JP2002155149A - Method for preparing carbonaceous powder molding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonaceous powder molding material that has good moldability and that enables the production of a molded article having a small electric resistance and a large mechanical strength. SOLUTION: The carbonaceous powder molding material is prepared by dry blending a carbonaceous powder, a phenolic resin powder and a silica powder. The carbonaceous powder and the phenolic resin power are blended in a weight ratio of 95/5-80/20, preferably 92/8-85/15. The silica powder is incorporated in an amount of 0.1-5 wt.%, preferably 0.3-2 wt.%, into the molding material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbonaceous powder molding material containing a carbonaceous powder and a phenol resin as main components. This molding material is suitable for molding a carbon electrode, a conductive separator between fuel cells, and the like.

[0002]

2. Description of the Related Art Conventionally, the production method of the above molding material includes:
(1) A method in which carbonaceous powder and a thermosetting resin are kneaded under heat and pressure, and then pulverized. (2) A method in which carbonaceous powder and phenol resin powder are dispersed in water, mixed, and then dried. (4) Wet mixing carbonaceous powder and thermosetting resin or thermoplastic resin using a solvent followed by drying, or dry mixing without using a solvent.

[0003] However, molded articles molded using the carbonaceous powder molding materials prepared by these methods have various inadequate characteristics. In the method (1), it is necessary to use a resin having the same mass as that of the carbonaceous powder in order to perform uniform kneading, and a molded article formed from such a molding material has a large electric resistance. In the method (2), the molding material must be heated and dried to remove water. However, since the curing reaction of the resin proceeds simultaneously by the heating and drying, high-temperature and long-time drying cannot be performed. Moisture tends to remain in the prepared molding material, and the strength of the molded product is reduced. The molding material of (3) can be easily molded in a cold state, but it is difficult to secure the strength of the molded product. In the method (4), the solvent must be removed by heating and drying the molding material. For the same reason as in the above (2), the solvent is likely to remain, and the strength of the molded article is reduced. On the other hand, in the case of dry mixing, it is difficult to produce a molding material in which carbonaceous powder and resin are uniformly dispersed. When a molding material having such non-uniform dispersion is used, insufficient filling of resin occurs during molding.

[0004]

As described above, the carbonaceous powder molding material obtained by the conventional production method is insufficient in the formability, the low electric resistance of the molded product and the mechanical strength. In view of the above problems, it is an object of the present invention to provide a carbonaceous powder molding material which has good moldability and can contribute to the production of a molded article having low electric resistance and high mechanical strength.

[0005]

In order to solve the above problems, the present invention produces a carbonaceous powder molding material by the following method. That is, it is characterized in that carbonaceous powder and phenol resin powder are blended in a mass ratio of 95/5 to 80/20, silica powder is contained in an amount of 0.1 to 5% by mass, and substantially dry-mixed. The content of the silica powder is preferably 0.3 to 2% by mass, and the mass ratio of the carbonaceous powder to the phenol resin powder is preferably 92/8 to 8%.
5/15. The carbonaceous powder is preferably at least one of expanded graphite powder and flaky graphite powder.

[0006] In order to reduce the electric resistance of a molded article molded using a carbonaceous powder molding material containing carbonaceous powder and a phenol resin as main components, the content of the resin may be reduced. However, if the content of the resin is reduced, the gap between the carbonaceous powder particles cannot be sufficiently filled with the resin.
The mechanical strength of the molded article decreases. So, in general,
The mass ratio of carbonaceous powder and phenolic resin is 70 / 30-5.
It is blended in the range of 0/50 so as to prevent one of the characteristics of electric resistance and mechanical strength from being extremely deteriorated. Therefore, the characteristics of both the electric resistance and the mechanical strength are insufficient.

The molding material produced by the method according to the present invention comprises:
The mass ratio of carbonaceous powder and phenol resin powder is 95/5 to 5/5.
Since the mixing ratio is 80/20 and the content of the resin is limited to a small value, a molded product having a small electric resistance can be molded. And, although the content of the resin is limited to a small amount, a molded article having high mechanical strength can be molded. The reason is presumed as follows.

When a carbonaceous powder molding material having a low resin content is used, the moldability is reduced and the mechanical strength of the molded article is reduced because the resin is sufficiently filled in the gaps formed between the carbonaceous powders. It is not done. The gap is formed because irregularities on the surface of the carbonaceous powder particles become obstacles and the carbonaceous powders cannot approach each other. According to the method of the present invention, the blended silica powder (having a high hardness) removes irregularities on the surface of the carbonaceous powder particles during dry mixing, reduces gaps formed between the carbonaceous powders, And phenol resin powder to promote uniform dispersion.
This contributes to ensuring good moldability and molding a molded article having good mechanical strength, despite the fact that the content of the resin is limited to a small amount.

The lower limit of the content of the silica powder is necessary for effectively removing irregularities on the surface of the carbonaceous powder particles, and the upper limit is set so as not to lower the mechanical strength of the molded product. Is necessary so as not to increase the electric resistance. The limitation of the mass ratio of the carbonaceous powder and the phenolic resin powder is to increase the resin content and not to increase the electric resistance of the molded article, and also to reduce the resin content and not to decrease the mechanical strength of the molded article. Is necessary for In the present invention, dry mixing does not exclude the addition of a small amount of a solvent or the like unless it is necessary to substantially dry after mixing, and such a case is also included in the concept of dry mixing.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the method according to the present invention,
As the carbonaceous powder, flaky graphite powder, expanded graphite powder,
Use artificial graphite powder, carbon fiber powder or the like. Above all,
It is desirable to use flaky graphite powder or expanded graphite powder or a mixture of flaky graphite powder and expanded graphite powder having excellent mechanical strength and conductivity. As the flaky graphite powder, a commercially available product can be used, and the particle size is preferably in the range of 5 to 100 μm. The expanded graphite powder can be manufactured by a known method. For example, scaly graphite is immersed in a mixed solution of sulfuric acid and nitric acid to obtain an acid compound, washed with water, and then rapidly heated at a temperature of 900 ° C. or more to obtain expanded graphite. Thereafter, the desired expanded graphite powder can be obtained by compression molding and pulverization.

Next, as the phenol resin powder, a solid resol-type phenol resin powder obtained by polycondensing phenols and formaldehyde as main components under an alkali catalyst is used. A normal commercial product may be used, but the smaller the particle size, the better, and preferably 75 μm or less.

Further, as the silica powder, fused silica powder, crystalline silica powder, spherical silica powder and the like are used. Ordinary commercial products can be used as they are or after surface treatment, and the average particle size is preferably 0.1 to 50 μm.

By directly dry-mixing these carbonaceous powder, phenolic resin powder and silica powder using a usual shaker, mixer, tumbler, ball mill, thunder crusher, etc., the moldability is excellent and the generation of gas during molding is small. ,
It is possible to obtain a carbonaceous powder molding material which can contribute to molding of a molded article having low electric resistance and good mechanical strength. At the time of the mixing, a solvent, a release agent, a surface treatment agent, and the like may be added as needed in an amount that does not require drying in a subsequent step.

[0014]

Examples 1 to 11 and Comparative Examples 1 to 4 Scale-like graphite powder (average particle size 15 μm) or expanded graphite powder (average particle size 30 μm) and solid resole type phenol resin powder (average particle size 30 μm, JIS- A plate flow of 34 mm according to K-6910) and crystalline silica powder (average particle size of 5 μm) were charged into a Henschel mixer in the composition shown in Tables 1 and 2, and dry-mixed for 3 minutes to obtain the desired carbonaceous powder molding material. Obtained. The amounts of the flaky graphite powder or expanded graphite powder and the phenolic resin powder shown in the table are the mass ratios of the two. The compounding amount of the silica powder is the mass% of the silica powder in the whole.

Conventional Example In the above embodiment, a liquid resol type phenol resin (solid content 3) was used instead of the solid resol type phenol resin powder.
(5% by mass) was charged into a Henschel mixer with the composition shown in Table 2 and mixed for 3 minutes. Upon mixing, methanol was added as a solvent. After mixing, the mixture was dried at 80 ° C. for about 3 hours to remove the solvent to obtain a carbonaceous powder molding material. The amounts of the flaky graphite powder and the phenolic resin shown in the table are the mass ratios of the liquid resol-type phenolic resin and the solid content.

The carbonaceous powder molding material obtained in each of the above examples is charged into a mold, and the temperature is 180 ° C., the pressure is 80 MPa, and the pressure is 10 m.
The product was molded under heat and pressure for 1 minute to obtain a molded product having dimensions of 125 × 10 × 4 mm. JIS-K-6911, JIS-C-2
According to 525, the bending strength and electric resistance of these molded products were measured, and the appearance of the molded products was evaluated. The result is
The results are shown in Tables 1 and 2.

[0017]

[Table 1]

[0018]

[Table 2]

From Tables 1 and 2, it can be seen that the molding materials obtained in the examples according to the present invention have a good molded product appearance due to good moldability.
In addition, it can be seen that it contributes to molding of a molded article having a small electric resistance and a large mechanical strength. In order to achieve the above effect, the carbonaceous powder and the phenol resin powder are mixed at a mass ratio of 95 /
It can be understood from the comparison between Examples 7 to 10 and Comparative Examples 3 and 4 that the mixing must be carried out at a ratio of 5 to 80/20, and that the silica powder must be contained at 0.1 to 5% by mass. It can be understood from the comparison between Examples 1 to 6 and Comparative Examples 1 and 2. The obtained molded article has a sufficiently small electric resistance without firing to carbonize the resin component.

In particular, when the content of the silica powder is 0.3 to 2% by mass, the effect of reducing the electric resistance of the molded article and increasing the mechanical strength is remarkable (Examples 1, 6 and 2). -5). Further, when the carbonaceous powder and the phenol resin powder are blended in a mass ratio of 92/8 to 85/15, the same effect as described above is remarkable (comparison between Examples 7, 10 and Examples 8, 3, 9).

[0021]

As described above, the carbonaceous powder molding material produced by the method according to the present invention has a good formability, an effect of contributing to the molding of a molded article having a small electric resistance and a high mechanical strength. Is great.

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Claims (4)

[Claims] A mixture of carbonaceous powder and phenol resin powder in a mass ratio of 95/5 to 80/20,
What is claimed is: 1. A method for producing a carbonaceous powder molding material, wherein the carbonaceous powder molding material is contained in an amount of about 5% by mass and substantially dry-mixed. 2. The method for producing a carbonaceous powder molding material according to claim 1, wherein the content of the silica powder is 0.3 to 2% by mass. 3. The method for producing a carbonaceous powder molding material according to claim 1, wherein the carbonaceous powder and the phenol resin powder are blended in a mass ratio of 92/8 to 85/15. 4. The method for producing a carbonaceous powder molding material according to claim 1, wherein at least one of expanded graphite powder and flaky graphite powder is selected as the carbonaceous powder.