JP6143299B2 - Microporous layer forming paste composition and method for producing the same - Google Patents

Description

  The present invention relates to a paste composition for forming a microporous layer, which is applied to the surface of a substrate made of a conductive porous material such as carbon paper to form a microporous layer of a gas diffusion layer, and a method for producing the same.

  In a fuel cell, in particular, a polymer electrolyte fuel cell, a cathode side electrode and an anode side electrode are formed on both sides of a polymer electrolyte membrane. Usually, the cathode side electrode and the anode side electrode are made of platinum or the like. An electrocatalyst layer made of carbon black and an ion exchange resin supporting a catalyst, and a conductive powder such as carbon particles for imparting conductivity to a base material made of a conductive porous material such as carbon cloth or carbon paper; It is composed of a gas diffusion layer formed by coating a water-repellent paste kneaded with a water-repellent resin such as polytetrafluoroethylene (hereinafter also referred to as “PTFE”) emulsion for imparting water repellency. . Emulsion (also referred to as “emulsion”) is also called an emulsion, and the original meaning is that the liquid particles form a milky form as colloidal particles or coarser particles (dispersed system). Although it is (Saburo Nagakura et al., “Iwanami Rikagaku Dictionary (5th edition)” page 152, published by Iwanami Shoten Co., Ltd. on February 20, 1998), in this specification and claims, it is more general. As used herein, the term “emulsion” is used herein as “in which solid or liquid particles are dispersed in a liquid”.

  In the base material of the gas diffusion layer of such a fuel cell, a water-repellent treatment is usually applied to a conductive porous material such as carbon paper and carbon cloth in order to quickly remove water generated in the electrode of the fuel cell. Applied. However, in a fuel cell in which a gas diffusion layer is formed by applying a paste-like mixture for forming a microporous layer on the surface of a carbon substrate such as carbon paper that has been subjected to water repellent treatment, When the mixture is composed of conductive powder such as carbon black, a water repellent resin such as PTFE emulsion, and a dispersant, the paste-like mixture for forming a microporous layer is applied to the surface of a carbon substrate that has been subjected to a water repellent treatment. There was a problem that the paste component escapes to the back surface of the carbon base material following the water moved to the back surface of the base material by the water repellent treatment. If the paste component escapes to the back surface of the carbon base material, the water repellency of the carbon base material is reduced at the back-through portion even though the carbon base material is water-repellent. The generated water is not smoothly removed, which adversely affects battery performance.

Therefore, in order to suppress the penetration of the paste component, a method of increasing the viscosity of the composition by adjusting the viscosity can be considered.
Here, as a technique for improving the viscosity of the composition, in Patent Document 1, it is located between the catalyst layer, the gas diffusion layer composed of a conductive substrate, and the catalyst layer and the gas diffusion layer. And a microporous layer containing a conductive material, a thickener which is a nonionic cellulose series compound selected from methylcellulose, ethylcellulose, hydroxypropylmethylcellulose and hydroxypropylethylcellulose, and a fluorine series resin. Yes.

JP 2006-19300 A

However, in Patent Document 1, the thickener is a nonionic cellulose-based compound, and the cellulose-based compound is not completely decomposed at a temperature of about 300 ° C. Therefore, it is necessary to increase the current drying / calcination temperature. -There arises a problem that the load during firing increases.
In addition, when the viscosity of the composition is improved by using a cellulose compound for viscosity adjustment, the fluidity of the composition deteriorates against the increase in viscosity, so the smoothness decreases and the unevenness of the coating film increases. In addition, it becomes difficult to ensure the smoothness of the microporous layer required for the diffusion layer in order to stabilize the output of the fuel cell, and the production efficiency cannot be increased.

  Therefore, the present invention has been made to solve such a problem, and can prevent the penetration of the paste component without increasing the load of the drying process more than necessary, and has excellent smoothness. It is an object of the present invention to provide a layer forming paste composition and a method for producing the same.

Microporous layer forming paste composition of the invention of claim 1 includes a conductive powder, a water-repellent resin, a dispersant, a paste composition containing a thickening agent, as the thickener, A low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination , and the total solid content of the conductive powder and the water repellent resin is 100 parts by weight. The low molecular weight polyethylene oxide has a solid content of 0.2 to 1.1 parts by weight, and the high molecular weight polyethylene oxide has a solid content of 0.3 to 1 part by weight. It is within the range of 0.0 part by weight .

Here, examples of the conductive material include carbon particles such as carbon black powder, graphite powder, and vapor growth carbon powder.
Examples of the water repellent resin include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene ( PCTFE), fluoropolymers such as ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), and polyvinylidene fluoride (PVdF).
Furthermore, examples of the dispersant include Triton X-100 and polyoxyethylene lauryl ether.
As the thickener, polyethylene oxide which is a water-soluble resin that is thermally decomposed at less than 300 ° C. even when the molecular weight is large is used. Low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and average molecular weight of 1.6 million or more Polyethylene oxide having an average molecular weight different from that of high molecular weight polyethylene oxide is used in combination. This combined use ensures a viscosity characteristic suitable for coating by a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million, and a viscosity characteristic that suppresses the back-through by a high molecular weight polyethylene oxide.

In the microporous layer forming paste composition according to the present invention, the low molecular weight polyethylene oxide has an average molecular weight in the range of 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight of 1,600,000 or more. It is in the range of ˜6.5 million or less .

The paste composition for forming a microporous layer according to the invention of claim 2 is a low porous composition having carbon particles as a conductive material, a PTFE emulsion as a water repellent resin, a dispersant, and an average molecular weight of less than 1.6 million as a thickener. It contains a polyethylene oxide having a molecular weight and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more, and the solid content of the low molecular weight polyethylene oxide is 100 parts by weight with respect to the total solid content of the carbon particles and the PTFE emulsion. The blending amount is in the range of 0.2 to 1.1 parts by weight, the solid content blending amount of the high molecular weight polyethylene oxide is in the range of 0.3 to 1.0 parts by weight, and at least the dispersing agent and the PTFE emulsion and the carbon particles, a predetermined time mixing and dispersing child in a planetary stirrer-deaerator By a microporous layer paste, it is applied to a substrate of a conductive porous material, and forms a microporous layer of the gas diffusion layer by drying and baking.

In the microporous layer forming paste composition according to the present invention, the low molecular weight polyethylene oxide has an average molecular weight in the range of 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight of 1,600,000 or more. It is in the range of ˜6.5 million or less .

The method for producing a microporous layer forming paste composition according to the invention of claim 3 is characterized in that carbon particles as a conductive material, PTFE emulsion as a water repellent resin, a dispersant, a dispersion medium, and an average as a thickener. A mixed material with a low molecular weight polyethylene oxide having a molecular weight of less than 1.6 million is mixed and dispersed for a predetermined time with a planetary stirring and defoaming device, and then a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more as a thickener. Is mixed with a stirrer to obtain a paste for a microporous layer, and the solid content of the low molecular weight polyethylene oxide is set to 0.1 part with respect to 100 parts by weight of the total solids of the carbon particles and the PTFE emulsion. The solid content of the high molecular weight polyethylene oxide is 0.3 fold in the range of 2 to 1.1 parts by weight. Part 1.0 is intended to be in the range of parts by weight.

In the method for producing a microporous layer forming paste composition according to the present invention, the low molecular weight polyethylene oxide has an average molecular weight in the range of 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight are those in the range of more than 1.6 million to 650 than 10,000.

The microporous paste of the method for manufacturing the microporous layer forming paste composition of the invention of claim 4, was subjected to a applied to a substrate made of a conductive porous material such as carbon cloth or carbon paper microporous layer It is characterized by this.

Microporous layer forming paste composition according to the invention of claim 1 includes a conductive powder, a water-repellent resin, a dispersant, a paste composition containing a thickening agent, as the thickener A low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more were used in combination.

The present inventors have conducted extensive experimental research in order to achieve both suppression of the back-through of the paste component on the back surface of the base material made of a conductive porous material and good smoothness to the base material of the paste, As a thickener, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination without unnecessarily increasing the load of the drying process. It was found that the penetration of the paste component to the back of the base material can be suppressed, and that a smooth microporous layer (coating film) of the gas diffusion layer without unevenness can be formed and the coating property is also good. The present invention has been completed based on the above.
That is, according to the experiments by the inventors, as a thickener, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination. The polyethylene oxide on the low molecular weight side with a molecular weight of less than 1.6 million can secure the viscosity characteristics suitable for coating, the polyethylene oxide on the high molecular weight side can secure the viscosity characteristics to suppress the back-through, and the back of the paste component on the back of the substrate Both omission control and good smoothness can be effectively ensured. And as a thickener, in order to ensure the characteristics required at the time of microporous layer formation by using polyethylene oxide of a water-soluble resin that thermally decomposes at less than 300 ° C. even when the molecular weight increases, The load is not increased more than necessary.
Therefore, according to the first aspect of the present invention, it is possible to suppress the penetration of the paste component required for the diffusion layer for the stabilization of the output of the fuel cell to the back surface of the substrate without increasing the load of the drying process more than necessary, and The smoothness of the microporous layer can be ensured. And by suppressing the penetration of the paste component, the water repellency of the back surface of the base material is not lowered, and further, a smooth microporous layer is obtained, so that gas diffusion can be made uniform, and the catalyst Since the adhesion to the layer is also increased, a stable output can be obtained in the fuel cell.

According to the microporous layer forming paste composition of the present invention, the low molecular weight polyethylene oxide has an average molecular weight in the range of from 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight of 160. It is in the range of 10,000 to 6.5 million.
Here, when the average molecular weight of the low molecular weight side of the polyethylene oxide is less than 600,000, there is a possibility that the sagging after coating or the penetration into the base material occurs and the power in the fuel cell is reduced. Further, if the average molecular weight of the polymer side exceeds 6.5 million, can not produce a uniform film on the flow characteristics becomes poor substrate, forming a smooth microporous layer becomes difficult. Furthermore, it becomes difficult to dissolve in a dispersion medium such as ion-exchanged water, so that the handleability is deteriorated and it is not suitable for practical use.
Therefore, when the average molecular weight of the polyethylene oxide on the low molecular weight side is in the range of 600,000 to less than 1.6 million, it prevents the penetration after coating and the penetration into the base material and has a viscosity characteristic suitable for coating. By ensuring that the average molecular weight of polyethylene oxide on the high molecular weight side is in the range of from 1.6 million to 6.5 million, it is easy to handle, and it is possible to secure a viscosity characteristic that suppresses through-through without causing a decrease in smoothness. .
Drunk, stable print-through suppression and good smoothness can be secured, the output of the fuel cell can also be further stabilized.

The paste composition for forming a microporous layer according to the invention of claim 2 is a low porous composition having carbon particles as a conductive material, a PTFE emulsion as a water repellent resin, a dispersant, and an average molecular weight of less than 1.6 million as a thickener. It contains polyethylene oxide having a molecular weight and high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more, and at least the carbon particles, the PTFE emulsion, and the dispersing agent are mixed and dispersed for a predetermined time by a planetary stirring and defoaming device. To paste the microporous layer.

That is, in the present invention, the thickener of the paste composition for forming a microporous layer is a low molecular weight having an average molecular weight of less than 1.6 million as polyethylene oxide of a water-soluble resin that is thermally decomposed at less than 300 ° C. even if the molecular weight is increased. Polyethylene oxide and high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination.
Viscosity suitable for coating with polyethylene oxide on the low molecular weight side by using a low molecular weight polyethylene oxide with an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide with an average molecular weight of 1.6 million or more as a thickener. The properties can be secured, and the viscosity property that suppresses the back-through by the high molecular weight polyethylene oxide can be secured, so that both the back-through suppression to the back of the base material of the paste component and good smoothness can be effectively secured. be able to.
And as a thickener, in order to ensure the characteristics required at the time of microporous layer formation by using polyethylene oxide of a water-soluble resin that thermally decomposes at less than 300 ° C. even when the molecular weight increases, The load is not increased more than necessary.
Therefore, according to the second aspect of the present invention, it is possible to suppress the penetration of the paste component required for the diffusion layer for the stabilization of the output of the fuel cell to the back surface of the substrate without increasing the load of the drying process more than necessary, and The smoothness of the microporous layer can be ensured. And by suppressing the penetration of the paste component, the water repellency of the back surface of the base material is not lowered, and further, a smooth microporous layer is obtained, so that gas diffusion can be made uniform, and the catalyst Since the adhesion to the layer is also increased, a stable output can be obtained in the fuel cell.

According to the microporous layer forming paste composition of the present invention, the low molecular weight polyethylene oxide has an average molecular weight in the range of from 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight of 160. It is in the range of 10,000 to 6.5 million.
Here, when the average molecular weight of the low molecular weight side of the polyethylene oxide is less than 600,000, there is a possibility that the sagging after coating or the penetration into the base material occurs and the power in the fuel cell is reduced. Further, if the average molecular weight of the polymer side exceeds 6.5 million, can not produce a uniform film on the flow characteristics becomes poor substrate, forming a smooth microporous layer becomes difficult. Furthermore, it becomes difficult to dissolve in a dispersion medium such as ion-exchanged water, so that the handleability is deteriorated and it is not suitable for practical use.
Therefore, when the average molecular weight of the polyethylene oxide on the low molecular weight side is in the range of 600,000 to less than 1.6 million, it prevents the penetration after coating and the penetration into the base material and has a viscosity characteristic suitable for coating. By ensuring that the average molecular weight of polyethylene oxide on the high molecular weight side is in the range of from 1.6 million to 6.5 million, it is easy to handle, and it is possible to secure a viscosity characteristic that suppresses through-through without causing a decrease in smoothness. .
Drunk, stable print-through suppression and good smoothness can be secured, the output of the fuel cell can also be further stabilized.

According to the method for producing the microporous layer forming paste composition of the invention of claim 3 , the carbon particles as the conductive material, the PTFE emulsion as the water repellent resin, the dispersant, the dispersion medium, and the thickener. As a thickening agent, a mixed material with a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million is mixed and dispersed for a predetermined time using a planetary stirring and defoaming device. Polyethylene oxide is blended and mixed with a stirrer to obtain a microporous layer paste.

That is, in the present invention, the thickener of the paste composition for forming a microporous layer is a low molecular weight having an average molecular weight of less than 1.6 million as polyethylene oxide of a water-soluble resin that is thermally decomposed at less than 300 ° C. even if the molecular weight is increased. Polyethylene oxide and high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination.
As a thickener, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination, so that the polyethylene oxide on the low molecular weight side is suitable for coating. Viscosity characteristics can be ensured, and the high-molecular-weight polyethylene oxide can ensure the viscosity characteristics to suppress the back-through, effectively ensuring both the back-through suppression of the paste component to the back of the substrate and good smoothness. can do.
In addition, high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more as a thickener is blended with other materials after stirring and mixed with a stirrer, so that high molecular weight polyethylene oxide is reduced in molecular weight by overdispersion. Can be prevented. When high molecular weight polyethylene oxide is added and dispersed simultaneously with other materials, the high molecular weight polyethylene oxide may have a low molecular weight. In this case, the desired characteristics may not be obtained.
Therefore, the high molecular weight polyethylene oxide is preferably blended after stirring other materials.
And as a thickener, in order to ensure the characteristics required at the time of microporous layer formation by using polyethylene oxide of a water-soluble resin that thermally decomposes at less than 300 ° C. even when the molecular weight increases, The load is not increased more than necessary.
Therefore, according to the invention of claim 3, the penetration of the paste component required for the diffusion layer for stabilizing the output of the fuel cell to the back surface of the base material is suppressed without increasing the load of the drying process more than necessary, and A microporous layer paste that can ensure the smoothness of the microporous layer is obtained. According to such a microporous layer paste, the back-through of the paste component is suppressed, so that the water repellency of the back surface of the base material is not lowered, and further, a smooth microporous layer is obtained. Can be made uniform and the adhesion to the catalyst layer can be increased, so that a stable output can be obtained in the fuel cell.

The method for producing a microporous layer forming paste composition according to the present invention is such that the low molecular weight polyethylene oxide has an average molecular weight in the range of 600,000 to less than 1.6 million, and the high molecular weight polyethylene oxide has an average molecular weight. It is within the range of 1.6 million to 6.5 million.
Here, when the average molecular weight of the low molecular weight side of the polyethylene oxide is less than 600,000, there is a possibility that the sagging after coating or the penetration into the base material occurs and the power in the fuel cell is reduced. On the other hand, when the average molecular weight on the polymer side exceeds 6.5 million, the flow characteristics are deteriorated and a uniform film cannot be produced on the substrate, and it becomes difficult to form a smooth microporous layer. Furthermore, it becomes difficult to dissolve in a dispersion medium such as ion-exchanged water, so that the handleability is deteriorated and it is not suitable for practical use.
Therefore, when the average molecular weight of the polyethylene oxide on the low molecular weight side is in the range of 600,000 to less than 1.6 million, it prevents the penetration after coating and the penetration into the base material and has a viscosity characteristic suitable for coating. By ensuring that the average molecular weight of polyethylene oxide on the high molecular weight side is in the range of from 1.6 million to 6.5 million, it is easy to handle, and it is possible to secure a viscosity characteristic that suppresses through-through without causing a decrease in smoothness. .
Drunk, stable print-through suppression and good smoothness can be ensured, also, microporous layer forming paste capable of output even further stabilize the fuel cell can be obtained.

Method for producing a microporous layer forming paste composition of the invention of claim 4, claim since it is obtained by coating the microporous paste on a substrate made of a conductive porous material such as carbon cloth or carbon paper In addition to the effects described in 3, it can be easily manufactured, and can be finished in any shape depending on the shape of the substrate.

FIG. 1 is a schematic configuration diagram of a polymer electrolyte fuel cell having a gas diffusion layer for a fuel cell using the microporous layer forming paste composition of the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the microporous layer forming paste composition according to the present embodiment will be described.
The microporous layer forming paste composition of the present embodiment is a paste composition containing a conductive material, a water repellent resin, a dispersant, and a thickener, and has an average molecular weight as the thickener. Is a combination of a low molecular weight polyethylene oxide having a molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more.

  Examples of the conductive material that can be used include powdered conductive materials such as carbon black powder, graphite powder, and vapor-grown carbon powder, and fibrous conductive materials such as carbon fibers. Among them, carbon black is preferable from the viewpoint of compatibility with the carbon base material used as the base material. Examples of the carbon black include carbon particles such as acetylene black, ketjen black, and furnace black. It has high purity and is easy to use, and is suitable for forming a coating layer used for an electrode of a fuel cell.

Examples of water-repellent resins include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene / tetra Fluorine resin emulsions such as fluorinated ethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), and polyvinylidene fluoride (PVdF) can be used, and it is particularly preferable to use an emulsion of PTFE.
Moreover, as a dispersing agent, Triton X-100, polyoxyethylene lauryl ether, etc. are used.

If the thickener remains in the microporous layer that forms the diffusion layer, it adversely affects the properties of the microporous layer, so it is thermally decomposed in the drying and drying process. Depending on the thermal decomposition temperature of the thickener, The temperature of the drying process needs to be higher than when no thickener is used, and the load increases. Therefore, in the present invention, the load in the drying process associated with the thermal decomposition of the thickener by using polyethylene oxide, which is a water-soluble resin that thermally decomposes at less than 300 ° C., is used as a thickener, compared to the case where no thickener is used. Therefore, the load can be suppressed without increasing more than necessary.
In the present invention, as a thickener, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination. As such polyethylene oxide, for example, those commercially available from Sumitomo Seika Co., Ltd. (trade name: PEO), Meisei Chemical Industry Co., Ltd. (trade name: Alcox) are used. be able to.

Here, the average molecular weight of the low molecular weight polyethylene oxide as the thickener is in the range of 600,000 to less than 1.6 million, and the average molecular weight of the high molecular weight polyethylene oxide is in the range of 1.6 million to 6.5 million. Is preferred.
When the average molecular weight of the polyethylene oxide on the low molecular weight side is less than 600,000, there is a possibility that the sagging after coating or penetration into the base material may occur, resulting in a decrease in power in the fuel cell. When the average molecular weight exceeds 6.5 million, it is difficult to dissolve in ion-exchanged water, the handleability is poor, and the smoothness is lowered, so that it is not suitable for practical use.

The blending amount of the thickening agent is such that the total solid content of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide is 0. 0 parts by weight based on the total solid content of the conductive material and the water-repellent resin. It is preferably within the range of 5 to 2.5 parts by weight.
When the total solid content of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as the thickener is less than 0.5 parts by weight, the amount of the thickener is small, and the through-through suppression and good smoothness are achieved. This is because the viscosity characteristics to be ensured cannot be obtained, and on the other hand, when it exceeds 2.5 parts by weight, the increase in viscosity tends to increase and the smoothness tends to decrease.
Furthermore, the solid content of the low molecular weight polyethylene oxide is in the range of 0.2 to 1.1 parts by weight with respect to 100 parts by weight of the total solids of the conductive material and the water repellent resin. The solid content of the high molecular weight polyethylene oxide is preferably in the range of 0.2 to 1.1 parts by weight.
When the solid content of the molecular weight polyethylene oxide is less than 0.2 parts by weight, the blending amount of the low molecular weight polyethylene oxide is small and the smoothness may be lowered, while the amount exceeds 1.1 parts by weight. In such a case, the flow characteristics are increased, the flow characteristics are deteriorated, and a uniform film cannot be produced on the substrate, so that it is difficult to form a smooth microporous layer.

  Thus, the microporous layer forming paste composition of the present embodiment has an average molecular weight of less than 1.6 million as a conductive material such as carbon particles, a water repellent resin such as PTFE emulsion, a dispersant, and a thickener. A low molecular weight polyethylene oxide and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are blended in a predetermined ratio. This microporous layer-forming paste composition is used as a fuel cell gas diffusion layer 14 (FIG. 1). When applied to a conductive material such as carbon particles, a water repellent resin such as PTFE emulsion, a dispersant, water such as ion-exchanged water as a dispersion medium, and an average molecular weight of less than 1.6 million as a thickener. The material mixed with low molecular weight polyethylene oxide was mixed with a planetary agitation / defoaming device with a specific value for revolution and rotation. And, then, to this mixture dispersed material, further average molecular weight blended 1,600,000 more high molecular weight polyethylene oxide as a thickener, to paste microporous layer by mixing it with a stirrer. Then, the microporous layer paste is applied to a base material 16 (see FIG. 1) obtained by subjecting the conductive porous material to a water repellent treatment, thereby forming a diffusion layer 14 (FIG. 1) formed with a microporous layer. Reference).

  1 is a schematic configuration diagram of FIG. 1 regarding the structure of a polymer electrolyte fuel cell (single cell) to which the fuel cell gas diffusion layer using the microporous layer forming paste composition according to the present embodiment is applied. This will be described with reference to FIG.

  As shown in the figure, in the fuel cell 1 using the microporous layer forming paste composition according to the present embodiment, an oxidizing gas such as oxygen gas reacts on one surface of an electrolyte membrane 11 that becomes the core of a single cell. The cathode electrode 12A is disposed on the surface of the cathode electrode 12A of the membrane-electrode assembly 10 and the membrane-electrode assembly 10 in which an anode electrode 12B on which the fuel gas such as hydrogen gas reacts is disposed on the other surface. The cathode-side separator 20A and the anode-side separator 20B disposed on the surface of the anode electrode 12B of the membrane-electrode assembly 10 are configured. The membrane-electrode assembly 10 is also called a membrane-electrode assembly, and the fuel gas and the oxidizing gas react to take out electric power between the cathode side separator 20A and the anode side separator 20B.

  The electrolyte membrane 11 made of a polymer membrane serving as an ion exchange group has a property of binding firmly to specific ions and selectively transmitting cations or anions. Electrodes 12 (cathode electrode 12A and anode electrode 12B) formed on both surfaces of electrolyte membrane 11 are composed of catalyst layer 13 (cathode side catalyst layer 13A and anode side catalyst layer 13B) and diffusion layer 14 (cathode side diffusion layer 14A). And the anode side diffusion layer 14B).

  The catalyst layer 13 (cathode side catalyst layer 13A or anode side catalyst layer 13B) with which the fuel gas or the oxidizing gas reacts is a catalyst-supported carbon in which a noble metal catalyst such as platinum, gold, palladium, etc. is supported by carbon, and this catalyst-supported carbon. And a resin that adheres to the electrolyte membrane 11. The diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) having gas permeability and water permeability is formed on the surface of the catalyst layer 13 (cathode side catalyst layer 13A or anode side catalyst layer 13B).

  The diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) includes a base material 16 (cathode side base material 16A or anode side base material 16B) and a surface layer 15 (microporous layer) as a microporous layer (microporous layer). Cathode side surface layer 15A or anode side surface layer 15B), and surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B) is catalyst layer 13 (cathode side catalyst layer 13A or anode side catalyst layer 13B). The substrate 16 (cathode side substrate 16A or anode side substrate 16B) is disposed on the surface of the surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B).

  With this configuration, when an oxidizing gas is supplied from the outside to the oxidizing gas channel 21A of the cathode-side separator 20A, a part of the oxidizing gas flowing along the oxidizing gas channel 21A is based on the cathode-side diffusion layer 14A. It penetrates into the inside from the surface of the material 16A. Other unreacted oxidizing gas flows along the oxidizing gas channel 21 </ b> A and is discharged to the outside of the fuel cell 1. Similarly, when fuel gas is supplied from the outside to the fuel gas passage 21B of the anode separator 20B, a part of the fuel gas flowing along the fuel gas passage 21B is the base material of the anode diffusion layer 14B. It penetrates from the 16B side surface. Other unreacted fuel gas flows along the fuel gas flow path 21B as it is, and is discharged to the outside of the fuel cell 1.

In the present embodiment, the present embodiment is applied to the base material 16 (cathode side base material 16A or anode side base material 16B) obtained by subjecting a conductive porous material such as carbon paper or carbon cloth to a water repellent treatment. By applying a microporous layer paste made of such a microporous layer paste composition, a surface layer 15 (cathode-side surface layer 15A or anode-side surface layer 15B) as a microporous layer is formed, and gas permeability is achieved. And a diffusion layer 14 having water permeability (cathode side diffusion layer 14A or anode side diffusion layer 14B).
At this time, the surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B) is electrically conductive by the conductive material of the microporous layer paste composition according to the present embodiment, for example, carbon particles such as carbon black. In addition, water repellency is imparted by a water repellent resin such as a PTFE emulsion.
Moreover, the base material 16 (cathode side base material 16A or anode side base material 16B) is formed by subjecting a conductive porous material such as carbon paper or carbon cloth to a water repellent treatment.

In this embodiment, the microporous layer is applied to a base material 16 (cathode side base material 16A or anode side base material 16B) obtained by subjecting a conductive porous material such as carbon paper or carbon cloth to a water repellent treatment. In the paste composition, a low molecular weight polyethylene oxide having an average molecular weight of less than 1,600,000 and a high molecular weight polyethylene oxide having an average molecular weight of 1,600,000 or more are used in combination as a thickener, thereby making the conductive porous material water repellent. Even if the coating is performed on the base material 16 that has been subjected to the treatment, a situation in which the paste component escapes to the back surface a of the base material 16 following the water moved to the back surface a of the base material 16 due to the water repellent treatment is prevented.
In addition, the low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and the high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination as a thickener, so that flow characteristics when applied to the substrate 16 are also achieved. The coating amount can be made uniform, and a smooth microporous layer (coating film) without unevenness can be formed. That is, smoothness is also good and production efficiency at the time of coating is also good.

  In this way, by using together a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 6.5 million or less as a thickener, it is possible to suppress the penetration of paste components during paste coating and The smoothness of the porous layer, that is, good smoothness can be achieved together with the low molecular weight side polyethylene oxide ensuring the viscosity characteristics suitable for coating and the high molecular weight side polyethylene oxide being the paste component. This is considered to be because it is possible to ensure the viscosity characteristic that suppresses the back-through of the film.

  Therefore, in the fuel cell in which the gas diffusion layer 14 is formed by applying the microporous layer paste made of the microporous layer paste composition of the present embodiment, the paste component escapes to the back surface a of the substrate 16. Since the back-through is suppressed, a decrease in water repellency of the back surface a of the substrate 16 is prevented. Further, by obtaining a smooth microporous layer in the surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B), gas diffusion can be made uniform, and the catalyst layer 13 (cathode side catalyst layer 13A or Adhesion with the anode catalyst layer 13B) is also increased. Therefore, a stable output can be obtained. In addition, since a smooth microporous layer can be obtained, workability (handling) at the time of manufacturing the fuel cell is also improved.

  Here, polyethylene oxide used as a thickener for the microporous layer forming paste composition of the present embodiment is a water-soluble resin, has a low decomposition temperature, and a difference in decomposition temperature depending on molecular weight is small. Even if it becomes larger, it is thermally decomposed at a firing temperature of less than 300 ° C. Therefore, even when a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1,600,000 or more are used in combination as a thickener, the firing load for decomposing and disappearing the polyethylene oxide is Since it does not increase more than necessary, an increase in the load of the drying process is suppressed. By the way, according to the experiments by the inventors, the relationship between the molecular weight and the heat resistance has the same molecular structure, the heat resistance improves as the molecular weight increases up to a certain molecular weight, but even if the molecular weight increases further. It was confirmed that the heat resistance did not change.

  Therefore, as a thickener for the microporous layer forming paste composition, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination, thereby reducing the load of the drying process. Without increasing it more than necessary, it is possible to suppress the penetration of the paste component, which is an important characteristic of the diffusion layer 14 that affects the power generation efficiency of the fuel cell, and to obtain good smoothness.

In addition, in the low molecular weight side polyethylene oxide and the high molecular weight side polyethylene oxide as thickeners, by adjusting the molecular weight and addition amount, respectively, it can be set to the viscosity characteristics that match the coating characteristics and match the coating conditions. Construction with high viscosity characteristics is possible.
In addition, the microporous layer-forming paste comprising the microporous layer-forming paste composition of the present embodiment has good flow characteristics and good production efficiency at the time of coating. is there.

  Next, the content and amount of each component of the paste composition for a microporous layer according to the embodiment of the present invention are specifically shown in Tables 1 and 2, and each example will be described.

[Example]
The paste composition for a microporous layer according to Example 1 is composed of carbon particle acetylene black (made by Denki Kagaku Kogyo Co., Ltd .: 75.0 g of trade name “Denka Black” as a conductive material, and PTFE as a water repellent resin. 41.7 g of emulsion (made by Daikin Industries, Ltd .: POLYFLON PTFE D-210C [solid content (resin content) 61%]) (solid content 25.4 g, moisture content 16.3 g), Triton X- as a dispersant 7.5 g of 100, 295.8 g of ion-exchanged water as a dispersion medium, and 1.25% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 to 1.5 million as a thickener 40.0 g (solid content 0.5 g, moisture content 39.5 g) in a planetary agitation set to revolution 600 rpm and rotation 600 rpm Deaerator (Kurabo Co., Ltd.: trade name "Mazerustar KK-1000W") for 3 min mixed and dispersed in, and evenly dispersed as aggregates of carbon particles is not.
Next, 40.0 g (0.5 g solid content, water content) of a 1.25% aqueous solution of high molecular weight polyethylene oxide (Esei-160, manufactured by Meisei Chemical Co., Ltd.) having an average molecular weight of 3.6 to 4 million as a thickener is added to this mixed material. Example 3 by blending 39.5 g), three propellers having a diameter of 10 cm to a three-one motor as a stirrer (manufactured by HEIDON: HEIDON 600G), rotating at 300 rpm, mixing, and degassing This was a microporous layer paste.
It should be noted that the stirring after the addition of the high molecular weight polyethylene oxide is concerned because the molecular weight of the high molecular weight polyethylene oxide may be lowered in the case of overdispersion.

  Example 2 is 40.0 g (solid content 0.3 g, moisture content) of a 0.75% aqueous solution of low molecular weight polyethylene oxide (PEO-4, manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 to 1,500,000 as a thickener. 39.7 g) and 40.0 g (solid content 0.3 g, moisture content 132.3 g) of a 0.75% aqueous solution of high molecular weight polyethylene oxide (Meisei Chemical E-160) having an average molecular weight of 3.6 to 4 million did. That is, the solid content blending amount of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as thickeners was reduced as compared with Example 1. A microporous layer paste of Example 2 was prepared under the same conditions as in Example 1 except that the blending amounts were different.

  In Example 3, 40.0 g of a 2.5% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 to 1,500,000 as a thickening agent (solid content: 1.0 g, water content) 30.0 g) and 40.0 g (solid content: 1.0 g, water content: 39.0 g) of 2.5% aqueous solution of high molecular weight polyethylene oxide (M-sei Chemical E-160) having an average molecular weight of 3.6 million to 4 million did. That is, the solid content compounding amount of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as the thickener was increased as compared with Example 1. A microporous layer paste of Example 3 was prepared under the same conditions as in Example 1 except that the blending amounts were different.

  Example 4 uses polyethylene oxide having an average molecular weight of 600,000 to 1,100,000 (PEO-3 manufactured by Sumitomo Seika Co., Ltd.) as the low molecular weight polyethylene oxide of the thickener, and the average molecular weight of the low molecular weight polyethylene oxide as the thickener is A microporous layer paste of Example 4 was prepared under the same conditions as in Example 1 except for the differences.

  Example 5 uses polyethylene oxide (PEO-8 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.7 to 2.2 million as the high molecular weight polyethylene oxide of the thickener, and the average molecular weight of the high molecular weight polyethylene oxide as the thickener is A microporous layer paste of Example 5 was prepared under the same conditions as in Example 1 except for the differences.

  Example 6 uses polyethylene oxide having an average molecular weight of 5.5 million to 6.5 million (E-300 manufactured by Meisei Chemical Co., Ltd.) as the high molecular weight polyethylene oxide as the thickener, and the average molecular weight of the high molecular weight polyethylene oxide as the thickener is different. The microporous layer paste of Example 6 was prepared under the same conditions as in Example 1 except for the above.

Next, the microporous layer pastes of Comparative Examples 1 to 9 produced for comparison will be described.
[Comparative example]
In Comparative Example 1, a microporous layer paste was prepared using only a low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 as a thickener.
That is, acetylene black of carbon particles as a conductive material (made by Denki Kagaku Kogyo Co., Ltd .: 75.0 g of trade name “Denka Black”, PTFE emulsion as a water-repellent resin (made by Daikin Industries, Ltd .: POLYFLON PTFE D) -210C [solid content (resin content) 61%]) 41.7 g (solid content 25.4 g, moisture content 16.3 g), Triton X-100 as a dispersant 7.5 g, ion exchange as a dispersion medium 290.0 g of water, 80.0 g of a 1.25% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 to 1,500,000 as a thickener (solid content 1.0 g, moisture Planetary agitation and defoaming device (manufactured by Kurashiki Boseki Co., Ltd .: trade name “Mazerusta”) KK-1000W ") was at 3 minutes mixing and dispersion of Comparative Example 1 by and defoamed microporous layer paste.

  Also in Comparative Example 2, only a low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 was used as a thickener, but a low molecular weight polyethylene oxide having an average molecular weight of 1,100,000 to 1,500,000 (PEO-4 manufactured by Sumitomo Seika Co., Ltd.). 80.0 g (solid content 2.0 g, moisture content 78.0 g), and a low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 as a thickener than Comparative Example 1 The amount of solid content was increased. A microporous layer paste of Comparative Example 2 was prepared under the same conditions as in Comparative Example 1 except that the blending amounts were different.

In Comparative Example 3, a microporous layer paste was prepared without using polyethylene oxide as a thickener.
That is, acetylene black of carbon particles as a conductive material (made by Denki Kagaku Kogyo Co., Ltd .: 75.0 g of trade name “Denka Black”, PTFE emulsion as a water-repellent resin (made by Daikin Industries, Ltd .: POLYFLON PTFE D) -210C [solid content (resin content) 61%]) 41.7 g (solid content 25.4 g, moisture content 16.3 g), Triton X-100 as a dispersant 7.5 g, ion exchange as a dispersion medium The material containing 375.8 g of water was mixed, dispersed and removed for 3 minutes using a planetary agitation and deaerator (trade name “Mazerustar KK-1000W” manufactured by Kurashiki Boseki Co., Ltd.) set at 600 rpm for revolution and 600 rpm for rotation. It was set as the microporous layer paste of the comparative example 3 by bubbling.

In Comparative Example 4, a microporous layer paste was prepared using only high molecular weight polyethylene oxide having an average molecular weight of 3.6 to 4 million as a thickener.
That is, acetylene black of carbon particles as a conductive material (made by Denki Kagaku Kogyo Co., Ltd .: 75.0 g of trade name “Denka Black”, PTFE emulsion as a water-repellent resin (made by Daikin Industries, Ltd .: POLYFLON PTFE D) -210C [solid content (resin content) 61%]) 41.7 g (solid content 25.4 g, moisture content 16.3 g), Triton X-100 as a dispersant 7.5 g, ion exchange as a dispersion medium Mix and disperse and degas for 3 minutes with a planetary agitation / deaerator (trade name “Mazerustar KK-1000W” manufactured by Kurashiki Boseki Co., Ltd.) set to revolution 8 and rotation 9. Next, an 80% 1.25% aqueous solution of high molecular weight polyethylene oxide (E-160, manufactured by Meisei Chemical Co., Ltd.) having an average molecular weight of 3.6 to 4 million is used as a thickener in this mixed material. 0g (solid content 1.0g, moisture content 79.0g) is blended and mixed with a three-one motor (HEIDON: HEIDON 600G) as a stirrer with a 10cm diameter propeller attached and rotated at 300rpm. By defoaming, the paste for the microporous layer of Comparative Example 4 was obtained.

  In Comparative Example 5, 40.0 g (0.5 g solid content, water content) of a 1.25% aqueous solution of low molecular weight polyethylene oxide (PEO-4, manufactured by Sumitomo Seika) having an average molecular weight of 1.1 to 1,500,000 as a thickener 39.5 g) and 40.0 g (solid content 0.1 g, water content 39.9 g) of a 0.25% aqueous solution of high molecular weight polyethylene oxide (Meisei Chemical E-160) having an average molecular weight of 3.6 million to 4 million did. That is, the microporous layer paste of Comparative Example 5 was prepared under the same conditions as in Example 1 except that the amount of the solid content of the high molecular weight polyethylene oxide was smaller than that of Example 1 and the amount was different. .

  In Comparative Example 6, 40.0 g (0.5 g solid content, water content) of a 1.25% aqueous solution of a low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 million to 1,500,000 as a thickener. 39.5 g) and 3 of high molecular weight polyethylene oxide (Esei-160, manufactured by Meisei Chemical Co., Ltd.) having an average molecular weight of 3.6 to 4 million. % Aqueous solution was blended in an amount of 40.0 g (solid content 1.2 g, moisture content 38.8 g). That is, the solid content blending amount of the high molecular weight polyethylene oxide was increased from that in Example 1, and the microporous layer paste of Comparative Example 6 was prepared under the same conditions as in Example 1 except that the blending amount was different.

  In Comparative Example 7, 40.0 g of a 3% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 to 1,500,000 as a thickener (solid content: 1.2 g, water content: 38. 80.0) and 2.5% aqueous solution of high molecular weight polyethylene oxide (E-160 manufactured by Meisei Chemical Co., Ltd.) having an average molecular weight of 3.6 million to 4 million was blended in an amount of 40.0 g (solid content 1.0 g, moisture content 39.0 g). That is, the solid content blending amount of the low molecular weight polyethylene oxide was increased as compared with Example 3, and the microporous layer paste of Comparative Example 7 was prepared under the same conditions as in Example 3 except that the blending amount was different.

  In Comparative Example 8, 40.0 g of a 2.5% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 1.1 million to 1,500,000 as a thickening agent (1.0 g of solid content, moisture) 30.0 g) and a 3% aqueous solution of a high molecular weight polyethylene oxide (E-160 manufactured by Meisei Chemical Co., Ltd.) having an average molecular weight of 3.6 million to 4 million was blended with 40.0 g (solid content 1.2 g, moisture content 38.8 g). . That is, the solid content blending amount of the high molecular weight polyethylene oxide was increased from that in Example 3, and the microporous layer paste of Comparative Example 8 was prepared under the same conditions as in Example 3 except that the blending amount was different.

  In Comparative Example 9, 40.0 g (0.5 g solid content, water content) of a 1.25% aqueous solution of low molecular weight polyethylene oxide (PEO-4 manufactured by Sumitomo Seika) having an average molecular weight of 1.1 to 1,500,000 as a thickener 30.0 g) and 40.0 g of a 0.125% aqueous solution of high molecular weight polyethylene oxide (PEO-27 manufactured by Sumitomo Seika Co., Ltd.) having an average molecular weight of 6 to 8 million (solid content 0.5 g, moisture content 39.5 g) Blended. That is, as high molecular weight polyethylene oxide, polyethylene oxide having a higher average molecular weight than those in Examples 1 and 6 was used, and the high molecular weight polyethylene oxide was the same as in Examples 1 and 6 except that the average molecular weight was different. The microporous layer paste of Comparative Example 9 was prepared under the above conditions.

And about the paste for microporous layer formation which consists of the paste composition for microporous layers of each Example and each comparative example, the evaluation test of smoothness and a strike-through was done.
Specifically, after impregnating with PTFE Marujon (Daikin Kogyo Co., Ltd .: POLYFLON PTFE D-210C [solid content (resin content) 61%]) so as to have a basis weight of 1 mg / cm ² , water repellent by drying. Various pastes on various carbon papers (CP1, CP2, CP3) as treated substrates 16 using a thin film coating tool (die head), carbon paper moving speed 1.0 m / min, basis weight 5.0 mg / cm ² applied. After the application, the diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) having a microporous layer formed on the surface layer 15 was produced by drying and baking at 300 ° C. for 30 minutes. Table 3 shows the thickness and the porosity of the carbon paper (CP1, CP2, CP3) as the base material 16 to which various pastes are applied. Here, the thickness and the porosity of the base material 16 are different. Various diffusion layers 14 were prepared using three types of carbon paper (CP1, CP2, CP3). In addition, the porosity of this carbon paper is the ratio of the space | gap when the cross section of carbon paper is observed by SEM.

The smoothness was evaluated by observing the uniformity of the surface appearance of the microporous layer formed as the surface layer 15 of the diffusion layer 14, that is, the presence or absence of irregularities. The film thickness of 5 points in total in the center and 4 corners of the surface layer 15 within the range of 3 cm in length and 3.6 cm in width was measured with a digital dial gauge at a pressure of 0.1 MPa, and each of the measured 5 points of film was measured. When the thickness was less than ± 20% with respect to the average film thickness, it was determined that there was no unevenness, and when the difference was ± 20% or more, it was determined that there was unevenness.
Moreover, about the back-through, the back side a of the paste application surface of the carbon paper (base material 16) was observed in the produced diffusion layer 14. On the back side a of the paste application surface, the presence or absence of carbon particles of acetylene black, which is a paste component, was visually confirmed. The case where no carbon particles were present was judged as ◯, and the case where carbon particles were present was judged as x. That is, when the paste was applied to carbon paper having a porosity of 80% or less, it was determined that the case where carbon particles were not present on the back side a of the application surface to the carbon paper was judged as ○, and the through-through was suppressed. .

  Tables 1 and 2 collectively show the blending compositions of these Examples and Comparative Examples, and the evaluation results of the smoothness and back-through. Table 3 shows the thickness and porosity of the carbon paper (CP1, CP2, CP3) used as the base material 16 to which the paste is applied.

In Examples 1 to 6, the prepared microporous layer forming paste has good flow characteristics, and can be applied smoothly and uniformly on the carbon paper as the substrate 16, and the microporous layer forming paste is applied. The microporous layer of the diffusion layer 14 obtained by drying and firing was smooth with no irregularities. Therefore, it was confirmed that the smoothness is good.
In addition, the presence of carbon particles as a paste component was confirmed on the back side a of the paste application surface of all the carbon papers (CP1, CP2, CP3) used as the base material 16, that is, the carbon paper having a porosity of 80% or less. In other words, the penetration of the paste component into the base material 16 was suppressed.
Thus, in Examples 1 to 6, it was confirmed that the penetration of the paste components was suppressed and the smoothness was also good.

  On the other hand, Comparative Example 1 and Comparative Example 2 are compositions using only low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 as a thickener. In Comparative Example 1 and Comparative Example 2, the microporous layer of the obtained diffusion layer 14 was smooth with no irregularities, and good smoothness was confirmed. However, the presence of carbon particles as the paste component was confirmed on the back side a of the paste application surface of all the carbon paper, and the back penetration of the paste component to the base material 16 occurred.

  Moreover, the comparative example 3 is a composition which does not use the polyethylene oxide as a thickener. In Comparative Example 3, since the flow characteristics of the microporous layer paste were poor and a uniform coating film could not be produced on the carbon paper as the substrate 16, the microporous layer of the obtained diffusion layer 14 was used. Had irregularities and poor smoothness. In addition, the presence of carbon particles as the paste component was confirmed on the back side a of the paste application surface of all the carbon papers, and the back-through of the paste component to the base material 16 was also caused.

  Furthermore, the comparative example 4 is a composition which uses only high molecular weight polyethylene oxide whose average molecular weight is 3.6 million to 4 million as a thickener. In Comparative Example 4, the effect of suppressing the breakthrough of the paste component was confirmed. However, since the flow characteristics of the microporous layer paste are poor and a uniform film could not be produced on the carbon paper as the base material 16, the microporous layer of the obtained diffusion layer 14 has irregularities, The smoothness was poor.

  Comparative Example 5 is a blend of low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 as a thickener and high molecular weight polyethylene oxide having an average molecular weight of 3.6 million to 4 million, but the solid content of acetylene black and PTFE emulsion. This is a composition in which the solid content of the low molecular weight polyethylene oxide is 0.5 parts by weight and the solid content of the high molecular weight polyethylene oxide is 0.1 parts by weight with respect to 100 parts by weight of the total solid content. In Comparative Example 5, the microporous layer of the obtained diffusion layer 14 was smooth without any irregularities, and good smoothness was confirmed. However, since the solid content of the high molecular weight polyethylene oxide is small, the penetration of paste components into the base material 16 is suppressed when applying paste to CP3 carbon paper (thickness 0.28 mm, porosity 78%). In the paste application to CP1 carbon paper (thickness 0.11 mm, porosity 80%) and CP2 carbon paper (thickness 0.19 mm, porosity 78%), on the back side a of the paste application surface The presence of carbon particles as the paste component was confirmed, and the back-through of the paste component to the base material 16 occurred.

  Comparative Example 6 is a blend of low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 and high molecular weight polyethylene oxide having an average molecular weight of 3,600,000 to 4,000,000 as a thickener, but acetylene black and PTFE emulsion. This is a composition in which the solid content of low molecular weight polyethylene oxide is 0.5 parts by weight and the solid content of high molecular weight polyethylene oxide is 1.2 parts by weight with respect to 100 parts by weight of the total solid content. In Comparative Example 6, the effect of suppressing the penetration of the paste component was confirmed. However, since the solid content of the high molecular weight polyethylene oxide is large, the flow characteristics of the microporous layer paste are lowered, making it difficult to produce a uniform film on the carbon paper as the substrate 16, and the diffusion layer 14 Concavities and convexities were likely to occur in the microporous layer, and the smoothness was poor.

  Furthermore, although the comparative example 7 mix | blends the low molecular weight polyethylene oxide whose average molecular weight is 1.1 million to 1.5 million and the high molecular weight polyethylene oxide whose average molecular weight is 3.6 million to 4 million as a thickener, it is solid of acetylene black and PTFE emulsion. This is a composition in which the solid content of low molecular weight polyethylene oxide is 1.2 parts by weight and the solid content of high molecular weight polyethylene oxide is 1.0 part by weight with respect to 100 parts by weight of the total amount. In Comparative Example 7, the effect of suppressing the breakthrough of the paste component was confirmed. However, since the amount of the solid content of the low molecular weight polyethylene oxide is large, the flow characteristics of the microporous layer paste are high, making it difficult to produce a uniform film on the carbon paper as the substrate 16, and the microlayer of the diffusion layer 14. Unevenness was likely to occur in the porous layer, and the smoothness was poor.

  Comparative Example 8 is a blend of low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 and high molecular weight polyethylene oxide having an average molecular weight of 3.6 million to 4 million as a thickener, but the total solid content of acetylene black and PTFE emulsion. This is a composition in which the solid content of low molecular weight polyethylene oxide is 1.0 part by weight and the solid content of high molecular weight polyethylene oxide is 1.2 parts by weight with respect to 100 parts by weight. In Comparative Example 8, the effect of suppressing the breakthrough of the paste component was confirmed. However, since the solid content of the high molecular weight polyethylene oxide is large, the flow characteristics of the microporous layer paste are lowered, making it difficult to produce a uniform film on the carbon paper as the substrate 16, and the diffusion layer 14 Concavities and convexities were likely to occur in the microporous layer, and the smoothness was poor.

In Comparative Example 9, a low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 as a thickener and a high molecular weight polyethylene oxide having an average molecular weight of 6 million to 8 million were blended, and solids of acetylene black and PTFE emulsion were mixed. This is a composition in which the solid content of low molecular weight polyethylene oxide is 0.5 parts by weight and the solid content of high molecular weight polyethylene oxide is 0.5 parts by weight with respect to 100 parts by weight of the total amount. In Comparative Example 9, the effect of suppressing the breakthrough of the paste component was confirmed. However, since the blended high molecular weight polyethylene oxide has a large average molecular weight, the flow characteristics of the microporous layer paste are deteriorated, making it difficult to produce a uniform film on the carbon paper as the base material 16. Concavities and convexities were likely to occur in the microporous layer, and the smoothness was poor.
In the above Examples and Comparative Examples, the drying and baking temperature was 300 ° C., and the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as the thickener were thermally decomposed. Therefore, an increase in load in the drying / firing process is suppressed.

  From the above results, by using a low molecular weight polyethylene oxide having an average molecular weight in the range of 600,000 to less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight in the range of 1.6 million to 6.5 million as a thickener. Since the flow characteristics are good and the coating amount on the substrate 16 can be made uniform, a smooth microporous layer (coating film) without unevenness can be formed, the smoothness is good, and the paste component is applied to the substrate 16. It becomes the paste for microporous layers which can suppress a back-through.

Here, according to the experimental study by the present inventors, when the average molecular weight of the polyethylene oxide on the low molecular weight side is less than 600,000, the sagging after coating and the penetration into the base material occur, resulting in a decrease in power in the fuel cell. There is a risk of inviting. Further, when the average molecular weight of the polyethylene oxide on the high molecular weight side exceeds 6.5 million, as shown in Comparative Example 9, it is difficult to produce a uniform film on the base material 16 due to a decrease in flow characteristics. Unevenness is likely to occur in the microporous layer of the layer 14. Moreover, since it is difficult to dissolve in ion-exchanged water and handling becomes difficult, it is not suitable for practical use.
Accordingly, the average molecular weight of the low molecular weight polyethylene oxide as a thickener is in the range of less than 600000 to 1600000, have an average molecular weight of the high molecular weight polyethylene oxide is in the range of 1 6 00,000 to 6,500,000 preferable.

Further, from the comparison between Example 1 to Example 6 and Comparative Example 5 to Comparative Example 8, the solid content of low molecular weight polyethylene oxide was 0 with respect to 100 parts by weight of the total solid content of acetylene black and PTFE emulsion. It is within the range of 2 parts by weight to 1.1 parts by weight, and the blending amount of the solid content of the high molecular weight polyethylene oxide is within the range of 0.3 parts by weight to 1.0 part by weight. And the paste for microporous layers which exhibits the remarkable strike-through suppression effect is obtained reliably.
That is, when the solid content of the low molecular weight polyethylene oxide is less than 0.2 parts by weight, the blending amount of the low molecular weight polyethylene oxide is small and the smoothness may be lowered. When the amount exceeds 50 parts, as shown in Comparative Example 7, since the blending amount of the low molecular weight polyethylene oxide is large, the flow characteristics are deteriorated, and it is difficult to produce a uniform film on the substrate 16. Concavities and convexities are easily generated in the microporous layer, and the smoothness is lowered.
Further, when the solid content of the high molecular weight polyethylene oxide is less than 0.2 parts by weight, as shown in Comparative Example 5, the amount of the high molecular weight polyethylene oxide is small enough to suppress the show-through. On the other hand, when it exceeds 1.1 parts by weight, as shown in Comparative Example 6 and Comparative Example 8, the increase in viscosity is large due to the large amount of high molecular weight polyethylene oxide. Therefore, it is difficult to produce a uniform film on the substrate 16, and unevenness is likely to occur in the microporous layer of the diffusion layer 14, resulting in a decrease in smoothness.
Therefore, the solid content of the low molecular weight polyethylene oxide is in the range of 0.2 to 1.1 parts by weight with respect to 100 parts by weight of the total solids of acetylene black and PTFE emulsion, and the high molecular weight polyethylene oxide The solid content is preferably in the range of 0.3 to 1.0 part by weight.

Further, as shown in Examples 1 to 6, the total solid content of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as the thickener is the total solid content of acetylene black and PTFE emulsion. It is preferable to be within the range of 0.5 to 2.5 parts by weight with respect to parts by weight.
According to the experimental study by the present inventors, the total solid content of low molecular weight polyethylene oxide and high molecular weight polyethylene oxide as a thickener is 100 parts by weight of the total solid content of acetylene black and PTFE emulsion. When the amount is less than 0.5 parts by weight, the blending amount of the thickener is small, and the viscosity characteristic that ensures the effect of suppressing the back-through and good smoothness cannot be obtained. It has been confirmed that the increase in viscosity increases and the smoothness decreases.
Therefore, the total solid content of the low molecular weight polyethylene oxide and the high molecular weight polyethylene oxide as the thickener is 0.5 parts by weight to 2 parts per 100 parts by weight of the total solids of the acetylene black and the PTFE emulsion. By being within the range of 5 parts by weight, it is possible to more reliably ensure the effect of suppressing the breakthrough and good smoothness.

In the above examples, the low molecular weight polyethylene oxide having an average molecular weight of 1.1 million to 1,500,000 and the high molecular weight polyethylene oxide having an average molecular weight of 6 million to 8 million were used as a thickener. It decomposes and volatilizes from the microporous layer and does not affect the characteristics of the microporous layer.
That is, the characteristics required for the microporous layer (coating film) such as suppression of paste component back-through and smoothness of the coating film can be achieved at the same time without increasing the load in the drying process.

Thus, in the fuel cell in which the gas diffusion layer 14 is formed by applying the microporous layer paste to the surface of the base material 16 (cathode side base material 16A or anode side base material 16B) such as carbon paper, the microporous layer is formed. Even when the paste composition contains a conductive material such as acetylene black, a water repellent resin such as PTFE emulsion, and a dispersant such as Triton X-100, the average molecular weight as a thickener in the paste composition for forming a microporous layer There by low molecular weight polyethylene oxide and an average molecular weight in the range of 600000 to 1500000 is used in combination high molecular weight polyethylene oxide in the range of 1 6 00000-6500000, the drying process can be dried at 300 ° C. Without increasing the load more than necessary, the penetration of paste components into the substrate 16 is suppressed. Is, moreover, possible to form a microporous layer of smooth gas diffusion layer 14 without irregularities.

  As described above, the microporous layer forming paste composition of the above embodiment includes a conductive powder such as carbon particles, a water repellent resin such as PTFE emulsion, a dispersant such as Triton X-100, and a thickener. A paste composition containing a low molecular weight polyethylene oxide having an average molecular weight of 1,500,000 or less and a high molecular weight polyethylene oxide having an average molecular weight of 1,700,000 or more as a thickener. Conductive powder such as PTFE emulsion, water repellent resin such as PTFE emulsion, dispersant such as Triton X-100, dispersion medium such as ion-exchanged water, and low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million as a thickener The mixed material is mixed and dispersed for a predetermined time with a planetary stirring and defoaming device, and then the average molecular weight is 1.6 million or more as a thickener. A high-molecular-weight polyethylene oxide is blended and mixed with a stirrer to form a microporous layer paste, which is applied to a base material 16 of a conductive porous material such as carbon paper, and dried and fired to form a gas diffusion layer. This is a manufacturing method for forming 14 microporous layers.

  The manufacturing method of the microporous layer forming paste composition of the above embodiment includes conductive powder such as carbon particles, water repellent resin such as PTFE emulsion, dispersant such as Triton X-100, ion-exchanged water, and the like. A mixture of the above dispersion medium and a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million as a thickener is mixed and dispersed for a predetermined time using a planetary stirring and defoaming device, and then further an average molecular weight as a thickener. Is a paste for a microporous layer by blending a high molecular weight polyethylene oxide of 1.6 million or more and mixing with a stirrer.

  In the above embodiment, as a thickener, a low molecular weight polyethylene oxide having an average molecular weight of less than 1.6 million and a high molecular weight polyethylene oxide having an average molecular weight of 1.6 million or more are used in combination, whereby the average molecular weight is less than 1.6 million. Polyethylene oxide on the low molecular weight side can ensure the viscosity characteristics suitable for coating, and the high molecular weight side polyethylene oxide can ensure the viscosity characteristics to suppress the back-through of the paste component, providing good smoothness and paste component base material It is possible to effectively secure both the back-through suppression to the back surface. And as a thickener, in order to ensure the characteristics required at the time of microporous layer formation by using polyethylene oxide of a water-soluble resin that thermally decomposes at less than 300 ° C. even when the molecular weight increases, Without increasing the load more than necessary, it is possible to satisfy both good smoothness and suppression of paste component penetration.

  Thus, in the above embodiment, the microporous layer and the microporous layer are prevented from passing through to the back surface of the base material of the diffusion layer required for stabilizing the output of the fuel cell without increasing the load of the drying process more than necessary. Smoothness can be ensured. Therefore, by suppressing the penetration of the paste component, the water repellency of the back surface of the base material is not lowered, and a smooth microporous layer can be obtained, so that gas diffusion can be made uniform and the adhesion to the catalyst layer can be improved. Therefore, a stable output can be secured in the fuel cell.

In carrying out the present invention, the composition, components, blending amount, material, etc. of other parts of the microporous layer-forming paste composition, and other steps of the method for producing the microporous layer-forming paste composition However, the present invention is not limited to this embodiment.
In addition, the numerical values listed in the embodiment of the present invention do not indicate critical values but indicate appropriate values suitable for implementation, and therefore, even if the numerical values are slightly changed, the implementation is denied. is not.

DESCRIPTION OF SYMBOLS 1 Fuel cell 11 Electrolyte membrane 10 Membrane-electrode assembly 12 Electrode (cathode electrode 12A, anode electrode 12B)
13 catalyst layer (cathode side catalyst layer 13A, anode side catalyst layer 13B)
14 diffusion layer (cathode side diffusion layer 14A, anode side diffusion layer 14B)
15 surface layers (cathode side surface layer 15A, anode side surface layer 15B)
16 base materials (cathode side base material 16A, anode side base material 16B)
a Back of base material

Claims (4)

Conductive powder and a water-repellent resin, a dispersant, a paste composition containing a thickening agent, as the thickener, low average molecular weight in the range of less than 600,000 or more to 160 ten thousand Combined use of molecular weight polyethylene oxide and high molecular weight polyethylene oxide having an average molecular weight in the range of from 1.6 million to 6.5 million ,
The solid content of the low molecular weight polyethylene oxide is in the range of 0.2 to 1.1 parts by weight with respect to 100 parts by weight of the total solids of the conductive powder and the water repellent resin, A paste composition for forming a microporous layer, wherein the solid content of the high molecular weight polyethylene oxide is in the range of 0.3 to 1.0 part by weight . Carbon particles as a conductive material, PTFE emulsion as a water repellent resin, a dispersant , a low molecular weight polyethylene oxide having an average molecular weight in the range of 600,000 to less than 1.6 million as a thickener, and an average molecular weight Containing high molecular weight polyethylene oxide in the range of 1.6 million to 6.5 million ,
The solid content of the low molecular weight polyethylene oxide is in the range of 0.2 parts by weight to 1.1 parts by weight with respect to 100 parts by weight of the total solids of the carbon particles and the PTFE emulsion. The solid content of polyethylene oxide having a molecular weight is in the range of 0.3 to 1.0 part by weight,
At least the dispersant and the carbon particles and the PTFE emulsion is microporous layer forming paste composition characterized in that the predetermined time mixed and dispersed in a planetary stirrer-deaerator. A mixed material of carbon particles as a conductive material, PTFE emulsion as a water repellent resin, a dispersant, and a low molecular weight polyethylene oxide having an average molecular weight in the range of 600,000 to less than 1.6 million as a thickener. Is mixed and dispersed for a predetermined time with a planetary stirring and defoaming device, and then blended with a high molecular weight polyethylene oxide having an average molecular weight in the range of 1.6 million to 6.5 million as a thickener and mixed with a stirrer. To make a paste for the microporous layer ,
The solid content of the low molecular weight polyethylene oxide is in the range of 0.2 to 1.1 parts by weight with respect to 100 parts by weight of the total solids of the carbon particles and the PTFE emulsion, and the high molecular weight The manufacturing method of the paste composition for microporous layer formation characterized by making solid content of polyethylene oxide into the range of 0.3 weight part-1.0 weight part . The method for producing a paste composition for forming a microporous layer according to claim 3, wherein the microporous layer paste is applied to a substrate made of a conductive porous material to form a microporous layer. .

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