JPH01264917A - Production of impermeable carbon material - Google Patents

Abstract

PURPOSE:To obtain the title gas-impermeable carbon material having excellent heat conductivity, electrical conductivity, chemical resistance, and mechanical strength by forming a mixture of mesophase globules or mesophase powder, a thermosetting resin, and infusibilized fiber, and calcining the formed product. CONSTITUTION:A mixture contg. 5-70wt.% mesophase globules or mesophase powder, 10-60wt.% thermosetting resin, and 3-60wt.% infusibilized fiber is formed. The formed product is calcined in a nonoxidizing atmosphere to obtain the desired carbon material. The thermosetting resin to be used is capable of providing a carbide by carbonization and calcination, and phenolic resin, furan resin, xylene resin, epoxy resin, etc., can be exemplified. However, the phenolic resin and furan resin having high carbonization yield are preferably used, and the resin having >=50wt.% carbonization yield is preferably selected. In addition, the mesophase powder can be produced from either petroleum pitch or coal pitch.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for producing a gas-impermeable carbon material having excellent thermal conductivity, electrical conductivity, and chemical resistance as well as high mechanical strength. It is something.

<Prior art and its challenges> In recent years, carbon molding materials have attracted attention as materials that are lightweight, and have excellent dimensional stability, heat resistance, electrical conductivity, thermal conductivity, and chemical resistance, and are used in semiconductor manufacturing. Its use is being promoted in many fields such as jigs and tools, nuclear reactor materials, and electrodes.

Among these, "gas-impermeable carbon materials" in particular are attracting attention for their application as "separator plates for phosphoric acid fuel cells" because they exhibit low electrical resistance and good chemical resistance in addition to gas permeation blocking physical properties. are collecting. This is because the separator plate in a phosphoric acid fuel cell serves as a partition between the hydrogen supplied as fuel and the fuel air, so it must have a function to prevent the two from mixing. Gas-impermeable carbon materials were required to be good conductors of electricity and heat, and to have excellent resistance to phosphoric acid at temperatures of about 200°C, but the physical properties of gas-impermeable carbon materials are extremely close to meeting these requirements. Because it was.

Therefore, various proposals have been made to realize gas-impermeable carbon materials with sufficiently satisfactory characteristics as "separation plates for phosphoric acid fuel cells" and the like.

For example, Japanese Patent Publication No. 56-22836 discloses that after molding and curing a mixture of a curable resin (thermosetting resin) and cured phenol resin fibers, the mixture is fired at a temperature of 800°C or higher. Carbon material is shown. However, since the carbon material disclosed in the publication is an amorphous carbonaceous material, it has problems such as inferior electrical and thermal conductivity and phosphoric acid resistance compared to graphite carbonaceous materials, as well as poor machinability (e.g. The workability of the grooves when processing into a ribbed separation plate was not fully satisfactory.

Therefore, as a carbon material with improved electrical conductivity, thermal conductivity, phosphoric acid resistance, and machinability, a material prepared by firing a raw material of thermosetting resin mixed with graphite powder was proposed (Japanese Unexamined Patent Application Publication No. 57-197). -72273, JP-A-59-195514, JP-A-59-232906, etc.).

However, these carbon materials are made by dispersing graphite powder, which is a good electrical and thermal conductor and has good phosphoric acid resistance and machinability, in a matrix of amorphous carbon (so-called "glassy carbon"). Therefore, it certainly had better electrical conductivity, thermal conductivity, phosphoric acid resistance, and machinability than amorphous carbon alone, but on the other hand, thermosetting resin During the carbonization and firing process of the above-mentioned carbon material used as a raw material, ``thermosetting resin shrinks significantly, but graphite does not shrink at all, and as a result, cracks occur at the interface between the two due to the difference in shrinkage rate.'''cannot be prevented'
Therefore, it was undeniable that the reliability of gas impermeability was poor.

<Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors have developed a technology that not only has excellent gas barrier properties but also has impeccable electrical conductivity, thermal conductivity,
We conducted research to provide an impermeable carbon material that has phosphoric acid resistance and machinability and can be used as a separator plate in phosphoric acid fuel cells. There was a strong interest in the fact that small spheres and mesophase powders contract during the carbonization and firing process.
``If mesophase small spheres or mesophase powder are mixed with a thermosetting resin that shows significant shrinkage during carbonization and firing, the mesophase small spheres or mesophase powder will shrink during carbonization and firing in the same way as the thermosetting resin. Based on this assumption, the formation of cracks due to the difference in shrinkage rate at the interface with the matrix thermosetting resin should be suppressed.
As a result of further research on carbon materials that use a mixture of thermosetting resin and mesophase spherules or mesophase powder as a starting material, we found that [the mixture obtained by carbonization and firing is "carbide derived from mesophase spherules or mesophase powder"] and"
There are no cracks at the interface between the two carbides derived from thermosetting substances, making it a carbon material with excellent impermeability, as well as electrical and thermal conductivity.

It was fully satisfactory in terms of phosphoric acid resistance and machinability, and furthermore, when infusible fibers having a carbonization shrinkage rate comparable to that of the thermosetting resin were mixed, the above-mentioned favorable characteristics were maintained. This led to the discovery that the mechanical strength of the material is further improved.

This invention was made based on the above findings,
"Mesophase spherules or mesophase powder: 5-70M
After molding a mixture of thermosetting resin: 10 to 60% by weight and infusible fiber: 3 to 60% by weight, the molded product is fired in a non-oxidizing atmosphere to provide excellent gas shielding. It is characterized by the ability to stably produce an impermeable carbon material that exhibits high strength, electrical conductivity, thermal conductivity, phosphoric acid resistance, and machinability.

Thermosetting resins targeted in the present invention are resins that can be carbonized to provide a carbide by carbonization firing, such as phenol resins, furan resins, xylene resins,
Examples include epoxy resins, but phenol resins and furan resins with high carbonization yields are preferred, preferably 5
It is better to choose one with a carbonization yield of 0% by weight or more. If such a resin is used as a starting material, a sufficiently excellent impermeable carbon material can be obtained.

Further, the mesophase powder may be produced from any petroleum-based or coal-based pitch. However, from the viewpoint of phosphoric acid corrosion resistance and stability of battery reactions, a carbon material with few impurities is required, so in the case of coal-based mesophase powder, it is preferable to refine the mesophase production raw material.

Usually petroleum or coal based heavy oil or pitch
When heat treated at 0 to 500℃, optically anisotropic spheres called spherulites are generated in the pinch matrix at the beginning of the heat treatment, and as the heat treatment continues, the spherulites repeatedly coalesce and grow. The entire pitch becomes an optically anisotropic material, the so-called "bulk mesophase." The above-mentioned spherulites and bulk mesophases differ depending on the heat treatment conditions, but - they do not show a softening point in boat fishing. In other words, it is a carbon precursor that has coke-like properties of being infusible, but also pitch-like properties of containing several percent by weight of volatile matter.

The mesophase microspheres targeted by the present invention are the above-mentioned "spherulites", and the mesophase powder is the above-mentioned "pulverized bulk mesophase".

For example, "the carbon content is 92% by weight or more,
Volatile content up to 900°C is 7-20% by weight.

"Mesophase microspheres with a linear shrinkage rate of 1% or more when heated to 500°C and an average particle size of 40 μm or less" or "Bulk mesophase having the same properties as the above mesophase microspheres with an average particle size of 4 μm or less" The preferred target is ``mesophase powder that has been ground into

If the carbon content is less than 92%, elements other than carbon will decompose and gasify during the firing process, resulting in increased weight loss, and atoms other than carbon will inhibit graphitization, resulting in poor thermal conductivity. , electrical conductivity and phosphoric acid resistance may not improve.

In addition, if the volatile content up to 900°C is less than 7% by weight, wettability with the thermosetting resin of the matrix will be poor during the firing process, and a gap (crank) will occur at the interface between the mesophase spherules or mesophase powder and the matrix. On the other hand, if it exceeds 13% by weight, a large amount of volatile matter generated from inside the mesophase spherules or mesophase powder will result in a foamed or porous body, resulting in a decrease in impermeability. This is becoming a concern.

And what is the linear shrinkage rate when heated to 500"C?
2t/c of mesophase small spheres or mesophase powder alone
This is a value measured by taking a sample from the molded product obtained by pressure molding at a pressure of II1 or higher. If this linear shrinkage rate is less than 1%, a gap will occur at the interface between the carbon particles derived from the mesophase small spheres or mesophase powder after carbonization and firing and the matrix carbon derived from the thermosetting resin, resulting in a decrease in impermeability. This is not desirable because it tends to occur.

The infusible fibers targeted by the present invention are fibers obtained by infusible treatment of organic fibers such as petroleum-based and coal-based pitch fibers, polyacrylonitrile (PAN) fibers, cellulose fibers, and phenol resin fibers. The method of infusibility treatment varies depending on the type of organic fiber, but usually 200 to 40
A method of air oxidation at a temperature of 0° C. is adopted.

Note that these infusible fibers may be in any form such as short fibers with a length of 0.5 to 10 mm, nonwoven fabric, mat cloth, etc.

Next, conditions for manufacturing an impermeable carbon material using mesophase small spheres or mesophase powder having such properties, a thermosetting resin, and infusible fibers will be explained.

The mesophase spherules or mesophase powder are blended in a proportion ranging from 5 to 70% by weight with respect to the mixture with the thermosetting resin and infusible fiber. This blending ratio is 5
When the amount is less than % by weight, the effect of blending the mesophase spherules or mesophase powder cannot be obtained, and thermal conductivity, electrical conductivity, phosphoric acid resistance, and machinability deteriorate. On the other hand, 70
If the amount exceeds % by weight, the surface area of the mesophase spherules or mesophase powder will increase, and the thermosetting resin will not be able to bind the mesophase spherules or mesophase powder uniformly, resulting in a decrease in strength.

Further, the infusible fiber is blended in an amount of 3 to 60% by weight with respect to the mixture of mesophase spherules or mesophase powder and thermosetting resin.

This is because if the blending ratio is less than 3% by weight, the blending effect of infusible fibers cannot be obtained and sufficient strength cannot be secured, whereas if the blending ratio exceeds 60% by weight, mesophase spherules or mesophase powder It depends on the blending ratio of
The surface area of the infusible fibers increases, making it impossible to bind the infusible fibers uniformly with the thermosetting resin, which also results in a decrease in strength.

In order to produce an impermeable carbon material from the above-mentioned raw materials, first, the raw material mixture blended as described above is charged into a mold, and 5-150 kg of the raw material mixture is usually placed at a temperature of 130-200°C.
The molded product is then pressure-molded by applying a pressure of 1.5 cm/cm. The molded product is then “post-cured” by heating at 130 to 200°C for 10 to 30 hours as necessary.The post-cured molded product is Carbonization is carried out in a non-oxidizing atmosphere (for example, under the flow of N2 gas or gauge gas) at a heating rate of 20.5 to 50°C/hr to at least 800°C, and if necessary, further graphitized to form impermeable carbon. It is considered as a material.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

<Examples> Example 1 Mesophase powder with carbon content: 93.3% by weight, volatile content up to 900°C: 10.3% by weight, linear shrinkage rate up to 500°C of 3%, and average particle size of 15 μm. 1000°
Phenol/novolac resin powder with a carbonization yield of 52x4% in C and infusible short fibers of PAN (length 111
) at the blending ratio shown in Table 1 (Table 1 only shows the blending ratio of mesophase powder and infusible fiber,
The remainder is a blended thermosetting resin), placed in a mold with a planar area of 1m x 1m, temperature: 180°C, pressure crab 80
Heated and pressure molded at kg/cm2 for 30 minutes to a thickness of lm.
A molded body of m is obtained, and then this molded body is heated for 20 hours.
After raising the temperature to 00°C, it was held at 200°C for 20 hours for "post-curing".

Next, the post-cured compact was carbonized by raising the temperature to 1000°C at a rate of 4°C/hr in a “vessel filled with coke powder”, and then carbonized at a rate of 4°C/min in an argon atmosphere. The temperature was raised to 2500°C to obtain a graphitized material with a thickness of 0.8 mm.

The physical properties of the obtained graphitized material were measured, and these results were used in the first
Shown in the table.

Note that "air permeability" in Table 1 is based on a differential pressure of 1 kg/c.
It was determined by measuring the amount of N2 gas passing through m2 at room temperature.

Moreover, "phosphoric acid resistance" is the weight loss rate with respect to the initial weight after being immersed in a 100% phosphoric acid solution at 200° C. for 1000 hours.

Machinability is 200mm in diameter, J! Cutting was performed by rotating a J-Sa2 Tsuru diamond blade at a speed of 243 rpm and moving the graphitized material at a feed rate of 111 m1n, and judgment was made based on the presence or absence of cracking of the graphitized material at this time.

Example 2 Mesophase spherules with a carbon content of 92.8% by weight, a volatile content of 712.0% by weight up to 900°C, a linear shrinkage rate of 5% up to 500°C, and an average particle size of 30 μm were made into mesophase powder. 1 of the cured phenolic resin fiber.
A graphitized material was obtained in exactly the same manner as in Example 1, except that a 011-length chopped fiber was used instead of the PAN infusible fiber.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Example 3 Mesophase powder with carbon content: 93.3% by weight, volatile content up to 900°C: 9.8% by weight, linear shrinkage rate up to 500°C of 2% and average particle size of 30 μm: 50 parts by weight To,
After kneading 25 parts by weight of the phenol/nozole resin liquid and 25 parts by weight of the infusible pinched fibers having a loam length, the mixture was dried at 80° C. for 10 minutes.

A graphitized product was produced in the same manner as in Example 1, except that the dry powder thus obtained was used as the starting mixture.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 1 Completely the same as Example 1 except that fixed carbon: 97.0% by weight, ash content: 2% by weight, volatile content: 1% by weight, and natural graphite with an average particle size of 10 μm was used instead of mesophase powder. A graphitized product was produced in the same manner.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 2 A graphitized product was produced in the same manner as in Example 1, using the same raw materials as in Example 1 and changing only the blending ratio.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 3 After mixing 50 parts by weight of phenol novolac resin and 50 parts by weight of 10 mm long Chiyo 7 fiber of cured phenol resin fiber [Kynol 11010: Gunei Chemical Co., Ltd., product name], It was molded, post-cured, carbonized, and graphitized in the same manner as in Example 1.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Note that machining was extremely difficult for both the obtained products fired at 1000°C and 2500°C.

<Summary of Effects> As explained above, according to the present invention, gas shielding properties,
It has excellent electrical conductivity, thermal conductivity, phosphoric acid resistance, strength, and machinability, and can provide an impermeable carbon material that is fully satisfactory even when applied to the separation plate of phosphoric acid fuel cells. Useful effects are produced.

Claims (1)

[Claims] Mesophase small spheres or mesophase powder: 5 to 70% by weight, thermosetting resin: 10 to 60% by weight, and infusible fiber:
A method for producing an impermeable carbon material, which comprises molding a 3-60% by weight mixture and then firing the molded product in a non-oxidizing atmosphere.