JP6439263B2 - Gas diffusion electrode manufacturing equipment - Google Patents

Description

  A fuel cell is a mechanism that electrically extracts energy generated when water is generated by reacting hydrogen and oxygen, and is expected to be clean energy because it has high energy efficiency and only emits water. The present invention relates to a gas diffusion electrode used for a fuel cell and a method for manufacturing the same, and more particularly, to a method and a method for manufacturing a gas diffusion electrode used for a polymer electrolyte fuel cell used as a power source for a fuel cell vehicle. Relates to the device.

  An electrode used in a polymer electrolyte fuel cell is sandwiched between two separators in a polymer electrolyte fuel cell, and is disposed between the two separators. On both surfaces of the polymer electrolyte membrane, the electrode is on the surface of the polymer electrolyte membrane. It has a structure comprising a formed catalyst layer and a gas diffusion layer formed outside the catalyst layer. A gas diffusion electrode is distributed as an individual member for forming a gas diffusion layer on the electrode. The performance required for the gas diffusion electrode includes, for example, gas diffusivity, conductivity for collecting electricity generated in the catalyst layer, and drainage for efficiently removing moisture generated on the surface of the catalyst layer. can give. In order to obtain such a gas diffusion electrode, generally, a conductive porous substrate having gas diffusion ability and conductivity is used.

  Specifically, carbon felt made of carbon fiber, carbon paper, carbon cloth, and the like are used as the conductive porous substrate, and carbon paper is most preferable from the viewpoint of mechanical strength.

  In addition, since a fuel cell is a system that electrically extracts energy generated when hydrogen and oxygen react to produce water, when the electrical load increases, that is, when the current taken out of the cell increases, a large amount of water ( When the water vapor is condensed and becomes water droplets at low temperatures, and the pores of the gas diffusion electrode are blocked, the amount of gas (oxygen or hydrogen) supplied to the catalyst layer decreases, and finally all If the pores are blocked, the power generation stops (this phenomenon is called flooding).

  In other words, in order to prevent the flooding from occurring as much as possible, the gas diffusion electrode is required to have drainage in order to increase the current value causing the flooding as much as possible. As means for improving the drainage, the water repellency is usually increased by using a gas diffusion electrode base material obtained by subjecting the conductive porous base material to water repellency treatment.

  Further, when the conductive porous substrate subjected to the water repellent treatment as described above is used as a gas diffusion electrode as it is, the fiber has a coarse mesh, so that when water vapor condenses, large water droplets are generated and flooding is likely to occur. For this reason, a layer called a microporous layer (microporous layer) is formed by applying a coating liquid in which conductive fine particles such as carbon black are dispersed on a conductive porous substrate that has been subjected to a water repellent treatment, followed by drying and sintering. May also be provided). In order to impart water repellency to this microporous layer, it is known to contain a fluorine-based resin as a water repellent material (Patent Documents 1, 2, and 3). In addition to the above, the role of the microporous layer is to prevent the catalyst layer from penetrating into the gas diffusion electrode base material with a coarse mesh (Patent Document 4), and the roughness of the conductive porous base material to the electrolyte membrane There is a retouching effect to prevent transfer.

  Since the water repellent material preferably has as high a water repellency as possible, a fluorine-based resin is preferably used. Among these, PTFE, FEP, etc., which can obtain particularly high water repellency, are preferably used. These fluororesins are usually marketed in a dispersion state in which they are dispersed in a water-based dispersion medium with a dispersant such as a surfactant. Water-based coating is also preferable from the viewpoint of reducing environmental burden.

  As described above, it is preferable that the conductive porous substrate is subjected to water repellent treatment to provide a microporous layer. A microporous layer is formed by applying a coating liquid in which conductive fine particles such as carbon black and a water repellent material such as fluororesin are mixed and dispersed on a conductive porous substrate. In order to disperse in a dispersion medium, a surfactant is usually used as a dispersant or a dispersion stabilizer.

  Further, as described above, it is desirable to apply the microporous layer to a certain degree of thickness in order to function the retouching effect for preventing the roughness of the conductive porous substrate from being transferred to the electrolyte membrane. In order to form a coating film having a large thickness, it is desirable that the viscosity is high within a range suitable for coating. Further, since the conductive porous substrate is porous, there is a possibility that the coating liquid may come off on the back side when a coating liquid having a low viscosity is applied to the surface. An organic compound may be used as a thickener in order to increase the viscosity of the microporous layer coating solution. If the surfactant used as the dispersant has a thickening action, it may be added in a large amount and used as a thickening agent.

  On the other hand, in order to improve the gas diffusibility and conductivity of the gas diffusion electrode, there are some dispersants for dispersing the water repellent material, dispersants for dispersing conductive fine particles such as carbon black in the microporous layer, and thickeners. Need to be removed by the method. By removing the gas, a gas diffusion path can be formed, and a water vapor or condensed water drainage path can be formed.

  Conventionally, as represented by Patent Document 1, a method for producing a gas diffusion layer is such that a conductive porous substrate is subjected to a water-repellent treatment, dried, if necessary, sintered, coated with a microporous layer, dried, and sintered. A process has been taken. Here, the significance of the sintering step is to remove the surfactant used as a dispersant and to melt the water repellent material such as a fluorine resin once to enhance the function as a binder.

Japanese Patent No. 3382213 JP 2002-352807 A JP 2000-123842 A Japanese Patent No. 3773325

  However, in order to enhance the dispersibility, dispersion stability, or thickening action of the coating solution for the microporous layer as described above, it is necessary to use a large amount of the surfactant used for this purpose. In a normal pigment dispersion coating solution, the surfactant used as a dispersing agent may be an addition amount of at most several percent of the pigment, but in the case of a coating solution for forming a gas diffusion layer, several tens of percent or more. A surfactant may be added. In such a case, it has not been clarified how to perform the above-described sintering step to obtain a gas diffusion electrode that is safe, efficient, and good in performance.

  For example, as described in Patent Document 1, after applying a microporous layer and drying water as a dispersion medium, when introduced into a sintering process at 360 ° C., the surfactant is rapidly decomposed and the combustible gas is generated. There is a risk that it will burn and ignite. Alternatively, when the fluororesin, which is a water repellent material, is semi-melted and bound to the conductive fine particles, if the undecomposed surfactant remains, the binding cannot be completed and the conductive fine particles fall off. Cheap. Furthermore, if the conductive fine particles and the fluororesin are not sufficiently bound, when the gas diffusion electrode is incorporated into the fuel cell, condensation of water vapor generated at the cathode on the surface of the conductive fine particles is likely to occur, resulting in a high current density. There is a possibility that the power generation performance will be reduced. Patent Document 2 discloses a technique for binding a fluororesin and conductive fine particles by hot pressing after sintering, but the voids in the microporous layer are crushed by pressing, and the microporous layer There was a problem that the diffusibility of the gas inside was impaired and the power generation performance was lowered.

  An object of the present invention is to provide a manufacturing method and a manufacturing apparatus capable of mass-producing a gas diffusion electrode having good power generation performance as a gas diffusion electrode with high safety and high productivity.

The gas diffusion electrode manufacturing method of the present invention employs the following means in order to solve the above problems. That is, a method for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell, in which a microporous layer is formed on at least one surface of a conductive porous substrate, wherein the conductive fine particles are formed on the conductive porous substrate. , A coating liquid coating process for coating a microporous layer coating liquid containing a water repellent resin, a dispersion medium and a surfactant, a coating liquid drying process for drying the microporous layer coating liquid to remove the dispersion medium, and a surfactant A first heat treatment step of heat-treating at a temperature capable of removing water, and a second heat treatment step of heat-treating the conductive porous substrate that has undergone the first heat treatment step at a temperature equal to or higher than the melting point of the water repellent. It is a manufacturing method of a gas diffusion electrode.
A method for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell in which a microporous layer is formed on at least one surface of an electrically conductive porous substrate,
An unwinding step of unwinding the conductive porous substrate from a wound body obtained by winding a long conductive porous substrate into a roll;
A coating liquid coating step of coating a microporous layer coating liquid containing conductive fine particles, a water-repellent resin, a dispersion medium and a surfactant on the conductive porous substrate;
A coating liquid drying step of drying the microporous layer coating liquid to remove the dispersion medium,
A first heat treatment step of heat treatment at a temperature at which the surfactant can be removed and less than 350 ° C .;
A second heat treatment step of heat treating the conductive porous substrate that has undergone the first heat treatment step at a temperature equal to or higher than the melting point of the water-repellent resin; and
Including a winding step of winding the gas diffusion electrode obtained through the second heat treatment step,
It is a manufacturing method of a gas diffusion electrode.

Moreover, in order to solve said subject, the manufacturing apparatus of the gas diffusion electrode of this invention employs one of the following means.
A device for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell in which a microporous layer is formed on at least one surface of a conductive porous substrate, which is a long conductive porous substrate wound in a roll shape A first heat treatment furnace for removing the surfactant from the conductive porous substrate that is unwound by the unwinder and unwinder for unwinding the material and previously formed with the microporous layer precursor; In order to wind up the gas diffusion electrode obtained through the second heat treatment furnace and the second heat treatment furnace for further heat-treating the conductive porous substrate through the heat treatment furnace and sintering the water-repellent resin. An apparatus for producing a gas diffusion electrode, wherein the first heat treatment furnace is a single-pass heat treatment furnace and the second heat treatment furnace is a hot air circulation heat treatment furnace.
A device for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell in which a microporous layer is formed on at least one surface of a conductive porous substrate, which is a long conductive porous substrate wound in a roll shape An unwinding machine for unwinding the material, a coating machine for applying a microporous layer coating liquid on the conductive porous substrate unwound by the unwinding machine, and a microporous material from the conductive porous substrate A dryer for drying the layer coating liquid, a first heat treatment furnace for removing the surfactant from the substrate dried by the dryer, and a conductive porous substrate through the first heat treatment furnace A second heat treatment furnace for heat treatment and sintering of the water repellent resin, and a winder for winding up the gas diffusion electrode obtained through the second heat treatment furnace, the first heat treatment furnace, It is a single-pass heat treatment furnace, and the second heat treatment furnace is a hot air circulation heat treatment furnace. An apparatus for manufacturing a gas diffusion electrode.

The following effects can be expected by using the gas diffusion electrode manufacturing method and manufacturing apparatus of the present invention.
-Gas diffusion electrodes can be manufactured without risk of ignition during manufacture.
・ Energy consumption can be reduced in manufacturing.
-A gas diffusion electrode with high gas diffusibility and good drainage can be produced, and when it is used, a fuel cell with high power generation performance can be obtained.

Schematic diagram of a take-up type transport device used in the examples Schematic of the water-repellent treatment apparatus used in Example 1 Schematic diagram of die coating equipment used in Example 1 Schematic diagram of die coating equipment used in Example 2 Schematic diagram of die coating equipment used in Examples 3, 4 and 5 Schematic which shows an example of the manufacturing apparatus of the gas diffusion electrode which concerns on this invention In this invention, it is a graph which shows the mode of the weight reduction at the time of thermogravimetric analysis (TG) about the sample after apply | coating and drying a microporous layer coating liquid. It is a graph which shows the mode of the temperature rising in the thermogravimetric analysis (TG) shown in FIG.

  The gas diffusion electrode produced in the present invention has a microporous layer formed on at least one surface of a conductive porous substrate.

  In a polymer electrolyte fuel cell, the gas diffusion electrode has a high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, and a high drainage for discharging the water generated by the electrochemical reaction to the separator. In order to take out the generated electric current, high conductivity is required. For this reason, a conductive porous base material, which is a base material made of a porous body having conductivity and an average pore diameter of usually 10 μm or more and 100 μm or less, is used for the gas diffusion electrode. Specific examples of the conductive porous base material include porous base materials containing carbon fibers such as carbon fiber papermaking bodies, carbon felt, carbon paper, and carbon cloth, foam sintered metal, metal mesh, and expanded metal. It is preferable to use a metal porous substrate such as. Among them, since the corrosion resistance is excellent, it is preferable to use a porous substrate such as carbon felt containing carbon fiber, carbon paper, carbon cloth, and moreover, a property of absorbing a dimensional change in the thickness direction of the electrolyte membrane, That is, since it is excellent in “spring property”, it is preferable to use a base material obtained by binding a carbon fiber papermaking body with a carbide, that is, carbon paper.

  The microporous layer comprises conductive fine particles such as carbon black, carbon nanotubes, carbon nanofibers, chopped fibers of carbon fibers, graphene, and graphite. As the carbon black, acetylene black is preferably used because it has few impurities and hardly reduces the activity of the catalyst. In addition, the microporous layer has characteristics such as conductivity, gas diffusivity, water drainage, moisture retention, and thermal conductivity, as well as strong acid resistance on the anode side inside the fuel cell and oxidation resistance on the cathode side. Therefore, the microporous layer contains a water-repellent resin such as a fluororesin in addition to the conductive fine particles. Examples of the water-repellent resin used for the microporous layer include PTFE (polytetrafluoroethylene) (for example, “Teflon” (registered trademark)), FEP (tetrafluoroethylene hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluoride). Resin), ETFA (ethylene tetrafluoride ethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc., but PTFE or FEP is particularly high in water repellency. Is preferred.

  In order to provide the microporous layer on the conductive porous substrate, a coating liquid coating step of coating a microporous layer coating liquid on the conductive porous substrate is employed. The microporous layer coating liquid comprises a dispersion medium such as water or alcohol and the above-described conductive fine particles, water-repellent resin, and a surfactant as a dispersant for dispersing the conductive fine particles in the dispersion medium. .

  From the viewpoint of productivity, the concentration of the conductive fine particles in the microporous layer coating solution is preferably 5% by mass or more, more preferably 10% by mass or more, with respect to the mass of the entire coating solution. There is no upper limit to the concentration if the viscosity, dispersion stability of the conductive particles, applicability of the coating liquid, and the like are appropriate, but in reality, if it exceeds 50% by mass, the suitability as a coating liquid may be impaired. . In particular, when acetylene black is used as the conductive fine particles, in the study by the present inventors, the upper limit is about 25% by mass in the case of an aqueous coating liquid. Percolation occurs, and the applicability of the coating liquid is impaired due to a sudden increase in viscosity.

  The role of the microporous layer is as follows: (1) protection of the catalyst, (2) re-dressing effect that prevents the surface of the rough conductive porous substrate from being transferred to the electrolyte membrane, and (3) water vapor generated at the cathode. This is an effect of preventing condensation. Among the above, a certain amount of thickness is required for the microporous layer in order to exhibit a re-dressing effect.

  In consideration of the roughness of the conductive porous substrate, the thickness of the microporous layer needs to be 10 μm or more in terms of the dry film thickness, but if it exceeds 60 μm, the electric resistance of the gas diffusion electrode itself is preferably increased. Absent.

  The microporous layer coating liquid is prepared by dispersing conductive fine particles in a dispersion medium (water in the case of an aqueous system) as described above. In order to disperse the conductive fine particles, a dispersant may be added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the conductive fine particles. However, it is effective to increase the amount of the surfactant added as a dispersing agent in order to stabilize this dispersion for a long time, prevent an increase in the viscosity of the coating liquid and prevent the liquid from separating.

  In addition, as described above, when the thickness of the microporous layer is 10 μm or more with a dry coating film, it is preferable to keep the viscosity of the coating liquid at least 1000 mPa · s or more. If the viscosity is lower than this, the coating liquid flows on the surface of the conductive porous substrate, and the coating liquid flows into the pores to cause back-through. On the other hand, if the viscosity is too high, the applicability deteriorates, so the upper limit is about 25 Pa · s. A preferable viscosity range is 3000 mPa · s or more and 20 Pa · s or less, and more preferably 5000 mPa · s or more and 15 Pa · s or less.

  In order to keep the viscosity of the coating liquid at a high viscosity as described above, it is effective to add a thickener. The thickener used here may be a well-known one. For example, surfactants such as methyl cellulose, polyethylene glycol, and polyvinyl alcohol are preferably used as the thickener.

  These dispersants and thickeners may have two functions for the same surfactant, or a surfactant suitable for each function may be selected. However, when the thickener and the dispersant are selected separately, it is necessary to select one that does not break the dispersion of conductive fine particles and the dispersion of a water-repellent resin such as a fluororesin. In any case, in the present invention, a surfactant is used as a dispersant and a thickener. In the scope of the present invention, the total amount of the surfactant is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, and further preferably more than 150 parts by mass per 100 parts by mass of the conductive fine particles. is there. The upper limit of the amount of the surfactant added is 500 parts by mass or less per 100 parts by mass of the conductive fine particles, and if it exceeds this, a large amount of vapor or decomposition gas is generated in the subsequent sintering step, safety, Productivity may be reduced, which is not preferable.

  The presence of metal contamination as a fuel cell member may reduce battery performance due to short circuit or catalyst degradation. Therefore, the surfactant used in the present invention is a nonionic (nonionic) material with a low metal ion content. ) Is preferred. From this point, methyl cellulose, polyethylene glycol, especially ethers of alkylphenol and polyethylene glycol, ethers of higher aliphatic alcohol and polyethylene glycol, polyvinyl alcohol, and the like are preferably used.

  Application of the microporous layer coating liquid to the conductive porous substrate can be performed using various commercially available coating machines. As the coating method, screen printing, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater coating, bar coating, blade coating, etc. can be used, but the surface roughness of the conductive porous substrate However, since the amount of coating can be quantified, die coating is preferred. The coating methods exemplified above are only for illustrative purposes, and are not necessarily limited thereto.

  After passing through the coating liquid coating process, it is subjected to a coating liquid drying process for drying the microporous layer coating liquid in order to remove the dispersion medium (water in the case of an aqueous system). The drying temperature is preferably a temperature at which the surfactant is not removed. Specifically, the drying temperature is preferably from room temperature (around 20 ° C.) to less than 150 ° C., more preferably from 60 ° C. to 120 ° C. The substrate that has undergone the coating liquid drying step becomes a substrate on which a microporous layer precursor containing conductive fine particles, a water-repellent resin, and a surfactant is formed by removing the dispersion medium.

  After the coating liquid drying process, sintering is generally performed for the purpose of removing the surfactant used to disperse the conductive fine particles and for the purpose of binding the conductive fine particles by once melting the water-repellent resin. However, in the present invention, after the coating liquid drying step, the first heat treatment step that mainly removes the surfactant, and the second step that mainly performs the melt-binding of the water-repellent resin, so-called sintering. These heat treatment steps are performed separately at each optimum temperature.

  The heat treatment temperature in the first heat treatment step for removing the surfactant is a temperature at which the surfactant can be removed, that is, a temperature at which the surfactant can be reduced by evaporation or thermal decomposition. In the study by the present inventors, in order to completely remove the surfactant used in the present invention by heat treatment in a short time, it is preferable to perform heat treatment at a temperature of 290 ° C. or higher, and heat treatment at a temperature of 300 ° C. or higher. It is more preferable to carry out. More preferably, when the heat treatment is first performed at a temperature of about 200 ° C. and then gradually heated to a temperature of 290 ° C. or more, the concentration of the decomposition gas does not increase rapidly, and the risk of ignition or the like is reduced. Become.

  As the upper limit of the temperature of the first heat treatment, it is not preferable that the water-repellent resin is decomposed by heat. Therefore, it is preferable to perform the heat treatment at a temperature equal to or lower than the decomposition temperature of the water-repellent resin. Hereinafter, it is more preferably less than 350 ° C., and it is particularly preferable to perform heat treatment at a temperature not higher than a substantial melting temperature of a water repellent resin described later.

  Depending on the characteristics of the surfactant used, the surfactant can be removed by heat treatment without the decomposition of the surfactant and the generation of gas, but in the vapor state of the surfactant itself. This is preferable because the air volume for discharging from the inside of the furnace to the outside of the furnace can be reduced. Therefore, when the decomposition temperature is sufficiently higher than the boiling point of the surfactant, the heat treatment temperature in the first heat treatment step is preferably not more than the decomposition temperature of the surfactant and not less than the boiling point of the surfactant.

  The heat treatment time in the first heat treatment step is as short as possible from the viewpoint of productivity, preferably within 20 minutes, more preferably within 10 minutes, and even more preferably within 5 minutes. If heat treatment is carried out, surfactant vapors and degradable organisms are rapidly generated. If it is carried out in the air, there is a risk of ignition, which is not preferable. Usually, 2 minutes or more is preferable.

  Hot air is preferable as the heat source in the first heat treatment step. Hot air is supplied to the heat treatment furnace from the air supply port, heated by a heater, etc., then introduced into the heat treatment furnace, heat is supplied to the substrate to be heated in the furnace, and the generated surfactant vapor and decomposition are generated. The product is discharged from the heat treatment furnace through the exhaust port. Sufficient air volume is supplied so that the concentration of gas such as surfactant vapor and decomposition products generated at this time does not exceed the explosion limit. In order to further improve safety, a so-called single-pass method is preferable in which hot air discharged from the exhaust port to the outside of the heat treatment furnace is not returned to the heating unit such as a heater.

  The second heat treatment step, so-called sintering step, needs to be performed at a temperature equal to or higher than the melting point of the water-repellent resin, but is preferably performed at a heat treatment temperature (sintering temperature) that exceeds a substantial melting temperature described later. . When PTFE is used as the water repellent resin, the melting point of PTFE is around 330 ° C., but sintering is performed at a sintering temperature exceeding 350 ° C., preferably at a sintering temperature of 370 ° C. or more for 30 seconds or more. It is good to do. When FEP is used as the water repellent resin, the melting point of FEP is around 240 ° C., but it is preferable to sinter at a sintering temperature exceeding 320 ° C.

  According to the study by the present inventors, when the sintering temperature of FEP is 240 ° C. or higher and 320 ° C. or lower, when the gas diffusion electrode is incorporated in a fuel cell to generate electric power, the drainage at low temperature (around 40 ° C.) can function sufficiently. In addition, it was found that the function as a binder for the conductive fine particles of FEP is not sufficiently exhibited, and there is a concern that the conductive fine particles may fall off. That is, the substantial melting temperature of FEP is 320 ° C., and the temperature suitable for sintering is a temperature range exceeding 320 ° C. Here, the substantial melting temperature can be obtained experimentally. That is, the temperature at which the power generation performance at low temperature is improved after applying and drying the microporous layer of the gas diffusion electrode, that is, the ability of the water repellent material to drain the condensed water generated inside the fuel cell. Determine the effective temperature. As a result of examination by the present inventors, the substantial melting temperature of PTFE is 350 ° C., and the substantial melting temperature of FEP is 320 ° C.

  Further, if the sintering temperature is too high, water repellent resin such as fluororesin may be decomposed. Therefore, the upper limit is usually about 400 ° C, and the sintering time is preferably over 1 minute. From the viewpoint of productivity, the upper limit is 60 minutes, and it is preferably less than 10 minutes, more preferably less than 5 minutes.

  Hot air is preferable as the heat source in the second heat treatment step. In order to increase energy efficiency, it is desirable to circulate hot air. In the first heat treatment step, combustible decomposition products are almost removed, and in the second heat treatment step, there is little risk of ignition even if hot air is circulated. That is, in the second heat treatment step, the hot air used for the heat treatment is heated by the heater and supplied into the furnace, most of the gas exhausted outside the furnace is returned to the heating part by the heater, and a part is outside the apparatus. It is preferable to use a so-called circulation system that exhausts air and supplies air commensurate with the exhausted gas.

  In the present invention, it is preferable that the conductive porous substrate subjected to the coating liquid coating process is subjected to a water repellent treatment. For the water repellent treatment, a water repellent dispersion in which a water repellent material such as a fluororesin is dispersed in a dispersion medium is usually used. Examples of the water repellent material include a fluororesin similar to the water repellent resin used in the above-mentioned microporous layer coating liquid, but PTFE or FEP exhibiting strong water repellency is preferable.

  These water repellent materials are used for water repellent treatment as a water repellent dispersion in a state of being dispersed in water or other dispersion medium. The dispersant (surfactant) used for this dispersion is the water repellent material itself. It is preferable that evaporation or decomposition can be performed at a temperature lower than the melting point.

  The amount of the water repellent material to be imparted by the water repellent treatment is not particularly limited, but is preferably about 0.1 to 20 parts by mass with respect to 100 parts by mass of the conductive porous substrate. If the amount is less than 0.1 parts by mass, the water repellency is not sufficiently exerted. If the amount exceeds 20 parts by mass, pores serving as gas diffusion paths or drainage paths may be blocked, or electrical resistance may increase. Absent.

  As a method of water repellent treatment, a coating technique such as die coating and spray coating can be applied in addition to a treatment technique of immersing a conductive porous substrate in a generally known water repellent dispersion. After the water-repellent treatment, before being subjected to the coating liquid coating process, a drying process and further a heat treatment process may be added as necessary. From the viewpoint of productivity, these drying process and heat treatment process are performed according to the coating liquid. It is desirable to carry out in a lump in the drying step after the coating step and the first heat treatment step.

  In the present invention, in order to efficiently manufacture the gas diffusion electrode, the conductive porous base material is wound in a long state and continuously processed until it is wound up. It is preferable. That is, before the first heat treatment step, the method includes a step of unwinding the conductive porous substrate from a wound body obtained by winding a long conductive porous substrate into a roll shape, and the second heat treatment step. After that, a winding step of winding the gas diffusion electrode obtained through the second heat treatment step is included. The long conductive porous base material to be a wound body may be a state in which the microporous layer coating liquid is not applied, or a microporous layer precursor may be formed. It is more preferable that it is before the coating liquid coating step because the process from the conductive porous substrate to which the coating liquid is not applied to the gas diffusion electrode can be continuously and consistently processed. In the unwinding step, a wound body in which a long conductive porous substrate is wound in a roll shape is unwound from an unwinding machine. A water-repellent treatment step is added between the unwinding step and the coating liquid coating step as necessary. After the second heat treatment step and before the winding step, the gas diffusion electrode obtained through the second heat treatment step may be cooled as necessary. In the winding process, the gas diffusion electrode is continuously wound by a winder. When winding up, in order to protect the coated surface, an interleaf may be wound together. Further, the winding may be performed after trimming the edge portion or slitting to the product width immediately before winding.

  In addition, there is an advantage that the processing apparatus can be made compact by winding and processing every several processing steps, such as water repellent treatment, winding, coating liquid application, drying and winding, heat treatment and winding. .

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  One aspect of a preferable manufacturing apparatus for realizing the manufacturing method of the present invention is as shown in FIG. 6, an unwinding machine 1 for unwinding a long conductive porous substrate wound in a roll shape, and a heat treatment furnace. There is a winder 6 for winding up the gas diffusion electrode obtained via B9 (second heat treatment furnace). During that time, the winder is unwound by the winder 1, and the conductive fine particles, water-repellent resin and Via a first heat treatment furnace (heat treatment furnace A8) for removing the surfactant from the conductive porous substrate on which the microporous layer precursor containing the surfactant is formed, and the first heat treatment furnace A second heat treatment furnace (heat treatment furnace B9) for further heat-treating the conductive porous substrate and sintering the water-repellent resin is installed in this order. The conductive porous substrate on which the microporous layer precursor is formed may be unwound from the unwinding machine 1, or the conductive porous substrate on which the microporous layer precursor is not formed may be unwound. The microporous layer precursor may be formed by appropriate processing (not shown) before unwinding from 1 and supplying to the first heat treatment furnace.

  The winder 6 is preferably provided with a slip paper unwinding machine 5 for winding the slip sheet 15 for protecting the coated surface of the product. Further, on the unwinding side, when the interleaf paper is wound together on the base material, it is preferable to install the interleaf paper winder 14. Between the unwinding machine 1 and 1st heat processing furnace A8, the guide roll 3 for making conveyance of a base material smooth is arrange | positioned suitably. The substrate is transported by driving the winder 6, but if necessary, the substrate may be nipped and transported while cutting the tension. It is also preferable to install a nip roll 2 for this purpose. Further, when it is not desired to bring the roll into contact with the coated surface of the product, it is more preferable to use a suction roll instead of the nip roll. The guide roll 3 may be non-driven. Further, after the heat treatment furnace B, a device such as a fan for cooling the base material may be installed, or a calender device for pressing the coating film may be installed if necessary.

  The first heat treatment furnace (heat treatment furnace A) is preferably capable of raising the temperature to 320 ° C., and more preferably capable of raising the temperature to about 400 ° C. As a heat source, hot air is preferable, a blower for sending outside air into the furnace, a heater for raising the temperature of air sent into the furnace, an air supply duct for introducing air into the furnace, and an exhaust duct for gas discharged from the furnace A blower or the like for sending out exhaust gas is appropriately installed. At this time, all the exhausted gas is directly trapped by a cooler, or diluted with air and discharged to the outside air, or sent to a combustion device and thermally decomposed. Here, it is preferable to adopt a so-called single pass system in which no exhausted gas is returned to the heater side. A single-pass heat treatment furnace is a heat treatment furnace of a type that does not supply gas exhausted from the heat treatment furnace to the heat treatment furnace.

  The second heat treatment furnace (heat treatment furnace B) preferably has the ability to raise the temperature to 400 ° C. As the heat source, hot air is preferable because temperature control is easy, and it is assumed that organic substances such as surfactants in the base material to be treated are removed by the first heat treatment. The gas discharged from the furnace is preferably circulated in such a manner that a part of the gas is returned to the processing apparatus and the other is returned to the heater and circulated. The circulation type heat treatment furnace is a heat treatment furnace in which at least a part of the gas exhausted from the heat treatment furnace is supplied again to the heat treatment furnace.

  FIG. 5 shows a more preferable aspect of the manufacturing apparatus of the present invention. That is, in addition to the apparatus shown in FIG. 1, between the unwinding machine 1 and the heat treatment furnace A8, the coating machine 12 for applying the microporous layer coating liquid and the microporous layer coating liquid is applied by the coating machine. The dryer 7 for drying a microporous layer coating liquid from the made conductive porous substrate is installed in this order. By doing in this way, a microporous layer coating liquid application | coating, drying, and heat processing can be performed now consistently with respect to a long electroconductive porous base material.

  Moreover, as shown in FIG. 5, by installing a device for water repellent treatment such as a spray 13 between the unwinding machine 1 and the coating machine 12, a long conductive porous substrate is formed. In contrast, water repellent treatment, microporous layer coating, drying, and heat treatment can be performed consistently, which makes a more preferable device.

  The gas diffusion electrode manufactured by the manufacturing method and manufacturing apparatus of the present invention is pressure-bonded so that the catalyst layer and the gas diffusion electrode are in contact with both sides of the electrolyte membrane provided with the catalyst layer on both sides, and a member such as a separator is assembled. The unit cell is assembled and used as a fuel cell. When using a gas diffusion electrode in which a microporous layer is provided only on one side, it is preferable to assemble the microporous layer and the catalyst layer in contact with each other.

  Hereinafter, the present invention will be described more specifically with reference to examples. Various evaluation methods used in the examples are shown below.

<Measurement of film thickness of substrate and microporous layer>
The thickness of the base material (gas diffusion electrode and conductive porous base material) was measured using a Mitutoyo Digimicro and applying a load of 0.15 MPa to the base material. The thickness of the microporous layer was measured by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode.

<Viscosity measurement>
In the viscosity measurement mode of the Spectris Borin rotary rheometer, the stress is measured using a circular cone plate having a diameter of 40 mm and an inclination of 2 ° while increasing the number of rotations of the plate (increase the share rate). At this time, the value of viscosity at 0.17 / sec.

<Evaluation of power generation performance>
The obtained gas diffusion electrode was formed by integrating an electrolyte membrane / catalyst layer integrated product (Nippon Gore's electrolyte membrane “Gore Select” (registered trademark) and Nippon Gore's catalyst layer “PRIMEA” (registered trademark) on both sides. The membrane electrode assembly (MEA) was manufactured by sandwiching the catalyst layer and the microporous layer so that the catalyst layer and the microporous layer were in contact with each other and hot pressing. This membrane electrode assembly is incorporated into a single cell for a fuel cell. The cell temperature is 40 ° C., the fuel utilization efficiency is 70%, the air utilization efficiency is 40%, the hydrogen on the anode side, and the air on the cathode side have dew points of 75 ° C. and 60 ° C., respectively. The value of current density (limit current density) at which power generation is stopped when the current density is increased by humidifying the temperature to be 0 ° C. is used as an index for flooding resistance. Further, the power generation performance under normal operating conditions (battery temperature 70 ° C.) was also measured.

Example 1
As schematically shown in FIG. 1, an unwinder 1, an infeed roll 2, a guide roll 3, a back roll 4, an interleaf unwinder 5, a winder 6, a dryer 7, and a heat treatment furnace A8 are provided. A take-up type transport device was prepared.

  Here, although the heat source in the heat treatment furnace A8 is hot air, air is introduced from the air supply port by a blower, is heated by the heater H, is sent into the furnace, is heated in the furnace, and is directly heated from the exhaust port to the outside of the furnace. A single pass system is used.

  An original fabric obtained by winding a carbon paper (TGP-R-060 manufactured by Toray Industries, Inc.), which is a conductive porous substrate having a width of about 400 mm, into a roll of 400 m was set in the unwinding machine 1.

  The raw material was conveyed by drive rolls installed at the unwinding unit, the winding unit, and the coater unit. In the transport apparatus shown in FIG. 1, the water repellent treatment apparatus shown in FIG. 2 in which a dipping stainless steel tank 10 is attached to the coater section is used, and a water repellent material dispersion (Daikin Industries PTFE dispersion D- 210C, which is diluted 5 times with purified water), transported so that the raw material is immersed therein, squeezed excess liquid with squeeze roll 11, and further set the temperature at 80 ° C. 7 And passed through a heat treatment furnace A8 at room temperature without raising the temperature, and then wound up. The drying time at this time was 2 minutes. The amount of the water repellent material was 5 parts by mass with respect to 100 parts by mass of the carbon paper.

  Using the die coating apparatus shown in FIG. 3, the water repellent treated raw material is set in the unwinding machine 1 and the water repellent treatment is not performed, and the microporous layer coating liquid is applied using a die coater as the coating machine 12. After coating, the moisture was dried with hot air at 100 ° C. in the dryer 7 and further subjected to the first heat treatment step in the heat treatment furnace A 8 set at a temperature of 320 ° C., and then wound up with the winder 6. The first heat treatment time was 5 minutes.

  Further, using the apparatus shown in FIG. 3, the web which has been subjected to the first heat treatment step is set on the unwinder 1 again and unwound, and the heat treatment set at 380 ° C. without performing the first heat treatment step. A second heat treatment step was performed through the furnace A8 and wound up. The second heat treatment time was 2 minutes.

  Here, although the heat source in the heat treatment furnace A8 is hot air, air is introduced from the air supply port by a blower, is heated by the heater H, is sent into the furnace, is heated in the furnace, and is directly heated from the exhaust port to the outside of the furnace. A single pass system is used.

  The microporous layer coating solution was prepared as follows.

  “Denka Black” (registered trademark), 7.7 parts by mass, manufactured by Denki Kagaku Kogyo Co., Ltd., 2.5 parts by mass of PTFE dispersion (Polyflon D-210C, manufactured by Daikin Industries, Ltd.), surfactant (Nacalai Tesque Co., Ltd.) “TRITON” (registered trademark) X-100: decomposition temperature 200 ° C. to 270 ° C.) 14 parts by mass and 75.8 parts by mass of purified water were kneaded with a planetary mixer to prepare a coating solution. The coating solution viscosity at this time was 9.5 Pa · s.

In applying the microporous layer coating liquid, the basis weight of the microporous layer after the second heat treatment was adjusted to 15 g / m ² . At this time, the thickness of the microporous layer (the value obtained by subtracting the thickness of the carbon paper from the thickness of the gas diffusion electrode) was about 30 μm.

  In addition, the gas diffusion electrode prepared as described above is thermocompression bonded to both sides of the electrolyte membrane provided with the catalyst layer on both sides, and incorporated into a single cell of the fuel cell, and the power generation performance (limits) at temperatures of 40 ° C and 70 ° C. Current density) was evaluated.

  FIG. 7 shows the relationship between the weight loss and the elapsed time when four samples having a diameter of 5 mm are punched from the base material just before the first heat treatment step and thermogravimetric analysis (TG) is performed. Show. As the thermogravimetric analyzer, Shimadzu Corporation thermal analyzer DTG-60 was used.

  For each sample, as shown in FIG. 8, the temperature is first raised from room temperature to 110 ° C. over about 25 minutes and dried. From here, the A sample is heated up to 200 ° C. and held as it is, the B sample is heated up to 260 ° C. and held, the C sample is heated up to 320 ° C. and held, and the D sample is held up to 380 ° C. The temperature was raised and held. Theoretically, the theoretical weight loss due to the decomposition and removal of the surfactant was 59%, but at least 290 ° C or more is necessary to reach this theoretical weight loss within 20 minutes after the temperature is raised to 200 ° C. It was necessary and it turned out that 300 degreeC or more is preferable. Based on this experiment, a first heat treatment temperature was set.

(Comparative Example 1)
In Example 1, a gas diffusion electrode was obtained in the same manner as in Example 1 except that the heat treatment temperature in the first heat treatment step was changed to 380 ° C. and the second heat treatment step was not performed. This gas diffusion electrode was incorporated into a single cell for a fuel cell in the same manner as in Example 1 to evaluate the power generation performance.

(Example 2)
In Example 1, the water repellent treatment using the water repellent treatment device shown in FIG. 2 was omitted, and instead, using the device shown in FIG. 4 in which a spray was installed in front of the die coater of the device shown in FIG. Water repellent material dispersion is applied by spraying, followed by water repellent treatment, and then the steps from the application of the microporous layer by the die coater to the first heat treatment process without drying and winding the water repellent material A gas diffusion electrode was prepared and evaluated in the same manner as in Example 1 except that the above was performed consistently.

(Comparative Example 2)
In Example 2, the gas diffusion electrode was prepared in the same manner as in Example 2 except that the temperature of the first heat treatment step was set to 380 ° C. and the second heat treatment step was omitted, and various evaluations were performed. .

Example 3
The apparatus shown in FIG. 5 in which a heat treatment furnace B9 is further added after the heat treatment furnace A8 of the die coating apparatus shown in FIG. The hot air as a heat source for the heat treatment furnace B9 was basically circulated through the atmosphere, partially supplied with air, introduced into the furnace, and discharged. Using this apparatus, in the same manner as in Example 2, the water repellent material was applied by spraying, the microporous layer was applied by a die coater, dried at 100 ° C., and further passed through a heat treatment furnace A set at 200 ° C. 6 was wound up. The heat treatment time was 2 minutes.

  The base material that has been subjected to the heat treatment at 200 ° C. is set again in the unwinding machine 1 of the apparatus shown in FIG. 5, and the temperature of the heat treatment machine A is set to 320 ° C. and the temperature of the heat treatment furnace B is set to 380 ° C. Then, it was heat-treated and wound up by a winder 6. Each heat treatment time was 2 minutes.

  In Example 3, the first heat treatment was performed in two stages of 200 ° C. and 320 ° C.

  The heat treatment furnace B is a system in which hot air is circulated as described above. However, since the surfactant vapor and decomposition products are substantially removed in the first heat treatment, a phenomenon such as ignition in the heat treatment furnace B is performed. Was not seen.

  A power generation evaluation was performed on the gas diffusion electrode thus prepared.

(Example 4)
In Example 3, when the apparatus shown in FIG. 5 is used for the first time, the temperature of the heat treatment furnace A is changed to 320 ° C., the temperature of the heat treatment furnace B is changed to 380 ° C., the first heat treatment, A gas diffusion electrode was prepared and evaluated for power generation in the same manner as in Example 3 except that each time of the heat treatment was changed to 3 minutes and the apparatus shown in FIG. 5 was not used for the second time.

(Example 5)
In Example 4, except that the temperature of the heat treatment furnace A was changed to 330 ° C., a gas diffusion electrode was prepared and power generation evaluation was performed in the same manner as in Example 4.

(Example 6)
In Example 4, the PTFE dispersion used as the water-repellent material in the water-repellent treatment and the water-repellent resin in the microporous layer coating liquid was FEP dispersion ("Polyflon" (registered trademark) ND-110 manufactured by Daikin Industries, Ltd.). The gas diffusion electrode was prepared and evaluated for power generation in the same manner as in Example 4 except that the temperature of the heat treatment furnace A was changed to 320 ° C. and the temperature of the heat treatment furnace B was changed to 350 ° C.

  Table 1 shows the results of power generation performance evaluation in each example and comparative example. It can be seen that the fuel cells using the gas diffusion electrodes prepared by the manufacturing method of the present invention all have better power generation performance than those prepared by the conventional technique.

  After removing the surfactant contained in the microporous layer and the conductive porous substrate by heat treatment by the production method of the present invention, the conductive agent in the microporous layer is heat-treated at a temperature equal to or higher than the melting point of the water repellent material. The water-repellent material is well bonded to the fine particles and the conductive porous substrate, which increases the gas diffusibility of the gas diffusion electrode and the drainage of water generated inside the fuel cell. It is considered that the performance is improved.

1 Unwinding machine 2 In-feed roll (nip roll)
3 Guide roll 4 Back roll 5 Interleaf unwinding machine 6 Winding machine 7 Drying machine 8 Heat treatment furnace A
9 Heat treatment furnace B
DESCRIPTION OF SYMBOLS 10 Tank 11 Squeezing roll 12 Coating machine 13 Spray 14 Interleaf winder 15 Interleaf H Heater SP Intake EX Exhaust

Claims (2)

An apparatus for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell, in which a microporous layer is formed on at least one surface of a conductive porous substrate, which is a long conductive porous substrate wound in a roll shape A first heat treatment furnace for removing the surfactant from the conductive porous substrate that has been unwound by the unwinding machine and the unwinding machine and previously formed with the microporous layer precursor, A second heat treatment furnace for further heat-treating the conductive porous substrate via the heat treatment furnace and sintering the water-repellent resin, and for winding the gas diffusion electrode obtained via the second heat treatment furnace A gas diffusion electrode manufacturing apparatus comprising a winder, wherein the first heat treatment furnace is a single-pass heat treatment furnace, and the second heat treatment furnace is a hot air circulation heat treatment furnace. An apparatus for producing a gas diffusion electrode for use in a polymer electrolyte fuel cell, in which a microporous layer is formed on at least one surface of a conductive porous substrate, which is a long conductive porous substrate wound in a roll shape An unwinding machine for unwinding, a coating machine for applying a microporous layer coating liquid on a conductive porous substrate unwound by an unwinding machine, and a microporous layer from a conductive porous substrate A dryer for drying the coating liquid, a first heat treatment furnace for removing the surfactant from the substrate dried by the dryer, and further heat-treating the conductive porous substrate via the first heat treatment furnace A second heat treatment furnace for sintering the water-repellent resin, and a winder for winding the gas diffusion electrode obtained via the second heat treatment furnace. It is a one-pass heat treatment furnace, and the second heat treatment furnace is a hot air circulation heat treatment furnace. Gas diffusion electrode manufacturing equipment.

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