JP2010061964A - Method for manufacturing carbon fiber base material used for diffusion layer of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent fluff of a carbon fiber base material used for a diffusion layer of a fuel cell from damaging a membrane-electrode assembly. <P>SOLUTION: Unnecessary fluff of the carbon fiber base material 7 is removed so that the carbon fiber base material 7 as a material of the diffusion layer is immersed into a water-repellent processing agent solution 2 filled into a vessel 1 and ultrasonic vibration 3 is given to the carbon fiber base material 7 immersed into the water-repellent processing agent solution 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon fiber base material used for a diffusion layer (GDL) of a fuel cell.

  The diffusion layer of a fuel cell is generally made of carbon fibers such as carbon paper, carbon cloth, carbon felt. This is because carbon fiber is a material suitable for a diffusion layer having a function of diffusing gas and moving hydrogen, air (oxygen), water, and electrons in the fuel cell because it is porous and has good conductivity.

  However, due to the inherent properties of the fiber, the carbon fiber is likely to fluff or the fluff may be detached from the carbon fiber substrate. In particular, carbon fiber base materials for production are generally supplied from the manufacturer in a tape form wound on a predetermined reel, and the carbon fiber base materials wound in a tape form on a reel are in a contact state before feeding. However, during the feeding from the feed reel to the take-up reel, the contact state is changed to the separated state. At this time, fluffing of the carbon fibers can often occur by rubbing the carbon fiber substrates in contact with each other or by partial contact between the carbon fiber substrates.

Furthermore, since the rigidity of the fluff of the carbon fiber substrate is generally higher than the rigidity of the electrolyte membrane, the fluff of the diffusion layer on the anode electrode side or the cathode electrode side made of the carbon fiber substrate may pierce the electrolyte membrane. More specifically, when the diffusion layer is subjected to a bonding pressure when it is bonded to the MEA (membrane electrode assembly), MEA is supported by the diffusion layer, and MEGA (membrane electrode diffusion layer bonding) is further supported by the separator. This is a case where a fuel cell is produced, fuel cells are stacked and subjected to a fastening pressure when the fuel cell stack is fastened in the overlapping direction.
If the fluff penetrates into the electrolyte membrane, the anode layer and the cathode electrode may be short-circuited, and the anode side hydrogen gas and / or the cathode side oxygen gas may be cross leaked. Bring to the fuel cell containing.
Therefore, in order to solve such a problem, an electrolyte membrane member such as MEA is sandwiched between two diffusion layers, and before the diffusion layer is joined to the MEA containing the electrolyte, at least the problem of the carbon fiber base material on the joining surface. There has been a need for a method of removing the fluffing that would cause the problem.

Note that Patent Document 1 discloses a first layer comprising a catalyst layer and a first solid polymer electrolyte for giving and receiving protons to the catalyst layer with respect to the fluff of the porous carbon fiber base material of the diffusion layer. The present invention proposes a method for preventing the above-mentioned problems by including a composite comprising a layer and a reinforcing agent for suppressing damage to the electrolyte by the diffusion layer. However, a method for directly removing fluff that is likely to be detached or detached from the carbon fiber substrate is not shown.
Japanese Patent Laid-Open No. 2004-220843

  In order to meet this demand, the present invention removes the fluff that is detached from the carbon fiber substrate used in the diffusion layer of the fuel cell or the fluff that is likely to be detached simultaneously with the acceleration of the water repellent treatment of the carbon fiber substrate. For the purpose.

Various aspects of the method for producing a diffusion layer for a fuel cell according to the present invention, and their functions and effects will be described in detail in the following section of the invention.

(Aspect of the Invention)
In the following, some of the aspects of the invention that are recognized as being claimable are illustrated and described. Each of the items (1) to (3) corresponds to each of claims 1 to 3.

(1) A method for producing a carbon fiber substrate used for a diffusion layer of a fuel cell, wherein the water repellent treatment is performed while moving the carbon fiber substrate in a water repellent treatment agent solution filled in a tank. A production method comprising applying ultrasonic vibration to a carbon fiber substrate immersed in an agent solution to remove fluff of the carbon fiber substrate.

  The carbon fiber base material is porous and conductive carbon paper, carbon cloth, carbon felt or the like. The water repellent solution preferably contains a fluorine resin such as PTFE. This is because such a material is suitable for repelling and draining water generated in the diffusion layer. When ultrasonic vibration is applied to the carbon fiber substrate immersed in the water repellent solution, the water repellent solution is easily impregnated into the pores of the carbon fiber substrate, and the entire carbon fiber is quickly made water repellent. To. And the fluff adhering to the carbon fiber base material is detached from the base material by the generation of fine bubbles generated by the ultrasonic vibration and the energy accompanying the cavitation. In particular, it is effective in rapidly impregnating a carbon fiber base material as thick as 500 μm with the water repellent treatment solution by the ultrasonic vibration.

In addition, by applying ultrasonic vibration to the carbon fiber substrate simultaneously with the water repellent solution, the water repellent solution is more easily penetrated into the carbon fiber substrate, and the penetration speed is improved. The fluff can be discharged to the outside of the carbon fiber substrate using the penetrating force as an inertial force.
The ultrasonic vibration propagates through the water-repellent treatment agent solution in the tank, but the ultrasonic vibrator so that the location (focal point) where the ultrasonic waves strengthen is substantially coincident with the surface of the carbon fiber base material to be pretreated. It is preferable to adjust the arrangement position.

(2) The production method according to (1), wherein a liquid flow in a certain direction is applied to the immersed carbon fiber substrate.
The mode described in this section is the mode (1), in which a liquid flow in a certain direction is applied to the soaked carbon fiber base material to prevent the fluff from reattaching, and preferably Forcibly moved to the bottom of the sonic tank so that it can be easily removed from the drain provided at the bottom of the ultrasonic tank.
The certain direction is desirably a direction along the ultrasonic treatment surface of the carbon fiber substrate. This is because the fluff adhering to the carbon fiber substrate that is merely upright needs only to be prone along the direction. On the other hand, the liquid flow in the direction intersecting the ultrasonic treatment surface, in particular in the direction perpendicular to the surface, causes further fluffing, and furthermore, meandering of the tape-like carbon fiber substrate and tape-like carbon fiber substrate. It tends to lead to disturbing the winding state of the material, which is undesirable.

(3) The water repellent solution in the tank is filtered, and the fluff is removed from the water repellent solution in the tank, and then the water repellent solution from which the fluff has been removed is returned to the tank. (1) The manufacturing method of any one of (2) characterized by the above-mentioned.

According to the aspect described in this section, the removed unnecessary fluff can be suitably discharged from the tank, and reattachment to the carbon fiber substrate can be prevented.
The fluff of the carbon fiber detached from the carbon fiber substrate by ultrasonic vibration has a higher specific gravity than the water repellent solution, and thus settles to the bottom of the tank. It is desirable that the detached fluff is appropriately discharged from the tank. This is because when the detached fluff is reattached to the carbon fiber substrate, the significance of removing the fluff with ultrasonic waves is lost.
Specifically, the water repellent treatment solution discharged from the drain together with the water repellent treatment agent solution or the water repellent treatment agent solution containing the discharged fluff is filtered out to remove the fluff by filtration, and then the water repellent treatment not including the fluff is removed. The agent solution is preferably reused by returning it to the tank.
It is preferable that the ultrasonic vibration device (ultrasonic vibrator) is disposed below the outside of the tank wall. Since the fluff settles in the water repellent solution and collects at the inner bottom of the tank, when the ultrasonic vibration device is arranged in this manner, the inner bottom of the tank becomes flat, and thus the fluff is detached from the carbon fiber base material. This is because unnecessary fluff is easily cleaned or removed from the drain provided at the bottom of the tank. In such a case, for example, a BRANSON tank with a vibrator (tank) suitable for industrial ultrasonic cleaning can be used.

  According to the present invention, while uniformly imparting a water repellent treatment agent to the entire carbon fiber base material used in the diffusion layer of the fuel cell, in particular, fluff that is likely to be detached from the base material is removed, and the carbon fiber base is removed. The joint surface of the material to the electrolyte membrane (or MEA) can be adjusted.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 to FIG. 4 are diagrams for illustrating an embodiment for carrying out a method for producing a carbon fiber base material used for a diffusion layer of a fuel cell according to the present invention. In the figure, the same reference numerals denote the same components, and the basic configuration is the same as the conventional one shown in the figure. The manufacturing method is not limited to the following embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

First Embodiment : FIG. 1 is a schematic view for explaining the concept of a method for producing a carbon fiber substrate used for a diffusion layer of a fuel cell according to the present invention.
In the manufacturing method, an apparatus as shown in FIG. 1 (hereinafter referred to as “ultrasonic apparatus”) is used. In the ultrasonic device 100 shown in FIG. 1, a carbon fiber base material used in a diffusion layer of a fuel cell in a tape shape (hereinafter referred to as “tape 7”) is first wound around a feed reel 5 and then tank 1 While being wound on the lower surface 8 of the center roll 4 arranged in the inside, the take-up reel 6 can take up. The tank 1 is preferably filled with a fluorine-based water repellent solution 9 so as to be at least above the lower surface 8 of the center roll 4. In addition, it is desirable that the ultrasonic generator (ultrasonic vibrator) 3 is disposed at the bottom inside the tank 1 so that the ultrasonic wave strengthening portion substantially coincides with the lower surface 8 of the center roll 4.

  The tape 7 in surface contact with the lower surface 8 of the center roll 4 is bent into a V shape by the arrangement of the feed reel 5, the center roll 4, and the take-up reel 6. Therefore, the fluff adhering to the tape 7 or the fluff that is likely to fall off the tape 7 is lifted from the surface of the tape 7 at this bent portion, and these fluffs are detached from the tape 7 by ultrasonic vibration. It becomes easy. However, if the V-shaped angle is too acute, it becomes easier to generate fluff that stands up unnecessarily. Therefore, when the tape 7 is particularly thick as 500 μm, it is desirable to set the angle to an obtuse angle.

  Thus, in the method for producing a carbon fiber substrate used for the diffusion layer of the fuel cell according to the present invention, the carbon fiber substrate 7 is immersed in the water repellent treatment agent solution 2 filled in the tank 1, The carbon fiber base material is moved in the water repellent treatment agent solution 2 filled in the tank, and the ultrasonic vibration 3 is applied to the carbon fiber base material 7 immersed in the water repellent treatment agent solution 2. While impregnating the water repellent solution 2 over the entire carbon fiber base material 7, unnecessary fluff of the carbon fiber base material 7 can be removed.

Second Embodiment : FIG. 2 shows an ultrasonic cleaning apparatus 200 (hereinafter referred to as “apparatus 200”) for carrying out the carbon fiber substrate manufacturing method according to the present invention. This is a device that can be adapted for mass production.
The apparatus 200 of FIG. 2 differs from the apparatus 100 of FIG. 1 in that the rotary rolls 10 and 11 are placed in the tank 1 with a constant span of 0 to increase the processing area of the tape 7 to be ultrasonically treated. This is the point that the ultrasonic treatment area is increased. Another difference is that the water repellent agent solution 9 is set so as to produce a constant flowing water by the discharge pump P1 and the suction pump P2 along the processing surface of the ultrasonically treated tape 7. The fluff pieces (carbon fiber pieces) which are disposed between the discharge pump P1 and the suction pump P2 and detached from the tape 7 are filtered by the filter F, and the water repellent agent The point is that no fluff is present in the solution 9.
Thereby, the tape 7 can be subjected to ultrasonic treatment over a wide range at a time. In addition, the fluff pieces removed and detached from the tape 7 can be prevented from reattaching to the tape 7 again.

Third Embodiment : FIG. 3 shows a nip roll in the apparatus 100 of FIG. 1 and the apparatus 200 of FIG. 2 after the tape 7 is fed by the feed reel 5 and before the tape 7 is wound by the take-up reel 6. 12A, 12B, and nip rolls 13A, 13B. Fluff that is likely to be detached soon or that has already detached and adhered to the tape 7 needs to be removed by the ultrasonic treatment, but it is upright with respect to the tape 7 that is fixed to the tape 7. The fluff that is being pressed is pressed from both sides of the tape 7 with the nip rolls 12A, 12B, 13A, and 13B, and is laid down parallel to the tape 7. As a result, it is not necessary to pierce the electrolyte membrane or other fluff in the fuel cell that is less rigid than the fluff.

Fourth Embodiment : This embodiment includes an apparatus that can be added to any one of the first to third embodiments.
Referring to FIG. 4, the impregnation of the water repellent solution and the ultrasonic treatment are completed, and the tape 7 that has come out of the solution into the atmosphere is dried with warm air using the blowers 14A and 14B. At this time, it is desirable that the direction of the warm air from the blowers 14A and 14B is inclined toward the downstream direction as shown in FIG. This is because the fluff wetted with the water repellent treatment agent solution tends to fall in the downstream direction. Next, a flexible resin film such as polyimide resin is backed up on the spare reel 15 to protect the ultrasonic treatment surface of the tape 7 (at this time, the surface of the film is preferably treated to prevent static electricity generation). In this way, it is wound on the take-up reel 17. Thereby, it becomes possible to further prevent fluffing of the tape 7 (carbon fiber base material) in the next step (step of bonding the diffusion layer to the MEA).

<Examples and Comparative Examples>
An ultrasonic treatment using the ultrasonic treatment apparatus 100 was used as an example, and a non-sonic treatment was used as a comparative example.
The processing conditions of the examples are as follows: the carbon fiber-based tape 7 has a thickness of 200 μm, the frequency of the ultrasonic vibrator is 44 kHz, and the distance from the ultrasonic vibrator to the carbon fiber base is set to about 1 cm. For 30 seconds, ultrasonic treatment was performed on the carbon fiber-based tape 7 in a fluorine solution, which is a water repellent solution, and the tape was naturally dried.
On the other hand, in the comparative example, the same tape 7 was used, and the same fluorine solution was impregnated only for the same time and dried naturally.

<Evaluation>
The two carbon fiber substrates obtained in the above examples and comparative examples were punched into a size of 13 cm ² to produce two carbon fiber substrates. Then, two carbon fiber base materials each having a substantially equal size MEA (membrane electrode assembly) sandwiched and joined were produced (respectively, MEGA (membrane electrode diffusion layer assembly) of the example, comparative example Called MEGA). The MEA electrolyte membrane was Nafion (trade name) manufactured by DuPont, and the MEA catalyst layer was obtained by uniformly fixing platinum-supported electrodes on both surfaces of the electrolyte membrane.
And as FIG. 5 shows, about MEGA of an Example and MEGA of a comparative example, it sandwiches with copper flat plates P1 and P2, applies 0.2V DC voltage between P1-P2, and after 1 minute, current In total A, the leakage current flowing between P1 and P2 was measured. By measuring the leakage current, current flows through the MEA film, that is, current leakage, and it can be determined whether the diffusion layers on both sides of the MEA that should be insulated on the anode and cathode sides are short-circuited. Table 1 shows the measurement results.

  As can be seen from Table 1, the leakage current value of the MEGA of the example was considerably smaller than the MEGA of the comparative example (2.5 mA). From the results of Table 1, according to the example, it can be determined that the leakage current can be significantly reduced and the fluff sticking to the MEA can be substantially prevented. On the other hand, from the results of the same table, according to the comparative example, it was determined that the leakage current was larger than that of the example (213 mA), and fluff was stuck into the MEA electrolyte membrane, causing the above-mentioned problems. It was.

<Modification>
The manufacturing method of the carbon fiber base material used for the diffusion layer of the fuel cell according to the present invention is not limited to the aspect described in the above embodiment, and various modifications may be adopted by those skilled in the art.
For example, in the method according to the present invention, a carbon fiber substrate is used as the material of the diffusion layer, but the same method can also be applied when a substrate made of conductive metal material or organic material fiber is used.
Further, in the method according to the invention, at least one side of the carbon fiber base material is subjected to ultrasonic treatment as a surface to be joined to the MEA. This is because it is sufficient that the separator on the one side of the carbon fiber base is in contact with a separator member that is more rigid than the carbon fiber. However, by arranging the ultrasonic transducers on both sides of the carbon fiber base material (tape 7) in the first or second embodiment described above, both surfaces of the tape 7 can be subjected to ultrasonic treatment.

  The manufacturing method of the carbon fiber base material used for the diffusion layer of the fuel cell according to the present invention can be used when the fluff of the carbon fiber base material of the diffusion layer is suitably treated before the production of the fuel cell.

It is a schematic sectional drawing for demonstrating 1st Embodiment concerning this invention. It is a schematic sectional drawing for demonstrating 2nd Embodiment which concerns on this invention. It is a schematic sectional drawing for demonstrating 3rd Embodiment based on this invention. It is a schematic sectional drawing for demonstrating 4th Embodiment based on this invention. It is a figure which shows the evaluation method of the carbon fiber base material pre-processed by the Example and the comparative example.

Explanation of symbols

1: Tank, 3: Ultrasonic vibrator, 7: Carbon fiber substrate, 9: Water repellent solution, 100, 200: Ultrasonic treatment apparatus

Claims (3)

A method for producing a carbon fiber substrate used for a diffusion layer of a fuel cell,
While moving the carbon fiber substrate in the water repellent treatment solution filled in the tank, ultrasonic vibration is applied to the carbon fiber substrate immersed in the water repellent treatment solution, and the carbon fiber substrate The manufacturing method characterized by removing the fluff.   The manufacturing method according to claim 1, wherein a liquid flow in a certain direction is applied to the immersed carbon fiber base material.   The water-repellent treatment agent solution in the tank is filtered, the fluff is removed from the water-repellent treatment solution in the tank, and then the water-repellent treatment solution from which the fluff has been removed is returned to the tank. The manufacturing method of any one of Claim 1 or Claim 2.

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