JP6578738B2 - Carbon fiber nonwoven fabric, gas diffusion electrode for polymer electrolyte fuel cell, and polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a carbon fiber nonwoven fabric suitable for an electrode substrate such as a polymer electrolyte fuel cell.

  Woven knitted fabrics and nonwoven fabrics made of carbon fibers are suitable for electrode substrates because they are chemically stable and have an appropriate compressive stress, and their application to gas diffusion electrodes for polymer electrolyte fuel cells has been investigated. Yes.

  When used for such applications, substrates such as woven and knitted fabrics and nonwoven fabrics made of carbon fibers are required to have high gas permeability. Thus, attempts have been made to improve gas permeability by forming voids in the substrate. For example, an electrode base material has been proposed in which an organic fiber sheet impregnated with a phenolic resin is sandwiched and bound between carbon fiber-made nonwoven fabrics, and pores are formed inside by firing to improve gas diffusibility and water discharge. (Patent Document 1). In addition, an electrode base material in which a non-woven fabric made of carbon fiber and a carbon fiber precursor fiber and an organic fiber sheet are entangled with a water jet or the like and fired, and the carbon fiber is arranged in a hole layer formed inside is proposed. (Patent Document 2).

On the other hand, as an electrode material for a redox flow battery, a base material that improves the permeability of a liquid rather than a gas due to a void is being studied. For example, braided or woven or knitted fabric made of organic fibers or natural fibers with a low residual carbon ratio after firing is used for the intermediate layer of the web made of carbon fiber precursor fibers to entangle with the carbon fiber precursor fibers, after firing, A carbon fiber nonwoven fabric having pores with a cross-sectional area of 0.3 mm ² or more in the sheet has been proposed by the disappearance of the intermediate layer portion (Patent Document 3).

JP 2007-269624 A JP 2013-206704 A JP 2013-144857 A

  The electrode substrate carbon fiber sheet disclosed in Patent Document 1 has sufficient gas permeability, but is weak in compression because the pore layer is formed of carbonized resin, and is incorporated into a polymer electrolyte fuel cell. There was a problem that it was easily destroyed by the fastening pressure.

  On the other hand, the electrode base material carbon fiber sheet disclosed in Patent Document 2 has carbon fibers in the pore layer, so that the compression resistance is improved compared to the case where the pore layer is formed of carbonized resin, Since the carbon fibers are bonded to the three-dimensional network carbon, the compression resistance is still insufficient. In addition, since the rigid carbon fibers are oriented in the thickness direction, when the thickness fluctuates due to the fastening pressure when incorporated into the polymer electrolyte fuel cell, the carbon fibers break through the electrolyte membrane, causing gas and There was a problem that current leaked.

Further, the carbon fiber nonwoven fabric disclosed in Patent Document 3, although the cross-sectional area is transparent liquid easy because it has a large void and 0.3 mm ² or more, the pore is large min, compression resistance is lowered Moreover, there is a problem that the apparent density is lowered and the conductivity is also lowered. In the first place, since the use of gas permeation is not envisaged, the pore size is too large and high pressure is required to permeate gas in the penetration direction. Therefore, for example, it is inconvenient when it is used for a gas permeable electrode such as a gas diffusion electrode substrate for a polymer electrolyte fuel cell.

  It is an object of the present invention to provide a carbon fiber nonwoven fabric having a low gas permeation resistance and excellent compression resistance, and in particular, providing a carbon fiber nonwoven fabric suitable for a gas diffusion electrode substrate for a polymer electrolyte fuel cell. .

The carbon fiber nonwoven fabric of the present invention for achieving the above-mentioned object includes carbon fibers formed from carbon fibers having a fiber length of 30 to 100 mm, in which carbon fibers are entangled and oriented in the thickness direction, is a carbon fiber nonwoven fabric having a hollow portion of the cross-sectional area formed on the surface almost parallel 350μm ² ~200000μm ^2.

  According to the present invention, the carbon fiber is entangled with each other and the carbon fiber oriented in the thickness direction is included so that the compression recovery rate in the thickness direction is excellent, and the gas permeation resistance is suppressed to be small by having the hollow portion. A carbon fiber nonwoven fabric suitable for a gas diffusion electrode substrate for a polymer electrolyte fuel cell can be provided.

It is an example of the scanning electron micrograph of the cross section of the carbon fiber nonwoven fabric of this invention (magnification: 200 times). It is a schematic diagram showing the single cell which set the carbon fiber nonwoven fabric of this invention to the gas flow path non-formation separator as a gas diffusion electrode.

  The type of carbon fiber constituting the carbon fiber nonwoven fabric of the present invention is not particularly limited, and polyacrylonitrile fiber, pitch fiber, polyvinyl alcohol fiber, cellulose fiber, lignin fiber, polyacetylene fiber, polyethylene A fired fiber such as fiber or polybenzoxazole-based fiber can be used. Among these, it is preferable to use polyacrylonitrile-based carbon fibers having relatively high mechanical strength such as tensile strength and compression strength.

  The fiber length of the carbon fiber is preferably 30 to 100 mm. When the fiber length is in this range, the fibers are easily entangled, and the carbon fibers can be oriented in the thickness direction when the fibers are entangled with a needle punch or a water jet punch. When the fiber length of the carbon fiber is less than 30 mm, the entanglement of the fiber tends to be weakened, and the compression recovery rate and the electrical resistance tend to decrease. In addition, since the fiber ends facing in the thickness direction increase, when used as a gas diffusion electrode substrate for a polymer electrolyte fuel cell, the carbon fiber penetrates the electrolyte membrane and leak current is likely to occur. Become. If the fiber length exceeds 100 mm, the card passing property tends to be poor and the formation of the nonwoven fabric tends to be difficult.

  In the present invention, the fiber diameter of the carbon fiber is not particularly limited, but if the fiber is thin, contact with the surroundings is easy and high conductivity is easily obtained, but it is difficult to obtain high gas and liquid permeability. It is. The example of a suitable fiber diameter is 3-30 micrometers, and it is more preferable that it is 5-20 micrometers.

Carbon fiber nonwoven fabric of the present invention has a hollow portion of the cross-sectional area 350μm ² ~200000μm ² formed approximately parallel and the nonwoven fabric surface (equivalent circle diameter 21~500μm). The hollow part as used in the field of this invention means the space in which the carbon fiber formed in the tunnel shape inside the carbon fiber nonwoven fabric does not exist, and has a length of 10 mm or more in the depth direction. Henceforth, when only calling the length of a cavity part, it shall mean the length of the said depth direction. Moreover, the cross-sectional area of the cavity portion means the area of a cross section perpendicular to the depth direction of the cavity portion described above. In the present invention, the carbon fiber nonwoven fabric is cut so that the cross section of the cavity appears, and the cross section in the range of 5 mm in the plane direction is arbitrarily observed, and the maximum inscribed circle among the cross sections of the cavity existing in the range. in cavity cross-section of the diameter is greatest, the area of the maximum inscribed circle if 350μm ² ~200000μm ^2, shall be deemed to have a hollow portion of the cross-sectional area 350μm ² ~200000μm ^2.

  Further, if the length of the cavity is less than 10 mm, the gas diffusibility and the water discharge are insufficient, and the performance as a gas diffusion electrode for a polymer electrolyte fuel cell is deteriorated. The length of the cavity is preferably 30 mm or more, and more preferably 50 mm or more. For the length of the cavity, for example, a test piece continuous in the depth direction of the cavity is created by cutting with an ion beam or a razor, and the cross section is observed with a scanning electron microscope, or X-ray CT is used. It can be determined by confirming that the cavity is continuous over 10 mm or more by a tomographic image or the like.

When used as a gas diffusion electrode substrate of a polymer electrolyte fuel cell, it is difficult to obtain a high gas or liquid permeability if the cross-sectional area of the cavity is too small. Therefore, the cross-sectional area of the cavity is 1000 μm ² or more. It is more preferable that it is 8000 μm ² or more. Liable becomes difficult to obtain the conductive cavity is too large, more preferably the cross-sectional area of the cavity portion is 180000Myuemu ² or less, and more preferably 160000Myuemu ² or less.

  The carbon fiber nonwoven fabric of the present invention preferably includes a plurality of cavities. In this case, the hollow portion may be formed intermittently (that is, independently). However, for example, when used for a gas permeable electrode such as a gas diffusion electrode for a polymer electrolyte fuel cell, a gas is used. It is preferable that the cavities are connected to each other and arranged in a mesh shape in order to effectively diffuse the water and discharge water. It is a particularly preferable aspect that the plurality of cavities are formed vertically and horizontally and arranged in a lattice shape, that is, a continuous lattice-like space is formed inside the carbon fiber nonwoven fabric as a whole. It can be determined from a tomographic image using X-ray CT that the plurality of cavities are arranged in a mesh or lattice pattern.

  In the carbon fiber nonwoven fabric of the present invention, carbon fibers are entangled with each other. Here, it is possible to confirm that the carbon fibers are entangled in the carbon fiber nonwoven fabric by observing that the carbon fibers curved on the nonwoven fabric surface are intertwined while intersecting each other.

  Moreover, the carbon fiber nonwoven fabric of this invention contains the carbon fiber orientated in the thickness direction. Here, the carbon fiber oriented in the thickness direction means that the carbon fiber nonwoven fabric is cut so that the cross section of the cavity portion appears, and the portion where the carbon fiber exists between the cavity portion and the cavity portion in the cross section is a scanning type. When observed with an electron microscope at a magnification of 200, it refers to a carbon fiber oriented at an angle of 10 to 90 ° with respect to the plane direction. By adopting such a structure, carbon fibers oriented in the thickness direction during compression become pillars, carbon fiber is less damaged by compression, and has a high thickness recoverability (compression recovery rate) when released from compression. A nonwoven fabric can be obtained. When used as a gas diffusion electrode base material for polymer electrolyte fuel cells, it is oriented in the thickness direction because it has a high effect on the durability against compression and the suppression of penetration of the electrolyte membrane by the carbon fiber during compression. The angle with respect to the surface direction of the fiber is preferably 20 to 80 °, and more preferably 30 to 70 °.

Basis weight of the carbon fiber nonwoven fabric of the present invention is not particularly limited, but is preferably ^{40~500g / m 2, 60~400g / m} 2 is more preferable. This is because if the basis weight is low, the process tension at the time of production cannot be endured, the handleability is poor, and if the basis weight is high, it is difficult to permeate gas or liquid when used as an electrode substrate. Here, the basis weight is the weight of the carbon fiber nonwoven fabric divided by the area.

  Although the thickness of the carbon fiber nonwoven fabric of this invention is not specifically limited, 80-1000 micrometers is preferable, 100-800 micrometers is more preferable, 150-700 micrometers is further more preferable. If the thickness is too thin, it cannot withstand the process tension at the time of manufacture, and if it is too thick, gas and liquid permeation becomes difficult and conductivity tends to be lowered. Here, the thickness of the carbon fiber nonwoven fabric refers to ten 5 cm × 5 cm test pieces according to JISL 1913 6.1 (thickness (Method A)), and is a fully automatic compression elasticity / thickness measuring instrument ( This is a value obtained by measuring the thickness of each test piece after 10 seconds under a pressure of 0.5 kPa using Daiei Kagaku Seiki Seisakusho Co., Ltd. (model: CEH-400).

While the apparent density of the carbon fiber nonwoven fabric of the present invention is not particularly limited, and is preferably 0.20~1.00g / cm ^3, more preferably 0.25~0.90g / cm ^3, 0.30~ 0.80 g / cm ³ is more preferable. When used as a gas diffusion electrode substrate of a polymer electrolyte fuel cell, it is difficult to obtain sufficient conductivity when the apparent density is less than 0.20 g / cm ³ , and the structure is destroyed by the applied pressure. In addition, if it exceeds 1.00 g / cm ³ , it tends to be difficult to obtain sufficient gas and liquid permeability. The apparent density of the carbon fiber nonwoven fabric is the basis weight divided by the thickness.

  When using the carbon fiber nonwoven fabric of this invention as a gas diffusion electrode base material, it is preferable to perform water-repellent treatment. When the surface of the gas diffusion electrode substrate has water repellency, when a fuel cell is constructed, it becomes possible to suppress clogging due to water generated in the power generation reaction, and supply sufficient substances necessary for the reaction. Power generation efficiency is improved.

  Moreover, a membrane electrode assembly (MEA) can be comprised by using the carbon fiber nonwoven fabric of this invention as a gas diffusion electrode base material, and arrange | positioning on both sides of an electrolyte membrane. The MEA can be further provided with separators on both sides to form a solid polymer fuel cell.

  As the separator, one having a groove on the surface that serves as a gas channel, such as a serpentine channel or a straight channel, is generally used. However, the MEA using the carbon fiber nonwoven fabric of the present invention as a gas diffusion electrode substrate has a gas flow path formed because the cavity inside the gas diffusion electrode can replace the function of the gas flow path of the separator. Electricity can be generated even when a fuel cell is combined with a separator. A polymer electrolyte fuel cell having a gas diffusion electrode for a polymer electrolyte fuel cell made of the carbon fiber nonwoven fabric of the present invention and a separator in which no gas flow path is formed contributes to a reduction in the manufacturing cost of the fuel cell. there is a possibility.

  Next, an example of using a polyacrylonitrile (PAN) -based carbon fiber will be described as a preferred production method for obtaining the carbon fiber nonwoven fabric of the present invention.

  As the precursor of the PAN-based carbon fiber, an acrylic copolymer composed of 90% by weight of acrylonitrile, preferably 95% by weight or more can be used. Comonomers that copolymerize with acrylonitrile include organic acids such as acrylic acid and itaconic acid, or methyl esters, ethyl esters, propyl esters, butyl esters, alkali metal salts, ammonium salts, or allyl sulfonic acids, methacrylates of these organic acids. Examples thereof include organic acids such as rylsulfonic acid and styrenesulfonic acid, and metal salts of these organic acids.

  The acrylic copolymer can be polymerized by a known method such as emulsion polymerization, bulk polymerization, or solution polymerization, and the spinning dope can be prepared with dimethylacetamide, dimethylsulfoxide, dimethylformamide, nitric acid, an aqueous rhodium soda solution, or the like. it can. The concentration of the acrylonitrile copolymer in the spinning dope is preferably 13 to 25% by weight, more preferably 15 to 20% by weight. When the concentration of the acrylonitrile copolymer is less than 13% by weight, unevenness due to fibrils appears on the surface of the fiber obtained by the dry and wet spinning method, and the strength characteristics of the obtained carbon fiber may be reduced. is there.

  Next, this spinning solution is once extruded from the die into the air, spun by a dry and wet spinning method in which the spinning solution is spun into a coagulation bath composed of a solvent and water, washed with water, and stretched in a bath. Here, in order to effectively suppress adhesion between the constituent single fibers, for example, it is preferable to apply a silicone-based oil agent containing amino-modified silicone as an essential component. Thereafter, it is dried and densified, and stretched in a heating medium such as pressurized steam as necessary to obtain acrylic copolymer fibers.

  The acrylic copolymer fiber thus obtained is heated in an air atmosphere at 200 to 300 ° C. while being stretched as necessary to obtain a flame-resistant fiber.

  The obtained flame-resistant fiber is made into a short fiber of 30 to 100 mm, and a dry web is produced by using carded fibers in parallel lay, cross lay, air lay, or the like.

  Such a web is laminated on one side or both sides of the fiber fabric, and needle punching and / or water jet punching are both performed. The fiber fabric functions as a spacer in the compression treatment described later, and its volume is reduced when it is carbonized by firing, whereby a cavity is formed in the traces of the fibers constituting the fiber fabric.

  When the carbonized yield of the fiber fabric is 20% or less, the volume is greatly reduced in the step of carbonizing the flame resistant fiber. Therefore, it is preferable because it becomes easy to control the shape of the cavity after firing, and high permeability in the gas surface direction and thickness direction can be obtained. The carbonization yield of the fiber fabric is more preferably 10% or less, and further preferably 5% or less. The carbonization yield here is the difference between the weight at room temperature and the weight at 800 ° C. by measuring the change in weight when the temperature is raised at 10 ° C./min in a nitrogen atmosphere by the thermogravimetry (TG) method. Is divided by the weight at room temperature.

  Examples of fibers constituting the fiber fabric include polyethylene fibers, polypropylene fibers, polyethylene terephthalate fibers, polylactic acid fibers, and polyamide fibers.

Fiber length of the fibers constituting the fiber fabric, the fiber diameter is appropriately adjusted so as to form a cavity of the cross-sectional area 350μm ² ~200000μm ² to reduce the volume at the time of carbonization. The fiber length is not particularly limited, and any of short fibers and long fibers of about 30 to 100 mm can be used. The larger the diameter of the fiber constituting the fiber fabric, the larger the diameter of the cavity, and the easier the permeation of gas or liquid, but it becomes difficult to obtain high conductivity.

  The form of the fiber fabric is not particularly limited, and examples thereof include woven fabrics, knitted fabrics, nonwoven fabrics, and net-like materials. For example, when priority is given to the conductivity in the thickness direction, the effect can be expressed by increasing the mesh opening of the fabric, and when priority is given to the permeability of gas or liquid, reducing the mesh opening of the fabric.

  The woven fabric may be, for example, a single structure such as plain weaving, satin weaving, or oblique weaving, a double structure such as ventilating weaving, a pile structure such as velvet or velvet, an entangled structure such as folds, a crest weaving, or a binding weaving. As the knitted fabric, for example, a horizontal knitting such as a flat knitting, a rubber knitting, a double-sided knitting, a lace knitting, and a vertical knitting such as a denby, an atlas, and a cord can be appropriately selected. The fiber fabric may be a nonwoven fabric, and may be either a wet nonwoven fabric or a dry nonwoven fabric. Also, in the fiber fabric, it is easier to form a uniform cavity when there is no difference in the thickness between the intersection of the fibers and the other locations. Therefore, the intersections of these fabrics are fused by a method such as hot pressing. This is also a preferred embodiment.

  By laminating the above-mentioned flame-resistant fiber web and fiber fabric and needle punching and / or water jet punching, the fibers are entangled with each other and penetrate through the opening of the fiber fabric in the thickness direction. The orientation proceeds. When a fiber fabric having a low opening ratio is used, the number of fibers penetrating through the fiber fabric and thickness-oriented is reduced, so that the compression resistance and the conductivity in the thickness direction of the carbon fiber nonwoven fabric obtained after firing tend to be inferior. In addition, when a fiber fabric having a high aperture ratio is used, the permeability of gas or liquid tends to be inferior. Therefore, the aperture ratio of the fiber fabric observed with a microscope or transmitted light is preferably 20 to 80%, more preferably 25 to 70%, and further preferably 30 to 65%.

Instead of the fiber fabric, arranged monofilaments or multifilaments having a fiber diameter that can form a cavity of the cross-sectional area 350μm ² ~200000μm ^2, sandwiched by the oxidized fiber web, subjected to needle punching and / or water jet punching May be.

  In the case of a needle punch, the fiber orientation can be adjusted by the shape of the needle and the number of driven needles. The number of fibers moving in the thickness direction increases as the number of barbs, the volume, and the needle density increase. In the case of a water jet punch, it becomes easy to move in the thickness direction by increasing the nozzle diameter and water pressure. The slower the web transport speed, the greater the effect of moving in the thickness direction. It is preferable to carry out only the needle punch because a drying step is unnecessary and high productivity can be expected.

  In order to avoid the fibers constituting the fiber fabric from being caught by the needle barb in the needle punching process, the fibers forming the fiber fabric are monofilaments having a relatively large fiber diameter or multifilaments having a twist number of 1000 to 4000 T / M. Preferably there is. The number of twists can be measured by a method defined in JIS L1096 (2005) 8.8.2, which is a general textile testing method.

  Lamination of the web made of flame-resistant fibers to the fiber fabric may be double-sided, single-sided, single-sheeted or plural-sheeted. From the viewpoint of uniformity between the front and back, it is preferable to laminate on both sides, and lamination on one side is preferred from the viewpoint that the process is simple and handling and cost reduction are easy.

Next, hot pressing is performed using a continuous press machine using a calendar roller or a press machine using a flat plate. Usually, the apparent density of the composite sheet obtained by needle punch and / or water jet punch is about 0.02 to 0.20 g / cm ³ , and if it is carbonized as it is, the conductivity necessary as an electrode substrate can be obtained. This is because it is difficult. At this time, the compression treatment is preferably performed so that the apparent density of the composite sheet is 0.3 to 1.3 g / cm ³ . In this case, although appropriate compression processing conditions vary depending on the raw material composition and spinning conditions, the temperature, pressure, and compression speed can be controlled while confirming the processing status. In general, in order to obtain the compression effect, it is preferably performed at 100 ° C. or higher, more preferably 130 ° C. or higher. In addition, when the temperature is too high, the fiber is likely to melt or deteriorate, and therefore, the temperature is preferably 400 ° C. or lower, more preferably 250 ° C. or lower. In particular, from the viewpoint of facilitating control of the shape of the cavity after firing, the compression treatment is preferably performed at a temperature at which the fiber fabric having a carbonization yield of 20% or less does not melt.

  Then, the composite sheet produced in this way is baked and the baking process which makes carbon fiber is performed. The firing method is not particularly limited as long as it is a commonly used method, but it is preferable to perform a heat treatment at 800 ° C. or higher under an inert atmosphere such as nitrogen or argon. When used, it is more preferable to perform graphitization at a temperature of 2000 ° C. or higher.

Incidentally, it is preferable to appropriately adjust the thermal press treatment conditions and sintering conditions of the composite sheeting so that the carbon fiber nonwoven fabric of density 0.2 to 1.0 g / cm ³ apparent after carbon fibers of.

  Moreover, the other manufacturing method of the carbon fiber nonwoven fabric of this invention is illustrated below.

  First, a flame resistant fiber having a fiber length of 30 to 100 mm is carded, and a dry web is produced by parallel lay, cross lay, air lay, or the like. Such a web is subjected to needle punching and / or water jet punching to form a flameproof fiber nonwoven fabric.

  This flame resistant fiber nonwoven fabric is heat-pressed with an embossing roll, or a metal plate with a concavo-convex pattern, fiber fabric, etc. is pressed against one side of the flame resistant fiber nonwoven fabric and hot pressed, so that only one surface of the flame resistant fiber nonwoven fabric is uneven. Form a pattern. Next, the concavo-convex pattern surfaces of the flame-resistant fiber nonwoven fabric formed with the concavo-convex pattern are bonded together and fired, or after firing the flame-resistant fiber nonwoven fabric into a carbon fiber nonwoven fabric, the concavo-convex pattern surfaces are joined together By bonding together, a carbon fiber nonwoven fabric having a cavity can be obtained.

  Embossing rolls that can be used to form a concavo-convex pattern and the concavo-convex pattern of a metal plate are not particularly limited, such as a dot shape, a lattice shape, a stripe shape, a staggered shape, or a tortoiseshell shape. It is preferable to use a grid-like or stripe-like embossing roll that is easy to form without being interrupted to both ends.

  The method for pasting the uneven surfaces is not particularly limited, but it is possible to apply heat-curing resin such as phenol resin, epoxy resin, acrylic resin by spraying or coating only on the uneven surface or impregnating the substrate after impregnation. A method of pasting the surfaces together by hot pressing can be given.

  The same method as described above can be used for the baking step after the uneven surfaces are bonded together.

  It is preferable that a binder adheres to the carbon fiber nonwoven fabric of the present invention in order to improve shape retention and handling properties. The binder is preferably applied as a precursor, and is not particularly limited as long as it is carbonized by firing, and examples thereof include a phenol resin, an epoxy resin, and an acrylic resin. Moreover, in order to improve electroconductivity, in the state of the binder precursor solution which disperse | distributed carbon black etc., it can provide by immersion or a spray. Since it shrinks during carbonization and changes its shape, and the smoothness of the surface tends to be impaired, the composite sheet can be carbonized and a carbon fiber nonwoven fabric that does not shrink any further, then a binder precursor is applied and carbonized again. From the viewpoints of form stability and surface smoothness.

  The binder precursor provided in the present invention preferably has a carbonization yield of 30% or more, and more preferably 40% or more in terms of productivity.

  Moreover, when using as a gas diffusion electrode base material for polymer electrolyte fuel cells, it is preferable to perform water-repellent treatment by applying a water-repellent substance in order to improve power generation efficiency.

  As the water repellent substance, it is preferable to use a fluororesin. The water repellent treatment can be performed by adhering the water repellent material to the carbon fiber nonwoven fabric in a proportion of 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less. Here, the fluororesin includes tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FEP), fluorinated ethylene tetrafluoroethylene resin (ETFE), etc. A resin having water repellency containing atoms.

  It is also a preferred aspect to provide a microporous layer on the surface of the carbon fiber nonwoven fabric. For carbon fiber nonwoven fabric that has been subjected to water repellent treatment, a paste obtained by adding a surfactant and water to fluororesin and carbon black is applied to the surface by a bar coat or die coat method, dried, and sintered, It is preferable to provide a water-repellent microporous layer. The fluororesin contained in such a microporous layer is preferably 1 to 80% by weight, more preferably 10 to 70% by weight, and still more preferably 20 to 60% with respect to carbon black. When the fluororesin contained in the microporous layer is 1% by weight or more, the binder effect of the fluororesin connecting the carbon black is increased, so that the strength of the carbon layer is increased. When the fluororesin is 80% by weight or less, high conductivity is obtained. Since the ratio of carbon black having the property increases, the conductivity is improved.

  Compared to the case where only water repellent treatment is performed, by providing such a microporous layer on the carbon fiber nonwoven fabric, water generated during the power generation of the polymer electrolyte fuel cell is effectively discharged from the inside of the gas diffusion electrode substrate. can do.

  When the carbon fiber nonwoven fabric of the present invention is used as a gas diffusion electrode substrate for a fuel cell, the carbon fibers are oriented in the thickness direction, so that the compression recovery rate is excellent despite having a hollow portion. Further, by utilizing the hollow portion as a gas or liquid flow path, it is possible to provide a cost-effective fuel cell in which it is not necessary to form a gas flow path in the separator.

  The physical property values in the examples were measured by the following methods.

1. Cross-sectional area of cavity and orientation in thickness direction A test piece was prepared by cutting with a carbon fiber nonwoven fabric and an ion beam so that the cross-section of the cavity appeared. The adjusted specimen is cross-sectionally observed at a magnification of 200 mm with a scanning electron microscope over a width of 5 mm, and the largest inscribed circle of the cavity section where the diameter of the largest inscribed circle is the largest among the cavity sections in the observation range. Was the cross-sectional area of the cavity. Further, when at least one fiber having an angle of 10 to 90 ° with respect to the thickness direction is present by observing the range, it is determined that the fibers are oriented in the thickness direction.

2. Formation of Cavity Part A test piece including a cavity part was prepared by cutting the carbon fiber nonwoven fabric to 10 mm × 6 mm with a razor with the depth direction of the formed cavity part as the long side direction. The long side direction of this test piece was cut into 2 mm increments, and five continuous 2 mm × 6 mm observation test pieces were produced. If both sides of the observation specimen are observed at 200 times with a scanning electron microscope and a void is observed at the same position on both sides of all five observation specimens, it is determined that a cavity is formed. did.

3. Apparent density In accordance with JIS L1913 6.1 (thickness (Method A)), 10 test pieces of 5 cm × 5 cm were collected and fully automatic compression elasticity / thickness measuring instrument (manufactured by Daiei Scientific Instruments Co., Ltd.) The thickness of each test piece after 10 seconds was measured under a pressure of 0.5 kPa using a model: CEH-400). And after calculating | requiring the average value of a measured value as thickness, the decimal density was rounded off from this thickness, a dimension (5 cm x 5 cm), and the weight, and the apparent density was calculated | required.

4). Gas permeation resistance A test piece (diameter 50 mm) obtained by cutting a carbon fiber nonwoven fabric subjected to water repellent treatment into a circle was sandwiched between discs having an inner diameter of 12 mm and an outer diameter of 100 mm, and pressurized to 1 MPa. Air was supplied to the hollow part of the disk on one side at a flow rate of 1.0 L / min, and the hollow part of the other disk was opened to the atmosphere. The supply side pressure (pressure difference from the open side) at this time was defined as gas permeation resistance.

5). Compression recovery rate Water-repellent treated carbon fiber nonwoven fabric test piece (20 mm x 20 mm) is sandwiched between 100 mm x 100 mm plates, and the test piece is pressurized so that the load received is 0.3 MPa. The thickness T1 of the piece was measured in units of 1 μm. Next, after raising the load to 2 MPa, the pressure was lowered to 0.3 MPa, and the thickness T2 was measured. Similarly, the thickness of ten test specimens collected from different locations was measured. The thickness recovery rate was calculated from the following equation, and the average value of 10 test pieces was taken as the compression recovery rate.

Thickness recovery rate (%) = T2 / T1 × 100
6). Power generation performance (1) Power generation with a serpentine flow separator Separation of platinum-supported carbon and Nafion on both sides of a fluorine-based electrolyte membrane “Nafion” 212 (manufactured by DuPont) (platinum amount 0.2 mg / cm ² ) Were joined by hot pressing to prepare a catalyst layer-coated electrolyte membrane (CCM).

  Two gas diffusion electrode substrates were placed on both sides of the CCM, and hot pressing was performed again to obtain a membrane electrode assembly (MEA). At this time, the gas diffusion electrode substrate was arranged so that the surface having the microporous layer was in contact with the catalyst side.

Around the gasket of the gas diffusion electrode (the thickness of the gasket MEA 80% thickness) was set MEA which arranged Electro Chem, Inc. of single-cell (5 cm ^2, serpentine flow path) to.

  When the cell temperature is 60 ° C., the dew point of hydrogen and air is 60 ° C., the flow rates are 100 cc / min and 250 cc / min, respectively, and the gas outlet is open (no pressurization) to generate electricity and the voltage is 0.2 V The current density was measured.

(2) Power generation with a gas channel non-forming separator A gasket (the thickness of the gasket is 80% of the thickness of the MEA) is arranged around the gas diffusion electrode of the MEA produced by the same method as described above, and gas is supplied to the MEA. A single cell (5 cm ² , non-flow channel) using a separator having the shape of FIG. 2 made of a resin-impregnated graphite material manufactured by Tokai Carbon Co., Ltd., which has no gas flow path and only gas introduction holes and discharge holes. Set).

  When the cell temperature is 60 ° C., the dew point of hydrogen and air is 60 ° C., the flow rates are 100 cc / min and 250 cc / min, respectively, and the gas outlet is open (no pressurization) to generate electricity and the voltage is 0.2 The current density was measured.

<Production Example 1 (Dry Web)>
Using a copolymer composed of 99.4 mol% of acrylonitrile and 0.6 mol% of methacrylic acid, a polyacrylonitrile (PAN) fiber bundle of 1 dtex and 12,000 filaments was obtained by a dry and wet spinning method. The obtained PAN-based fiber bundle was heated at a draw ratio of 1.05 in air at a temperature of 240 to 280 ° C. to obtain a PAN-based flame resistant yarn (density 1.38 g / cm ³ ).

Next, the PAN flame resistant yarn was crimped by a push-in crimper. The zigzag crimped yarn obtained had a number of crimps of 7.1 / 25 mm and a crimp rate of 12.7%. The flame resistant yarn was cut into a number average fiber length of 76 mm, and then a dry web of 60 g / m ² was obtained using a card and a cross wrapper.

<Production Example 2 (Dry Web)>
A dry web of 60 g / m ² was prepared in the same manner except that the number average fiber length of the flame resistant yarn of Production Example 1 was changed to 38 mm.

<Production Example 3 (woven fabric)>
A PET (polyethylene terephthalate) component having an intrinsic viscosity of 0.66 was spun and drawn to obtain 40 dtex 48 filament fibers. This was twisted by S twisting at 2400 T / m and steam set at 75 ° C. Similarly, a yarn that was twisted at 2400 T / m by Z twisting and steam-set at 75 ° C. was produced. S warp yarn and Z twist yarn are alternately arranged on the warp yarn, the S twist yarn is used for the weft yarn, the weave structure is plain weave, and a fabric is produced with a weave density of 93 × 64 / 2.54 cm. Thus, a fabric with a basis weight of 43 g / m ² was produced.

<Production Example 4 (woven fabric)>
A PET (polyethylene terephthalate) component having an intrinsic viscosity of 0.66 was spun and drawn to obtain 56 dtex 48 filament fibers. This was twisted by S twisting at 2400 T / m and steam set at 75 ° C. Similarly, a yarn that was twisted at 2400 T / m by Z twisting and steam-set at 75 ° C. was produced. S warp yarn and Z twist yarn are alternately arranged on the warp yarn, the S twist yarn is used for the weft yarn, the weave structure is plain weave, and a fabric is produced with a weave density of 93 × 64 / 2.54 cm. Thus, a fabric with a basis weight of 60 g / m ² was produced.

<Production Example 5 (monofilament fabric)>
A monofilament of polyamide 6 having a fiber diameter of 480 μm and 2040 dtex was used, a woven structure was made into a plain weave, and a woven fabric was produced at a woven density of 20 × 15 pieces / 2.54 cm to produce a woven fabric having a basis weight of 65 g / m ² .

<Manufacture example 6 (resin imparting wet web)>
Using a copolymer composed of 99.4 mol% of acrylonitrile and 0.6 mol% of methacrylic acid, a polyacrylonitrile (PAN) fiber bundle of 1 dtex and 12,000 filaments was obtained by a dry and wet spinning method. The obtained PAN fiber bundle was heated at a draw ratio of 1.05 in air at a temperature of 240 to 280 ° C. to obtain a PAN flame resistant yarn (density 1.38 g / cm ³ ), and then 1500 ° C. in a nitrogen atmosphere. And PAN-based carbon fiber (density 1.77 g / cm ³ ).

Next, 70 parts by weight of PAN-based carbon fibers cut to 5 mm and 30 parts by weight of PVA fibers having a fiber length of 5 mm as a binder were mixed together, and then paper-made to obtain a wet web of 36 g / m ² . phenolic resin and graphite, ^{respectively,} 40 g / m 2, was 12 g / ^{m 2} applied was sandwiched in a press heated to 200 ° C., to cure the phenolic resin and the resin applied wet web.

[Example 1]
The fabric of Production Example 3 is laminated on the dry web of Production Example 1, the dry web of Production Example 1 is further laminated thereon, and the dry web is constructed by alternately needle punching both sides of the dry web. The fibers that had been pierced to the other surface of the woven fabric were obtained to obtain a composite nonwoven fabric with an apparent density of 0.13 g / cm ³ .

The obtained composite nonwoven fabric was compressed with a press machine heated to 240 ° C. to give an apparent density of 0.55 g / cm ³ .

  Subsequently, the carbon fiber nonwoven fabric was obtained by baking at 2400 degreeC in argon atmosphere in an electric furnace.

This carbon fiber nonwoven fabric, respectively phenolic resin and ^graphite, 40 g / m 2, was 12 g / ^{m 2} applied was sandwiched in a press heated to 200 ° C., to cure the phenolic resin.

  This was fired again in an electric furnace at 2400 ° C. under an argon atmosphere to obtain a carbon fiber nonwoven fabric reinforced with a phenolic resin carbide.

When the obtained carbon fiber non-woven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope, a cavity with a cross-sectional area of 3848 μm ² was formed at the location where the woven fabric was present by firing. It was confirmed that there were fibers oriented at an angle of 45 ° to the direction.

  Moreover, it has confirmed that the space | gap was continuing over 10 mm in length, and the cavity part was formed.

  PTFE resin aqueous dispersion ("Polyflon" (registered trademark) PTFE dispersion D-1E (manufactured by Daikin Industries, Ltd.)) was used to give 5% by weight of PTFE to the carbon fiber nonwoven fabric. Water repellent treatment was performed.

Next, an aqueous dispersion containing 7.7% by weight of acetylene black “Denka Black” (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd.) and PTFE resin (60 parts by mass of PTFE resin) on one side of the carbon fiber nonwoven fabric. "Polyflon" (registered trademark) PTFE dispersion D-1E (manufactured by Daikin Industries, Ltd.) 2.5% by weight, surfactant "TRITON" (registered trademark) X-100 (manufactured by Nacalai Tesque) ) A mixture consisting of 14.0 wt% and pure water 75.8 wt% was applied using a slit die coater. After the carbon coating solution was applied, it was heated at 120 ° C. for 10 minutes and at 380 ° C. for 10 minutes to form a microporous layer having a basis weight of 20 g / m ² on the carbon fiber nonwoven fabric. Thus, MEA was produced using the obtained gas diffusion electrode, and power generation performance was evaluated using a serpentine channel separator. The evaluation results are as shown in Table 1. The gas permeation resistance was low, the compression recovery rate, and the current density during power generation were high.

[Example 2]
A carbon fiber nonwoven fabric reinforced with a phenol resin carbide was obtained in the same manner as in Example 1 except that the woven fabric of Production Example 4 was used.

The obtained carbon fiber nonwoven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope. As a result, a cavity with a cross-sectional area of 3920 μm ² was formed at the location where the woven fabric was present by firing. It was confirmed that there were fibers oriented at an angle of 48 ° to the direction. Moreover, it has confirmed that the space | gap was continuing over 10 mm in length, and the cavity part was formed. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.
The evaluation results are as shown in Table 1. The gas permeation resistance was low, the compression recovery rate, and the current density during power generation were high.

[Example 3]
Polyamide 6 monofilaments having a fiber diameter of 480 μm are arranged at 1 cm intervals on the dry web of Production Example 2, and one dry web of Production Example 1 is stacked thereon to perform needle punching, with an apparent density of 0.02 g / cm ^3. A composite nonwoven fabric was obtained.

The obtained composite sheet was compressed with a press machine heated to 240 ° C. to make the apparent density 0.21 g / cm ³ .

  Subsequently, the PAN type | system | group carbon fiber nonwoven fabric was obtained by baking at the temperature of 2400 degreeC by argon atmosphere in an electric furnace.

When the obtained carbon fiber nonwoven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope, a cavity with a cross-sectional area of 170191 μm ² was formed at the location where the woven fabric was present by firing, and the thickness It was confirmed that there were fibers oriented at an angle of 48 ° to the direction. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.
The evaluation results are as shown in Table 1. The gas permeation resistance was low, the compression recovery rate, and the current density during power generation were high.

[Example 4]
The dry web of Production Example 1 was needle punched to obtain a nonwoven fabric with an apparent density of 0.06 g / cm ³ . The obtained non-woven fabric was placed on a grid-like metal plate having depressions of 100 μm in depth and 130 μm square formed on the entire surface at a pitch of 180 μm, and compressed by a press machine heated to 240 ° C., and an apparent density of 0.31 g / cm ^3. The nonwoven fabric was made.

  Subsequently, the carbon fiber nonwoven fabric was obtained by baking at 2400 degreeC in argon atmosphere in an electric furnace. This carbon fiber non-woven fabric had grooves in which the lattice shape of the metal plate was transferred.

This carbon fiber nonwoven fabric, respectively phenolic resin and graphite, was ^{40g / m 2, 12g / m} 2 applied, sandwiched in a press heated to 200 ° C. The combined grooved surfaces of the two carbon fiber nonwoven fabric, Two carbon fiber nonwoven fabrics were bound.

  Firing was performed again in an electric furnace at 2400 ° C. under an argon atmosphere to obtain a carbon fiber nonwoven fabric reinforced with a phenolic resin carbide.

When the obtained carbon fiber non-woven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope, it was confirmed that a cavity having a cross-sectional area of 27300 μm ² was formed at the location where the woven fabric was present by firing. did it. Further, it was confirmed that the fibers were entangled with each other and there were fibers oriented at an angle of 32 ° with respect to the thickness direction. Moreover, it has confirmed that the space | gap was continuing over 10 mm in length, and the cavity part was formed. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.
The evaluation results are as shown in Table 1. The gas permeation resistance was low, the compression recovery rate, and the current density during power generation were high.

[Example 5]
A composite nonwoven fabric having an apparent density of 0.07 g / cm ³ is formed by laminating the fabric of Production Example 5 on the dry web of Production Example 1 and then stacking one of the dry webs of Production Example 1 on the dry web. Got. The obtained composite sheet was compressed by a press machine heated to 220 ° C. to make the apparent density 0.48 g / cm ³ .

  Subsequently, the PAN type | system | group carbon fiber nonwoven fabric was obtained by baking at the temperature of 2400 degreeC by argon atmosphere in an electric furnace.

When the obtained carbon fiber non-woven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope, a cavity having a cross-sectional area of 168500 μm ² was formed at the location where the woven fabric was present by firing, and the thickness It was confirmed that there were fibers oriented at an angle of 50 ° to the direction. Using this carbon fiber nonwoven fabric, a gas diffusion electrode and an MEA were produced in the same manner as in Example 1, and the power generation performance was evaluated using a gas channel non-formed separator.
The evaluation results are as shown in Table 1. The gas permeation resistance was low, the compression recovery rate was high, and power generation was possible despite the separator having no gas flow path.

[Comparative Example 1]
A carbon fiber nonwoven fabric was obtained in the same manner as in Example 1 except that needle punching was performed without laminating the fabric of Production Example 4. Evaluation results of the resulting carbon fiber nonwoven fabric are shown in Table 1, it did not form a hole having a cavity cross-sectional area 350μm ² ~200000μm ^2. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.

  The evaluation results are as shown in Table 1. The gas permeation resistance was high and the current density at the time of power generation was inferior as compared with the carbon fiber non-woven fabric in which the hollow portion was formed.

[Comparative Example 2]
A 30 wt% polyamide 6 monofilament sheet (mesh sheet) with 30 wt% phenolic resin applied on both sides is placed with the resin-added wet web of Production Example 6 and compressed with a press machine heated to 200 ° C. Was cured.

  Subsequently, a PAN-based wet carbon fiber nonwoven fabric was obtained by firing at 2400 ° C. in an electric furnace in an argon atmosphere.

The resulting carbon fiber nonwoven fabric, observation of the cross section using a scanning electron microscope was cut by ion beam, confirmed that the cavity sectional area 7800Myuemu ² at positions fabric is present is formed by firing However, there was no mutual entanglement between the straight carbon fibers just crossing and contacting with each other, and fibers having an angle of 10 ° or more with respect to the thickness direction could not be confirmed. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.
The evaluation results are as shown in Table 1, and the walls between the cavities are made only of phenolic resin, so they are weak against compression, have a low compression recovery rate, and have a high electrical resistance, resulting in poor current density during power generation. .

[Comparative Example 3]
Polyamide 6 monofilaments having a fiber diameter of 710 μm are arranged at 1 cm intervals on the dry web of Production Example 1, and one dry web of Production Example 1 is stacked thereon to perform needle punching, with an apparent density of 0.03 g / cm ^3. A composite nonwoven fabric was obtained.

The obtained composite sheet was compressed with a press machine heated to 240 ° C. to make the apparent density 0.17 g / cm ³ .

  Subsequently, the PAN type | system | group carbon fiber nonwoven fabric was obtained by baking at the temperature of 2400 degreeC by argon atmosphere in an electric furnace.

When the obtained carbon fiber non-woven fabric was cut with an ion beam and the cross section was observed using a scanning electron microscope, a cavity having a cross-sectional area of 373194 μm ² was formed at the location where the woven fabric was present by firing. It was confirmed that there were fibers oriented at an angle of 56 ° with respect to the direction. Using this carbon fiber nonwoven fabric, the power generation performance was evaluated in the same manner as in Example 1.

  The evaluation results are as shown in Table 1. Since the cavity portion was large and easily crushed, the compression recovery rate was low, and the electric resistance was large. Therefore, the current density during power generation was inferior.

[Comparative Example 4]
Using the MEA of Comparative Example 1, power generation evaluation was performed in the same manner as in Example 5. However, since the gas diffusivity in the surface is low, power is generated in combination with a separator that does not form a gas flow path. I could not.

1 Example of carbon fiber oriented in the thickness direction of carbon fiber nonwoven fabric 3 Gas introduction hole 4 Gas discharge hole

Claims (6)

Fiber length is formed from carbon fiber 30 to 100 mm, entangled carbon fibers, and with containing carbon fibers oriented in the thickness direction, the cross-sectional area formed on the surface almost parallel 350μm ² ~200000μm ² A carbon fiber nonwoven fabric having a hollow portion. The carbon fiber nonwoven fabric according to claim 1, wherein the carbon fiber nonwoven fabric includes a plurality of the hollow portions, and the hollow portions are connected to each other and arranged in a mesh shape. The carbon fiber nonwoven fabric according to claim 1 or 2, wherein the carbon fibers oriented in the thickness direction are oriented at an angle of 20 to 80 ° with respect to the plane direction. 0.20~1.00g / cm has an apparent density of ^3, claim 1 carbon fiber nonwoven fabric according to any one of claims 3. A gas diffusion electrode for a polymer electrolyte fuel cell, wherein the carbon fiber nonwoven fabric according to any one of claims 1 to 4 is used as a base material. A polymer electrolyte fuel cell comprising the gas diffusion electrode for a polymer electrolyte fuel cell according to claim 5 and a separator in which no gas flow path is formed.