP absorption is within the range of 32 ml/100 g to 48 ml/100 g, and further, where the iodine adsorption amount of the first carbon black is within the range of 85 mg/g to 97 mg/g. The present invention discloses a paste composition for forming a microporous layer in which the second carbon black has an iodine adsorption amount within a range of 15 mg/g to 20 mg/g.

According to the technology disclosed in Patent Document 1, by increasing the DBP oil absorption of carbon to form a microporous layer (hereinafter sometimes abbreviated as "MPL"), the MPL coating liquid is impregnated into the carbon sheet. According to the technology of Patent Document 2, by combining carbon blacks with specific differences in the degree of structure development and controlling the chain structure and three-dimensional structure of carbon particles, It is said that it can suppress cracks in MPL.

In Patent Document 1 and Patent Document 2, regarding the carbon mixed in the coating paste for forming MPL, if the structure is small and the DBP absorption is small, conductive porous material made of carbon sheet etc. The use of carbon with a high DBP absorption rate has been proposed because it tends to penetrate the conductive porous substrate and strike through when applied to the substrate, and is also weak in strength and prone to cracks.

International Publication No. 2016/076132 JP 2019-040791 (Patent No. 6932447)

However, carbon with a high DBP absorption rate tends to have structures (aggregates) that become entangled with each other, resulting in excessive structure development (the diameter of secondary aggregation is several tens of micrometers or more), generating aggregates (agglomerated particles), and resin content. By adsorbing and retaining a large amount of solvent, the dispersibility is poor, leading to an increase in the viscosity of the paint and a decrease in coating properties, resulting in surface defects of the gas diffusion electrode (decreased surface smoothness and reduced coating width). ) and also reduce productivity.
In addition, carbon products often contain foreign substances (impurities) such as sulfur, metals (potassium, lead, sodium, iron, etc.), calcium, chlorine, etc. These foreign substances, especially iron foreign substances, , the durability and life of the catalyst layer adjacent to the gas diffusion layer are likely to be reduced, leading to a decline in battery performance and battery life. However, when carbon with a high DBP absorption is added to the coating paste for forming MPL, , the aggregates clog the fine-mesh filtration filter used to remove foreign matter, especially iron foreign matter, in carbon products, reducing the permeability to the filtration filter and causing battery damage. There is also the problem that it is difficult to remove iron foreign substances that reduce the durability and life of the steel.

Therefore, the use of carbon with a high DBP absorption amount causes aggregation and increases the viscosity of the coating paste. There was a limit to the ability to improve the performance of the gas diffusion layer, such as its diffusivity.

Therefore, the present invention provides a coating paste for forming a microporous layer that can improve the performance of the gas diffusion layer by forming a microporous layer with a high porosity, a method for manufacturing the same, and a gas diffusion layer for fuel cells. This is an issue to be addressed.

The coating paste 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 300 ml/100 g to 500 ml/ The secondary aggregation size is such that 100 g of carbon black passes through a mesh with an opening of 34 to 154 μm, and is applied to the surface of a conductive porous base material such as a carbon fiber sheet and dried.・It forms a microporous layer of a gas diffusion layer for a fuel cell by being fired.

As the carbon black, for example, furnace black, thermal black, Ketjen black, acetylene black, etc. can be used, but acetylene black is preferable because it can form a microporous layer with high gas diffusivity, strength, and conductivity. It is.
Carbon black with a DBP absorption amount of 300 ml/100 g to 500 ml/100 g passes through a mesh with an opening of 34 to 154 μm. Secondary aggregates (several tens of μm) of carbon black in the range of 100 g or more and 500 ml/100 g or less are dispersed with high shear to form a mesh with an opening of 34 μm or more and 154 μm or less, that is, 100 mesh or more and 400 mesh or less. This means that the particles have been disintegrated (deagglomerated) to a secondary aggregation diameter (several μm) that can pass through. That is, secondary aggregates of carbon black whose DBP absorption amount is within the range of 300 ml/100 g or more and 500 ml/100 g or less are crushed and can pass through a mesh with an opening of 34 to 154 μm (100 to 400 mesh). This means that it has the following agglomeration diameter.

Here, "DBP absorption amount" is measured in accordance with JIS K6217-4. The absorption amount (oil absorption amount) of DBP is determined by using the fact that the porosity between aggregates of carbon black has a positive correlation with the structure, and by absorbing DBP (dibutyl phthalate) into the pores. The structure is indirectly quantified using This indicates that the structure is not very developed and the structure is low. Note that the term "structure" refers to the degree of development of a chain-like aggregate made up of several or tens of carbon black particles, that is, the degree of development of the connections between carbon black particles. If the number of carbon particles constituting the aggregate is large or the carbon particles have a complicated shape, the amount of DBP absorbed will be high.
Note that in this specification and claims, the opening of the mesh is the opening of the mesh according to the JIS G 3556 standard.

The carbon black and the water-repellent resin in the coating paste for forming a microporous layer of the invention according to claim 2 have a solid content weight ratio of 9/1≦carbon black/water-repellent resin≦5/5. be.

The coating paste for forming a microporous layer according to the invention of claim 3 has a viscosity at a shear rate of 50 [1/s] of 0.05 Pa·s or more and 1.0 Pa·s or less, more preferably 0.1 Pa·s. It is in the range of 0.9 Pa·s or less, more preferably 0.1 Pa·s or more and 0.5 Pa·s or less.

In the gas diffusion layer for fuel cells according to the invention of claim 4, the carbon black of the microporous layer formed on the surface of the conductive porous base material and composed of carbon black and water-repellent resin has a DBP absorption amount of 300 ml/100 g to 500 ml. The secondary agglomeration diameter is such that carbon black within the range of /100g passes through a mesh with an opening of 34 to 154 μm.

The conductive porous base material is a gas diffusion layer electrode base material, and is a porous body that has conductivity and has a larger average pore diameter than the microporous layer, such as carbon fiber fabric, carbon fiber Porous substrates made of carbon fibers (e.g., graphite fibers, etc.) such as paper bodies, carbon fiber nonwoven fabrics, carbon felt, carbon paper, and carbon cloth, and metal porous substrates such as foamed sintered metals, metal meshes, and expanded metals. material is used.
The microporous layer is formed by applying a coating paste for forming a microporous layer containing carbon black and a water-repellent resin onto the surface of the conductive porous base material, and drying and baking the coating paste to repel the carbon black. The carbon black is bound with a water-based resin, and the carbon black has a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g. It is of the agglomerate size.

Here, as the above-mentioned carbon black, for example, furnace black, thermal black, Ketjen black, acetylene black, etc. can be used, but acetylene black Black is preferred.
Carbon black with a DBP absorption amount of 300 ml/100 g to 500 ml/100 g passes through a mesh with an opening of 34 to 154 μm. Secondary aggregates (several tens of μm) of carbon black in the range of 100 g or more and 500 ml/100 g or less are dispersed with high shear to form a mesh with an opening of 34 μm or more and 154 μm or less, that is, 100 mesh or more and 400 mesh or less. This means that the particles have been disintegrated (deagglomerated) to a secondary aggregation diameter (several μm) that can pass through. That is, secondary aggregates of carbon black whose DBP absorption amount is within the range of 300 ml/100 g or more and 500 ml/100 g or less are crushed and can pass through a mesh with an opening of 34 to 154 μm (100 to 400 mesh). This means that it has the following agglomeration diameter.

The carbon black and the water-repellent resin in the microporous layer of the gas diffusion layer for a fuel cell according to the invention of claim 5 have a solid content weight ratio of 9/1≦carbon black/water-repellent resin≦5/5. It is something.

The method for producing a coating paste for forming a microporous layer according to the invention of claim 6 is such that a dispersant is mixed into a solvent in which the dispersant is dissolved and mixed, and a DBP absorption amount is in a range of 300 ml/100 g or more and 500 ml/100 g or less. Carbon black and water-repellent resin are mixed together and stirred using a thin film swirling method.

Here, the above-mentioned thin film swirling method is a method in which the processed material (compounded material) is pressed against the inner wall surface of the device in a thin cylindrical shape by centrifugal force and rotated at high speed, and the speed difference between the centrifugal force and the swirling flow on the inner wall surface of the device is By applying the shear stress generated by this to the dispersed material (compounded material), the entire tank is brought into a high-energy turbulent state, and the agglomerated particles in the thin cylindrical processed material (compounded material) are dispersed. It's a method. As a swirling thin film type high speed stirrer that utilizes such a high speed swirling thin film flow, for example, a thin film swirling type high speed mixer "Filmix" (registered trademark) series (manufactured by Primex Co., Ltd.) can be suitably used. The stirring conditions at this time are preferably such that stirring is performed at a circumferential speed of 25 m/s or more at the tip of the stirring blade, and the upper limit value is 25 m/s or more, considering the performance limit of the machine. , 60 m/s or less.
Further, as the above-mentioned carbon black, for example, furnace black, thermal black, Ketjen black, acetylene black, etc. can be used, but acetylene black is suitable.

The method for producing a coating paste for forming a microporous layer according to the invention of claim 7 is to add a dispersant to a solvent in which the dispersant is dissolved and mixed, and a DBP absorption amount in a range of 300 ml/100 g or more and 500 ml/100 g or less. Carbon black and water-repellent resin are mixed and stirred at a circumferential speed of 25 m/s or more and 60 m/s or less.

Here, stirring at the circumferential speed of 25 m/s or more is performed by controlling the circumferential speed at the tip of the stirring blade using a high-speed stirrer such as Homo Mixer, Homo Dispa, Neokaiser (registered trademark), Neomixer (registered trademark), thin film swirl type high-speed mixer, or Homomixer. The stirring speed is 25 m/s or more, and the upper limit thereof is 60 m/s or less considering the performance limit of the machine. Among these, a thin film swirl type high speed mixer "Filmix" (registered trademark) series (manufactured by Primex Co., Ltd.) can be suitably used.
Further, as the above-mentioned carbon black, for example, furnace black, thermal black, Ketjen black, acetylene black, etc. can be used, but acetylene black is suitable.

In the method for producing a coating paste for forming a microporous layer according to the invention of claim 8, after the stirring, a mesh having an opening of 34 to 154 μm (100 to 400 mesh), preferably a mesh having an opening of 45 to 154 μm ( 100 to 300 mesh), more preferably through a mesh with an opening of 45 to 150 μm (100 to 300 mesh).

In the method for producing a coating paste for forming a microporous layer according to the invention of claim 9, a dispersant is mixed into a solvent in which the dispersant is dissolved and mixed, and a DBP absorption amount is in a range of 300 ml/100 g or more and 500 ml/100 g or less. Carbon black and a water-repellent resin are mixed, pre-stirred using a disper or turbine stator type stirrer, and then stirred by a thin film swirling method or at a circumferential speed of 25 m/s or more and 60 m/s or less.

Here, the above-mentioned disper stirs the processed material (compounded material) by generating shear through high-speed rotation of stirring blades such as a disk turbine or a dissolver (disper).
Further, the above-mentioned stirring turbine/stator type stirs the processed material (compounded material) by applying shear force in the gap between the turbine and the stator.

The method for producing a coating paste for forming a microporous layer according to the invention of claim 10 is such that a dispersant is mixed into a solvent in which the dispersant is dissolved and mixed, and a DBP absorption amount is in a range of 300 ml/100 g or more and 500 ml/100 g or less. Carbon black and water-repellent resin are mixed and pre-stirred at a circumferential speed of 1 m/s or more and 20 m/s or less, and then stirred by thin film swirling method or at a circumferential speed of 25 m/s or more and 60 m/s or less. It is something to do.

Here, in the above-mentioned stirring at a peripheral speed of 1 m/s or more and 20 m/s or less, the peripheral speed at the tip of the stirring blade is controlled by a stirrer to be 1 m/s or more and 20 m/s or less, preferably 10 m/s or more. For example, a disper or turbine stator type stirrer can be used.

In the method for producing a coating paste for forming a microporous layer according to the invention of claim 11, the carbon black and the water-repellent resin have a solid content weight ratio of 9/1≦carbon black/water-repellent resin≦5/5. It is something.

The coating paste for forming a microporous layer in the method for producing a coating paste for forming a microporous layer according to the invention of claim 12 has a viscosity of 0.05 Pa·s or more and 1.0 Pa at a shear rate of 50 [1/s].・s or less, more preferably 0.1 Pa·s or more and 0.9 Pa·s or less, still more preferably 0.1 Pa·s or more and 0.5 Pa·s or less.

According to the coating paste for forming a microporous layer according to the invention of claim 1, the coating paste contains carbon black, a water-repellent resin, a dispersant, and a solvent, and the carbon black has a DBP absorption amount of 300 ml/100 g. As mentioned above, carbon black within the range of 500 ml/100 g or less has a secondary agglomerate diameter that passes through a mesh with an opening of 34 to 154 μm, and the secondary agglomerates of carbon black with high DBP absorption are dissolved. Because it is crushed, the increase in viscosity of the paste is suppressed, and it can be applied to the surface of the conductive porous substrate with good coating properties, and is formed by drying and baking the applied paste. In the microporous layer, the carbon black having a high DBP absorption amount has a high porosity due to a high structure, resulting in a high void ratio (porosity).

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with an opening of 34 to 154 μm, due to the good coating properties of the paste. In addition to ensuring good surface smoothness in the microporous layer, it is also possible to achieve both high porosity and coating film strength that does not easily cause cracks. That is, it is possible to form a microporous layer that has a high porosity, good surface smoothness, few cracks, and good adhesion to the catalyst layer. Therefore, such a microporous layer is difficult to accumulate moisture, has high drainage performance, maintains high gas diffusivity well, and has good durability.
In addition, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with an opening of 34 to 154 μm, and the durability of the catalyst layer that performs the battery reaction is The size of the battery is such that it can pass through a fine mesh filter that removes foreign substances such as iron that affect the battery's durability and lifespan, so it does not easily reduce the durability and lifespan of the battery.
In this way, according to the coating paste for forming a microporous layer according to the invention of claim 1, a microporous layer is formed that has a high porosity and can improve the performance of gas diffusion and moisture management of the gas diffusion layer. can.

According to the coating paste for forming a microporous layer according to the invention of claim 2, since the carbon black and the water-repellent resin are in a weight ratio of 9/1 to 5/5, the microporous layer to be formed is In the cured coating film, the adhesion (binding property, binder effect) due to the resin component is good and cracks are less likely to occur, and the clogging of voids due to the excessive resin component is suppressed. Therefore, in addition to the effects described in claim 1, it is possible to form a microporous layer that can achieve both coating film strength and gas and moisture permeability.

According to the coating paste for forming a microporous layer according to the invention of claim 3, the viscosity at a shear rate of 50 s ^-1 is within the range of 0.05 Pa·s to 1.0 Pa·s, so that the coating paste forms a gas diffusion layer. It is possible to suppress paste bleed-through (a phenomenon in which the paste bleeds through to the back side of the conductive porous base material on the opposite side from the applied surface) when applying it to the conductive porous base material, and to maintain the desired coating width. A cured coating film of a microporous layer with good smoothness can be formed, resulting in good coating properties. Therefore, a smooth microporous layer can be obtained without reducing the porosity of the conductive porous base material, and the adhesion to the catalyst layer can be improved. A microporous layer that can better exhibit the performance of the diffusion layer can be formed.

According to the gas diffusion layer for fuel cells according to the invention of claim 4, the carbon black in the microporous layer made of carbon black and water-repellent resin formed on the surface of the conductive porous base material made of conductive fibers, etc. Carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation diameter that passes through a mesh with an opening of 34 μm or more and 150 μm or less, and the secondary carbon black with high DBP absorption Since the aggregates were crushed, the increase in viscosity of the paste forming the microporous layer was suppressed, and the microporous layer was formed with good coating properties on the surface of the conductive porous substrate. Carbon black with a high DBP absorption amount has a high porosity due to a high structure, resulting in a high porosity.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with an opening of 34 to 154 μm, due to the good coating properties of the paste. The microporous layer has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, a microporous layer with high porosity, good surface smoothness, few cracks, and good adhesion to the catalyst layer is difficult for moisture to accumulate, has high drainage performance, and maintains high gas diffusivity. and has good durability.
In addition, carbon black with DBP absorption within the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with openings of 34 μm or more and 150 μm or less, and the durability of the catalyst layer that performs the battery reaction is Since the size of the battery is such that it can pass through a fine mesh filter that makes it possible to remove foreign substances such as iron that affect the battery life, it does not easily reduce the durability and life of the battery.
In this way, according to the gas diffusion layer for a fuel cell according to the invention of claim 4, since it has a microporous layer with a high porosity, it is possible to improve the performance of the gas diffusion property and moisture management property of the gas diffusion layer. It is something.

According to the gas diffusion layer for fuel cells according to the invention of claim 5, since the carbon black and the water-repellent resin have a weight ratio in the range of 9/1 to 5/5, the cured coating of the microporous layer is In the film, the adhesion (bonding, binder effect) due to the resin content is good, making cracks less likely to occur, and clogging of voids due to excessive resin content is suppressed. Therefore, in addition to the effect described in claim 4, the microporous layer can achieve both coating film strength and gas and moisture permeability.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 6, carbon black having a DBP absorption within the range of 300 ml/100 g to 500 ml/100 g is added to the solvent mixed with the dispersant. A water-repellent resin is mixed and stirred using a thin film swirling method. By dispersing the compounded materials with high shear using the thin film swirling method, secondary aggregates of carbon black with high DBP absorption can be broken up. It is possible to suppress the increase in viscosity of the paste. Therefore, according to the coating paste for forming a microporous layer in which the secondary aggregates of carbon black with a high DBP absorption amount are crushed and the viscosity increase is suppressed, the coating paste can be coated well on the surface of the conductive porous substrate. In the microporous layer formed by drying and firing the applied paste, carbon black with high DBP absorption has a high porosity due to its high structure. ) will be high.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with an opening of 34 to 154 μm, due to the good coating properties of the paste. The microporous layer has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. That is, it is possible to form a microporous layer that has a high porosity, good surface smoothness, few cracks, and good adhesion to the catalyst layer. Therefore, such a microporous layer is difficult to accumulate moisture, has high drainage performance, maintains high gas diffusivity well, and has good durability.
Therefore, according to the method for producing a coating paste for forming a microporous layer according to the invention of claim 6, the microporous layer has a high porosity and can improve the diffusivity and moisture management performance of the gas diffusion layer. A coating paste is obtained that can form a coating paste.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 7, carbon black having a DBP absorption within the range of 300 ml/100 g to 500 ml/100 g is added to the solvent mixed with the dispersant. Water-repellent resin is mixed and stirred at a circumferential speed of 25 m/s or more and 60 m/s or less, and by dispersing the compounded materials with high shear by stirring at a circumferential speed of 25 m/s or more and 60 m/s or less, Secondary aggregates of carbon black with a high DBP absorption amount can be disintegrated, and an increase in the viscosity of the paste can be suppressed. Therefore, according to the coating paste for forming a microporous layer in which the secondary aggregates of carbon black with a high DBP absorption amount are crushed and the viscosity increase is suppressed, the coating paste can be coated well on the surface of the conductive porous substrate. In the microporous layer formed by drying and firing the applied paste, carbon black with high DBP absorption has a high porosity due to its high structure. ) will be high.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation size that passes through a mesh with an opening of 34 to 154 μm, due to the good coating properties of the paste. The microporous layer has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. That is, it is possible to form a microporous layer that has a high porosity, good surface smoothness, few cracks, and good adhesion to the catalyst layer. Therefore, such a microporous layer is difficult to accumulate moisture, has high drainage performance, maintains high gas diffusivity well, and has good durability.
Therefore, according to the method for producing a coating paste for forming a microporous layer according to the invention of claim 7, the microporous layer has a high porosity and can improve the diffusivity and moisture management performance of the gas diffusion layer. A coating paste is obtained that can form a coating paste.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 8, the durability of the catalyst layer is further improved by passing the coating paste through a mesh having an opening in the range of 34 to 154 μm after the stirring. It is possible to obtain products with less foreign substances such as iron that affect durability and lifespan. Therefore, in addition to the effects described in claim 6 or claim 7, a coating paste can be obtained that can form a microporous layer without reducing the durability and life of the battery.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 9, before the stirring, the mixture of the dispersant, solvent, carbon black, and water-repellent resin is stirred using a disper or turbine stator type stirring system. Pre-stir with. In this way, when pre-stirring is performed using a disper or turbine stator type stirring system, and then the thin film swirling method or stirring is performed at a circumferential speed of 25 m/s or more and 60 m/s or less, the pre-stirring can improve the compatibility between the carbon black and the solvent. Furthermore, by being able to improve the temperature and degassing by stirring, it is possible to suppress variations in the distribution of the secondary aggregation diameter of carbon black, and also to reduce the number of air bubbles. Therefore, in addition to the effects described in claim 6 or claim 7, a coating paste can be obtained that can form a more uniform microporous layer in which variations in the distribution of voids are suppressed.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 10, before the stirring, a mixture of a dispersant, a solvent, carbon black, and a water-repellent resin is heated at a circumferential speed of 1 m/s or more. Pre-stir at a speed of 20 m/s or less. In this way, for products that are pre-stirred with low shear and then diffused with high shear, pre-stirring can improve the compatibility between carbon black and the solvent, and it is possible to suppress variations in the distribution of the secondary agglomerate diameter of carbon black. It is. Therefore, in addition to the effects described in claim 6 or 7, a coating paste can be obtained that can form a microporous layer in which variation in the distribution of voids is suppressed.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 11, since the carbon black and the water-repellent resin are in a weight ratio of 9/1 to 5/5, the formation In the cured coating film of the microporous layer, the adhesion (binding property, binder effect) due to the resin content is good, and cracks are less likely to occur, and the clogging of voids due to excessive resin content is suppressed. Therefore, in addition to the effects described in claim 6 or 7, a coating paste can be obtained that can form a microporous layer that has both coating film strength and gas and moisture permeability.

According to the method for producing a coating paste for forming a microporous layer according to the invention of claim 12, since the viscosity at a shear rate of 50 s ^-1 is within the range of 0.05 Pa.s to 1.0 Pa.s, gas diffusion is prevented. When applying the paste to the conductive porous base material that makes up the layer, it is possible to suppress paste strike-through (a phenomenon in which the paste escapes to the back side of the conductive porous base material on the opposite side from the applied surface), and to achieve the desired coating. It is possible to form a cured coating film of a microporous layer with good smoothness in the width of the coating, resulting in good coating properties. Therefore, a smooth microporous layer can be obtained without reducing the porosity of the conductive porous base material, and the adhesion to the catalyst layer can be improved. In addition, a coating paste can be obtained that can form a microporous layer that can better exhibit the performance of the gas diffusion layer.

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

Embodiments of the present invention will be described below with reference to the drawings.
Note that in the embodiments, the same symbols and the same reference numerals mean the same or corresponding functional parts in the embodiments, and therefore, redundant detailed explanations will be omitted here.

[Embodiment]
First, the structure of a polymer electrolyte fuel cell (single cell) in which a fuel cell gas diffusion layer in which a microporous layer is formed by applying the coating paste for forming a microporous layer according to the present embodiment is incorporated is shown in FIG. This will be explained with reference to a schematic configuration diagram of No. 1. In addition, in the figure, the anode side is designated as A, and the cathode side is designated as K.

As shown in FIG. 1, the gas diffusion layer 14 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A) is made of catalyst-supported carbon in which precious metal catalysts such as platinum, gold, palladium, etc. are supported on carbon and ion exchange resin. It is joined to the catalyst layer 13 (cathode side catalyst layer 13K, anode side catalyst layer 13A) with which oxidizing gas or fuel gas reacts, and together constitutes the electrode 12 (cathode electrode 12K, anode electrode 12A). The gas diffusion layer 14 is disposed together with the catalyst layer 13 on both sides of the polymer electrolyte membrane 11 (the core of the single cell) that selectively transmits specific ions, thereby forming a membrane/electrode assembly (MEGA) 10. do.
This membrane/electrode assembly 10 includes a cathode-side separator 20K provided with an oxidizing gas flow path 21K for supplying an oxidizing gas serving as an oxidizing agent on the outside of the cathode-side gas diffusion layer 14K, and also on the outside of the anode-side gas diffusion layer 14A. It is sandwiched between an anode-side separator 20A provided with a fuel gas flow path 21A for supplying fuel gas, thereby forming 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 coating paste for forming a microporous layer according to the present embodiment is applied is used, an oxidizing gas such as oxygen gas is present on one surface of the polymer electrolyte membrane 11. A cathode electrode 12K composed of a reacting cathode catalyst layer 13K and a cathode gas diffusion layer 14K is disposed, and an anode catalyst layer 13A and an anode gas diffusion layer are provided on the other surface, and an anode catalyst layer 13A and an anode gas diffusion layer are provided on the other surface. A membrane/electrode assembly 10 having an anode electrode 12A configured by a layer 14A and forming a power generation section, and a cathode side separator 20K and a membrane disposed on the surface of a cathode electrode 12K of the membrane/electrode assembly 10. /anode side separator 20A disposed on the surface of the anode electrode 12A of the electrode assembly 10.

Here, in the gas diffusion layer 14 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A) according to the present embodiment, a coating paste for forming a microporous layer, which will be described later, is applied to the conductive porous base material 16 (cathode side gas diffusion layer 14K, anode side gas diffusion layer 14A). The microporous layer (microporous layer) 15 (cathode side microporous layer 15K, The anode side microporous layer 15A) is formed on one side of the conductive porous base material 16 (cathode side conductive porous base material 16K, anode side conductive porous base material 16A).
The gas diffusion layer 14 composed of the microporous layer 15 and the conductive porous base material 16 has the microporous layer 15 side adjacent to the catalyst layer 13 and the conductive porous base material 16 side adjacent to the separator 20. The fuel cell 1 is assembled in such a manner that the fuel cell 1 is disposed therein.

With such a cell configuration, when oxidizing gas is supplied from the outside to the oxidizing gas flow path 21K of the cathode-side separator 20K, a portion of the oxidizing gas flowing along the oxidizing gas flow path 21K reaches the cathode-side gas diffusion layer. It penetrates into the inside of the 14K conductive porous base material from the 16K side surface. Note that 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, part of the fuel gas flowing along the fuel gas flow path 21A is absorbed by the conductivity of the anode side gas diffusion layer 14A. It penetrates into the inside of the porous base material 16A side surface. 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, as the oxidizing gas and the fuel gas react, electric power is extracted between the cathode side separator 20K and the anode side separator 20A. Note that the microporous layer 15 may be formed on both the front and back surfaces of the conductive porous base material 16.

Next, a microporous layer 15 to be 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 prepared. The coating paste for forming a porous layer will be explained.

The coating paste for forming a microporous layer (hereinafter sometimes abbreviated as "MPL coating paste") of this embodiment includes carbon black, which is a conductive material, a water-repellent resin, a solvent, carbon black, and a water-repellent material. It contains a dispersant and the like to disperse the resin.

The carbon black blended into the MPL coating paste of this embodiment has a DBP absorption of 300 ml/100 g or more and 500 ml/100 g or less, preferably 300 ml/100 g or more and 480 ml/100 g or less, More preferably, it is within the range of 300 ml/100 g or more and 450 ml/100 g or less. Such high DBP absorption carbon black has an average primary particle size in the range of about 25 nm to 45 nm, preferably in the range of 30 nm to 45 nm.

As carbon black, furnace black, thermal black, acetylene black, Ketjen black, etc. can be used, but acetylene black is preferable. Acetylene black has a high structure, is highly pure, has few impurities such as metals, has few surface functional groups, and is highly crystalline, so it has high gas diffusivity, strength, and conductivity. A microporous layer 15 (hereinafter sometimes abbreviated as "MPL15") can be formed.
In addition, such carbon black has a structural structure in which primary particles are connected in a chain, that is, an aggregate structure in which the primary particles are fused together. Agglomerates (secondary aggregates) bonded together are aggregated and exist as a powder or granular aggregate structure. Incidentally, carbon blacks such as acetylene black and Ketjen black exhibit electrical conductivity through the movement of π electrons in their condensed benzene rings.
Furthermore, since carbon black is inexpensive compared to other carbons, the material cost can also be kept low.

In addition, examples of water-repellent resins to be added to the MPL coating paste include polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), perfluoroalkoxyfluororesin (PFA), Fluorine resins such as polychlorotrifluoroethylene (PCTFE), ethylene/tetrafluoroethylene copolymer (ETFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVdF), and silicone resins etc. can be used. These can be used alone or in an appropriate combination of two or more.

Among these, fluorine-based polymer materials are preferred because they have excellent water repellency and corrosion resistance during electrode reactions, and PTFE, which is a fluororesin that provides high water repellency, is particularly preferred. PTFE as the water-repellent resin may be a homopolymer of tetrafluoroethylene, halogenated olefins such as chlorotrifluoroethylene and hexafluoropropylene, and other fluorine-based monomers such as perfluoro(alkyl vinyl ether). It may also be a modified PTFE containing units derived from.

Further, the water-repellent resin preferably has an average molecular weight within the range of 50,000 to 1,000,000. If a material having an average molecular weight that is too low is used, the binding property as a binder for binding carbon black particles will be low, and cracks will easily occur in the formed MPL 15. On the other hand, if a material with an average molecular weight that is too large is used, it tends to become fibrous when mixed with other raw materials, resulting in poor dispersion and reduce the stability of the paste, or it may become fibrous and harden due to the shearing force during stirring. This can cause concentration changes, clogging of piping, pumps, foreign matter removal filters, etc., poor adhesion of paint films, and surface defects. Note that when the water-repellent resin is a fluoropolymer, it is difficult to measure the average molecular weight using melt viscosity because the fluoropolymer is difficult to dissolve in a solvent. For this reason, the specific gravity method is applied to determine the average molecular weight from the relationship between specific gravity and number average molecular weight.

Generally, water-repellent resins such as fluororesins do not disperse in water as they are, so they can be dispersed in water using an appropriate dispersant (surfactant), such as fluororesins such as PTFE emulsion. It is formulated in the form of an emulsion in which a water-repellent resin is emulsified, or a dispersion in which a water-repellent resin such as a fluororesin is dispersed. That is, a dispersant may be included in advance in the water-repellent resin emulsion or the like that is mixed as a composition raw material.

Incidentally, an emulsion (also referred to as an "emulsion") is also called an emulsion, and its original meaning is a system in which liquid particles form a milky state as colloidal particles or coarser particles (a dispersion system). However, in this specification, it is generally used in a broader sense. The term "emulsion" is used here as "a substance in which solid or liquid particles are dispersed in a liquid."

Further, in the MPL coating paste of this embodiment, a dispersant is used to disperse and stabilize compounding materials such as carbon black and water-repellent resin in a solvent. Examples of the dispersant include polyoxyethylene tridecyl ether, polyoxyethylene alkylphenyl ether (Triton X-100, etc.), polyoxyethylene lauryl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene alkylene alkyl ether , nonionic surfactants such as polyethylene glycol alkyl ether, cationic surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium chloride, alkylpyridium chloride, polyoxyethylene fatty acid ester, acidic group-containing structure Surfactants such as anionic surfactants such as modified polyacrylates, polyethylene oxide-based, methylcellulose-based, hydroxyethylcellulose-based, polyethylene glycol-based (for example, ethers of alkylphenols and polyethylene glycol, ethers of higher aliphatic alcohols and polyethylene glycol) etc.), polyvinyl alcohol-based thickeners, etc. can be used.

Among these, nonionic (nonionic) surfactants are preferable because they have a low content of metal ions and are less likely to cause deterioration in battery performance due to short circuits, etc., and are particularly suitable for carbon black and water-repellent resins. When dispersing a PTFE emulsion in a solvent, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene alkyl is used to improve the wettability and dispersibility of these carbon black particles and PTFE particles. Phenyl ether (Triton X-100) and the like are preferably used.
Note that the type of dispersant such as a surfactant or a thickener is selected depending on the characteristics required for MPL15 and the compounded materials, and the dispersant may have both dispersing and thickening functions.
Furthermore, if necessary, a thickener such as polyvinyl alcohol may be added to adjust the viscosity.

As the solvent for the MPL coating paste of this embodiment, an aqueous solvent such as ion-exchanged water is used. When using an aqueous solvent such as ion-exchanged water, the dispersibility of water-repellent resins such as PTFE emulsion is better than when using organic solvents, and the water-repellent resin does not separate, resulting in good film-forming properties. is obtained. In addition, it has good workability during coating and firing, and there is no risk of ignition. Furthermore, it does not cause any environmental burden and is low cost.

In the MPL coating paste of the present embodiment, carbon black having a DBP absorption amount of 300 ml/100 g or more and 500 ml/100 g or less in terms of solid content is preferably 55 to 90% by mass, more preferably is within the range of 70 to 85% by mass, more preferably 75 to 80% by mass, and the water repellent resin is preferably within the range of 10 to 45% by mass, more preferably 15 to 30% by mass, even more preferably is within the range of 20 to 25% by weight, and the dispersant is preferably 5 to 30 parts by weight, more preferably 8 to 20 parts by weight, even more preferably 10 to 15 parts by weight, based on 100 parts by weight of carbon. It is blended within the range of 50%.

The MPL coating paste of this embodiment includes a dispersant mixing/dissolving step in which a solvent and a dispersant are mixed and stirred, and a DBP absorption amount of 300 ml/100 g or more and 500 ml in a solvent in which the dispersant is mixed and dissolved. /100g or less of carbon black (usually powder or granules) and a water-repellent resin (usually resin emulsion or resin dispersion) are mixed, and the mixture is stirred at a circumferential speed of 25m/100g using a thin-film rotary stirrer or the like. It is obtained through a stirring step of stirring at a stirring speed of s or more, and a filtration step of filtering the paste in which the ingredients are dispersed by stirring through a mesh filter of a predetermined size to remove foreign substances.

That is, in this embodiment, first, a dispersant mixing/dissolving step is performed in which the dispersant is mixed and dissolved in the solvent by mixing and stirring the dispersant and the solvent. The stirring means and stirring conditions at this time are not particularly limited as long as the dispersant can be uniformly mixed and dissolved in the solvent. For example, if the dispersant is soluble in water, stirring with a stirrer (for example, rotation speed: 100 to 1500 rpm) (rotations/min) and stirring conditions (stirring time: about 1 to 15 minutes), a uniform solution can be obtained.

Next, a water-repellent resin and carbon black whose DBP absorption amount is within the range of 300 ml/100 g or more and 500 ml/100 g or less are mixed with the solvent in which the dispersant has been mixed and dissolved, and then mixed with a thin film swirl type stirrer or the like. A stirring step of stirring at a circumferential speed of 25 m/s or more is carried out.
In the above-mentioned stirring process at a circumferential speed of 25 m/s or more, the circumferential speed at the tip of the stirring blade is Stir at 25 m/s or more.
In particular, stirring using a thin film swirling type stirrer is called a thin film swirling method, and the entire interior of the tank of the stirrer is brought into a high-energy turbulent state. According to such a stirring method, the agglomerated particles are pressed against the tank wall surface by the swirling flow that creates a turbulent flow, and perform a swirling motion along the wall surface, and at this time, the particles are stretched thinly by the rotation of the turbine and the liquid flow of the solvent. A swirling thin film is formed, and the carbon black aggregates are broken up by the shear stress of the centrifugal force pressed against the wall and the force of the swirling flow. Furthermore, in stirring using such a thin film swirling method, re-agglomeration (flocculation) of secondary aggregates is prevented by stabilizing the droplet interface, etc., and the disintegration state of secondary aggregates is stabilized. becomes. Carbon black with a high DBP absorption amount can be highly dispersed and the dispersion can be stabilized with a simple process without taking much time. Furthermore, a dispersant can also prevent the re-agglomeration (flocculation) of the finely dispersed secondary aggregates due to such strong shearing and stabilize the crushed state of the secondary aggregates. .

The conditions for stirring using a thin film swirl type stirrer, etc., have been determined through experimental research by the present inventors.If the circumferential speed of the stirring section is too slow or the stirring time is too short, carbon black aggregates will not be sufficiently broken down. Since it has been confirmed that it is difficult to pass through a mesh filter with a predetermined opening under a predetermined pressure condition, it is preferable that the circumferential speed of the stirring section is 25 m/s or more, and the stirring time is The time is preferably 20 seconds or more, more preferably 25 seconds or more, and even more preferably 30 seconds or more. Note that the upper limit of the circumferential speed is a finite value at the performance limit (maximum circumferential speed) of the stirrer, and is approximately 60 m/s, but according to the experimental research of the present inventors, the specified value can be achieved even at a circumferential speed of 50 m/s or more. It has been confirmed that the desired viscosity characteristics can be obtained with a stirring time of . In particular, in diffusion using such thin film swirling method, it is possible to control the diameter of secondary agglomeration by changing the circumferential speed and stirring time conditions, and the diameter of secondary agglomeration of carbon black can be designed according to the desired characteristics of MPL15. It is also possible.

Here, if the stirring time using a thin film swirl type stirrer or the like is too long, the diameter of the secondary agglomeration of carbon black becomes fine and the viscosity of the paste decreases greatly, and the conductive porous base constituting the gas diffusion layer 14 When applied to the conductive porous base material 16, strike-through that penetrates the conductive porous base material 16 and passes through its thickness is likely to occur. Therefore, it becomes necessary to increase the viscosity by adding a large amount of thickener. However, when a large amount of thickener is added, the burden of decomposing and removing the thickener during the baking and drying steps after applying the paste increases. In other words, if the thickener is not sufficiently decomposed by heating during the baking and drying process, water repellency will deteriorate, so if a large amount of thickener is added, it is necessary to take longer drying and baking times. This results in an increase in the load on the firing and drying processes.
The peripheral speed of the stirring section is preferably 25 m/s or more, and the stirring time is preferably about 20 seconds to 200 seconds, more preferably 25 seconds to 150 seconds, and still more preferably about 30 seconds to 100 seconds. For example, it is possible to obtain desired viscosity characteristics within the range of 0.05 to 1.0 Pa·S at a shear rate of 50 S ^-1 without requiring the addition of a large amount of thickener.

Then, by stirring for a predetermined time using a thin film swirling method or the like, the carbon black is heated to a size that allows the paste to pass through a mesh with an opening of 154 μm or less, that is, 100 mesh or more, which can remove metal foreign substances contained in the carbon black product. It is sufficient if the secondary aggregates can be broken up. However, even if it is crushed to a size that allows it to pass through a filter that is too fine, productivity will decrease. Hereinafter, preferably a mesh with an opening of 45 μm or more and 154 μm or less, i.e., 100 mesh or more and 300 mesh or less, more preferably a mesh with an opening of 45 μm or more and 150 μm or less, i.e. 100 mesh or more, 300 mesh It is sufficient if it can be dispersed to a size that can pass through the mesh.

By the way, when carrying out the present invention, if necessary, pre-stirring (pre-dispersion) may be performed by stirring with a disper type or turbine stator type stirrer before stirring with a thin film swirl type stirrer or the like. .
By stirring with a disper type or turbine stator type stirrer, etc. before stirring with a thin film swirl type stirrer, etc., the compounded materials are roughly dispersed, and the secondary carbon black after stirring with a thin film swirl type stirrer etc. It is possible to suppress variations in the distribution of agglomerate diameters (sharply adjust the particle size distribution) and stabilize dispersion, resulting in higher stability, and also suppresses variations in the distribution of voids in MPL15, resulting in stable performance. , it becomes possible to obtain uniform diffusivity. This improves the wettability of carbon black by stirring at a low shear using a disper type or turbine stator type stirrer before stirring at a high shear using a thin film swirl type stirrer. This is thought to be because the compatibility between the carbon black and the water solvent is improved, and the dispersibility can be improved by high-shear stirring. It can also be assumed that carbon black with a highly developed structure has a large specific surface area, so it easily absorbs moisture and becomes wet. Note that it is also possible to improve the wettability of carbon black by using a dispersant.

Incidentally, a disper-type stirrer generates shear force by rotating a high-speed stirring blade called a disk turbine or a dissolver at high speed. In addition, a turbine-stator type agitator consists of turbine blades (homo mixer) that rotate at high speed and a stator (fixed ring) that surrounds the turbine blades and does not rotate. For example, a homomixer, a comb-teeth turbine stator, or an in-line type (turbine stator type stirrer installed in a casing) type stirrer can be used. Note that a composite stirrer in which a disper type stirrer and a turbine stator side stirrer are combined may be used. All of these generate shearing force by applying local energy.
In particular, a disperser type or turbine stator type stirrer can produce a paste that can form a uniform coating film with few air bubbles by stirring and defoaming.

The stirring conditions for the disper type or turbine stator type stirrer or the like are a circumferential speed of 1 m/s or more and a circumferential speed of 20 m/s or less, preferably a circumferential speed of 10 m/s or more and a circumferential speed of 20 m/s or less. If the peripheral speed (rotation speed) of the stirrer at this time is too low, the wettability of carbon black particles cannot be sufficiently improved, and variations in the distribution of secondary agglomerate diameters of carbon black can be effectively suppressed. I can't. On the other hand, if the rotation speed of the stirrer exceeds a certain level, even if the peripheral speed (rotation speed) or stirring time is increased too much, idle operation (vortex) will occur, and the effect of improving wettability and dispersibility will not be affected. This only increases the load and energy consumption of the machine. Within the above range, variations in the distribution of secondary agglomerate diameters of carbon black can be effectively suppressed with good productivity and low energy consumption.
Note that if a large amount of foam is generated by these stirrings, a defoaming step may be provided before or after the stirring.

In this embodiment, after stirring with the thin film swirl type stirrer, a filtration step is performed in which the stirred paste is filtered through a mesh filter with a predetermined mesh size to remove foreign substances such as iron. .
In this filtration step, the stirred paste is passed through a filter with a mesh opening of 154 μm or less, ie, 100 mesh or more, using a ram press (pressurized extrusion device) or the like. This removes foreign substances contained in the paste compounding materials, especially metal foreign substances such as iron contained in carbon black products that cause short circuits and adversely affect the durability of the catalyst layer 13 and the lifespan of the battery 1. be done. If the mesh is too fine, the productivity will decrease, so it is preferable to use a mesh with an opening of 34 μm or more and 154 μm or less, i.e., 100 mesh or more and 400 mesh or less, preferably a filter with an opening of 45 μm or more, and a mesh with an opening of 45 μm or more. Any mesh with an opening of 154 μm or less, ie, 100 mesh or more and 300 mesh or less, more preferably a mesh with an opening of 45 μm or more and 150 μm or less, ie, 100 mesh or more and 300 mesh or less, is sufficient.

At this time, if the viscosity of the paste after stirring at a shear rate of 50 S ^-1 exceeds 1.0 Pa·S, pressure loss will increase when passing through a fine mesh for removing foreign matter, resulting in a decrease in productivity. Therefore, if the viscosity of the paste at a shear rate of 50 S ^-1 exceeds 1.0 Pa·S after stirring, a solvent may be added before passing through a predetermined filter to reduce the viscosity to 1.0 Pa·S at a shear rate of 50 S ^-1 . It is preferable to adjust the viscosity to reduce the viscosity to 0 Pa·S or less. More preferably, the viscosity at a shear rate of 50 S ^-1 is adjusted to 0.9 Pa.S or less, and even more preferably 0.5 Pa.S or less.

Furthermore, in order to prevent the paste from bleed-through when the MPL coating paste is applied to the conductive porous base material 16, the shear rate of the MPL coating paste applied to the conductive porous base material 16 is set to 50S ^-1 . The viscosity is preferably 0.05 Pa·S or more, more preferably 0.1 Pa·S or more.
That is, if the viscosity of the paste passed through a filter with a predetermined opening (mesh) is too low, the paste will become conductive porous when applied to the conductive porous base material 16 constituting the gas diffusion layer 14. A strike-through occurs that penetrates into the base material 16, passes through the conductive porous base material 16, and reaches the back surface opposite to the coated surface, and the paste component closes the voids in the conductive porous base material 16 and removes gas and moisture. This will reduce the permeability of

Therefore, if the viscosity of the paste at a shear rate of 50S ^-1 after filtration through a filter with a predetermined opening (mesh) is less than 0.05 Pa・S, by adding ^a thickener, The viscosity is preferably adjusted to be within the range of 0.05 Pa·S or more and 1.0 Pa·S or less. If the viscosity at a shear rate of 50 S ^-1 is increased too much by adding a thickener, the coatability of the MPL coating paste will decrease, and as mentioned above, the baking and drying steps to decompose the thickener will be difficult. Since this will increase the load, the viscosity of the MPL coating paste applied to the conductive porous substrate 16 at a shear rate of 50S ^-1 should be within the range of 0.05 Pa.S or more and 1.0 Pa.S or less. It is preferably within the range of 0.1 Pa·S or more and 0.9 Pa·S or less, and even more preferably 0.1 Pa·S or more and 1.0 Pa·S or less.

If the viscosity of the MPL coating paste applied to the conductive porous base material 16 at a shear rate of 50S ^-1 is within the range of 0.05 Pa·S or more and 1.0 Pa·S or less, the conductive porous base material 16 It is possible to prevent the paste from bleed-through when applied to the conductive porous base material 16, thereby exhibiting good performance of the conductive porous base material 16, and without increasing the load of the firing and drying process. Since the coatability to the substrate 16 (surface smoothness, etc.) is good, the adhesion to the catalyst layer 13 is also good, and MPL15 exhibits good moisture management properties and gas diffusivity. Note that the solid content will vary depending on the intended viscosity setting.

The MPL coating paste prepared in this manner is applied to the surface of the conductive porous base material 16 that constitutes the gas diffusion layer 14 for the fuel cell 1, and then dried and fired to constitute the MPL 15. It becomes a hardened coating film. As shown in FIG. 1, the gas diffusion layer of the fuel cell electrode is formed by the conductive porous base material 16 as the gas diffusion layer electrode base material and the cured coating film MPL 15 formed on one or both sides of the conductive porous base material 16. 14.

Here, the conductive porous base material 16 to which the MPL coating paste of this embodiment is applied is generally used in the gas diffusion layer 14 of the conventional fuel cell 1 (particularly, the polymer electrolyte fuel cell 1). For example, carbon materials such as metals and graphite (including nanocarbon materials) are used in porous forms such as fibrous, particulate, woven fabric, nonwoven fabric, mesh, lattice, punched bodies, and foamed bodies. A material configured in the form of a solid body can be used, and a porous base material having gas permeability and electrical conductivity is used. In particular, from the viewpoint of gas permeability, carbon fibers (also called carbon fibers, carbon-based fibers, carbon-based fibers) are preferable, and examples of graphite fibers include polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers. Fibers, phenolic carbon fibers, etc. are used. Carbon fiber sheets such as carbon paper, carbon cloth, and carbon felt (carbon nonwoven fabric) are preferably used as the base material. These are selected in consideration of the usage environment, operating conditions, etc. of the fuel cell 1. Such a conductive porous base material 16 is usually a porous body having a peak pore diameter within a range of 10 μm or more and 100 μm or less.

Note that, if necessary, the conductive porous base material 16 such as carbon paper, carbon cloth, or carbon felt is subjected to water repellent treatment in order to improve the water repellency of the gas diffusion layer 14 or the like. The method for water repellent treatment is not particularly limited, and for example, the conductive porous base material 16 may be immersed in an emulsion, dispersion, etc. containing a water repellent, or the conductive porous base material 16 may be treated with a water repellent by die coating, spray coating, etc. Water-repellent treatment can be performed by applying a water-repellent agent or processing by a dry process such as sputtering of fluororesin. Note that after the water repellent treatment, drying and baking may be performed as necessary. The water repellent used in this water repellent treatment is the same as the above-mentioned water repellent resin that can also be used in the MPL coating paste. The amount of water repellent at this time is not particularly limited, but from the viewpoint of achieving both water repellency and a good gas diffusion path and drainage path, it is preferably included in 100% by mass of the entire conductive porous base material 16. It is within the range of 0.1% by mass to 20% by mass.

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 of the fuel cell 1 and the required performance. If the layer 16 is too thin, the strength may be insufficient and the performance of the gas diffusion layer 14 such as stable gas diffusion, moisture management, and electrical conductivity may not be obtained, and the ease of handling may be poor and the catalyst layer 13 and This may cause the position of the battery to shift, resulting in a decrease in battery performance. Furthermore, if the conductive porous base material 16 is too thick, gas diffusivity will decrease due to increased resistance, making it impossible to obtain high battery performance. For this reason, a thickness of, for example, 2 μm or more and 500 μm or less, preferably 10 μm or more and 250 μm or less, more preferably 70 μm or more and 150 μm or less is used.

Further, as a coating method for applying the MPL coating paste of this embodiment to the conductive porous base material 16, brush coating, brush coating, roll coater method, bar coater method, die coater method, blade method, knife coater method, spin coater etc. method, screen printing, rotary screen printing, curtain coating method, dip coater method, spray coater method, gravure coater method, applicator, spray atomization, etc. In particular, the die coater method is suitable because the coating amount can be quantified regardless of the surface roughness of the conductive porous base material 16, but it is not necessarily limited thereto.

The MPL coating paste of this embodiment is applied to the surface of the conductive porous base material 16, dried and fired, and the solvent is removed by drying. MPL15 is formed, but the temperature for drying and baking at this time may be any temperature that can decompose and remove dispersants and thickeners such as surfactants, and that does not thermally decompose the water-repellent resin. For example, , heat-treated within the range of 250 to 400°C for 5 to 20 minutes.
If the drying and firing temperature at this time is too low, even if the drying and firing time is prolonged, the dispersant, etc. cannot be sufficiently thermally decomposed and volatilized to be removed, and the dispersant remains and becomes hydrophilic. Since moisture is captured by the chemical groups, the formed gas diffusion layer 14 cannot exhibit sufficient water repellency. On the other hand, if the drying/baking temperature is too high, coating film components such as water-repellent resin may be thermally decomposed and the components of MPL15 may deteriorate, or large temperature changes may increase the deformation of MPL15 and reduce smoothness. , cracks may occur, making it difficult to form an MPL 15 that satisfies the desired required performance. Furthermore, the load in the drying and firing process and the load on the natural environment increases, and the manufacturing cost also increases. By drying and baking in a specified temperature range, dispersants and thickeners such as surfactants contained in the MPL coating paste can be removed, and water repellency can be prevented from being inhibited by dispersants and thickeners such as surfactants. Furthermore, by melting the water repellent, carbon black can be bound to form an MPL 15 having a desired strength.

For example, if the dispersant is polyoxyethylene tridecyl ether, polyoxyethylene alkylphenyl ether (Triton X-100), etc., the drying/calcination temperature is set in the range of 250 to 350°C. Within this range, the dispersant and the like can be sufficiently decomposed and volatilized, thereby ensuring water repellency, which is an important characteristic of the gas diffusion layer 14 that greatly affects power generation efficiency, and forming an MPL 15 with desired characteristics. In addition, good bondability with the conductive porous base material 16 can be ensured. In addition, in the drying and baking process involving such heat treatment, the order of drying and baking is not particularly limited, and drying and baking may be performed simultaneously. It is also possible to perform each heat treatment separately by changing the temperature and time conditions for the heat treatment mainly for decomposing and removing the dispersant and the heat treatment mainly for binding by melting the water-repellent resin. be.

The coating thickness when applying the MPL coating paste of this embodiment to the conductive porous base material 16 is set in consideration of the operating conditions of the fuel cell 1 and the performance required of the MPL 15. For example, the thickness of the cured coating film after applying the MPL coating paste to the conductive porous substrate 16, drying and baking, that is, the thickness of the dry film thickness of the MPL 15, is preferably within the range of 1 to 300 μm. is set within the range of 10 to 100 μm.
If the thickness of the MPL 15 (the dry film thickness of the cured coating film) is too thin, the effect of suppressing the formation of a liquid film at the interface with the catalyst layer 13 will be small, and the unevenness of the conductive porous base material 16 will not be absorbed. Moreover, the effect of preventing the fibers of the conductive porous base material 16 from penetrating the electrolyte membrane 11 cannot be obtained. On the other hand, if the coating film thickness of the MPL coating paste is too thick, the surface smoothness tends to decrease due to shrinkage due to drying and baking, and the contact resistance with the catalyst layer 13 increases, resulting in a decrease in moisture management due to a decrease in adhesion. This may lead to a decrease in conductivity. Furthermore, if the dry film thickness is too thick, the electrical resistance in the thickness direction will increase, and the gas diffusion resistance will also increase.

If the thickness of the cured coating film after applying the MPL coating paste to the conductive porous substrate 16, drying and baking, that is, the dry film thickness of the MPL 15, is within the range of 1 to 300 μm, the surface smoothness is determined. A high MPL of 15 can be obtained, and good gas and moisture permeability and conductivity performance can be ensured. Preferably, it is within the range of 10 to 100 μm. Further, it is desirable that the thickness of the MPL 15 is 50% or less of the thickness of the conductive porous base material 16. If 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, so that good moisture management and conductivity are exhibited due to good adhesion with the catalyst layer 13.

By applying the MPL coating paste to the conductive porous substrate 16 in this way, and drying and baking it, the dispersant, thickener, and solvent (moisture) in the MPL coating paste are removed. A cured coating film as MPL 15 in which carbon black is bound by a water-repellent resin is formed on the conductive porous substrate 16. At this time, the MPL coating paste is dried and fired together with the conductive porous base material 16, so that a part of the water-repellent resin in the MPL coating paste is melted, and the carbon blacks are bound together by the water-repellent resin. At the same time, by bonding the carbon black with a conductive material such as carbon fiber of the conductive porous base material 16, the adhesion with the conductive porous base material 16 is improved, and the formed MPL 15 is made stronger. shall be.

In this way, the MPL coating paste containing carbon black, water-repellent resin, dispersant, and solvent is coated on the conductive porous base material 16 and dried and fired. MPL15, the cured coating film formed in Also, it has water repellency due to the water repellent resin, and also has moisture and gas permeability due to the pores (voids).

Then, an MPL coating paste is applied to the surface of the conductive porous base material 16, and the MPL 15 is formed on the conductive porous base material 16 by drying and baking. According to , in the fuel cell 1 incorporating the MPL 15, the presence of the MPL 15 makes it difficult for moisture to accumulate at the boundary with the adjacent catalyst layer 13, improving gas diffusivity and moisture management, and stabilizing power generation performance. Further, by adjusting the components of the MPL 15, it is possible to obtain fine controllability of performance in accordance with the usage environment, operating conditions, etc. of the battery, which is difficult with the conductive porous base material 16 alone. Furthermore, the MPL 15 absorbs the undulations of the conductive porous base material 16 to obtain a smooth surface. That is, the MPL 15 can prevent short circuits caused by fraying or fuzzing of the carbon fibers of the conductive porous base material 16 penetrating or coming into contact with the catalyst layer 13 or the polymer electrolyte membrane 11.

In particular, according to the MPL coating paste of this embodiment, secondary aggregates of carbon black with a high DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g are crushed. Because of this, the increase in viscosity of the paste is suppressed, and the desired wide coating width can be applied to the surface of the conductive porous substrate 16, and coating streaks are less likely to occur and good coating properties are obtained, which improves productivity. Sex is also good. Furthermore, the MPL 15 formed from the MPL coating paste of this embodiment has less unevenness and undulations such as coating streaks, has good surface smoothness, and has good adhesion to the catalyst layer 13. There is little biting into the material, so it is difficult to apply mechanical stress. In addition, secondary aggregates of carbon black with a high DBP absorption amount are broken up by high shear dispersion using a thin film swirling method at a circumferential speed of 25 m/s or more, so the aggregates are less likely to re-agglomerate and can be stored. Stability is also good.

Since the carbon black with high DBP absorption has a high porosity due to its high structure, the formed MPL15 has a high porosity (porosity), and the pores can be uniformly distributed, allowing gas and moisture to be absorbed due to the high structure. By forming the passages, it is possible to improve the diffusion and drainage of gas and moisture. Therefore, flatting (a phenomenon in which generated water accumulates in the MPL) is less likely to occur, and gas diffusivity is prevented from being inhibited by flatting, and moisture accumulated at the boundary with the catalyst layer 13 is prevented from freezing Obstruction of gas diffusibility and deterioration of MPL 15 are prevented, and battery output can be stabilized.

In addition, carbon black with DBP absorption within the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration diameter that allows it to pass through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Due to the good coating properties of the paste, good surface smoothness can be ensured in MPL15, and it is also possible to achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, by forming the MPL 15 which has a high porosity but has good surface smoothness, is less prone to cracking, and has good adhesion to the catalyst layer 13, the MPL 15 is less likely to accumulate moisture, that is, less likely to cause flatting. As a result, stable drainage properties and gas diffusion properties can be obtained, and the coating film is less likely to be chipped and has good durability. By having good adhesion with the catalyst layer 13, the contact resistance at the contact surface can be reduced, and since cracks are less likely to occur and good conductivity can be exhibited, power generation efficiency can also be improved. Furthermore, it is able to withstand the clamping force from the separators of stacking, and the gaps are not easily crushed even by the clamping force from the separators.
Therefore, it is possible to form an MPL 15 with a high porosity and to improve the gas and moisture permeability of the MPL 15, thereby improving the performance of gas diffusion and moisture management of the gas diffusion layer 14 in which the MPL 15 is formed. Is possible.

Carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation diameter that allows it to pass through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Since it is of a size that can pass through a fine mesh filter that makes it possible to remove foreign substances such as iron that affect the durability and life of the catalyst layer 13 that performs the battery reaction, the yield is good and the mesh opening is 34 μm or more. By filtering with a filter having a mesh size of 154 μm or less (100 mesh or more, 400 mesh or less), foreign substances such as iron can be removed, making it difficult to reduce the durability and life of the battery.

Next, regarding an example of the MPL coating paste according to the present embodiment, and an example of the gas diffusion layer (gas diffusion electrode) 14 for a fuel cell manufactured using the MPL coating paste of the present embodiment, This will be explained along with a comparative example.
The MPL coating pastes of Examples and Comparative Examples contain carbon black, a water-repellent resin, a dispersant, and a solvent.

As the carbon black, acetylene black (for example, "Denka Black (registered trademark)" manufactured by Denki Kagaku Kogyo Co., Ltd.) was used, and as the water-repellent resin, an emulsion of PTFE, a fluororesin (manufactured by Daikin Industries, Ltd.) was used. : POLYFLON PTFE D-210C [solid content (resin content) 61%]), the surfactant Triton X-100 was used as the dispersant (10% carbon ratio), and the solvent was ion Exchange water was used. Note that the PTFE emulsion also contains a nonionic surfactant (dispersant) for stabilizing the PTFE fine particles as a water-repellent resin.

In each Example and Comparative Example, first, the solvent and the dispersant were mixed and stirred using a stirrer at a stirring speed of 300 rpm for about 10 minutes to dissolve the dispersant in the solvent (dispersant mixing/dissolving step). . Next, the specified carbon black shown in Table 1 and the PTFE emulsion are mixed into the solvent in which the dispersant is dissolved, and the mixture is mixed with a homomixer, which is a turbine stator type high-speed stirrer ("Homomixer MARK II" manufactured by Primix Co., Ltd.). 2.5 type) using 30
After stirring at 00 rpm for about 30 minutes, the mixture was stirred under the predetermined conditions shown in Table 1 using Filmix R ("Filmix R56-L type" manufactured by Primix Co., Ltd.), which is a thin film rotating high-speed stirrer. (Stirring process).

In Examples 1 to 4, Example 7, Comparative Example 1, and Comparative Example 2, the viscosity of the paste after stirring by the thin film swirling method was measured, and the viscosity at a shear rate of 50S ^-1 was 0.5 Pa・s or less. For pastes within this range, without adjusting the viscosity, they are passed through a filter with a mesh opening of 45 μm (300 mesh) using a ram press machine under a pressure of 0.45 MPa (pressing force). Filter filtration was performed to remove foreign substances and the like (filtration step). Furthermore, the viscosity of the paste after passing through the filter is measured, and if the viscosity at a shear rate of 50S ^-1 is within the range of 0.1 Pa・s or more and 0.5 Pa・s or less, it is used as it is for MPL coating with the finished viscosity. If the paste is less than 0.1 Pa・s, a thickener is added to adjust the viscosity so that the finished viscosity is within the range of 0.1 Pa・s or more and 0.5 Pa・s or less. An MPL coating paste with a viscosity of 0.1 Pa·s or more and 0.5 Pa·s or less was obtained.

On the other hand, if the viscosity of the paste after stirring by the thin film swirling method exceeds 0.5 Pa·s at a shear rate of 50 S ^-1 , a solvent (ion-exchanged water) may be added to reduce the viscosity to 0.1 Pa·s. After adjusting the viscosity so that it is within the range of s or more and 0.5 Pa・s or less, use a ram press machine to apply a filter with a mesh opening of 45 μm (300 mesh) under a pressure of 0.45 MPa (pressing force). was passed through a filter to remove iron foreign substances, etc. (filtration step). Furthermore, the viscosity of the paste after passing through the filter is measured, and as mentioned above, if the viscosity at a shear rate of 50S ^-1 is within the range of 0.1 Pa・s or more and 0.5 Pa・s or less, it is used as the finished viscosity. MPL coating paste is used, and if it is less than 0.1 Pa・s, a thickener is added to adjust the viscosity so that the finished viscosity is within the range of 0.1 Pa・s or more and 0.5 Pa・s or less. An MPL coating paste with a finished viscosity of 0.1 Pa·s or more and 0.5 Pa·s or less was obtained.

Regarding Example 5, after stirring by the thin film swirling method, iron foreign substances etc. were removed by passing through a filter with a mesh opening of 45 μm (300 mesh) under a pressure of 0.45 MPa (pressing force) using a ram press machine. After performing filter filtration (filtration step), a solvent is added so that the finished viscosity is 0.05 Pa s at a shear rate of 50 S ^-1 , and the finished viscosity is at a shear rate of 50 S ^-1 . An MPL coating paste with a pressure of 0.05 Pa·s was obtained.
In Example 6, after stirring by the thin film swirling method, a thickener was added so that the finished viscosity was 1.0 Pa·s at a shear rate of 50 S ^-1 , and then 0.0 Pa·s was added using a ram press machine. Filtration was performed under a pressure of 45 MPa (pressing force) to remove iron foreign substances by passing through a filter with a mesh opening of 45 μm (300 mesh) (filtration process), and the finished viscosity was determined at a shear rate of 50 S ^-1. An MPL coating paste with a viscosity of 1.0 Pa·s was obtained.

Here, in Examples 1 to 6, carbon black A (“Denka Black Li-250” manufactured by Denki Kagaku Kogyo Co., Ltd.) with a DBP absorption amount of 315 ml/100 g, average primary particle diameter: 37 nm, specific surface area: 58 m ² /g, iodine adsorption amount: 82 mg/g) (hereinafter abbreviated as "carbon A") to prepare an MPL coating paste.

In Example 1, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 9/1, and stirring by the thin film swirling method was performed at a circumferential speed of 25 m/s. The MPL coating paste was stirred for 30 seconds and had a finished viscosity of 0.5 Pa·s at a shear rate of 50 S ^-1 . In addition, in the MPL coating paste according to Example 1, the solid content ratio of carbon black, fluororesin, dispersant, etc. is 15%.
In Example 2, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 9/1, and stirring by the thin film swirling method was performed at a circumferential speed of 30 m/s. This is an MPL coating paste that is stirred for seconds and has a finished viscosity of 0.1 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 2 is also 15%.
In Example 3, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 5/5, and stirring by the thin film swirling method was performed at a circumferential speed of 25 m/s. This is an MPL coating paste that is stirred for seconds and has a finished viscosity of 0.1 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 3 is also 15%.

In Example 4, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 5/5, and stirring by the thin film swirling method was performed at a circumferential speed of 30 m/s. This is an MPL coating paste that is stirred for seconds and has a finished viscosity of 0.5 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 4 is 20%.

In Example 5, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 9/1, and stirring by the thin film swirling method was performed at a circumferential speed of 30 m/s. This is an MPL coating paste that was stirred for seconds to give a finished viscosity of 0.05 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 5 is 12%.
In Example 6, carbon A with a DBP absorption amount of 315 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 9/1, and stirring by the thin film swirling method was performed at a circumferential speed of 30 m/s. This is an MPL coating paste that was stirred for seconds to give a finished viscosity of 1.0 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 6 is 15%.

Furthermore, in Example 7, carbon black B (“Denka Black Li-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) with a DBP absorption amount of 425 ml/100 g, average primary particle diameter: 35 nm, specific surface area: 68 m ² /g, An MPL coating paste was prepared using iodine adsorption amount: 92 mg/g) (hereinafter abbreviated as "carbon B").
In Example 7, carbon B with a DBP absorption amount of 425 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 9/1, and stirring by the thin film swirling method was performed at a circumferential speed of 30 m/s. This is an MPL coating paste that is stirred for seconds and has a finished viscosity of 0.5 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Example 7 is 8%.

On the other hand, in Comparative Example 1, carbon black C (“Denka Black Li-400” manufactured by Denki Kagaku Kogyo Co., Ltd.) with a DBP absorption amount of 220 ml/100 g, average primary particle diameter: 48 nm, specific surface area: 39 m ² /g , iodine adsorption amount: 52 mg/g) (hereinafter abbreviated as "carbon C") to prepare an MPL coating paste.
Comparative Example 1 uses carbon C with a DBP absorption of 220 ml/100 g, the blending ratio of carbon/fluororesin (solid content) is 9/1, and stirring by the thin film swirling method is performed at a circumferential speed of 10 m/s. The MPL coating paste was stirred for 30 seconds and had a finished viscosity of 0.5 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Comparative Example 1 is 13%.

In addition, in Comparative Example 2, carbon D (“Denka Black Li-435” manufactured by Denki Kagaku Kogyo Co., Ltd.) with a DBP absorption amount of 510 ml/100 g, average primary particle diameter: 23 nm, specific surface area: 133 m ² /g, An MPL coating paste was prepared using iodine adsorption amount: 180 mg/g) (hereinafter abbreviated as "Carbon D").
In this comparative example 2, carbon D with a DBP absorption amount of 510 ml/100 g was used, the blending ratio of carbon/fluororesin (solid content) was 5/5, and the stirring by the thin film swirling method was performed at a circumferential speed of 10 m/s. The MPL coating paste was stirred for 30 seconds and had a finished viscosity of 0.5 Pa·s at a shear rate of 50 S ^-1 . Note that the solid content ratio of the MPL coating paste according to Comparative Example 2 is 13%.

The DBP absorption amount (ml/100g) of the above carbon black is determined based on JIS K 6217-4 using an S-500 absorption measuring device (manufactured by Asahi Souken Co., Ltd.). ) was detected, and the amount of DBP added at 70% of the maximum torque was calculated per 100 g of sample.
Further, the above viscosity was measured using an E-type viscometer (manufactured by Toki Sangyo).

Here, the MPL coating pastes of each example and comparative example were evaluated for their permeability through a predetermined filter for removing iron foreign matter and the like. As mentioned above, the MPL coating paste of each Example and Comparative Example was extruded and passed through a 300-mesh filter with an opening of 45 μm using a ram press at a pressing force of 0.45 MPa. However, at that time, the MPL coating paste was able to pass through a 300 mesh filter with an opening of 45 μm without being deformed at all under an extrusion pressure of 0.45 MPa. Clogging of the conductive porous base material 16 is suppressed, and the carbon black product can easily pass through a fine-mesh filter for removing iron foreign substances contained in the product, resulting in good productivity. A rating of ◎ is given if the viscosity characteristics (flow characteristics) are good during application and coating properties with good smoothness are obtained.If the filter is slightly deformed during extrusion of the MPL coating paste, it is evaluated as ◎. It was evaluated as 〇, and those with broken filters were evaluated as × because productivity decreased and the removal rate of iron foreign substances etc. decreased. The evaluation results at this time are as shown in the lower part of Table 1.

Furthermore, the MPL coating paste according to each example and comparative example was applied to a conductive porous substrate using a thin film coating tool (die head) at a moving speed of 1.0 m/min and a basis weight of 3.5 mg/cm ² . As No. 16, it was coated on one side of a nonwoven carbon fiber sheet that had been impregnated with a fluororesin solution to make it water repellent, and dried and baked at 300° C. for 10 minutes. From this, a cured coating film to become MPL 15 is formed from the MPL coating paste applied to the surface of the water-repellent nonwoven carbon fiber sheet as the conductive porous substrate 16, and a conductive porous film made of the nonwoven carbon fiber sheet is formed. A gas diffusion layer 14 was prepared, which was composed of a solid base material 16 and an MPL 15 made of a cured coating film formed from an MPL coating paste.

At this time, regarding the MPL coating pastes according to each example and comparative example, the viscosity characteristics of the paste when applied to the water-repellent nonwoven carbon fiber sheet as the conductive porous substrate 16 were determined by The phenomenon was observed from the viewpoint of the phenomenon in which the conductive porous substrate 16 was leaked to the back side of the conductive porous base material 16 on the side opposite to the coated surface. In the MPL coating paste of each example and comparative example, when the MPL coating paste was applied to a water-repellent non-woven carbon fiber sheet, even if the MPL coating paste penetrated into the water-repellent non-woven carbon fiber sheet, the non-woven fabric If the circumscribed circle of the permeated portion of the MPL coating paste is 6 mm ² /piece or less on the surface opposite to the coated surface of the carbon fiber sheet, the components of the MPL coating paste are the conductive porous base material 16. It is rated as ◎ because it suppresses the decrease in permeability of moisture and gas due to filling the voids (pores) of the paste, and has moderately high viscosity characteristics (flow characteristics) that can suppress the bleed-through of paste components. Those in which the number exceeding 6 mm ² /piece was 3 pieces/m ² or less were evaluated as ○.

Furthermore, regarding the cured coating film as MPL15 formed on the nonwoven carbon fiber sheet by applying the MPL coating paste of each example and comparative example to a water-repellent treated nonwoven carbon fiber sheet, drying and baking, The presence or absence of surface cracks was confirmed using an optical microscope. Specifically, optical micrographs with a size of 10 mm x 10 mm were taken one by one at 10 arbitrary locations of the cured coating film as MPL15 formed on a nonwoven carbon fiber sheet, and out of the 10 arbitrary locations. , If there are 2 or less cracks (cracks in the paint film) with a major axis length of 0.5 mm or more in 9 or more places, the film is judged to have excellent strength and is evaluated as ◎, and in 8 or more places. If there were three or more cracks with a major axis length of 0.5 mm or more, it was judged to be impractical and rated as ×.

In addition, a nonwoven fabric was prepared by applying the MPL coating paste of each example and comparative example to a water-repellent nonwoven carbon fiber sheet, and drying and baking to form a cured coating film on the nonwoven carbon fiber sheet. The gas diffusion resistance of the gas diffusion layer 14 composed of the conductive porous base material 16 made of a carbon fiber sheet and the MPL 15 made of a cured coating film formed from an MPL coating paste was measured to determine the gas diffusion property. was evaluated. Specifically, a circular sample with a diameter of 4.7 cm was cut out from the prepared gas diffusion layer 14, and air was blown at 58 cc/min/cm ² from the surface of the gas diffusion layer sample on the MPL 15 side to the opposite surface. Gas diffusion resistance was investigated by measuring the differential pressure between the surface on the MPL 15 side and the surface on the opposite side (the surface of the nonwoven carbon fiber sheet) with a differential pressure gauge when the gas was permeated at a flow rate of . It can be said that the smaller the differential pressure at this time, the lower the gas diffusion resistance and the higher the gas diffusion (gas permeability).If the gas diffusion resistance is 25 mmAq or less, it is judged to have excellent gas diffusion and is evaluated as ◎. , those exceeding 25 mmAq and 50 mmAq or less were evaluated as ×.
These evaluation results are shown in the lower part of Table 1.

As shown in Table 1, carbon black whose DBP absorption is within the range of 300ml/100g to 500ml/100g, specifically carbon A whose DBP absorption is 315ml/100g and carbon black whose DBP absorption is 425ml/100g. The MPLs of Examples 1 to 7 were prepared by using Carbon B, which is carbon B, and stirring the compounded materials with a turbine stator type stirring system, and then stirring with a high shear at a circumferential speed of 25 m/s or more using the thin film swirling method. All of the coating pastes could easily pass through a filter with a mesh opening of 45 μm (300 mesh) under a pressing force of 0.45 MPa without significantly deforming the filter, that is, without causing clogging. It was something.

In addition, the MPL coating pastes of Examples 1 to 7 all had little paste bleed-through when applied to the nonwoven carbon fiber sheet as the conductive porous substrate 16, and had appropriate viscosity characteristics. It had excellent coatability.
Furthermore, the cured coating film of MPL15, which was formed by applying the MPL coating paste of Examples 1 to 7 to a water-repellent treated nonwoven carbon fiber sheet, drying and baking it, had fewer cracks on the surface and was coatable. The film had excellent strength.

According to the MPL coating pastes of Examples 1 to 7 using carbon black having a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g, a gas diffusion layer 14 having excellent gas diffusion properties is obtained. I was able to do that.
That is, the MPL coating pastes of Examples 1 to 7 using carbon black having a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g were applied to a water-repellent nonwoven carbon fiber sheet. The gas diffusion layer 14 is composed of the MPL 15, which is a cured coating film prepared by drying and baking, and the conductive porous base material 16, which is a nonwoven carbon fiber sheet. Compared to Comparative Example 1 using black, the differential pressure was small, gas permeability was improved, and gas diffusivity was excellent.
This is because carbon black, whose DBP absorption is within the range of 300ml/100g to 500ml/100g, has a well-developed structure, so even if it is dispersed with a high shear, its primary aggregate maintains high voids. This is because it was possible to increase the porosity of MPL15 formed as a cured coating film of the MPL coating paste.

On the other hand, in the MPL coating paste of Comparative Example 1 using carbon black with a DBP absorption amount of less than 300 ml/100 g, specifically, carbon C with a DBP absorption amount of 220 ml/100 g, the shear rate was 50 S ^-1 Even if the finished viscosity was 0.5 Pa·S, the obtained gas diffusion layer 14 was inferior in gas diffusivity.

In addition, in the cured coating film of MPL15 formed from the MPL coating paste of Comparative Example 2 using carbon black with a DBP absorption amount of more than 500 ml/100 g, specifically, carbon D with a DBP absorption amount of 510 ml/100 g. Many cracks were observed and the coating film strength was poor.
This is because carbon black with a DBP absorption of more than 500ml/100g has a highly developed structure, so even if it is dispersed with a high shear and the secondary aggregates are crushed, the primary aggregates have a high porosity. was maintained, and it can be assumed that in carbon black with a DBP absorption amount exceeding 500 ml/100 g, the porosity of MPL15 became too high, resulting in a decrease in coating film strength and the occurrence of many cracks.

That is, if the DBP absorption amount is too high, the porosity becomes too high and the cured coating film of MPL15 becomes brittle, but if the cured coating film of MPL15 is brittle, the adhesion with the catalyst layer 13 also decreases. , flatting in which generated water accumulates in the MPL 15 is likely to occur, gas diffusivity and drainage properties are reduced, and battery performance is reduced. In other words, if there are many surface cracks on the MPL 15, the adhesion between the catalyst layer 13 and the gas diffusion layer 14 will decrease when it is assembled into the fuel cell 1, and voids will be created between these layers, where liquid water will accumulate and moisture will be absorbed. This will reduce manageability. On the other hand, it is possible to obtain a certain level of strength by increasing the thickness of the coating film, but increasing the thickness of MPL15 increases gas diffusion resistance and reduces gas diffusivity, leading to a decrease in battery performance. will be invited.
On the other hand, according to the MPL coating pastes of Examples 1 to 7, the strength of the coating film that makes it difficult for MPL15 to crack can be obtained, and the adhesion with the catalyst layer 13 is also good, so that flatting can be suppressed. This makes it possible to obtain stable battery performance without deteriorating gas and moisture permeability and moisture management.

Thus, in the MPL coating pastes of Examples 1 to 7, carbon black having a DBP absorption amount within the range of 300 ml/100 g to 500 ml/100 g is used, and the carbon black and the fluororesin as the water-repellent resin are used. By mixing these with water in which a dispersant is dissolved and stirring them at a high shear using a thin-film swirl type high-speed stirrer, even if the carbon black has a highly developed structure, its secondary aggregates can be reduced to a few micrometers. By being crushed, it is possible to pass through a fine-mesh filter with an opening of 45 μm (300 mesh) that can remove foreign substances such as metal under a pressure of 0.45 MPa without clogging. can. Therefore, it is possible to remove foreign substances such as metals from carbon black products that cause a decrease in battery durability and life without reducing productivity, and it is possible to improve battery durability. can.

Carbon black, whose DBP absorption is within the range of 300ml/100g to 500ml/100g, has a high porosity in its structure, so even if the secondary aggregates are broken down to several micrometers, In MPL15, a cured coating film formed by coating the conductive porous substrate 16 with the MPL coating paste containing MPL, and drying and baking, the high porosity of carbon black with high DBP absorption prevents gas and moisture. It has excellent permeability, and provides excellent gas diffusivity and moisture management.

In particular, carbon black with a DBP absorption within the range of 300 ml/100 g to 500 ml/100 g can achieve both high porosity and crack resistance. That is, if the porosity of the MPL 15 is too high, cracks will easily occur in the MPL 15, and if there are cracks in the MPL 15, the durability will be low, and the characteristics of the MPL 15 will not be fully exhibited, and the bond between the catalyst layer 13 and the catalyst layer 13 will be reduced. Since moisture tends to accumulate between the two, moisture controllability deteriorates, making it difficult to obtain stable battery performance. In addition, the water accumulated at the interface between the crack and the catalyst layer 13 freezes at subzero temperatures, causing the MPL 15 and the catalyst layer 13 to separate and part of them to be missing, which adversely affects the performance of the fuel cell 1 and fuel There is also a risk that the life of the battery 1 will be shortened.

If the carbon black has a DBP absorption amount within the range of 300 ml/100 g to 500 ml/100 g, high porosity and coating film strength are compatible, and good coating film strength also improves adhesion to the catalyst layer 13. At best, it can reduce unevenness in contact resistance and create a uniform thickness, which results in good conductivity, prevents cracks and flatting where generated water collects inside the MPL15, and has a compressive strength that can withstand the pressure of stacking. Since low compression creep property is obtained, the gas diffusion layer 14 stably exhibits excellent gas diffusivity and moisture management property, and stable and high battery performance can be obtained. Furthermore, as mentioned above, the battery can be passed through a fine-mesh filter that can remove foreign substances such as metal without reducing productivity. Longer life and durability can also be achieved. Furthermore, carbon black with a high DBP absorption can be expected to have an effect of improving conductivity due to a highly developed structural network.

According to the experimental research conducted by the present inventors, the ratio of carbon black to water-repellent resin (solid content) is preferably within the range of 9/1 to 5/5 by weight. If the blending ratio of water-repellent resin (solid content) to carbon black is too low, the binding of carbon black by the resin content will be weak, and the cured coating film of MPL15 will be prone to cracking, resulting in a decrease in coating strength. Furthermore, the binding property between the MPL 15 and the conductive porous base material 16 also decreases, and the contact resistance increases. On the other hand, if the blending ratio of water-repellent resin (solid content) to carbon black is too high, the resin content will become too large and the resin content will close the voids (spaces between carbon particles), resulting in a decrease in porosity and gas diffusivity. decreases. If the ratio of carbon black and water-repellent resin (solid content) is preferably within the range of 9/1 to 5/5 by weight, cracks will not easily occur, the coating will have high strength, and gas diffusivity will be achieved. A cured coating film with a high microporous layer can be obtained.

Further, according to the experimental research conducted by the present inventors, the solid content ratio of the MPL coating paste is preferably 5% by mass or more and 40% by mass or less. If the solid content ratio of carbon, water-repellent resin, etc. is too small, the shrinkage stress during MPL film formation may become large, making the cured coating film of MPL15 more likely to crack, resulting in a decrease in coating film strength. On the other hand, if the solid content ratio is too large, the porosity decreases and gas diffusivity decreases. If the solid content ratio of the MPL coating paste is preferably 5% by mass or more and 40% by mass or less, a cured coating film of MPL15 that is difficult to crack, has high coating strength, and has high gas diffusivity can be obtained. can get. More preferably, it is 5% by mass or more and 30% by mass or less, and still more preferably 5% by mass or more and 25% by mass or less.

Further, according to the experimental research conducted by the present inventors, in stirring by the thin film swirling method, it is preferable that the circumferential speed is 25 m/s or more. If the circumferential speed is too slow, the secondary aggregates of carbon with a high DBP absorption amount will not be sufficiently broken down, and iron foreign substances will be generated which will impair the durability of the catalyst layer 13, that is, the durability and life of the battery. When passing through a fine filter with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less) for removal, it may become clogged, reducing productivity or preventing the filter from passing through. If this becomes difficult, the durability and life of the battery will be reduced. Further, the coating properties are reduced, the cured coating film has a surface defect, and the adhesion with the catalyst layer 13 is reduced, so that generated water is likely to accumulate in the MPL 15, causing flatting, and the drainage performance is reduced. On the other hand, as shown in Example 2, even when the circumferential speed is 50 m/s, the paste hardly bleeds through even when applied to the conductive porous substrate 16 and has excellent gas diffusivity. . In particular, by increasing the circumferential speed, it is possible to miniaturize the diameter of the secondary agglomerates, and also to make the diameters of the secondary agglomerates uniform, thereby making it possible to make the cured coating film uniform.

Considering the performance limits of high-speed stirrers for the thin film swirling method, if the circumferential speed during stirring by the thin film swirling method is 25 m/s or more and 60 m/s or less, mesh with an opening of 34 μm or more and 154 μm or less (100 mesh The secondary aggregates of carbon with a high DBP absorption amount are sufficiently broken down to a size that allows them to pass through a fine-mesh filter (400 mesh or less), resulting in good viscosity characteristics (flow characteristics). As a result, surface defects are less likely to occur during coating and a sufficient coating width can be obtained, resulting in good coating properties, resulting in good adhesion with the catalyst layer 13, and stable battery performance due to stable moisture management. In addition, the durability and life of the battery can be ensured favorably.

Further, according to the experimental research of the present inventors, in stirring at the above peripheral speed by the thin film swirling method, the stirring time is preferably 20 seconds or more, more preferably 25 seconds or more, and even more preferably 30 seconds or more. It is preferable that If the stirring time is too short, the secondary aggregates of carbon with a high DBP absorption amount will not be sufficiently broken down, and iron foreign substances will be generated which will impair the durability of the catalyst layer 13, that is, the durability and life of the battery. When passing through a fine filter with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less) for removal, it may become clogged, reducing productivity or preventing the filter from passing through. If this becomes difficult, the durability and life of the battery will be reduced. On the other hand, if the stirring time is too long, the viscosity decreases excessively, resulting in strike-through of the paste components during application onto the conductive porous substrate 16. The viscosity can be increased by adding a thickener, but the use of a thickener increases the firing time to decompose it, resulting in higher costs and higher costs due to the use of the thickener and the high load of firing. This will lead to a decrease in productivity. If the stirring time in the thin film swirling method is preferably 20 seconds or more and 200 seconds or less, more preferably 25 seconds or more and 150 seconds or less, and even more preferably 30 seconds or more and 100 seconds or less, productivity may be reduced. Secondary coagulation of carbon with high DBP absorption to a size that allows it to pass through a fine filter with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less) without increasing cost. By sufficiently crushing the aggregates, good viscosity properties (flow properties) ensure good coating properties that prevent surface defects from occurring during coating and ensure a sufficient coating width. Adhesion is also good, and by ensuring stable moisture management, stable battery performance can be obtained, and the durability and life of the battery can also be ensured favorably.

In addition, according to the experimental research conducted by the present inventors, the viscosity of the MPL coating paste at a shear rate of 50 S ^-1 is preferably 0.05 Pa·s or more and 1.0 Pa·s or less, more preferably 0. .1 Pa·s or more and 0.9 Pa·s or less, more preferably 0.1 Pa·s or more and 0.5 Pa·s or less. If the viscosity is too low, the paste will bleed through when applied to the conductive porous base material 16, closing the voids in the conductive porous base material 16 and reducing the permeability of gas and moisture. On the other hand, if the viscosity is too high, the surface smoothness will decrease when coating the conductive porous substrate 16, and it will also become difficult to coat with the desired coating width, reducing productivity. It is not possible to obtain good coating properties. Further, when passing through a fine mesh filter with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less) that can remove foreign substances such as metals that may impair the durability of the catalyst layer 13. The pressure loss is large and it is difficult to pass through the filter. The viscosity of the MPL coating paste at a shear rate of 50 S ^-1 is preferably 0.05 Pa·s or more and 1.0 Pa·s or less, more preferably 0.1 Pa·s or more and 0.9 Pa·s or less, and further Preferably, if the viscosity is 0.1 Pa·s or more and 0.9 Pa·s or less, it has good viscosity characteristics that can pass through a fine mesh filter with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). It is possible to obtain good productivity, and also to obtain good coating properties that prevent surface defects from occurring during coating and ensure a sufficient coating width, and to have good adhesion to the catalyst layer 13 and stable moisture management. By ensuring this, stable battery performance can be obtained, and furthermore, good durability and service life of the battery can be ensured.

As explained above, the coating paste for forming a microporous layer of the above embodiment is a coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent. Therefore, the carbon black has a DBP absorption amount of 300 ml/100 g or more and 500 ml/100 g or less and passes through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). It is of the agglomerate size.

Therefore, according to the coating paste for forming a microporous layer of the present embodiment, since the secondary aggregates of carbon black with a high DBP absorption amount are crushed, the viscosity increase of the paste is suppressed, MPL15 can be formed on the surface of the conductive porous base material 16 with good coating properties. In addition, the voids are uniformly distributed, and the highly structured structure forms passages for gas and moisture, which improves the diffusion and drainage of gas and moisture. Furthermore, by making the MPL 15 have good smoothness, good adhesion with the catalyst layer 13 can be obtained. Therefore, flatting is less likely to occur, and the gas diffusion properties and moisture management properties of the gas diffusion layer 14 can be improved, and battery output, stabilization of power generation performance, and improvement of battery performance can be achieved.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration size that passes through a mesh with openings of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Due to the good coating properties of the paste, good surface smoothness can be ensured in MPL15, and it is also possible to achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, by forming the MPL 15 which has a high porosity, has good surface smoothness, is less prone to cracking, and has good adhesion to the catalyst layer 13, the MPL 15 has a high porosity, is difficult to accumulate moisture, has high drainage performance, and has a high gas flow rate. Diffusibility is maintained, and durability is also improved.

In addition, carbon black with DBP absorption within the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration diameter that allows it to pass through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Since it is of a size that can pass through a fine mesh filter that makes it possible to remove foreign substances such as iron that affect the durability and lifespan of the catalyst layer 13 that performs battery reactions, it reduces the durability and lifespan of the battery. It is difficult to do so.
Therefore, it is possible to form an MPL 15 with a high porosity, and it is possible to improve the gas and moisture permeability of the MPL 15, thereby improving the performance of gas diffusion and moisture management of the gas diffusion layer 14 in which the MPL 15 is formed. becomes possible.

Furthermore, in the coating paste for forming a microporous layer of the above embodiment, if the weight ratio of carbon black and water-repellent resin is within the range of 9/1 to 5/5, it will be effective in the cured coating film of MPL15 to be formed. The adhesive properties (binding properties) due to the resin content are good, making it difficult for cracks to occur, and the clogging of voids due to excessive resin content is suppressed, making it possible to achieve both the coating strength of MPL15 and the permeability of gas and moisture. , the gas diffusion layer 14 can exhibit high gas diffusivity and moisture management performance better.

In addition, in the coating paste for forming a microporous layer of the above embodiment, if the viscosity at a shear rate of 50 s ^-1 is within the range of 0.05 Pa·s to 1.0 Pa·s, the gas diffusion layer 14 can be formed. When applying the paste to the conductive porous base material 16 to be coated, it is possible to suppress paste strike-through (a phenomenon in which the paste escapes to the back side of the conductive porous base material on the opposite side from the applied surface), and to achieve the desired coating width. A cured coating film of MPL15 with good smoothness can be formed and the coating properties are good. Therefore, a smooth MPL 15 can be obtained without reducing the porosity of the conductive porous base material 16, and the adhesion to the catalyst layer 13 can be improved, so that the gas diffusion properties and moisture management properties of the gas diffusion layer 14 can be improved. becomes more stable.

Further, the above embodiment is a method for producing a coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent, in which the solvent mixed with the dispersant contains This invention can be considered as an invention of a method for producing a coating paste for forming a microporous layer, in which carbon black with a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g and a water-repellent resin are mixed and stirred by a thin film swirling method. .

According to the method for producing a coating paste for forming a microporous layer according to the embodiment described above, secondary aggregates of carbon black having a high DBP absorption amount are disintegrated by dispersing the compounded material with high shear using the thin film swirling method. It is possible to suppress the increase in viscosity of the paste. Preferably, by dispersing the blended materials by stirring at a circumferential speed of 25 m/s to 60 m/s, secondary aggregates of carbon black with a high DBP absorption amount can be crushed with high efficiency.

Therefore, according to the coating paste for forming a microporous layer in which the secondary aggregates of carbon black having a high DBP absorption amount are disintegrated and the increase in viscosity is suppressed, good coating on the surface of the conductive porous substrate 16 is achieved. In MPL15, which can be applied manually and is formed by drying and firing the applied paste, carbon black with high DBP absorption has a high porosity due to its high structure, resulting in a high porosity. In addition, the voids are uniformly distributed. Therefore, the diffusion and drainage properties of gas and moisture can be improved by forming gas and moisture passages through the highly structured structure. Furthermore, by making the MPL 15 have good smoothness, good adhesion with the catalyst layer 13 can be obtained. Therefore, flatting is less likely to occur, and the gas diffusion properties and moisture management properties of the gas diffusion layer 14 can be improved, and the battery output and power generation performance can be stabilized.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration size that passes through a mesh with openings of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Due to the good coating properties of the paste, MPL15 has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, by forming the MPL 15 which has a high porosity, has good surface smoothness, is less prone to cracking, and has good adhesion to the catalyst layer 13, the MPL 15 has a high porosity, is difficult to accumulate moisture, has high drainage performance, and has a high gas flow rate. Diffusibility is maintained, and durability is also improved.
Therefore, the MPL coating paste can form an MPL 15 that has a high porosity and can improve the performance of the gas diffusion layer 14 in terms of diffusivity and moisture management.

Further, the above embodiment is a method for producing a coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent, in which the solvent mixed with the dispersant contains A coating paste for forming a microporous layer in which carbon black with a DBP absorption amount within the range of 300 ml/100 g to 500 ml/100 g and a water-repellent resin are mixed and stirred at a peripheral speed of 25 m/s or more and 60 m/s or less. It can also be regarded as an invention of a manufacturing method.

According to the method for producing a coating paste for forming a microporous layer according to the embodiment described above, by dispersing the compounded material at a high shear at a circumferential speed of 25 m/s or more and a circumferential speed of 60 m/s or less, a high DBP absorption amount can be achieved. It is possible to disintegrate secondary aggregates of carbon black, and it is possible to suppress an increase in the viscosity of the paste. Preferably, by dispersing the blended materials by stirring at a circumferential speed of 25 m/s to 60 m/s, secondary aggregates of carbon black with a high DBP absorption amount can be crushed with high efficiency.

Therefore, according to the coating paste for forming a microporous layer in which the secondary aggregates of carbon black having a high DBP absorption amount are disintegrated and the increase in viscosity is suppressed, good coating on the surface of the conductive porous substrate 16 is achieved. In MPL15, which can be applied manually and is formed by drying and firing the applied paste, carbon black with high DBP absorption has a high porosity due to its high structure, resulting in a high porosity. In addition, the voids are uniformly distributed. Therefore, the diffusion and drainage properties of gas and moisture can be improved by forming gas and moisture passages through the highly structured structure. Furthermore, by making the MPL 15 have good smoothness, good adhesion with the catalyst layer 13 can be obtained. Therefore, flatting is less likely to occur, and the gas diffusion properties and moisture management properties of the gas diffusion layer 14 can be improved, and the battery output and power generation performance can be stabilized.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration size that passes through a mesh with openings of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Due to the good coating properties of the paste, MPL15 has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, by forming the MPL 15 which has a high porosity, has good surface smoothness, is less prone to cracking, and has good adhesion to the catalyst layer 13, the MPL 15 has a high porosity, is difficult to accumulate moisture, has high drainage performance, and has a high gas flow rate. Diffusibility is maintained, and durability is also improved.
Therefore, the MPL coating paste can form an MPL 15 that has a high porosity and can improve the performance of the gas diffusion layer 14 in terms of diffusivity and moisture management.

Furthermore, in the method for producing a coating paste for forming a microporous layer according to the above embodiment, a dispersant, a solvent, carbon black, When the mixture of water-repellent resin and water-repellent resin is pre-stirred with a stirrer such as a Disper or a turbine stator type stirrer or at a circumferential speed of 1 m/s to 20 m/s, that is, agitator such as a Disper or a turbine stator type stirrer is used. In the case of low shear dispersion at a circumferential speed of 1 m/s to 20 m/s using a machine, and then high shear dispersion at a circumferential speed of 25 m/s to 60 m/s using a thin film swirling method, etc., the secondary dispersion of carbon black It is possible to suppress variations in the distribution of aggregate diameters, suppress variations in the distribution of voids, form a homogeneous MPL 15, and obtain stable gas and moisture permeability. Therefore, it becomes an MPL coating paste that can form MPL 15 that can suppress variations in the distribution of voids and obtain stable performance. In particular, if a stirrer such as a disper or a turbine stator type stirrer is used for the pre-stirring at this time, a paste with few air bubbles can be obtained by stirring and degassing.

In addition, according to the method for producing a coating paste for forming a microporous layer according to the above embodiment, after stirring at a circumferential speed of 25 m/s to 60 m/s by a thin film swirling method or the like, the opening of the mesh is 34 μm or more. , 154 μm or less mesh (100 mesh or more, 400 mesh or less), it is possible to obtain a catalyst layer 13 with less foreign matter such as iron that affects its durability and life. Therefore, the durability of the fuel cell 1 can be maintained satisfactorily. That is, the MPL coating paste can form the MPL 15 without reducing the durability and life of the fuel cell 1.

In addition, in the above method for producing a coating paste for forming a microporous layer, if the weight ratio of carbon black and water-repellent resin is within the range of 9/1 to 5/5, the resin may be used in the cured coating film of MPL15 to be formed. The resin has good adhesion (binding ability) and is less likely to cause cracks, and the clogging of voids due to excessive resin content is suppressed. Therefore, it becomes an MPL coating paste that can form MPL15 that can achieve both coating film strength and gas and moisture permeability.

In addition, in the above method for producing a coating paste for forming a microporous layer, if the viscosity at a shear rate of 50 ^s is within the range of 0.05 Pa s to 1.0 Pa s, the gas diffusion layer 14 is formed. It is possible to suppress paste bleed-through during application to the conductive porous substrate 16, and to form a cured coating film of MPL 15 with good smoothness in a desired coating width, resulting in good coating properties. . Therefore, a smooth MPL 15 can be obtained without reducing the porosity of the conductive porous base material 16, and the adhesion to the catalyst layer 13 can be improved, so the MPL coating can form an MPL 15 that can ensure stable performance. It becomes a paste.

Furthermore, the above embodiment is composed of a conductive porous base material 16 made of conductive fibers or the like, and an MPL 15 made of carbon black and water-repellent resin formed on the surface of the conductive porous base material 16. In the gas diffusion layer 14 for fuel cells, the carbon black of MPL15 has a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g. , 400 mesh or less).

According to the fuel cell gas diffusion layer 14 of the present embodiment, the carbon black formed on the surface of the conductive porous base material 16 made of conductive fibers and the like and the carbon black of the MPL 15 made of a water-repellent resin are DBP. Carbon black with an absorption amount within the range of 300ml/100g to 500ml/100g has a secondary aggregation diameter that passes through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less), and has a high DBP. Since the secondary aggregates of the absorbed amount of carbon black are crushed, the increase in viscosity of the paste forming MPL 15 is suppressed, and it has good coating properties on the surface of the conductive porous base material 16. In the formed MPL 15, carbon black with a high DBP absorption amount has a high porosity due to a high structure, so that the porosity (porosity) is high and the pores are uniformly distributed. Therefore, the diffusion and drainage properties of gas and moisture can be improved by forming gas and moisture passages through the highly structured structure. Furthermore, by making the MPL 15 have good smoothness, good adhesion with the catalyst layer 13 can be obtained. Therefore, flatting is less likely to occur, and the gas diffusion properties and moisture management properties of the gas diffusion layer 14 can be improved, and the battery output and power generation performance can be stabilized.

In particular, carbon black with DBP absorption in the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration size that passes through a mesh with openings of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Due to the good coating properties of the paste, MPL15 has good surface smoothness, and can achieve both high porosity and coating film strength that does not easily cause cracks. Therefore, in MPL15, which has a high porosity but has good surface smoothness, is difficult to crack, and has good adhesion to the catalyst layer 13, it is difficult for water to accumulate, has high drainage performance, maintains high gas diffusivity, and , the durability is also good.

In addition, carbon black with DBP absorption within the range of 300 ml/100 g to 500 ml/100 g has a secondary agglomeration diameter that allows it to pass through a mesh with an opening of 34 μm or more and 154 μm or less (100 mesh or more and 400 mesh or less). Since it is of a size that can pass through a fine mesh filter that makes it possible to remove foreign substances such as iron that affect the durability and lifespan of the catalyst layer 13 that performs battery reactions, it reduces the durability and lifespan of the battery 1. This is difficult to lower.
Therefore, according to the fuel cell gas diffusion layer 14 of the above embodiment, since it has the MPL 15 with a high porosity, it is possible to improve gas and moisture permeability, and improve gas diffusivity and moisture management performance. It is possible to improve the performance of

Furthermore, in the fuel cell gas diffusion layer 14 of the above embodiment, if the weight ratio of carbon black and water-repellent resin in MPL15 is within the range of 9/1 to 5/5, the resin content in the cured coating film of MPL15 will be reduced. It has good adhesion (binding) properties, making it more difficult for cracks to occur, and also suppressing the clogging of voids due to excessive resin content. Therefore, the gas diffusion layer 14 exhibits good moisture and gas permeability.

Note that the MPL coating paste of this embodiment and the fuel cell gas diffusion layer 14 produced using the same are applicable not only to the polymer electrolyte fuel cell 1 but also to other fuel cells such as a direct methanol fuel cell. is also applicable.
Furthermore, when carrying out the present invention, the composition, components, blending amounts, materials, and other manufacturing processes of the MPL coating paste and other parts of the fuel cell gas diffusion layer 14 are limited to the present embodiment. It's not a thing.
Further, the above-mentioned numerical range is not strict, but is an approximate value that naturally includes errors due to measurement, etc., and does not deny an error of several tenths. Further, the numerical values listed in the embodiments of the present invention do not indicate critical values, but indicate appropriate values suitable for implementation, so even if the above numerical values are slightly changed, the implementation thereof will be denied. isn't it.

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

Claims (12)

A coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent,
The carbon black is characterized in that the carbon black having a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g has a secondary aggregation diameter that allows the carbon black to pass through a mesh with an opening in the range of 34 to 154 μm. Coating paste for forming microporous layers. The coating paste for forming a microporous layer according to claim 1, wherein the weight ratio of the carbon black and the water-repellent resin is within a range of 9/1 to 5/5. The microporous layer forming coating paste according to claim 1, wherein the coating paste for forming a microporous layer has a viscosity within a range of 0.05 Pa·s to 1.0 Pa·s at a shear rate of 50 s ⁻¹ . Coating paste. A gas diffusion layer for a fuel cell, comprising a conductive porous base material and a microporous layer formed on the surface of the conductive porous base material and made of carbon black and a water-repellent resin,
The carbon black of the microporous layer has a secondary agglomeration diameter that allows carbon black with a DBP absorption amount in the range of 300 ml/100 g to 500 ml/100 g to pass through a mesh with an opening in the range of 34 to 154 μm. A gas diffusion layer for fuel cells characterized by: 5. The gas diffusion layer for a fuel cell according to claim 4, wherein the carbon black and the water-repellent resin have a weight ratio of 9/1 to 5/5. A method for producing a coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent, the method comprising:
Formation of a microporous layer characterized by mixing a water-repellent resin and carbon black whose DBP absorption is within the range of 300 ml/100 g to 500 ml/100 g in a solvent mixed with a dispersant, and stirring the mixture by a thin film swirling method. Method for producing coating paste for use. A method for producing a coating paste for forming a microporous layer containing carbon black, a water-repellent resin, a dispersant, and a solvent, the method comprising:
Carbon black and water-repellent resin having a DBP absorption within the range of 300 ml/100 g to 500 ml/100 g are mixed in a solvent mixed with a dispersant, and stirred at a peripheral speed of 25 m/s or more and 60 m/s or less. A method for producing a coating paste for forming a microporous layer, characterized by: The method for producing a coating paste for forming a microporous layer according to claim 6 or 7, characterized in that after the stirring, the paste is passed through a mesh having an opening within a range of 34 to 154 μm. The method for producing a coating paste for forming a microporous layer according to claim 6 or 7, characterized in that, before the stirring, pre-stirring is performed using a disper or a turbine stator type stirrer. The method for producing a coating paste for forming a microporous layer according to claim 6 or 7, characterized in that, before the stirring, pre-stirring is performed at a peripheral speed of 1 m/s or more and 20 m/s or less. Production of a coating paste for forming a microporous layer according to claim 6 or 7, wherein the carbon black and the water-repellent resin are in a weight ratio of 9/1 to 5/5. Method. The microporous layer-forming coating paste according to claim 6 or 7, wherein the viscosity at a shear rate of 50 s ^-1 is within the range of 0.05 Pa.s to 1.0 Pa.s. A method for producing a coating paste for forming a microporous layer.

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