JP6500421B2 - Carbon fiber non-woven fabric - Google Patents

Description

  The present invention relates to a carbon fiber non-woven fabric suitable for an electrode substrate such as a polymer electrolyte fuel cell and a method for producing the same.

  A carbon fiber woven or knitted fabric and a carbon fiber non-woven fabric are applied to a gas diffusion electrode for a polymer electrolyte fuel cell because they have corrosion resistance and can achieve both gas permeation and conductivity at a high level.

  In a polymer electrolyte fuel cell, high power generation efficiency may not be obtained due to the occurrence of so-called flooding in which water produced by the reaction blocks the pores of the catalyst layer and the gas diffusion electrode and hinders transport of hydrogen and air. . On the other hand, humidification of the electrolyte membrane and catalyst layer to the ionomer is not sufficient, and high drying efficiency can not be obtained even when drying progresses, that is, when drying out occurs. From this, it is possible to maintain the wet state of the electrolyte membrane and the ionomer of the catalyst layer with the hydrogen that is supplied by the reaction with the supplied hydrogen and the moisture added to the air, and the excess water does not disturb the transport of hydrogen and air. It needs to be discharged to the channel promptly. Therefore, attempts have been made to improve water discharge by a method in which the gas diffusion electrode is subjected to water repellent treatment with a fluorine resin or the like, or a method in which a gas diffusion electrode is formed with a microporous layer consisting of a fluorine resin and conductive particles. This is not sufficient, and further performance improvement is required.

  For example, Patent Documents 1 and 2 disclose a technology capable of smoothly discharging water from the holes by using carbon paper having a hole having an opening on the channel side as a gas diffusion electrode.

  In Patent Documents 2 and 3, by forming non-through holes with a depth of 20 to 80% of the thickness by laser processing, it is possible to balance the drainage from the gas diffusion electrode and the moisture retention of the ionomer of the electrolyte membrane or catalyst layer. Technology is disclosed.

JP-A-8-111226 JP, 2009-211928, A JP, 2011-96385, A

  Patent Document 1 describes the provision of through holes in the thickness direction of the gas diffusion electrode base material as a preferred embodiment. This has the effect of improving drainage, but facilitates drying of the electrolyte membrane and the ionomer of the catalyst layer.

  Patent Documents 2 and 3 disclose a technique for forming a non-through hole in a gas diffusion electrode substrate by laser or mechanical processing. Although such a non-through hole facilitates controlling the balance between drainage from the gas diffusion electrode and the suppression of drying of the electrolyte membrane and ionomer of the catalyst layer, the carbon fiber is partially damaged at the time of hole formation and loses continuity. There is a problem that the conductivity and the thermal conductivity decrease.

In the present invention for achieving the above object, a plurality of non-through holes having an open area larger than the average pore area of a carbon fiber non-woven fabric are dispersedly formed on the surface, and carbon forming the wall surface of the non-through holes It is a carbon fiber nonwoven fabric in which at least a part of carbon fibers among the fibers are oriented in the height direction of the non-through holes. Moreover, the present invention for obtaining such a carbon fiber non-woven fabric is
Step A: A step of forming a non-through hole on the surface of the carbon fiber precursor fiber non-woven fabric, wherein the shaping member having a convex portion corresponding to the non-through hole is pressed against the surface of the carbon fiber precursor fiber non-woven fabric Forming a non-through hole;
Step B: A carbon fiber non-woven fabric manufacturing method comprising the step of carbonizing the carbon fiber precursor fiber non-woven fabric obtained in Step A.

  According to the present invention, it is possible to provide a carbon fiber non-woven fabric suitable for a gas diffusion electrode, which is excellent in conductivity and thermal conductivity and is compatible with drainage of the gas diffusion electrode and moisture retention of the electrolyte membrane and ionomer of the catalyst layer at high levels. .

It is a scanning electron micrograph of the cross section of the carbon fiber nonwoven fabric of this invention obtained in Example 1. FIG.

<Carbon fiber non-woven fabric>
[Carbon fiber non-woven fabric]
Hereinafter, the case where the carbon fiber nonwoven fabric of the present invention is mainly used as a fuel cell gas diffusion electrode base material will be described as an example.

  In the present invention, the carbon fiber non-woven fabric is a web or sheet composed of carbon fibers. A carbon fiber is a carbon fiber precursor fiber heated and carbonized in an inert gas atmosphere, and a carbon fiber nonwoven fabric is a carbon fiber precursor fiber nonwoven heated and carbonized in an inert gas atmosphere It is. The carbon fiber precursor fiber will be described later. As the web, a dry parallel laid web or crosslaid web, an air laid web, a wet papermaking web, an extrusion spunbond web, a meltblown web, an electrospinning web, etc. can be used. Further, as the sheet, a sheet mechanically interlocking these webs, a sheet fused by heating, a sheet bonded with a binder, or the like can be used.

  The carbon fiber non-woven fabric preferably includes carbon fibers having a curved portion with a radius of curvature of 1 mm or less. Generally, the conductivity and thermal conductivity of carbon fibers are better in the fiber axis direction than in the fiber cross-sectional direction, and fibers having curved portions with a small radius of curvature have longer fiber lengths within a certain area, so carbon fiber non-woven fabrics It can be expected to impart high conductivity and thermal conductivity to the The carbon fiber non-woven fabric of the present invention more preferably includes carbon fibers having a curved portion with a radius of curvature of 500 μm or less, and further preferably includes carbon fibers having a curved portion with a radius of curvature of 200 μm or less.

  The inclusion of the carbon fiber having such a curved portion can be confirmed by observing the carbon fiber on the surface of the carbon fiber nonwoven fabric. The radius of curvature of the carbon fiber can be determined as the radius of the circumscribed circle of the three points by observing the carbon fiber on the surface of the non-woven carbon fiber fabric with an optical microscope or an electron microscope and taking any three points in the curved portion of the carbon fiber . In the present invention, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber non-woven fabric is observed with an optical microscope or an electron microscope, ten or more carbon fibers having a curved portion with such a radius of curvature can be confirmed. Preferably, 30 or more lines can be confirmed. Also, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber non-woven fabric is observed with an optical microscope or an electron microscope and this field of view is divided into 25 areas of 0.3 mm × 0.3 mm, such It is preferable that the area | region which can confirm the curved part of a curvature radius is five or more, and it is more preferable that it is ten or more.

  In the carbon fiber non-woven fabric, when carbide as a binder is attached to the contact between carbon fibers, the contact area becomes larger at the contact between carbon fibers, and excellent conductivity and thermal conductivity can be obtained. As a method of applying such a binder, a method of impregnating or spraying a binder solution on a carbon fiber non-woven fabric after carbonization treatment, and heat treating again in an inert atmosphere to carbonize the binder can be mentioned. In this case, thermosetting resins such as phenol resin, epoxy resin, melamine resin and furan resin can be used as the binder, and among them, phenol resin is particularly preferable in view of high carbonization yield. In addition, as described later, a method in which a thermoplastic resin is blended with a carbon fiber precursor nonwoven fabric is also preferable.

  The average pore diameter of the carbon fiber non-woven fabric of the present invention is not particularly limited, but is preferably 2 to 45 μm, and more preferably 5 to 30 μm. If it is less than 2 μm, flooding tends to occur easily, and if it is 45 μm or more, dryout tends to occur easily. Here, the average pore size of the carbon fiber non-woven fabric is a value calculated as an average flow pore size (Mean Flow Pore Size) by the method of ASTM F316-86.

[Non-through hole]
The carbon fiber non-woven fabric of the present invention is formed by dispersing and forming on the surface a plurality of non-through holes having an open area larger than the average pore area of the carbon fiber non-woven fabric. The non-through holes are holes (recesses) having an opening on one side of the carbon fiber non-woven fabric and not reaching the other side. Here, the average pore area of the carbon fiber non-woven fabric refers to the area of a circle whose diameter is the average pore diameter of the carbon fiber non-woven fabric described above.

  The open area of the non-penetrating holes as referred to in the present invention is the thickness of the carbon fiber non-woven fabric when the carbon fiber non-woven fabric is pressurized at 1 MPa in the thickness direction (hereinafter simply referred to This refers to the open area when it is assumed that the non-through hole forming surface of the carbon fiber non-woven fabric is trimmed to the same thickness as the thickness when pressed. The thickness of the carbon fiber non-woven fabric cut into 2.5 cm × 2.5 cm at the time of pressurization is sandwiched by a metal plate with a surface of 3 cm or more × 3 cm or more and a thickness of 1 cm or more, and a pressure of 1 MPa is applied to the carbon fiber non-woven fabric Ask for. In addition, the open area of the non-through hole is to observe the surface of the carbon fiber non-woven fabric with a laser microscope or the like, and measure the cross-sectional area of each non-through hole at a height corresponding to the thickness when pressurized using a shape analysis application. You can ask for If the non-through holes are eliminated by trimming the non-through hole forming surface of the carbon fiber non-woven fabric until the thickness becomes the same as the thickness when pressurized, or the peripheral edge of the holes can not be recognized, the non-through holes Judged as not being formed. Moreover, when the shape of the non-through hole is referred to in the following description, it is assumed that the non-through hole forming surface of the carbon fiber non-woven fabric is trimmed to the thickness at the time of pressing, unless otherwise specified. It shall be a value about a through hole.

Open area of a single non-through-hole, in order to ensure the drainage, preferably at 1000 .mu.m ² or more, and more preferably 2000 .mu.m ² or more. Further, from the viewpoint of securing a contact area with the separator and having sufficient conductivity and thermal conductivity, it is preferably 100 mm ² or less, more preferably 10 mm ² or less, and 1 mm ² or less. Is more preferred.

  The cross-sectional shape of the non-through hole (the cross-sectional shape when cut in the in-plane direction of the carbon fiber non-woven fabric) is not particularly limited, and circular, oval, square, triangle, polygon, star or the like can be arbitrarily selected.

  The longitudinal cross-sectional shape (the cross-sectional shape when cut in the direction perpendicular to the surface of the carbon fiber non-woven fabric) of the non-through hole is not particularly limited, and the diameter in the depth direction is approximately rectangular even if the diameter does not change in the depth direction The shape may be a substantially trapezoidal shape, a substantially triangular shape, or a substantially arc shape that changes, but it is preferable to configure it as an inverted trapezoidal shape or an arch shape in which the diameter decreases with increasing depth. It is preferable that such non-through holes have an arc shape with an upper chord cross-section in the depth direction in terms of the easiness of hole formation. That is, it is preferable that the non-through hole be a substantially spherical recess.

  The depth of the non-through holes is not particularly limited, but is preferably 5% or more, and more preferably 10% or more with respect to the thickness of the carbon fiber non-woven fabric under pressure, from the viewpoint of securing drainage. The absolute value of the depth of the non-through holes is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more.

  The upper limit of the depth of the non-through holes is not particularly limited and may be appropriately set according to the thickness of the carbon fiber non-woven fabric, but from the viewpoint of securing the strength of the carbon fiber non-woven fabric and from the viewpoint of maintaining uniformity of gas supply It is preferable that it is 80% or less with respect to the thickness at the time of pressurization of a fiber nonwoven fabric, and it is more preferable that it is 50% or less. In addition, the carbon fiber non-woven fabric is preferably thin as long as the carbon fiber non-woven fabric exhibits its function, since the size of the fuel cell is increased if the thickness of the carbon fiber non-woven fabric itself is increased. Therefore, the depth of the non-through holes is preferably 400 μm or less, more preferably 300 μm or less, corresponding to the thickness of the carbon fiber non-woven fabric.

  The depth of the non-penetrating hole means the depth when it is assumed that the non-penetrating hole forming surface of the carbon fiber non-woven fabric is trimmed to the thickness at the time of pressurization as the opening area. The depth of such a non-through hole is observed by a laser microscope etc., and a height equivalent to the thickness of the carbon fiber non-woven fabric from the non-opening face of the non-through hole is used. Assuming a flat surface on the side, it can be obtained by measuring the depth of a portion of the non-through hole which is located on the non-opening side with respect to this flat surface.

  In the carbon fiber non-woven fabric of the present invention, the non-through holes are dispersedly formed on at least one surface. “Dispersed” means that a plurality of non-through holes are disposed on the surface of the carbon fiber non-woven fabric without the peripheries of the openings being in contact with each other. Although the arrangement pattern of the non-through holes is not particularly limited, it is preferable that the non-through holes be formed to be substantially uniformly distributed in the plane.

  The aperture ratio of the non-through holes is preferably 1.5% to 60%. When the aperture ratio of the non-through holes is 1.5% or more, sufficient drainage performance can be secured, and by being 60% or less, the conductivity and thermal conductivity should be excellent. Can. The open area ratio of the non-through holes is more preferably 3% or more, and more preferably 40% or less. The aperture ratio of the non-through holes is obtained by observing the non-through hole forming surface of the carbon fiber non-woven fabric with a laser microscope or the like, and using the shape analysis application, removing the sum of the open areas of the non-through holes in a certain field of view Can be asked.

The number of non-through holes is preferably 30 ^/ cm 2 ~ 5000 pieces / cm ² per unit area, and more preferably 100 ^/ cm 2 to 1500 pieces / cm ^2.

Furthermore, the non-through hole of the present invention preferably has an opening circumferential length per unit area of 0.1 to 20 km / m ² , and more preferably 0.5 to 10 km / m ² . When the opening circumference is 0.1 km / m ² or more, a high drainage effect can be obtained, and when the opening circumference is 10 km / m ² or less, a high moisturizing effect can be obtained.

  In the carbon fiber non-woven fabric of the present invention, at least a part of the carbon fibers constituting the wall surface of the non-through hole is oriented in the height direction of the non-through hole. The carbon fiber which comprises the wall surface of the non-through hole is a carbon fiber in which at least a part of the fiber is exposed to the inner wall surface of the non-through hole. And the said carbon fiber is orientating to the height direction of a non-penetrating hole, when the non-penetrating hole is equally divided into 3 in the height direction, the carbon fiber has two equally divided faces (carbon fiber non-woven fabric surface And both parallel planes are meant to penetrate.

  The presence of carbon fibers oriented in the height direction of the non-penetrating holes means that the surface of the carbon fiber non-woven fabric is observed with a laser microscope or the like, and the shape analysis application is used. Carbon fiber crossing both the intersection line of the dividing surface and the inner wall surface of the non-through hole and the intersection line of each 2 / 3-depth dividing surface of the non-through hole and the inner wall surface of the non-through hole is observed It can confirm by. In addition, the carbon fiber non-woven fabric crosses the non-penetrating hole at a position of 1/3 and 2/3 of the depth of the non-penetrating hole by observing any cross section including the non-penetrating hole of the carbon fiber non-woven fabric with a scanning electron microscope etc. After drawing two straight lines parallel to the surface, it can also be confirmed by observing carbon fibers intersecting with both of the two straight lines. Preferably, two or more such carbon fibers are present in one non-through hole, and more preferably five or more.

  In general, when a hole is formed, the contact area with a member (for example, a separator) on the gas supply side is smaller than in the case where the hole is not formed, and the conductivity and the thermal conductivity are reduced. However, since the carbon fiber is more excellent in conductivity and thermal conductivity in the fiber axis direction than in the fiber cross-sectional direction, the carbon fiber constituting the wall surface of the non-through hole is oriented in the height direction of the non-through hole In this case, the conductivity and heat conductivity of the carbon fiber non-woven fabric in the thickness direction can be improved, and the decrease in conductivity and heat conductivity due to the formation of holes can be compensated.

  It is preferable that such a carbon fiber similarly penetrates all of the three equal divisions in the case of dividing the non-through hole into four in the height direction, and the four equal divisions in the case of five equal divisions. More preferably, all of the faces are penetrated. It is preferable that at least a part of the carbon fibers constituting the wall surface of the non-through hole be continuous along the wall surface at least from the opening of the non-through hole to the bottom.

  In addition, when the carbon fibers oriented in the height direction of the non-through hole are continuous to the bottom of the non-through hole, the effect of improving the conductivity and thermal conductivity in the height direction of the non-through hole is obtained. It is preferable because it becomes high. The carbon fiber being continuous to the bottom of the non-penetrating hole means that the tip of the carbon fiber non-woven fabric bottom side of the carbon fiber constituting the wall surface of the non-penetrating hole is bent or curved, and at least one of the carbon fibers It refers to the state where the part is also exposed to the bottom of the non-through hole. In the case where the non-through hole is spherical or the like, and the wall surface and the bottom surface can not be distinguished in the non-through hole, the deepest portion of the non-through hole is considered as the bottom. When a cross section of the carbon fiber non-woven fabric is observed, at least a part of carbon fibers among carbon fibers constituting one wall surface of the non-penetrating hole continue to the bottom surface of the non-penetrating hole and another wall surface It is also preferable to configure. That is, it is preferable that the carbon fiber which comprises a wall surface in two places in a non-penetration hole, and is continued to the bottom face exists.

  In the present invention, all the carbon fibers constituting the wall surface of the non-through hole need not be oriented in the height direction of the non-through hole, and such carbon fibers may be present. Moreover, it is preferable that such carbon fibers can be confirmed in each non-through hole, but the presence of non-through holes in which such carbon fibers can not be confirmed is not outside the scope of the present invention.

<Method of manufacturing carbon fiber non-woven fabric>
The carbon fiber non-woven fabric of the present invention includes, as an example, step A: a step of pressing the surface of the carbon fiber precursor fiber non-woven fabric to form non-penetrating holes; and step B: a carbon fiber precursor fiber non-woven fabric obtained in step A And a step of carbonizing the carbon fiber non-woven fabric.

[Carbon fiber precursor fiber non-woven fabric]
The carbon fiber precursor fiber is a fiber to be carbonized by carbonization, preferably a fiber having a carbonization ratio of 15% or more, and more preferably 30% or more. The carbon fiber precursor fiber used in the present invention is not particularly limited, and polyacrylonitrile (PAN) fiber, pitch fiber, lignin fiber, polyacetylene fiber, polyethylene fiber, and fibers obtained by infusible these, polyvinyl Alcohol fibers, cellulose fibers, polybenzoxazole fibers and the like can be mentioned. Among them, it is particularly preferable to use a PAN-based flame resistant fiber in which PAN having high strength and elongation and good processability is infusible. The timing of infusibilization of the fibers may be before or after the production of the non-woven fabric, but it is preferable to infusibilize the fibers before forming into a sheet, since the infusibilization process can be easily controlled uniformly. When using a non-infusible carbon fiber precursor fiber non-woven fabric, infusibilization treatment can be performed after step A described later, but from the viewpoint of minimizing deformation in step A, it is infusible Preferably, the carbon fiber precursor fiber non-woven fabric is subjected to step A.
The carbonization rate can be determined from the following equation.
Carbonization ratio (%) = weight after carbonization / weight before carbonization × 100 The carbon fiber precursor fiber non-woven fabric is a web or a sheet formed of carbon fiber precursor fibers. As the web, a dry parallel laid web or crosslaid web, an air laid web, a wet papermaking web, an extrusion spunbond web, a meltblown web, an electrospinning web can be used. Further, as the sheet, a sheet mechanically interlocking these webs, a sheet fused by heating, a sheet bonded with a binder, or the like can be used. When PAN-based fibers obtained by the solution spinning method are infusible and made into a web, a dry web or a wet web is preferable because it is easy to obtain a uniform sheet, and in particular, it is easy to obtain form stability in the process. Particularly preferred is a sheet mechanically interlocked with a dry web.

  In order to impart high conductivity and thermal conductivity to the carbon fiber non-woven fabric after carbonization, in the carbon fiber precursor fiber non-woven fabric, the carbon fiber precursor fiber preferably includes a curved portion having a curvature radius of 1 mm or less . The carbon fiber precursor fiber non-woven fabric more preferably has a curved portion with a radius of curvature of 500 μm or less, and more preferably has a curved portion with a radius of curvature of 200 μm or less. Specifically, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber precursor fiber nonwoven fabric is observed with an optical microscope or an electron microscope, the carbon fiber precursor fiber having a curved portion with such a radius of curvature is It is preferable that 10 or more can be confirmed, and it is more preferable that 30 or more can be confirmed. In addition, when the area of 1.5 mm × 1.5 mm of the carbon fiber precursor fiber non-woven fabric surface is observed with an optical microscope or an electron microscope, this field of view is divided into 25 areas of 0.3 mm × 0.3 mm, It is preferable that the area | region which can confirm the curved part of such a radius of curvature is five or more, and it is more preferable that it is ten or more.

  As a method of obtaining a carbon fiber precursor fiber non-woven fabric containing a carbon fiber precursor fiber having a curved portion with a radius of curvature of 1 mm or less, carbon that has been crimped in advance by a push-in type (using stuffing box) A method of forming a non-woven fabric using a fiber precursor fiber, and a method of entanglement of the fiber and bending the fiber by mechanical processing such as needle punching or water jet punching after a web is made of carbon fiber precursor fibers Can. It is a more preferable method to use a carbon fiber precursor fiber non-woven fabric further subjected to needle punching or water jet punching to the web obtained by applying crimp.

  Further, as described above, the carbon fiber precursor fiber non-woven fabric preferably contains a binder because the conductivity and thermal conductivity are excellent when carbides adhere to the intersections of carbon fibers of the carbon fiber non-woven fabric. The method of incorporating the binder into the carbon fiber precursor fiber non-woven fabric is not particularly limited. However, a method of impregnating or spraying the carbon fiber precursor fiber non-woven fabric with the binder solution, or a thermoplastic resin used as a binder in advance to the carbon fiber precursor fiber non-woven fabric The method of mixing fibers is mentioned.

  When impregnating or spraying a binder solution onto a carbon fiber precursor fiber non-woven fabric, a thermosetting resin such as a phenol resin, an epoxy resin, a melamine resin, or a furan resin can be used as a binder, and phenol has high carbonization yield. Resins are preferred. However, when the binder resin solution is impregnated, the smoothness of the carbon fiber non-woven fabric is likely to be deteriorated due to the difference in shrinkage behavior between the carbon fiber precursor fiber and the binder resin in the carbonization step, and when the binder is dried. Since the migration phenomenon that the solution moves to the surface of the carbon fiber non-woven fabric is also apt to occur, uniform treatment tends to be difficult.

  On the other hand, in the method in which the thermoplastic resin fiber serving as the binder is blended with the carbon fiber precursor fiber nonwoven fabric in advance, the ratio of the carbon fiber precursor fiber to the binder resin can be made uniform in the nonwoven fabric. It is the most preferable method because the difference in shrinkage behavior between the fiber precursor fiber and the binder resin hardly occurs. As such thermoplastic resin-made fibers, relatively inexpensive polyester fibers, polyamide fibers and polyacrylonitrile fibers are preferable.

  The compounding amount of the binder is preferably 0.5 parts by mass or more, and 1 part by mass or more, with respect to 100 parts by mass of the carbon fiber precursor fiber, in order to improve the strength, the conductivity and the thermal conductivity of the carbon fiber non-woven fabric. It is more preferable that Moreover, in order to improve drainage, it is preferably 80 parts by mass or less, and more preferably 50 parts by mass or less.

  The binder can also be applied by impregnating or spraying a binder solution after shaping non-through holes in the carbon fiber precursor fiber nonwoven fabric in step A described later. Moreover, it can also carry out by passing through the process of impregnating or spraying a binder solution on the carbon fiber nonwoven fabric which performed carbonization processing in the process B mentioned later, and carrying out carbonization processing again. However, when the binder is applied after the formation of the non-through holes, the binder solution tends to be accumulated around the holes and the adhesion amount tends to be nonuniform. Therefore, it is preferable to perform before forming the holes.

  It is more preferable from the viewpoint of conductivity improvement to add a conductive auxiliary agent to a thermoplastic resin fiber serving as a binder and a solution to be impregnated or sprayed. As such a conductive support agent, carbon black, carbon nanotubes, carbon nanofibers, milled fibers of carbon fibers, graphite or the like can be used.

[Step A]
Step A is a step of forming non-through holes on the surface of the carbon fiber precursor fiber non-woven fabric to obtain a carbon fiber precursor fiber non-woven fabric having non-through holes. Conventionally, such non-through holes are generally formed by performing laser processing or machining on a carbon fiber non-woven fabric after carbonization, but this method is based on the wall surface of non-through holes at the time of hole formation. There is a problem in that the conductivity and the thermal conductivity are lowered because the carbon fibers are inevitably cut.

  In step A, the surface of the carbon fiber precursor fiber non-woven fabric is pressed to form non-penetrating holes. The method of pressing is not particularly limited as long as it does not involve cutting of carbon fiber, and a method of pressing a shaping member having a convex portion corresponding to the non-penetrating hole, a method of pressing by a needle member, or water A method of pressing can be used.

  Among them, preferred is a method of pressing a shaping member having a convex portion corresponding to the non-through hole to be formed on the surface of the carbon fiber precursor fiber nonwoven fabric. In this method, it is possible to form non-penetrating holes while preventing cutting of the carbon fiber precursor fiber by physically pressing a part of the surface of the carbon fiber precursor fiber non-woven fabric with the shaping member. As a result, at least a part of carbon fibers among the carbon fiber precursor fibers constituting the wall surface of the non-through hole is oriented in the height direction of the non-through hole.

  More specific means is not particularly limited, but embossing is preferable, and a method of continuously pressing with an embossing roll and a flat roll having a convex shape corresponding to the non-through hole, a plate and a flat plate having a similar convex shape Methods of batch pressing. At the time of pressing, it is preferable to use a heated roll or plate so that the form is not restored (no non-through holes are eliminated) in the carbonization treatment in step B described later. The heating temperature at this time is preferably 160 ° C. to 280 ° C., and more preferably 180 ° C. to 260 ° C., from the viewpoint of the form stability of the non-through holes formed in the nonwoven fabric structure of carbon fiber precursor fibers.

  Moreover, in order to control the density and thickness of the carbon fiber nonwoven fabric finally obtained, it is also a preferable aspect to implement the press in the roll and plate without a convex part before or after the process A.

In addition, in order to shape a non-penetrating hole without causing fiber breakage, it is preferable to deform a carbon fiber precursor fiber non-woven fabric having a relatively low density, so the carbon fiber precursor before being subjected to step A fiber nonwoven fabric is preferably an apparent density of 0.02~0.20g / cm ^3, more preferably 0.05~0.15g / cm ^3.

Further, the carbon fiber non-woven fabric used for the gas diffusion electrode can obtain excellent conductivity and thermal conductivity, so the apparent density is preferably 0.20 g / cm ³ or more, and the gas diffusibility is excellent, Preferably, the apparent density is 1.00 g / cm ³ or less. For that purpose, it is preferable to make the apparent density of a carbon fiber precursor fiber non-woven fabric 0.20 to 1.00 g / cm ³ . In order to control the apparent density of the carbon fiber precursor fiber non-woven fabric, after performing step A, it can be adjusted by pressing with a flat roll or flat plate, but from the viewpoint of controlling the shape of non-penetrating holes, In the step A, it is preferable to set the apparent density of the carbon fiber precursor fiber non-woven fabric to 0.20 to 1.00 g / cm ³ by simultaneously pressing not only the non-through hole portion but the entire carbon fiber precursor non-woven fabric.

[Step B]
Process B is a process of carbonizing the carbon fiber precursor fiber non-woven fabric obtained in Process A. The method of carbonization treatment is not particularly limited, and any known method in the field of carbon fiber materials can be used, but baking under an inert gas atmosphere is preferably used. The baking in an inert gas atmosphere is preferably performed by carbonizing at 800 ° C. or higher while supplying an inert gas such as nitrogen or argon. The firing temperature is preferably 1500 ° C. or more, more preferably 1900 ° C. or more, because it is easy to obtain excellent conductivity and thermal conductivity. On the other hand, when the viewpoint of the operating cost of a heating furnace is considered, it is preferable that it is 3000 degrees C or less.

  When using a carbon fiber non-woven fabric as a gas diffusion electrode of a polymer electrolyte fuel cell, it is preferable to adjust the form of carbon fiber precursor fiber non-woven fabric and carbonization treatment conditions so that the thickness becomes 30 to 400 μm after carbonization.

In the case where the carbon fiber precursor nonwoven fabric is formed of carbon fiber precursor fibers before infusibilization, it is preferable to perform the infusibilization step before the step B. Such an infusibilization step usually brings the treatment time to 10 to 100 minutes and the temperature to 150 to 350 ° C. in air. In the case of PAN-based infusible fiber, it is preferable to set the density to be in the range of 1.30 to 1.50 g / cm ³ .

[Others]
The carbon fiber non-woven fabric of the present invention can be used as it is as a gas diffusion electrode of a polymer electrolyte fuel cell, but it is said to be water repellent treatment with a fluorine resin and / or MPL because it excels in water management during power generation. It is preferable to form a layer composed of a fluorine-based resin and a carbonaceous conductive aid on one side.

Physical property values in the examples were measured by the following methods.
1. Fiber Structure (1) Number of Carbon Fibers Having Curved Portions with a Curvature Radius of 1 mm or Less The area of 500 μm × 500 μm of the carbon fiber non-woven fabric surface was observed with a scanning electron microscope. Three points were taken at the curved portion of the carbon fiber, and the radius of curvature of the curved portion was determined as the radius of the circumscribed circle of the three points. When 10 or more fibers having a curved portion with a radius of curvature of 1 mm or less could be confirmed, the number was determined to be large, and in the case of less than 10, the number was actually measured. The smallest radius of curvature among the radii of curvature measured on the target carbon fiber was taken as the radius of curvature of the carbon fiber.
(2) Shape of non-through hole The opening area and depth of non-through hole are observed with a laser microscope (VK-9710, manufactured by Keyence Corporation), and a shape analysis application (VK-Analyzer Plus, manufactured by Keyence Corporation) ) Was used. Conduct measurement analysis of the uneven part with a field of view of 1000 μm × 1400 μm, and assume a plane that exists from the non-opening face of the non-through hole to the opening face side by the height equivalent to the thickness of the carbon fiber non-woven fabric under pressure. The average value of the cross-sectional area of the non-through holes in the plane was taken as the open area of the non-through holes, and the average value of the depth of the portion present on the non-opening side from the plane was taken as the depth (absolute value) of the non-through holes. At this time, the threshold value of the height was taken as the value of the thickness of the carbon fiber non-woven fabric when pressurized at 1 MPa. An area smaller than 1000 μm ² was ignored as a minute area. Also, the open area ratio was determined as a percentage of the total area of the open areas of all non-through holes to the area of the carbon fiber non-woven fabric.
(3) Orientation of carbon fibers in the height direction on the wall surface of the non-through hole Whether the carbon fibers constituting the wall surface of the non-through hole are oriented in the height direction of the non-through hole can be determined by laser microscopy ( It observed by VK-9710 (made by Keyence Corporation), and judged using shape analysis application (VK-Analyzer Plus, made by Keyence Corporation). Observe a field of view of 1000 μm × 1400 μm, and the line of intersection between the 1⁄3 deep isosection of the non-through hole and the inner wall surface of the non-through hole, and the 1⁄3 deep equal division and inner wall surface of the non-through hole If even one carbon fiber crossing both lines of intersection was observed, it was judged that there was a fiber oriented in the height direction of the non-through hole.
(4) Average pore size of carbon fiber non-woven fabric
The average flow pore diameter was determined by the method of ASTM F316-86, and was taken as the average pore diameter of the carbon fiber non-woven fabric.
2. Power generation performance A catalyst layer (0.2 mg / cm ² platinum content) consisting of platinum-supported carbon and Nafion is joined by hot pressing on both sides of a fluorine-based electrolyte membrane Nafion 212 (manufactured by DuPont), and a catalyst layer-coated electrolyte membrane (CCM) It was created. Gas diffusion electrodes were disposed on both sides of this CCM, and hot pressing was performed again to obtain a membrane electrode assembly (MEA). An MEA having a gasket (70 μm thick) disposed around the gas diffusion electrode was set in a single cell (5 cm ² , serpentine flow path) manufactured by Electrochem. At this time, the surface on which the fluorine-based resin (PTFE) and the conductive auxiliary agent (carbon black) of the gas diffusion electrode were applied was set facing the MEA side.
(1) Voltage under humidification conditions The cell temperature is 60 ° C, the dew point of hydrogen and air is 60 ° C, the flow rates are 100cc / min and 250cc / min, and the gas outlet is open (no pressure), 0.6A / Electricity was generated at a current density of cm ² , and the voltage at that time was taken as the voltage under humidification conditions.
(2) Voltage under low humidification conditions Cell temperature is 90 ° C, dew point of hydrogen and air is 60 ° C, flow rate is 1000cc / min and 2500cc / min, gas outlet is open (no pressure), 0.6A Power was generated at a current density of 1 / cm ² , and the voltage at that time was taken as the voltage under the low humidification condition.

Example 1
The crimped yarn of PAN-based flame resistant yarn was cut into a number average fiber length of 76 mm, sheeted with a card and cloth layer, and needle punched at a needle density of 100 / cm ² to obtain a carbon fiber precursor fiber non-woven fabric .

  Cylindrical convex parts with a diameter of 150 μm and a height of 150 μm are dispersedly formed on one surface of this carbon fiber precursor fibrous nonwoven fabric, and the pitch of the convex parts is 0.5 mm for both MD and CD, elemental fiber precursor fibrous nonwoven fabric Embossing was performed using a metal embossing roll made of a dot pattern in which the area ratio of the projections to the area of 3% was 3%, and a metal flat roll. The heating temperature of the embossing roll and the flat roll was 220 ° C., and the linear pressure was 50 kN / m.

  Thereafter, carbonization was performed by raising the temperature to 1500 ° C. from room temperature over 3 hours and heating at 1500 ° C. for 15 minutes in a nitrogen atmosphere to obtain a carbon fiber non-woven fabric having non-penetrating holes shown in FIG. . The carbonization ratio calculated from the weight change before and after carbonization was 52%.

  The carbon fiber non-woven fabric was impregnated with PTFE so that the solid content adhesion amount was 5%, and dried. Furthermore, a paste consisting of carbon black and PTFE was applied to a smooth surface (surface without non-through holes), dried, and then heat treated at 380 ° C. for 15 minutes to obtain a gas diffusion electrode.

Example 2
The carbon fiber precursor fiber non-woven fabric obtained in the same manner as in Example 1 was impregnated with a phenol resin so that 10% by weight of solid content was adhered. Then, the process after embossing was implemented similarly to Example 1, and the carbon fiber nonwoven fabric was obtained. The carbon fiber nonwoven fabric was subjected to the same treatment as in Example 1 to obtain a gas diffusion electrode.

[Example 3]
After blending a number average fiber length 76 mm flame resistant yarn obtained in the same manner as in Example 1 and a number average fiber length 37 mm nylon staple at a ratio of 80% by weight and 20% by weight respectively, the card, cross layer and needle density A needle punch of 100 / cm ² was performed to obtain a carbon fiber precursor fiber non-woven fabric. A carbon fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the carbon fiber precursor fiber nonwoven fabric was used.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

Example 4
A wet nonwoven fabric was obtained by a paper-making method using a PAN-based flame resistant yarn with a fiber length of 10 mm. The wet non-woven fabric was impregnated with 10% by weight of phenol resin to obtain a carbon fiber precursor fiber non-woven fabric. A carbon fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the carbon fiber precursor fiber nonwoven fabric was used.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

Comparative Example 1
A carbon fiber precursor fiber non-woven fabric obtained in the same manner as in Example 3 was irradiated with a YAG laser having a beam diameter of 100 μm, and holes were formed at a frequency of one hole at 0.5 mm for both MD and CD. Thereafter, carbonization was performed by heating at 1500 ° C. for 15 minutes in a nitrogen atmosphere to obtain a carbon fiber non-woven fabric. The average pore diameter of the obtained carbon fiber non-woven fabric was 12.5 μm.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

Comparative Example 2
A carbon fiber nonwoven fabric was obtained in the same manner as in Comparative Example 1 except that the carbon fiber precursor fiber nonwoven fabric obtained in the same manner as in Example 4 was used.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

Comparative Example 3
10% by weight of a phenolic resin was impregnated and applied to a plain woven fabric obtained from a strand of PAN-based flame resistant yarn staple having a fiber length of 51 mm to obtain a carbon fiber precursor fibrous plain woven fabric. A carbon fiber plain woven fabric was obtained in the same manner as in Example 1 except that this carbon fiber precursor fibrous flat woven fabric was used instead of the carbon fiber precursor fibrous nonwoven fabric.

  Subsequently, a gas diffusion electrode was obtained using the carbon fiber plain weave in the same manner as in Example 1.

Comparative Example 4
In the same manner as in Example 3, a carbon fiber precursor fiber non-woven fabric was obtained. A carbon fiber non-woven fabric was obtained in the same manner as in Comparative Example 1 except that the irradiation time of the YAG laser was 10 times as large as that of Comparative Example 1 to the obtained carbon fiber precursor fiber non-woven fabric. The holes formed in the obtained carbon fiber non-woven fabric were through holes.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

Comparative Example 5
The carbon fiber precursor fiber non-woven fabric obtained in the same manner as in Example 1 was pressed with a pair of flat rolls. The heating temperature of the pair of flat rolls was 220 ° C., the linear pressure was 50 kN / m, and the processing speed was 50 cm / min. The apparent density after press working was 0.40 g / cm ³ . Thereafter, carbonization was performed by heating at 1500 ° C. for 15 minutes in a nitrogen atmosphere to obtain a carbon fiber non-woven fabric. The same carbon fiber non-woven fabric was subjected to the same embossing as in Example 1.

  Subsequently, using the carbon fiber non-woven fabric, a gas diffusion electrode was obtained in the same manner as Example 1.

  The structure of the base material of the gas diffusion electrode prepared in each Example and Comparative Example and the power generation performance of the fuel cell are shown in Table 1.

Claims (7)

A plurality of non-through holes including an open area larger than the average pore area of a carbon fiber non-woven fabric including carbon fibers having a curved portion with a curvature radius of 1 mm or less are dispersedly formed on the surface, and the wall surface of the non-through holes is configured. A carbon fiber non-woven fabric in which at least a part of carbon fibers among the carbon fibers being oriented are oriented in the height direction of the non-through holes. The carbon fiber non-woven fabric according to claim 1, wherein the carbon fiber oriented in the height direction of the non-through hole is continuous to the bottom surface of the non-through hole. The carbon fiber non-woven fabric according to claim 1 or 2 , wherein the total of the open areas of the non-through holes in a plan view is 1.5% to 60% of the area of the carbon fiber non-woven fabric. The opening area of the non-penetrating pores is 1000 .mu.m ² 500 mm ^2, the carbon fiber nonwoven fabric according to any one of claims 1 to 3. The carbon fiber non-woven fabric according to any one of claims 1 to 4 , wherein the depth of the non-through holes is 10 to 500 m. The base material for electrodes which uses the carbon fiber nonwoven fabric in any one of Claims 1-5 . A gas diffusion electrode for a fuel cell, comprising the electrode substrate according to claim 6 .