JPH11310460A - Water repellent carbonaceous electrode material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-repellent carbonaceous electrode material by using C/C material capable of exhibiting mechanical strength, having water repellency equivalent to or larger than that of polytetrafluoroethylene without mixing polytetrafluoroethylene therein, usable for various electrodes such as electrode of fuel cell and electrode of electric scalpel tip, of the like, and having water repellency and mechanical strength simultaneously imparted thereto. SOLUTION: A carbon fiber-reinforced carbon composite material having >=108 degree, preferably >=110 degree contact angle with water is prepared. The method for producing a water-repellent carbonaceous electrode material comprises forming carbon matrix in carbon fiber by resin char method, subjecting the materials to heat history of at least 2,000-2,800 deg.C, introducing an inert gas therein and replacing the generated gas with the inert gas so that generated gas concentration in furnace in the backing step becomes <=5 g/m<3> , preferably <=1 g/m<3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-repellent carbonaceous electrode material, and more particularly to a water-repellent carbonaceous electrode material used for an electrode of a fuel cell or a medical electric knife.

[0002]

2. Description of the Related Art Carbonaceous materials have long been used as electrode materials because of their excellent conductivity and chemical corrosion resistance.

For example, an electrode material such as a phosphoric acid type fuel cell requires a highly water-repellent electrode material.
Japanese Patent Application No. -143751 describes a method for forming a highly water-repellent electrode by depositing a water-repellent functional group on a carbonaceous material. Japanese Patent Application Laid-Open No. 7-78617 discloses a polymer electrolyte battery using a sheet in which acetylene black as a water-repellent carbon black, polytetrafluoroethylene having water repellency and chopped or milled carbon fiber are mixed. Electrodes are shown.

[0004] The carbonaceous material described above has low elongation and low tensile strength. Therefore, a composite material reinforced with carbon fiber (carbon fiber reinforced carbon composite material: Carbon fiber reinforced carbon com.
posites Hereinafter, abbreviated as C / C. ) Have been proposed,
JP-A-4-97948 discloses a method for producing C / C for a phosphoric acid type fuel cell electrode material.

As another application utilizing the water repellency of C / C, if C / C is used for an electrocautery electrode material, the adhesion of carbides of proteins and oils and fats of living tissue at the time of incision can be achieved by using a stainless steel knife. It is disclosed in Japanese Patent Application Laid-Open No. 8-196542 that the adhesion of the carbide is smaller than that in the case of using the polytetrafluoroethylene coated product.

[0006]

The conventional C / C has insufficient water repellency when viewed as an electrode material. For this reason, materials mixed with or coated with polytetrafluoroethylene have been proposed in order to increase water repellency. However, when the temperature exceeds 800 ° C., decomposition of polytetrafluoroethylene occurs, and the problem of loss of water repellency or generation of decomposition gas occurs. was there. For this reason, it was necessary to increase the water repellency of C / C itself.

As described above, the C / C knife disclosed in Japanese Patent Application Laid-Open No. 8-196542 is known. In the C / C knife described in the publication, although the carbide adheres to the knife tip at the same level as that of the polytetrafluoroethylene-coated product, the carbide may adhere to the knife, and this point is sufficiently satisfactory. It wasn't going. Further, the method of producing the C / C composite is a known method formed by firing a reinforcing fiber impregnated with a phenol resin, and thus has a disadvantage that high water repellency is hardly obtained.

[0008] Conventionally, the conventional C / C production method is a chemical vapor deposition method (Chemical Vapor Deposition) in which a low-carbon hydrocarbon decomposition product represented by methane or propylene is deposited in a gas layer around carbon fibers. ) And a resin method in which a thermosetting resin or a thermoplastic resin is attached to carbon fibers to form a carbon fiber reinforced resin composite material (hereinafter abbreviated as CFRP), and then the resin component is heated and carbonized in an inert gas. (Resi
n Char) is known.

In the resin method, since the resin component is previously attached to the carbon fiber, the conventional CFRP manufacturing technology can be used as it is, the carbonization efficiency is high, and the running cost can be reduced relatively. It is excellent in such points, and is widely adopted. Also, once carbonized, the porous matrix is repeatedly impregnated with a high carbonization yield pitch or the like and further heated and carbonized, so-called densification treatment is performed to the required density. Enhancing is done.

However, according to the study of the present inventors, such a conventional resin method has not obtained a highly water-repellent C / C material suitable as an electrode material.

Therefore, an object of the present invention is to provide a high water repellency,
Another object of the present invention is to provide a water-repellent carbonaceous electrode material which has high mechanical strength and can be widely used as an electrode material even at high temperatures.

[0012]

To solve the above-mentioned problems, the present invention has the following arrangement.

That is, the water-repellent carbonaceous electrode material of the present invention comprises:
It is made of a carbon fiber reinforced carbon composite material having a contact angle with water of at least 108 degrees, preferably at least 110 degrees.

For the purpose of enhancing the mechanical strength of the water-repellent carbonaceous electrode material of the present invention, it is desirable that the carbon fibers used are continuous fibers and oriented in one or two directions. .

In the method for producing a water-repellent carbonaceous electrode material of the present invention, a carbon matrix is formed on a carbon fiber by a resin method, and at least two
An inert gas is introduced and replaced so as to receive a heat history of 2,000 to 2800 ° C. and to generate a gas concentration of 5 g / m ³ or less, preferably 1 g / m ³ or less in the furnace in the firing step. And

According to the present invention, C / C having higher water repellency (large contact angle) and higher mechanical strength than conventional C / C can be obtained, which is suitable for use as an electrode material.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The water-repellent carbonaceous electrode material of the present invention is made of a composite material reinforced with carbon fibers and using carbon as a matrix.

The carbon fibers used in the water-repellent carbonaceous electrode material of the present invention are rayon, polyacrylonitrile,
It is a fiber obtained by carbonizing fibers such as pitch by a known method, or a graphite fiber which is further heat-treated at a high temperature.

The carbon fiber has a tensile strength of 100 kgf / m
Those having properties of at least m ² and a tensile modulus of elasticity of at least 10 × 10 ³ kgf / mm ² are preferred. The diameter of the carbon fiber is preferably 1 to 20 μm, more preferably 4 to 7 μm.
m.

The carbon fibers are usually bundled with about 500 to 100,000 filaments. The surface of the carbon fiber is usually subjected to a surface treatment by an electrolytic oxidation method, a chemical liquid oxidation method, or the like, but a carbon fiber that has not been subjected to a surface treatment may be used.

In general, a sizing agent is attached to the carbon fiber bundle in order to maintain good handling properties in the subsequent process and interface characteristics with the matrix resin. can do.

The form of the carbon fiber may be any of milled fiber, short fiber or long fiber (continuous fiber).

The structure made of carbon fibers may be paper-like, felt-like, woven or knitted, or a sheet aligned in one direction. Further, these may be a single layer or a stacked layer. In particular, in order to obtain a high-strength electrode material, it is preferable to use a continuous fiber that is oriented in one or two directions.

As the thermosetting resin used in the resin method of the present invention, phenol resin, furan resin, epoxy resin, bismaleide resin, polyimide resin and the like are used. In particular, when carbon fiber is impregnated with a matrix resin and molded and cured, a phenol resin, a furan resin or the like having a high carbonization yield is suitable. As the thermoplastic resin, coal-based or petroleum-based pitch or the like is used, and these are suitable as a densification resin because of their low melt viscosity and high carbonization yield.

The C / C matrix is formed by the resin method by impregnating carbon fiber with a resin to form a cured product having a predetermined shape, so-called CFRP, and then heating it in an inert gas to carbonize or densify it. can get.

The CFRP can be formed into various shapes such as a flat plate, a curved plate, a pipe, and the like.
(Carbon fiber) and a method of obtaining a molded product directly from resin, or forming an intermediate material such as prepreg, SMC, stampable sheet, etc., and then molding the molded product using molding means such as autoclave molding, matched die molding or hot press molding. In some cases, any molding method may be used.

Next, the CFRP is calcined in an inert gas such as nitrogen at 600 to 1500 ° C. in a calcining furnace to carbonize a resin phase as a matrix, and to carry out C / C before densification.
Get.

In order to obtain a high-density or high-strength electrode material, the C / C before densification is further impregnated with a molten pitch or the like.
The densification step consisting of re-carbonization is repeatedly performed until predetermined characteristics are obtained.

In this densification step, 1600 ° C. to 2 ° C. in an inert gas is used to promote densification or improve conductivity.
Heating at a temperature of 800 ° C. to make the matrix graphite.

In the present invention, the degree of densification is determined by the specifications of the electrode material to be applied. When higher strength is required, the number of densifications is increased, and when emphasis is placed on gas permeability, the number of densifications is reduced. The bulk density of C / C can be set to an arbitrary value according to the number of densifications, and the number of densifications is determined according to the specifications of the electrode material to be applied so that a desired bulk density is obtained.

In the present invention, in order to obtain an electrode material having high water repellency, maintaining the concentration of generated gas in the furnace in the firing step as low as possible can reduce the influence of re-adhesion of the thermal decomposition product to the object to be processed. It is effective.

The generated gas concentration is measured in accordance with the method for measuring the concentration of dust in exhaust gas according to JIS Z8808. That is, gas is sampled by constant-velocity suction from a gas suction nozzle provided in the direction opposite to the gas flow inside the firing furnace,
The generated gas concentration is calculated as the mass of the generated gas solid content per 1 m ^{3 of the} flow rate from the generated gas solid content filtered and collected by the gas collector and the amount of gas sucked at the same time.

The gas collector is based on filtration and collection, and the performance thereof must be 99% or more and does not cause a chemical change in use. As the gas collector, a circular filter paper, a cylindrical filter paper, or a dust tube can be used. The gas is cooled to 500 ° C. or less at the stage of being filtered and collected by the gas collector. A glass fiber or a silica fiber is used as a filtering material. The amount of suction gas is selected based on the amount of generated gas solids collected by the gas collector. That is, in the case of the circular filter paper, the collection amount is about 0.5 mg / cm ² , and in the case of the cylindrical filter paper, the total collection amount is 5 mg.
mg or more, and in the case of a dust tube, the total collection amount is about 50 mg. The constant-velocity suction of the gas can be achieved by adjusting the flow rate of the suction gas such that the dynamic pressure of the gas at the measurement point is equal to the dynamic pressure of the suction gas.

The generated gas concentration C in the inert gas is represented by the mass of the generated gas solid contained in 1 m ^{3 of} the gas flow rate converted to a standard condition (temperature: 0 ° C., pressure: 760 mmHg). Is defined by

[0036]

(Equation 1)

Here, m is the mass of collected generated gas solids, and Q is the amount of gas sucked in the standard state.

The concentration of the generated gas varies depending on the capacity of the firing furnace, the amount of the object to be treated, and the amount of the thermal decomposition component of the object to be treated.
In any case, in the final baking step, an inert gas is supplied so as to receive a heat history of at least 2000 to 2800 ° C. and to generate a gas concentration of 5 g / m ³ or less in the furnace in the baking step. Introduce and replace.
When the generated gas concentration is 1 g / m ³ or less, it is more preferable to increase the water repellency.

When the concentration of the generated gas exceeds 5 g / m ³ , the thermal decomposition product is re-adhered to the object to be processed, and the water repellency is reduced. If the firing temperature at this time is lower than 2000 ° C.,
The graphitization of the matrix is not sufficient, and the water repellency decreases.
If the temperature exceeds 2800 ° C., the graphitization of the matrix proceeds excessively, and the mechanical strength decreases, which is not preferable.

In the final firing step, at least 2000
Graphite is formed by receiving a heat history of up to 2800 ° C., and by introducing an inert gas so that the generated gas concentration is equal to or lower than a specified value, the atmosphere in the firing furnace is kept clean to form graphite. It is effective in continuously and rapidly replacing decomposition gases and reaction products generated in the process, and preventing a decrease in water repellency of the C / C surface.

As such an inert gas, known gases such as nitrogen gas and argon gas can be used, but inexpensive nitrogen gas is preferable.

It is extremely important to carry out this inert gas introduction operation at least in the final baking step in order to enhance water repellency. If this operation is not performed in the final baking step, even if a clean C / C surface is formed up to that point, it will be offset in the final step, and it will be difficult to develop water repellency.

In the present invention, the contact angle, which is an index indicating the water repellency of C / C, is defined as follows.

That is, the object to be measured was washed with acetone for 10 minutes.
After washing for 10 minutes and ethanol washing for 10 minutes,
Dry at 05 ° C for 60 minutes, store in a desiccator for 12 hours or more, and adjust the condition.

Using water as a test solution, one drop (10 μl) is dropped on the flat surface of the test piece. Then the microscope V
Using a H-6110 (trade name: manufactured by KEYENCE CORPORATION), the droplet is enlarged on a monitor television, and the height h of the droplet, an orthogonal point between the apex of the droplet and the horizontal plane and the droplet are determined by image processing. The distance a to the intersection of the horizontal plane is measured, and the contact angle θ is determined by the following equation (2).

[0046]

(Equation 2)

According to the present invention, it is possible to obtain a highly water-repellent C / C having a contact angle of 108 degrees or more, and more preferably 110 degrees or more.

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

[0049]

EXAMPLES In the examples, each measured value is obtained as follows. The concentration of the decomposition gas and the contact angle are obtained by the above-described equations (1) and (2).

In the measurement of bulk density, a C / C flat plate having a thickness of 2 mm was wet-cut to a size of 30 mm in width and 30 mm in length using a diamond cutter, and the cut surface was sandpaper # 1.
After polishing at 000, dried at 105 ° C. for 60 minutes, and stored in a desiccator for 12 hours or more, was used as a test piece. The bulk density d was calculated by the following equation (3).

[0051]

(Equation 3)

Here, W is the dry weight of the test piece, and V is the volume of the test piece.

The bending strength is a three-point bending strength in accordance with JIS-K7074. A C / C flat plate having a thickness of 2 mm is wet-processed using a diamond cutter to a width of 15 mm and a length of 100 mm.
mm size and the cut surface is sandpaper # 1000
, And dried at 105 ° C for 60 minutes, and stored in a desiccator for 12 hours or more to obtain a test piece. The test was performed using a universal testing machine at a test speed of 5 mm / min and a span length / thickness ratio (L / h) of 40. The bending strength σ _b was calculated by the following equation (4).

[0054]

(Equation 4)

Here, P _max is the load at break or the maximum load, L is the distance between fulcrums, b is the width of the test piece, and h is the thickness of the test piece.

The measurement of the volume resistivity was performed by Mitsubishi Motors
AP (trade name) was used. A C / C flat plate having a thickness of 2 mm is wet-cut with a diamond cutter to dimensions of 100 mm in width and 100 mm in length, and the cut surface is sandpaper #
After being polished at 1000, dried at 105 ° C. for 60 minutes and stored in a desiccator for 12 hours or more. Then, a silver paste was applied to the cut surface parallel to the fiber direction and a silver paste was applied to the fiber at right angles to the fiber direction. did. The volume resistivity was measured based on the four probe resistivity measurement method.

Example 1 Using a carbon fiber strand (Vesfite UM46: registered trademark, manufactured by Toho Rayon Co., Ltd.) having no surface treatment and having no elasticity and having a modulus of elasticity of 46,000 kgf / mm ² , Using a resol type phenol resin (PR9480: trade name, manufactured by Sumitomo Durez Co., Ltd.) as a matrix resin, a prepreg was prepared in one direction using acetone as a diluent. The weight of the carbon fiber of the obtained prepreg is 150 g /
m ² , the resin content was 47% by weight.

The prepreg was cut into a size of 150 × 150 mm, 16 sheets were laminated in a mold, and one-way CFRP was formed using a hot press at 150 ° C. × 5 kgf / cm ² × 30 minutes. A laminated material was obtained. The CFRP laminate was kept in a nitrogen atmosphere with a diameter of 30 cm and a height of 30 cm.
m, and fired at 1000 ° C. to obtain C / C before densification.

The pitch of the C / C before densification is set to 10% in a firing furnace maintained in a nitrogen atmosphere by using a resin as a densification resin.
The operation of firing at 00 ° C. was repeated twice. Next, firing is performed once at 2600 ° C. in a firing furnace maintained in a nitrogen atmosphere without using a densifying resin, and further, in a firing furnace maintained in a nitrogen atmosphere, the pitch is set to 1000 as a densifying resin.
Calcination was performed once at ℃ to obtain C / C after densification.

After the densification, the C / C is further subjected to a firing temperature of 2600.
The final baking was performed by introducing nitrogen gas so as to maintain the gas concentration at 3 ° C. and 3 g / m ³ . In this case, the amount of nitrogen gas introduced was 200 L / min. C / C obtained
Are shown in Table 1 below.

The bulk density of C / C in Example 1 was 1.81 g.
/ Cm ³ , the three-point bending strength according to JIS-K7074 is 569 MPa, and the volume resistivity is 9 × 1 in the fiber direction.
0 ^-6 Ωm, and 58 × 10 ^-6 Ωm in the direction perpendicular to the fiber. The contact angle of the C / C by the dropping method was 110.
Degree.

[Example 2] As in Example 1, except that nitrogen gas was introduced so as to maintain the generated gas concentration in the firing furnace at 0.5 g / m ^3. And C / C was produced.

The basic characteristics of the obtained C / C are shown in Table 1 below.

The bulk density of C / C in Example 2 was 1.82 g.
/ Cm ³ , the flexural strength was 572 MPa, and the volume resistivity was 8 × 10 ⁻⁶ Ωm in the fiber direction and 57 × 10 ⁻⁶ Ωm in the direction perpendicular to the fiber. The contact angle of the C / C by the dropping method was 113 degrees.

[Comparative Example 1] In Example 1, the final firing temperature was 1000 ° C and the generated gas concentration was 10 g / m ^3.
C / C was manufactured in the same manner as in Example 1 except that nitrogen gas was introduced so as to maintain the temperature.

Table 1 below shows the basic characteristics of the obtained C / C.

The bulk density of C / C in Comparative Example 1 was 1.82 g /
cm ³ , bending strength was 589 MPa, and volume resistivity was 30 × 10 ⁻⁶ Ωm in the fiber direction and 100 × 10 ⁻⁶ Ωm in the direction perpendicular to the fiber. In addition, C / C of Comparative Example 1
Was 98 degrees by a dropping method.

Comparative Example 2 A C / C was manufactured in the same manner as in Example 1 except that the final firing temperature was changed to 1000 ° C. in Example 1.

Table 1 below shows the basic characteristics of the obtained C / C.

The bulk density of C / C in Comparative Example 2 was 1.83 g /
cm ³ , the bending strength was 595 MPa, and the volume resistivity was 28 × 10 ⁻⁶ Ωm in the fiber direction and 97 × 10 ⁻⁶ Ωm in the direction perpendicular to the fiber. The contact angle of the C / C dropping method of Comparative Example 2 was 101 degrees.

Comparative Example 3 The same as in Example 1 except that nitrogen gas was introduced in the final baking step in Example 1 so as to maintain the generated gas concentration at 10 g / m ^3. And C / C was produced.

Table 1 below shows the basic characteristics of the obtained C / C.

The bulk density of C / C in Comparative Example 3 was 1.80 g /
cm ³ , bending strength was 559 MPa, and volume resistivity was 12 × 10 ⁻⁶ Ωm in the fiber direction and 70 × 10 ⁻⁶ Ωm in the direction perpendicular to the fiber. Further, the contact angle of the C / C dropping method of Comparative Example 3 was 102 degrees.

[0074]

[Table 1]

[0075]

The water-repellent carbonaceous electrode material of the present invention has a water repellency higher than that of polytetrafluoroethylene without mixing a water-repellent material such as polytetrafluoroethylene, and has excellent mechanical strength. And high-temperature characteristics and conductivity. Therefore, it is useful as an electrode of a fuel cell and various electrodes such as an electrode material at the tip of an electric knife.

Claims (5)

[Claims] 1. A water-repellent carbonaceous electrode material comprising a carbon fiber reinforced carbon composite material having a contact angle with water of at least 108 degrees. 2. The water-repellent carbonaceous electrode material according to claim 1, comprising a carbon fiber reinforced carbon composite material having a contact angle with water of 110 degrees or more. 3. The water-repellent carbonaceous electrode material according to claim 1, wherein the carbon fibers are continuous fibers and are oriented in one direction or two directions. 4. A carbon matrix is formed on a carbon fiber by a resin-charging method, receives a heat history of at least 2000 to 2800 ° C. in a final firing step, and generates a gas having a concentration of 5 g / g in the furnace in the firing step. A method for producing a water-repellent carbonaceous electrode material, which comprises introducing and replacing an inert gas so as to have an m ³ or less. 5. The water-repellent carbonaceous electrode material according to claim 4, wherein an inert gas is introduced and replaced so that a generated gas concentration in the furnace in the firing step becomes 1 g / m ³ or less. Production method.