JP4187683B2 - Porous carbon electrode substrate for fuel cells - Google Patents

Description

The present invention, fuel cell electrode substrates, and particularly to a solid polymer fuel cell electrode substrate.

  Compared with the electrodes for phosphoric acid fuel cells, the electrodes for polymer electrolyte fuel cells have gas diffusion / permeability, strength to withstand handling, flexibility, electrode manufacturing and when the electrodes are assembled Strength that can withstand compression is required. In addition, since the polymer electrolyte fuel cell is required to be smaller than the phosphoric acid fuel cell, the electrode is also required to be thin. As an electrode for such a polymer electrolyte fuel cell, a mainstream is an electrode produced by making a short carbon fiber, impregnating with a thermosetting resin, curing, and firing. In order to improve the productivity of the battery, the electrode needs to be flexible enough to be wound into a roll. However, the electrodes so far are thick, and many of them break immediately when bent. In addition, since the electrodes so far have a small number of binding points between carbon fibers, there is a problem that when the porosity is increased, the conductivity is deteriorated.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 7-14068) shows a porous carbon electrode base material having good conductivity by mixing carbon milled fiber, but it is thick and used for a polymer electrolyte fuel cell. To be inflexible.

Patent Document 2 (Japanese Patent Laid-Open No. 9-157052) describes an invention of a porous carbon plate and a method for producing the same, but the electrode of the present invention has a low bulk density, and therefore has sufficient conductivity. I can't say that.
Japanese Patent Laid-Open No. 7-14068 Japanese Patent Laid-Open No. 9-157052

An object of the present invention is to overcome the above-described problems and to provide a fuel cell electrode substrate having high conductivity and flexibility.

In the present invention, the thickness is 0.05 to 0.5 mm, the bulk density is 0.3 to 0.8 g / cm ³ , the strain rate is 10 mm / min, the distance between fulcrums is 2 cm, and the specimen width is 1 cm. The porous carbon electrode substrate for a fuel cell having a bending strength of 10 MPa or more and a bending deflection of 1.5 mm or more in a three-point bending test.

  In the electrode base material of the present invention, it is preferable that the length is 1 m or more and the film can be wound around a roll having an outer diameter of 50 cm or less. Moreover, it is preferable that an electrode base material contains carbon fiber and this carbon fiber is only a polyacrylonitrile-type carbon fiber. Further, the electrode substrate contains carbon fibers, the carbon fibers have an average diameter of more than 3 μm and less than 5 μm, an average fiber length of 3 to 10 mm, an average diameter of 5 μm or more and less than 9 μm, and an average fiber length of 3 to 3 mm. A mixture with 10 mm thick fibers is preferred. It is also preferred that the electrode substrate contains carbon fibers, and the fine fibers are contained in an amount of 40% by mass or more in the total carbon fibers contained.

Fuel porous carbon electrode substrate for a battery of the present invention, resistant to bending and excellent flexibility, a high substrate productivity, etc. may be wound into a roll.

  The present invention is described in further detail below.

  The carbon fiber paper of the present invention comprises carbon fibers containing fine carbon short fibers having an average diameter of less than 5 μm and an average fiber length of 3 mm to 10 mm and an organic polymer compound as a binder.

  In the present invention, the bending strength and flexibility of the porous electrode substrate can be improved by using short carbon fibers having an average diameter of less than 5 μm, preferably more than 3 μm and 4.5 μm or less. If only carbon fibers having an average diameter larger than 5 μm are used, the flexibility is insufficient and the number of binding points between the fibers is small, and the resistance of an electrode manufactured using such carbon fiber paper increases. Further, it is preferable to make the average diameter thicker than 3 μm because it is possible to prevent the carbon fiber paper from becoming dense and the gas permeability from being lowered.

  Further, the average fiber length of the carbon fibers is preferably 3 mm to 10 mm, more preferably about 3 to 9 mm, from the viewpoint of the strength and smoothness of the base material. When the average fiber length is less than 3 mm, the entanglement between the fibers decreases, and the strength of the base material becomes weak. On the other hand, when the thickness exceeds 10 mm, the dispersibility of the fibers in the dispersion medium decreases, and the carbon fiber paper becomes uneven.

  The fine fibers having an average diameter of less than 5 μm and an average fiber length of 3 to 10 mm are preferably 40% by mass or more of the total carbon fibers. That is, among all the carbon fibers, fine fibers having an average diameter of less than 5 μm and an average fiber length of 3 to 10 mm are 40% by mass or more, and mixed carbon fibers in which carbon fibers having an average diameter of 5 μm or more are 60% by mass or less are used in the present invention. It can be used for carbon fiber. In order to maintain flexibility and high conductivity of the electrode substrate, it is preferable that 40% by mass or more of the fine fibers having an average diameter of less than 5 μm are included.

  Except for carbon fibers having an average fiber diameter of less than 5 μm and an average fiber length of 3 to 10 mm, carbon fibers having an average fiber diameter of 5 μm or more are preferably used, and carbon fibers having an average fiber diameter of 7 μm or more are more preferably used. preferable.

  Carbon fibers contained in the carbon fiber paper are fine fibers having an average diameter of more than 3 μm and less than 5 μm and an average fiber length of 3 to 10 mm, and thick fibers having an average diameter of 5 μm to less than 9 μm and an average fiber length of 3 to 10 mm It is also preferred that it is a mixture of The small-diameter carbon fiber contributes to imparting flexibility to the electrode and improving conductivity, while the large-diameter carbon fiber contributes to improving dispersibility and gas permeability of the fiber substrate. Accordingly, a carbon fiber paper obtained by mixing these in an appropriate amount is preferable because it can have the above-mentioned advantages.

  The carbon fiber used in the present invention may be any of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber and the like. However, polyacrylonitrile-based carbon fibers having a relatively high mechanical strength are preferable, and it is particularly preferable that the carbon fibers to be used consist only of polyacrylonitrile-based carbon fibers.

  The polyacrylonitrile-based carbon fiber is manufactured using a polymer mainly composed of acrylonitrile as a raw material. Specifically, a spinning process for spinning acrylonitrile fibers, a flameproofing process for heating and firing the fibers in an air atmosphere at 200 to 400 ° C. to convert them into oxidized fibers, and in an inert atmosphere such as nitrogen, argon, helium, etc. In addition, the carbon fiber can be obtained through a carbonization step of carbonizing by heating to 300 to 2500 ° C., and is suitably used as a composite material reinforcing fiber. Therefore, it is possible to form a carbon fiber paper that has higher strength and higher mechanical strength than other carbon fibers.

  As a papermaking method for producing carbon fiber paper, a wet method in which carbon short fibers are dispersed in a liquid medium for paper making, or a dry method in which carbon short fibers are dispersed in air to be deposited can be applied. Moreover, it is preferable to mix an appropriate amount of an organic polymer substance as a binder for binding carbon fibers together. Thus, the strength of the carbon fiber paper can be maintained, and the carbon fiber can be prevented from peeling off from the carbon fiber paper during the production or the orientation of the carbon fiber can be prevented from changing.

  The organic polymer compound is preferably polyvinyl alcohol, or an acrylonitrile-based polymer pulp or short fiber. Acrylonitrile-based polymer pulps or short fibers are particularly preferred because their own fired product serves as a conductor. Polyvinyl alcohol is preferable as a binder because it has excellent binding power in the paper making process, and the short carbon fibers do not fall off. Polyvinyl alcohol is mostly decomposed and volatilized in the final stage of carbonization process for producing an electrode substrate to form pores. The presence of these pores is preferable because the permeability of water and gas is improved.

  A pulp-like material has a structure in which a large number of fibrils having a diameter of several μm or less are branched from a fibrous trunk, and a sheet-like material made from this pulp-like material has an efficient entanglement between fibers and is thin. -Even if it is a toroid, it has the advantage that it is excellent in its handleability. Moreover, the short fiber of an acrylonitrile-type polymer can be obtained by cutting the fiber yarn which consists of an acrylonitrile-type polymer, or the fiber tow into predetermined length.

  The content of the organic polymer compound in the carbon fiber paper is preferably in the range of 5 to 40% by mass. More preferably, it is the range of 15-30 mass%. In order to reduce the electric resistance of the electrode base material obtained by impregnating carbon fiber paper with resin and firing, the content of the polymer compound is preferably small, and the content is preferably 40% by mass or less. From the viewpoint of maintaining the strength and shape of the carbon fiber paper, the content is preferably 5% by mass or more.

  There are two methods for mixing pulp fibers or short fibers of these organic polymer compounds into carbon fibers: stirring and dispersing together with carbon fibers in water and mixing directly. The method of diffusing and dispersing with is preferable.

  After making the carbon fiber paper, it is hot-pressed with a heat and pressure roll, so that the orientation and thickness of the carbon fiber can be made uniform, and the fluff peculiar to the carbon fiber can be minimized. The heating temperature of the heating and pressing roll is preferably 100 ° C to 150 ° C, and the pressure is preferably 0.5 MPa to 20 MPa.

The porous carbon electrode substrate for a fuel cell according to the present invention has a thickness of 0.05 to 0.5 mm and a bulk density of 0.3 to 0.8 g / cm ³ , a strain rate of 10 mm / min, and a fulcrum distance of 2 cm. A porous carbon electrode substrate for a fuel cell having a bending strength of 10 MPa or more and a bending deflection of 1.5 mm or more in a three-point bending test under the condition of a test piece width of 1 cm.

The porous carbon electrode substrate for a fuel cell is mainly composed of a carbonaceous material such as carbon fiber, and is a substrate having water or gas permeability and conductivity sufficient to function as an electrode of a fuel cell. The gas permeability of the porous electrode substrate is preferably 200 ml · mm / hr · cm ² · mmAq or more. The conductivity is 10 mΩ · cm ² when the electrode substrate is sandwiched between copper plates, pressed at 1 MPa from the top and bottom of the copper plate, and measured for resistance when a current density of 10 mA / cm ² is passed. The following is preferable.

The thickness of the porous carbon electrode base material needs to be 0.05 to 0.5 mm, preferably 0.1 mm to 0.3 mm, from the viewpoint of the resistance value. When the thickness is less than 0.05 mm, the strength in the thickness direction is weakened, and it becomes impossible to withstand handling when the cell stack is assembled. On the other hand, when the thickness exceeds 0.5 mm, the electric resistance increases, and the total thickness increases when the stack is stacked. The bulk density is required to be 0.3 to 0.8 g / cm ^3, preferably 0.4 to 0.7 g / cm ^3. When the bulk density is less than 0.3 g / cm ³ , the electrical resistance increases and satisfactory flexibility cannot be obtained. On the other hand, if it exceeds 0.8 g / cm ³ , the gas permeability is deteriorated and the performance of the fuel cell is lowered.

  The bending strength of the porous carbon electrode substrate of the present invention is 10 MPa or more, preferably 40 MPa or more, under the conditions of a strain rate of 10 mm / min, a fulcrum distance of 2 cm, and a test piece width of 1 cm. When it is less than 10 MPa, handling becomes difficult and, for example, it is easy to break when wound on a roll. Further, by setting the bending strength to 10 MPa or more, it is possible to prevent cracks from being generated when the electrode base material is bent. Furthermore, the bending at the time of bending is 1.5 mm or more, preferably 2.0 mm or more. When the bending deflection is less than 1.5 mm, it is easy to break when continuously wound on a roll, and it becomes difficult to produce and handle a long electrode substrate.

  The porous carbon electrode substrate for a fuel cell in the present invention is preferably 1 m or more in length and can be wound around a roll having an outer diameter of 50 cm or less. If the electrode substrate is long and can be wound on a roll, not only the productivity of the electrode substrate is increased, but also MEA (Membrane / Electrode Assembly) production in the subsequent process can be continuously performed. This can greatly contribute to cost reduction of the fuel cell. Also for this purpose, it is preferable that it is flexible enough to be wound around a roll having an outer diameter of 50 cm or less, more preferably 40 cm or less. A carbon electrode base material that can be wound around a roll having an outer diameter of 50 cm or less is preferable because it has excellent flexibility and is easy to pass through the MEA production process as a subsequent process. Furthermore, if it can be wound on a roll having an outer diameter of 50 cm or less, the product form as the carbon electrode substrate can be made compact, which is advantageous in terms of packaging and transportation costs. Moreover, it is preferable that roll radius R (cm) satisfies the following Formula from a viewpoint of preventing destruction of an electrode base material.

  In the present invention, a fuel is obtained by impregnating a carbon fiber paper containing fine carbon fibers having an average diameter of less than 5 μm and an average fiber length of 3 to 10 mm with a thermosetting resin, curing by heating and pressing, and then carbonizing. A porous carbon electrode substrate for a battery is used.

  The thermosetting resin used in the present invention is preferably a substance that exhibits adhesiveness or fluidity at room temperature and remains as a conductive substance even after carbonization, and a phenol resin, a furan resin, or the like can be used. As the phenol resin, a resol type phenol resin obtained by reaction of phenols and aldehydes in the presence of an alkali catalyst can be used. In addition, a novolac type phenolic resin showing solid heat-fusibility, which is produced by a reaction of phenols and aldehydes under an acidic catalyst by a known method, can be dissolved and mixed in a resol type flowable phenolic resin. In this case, a self-crosslinking type containing a curing agent such as hexamethylenediamine is preferred.

  As phenols, for example, phenol, resorcin, cresol, xylol and the like are used. As aldehydes, for example, formalin, paraformaldehyde, furfural and the like are used. Moreover, these can be used as a mixture. These can also use a commercial item as a phenol resin.

  A preferable ratio of the resin in the resin-impregnated carbon fiber paper used in the present invention is 30% by mass to 70% by mass. 30 mass% or more is preferable at the point that the structure of a porous carbon electrode base material becomes dense and the intensity | strength of the electrode base material obtained is high. Moreover, it is preferable to set it as 70 mass% or less at the point of maintaining the porosity and gas permeability of the electrode base material obtained. Here, the resin-impregnated carbon fiber paper refers to a paper obtained by impregnating a carbon fiber paper with a resin before heating and pressurization. When a solvent is used during resin impregnation, the carbon fiber paper is obtained by removing the solvent.

  In the thermosetting resin impregnation step, a conductive substance can be mixed into the thermosetting resin. Examples of the conductive material include carbonaceous milled fiber, carbon black, acetylene black, and isotropic graphite powder. The mixing amount when the conductive substance is mixed in the resin is preferably 1% by mass to 10% by mass with respect to the resin. If the mixing amount is less than 1% by mass, it is disadvantageous in that the effect of improving the conductivity is small, and if it exceeds 10% by mass, the effect of improving the conductivity tends to saturate, and the cost increases. It is disadvantageous in terms.

  As a method for impregnating carbon fiber paper with resin or a mixture of resin and conductor, a method using a drawing device or a method of superposing a thermosetting resin film on carbon fiber paper is preferable. In the method using the squeezing device, the carbon fiber paper is impregnated in the resin solution or mixed solution, and the squeezing device applies the liquid to the entire carbon fiber paper uniformly, and the amount of liquid changes the roll interval of the squeezing device. It is a method to adjust with. If the viscosity is relatively low, a spray method or the like can also be used.

  In the method using a thermosetting resin film, first, a thermosetting resin is once coated on a release paper to obtain a thermosetting resin film. Thereafter, the film is laminated on carbon fiber paper and subjected to heat and pressure treatment to transfer the thermosetting resin.

  The heating and pressing step in the present invention is preferably performed continuously over the entire length of the carbon fiber paper from the viewpoint of productivity. Moreover, it is preferable to perform preheating prior to heating and pressurization. In this preheating step, the thermosetting resin is softened, and in the subsequent heating and pressing step, the thickness of the electrode base material can be well controlled by pressing. An electrode base material having a desired thickness and density can be obtained by pressing the preheated resin-impregnated carbon fiber paper at a temperature higher by 50 ° C. or more than the preheating temperature. Further, in order to obtain an electrode base material having a desired thickness and density, a plurality of resin-impregnated carbon fiber papers may be stacked and heated and pressurized.

  The heating and pressing described above is preferably performed using a continuous heating roll press apparatus or a continuous heating press apparatus having a pair of endless belts. In the latter continuous heating press apparatus, since the base material is sent out by a belt, the base material is hardly tensioned. Therefore, destruction of the base material during production hardly occurs and the process passability is excellent. Moreover, the former continuous heating roll press apparatus has a simple structure and a low running cost. As described above, the two heating and pressurizing methods are suitable methods for continuously curing the resin, and are preferably used for producing the electrode substrate of the present invention.

The pressurizing pressure when using the above-described continuous press apparatus is preferably 1.5 × 10 ⁴ to 1 × 10 ⁵ N / m. Heating and pressurization is a process necessary for sufficiently impregnating the resin in the fiber and increasing the bending strength. Sufficient electrical conductivity and flexibility can be produced by applying a pressure of 1.5 × 10 ⁴ N / m or more when the resin is thermally cured. Further, by applying a pressure of 1 × 10 ⁵ N / m or less, the vapor generated from the resin can be sufficiently released to the outside at the time of curing, and the generation of cracks can be suppressed.

  The heating temperature in the heat and pressure treatment is preferably 140 ° C. or higher from the viewpoint of the curing treatment time or productivity, and is preferably 320 ° C. or lower from the viewpoint of cost for equipment such as a heat and pressure apparatus. More preferably, it is the range of 160-300 degreeC. The preheating temperature is preferably in the range of 100 to 180 ° C.

  In the present invention, it is preferable that the carbonization following the resin curing is continuously performed over the entire length of the carbon fiber paper. If the electrode base material is long, not only the productivity of the electrode base material is increased, but also MEA production in the subsequent steps can be performed continuously, which can greatly contribute to cost reduction of the fuel cell. Specifically, the carbonization is preferably performed by continuous firing over the entire length of the carbon fiber paper in a temperature range of 1000 to 3000 ° C. in an inert treatment atmosphere. In the carbonization of the present invention, a pretreatment by firing in an inert atmosphere of about 300 to 800 ° C., which is performed before a carbonization treatment in a temperature range of 1000 to 3000 ° C. in an inert atmosphere, is performed. You can go.

  The electrode substrate finally obtained from the above is preferably wound on a roll having an outer diameter of 50 cm or less, more preferably an outer diameter of 40 cm or less. If it can be wound on a roll having an outer diameter of 50 cm or less, the product form as the electrode substrate can be made compact, which is advantageous in terms of packaging and transportation costs.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  Each physical property value in the examples was measured by the following method.

1) Carbon fiber diameter The diameter of the carbon fiber was measured by a helium-neon laser described in JIS R-7601 (an SLB DIA MEASURING SYSTEM manufactured by Anritsu). The said measurement was performed about 100 carbon fibers, and the average value was made into the average diameter of carbon fiber.

2) Thickness A thickness measuring device dial thickness gauge 7321 (manufactured by Mitutoyo Corporation) was used for measurement. The size of the probe at this time is 10 mm in diameter and the measurement pressure is constant at 1.5 kPa.

3) Bending strength of electrode base material It measures using a bending strength test apparatus. The distance between the fulcrums was set to 2 cm, a load was applied at a strain rate of 10 mm / min, and the breaking load of the pressure wedge when the test piece broke from the point at which the load began to be applied was measured and obtained from the following equation.

  In addition, about the continuous sample, the value of the longitudinal direction was measured.

4) Deflection of electrode base material It measured using the bending strength test apparatus. The distance between the fulcrums was 2 cm, and a load was applied at a strain rate of 30 mm / min. The distance was measured by measuring the moving distance of the pressure wedge when the test piece broke from the point where the load began to be applied.

5) Gas Permeability Coefficient Based on JIS-P8117, a Gurley densometer was used, and the time required for 200 mm ³ gas to pass through was measured and calculated.

6) Measurement of penetration resistance A sample was sandwiched between copper plates, pressed from above and below the copper plate at 1 MPa, a current value was measured at a current density of 10 mA / cm ² , and a resistance value was obtained from the following equation.

Example 1
A fiber bundle of polyacrylonitrile (PAN) -based carbon fibers having an average fiber diameter of 4 μm was cut to obtain short fibers having an average fiber length of 3 mm.

Next, this short fiber bundle is defibrated in water, and when fully dispersed, the short fiber of polyvinyl alcohol (PVA) as a binder (VBP105-1 manufactured by Kuraray Co., Ltd., cut length: 3 mm) is the sum of carbon fiber and PVA. It is dispersed uniformly so as to be 15% by mass with respect to the amount, and manually performed in accordance with JIS P-8209 method using a standard square sheet machine (No. 2555 standard square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd.). The paper was made and dried to obtain a carbon fiber paper. The PVA fibers were in a melted state in which they were half dissolved, and the carbon fibers were bonded to each other. The obtained carbon fiber paper had a mass (unit weight) per unit area of 60 g / m ² .

  This carbon fiber paper is immersed in a 15% by mass ethanol solution of a phenol resin (Register Top PL-2211, manufactured by Gunei Chemical Co., Ltd.) and pulled up, and 100 parts by mass of the phenol resin is attached to 100 parts by mass of the carbon fiber. After being dried with hot air, it was sandwiched between fluorinated iron plates and placed in a batch press apparatus at 170 ° C. and 15 MPa for 15 minutes to cure the phenolic resin.

  Then, the said intermediate base material was heated at 2000 degreeC for 1 hour in the batch carbonization furnace in nitrogen gas atmosphere, and the porous carbon electrode base material was obtained by carbonizing. Both bending strength and deflection were good results.

  Table 1 shows the production conditions of the carbon fiber paper in each example and comparative example, Table 2 shows the production conditions of the electrode substrate, and Table 3 shows the evaluation results of the electrode substrate.

Example 2
An electrode substrate was obtained in the same manner as in Example 1 except that continuous papermaking was performed as follows.

The carbon short fiber bundle is defibrated in water in a slurry tank of a wet continuous paper making machine, and the polyvinyl alcohol (PVA) short fiber (used in Example 1) as a binder is uniformly dispersed in a sufficiently dispersed place. , Sent out. The fed web was passed through a short mesh plate and dried with a dryer to obtain a carbon fiber paper having a length of 20 m. The obtained carbon fiber paper had a mass per unit area of 60 g / m ² . In addition, this long carbon fiber paper was cut to a length of 25 cm for the subsequent process.

  The electrode base material of this example had remarkably strong bending strength and good deflection due to continuous papermaking.

Example 3
A long carbon fiber paper was prepared in the same manner as in Example 2, and this carbon fiber paper was impregnated with a thermosetting resin by the dip-nip method. That is, this carbon fiber paper is continuously fed into a tray of a phenol resin (Phenolite J-325, manufactured by Dainippon Ink Chemical Co., Ltd.) in a 20% by weight methanol solution, and the resin is squeezed continuously by a squeezing device. Hot air was blown onto the substrate and dried to obtain a resin-impregnated carbon fiber paper. At this time, 100 mass parts of phenol resin was attached to 100 mass parts of carbon fibers.

Next, this resin-impregnated carbon fiber paper was continuously heated and pressed by the continuous heating roll press apparatus shown in FIG. 1 to obtain a resin-cured carbon fiber paper. That is, the resin-impregnated carbon fiber paper 1 is fed out from a roll, and is fed between the release agent coating substrate 2 and then sent to the preheating zone 4 and subsequently to the heating and pressing zone 5, and then the release agent coating substrate 2. And the obtained resin-cured carbon fiber paper was wound up on a roll. At this time, the preheating temperature in the preheating zone was 150 ° C., the preheating time was 5 minutes, the temperature in the heating and pressing zone was 250 ° C., and the pressing pressure was a linear pressure of 1.5 × 10 ⁴ N / m.

  Thereafter, the resin-cured carbon fiber paper obtained 20 m with a width of 30 cm was cut by 25 cm and fired in the same manner as in Examples 1 and 2 to obtain an electrode substrate. Both bending strength and deflection were good results.

Example 4
An electrode substrate was obtained in the same manner as in Example 3 except that the press pressure of the roll press apparatus was increased to a linear pressure of 7.5 × 10 ⁴ N / m. Due to the strong press pressure, it was thin, the bending strength was strong, and the deflection was large.

Example 5
Resin-cured carbon fiber paper obtained by papermaking, resin impregnation and roll pressing in the same manner as in Example 4 was heated for 10 minutes in a continuous firing furnace at 2000 ° C. in a nitrogen gas atmosphere, and carbonized. As a result, a carbon electrode substrate having a length of 20 m was continuously obtained and wound around a cylindrical paper tube having an outer diameter of 30 cm. It was thin, strong in bending strength, and large in deflection.

Example 6
A continuous hot press apparatus comprising the pair of endless belts shown in FIG. 2 after continuous paper making and resin impregnation in the same manner as in Example 3 except that the basis weight is 100 g / m ² . (Double belt press apparatus: DBP) was continuously heated and pressed to obtain a resin-cured carbon fiber paper. That is, the resin-impregnated carbon fiber paper 1 is disposed between the release agent coating base material 2, and the resin-impregnated carbon fiber paper 1 and the release agent coating base material 2 are sent between the connecting belt devices 3a and 3b to preheat. It was sent to zone 4 and subsequently to heat and pressure zone 5. Thereafter, as in the roll press apparatus of FIG. 1, the release agent coating substrate 2 was removed, and the obtained resin-cured carbon fiber paper was wound up on a roll. The continuous belt devices 3a and 3b each convey the resin-impregnated carbon fiber paper 1 and the like by rotating. At this time, the preheating temperature in the preheating zone was 160 ° C., the preheating time was 5 minutes, the temperature in the heating and pressing zone was 280 ° C., and the press pressure was a linear pressure of 1.5 × 10 ⁴ N / m. It was. Then, this base material obtained by 20 cm with a width of 30 cm was cut every 25 cm and fired in the same manner as in Examples 1 and 2 to obtain an electrode base material. It was smooth and had good bending strength and deflection.

Example 7
An electrode substrate was obtained in the same manner as in Example 6 except that the press pressure of the double belt press (DBP) apparatus was increased to a linear pressure of 7.5 × 10 ⁴ N / m. Due to the strong press pressure, it was thin, the bending strength was strong, and the deflection was large.

Example 8
Papermaking and resin impregnation were continuously performed in the same manner as in Example 7 except that the carbon fiber paper was continuously obtained by adjusting the mass per unit area to be 30 g / m ² . In the double belt press, the obtained resin-impregnated carbon fiber paper was heated and pressurized in the same manner as in Example 7 except that two sheets were stacked and pressed so that the same paper-making surface was inside. The obtained base material was not cut, and was pre-carbonized in a 300-600 ° C. furnace in a nitrogen gas atmosphere for 5 minutes, then heated in a continuous baking furnace at 1600-2000 ° C. for 10 minutes, and carbonized. Thus, a carbon electrode substrate having a length of 20 m was continuously obtained and wound around a paper tube having a diameter of 30 cm. The obtained base material had no warp, was thin, had high bending strength, and had a large deflection.

Example 9
A carbon electrode substrate in the same manner as in Example 8 except that short fibers having an average fiber diameter of 4 μm and an average fiber length of 3 mm were used instead of short carbon fibers having an average fiber diameter of 4 μm and an average fiber length of 3 mm. Got. Although dispersibility was relatively poor, strength, deflection, and gas permeability were good values.

Example 10
A fiber bundle of polyacrylonitrile (PAN) -based carbon fibers having an average fiber diameter of 4 μm was cut to obtain short fibers having an average fiber length of 3 mm. On the other hand, a fiber bundle of PAN-based carbon fibers having an average fiber diameter of 7 μm was cut to obtain short fibers having an average fiber length of 6 mm. Next, these fiber bundles are defibrated in water so that the ratio of short fibers having a fiber diameter of 4 μm and 7 μm is 4 μm / 7 μm = 8/11, and when sufficiently dispersed, polyvinyl alcohol (PVA) as a binder is dispersed. Short fibers (used in Example 1) are uniformly dispersed so as to be 5% by mass with respect to the total amount of carbon fiber and PVA, and a standard square sheet machine (used in Example 1) is used. The paper was made according to JIS P-8209 method. Except this, resin impregnation, batch press, and batch carbonization were performed in the same manner as in Example 1 to obtain an electrode substrate. Good results were obtained for both bending and deflection.

Example 11
Except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper making was performed by a wet continuous paper machine as in Example 2, and resin impregnation, batch press, and batch carbonization were performed to obtain an electrode substrate. . Compared with Example 10, the bending strength was remarkably increased, and the deflection was also good.

Example 12
As in Example 3, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper was made with a wet continuous paper machine, continuously impregnated with resin, dried, and then subjected to roll press, batch carbonization, An electrode substrate was obtained. Both bending strength and deflection were good results.

Example 13
As in Example 4, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper was made with a wet continuous paper machine, continuously impregnated with resin, and dried, followed by roll press and batch carbonization. An electrode substrate was obtained. Since pressing was performed at a pressure higher than that of Example 12, the electrode substrate of Example 12 was thinner, the bending strength was higher, and the deflection was larger.

Example 14
As in Example 5, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper was made with a wet continuous paper machine, continuously impregnated with resin, dried, and then subjected to roll press and continuous firing. An electrode base material having a length of 30 cm and a length of 20 m was wound around a cylindrical paper tube having an outer diameter of 30 cm. It was thin, strong in bending strength, and large in deflection.

Example 15
As in Example 6, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper was made by a wet continuous paper machine, continuously impregnated with resin and dried, then double belt press (DBP), batch Carbonization was performed to obtain an electrode base material. Both bending strength and deflection were good results.

Example 16
As in Example 7, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper was made by a wet continuous paper machine, continuously impregnated with resin, dried, then double belt press (DBP), batch Carbonization was performed to obtain an electrode base material. Since pressing was performed at a pressure higher than that of Example 15, it was thinner, stronger in bending strength, and larger in deflection than the electrode substrate of Example 15.

Example 17
As in Example 8, except that carbon short fibers and PVA were blended in the same formulation as in Example 10, paper making was performed by a wet continuous paper machine, continuously impregnated with resin and dried, then double belt press (DBP), continuous firing The electrode substrate having a width of 30 cm and a length of 20 m was wound around a cylindrical paper tube having a diameter of 30 cm. The obtained base material had no warp, was thin, had high bending strength, and had a large deflection.

Example 18
A carbon electrode substrate in the same manner as in Example 17 except that short fibers having an average fiber diameter of 4 μm and an average fiber length of 6 mm were used instead of short carbon fibers having an average fiber diameter of 4 μm and an average fiber length of 3 mm. Got. The dispersibility was relatively poor, but the strength and deflection showed good values, and the gas permeability was good.

Example 19
An electrode substrate was obtained in the same manner as in Example 1 except that polyacrylonitrile (PAN) pulp was used instead of PVA as the binder to be used for papermaking. Although the binding force of the short carbon fibers was smaller than when PVA was used, good results were obtained in both bending and deflection.

Example 20
Similar to Example 1, except that carbon black MA100 (manufactured by Mitsubishi Chemical Co., Ltd.) as a conductive substance in the resin solution was mixed with 1% by mass of the phenol resin and impregnated into the carbon fiber paper. The electrode base material was obtained by the method. A good value was exhibited in conductivity.

Example 21
An electrode base material was obtained in the same manner as in Example 8, except that 65 parts by mass of phenol resin was attached to 35 parts by mass of carbon fiber. Although the gas permeability was slightly reduced, the bending strength was also good.

Example 22
After continuously obtaining carbon fiber paper in the same manner as in Example 2, the phenol resin (Phenolite 5900 manufactured by Dainippon Ink & Chemicals, Inc.) was desolvated, and then coated on the release paper with a coater. A long phenol resin film having a weight of 30 g / m ² was obtained. This phenolic resin film was layered on the carbon fiber paper from above and below, and the phenol resin was transferred to the carbon fiber paper.

  Except that the obtained resin-impregnated carbon fiber paper was not overlapped, it was press-cured by a double belt apparatus and continuously carbonized in the same manner as in Example 8 to obtain a 30 cm wide, 20 m electrode base material. Excellent gas permeability and good bending strength deflection.

Comparative Example 1
Using only PAN-based carbon short fibers (used in Example 10) having an average fiber diameter of 7 μm as carbon fibers, continuous paper making was performed in the same manner as in Example 2 to obtain a carbon fiber paper of 60 g / m ² . . Also, resin impregnation was performed in the same manner as in Example 3, and belt press and continuous carbonization were performed in the same manner as in Example 22 to obtain an electrode base material. The gas permeability coefficient increased, but the deflection was small and cracked when wound on a roll.

Comparative Example 2
As in Comparative Example 1, only PAN-based short carbon fibers having an average fiber diameter of 7 μm were used as carbon fibers, and continuous paper making was performed in the same manner as in Example 8 to obtain 30 g / m ² of carbon fiber paper. Next, resin impregnation was performed in the same manner as in Example 3, but continuous curing was performed at 180 ° C. without performing pressing, and carbonization was performed as it was. The obtained electrode base material has become very brittle.

Comparative Example 3
An electrode substrate was prepared in the same manner as in Example 1 except that pitch-based carbon fibers having an average fiber length of 11 mm were used in place of the PAN-based carbon fibers. Bending strength was weak and brittle.

FIG. 1 is an example of a continuous heating roll press apparatus that can be suitably used in the production method of the present invention. FIG. 2 is an example of a continuous hot press apparatus having a pair of endless belts that can be suitably used in the production method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Resin impregnated carbon fiber paper 2 ... Release agent coating base material 3a, 3b ... Endless belt 4 ... Preheating zone 5 ... Heating and pressing zone

Claims (5)

Three-point bending under the conditions of a thickness of 0.05 to 0.5 mm, a bulk density of 0.3 to 0.8 g / cm ³ , a strain rate of 10 mm / min, a fulcrum distance of 2 cm, and a specimen width of 1 cm. A porous carbon electrode substrate for a fuel cell, wherein the bending strength is 10 MPa or more in the test, and the deflection during bending is 1.5 mm or more. Is not less than 1m in length, and can be wound up in the following roll outer diameter 50cm claim 1 for a fuel cell porous carbon electrode substrate according. The porous carbon electrode substrate for fuel cells according to claim 1 or 2 , comprising carbon fibers, wherein the carbon fibers are only polyacrylonitrile-based carbon fibers. A carbon fiber containing a fine fiber having an average diameter of more than 3 μm and less than 5 μm and an average fiber length of 3 to 10 mm and a thick fiber having an average diameter of 5 μm to less than 9 μm and an average fiber length of 3 to 10 mm. The porous carbon electrode substrate for a fuel cell according to any one of claims 1 to 3 , which is a mixture. Containing carbon fibers, the carbon fiber in an average diameter 3μm to exceed average fiber length of less than 5μm is 3~10mm fine fibers according to any one of claims 1 to 4 included more than 40 wt% Porous carbon electrode substrate for fuel cells.

Images