JPH07142068A - Porous electrode base material and its manufacture - Google Patents

Abstract

PURPOSE:To utilize effectively electric conductivity in the width direction of carbon fiber, and provide a porous electrode base material excellent in thickness directional electric conductivity by making carbonaceous milled fiber having a prescribed fiber length exist in the vertical direction to the surface of the electrode base material in a matrix part of the electrode base material. CONSTITUTION:Carbonaceous milled fiber is manufactured by pulverizing ordinary carbon fiber (containing graphite fiber), and though a fiber length is not more than 1.0mm, in this case, fiber not more than 0.1mm is particularly used. When the fiber length becomes longer than 0.1mm, inflow of a porous carbon fiber sheet-like material in the void is hindered. Here, resin solution or melting solution in which carbonaceous milled fiber having a fiber length of not more than 0.1mm and bulk density of 0.2 to 0.5g/cm<3> is mixed by a prescribed quantity is injected into the void of the carbon fiber sheet-like material of a porous structure. Then, when the carbonaceous milled fiber is flowed in, shearing stress acts, and mixed solution or the like flows in abundantly from the vertical direction to a surface, and is arranged in the vertical direction to a surface of the sheet-like material. Thereby, thickness directional electric conductivity of an electrode base material is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous electrode base material mainly used for phosphoric acid type fuel cells and a method for producing the same.

[0002]

2. Description of the Related Art Recently, a new type of secondary battery is used to store surplus power at night and to cope with the increase in demand during the daytime. The development of fuel cells is progressing, and both are in the stage of verification test. Porous plates of carbon fiber are used for the electrode base material of these batteries because of their excellent high-temperature characteristics, electrical conductivity, chemical resistance, and thermal oxidation resistance. It is excellent in the axial direction but not necessarily high in the cross-sectional direction, and the molded product obtained by lengthening the fiber length in relation to the strength is easy to arrange in parallel in the plane direction,
The conductivity of the electrode base material in the thickness direction was not necessarily high.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the prior art and to provide a porous electrode substrate having excellent conductivity in the thickness direction and a method for producing the same.

[0004]

The present invention adopts the following means in order to solve the above problems. That is, the first gist of the present invention is that a carbonaceous milled fiber having a fiber length of 0.1 mm or less is added to the surface of the electrode base material in the matrix portion of the electrode base material having a porous structure composed of carbon fiber-carbon. In a porous electrode substrate characterized by being present in the vertical direction,

The second gist is that the fiber length is 0.1 mm in the void of the sheet-like material having a porous structure made of carbon fiber.
10 to 1 w of carbonaceous milled fiber having a bulk density of 0.2 to 0.5 g / cm ³ below.
A porous material characterized by injecting a thermosetting resin solution containing t%, removing the solvent, laminating it to a predetermined thickness to heat-harden it, and further heat-treating it at a temperature of 2000 ° C. or more in an inert atmosphere. In the manufacturing method of the electrode base material,

A third gist is a sheet-like material having a porous structure made of carbon fibers, a fiber length of 0.1 mm or less, and a bulk density of carbonaceous milled fibers of 0.2 to 0.5 g. / Cm ³ of thermosetting resin film containing carbonaceous milled fibers are alternately laminated, heat-melted, injected under pressure into the voids of the sheet-like material, then cured, and further in an inert atmosphere. A method for producing a porous electrode substrate is characterized by performing heat treatment at a temperature of 2000 ° C. or higher.

The present invention will be described in more detail. A resin solution or a melt containing a predetermined amount of carbonaceous milled fibers having a fiber length of 0.1 mm or less and a bulk density of 0.2 to 0.5 g / cm ³ is prepared by porosity. When it is injected into the voids of a carbon fiber sheet-like material with a fine structure, shear stress acts when the carbonaceous milled fiber flows in, and in the case of a sheet-like material, the inflow of a mixed solution or melt from the direction perpendicular to the surface is overwhelming. Most of them are arranged in the direction perpendicular to the surface of the porous carbon fiber sheet. This improves the conductivity of the electrode base material in the thickness direction.

The carbonaceous milled fiber is produced by crushing ordinary carbon fiber (including graphite fiber) and has a fiber length of 1.0 mm.
The followings are used, but those of 0.1 mm or less are used in the present invention. The carbonaceous material may be either polyacrylonitrile, phenol, carbon fiber obtained by firing an organic material such as cellulose, or carbon fiber obtained from an inorganic material such as petroleum or coal, but the fiber length is 0.1 m.
If it is longer than m, the porous carbon fiber sheet-like material is prevented from flowing into the voids. If the bulk density is less than 0.2 g / cm ³ , it becomes difficult to mix it with the resin liquid, and 0.5 g / cm ³
If it is larger than the above range, the dispersibility in the resin impregnating liquid becomes poor and it causes unevenness, which is not preferable. The diameter of the fiber is not particularly limited, but the normal carbon fiber diameter is preferably in the range of 3 to 12 μm.

The sheet-like material (sheet, paper, felt, woven fabric, knitted material, etc.) having a porous structure made of carbon fiber (including graphite fiber) used in the present invention is an organic material such as polyacrylonitrile, phenol resin, cellulose and the like. The carbon fiber obtained by firing, and the pitch-based carbon fiber obtained by firing a pitch-based fiber made of an inorganic material from petroleum, coal as a raw material, but in terms of strength characteristics and processing characteristics Those from the acrylonitrile series are excellent.

The thermosetting resin used in the present invention is adhesive or fluid at room temperature, and a phenol resin, a furan resin or the like is used. As the phenol resin, a resol-type phenol resin obtained by reacting a phenol with an aldehyde in the presence of an alkali catalyst can be used. It is also possible to dissolve and mix a solid, heat-fusible novolak type phenolic resin produced by the reaction of phenols and aldechts with an acidic catalyst by a known method in a resol type fluid phenolic resin. In this case, a self-crosslinking type containing a hardening material such as hexamethylenediamine is preferable.

As the phenols, for example, phenol, resorcin, cresol, xylol, etc. are used. As the aldechts, formalin, paraformaldehyde, furfural, etc. are used. Also, these can be used as a mixture. It is also possible to use commercially available products as these phenolic resins.

A furan resin initial condensate is used as the furan resin. A furfuryl alcohol condensate and a furfuryl alcohol-furfural cocondensate are used as the furan resin initial condensate. In this case, furfuryl alcohol or a furfuryl alcohol-furfural mixture is added with an acidic catalyst and heated to a proper viscosity,
It is recommended to use it after cooling. It is also possible to eliminate the catalytic activity from these initial condensates at room temperature by means such as volatilization or neutralization.

The resin concentration of the preferred resin impregnating liquid used in the present invention is 5 wt% to 40 wt%. If the concentration is lower than 5 wt%, the structure of the porous carbon fiber sheet material becomes a rough structure and the strength characteristics of the electrode substrate deteriorate, which is not preferable. When the concentration is higher than 40 wt%, the structure of the porous carbon fiber sheet-like material becomes dense and the strength of the electrode substrate increases, but the porosity becomes small and the gas permeability becomes poor, which is not preferable.

In the present invention, the amount of carbonaceous milled fiber mixed in the resin liquid is preferably 1 to 10 wt%. If the amount of the milled fibers mixed is less than 1 wt%, the effect of improving the conductivity in the thickness direction is small, and if it exceeds 10 wt%, the effect of improvement reaches the equilibrium, and if it is more, it becomes a factor of cost increase, which is not preferable.

When the resin solution containing the carbonaceous milled fibers is injected into the voids of the porous carbon fiber sheet-like material, when the solution viscosity is relatively low, is it sprayed vertically to the surface of the sheet-like material? A means such as a vacuum adsorption method in which the impregnating liquid is allowed to flow from the front surface to the back surface can be used. When it is in a molten state and has a relatively high viscosity, it is necessary to inject it under pressure, but there is no particular limitation as long as it is a method in which it is easy to flow into the void.

In the voids of the porous carbon fiber sheet,
The injection amount of the resin impregnating liquid mixed with the carbonaceous milled fiber is 500 to 2000%, preferably 800 to 1200 wt% with respect to the weight of the sheet material. If it is less than 500%, the porosity increases and the strength characteristics deteriorate, resulting in 2000
When it is more than%, the gas permeability is deteriorated, which is not preferable.

In order to control the injection amount of the resin solution into the voids of the sheet-like material, the suction method is preferable to the method using compression or squeezing with a roll because the fibers are easily arranged in the thickness direction. Desolvation is preferably performed in a vacuum dryer at a temperature of 70 ° C. or lower at which heat curing does not occur, but if the temperature is extremely short, a temperature of about 90 ° C. does not cause any particular problem. Lamination curing is usually carried out by a known method using a press molding machine or an autoclave while effectively removing the reaction gas.

Then, the temperature is raised to 200 at a heating rate of 10 ° C./min or less in an atmosphere of an inert gas such as nitrogen or argon.
By heat-treating at a temperature of 0 ° C. or more for a time of 10 seconds or more, it is possible to manufacture the electrode substrate having a porous structure of the present invention, which has excellent conductivity in the thickness direction.

[0019]

EXAMPLES The present invention will be described in more detail with reference to examples below. The physical properties and the like in the examples were measured by the following methods. That is,

The "air permeability" of the electrode base material is JIS P8.
The number of seconds (t) through which 100 cc of air passes was measured and calculated according to the following formula. Permeability (cc / sec.cm ² .cmAq) = 100 / t × 0.64 (permeation area) × 13.2 (permeation pressure)

The "specific resistance in the thickness direction" of the electrode base material was obtained from the following equation by measuring the resistance value when the sample was sandwiched between copper plates and a current was applied. Specific resistance value (Ωcm) = measured resistance value (Ω) × sample area (cm ² ) / sample thickness (cm)

The "bending strength" of the electrode substrate is the measurement span (L
mm) and the thickness (tmm) of the sample with 32 as a standard, the strain rate was measured by the three-point bending method at 300 mm / min, and the value was calculated by the following formula. Bending strength (kg / cm ² ) = 3P (breaking load) L (span) / 2W (width of sample) t
² (thickness)

The "porosity" of the electrode base material was calculated from the following equation. Porosity (%) = {1-W (weight of sample) / ρ (true density of sample) V (volume of sample) 100

(Example 1) Paper was made by a Fourdrinier method using chopped fibers having a fiber length of 12 mm and made of polyacrylonitrile (hereinafter abbreviated as PAN) -based carbon fiber having an elastic modulus of 24 t / mm ² , and a mass per unit area was 30 g. / M ² of carbon fiber paper was produced. Phenol resin (Phenolite 5
900. (Manufactured by Dainippon Ink KK) 30 wt% methanol solution, average fiber length 70 μm, bulk density 0.35 g / cm
^The impregnating solutions (1) to (4) were prepared by mixing PAN-based carbonaceous milled fiber (3) at the concentration shown in Table 1.

For comparison, an impregnation solution (5) containing no carbonaceous milled fiber was also prepared. Carbon fiber paper is impregnated with a resin impregnating solution, and a sufficient amount is filled into the voids of the paper and adsorbed by a suction device.
After adsorbing 0 times the amount of the resin solution, the solvent was removed with a vacuum dryer at a temperature of 60 ° C. to prepare prepregs 1 to 5.

50 cm × 50 each of the above prepregs
It was cut into a size of cm, and 16 sheets were laminated and heat-cured at a pressing pressure of 5 kg / cm ² , a temperature of 180 ° C., and a time of 30 minutes. Further, it was fired at a temperature of 2400 ° C. in a nitrogen atmosphere to produce an electrode substrate having a porous structure. The performance of each electrode substrate is shown in Table 1.

[0027]

[Table 1]

Example 2 PA having an elastic modulus of 22 t / mm ²
20 g of mass per unit area is produced by the Fourdrinier method using chopped fibers made of N-based carbon fibers and having a fiber length of 24 mm.
/ M ² of carbon fiber paper was produced. In a methanol solution containing 20 wt% of the phenol resin of Example 1, the fiber length was 50.
A PAN-based carbonaceous milled fiber having a particle size of 0.4 μm and a bulk density of 0.40 g / cm ³ was mixed at 3 wt%. Using a spray, the carbon fiber paper was vertically sprayed and injected into the voids of the paper so as to have 12 times the weight of the carbon fiber, and dried in hot air at 90 ° C. for 10 minutes to obtain a prepreg.

This prepreg was cut into 1.2 m × 1.2 m, and heat-cured using a large press without laminating. Then, it was fired at 2000 ° C. in an inert gas to manufacture a porous electrode base material having a thickness of 0.1 mm. The obtained porous electrode substrate has a porosity of 75% and an electrical resistivity of 0.04Ω.
cm, air permeability is 6 cc / sec. cm ² . cmAq
And had sufficient performance as an electrode base material.

(Example 3) A phenol resin (Phenolite 5900) in a 60 wt% methanol solution was added with a fiber length of 5
0 μm. 18 wt% of carbonaceous milled fiber having a bulk density of 0.40 g / cm ³ is mixed, stirred well, and spread on a glass plate to prepare a film made of a resin mixed with milled fiber having a mass per unit area of 30 g / m ² Then, it was cut into 50 × 50 cm.

On the other hand, the thickness is 4 mm. Mass per unit area 4
A carbon fiber felt of 0 g / m ² is cut into 50 × 50 cm, one resin film is laminated on each side of the felt, and the pressure is 10 kg / cm ² at a temperature of 80 ° C. using a press.
The resin film was poured into the felt cavity. Then, the temperature was raised to 180 ° C. and heat-cured. Further N ²
Firing was performed at 2200 ° C. in a gas atmosphere to manufacture a porous electrode base material having a thickness of 0.2 mm.

The porosity of the obtained porous electrode substrate is 70.
%, Electrical resistivity 0.03 Ωcm, air permeability 2.8.
cc / sec. cm ² . cmAq, bending strength is 370k
It was g / cm ² and had sufficient performance as an electrode base material.

[0033]

According to the present invention constructed as described above,
Since the carbonaceous milled fiber having a fiber length of 0.1 mm or less was present in the matrix portion of the electrode base material in the direction perpendicular to the surface of the electrode base material, the electrical conductivity in the axial direction of the carbon fiber was effectively utilized. In addition, the porous electrode substrate having excellent conductivity in the thickness direction can be obtained.

Claims (3)

[Claims] 1. A carbonaceous milled fiber having a fiber length of 0.1 mm or less is present in a matrix portion of a carbon fiber-carbon porous structure electrode base material in a direction perpendicular to a surface of the electrode base material. A porous electrode substrate characterized by: 2. The fiber length is 0.1 mm or less in the voids of the sheet-like material having a porous structure made of carbon fibers,
In addition, the bulk density of the carbonaceous milled fiber is 0.2 to 0.5 g /
After injecting a thermosetting resin solution containing 1 to 10 wt% of carbonaceous milled fiber of ³ cm3, after removing the solvent, it is laminated to a predetermined thickness to be thermoset, and further in an inert atmosphere at a temperature of 2000 ° C or more. A method for producing a porous electrode base material, which comprises heat-treating. 3. A sheet-like material having a porous structure composed of carbon fibers, carbon having a fiber length of 0.1 mm or less, and a carbonaceous milled fiber having a bulk density of 0.2 to 0.5 g / cm ³ . Thermosetting resin film containing fine milled fibers are alternately laminated, heat-melted, injected under pressure into the voids of the sheet-like material, then cured, and further cured in an inert atmosphere at 200
A method for producing a porous electrode substrate, which comprises performing a heat treatment at a temperature of 0 ° C. or higher.