JP4004180B2 - Method for producing carbon / graphite composite molded body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention molds and carbonizes a fine particle mixture mainly composed of carbonaceous carbon compound fine particles having self-sintering properties and at least one kind of graphitic carbon fine particles selected from the group consisting of natural graphite and artificial graphite. Do Carbon / graphite composite molded body Manufacturing method About.
In particular, the present invention is a carbon / graphite composite molding that satisfies the characteristics required for separator plates of solid polymer type and phosphoric acid type fuel cells such as bending strength, electrical conductivity, thermal conductivity, gas permeability, and corrosion current. body Manufacturing method Is to provide.
Furthermore, the present invention can be put to practical use by omitting complicated post-processing steps by simply carbonizing a molded product having a complicated shape found in a grooved separator plate of a fuel cell with a press. Carbon / graphite composite molded body Manufacturing method Is to provide.
[0002]
[Prior art]
Various methods for producing composite materials composed of carbonaceous carbon and graphitic carbon have been proposed, and at least one kind of carbonaceous carbon powder selected from organic carbon and carbonaceous carbon, artificial graphite, and natural graphite were selected. Many use at least one type of graphitic carbon powder.
Although there are various purposes for combining carbonaceous carbon and graphitic carbon, it is generally possible to impart the characteristics of graphite to a molded body obtained by firing at around 1000 ° C. by combining these. In addition, the weakness of graphitic carbon can be compensated with carbonaceous carbon.
[0003]
For example, in the examples described in JP-A-59-26907, 20 parts by weight of a resol-based phenol resin are mixed at room temperature with 80 parts by weight of graphite fine powder containing 99% of a particle size of 44 μm or less previously heat-treated at 3000 ° C. The paste thus obtained is roll-formed (peripheral speed 0.3 m / min) to form a 4 mm-thick sheet, which is cured, and then heat-treated at a maximum temperature of 1000 ° C. at a rate of 1000 ° C./10 hours to obtain a product. Pressure curing after roll forming (0.1kg / cm ² ) Product characteristics when
Size: 300mm x 400mm x thickness 3.2mm
Bulk density: 1.703 (g / cm ^Three )
Specific resistance: 165 × 10 ^-Five (Ω · cm)
Bending strength: 323 (kg / cm ² )
Air permeability: 3.5 × 10 ^-Five (Cm ² / Sec)
It is described that it was.
[0004]
In this publication, for the purpose of combining organic carbon and graphitic carbon, the graphitic carbon shares the low specific resistance value required for the phosphoric acid fuel cell separator plate, and the low air permeability is reduced by the carbide of resol-based phenolic resin, ie, glassy. The carbon is assigned to give the desired function.
The publication also discloses a method of forming a grooved separator plate by using a grooved roll or a grooved steel plate that is suppressed during hardening.
The combination of a flat separator plate and a grooved porous electrode plate is common in a phosphoric acid fuel cell at a practical level in recent years. In a system using organic carbon that has a large shrinkage during carbonization, such as a phenol resin, a groove is used. It is clear that it is not suitable for the production of a complex shaped product such as a separator with a flange.
[0005]
One of the inventors of the present invention disclosed in JP-A-61-199737, quinoline insoluble matter; 70% by weight or less, mesophase content; 40% or more, heating melting temperature upper limit; carbonization yield at 400 ° C. and 1000 ° C .; A powder obtained by mixing a mesophase-containing pitch having a property of 70% and graphite powder is preferably heated to a temperature equal to or higher than the heating and melting temperature of the pitch and then pressure-molded, and then fired at an appropriate temperature in an inert atmosphere. , Volume change during firing at 1000 ° C .; dimensional stability with linear shrinkage of less than 1% between 3% or less raw product and fired product, volume resistivity: 5.0 mΩ · cm, flexural strength ;> 200kg / cm ² The manufacturing method of the graphite molded object which has the characteristic suitable for a separator board is proposed.
[0006]
Japanese Patent Publication No. 7-35250 discloses a tar fraction containing a mesophase pitch precursor in which fine graphite powder is suspended as a method for producing a graphite molded body having the same characteristics as disclosed in JP-A-61-199737. A carbon fraction obtained by blowing off a light fraction in a fraction by blowing an inert gas and heating to 350 to 500 ° C. to deposit a mesophase-containing pitch containing 5 to 90% by weight of a quinoline soluble component on the surface of the graphite fine powder. A method using a precursor is disclosed.
[0007]
In Japanese Patent Publication No. 4-75189,
(1) suspending graphite powder in a tar fraction containing a mesophase pitch precursor;
(2) A step of obtaining a carbonaceous precursor in which mesophase pitch is produced on graphite particles by heat-treating the above suspension with an inert gas (eg, nitrogen gas, carbon dioxide gas, argon, etc.) at 350 to 500 ° C. ,
(3) A step of pressure-molding the carbonaceous precursor at 400 to 800 ° C. to form a generated shape,
(4) A step of carbonizing or graphitizing the generated shaped body in an inert atmosphere
A method for producing a graphite molded body is disclosed.
[0008]
This manufacturing method discloses a method of hot pressing as a technique for forming a carbonaceous precursor to obtain a formed body.
[0009]
(3) shows the distortion and residual stress of the carbonized product caused by subtle differences in the linear shrinkage rate generated in the process of firing a raw product obtained by molding a carbonaceous precursor powder into a complex shape such as a grooved separator plate. It can be eliminated by the hot press process shown.
In JP-B-6-102630, the step (3) described in JP-B-4-75189 is omitted, and a graphite mold or the like is used, and a vacuum or an inert gas atmosphere is used. Discloses a method for producing a graphite molded body by pressure molding.
[0010]
According to this invention, it becomes possible to mold a grooved separator having a large number of grooves perpendicular to the front and back surfaces. At the same time, the characteristics required for the fuel cell separator plate such as gas impermeability, thermal conductivity and electrical conductivity can be satisfied.
Japanese Patent Application Laid-Open No. 62-187167 discloses a method for producing a graphite molded body excellent in gas impermeability, which can be used as a gas separation plate of a phosphoric acid fuel cell, in a simplified process. Quinoline insoluble matter obtained by heat treatment of decomposition residue, etc. at about 350 to 550 ° C .; 95 wt% or less, mesophase content; 35 wt% or less, carbonization yield at 1000 ° C .; mesophase content of 70 wt% or more The pitch is added in an amount of 5 to 60 parts by weight with respect to 100 parts by weight of graphite powder selected from flaky natural graphite or artificial graphite, and then the mixture is heated at a rate of temperature rise of 150 to 3000 ° C./in vacuum or under an inert gas atmosphere. Heat to 700-3000 ° C in about an hour, pressure 50-2000kg / cm ² A method of pressure forming to the extent is proposed.
Japanese Patent No. 2566589 discloses the production of a carbon-based composite molded body raw material comprising one or more materials selected from graphitic carbon, carbonaceous carbon, inorganic compounds, metals and metal compounds, and mesophase-containing pitch. In the method
(1) A slurry is prepared by suspending in a tar fraction containing one or more materials selected from graphitic carbon, carbonaceous carbon, inorganic compounds, metals and metal compounds and a mesophase pitch precursor. Process,
(2) The suspension slurry was selected from the group consisting of (a) an aliphatic or alicyclic hydrocarbon having 5 to 20 carbon atoms and (b) an aliphatic or alicyclic ketone compound having 3 to 5 carbon atoms. One or more solvents are added at a ratio of solvent ratio (Sn) of 2 to 15 (solvent weight / raw material tar weight) and treated at 0 to 60 ° C. to thereby include a polycyclic aromatic containing a mesophase precursor on the surface of the material. The slurry obtained by precipitating the polymer and separating the treatment solvent was washed at 0 to 60 ° C. at a ratio of solvent ratio for rinsing (Sr) of 1 to 15 (solvent weight / raw material tar weight), Separating a mixture comprising a polycyclic aromatic polymer containing a mesophase precursor;
(3) A step of heat-treating the mixture at 350 to 520 ° C. in an inert gas atmosphere to form a polycyclic aromatic polymer into a mesophase-containing pitch,
A method for producing a raw material of a carbon-based composite molded body characterized by using these three steps is disclosed.
[0011]
In this method, not only graphite carbon and carbonaceous carbon but also SiC, AlN, B _Four C, TiC, Si _Three N _Four It is possible to completely coat the surface of a powder such as a mesophase-containing pitch. Therefore, it has the characteristic that a uniform pitch coating | cover can be performed on the surface of several composition containing powder. Moreover, acetone, heptane, etc. are mentioned as a solvent used, but it has the characteristics which can be collect | recovered and reused easily.
In addition, in Patent No. 2566595, a complex shaped precision molded body that has not been conceived in the past is taken as an example of a composite powder made of graphitic carbon coated with a mesophase-containing pitch prepared in the above-mentioned Patent No. 2566589. Discloses a method for granulating carbon powder, which is essential for carbonization and mass production.
[0012]
The granulating method comprises a binder comprising a self-sintering carbon-based powder and optionally a carbon-based powder containing at least one powder selected from the group consisting of graphitic carbon, carbonaceous carbon, metal and inorganic compounds. And a method of granulating the slurry dispersed in water in the presence of a wetting agent by spray drying in heated air that may contain heated steam.
(1) The binder is an organic compound that does not form a foam when carbonized at 1000 ° C. and has a residual carbon yield of 10% by weight or more, and the amount used is 0 with respect to 100 parts by weight of the carbon-based powder. .01 to 5 parts by weight,
(2) The wetting agent is a nonionic surfactant having a cloud point range of 25 ° C. or higher, and the amount used is 0.01 to 3 parts by weight with respect to 100 parts by weight of the carbon-based powder. There is,
It is characterized by.
[0013]
The powder to be used for granulation can be any powder obtained by the above-mentioned prior invention of the present inventor.
A granulated product having an average particle diameter of 114 μm obtained by granulating a carbon-based composition having a scaly graphite surface coated with a mesophase-containing pitch having a quinoline insoluble content of 97% by weight has a bottom having a thickness of 1.2 mm. A hollow box-shaped thin-walled product having partitions between vertical and horizontal characters could be continuously produced with a rotary press. Further, the product obtained by carbonizing to 1000 ° C. at a heating rate of 9 hours was finished to the same dimensions as the mold dimensions, and no shrinkage cracks were observed at the bottom part, and a yield rate of nearly 100% was obtained.
Patents Nos. 2566589 and 2566595 are incorporated into the United Kingdom (308824: 922.12.23), US (4985184: 91.115), Germany (P3876913.1; 922.113), and France (308824). : 92.12.23) Registered in 4 countries.
[0014]
In JP-A-6-192660, when a pitch precursor composition or a mixture of the pitch precursor composition and aggregate is heat-treated, a special static agent is optionally added in the presence of a dispersant. The manufacturing method of the pitch containing composition which processes by combining a radiant heating technique with an in-situ reaction container is disclosed.
[0015]
In this method, various dispersants are used that have an affinity between a locally hydrophilic material containing many surface active sites such as hydroxyl groups and carboxyl groups on the crystal surface of fine graphite particles and a lipophilic mesophase-containing pitch. As a result, it can be improved epoch-makingly, and the composite characteristics have been dramatically improved. Moreover, by using radiant heating well, by suppressing the variation in the large-scale reactor of the heat treatment temperature, which is an important governing factor of the composite compact strength, to ± 2 ° C or less, it is possible to produce homogeneous composite materials on an industrial scale. Mass production became possible.
[0016]
[Problems to be solved by the invention]
The separator plate manufacturing technology that satisfies the characteristics required for the grooved separator plate of the phosphoric acid fuel cell disclosed in the prior patent of the present inventor has been attracting attention in recent years due to global environmental problems. It can be easily understood that the characteristics of the grooved separator plate, which is a member used therefor, can be easily understood because the solid polymer type has a lower operating temperature of around 80 ° C. than the phosphoric acid type 170-200 ° C. .
[0017]
However, since the prior art is a production technology aimed at a grooved separator plate of a phosphoric acid fuel cell as a large power generator, a solid polymer fuel cell as a power generator for automobiles or a small stationary generator for home use In order to meet the low prices required by the company and the huge production volume of millions or more, it is necessary to overcome various hurdles.
In particular, according to the prior art disclosed by the present inventor, the cost for producing mesophase-containing pitch-coated graphite composite powder suitable for a fuel cell separator plate is a significant wall.
Mesophase-containing pitch-coated graphite exhibits favorable characteristics by hot pressing at 800 to 900 ° C., but there are problems in mass productivity and production equipment.
In addition, a granulation method suitable for mass automatic unattended press molding is an epoch-making technique, but it requires a spray drying apparatus with poor productivity, leading to an increase in cost.
[0018]
On the other hand, products made of a mixture of mesophase-containing pitch powder and graphite powder have a problem to be solved in terms of productivity and cost because they require a heating press at 300 ° C. or higher.
That is, the problem to be solved by the present invention is to eliminate the difference between the low-priced product price demanded by the times and the product price created by the existing technology by creating a new technology.
[0019]
[Means for Solving the Problems]
The inventors of the present invention conducted intensive research to create a new technique for producing a low-priced product and exhibiting the physical properties shown in the prior art.
The following requirements concerning productivity and physical properties required for a separator plate with a polymer electrolyte fuel cell groove as a major premise of research and development must be satisfied.
productivity
(B) The ability to mass-produce 200-500 mm square and 1-5 mm thick plates.
(B) A fuel and air supply groove having a depth of 1 mm and a width of 1 to 2 mm can be easily installed on the plate surface or both the front and back surfaces, preferably by a single press molding.
Physical property value
(C) Mechanical dimensions such as surface smoothness and warpage
(D) Bending strength, compressive strength
(E) Volume resistivity
(F) Corrosion current
(G) Gas permeability
[0020]
The present inventors considered that low-priced products can be mass-produced by satisfying the following items regarding materials and production techniques.
(1) Products that combine materials that are mass-produced and stably supplied to the market
(2) Granulated powder that can be used for automatic unmanned press operation
(3) Build all processes with high production efficiency equipment
It is obvious to those skilled in the art that high cost is unavoidable in the cutting method of a complex-shaped graphite molded body and the manufacturing method of a glassy carbon molded body in the prior art.
[0021]
The inventors have obtained a formed form from graphite powder and self-sintering carbonaceous compound powder that are mass-produced and supplied to the market abundantly or can be supplied on demand. Based on the basic concept of producing solid polymer type and phosphoric acid type fuel cell separator plates by a simple method to obtain a product by carbonization, we proceeded with intensive studies.
[0022]
If a granulated product of mesophase-containing pitch-coated graphite is used among the prior arts of the present inventor, desired product productivity and carbonized product property values can be obtained. On the other hand, in this technique, it is necessary to newly provide a pitch coating process, and there is a problem that an extremely expensive material must be used in accordance with the production amount. On the other hand, in the method of molding a mesophase-containing pitch mixed with graphite powder in a grinding mill without the pitch coating process, the productivity is low, and in order to obtain the desired bending strength, the cost increase factor that requires hot press molding There is.
[0023]
One of the inventors of the present invention disclosed in Japanese Patent Application No. 11-24537, as a technique for developing high strength in a mixed system of ceramic powder and metamorphic coke powder, the metamorphic coke powder was made into fine particles of about 3 μm and ceramic powder of about 1 μm. A method of uniform mixing was proposed. In this method, the ceramic strength was coated with the modified coke fine particles, and the bending strength could be increased to an unprecedented level.
However, in the method of the present invention, when the formed body becomes a sintered molded body, linear shrinkage of 10% or more occurs. Therefore, the formed body and the carbonized molded body targeted by the present invention have the same dimensions, that is, a molded body having substantially zero linear shrinkage. It was not directly related to the manufacturing method.
[0024]
The present inventors produce an excellent carbon / graphite composite molded body by solving the above-mentioned universal problems related to the production of a carbon / graphite composite molded body without using expensive equipment and raw materials. As a result of intensive research, we have been able to solve the problems described below by the manufacturing method at once, even if the prior art can be partially solved by combining simple operating conditions. As a result, the present invention was completed.
[0025]
In the present invention, 10-50 parts by weight of self-sintering carbonaceous compound fine particles having an average particle size of 10 μm or less, preferably 1-7 μm, and graphitic carbon fine particles 90 having an average particle size of 10-70 μm, preferably 15-50 μm. Water-soluble carbonaceous carbon compounds such as polyethylene glycol, sucrose, methylcellulose, and polymer flocculants, and graphite, if necessary, in a mixture obtained by stirring and mixing fine particles mainly comprising -50 parts by weight in a dry state A granulated product having a maximum particle size of 0.5 mm or less by adding an aqueous solution or water containing at least one additive for mutual adhesion selected from a group of compounds having adhesiveness to carbonaceous materials and stirring and granulating the mixture. After the product is dried, it is filled with a die having a die pressing plate with various shapes as necessary, and the resulting shaped product is molded under an inert atmosphere 1100. 1800 ° C., sintered at preferably 1200 to 1600 ° C. It is characterized by Carbon / graphite composite molded body Manufacturing method Is a summary.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The embodiment will be described roughly by dividing into raw materials, mixing / granulation, molding, and firing system.
Raw material system
(1) As the graphitic carbon fine particles, at least one kind of graphitic carbon fine particles selected from the group consisting of scale-like and earthy natural graphite and artificial graphite can be used.
Artificial graphite is more preferable in terms of both physical properties and supply stability of graphite.
Examples of preferable artificial graphite include KS series manufactured by Timcal Corporation. Various artificial graphites supplied from the graphite molded body manufacturing industry can also be selected.
(2) The particle diameter of the graphite fine particles can be widely selected from the viewpoint of moldability.
However, from the viewpoint of simultaneously satisfying various physical properties such as volume resistivity, thermal conductivity, strength of the molded body, dimensional stability and gas permeability of the formed and fired molded body, the object of the present invention Will not match.
The average particle size of the graphite fine particles can be selected from the range of 10 to 70 μm, preferably 15 to 50 μm.
When the shape of the groove portion of the separator plate becomes finer and the requirements for dimensional accuracy and gas permeability become severe, small particle size graphite is selected. The smaller the graphite particle size is, the more the self-sintering carbonaceous compound is selected from the strength development mechanism described later, or the average particle size is selected to be small.
Typical marketed products that can be used in the present invention include KS44 from Teimcal for artificial graphite, and CPB and CPB refined products from Nippon Graphite for natural graphite.
[0027]
(3) The graphite content can be selected widely, but 90-50 parts by weight of the mixture, more preferably 85-60 parts by weight, in order to set the dimensions of the formed product and the carbonized molded product to be the same. More preferably, 80 to 65 parts by weight can be selected.
This graphite content range is a factor governed by the physical properties of the self-sinterable carbonaceous compound during carbonization, and is comprehensively determined based on the characteristics of the self-sinterable carbon compound.
As a matter of course, there is room for improving the graphite-derived characteristics such as electric conductivity and thermal conductivity as the graphitic carbon content increases. However, if the sintering characteristics of the self-sintering carbonaceous compound and the average particle size described later are inappropriate, the graphitic carbon may swell during carbonization, making it impossible to take advantage of the characteristics inherent to the graphitic carbon. So it needs proper design.
[0028]
(4) Various self-sintering carbonaceous compounds that can be used in the present invention are commercially available. β A self-sintering carbonaceous compound having a component (quinoline-soluble toluene-insoluble component) content of 3 to 30% by weight, preferably 5 to 25% by weight, is used as a starting material for the carbon / graphite composite molded body of the present invention. it can.
β If the component content is too small, the desired strength cannot be expressed within the required range of the predetermined physical property values. On the other hand, if it is too high, it melts at 100 ° C. or lower, such as coal tar, which causes the shape of the molded body to be retained and the self-sintering carbonaceous compound to be unevenly distributed.
[0029]
Examples of commercially available self-sintered carbonaceous compounds that can be used in the present invention include TGP series, MPC series, Osaka Gas Co., Ltd. MCMB, Kawasaki Steel Corporation KMFC, Kureha Chemical Co., Ltd. KS, and the like.
Also, the high softening point pitch β If the component content is satisfied, it can be used.
Required by the present invention β As long as the component content range is satisfied, there is no problem whether the self-sintering carbonaceous compound is made of coal tar or petroleum heavy oil as a starting material.
Moreover, there is no problem even if it is a material whose oxygen content is increased by air oxidation such as MPC-1 manufactured by Osaka Kasei Co., Ltd.
[0030]
(5) The average particle size of the self-sintering carbonaceous compound is an important factor governing the bending strength, gas permeability and corrosion current value of the carbon / graphite composite molded body in the practice of the present invention. The particle size effect of the product “TGP3000” marketed by Osaka Kasei is shown below.
TGP3000 is β It is positioned as a pulverized product (300 mesh sieve product) of a self-sintering mesophase-containing pitch having a component content of 21%.
Even if TGP3000 is used as it is, a sintered body can be obtained.
However, the bending strength of the 1000 ° C. fired product of the composite formed body obtained by mixing with “TGP3000 (300 mesh under sieve) / artificial graphite powder having an average particle size of 25 μm = 3/7” is 100 kg / cm. ² The bending strength value required for the fuel cell separator plate could not be satisfied.
The gas permeability and corrosion current value of the product were also inadequate areas.
[0031]
“TGP3000” was subjected to jet mill pulverization to obtain a pulverized product having an average particle size of 10, 7, 3, 1 μm, and a molded body was formed at the above ratio. When the molded product was 3 μm, the bending strength was 250 kg / cm. ² The gas permeability and corrosion current also decreased in proportion to the decrease in particle size. A preferable average particle diameter capable of comprehensively satisfying various physical properties was 7 μm or less. A particularly preferable average particle diameter was 3 μm or less.
This phenomenon can be attributed to the fact that the particle size of the self-sintering carbon fine particles is reduced, and the surface of the large graphite particles is filled with the self-sintering carbon powder without gaps.
[0032]
That is, when 70% graphite particles (specific gravity = 2.2) having an average particle size = 25 μm and 30% self-sintering carbon particles (specific gravity = 1.8) having an average particle size = 50 μm exist, self-sintering carbon There is a calculation result that there are 15 graphite grains per grain.
Therefore, it is clear that the existence effect of the self-sintering carbon particles responsible for the sinterability cannot be expected so much in the above particle size relationship.
By changing the average particle size of the self-sintering carbon particles to 10, 7, and 3 μm, it is calculated that there are 8, 24, and 303 self-sintering carbon particles per graphite particle. In the case of 10 μm, self-sintering carbon covers 1/3 of the surface of one graphite particle. In the case of 7, 3 μm, it is calculated that the surface of 1/2, 1 is covered with self-sintering carbon particles.
From the experimental results, it can be seen that the required values of bending strength, corrosion current, and gas permeability are satisfied in a situation where a calculated value is obtained in which carbon particles cover 1/2 of the graphite particle surface. In addition, the effect becomes more complete with a 3 μm product.
[0033]
On the other hand, when the coverage of the carbon component is increased, the electric resistance value is increased and the resistance loss inside the fuel cell is expected to increase. However, the volume resistivity value measured by “Loresta” manufactured by Yuka Denshi Co., Ltd. is 1.5 to 1.7 mΩ · cm for a product with an average particle size of 3 μm of TGP, which can satisfy the required separator value.
Even if the average particle size was 1 μm, the effect was the same as that of the 3 μm product.
Therefore, the particle size of the self-sintering carbon required for the surface coating varies depending on the variation of the graphite particle size, but this can be predicted by a simple calculation.
[0034]
Therefore, it is possible to obtain the maximum particle diameter at which the coverage in the above calculation can satisfy about 1.
It seems that the same effect can be obtained even if the graphite particles are larger than 7 μm, but in reality, if too large graphite particles are used in the groove portion of the molded product, the gas permeability and the smoothness of the groove are not acceptable. Therefore, the particle diameter itself of the graphite particles is also limited, and as a result, the average particle diameter of the self-sintering carbon is preferably 7 μm.
[0035]
Mixing / granulating system
The thickness of the separator is a weight controlling factor of the fuel cell system, and is an important factor governing the internal heat loss due to the volume resistivity.
The present inventors diligently studied a technique for automatically press-forming a thin plate. The powder flowability is an extremely important controlling factor for molding by automatic pressing, and granulated powder is usually used to ensure quick and uniform flowability in an automatic press mold. The objective cannot be achieved with a simple mixture of graphite powder and carbon powder.
[0036]
The spray-drying granulation method disclosed in Japanese Patent No. 2566595 proposed by one of the present inventors can supply a graphite / carbon composite powder with high flowability that satisfies the characteristics required for automatic pressing. . If the slurry aqueous solution of graphite / carbon composite powder using methylcellulose and surfactant as auxiliary agents is spray-dried in the air with water vapor as a heat source in accordance with the method of the present invention, granulation rich in flowability with a desired particle size Powder can be manufactured.
The present invention includes a granulated powder production method according to the method disclosed in Japanese Patent No. 2566595 as one form of carrying out the invention.
The present inventors further examined the mixing and granulation methods.
[0037]
(6) In the present invention, the success or failure of the operation of uniformly mixing the fine self-sintering carbonaceous compound of 1 to 10 μm and the graphite particles of 10 to 70 μm is formed by coating the surface of the graphite particles with the self-sintering carbon particles. It is extremely important for the body to develop the required characteristics.
This uniform mixing of fine particles involves considerable difficulty.
That is, when a mixing device with compression such as a grinder is used, it is remarkable for graphite particles having a scale-like structure and exhibiting self-molding property by compression, especially natural graphite having huge scales. Prior to mixing with the sinterable carbonaceous compound particles, the graphitic carbon particles adhere to each other and the desired properties cannot be expressed. On the other hand, in a mixer such as a ball mill where priority is given to the pulverization function, the raw material itself is pulverized, and it becomes difficult to express the performance of the compact designed with a predetermined mixing ratio.
[0038]
In a stirring and mixing apparatus represented by a high-speed mixer, the above-described problems are unlikely to occur because the powder is mixed in a freely floating state using rotating blades.
The present inventors searched for mixing conditions with a high speed mixer (Fukae Pautech Co., Ltd.). As a result, both carbon powder and graphite powder are dried at 50 ° C. or more, preferably around 100 ° C., and then purged with dry air or nitrogen gas so that moisture does not enter the mixing tank in the temperature range from room temperature to 100 ° C. It has been found that a very good mixing state can be achieved in a few minutes by mixing with the use of.
[0039]
(7) The granulated product obtained by granulating this mixed powder with the same machine and then removing moisture by drying has a particle size of 0.5 mm or less. Specifically, spherical particles passing almost 100% through a sieve having a sieve mesh <0.425 mm were obtained.
In this case as well, it has been found that the desired fine spherical particles can be produced with good reproducibility by subjecting the agitator to rotation at a higher speed than conventional common sense.
These new discoveries have led to the completion of a simple and highly productive mixing and granulation method.
(8) Granulation is achieved by adding a granulation liquid to the powder after mixing in a stirred state. Various forms of the granulation liquid can be selected.
The simplest granulating liquid is water. However, in the case of water granulation, the granulated body obtained after drying tends to collapse. Therefore, although it is not suitable for a production form in which the granulated powder is transported in a large container, a desired function can be obtained even with water granulation in a factory where granulation, drying and molding are systemized.
Further, by adding various compounds having water solubility and caking property such as polymer flocculant, polyethylene glycol, methyl cellulose, and sucrose to water as caking aid, a granulated body having higher strength can be obtained.
[0040]
The object is achieved by selecting a caking aid that does not contain an element that remains in the separator and participates in the electrochemical reaction and causes corrosion and heat generation.
However, if the strength of the granulated body obtained here is too high, the grains will not collapse even if molded at a predetermined pressure in the press molding process. In an extreme case, the cross section of the compact is observed as a combination of granulated particles. In such a case, desired physical properties represented by gas permeability cannot be satisfied.
[0041]
Therefore, it is necessary to optimize the addition amount of the caking aid in accordance with each physical property. Specifically, in the case of methyl cellulose, a polymer flocculant, or a polyethylene glycol type, 0.05 to 1.0%, preferably 0.1 to 0.5% is selected as the outer ratio regardless of the degree of polymerization.
In the case of sucrose, 0.1 to 10%, preferably 0.5 to 5%, more preferably 1 to 3% is selected as the outer ratio.
The difference in addition amount is due to the fact that polyethylene glycol forms a strong film in the dry state, whereas sucrose forms a film with innumerable cracks.
[0042]
That is, in polyethylene glycol, a strong film works in the direction of preventing the collapse of grains during pressurization, so it is necessary to reduce the addition amount as much as possible.
On the other hand, when polyethylene glycol is added, the particles are unlikely to disintegrate during normal handling, so extremely stable flowability is ensured. This granulated body can sufficiently cope with a general material uniform filling method in an automatic press.
The same effect can be expected with sucrose and methylcellulose. Further, in these systems, a part of the carbon remains in the molded body as carbon and acts as a binder for carbon particles and graphite particles, thereby contributing to improvement of the strength of the molded body. It also contributes to an increase in the density of carbonized products.
[0043]
(9) On an industrial scale, it is preferable to perform mixing and granulation separately. As a result, complicated steps such as drying of the mixing tank and removal of deposits when the dry powder is introduced into the apparatus using water can be omitted, and the mixing and granulation steps can be operated almost unattended.
The granulated product is subjected to press molding after undergoing a drying process. It is obvious to those skilled in the art that it can be molded even while it contains moisture, but it is not suitable for automatic molding. The granulated product can be dried by applying a magnetron dryer to a device such as a high speed mixer. In this case, since water evaporates from the inside, innumerable pores can be formed inside the granulated powder, and the collapse of the particles is further promoted by the forming pressure, which contributes to the improvement of the gas impermeability of the formed body.
[0044]
Molding system
Many fuel cell separator plates form a complex-shaped flow path of fuel gas (hydrogen) and oxidant (air) on the surface thereof. The shape varies from the information disclosed in the patent. Many proposals have been made by manufacturers, such as those in which a flow path is formed only on one side and those formed on both sides.
It is obvious to those who handle carbon molding materials, but it is extremely difficult to form such complex shapes on carbonized or graphitized plates, resulting in expensive products as a result of occupying machine tools for a long time. It must be.
Moreover, mass production is extremely difficult for high-hardness materials such as glassy carbon.
[0045]
An object of the present invention is to form a complicated shape in a single shot at the time of automatic press molding by imprinting such a complicated shape on a pressing die pressing surface in advance.
Of course, difficult to set in the press molding operation, such as holes on the side, will be formed by post-processing, but if you use a one-shot molding method, if you have a press die that matches the manufacturer's proposal, a lot of complex shaped products Production can be performed at low cost.
Although it is technically possible to give a complicated shape by a single molding, the complicated shape is often destroyed by shrinkage that occurs during carbonization. In reality, problems such as deformation of the entire plate occur and it is not suitable for practical use.
[0046]
A method proposed by one of the present inventors, for example, Japanese Patent Publication No. 6-102530, discloses a method of forming a fuel cell separator using a graphite mold.
Japanese Patent No. 256659 discloses a method for mass-producing a thin-bottomed complex molded body by combining granulation means.
In the present invention, a self-sintering carbonaceous compound having a β-component content of about 21% derived from coal tar called TGP3000 is used as a representative example in combination with graphite. Whether or not a composite powder for body can be obtained was examined.
[0047]
(10) TGP3000 is a material that generates a large amount of cracked gas components at 200 to 400 ° C., and has unique properties as a mesophase-containing pitch. However, a TGP-only molded body has the characteristics of extremely high strength.
TGP3000 pulverized to the various particle sizes described above was mixed with artificial graphite “KS44” manufactured by Temcal Co. at various ratios using a high-speed mixer, granulated with 2% sucrose, and dried powder at a molding pressure of 1 ton / cm. ² Then, the temperature was increased to 1200 ° C. at a temperature increase rate of 1 ° C./min in an inert gas atmosphere to obtain a carbonized molded body, and dimensional changes before and after firing were observed.
[0048]
As a result, TGP3000 having an average particle diameter of 3 μm had TGP3000 = 30% and KS44 = 70%, and the linear shrinkage rate before and after firing was substantially zero. Further, the linear shrinkage rate was less than 1% even within the range of TGP3000 = 27-30%.
Although the optimum value slightly fluctuated depending on the change in the average particle diameter of TGP3000, a composition having a substantially zero linear shrinkage rate could be set within the range of TGP3000 = 26 to 30%.
It was confirmed that the composition with a zero linear shrinkage rate could be set, so that one-shot molding of a complex shaped product similar to the previous invention was possible with a re-pulverized product of TGP3000 which is special but mass-produced.
The same test was performed with a commercially available TGP2000 (200 mesh sieve product) and similar results were obtained. That is, it has been found that a composition called TGP2000 meets the purpose of the present invention.
[0049]
The present inventors have used dry-granulated powder prepared through the processes of dry mixing and wet granulation, which are constituent elements of the present invention, using "KMFC" and "MCMB" which are commercially available self-sintering carbon materials. A similar test was conducted on the body, and a composition with a zero linear shrinkage rate was found, similar to TGP3000.
In automatic press molding, after putting a little more amount into the mold frame than the preset amount of granulated powder based on the bulk density of the granulated powder and the pressure density at the time of molding, the lower frame is moved to a predetermined position. A general method is to brush the granulated body that has been pushed up and overflowed to the upper surface of the mold, determine the filling amount, and move to a predetermined pressurizing operation.
[0050]
In this case, it is important for the product thickness to be constant that the bulk density of the granulated powder is constant. In addition, the flowability that can be easily and uniformly filled in the mold frame is also an important factor.
The granulated powder of the present invention can satisfy such a demand. In particular, a powder obtained by wet granulation using polyethylene glycol, sucrose and methylcellulose can give excellent flowability and uniform particle size distribution.
The so-called springback phenomenon, in which the shaped body obtained by molding gives dimensions slightly larger than the mold, is well known. When this phenomenon occurs, it is known that the probability of breakage when the molded body is pulled out from the mold increases, but as a countermeasure, it is a technology within the common sense of the industry, but a small amount called the allowance for the mold. To taper.
[0051]
It is most effective to prevent the deformation of the groove and the like by making the dimensions of the formed body with the spring back substantially the same as the dimension of the carbonized molded body, but when the spring back linear expansion coefficient is around 1% The mold size can be shrunk. In this case, the material ratio can be easily designed by increasing the mixing ratio of the self-sintering carbon material by a predetermined amount to give the desired linear shrinkage rate. Obtainable.
It was experimentally confirmed that the amount of springback is hardly affected by the molding pressure. The molding pressure is 0.5 ton / cm. ² ~ 2 tons / cm ² It was also confirmed that the linear shrinkage rate during carbonization was not affected in the range of.
[0052]
These two features make it possible to imprint a complex shape on a generated shape when molding a mold as an embodiment of the present invention. In other words, when a large number of grooves with a width of 1 mm and a depth of 1 mm are installed on the surface like a grooved separator, the amount of granulated powder is finely adjusted according to the presence or absence of grooves, and a uniform molding pressure is applied to the entire molding surface. This is because it is practically impossible to secure this. Therefore, the molding pressure always fluctuates in the groove portion, and as long as this directly affects the linear shrinkage rate at the time of carbonization, the complex shape cannot be stamped on the generated shape.
It is speculated that the expansion and contraction during heating of the graphite acts as a buffer mechanism to absorb the fluctuations in the molding pressure in the above range, but the discovery that the difference in molding pressure does not affect the linear shrinkage is a groove as needed. The attached separator plate can be manufactured by a single press molding.
[0053]
Firing system
In the present invention, a product can be obtained by performing a heat treatment in an inert atmosphere up to a temperature at which the self-sintering carbonaceous compound becomes carbonaceous carbon.
It is generally known that self-sintering carbonaceous compounds terminate carbonization by releasing hydrogen at around 900 ° C. Therefore, the carbonization is completed if the heat treatment is performed up to 1000 ° C. which is known as a normal carbonization temperature.
However, the carbonization temperature in the present invention is selected from 1100 to 1800 ° C, preferably 1150 to 1600 ° C, more preferably 1200 to 1500 ° C.
The reason for selecting a temperature higher than the conventional carbonization temperature is to reduce the corrosion current.
[0054]
That is, in a proton type fuel cell, whether it is phosphoric acid or a solid polymer type polymer in which a sulfate group is fixed to the polymer membrane, current flows through the separator plate in an operating state, and moisture and proton coexist. Regardless of the difference in operating temperature, an electrochemical reaction occurs at the functional group present on the end face of the graphite or carbon crystal, which is observed as a corrosion current. In addition, a phenomenon that the separator plate is broken in an extreme case is caused by destruction of the crystal structure of graphite or carbon by the corrosion current.
In particular, it is well known that the end face of graphite crystal has many functional groups, and this is the source of corrosion current. Moreover, when carbonaceous carbon is also insufficiently carbonized, a corrosive current reaction is caused by the remaining functional groups.
[0055]
There are two types of corrosion current countermeasures of the present invention. First, regarding the reaction inhibition of the graphite crystal end face functional group, the graphite end face is coated with self-sintering carbonaceous compound fine particles at the time of mixing / granulation, and the self-sintering carbonaceous compound fine particles are melt-sintered during carbonization. The graphite crystal end face is protected to reduce its reactivity.
Next, by setting the carbonization temperature within the above range, the functional groups of the carbonaceous carbon crystal and the graphitic carbon crystal are removed in advance, and the acceleration of the electrochemical reaction that occurs when a large amount of functional groups remain is suppressed. It is to ensure long-term stability.
When a particularly preferable temperature range of 1200 to 1500 ° C. is selected, the initial corrosion current value is drastically reduced to 1/10 or less of that when firing at 1000 ° C., and the current value remains within the allowable range even during long-time operation.
[0056]
On the other hand, BN used at the time of molding can be cited as a cause of increasing the initial corrosion current value. Therefore, it is preferable not to use this or to reduce the amount of use as much as possible.
Self-sintering carbonaceous compounds are their starting materials, heat treatment methods and β Although the range varies slightly depending on the component content, it is well known that the gas transitions to carbonaceous carbon while releasing cracked gas in a carbonization temperature range of about 200 to 500 ° C.
If the amount of gas generated per unit time from the molded body at 200 to 500 ° C. is too large, the molded body will swell due to the gas pressure, and only deteriorate the physical properties such as bending strength, gas permeability, and electrical conductivity. Rather, it sometimes loses its product form.
[0057]
The rate of temperature increase is the content of the self-sintering carbonaceous compound in the mixture for moldings, β Optimized by component content, molding area and molding pressure. These techniques are within the technical range known to those skilled in the art, but the carbonization temperature range of 150 to 600 ° C. of the temperature rise rate of the formed form of the present invention is 0.01 to 5 ° C./min, preferably 0.1 It is required to set in the range of ˜3 ° C./min, more preferably in the range of 0.2˜2 ° C./min.
When oxygen comes into contact with the molded body from the outside during firing, the self-sintering carbonaceous compound absorbs oxygen and changes into an oxygen-containing carbonaceous compound in the temperature range of 200 to 500 ° C. In this case, since there is a difference in the linear shrinkage rate at the time of carbonization with a compound that has not undergone oxidation, it will cause distortion and destruction of the product, so it is necessary to suppress the entry of oxygen during firing in that temperature range become.
[0058]
As a method for suppressing oxygen intrusion in this temperature range, which is a conventionally known technique, carbonization under an inert gas (preferably nitrogen gas) atmosphere can be mentioned.
In addition, since “Coke Breeze”, which is a carbonized filler that is usually used, does not have the ability to suppress oxygen intrusion in this temperature range, the present inventors have added linseed oil to the coke breeze disclosed in Japanese Patent Laid-Open No. 5-186265. It is also possible to use a method in which an oxygen permeation inhibiting layer obtained by mixing the above is placed on the top of the container so that oxygen intrusion up to 500 ° C. is substantially zero. The same effect can be obtained by mixing a suitable ground product of TGP with coke breeze instead of linseed oil.
Carbonization at 600 ° C. or higher can be arbitrarily selected from the range of 1 ° C. to 10 ° C./min. Here, desorption of hydrogen occurs at the final stage of carbonization, but it is desorption at a stage where the strength has already been improved, and since a gas flow path is also secured, a slow temperature increase is not required.
It should be noted that the carbonized carbon / graphite composite molded body produced in the present invention can be optionally produced by subjecting the carbonized carbon / graphite composite molded body to cutting using a normal cutting machine. Needless to say.
[0059]
Example
The contents of the present invention will be described more specifically with reference to the following examples.
Example 1
75 g of self-sintering carbonaceous compound fine particles (pulverized with TGP3000 made by Osaka Kasei Co., Ltd. with a jet mill) that reached a constant weight of drying with a hot air circulation dryer maintained at 110 ° C. Artificial graphite manufactured by Temcal Co., Ltd. with an average particle size of 25 μm while being fed into a speed mixer (LFS-GS-2J type), blown dry nitrogen from the agitator and chopper shaft, and stirred at an agitator rotation speed of 500 rpm and chopper rotation speed average of 1000 rpm. (KS44) 175 g was charged with a spatula in 5 minutes, and stirring was further continued for 5 minutes. The powder was smoothly mixed when observed through the viewing window of the lid.
[0060]
An aqueous solution for granulation composed of 5 g of sucrose and 75 g of water was poured into the above mixture being mixed at an agitator rotation speed of 2000 rpm and chopper rotation speed of 500 rpm in 2 minutes, and granulation was continued for 3 minutes.
The obtained granulated material was dried with a hot air circulating dryer at 105 ° C. and cooled to room temperature. The top of the sieve was separated with a sieve having a mesh of 0.425 mm. More than 99% was recovered as a sieve. A 200.0 mm long x 200.0 mm wide die is installed in a biaxial 600 ton type press, and a groove having a width of 1 mm, a depth of 1 mm, and a groove interval of 2 mm is vertically cut in the center portion of the molded body on the upper pressing die surface. Five were installed. 216 g of granulated material under sieving was charged, and after degassing operation, 1 ton / cm ² The molded body with a groove having a thickness of 3.2 mm was obtained.
[0061]
The upper and lower parts of the molded product were sandwiched between 50 mm thick graphite plates having a smooth surface and placed in a stainless steel container, the periphery was covered with coke breeze, and an antioxidation layer in which linseed oil was mixed with coke breeze was installed on the upper part. A container is installed in a muffle furnace and heated to 1200 ° C. at a heating rate of 1 ° C. per minute while supplying nitrogen from an alumina pipe introduced into the breath layer from the top of the lid at a supply rate of 5 L / min. And then cooled in the furnace. The obtained carbonized compact gave a linear shrinkage of 0.4% compared to the mold size. The groove formed by the mold was carbonized as it was, and no distortion or destruction was observed. A test piece having a length of 100 mm and a width of 10 mm was cut out from the flat surface by cutting and subjected to a three-point bending test to obtain a bending strength of 2.5 kgf / mm. ² Got.
[0062]
Cut out a 25mm square test piece from the flat part and use nitrogen to back pressure 1kg / cm ² The gas permeability is obtained with 3 × 10 ^-Five Ncc / min / cm ² Got.
Further, the volume resistivity of the test piece was measured using an oiled electronics Loresta, and 1.6 mΩ · cm was obtained.
A 10 mm × 10 mm test piece was cut out from the flat surface, and the corrosion current was measured. After 1000 minutes, 80 μA / cm ² Got.
[0063]
【The invention's effect】
The present invention is a carbon having a complicated shape that satisfies various characteristics required for separator plates of solid polymer type and phosphoric acid type fuel cells such as bending strength, electrical conductivity, thermal conductivity, gas permeability, and corrosion current. -It makes it possible to provide a graphite composite molded body at low cost.

Claims (8)

At least one average particle size selected from the group consisting of 10 to 50 parts by weight of carbonaceous carbon compound fine particles having a component having self-sintering property during carbonization and having an average particle size of 10 μm or less, natural graphite, and artificial graphite A homogeneous mixed powder obtained by drying and dehydrating fine particles mainly composed of 90 to 50 parts by weight of graphitic carbon fine particles having a particle size of 10 to 70 μm and then stirring and mixing in a dry state is a water-soluble, carbonaceous carbon compound and graphite A granulated product having a maximum particle size of 0.5 mm or less by adding an aqueous solution or water containing at least one kind of particle-binding additive selected from the group consisting of compounds having adhesion to carbon and stirring and granulating the mixture. Next, the dried granulated product obtained by removing moisture is formed with one molding machine selected from a uniaxial press, a biaxial press, a rotary press, a wet isostatic press, a dry isostatic press, etc. A method for producing a 200-500 mm square carbon / graphite composite molded article , wherein the resulting shaped product is carbonized in a non-oxygen atmosphere . An average particle size of 10 to 70 μm selected from the group consisting of carbonaceous carbon compound fine particles containing a component having self-sintering properties during carbonization and having an average particle size of 10 μm or less, natural graphite, and artificial graphite A group consisting of a water-soluble and carbonaceous carbon compound and a compound having adhesiveness to graphitic carbon obtained from a homogeneous mixed powder obtained by drying and dewatering fine particles mainly composed of graphitic carbon fine particles and then stirring and mixing in a dry state. Add an aqueous solution or water containing at least one kind of particle-binding additive selected from the above and stir to mix and granulate to obtain a granulated product having a maximum particle size of 0.5 mm or less, and then remove the moisture. The resulting dried granulated product is molded into a non-oxygen atmosphere by molding with one molding machine selected from uniaxial press, biaxial press, rotary press, wet isostatic press, dry isostatic press, etc. A method for producing a 200 to 500 mm square carbon / graphite composite molded body, which is carbonized at 1100 to 1800 ° C. under an atmosphere. The carbon / graphite composite molded body according to claim 1 or 2, wherein the carbonaceous carbon compound fine particle containing a component having self-sintering property has a γ component (quinoline-soluble toluene insoluble component) content of 3 to 30% by weight. Manufacturing method. 3. The carbon / carbon composition according to claim 2, wherein the main component is a fine particle containing 10 to 50 parts by weight of carbonaceous carbon compound fine particles containing a component having self-sintering properties and 90 to 50 parts by weight of graphitic carbon fine particles. A method for producing a graphite composite molded body . 3. The carbon-based carbon according to claim 1, wherein the average particle size of the carbonaceous carbon compound fine particles containing a component having self-sintering properties is 1 to 7 μm, and the average particle size of the graphitic carbon fine particles is 15 to 50 μm. A method for producing a graphite composite molded body . The method for producing a carbon / graphite composite molded article according to claim 1 or 2, wherein the particle bonding additive is at least one compound selected from the group consisting of a polymer flocculant, polyethylene glycol, sucrose, and methylcellulose . 7. The carbonization under a non-oxygen atmosphere is carried out in a system in which the formed form is embedded in a coke plain of a gas-impermeable container and the upper part of the container is coated with linseed oil-impregnated coke plain. Of carbon / graphite composite molded body . At least one average particle size selected from the group consisting of 10 to 50 parts by weight of carbonaceous carbon compound fine particles having a component having self-sintering property during carbonization and having an average particle size of 10 μm or less, natural graphite, and artificial graphite A homogeneous mixed powder obtained by drying and dehydrating fine particles mainly composed of 90 to 50 parts by weight of graphitic carbon fine particles having a particle size of 10 to 70 μm and then stirring and mixing in a dry state is a water-soluble, carbonaceous carbon compound and graphite A granulated product having a maximum particle size of 0.5 mm or less by adding an aqueous solution or water containing at least one kind of particle-binding additive selected from the group consisting of compounds having adhesion to carbon and stirring and granulating the mixture. Next, the dried granulated product obtained by removing moisture is formed with one molding machine selected from a uniaxial press, a biaxial press, a rotary press, a wet isostatic press, a dry isostatic press, etc. The method for producing a shaped product for producing a carbon / graphite composite shaped product according to claim 1, wherein the shaped product is produced.