JPH0127967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an impermeable carbon molded body.

Impermeable carbon molded bodies, which are highly impermeable to gases and liquids, have low electrical resistance and excellent chemical resistance in addition to these properties, making them widely used in industrial fields such as electronics, nuclear power, and aerospace. Among these, due to the above-mentioned characteristics,
It can be suitably used as a separation plate for phosphoric acid fuel cells, which have been attracting attention in recent years.

In a phosphoric acid fuel cell, for example, a pair of porous electrode plates carrying a required catalyst are arranged with a matrix impregnated with phosphoric acid as an electrolyte sandwiched between them, and a separating plate is arranged on the outside of each porous electrode plate. A unit cell is formed and a large number of unit cells are stacked. For example, in the case of a fuel cell called a ribbed electrode type, ribs are formed on the separation plate side of each of the electrodes, and fuel gas or oxidant gas is supplied to the grooves between these ribs. That is, a gaseous fuel such as hydrogen gas is supplied to the grooves of one electrode, and a gaseous oxidant such as air or oxygen is supplied to the grooves of the other electrode.
A battery reaction takes place. Therefore, since one separator plate is supplied with fuel on one side and oxidizer on the other side, the separator plate must be gas-impermeable to prevent these gases from mixing. In addition, in order to function as a current collector for a fuel cell constructed by stacking unit cells as described above, it is necessary to have high conductivity, and to have a thin plate shape with large stack compression. It is necessary to have strength and bending strength.

However, all of the conventionally known impermeable carbon molded bodies are insufficient in the above-mentioned required properties. For example, in JP-A No. 54-20991, fine powder of a cured phenolic resin and an initial condensate of phenols and aldehydes are kneaded, molded and hardened, and then carbonized and fired to produce a mixture containing substantially only vitreous carbon. A method for obtaining a carbon molded body comprising: However, the molded product obtained in this way lacks compactness as a molded product because the resin undergoes significant volumetric shrinkage during the firing process.
Therefore, the gas impermeability is not sufficient, and furthermore, when the thickness is reduced to about 0.4 to 1.5 mm, which is preferable for an actual separation plate, the strength is poor.

On the other hand, various impermeable carbon molded bodies whose carbonaceous substance is graphite are already known. For example, an impermeable carbon molded body is obtained by impregnating the voids of a graphite molded body obtained by carbonization firing with an impregnating agent such as pitch, tar, or resin, and then firing it again to carbonize the impregnating material. Although the method is known,
According to this method, fine cracks often occur in the resulting carbonized and fired product due to the difference in thermal shrinkage rate between the graphite compact and the impregnated material.

Furthermore, JP-A No. 57-72273 discloses a method of molding graphite powder with a phenol resin liquid as a binder and firing it at a high temperature to obtain an impermeable carbon molded body made entirely of graphite. However, when this method is used, fine cracks tend to occur frequently during firing due to the difference in heat shrinkage rate between the graphite in the molded body and the binder, and furthermore, the fired product does not have good quality. In order to provide gas impermeability, it is necessary to impregnate the binder repeatedly, which increases the number of steps and increases the manufacturing cost.

Furthermore, in order to obtain an impermeable carbon molded body with a predetermined shape, the above-mentioned publication describes that a casting method or an extrusion molding method is used. For example, if the separation plate for fuel cells as described above is
In order to obtain a wide thin plate-shaped molded product with a thickness of about 0.4 to 1.5 mm, it is necessary to further cut the molded product larger than the predetermined dimensions, which requires processing costs and is also costly from a material standpoint. In addition to being economical, precision cutting of the entire plate surface is required to obtain the required flatness. As described above, according to the conventional methods, there are various problems in manufacturing an impermeable carbon molded body, including the molding method.

The present invention has been made in order to solve the various problems described above, and is an impermeable carbon molding having excellent gas and liquid impermeability and particularly suitable for obtaining a wide and thin plate-like molded product. The purpose is to provide a method for manufacturing the body.

The method for producing an impermeable carbon molded body according to the present invention involves extruding a kneaded composition containing a thermosetting resin into a flat plate, rolling it with rolls, drying it, and then curing it in a non-oxidizing atmosphere. It is characterized by being carbonized and fired.

In the present invention, the kneading composition containing a thermosetting resin is preferably a kneading composition containing a thermosetting resin liquid and at least one selected from both a thermosetting resin powder and a carbon powder. It particularly preferably contains 100 parts by weight of thermosetting resin powder, 0 to 50 parts by weight of carbon powder, and thermosetting resin liquid.
More preferably, the kneading composition in the present invention is
As will be described later, an organic thickener that is soluble in the thermosetting resin liquid and that can be decomposed and volatilized during carbonization and firing of the cured molded product of the kneaded composition is added to one part of the kneaded composition.
It is a composition containing in the range of ~20% by weight.

In the present invention, as the thermosetting resin liquid, water-based or oil-based adhesives such as phenolic resins, xylene-based resins, melamine-based resins, urea-based resins, epoxy-based resins, and furan-based resins are used.
Note that the thermosetting resin liquid includes not only solutions but also emulsions and suspensions. In the present invention, although not particularly limited, an aqueous resin liquid is preferably used for convenience of drying.

In the present invention, thermosetting resin powder refers to thermosetting resin powder that changes into vitreous carbon by carbonization firing at a temperature of 800 to 2000°C, preferably 1000 to 1500°C in a non-oxidizing atmosphere. Generally, resin powders such as phenolic resins, furan resins, xylene resins, melamine resins, and aniline resins are used, and powders of phenolic resins are particularly preferably used.

In the present invention, as described above, the kneading composition consists of a thermosetting resin powder and/or carbon powder together with a thermosetting resin liquid; Alone,
Or it can be used as a mixture of two or more types. However, it is desirable that the resin components in the thermosetting resin powder and the resin liquid are the same resin. The thermosetting resin liquid facilitates kneading and molding of the composition containing the thermosetting resin powder and carbon powder into a desired shape, and after heating and curing, it is baked together with the thermosetting resin powder to form an amorphous state. Vitreous carbon is formed, and when the kneading composition contains carbon powder, a matrix of carbon powder is formed.

The carbon powder provides a high packing density to the resulting impermeable carbon molded body, and therefore provides an impermeable carbon molded body with excellent properties such as mechanical strength, electrical conductivity, and thermal conductivity. Here, carbon powder means crystalline carbon powder, such as graphite powder, and amorphous carbon powder, such as carbon black, and in particular,
Graphite powder is preferably used. The amount of carbon powder blended is 50 parts by weight or less per 100 parts by weight of thermosetting resin powder. When blending in a large amount exceeding 50 parts by weight, fine cracks are likely to occur when the kneaded composition is molded and carbonized and fired, which is not preferable.

Furthermore, the smaller the particle size of the thermosetting resin powder and carbon powder, the better the impermeability of the resulting molded product to gases and liquids. Therefore, in the present invention, the thermosetting resin powder has an average particle size of 50 μm.
or less, and the carbon powder preferably has an average particle size of 1/2 or less of the average particle size of the thermosetting resin powder. When the average particle size of the thermosetting resin powder exceeds 50 μm, it is difficult to obtain a dense and strong molded body. If the average particle size of the carbon powder is larger than 1/2 of the average particle size of the thermosetting resin powder used, internal stress will occur when the cured thermosetting resin and resin liquid are carbonized and fired, resulting in a similar problem. This will reduce the strength of the molded product.

In the method of the present invention, the moldability of the kneaded product containing preferably thermosetting resin powder and carbon powder together with the thermosetting resin liquid, particularly the slipperiness and shape retention during extrusion molding, and the roll Improves elongation during rolling, prevents the occurrence of minute cracks, and thus
In order to obtain a thin plate-like impermeable carbon molded body with excellent gas impermeability, an organic thickener that is soluble in the thermosetting resin liquid and that can be decomposed and volatilized during carbonization and firing of the molded composition of the kneaded composition is used. It is preferable to mix the agent into the kneading composition. This organic thickener needs to be water-soluble when an aqueous resin liquid as described above is used as the thermosetting resin liquid. Therefore, preferable thickeners include, for example,
Methyl cellulose, carboxymethyl cellulose, carboxymethyl starch, hydroxyethyl cellulose, hydroxypropyl cellulose,
Sodium ligninsulfonate, calcium ligninsulfonate, polyvinyl alcohol, polyacrylate, polymethacrylate,
Guar gum, alginates, etc. can be mentioned.

In order for the thickener to have the above-mentioned effects, it is desirable that the thickener be contained in the kneaded composition at least 1% by weight, but on the other hand, when it is contained in a large amount exceeding 20% by weight. This is not preferable because the impermeability of the resulting molded product is reduced and its strength is also reduced.

In the method of the present invention, the kneaded composition is extruded and rolled to form a molded article of a desired shape, dried to volatilize the solvent of the resin liquid, and then heated to harden the resin.

The method of kneading the mixture consisting of a thermosetting resin liquid, preferably a thermosetting resin powder and/or carbon powder, and an organic thickener is not particularly limited, and may be any conventionally known conventional method. Any kneading device may be used. The kneaded composition is then extruded into a predetermined plate shape using an extruder. For this extrusion molding, a conventional extrusion molding machine is used.
For example, a screw type extrusion molding machine or a plunger type extrusion molding machine can be used. In addition, when using a screw type extrusion molding machine, the preparation of the kneaded product can be performed at the same time.

The extruded product is then rolled by roll rolling, and according to the method of the present invention, rolling is performed at least twice or more times at a rolling rate of 1/5 or more. It is preferable to do so. If rolled to a predetermined thickness at once, air may be drawn into the molded product, or the resin powder or carbon powder may have directionality, resulting in an uneven layer that tends to cause microscopic cracks with directionality. It is.
Furthermore, in the method of the present invention, when rolling is performed multiple times, it is preferable to perform roll rolling at least once in a direction perpendicular to the extrusion direction in order to eliminate the above-mentioned directionality in the molded product.

Furthermore, during roll rolling, the thermosetting resin liquid tends to adhere to the roll surface, making it difficult for the rolled plate to release from the roll after rolling. Therefore, interposing a release sheet between the extrusion plate to be rolled and the roll and/or subjecting the roll surface to a release treatment in advance is a preferred method in order to smoothly obtain the rolled plate. In particular, by forming the release sheet from polytetrafluoroethylene and performing the roll release treatment using this polymer, it is possible not only to obtain a rolled plate extremely smoothly, but also to obtain an impermeable carbon material. This is preferable because the molded article has excellent flatness.

FIG. 1 shows a preferred example of roll rolling according to the method of the present invention. A feed belt 3 and a feed belt 4 made of polytetrafluoroethylene are disposed close to the opposing rolling rolls 1 and 2, and a workpiece 5 to be rolled is fed between the rolling rolls by the feeding belt and rolled to a predetermined thickness. The rolled plate 6 is transported out by a delivery roll. In order to prevent the rolling plate from adhering to the upper and lower rolls, release sheets 7 and 8 made of polytetrafluoroethylene sheets are appropriately supported, and while being in contact with the rolling rolls, release sheets 7 and 8 are appropriately supported. They are forced to travel at the same speed.

The rolled plate thus rolled is then dried to volatilize the solvent of the thermosetting resin liquid, and then heated to harden the thermosetting resin. The temperature for curing this thermosetting resin is appropriately selected depending on the resin used, the shape of the molded product, etc., but is usually 100 to 180°C. Incidentally, after the thermosetting resin is heat-cured to obtain a molded body, the molded body may be further impregnated with a resin liquid, dried, and heat-cured, if necessary.

The molded body thus formed is then
Carbonized and fired in a non-oxidizing atmosphere. As the atmosphere, helium, argon, nitrogen, etc. are usually used. Heating for carbonization and firing to obtain an impermeable carbon compact is described, for example, in the above-mentioned JP-A-57-
As stated in Publication No. 72273, approximately 200℃
From about 500°C to about 700°C, it is desirable to heat at a slow temperature increase rate of about several tens of degrees C/hour. Thereafter, the impermeable carbon molded body of the present invention is obtained by heating to a predetermined carbonization firing temperature at a heating rate within the above range or higher and firing for a certain period of time. The carbonization firing temperature is required to be at least 800°C, preferably in the range of 1000 to 1500°C.
The required firing time depends on the shape and dimensions of the molded product, and virtually all of the thermosetting resin is carbonized.
The firing time may be sufficient to change into vitreous carbon, but it is usually several hours to several tens of hours. During this carbonization firing, the organic thickener is decomposed and volatilized.

In the present invention, in order to further increase the strength of the obtained molded product, a substance having good bonding properties to the carbon matrix of the molded product, for example, a metal carbide such as silicon carbide, titanium carbide, or tungsten carbide, is used. , carbon fiber, etc. can be added in appropriate amounts to a molding raw material consisting of thermosetting resin powder, carbon powder, and thermosetting resin liquid, and this can be molded, dried, and fired as described above.

As described above, according to the present invention, since the kneaded composition is extruded and further rolled, a thin plate-like impermeable carbon molded body can be easily obtained, and in particular,
By adding an organic thickener to the kneading composition,
Since the formability in extrusion molding and roll rolling is improved, a thin plate-like impermeable carbon molded body can be obtained without the occurrence of minute cracks. In this case, further according to the present invention, by performing roll rolling a plurality of times, and preferably at least once in a direction perpendicular to the extrusion direction, the occurrence of fine cracks can be more effectively prevented. . Thus, according to the method of the present invention, unlike conventional methods, it is not necessary to cut the molded product again to the required thickness after firing, or to cut the entire surface to obtain the required flatness. A plate-shaped impermeable carbon molded body having high strength, uniformity, and excellent plate thickness accuracy and flatness can be obtained.

Further, according to the method of the present invention, a kneaded composition containing a predetermined amount of an organic thickener and carbon powder is molded with respect to thermosetting resin powder, and carbonized and fired, thereby making the carbon powder thermosetting. It is uniformly dispersed in the glassy carbon matrix formed by carbonizing and firing the resin, giving a dense carbon molded body without cracking, and the impermeable carbon molded body thus obtained is impermeable to gases and liquids. Not only does it have excellent properties, but it also has excellent strength such as laminated compressive strength and bending strength, as well as electrical conductivity.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in the following, parts mean parts by weight.

Example 1 100 parts of phenol-formaldehyde resin powder with an average particle size of 39 μm, 10 parts of graphite powder with an average particle size of 12 μm with 99% or more of fixed carbon, 9 parts of carboxymethyl cellulose and 3 parts of hydroxypropyl cellulose as water-soluble organic thickeners. , and 23 parts of an aqueous phenolic resin liquid (concentration 50% by weight) were kneaded and extruded into a plate having a cross section of 500 mm in width and 20 mm in thickness using a plunger extruder. Then set this to 400
Using a 2-mm diameter rolling mill, the first stage rolls the product to a thickness of 7.0 mm in the direction perpendicular to the extrusion direction, the second stage rolls the product to a thickness of 3.2 mm in the extrusion direction, and the third stage rolls the product to a thickness of 3.2 mm. It was rolled to a thickness of 1.0 mm in a direction perpendicular to the extrusion direction.

Next, this rolled plate was placed in a heat insulating tank at 40°C for 8 hours, and then heated at a temperature of 110°C for 12 hours to harden the thermosetting resin. After that, charge it into the firing furnace,
Heating under argon atmosphere at a heating rate of 40°C/hour to a temperature of 700°C, then to a temperature of 130°C.
After heating at a rate of 100° C./hour, the mixture was maintained at this temperature for 2 hours to obtain a thin plate-like impermeable carbon molded body having a thickness of 0.6 mm, a width of 500 mm, and a length of 500 mm.

The molded body thus obtained had a flatness within ±0.02. In addition, when there was a differential pressure of 1 Kg/cm ² , the nitrogen permeability was 4×10 ^-4 cc/min·cm ² , the electrical resistivity was 3.5×10 ^-3 Ωcm, and the three-point bending strength was 721 Kg/cm ² . .

Example 2 An impermeable carbon molded body with the same dimensions was obtained in the same manner as in Example 1, except that a furan resin liquid (48% by weight) was used instead of the phenol resin liquid as the resin liquid. Ta.

This compact also had a flatness within ±0.02. In addition, the nitrogen permeability is 6×10 ^-4 cc/min・cm ² , the electrical resistivity is 3.8×10 ^-3 Ωcm, and the three-point bending strength is 704 Kg/
It was warm in ^cm2 .

Example 3 The same procedure as in Example 1 was carried out except that the amount of the mixture of carboxymethyl cellulose and hydroxypropyl cellulose as a water-soluble organic thickener was varied in the kneaded composition. A transparent carbon molded body was obtained. The gas permeability of the molded body thus obtained was examined. The results are shown in Figure 2. When the amount of thickener blended is less than 2% by weight of the kneaded composition, not only the gas permeability is poor, but also many fine cracks are observed on the surface of the molded product. It was confirmed that when the amount exceeds 20% by weight of the kneaded composition, the density of the obtained molded product is low, porous defects are observed, and the gas permeability is also poor.

Example 4 100 parts of the same phenol-formaldehyde resin powder as in Example 1, 23 parts of carbon black, the same aqueous phenol resin liquid as in Example and 8 parts of methylcellulose were kneaded in the same manner as in Example 1, and this kneaded composition was prepared. An impermeable carbon molded body was obtained by processing in the same manner as in Example 1.

The nitrogen permeability of this molded body is 10 ^-4 cc/min.cm ² , the electrical resistivity is 7×10 ^-3 Ωcm, and the three-point bending strength is 724 kg/cm 2 .
It was warm in ^cm2 .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a rolling apparatus suitable for carrying out the method of the present invention, and FIG. 2 is a graph showing the relationship between an organic thickener and the gas permeability of the impermeable carbon compact obtained. . 1, 2... Rolling roll, 3... Feeding belt, 4... Feeding belt, 5... Rolled object, 6
...Rolled plate, 7...Release sheet.

Claims (1)

[Scope of Claims] 1. After extrusion molding a kneaded composition containing at least one selected from thermosetting resin powder and carbon powder and thermosetting resin liquid into a flat plate shape, roll rolling is performed. is carried out twice or more, and the rolling rate per time is 1/5 or more, and then,
1. A method for producing an impermeable carbon molded body, which comprises drying and hardening and then carbonizing and firing in a non-oxidizing atmosphere. 2. The method for producing an impermeable carbon molded body according to claim 1, wherein the kneaded composition is rolled at least once in a direction perpendicular to the extrusion direction.