JP6818223B2 - Manufacturing method of carbon fiber woven fabric for fuel cells - Google Patents

Description

The present invention relates to a method for producing a carbon fiber woven fabric for a fuel cell used in transportation such as a vehicle, a ship, and an aircraft.

Conventionally, power generation by fuel cells has been attracting attention as a new energy source due to high concern about environmental problems, and carbon fiber woven fabric is useful as an electrode thereof. Among them, polymer electrolyte fuel cells (hereinafter referred to as fuel cells or FC), which are the mainstream for home use and vehicles, are membrane-catalyst conjugates (hereinafter referred to as CCM) in which electrodes are bonded to both sides of a polymer membrane. A unit unit (hereinafter referred to as a cell) consisting of a gas diffusion layer (hereinafter referred to as GDL) that guides fuel gas and oxidant gas to the electrode reaction region, a separator having a gas introduction / discharge groove, a sealing material, etc. ) Are repeatedly laminated, and several hundred cells are laminated and assembled in an area of approximately A4 size, and these are fastened with plates from both sides.

GDL is a member generally formed in the form of a thin sheet of 1 mm or less, and has a function of smoothly supplying two reaction gases, a fuel gas containing hydrogen and an oxidant gas containing oxygen, to the electrode catalyst layer from the outside. Having is the first. In addition to this, the basic functions of GDL are 1) low electrical resistance to efficiently extract electrical energy, 2) sufficient gas permeability to extract large current, and battery generation. It has good diffusivity due to the discharge of generated water, 3) has cushioning property (elasticity) that can absorb uneven thickness of laminated members, and 4) has corrosion resistance that can withstand strong acidity and strong alkalinity. Things, etc. are required.

Therefore, GDL, which is stably provided in the market at present, has a "flame resistance" pretreatment process in which acrylic fibers are heat-treated at about 220 to 260 ° C., and "flame resistance" is performed in an inert gas atmosphere at a high temperature of 900 to 2800 ° C. After obtaining carbon fibers by "carbonization" and "graphitization", they are further trimmed to the desired length, then made into a paper shape in the papermaking process, fastened with a thermosetting resin, and carbonized to further increase conductivity. Since heat treatment is performed multiple times, a large amount of energy is required, and the process is complicated and costly.

Further, since such a GDL has a paper structure, the above-mentioned gas permeability is insufficient, the cushioning property for absorbing thickness unevenness is low, and above all, there are many steps that consume energy, so that the manufacturing cost is high. There was a problem. Therefore, in order to popularize the fuel cell system, it is crucially important to have low electric resistance, sufficient gas diffusivity, appropriate cushioning property, sufficient corrosion resistance, energy saving process and low cost.

Therefore, in Patent Document 1, short carbon fibers are made into a paper shape, then impregnated with a thermosetting resin to obtain a resin-impregnated paper, and heat-press molded to obtain a resin-cured sheet. It is said that a porous carbon electrode is obtained by running the resin in a firing furnace in an active atmosphere and firing the resin-cured sheet.

Further, Patent Document 2 discloses a technique for producing a thick carbon fiber woven fabric of 1000 denier or more, which is made of long acrylic fibers as a woven fabric and then flame-resistant, carbonized, and graphitized to easily obtain a free curved surface for high-strength general parts. ing.

Further, in Patent Document 3, the acrylic spun yarn is made into a flame-resistant fiber and then made into a woven fabric, which is then pressed to be carbonized or graphitized so that the cross-sectional shape of the fiber of the woven fabric has a major axis in the surface direction and a thickness direction. It is explained that the minor axis can be approximated by an elliptical shape with a major axis / minor axis ratio of 2 or more.

Japanese Unexamined Patent Publication No. 2011-06592 Japanese Unexamined Patent Publication No. 56-101917 Japanese Unexamined Patent Publication No. 2004-100102

However, the paper-like carbon fiber disclosed in Patent Document 1 uses a large amount of energy for producing carbon fiber having higher strength than necessary, and has not reached the target price for popularizing FC automobiles. .. Further, since the carbon fiber has a paper structure, the gas diffusibility is insufficient, a large current cannot be taken out for vehicle use, and the cushioning property is also insufficient.

Further, the carbon fiber woven fabric disclosed in Patent Document 2 is not a GDL for FC use, which is a woven fabric, and is not described for flattening or electrical resistance, and is a fuel cell that is thin and has good electrical resistance. There was a problem that it was not suitable for GDL.

Further, the woven fabric disclosed in Patent Document 3 is insufficient to reduce the contact resistance with the CCM and the separator, and there is a problem that it is necessary to increase the contact area with them. Further, since the fiber undergoes a flame resistance process, there is a problem that the energy cost and the equipment cost are higher than the direct flame resistance of the woven fabric.

Therefore, an object of the present invention is to provide a method for producing a carbon fiber woven fabric for a fuel cell, which can reduce the thickness when laminated in a fuel cell and reduce the electric resistance at the time of contact. At the same time, it is an object of the present invention to provide a method for producing a carbon fiber woven fabric for a fuel cell, which has excellent gas diffusibility in the fuel cell and can generate a large current.

In order to solve the above-mentioned problems, the present inventor has a composite yarn in which a sliver of acrylic fiber is wound so as to be wrapped with vanishing fiber as a method for producing a carbon fiber woven fabric for a fuel cell, and the vanishing fiber is substantially in the center. For fuel cells, use either spun yarn around which untwisted acrylic fiber is wound, or synthetic yarn in which the number of upper twists of lost fibers is approximately the same as the number of lower twists of acrylic fibers and twisted in the opposite direction. The first step of weaving the carbon fiber woven material, the second step of removing the lost fibers from the carbon fiber woven material for fuel cells using water or an organic solvent, and then the oxidation of the carbon fiber woven material for fuel cells. A method for producing a carbon fiber woven fabric for a fuel cell, which comprises a third step of flame-resistant treatment in an atmosphere and a fourth step of carbonizing the carbon fiber woven material for the fuel cell thereafter.

Further, in the fourth step of performing the carbonization treatment, the treatment may be carried out with a load applied on the carbon fiber woven fabric material for a fuel cell. At that time, the load applied to the carbon fiber woven fabric material for the fuel cell can be in the range of 0.1 to 5 N per 1 cm ² .

Since the yarn bundle constituting the carbon fiber woven fabric for a fuel cell according to the manufacturing method of the present invention is substantially untwisted, the fiber cross section can be deformed flat and thin, and the dimensions in the stacking direction of the fuel cell can be adjusted. Can be shortened. Further, since the contour line of the thread bundle cross section is flattened while having a straight portion so that the contact area with the sandwiched member can be increased, the contact electrical resistance can be reduced, and the fuel cell becomes highly efficient. .. In addition, as compared with twisted fibers, fine gaps can be secured between single fibers, excellent gas diffusibility can be obtained, and the effect of being suitable for power generation of a large current is achieved.

It is an enlarged view of the raw material yarn before carbonization that the spun yarn is untwisted and wound around the vanishing fiber. It is an enlarged view for explanation for the raw material yarn of the spun twin yarn which gave the same number of upper twists as the lower twist. In another embodiment, it is an enlarged cross-sectional view after carbonization and curing. It is a schematic cross-sectional view of the uniform load type manufacturing apparatus used when manufacturing the carbon fiber woven fabric for a fuel cell of this invention. It is a schematic cross-sectional view of the constant tension type manufacturing apparatus used when manufacturing the carbon fiber woven fabric for a fuel cell of this invention.

An example of the embodiment of the present invention will be described with reference to the drawings together with the manufacturing process. The carbon fiber woven fabric for a fuel cell of the present invention is roughly divided into (1) a yarn-making step, (2) a weaving step, (3) a carbonization step, and (4) a curing treatment step. Hereinafter, each of the above steps (1) to (4) will be described in detail.

(1) Thread-making process First, the fibers used as starting materials are natural cellulose (cotton, bamboo fiber, etc.), regenerated cellulose (rayon, acetate), polyacrylonitrile-based, pitch-based, polynosic-based, phenol-resin-based, polyparaphenylene terephthal. Fibers consisting of amides or mixtures thereof can be used.

Here, cotton having a residual weight ratio of 30% or less by firing but having excellent marketability, and fibers containing polyacrylonitrile as a main component, which requires a flame resistance process but is stable in strength, are starting materials. Desirable as. Furthermore, since GDL for fuel cells is used in a stacked manner, compressive strength and bending strength are more important than tensile strength, and carbon fiber strength used as a structural strength material is not required more than necessary. Therefore, acrylic fiber is used. If the woven fabric is then subjected to a flame resistance step, a carbonization step, and a hardening treatment, the total energy cost can be reduced as compared with the case where the flame proof fiber is made into a woven fabric.

Next, as a yarn-making method, when a spun yarn is used as the material of the woven fabric, the spun yarn B having the lower twist number A and the twist direction Z and the fiber C disappearing after weaving can be combined. The number of upper twists at that time is also substantially the same as A, and the twist direction S (direction for returning the lower twist) may be used. According to (Fig. 1 raw material for untwisted yarn), the straight fiber in the center is the fiber C that disappears after weaving, and it is the twist angle that does not contribute to the tensile strength, which is substantially untwisted. It is a spun yarn B.

Here, the lost fibers contribute to the stabilization of the weaving process, and after that, they can be easily lost with water or an organic solvent, and the cost may be low. The shape may be a filament or a spun yarn, and the raw material is preferably a fiber similar to the glue used to secure the strength of the warp, and PVA fiber or starch may be used as a fiber and washed off after weaving. Alternatively, an alkali-soluble SST polymer fiber (dimethyl 5-sodium sulfoisophthalate) may be used. Alternatively, the spun yarn fixed with starch paste that can be dissolved in warm water may be twisted back and woven. Further, a composite yarn in which the spun sliver after drafting is wrapped so as to be wrapped with vanishing fibers may be used. That is, it is not limited as long as it can be dissolved and removed after weaving. PVA fiber is preferable from the viewpoint of environmental load of the dissolved residual liquid, cost, and stable technology.

Further, even when twin yarns are used as the material of the woven fabric, the fibers can be easily flattened if the conditions are appropriately selected. The number of top twists is 300 times / m to 1000 times / m, preferably 800 times / m or less per 1 m of fiber length. If the number of lower twists is small, the number of fluffs tends to be large, and if the number of lower twists is large, the probability of yarn breakage during twisting increases and the thickness unevenness may increase. Here, when the number of fluffs per unit length is large, it is desirable to include a fluff baking step. If the number of upper twists is almost the same as the number of lower twists and the yarns are twisted in the opposite directions to combine the yarns, the twists of each single yarn are rewound as shown in (Fig. 2 twin yarn), and both single yarns are wound. The yarn bundles are wound around each other, which is not practically untwisted, but each single yarn is wound around each other, arranged substantially parallel in the longitudinal range of the pitch, and then compressed into a woven fabric. It is crushed flat in the thickness direction, and it becomes easy to obtain a straight portion on the contour line of the thread bundle cross section. (Fig. 3 Flat cross section)

On the other hand, in a woven fabric made of twisted single yarn having tensile strength, since the single yarn group cannot be deformed flatly, it is not thinned, the contact area is small, and the electric resistance remains high. Needless to say, in FIG. 1, it is desirable that the weaving pitch is shorter than the twist pitch that is wound around each other.

Further, in the case of long fibers, it goes without saying that a woven fabric made of threads having a small number of entanglements is a carbon fiber woven fabric that is substantially untwisted and easily deformed flat. However, although the acrylic long fibers mentioned above are desirable starting materials, long fibers up to 250 dtex have limited applications and are not marketable. In addition, if the number of entangled fibers is small, long fibers have many price problems such as single yarn breakage. This is the reason why spun yarn, which is more marketable than long fibers, is desirable.

The shape of the material used may be either twin yarn or single fiber as long as it is a spun yarn, but in general, twin yarn has a higher tensile strength of the fiber than single fiber.

Regarding the thickness of the spun yarn, the thickness in the case of a single yarn is expressed in meters, the thicker one is 1/20 Nm or less, preferably 1/30 Nm or less, and the thinner one is usually 1/100 Nm. As mentioned above, it is preferably 1/64 Nm or more. In the case of twin yarn, the metric count is displayed, the thicker one is usually 2/26 Nm or less, preferably 2/34 Nm or less, and the thinner one is usually 2/120 Nm or more, preferably 2/100 Nm or more. Is.

Further, the number of twists of the spun yarn is based on JIS L1095 (general spun yarn test method). In the case of a single yarn, the number of twists per 1 m of fiber length is usually 300 times / m to 1000 times / m, but in order to flatten the cross section of the yarn bundle, it is desirable that the number is as small as possible. Here, a spun yarn having a small number of twists that does not become a yarn is defined as a substantially untwisted yarn, and by compressing in a process after obtaining a woven fabric made of this fiber, a yarn bundle cross section made of a large number of single fibers can be obtained. It can be deformed flat.

(2) Weaving process In this process, it can be selected for a fuel cell according to its purpose. The weaving method may be plain weave or twill weave, but it is desirable that the woven surface is smooth with respect to the CCM surface, and 3, 4, or 5 satin weaves are used, and the above-mentioned substantially untwisted or near-untwisted yarn bundle is used. It is desirable that each single fiber spreads so as to increase the contact area and hits the CCM surface. However, eight satin weaves should be avoided because the flying part is long and unstable.

Next, the density of the woven fabric is defined as the woven fabric cover factor Kc, which is the sum of the thickness of the yarn and the cover factors of the warp and weft yarns, which consist of the number of threads to be driven.
Kt = warp cover factor = ntx√10000 / Nt
Ky = Weft Cover Factor = nyx√10000 / Ny
nt = warp density per inch, ny = weft density per inch Nt = metric count of warp, Ny = metric count of weft

Although it depends on the woven fabric structure, for example, in the case of 5 pieces of Zhu Xi, Kc = 700 to 2500, preferably 1000 to 2500. Plain weave has a smaller Kc range, and satin weave has a larger Kc range. Twill is in the middle range. The relationship between the count of spun yarn and the density of warp and weft fabrics is the same for twin yarns. Since the long fibers have an apparent thickness smaller than that of the spun yarn, the range of Kc is set to be slightly higher. In the case of long fibers, flat yarn may be used, but bulky processing may be applied. The cover factors of the warp and weft have never been aligned, and the weight of the fiber that disappears after weaving as described above is excluded.

(3) Carbonization process 95% or more of commercially available carbon fibers are made of acrylic fibers flame-resistant, carbonized, and graphitized, but for fuel cells that require good electrical characteristics and corrosion resistance, in order to increase rigidity. Graphitization is not essential, but rather highly commercially available and inexpensive cellulose fibers and acrylic fibers are desirable. Other than that, the materials described in the section of starting material may be used, and these may be carbonized at 800 ° C. to 1200 ° C. in an inert gas. Further, a cellulose fiber woven fabric such as rayon was manufactured in 1958, and this method may be followed, and a method of interweaving flame-resistant fibers and cotton may be used. In the case of acrylic fiber, this is used as a woven fabric, and after undergoing flame resistance treatment at 235 ° C to 260 ° C for 2 hours to 5 hours while allowing shrinkage in an oxidizing atmosphere, the temperature is 800 ° C to 1200 ° C in an inert gas. It may be carbonized with.

The details of the step of carbonizing the carbon fiber woven fabric for a fuel cell obtained in the woven fabric step and the flameproofing step described above will be described with reference to FIG. In the firing (carbonization) device 100, a flat plate 16 having a flatness of 0.1 mm or less, which is smooth and preferably 0.1 mm or less, is laid on the bottom plate 11b of the firing box 11 having the upper opening 11a, and a metal such as iron is interposed therein. The above-mentioned carbon fiber woven fabric for fuel cells (hereinafter referred to as woven fabric) 20 is placed so as not to wrinkle and protrude. The same ceramic plate and the woven fabric 20 are sequentially and repeatedly stacked on the same, and the weight 17 is placed on the uppermost stage so that a uniform load is applied. The firing box 11 is housed in the main body 2 of the firing heating furnace 1 having the upper opening 11a. The upper opening 11a of the firing and heating furnace 1 is closed by a lid 3, and the lid 3 is sandwiched and screwed by bolts 5a and nuts 5b via a seal 4 of a graphite sheet to be sealed.

Next, the gas supply pipe 6 is connected to the main body 2 of the firing and heating furnace 1, so that the inert gas can be supplied from a gas source (not shown). Further, a gas discharge port 7 is connected to the main body 2, and is connected to the exhaust gas trap 31 through a pipe 8. Water 34 is put into the main body 32 of the exhaust gas trap 31, and the tip 8a of the pipe 8 is submerged in the water 34. The main body 32 of the exhaust gas trap 31 is sealed by a lid 33 having an exhaust gas trap discharge port 35. The exhaust gas trap discharge port 35 is connected to a purification device 37 or the like via a pipe 36 so as to discharge harmless exhaust gas to the outside. It is preferable that the exhaust gas trap 31 is provided with a valve for visually recognizing the liquid level of water or detecting components, checking the temperature and pressure in the firing and heating furnace, and analyzing the gas generated by decomposition. It is even better to provide an exhaust gas combustion device. In the carbonization treatment using such an apparatus configuration, an inert gas is charged into the firing box 11, and the gas decomposed and generated in the firing box 11 is discharged to a temperature of 800 to 1200 ° C. where carbonization is possible. It is carried out by heating, holding for 10 minutes to 1 hour, and then cooling.

The amount of the inert gas input is preferably 1 kPa and the volume of gas in the firing and heating furnace 1 per 3 minutes, and the oxygen concentration is preferably 5 ppm or less at 150 ° C. or higher. The load applied to the woven fabric 20 by the flat plate 16 is 0.1 to 5 N / cm ² , more preferably 0.4 to ² N / cm ² . Further, the flatness (smoothness) of the flat plate 16 is preferably 0.1 mm or less per A4 plate size, and the surface accuracy of the cold rolled plate is sufficient without any scratches. Here, if a shim 10 to 50% thinner than the finished thickness of the woven fabric 20 is sandwiched around the woven fabric 20, the thickness unevenness is small and the problem of woven fabric cracking due to heat shrinkage is also reduced. Further, the woven fabric 20 is contracted and deformed during carbonization. At this time, the contour line made of single fibers is crushed so as to have a straight portion in the cross section of the yarn bundle, and the single fibers are heat-fixed so as to line up in the longitudinal direction of the fibers. is important.

Next, FIG. 5 shows an example of a step of applying a constant tension to the woven fabric obtained in the woven fabric step or the above-mentioned flame resistance step to carbonize the woven fabric. The apparatus and the firing method at this time are the same as the carbonization method of constant pressure shown in FIG. 4 up to the firing box 21, and the contents (contents) thereof may be replaced. First, a long woven fabric 20 to be carbonized is folded back and hung on a plurality of upper round bars 24 and lower round bars 26 arranged one above the other to obtain a constant tension with respect to the woven fabric 20.

Grooves 25 having a U-shape or a V-shape are provided at equal intervals on both upper sides of the firing box 21 having the upper opening 21a in the longitudinal direction. An upper round bar 24 is placed in the groove 25. Clips 22 and 23 are provided at both upper ends in the longitudinal direction. Further, elongated holes 27 having a major axis in the vertical direction are provided at equal intervals below both side surfaces in the longitudinal direction of the firing box 21. Both ends of the lower round bar 26 are inserted into the elongated holes 27. The groove 25 and the elongated hole 27 are provided with a deviation of half a pitch.

One side of the long woven fabric 20 is held by the clip 22, the other side of the woven fabric 20 is passed through in the order of the lower round bar 26 and the upper round bar 24 while being folded back in order, and fixed by the clip 23 at the other end. In fixing, the lower round bar 26 is prevented from touching the upper end or the lower end of the elongated hole 27 before and after firing. As a result, even if the woven fabric 20 is stretched or contracted during firing in the firing heating furnace 1, a constant tension can be applied to the woven fabric 20 by the load of the lower round bar 26. Further, the tension applied to the fiber direction of the woven fabric 20 can be adjusted by adding weights to both ends of the lower round bar 26. Further, the lower round bar 26 is movable up and down, but is regulated so as not to swing in the left-right direction. Further, both ends of the lower round bar 26 are bent at right angles so as not to come off from the elongated holes 27 of the firing box 21.

Here, the length of the woven fabric 20 to be put in may be adjusted so that the lower round bar 26 is not lifted any more at the upper limit of the elongated hole 27, the shrinkage length may be regulated, and wrinkles may be reduced. The tension is preferably 5 × 10-6 to 200 × 10-6 cN / denier by converting the count and the total number of fibers of the woven fabric 20 into denier, and is 2 × 10 ^{-6 to} 300 × 10 ^−. The tension is preferably ⁶ cN / denier. Of course, instead of the upper round bar 24, positioning may be performed using a woven fabric sandwich with pins at appropriate intervals. The lower round bar 26 and the upper round bar 24 are preferably ceramic or heat-resistant titanium alloy rods or thin-walled pipes having a smooth surface without scratches.

Further, if pins are implanted in the lower round bar 26 and the upper round bar 24 at equal intervals, the woven fabric 20 is inserted into the pins with an assumed shrinkage allowance, and the fabric 20 is fired, the shrinkage width in the vertical direction can be substantially made uniform. In mass production, the firing boxes 11 shown in FIG. 4 and the firing boxes 21 shown in FIG. 5 may be continuously charged into a continuous carbonization furnace capable of ensuring an inert atmosphere, and heated and cooled. Further, it may be carried by heating on a heat-resistant mesh belt having a surface that does not get caught in a continuous carbonization furnace, and may be fired without wrinkles while allowing shrinkage in the warp and weft directions, and then taken out.

(4) Hardening process Since GDL (carbon fiber woven fabric for fuel cells) is pressed against the CCM with a separator having concave grooves, the carbon fiber woven fabric for fuel cells is pressed so that an appropriate contact pressure is applied to the CCM from the GDL even in the grooves. Hardening treatment is required. That is, the carbon fiber woven fabric for fuel cells obtained in the above step is impregnated with a liquid in which a resole-type thermosetting resin is dispersed, dried, and then compressed with a smooth plate in an inert gas atmosphere to be heated and cooled. By doing so, the thread bundle is hardened so as to be flatly deformed. At this time, the pressure is applied in the same manner as in the carbonization treatment, and the resin is fired in a temperature range of 300 ° C. to 800 ° C. in which the resin has low resistance in an inert gas.

Further, water phenol is preferable as the resol type thermosetting resin. If a liquid (ink) in which carbon black or graphite is uniformly dispersed is applied to the surface of the carbon fiber woven fabric for a fuel cell, appropriate electric resistance can be secured even if the firing temperature is lowered to about half of the above. The coating method may be a gravure printing method, a doctor blade method, or a direct coating method using a die having a uniform base width. In either method, it is desirable that the weight of the carbon fiber woven fabric for the fuel cell is increased by 5 to 50% after the dispersion is applied and heat-cured.

Summarizing the steps so far, since the yarn bundle is substantially untwisted, the yarn bundle tends to have a flat cross section, and for applications that do not require hardening treatment, it may be flattened during carbonization under constant pressure, and hardening treatment is required. In this application, a carbon fiber woven fabric carbonized at a constant tension may be cured with a binder.

Claims (3)

Composite yarn in which a sliver of acrylic fiber is wrapped so as to be wrapped with vanishing fiber, spun yarn in which there is vanishing fiber in the center and substantially untwisted acrylic fiber is wound around the vanishing fiber, vanishing fiber with respect to the number of lower twists of acrylic fiber By making the number of upper twists of the fibers substantially the same and twisting them in opposite directions, the twists of the acrylic fibers are untwisted and the yarn bundles of the acrylic fibers and the disappearing fibers are wound around each other . A first step of weaving a carbon fiber woven material for a fuel cell using any of the above, and a second step of removing the lost fiber from the carbon fiber woven material for a fuel cell using water or an organic solvent after the first step. A third step of flame-resistant treatment of the carbon fiber woven material for fuel cells in an oxidizing atmosphere after the second step, and a fourth step of carbonizing the carbon fiber woven material for fuel cells after the third step. A method for producing a carbon fiber woven fabric for a fuel cell, which comprises. The method for producing a carbon fiber woven fabric for a fuel cell according to claim 1, wherein in the fourth step, carbonization treatment is performed on the carbon fiber woven fabric material for a fuel cell in a state where a load is applied. The method for producing a carbon fiber woven fabric for a fuel cell according to claim 2, wherein the load applied to the carbon fiber woven fabric material for a fuel cell is in the range of 0.1 to 5 N per 1 cm ² .

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