WO2013147174A1 - 多孔質電極基材、その製造方法及び前駆体シート - Google Patents
多孔質電極基材、その製造方法及び前駆体シート Download PDFInfo
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Definitions
- the present invention relates to a porous electrode substrate that can be used for a fuel cell, a method for producing the same, and a precursor sheet used for producing the porous electrode substrate.
- This application is based on Japanese Patent Application No. 2012-079928 filed in Japan on March 30, 2012 and Japanese Patent Application No. 2012-164774 filed in Japan on July 25, 2012. Insist and use the contents here.
- gas diffusion electrode base materials installed in fuel cells are made of short carbon fibers and then bonded with a thermosetting resin, and then fired at a high temperature to increase mechanical strength. It was the porous electrode base material which consists of a paper-like carbon / carbon composite carbonized (refer patent document 1).
- Patent Document 1 tends to have a complicated manufacturing process, and may be expensive.
- the method of Patent Document 2 can certainly reduce the specific resistance in the thickness direction.
- paper-like carbon / carbon composites are rarely used as they are in fuel cells.
- MPL fluororesin or surface densification
- Layer is applied and then mounted on the cell.
- MPL fluororesin or surface densification
- the present invention has been made in view of the above points, and has a low manufacturing cost, sufficient conductivity, and a porous electrode substrate that exhibits good power generation performance without MPL and a method for manufacturing the same The purpose is to provide.
- the present inventors have found that the above problems can be solved by the following inventions (1) to (15).
- the following (1) to (4) are production methods of the present invention, and the following (5) to (10) are porous electrode substrates that can be produced by the production method of the present invention.
- (15) is a precursor sheet produced during the production method of the present invention.
- a step of dispersing the short carbon fibers (A) to form a sheet [2] A step of adding at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin together with the carbon powder (d) to the sheet-like material to form a precursor sheet
- the method includes a step [4] of confounding the sheet-like material between the step [1] and the step [2], and the sheet-like material is dried between the step [4] and the step [2].
- the average particle size of the substantial particles or aggregates of the carbon powder (d) is 0.1 to 50 ⁇ m.
- a water repellent treatment in which after the step [3], a fluororesin dispersion having a solid content of 1 to 30% by mass is added to the porous electrode substrate, followed by drying and heat treatment at 300 to 390 ° C.
- the carbon short fiber (A) includes a sheet-like structure bound by a resin carbide (C) derived from at least one selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin. It is a porous electrode base material, Comprising: The porous electrode base material with which carbon powder (d) is unevenly distributed in the surface layer vicinity of the single side
- a porous electrode substrate including a sheet-like structure in which short carbon fibers (A) are bound by a resin carbide (C), wherein carbon is disposed near the surface layer on one or both sides of the sheet-like structure.
- a porous electrode substrate including a sheet-like structure in which short carbon fibers (A) are bound by a resin carbide (C), wherein carbon is disposed near the surface layer of one or both surfaces of the sheet-like structure. It has a region where the short fibers (A) and the carbon powder (d) are bound by the resin carbide (C), and the void occupation ratio in the region X from the surface having the region to the depth of 20 ⁇ m is 30%.
- a porous electrode base material having a void occupancy ratio of 50 to 90% in a region Y of 40 ⁇ m in the thickness direction of the central portion of the sheet-like structure.
- a porous electrode base material comprising a sheet-like structure bound with a carbide (C), wherein the carbon short fibers (A) form a three-dimensional entangled structure in the sheet-like structure, A porous electrode base material in which carbon powder (d) is unevenly distributed in the vicinity of one or both surface layers of a sheet-like structure.
- a porous electrode base material comprising a sheet-like structure in which carbon short fibers (A) are bound by carbon fibers (B) having a fiber diameter of 0.1 to 5 ⁇ m and resin carbide (C).
- the carbon short fibers (A) form a three-dimensional entangled structure in the sheet-like structure, and the carbon short fibers (A) and carbon powder ( d) A porous electrode base material in which the region bound by the resin carbide (C) is unevenly distributed.
- a porous electrode base material comprising a sheet-like structure in which short carbon fibers (A) are bound by carbon fibers (B) having a fiber diameter of 0.1 to 5 ⁇ m and resin carbide (C).
- the short carbon fibers (A) form a three-dimensional entangled structure in the sheet-like structure, and the short carbon fibers (A) and the carbon powder (d ) Has a region bound by the resin carbide (C), and the occupation ratio of the voids in the region X from the surface having the region to the depth of 20 ⁇ m is less than 30%, and the sheet-like structure A porous electrode base material in which a void occupation ratio in a region Y of 40 ⁇ m in the thickness direction of the central portion is 50 to 90%.
- the carbon short fiber (A) is a precursor sheet containing a sheet-like structure bound by a phenol resin (c), and carbon powder (in the vicinity of the surface layer on one or both sides of the sheet-like structure) A precursor sheet in which d) is unevenly distributed.
- a precursor sheet comprising a sheet-like structure in which the carbon short fibers (A) are bound by a phenol resin (c), wherein the carbon short fibers are disposed near the surface layer on one or both sides of the sheet-like structure.
- a precursor sheet comprising a sheet-like structure in which the carbon short fibers (A) are bound by a phenol resin (c), wherein the carbon short fibers are disposed near the surface layer on one or both sides of the sheet-like structure.
- (A) and the carbon powder (d) have a region bound by the phenol resin (c), and the occupation ratio of the void in the region X from the surface having the region to a depth of 20 ⁇ m is less than 25%
- a precursor sheet having a void occupation ratio of 35 to 70% in the region Y of 40 ⁇ m in the thickness direction of the central portion of the structure.
- a precursor sheet including a sheet-like structure in which the carbon short fibers (A) and the carbon fiber precursor short fibers (b) are bound by a phenol resin (c), the sheet-like structure
- the short carbon fibers (A) form a three-dimensional entangled structure, and the short carbon fibers (A) and the carbon powder (d) are in the vicinity of the surface layer on one or both sides of the sheet-like structure.
- the phenol resin (c) is at least one selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin. Sheet.
- the following (16) to (31) are also embodiments of the present invention.
- (16) The production method according to (1), wherein the step [1] is a step of dispersing the short carbon fibers (A) and the fibrillar fibers (b ′) to form a sheet-like product.
- the step [2] at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin and carbon powder (d) are mixed in the sheet-like material.
- the dispersion liquid (e) is added to obtain a precursor sheet.
- step [2] at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin is sprayed and dropped onto the sheet-like material together with the carbon powder (d).
- any of the above (1) to (4) and (16) to (24), wherein the viscosity of the phenol resin (c) is 0.2 mPa ⁇ s or more and 500 mPa ⁇ s or less
- the addition amount of the carbon powder (d) is such that the mass ratio of the carbon powder (d) to the solid content of the phenol resin (c) is 0.001 to 3.0.
- the carbon short fiber (A) and the carbon fiber precursor short fiber (b) are bound by at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin.
- the short carbon fibers (A) form a three-dimensional entangled structure in the sheet-like structure, and carbon powder ( A precursor sheet in which d) is unevenly distributed.
- a porous electrode base material having a low manufacturing cost, sufficient conductivity, and good power generation performance even without an MPL, and a method for manufacturing the same.
- a membrane-electrode assembly and a polymer electrolyte fuel cell including the porous electrode substrate can be provided.
- FIG. 1 It is a figure which shows an example of the scanning electron micrograph of the porous electrode base material surface of this invention. It is an example of the scanning electron micrograph of the cross section of the porous electrode base material of this invention, and is a figure for demonstrating the measuring method of the angle of a carbon short fiber and a horizontal surface. It is an example of the scanning electron micrograph of the porous electrode base material cross section of this invention, and is a figure for demonstrating uneven distribution to the surface layer vicinity of carbon powder. It is an example of the scanning electron micrograph of the porous electrode base material cross section of the comparative example of this invention.
- the production method of the present invention includes the following steps [1] to [3].
- [1] A step of dispersing carbon short fibers (A) to form a sheet (sheet-like product manufacturing step [1]).
- [2] A step of adding at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin together with the carbon powder (d) to the sheet-like material to form a precursor sheet (Resin addition step [2]).
- a process [4] (entanglement process process [4]) for entanglement treatment of the sheet-like material may be included.
- the step [1] is a step for producing a sheet-like material in which the short carbon fibers (A) and the fibrillar fibers (b2) are dispersed, or the step [1] and the step [2].
- the step [4] of entanglement of the sheet-like material in which the short carbon fibers (A) are dispersed the short carbon fibers (A) are helped to open into single fibers, and the precursor The strength of the sheet can be easily increased.
- the sheet-like material refers to a sheet-like material in which at least carbon short fibers (A) are dispersed (precursor fibers (b) described later may be dispersed).
- the manufacturing method of this invention has the said process [4], between the said process [1] and the said process [4], and between the said process [4] and the said process [2]
- One or both of them may include a step [7] of drying the sheet.
- this sheet-like material when the step [7] is performed between the steps [1] and [4], at least the carbon short fibers (A) are dispersed (precursor fibers (b described later) )
- step [7] is performed between step [4] and step [2]
- the process [5] heat pressurization process [5] which heat-presses a precursor sheet at the temperature of 100 degreeC or more and 250 degrees C or less between the said process [2] and the said process [3] may be included. it can.
- a step [6] (drying step [6]) for drying the precursor sheet may be included between the step [2] and the step [5].
- ⁇ Sheet product manufacturing process [1]> In manufacturing a sheet-like material, a wet method in which a short carbon fiber (A) is dispersed in a liquid medium for paper making, a dry method in which the short carbon fiber (A) is dispersed in an air, and the like is deposited. The papermaking method can be applied. From the viewpoint of sheet strength and fiber dispersion uniformity, the wet method is preferred.
- a precursor fiber (b) can also be disperse
- the precursor fiber (b) means one or both of the carbon fiber precursor short fiber (b1) and the fibrillar fiber (b2).
- a small amount of an organic polymer compound may be used as a binder for these sheet-like materials.
- the method for adding the binder to the sheet is not particularly limited.
- carbon short fibers (A) or precursor fibers (b) and a binder may be dispersed together, or after forming a sheet-like material containing carbon short fibers (A), A binder may be added later.
- the organic polymer compound used as the binder is not particularly limited, and examples thereof include water-soluble binders such as polyvinyl alcohol (PVA), polyacrylic acid, carboxymethyl cellulose, and heat-fused polyester or polyolefin binders. It is done.
- the binder may be solid such as fibers and particles, or may be liquid.
- Examples of the medium in which the fibrous materials such as the short carbon fibers (A) and the precursor fibers (b) are dispersed include, for example, a medium in which these fibrous materials do not dissolve, such as water and alcohol. From the viewpoint, water is preferable.
- the sheet-like material can be produced by either a continuous method or a batch method, but it is preferably produced by a continuous method from the viewpoint of the productivity and mechanical strength of the sheet-like material.
- the basis weight of the sheet-like material is preferably about 10 to 200 g / m 2 .
- the thickness of the sheet is preferably about 20 to 400 ⁇ m.
- ⁇ Resin addition process [2]> As a method for producing a precursor sheet by adding at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin together with carbon powder (d) to a sheet-like material, If it is a method which can provide these phenol resins and carbon powder (d) to a shape, it will not specifically limit.
- at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin may be referred to as a phenol resin (c) or a resin (c).
- a dispersion (e) in which the resin (c) and the carbon powder (d) are mixed is prepared.
- the dispersion liquid (e) is prepared by adding the carbon powder (d) to at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin and stirring.
- a single carbon powder (d) may be used, or a plurality of different types of carbon powder may be used in combination.
- the resin (c) penetrates to the back side, while the carbon powder (d) does not reach the back side but is unevenly distributed on the added side.
- the viscosity of the base resin (c) is preferably 0.2 mPa ⁇ s or more from the viewpoint that the solvent or dispersion medium water exists in a liquid state, and 500 mPa ⁇ s or less from the viewpoint of permeability to the sheet-like material. preferable.
- the resin (c) is a water-soluble phenol resin
- the stock solution viscosity is 500 mPa ⁇ s or less.
- the resin (c) is a water-dispersible phenol resin
- the stock solution viscosity exceeds 500 mPa ⁇ s. In such a case, it may be used after diluting with a solvent such as water.
- the solid content concentration of the resin (c) is preferably 1% by mass or more from the viewpoint of mechanical strength and electrical conductivity when it is used as a porous electrode base material, in order to obtain a dispersion with low viscosity and high permeability. It is preferably 40% by mass or less, and more preferably 5 to 35% by mass.
- the resin (c) may be used as it is after diluting a commercially available product with a solvent such as water, or in order to help disperse the solid content of the resin (c) and the carbon powder (d). Also good.
- the addition amount of the surfactant is preferably 0 to 3% by mass with respect to the dispersion in order to suppress foaming as much as possible.
- the amount of carbon powder (d) added to the dispersion is such that the viscosity of the dispersion (e) does not become too high and the gas permeability of the porous electrode substrate does not become too low.
- the mass ratio of the carbon powder (d) to the solid content is preferably 3.0 or less, and preferably 0.001 or more from the viewpoint of improving the conductivity of the porous electrode substrate. It is more preferably from 0.01 to 2.0, and particularly preferably from 0.1 to 1.0.
- the carbon powder (d) commercially available carbon black, graphite, milled fiber, or the like can be used, but the size of the particles or aggregates can be easily distributed on the surface of the porous electrode substrate. Is preferably about 0.1 to 50 ⁇ m, and from the viewpoint of the conductivity of the porous electrode substrate, for example, pyrolytic graphite, scaly graphite, spherical graphite, acetylene black, ketjen black, etc. may be used. preferable.
- the total addition amount of the solid content of the phenol resin (c) and the carbon powder (d) is 20 to 180 parts by mass with respect to 100 parts by mass of the sheet (solid content).
- the addition amount is controlled by the nip (squeezing) regardless of the addition method.
- the addition method of the dispersion liquid (e) can be applied by discharging (spraying, dropping, flowing down) the phenol resin (c) and the carbon powder (d) onto the sheet-like material.
- a method of spraying or dripping the resin (c) and the carbon powder (d) on the surface of the sheet-like material using a spray nozzle, or a resin (c) on the surface of the sheet-like material using a discharge type coater such as a curtain coater For example, a method of uniformly coating by flowing down can be used.
- the method for supplying the liquid agent including the phenol resin (c) and the carbon powder (d) is not particularly limited.
- a pressure supply by a pressurized tank, a quantitative supply by a pump, a liquid agent suction method using self-priming pressure, or the like is used. Can do.
- the spray nozzle it is preferable to use a two-fluid nozzle in which the liquid agent flow path and the gas flow path are separated from the viewpoint of easy clogging and easy maintenance.
- a nozzle for example, a double tube nozzle or a vortex nozzle disclosed in Japanese Patent Application Laid-Open No. 2007-244997 can be used.
- the gas used for spraying is not particularly limited as long as it does not react with the phenol resin (c) or the carbon powder (d) or accelerate the curing of the phenol resin (c), but it is usually preferable to use compressed air.
- a needle-shaped nozzle generally known as a dropping needle, the spray nozzle, and a high-pressure liquid jet nozzle can be used. It is preferable to use a caliber that does not clog the phenol resin (c) or the carbon powder (d).
- a (nip) device can be used in combination. Further, instead of the nip, by blowing gas on the sheet-like object surface discharged (for example, sprayed) resin (c) and carbon powder (d), or by sucking from the back side of the discharged sheet-like object surface, The resin (c) may be penetrated into the sheet-like material. At that time, it is better that the carbon powder (d) does not move inside the sheet-like material together with the resin (c) but is unevenly distributed on the discharged surface. By continuously performing these steps, the amount of the resin (c) and the carbon powder (d) attached to the sheet can be made constant. Furthermore, you may perform a drying process, after adding resin (c) and carbon powder (d).
- the addition of resin (c) and carbon powder (d) may be repeated multiple times. That is, after adding the resin (c) and the carbon powder (d), the resin (c) and the carbon powder (d) may be further added after the dispersion medium is dried, or the resin being made The carbon powder-added sheet may be turned over, and the resin (c) and carbon powder (d) may be added from the opposite side. These operations may be repeated.
- the number of additions of the resin (c) and the carbon powder (d) is not particularly limited, but it is preferable to reduce the number of additions from the viewpoint of reducing manufacturing costs. When the number of times of addition is multiple, the same phenol resin (c) may be used, or the resin composition and concentration may be different, and the same carbon powder (d) may be used. Alternatively, different types and compositions may be used. Further, the addition amount of the resin (c) and the carbon powder (d) may be uniform in the thickness direction of the sheet or may have a concentration gradient.
- At least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin is added to the sheet material together with the carbon powder (d) to obtain a precursor sheet.
- carbon powder (d) is unevenly distributed in the surface layer vicinity of the single side
- both sides of the dispersion (e) of the resin (c) and the carbon powder (d) are applied to only one side of the precursor sheet.
- the carbon powder (d) is unevenly distributed on both surfaces of the precursor sheet.
- the carbon powder (d) is unevenly distributed in the vicinity of one or both surface layers of the sheet-like structure” means that the surface of the precursor sheet, or the surface and the surface layer, compared to the inside (inner layer) of the precursor sheet. It means that a lot of carbon powder (d) exists in the vicinity.
- the “surface” is a surface that can be observed without performing a special treatment such as cutting or polishing, while the “surface vicinity” is a region including the surface and having a width in the thickness direction. is there. Specifically, (i) when observing the cross section of the precursor sheet, the void area is relatively low because the voids are filled with the carbon powder (d) in the vicinity of the surface layer, and the fibers are one by one.
- the inner layer has a relatively high occupancy ratio of the voids, and it is easy to distinguish each fiber.
- the vicinity of the surface layer is (ii) the surface of the precursor sheet is covered with a mixture of resin (c) and carbon powder (d), and fibers and voids other than the outermost surface are present. A state that is almost invisible is preferable.
- the cross-section polisher (CP) and focused ion beam device (FIB) based on the ion etching method should be used because the cross-section of the precursor sheet is likely to cause sagging of the polishing flaw and the material bonding interface with normal mechanical polishing. Is preferred.
- Observation of the cross section or surface of the precursor sheet is not particularly limited as long as it is a method that can easily identify fibers and particles, but it is preferable to use a scanning electron microscope having a deep depth of field.
- the observation magnification of the cross section is preferably a magnification that covers the entire surface in at least the thickness direction (from one surface layer to the other surface layer fits in one photograph).
- image analysis software capable of binarization and area calculation of a gray scale image for calculation of the porosity in the observation photograph.
- the “state in which fibers and voids other than the outermost surface are hardly visible” in (ii) above means that the occupied area of the mixture of the resin (c) and the carbon powder (d) is other than the outermost surface in the surface observation photograph of the precursor sheet It is larger than the occupied area of fibers and voids. At that time, fibers and voids other than the outermost surface may be partially visible.
- any method may be used as long as it is carbonized by continuous temperature rise from room temperature, and the temperature is 1000 ° C. or higher.
- the carbonization treatment is preferably performed in a temperature range of 1000 ° C. or higher and 2400 ° C. or lower in an inert atmosphere.
- the porous electrode base material is long, the productivity of the porous electrode base material will be high, and the subsequent manufacture of the membrane-electrode assembly (MEA: MEMBRANE ELECTRODE ASSEMBLY) can also be performed continuously. The manufacturing cost of the battery can be reduced. Moreover, it is preferable to wind up the manufactured porous electrode base material continuously from the viewpoint of productivity and manufacturing cost of the porous electrode base material and the fuel cell.
- ⁇ Entanglement process [4]> By performing the entanglement treatment on the sheet-like material, a sheet (entangled structure sheet) having an entangled structure in which the carbon short fibers (A) are entangled three-dimensionally can be formed.
- the precursor fiber (b) is dispersed together with the carbon fiber (A) in the sheet-like material production process [1]
- the carbon short fiber (A) and the precursor fiber are entangled with the sheet-like material.
- a sheet (entangled structure sheet) having an entangled structure in which (b) is entangled three-dimensionally can be formed.
- the entanglement process can be selected as needed from the method of forming the entangled structure, and is not particularly limited.
- a mechanical entanglement method such as a needle punching method, a high pressure liquid injection method such as a water jet punching method, a high pressure gas injection method such as a steam jet punching method, or a combination thereof can be used.
- the high-pressure liquid jet method is preferable in that the breakage of the short carbon fibers (A) in the entanglement treatment step can be easily suppressed and appropriate entanglement can be easily obtained.
- this method will be described in detail.
- the high-pressure liquid ejecting process is a process in which a sheet-like material is placed on a substantially smooth support member, and a liquid columnar flow, a liquid fan-shaped flow, a liquid slit flow, or the like ejected at a pressure of 1 MPa or more, for example, It is the processing method which makes the carbon short fiber (A) in a sheet-like material entangle.
- the sheet-like product manufacturing step [1] when the precursor fiber (b) is dispersed together with the carbon fiber (A), the short carbon fiber (A) and the precursor fiber (b) are entangled.
- the support member having a substantially smooth surface is selected as necessary from the one in which the pattern of the support member is not formed on the resulting entangled structure and the ejected liquid is quickly removed.
- the entanglement process by high-pressure liquid injection of the sheet-like material may be repeated a plurality of times. That is, after performing the high-pressure liquid injection treatment of the sheet-like material, the sheet-like material may be further laminated and the high-pressure liquid injection treatment may be performed, or the sheet-like material having an entangled structure (entangled structure sheet shape) The object) may be turned over, and the high-pressure liquid injection process may be performed from the opposite side. These operations may be repeated.
- the liquid used for the high-pressure liquid jet treatment is not particularly limited as long as it is a solvent that does not dissolve the fiber to be treated, but it is usually preferable to use water.
- the water may be warm water.
- each jet nozzle diameter in the high-pressure liquid jet nozzle is preferably 0.06 to 1.0 mm, and more preferably 0.1 to 0.3 mm.
- the distance between the nozzle injection hole and the laminate is preferably 0.5 to 5 cm.
- the pressure of the liquid is preferably 1 MPa or more from the viewpoint of fiber entanglement, more preferably 1.5 MPa or more, and the entanglement treatment may be performed in one or more rows. When performing multiple rows, it is effective to increase the pressure in the second and subsequent high-pressure liquid ejection processes from the first row from the viewpoint of maintaining the sheet form.
- the trajectory pattern can be suppressed by vibrating a high-pressure liquid jet nozzle including one or more rows of nozzle holes in the width direction of the sheet.
- the tensile strength can be expressed in the sheet width direction.
- the frequency of vibrating the high-pressure liquid jet nozzles in the width direction of the sheet and the phase difference thereof are controlled so that the entangled structure sheet It is also possible to suppress the periodic pattern appearing in.
- the tensile strength of the sheet is improved by the entanglement treatment step, it is not necessary to use a binder such as polyvinyl alcohol usually used in papermaking, and the tensile strength of the sheet can be maintained even in water or in a wet state. Thereby, it becomes possible to add a phenol resin (c) continuously to the sheet entangled. Furthermore, since it is not necessary to recover the organic solvent by using the phenol resin (c), the manufacturing equipment can be simplified as compared with the conventional case, and the manufacturing cost can be reduced.
- a binder such as polyvinyl alcohol usually used in papermaking
- ⁇ Heating and pressing step [5]> Reduces unevenness in the thickness of the porous electrode substrate, and further suppresses fluffing in the vicinity of the sheet surface of the fiber that has become fluffy due to the entanglement treatment. From the viewpoint of suppressing, it is preferable to heat and press the precursor sheet at a temperature of 100 ° C. or higher and 250 ° C. or lower.
- the heating and pressing process [5] is performed by using the short carbon fiber (A) as the precursor fiber. It also has the effect of being fused in (b).
- Any method can be applied as a method of heating and pressing as long as it is a technology that can uniformly heat and press the precursor sheet.
- a method of hot pressing a flat rigid plate on both sides of the precursor sheet a method of using a hot roll press device or a continuous belt press device can be mentioned.
- a method using a hot roll press device or a continuous belt press device is preferable. Thereby, the carbonization process [3] mentioned above can be performed continuously.
- the heating temperature in the heating and pressurization is preferably 100 to 250 ° C., more preferably 120 to 230 ° C., in order to effectively smooth the surface of the precursor sheet.
- the time for heating and pressing can be, for example, 30 seconds to 10 minutes.
- the pressure in the heating and pressurization is not particularly limited, but when the content ratio of the short carbon fibers (A) in the precursor sheet is low (for example, 15% by mass or more and 50% by mass or less), it is easy even if the pressure is low.
- the surface of the precursor sheet can be easily smoothed.
- the pressure in the heating and pressing is preferably 20 kPa to 10 MPa. When the pressure is 10 MPa or less, it is possible to easily prevent the short carbon fibers (A) from being destroyed during heating and pressurization, and it is possible to easily impart appropriate denseness to the porous electrode substrate. If the pressure is 20 kPa or more, the surface can be easily smoothed.
- a release agent is applied in advance so that fibrous materials do not adhere to the rigid plate, roll, or belt. It is preferable to coat or release paper between a precursor sheet and a rigid plate, a heat roll, or a belt.
- the production method of the present invention may further include a step [6] of drying the precursor sheet between the step [2] and the step [5]. This is preferable because energy for removing the dispersion medium and unreacted monomer in step [5] can be easily reduced.
- the precursor sheet it is preferable to dry the precursor sheet at a temperature of 20 to 140 ° C.
- the drying process time can be, for example, 1 minute to 24 hours.
- the drying method is not particularly limited, and heat treatment using a high-temperature atmosphere furnace or far-infrared heating furnace, direct heat treatment using a hot plate, a hot roll, or the like can be applied.
- the drying process by a high temperature atmosphere furnace or a far-infrared heating furnace is preferable at the point which can suppress adhesion of the phenol resin (c) to a heating source.
- the production method of the present invention can include a step [7] of drying the sheet-like material between the steps [1] and [2].
- the manufacturing method of this invention has process [4] either between process [1] and process [4] and between process [4] and process [2] or Both can further include a step [7] of drying the sheet.
- the drying process [7] is performed between the process [4] and the process [2]
- the drying process is performed on the entangled sheet (entangled structure sheet).
- the sheet-like material in the present invention does not include a precursor sheet.
- drying treatment steps [7] it is preferable to dry the sheet material at 20 to 140 ° C. from the viewpoint of removing the dispersion medium from the sheet material to be subjected to the drying treatment.
- the drying process time can be, for example, 1 minute to 24 hours.
- a complete dehydration method using a vacuum dehydrator can be applied.
- a heat treatment using a high-temperature atmosphere furnace or a far-infrared heating furnace, or a direct heat treatment using a hot plate or a hot roll. Etc. are applicable.
- drying treatment step [7] is performed between the step [4] and the step [2] in that the fibers constituting the entangled sheet can be prevented from adhering to the heating source
- a high temperature atmosphere furnace or a far infrared ray is used.
- a drying treatment using a heating furnace is preferred.
- Water repellent treatment process [8]>
- humidified fuel is supplied to suppress drying of the polymer electrolyte membrane and maintain appropriate proton conduction.
- water (water vapor) as an electrode reaction product is generated on the cathode side, but this may condense and become liquid water, which may block gas permeation by closing voids in the porous electrode substrate. Therefore, in order to ensure gas permeability, water repellent treatment is often performed with a water repellent polymer.
- water-repellent polymers examples include fluorine resins and silicon resins (silicones) that are chemically stable and have high water repellency. Silicones have low acid resistance and are in contact with highly acidic polymer electrolyte membranes. Fluorine-based resin is exclusively used because it cannot be made.
- the fluororesin is not particularly limited, but tetrafluoroethylene (TFE), hexafluoropropylene (HFP), vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), vinyl fluoride, perfluoroalkyl vinyl ether, par Using a homopolymer or copolymer of a fluoromonomer such as fluoro (allyl vinyl ether), perfluoro (butenyl vinyl ether) (PBVE), perfluoro (2,2-dimethyl-1,3-dioxole) (PDD) be able to.
- TFE tetrafluoroethylene
- HFP hexafluoropropylene
- VDF vinylidene fluoride
- CTFE chlorotrifluoroethylene
- vinyl fluoride vinyl fluoride
- perfluoroalkyl vinyl ether par Using a homopolymer or copolymer of a fluoromonomer such as fluor
- an ethylene-tetrafluoroethylene copolymer ETFE
- an ethylene-chlorotrifluoroethylene copolymer ECTFE
- ethylene ethylene-chlorotrifluoroethylene copolymer
- a form of these fluororesins those dissolved in a solvent and those dispersed in a dispersion medium such as water or alcohol in a granular form are preferable from the viewpoint of impregnation.
- PTFE polytetrafluoroethylene
- FEP tetrafluoroethylene-hexafluoropropylene copolymer
- PVDF polyvinylidene fluoride
- an impregnation method in which the porous electrode base material is immersed in a dispersion liquid (dispersion) in which fine particles of fluororesin are dispersed, or a dispersion liquid is sprayed.
- a spray method or the like can be used.
- the concentration of the fluororesin dispersion is not particularly limited, but is preferably about 1 to 30% by weight of solid content in order to uniformly deposit the fluororesin without filling the voids of the porous electrode substrate. 10 to 30% by weight is more preferable, and 15 to 25% by weight is particularly preferable.
- the sintering temperature must be within a temperature range in which PTFE softens and binds to short carbon fibers (A), carbon powder (d), and resin carbide (C), and PTFE does not thermally decompose. 300 to 390 ° C is more preferable, and 320 to 360 ° C is particularly preferable.
- the fluororesin is applied so that the macroscopic conductive path in the porous electrode base material in which the carbon short fibers (A) and the carbon powder (d) are bound by the resin carbide (C) is covered from the outside. . That is, the fluorine-based resin is present on the surface of the conductive path without dividing the conductive path composed of the short carbon fibers (A), the carbon powder (d), and the resin carbide (C). However, most of the fluorine-based resins are aggregated in the vicinity of the intersection of the fibers, and the surface of the short carbon fibers (A), carbon powder (d), and resin carbide (C) constituting the porous electrode substrate has no gaps. It is not necessarily coated with a fluororesin. Therefore, even after the water repellent treatment, a conductive path that continues from the substrate surface to the inside of the substrate is secured, and both water repellency and conductivity can be achieved.
- the number of additions of the fluororesin is not particularly limited, but it is preferable from the viewpoint of reducing the manufacturing cost to reduce the number of additions.
- the same fluororesin slurry may be used, or slurries with different slurry concentrations or different fluororesin types may be used.
- the addition amount of the fluorine-based resin may be uniform in the thickness direction of the porous electrode substrate or may have a concentration gradient.
- the short carbon fiber (A) which is one fiber constituting the porous electrode substrate, can be entangled in the thickness direction in the sheet-like material, the precursor sheet, and the porous electrode substrate.
- Examples of the short carbon fibers (A) include those obtained by cutting carbon fibers such as polyacrylonitrile-based carbon fibers (hereinafter referred to as “PAN-based carbon fibers”), pitch-based carbon fibers, and rayon-based carbon fibers to an appropriate length. Is mentioned. From the viewpoint of the mechanical strength of the porous electrode substrate, PAN-based carbon fibers are preferred.
- the average fiber length of the short carbon fibers (A) is preferably 2 to 12 mm from the viewpoint of dispersibility.
- the average fiber diameter of the short carbon fibers (A) is preferably 3 to 9 ⁇ m from the viewpoint of production cost and dispersibility of the short carbon fibers, and 4 to 8 ⁇ m from the smoothness of the porous electrode substrate. More preferably.
- the average fiber length can be measured with a commercially available fiber length measuring machine (for example, HiRes-FQA (trade name) manufactured by Nomura Corporation), and the average fiber diameter is measured with a commercially available fiber diameter measuring machine (for example, , Manufactured by Diatron, FDAS765 (trade name), etc.).
- Precursor fiber (b) As described above, in the present invention, one or both of the carbon fiber precursor short fiber (b1) and the fibrillar fiber (b2) are used as the precursor fiber (b).
- the carbon fiber precursor short fiber (b1) can be obtained by cutting a carbon fiber precursor fiber having a long fiber shape into an appropriate length. Moreover, this long-fiber-like carbon fiber precursor fiber can be comprised from the polymer (for example, acrylic polymer) mentioned later.
- the average fiber length of the carbon fiber precursor short fibers (b1) is preferably 2 to 20 mm from the viewpoint of dispersibility.
- the cross-sectional shape of the carbon fiber precursor short fiber (b1) is not particularly limited, a high roundness is preferable from the viewpoint of mechanical strength after carbonization and production cost.
- the average fiber diameter of the carbon fiber precursor short fibers (b1) is 5 ⁇ m or less in order to easily suppress breakage due to shrinkage in the heating and pressurizing step [5] and the carbonizing step [3]. preferable. From the viewpoint of spinnability, the average fiber diameter of the carbon fiber precursor short fibers (b1) is preferably 1 ⁇ m or more.
- the polymer constituting the carbon fiber precursor short fiber (b1) preferably has a residual mass of 20% by mass or more in the carbonization treatment step.
- examples of such polymers include acrylic polymers, cellulose polymers, and phenolic polymers.
- the acrylic polymer used for the carbon fiber precursor short fiber (b1) may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and other monomers.
- the monomer copolymerized with acrylonitrile is not particularly limited as long as it is an unsaturated monomer constituting a general acrylic fiber.
- Methacrylic acid esters acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, N-methylol acrylamide, diacetone acrylamide, styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinylidene bromide, vinyl fluoride, And vinylidene fluoride.
- the short carbon fibers (A) can be bound to each other from spinnability and low temperature to high temperature, the remaining mass at the time of carbonization treatment is large, and the fiber elasticity and fiber strength at the time of performing the above-described entanglement treatment In view of the above, it is preferable to use an acrylic polymer containing 50% by mass or more of acrylonitrile units.
- the weight average molecular weight of the acrylonitrile-based polymer used for the carbon fiber precursor short fiber (b1) is not particularly limited, but is preferably 50,000 to 1,000,000. When the weight average molecular weight is 50,000 or more, the spinnability is improved and the yarn quality of the fiber tends to be good. When the weight average molecular weight is 1,000,000 or less, the polymer concentration that gives the optimum viscosity of the spinning dope increases, and the productivity tends to improve.
- One type of carbon fiber precursor short fiber (b1) may be used, or two or more types of carbon fiber precursor short fibers (b1) having different fiber diameters and polymer types may be used.
- the precursor fibers ( The ratio which remains as carbon fiber (B) derived from b) can be adjusted.
- the carbon short fiber (A) in the porous electrode base material and the carbon fiber (B) after carbonization have the following blending ratio.
- the content of carbon fiber (B) in the porous electrode substrate is 1% by mass or more from the viewpoint of binding of carbon short fiber (A) to the total of carbon short fiber (A) and carbon fiber (B). From the viewpoint of the mechanical strength of the porous electrode substrate, it is preferably 50% by mass or less.
- the carbon fiber (B) content in the porous electrode base material is such that the carbon short fiber (A) and the carbon fiber (B) 4 to 25% by mass is more preferable based on the total of
- the fibrillar fibers (b2) can be dispersed together with the short carbon fibers (A) to prevent refocusing of the short carbon fibers (A) and make the sheet-like material stand as a self-supporting sheet.
- Some resins for example, phenol resin (c)
- the fibrillar fibers can be expected to absorb and discharge the water. Therefore, what is excellent also in the affinity with water is preferable.
- Specific examples of the fibrillar fiber (b2) include synthetic pulp such as fibrillated polyethylene fiber, acrylic fiber, and aramid fiber.
- the fibrillar fiber (b2) may be one with carbon residue after carbonization treatment (one that remains as carbon), or one that does not have carbon residue after carbonization treatment (one that does not remain as carbon). good.
- the short carbon fibers (A) and the fibrillar fibers (b2) are entangled well in the precursor sheet, and it is easy to obtain a precursor sheet with excellent mechanical strength. It becomes.
- the freeness of the fibrillar fibers (b2) is not particularly limited, but generally, the use of fibrillar fibers having a low freeness improves the mechanical strength of the precursor sheet, but the gas permeation of the porous electrode substrate is improved. Tend to decrease.
- the two fibrillar fibers (b2) may be referred to as fibers (b2-1) and fibers (b2-2), respectively.
- the fibrillar fiber (b2) one type of fiber (b2-1) or two or more types of fibers (b2-1) having different freeness, fiber diameter, or polymer type may be used.
- one type of fiber (b2-2) or two or more types of fibers (b2-2) having different freeness, fiber diameter, or polymer type may be used, or these may be used in combination.
- the two fibrillar fibers (b2) will be described in detail.
- Carbon precursor fiber having a structure in which many fibrils are branched (b2-1) From the viewpoint of establishing the structure of the porous electrode substrate together with the short carbon fiber (A) after the carbonization, the polymer constituting the fiber (b2-1) has a residual mass of 20% by mass or more in the carbonization treatment step. Preferably there is.
- examples of such a polymer include an acrylic polymer, a cellulose polymer, and a phenol polymer.
- the acrylic polymer used for the fiber (b2-1) the acrylic polymer used for the carbon fiber precursor short fiber (b1) described above can be similarly used.
- the short carbon fibers (A) can be bound to each other from spinnability and low temperature to high temperature, the remaining mass at the time of heating and pressurization and carbonization treatment is large, and further entangled with the short carbon fibers (A).
- the method for producing the fiber (b2-1) is not particularly limited, but it is preferable to use an injection coagulation method in which the freeness can be easily controlled.
- the average fiber length of the fibers (b2-1) is preferably 0.1 mm or more from the viewpoint of ensuring the mechanical strength of the porous electrode substrate, and 3 mm from the viewpoint of dispersibility in the precursor sheet. The following is preferable.
- the diameter (average fiber diameter) of the fiber (b2-1) is preferably 0.01 ⁇ m or more from the viewpoint of ensuring dehydrability during production of the precursor sheet and gas permeability of the porous electrode substrate. From the viewpoint of suppressing breakage due to shrinkage during heat treatment, the thickness is preferably 30 ⁇ m or less.
- the fiber (b2-2) can be obtained by beating a long-fiber easily split sea-island composite fiber into an appropriate length and beating it with a refiner, a pulper, or the like.
- the easily split sea-island composite fibers are fibrillated by beating.
- the long-fiber easily splittable sea-island composite fibers can be produced using two or more different types of polymers that are soluble in a common solvent and are incompatible.
- at least one polymer has a residual mass in the carbonization treatment step of 20% by mass or more. Is preferred.
- those having a residual mass of 20% by mass or more in the carbonization process include, for example, acrylic polymers, cellulose polymers, and phenol polymers.
- the acrylic polymer used for the easily splittable sea-island composite fiber may be the same acrylic polymer used for the carbon fiber precursor short fiber (b1) described above. Among them, it is preferable to use an acrylic polymer containing 50% by mass or more of an acrylonitrile unit from the viewpoint of spinnability and the remaining mass in the carbonization treatment step.
- the weight average molecular weight of the acrylonitrile-based polymer used for the easily split sea-island composite fiber is not particularly limited, but is preferably 50,000 to 1,000,000. When the weight average molecular weight is 50,000 or more, the spinnability is improved and the yarn quality of the fiber tends to be good. When the weight average molecular weight is 1,000,000 or less, the polymer concentration that gives the optimum viscosity of the spinning dope increases, and the productivity tends to improve.
- the acrylic polymer described above is used. It is desirable that the polymer (1) be stable when dissolved in the same solvent as the acrylonitrile polymer and used as a spinning dope. In other words, it is desirable that the other polymer is incompatible with the acrylonitrile polymer when dissolved in the same solvent as the acrylonitrile polymer, and has a miscibility enough to form a sea-island structure during spinning. It is.
- polymers that satisfy these requirements include, for example, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl pyrrolidone, cellulose acetate, acrylic resin, methacrylic resin, phenolic resin, etc. Resins and methacrylic resins can be preferably used in view of the above-mentioned balance of demand.
- the other polymer may be one type or two or more types.
- the splittable sea-island composite fiber used for the fiber (b2-2) can be produced by a normal wet spinning method.
- an easily split sea-island composite fiber can be produced by the following method. First, the acrylonitrile-based polymer and another polymer are mixed and then dissolved in a solvent to obtain a spinning dope for an easily splittable sea-island composite fiber.
- a spinning stock solution obtained by dissolving an acrylonitrile-based polymer in a solvent and a spinning stock solution obtained by dissolving another polymer in a solvent are mixed with a static mixer or the like, and a spinning stock solution of an easily splittable sea-island composite fiber.
- a solvent organic solvents such as dimethylamide, dimethylformamide, dimethyl sulfoxide and the like can be used.
- the cross-sectional shape of the easily splittable sea-island composite fiber is not particularly limited.
- the fineness of the easily split sea-island composite fiber is preferably 1 to 10 dtex.
- the average fiber length of the splittable sea-island composite fiber is preferably 1 to 20 mm from the viewpoint of dispersibility.
- the easily splittable sea-island composite fiber is beaten by peeling of the phase separation interface by mechanical external force, and at least a part thereof is split and fibrillated.
- the beating method is not particularly limited, and examples thereof include a refiner, a pulper, a beater, or a method of fibrillation by jetting a pressurized water stream (water jet punching).
- the fibrillation state changes depending on the beating method and beating time.
- the degree of fibrillation can be evaluated by the freeness.
- the freeness can be determined by a method based on P8121 (pulp freeness test method: Canadian standard type) using a Canadian Standard Freeness (CSF) tester.
- P8121 pulse freeness test method: Canadian standard type
- CSF Canadian Standard Freeness
- the freeness of the splittable sea-island composite fiber is not particularly limited. However, as the freeness decreases, the carbon fiber (B) having a three-dimensional network structure is likely to be formed. Moreover, when an easily split sea-island composite fiber with a high freeness is not used without sufficient beating, carbon fibers (B) having a fiber structure are easily formed.
- the average fiber length of the fiber (b2-2) is preferably 1 mm or more from the viewpoint of securing the mechanical strength of the precursor sheet, and preferably 20 mm or less from the viewpoint of dispersibility.
- the average fiber diameter of the trunk of the fiber (b2-2) is preferably 1 ⁇ m or more from the viewpoint of dispersibility, and is preferably 50 ⁇ m or less from the viewpoint of suppressing breakage due to shrinkage during heat treatment.
- the average fiber diameter of the fibril part of the fiber (b2-2) is preferably 0.01 ⁇ m or more from the viewpoint of ensuring dehydrability during production of the precursor sheet and gas permeability of the porous electrode substrate. From the viewpoint of dispersibility, it is preferably 30 ⁇ m or less.
- the carbon fiber (B) is a carbon fiber obtained by carbonizing a carbon fiber precursor short fiber (b1) or a fibrillar fiber (b2) having residual carbon (remaining as carbon).
- the carbon fiber precursor short fiber (b1) can be obtained by cutting a carbon fiber precursor fiber having a long fiber shape into an appropriate length.
- the average fiber diameter of the carbon fiber (B) is preferably 5 ⁇ m or less from the viewpoint of forming a void suitable for gas permeability and moisture management (moisturizing property, drainage property). Further, from the viewpoint of mechanical strength, the average fiber diameter of the carbon fiber (B) is preferably 0.1 ⁇ m or more. More preferably, it is 0.5 ⁇ m or more and 3 ⁇ m or less.
- phenol resin (c) As described above, in the present invention, one or both of a water-soluble phenol resin and a water-dispersible phenol resin is used as the phenol resin (c).
- Water-dispersible phenolic resin examples include phenol resin emulsions (emulsions) and phenol resin suspensions (suspensions) disclosed in JP 2004-307815 A, JP 2006-56960 A, and the like.
- phenol resin emulsions emulsions
- phenol resin suspensions suspensions
- a known water-dispersible phenolic resin called an aqueous dispersion can be used.
- the resol type phenol resin before crosslinking is often a liquid in a temperature / pressure range where water exists as a liquid, the aqueous dispersion often becomes an emulsion (emulsion).
- novolak-type phenol resins generally have a higher molecular weight than resol-type phenol resins, and are often solid in the temperature and pressure range where water exists as a liquid, so that the aqueous dispersion becomes a suspension.
- the average particle size of the phenol resin is preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less from the viewpoint of permeating into the inner layer of the sheet-like material.
- a phenol resin powder not intended to be dispersed in water is preferable because it cannot be expected to quantitatively penetrate into the inner layer of the sheet-like material even if it is forcibly dispersed in water.
- Absent trade names of DIC Corporation: Phenolite TD-4304 and PE-602, trade names of Sumitomo Bakelite Co., Ltd .: Sumilite Resin PR-14170, PR-55464, PR-50607B Trade name: Shounol BRE-174 manufactured by Showa Denko K.K.
- the water-dispersible phenol resin tends to bind the short carbon fibers (A) at the stage of carbonization and remains as a conductive substance, as is the case with general phenol resins using methanol or methyl ethyl ketone as a solvent.
- the water-dispersible phenol resin As a form of obtaining the water-dispersible phenol resin, it is preferable to use an aqueous dispersion or a granular form that is easy to procure a commercially available product from the viewpoints of handleability and manufacturing cost.
- Commercially available water-dispersible phenolic resins have fewer organic solvents and unreacted monomers that remain without being removed at the time of manufacture than general phenolic resins. That is, since there are few organic solvents and unreacted monomers that volatilize during the drying process and the heating and pressurizing process, the manufacturing cost can be reduced, for example, the exhaust equipment can be simplified.
- Water-soluble phenolic resin As the water-soluble phenol resin used in the present invention, a known water-soluble phenol resin such as a resol-type phenol resin having good water solubility described in JP-A-2009-84382 can be used. Specifically, the product names manufactured by Gunei Chemical Co., Ltd .: Resitop PL-5634, the product names manufactured by Sumitomo Bakelite Co., Ltd .: Sumilite Resins PR-50781, PR-9800D, PR-55386, Showa Denko Trade name: Shonor BRL-1583, BRL-120Z, etc.
- the water-soluble phenol resin tends to bind the carbon short fibers (A) at the stage of carbonization and remains as a conductive substance, as in the case of general phenol resins using methanol or methyl ethyl ketone as a solvent.
- the water-soluble phenol resin As a form of obtaining the water-soluble phenol resin, it is preferable to use a commercially available product in the form of an aqueous solution from the viewpoint of handleability and manufacturing cost.
- Commercially available water-soluble phenolic resins have fewer organic solvents and unreacted monomers that remain without being removed at the time of manufacture than general phenolic resins. That is, since there are few organic solvents and unreacted monomers that volatilize during the drying process and the heating and pressurizing process, the manufacturing cost can be reduced, for example, the exhaust equipment can be simplified.
- the phenol resin (c) used in the resin addition step [2] described above is preferably a dispersion (emulsion or suspension) or an aqueous solution from the viewpoint of permeability to the sheet.
- concentration of the solid content of the phenol resin (c) in the dispersion or in the aqueous solution is preferably 1% by mass or more from the viewpoint of the strength and conductivity of the porous electrode substrate, and the dispersion is low in viscosity and high in permeability. Therefore, it is preferably 40% by mass or less, and more preferably 5 to 35% by mass.
- a medium for diluting or dispersing the obtained phenol resin (c) it is preferable to use water, alcohol or a mixture thereof from the viewpoints of handleability and production cost. Moreover, it is more preferable that water is a main component from the viewpoint of productivity, the viewpoint of protecting the air environment, and the viewpoint of protecting the human body environment.
- the resin carbide (C) is used alone or by binding the carbon short fibers (A) to the carbon powder (d) with the resin carbide (C) and the carbon fibers (B). It is an amorphous material made by carbonizing a carbon precursor resin.
- the carbon precursor resin those having strong binding force with carbon fibers such as phenol resin and a large residual mass upon carbonization are preferable, but are not particularly limited.
- the ratio of the resin carbide (C) remaining as a carbide in the porous carbon electrode substrate finally differs depending on the type of carbon precursor resin and the amount of carbon fiber paper impregnated.
- the resin carbide (C) therein is preferably 5 to 25% by mass, and more preferable lower and upper limits are 10% by mass and 20% by mass, respectively.
- the resin carbide (C) includes a resin carbide (C) derived from at least one selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin.
- Carbon powder (d) As the carbon powder (d), graphite powder, carbon black, milled fiber, or a mixture thereof is preferably used from the viewpoint of conductivity.
- Graphite powder has a highly crystalline graphite structure, and the average primary particle size is generally several micrometers to several hundred micrometers.
- the resin (c) penetrates in the thickness direction of the sheet-like material and penetrates to the back surface. Therefore, it hardly penetrates in the thickness direction and can be unevenly distributed in the vicinity of the surface layer.
- the graphite powder pyrolytic graphite, spherical graphite, scaly graphite, massive graphite, earth graphite, artificial graphite, expanded graphite, etc. can be used, but from the viewpoint of conductivity development, pyrolytic graphite, spherical graphite or Scaly graphite is preferred.
- Carbon black generally exists as a structure (agglomerate) in which primary particles having an average particle size of several tens of nanometers are fused together to form a structure, and the structures are bonded by van der Waals force. Carbon black has a significantly larger number of particles per unit mass than graphite powder, and agglomerates form a three-dimensional network at a certain critical concentration or more to form a macroscopic conductive path. Therefore, when an additive solution in which carbon black is mixed with liquid resin (c) at a critical concentration or more is added to the sheet material, the resin (c) penetrates in the thickness direction of the sheet material and penetrates to the back surface. Carbon black hardly penetrates in the thickness direction and can be unevenly distributed on the surface. As carbon black, for example black, channel black, acetylene black, lamp black, thermal black, ketjen black and the like can be used, and acetylene black or ketjen black having excellent electrical conductivity is preferable.
- Milled fiber may be produced by pulverizing virgin carbon fiber, or manufactured from recycled products such as carbon fiber reinforced thermosetting resin molded products, carbon fiber reinforced thermoplastic resin molded products, and prepregs. May be used.
- the phenol resin (c) and the carbon powder (d) include a carbon short fiber (A) described later, one or more kinds of oxidized fiber precursor short fibers (b), and one or more kinds of fibrillated oxidized fiber precursors. From the viewpoint of permeability to a sheet-like material comprising at least one selected from the group consisting of fibers (b ′), it is preferably a slurry.
- the dispersion solvent it is preferable to use water, alcohol, dimethylformamide, dimethylacetamide, or a mixture thereof from the viewpoints of handleability and production cost.
- a dispersant such as a surfactant can be used to disperse the phenol resin (c) and the carbon powder (d).
- polyethers such as polyoxyethylene alkylphenyl ether, aromatic sulfonates such as naphthalene sulfonate, and the like can be used.
- Dispersants containing metal ions such as sodium remain in the precursor sheet and may be scattered in the furnace in the subsequent carbonization step and damage the furnace, so it is preferable to avoid use.
- the mass ratio of the carbon powder (d) to the solid content of the phenol resin (c) is such that the particle size distribution and viscosity of the phenol resin (c) and the particle size distribution and bulkiness of the carbon powder (d) are easy to aggregate.
- it is preferably 0.001 to 3.0, more preferably 0.01 to 2.0, and particularly preferably 0.1 to 1.0 from the viewpoint of conductivity expression and handling properties. preferable.
- this ratio is too small, sufficient electrical conductivity cannot be obtained, or carbon powder permeates through the back of the sheet and is not unevenly distributed on the surface. If this ratio is too small or too large, the viscosity of the dispersion (e) is too high for any combination of phenol resin (c) and carbon powder (d), and the phenol resin (c) component also penetrates the sheet. It will disappear.
- the average particle diameter of the substantial particles or aggregates of the carbon powder (d) is on a sheet-like material comprising at least one selected from the group consisting of short carbon fibers (A) and precursor fibers (b). From the viewpoint of remaining unevenly on the surface, the thickness is preferably about 0.1 to 50 ⁇ m, more preferably 1 to 20 ⁇ m.
- the “substantial particles” are stably present in the dispersion (e) of the resin (c) and the carbon powder (d) in an environment where there is no strong shear that destroys the aggregates. Refers to particles. In the case of graphite powder or milled fiber, it corresponds to primary particles, and in the case of carbon black, it refers to a structure or agglomerate in which primary particles are aggregated.
- the porous electrode substrate can take a shape such as a flat plate shape or a spiral shape.
- the basis weight of the sheet-like porous electrode substrate is preferably 15 g / m 2 or more, and preferably 100 g / m 2 or less from the viewpoint of handleability.
- the porosity of the sheet-like porous electrode substrate is preferably 50% or more from the viewpoint of gas diffusibility, and preferably 90% or less from the viewpoint of mechanical strength.
- the thickness of the sheet-like porous electrode substrate is preferably 50 ⁇ m or more and preferably 300 ⁇ m or less from the viewpoint of handleability.
- the waviness of the sheet-like porous electrode base material is preferably 5 mm or less from the viewpoint of uniformly performing post-treatment such as water repellent treatment.
- Gas permeability of the porous electrode substrate is preferably from the standpoint of gas diffusibility 10mL / hr / cm 2 / Pa or more, from the viewpoint of preventing drying of the electrolyte membrane 3000mL / hr / cm 2 / Pa or less Preferably there is.
- the electrical resistance (through-direction resistance) in the thickness direction of the porous electrode substrate is preferably 50 m ⁇ ⁇ cm 2 or less from the viewpoint of efficiently collecting electrons generated in the electrode catalyst.
- the measuring method of the gas permeability and penetration direction resistance of a porous electrode base material is later mentioned in the Example column.
- ⁇ 1> A sheet in which short carbon fibers (A) are bound by a resin carbide (C) derived from at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin.
- ⁇ 2> A sheet-like structure in which the carbon short fibers (A) are bound by the resin carbide (C), and the carbon short fibers (A) and carbon powder ( d) A porous electrode base material in which the region bound by the resin carbide (C) is unevenly distributed.
- the carbon short fiber (A) is at least one phenol resin (c) selected from the group consisting of a carbon fiber (B) having a fiber diameter of 0.1 to 5 ⁇ m, a water-soluble phenol resin, and a water-dispersible phenol resin. ) Derived from the resin carbide (C) derived from the above, wherein the short carbon fibers (A) form a three-dimensional entangled structure in the structure, and one side of the structure Or the porous electrode base material in which the carbon powder (d) is unevenly distributed in the surface layer vicinity of both surfaces.
- the short carbon fibers (A) form a three-dimensional entangled structure, and the short carbon fibers (A) and the carbon powder (d) are bound by resin carbide (C) in the vicinity of the surface layer on one or both sides of the structure.
- ⁇ 6> A sheet-like structure in which the carbon short fibers (A) are bound by carbon fibers (B) having a fiber diameter of 0.1 to 5 ⁇ m and resin carbide (C),
- the short fibers (A) form a three-dimensional entangled structure, and the carbon short fibers (A) and the carbon powder (d) are bound by the resin carbide (C) in the vicinity of the surface layer on one or both surfaces of the structure.
- the occupation ratio of the void in the region X from the surface of the surface having the region to the depth of 20 ⁇ m is less than 30%, and the void in the region Y of 40 ⁇ m in the thickness direction of the center of the structure
- a porous electrode substrate having an occupation ratio of 50 to 90%.
- the carbon powder (d) is unevenly distributed in the vicinity of the surface layer on one side or both sides of the sheet-like structure” means that it is more porous than the inside (inner layer) of the porous electrode substrate. It means that a large amount of carbon powder (d) is present on the surface of the electrode substrate or in the vicinity of the surface and the surface layer.
- the “surface” is a surface that can be observed without performing a special treatment such as cutting or polishing, while the “surface vicinity” is a region including the surface and having a width in the thickness direction. is there.
- the void area is relatively low because the voids are filled with carbon powder (d) in the vicinity of the surface layer.
- the inner layer has a relatively high space occupation ratio, and indicates a state in which individual fibers can be easily discriminated.
- the surface of the porous electrode substrate is covered with a mixture of resin carbide (C) and carbon powder (d), and the surface is observed. It is preferable that fibers and voids other than the outermost surface are hardly visible.
- the occupancy ratio of the voids is relatively low and it is difficult to discriminate each fiber.
- the inner layer has a relatively high occupancy ratio of the voids. It can be determined from the cross-sectional observation photograph that the book is easily discriminated.
- the above-mentioned “surface vicinity is filled with carbon powder (d) so that the void occupancy is relatively low and it is difficult to discriminate each fiber, whereas the inner layer has a void occupancy.
- X is a region from the outermost layer of the porous electrode substrate to a depth of 20 ⁇ m, and the porous electrode
- the void occupation ratio in the region X is preferably less than 30%, and the void occupation ratio in the region Y is preferably 50 to 90%. More preferably, the void occupation ratio in X is less than 25%, and the void occupation ratio in region Y is 60 to 80%.
- the above-mentioned “void occupation ratio” is a value obtained by a calculation method described later.
- Cross-sectional polisher CP or focused ion beam device (FIB) based on ion etching method is used for the cross-section of the porous electrode base material because it is easy to cause polishing wrinkles and sagging of the material bonding interface with normal mechanical polishing. It is preferable to use it.
- the observation of the cross section or surface of the porous electrode substrate is not particularly limited as long as it is a method capable of easily discriminating fibers and particles, but it is preferable to use a scanning electron microscope having a deep depth of field.
- the observation magnification of the cross section is preferably such a magnification that covers the whole at least in the thickness direction (from one surface layer to the other surface layer fits in one photograph) and can distinguish fibers and voids. Specifically, it is about 200 to 500 times.
- image analysis software that can calculate the area of each part by dividing the gap part and the other part by binarizing the gray scale image.
- the “state in which fibers and voids other than the outermost surface are hardly seen” in the above (ii) means that the occupied area of the mixture of the resin carbide (C) and the carbon powder (d) in the surface observation photograph of the porous electrode substrate is It means that it is larger than the occupied area of fibers and voids other than the outermost surface. At that time, fibers and voids other than the outermost surface may be partially visible.
- the occupied area of the mixture of the resin carbide (C) and the carbon powder (d) in the surface observation photograph is preferably 50% or more, more preferably 70% or more, and particularly preferably 90%. That's it.
- the region where the carbon short fibers (A) and the carbon powder (d) are bound by the resin carbide (C) is unevenly distributed in the vicinity of the surface layer on one or both sides of the structure.
- “has” refers to a state in which (iii) the particle shape derived from the carbon powder (d) can be discriminated in the surface observation photograph of the porous electrode substrate.
- porous electrode substrate of the present invention is manufactured by the above-described manufacturing method, it has the following characteristics.
- the bulk density of the porous electrode substrate can be calculated as follows from the basis weight of the porous electrode substrate and the initial thickness of the porous electrode substrate described later in detail.
- Bulk density (g / cm 3 ) weight per unit area (g / m 2 ) / initial thickness ( ⁇ m)
- the bulk density is 0.20 g / cm 3 or more, it can be a porous electrode substrate that is easy to handle and has low resistance in the penetration direction, and if it is 0.45 g / cm 3 or less, sufficient gas permeability is obtained. It can be set as the porous electrode base material which has this. Further, the mechanical strength and bulk density from the viewpoint of the cushion property 0.25 g / cm 3 or more, and more preferably 0.45 g / cm 3 or less.
- ⁇ Three-dimensional entanglement structure> whether or not the short carbon fibers (A) form a three-dimensional entangled structure is obtained by observing a cross section of the sheet-like measurement object (porous electrode base material), and the short carbon fibers (A ) And the sheet surface.
- the cross section which performs cross-sectional observation is a cross section perpendicular
- the angle between the measured short carbon fiber (A) and the horizontal plane is 3 ° or more on average, or the maximum angle between the measured short carbon fiber (A) and the horizontal plane is 10 ° or more, it is three-dimensional. It is determined that an entangled structure is formed (has a three-dimensional entangled structure). When the average angle between the measured short carbon fiber (A) and the horizontal plane is less than 3 ° and the maximum angle between the measured short carbon fiber (A) and the horizontal plane is less than 10 ° It is determined that a three-dimensional entangled structure is not formed (no three-dimensional entangled structure). Specifically, as shown in FIG.
- a straight line 1 in FIG. 2 is a line parallel to the sheet surface.
- the porous electrode substrate of the present invention can be suitably used for a membrane-electrode assembly of a polymer electrolyte fuel cell.
- the membrane-electrode assembly using the porous electrode substrate of the present invention can be suitably used for a polymer electrolyte fuel cell.
- a precursor sheet is produced in a stage before the carbonization treatment step [3].
- the following [1] to [6] can be mentioned.
- [1] A sheet-like structure in which the short carbon fibers (A) are bound by at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin, A precursor sheet in which carbon powder (d) is unevenly distributed in the vicinity of the surface layer on one or both surfaces of the structure.
- [2] A sheet-like structure in which the short carbon fibers (A) are bound by the phenol resin (c), and the short carbon fibers (A) and the carbon powder ( A precursor sheet in which a region where d) is bound by a phenol resin (c) is unevenly distributed.
- a sheet-like structure in which the short carbon fibers (A) are bound by the phenol resin (c), and the short carbon fibers (A) and carbon powder ( d) has a region bound by the phenol resin (c), and the occupation ratio of the void in the region X from the surface having the region to the depth of 20 ⁇ m is less than 25%, and the center of the structure Precursor sheet having an occupancy ratio of 35 to 70% in the area Y of 40 ⁇ m in the thickness direction of the part.
- the short carbon fiber (A) and the short carbon fiber precursor fiber (b) are bound by at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin.
- the carbon short fibers (A) form a three-dimensional entangled structure in the structure, and the carbon powder (d) is unevenly distributed in the vicinity of one or both surface layers of the structure.
- Precursor sheet [5] A sheet-like structure in which the carbon short fibers (A) and the carbon fiber precursor short fibers (b) are bound by the phenol resin (c), and the carbon short fibers (A ) Form a three-dimensional entangled structure, and the region where the short carbon fibers (A) and the carbon powder (d) are bound by the phenol resin (c) is unevenly distributed in the vicinity of the surface layer on one or both surfaces of the structure. Precursor sheet.
- the void occupation ratio in the region X from the surface having the region to the depth of 20 ⁇ m is less than 25%, and the void occupation ratio in the region Y of 40 ⁇ m in the thickness direction of the central portion of the structure is 35.
- the phenol resin (c) is preferably at least one phenol resin (c) selected from the group consisting of a water-soluble phenol resin and a water-dispersible phenol resin.
- the carbon powder (d) is unevenly distributed in the vicinity of the surface layer on one or both sides of the sheet-like structure” means that the precursor sheet is in comparison with the inside (inner layer) of the precursor sheet. It means that a large amount of carbon powder (d) is present on the surface or in the vicinity of the surface and the surface layer.
- the “surface” is a surface that can be observed without performing a special treatment such as cutting or polishing, while the “surface vicinity” is a region including the surface and having a width in the thickness direction. is there.
- the void area is relatively low because the voids are filled with the carbon powder (d) in the vicinity of the surface layer, and the fibers are one by one. Is difficult, whereas the inner layer has a relatively high void occupancy rate, and it is easy to distinguish each fiber.
- the surface of the porous electrode substrate is covered with a mixture of the resin carbide (C) and the carbon powder (d), and the outermost surface is observed when the surface is observed. It is preferable that fibers and voids other than those are hardly visible.
- X is a region from the outermost layer of the porous electrode substrate to a depth of 20 ⁇ m, and the porous electrode
- the void occupation ratio in the region X is preferably less than 25%, and the void occupation ratio in the region Y is preferably 35 to 70%. More preferably, the void occupation ratio in X is less than 20%, and the void occupation ratio in region Y is 40 to 65%.
- the region where the carbon short fibers (A) and the carbon powder (d) are bound by the phenol resin (c) is unevenly distributed in the vicinity of the surface layer on one or both surfaces of the structure.
- "" Refers to a state in which (iii) in addition to the above (i) and (ii), the particle shape derived from the carbon powder (d) can be identified in the surface observation photograph of the precursor sheet.
- Gas permeability Determined by a method based on JIS standard P-8117. Using a Gurley densometer, the test piece (porous electrode substrate) was sandwiched between cells having a hole with a diameter of 3 mm, and 200 mL of air was passed through the hole at a pressure of 1.29 kPa, and it took for the air to permeate. Time was measured and calculated from the following formula.
- Gas permeability (mL / hr / cm 2 / Pa) gas permeation amount (mL) / permeation time (hr) / permeation pore area (cm 2 ) / permeation pressure (Pa).
- the electrical resistance in the thickness direction of the porous electrode substrate (through-direction resistance) is obtained by sandwiching the porous electrode substrate between gold-plated copper plates and pressurizing at 0.6 MPa from the upper and lower sides of the copper plate.
- the resistance value when a current was passed at a current density of cm 2 was measured and obtained from the following formula.
- Penetration direction resistance (m ⁇ ⁇ cm 2 ) measured resistance value (m ⁇ ) ⁇ sample area (cm 2 ).
- the thickness of the porous electrode substrate was measured as follows using a micro autograph small test piece compression tester (manufactured by Shimadzu Corporation, trade name: MST-I).
- the load rod was lowered at a stroke speed of 0.4 mm / min without interposing anything between the upper platen (fixed type) with a diameter of 50 mm and the lower platen (ball seat type) with a diameter of 50 mm. .
- the stroke of the load rod was immediately stopped, and the values of the displacement gauges between the three platens were all set to zero.
- Example 1 As the carbon short fiber (A), a PAN-based carbon fiber having an average fiber diameter of 7 ⁇ m and an average fiber length of 3 mm was prepared. Moreover, as carbon fiber precursor short fibers (b1), acrylic short fibers (Mitsubishi Rayon Co., Ltd., trade name: D122) having an average fiber diameter of 4 ⁇ m and an average fiber length of 3 mm were prepared. Further, as the fibrillar fiber (b2), a polyacrylonitrile pulp (b2-1) produced by spray coagulation in which many fibrils having a diameter of 3 ⁇ m or less were branched from the fibrous trunk was prepared.
- carbon fiber precursor short fibers (b1) acrylic short fibers (Mitsubishi Rayon Co., Ltd., trade name: D122) having an average fiber diameter of 4 ⁇ m and an average fiber length of 3 mm were prepared.
- the fibrillar fiber (b2) a polyacrylonitrile pulp (b2-1) produced by spray coagulation in which many fibrils having a diameter of 3 ⁇
- the production of the sheet-like material and the production of the three-dimensional entangled structure sheet by the entanglement treatment were performed by the following wet continuous papermaking method and the entanglement treatment method by the continuous pressurized water jet treatment.
- Wet continuous papermaking method (1) Disaggregation of short carbon fibers (A) PAN-based carbon fibers with an average fiber diameter of 7 ⁇ m and an average fiber length of 3 mm are put into water so that the fiber concentration is 1% (10 g / L). Dispersed and disaggregated through a disk refiner (manufactured by Kumagai Riki) to obtain disaggregated slurry fibers (SA).
- SA disaggregated slurry fibers
- % (10 g / L) was dispersed in water to obtain a disaggregated slurry fiber (Sb2).
- the carbon short fibers (A), the carbon fiber precursor short fibers (b1), and the fibrillar fibers (b2) have a mass ratio of 60:20:20, and Dispersion slurry fiber (SA), disaggregation slurry fiber (Sb1), disaggregation slurry fiber (Sb2) and dilution water are weighed so that the concentration of the fiber (hereinafter abbreviated as floc) is 1.7 g / L, and the slurry is supplied. It was put into the tank.
- SA Dispersion slurry fiber
- floc concentration of the fiber
- Processing device A sheet drive unit consisting of a net drive unit and a net made of a net 60m x 585cm plastic net woven mesh connected together in a belt and continuously rotated, slurry supply unit width 48cm, amount of slurry supplied Is made up of a papermaking slurry supply apparatus having a pressure of 30 L / min, a vacuum dehydration apparatus disposed under the net, and a pressurized water jet treatment apparatus shown below.
- As the water jet nozzle three types of two nozzles were used as shown in Table 1.
- Step [4] Entangling treated sheet a pin tenter tester (TSUJII dyeing machine, trade name: PT-2A-400) by by drying at 0.99 ° C. ⁇ 3 minutes (step [7]), 3 having a basis weight of 64 g / m 2 A dimensionally entangled structure sheet was obtained.
- the dispersion state of the carbon fiber precursor short fibers (b1) and the fibrillar fibers (b2) in the obtained three-dimensional entangled structure sheet was good.
- a resin (c) used in the dispersion (e) two kinds of aqueous dispersions of resol type phenol resins (trade names: PR-14170, PR, manufactured by Sumitomo Bakelite Co., Ltd.) -55464) was prepared and diluted with pure water so that the resin solid content ratio was 7: 3 and the total resin solid content was 10% by mass of the resin aqueous dispersion. Further, pyrolytic graphite (made by Ito Graphite Industries Co., Ltd., trade name: PC-H) was added as carbon powder (d) so that the carbon powder / resin solid content ratio was 1.0, and the additive liquid was added. It was.
- pyrolytic graphite made by Ito Graphite Industries Co., Ltd., trade name: PC-H
- This additive solution is allowed to flow down on both sides of the three-dimensional entangled structure sheet (step [2]), the excess resin (c) and carbon powder (d) are removed by a nip, and then the water in the sheet is heated at 80 ° C. Was sufficiently dried (step [6]) to obtain a precursor sheet to which a total of 48% by mass of the non-volatile content of the resin and the carbon powder was adhered.
- Step [5] Heating and pressurizing
- a continuous heating press device double belt press device: DBP
- DBP double belt press device having a pair of endless belts disclosed in, for example, Japanese Patent No. 3699447.
- Step [5] an intermediate base material (sheet thickness: 240 ⁇ m, width 40 cm) having a smooth surface was obtained.
- the preheating temperature in the preheating zone was 150 ° C.
- the preheating time was 5 minutes
- the temperature in the heating and pressing zone was 230 ° C.
- the press pressure was 8.0 ⁇ 10 4 N / m.
- DBP was passed between two release sheets.
- the intermediate base material is carbonized at 2200 ° C. in an inert gas (nitrogen) atmosphere (step [3]), and the carbon short fibers (A) are fibrous resin carbides (carbon fibers ( A porous carbon electrode base material bound by B)) and an irregular resin carbide (C) was obtained.
- a surface observation photograph of the obtained porous carbon electrode substrate by a scanning electron microscope is shown in FIG. 1, and a cross-sectional observation photograph is shown in FIG.
- the obtained porous electrode substrate had no in-plane shrinkage during heat treatment, and the thickness and penetration direction resistance were good. As shown in FIG.
- the short carbon fibers (A) dispersed in the three-dimensional structure are bound together by a fibrous resin carbide (carbon fiber (B)) and an amorphous resin carbide (C). It was confirmed that the carbon powder (d) was unevenly distributed on the surface. Even when a compressive load having a surface pressure of 3 MPa was applied to the porous electrode substrate, the sheet form could be maintained.
- Example 2 A porous electrode substrate was obtained in the same manner as in Example 1 except for the following points.
- -As the fibrillar fiber (b2) used for the production of the sheet-like material an easily splitable acrylic sea-island composite short fiber (Mitsubishi Rayon Co., Ltd.) consisting of an acrylic polymer that is fibrillated by beating and diacetate (cellulose acetate)
- the product used is a product (fiber (b2-2)) obtained by beating a manufactured product name: Bonnell MVP-C651, average fiber length: 3 mm).
- the mass ratio of the short carbon fiber (A), the short carbon fiber precursor fiber (b1) and the fibrillar fiber (b2) used for the production of the sheet is 70:10:20, and the target weight is 55 g / m 2 and the points.
- a point where the pressurized water jet pressure in the entanglement process is 2 MPa (nozzle 1), 2 MPa (nozzle 2), and 2 MPa (nozzle 3).
- nozzle 1 A point where the pressurized water jet pressure in the entanglement process is 2 MPa (nozzle 1), 2 MPa (nozzle 2), and 2 MPa (nozzle 3).
- -Prepare two types of aqueous resol type phenolic resin dispersions (trade name: PR-14170, PR-55464, manufactured by Sumitomo Bakelite Co., Ltd.) as resin aqueous dispersions used in the resin additive. The ratio was 5: 5.
- Example 3 A porous electrode substrate was obtained in the same manner as in Example 1 except for the following points. -When preparing the papermaking slurry, the mass ratio of the short carbon fiber (A), the short carbon fiber precursor fiber (b1), and the fibrillar fiber (b2) was 80: 0: 20. -Prepare one kind of resol type phenol resin aqueous dispersion (manufactured by Sumitomo Bakelite Co., Ltd., trade name: PR-55464) as the resin aqueous dispersion used for the resin additive, and the resin solids in the resin additive The point at which the concentration was 12% by mass. -The point which made carbon powder / resin solid content ratio 0.8.
- a vortex atomization nozzle installed in the discharge section using a roller pump (trade name: RP-1000, manufactured by Tokyo Rika Kikai Co., Ltd.)
- the point using the method of spraying air pressure 0.2MPa) from (Atomax Co., Ltd. make, brand name: AM45).
- the heating and pressurization was performed by a batch press method, the temperature was 180 ° C., the preheating time was 0 second, the pressure was 6 MPa, and the heating and pressing time was 1 minute.
- Example 4 A porous electrode substrate was obtained in the same manner as in Example 1 except for the following points.
- the mass ratio of the short carbon fibers (A), the short carbon fiber precursor fibers (b1), and the fibril fibers (b2) is 50:30:20, and the target The basis weight is 50 g / m 2 .
- a point where the pressurized water jet pressure in the entanglement process is 2 MPa (nozzle 1), 2 MPa (nozzle 2), and 2 MPa (nozzle 3).
- Example 1 A porous electrode substrate was obtained in the same manner as in Example 1 except for the following points.
- the fibrillar fiber (b2) used for the production of the sheet-like material an easily splitable acrylic sea-island composite short fiber (Mitsubishi Rayon Co., Ltd.) consisting of an acrylic polymer that is fibrillated by beating and diacetate (cellulose acetate)
- the product used is a product (fiber (b2-2)) obtained by beating a manufactured product name: Bonnell MVP-C651, average fiber length: 3 mm).
- a vortex atomization nozzle installed in the discharge section using a roller pump (trade name: RP-1000, manufactured by Tokyo Rika Kikai Co., Ltd.)
- the point using the method of spraying air pressure 0.2MPa) from (Atomax Co., Ltd. make, brand name: AM45).
- Example 5 Production of membrane-electrode assembly (MEA) Two sets of porous electrode substrates obtained in Example 1 were prepared as cathode electrode and anode electrode porous electrodes. Further, a catalyst layer (catalyst layer area: 25 cm 2 , Pt) composed of catalyst-supported carbon (catalyst: Pt, catalyst support amount: 50 mass%) on both surfaces of a perfluorosulfonic acid polymer electrolyte membrane (film thickness: 30 ⁇ m). The laminated body which formed the adhesion amount: 0.3 mg / cm ⁇ 2 >) was made easy. This laminate was sandwiched between porous electrode substrates for cathode and anode, and joined to obtain an MEA.
- a catalyst layer catalyst layer area: 25 cm 2 , Pt
- catalyst support amount catalyst-supported carbon
- Example 5 Polyacrylonitrile (PAN) carbon short fiber bundles with an average diameter of 7 ⁇ m cut to a length of 3 mm are defibrated in water, and when 80 parts by mass of the short fiber bundles are sufficiently dispersed, polyvinyl alcohol (PVA) as a binder ( 20 parts by mass of short fibers (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) were uniformly dispersed, and papermaking was performed using a standard square sheet machine. The obtained carbon fiber paper had a mass per unit area of 43 g / m 2 .
- PVA polyvinyl alcohol
- an aqueous phenol resin solution (manufactured by Sumitomo Bakelite Co., Ltd., trade name: PR-9800D) is prepared as the resin (c) used in the dispersion (e), and the resin solid content ratio is 10 mass of the dispersion (e). It diluted with pure water so that it might become%. Further, ketjen black (manufactured by Lion Corporation, trade name: carbon ECP) is added as carbon powder (d) so that the carbon powder / resin solid content ratio is 0.01, and dispersion (e) It was. This dispersion (e) is dropped onto the carbon fiber paper from both sides (step [2]), and water in the sheet is sufficiently dried at 80 ° C. (step [6]).
- a precursor sheet with a total of 112 mass% adhered was obtained.
- the precursor sheet is batch-pressed by applying a pressure of 6 MPa for 3 minutes at 180 ° C. without preheating to cure the resin (c), and carbon at 2000 ° C. in an inert gas (nitrogen) atmosphere. (Step [3]) to obtain a porous carbon electrode substrate.
- Example 6 A porous electrode substrate was obtained in the same manner as in Example 5 except for the following points. -Denka black (made by Denki Kagaku Kogyo Co., Ltd., a brand name: Denka black granular product) was used as carbon powder (d). -The point which made carbon powder / resin solid content ratio 0.1. -The point which made the addition method to the carbon fiber paper the dispersion liquid (e) sprayed.
- Example 7 Except for the following points, a porous electrode substrate was obtained in the same manner as in Example 6. -A phenol resin aqueous dispersion (manufactured by Sumitomo Bakelite Co., Ltd., trade name: PR-14170) was used as the resin (c). -The point which made carbon powder / resin solid content ratio 0.001.
- Example 8 A porous electrode substrate was obtained in the same manner as in Example 7 except for the following points. -The point which used Vulcan as carbon powder (d). -The point which made carbon powder / resin solid content ratio 0.1.
- Example 9 A porous electrode substrate was obtained in the same manner as in Example 5 except for the following points.
- -A phenol resin aqueous dispersion manufactured by Sumitomo Bakelite Co., Ltd., trade name: PR-554614 was used as the resin (c).
- a point of using scaly graphite manufactured by Ito Graphite Industries Co., Ltd., trade name: Z-5F as the carbon powder (d).
- Example 10 A porous electrode substrate was obtained in the same manner as Example 9 except for the following points.
- Table 2 shows the sheet-like materials used for producing the porous electrode substrates of Examples 1 to 10 and Comparative Example 1, the composition of the precursor sheet, the production conditions, and the evaluation results of the porous electrode substrate. .
- Example 11 ⁇ Example of precursor sheet> About the precursor sheet
- ImagePro image analysis software
- Example 12 ⁇ Example of water repellent treatment> Prepare a dispersion of polytetrafluoroethylene (PTFE) fine particles (Mitsui / Dupont Fluoro Chemical Co., Ltd., trade name: 31-JR), and add pure water so that the solid content is 20% by mass. Diluted.
- the porous electrode substrate obtained in Example 1 was impregnated with the diluted PTFE dispersion, nipped, and then placed in a far infrared furnace set at 120 ° C. and dried. Next, PTFE was sintered by applying a heat treatment for 20 minutes using an atmospheric furnace set at 360 ° C., to obtain a water-repellent treated porous electrode substrate.
- PTFE polytetrafluoroethylene
- the porous electrode substrate of the present invention is low in production cost, has sufficient conductivity, and exhibits good power generation performance even without MPL. Therefore, the membrane-electrode assembly and the polymer electrolyte fuel cell It is useful for the production of
- A Carbon short fiber (A) B: Carbon fiber (B) C: Resin carbide (C) D: Carbon powder (d) 1: Line parallel to the sheet surface
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Abstract
Description
本発明は、上記の点を鑑みて行われたものであり、製造コストが低く、十分な導電性を有し、MPLがなくても良好な発電性能を示す多孔質電極基材およびその製造方法を提供することを目的とする。
(1)以下の[1]~[3]の工程を含む、多孔質電極基材の製造方法。
[1]炭素短繊維(A)を分散し、シート状物とする工程、
[2]前記シート状物に、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を炭素粉(d)と共に添加し、前駆体シートとする工程、および
[3]工程[2]の後に、前駆体シートを1000℃以上の温度で炭素化処理する工程。
(2)前記工程[1]と前記工程[2]の間にシート状物を交絡処理する工程[4]を含み、前記工程[4]と前記工程[2]の間にシート状物を乾燥処理する工程[7]を含み、前記工程[2]と前記工程[3]の間に、前駆体シートを100~250℃の温度で加熱加圧する工程[5]を含み、前記工程[2]と前記工程[5]の間に、前記前駆体シートを乾燥処理する工程[6]を含む、上記(1)に記載の製造方法。
(3)前記工程[2]において、炭素粉(d)の実質的な粒子あるいは凝集体の平均粒径が、0.1~50μmであることを特徴とする上記(1)または(2)に記載の製造方法。
(4)前記工程[3]の後に、多孔質電極基材に固形分1~30質量%のフッ素系樹脂ディスパージョンを添加し、さらに乾燥して300~390℃にて熱処理を行う撥水処理工程[8]を有することを特徴とする上記(1)~(3)のいずれか1つに記載の製造方法。
(5)炭素短繊維(A)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つに由来する樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
(6)炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
(7)炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、前記領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、前記シート状構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
(8)炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つに由来する樹脂炭化物(C)とにより結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
(9)炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)とにより結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
(10)炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、前記領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、前記シート状構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
(11)炭素短繊維(A)が、フェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している前駆体シート。
(12)炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域が偏在する前駆体シート。
(13)炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が前記フェノール樹脂(c)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が25%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が35~70%である前駆体シート。
(14)炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、フェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が前記フェノール樹脂(c)により結着された領域が偏在する前駆体シート。
(15)フェノール樹脂(c)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つである上記(12)~(14)のいずれか1つに記載の前駆体シート。
なお、下記の(16)~(31)も本発明の実施形態の一つである。
(16)前記工程[1]が、炭素短繊維(A)とフィブリル状繊維(b’)とを分散し、シート状物とする工程である、上記(1)に記載の製造方法。
(17)前記工程[2]において、シート状物に、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)と炭素粉(d)とが混在した分散液(e)を添加し、前駆体シートとすることを特徴する上記(1)または(16)に記載の製造方法。
(18)前記工程[1]と前記工程[2]の間に、シート状物を交絡処理する工程[4]を含む、上記(1)、(16)、(17)のいずれか1つに記載の製造方法。
(19)前記工程[1]と前記工程[2]の間に、シート状物を乾燥処理する工程[7]を含む、上記(1)、(16)~(18)のいずれか1つに記載の製造方法。
(20)前記工程[1]が、炭素短繊維(A)と、炭素繊維前駆体短繊維(b1)およびフィブリル状繊維(b2)のうちの一方または両方とが分散したシート状物を製造する工程である、上記(1)、(16)~(19)のいずれか1つに記載の製造方法。
(21)前記工程[2]と前記工程[3]の間に、前駆体シートを100~250℃の温度で加熱加圧する工程[5]を含む、上記(1)、(16)~(20)のいずれか1つに記載の製造方法。
(22)前記工程[2]と前記工程[5]の間に、前駆体シートを100~250℃の温度で加熱加圧する工程[5]を含む、上記(21)に記載の製造方法。
(23)前記工程[1]において、シート状物における水溶性バインダーの含有量が10g/m2以下である、上記(1)~(4)、(16)~(22)のいずれか1つに記載の製造方法。
(24)前記工程[2]において、シート状物に、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を炭素粉(d)と共に噴霧、滴下または流下して添加する、上記(1)~(4)、(16)~(23)のいずれか1つに記載の製造方法。
(25)前記工程[2]において、フェノール樹脂(c)の粘度が、0.2mPa・s以上、500mPa・s以下である上記(1)~(4)、(16)~(24)のいずれか1つに記載の製造方法。
(26)前記工程[2]において、炭素粉(d)の添加量は、フェノール樹脂(c)の固形分に対する炭素粉(d)の質量比が0.001~3.0であることを特徴とする上記(1)~(4)、(16)~(25)のいずれか1つに記載の製造方法。
(27)上記(1)~(4)、(16)~(26)のいずれか1つに記載の方法で製造される多孔質電極基材。
(28)上記(5)~(15)のいずれか1つに記載の多孔質電極基材を用いた膜-電極接合体。
(29)上記(28)に記載の膜-電極接合体を用いた固体高分子型燃料電池。
(30)炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)により結着されたシート状構造体であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している前駆体シート。
(31)炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、フェノール樹脂(c)により結着されたシート状構造体であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域を有し、前記領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が25%未満であり、前記シート状構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が35~70%である前駆体シート。
本発明の製造方法は、以下の[1]~[3]の工程を含む。
[1]炭素短繊維(A)を分散し、シート状物とする工程(シート状物製造工程[1])。
[2]前記シート状物に、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を炭素粉(d)と共に添加し、前駆体シートとする工程(樹脂添加工程[2])。
[3]工程[2]の後に、前駆体シートを1000℃以上の温度で炭素化処理する工程(炭素化処理工程[3])。
シート状物を製造するにあたっては、液体の媒体中に、炭素短繊維(A)を分散させて抄造する湿式法、空気中に、炭素短繊維(A)を分散させて降り積もらせる乾式法などの抄紙方法を適用できる。シート強度や繊維分散の均一性の観点から、好ましくは湿式法である。
水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を炭素粉(d)と共にシート状物に添加して前駆体シートを製造する方法としては、シート状物にこれらのフェノール樹脂および炭素粉(d)を付与することができる方法であれば特に限定されない。以降、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を、フェノール樹脂(c)または樹脂(c)と称することがある。
分散液(e)の攪拌方法は、樹脂(c)の固形分や炭素粉(d)が沈降しない程度の緩やかな攪拌を行えば十分である。攪拌の剪断力が大きすぎると、むしろ樹脂(c)の固形分や炭素粉(d)の凝集を促したり、著しく起泡したりするため好ましくない。
前駆体シートを炭素化処理する方法としては、室温からの連続昇温により炭素化するような方法であればよく、1000℃以上の温度で行う。なお、十分な導電性付与の観点から、炭素化処理は、不活性雰囲気下にて1000℃以上2400℃以下の温度範囲で行うことが好ましい。なお、炭素化処理工程を行う前に、不活性雰囲気下にて300℃以上1000℃未満の温度範囲で前炭素化処理を行っても良い。前炭素化処理を行うことで炭素化初期段階において発生する分解ガスを容易に出し切ることができ、炭素化炉内壁への分解物の付着や堆積を容易に抑制することができるため好ましい。
シート状物を交絡処理することで、炭素短繊維(A)が3次元に交絡した交絡構造を有するシート(交絡構造シート)を形成することができる。シート状物製造工程[1]において、炭素繊維(A)と共に、前駆体繊維(b)を分散させた場合は、シート状物を交絡処理することで、炭素短繊維(A)と前駆体繊維(b)とが3次元に交絡した交絡構造を有するシート(交絡構造シート)を形成することができる。
多孔質電極基材の厚みむらを低減させ、さらに、交絡処理によりシート表面に毛羽立った状態となった繊維の、シート表面近傍における毛羽立ちを抑制し、燃料電池として組み込んだ際の短絡電流やガスリークを抑制するという観点から、前駆体シートを100℃以上250℃以下の温度で加熱加圧することが好ましい。
本発明の製造方法は、工程[2]と工程[5]との間に、前駆体シートを乾燥処理する工程[6]をさらに含むことができる。これにより、工程[5]で分散媒や未反応モノマーを除去するためのエネルギーを容易に低減することができ好ましい。
本発明の製造方法は、工程[1]と工程[2]との間に、シート状物を乾燥処理する工程[7]を含むことができる。また、本発明の製造方法が工程[4]を有する場合は、工程[1]と工程[4]との間、および、工程[4]と工程[2]との間、のうちの一方または両方に、シート状物を乾燥処理する工程[7]をさらに含むことができる。工程[4]と工程[2]との間に乾燥処理工程[7]を行う場合は、乾燥処理は、交絡処理したシート状物(交絡構造シート)に対して行われる。なお、本発明におけるシート状物は、前駆体シートを含まない。
また、工程[4]と工程[2]の間に、乾燥処理工程[7]を行う場合は、例えば、高温雰囲気炉や遠赤外線加熱炉による熱処理や、熱板や熱ロールなどによる直接加熱処理などが適用できる。交絡処理したシートを構成する繊維の、加熱源への付着を抑制できる点で、工程[4]と工程[2]の間に乾燥処理工程[7]を行う場合は、高温雰囲気炉や遠赤外線加熱炉による乾燥処理が好ましい。
固体高分子型燃料電池は、高分子電解質膜の乾燥を抑制して適度なプロトン伝導を維持するために、加湿された燃料が供給される。さらに、カソード側においては電極反応生成物としての水(水蒸気)が発生するが、これが凝縮して液体水となり、多孔質電極基材の空隙を塞いでガス透過を妨げる場合がある。そこで、ガス透過性を確保するため、撥水性高分子によって撥水処理を施されることが多い。
多孔質電極基材を構成する1つの繊維である炭素短繊維(A)は、シート状物、前駆体シート、ならびに多孔質電極基材中で厚み方向に交絡されることができる。炭素短繊維(A)としては、例えば、ポリアクリロニトリル系炭素繊維(以下「PAN系炭素繊維」と称する)、ピッチ系炭素繊維、レーヨン系炭素繊維等の炭素繊維を適当な長さに切断したものが挙げられる。多孔質電極基材の機械的強度の観点から、PAN系炭素繊維が好ましい。
上述したように、本発明では、前駆体繊維(b)として、炭素繊維前駆体短繊維(b1)およびフィブリル状繊維(b2)のうちの一方、または両方を用いる。
炭素繊維前駆体短繊維(b1)は、長繊維状の炭素繊維前駆体繊維を適当な長さにカットしたものであることができる。また、この長繊維状の炭素繊維前駆体繊維は、後述するポリマー(例えば、アクリル系ポリマー)から構成されることができる。
フィブリル状繊維(b2)は、炭素短繊維(A)と一緒に分散し、炭素短繊維(A)の再集束を防止すると共に、シート状物を自立シートたらしめる役割を果たすことができる。また、使用する樹脂(例えば、フェノール樹脂(c))によっては、樹脂の硬化に縮合水を生成するものもあるが、フィブリル状繊維には、その水を吸収、排出する役割も期待できる。そのため、水との親和性にも優れているものが好ましい。具体的なフィブリル状繊維(b2)としては、例えば、フィブリル化されたポリエチレン繊維、アクリル繊維、アラミド繊維などの合成パルプが挙げられる。フィブリル状繊維(b2)は、炭素化処理後に残炭があるもの(炭素として残るもの)であっても良いし、炭素化処理後に残炭がないもの(炭素として残らないもの)であっても良い。
フィブリル状繊維(b2)としては、繊維(b2-1)を1種類または濾水度、繊維直径またはポリマー種が異なる繊維(b2-1)を2種類以上用いることもできる。また、繊維(b2-2)を1種類または濾水度、繊維直径またはポリマー種が異なる繊維(b2-2)を2種類以上用いることもでき、これらを組み合わせて用いることもできる。
以下に、この2つのフィブリル状繊維(b2)について詳しく説明する。
・フィブリルが多数分岐した構造を有する炭素前駆体繊維(b2-1)
繊維(b2-1)を構成するポリマーは、炭素化後に、炭素短繊維(A)と共に多孔質電極基材の構造を成立させる観点から、炭素化処理する工程における残存質量が20質量%以上であることが好ましい。このようなポリマーとしては、例えばアクリル系ポリマー、セルロース系ポリマー、フェノール系ポリマーを挙げることができる。
なお、繊維(b2-1)の平均繊維長は、多孔質電極基材の機械的強度を確保する観点から0.1mm以上とすることが好ましく、前駆体シート内での分散性の観点から3mm以下とすることが好ましい。また、繊維(b2-1)の直径(平均繊維径)は、前駆体シート製造時の脱水性や多孔質電極基材のガス透過性を確保する観点から0.01μm以上とすることが好ましく、熱処理時の収縮による破断を抑制する観点から30μm以下とすることが好ましい。
繊維(b2-2)は、長繊維状の易割繊性海島複合繊維を適当な長さにカットしたものを、リファイナーやパルパーなどによって叩解しフィブリル化したものであることができる。易割繊性海島複合繊維は、叩解によってフィブリル化する。長繊維状の易割繊性海島複合繊維は、共通の溶剤に溶解し、かつ非相溶性である2種類以上の異種ポリマーを用いて製造することができる。その際、炭素化後に、炭素短繊維(A)と共に多孔質電極基材の構造を成立させる観点から、少なくとも1種類のポリマーは、炭素化処理する工程における残存質量が20質量%以上であることが好ましい。
炭素繊維(B)は、炭素繊維前駆体短繊維(b1)、またはフィブリル状繊維(b2)のうち残炭があるもの(炭素として残るもの)を炭素化処理することによって得られる炭素繊維である。炭素繊維前駆体短繊維(b1)は、長繊維状の炭素繊維前駆体繊維を適当な長さにカットしたものであることができる。
上述したように、本発明では、フェノール樹脂(c)として、水溶性フェノール樹脂および水分散性フェノール樹脂のうちの一方または両方を用いる。
本発明で使用する水分散性フェノール樹脂は、例えば特開2004-307815号公報、特開2006-56960号公報等に示されるフェノール樹脂乳濁液(エマルション)やフェノール樹脂懸濁液(サスペンション)、あるいは水系ディスパージョンとも呼ばれる公知の水分散性フェノール樹脂を使うことができる。なお、架橋前のレゾール型フェノール樹脂は、水が液体として存在する温度・圧力範囲において、液体であることが多いため、水分散液は乳濁液(エマルション)となることが多い。一方、ノボラック型フェノール樹脂は一般にレゾール型フェノール樹脂に比べ分子量が高く、水が液体として存在する温度・圧力範囲において固体であることが多いため、水分散液は懸濁液(サスペンション)となることが多い。乳濁液、懸濁液のいずれの場合でも、フェノール樹脂の平均粒径は、シート状物内層に浸透させる観点から10μm以下であることが好ましく、5μm以下であることがより好ましい。例えば、塊状重合後に破砕して得たような、水への分散を意図していないフェノール樹脂粉末を、無理やり水に分散させても、シート状物内層への定量的な浸透が期待できないため好ましくない。具体的には、DIC(株)製の商品名:フェノライトTD-4304、PE-602や、住友ベークライト(株)製の商品名:スミライトレジンPR-14170、PR-55464、PR-50607Bや、昭和電工(株)製の商品名:ショウノールBRE-174等である。水分散性フェノール樹脂は、メタノールやメチルエチルケトンを溶媒とする一般的なフェノール樹脂と同様に、炭素化した段階で炭素短繊維(A)を結着しやすく、かつ導電性物質として残存しやすい。
本発明で使用する水溶性フェノール樹脂は、例えば特開2009-84382号公報等に示される水溶性が良好なレゾール型フェノール樹脂のような、公知の水溶性フェノール樹脂を使うことができる。具体的には、群栄化学(株)製の商品名:レヂトップPL-5634や、住友ベークライト(株)製の商品名:スミライトレジンPR-50781、PR-9800D、PR-55386や、昭和電工(株)製の商品名:ショウノールBRL-1583、BRL-120Z等である。水溶性フェノール樹脂は、メタノールやメチルエチルケトンを溶媒とする一般的なフェノール樹脂と同様に、炭素化した段階で炭素短繊維(A)を結着しやすく、かつ導電性物質として残存しやすい。
本発明において、樹脂炭化物(C)とは、単独で、又は、樹脂炭化物(C)と炭素繊維(B)とにより、炭素短繊維(A)同士と炭素粉(d)とを結着する、炭素前駆体樹脂を炭化してできた不定形な物質である。
炭素前駆体樹脂としては、フェノール樹脂など炭素繊維との結着力が強く、炭化時の残存質量が大きいものが好ましいが特に限定はされない。
この樹脂炭化物(C)は、炭素前駆体樹脂の種類や炭素繊維紙への含浸量により、最終的に多孔質炭素電極基材に炭化物として残る割合が異なる。多孔質電極基材を100質量%とした時に、その中の樹脂炭化物(C)が5~25質量%であることが好ましく、更に好ましい下限及び上限は、それぞれ10質量%及び20質量%である。
樹脂炭化物(C)には、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つに由来する樹脂炭化物(C)が含まれる。
炭素粉(d)としては、黒鉛粉、カーボンブラック、ミルドファイバーまたはこれらの混合物を用いることが、導電性発現の点で好ましい。
多孔質電極基材は、平板状、渦巻き状等の形状をとることができる。シート状の多孔質電極基材の目付は、取扱性の観点から15g/m2以上が好ましく、100g/m2以下が好ましい。シート状の多孔質電極基材の空隙率は、ガス拡散性の観点から50%以上が好ましく、機械的強度の観点から90%以下が好ましい。シート状の多孔質電極基材の厚みは、取扱性の観点から50μm以上が好ましく、300μm以下が好ましい。また、シート状の多孔質電極基材のうねりは、撥水処理等の後処理を均一に行えるようにする観点から5mm以下が好ましい。
<1> 炭素短繊維(A)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)に由来する樹脂炭化物(C)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
<2> 炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
<3> 炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
<4> 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)に由来する樹脂炭化物(C)とにより結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
<5> 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)とにより結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
<6> 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)により結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
本発明において、多孔質電極基材の嵩密度は、多孔質電極基材の目付と、詳細については後述する多孔質電極基材の初期厚みとから、以下のように算出できる。
嵩密度(g/cm3)=目付(g/m2)/初期厚み(μm)
本発明において、炭素短繊維(A)が3次元交絡構造を形成しているか否かは、シート状の測定対象物(多孔質電極基材)の断面観察を行い、断面における炭素短繊維(A)とシート面との角度を測定することにより判定できる。なお、断面観察を行う断面は、シート状の測定対象物のシート面に対して垂直方向の断面である。
本発明の多孔質電極基材は、固体高分子型燃料電池の膜-電極接合体に好適に用いることができる。また本発明の多孔質電極基材を用いた膜-電極接合体は、固体高分子型燃料電池に好適に用いることができる。
本発明の製造方法の過程で、炭素化処理工程[3]の前の段階において、前駆体シートが製造される。例えば、下記〔1〕~〔6〕が挙げられる。
〔1〕 炭素短繊維(A)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に炭素粉(d)が偏在している前駆体シート。
〔2〕 炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域が偏在する前駆体シート。
〔3〕 炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体であって、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が25%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が35~70%である前駆体シート。
〔4〕 炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)により結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に炭素粉(d)が偏在している前駆体シート。
〔5〕 炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、フェノール樹脂(c)により結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域が偏在する前駆体シート。
〔6〕 炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、フェノール樹脂(c)により結着されたシート状構造体であって、該構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、該構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が25%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が35~70%である前駆体シート。
前記「表層近傍は炭素粉(d)により空隙が埋まっているために空隙の占有率が相対的に低く、繊維一本一本の判別が困難であるのに対し、内層は空隙の占有率が相対的に高く、繊維一本一本の判別が容易である状態」としては、より具体的には、多孔質電極基材の最表層から深さ20μmまでの領域をXとし、また多孔質電極基材中心部の厚み方向に40μmの領域Yとすると、領域Xにおける空隙の占有率が25%未満であり、かつ、領域Yにおける空隙の占有率が35~70%であることが好ましく、領域Xにおける空隙の占有率が20%未満であり、かつ、領域Yにおける空隙の占有率が40~65%であることがより好ましい。
JIS規格P-8117に準拠した方法によって求められる。ガーレーデンソメーターを使用して試験片(多孔質電極基材)を直径3mmの孔を有するセルに挟み、孔から1.29kPaの圧力で200mLの空気を流し、その空気が透過するのにかかった時間を測定し、以下の式より算出した。
ガス透過度(mL/hr/cm2/Pa)=気体透過量(mL)/透過時間(hr)/透過孔面積(cm2)/透過圧(Pa)。
多孔質電極基材の厚さ方向の電気抵抗(貫通方向抵抗)は、金メッキした銅板に多孔質電極基材を挟み、銅板の上下から0.6MPaで加圧し、10mA/cm2の電流密度で電流を流したときの抵抗値を測定し、次式より求めた。
貫通方向抵抗(mΩ・cm2)=測定抵抗値(mΩ)×試料面積(cm2)。
多孔質電極基材の嵩密度は、多孔質電極基材の目付と、後述する多孔質電極基材の初期厚みから、以下のように算出した。
嵩密度(g/cm3)=目付(g/m2)/初期厚み(μm)。
多孔質電極基材の厚みは、マイクロオートグラフ小形試験片圧縮試験装置((株)島津製作所製、商品名:MST-I)を使用して、以下のように測定した。あらかじめ平行度を調整した直径50mmの上圧盤(固定式)と、直径50mmの下圧盤(球座式)の間に何も挟まず、ストローク速度0.4mm/minにて負荷ロッドを下降させた。3MPaの圧力が印加されたら、直ちに負荷ロッドのストロークを停止し、3点の圧盤間変位計の値をすべてゼロに設定した。次いで、上圧盤と下圧盤の間に、直径25mmの試験片(多孔質電極基材)を置き、ストローク速度0.4mm/minにて負荷ロッドを下降させた。試験片に0.05MPaの圧力が印加されたら、直ちに負荷ロッドのストロークを停止し、30秒後の圧盤間変位計の値を3点で読み取り、その平均値を厚みとした。
(5)断面観察写真の領域Xまたは領域Yにおける空隙率
クロスセクションポリッシャで切り出した多孔質電極基材の断面観察写真について、領域Xまたは領域Yにおける空隙率は以下のように測定した。前記断面を倍率300倍で撮影した走査型電子顕微鏡写真を、画像解析ソフトウェア(ImagePro)で開き、二値化により、空隙部とそれ以外とに分画し、空隙部の面積が全体に占める割合を算出した。
炭素短繊維(A)として、平均繊維径が7μm、平均繊維長が3mmのPAN系炭素繊維を用意した。また、炭素繊維前駆体短繊維(b1)として、平均繊維径が4μm、平均繊維長が3mmのアクリル短繊維(三菱レイヨン(株)製、商品名:D122)を用意した。また、フィブリル状繊維(b2)として、繊維状の幹より直径が3μm以下のフィブリルが多数分岐した、噴射凝固によって作製したポリアクリロニトリル系パルプ(b2-1)を用意した。シート状物の製造および交絡処理による3次元交絡構造シートの製造は、以下のような湿式連続抄紙法と、連続加圧水流噴射処理による交絡処理法により行った。
*湿式連続抄紙法
(1)炭素短繊維(A)の離解
平均繊維径が7μm、平均繊維長が3mmのPAN系炭素繊維を、繊維濃度が1%(10g/L)になるように水中へ分散して、ディスクリファイナー(熊谷理機製)を通して離解処理し、離解スラリー繊維(SA)とした。
(2)炭素繊維前駆体短繊維(b1)の離解
炭素繊維前駆体短繊維(b1)として、平均繊維径が4μm、平均繊維長が3mmのアクリル短繊維(三菱レイヨン(株)製、商品名:D122)、を、繊維濃度が1%(10g/L)になるように水中へ分散し、離解スラリー繊維(Sb1)とした。
(3)フィブリル状繊維(b2)の離解
フィブリル状繊維(b2)として、繊維状の幹より直径が3μm以下のフィブリルが多数分岐した、噴射凝固によって作製したポリアクリロニトリル系パルプを、繊維濃度が1%(10g/L)になるように水中へ分散し、離解スラリー繊維(Sb2)とした。
(4)抄紙用スラリーの調製
炭素短繊維(A)と炭素繊維前駆体短繊維(b1)とフィブリル状繊維(b2)とが、質量比60:20:20となるように、かつスラリー中の繊維(以下、フロックと略す)の濃度が1.7g/Lとなるように、離解スラリー繊維(SA)、離解スラリー繊維(Sb1)、離解スラリー繊維(Sb2)および希釈水を計量し、スラリー供給タンクに投入した。さらに、ポリアクリルアマイドを添加して粘度22センチポイズの抄紙用スラリーを調製した。
*処理装置
ネット駆動部および幅60cm×長さ585cmのプラスチックネット製平織メッシュをベルト状につなぎあわせて連続的に回転させるネットよりなるシート状物搬送装置、スラリー供給部幅が48cm、供給スラリー量が30L/minである抄紙用スラリー供給装置、ネット下部に配置した減圧脱水装置、と下記に示す加圧水流噴射処理装置からなる。ウォータージェットノズルとしては,表1のごとく2種類のノズルを3本用いた。
前記処理装置のネット上に上記抄紙用スラリーを定量ポンプによりネット上に供給した。抄紙用スラリーは均一な流れに整流するためのフローボックスを通して所定サイズに拡幅して供給した。その後静置、自然脱水する部分を通過して、減圧脱水装置により完全脱水し、目標目付65g/m2の湿紙ウエッブをネット上に積載した(工程[1]及び工程[7])。この処理が完了すると同時に、試験機後方のウォータージェットノズルより、加圧水流噴射圧力を3MPa(ノズル1)、圧力3MPa(ノズル2)、圧力4MPa(ノズル3)の順で通過させて交絡処理を加えた(工程[4])。
交絡処理されたシート状物をピンテンター試験機(辻井染色機製、商品名:PT-2A-400)により150℃×3分で乾燥させることで(工程[7])、目付64g/m2の3次元交絡構造シートを得た。得られた3次元交絡構造シート中での炭素繊維前駆体短繊維(b1)およびフィブリル状繊維(b2)の分散状態は良好であった。
次に、分散液(e)に用いる樹脂(c)として2種のレゾール型フェノール樹脂の水分散液(住友ベークライト(株)製、商品名:PR-14170、PR-55464)を用意し、これらの樹脂固形分比率が7:3で、かつ樹脂固形分の合計が樹脂水分散液の10質量%となるように純水で希釈した。さらに、炭素粉(d)として熱分解黒鉛(伊藤黒鉛工業(株)製、商品名:PC-H)を、炭素粉/樹脂固形分比が1.0となるように添加して、添加液とした。この添加液を前記3次元交絡構造シートに片面ずつ両面から流下し(工程[2])、ニップにより余分な樹脂(c)と炭素粉(d)を除去した後、80℃でシート中の水を十分に乾燥させ(工程[6])、樹脂の不揮発分と炭素粉の合計で48質量%付着させた前駆体シートを得た。
前記前駆体シートを、例えば特許第3699447号に開示される、一対のエンドレスベルトを備えた連続式加熱プレス装置(ダブルベルトプレス装置:DBP)にて連続的に加熱加圧し(工程[5])、表面が平滑化された中間基材(シート厚み:240μm、幅40cm)を得た。このときの予熱ゾーンでの予熱温度は150℃、予熱時間は5分であり、加熱加圧ゾーンでの温度は230℃、プレス圧力は線圧8.0×104N/mであった。なお、前駆体シートがベルトに貼り付かないように、2枚の離型紙の間に挟んでDBPを通した。
前記中間基材を、不活性ガス(窒素)雰囲気中、2200℃で炭素化して(工程[3])、炭素短繊維(A)が繊維状の樹脂炭化物(炭素繊維(B))と不定形な樹脂炭化物(C)とで結着された多孔質炭素電極基材を得た。得られた多孔質炭素電極基材の走査型電子顕微鏡による表面観察写真を図1に、断面観察写真を図2に、それぞれ示す。得られた多孔質電極基材は、熱処理時における面内の収縮がなく、厚みおよび貫通方向抵抗は、それぞれ良好であった。図1に示すように、3次元構造体中に分散された炭素短繊維(A)同士が、繊維状の樹脂炭化物(炭素繊維(B))と、不定形な樹脂炭化物(C)とによって結着されており、さらに表面に炭素粉(d)が偏在していることを確認できた。この多孔質電極基材に面圧3MPaの圧縮荷重を印加しても、シート形態を保つことができた。
以下の点以外は、実施例1と同様にして多孔質電極基材を得た。
・シート状物の作製に用いるフィブリル状繊維(b2)として、叩解によってフィブリル化するアクリル系ポリマーとジアセテート(酢酸セルロース)とからなる易割繊性アクリル系海島複合短繊維(三菱レイヨン(株)製、商品名:ボンネルM.V.P.-C651、平均繊維長:3mm)を叩解処理したもの(繊維(b2-2))を用いた点。
・シート状物の作製に用いる炭素短繊維(A)と炭素繊維前駆体短繊維(b1)とフィブリル状繊維(b2)との質量比を、70:10:20にし、かつ目標目付を55g/m2とした点。
・交絡処理における加圧水流噴射圧力を2MPa(ノズル1)、2MPa(ノズル2)、2MPa(ノズル3)とした点。
・樹脂添加液に用いる樹脂水分散液として2種のレゾール型フェノール樹脂の水分散液(住友ベークライト(株)製、商品名:PR-14170、PR-55464)を用意し、これらの樹脂固形分比率を5:5とした点。
以下の点以外は、実施例1と同様にして多孔質電極基材を得た。
・抄紙用スラリーを調製する際に、炭素短繊維(A)と炭素繊維前駆体短繊維(b1)とフィブリル状維(b2)との質量比を80:0:20となるようにした点。
・樹脂添加液に用いる樹脂水分散液として1種類のレゾール型フェノール樹脂の水分散液(住友ベークライト(株)製、商品名:PR-55464)を用意し、樹脂添加液中の樹脂の固形分濃度を12質量%とした点。
・炭素粉/樹脂固形分比を0.8とした点。
・樹脂添加方法として、ローラーポンプ(東京理化器械(株)製、商品名:RP-1000)を用いて添加液を送液(ポンプ回転数80rpm)し、吐出部に設置した渦流式微粒化ノズル((株)アトマックス製、商品名:AM45)から噴霧(エア圧0.2MPa)する方法を用いた点。
・加熱加圧をバッチプレス方式で行い、温度を180℃、予熱時間を0秒、圧力を6MPa、加熱加圧時間を1分とした点。
以下の点以外は、実施例1と同様にして多孔質電極基材を得た。
・抄紙用スラリーを調製する際に、炭素短繊維(A)と炭素繊維前駆体短繊維(b1)とフィブリル状維(b2)との質量比を50:30:20となるようにし、かつ目標目付を50g/m2とした点。
・交絡処理における加圧水流噴射圧力を2MPa(ノズル1)、2MPa(ノズル2)、2MPa(ノズル3)とした点。
・樹脂添加液に用いる樹脂水分散液として1種類のレゾール型フェノール樹脂の水分散液(住友ベークライト(株)製、商品名:PR-14170)を用意し、樹脂添加液中の樹脂の固形分濃度を8質量%とした点。
・炭素粉(d)としてケッチェンブラック(ライオン(株)製、商品名:カーボンECP)炭素粉/樹脂固形分比を0.5とした点。
・加熱加圧をバッチプレス方式で行い、温度を180℃、予熱時間を0秒、圧力を4.5MPa、加熱加圧時間を3分とした点。
以下の点以外は、実施例1と同様にして多孔質電極基材を得た。
・シート状物の作製に用いるフィブリル状繊維(b2)として、叩解によってフィブリル化するアクリル系ポリマーとジアセテート(酢酸セルロース)とからなる易割繊性アクリル系海島複合短繊維(三菱レイヨン(株)製、商品名:ボンネルM.V.P.-C651、平均繊維長:3mm)を叩解処理したもの(繊維(b2-2))を用いた点。
・炭素粉(d)を添加しなかった点。
・樹脂添加方法として、ローラーポンプ(東京理化器械(株)製、商品名:RP-1000)を用いて添加液を送液(ポンプ回転数80rpm)し、吐出部に設置した渦流式微粒化ノズル((株)アトマックス製、商品名:AM45)から噴霧(エア圧0.2MPa)する方法を用いた点。
(1)膜-電極接合体(MEA)の製造
実施例1で得られた多孔質電極基材2組を、カソード用およびアノード用の多孔質電極基材として用意した。また、パーフルオロスルホン酸系の高分子電解質膜(膜厚:30μm)の両面に触媒担持カーボン(触媒:Pt、触媒担持量:50質量%)からなる触媒層(触媒層面積:25cm2、Pt付着量:0.3mg/cm2)を形成した積層体を容易した。この積層体を、カソード用およびアノード用の多孔質電極基材で挟持し、これらを接合して、MEAを得た。
(2)MEAの燃料電池特性評価
得られたMEAを、蛇腹状のガス流路を有する2枚のカーボンセパレーターによって挟み、固体高分子型燃料電池(単セル)を形成した。この単セルの電流密度-電圧特性を測定することによって、燃料電池特性評価を行った。燃料ガスとしては水素ガスを用い、酸化ガスとしては空気を用いた。単セルの温度を80℃、燃料ガス利用率を60%、酸化ガス利用率を40%とした。また、燃料ガスと酸化ガスへの加湿は50℃のバブラーにそれぞれ燃料ガスと酸化ガスを通すことによって行った。その結果、電流密度が0.4A/cm2のときの燃料電池セルのセル電圧が0.610V、セルの内部抵抗が5.9mΩであり、良好な特性を示した。
長さ3mmにカットした平均直径7μmのポリアクリロニトリル(PAN)系炭素短繊維束を水中で解繊し、この短繊維束80質量部が十分に分散したところにバインダーであるポリビニルアルコール(PVA)(商品名:VBP105-1、クラレ株式会社製)の短繊維20質量部を均一に分散させ、標準角形シートマシンを用いて抄紙を行った。得られた炭素繊維紙は単位面積当たりの質量が43g/m2であった。
次に、分散液(e)に用いる樹脂(c)としてフェノール樹脂水溶液(住友ベークライト(株)製、商品名:PR-9800D)を用意し、樹脂固形分比率が分散液(e)の10質量%となるように純水で希釈した。さらに、炭素粉(d)としてケッチェンブラック(ライオン(株)製、商品名:カーボンECP)を、炭素粉/樹脂固形分比が0.01となるように添加して、分散液(e)とした。
この分散液(e)を前記炭素繊維紙に両面から滴下し(工程[2])、80℃でシート中の水を十分に乾燥させ(工程[6])、樹脂の不揮発分と炭素粉の合計で112質量%付着させた前駆体シートを得た。
前記前駆体シートに対し、180℃の温度で、予熱なしで6MPaの圧力を3分間加えてバッチプレスを行い、樹脂(c)を硬化させ、不活性ガス(窒素)雰囲気中、2000℃で炭素化して(工程[3])、多孔質炭素電極基材を得た。
以下の点以外は、実施例5と同様にして多孔質電極基材を得た。
・炭素粉(d)としてデンカブラック(電気化学工業(株)製、商品名:デンカブラック粒状品)を用いた点。
・炭素粉/樹脂固形分比を0.1とした点。
・分散液(e)の炭素繊維紙への添加方法を噴霧とした点。
以下の点以外は、実施例6と同様にして多孔質電極基材を得た。
・樹脂(c)としてフェノール樹脂水分散液(住友ベークライト(株)製、商品名:PR-14170)を用いた点。
・炭素粉/樹脂固形分比を0.001とした点。
以下の点以外は、実施例7と同様にして多孔質電極基材を得た。
・炭素粉(d)としてバルカンを用いた点。
・炭素粉/樹脂固形分比を0.1とした点。
以下の点以外は、実施例5と同様にして多孔質電極基材を得た。
・樹脂(c)としてフェノール樹脂水分散液(住友ベークライト(株)製、商品名:PR-55464)を用いた点。
・炭素粉(d)として鱗片状黒鉛(伊藤黒鉛工業(株)製、商品名:Z-5F)を用いた点。
・炭素粉/樹脂固形分比を2.0とした点。
・分散液(e)の炭素繊維紙への添加方法を噴霧とした点。
以下の点以外は、実施例9と同様にして多孔質電極基材を得た。
・炭素粉(d)として球状黒鉛(伊藤黒鉛工業(株)製、商品名:SG-BL40)を用いた点。
・炭素粉/樹脂固形分比を3.0とした点。
実施例1の多孔質電極基材を得る途中の前駆体シートについて、クロスセクションポリッシャで断面を出し、走査型電子顕微鏡を用いて倍率300倍で断面観察写真を得た。前記写真を、画像解析ソフトウェア(ImagePro)で開き、二値化により、空隙部とそれ以外とに分画し、空隙部の面積が全体に占める割合を算出したところ、領域Xにおける空隙率は3%であり、領域Yにおける空隙率は44%であった。
(実施例12)<撥水処理の実施例>
ポリテトラフルオロエチレン(PTFE)の微粒子が分散したディスパージョン(三井・デュポンフロロケミカル(株)製、商品名:31-JR)を用意し、固形分が20質量%となるように純水を加えて希釈した。実施例1で得られた多孔質電極基材を、前記希釈したPTFEディスパージョンに含浸し、ニップした後に、120℃に設定した遠赤外線炉に入れて乾燥した。次いで、360℃に設定した雰囲気炉を用いて20分熱処理を加えることにより、PTFEを焼結して、撥水処理済み多孔質電極基材を得た。
B :炭素繊維(B)
C :樹脂炭化物(C)
D :炭素粉(d)
1 :シート面と平行な線
Claims (15)
- 以下の[1]~[3]の工程を含む、多孔質電極基材の製造方法。
[1]炭素短繊維(A)を分散し、シート状物とする工程、
[2]前記シート状物に、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つのフェノール樹脂(c)を炭素粉(d)と共に添加し、前駆体シートとする工程、および
[3]工程[2]の後に、前駆体シートを1000℃以上の温度で炭素化処理する工程。 - 前記工程[1]と前記工程[2]の間にシート状物を交絡処理する工程[4]を含み、前記工程[4]と前記工程[2]の間にシート状物を乾燥処理する工程[7]を含み、前記工程[2]と前記工程[3]の間に、前駆体シートを100~250℃の温度で加熱加圧する工程[5]を含み、前記工程[2]と前記工程[5]の間に、前記前駆体シートを乾燥処理する工程[6]を含む、請求項1に記載の製造方法。
- 前記工程[2]において、炭素粉(d)の実質的な粒子あるいは凝集体の平均粒径が、0.1~50μmであることを特徴とする請求項1または2に記載の製造方法。
- 前記工程[3]の後に、多孔質電極基材に固形分1~30質量%のフッ素系樹脂ディスパージョンを添加し、さらに乾燥して300~390℃にて熱処理を行う撥水処理工程[8]を有することを特徴とする請求項1~3のいずれか1項に記載の製造方法。
- 炭素短繊維(A)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つに由来する樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
- 炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
- 炭素短繊維(A)が樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、前記領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、前記シート状構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
- 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つに由来する樹脂炭化物(C)とにより結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している多孔質電極基材。
- 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)とにより結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域が偏在している多孔質電極基材。
- 炭素短繊維(A)が、繊維径0.1~5μmの炭素繊維(B)と、樹脂炭化物(C)により結着されたシート状構造体を含む多孔質電極基材であって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が樹脂炭化物(C)により結着された領域を有し、該領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が30%未満であり、該構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が50~90%である多孔質電極基材。
- 炭素短繊維(A)が、フェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に炭素粉(d)が偏在している前駆体シート。
- 炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)がフェノール樹脂(c)により結着された領域が偏在する前駆体シート。
- 炭素短繊維(A)がフェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が前記フェノール樹脂(c)により結着された領域を有し、前記領域を有する面の表面から深さ20μmまでの領域Xにおける空隙の占有率が25%未満であり、前記シート状構造体の中心部の厚み方向に40μmの領域Yにおける空隙の占有率が35~70%である前駆体シート。
- 炭素短繊維(A)と、炭素繊維前駆体短繊維(b)が、フェノール樹脂(c)により結着されたシート状構造体を含む前駆体シートであって、前記シート状構造体中で炭素短繊維(A)が3次元交絡構造を形成しており、前記シート状構造体の片面または両面の表層近傍に、炭素短繊維(A)および炭素粉(d)が前記フェノール樹脂(c)により結着された領域が偏在する前駆体シート。
- フェノール樹脂(c)が、水溶性フェノール樹脂および水分散性フェノール樹脂からなる群から選択される少なくとも1つである請求項12~14のいずれか1項に記載の前駆体シート。
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WO2018124581A1 (ko) * | 2016-12-29 | 2018-07-05 | 코오롱인더스트리(주) | 펴짐성이 우수한 롤 타입 가스확산층의 제조방법 |
US10923732B2 (en) | 2016-12-29 | 2021-02-16 | Kolon Industries, Inc. | Method for producing roll-type gas diffusion layer having excellent spreading property |
JP2018152270A (ja) * | 2017-03-14 | 2018-09-27 | アイシン化工株式会社 | 燃料電池用ガス拡散層及びその製造方法 |
US10978716B2 (en) | 2018-06-07 | 2021-04-13 | Panasonic Intellectual Property Management Co., Ltd. | Gas diffusion layer for fuel battery, membrane electrode assembly, and fuel battery |
Also Published As
Publication number | Publication date |
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CA2866288C (en) | 2018-08-07 |
JPWO2013147174A1 (ja) | 2015-12-14 |
KR20160110564A (ko) | 2016-09-21 |
JP2014207240A (ja) | 2014-10-30 |
CN104205448B (zh) | 2017-03-29 |
EP2833450A1 (en) | 2015-02-04 |
CN104205448A (zh) | 2014-12-10 |
KR20140141607A (ko) | 2014-12-10 |
EP2833450A4 (en) | 2015-04-01 |
CA2866288A1 (en) | 2013-10-03 |
JP5621923B2 (ja) | 2014-11-12 |
US9716278B2 (en) | 2017-07-25 |
US20150086901A1 (en) | 2015-03-26 |
JP6086096B2 (ja) | 2017-03-01 |
KR101867747B1 (ko) | 2018-07-23 |
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