JP2016179923A - Manufacturing method of carbon material, and carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a carbon material, with which the inexpensive carbon material having excellent flexure strength can be obtained.SOLUTION: A manufacturing method of a carbon material includes: a process for mixing an aggregate with a binder therefor; a process for heating and molding the mixture; and a process for carbonizing the molded body. In the manufacturing method of the carbon material, the binder contains ashless coal obtained by a solvent extraction treatment of coal, and polyimide, and the content of polyimide in the mixture is 1 mass% to 15 mass%. A heating temperature of the mixture in the carbonization process is preferably 500°C to 3,000°C. The aggregate is preferably ashless coal coke obtained by dry distillation of the ashless coal. The carbonization process preferably includes a process for carbonizing the molded body and a process of graphitizing the molded body.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a carbon material and a carbon material.

  The carbon material is produced by forming a mixture of coke (aggregate) and pitch (binder) and carbonizing the mixture (see Japanese Patent Application Laid-Open Nos. 8-26709 and 2005-298231). In the production of such a carbon material, voids are likely to remain in the molded body in a single carbonization treatment. Therefore, after carbonization of the mixture, it is generally performed to impregnate the pitch and carbonize again. Furthermore, this carbonization process is often repeated.

  By the way, the pitch derived from petroleum has a disadvantage that the content of impurities such as sulfur and metal is high. In view of this, a carbon material production method using ashless coal that is relatively inexpensive and has few impurities, that is, low sulfur content and low ash content, has been proposed (see JP 2011-1240 A). However, when ashless coal is used as the binder, the bending strength of the carbon material is improved to some extent. However, since the bulk density is difficult to increase, there is a limit to the improvement of the bending strength.

  On the other hand, polyimide is used as a binder for the purpose of obtaining a carbon material having high bending strength. However, since polyimide is expensive, there is a disadvantage that the manufacturing cost of the carbon material is increased.

JP-A-8-26709 JP 2005-298231 A JP 2011-1240 A

  This invention is made | formed based on the above situations, and aims at provision of the carbon material which is excellent in bending strength at low cost, and its manufacturing method.

  The invention made to solve the above problems is a method for producing a carbon material comprising a step of mixing an aggregate and a binder thereof, a step of thermoforming the mixture, and a step of carbonizing the molded body. And the binder contains ashless coal obtained by solvent extraction treatment of coal and polyimide, and the content of the polyimide in the mixture is from 1% by mass to 15% by mass. Is the method.

  In the manufacturing method of the carbon material, the binder contains ashless coal and polyimide, and the content of the polyimide in the above mixture is within a specific range, so that the ashless coal molecule is entangled with the polyimide molecule, and in the carbon material. The bending strength of the structure derived from the binder is improved. Moreover, since the binder is efficiently filled into the space between the aggregates, the carbon density can be improved and the carbon material exhibiting high bending strength can be obtained. Furthermore, the cost concerning manufacture of a carbon material can be reduced by mixing and using an inexpensive ashless coal and an expensive polyimide.

  As heating temperature of the said mixture in the said carbonization process, 500 degreeC or more and 3000 degrees C or less are preferable. By making the heating temperature of the said compound into the said range, an aggregate and a binder can be carbonized efficiently and the bending strength of the carbon material obtained can be raised easily and reliably.

  The aggregate may be ashless coal coke obtained by dry distillation of ashless coal. Thus, by using ashless coal coke as an aggregate, the adhesive force between the aggregate and the binder is improved due to the similarity in carbon structure between the aggregate and the ashless coal in the binder. As a result, the bending strength of the obtained carbon material is further improved.

  The mixing step includes a step of mixing a solution containing ashless coal and a solution containing a polyamic acid polymer, a step of volatilizing a solvent in the mixed solution to obtain a powder, and heating the mixed solution to form the polyamic acid. It is good to provide the process of imidating a polymer, and the process of mixing the said powder and aggregate. When the manufacturing method includes the above steps, a carbon material having excellent bending strength can be obtained at a low cost by a simple procedure.

  The carbonization step may include a step of carbonizing the molded body and a step of graphitizing the carbonized molded body. Thus, by performing carbonization and graphitization, the bending strength of the carbon material can be more reliably increased.

  Another invention made to solve the above-mentioned problems is a carbon material formed by molding and carbonization of a mixture containing an aggregate and its binder, and the ashless coal is obtained by dry distillation of ashless coal as the aggregate. Charcoal coke is used, ashless coal and polyimide obtained by solvent extraction treatment of coal are used as the binder, and the polyimide content in the mixture is 1% by mass or more and 15% by mass or less. It is a characteristic carbon material.

  The carbon material uses ashless coal coke as an aggregate, uses ashless coal and polyimide as a binder, and has an excellent bending strength by setting the content of the polyimide in the above-mentioned mixture within a specific range. Inexpensive.

  As described above, the carbon material manufacturing method of the present invention can provide a carbon material that is low in cost and excellent in bending strength. Moreover, since the carbon material of the present invention is low in cost and excellent in bending strength, it can be suitably used as a structural member, an electric / electronic component, a metal reducing agent, or the like.

  Hereinafter, an embodiment of a method for producing a carbon material according to the present invention will be described.

[Method for producing carbon material]
The method for producing the carbon material includes a step of mixing an aggregate and its binder (mixing step), a step of thermoforming the mixture (heat forming step), and a step of carbonizing the molded body (carbonization step). Prepare. The carbonization step further includes a step of carbonizing the molded body (carbonization step) and a step of graphitizing the carbonized molded body (graphitization step).

[Mixing process]
In the mixing step, the aggregate and its binder are mixed. The mixing step includes a step of mixing a solution containing ashless coal and a solution containing a polyamic acid polymer (solution mixing step), and a step of volatilizing the solvent in the mixed solution to obtain a powder (powder acquisition step). ), Heating the mixed solution to imidize the polyamic acid polymer (imidation process), and mixing the powder and aggregate (aggregate mixing process). A powdery binder containing ashless coal and polyimide is obtained by the solution mixing step, the powder acquisition step, and the imidization step.

<Ashless charcoal>
Ashless coal (Hypercoal, HPC) is a type of modified coal obtained by modifying coal, and is a modified coal obtained by removing as much ash and insoluble components as possible from coal using a solvent.

  The upper limit of the ash content of ashless coal is generally 5% by mass, preferably 2% by mass. Moreover, as an upper limit of the ash content of ashless coal, 5000 ppm (mass basis) is more preferable, and 2000 ppm is further more preferable. Here, “ash” means a value measured in accordance with JIS-M8812 (2004).

  As a minimum of softening start temperature of ashless coal, 150 ° C is preferred and 160 ° C is more preferred. On the other hand, the upper limit of the softening start temperature is preferably 220 ° C, more preferably 210 ° C. If the softening start temperature is smaller than the lower limit, the mixture may be excessively softened and difficult to be molded when the mixture of aggregate and binder is thermoformed. On the contrary, when the softening start temperature exceeds the upper limit, the mixture is difficult to soften, and the density and bending strength of the obtained carbon material may be insufficient. Here, “softening start temperature” is a value measured in accordance with the JIS-M8801 (2004) Gisela plastometer method.

(Method for producing ashless coal)
As raw material coal of ashless coal used in the method for producing the carbon material, the concentration of residual inorganic substances (silicic acid, alumina, iron oxide, lime, magnesia, alkali metal, etc.) when heated and incinerated at 815 ° C. Very few are preferred. In addition, ashless coal has a moisture content of approximately 0.5% by mass or less, and exhibits higher thermal fluidity than raw coal.

  The ashless coal can be obtained by various known production methods, for example, by removing the solvent from the solvent extract of coal. Ashless coal can be obtained, for example, by a production method including a slurry preparation step, a slurry heating step, a separation step, and an ashless coal recovery step.

(Slurry preparation process)
In the slurry preparation step, coal as an ashless coal raw material and an aromatic solvent are mixed to prepare a slurry.

  The kind of said coal is not specifically limited, For example, various well-known coals, such as bituminous coal, subbituminous coal, lignite, lignite, can be used. Among these, bituminous coal is preferable from the viewpoint of the bending strength of the carbon material.

  The aromatic solvent is not particularly limited as long as it has a property of dissolving coal, and examples thereof include monocyclic aromatic compounds such as benzene, toluene, and xylene, naphthalene, methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, and the like. A bicyclic aromatic compound or the like can be used. The bicyclic aromatic compound includes naphthalene having an aliphatic chain and biphenyl having a long aliphatic chain.

  Among the aromatic solvents, a bicyclic aromatic compound which is a coal derivative purified from a coal dry distillation product is preferable. The bicyclic aromatic compound of the coal derivative is stable even in a heated state and has an excellent affinity with coal. Therefore, by using such a bicyclic aromatic compound as an aromatic solvent, the ratio of coal components extracted into the solvent (hereinafter also referred to as “extraction rate”) can be increased, and by a method such as distillation. The solvent can be easily recovered and recycled.

  The boiling point of the aromatic solvent is preferably 180 ° C. or higher and 330 ° C. or lower. When the boiling point of the aromatic solvent is smaller than the above lower limit, the extraction rate may decrease during the heat extraction and the required pressure may increase. In addition, the required pressure increases even in the separation step described later, and loss due to volatilization increases in the step of recovering the aromatic solvent, which may reduce the recovery rate of the aromatic solvent. Conversely, if the boiling point of the aromatic solvent exceeds the above upper limit, it becomes difficult to separate the aromatic solvent from the liquid component or solid component in the separation step, and the solvent recovery rate is reduced.

  The lower limit of the mixing ratio of coal with respect to the aromatic solvent in the slurry is preferably 10% by mass and more preferably 20% by mass based on dry coal. On the other hand, the upper limit of the mixing ratio is preferably 50% by mass, and more preferably 35% by mass. If the mixing ratio is less than the lower limit, the amount of coal components extracted with respect to the amount of the aromatic solvent decreases, which is not economical. On the other hand, when the mixing ratio exceeds the upper limit, the viscosity of the slurry is increased, and it may be difficult to separate the liquid component and the solid component in the slurry movement or separation process.

(Slurry heating process)
In the slurry heating step, the slurry is heat-treated to extract coal-soluble components into an aromatic solvent.

  As a minimum of heating temperature (extraction temperature) of a slurry, 350 ° C is preferred and 380 ° C is more preferred. On the other hand, the upper limit of the heating temperature of the slurry is preferably 470 ° C, more preferably 450 ° C. If the heating temperature of the slurry is lower than the above lower limit, the bonds between the molecules constituting the coal cannot be sufficiently weakened. For example, when low grade coal is used as the raw coal, it is recovered in the ashless coal recovery step described later. There is a possibility that the resolidification temperature of the ashless coal to be produced cannot be increased. On the other hand, when the heating temperature of the slurry exceeds the above upper limit, the thermal decomposition reaction of coal becomes very active and recombination of generated thermal decomposition radicals occurs, which may reduce the extraction rate.

  The lower limit of the heating time (extraction time) of the slurry is preferably 10 minutes. On the other hand, the upper limit of the heating time (extraction time) of the slurry is preferably 120 minutes, more preferably 60 minutes, and even more preferably 30 minutes. If the heating time of the slurry is smaller than the above lower limit, extraction of the soluble component of coal may be insufficient. On the other hand, if the heating time of the slurry exceeds the above upper limit, the thermal decomposition reaction of coal proceeds too much and the radical polymerization reaction proceeds, which may reduce the extraction rate.

  After heating the slurry, it is preferable to cool the slurry in order to suppress the thermal decomposition reaction. The cooling temperature of the slurry is preferably 300 ° C. or higher and 370 ° C. or lower. If the cooling temperature of the slurry is lower than the above lower limit, the dissolving power of the aromatic solvent is lowered, and the coal component once extracted may be reprecipitated, and the recovery rate of ashless coal may be lowered. On the contrary, if the cooling temperature of the slurry exceeds the above upper limit, the thermal decomposition reaction may not be sufficiently suppressed.

  The slurry is preferably extracted by heating in a non-oxidizing atmosphere. Specifically, it is preferable to perform heat extraction of the slurry in the presence of an inert gas such as nitrogen. By using an inert gas such as nitrogen, it is possible to prevent the slurry from coming into contact with oxygen and igniting at low cost during the heat extraction.

  Although the pressure at the time of heat extraction of a slurry is based also on heating temperature and the vapor pressure of the aromatic solvent to be used, it can be 1 MPa or more and 2 MPa or less, for example. When the pressure at the time of heat extraction is lower than the vapor pressure of the aromatic solvent, the aromatic solvent volatilizes and the soluble component of coal cannot be confined in the liquid phase, and the soluble component cannot be extracted. On the other hand, if the pressure at the time of heating extraction is too high, the cost of the equipment, the operating cost, etc. increase.

(Separation process)
In the separation step, the slurry heated in the slurry heating step is separated into a liquid component and a solid component. The liquid component of the slurry is a solution portion containing a coal component extracted into an aromatic solvent. The solid component of the slurry is a portion containing ash and coal components that are insoluble in the aromatic solvent.

  A method for separating the slurry into a liquid component and a solid component is not particularly limited, and a known separation method such as a filtration method, a centrifugal separation method, or a gravity sedimentation method can be employed. Among these, the gravity sedimentation method which can continuously operate the fluid and is suitable for a large amount of processing at a low cost is preferable. In the gravity sedimentation method, a supernatant liquid, which is a liquid component containing coal components extracted into an aromatic solvent, is separated at the top of the gravity sedimentation tank, and ash and coal components insoluble in the solvent as solid components are separated at the bottom of the gravity sedimentation tank. The solid concentrate containing is separated.

(Ashless coal recovery process)
In the ashless coal recovery step, the aromatic solvent is separated from the liquid component of the slurry obtained in the separation step to recover ashless coal with a very low ash content.

  The method for separating the aromatic solvent from the liquid component of the slurry is not particularly limited, and a general distillation method, evaporation method (for example, spray drying method), or the like can be used. The aromatic solvent separated and recovered can be recycled as described above. Ash liquid is obtained from the liquid component by separating the aromatic solvent.

  In addition, in the manufacturing method of ashless coal, you may add various process steps as needed. Specifically, within a range that does not adversely affect the respective steps, for example, a step of pulverizing raw coal, a step of removing foreign matter, etc., a step of drying the obtained ashless coal, etc. These steps may be included.

  Moreover, you may manufacture the byproduct charcoal by which the aromatic solvent was isolate | separated from the solid component of the slurry and the ash content was concentrated as needed. As a method for separating the aromatic solvent from the solid component, a general distillation method or evaporation method can be used as in the method for obtaining ashless coal from the liquid component.

  Although the particle size of the ashless coal used at this process is not specifically limited, As a minimum of the median diameter of ashless coal, 1 micrometer is preferable and 10 micrometers is more preferable. On the other hand, the upper limit of the median diameter is preferably 100 μm, and more preferably 50 μm. If the median diameter of ashless coal is smaller than the lower limit, the handleability and production efficiency may be reduced. If the median diameter of the ashless coal exceeds the above upper limit, the mixed state with the ashless coal coke becomes non-uniform, and there is a possibility that the molding failure of the mixture or the bending strength of the carbon material is insufficient. Here, the “median diameter” means a particle diameter at which the volume integrated value is 50% in the particle size distribution obtained by the laser diffraction scattering method.

<Solution mixing process>
In the solution mixing step, a solution containing ashless coal and a solution containing a polyamic acid polymer are mixed to obtain a mixed solution. Moreover, you may further mix other arbitrary components in the range which does not impair the effect of this invention.

  As a method for preparing a solution containing ashless charcoal, a known method can be used. For example, a method in which ashless charcoal is dispersed in a solvent, heated and stirred, and then filtered while maintaining a high temperature. The lower limit of the heating temperature when using this method is preferably 80 ° C, more preferably 90 ° C. On the other hand, the upper limit of the heating temperature is preferably 150 ° C, more preferably 130 ° C. When the heating temperature is lower than the lower limit, components soluble in the solvent in the ashless coal may not be sufficiently dissolved in the solvent. Conversely, if the heating temperature exceeds the upper limit, the solvent volatilizes and a sufficient amount of solution may not be obtained.

  As a minimum of the content rate of ashless coal in the solution containing ashless coal, 5 mass% is preferred and 10 mass% is more preferred. On the other hand, as an upper limit of the said content rate, 40 mass% is preferable and 30 mass% is more preferable. When the said content rate is smaller than the said minimum, there exists a possibility that the cost at the time of removing a solvent may increase in the powder acquisition process mentioned later. On the other hand, when the content ratio exceeds the upper limit, the solution containing the polyamic acid polymer and the solution containing ashless coal may not be sufficiently mixed.

(Polyamide acid polymer)
The polyamic acid polymer is a polyimide precursor that is a resin having an imide bond in the molecule. The polyamic acid polymer can be obtained, for example, by polycondensing a tetracarboxylic acid or an anhydride thereof as an acid component and a diamine compound as an amine component.

  As the tetracarboxylic acid or an anhydride thereof, a known compound can be used, but an aromatic tetracarboxylic acid or an anhydride thereof is preferable.

  Examples of the aromatic tetracarboxylic acid or anhydride thereof include 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride Anhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-paraterphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-meta Examples include terphenyl tetracarboxylic dianhydride.

  Among these tetracarboxylic acids or anhydrides thereof, 4,4′-biphenyltetracarboxylic dianhydride, 4,4′-benzophenone tetracarboxylic dianhydride, and pyromellitic dianhydride are more preferable. Preferably, pyromellitic dianhydride is more preferable.

  A known compound can be used as the diamine compound, but an aromatic diamine compound is preferable.

  Examples of the aromatic diamine compound include paraphenylene diamine, metaphenylene diamine, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfide, 4,4′-diaminodiphenylsulfide, 1,3-bis (4-aminophenoxy) benzene, 1 , 4-bis (4-aminophenoxy) benzene, 2,2-bis (trifluoromethyl) benzidine, 9,9'-bis (4-aminophenyl) fluorene 4,4'-diaminodiphenylamine, 3,4'- Diaminodiphenylamine, 3,3′- Aminodiphenylamine, 2,4'-diaminodiphenylamine, 4,4'-diaminodibenzylamine, 2,2'-diaminodibenzylamine, 3,4'-diaminodibenzylamine, 3,3'-diaminodibenzylamine N, N′-bis- (4-amino-3-methylphenyl) ethylenediamine, 4,4′-diaminobenzanilide, 3,4′-diaminobenzanilide, 3,3′-diaminobenzanilide, 4,3 '-Diaminobenzanilide, 2,4'-diaminobenzanilide, N, N'-p-phenylenebis-p-aminobenzamide, N, N'-p-phenylenebis-m-aminobenzamide, N, N'- m-phenylenebis-p-aminobenzamide, N, N′-m-phenylenebis-m-aminobenzamide, N, N -Dimethyl-N, N'-p-phenylenebis-p-aminobenzamide, N, N'-dimethyl-N, N'-p-phenylenebis-m-aminobenzamide, N, N'-diphenyl-N, N Examples include '-p-phenylenebis-p-aminobenzamide, N, N'-diphenyl-N, N'-p-phenylenebis-m-aminobenzamide, and the like.

  Among these, diamine compounds include paraphenylene diamine, metaphenylene diamine, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, and 3,3′-diaminodiphenyl sulfone. 4,4′-diaminodiphenyl sulfone, 9,9′-bis (4-aminophenyl) fluorene, and 4,4′-diaminobenzanilide are more preferable, and 4,4′-diaminodiphenyl ether is more preferable.

  As a minimum of the content rate of the polyamic acid in the solution containing a polyamic acid polymer, 5 mass% is preferable and 10 mass% is more preferable. On the other hand, as an upper limit of the said content rate, 40 mass% is preferable and 30 mass% is more preferable. When the said content rate is smaller than the said minimum, there exists a possibility that the cost at the time of removing a solvent may increase in the powder acquisition process mentioned later. On the other hand, when the content ratio exceeds the upper limit, the solution containing the polyamic acid polymer and the solution containing ashless coal may not be sufficiently mixed.

  Moreover, you may use a commercial item as said polyamic-acid polymer.

(solvent)
The solvent is not particularly limited as long as it can disperse ashless charcoal or can dissolve the polyamic acid polymer, but is preferably an organic solvent, more preferably a polar organic solvent, N- More preferred is methyl-2-pyrrolidone.

  In addition, the solvent in the solution containing ashless coal and the solvent in the solution containing the polyamic acid polymer may be the same or different, but it is easy to adjust the conditions when removing the solvent. From this point, the same is preferable.

  The lower limit of the total content of the ashless charcoal and the polyamic acid polymer in the mixed solution of the solution containing the ashless charcoal and the solution containing the polyamic acid polymer is preferably 5% by mass, and more preferably 10% by mass. On the other hand, as an upper limit of the said total content rate, 40 mass% is preferable and 30 mass% is more preferable. When the said content rate is smaller than the said minimum, there exists a possibility that the cost at the time of removing a solvent may increase in the powder acquisition process mentioned later. On the contrary, when the said content rate exceeds the said upper limit, there exists a possibility that it may become difficult to mix ashless coal and a polyamic-acid polymer in a mixed solution equally.

<Powder acquisition process>
In the powder acquisition step, the solvent in the mixed solution is removed by heating. Thereby, a mixed powder of the polyamic acid polymer and ashless coal is obtained.

  The heating temperature in this step can be appropriately adjusted depending on the pressure during heating, the solid content concentration in the mixed solution, etc. For example, when the solid content concentration is 20% by mass, the lower limit of the heating temperature is preferably 90 ° C. 100 ° C. is more preferable. On the other hand, the upper limit of the heating temperature is preferably 200 ° C and more preferably 180 ° C. If the heating temperature is lower than the lower limit, the solvent in the mixed solution may not be sufficiently removed. On the other hand, when the heating temperature exceeds the upper limit, polyamic acid or ashless carbonization occurs, and the mixture may not function as a binder.

  The heating time in this step can be adjusted as appropriate depending on the solid content concentration in the mixed solution. For example, when the solid content concentration is 20% by mass, the lower limit of the heating time is preferably 30 minutes, more preferably 45 minutes. preferable. On the other hand, the upper limit of the heating time is preferably 2 hours, more preferably 90 minutes. If the heating time is smaller than the lower limit, the solvent in the mixed solution may not be sufficiently removed. Conversely, when the heating time exceeds the upper limit, unnecessary heating continues even after the solvent is removed, which may increase the production cost of the binder.

  This step is preferably performed under vacuum conditions. Specifically, the lower limit of the pressure in this step is preferably -90 kPaG (gauge pressure), more preferably -80 kPaG. On the other hand, the upper limit of the pressure is preferably −30 kPaG, and more preferably −40 kPaG. When the pressure is smaller than the lower limit, the cost and time for reducing the pressure are unnecessarily increased, and the production efficiency of the binder may be lowered and the production cost may be increased. Conversely, when the pressure exceeds the upper limit, the temperature necessary for removing the solvent becomes unnecessarily high, which may increase the production cost of the binder.

  The lower limit of the maximum particle size of the mixed powder is preferably 1 μm and more preferably 10 μm. On the other hand, the upper limit of the maximum particle size is preferably 100 μm, and more preferably 80 μm. If the maximum particle size is smaller than the lower limit, the handleability of the mixed powder and the production efficiency of the carbon material may be reduced. On the other hand, when the maximum particle size exceeds the upper limit, the mixing state when the binder is mixed with the aggregate becomes non-uniform, and there is a possibility that the molding failure of the mixture, the bending strength of the carbon material, or the like may occur. Here, the “maximum particle size” means the maximum particle size in the particle size distribution obtained by the laser diffraction scattering method.

<Imidization process>
In the imidization step, the mixed powder is heated, and the polyamic acid polymer is dehydrated and closed to synthesize polyimide. Thereby, the binder containing a powdery ashless coal and a polyimide is prepared.

  Although the heating temperature in this process can be adjusted suitably, as a minimum of heating temperature, 100 degreeC is preferable and 180 degreeC is more preferable. On the other hand, the upper limit of the heating temperature is preferably 300 ° C, and more preferably 280 ° C. If the heating temperature is lower than the lower limit, imidation of the polyamic acid polymer may be insufficient. On the other hand, when the heating temperature exceeds the upper limit, polyamic acid or ashless carbonization occurs, and the mixture may not function as a binder.

  The heating time in this step can be adjusted as appropriate, but the lower limit of the heating time is preferably 45 minutes and more preferably 1 hour. On the other hand, the upper limit of the heating time is preferably 5 hours, and more preferably 3 hours. If the heating time is shorter than the lower limit, imidation of the polyamic acid may be insufficient. On the other hand, if the heating time exceeds the upper limit, unnecessary heating continues even after the imidization is completed, which may increase the production cost of the binder.

  In addition, this step is preferably performed in a non-oxidizing atmosphere, and more preferably in a nitrogen atmosphere.

<Binder>
The said binder joins aggregates and can be carbonized by heating, after mixing with an aggregate. The binder contains ashless charcoal and polyimide as described above. Furthermore, the binder may contain other components as long as the effects of the present invention are not impaired, but it is preferably composed of ashless coal and polyimide alone.

  As a minimum of the content rate of polyimide in a binder, 5 mass% is preferred, 10 mass% is more preferred, 15 mass% is still more preferred, and 18 mass% is especially preferred. On the other hand, as an upper limit of the said content rate, 45 mass% is preferable, 42 mass% is more preferable, 40 mass% is further more preferable, 38 mass% is especially preferable. When the said content rate is smaller than the said minimum, there exists a possibility that the bending strength of the carbon material obtained may become difficult to improve. On the other hand, when the content ratio exceeds the upper limit, the fluidity of the binder when the binder is mixed with the aggregate becomes insufficient, and it may be difficult to form the mixture.

  As a minimum of the content rate of ashless coal in a binder, 55 mass% is preferred, 58 mass% is more preferred, 60 mass% is still more preferred, and 62 mass% is especially preferred. On the other hand, as an upper limit of the said content rate, 95 mass% is preferable, 90 mass% is more preferable, 85 mass% is further more preferable, 72 mass% is especially preferable. When the said content rate is smaller than the said minimum, there exists a possibility that the cost of the carbon material obtained may increase. On the contrary, when the said content rate exceeds the said upper limit, there exists a possibility that the bending strength of the carbon material obtained may become difficult to improve.

  Examples of the shape of the binder include solids such as powders, liquids obtained by dissolving powders in a solvent, and the like, but powders are preferable because they are easy to handle in the molding process described below.

  When the binder is powdery, the lower limit of the maximum particle size of the binder is preferably 1 μm and more preferably 10 μm. On the other hand, the upper limit of the maximum particle size is preferably 100 μm, and more preferably 80 μm. If the maximum particle size is smaller than the lower limit, the handleability and production efficiency may be reduced. On the other hand, when the maximum particle size exceeds the upper limit, the mixed state at the time of mixing with the aggregate becomes non-uniform, and there is a possibility that the molding failure of the mixture or the bending strength of the carbon material is insufficient.

[Aggregate mixing process]
In the aggregate mixing step, the powdered binder and the aggregate are mixed to obtain a mixture. This mixture may be solid or liquid, but is preferably a solid and more preferably a powder.

<Aggregate>
The aggregate forms the main skeleton of the carbon material. The aggregate is not particularly limited as long as it contains carbon and is carbonized by a heating process described later, and generally used as an aggregate of a carbon material can be applied, but ashless coke (HPCC) is preferable. .

  Ashless coal coke is carbonized ashless coal. Specifically, ashless coal is heat-treated at a temperature of 600 ° C. or more and 1200 ° C. or less in an inert atmosphere such as nitrogen. In addition, since the expansibility of ashless coal lose | disappears at 500 degreeC vicinity, heating temperature is made the said range. Moreover, in the manufacturing method of the said carbon material, although the same thing as the ashless coal used for the said binder is preferable as a raw material of ashless coal coke, you may use different ashless coal.

  The method for producing ashless coal coke is not particularly limited, and can be performed using a known carbonization technique. The rate of temperature increase during heating can be, for example, 0.1 ° C./min or more and 5 ° C./min or less. Further, carbonization of ashless coal may be performed under pressure using a hot isostatic press or the like. Further, asphalt pitch, tar, and the like may be added to the ashless coal as necessary, but it is preferable not to add these components in order to enhance the effect of the present invention. Further, ashless coal may be appropriately formed and then subjected to carbonization. The heat treatment furnace used for carbonization is not particularly limited, and a known furnace can be used. Examples of such a heat treatment furnace include a pot furnace, a lead hammer furnace, a kiln, a rotary kiln, a shaft furnace, and a chamber furnace.

  The median diameter of the ashless coal coke is not particularly limited, but the upper limit of the median diameter of the ashless coal coke is preferably 80 μm, and more preferably 40 μm. On the other hand, the lower limit of the median diameter is preferably 1 μm and more preferably 10 μm. When the median diameter of the ashless coal coke exceeds the above upper limit, the inside of the ashless coal coke is not sufficiently carbonized and the bending strength of the carbon material may be insufficient. Conversely, when the median diameter of ashless coal coke is less than the above lower limit, the handleability and production efficiency of the aggregate may be reduced.

  As a minimum of the maximum particle size of ashless coal coke, 1 micrometer is preferred and 10 micrometers is more preferred. On the other hand, the upper limit of the maximum particle size is preferably 100 μm, and more preferably 80 μm. If the maximum particle size is smaller than the lower limit, the handleability and production efficiency may be reduced. On the other hand, when the maximum particle size exceeds the upper limit, the mixed state at the time of mixing with the binder becomes non-uniform, and there is a possibility that molding failure of the mixture or insufficient bending strength of the carbon material may occur.

  Moreover, it is good to make the median diameter of the ashless coal of a binder smaller than the median diameter of ashless coal coke. Thereby, the effect of the binder containing ashless coal can be improved more.

  Specifically, the lower limit of the ratio of the median diameter of the ashless coal coke to the median diameter of the ashless coal as the binder is preferably 1.2 times and more preferably 2 times. On the other hand, the upper limit of the ratio is preferably 5 times, and more preferably 4 times. When the ratio is smaller than the lower limit, the degree of improvement in the bending strength of the carbon material, which is an effect of the binder, may be reduced. Conversely, if the ratio exceeds the upper limit, it may be difficult to uniformly mix the binder and the aggregate.

  As a minimum of mass mixing ratio of an aggregate and a binder, 50:50 is preferred, 55:45 is more preferred, and 60:40 is still more preferred. On the other hand, the upper limit of the mass mixing ratio is preferably 85:15, more preferably 80:20, and even more preferably 75:25. If the mass mixing ratio is smaller than the lower limit, the content ratio of polyimide in the raw material of the carbon material is increased, which may make it difficult to form a mixture of the aggregate and the binder, and may increase the manufacturing cost of the carbon material. There is. Conversely, if the mass mixing ratio exceeds the upper limit, the bending strength of the resulting carbon material may be difficult to improve.

  The lower limit of the content of polyimide in the aggregate and binder mixture is 1% by mass, preferably 5% by mass, and more preferably 7% by mass. On the other hand, the upper limit of the content is 15% by mass, preferably 14% by mass, and more preferably 13% by mass. When the content is less than the lower limit, the bending strength of the obtained carbon material may be difficult to improve. On the other hand, if the content exceeds the upper limit, the fluidity of the binder in the mixture is lowered, the mixture of aggregate and binder may be difficult to mold, and the production cost of the resulting carbon material may be increased. There is.

  As a minimum of content of ashless charcoal in a mixture of an aggregate and a binder, 20 mass% is preferred and 21 mass% is more preferred. On the other hand, the upper limit of the content is preferably 35% by mass, more preferably 33% by mass, further preferably 30% by mass, and particularly preferably 28% by mass. If the content is less than the lower limit, the production cost of the resulting carbon material may increase. Conversely, if the content exceeds the upper limit, the bending strength of the resulting carbon material may be difficult to improve.

  The method for mixing the aggregate and the binder is not particularly limited, and for example, a method in which the aggregate and the binder are put into a known mixer and stirred while being pulverized by a conventional method can be used. By using this method, secondary particles in which aggregates or binders are aggregated can be pulverized, and these can be pulverized into granules. In addition, you may mix the aggregate and binder which were grind | pulverized previously.

  In the mixture of aggregate and binder, if necessary, a binder other than ashless coal and polyimide and an aggregate other than ashless coal coke may be mixed. Examples of binders other than the ashless coal and polyimide include coal pitch. By adding this coal pitch, the melting point of the binder can be lowered. Moreover, as an upper limit of the mixing ratio with respect to ashless coal of binders other than ashless coal and a polyimide, 10 mass% is preferable and 5 mass% is more preferable. If the mixing ratio of binders other than ashless charcoal and polyimide exceeds the above upper limit, the bending strength of the resulting carbon material may be insufficient.

[Heat forming process]
In the heat forming step, the mixture of the aggregate and the binder is formed into a desired shape by heating. By molding the mixture, the bond between the carbon materials can be further strengthened by the binder effect of ashless coal and polyimide, and the bending strength of the carbon material can be improved. Moreover, the powdering of a carbon material and the fall of a bulk density can be suppressed.

  The molding method of the mixture is not particularly limited. For example, a molding method using a double roll (double roll) molding machine having a flat roll, a double roll molding machine having an almond pocket, a press molding machine, an extrusion molding machine, or the like. Can be used. Among these, it is preferable to form the mixture into a briquette-shaped or sheet-shaped molded body using a double roll type molding machine.

  In this step, hot forming is performed in which the mixture is formed while being heated. Thus, by pressing the mixture under high temperature, the ashless coal and polyimide are plastically deformed after being softened to fill the gaps between the ashless coal coke, and a further compacted compact can be obtained. .

  As a minimum of heating temperature in this process, 200 ° C is preferred and 230 ° C is more preferred. On the other hand, the upper limit of the heating temperature is preferably 380 ° C, more preferably 350 ° C. If the heating temperature is lower than the lower limit, the mixture may not be sufficiently molded. Conversely, if the heating temperature exceeds the upper limit, thermal decomposition of ashless coal or the like may occur.

  Moreover, when the softening start temperature of ashless coal is set to T1 (degreeC), as a minimum of the heating temperature of the mixture in this thermoforming process, T1 + 20 degreeC is preferable and T1 + 30 degreeC is more preferable. When the heating temperature of the mixture is less than the above lower limit, the deformability of ashless coal becomes insufficient, and the density of the carbon material may be insufficient.

Molding pressure during the molding is not particularly limited, the lower limit of the molding pressure is preferably ^{0.5ton / cm 2, 1ton / cm} 2 is more preferable. On the other hand, the upper limit of the molding pressure is preferably ^{5ton / cm 2, 4ton / cm} 2 is more preferable. If the molding pressure is less than the lower limit, the density of the molded body becomes insufficient, and the bulk density of the resulting carbon material may be reduced. On the other hand, if the molding pressure exceeds the upper limit, there is a risk that cracks or the like occur in the molded body.

[Carbonization process]
In the carbonization step, a carbon material is obtained by heating the shaped body of the mixture. This step includes a carbonization step of performing carbonization in the mixture, and a graphitization step of further heating and graphitizing the carbonization mixture.

<Carbonization process>
In the carbonization step, the molded body obtained in the molding step is carbonized. Carbonization of the molded body is performed by heating in a non-oxidizing atmosphere. Specifically, the molded body is charged into an arbitrary heating device such as an electric furnace, the inside is replaced with a non-oxidizing gas, and then heated while blowing the non-oxidizing gas into the heating device. The ashless coal and polyimide are softened and melted by heating to be re-solidified, and the ashless coal coke voids are filled with ashless coal and polyimide.

  The heating temperature in this step may be appropriately set depending on the characteristics required for the carbon material, and is not particularly limited, but the lower limit of the heating temperature is preferably 500 ° C, more preferably 700 ° C. On the other hand, as an upper limit of heating temperature, 3000 degreeC is preferable and 2800 degreeC is more preferable. When the heating temperature is less than the above lower limit, carbonization may be insufficient. On the other hand, when the heating temperature exceeds the above upper limit, the production cost may increase from the viewpoint of improving the heat resistance of the equipment and fuel consumption.

  Moreover, as a minimum of the temperature increase rate in this process, 0.01 degree-C / min is preferable and 0.1 degree-C / min is more preferable. On the other hand, the upper limit of the heating rate is preferably 1 ° C./min, and more preferably 0.8 ° C./min. When the rate of temperature increase is smaller than the lower limit, the time required for carbonization increases and the production efficiency of the carbon material may be reduced. On the other hand, if the rate of temperature rise exceeds the upper limit, there is a risk that cracks or the like may occur in the molded body due to a rapid temperature change.

  In this step, the temperature holding time after the temperature rise may be appropriately set depending on the characteristics required of the carbon material, and the process may be shifted to the graphitization step immediately after the temperature rise. In this step, when the temperature is held after the temperature rise, the upper limit of the heating time of the holding time is preferably 10 hours, and more preferably 8 hours. When the said holding time exceeds the said upper limit, there exists a possibility that the production efficiency of a carbon material may fall.

  The non-oxidizing gas is not particularly limited as long as the oxidation of the carbon material can be suppressed, but an inert gas is preferable, and nitrogen gas is more preferable from the economical viewpoint among the inert gases.

<Graphitization process>
In the graphitization step, the molded body carbonized in the carbonization step is further graphitized. Graphitization of the molded body is performed by heating at a higher temperature than the carbonization step in a non-oxidizing atmosphere similar to the carbonization step. In the graphitization step, the same heating device as that in the carbonization step can be used.

  The heating temperature in this step may be appropriately set depending on the characteristics required for the carbon material, and is not particularly limited. However, the lower limit of the heating temperature is preferably 2000 ° C and more preferably 2200 ° C. On the other hand, as an upper limit of heating temperature, 3000 degreeC is preferable and 2800 degreeC is more preferable. When the heating temperature is less than the lower limit, graphitization may be insufficient. On the other hand, when the heating temperature exceeds the above upper limit, the production cost may increase from the viewpoint of improving the heat resistance of the equipment and fuel consumption.

Moreover, as a minimum of the temperature increase rate in this process, 0.01 degree-C / min is preferable, 0.1 degree
C / min is more preferable. On the other hand, the upper limit of the heating rate is preferably 3 ° C./min, and more preferably 2 ° C./min. When the rate of temperature increase is smaller than the lower limit, the time required for graphitization becomes long, and the production efficiency of the carbon material may be reduced. On the other hand, if the rate of temperature rise exceeds the upper limit, the graphite structure may be difficult to grow.

  The temperature holding time after the temperature increase in this step may be appropriately set depending on the characteristics required of the carbon material and is not particularly limited, but the lower limit of the holding time is preferably 30 minutes and more preferably 45 minutes. On the other hand, the upper limit of the holding time is preferably 10 hours, and more preferably 5 hours. If the holding time is smaller than the above lower limit, graphitization may be insufficient. Conversely, if the holding time exceeds the above upper limit, the production efficiency of the carbon material may be reduced.

<Carbon material>
The carbon material thus obtained is excellent in bending strength. The upper limit of the ash content of the carbon material is preferably 5000 ppm and more preferably 3000 ppm. The lower limit of the bulk density of the carbon material is preferably 1.5 g / cm ^3, more preferably 1.6 g / cm ^3, more preferably 1.63 g / cm ^3, especially 1.66 g / cm ³ preferable. Since the ash content of the carbon material is not more than the above lower limit and the bulk density is not less than the above lower limit, the carbon material is prevented from cracking and cracking and carbonized without being expanded, deformed, powdered, or the like. The shape of the previous molded body can be maintained.

<Advantages>
In the manufacturing method of the carbon material, the binder contains ashless coal and polyimide, and the content of the polyimide in the above mixture is within a specific range, so that the ashless coal molecule is entangled with the polyimide molecule, and in the carbon material. The bending strength of the structure derived from the binder is improved. Moreover, since the binder is efficiently filled into the space between the aggregates, the carbon density can be improved and the carbon material exhibiting high bending strength can be obtained. Furthermore, the cost concerning manufacture of a carbon material can be reduced by mixing and using an inexpensive ashless coal and an expensive polyimide.

[Other Embodiments]
The method for producing the carbon material is not limited to the above embodiment. In the above embodiment, a solution containing ashless charcoal and polyimide is obtained by mixing a solution containing ashless charcoal and a solution containing a polyamic acid polymer. After the synthesis, the polyimide and ashless coal may be mixed to obtain a binder.

  Further, a solution containing ashless coal and a solution containing a polyamic acid polymer and an ashless coal coke as an aggregate are mixed and then heated to imidize the polyamic acid polymer, and the aggregate and binder A mixture of

  Further, the aggregate and ashless coal may be mixed first, and then the polyamic acid polymer or polyimide may be added. Conversely, the aggregate and the polyamic acid polymer or polyimide may be mixed first, and then ashless charcoal may be added.

  In preparing the binder, the solvent removal step and the imidization step may be performed simultaneously. In this case, the pressure and temperature during heating can be adjusted as appropriate.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Example 1]
<Manufacture of ashless coal>
An Australian bituminous coal was used as a raw coal of ashless coal, and 1 kg (dry coal equivalent mass) of this raw coal and 4 times amount (4 kg) of 1-methylnaphthalene as a solvent were mixed to prepare a slurry. This slurry was put into a batch type autoclave having an internal volume of 10 L, nitrogen was introduced, the pressure was increased to 0.2 MPa, and the mixture was heated at 410 ° C. for 1 hour. This slurry is separated into a supernatant and a solid concentrate in the gravity settling tank maintained at the above temperature and pressure, and the solvent is separated and recovered from the supernatant by distillation. 0.4 kg of ashless I got charcoal. The softening start temperature of this ashless coal measured according to the JIS-M8801 (2004) Gisela plastometer method was 190 ° C.

<Preparation of binder>
(Solution containing polyamic acid polymer)
40.0 g of 4,4′-diaminodiphenyl ether (Wako Pure Chemical Industries) was added to 316.4 g of N-methyl-2-pyrrolidone (Wako Pure Chemical Industries) as a solvent, and pyromellitic dianhydride (Japanese) A solution containing a polyamic acid polymer was obtained by gradually adding 43.6 g of Kojunkaku Kogyo Co., Ltd. with stirring. The concentration of the polyamic acid polymer in the obtained solution was 20% by mass.

(Preparation of solution containing ashless coal)
The ashless coal and N-methyl-2-pyrrolidone as a solvent were mixed so as to be 25:75 (mass ratio), heated to 100 ° C., and stirred for 30 minutes. Then, it filtered in the state hold | maintained at 100 degreeC, the filtrate and the residue were fractionated, and the solution (filtrate) containing ashless coal was obtained. The concentration of ashless coal in this filtrate was 19.9% by mass.

(Solution mixing, solvent removal and imidization)
The solution containing the polyamic acid polymer and the solution containing ashless coal were mixed and stirred for 30 minutes. Subsequently, it heated at 120 degreeC in vacuum (-76kPaG), and was hold | maintained for 1 hour, the solvent in a mixed solution was removed, and powder was obtained. Thereafter, this powder was heated to 250 ° C. in a nitrogen atmosphere and held for 2 hours to imidize the polyamic acid polymer. The heated powder was pulverized so that the maximum diameter was 75 μm or less to obtain a powdery binder. The contents of ashless charcoal and polyimide in this binder were 91.4% by mass and 8.6% by mass, respectively.

<Preparation of aggregate (ashless coal coke)>
The ashless charcoal was heated at a rate of 0.5 ° C./min in a nitrogen atmosphere and heated to 1000 ° C. for carbonization. Then, it grind | pulverized so that a maximum diameter might be set to 75 micrometers or less, and the ashless coal coke as an aggregate was obtained.

<Molding, carbonization and graphitization>
65% by mass of ashless coal coke and 35% by mass of binder powder were mixed, this mixture was put in a mold, heated to 280 ° C., and pressed at a pressure of 3 ton / cm ² for 3 minutes to be molded. This molded product was put into a heating furnace, heated at a rate of 0.5 ° C./min in a nitrogen atmosphere, and heated to 1000 ° C. to be carbonized. Thereafter, the temperature was further increased to 2500 ° C. at a rate of 1 ° C./min and graphitized by holding at 2500 ° C. for 1 hour to obtain the carbon material of Example 1.

[Examples 2 to 4 and Comparative Examples 1 and 2]
Carbon materials of Examples 2 to 4 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1 except that the blending amounts of ashless coal, polyimide and ashless coal coke used were as shown in Table 1.

(Evaluation)
About the carbon material of the said Examples 1-4 and the comparative examples 1 and 2, the bulk density was measured based on JIS-K2151 (2004). Moreover, the bending strength of the obtained carbon material was measured based on JIS-R7222 (1997), and the following criteria evaluated. These results are shown in Table 2. In Table 2, “-” indicates that the mixture of aggregate and binder could not be molded and measurement was impossible.
A: The bending strength is 55 MPa or more.
B: Bending strength is 50 MPa or more and less than 55 MPa.
C: The bending strength is less than 50 MPa.

  As shown in Table 2, in Examples 1 to 4, in which ashless coal and polyimide are used as the binder, and the polyimide content is 15% by mass or less, the carbon material of Comparative Example 1 is excellent in bending strength. The bulk density was further improved. In particular, in Examples 3 and 4 in which the polyimide content was 7% by mass or more and 13% by mass or less, the bending strength was superior.

  On the other hand, in Comparative Example 1 using only ashless coal as the binder, the bending strength was inferior to the carbon material of the example. Moreover, in the comparative example 2 in which content of a polyimide exceeds 15 mass%, the mixture of a binder and an aggregate could not be shape | molded.

  As described above, the carbon material manufacturing method of the present invention can obtain a carbon material having excellent bending strength at low cost. Such a carbon material can be suitably used as a structural member, an electric / electronic component, a metal reducing material, or the like.

Claims (6)

Mixing the aggregate and its binder;
A step of thermoforming the mixture;
A carbon material production method comprising: carbonizing the molded body,
The binder contains ashless coal and polyimide obtained by solvent extraction treatment of coal,
Content of the polyimide in the said mixture is 1 mass% or more and 15 mass% or less, The manufacturing method of the carbon material characterized by the above-mentioned.   The method for producing a carbon material according to claim 1, wherein in the carbonization step, the mixture is heated at 500 ° C. or more and 3000 ° C. or less.   The method for producing a carbon material according to claim 1 or 2, wherein the aggregate is ashless coal coke obtained by carbonizing ashless coal.   The mixing step includes a step of mixing a solution containing ashless coal and a solution containing a polyamic acid polymer, a step of volatilizing a solvent in the mixed solution to obtain a powder, and heating the mixed solution to form the polyamic acid. The method for producing a carbon material according to claim 1, 2 or 3, comprising a step of imidizing a polymer and a step of mixing the powder and the aggregate.   The method for producing a carbon material according to any one of claims 1 to 4, wherein the carbonizing step includes a step of carbonizing the formed body and a step of graphitizing the carbonized formed body. A carbon material formed by molding and carbonization of a mixture containing an aggregate and its binder,
As the above aggregate, ashless coal coke obtained by carbonizing ashless coal is used,
As the binder, ashless coal and polyimide obtained by solvent extraction treatment of coal are used,
A carbon material, wherein the content of the polyimide in the mixture is 1% by mass or more and 15% by mass or less.