JPH042546B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a porous carbon material that is excellent for various uses such as electrode materials, overmaterials, and diffusers for blowing diffusion, and in particular, as electrodes for fuel cells. A conventional method for producing porous carbon materials is to mix and knead aggregates such as petroleum coke with a binder such as tar pitch and a foaming material, mold the mixture, and then sinter or graphitize it. Ammonium salts, carbonates, sawdust, etc. are used as foaming materials.
However, the carbon material produced by this method has the disadvantage that not only its mechanical strength is weak, but also a portion of the additive remains. Furthermore, the fuel electrode is required to have a specific pore distribution, but it is difficult to control the pore distribution using the above method. The electrode of a fuel cell is required to hold an electrolyte in its pores and to allow reactive gases such as hydrogen and oxygen to permeate therethrough. It is said that the former should have relatively large pores with uniform diameters distributed, and the latter should have pores with small diameters distributed. It is also desirable that these pores are uniformly distributed. In other words, there are two peaks with sharp pore distribution. It has been difficult to create conventional porous carbon materials with such a pore distribution. An object of the present invention is to facilitate control of the pore distribution of a porous carbon material including such a fuel cell electrode. As a result of researching various additives for this purpose, the inventor of the present invention found that by using a thermosetting resin as a binder for the carbon material, adding styrene resin powder to this, and adjusting the particle size of this powder, It was discovered that the pores of carbon materials can be easily controlled. That is, the present invention is a method in which a thermosetting resin is added to carbon powder such as graphite, and styrene resin powder whose particle size has been adjusted is further added, the mixture is thoroughly kneaded, and then molded, and the molded product is hardened and fired. . The carbon powder may be coke powder, graphite powder, carbon black, etc., and is selected depending on the use of the porous carbon material. Graphite powder is used for materials that require electrical conductivity, such as electrode materials. Also, for overfill materials, coke or carbon black powder may be used. The finer the particle size of the carbon powder, the higher the strength of the carbon material. Normally, 200 mesh or less is better, and if you want to increase the strength of the carbon material, 325 mesh or less is better. Thermosetting resin is used as the bonding material. Although tar pitch is often used as a general carbon material, it is not preferred in the present invention. This is thought to be related to the mechanism of action with the styrene resin during the heating process. Pores cannot be controlled if the binder melts at the same time as the styrene resin and becomes a single unit. Tar pits are considered undesirable because they melt in almost the same temperature range as styrene resins. Among thermosetting resins, phenolic resins are particularly preferred. The thermosetting resin must be well miscible with the carbon powder;
It is necessary that the mixed paste has good moldability and a high carbonization rate. For this reason, a resin that is liquid at room temperature and has a certain degree of viscosity is desirable. Liquid phenolic resins with a viscosity of 27,000 centipoise or higher are particularly suitable. Styrene resins include styrene and α-
Polymers of styrene derivatives such as α-substituted styrene such as methylstyrene, vinyltoluene, and substituted styrene such as 0-chlorostyrene, and monomers mainly copolymerizable with these monomers, such as acrylonitrile and acrylic acid. and vinyl compounds such as methacrylic acid, their methyl or ethyl esters, vinyl heterocyclic compounds such as vinylpyridine and vinylcarbazole, butadiene,
One or two conjugated diene compounds such as isoprene
Interpolymers obtained from monomer mixtures of two or more species and thermoplastic resin compositions containing the above-mentioned polymers as a substantial component can be used. These are then used in powder form. The powder used is one made by crushing a molded body or one made by spraying a polymer. The particle size is selected according to the pore distribution of the intended product. If mixed powder of each particle size is used,
A porous carbon material having a pore distribution corresponding to this can be obtained. Although the particle size of the styrene resin powder and the size of the pores in the carbon material are not exactly the same, there is a certain correspondence, so it is possible to create the desired pores in the carbon material by adjusting the particle size of the resin powder. It is. The particle size of the powder is generally in the range of 42 to 325 mesh. In the present invention, since a thermosetting resin and a styrene resin are combined, the thermosetting resin is first hardened during the heat treatment process, and the skeleton of the molded article is formed. It is thought that as the material is further heated, the styrene resin powder dispersed therein melts, carbonizes the skeleton, decomposes and volatilizes, and leaves pores. Since the size of the pores can be controlled by the particle size of the styrene resin powder, it is considered that the powder particles are not melted and agglomerated. It is presumed that the presence of a considerable amount of carbon powder in the compact is also responsible for this. Powders of polyethylene, polypropylene, vinyl chloride, etc., instead of styrene resin did not have the above effect. The reason for this is thought to be that these resins had a large amount of residual carbonization during the firing process and the resin powder itself became porous, making it impossible to create pores with the desired diameter. The mixing ratio of each of the above raw materials varies depending on the intended product, but in order to use it as a porous material and to have practical strength, carbon powder is generally
Suitable amounts are 15 to 30 parts by weight of thermosetting resin powder and 10 to 15 parts by weight of styrene resin powder per 100 parts by weight. If the amount of thermosetting resin is too large relative to the carbon powder, the base material will become dense and will not function as a porous material, and if it is too small, the strength characteristics of the porous material will be significantly reduced. If the amount of styrene resin is too large, the strength of the carbon material will naturally decrease, and if it is too small, sufficient pores will not be formed. The mixture is sufficiently kneaded using a mixer such as a Henschel mixer or a pressure kneader to form a uniform paste. A suitable temperature range is room temperature to 50°C. Forming may be done by molding, but if it is a plate-like object, it is more efficient to do it continuously by passing it between rolls or the like. At this time, if the roll is grooved, a grooved molded plate can be obtained, which is suitable for battery electrodes. The molded body is cured according to a conventional method. When a phenolic resin is used as the thermosetting resin, a dehydration condensation reaction occurs during the curing reaction. Furthermore, since water is included as a solvent, if this water is rapidly vaporized by heating, it will cause tissue deterioration. To prevent this, it is effective to pressurize the atmosphere to a pressure higher than the water vapor pressure at the processing temperature. This increases the strength approximately twice as much as when no pressure is applied. In the case of phenolic resin, curing may be performed at about 130 to 150°C for 1 to 5 hours. And in this temperature range, the pressure is 2 to 5 Kg/cm ²
The position is appropriate. The cured compact is fired in a non-oxidizing atmosphere. This firing requires sufficient time to raise the temperature. Desirably it is 20°C/Hr or less.
The firing temperature is determined depending on the intended use of the product, but if it is something like an overfill material, it can be carbonized at around 800 to 1000℃, and if high conductivity is required like an electrode, it can be graphitized. You can also do that. Example 325 mesh of artificial graphite powder was used as the carbon powder. The binding material is a liquid phenolic resin with a viscosity of approximately 30,000 centipoise (manufactured by Showa Union Gosei Co., Ltd.).
BXL-274) was used. The styrene-based resin used was polystyrene (trade name: S-Bright GP) which was pulverized to adjust the particle size. These raw materials were mixed in the proportions shown in Table 1 and kneaded at room temperature using a pressure kneader to form a paste. This paste was passed between rolls and formed into a plate shape. The thickness is approximately 4 mm. The molded body has an air pressure of 3
Kg/cm ² and held at 140°C for 2 hours to cure.
It was then heated to 800° C. for 48 hours under a N ₂ gas atmosphere. Table 2 shows the properties of the obtained porous carbon plate. (Measurement of pores is by mercury intrusion method).

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Claims (1)

[Scope of Claims] 1. A method for producing a porous carbon material, which comprises mixing carbon powder, styrene resin powder, and thermosetting resin powder, kneading, shaping, then hardening and firing. 2 Claim 1 for electrodes of fuel cells
A method for producing a porous carbon material as described in Section 1. 3. The method for producing a porous carbon material according to claim 1, wherein the thermosetting resin is a phenolic resin. 4. The method for producing a porous carbon material according to claim 1, wherein the curing is performed under pressure with gas.