JP2004084147A - Carbonaceous fiber woven cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbonaceous fiber woven cloth having well-balanced gas permeability, electrical conductivity, water retention, drainage properties, evenness of thickness, etc., and suitable as a material for a gas diffusion layer of a solid polymer-type fuel cell. <P>SOLUTION: This carbonaceous fiber woven cloth is mainly composed of carbonaceous fiber yarn, wherein the woven cloth has a Metsuke (areal density) of 50-200 g/m<SP>2</SP>, a thickness of 0.05-2 mm, a bulk density of 0.2-0.6 g/cc, a volume resistivity of ≤0.15 Ωcm, when measured in the surfacial direction of the cloth, and a coefficient of variation of ≤3.2% in thicknesses of the cloth at 20 points, when measured so that a square cloth in which one of the sides is parallel to the warp and the other is parallel to the weft is sampled, two diagonal lines of the square are each equally divided into 11 parts, and the thicknesses at the 20 points in total corresponding to the equally divided parts are measured to calculate the coefficient, and further weft and warp threads composing the woven cloth each have such a cross section that a ratio of the major axis of the cross section to the minor axis is 2 or more. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carbonaceous fiber woven fabric.
[0002]
[Prior art]
In recent years, great efforts have been put into the development of fuel cells.
Fuel cells are classified into alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, solid polymer type, etc., depending on the type of electrolyte used. 2. Description of the Related Art A polymer electrolyte fuel cell that is easy and has a high output density has attracted attention for applications such as electric vehicles and home power supplies. The development of solid polymer fuel cells into cogeneration systems that improve the overall thermal efficiency by utilizing the heat generated during power generation for heating, hot water supply, etc., is being studied.
[0003]
The main components of a single cell for a polymer electrolyte fuel cell are usually a membrane electrode assembly and a grooved separator. The basic structure of the membrane electrode assembly is such that a catalyst layer, a gas diffusion layer, and a current collector are sequentially joined to both surfaces of a polymer solid electrolyte membrane (ion exchange membrane). The catalyst layer mainly comprises a mixture of a catalyst and carbon black. Further, the gas diffusion layer may also have the function of a current collector. By joining grooved separators to both surfaces of the membrane electrode assembly, a single cell of a polymer electrolyte fuel cell is formed.
[0004]
In the polymer electrolyte fuel cell, a fuel (hydrogen gas) is supplied to the anode-side catalyst layer and an oxidant (oxygen-containing gas) is supplied to the cathode-side catalyst layer via the grooves of the grooved separator to cause a cell reaction. At this time, the flow of electrons generated through the membrane electrode body is extracted to the outside as electric energy. Therefore, the following is desired as a gas diffusion layer material.
(1) To operate this mechanism efficiently, supply fuel and oxidant to the membrane electrode assembly smoothly and evenly.
(2) having sufficient conductivity (that is, low volume resistivity) so as not to lower the extraction efficiency of electric energy as much as possible;
{Circle around (3)} The solid electrolyte membrane in the center of the membrane electrode body holds an appropriate amount of water so that proton conductivity can be exhibited (water retention);
{Circle around (4)} The water generated by the battery reaction can be discharged smoothly (drainage).
[0005]
However, water retention and drainage are contradictory, and it is generally difficult to satisfy both at the same time.
As a material of the gas diffusion layer (which may also serve as a current collector), mainly carbon paper is used, but recently a carbon fiber woven fabric made by weaving carbon fibers has been studied. Have been.
[0006]
Compared to carbon paper, carbonaceous fiber woven fabric has high air permeability, facilitates smooth and uniform supply of fuel to the membrane electrode assembly, easily lowers volume resistivity, and has a thickness depending on the material and weaving method. Since it is possible to provide elasticity in the direction, there is no mechanical brittleness, and it is easy to control water retention and drainage, there are advantages that carbon paper does not have.
[0007]
However, in the carbonaceous fiber woven fabric, since the warp and the weft of the woven fabric intersect, minute thickness unevenness is easily generated as compared with the carbon paper. Therefore, a slight difference occurs in the contact state between the separator and the carbon cloth as the gas diffusion layer material, so that the electric resistance at that portion is not stable, and as a result, the electric resistance of the entire woven fabric is also unstable. There is a problem that it is easy to become.
[0008]
Several methods have been proposed for solving this problem of carbonaceous fiber woven fabrics. For example, JP-A-58-165254 describes filling a void of a carbonaceous fiber woven fabric with a mixture of a fluororesin and carbon black. Japanese Patent Application Laid-Open No. 10-261421 describes that a layer composed of a fluororesin and carbon black is formed on the surface of a carbonaceous fiber woven fabric. These methods are expected to have the effect of reducing thickness unevenness by forming a mixed phase of fluororesin / carbon black on the cloth surface.
[0009]
However, these methods are intended to adjust the water retention, drainage, gas permeability, etc. of the gas diffusion layer by filling the carbonaceous fiber woven fabric with a fluororesin, carbon black or the like. There are disadvantages such as an increase in resistance and a decrease in battery characteristics, and a decrease in gas permeability, which is an advantage of the carbonaceous fiber woven fabric.
[0010]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a carbonaceous fiber woven fabric in which properties desired as a gas diffusion layer material such as gas permeability, conductivity (low resistance), water retention, drainage, etc. are balanced. Another object of the present invention is to provide a carbonaceous fiber woven fabric which is uniform and has particularly small thickness unevenness and which is suitable as a gas diffusion layer material for a polymer electrolyte fuel cell.
[0011]
[Means for Solving the Problems]
That is, the gist of the present invention is a woven fabric mainly composed of carbon fiber yarns, and has a basis weight of 50 to 200 g / m2. ² The thickness is 0.05 to 2 mm, the bulk density is 0.2 to 0.6 g / cc, the volume resistivity in the surface direction is 0.15 Ωcm or less, and the woven fabric is defined by the sides in the warp direction and the weft direction. When cut into squares, the coefficient of variation of the thickness of the woven fabric at a total of 20 division points obtained by dividing the two diagonal lines into 11 equal parts is 3.2% or less, and the warp constituting the woven fabric And the weft yarn is in a carbonaceous fiber woven fabric characterized in that the major axis of the cross section is at least twice the minor axis.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
The carbonaceous fiber woven fabric of the present invention is a woven fabric mainly composed of carbonaceous fiber yarns, and the basis weight, thickness and its variation coefficient, bulk density, and surface specific volume resistivity are in specific ranges. The cross section of the warp and the weft constituting the woven fabric has a specific shape.
[0013]
The method for producing a carbonaceous fiber woven fabric of the present invention is not particularly limited as long as a material satisfying specific physical properties is obtained.For example, a carbonaceous precursor fiber was woven, and the obtained woven fabric was pressed. Thereafter, it can be produced by carbonization treatment and, if desired, further graphitization.
Hereinafter, this manufacturing method will be described in detail.
[0014]
(Carbon precursor fiber)
As the carbonaceous precursor fiber as a starting material, any known carbonaceous precursor fiber such as polyacrylonitrile-based, pitch-based, cellulose-based, polynosic-based, phenolic resin-based, or a mixture thereof can be used. Usually, a pitch type or polyacrylonitrile type is used. Among them, it is preferable to use a polyacrylonitrile-based carbonaceous precursor fiber. The polyacrylonitrile-based carbonaceous precursor fibers are made of a raw material of polyacrylonitrile of almost 100% acrylonitrile or a raw material of an acrylonitrile-based copolymer containing 50% or more of acrylonitrile, depending on the content ratio of acrylonitrile units. And various types of acrylonitrile-based copolymers containing acrylonitrile containing 20 to 50% of acrylonitrile as raw materials, and carbonaceous precursor fibers using any of these as raw materials may be used. it can.
[0015]
(Flame-resistant treatment)
Prior to weaving the carbonaceous precursor fiber into a woven fabric, a flameproofing treatment can be performed.
The flame-resistance treatment (infusibility treatment) is a chemical reaction in which oxygen atoms are introduced into the molecular structure of pitch or polyacrylonitrile. This is done by contacting for minutes. In general, the larger the amount of oxygen introduced into the molecular structure, the greater the effect of preventing fusion during the subsequent carbonization treatment. As the index, a limit oxygen concentration, which is generally required to burn fibers, is referred to as an LOI value. In order not to cause fusion as in the case of producing ordinary carbonaceous fibers, it is supposed that a flame-proof treatment should be performed so that the LOI value is 35 to 60. Also in the production of the carbonaceous fiber woven fabric of the present invention, it is preferable to carry out a flameproofing treatment so that the LOI value of the carbonaceous precursor is 35 to 60.
[0016]
That is, in the case where the carbonaceous fibers constituting the woven fabric are not fused, it is only necessary to perform the flameproofing treatment so that the LOI value becomes 35 to 60. Conversely, when it is desired to improve the characteristics of the fuel cell by fusing the fibers into a woven fabric having rigidity, the flame resistance treatment may be performed so that the LOI value is less than 35, particularly 33 or less. . If the LOI value is too small, the fusion becomes so intense during the subsequent carbonization treatment that the resulting carbonaceous fiber woven fabric becomes brittle, so that the oxidization treatment is carried out so that the LOI value becomes 20 or more, especially 25 or more. Is preferably performed. The LOI value can be adjusted by changing the contact temperature and contact time with oxygen during the oxidation treatment.
[0017]
For example, in one of the preferable methods, an oxidized fiber obtained by oxidizing a polyacrylonitrile fiber at 200 to 300 ° C. in air is used. The polyacrylonitrile-based fiber to be subjected to the flame-resistant treatment may be either a long fiber or a spun short fiber, and the yarn may be a single yarn or a double yarn. In addition, at the time of the flame-proofing treatment, the fiber can be stretched to improve the toughness of the fiber.
[0018]
(Carbon precursor fiber yarn)
The yarn to be used for weaving may be either a filament yarn or a spun yarn, but a spun yarn is preferable because a dense and uniform woven fabric structure is obtained and the yarn productivity is high. As a spinning method for obtaining a spun yarn, any known method can be applied, and examples thereof include a spinning method such as cotton spinning, 2 inch spinning, carded spinning, woolen spinning, and direct spinning. In the case of the polyacrylonitrile-based flame-resistant fiber, it is preferable to use a spun yarn obtained by spinning a sliver obtained by cutting a continuous filament tow of polyacrylonitrile by carding spinning.
[0019]
(Type of thread)
The yarn to be used in the weaving may be any one of a single yarn, a twin yarn, a three-ply yarn, a filament yarn, and a composite yarn composed of carbonaceous precursor fibers of different raw materials.
The spun yarn may be either a twin yarn or a single yarn, but in general, a twin yarn has a higher tensile strength than a single yarn, so that a woven fabric having a uniform thickness can be produced. It is preferable because it is possible.
[0020]
(Yarn fineness (count))
The fineness of the yarn is metric count, usually 14 count or more, preferably 16 count or more, more preferably 18 count or more, and is usually 50 count or less, preferably 45 count or less.
In the case of a single yarn, it is usually 1/14 Nm or more, preferably 1/16 Nm or more, more preferably 1/18 Nm or more, and usually 1/50 Nm or less, preferably 1/45 Nm or less. In the case of twin yarn, the yarn count is usually 2/28 Nm or more, preferably 2/32 Nm or more, more preferably 2/36 Nm or more, and usually 2/100 Nm or less, preferably 2/90 Nm or less.
[0021]
In the case of a thicker count than 1/14 Nm or 2/28 Nm, the number of fluffs per unit length tends to increase. Further, when the yarn count is smaller than 1/50 Nm or 2/100 Nm, the tensile strength of the yarn tends to be low.
(Number of twists of yarn)
The number of twists of the yarn is measured according to JIS L 1095 (General spun yarn test method).
[0022]
The number of twists in the case of a single yarn is usually 300 times / m or more, preferably 500 times / m or more, and usually 800 times / m or less, preferably 700 times / m or less per 1 m of yarn length. . The preferred number of twists slightly varies depending on the yarn count, but if it is less than 300, the number of fluffs of the yarn tends to increase. On the other hand, if the number of twists is too large, yarn breakage tends to occur during twisting. When the number of twists is increased, the number of fluffs is reduced. However, when the number of twists is 700 or more, the effect of fluff reduction by increasing the number of twists is almost saturated.
[0023]
In the case of a twin yarn, the number of twists is usually 300 turns / m or more, preferably 400 turns / m or more, and usually 800 turns / m or less, preferably 750 turns / m or less per 1 m of yarn length. is there. If the number of twists is small, the number of fluffs tends to increase. Further, when the number of twists is large, the probability of yarn breakage during twisting increases, and the thickness unevenness may increase. The number of twists is usually 500 times / m or more, preferably 600 times / m or more, and is usually 900 times / m or less, preferably 850 times / m or less. If the number of ply twists is small, the number of fluffs tends to increase. In addition, when the number of twists is large, the probability of occurrence of yarn breakage during twisting tends to increase.
[0024]
(Weaving)
The above-mentioned polyacrylonitrile-based oxidized fiber or the like, the oxidized carbonaceous precursor fiber may be woven to form an oxidized-resistant fabric, or the polyacrylonitrile-based fiber itself or the like, which is not subjected to the oxidized-treated carbonaceous precursor fiber. The body fiber may be woven into a woven fabric, which may be subjected to a flame-resistant treatment to form a flame-resistant woven fabric. In this case, the woven fabric may be brought into contact with an oxidizing gas such as air, ozone, or nitrogen oxide, sulfuric acid, nitric acid, or the like to obtain a flame-resistant woven fabric having a suitable LOI value.
[0025]
(Weaving)
The structure of the woven fabric may be plain weave, oblique weave, satin weave, or any other structure, but since plain weave has the largest number of intersections per unit area of warp and weft, the volume resistivity of the woven fabric is low. It is preferable because it becomes smaller.
(Background density)
The weft density (the number of warp yarns and weft yarns per unit length) in the case of plain weave is generally 20 to 60 yarns per inch. It is appropriately selected according to the situation.
[0026]
(Carbon precursor fiber woven fabric)
The basis weight of the carbonaceous precursor fiber woven fabric, that is, the mass per unit area is usually 50 g / m ² Or more, preferably 60 g / m ² Or more, more preferably 80 g / m ² And usually 350 g / m ² Or less, preferably 250 g / m ² It is as follows. If the basis weight is too small, the rigidity and the tensile strength are reduced, and if the basis weight is too large, the clogging is too clogged and the gas diffusivity is reduced.
[0027]
The thickness of the woven fabric is usually at least 0.05 mm, preferably at least 0.10 mm, more preferably at least 0.20 mm, and is usually at most 5 mm, preferably at most 3 mm. If the thickness is too small, the tensile strength will decrease, and if it is too large, the clogging will be too tight and the gas permeability will decrease.
The bulk density of the woven fabric is usually 0.2 g / cc or more, preferably 0.25 g / cc or more, and is usually 0.8 g / cc or less, preferably 0.7 g / cc or less. If the bulk density is too low, the tensile strength decreases, and if the bulk density is too high, the clogging becomes too clogged and the gas permeability decreases.
[0028]
The width of the woven fabric is usually 5 cm or more, preferably 10 cm or more, and is usually 250 cm or less, preferably 200 cm or less, and more preferably 100 cm or less. If the width is too small, the shrinkage of the woven fabric in the width direction may increase, resulting in wrinkles and uneven thickness. On the other hand, if the width is too large, it is difficult to perform the carbonization and graphitization uniformly, and in particular, uneven shrinkage is likely to occur due to uneven shrinkage during the carbonization.
[0029]
The length of the woven fabric is usually at least 50 cm, preferably at least 100 cm, and is usually at most 300 m, preferably at most 200 m. If the length is too short, the shrinkage in the length direction (long direction) may increase, and wrinkles may occur, resulting in uneven thickness. In addition, the longer the length is, the more the woven fabric is used for the gas diffusion layer material (when the filling process is continuously performed by applying a paste containing carbon black as a main component to the woven fabric). Although it is preferable to reduce the number of times of connection (the number of times of connecting the ends of the woven fabric), in practice, a long wound material having a length of 300 m or more is wound up in order to prevent the occurrence of thickness unevenness. There is substantially no winding equipment capable of controlling and winding stably from the start to the end of winding.
[0030]
(Press working)
Press processing is performed to reduce the thickness unevenness of the carbonaceous precursor fiber woven fabric. Usually, it is often conceived that press working of carbonized (graphitized) woven fabric can suppress thickness unevenness. However, as shown in Comparative Examples 3 and 4 described below, fiber Pressing under mild pressing conditions to maintain the shape increases the thickness unevenness. On the other hand, if strong pressing conditions are used to eliminate thickness unevenness, the fiber itself cannot maintain its original shape. Therefore, the woven fabric having the specific physical properties of the present invention can be obtained by performing the specific press working.
[0031]
(Type of press machine)
Examples of the press machine for performing press working include a flat press machine having a flat press surface, a roll press machine for performing press working with a roll, and the like. A roll-type press is preferable because the cloth can be continuously pressed. The pressurizing method of the press may be a hydraulic type, a pneumatic type, a spring pressure type, or the like, and any type may be used, but a hydraulic type capable of high-pressure pressing is generally preferable.
[0032]
(Roll type press)
In a roll-type press, generally, a woven fabric is sandwiched between a rotating upper roll and a lower roll made of metal to perform a continuous press working. The roll diameter of the roll-type press is usually about 10 to 80 cm, and the width of the contact portion between the roll and the woven fabric is about 2 to 10 mm, depending on the roll diameter. The effective length of the roll is preferably about 50 to 200 cm in order to perform press working with a uniform pressure. The pressure per unit roll length, which is obtained by dividing the total load applied by hydraulic pressure or the like by the effective roll length, is 50 to 500 kg / cm, preferably 100 to 400 kg / cm. If it is less than 50 kg / cm, the thickness unevenness is reduced, but the reduction is small. On the other hand, if it exceeds 500 kg / cm, it slightly differs depending on the thickness of the woven fabric before pressing, the thickness unevenness, the thickness of the yarn, the weft density of the woven fabric, etc. The strength of the cloth may be significantly reduced. The passing speed of the woven fabric between the press rolls depends on the press pressure, but is usually preferably about 2 to 20 m / min. Outside this range, uniform pressing may not be performed.
[0033]
The number of times of the press processing is not limited to one, and may be repeated about 2 to 10 times.
(Flat plate press)
In the case of a flat-plate type press, the press pressure during press working is 20 to 2000 kg / cm in terms of surface pressure. ² Is preferred. 20kg / cm ² Even if the thickness is less than the above, the thickness unevenness is reduced, but the reduction amount is small. Also, 2000kg / cm ² If it exceeds, the thickness of the woven fabric before pressing, the thickness unevenness, the thickness of the yarn, the weft density of the woven fabric, etc. slightly vary, but the fibers of the woven fabric are partially compressed and destroyed, and the strength of the woven fabric is reduced. It may be significantly reduced.
[0034]
The time for pressurizing at a predetermined pressure is usually preferably 10 seconds to 10 minutes. If the time is less than 10 seconds, the effect of reducing thickness unevenness is small. On the other hand, even if the pressing is performed for a long time exceeding 10 minutes, the effect is small.
In any case, the number of woven fabrics to be pressed by the press is usually one by one. However, in order to increase productivity, about 2 to 20 woven fabrics may be stacked and pressed. However, when the number of sheets is 20 or more, the effect of reducing thickness unevenness may not be observed in the woven fabric after the press working.
[0035]
In addition, in order to enhance the effect of reducing thickness unevenness, the woven fabric before press working, polyvinyl alcohol, a paste such as starch paste, or phenol resin, furan resin, polyimide resin, polyethylene resin, polypropylene resin, polyimide resin, A thermosetting resin such as a polyamide resin or a thermoplastic resin dissolved with an organic solvent or the like, or a finely pulverized product of these resins may be attached.
[0036]
Further, at the time of press working, the temperature of the press surface may be raised to a temperature higher than room temperature (for example, about 50 to 500 ° C., preferably about 100 to 300 ° C.) to perform the press working. In this case, more uniform pressing can be performed because the above-described resin is melted and hardened, or moisture or the like contained in the woven fabric is removed.
By performing the press working as described above, not only the thickness unevenness is reduced, but also a fluff having a length of about several mm existing on the surface of the carbonaceous fiber woven fabric, which can be one of the factors of the voltage drop of the fuel cell. The effect of reducing fluffing can also be expected.
[0037]
(Carbonization treatment)
Subsequent to the press working, the carbonaceous precursor fiber woven fabric is carbonized.
The carbonization treatment may be performed by heating at 400 ° C. or higher, preferably 600 ° C. or higher, and 1400 ° C. or lower, preferably 1300 ° C. or lower in an inert gas. From the viewpoint of the conductivity of the woven fabric, the woven fabric is preferably heated to 700 ° C or higher, more preferably 800 ° C or higher, and more preferably 900 ° C or higher.
[0038]
In the carbonization treatment, carbonization is performed at 800 to 1400 ° C. via a thermal decomposition temperature of about 300 to 750 ° C. The rate of temperature rise during the thermal decomposition process is preferably 5 to 300 ° C./min, and the temperature holding time during the carbonization process is preferably 1 minute or more and 4 hours or less. Also, depending on the heat capacity of the heat treatment furnace and the speed of transporting the raw woven fabric into the furnace, the woven fabric is put into the carbonization zone at a constant temperature from the beginning without providing a pyrolysis zone at 750 ° C or lower, The heat received by the fabric from the carbonization zone may cause the temperature of the woven fabric to rise, resulting in thermal decomposition, followed by carbonization. In any case, the gas atmosphere in the furnace is preferably an inert atmosphere having an oxygen concentration of 100 ppm or less.
[0039]
The carbonization furnace for performing the carbonization treatment may be either a batch-type heat treatment furnace or a continuous-type heat treatment furnace, but a continuous furnace is advantageous in that the carbonization treatment can be performed continuously and uniformly on a long woven fabric. preferable.
A continuous heat treatment furnace is a horizontal continuous heating furnace or a vertical continuous heating furnace equipped with a plurality of heating means, and the horizontal type is more deformed and uneven due to the weight of the woven fabric than the vertical type. It is preferable because it is difficult. In the furnace, the object to be processed is usually placed directly on a metal (steel, stainless steel, etc.) mesh or meshless belt, and is transported by moving the belt at a constant speed by external control. preferable.
[0040]
(Graphitization)
Subsequent to the carbonization treatment, further graphitization treatment can be performed.
The temperature of the graphitization treatment is usually 1400 ° C. or higher, preferably 1600 ° C. or higher, and is usually 3000 ° C. or lower, preferably 2500 ° C. or lower. When the temperature is 1400 ° C. or higher, the volume resistivity of the woven fabric is further reduced, which is more preferable as a gas diffusion layer material. It should be noted that the volume resistivity after the heat treatment in the treatment up to about 3000 ° C. has no problem in use as a gas diffusion layer material.
[0041]
The graphitization time is usually at least 10 minutes, preferably at least 20 minutes, and is usually at most 4 hours, preferably at most 2 hours. If the treatment time is less than 10 minutes, the graphitization may not be completed uniformly. On the other hand, when the treatment time is long, the productivity and the thermal efficiency are low, and the woven fabric may be contaminated with impurities generated from the heat insulating material, the heating element and the like of the graphitization furnace.
[0042]
(Other processing)
The carbonaceous fiber woven fabric obtained above is composed of 100% by weight of carbonaceous fibers, and further contains conductive substances such as powdered activated carbon, conductive carbon black, and carbides of various pitches. You can also. For example, the pitch is dissolved in an organic solvent to form a pitch solution, and a suspension of powdered activated carbon or conductive carbon black is applied to the woven fabric obtained above, and then heated in an inert gas. A carbonized pitch can be used. Even in that case, the proportion of the carbonaceous fiber in the woven fabric is at least 60% by weight, preferably at least 80% by weight.
[0043]
The carbonaceous fiber woven fabric obtained as described above can be used as it is as a material for a gas diffusion layer of a fuel cell, but it can be further processed and used as a material for a gas diffusion layer. For example, to obtain a suitable amount of water in the membrane electrode body constituting the battery, or to remove the impurities contained in the fuel and the oxidizing agent supplied to the battery to prevent the deterioration of the battery characteristics, to obtain the above obtained The carbonaceous fiber woven fabric is brought into contact with water vapor or carbon dioxide at about 800 to 1200 ° C. or air at about 300 to 500 ° C. to gasify part of the carbonaceous material to generate fine pores in the carbonaceous fiber, It can be a woven fabric made of porous carbonaceous fibers.
[0044]
(Physical properties of carbonaceous fiber woven fabric)
The basis weight of the obtained carbonaceous fiber woven fabric is 50 g / m ² Or more, preferably 60 g / m ² And 200 g / m ² Or less, preferably 180 g / m ² It is as follows. If the basis weight is too small, the tensile strength will be low and cannot be used as a gas diffusion layer material. If the basis weight is too large, the gas permeability becomes too small.
[0045]
The bulk density (g / cc) of the carbonaceous fiber woven fabric is obtained by dividing the basis weight of the woven fabric by the thickness of the woven fabric. The bulk density of the woven fabric is 0.2 g / cc or more, preferably 0.25 g / cc or more, and 0.6 g / cc or less, preferably 0.55 g / cc or less. If the bulk density is less than 0.2 g / cc, the tensile strength of the woven fabric is weak, which is not practical. On the other hand, if the bulk density is too large, the gas diffusivity is reduced.
[0046]
The volume resistivity in the plane direction of the carbonaceous fiber woven fabric is 0.15 Ωcm or less, preferably 0.10 Ωcm or less. This value is preferably as low as possible, but if it is about 0.05 Ωcm or less, the volume resistivity is sufficiently low as a gas diffusion layer material.
The fineness of the yarn constituting the woven fabric is metric count, usually 16 count or more, preferably 18 count or more, more preferably 20 count or more, and is usually 60 count or less, preferably 55 count or less.
[0047]
In the case of a single yarn, it is usually 1/16 Nm or more, preferably 1/18 Nm or more, more preferably 1/20 Nm or more, and usually 1/60 Nm or less, preferably 1/55 Nm or less. In the case of a twin yarn, the yarn count is usually 2/32 Nm or more, preferably 2/36 Nm or more, more preferably 2/40 Nm or more, and usually 2/120 Nm or less, preferably 2/110 Nm or less.
[0048]
When the count is thicker than 1/16 Nm or 2/32 Nm, the number of fluffs per unit length tends to increase. Further, when the yarn count is smaller than 1/60 Nm or 2/120 Nm, the tensile strength of the yarn tends to be low.
In addition, the carbonaceous fiber is obtained through a process of spinning, flame resistance, carbonization, and (graphitization). In the process of carbonizing and further graphitizing the flame resistant yarn, the fineness is about 10 to 20%. Decrease. In the present invention, the fineness of the yarn constituting the woven fabric is about the yarn of the woven fabric finally obtained, and can be measured by extracting the yarn from the woven fabric and measuring.
[0049]
The weft density (number of warp yarns and weft yarns per unit length) of the carbonaceous fiber woven fabric in the case of plain weave has a fineness of about 10 in the process of carbonizing and graphitizing the yarn (flame-resistant yarn) constituting the woven fabric. In general, the number is 30 to 70 yarns per inch to reduce by about%, but specifically, it is appropriately selected according to the difference between single yarn and double yarn and the thickness of yarn. For example, when the 2/40 Nm spun yarn is used for the warp and the weft, the weft density is usually 100 to 300 yarns / 10 cm for both the warp and the weft per 10 cm length of the woven fabric, and preferably 180. ２５０250 lines / 10 cm. Further, when the gap between the yarns of the warp and the weft is observed with a scanning electron microscope, the pore diameter corresponding to the gap between the yarns is 10 to 150 μm, which is used for a gas diffusion layer of a fuel cell. It is preferable to ensure water retention and drainage.
[0050]
An example of a preferable woven fabric is obtained by plain weaving a double yarn of 40 to 60 count yarn consisting of a single fiber having a diameter of 7 to 10 μm with a density of 30 to 70 warp yarns and weft yarns per inch. .
The thickness (average value) and thickness unevenness (coefficient of variation) of the carbonaceous fiber woven fabric are determined as follows. From the woven fabric, a square having sides in the warp direction and the weft direction is cut out so as not to include a portion up to 5 mm from the end, preferably up to 10 mm, and two diagonal lines thereof are each divided into 11 equal parts, for a total of 20 divisions. Measure the thickness of the woven fabric at the point. From the measured values, the average value and the coefficient of variation of the thickness (standard deviation of woven fabric thickness / average of woven fabric thickness x 100%) are determined. The size of the woven fabric to be cut varies depending on the width of the woven fabric, but it is standard to cut the fabric into a square with a cloth width of 40 to 98% excluding the end portion, and particularly with a cloth width of about 70 to 90%. Although not limited, a square of 10 to 40 cm square is preferable.
[0051]
The thickness was measured using a disk-shaped terminal with a diameter of 5 mm at about 10 g / cm. ² And the thickness was measured by contacting the surface of the woven fabric with the weight. The above measurement is carried out every 5 to 50 m so as not to include the portion up to 5 mm from the end, preferably up to 10 mm from the end in the length direction of the woven fabric, but when the woven fabric length is less than 5 m, The thickness of the carbonaceous fiber woven fabric and the coefficient of variation of the thickness are determined from the measured values obtained by cutting out one arbitrary point into a square. When the length is 5 m or more, the thickness is divided into five equal parts in the length direction, and one point is cut out of each part into a square to obtain the thickness and the coefficient of variation of the thickness for a total of five points. The thickness and the coefficient of variation of the thickness of the long carbonaceous fiber woven fabric.
[0052]
The thickness of the carbonaceous fiber woven fabric is 0.05 mm or more, preferably 0.1 mm or more, and 2 mm or less, preferably 1 mm or less, more preferably 0.35 mm or less. If the thickness is less than 0.05 mm, the tensile strength is low and the material is insufficient as a gas diffusion layer material. On the other hand, if the thickness exceeds 2 mm, the gas permeability decreases and the gas diffusion layer material is insufficient.
[0053]
The coefficient of variation of the thickness of the carbonaceous fiber woven fabric is 3.2% or less, preferably 3% or less, more preferably 2.8% or less. The smaller the coefficient of variation, the better, but about 1% is sufficient.
(Cross-sectional shape of warp and weft constituting woven fabric)
In an ordinary woven fabric that has not been subjected to press working, the overall cross-sectional shape of the yarn after weaving can be approximated by a substantially perfect circle or an ellipse having a ratio of major axis / minor axis close to 1. On the other hand, the cross-sectional shape of the thread of the woven fabric after the press working can be approximated by an ellipse having a major axis in the plane direction, a minor axis in the thickness direction, and a major / major axis ratio of 2 or more.
[0054]
The method of observing the cross-sectional shape of the yarn in the woven fabric is not particularly limited.For example, a cut surface of the woven fabric is cut in parallel with a warp or a weft, and the cut cross section is taken from a photograph taken with a microscope such as a scanning electron microscope. You can ask. It is possible to use scissors with sharp blades to cut the woven fabric, but in addition, embed the woven fabric in a thermosetting resin with small dimensional change after curing, completely cure, and then May be cut out with a cutting instrument to obtain a sample to be observed.
[0055]
The value of the ratio of the major axis / minor axis of the cross section of the warp and weft constituting the woven fabric may vary slightly depending on the thickness of the yarn (yarn count), the number of twists of the yarn, whether it is twin yarn or single yarn, or the weft density of the woven fabric. Although different, it must be 2 or more, preferably 2.5 or more, more preferably 3 or more. If the ratio of major axis / minor axis is less than 2, the effect of reducing thickness unevenness is small. The ratio of the major axis / minor axis is usually 10 or less, and preferably 8 or less. If the ratio exceeds 10, a portion where the thickness of the woven fabric becomes extremely thin may occur, and the thickness unevenness may increase.
[0056]
The measured values of the major axis and the minor axis are slightly different depending on the thickness (yarn count) of the yarn, the number of twists of the yarn, the twin yarn or the single yarn, or the weft density of the woven fabric, but the major diameter is usually 200 to 800 μm. Yes, and the minor axis is usually 80 to 200 μm.
(Gas permeability)
The gas permeability was measured by a breathability test (Fragile method) according to JIS L 1096 (General Fabric Test Method). The measured value of gas permeability obtained by this evaluation method reflects the degree of gas permeability and water retention when carbonaceous fibers are used as a gas diffusion layer material for a fuel cell.
[0057]
The gas permeability of the woven fabric is typically 200 cm ³ / Cm ² * Sec or less, preferably 150 cm ³ / Cm ² ・ Second or less. The lower the gas permeability, the better the water retention is, which is preferable. However, for use as a gas diffusion layer material, 30 cm ³ / Cm ² 50 seconds when used in high-power applications requiring instantaneous generation of a large current, such as a polymer electrolyte fuel cell for automobiles ³ / Cm ² -Sec or more is preferable.
[0058]
(Size of carbon fiber monofilament)
The diameter of the single fiber of the carbonaceous fiber is usually in the range of 6 to 50 μm, preferably 6 to 30 μm. In particular, a woven fabric obtained from a spun yarn made of a single fiber having a diameter of 7 to 15 μm is preferable because unevenness in thickness hardly occurs due to the above carbonization treatment and graphitization treatment.
(Metal impurities in carbonaceous fiber woven fabric)
Metal impurities in the woven fabric are preferably reduced as much as possible because they cause a reduction in cell characteristics due to an electrolysis reaction of generated water during operation of the fuel cell. For example, iron is preferably 50 μg / g or less, nickel is preferably 50 μg / g or less, and sodium is preferably 100 μg / g or less. The content of metal impurities in the woven fabric can be reduced by washing the woven fabric or the carbonaceous fiber of the raw material, and further, the raw material yarn with an acid such as hydrochloric acid or acetic acid.
[0059]
(Gas diffusion layer material for polymer electrolyte fuel cells)
The carbonaceous fiber woven fabric of the present invention can be suitably used as a gas diffusion layer of a fuel cell. For example, a paste obtained by mixing a dispersion of polytetrafluoroethylene, a catalyst and carbon black is applied to a polymer solid electrolyte membrane to form a joined body of the polymer solid electrolyte membrane and the catalyst layer, and By bonding the carbonaceous fiber woven fabric of the present invention as a gas diffusion layer, a membrane electrode body can be formed. The formation of the bonded body of the polymer solid electrolyte membrane and the catalyst layer is performed by applying a paste of a dispersion of polytetrafluoroethylene, a catalyst and carbon black on a release sheet, forming a catalyst layer, and forming a catalyst layer. It can also be formed by joining a molecular solid electrolyte membrane with a hot press. Conversely, a catalyst paste is applied to the carbonaceous fiber woven fabric of the present invention to form a joined body of the gas diffusion layer and the catalyst layer, and this is joined to the polymer solid electrolyte membrane by hot pressing to obtain a membrane electrode. It can also form a body. Regardless of which method is used, the carbonaceous fiber woven fabric of the present invention has an appropriate rigidity and is easy to handle.
[0060]
The polymer electrolyte fuel cell using the carbonaceous fiber woven fabric of the present invention is suitably used as a power source for an automobile or a power source for a cogeneration power generation system.
[0061]
【Example】
Next, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist is not exceeded.
[Example 1]
(Carbon precursor fiber woven fabric)
A polyacrylonitrile flame-resistant spun yarn having a LOI value of 50 of a metric count 40-count double yarn (2/40 Nm) was plain woven. The size of the woven fabric is 100 cm in width and 150 m in length, the thickness is 0.318 mm (average value), and the basis weight is 171 g / m. ² (Average value), bulk density was 0.538 g / cc.
[0062]
(Press processing)
The carbonaceous precursor fiber woven fabric is brought into contact with a gap between an upper roll and a lower roll of a roll-type press at a contact pressure of 300 kg / cm, and passed through the woven fabric once at a transport speed of 10 m / min. Processing was performed.
The thickness of the woven fabric after pressing is 0.299 mm (average value), and the basis weight is 171 g / m. ² (Average value), bulk density was 0.572 g / cc.
[0063]
(Carbonization treatment)
The press-processed carbonaceous precursor fiber woven fabric was cut out at a width of 50 cm, and carbonized at 950 ° C. in a horizontal continuous carbonization furnace in a nitrogen atmosphere.
(Physical properties of carbonaceous fiber woven fabric after carbonization)
The physical properties of the carbonaceous fiber woven fabric after carbonization were measured according to the methods described above. However, the size of a square cut out using the warp direction and the weft direction of the woven fabric as sides for measuring the thickness of the woven fabric was 40 cm square.
[0064]
The thickness of the carbonaceous fiber woven fabric after carbonization is 0.234 mm, the coefficient of variation of the thickness is 2.6%, and the basis weight is 112 g / m. ² , Bulk density 0.479 g / cc, volume resistivity 0.12 Ωcm, gas permeability 98 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 5.5 for the warp and 5.7 for the weft.
(Graphitization)
The wound carbonized fiber woven fabric after carbonization was graphitized in a vacuum graphitization furnace at 2000 ° C. or higher to obtain a graphitized woven fabric.
[0065]
(Physical properties of carbonized fiber woven fabric after graphitization)
The physical properties of the graphitized carbonaceous fiber woven fabric were measured according to the method described above. However, the size of a square cut out using the warp direction and the weft direction of the woven fabric as sides for measuring the thickness of the woven fabric was 40 cm square.
The thickness of the carbonized fiber woven fabric after graphitization is 0.208 mm, the coefficient of variation of the thickness is 2.6%,
The basis weight is 96 g / m ² , Bulk density is 0.462 g / cc, volume resistivity is 0.02 Ωcm, gas permeability is 92 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 5.0 for the warp and 5.2 for the weft.
[0066]
[Example 2]
(Carbon precursor fiber woven fabric)
A polyacrylonitrile flame-resistant spun yarn having an LOI value of 50 of a 35-meter metric twin yarn (2/35 Nm) was plain woven. The size of the woven fabric was the same as in Example 1, the thickness was 0.352 mm, and the basis weight was 199 g / m. ² And the bulk density was 0.565 g / cc.
[0067]
(Press processing)
The above carbonaceous precursor fiber The woven fabric was pressed in the same manner as in Example 1 except that the pressing was repeated twice.
The thickness of the woven fabric after pressing is 0.318 mm (average value), and the basis weight is 198 g / m. ² (Average value), bulk density was 0.623 g / cc.
[0068]
(Carbonization treatment)
Carbonization treatment was performed in the same manner as in Example 1.
(Physical properties of carbonaceous fiber woven fabric after carbonization)
Physical properties of the carbonaceous fiber woven fabric after carbonization were measured in the same manner as in Example 1.
The thickness of the carbonaceous fiber woven fabric after carbonization is 0.264 mm, the coefficient of variation of the thickness is 2.7%, and the basis weight is 134 g / m. ² , Bulk density 0.508 g / cc, volume resistivity 0.13 Ωcm, gas permeability 75 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 5.4 in the warp and 5.5 in the weft.
[0069]
(Graphitization)
Graphitization was performed in the same manner as in Example 1.
(Physical properties of carbonized fiber woven fabric after graphitization)
The physical properties of the carbonized fiber woven fabric after graphitization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after graphitization is 0.290 mm, the coefficient of variation of the thickness is 2.8%,
The basis weight is 123 g / m ² , Bulk density is 0.424 g / cc, volume resistivity is 0.02 Ωcm, gas permeability is 70 cm ³ / Cm ² Sec, the volume resistivity was 0.02 Ωcm, and the ratio of the major axis / minor axis of the yarn was 5.1 for the warp and 5.3 for the weft.
[0070]
[Example 3]
(Carbon precursor fiber woven fabric)
The same carbonaceous precursor fiber woven fabric as in Example 1 was used.
(Press processing)
Press working was performed using a flat plate press.
[0071]
The carbonaceous precursor fiber woven fabric cut out to a size of 50 cm × 50 cm is placed on a square flat press plate having an effective size of about 60 cm square, and the surface pressure of the press surface is reduced from normal pressure to 100 kg / cm. ² After the pressure is increased to about 1 minute in about 1 minute, 100 kg / cm ² After maintaining the surface pressure for 2 minutes, the pressure was released to return to normal pressure.
The thickness of the woven fabric after pressing is 0.307 mm (average value), and the basis weight is 170 g / m. ² (Average value), bulk density was 0.554 g / cc.
[0072]
(Carbonization treatment)
Carbonization treatment was performed in the same manner as in Example 1.
(Physical properties of carbonaceous fiber woven fabric after carbonization)
Physical properties of the carbonaceous fiber woven fabric after carbonization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after carbonization is 0.255 mm, the coefficient of variation of the thickness is 2.6%, and the basis weight is 111 g / m. ² , Bulk density 0.435 g / cc, volume resistivity 0.13 Ωcm, gas permeability 98 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 4.5 for the warp and 4.7 for the weft.
[0073]
(Graphitization)
Graphitization was performed in the same manner as in Example 1.
(Physical properties of carbonized fiber woven fabric after graphitization)
The physical properties of the carbonized fiber woven fabric after graphitization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after graphitization is 0.220 mm, the coefficient of variation of the thickness is 2.7%,
The basis weight is 96 g / m ² , Bulk density is 0.436 g / cc, volume resistivity is 0.02 Ωcm, gas permeability is 92 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 4.0 for the warp and 4.3 for the weft.
[0074]
[Comparative Example 1]
(Carbon precursor fiber woven fabric)
The same carbonaceous precursor fiber woven fabric as in Example 1 was used.
(Press processing)
No pressing was performed.
[0075]
(Carbonization treatment)
Carbonization treatment was performed in the same manner as in Example 1.
(Physical properties of carbonaceous fiber woven fabric after carbonization)
Physical properties of the carbonaceous fiber woven fabric after carbonization were measured in the same manner as in Example 1.
The thickness of the carbonaceous fiber woven fabric after carbonization is 0.255 mm, the coefficient of variation of the thickness is 3.4%, and the basis weight is 118 g / m. ² , Bulk density is 0.463 g / cc, volume resistivity is 0.13 Ωcm, gas permeability is 100 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 1.7 for the warp and 1.8 for the weft.
[0076]
(Graphitization)
Graphitization was performed in the same manner as in Example 1.
(Physical properties of carbonized fiber woven fabric after graphitization)
The physical properties of the carbonized fiber woven fabric after graphitization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after graphitization is 0.246 mm, the coefficient of variation of the thickness is 3.5%,
The basis weight is 101 g / m ² , Bulk density 0.411 g / cc, volume resistivity 0.02 Ωcm, gas permeability 105 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 1.8 for the warp yarn and 1.9 for the weft yarn.
[0077]
[Comparative Example 2]
(Carbon precursor fiber woven fabric)
The same carbonaceous precursor fiber woven fabric as in Example 2 was used.
(Press processing)
No pressing was performed.
[0078]
(Carbonization treatment)
Carbonization treatment was performed in the same manner as in Example 2.
(Physical properties of carbonaceous fiber woven fabric after carbonization)
Physical properties of the carbonaceous fiber woven fabric after carbonization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after carbonization is 0.301 mm, the coefficient of variation of the thickness is 3.5%, and the basis weight is 139 g / m. ² , Bulk density is 0.462 g / cc, volume resistivity is 0.13 Ωcm, gas permeability is 82 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 1.7 for the warp yarn and 1.9 for the weft yarn.
[0079]
(Graphitization)
Graphitization was performed in the same manner as in Example 1.
(Physical properties of carbonized fiber woven fabric after graphitization)
The physical properties of the carbonized fiber woven fabric after graphitization were measured in the same manner as in Example 1.
The thickness of the carbonized fiber woven fabric after graphitization is 0.320 mm, the coefficient of variation of the thickness is 3.6%,
The basis weight is 124 g / m ² , Bulk density is 0.388 g / cc, volume resistivity is 0.02 Ωcm, gas permeability is 75 cm ³ / Cm ² Sec, the ratio of the major axis / minor axis of the yarn was 1.8 for both the warp and weft yarns.
[0080]
[Comparative Example 3]
The graphitized carbonaceous fiber woven fabric obtained in Comparative Example 1 was pressed by the roll press of Example 1 under the same pressure conditions as in Example 1. Most of the woven fabric after pressing was broken, and the tensile strength of the woven fabric was significantly reduced, so that it could not be used substantially as a gas diffusion layer material.
[0081]
[Comparative Example 4]
The graphitized carbonaceous fiber woven fabric obtained in Comparative Example 1 was pressed using the same flat plate press as in Example 3.
A carbon fiber woven fabric cut out to a size of 50 cm × 50 cm is placed on a square flat press plate having an effective size of about 60 cm square, and the surface pressure of the press surface is reduced from normal pressure to 10 kg / cm. ² 10kg / cm ² After maintaining the surface pressure for 2 minutes, the pressure was released to return to normal pressure.
[0082]
The thickness of the woven fabric immediately after the press working was 0.19 mm, but it was 0.231 mm after 30 minutes. The coefficient of variation of the thickness of this product (30-minute product) is 3.6%, and the basis weight is 102 g / m. ² The bulk density was 0.442 g / cc, the volume resistivity was 0.02 Ωcm, and the ratio of the major axis / minor axis of the yarn was 2.0 warp yarn and 2.0 weft yarn.
[0083]
【The invention's effect】
According to the present invention, properties desired as a gas diffusion layer material such as gas permeability, conductivity (low resistance), water retention, drainage, uneven thickness (smoothness) and the like are balanced, and especially for polymer electrolyte fuel cells. A carbonaceous fiber woven fabric suitable as a gas diffusion layer material is provided.

Claims (10)

A woven fabric mainly composed of carbon fiber yarns, having a basis weight of 50 to 200 g / m ² , a thickness of 0.05 to ² mm, a bulk density of 0.2 to 0.6 g / cc, and a surface direction Is less than or equal to 0.15 Ωcm, and when the woven fabric is cut into a square having sides in the warp direction and the weft direction, two diagonal lines are each divided into 11 equal parts, for a total of 20 division points. A carbon fiber woven fabric characterized in that the coefficient of variation of the thickness of the woven fabric is 3.2% or less, and the warp and weft constituting the woven fabric have a cross section whose major axis is at least twice the minor axis. cloth. The carbonaceous fiber woven fabric according to claim 1, wherein the yarn fineness is constituted by a yarn having a metric count of 16 to 60. The carbonaceous fiber woven fabric according to claim 1, wherein the woven fabric has a gas permeability of 30 to 200 cm ³ / cm ² · sec. The carbonaceous fiber woven fabric according to any one of claims 1 to 3, wherein the structure of the woven fabric is plain weave, and the warp and weft yarns have a weft density of 30 to 70 yarns per inch. The carbonaceous fiber woven fabric according to any one of claims 1 to 4, wherein the diameter of the single fiber of the carbonaceous fiber is 6 to 50 µm. The carbonaceous fiber woven fabric according to any one of claims 1 to 5, wherein the yarn constituting the woven fabric is a spun yarn. 7. The carbonaceous fiber woven fabric according to claim 6, wherein the warp yarn and / or the weft yarn constituting the woven fabric are twin yarns. The carbonaceous fiber woven fabric according to claim 6, wherein the yarn constituting the woven fabric is a double yarn having a metric count of 2/32 to 2 / 120Nm or a single yarn having a metric count of 1/16 to 1 / 60Nm. The carbonaceous fiber woven fabric according to any one of claims 1 to 8, wherein the carbonaceous fibers are carbonized acrylic fibers obtained by spinning a polymer of a monomer containing acrylonitrile. The carbonaceous fiber woven fabric according to any one of claims 1 to 9, which is produced through a step of weaving and carbonizing a carbonaceous precursor fiber.