JP6958347B2 - Gas diffusion layer for fuel cells and its manufacturing method - Google Patents

Description

The present invention relates to a fuel cell gas diffusion layer and a method for producing the same. More specifically, the present invention relates to a fuel cell gas diffusion layer capable of forming a water-repellent layer having a uniform film thickness on the surface of a conductive substrate by a dry process. The present invention relates to a method for producing a layer and a gas diffusion layer for a fuel cell produced by such a method.

Conventionally, in the gas diffusion layer for a fuel cell, a conductive base material such as carbon paper or carbon cloth is water-repellent treated, and a water-repellent layer forming paste is applied to the surface thereof, and the temperature is about 300 ° C. to 400 ° C. Manufactured by firing in. Usually, the water-repellent layer-forming paste is prepared by mixing and dispersing carbon particles, a dispersant, a polytetrafluoroethylene (PTFE) dispersion, and water, and then adding and mixing polyethylene oxide as a thickener. Manufactured.

In order to prepare an ink by dispersing water-repellent particles such as PTFE in a solvent, a surfactant is indispensable as an additive. Further, after the ink is applied, a firing treatment for removing the surfactant is indispensable. Therefore, in the wet process of forming a water-repellent layer using ink, problems such as complicated manufacturing process, long manufacturing time, and increased manufacturing cost occur. Further, since there is a problem that the pyrolyzed product generated during firing pollutes the environment, a process for treating the pyrolyzed product is required, which has been a factor that significantly impairs productivity.

Therefore, in order to solve this problem, various proposals have been made conventionally.
For example, in Patent Document 1,
(A) Subatomic particles having an average particle size of 5 μm containing acetylene black powder and water-repellent PTFE fine particles are granulated.
(B) A catalyst layer having an average thickness of 10 μm is formed by depositing a conductor carrying a catalyst on both the front and back surfaces of a polymer electrolyte membrane using an electrostatic coating method, and the catalyst layer is formed using a hot roller at 150 ° C. Established,
(C) A water-repellent layer having an average thickness of 5 μm is formed by depositing the secondary particles of (a) on the surface of the catalyst layer by an electrostatic coating method, and the water-repellent layer is fixed using a hot roller at 150 ° C. ,
(D) A method for producing a membrane electrode assembly (MEA) in which carbon paper is laminated so as to be in contact with a water-repellent layer and hot-pressed is disclosed.

In addition, in the same document,
(A) A polymer electrolyte membrane is placed in the upper opening of the dispersion chamber, and the polymer electrolyte membrane is charged to the positive electrode.
(B) The electrode catalyst powder is put into the lower part of the dispersion chamber, the electrode catalyst powder is stirred by a stirring blade, and the electrode catalyst powder is self-triboelectrically charged to the negative electrode.
(C) An electrostatic coating method for adsorbing an electrode catalyst powder on the surface of a polymer electrolyte membrane installed on the upper surface is disclosed.

In the same document,
(A) Since the electrodes can be formed by a complete dry process, there is no danger of harmful substances such as organic solvents, and the electrode catalyst powder can be stably stored.
(B) Since only one or two particle layers can be deposited on the surface of the polyelectrolyte film, it is described that the particle size of the deposited powder particles is approximately the thickness of the deposited layer. ..

Patent Document 2 describes a screen arranged above an object, a sponge roller arranged on the screen, and a hopper that supplies powder onto the sponge roller, although it is not an apparatus for manufacturing a gas diffusion layer. Disclosed is an electrostatic screen printing device including a voltage applying device for applying a voltage between a screen and an object, and a roller cover having an inner peripheral surface shaped along the outer peripheral surface of the sponge roller. ..
In the same document,
(A) Since the powder is carried to the screen while being sandwiched between the roller cover and the sponge roller, the powder hardly spills from the sponge roller onto the screen, and
(B) It is described that this causes almost all of the powder supplied from the hopper to be rubbed against the screen by the sponge roller.

Although Patent Document 3 does not describe a method for producing a gas diffusion layer,
(A) A high-viscosity binder is applied to the surface of the electrolyte membrane by screen printing.
(B) Platinum catalyst is applied to the binder application part by electrostatic screen printing.
(C) An electrode manufacturing method in which a platinum electrode is heat-fixed to an electrolyte membrane by a heating roller is disclosed.
In the same document,
(A) By controlling the applied electric field, the film thickness of each electrode site can be controlled.
(B) The applied electric field can guide the electrode material dropped from the conductive screen to the surface of the electrolyte membrane almost uniformly, and
(C) It is described that the screen makes the particle size of the electrode material uniform.

Further, in Patent Document 4,
(A) A catalyst layer slurry containing platinum-supported carbon and an electrolyte is spray-dried using a spray dryer to prepare a catalyst layer powder.
(B) A slurry containing spherical carbon and polyvinylidene fluoride (PVDF) is spray-dried using a spray dryer to prepare a powder for a microporous layer (MPL) layer.
(C) The powder for the catalyst layer and the powder for the MPL layer are mixed to prepare a powder for the intermediate layer.
(D) The catalyst layer powder, the intermediate layer powder, and the MPL layer powder are deposited on the surface of the electrolyte film using an electrostatic screen printing device in this order.
(E) A method for manufacturing a fuel cell in which a diffusion layer base material is placed on an MPL layer and hot-pressed at 140 ° C. is disclosed.

Patent Document 1 discloses an electrostatic coating method in which a positively charged base material is placed in the upper part of the dispersion chamber, the particles are negatively charged in the lower part of the dispersion chamber, and the charged particles are attached to the lower surface of the base material. Has been done. However, in this method, the adhesion strength of the charged particles is weak, and the particles that can be deposited are one or two particle layers. Therefore, the film thickness depends on the particle size and is not suitable for forming a thick film.
On the other hand, Patent Document 4 discloses a method in which a catalyst layer, an intermediate layer and a water-repellent layer (MPL layer) are attached to the surface of an electrolyte film by using an electrostatic screen printing apparatus, and then hot-pressed. .. However, in order to enhance the adhesion of the water-repellent layer, it is necessary to bake the water-repellent material near the melting point. Therefore, the applicable water repellent material is limited to a low melting point water repellent material such as PVDF, and cannot be applied to a high melting point water repellent material such as PTFE which is usually used.

International Publication No. WO2001 / 099216 Japanese Unexamined Patent Publication No. 2014-208405 Japanese Unexamined Patent Publication No. 2004-281221 JP-A-2009-193777

The problem to be solved by the present invention is a method for producing a gas diffusion layer for a fuel cell capable of forming a water-repellent layer having a uniform thickness on the surface of a conductive base material by a dry process, and such a method for producing a gas diffusion layer for a fuel cell. The purpose is to provide a gas diffusion layer for a fuel cell manufactured by the method.
Another problem to be solved by the present invention is a method for producing a gas diffusion layer for a fuel cell capable of forming a thick (or thick) water-repellent layer, and a method for producing the gas diffusion layer for a fuel cell. The purpose is to provide a gas diffusion layer for a fuel cell.
Further, another problem to be solved by the present invention is a method for producing a gas diffusion layer for a fuel cell, which can be applied even if it is a high melting point water repellent material, and a gas for a fuel cell produced by such a method. The purpose is to provide a diffusion layer.

In order to solve the above problems, the method for manufacturing a gas diffusion layer for a fuel cell according to the present invention is
A granulation process in which conductive particles and water-repellent particles are treated with mechanochemicals to obtain composite particles.
A film forming process of applying the composite particles to the surface of a conductive base material using an electrostatic screen printing device to obtain a coating film, and
The gist is that the coating film is pressed to obtain a water-repellent layer.

In the film forming step, it is preferable that a screen is placed above the conductive substrate, the composite particles are placed on the screen, and the composite particles are rubbed against the screen using a pressing member.

The gas diffusion layer for a fuel cell according to the present invention is
With a conductive base material
A water-repellent layer formed on the surface of the conductive base material is provided.
The water-repellent layer contains composite particles of conductive particles and water-repellent particles.
The gist is that the average film thickness of the water-repellent layer is 5 μm or more and 50 μm or less.

By mechanochemical treatment of the conductive particles and the water-repellent particles, it is possible to obtain composite particles in which both are uniformly dispersed without using a solvent. Next, when composite particles are applied to the surface of the conductive substrate using an electrostatic screen printing device and the coating film is pressed, a water-repellent layer can be formed without using a solvent. At this time, when the screen is arranged above the conductive base material and the charged composite particles are dropped from the screen toward the conductive base material, a coating film having a film thickness exceeding the average particle size of the composite particles is formed. be able to. Further, since a high melting point material is usually used for the conductive base material, high temperature hot pressing using a high melting point water repellent material is also possible.

It is a schematic diagram of the mechanochemical processing apparatus. It is a schematic diagram of the electrostatic screen printing apparatus. It is an appearance photograph of the gas diffusion layer obtained in Example 1.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Manufacturing method of gas diffusion layer for fuel cells]
The method for manufacturing a gas diffusion layer for a fuel cell according to the present invention is as follows.
A granulation process in which conductive particles and water-repellent particles are treated with mechanochemicals to obtain composite particles.
A film forming process of applying the composite particles to the surface of a conductive base material using an electrostatic screen printing device to obtain a coating film, and
It includes a pressing step of pressing the coating film to obtain a water-repellent layer.
The method for producing the gas diffusion layer for a fuel cell may further include a firing step of firing the water-repellent layer after the pressing step.

[1.1. Granulation process]
First, the conductive particles and the water-repellent particles are mechanochemically treated to obtain composite particles (granulation step).

[1.1.1. Conductive particles]
The material of the conductive particles is not particularly limited as long as it has the desired conductivity. Examples of the conductive particles include carbon black, VGCF (registered trademark), carbon nanofibers, carbon nanotubes, and carbon nanohorns. Any one of these may be used as the conductive particles, or two or more of them may be used in combination.

[1.1.2. Water repellent particles]
The material of the water-repellent particles is not particularly limited as long as it has the desired water repellency. The water-repellent particles are preferably made of a material having a melting point of more than 140 ° C.
Examples of the water-repellent particles include PTFE, polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polyhexafluoropropylene (FEP) and the like. Any one of these may be used as the water-repellent particles, or two or more of them may be used in combination.

[1.1.3. Blending amount]
The blending amount of the conductive particles and the water-repellent particles is not particularly limited, and the optimum blending amount can be selected according to the purpose.
Generally, if the amount of the water-repellent particles is too small, the water repellency becomes insufficient. Therefore, the blending amount of the water-repellent particles is preferably 10 wt% or more. The blending amount is preferably 20 wt% or more, more preferably 40 wt% or more.
On the other hand, if the amount of the water-repellent particles is excessive, the conductivity is lowered. Therefore, the blending amount of the water-repellent particles is preferably 70 wt% or less. The blending amount is preferably 60 wt% or less, more preferably 50 wt% or less.

[1.1.4. Mechanochemical treatment]
[A. Definition]
"Mechanochemical treatment" is the application of mechanical energy such as friction and compression to a plurality of solid substances to cause chemical reactions such as crystallization reaction, solid dissolution reaction, and phase transition reaction between the solid substances. Refers to processing.

When a mixture of conductive particles and water-repellent particles is subjected to mechanochemical treatment, composite particles in which the two are bonded with a force stronger than the Van der Waals force can be obtained. Various methods are known as methods for mechanochemical treatment. In the present invention, the method of mechanochemical treatment is not particularly limited, and any method may be used.

[B. Concrete example]
FIG. 1 shows a schematic view of a mechanochemical processing apparatus. In FIG. 1, the mechanochemical processing apparatus 10 includes a container 12, a stirring blade 14, and a motor 16. A raw material input port 12a is provided in the upper part of the container 12, and a processed powder take-out port 12b is provided in the lower part of the container 12.
The stirring blade 14 is inserted in the container 12. A gap is provided between the inner wall of the container 12 and the tip of the stirring blade 14, and the size of the gap can be arbitrarily set. Further, the rotating shaft of the stirring blade 14 is connected to the motor 16.

The treatment using the mechanochemical treatment apparatus 10 shown in FIG. 1 is performed as follows. First, the gap between the inner wall of the container 12 and the tip of the stirring blade 14 is set at a predetermined interval. In this state, the raw material is charged from the charging port 12a, and the stirring blade 14 is rotated at a predetermined rotation speed. This pushes the raw material powder between the gaps and applies mechanical energy between the particles. As a result, composite particles in which the conductive particles and the water-repellent particles are firmly adhered and are sized to an appropriate particle size can be obtained. After the treatment is completed, the composite particles are discharged from the take-out port 12b.

[1.2. Film formation process]
Next, the composite particles are coated on the surface of the conductive base material using an electrostatic screen printing device to obtain a coating film (film formation step).

[1.2.1. Conductive base material]
In the present invention, the conductive base material coated with the composite particles is a main component of the gas diffusion layer of the fuel cell, and is required to have high conductivity and high gas diffusivity. The material of the conductive base material is not particularly limited as long as it has the desired conductivity and gas diffusivity. As the conductive base material, for example,
(A) Carbon porous material such as carbon paper, carbon cloth, and glassy carbon,
(B) There are metal meshes, metal porous bodies such as foamed metals, and the like. The conductive base material may have a water-repellent treatment on the surface in advance.

[1.2.2. Electrostatic screen printing device]
[A. Definition]
The "electrostatic screen printing device" refers to a device that uses static electricity to attach particles to the surface of a base material. In the present invention, the main component of the gas diffusion layer, that is, the conductive base material is used as the base material. There are various methods of electrostatic screen printing. In the present invention, any method may be used.

However, as described in Patent Document 1, in the method of adhering the particles to the lower surface of the base material arranged above, only one or two particle layers are attached to the base material, and the film thickness is increased. Can not do it. In order for the particle layer on the surface of the base material to function as a water-repellent layer, the film thickness of the water-repellent layer needs to be about 3 to 15 μm. In order to form a water-repellent layer having such a film thickness by using the method described in Patent Document 1, it is necessary to set the particle size of the composite particles to 3 to 15 μm. Usually, the pore size distribution of the water-repellent layer controls the physical properties of the gas diffusion layer. Therefore, in order to control the performance of the gas diffusion layer, a method capable of coating composite particles having an arbitrary particle size is preferable.

Therefore, in the film forming step, it is preferable that a screen is placed above the conductive base material, the composite particles are placed on the screen, and the composite particles are rubbed against the screen using a pressing member. By using such a method, composite particles having an arbitrary particle size can be applied, and the thickness of the coating film can be arbitrarily controlled.

[B. Concrete example]
FIG. 2 shows a schematic view of an electrostatic screen printing apparatus having the above-mentioned functions. In FIG. 2, the electrostatic screen printing device 20 includes a pedestal 22, a screen 24, and a high voltage generator 26.
The pedestal 22 is for placing the printed matter (conductive base material) 30 on the pedestal 22. Above the pedestal 22, screens 24 are arranged at predetermined intervals.

The screen 24 is composed of a mesh net 24b provided substantially in the center of the frame portion 24a. The opening diameter of the mesh net 24b is not particularly limited, and the optimum opening diameter can be selected according to the purpose. Further, the gap G between the printed matter 30 placed on the pedestal 22 and the screen 24 can be arbitrarily adjusted.
The high voltage generator 26 positively charges the pedestal 22 and the printed matter 30 placed on the pedestal 22, and negatively charges the screen 24 and the composite particles (not shown) placed on the screen 24. Is for. The positive pole of the high voltage generator 26 is connected to the pedestal 22, and the negative pole is connected to the screen 24.

The film formation using the electrostatic screen printing apparatus 20 shown in FIG. 2 is performed as follows. First, the printed matter (conductive base material) 30 is placed on the pedestal 22, and the gap G between the printed matter 30 and the screen 24 is adjusted. Next, the composite particles are placed on the screen 24 with an electric field applied between the pedestal 22 and the screen 24, and the composite particles are transferred to the mesh net 24b of the screen 24 by using a pressing member (for example, a squeegee, a printing brush, etc.) (not shown). Rub in. As a result, composite particles having a particle size smaller than the opening diameter of the mesh net 24b fall from the mesh net 24b toward the pedestal 22.

Since the composite particles are negatively charged, they are accelerated by the electric field and collide with the surface of the positively charged printed matter 30. As a result, a coating film 32 having a shape corresponding to the shape of the mesh net 24b is formed on the surface of the printed matter 30.

[1.2.3. Printing conditions]
The film forming conditions when performing electrostatic screen printing affect the characteristics of the coating film. In particular, the electric field strength has a great influence on the characteristics of the coating film.

[A. gap]
In general, if the gap G between the screen and the conductive substrate becomes too small, the coating of the composite particles itself becomes difficult. Therefore, the gap G is preferably 1 mm or more. The gap G is preferably 1.5 mm or more, more preferably 2 mm or more.
On the other hand, if the gap G becomes too large, the coated surface becomes non-uniform. Therefore, the gap G is preferably 5.0 mm or less.

[B. Applied voltage]
Generally, if the applied voltage at the time of coating becomes too small, the coated surface becomes non-uniform. Therefore, the applied voltage is preferably 1.0 kV or more.
On the other hand, if the applied voltage becomes too large, it becomes difficult to coat the composite particles. Therefore, the applied voltage is preferably 3.0 kV or less.

[C. Average film thickness]
By using the method described above, the average film thickness of the coating film can be arbitrarily controlled regardless of the particle size of the composite particles. However, when the coating film coated in this way is pressed to form a water-repellent layer of a gas diffusion layer, if the average film thickness of the coating film becomes too thin, sufficient water repellency cannot be obtained. Therefore, the average film thickness of the coating film is preferably 5 μm or more. The average film thickness is preferably 10 μm or more, more preferably 20 μm or more.
On the other hand, if the average film thickness of the coating film becomes too thick, the gas diffusion performance deteriorates. Therefore, the average film thickness is preferably 50 μm or less. The average film thickness is preferably 40 μm or less, more preferably 30 μm or less.

[1.3. Press process]
Next, the coating film is pressed to obtain a water-repellent layer (pressing step).

[13.1. Press pressure]
Press pressure affects the properties of the water repellent layer. If the press pressure becomes too small, the adhesion between the base material and the water-repellent layer is low, and the base material and the water-repellent layer are easily peeled off. Therefore, the press pressure is preferably 0.1 kgf / cm ² (9.8 × 10 ^-3 MPa) or more. The press pressure is preferably 0.5 kgf / cm ² (4.9 × 10 ⁻² MPa) or more, and more preferably 1.0 kgf / cm ² (9.8 × 10 ⁻² MPa) or more.
On the other hand, if the press pressure becomes too high, the conductive base material undergoes plastic deformation or buckling. Therefore, the press pressure is preferably less than the plastic collapse load of the conductive substrate. The press pressure is preferably 80% or less, more preferably 60% or less of the plastic collapse load.

[1.3.2. Press temperature]
Generally, the higher the press temperature, the better the adhesion of the water repellent layer. In order to obtain such an effect, the press temperature is preferably room temperature or higher. The press temperature is preferably 300 ° C. or higher, more preferably 360 ° C. or higher.
On the other hand, if the press temperature is too high, the water-repellent particles may decompose. Therefore, the press temperature is preferably lower than the decomposition temperature of the water-repellent particles. The press temperature is preferably 90% or less, more preferably 80% or less of the decomposition temperature.
Further, when the melting point of the water-repellent particles is more than 140 ° C., the press temperature is preferably more than 140 ° C. and lower than the decomposition temperature of the water-repellent particles.

[1.4. Baking process]
After pressing the coating film to form a water-repellent layer, the water-repellent layer may be further fired (firing step). By firing the water-repellent layer, the adhesion of the water-repellent layer can be improved.

The firing temperature is not particularly limited, and the optimum temperature can be selected according to the purpose. Generally, if the firing temperature is too low, a sufficient effect cannot be obtained. Therefore, the firing temperature is preferably 300 ° C. or higher. The firing temperature is preferably 330 ° C. or higher, more preferably 360 ° C. or higher.
On the other hand, if the firing temperature is too high, the water-repellent molecules may be decomposed. Therefore, the firing temperature is preferably 400 ° C. or lower. The firing temperature is preferably 390 ° C. or lower, more preferably 380 ° C. or lower.
The optimum firing time is selected according to the firing temperature. Generally, the higher the firing temperature, the shorter the time required to improve the adhesion.

[2. Gas diffusion layer for fuel cells]
The gas diffusion layer for a fuel cell according to the present invention is
With a conductive base material
It is provided with a water-repellent layer formed on the surface of the conductive base material.

[2.1. Conductive base material]
The conductive substrate is the main component of the gas diffusion layer. The details of the conductive base material are as described above, and thus the description thereof will be omitted.

[2.2. Water repellent layer]
The water-repellent layer contains composite particles of conductive particles and water-repellent particles.
[2.1.1. Conductive particles, water-repellent particles, composite particles]
The details of the conductive particles, the water-repellent particles, and the composite particles are as described above, and thus the description thereof will be omitted. Further, since the blending amount of the water-repellent particles contained in the water-repellent layer is also as described above, the description thereof will be omitted.

[2.2.2. Average film thickness]
The average film thickness of the water repellent layer affects the water repellency of the gas diffusion layer. If the average film thickness of the water-repellent layer is too thin, sufficient water repellency cannot be obtained. Therefore, the average film thickness of the water-repellent layer is preferably 5 μm or more. The average film thickness is preferably 10 μm or more, more preferably 20 μm or more.
On the other hand, if the average film thickness of the water-repellent layer becomes too thick, the gas diffusion performance deteriorates. Therefore, the average film thickness is preferably 50 μm or less. The average film thickness is preferably 40 μm or less, more preferably 30 μm or less.

[2.3. Penetration]
The gas diffusion layer for a fuel cell according to the present invention is characterized in that the water-repellent layer does not penetrate into the conductive substrate. Generally, when an ink-like water-repellent layer is applied to a porous base material, the ink permeates the base material and the porosity of the base material is lost. Therefore, there is a problem that the gas diffusibility is lowered. On the other hand, since the present invention is a dry process that does not use ink, the water-repellent layer does not penetrate into the conductive substrate.

[3. Action]
By mechanochemical treatment of the conductive particles and the water-repellent particles, it is possible to obtain composite particles in which both are uniformly dispersed without using a solvent. Next, when composite particles are applied to the surface of the conductive substrate using an electrostatic screen printing device and the coating film is pressed, a water-repellent layer can be formed without using a solvent. At this time, when the screen is arranged above the conductive base material and the charged composite particles are dropped from the screen toward the conductive base material, a coating film having a film thickness exceeding the average particle size of the composite particles is formed. be able to. Further, since a high melting point material is usually used for the conductive base material, high temperature hot pressing using a high melting point water repellent material is also possible.
By using the method according to the present invention, composite particles having an arbitrary particle size and a water-repellent layer having an arbitrary film thickness can be formed by a complete dry process.

(Examples 1 to 5, Comparative Examples 1 to 5)
[1. Preparation of sample]
[1.1. Fabrication of composite particles]
As the conductive particles, carbon black (manufactured by Denka Co., Ltd.) having a primary particle diameter of 35 nm was used. As the water-repellent particles, PTFE (manufactured by 3M) having an average particle diameter of 4 μm was used. By treating these with mechanochemicals, composite particles having a particle size of about 0.1 to 20 μm were produced. The mechanochemical treatment apparatus shown in FIG. 1 (trade name: Nobilta (registered trademark), manufactured by Hosokawa Micron Co., Ltd.) was used to prepare the composite particles.

40 g of a raw material having a carbon black: PTFE weight ratio of 6: 4 was put into a processing apparatus and subjected to mechanochemical treatment. The rotation speed of the stirring blade was 3000 rpm, and the stirring time was 15 min. The gap between the stirring blade and the inner wall of the container was set to 1.5 mm. Further, the inside of the container has an inert atmosphere.

[1.2. Electrostatic screen printing]
Using the electrostatic screen printing apparatus shown in FIG. 2, a coating film composed of composite particles was formed on the surface of a conductive substrate. The mesh mesh opening was set to 100 μm. Water-repellent treated carbon paper F (manufactured by Electrochem, USA) was used as the conductive base material.
An amount of composite particles equivalent to the target film thickness (film thickness: 20 μm) was placed on the mesh net. A voltage was applied between the conductive substrate and the screen, and the composite particles were rubbed into the screen using a squeegee for coating. The voltage was 1 to 4 kV, and the gap between the screen and the conductive substrate was 0.5 to 10 mm.

[1.3. Coating film pressing and firing]
The obtained coating film was pressed. Pressing pressure, and ^{1~15kgf / cm 2 (9.8 × 10} -2 MPa~1.47MPa), the pressing temperature was room temperature (25 ℃) ~300 ℃.
Further, some samples were calcined at 300 ° C. after pressing.

[2. evaluation]
The adhesion and appearance of the water-repellent layer were evaluated. Here, the judgment as to whether or not the adhesion is possible is that the water-repellent layer does not peel off when the base material is tilted 90 degrees. In addition, the judgment as to whether or not the appearance is possible was based on the fact that the coated edges are in order, the coated surface is uniform, and there is no turning.

Table 1 shows the results. Further, FIG. 3 shows an external photograph of the gas diffusion layer obtained in Example 1. The following can be seen from Table 1 and FIG.
In Table 1, “◯” indicates that the water-repellent layer does not peel off when the base material before pressing is tilted 90 degrees after electrostatic screen printing. “X” indicates that the water-repellent layer peels off when the base material is tilted 90 degrees.
Further, regarding the appearance, “◯” indicates a state in which the coated surface is uniform and uniform, and the coated area is within 125% of the screen area. Further, "x" represents a state in which the coated surface is uneven and turned over, or a state in which the coated area has an area of more than 125% with respect to the screen area.

(1) When the applied voltage at the time of coating was 4 kV (Comparative Example 1), the coating itself could not be performed. It is considered that this is because an electric field strength higher than the dielectric strength of air was applied, dielectric breakdown occurred, and the screen and the pedestal became conductive. On the other hand, when the applied voltage was 0 kV (Comparative Example 3), poor appearance occurred. It is considered that this is because the coated surface becomes non-uniform because the composite particles are coated on the base material by free fall.
(2) When the gap at the time of coating was 0.5 mm (Comparative Example 2), the coating itself could not be performed. It is considered that this is because the screen and the pedestal are made conductive by the falling composite particles because the gap is small. On the other hand, when the gap was 10 mm (Comparative Example 4), poor appearance occurred. It is considered that this is because the coated surface is uneven and uneven due to the large gap.

(3) Even when the press pressure was 1 kgf / cm ² (9.8 × ^10-2 MPa) (Example 5), good adhesion was obtained. On the other hand, when the press pressure was 15 kgf / cm ² (1.47 MPa) (Comparative Example 5), poor appearance occurred. This is because the conductive base material is deformed because the press pressure is too high.
(4) The applied voltage during coating is 1 to 3 kV, the gap is 1 to 5 mm, the press pressure is 1 to ^{10 kgf / cm 2} (9.8 × 10 ^{−2 to} 0.98 MPa), and the press temperature is 25 to 300 ° C. Then, a gas diffusion layer having good adhesion and appearance was obtained.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The fuel cell gas diffusion layer according to the present invention can be used as a fuel cell gas diffusion layer used in an in-vehicle power source, a stationary power generator, or the like.

Claims (8)

A granulation process in which conductive particles and water-repellent particles are treated with mechanochemicals to obtain composite particles.
A film forming process of applying the composite particles to the surface of a conductive base material using an electrostatic screen printing device to obtain a coating film, and
A method for producing a gas diffusion layer for a fuel cell, comprising a pressing step of pressing the coating film to obtain a water-repellent layer. The first aspect of the film forming step comprises arranging a screen above the conductive substrate, placing the composite particles on the screen, and rubbing the composite particles onto the screen using a pressing member. The method for manufacturing a gas diffusion layer for a fuel cell according to the above method. In the film forming step, the gap between the screen of the electrostatic screen printing apparatus and the conductive substrate at the time of coating is 1 mm or more and 5 mm or less, and the applied voltage is 1.0 kV or more and 3.0 kV or less. It consists of coating the composite particles under certain conditions.
In the pressing step, the pressing pressure is 0.1 kgf / cm ² (9.8 × 10 ^-3 MPa) or more and less than the plastic decay load of the conductive substrate, and the pressing temperature is room temperature or more and the decomposition temperature of the water-repellent particles. The method for producing a gas diffusion layer for a fuel cell according to claim 1 or 2, wherein the pressing is performed under the condition of less than. The fuel cell according to any one of claims 1 to 3, wherein the film forming step comprises coating the composite particles so that the average film thickness of the coating film is 5 μm or more and 50 μm or less. A method for manufacturing a gas diffusion layer. The water-repellent particles are made of a material having a melting point of more than 140 ° C.
The method for producing a gas diffusion layer for a fuel cell according to any one of claims 1 to 4, wherein the pressing step comprises performing the pressing at a temperature higher than 140 ° C. and lower than the decomposition temperature of the water-repellent particles. .. With a conductive base material
A water-repellent layer formed on the surface of the conductive base material is provided.
The water-repellent layer contains composite particles of conductive particles and water-repellent particles.
A gas diffusion layer for a fuel cell having an average film thickness of 5 μm or more and 50 μm or less. The gas diffusion layer for a fuel cell according to claim 6, wherein the water-repellent particles are made of a material having a melting point of more than 140 ° C. The gas diffusion layer for a fuel cell according to claim 6 or 7, wherein the water-repellent layer does not penetrate into the conductive substrate.

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