JP2004227815A - Pelletisation object and its manufacturing method, and separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a manufacturing process of a separator for a fuel cell, and form the separator for the fuel cell which is superior in electric and mechanical characteristics. <P>SOLUTION: A carbon mixture containing a carbon material (1) 70 to 95 pts. wt, a thermoplastic resin (2) 5 to 30 pts. wt, and an extender (3) 0.1 to 5 pts. wt is supplied to a heat kneading machine and the carbon mixture is passed through a high-temperature region in which a temperature is higher than that of the melting point of the thermoplastic resin (2), an intermediate-temperature region in which a temperature is higher than that of the softening point of the thermoplastic resin (2), and a low-temperature region in which a temperature is lower than that of the softening point of the thermoplastic resin (2). While continuing kneading, and when this is passed through the high-temperature region, the thermoplastic resin (2) melts and when this is passed through the intermediate-temperature region and the low-temperature region, the thermoplastic resin (2) is gradually solidified and a shaped body is formed. By cutting the shaped body in a desired size, a pelletized material in which the carbon material (1) is dispersed homogeneously can be obtained. When forming the separator for a fuel cell from the pelletized material, a calcining process to carbonize it at a high temperatures is not needed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pelletized product containing a conductive carbon material, a binder resin and an extender, a method for producing the same, and a fuel cell separator formed from the pelletized product.
[0002]
[Prior art]
A fuel cell that obtains electric energy by an electrochemical reaction between oxygen and hydrogen is environmentally friendly and has inexhaustible raw materials to be used. Therefore, it is expected as a next-generation energy alternative to petroleum and the like. In particular, application to automobiles that do not emit exhaust gas to the atmosphere is already in the practical stage.
[0003]
Fuel cells have a flat cathode that decomposes hydrogen gas into hydrogen ions and electrons, a flat anode that reacts oxygen gas, hydrogen ions and electrons to produce water, and a cathode plate and an anode plate. An electrolyte comprising a cation exchange membrane and the like arranged, a fuel cell unit is formed by the cathode, anode and electrolyte. In a fuel cell, a plurality of fuel cell units can be overlapped to obtain necessary power, and a conductive flat separator is interposed between the fuel cell units. The separator is electrically connected between the fuel cell units and separates hydrogen gas and oxygen gas flowing through flow paths formed on both main surfaces.
[0004]
The conventional separator disclosed in Patent Literature 1 includes 100 parts by weight of a binder such as phenol that can be carbonized or graphitized, 10 to 75 parts by weight of carbon fibers, and 50 to 150 parts by weight of conductive carbonaceous particles. It is formed from a carbonaceous composition. The carbonaceous composition is kneaded with an organic solvent such as acetone, and a sheet having a thickness of 2 mm and a size of 300 mm × 300 mm is formed in a molding die. Then, the temperature is raised to 2000 ° C. in a nitrogen gas atmosphere to bake the binder or the like. A separator is obtained by graphitizing and firing.
[0005]
Patent Document 2 discloses that after injection molding of a material obtained by adding 2 to 60% of a carbon material such as natural graphite powder to a phenol resin, the molded product is carbonized and fired at 1500 ° C. in a vacuum or an inert gas atmosphere. A fuel cell separator having a length of 100 mm, a width of 100 mm, and a thickness of 2 mm is disclosed.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 4-214072 (Claims, Examples)
[Patent Document 2]
JP 2001-143719 A (Claims, Examples)
[0007]
[Problems to be solved by the invention]
As described above, the conventional separator includes a relatively large amount of a binder such as a phenol resin for the conductive carbon material, and joins the particles of the carbon material while heating and melting the binder by an injection molding process. A flat separator is formed. Since the inside of the molded separator contains a large amount of the hardened non-conductive binder and the carbon material and the binder are not completely and uniformly dispersed, it is necessary to improve the electrical characteristics of the separator by firing the binder. There is.
[0008]
However, in order to completely carbonize and graphitize the binder, it is necessary to heat the separator at a temperature of 2000 ° C. or more for a long time in a vacuum or in the presence of an inert gas using a large-scale facility for firing the separator. Patent Document 1 describes that a separator is fired at a temperature rising rate of 10 ° C. or less per hour for 200 hours.
[0009]
The firing improves the conductivity of the separator. However, when the resin is carbonized and graphitized by firing, gas is generated inside the separator and a large amount of fine pores are formed. No improvement can be expected. Further, if the carbon material and the binder are not sufficiently uniformly dispersed, large pores or voids are formed, and conversely, the sintering deteriorates the conductive performance of the separator. When the electrical conductivity of the separator connecting the fuel cell units decreases, the power conversion efficiency of the fuel cell decreases and the amount of heat generated by the separator increases.
[0010]
When a large amount of pores are formed inside the separator to make it porous, the mechanical strength is reduced due to the decrease in density, and a separator having low impact resistance and vibration resistance is formed. Further, the gas easily permeates, and there is a possibility that hydrogen and oxygen of the fuel gas cannot be completely separated and react inside. Further, conventionally, a phenol resin is used as a binder and an organic solvent is used at the time of kneading, so that a harmful gas is generated by heating, which is not preferable in a working environment.
[0011]
Accordingly, an object of the present invention is to provide a pelletized product which can be produced without a firing step, a method for producing the same, and a fuel cell separator.
Another object of the present invention is to provide a pelletized product for forming a fuel cell separator having excellent electrical characteristics, mechanical characteristics and gas separation properties, and a method for producing the same.
It is still another object of the present invention to provide a pelletized product which can be safely manufactured without emitting harmful gas, a method for producing the same, and a fuel cell separator.
[0012]
[Means for Solving the Problems]
The pelletized product according to the present invention comprises 70 to 95 parts by weight of one or more kinds of finely divided carbon materials (1) selected from carbon black, artificial graphite and natural graphite, polyvinyl acetate, polymethyl methacrylate, One or more thermoplastic resins selected from polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polycarbonate, polyester resin, polystyrene, polyvinyl butyral, styrene acryl, liquid crystal polyester (LCP) and polyphenylene sulfide (2) 5 to 30 parts by weight, and 0.1 to 5 parts by weight of one or more kinds of fine particulate extender (3) selected from silica, barium sulfate, calcium carbonate, kaolin, bentonite and aluminum hydroxide Including. The fine-grained carbon material (1) and the fine-grained extender (3) are uniformly dispersed in the pellet structure and are firmly bound by the thermoplastic resin (2).
[0013]
Since 5 to 30 parts by weight of the thermoplastic resin (2) is smaller than 70 to 95 parts by weight of the carbon material (1), the thermoplastic resin (2) does not require firing at a high temperature and has a predetermined electric resistivity. The separator can be formed from pelletized material, and the manufacturing process can be simplified. Further, since the separator is not fired so as to be porous, a separator having a high density and high conductivity can be obtained, and the thermoplastic resin (2) remaining between the fine particles of the carbon material (1) allows the carbon material to be removed. (1) The space is firmly bonded, the mechanical strength of the separator can be improved, and a separator having excellent gas separation properties, vibration resistance and impact resistance is used as a partition wall, and the oxygen-containing gas and the hydrogen-containing gas are separated. Can be completely airtightly separated.
[0014]
If the carbon material (1) is less than 70 parts by weight, the conductive performance of the separator and the power conversion efficiency of the fuel cell decrease, and the calorific value of the separator increases. When the proportion of the carbon material (1) is increased beyond 95 parts by weight, the conductive performance is improved, but the mechanical strength of the formed separator is reduced because the carbon material (1) is brittle and vulnerable to impact. If the amount of the thermoplastic resin (2) is less than 5 parts by weight, the thermoplastic resin (2) does not easily enter the gaps between the particles of the carbon material (1), and the mechanical strength of the separator decreases. If the thermoplastic resin (2) exceeds 30 parts by weight, the mechanical strength is improved, but the electrical resistance of the separator is increased and the output of the fuel cell is reduced. If the extender pigment (3) acting as a reinforcing material is less than 0.1 part by weight, the strength of the separator is reduced, and if it exceeds 5 parts by weight, the conductivity of the separator is reduced.
[0015]
In the embodiment according to the present invention, a number of carbon fibers (4) in the form of short filaments having a length of 15 mm or less are uniformly dispersed in the pellet structure. The average particle diameter of the carbon material (1) is 0.05 to 200 μm, the average particle diameter of the thermoplastic resin (2) is 10 to 200 μm, and the average particle diameter of the extender (3) is 0.01 to 10 μm. is there.
[0016]
The fuel cell separator according to the present invention is formed into a plate shape from the pelletized product, and has a specific resistance of 1 × 10 ⁻³ to 10 × 10 ⁻³ Ωcm, a tensile strength of 10 to 20 MPa, and a bending strength of 10 to 250 MPa.
[0017]
An embodiment of the method for producing a pelletized product according to the present invention is a heat kneading controllable to a temperature between a high temperature range higher than the melting point of the thermoplastic resin (2) and a low temperature range lower than the softening point of the thermoplastic resin (2). Kneading a carbon mixture containing a fine-grained carbon material (1), a fine-grained thermoplastic resin (2) and a fine-grained extender (3) in a heat kneader while maintaining the machine in a high-temperature range; The method includes the steps of solidifying the thermoplastic resin (2) while controlling the temperature of the heat kneader to a low temperature range, forming a molded body of the carbon mixture, and forming the molded body of the carbon mixture into pellets.
[0018]
When the carbon mixture is kneaded by heating the heat kneader in a high temperature region where the thermoplastic resin (2) in the carbon mixture melts, the molten thermoplastic resin (2) infiltrates between the particles of the carbon material (1). Thus, the components are very uniformly dispersed and mixed. Further, by sufficient kneading, the thermoplastic resin (2) is given a molecular orientation by shearing, and in a molten state or a solid state, linear molecules can be arranged in a certain direction by the action of an external force. The molecular orientation can suppress the deterioration of the thermoplastic resin (2) in a later step and improve the mechanical properties of the separator. In addition, while controlling the temperature of the heat kneading machine in a low temperature range, the thermoplastic resin (2) is solidified in a continuous production line, and the carbon mixture is formed into a molded body, and then formed into a pellet. . Therefore, each pellet has a structure in which the carbon material (1), the thermoplastic resin (2), and the extender (3) are uniformly and densely dispersed without unevenness.
[0019]
The embodiment according to the present invention includes a step of kneading the carbon mixture in a high temperature range and then further kneading the carbon mixture by controlling a heat kneader in a middle temperature range higher than the softening point of the thermoplastic resin (2). In the kneading step, the carbon mixture is kneaded by a heat kneader of an intermeshing type twin-screw rudder (kneader), and the intermeshing type twin-screw rudder is moved along a flow of the carbon mixture into three temperature regions of a high temperature region, a medium temperature region and a low temperature region. Including the step of controlling the temperature, the step of forming into a pellet, the step of forming the molded body of the carbon mixture into a linear shape, and cutting the linear molded body into a predetermined length to form a pellet shape And a step.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a pelletized product according to the present invention, a method for producing the same, and a fuel cell separator using the pelletized product will be described with reference to FIGS.
[0021]
As shown in the enlarged view of FIG. 3, the pelletized product according to the present invention contains 70 to 95 parts by weight of the carbon material (1), 5 to 30 parts by weight of the thermoplastic resin (2), and 0.1% of the extender pigment (3). To 5 parts by weight, preferably 80 to 85 parts by weight of the carbon material (1), 15 to 20 parts by weight of the thermoplastic resin (2), and 2 to 5 parts by weight of the extender (3). The fine-grained carbon material (1) and the fine-grained extender (3) are uniformly dispersed in the pellet structure and are firmly bound by the thermoplastic resin (2). The carbon material (1), the thermoplastic resin (2), and the extender (3) have average particle sizes of 0.05 to 200 μm, 10 to 200 μm, and 0.01 to 10 μm, respectively. If the particle size of the carbon material (1) is less than 0.05 μm, it is scattered and difficult to handle, and if it exceeds 200 μm, the gap between the particles of the carbon material (1) becomes large and the fuel cell is formed from pellets. The electrical resistance of the separator increases. It is difficult to form a thermoplastic resin (2) having a particle size of less than 10 μm, and if it exceeds 200 μm, the thermoplastic resin (2) may not be completely melted inside. If the particle size of the extender (3) is less than 0.01 μm, it is scattered and handling is inconvenient. If it exceeds 10 μm, dispersion is insufficient and mechanical strength is reduced.
[0022]
The carbon material (1) has high conductivity and is selected from carbon black, artificial graphite and natural graphite. For example, natural gas, hydrocarbon gas, or the like is subjected to gas phase pyrolysis or incomplete combustion to obtain carbon black, and amorphous carbon is heated (graphitized) to 3000 ° C. or higher to obtain artificial graphite. It is preferable to use artificial graphite and natural graphite, which have lower electric resistance than carbon black.
[0023]
The thermoplastic resin (2) acts as a binder for joining the fine particles of the carbon material (1), and improves the mechanical strength of the fuel cell separator obtained by molding the pelletized product. In the present embodiment, the uniform dispersibility of the carbon material (1) and the thermoplastic resin (2) is enhanced to realize a fuel cell separator having a high strength and a low electric resistance in a contradictory relationship. Thermoplastic resin selected from polyvinyl acetate, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polycarbonate, polyester resin, polystyrene, polyvinyl butyral, styrene acrylic, liquid crystal polyester (LCP) and polyphenylene sulfide ( Use 2).
[0024]
The extender (3) acts as a reinforcing material and is selected from silica, barium sulfate, calcium carbonate, kaolin, bentonite and aluminum hydroxide.
Most preferred is a pelletized product containing 80 to 85 parts by weight of the artificial graphite (1), 15 to 20 parts by weight of the liquid crystal polyester (2), and 2 to 5 parts by weight of the silica (3). In order to prevent the fuel cell separator from being broken by impact or vibration, a large number of short filament (filament) carbon fibers (4) having a thickness of 1 to 20 μm and a length of 15 mm or less, preferably 0.1 to 10 mm are pelletized. Disperse evenly throughout the tissue.
[0025]
In producing the pelletized product, first, artificial graphite (1) as a carbon material, liquid crystal polyester (2) as a thermoplastic resin (2), and silica (3) as an extender are charged into a dry mixer. Then, the mixture is stirred and mixed to obtain a carbon mixture. Dry mixers such as a V-type mixer, a cylindrical mixer, a screw mixer, a ribbon mixer, a fluidized-bed mixer, an edge runner, a Henschel mixer, and a ball mill can be used, and the stirring speed is 200 to 1500 rpm, preferably 500 to 800 rpm. And However, as shown in FIG. 1, the artificial graphite (1), the liquid crystal polyester (2), and the silica (3) in the carbon mixture stirred by the dry mixer are not completely dispersed.
[0026]
Next, the carbon mixture is charged into a heat kneader capable of controlling the temperature. As the heat kneader, a Banbury mixer, a twin-screw ruder, a hot roll or the like can be used, but a twin-screw ruder, particularly a meshing twin-screw ruder (kneader) is most preferable.
[0027]
Although not shown, the biaxial rudder used in the present embodiment controls the temperature between a high temperature range higher than the melting point of the thermoplastic resin (2) and a low temperature range lower than the softening point of the thermoplastic resin (2). It is possible. The inlet and outlet of the cylinder formed on the two-axis rudder are set to a high temperature range and a low temperature range, respectively, and the middle portion of the cylinder is set to a middle temperature range higher than the softening point of the thermoplastic resin (2). The carbon mixture is kneaded and passed in the order of the inlet, the middle and the outlet of the cylinder, and at the same time, the carbon mixture is continuously controlled along the flow into three temperature ranges of a high temperature range, a medium temperature range and a low temperature range. The high, middle and low temperature ranges are 150-400 ° C, 100-300 ° C and 50-200 ° C, respectively.
[0028]
When the carbon mixture passes through the cylinder inlet of the biaxial ruder maintained at a high temperature range, the liquid crystal polyester (2) in the carbon mixture melts. At this time, the liquid crystal polyester (2) penetrates between the artificial graphite (1) particles, and the artificial graphite (1) is dispersed as shown in FIG. 2 due to a synergistic effect with kneading. In the present invention, a harmful substance is not used as a binder and an organic solvent is not added and kneaded, so that even when heated, a harmful gas is not generated from the carbon mixture, and a favorable working environment can be maintained.
[0029]
After the carbon mixture passes through the high temperature range, when the liquid crystal polyester (2) in the molten state passes through the middle portion of the cylinder controlled at the medium temperature range, the viscosity of the liquid crystal polyester (2) gradually increases, and the liquid crystal polyester (2) increases. ) Is used as a binder to bind the fine particles of the artificial graphite (1) to each other. By continuing the kneading vigorously during this time, the artificial graphite (1) and the liquid crystal polyester (2) are dispersed. Further, when the carbon mixture is passed near the outlet of the cylinder set to a temperature in a low temperature range, the liquid crystal polyester (2) solidifies and is integrated with the artificial graphite (1) and silica (3) to form a molded body. Become.
[0030]
The molded product is formed into a linear shape while kneading, and cut into a predetermined length while being extruded from a biaxial ruder, thereby forming a pelletized product according to the present invention. A pelletizer, a cutting machine, a hot cutting machine, or the like connected to a twin-screw rudder is used for forming a pelletized product. As shown in the enlarged cross-sectional view of FIG. 3, the formed pelletized product is in a state where artificial graphite (1), silica (3), and carbon fiber (4) are uniformly dispersed in solidified liquid crystal polyester (2). Become.
[0031]
When the pelletized product is filled into an injection molding machine and molded, a fuel cell separator according to the present invention is obtained. This separator has physical properties of specific resistance of 1 × 10 ⁻³ to 10 × 10 ⁻³ Ωcm, tensile strength of 10 to 20 MPa and bending strength of 10 to 250 MPa, and has high power conversion efficiency and can reduce the size of a fuel cell. Excellent in shock resistance and vibration resistance. In the conventional method for producing a separator, a baking step for improving the conductive performance by carbonizing and graphitizing the resin was required because the binder resin contained a large amount and each substance was not uniformly dispersed. As compared with the case where the content of the thermoplastic resin (2) is small and the molten thermoplastic resin (2) is sufficiently kneaded, the dispersibility of the carbon material (1) and the thermoplastic resin (2) is extremely high. For this reason, sufficient electrical and mechanical characteristics can be obtained without requiring a firing step of heating at a high temperature of about 2000 ° C. for a long time.
[0032]
【Example】
Examples of the pelletized product and the fuel cell separator according to the present invention will be described below.
[Example 1]
70 parts by weight of carbon black (1) having an average particle size of 0.1 μm, 30 parts by weight of polyvinyl chloride (2) having an average particle size of 50 μm, 10 parts by weight of barium sulfate (3) having an average particle size of 1 μm, 6 μm and 1 part by weight of a carbon fiber (4) having a length of 6 mm were weighed and charged into a cylindrical mixer, followed by stirring and mixing at 200 rpm for 30 minutes to obtain a carbon mixture. Next, a twin-screw router in which the vicinity of the cylinder inlet is set to a high temperature region of 200 ° C., the middle portion of the cylinder is set to a medium temperature region of 150 ° C., and the cylinder outlet portion (die diameter: 3 mm) is set to a low temperature region of 80 ° C. And a carbon mixture was charged and kneaded to obtain a molded body. The obtained molded body is cut into a pellet having a diameter of 3 mm and a length of 5 mm by a pelletizer to form a pellet, and the pellet is injection-molded, and has a specific resistance of 2 × 10 ⁻³ Ωcm, a tensile strength of 150 MPa, and a bending strength. A fuel cell separator having a physical property of a strength of 200 MPa and a length of 275 mm × width 225 mm × thickness 1 mm was obtained.
[0033]
[Example 2]
90 parts by weight of artificial graphite (1) having an average particle size of 100 μm, 10 parts by weight of a liquid crystal polyester (2) having an average particle size of 90 μm, 2 parts by weight of silica (3) having an average particle size of 0.02 μm, thickness of 2 μm and length 6 parts by weight of a carbon fiber (4) having a thickness of 9 mm was weighed and charged into a Henschel mixer, and stirred and mixed at 1100 rpm for 5 minutes to obtain a carbon mixture. Next, the vicinity of the cylinder inlet was set to a high temperature range of 300 ° C., the middle of the cylinder was set to a medium temperature range of 240 ° C., and the cylinder outlet (diameter of the die was 3 mm) was set to a low temperature range of 190 ° C. The carbon mixture was charged into the shaft ruder and kneaded to obtain a molded body. The obtained molded body is cut into a pellet having a diameter of 3 mm and a length of 5 mm by a pelletizer to form a pelletized product. The pelletized product is injection-molded, and has a specific resistance of 7 × 10 ⁻³ Ωcm, a tensile strength of 40 Mpa and a bending strength. A fuel cell separator having a physical property of a strength of 70 MPa and a length of 275 mm × width 225 mm × thickness 1 mm was obtained.
[0034]
The fuel cell unit was formed by installing the separators obtained in Examples 1 and 2 outside each of the cathode and the anode with the electrolyte membrane interposed therebetween. As a result of mounting and operating each of the 550 fuel cell units having these 550 fuel cell units mounted on an automobile, constant power can be obtained without abnormality for a long time, and the fuel cell separator according to the present embodiment can be sufficiently applied to automobiles. Was confirmed.
[0035]
【The invention's effect】
As described above, since the present invention does not require a firing step, the manufacturing steps of the fuel cell separator can be simplified, the manufacturing time can be reduced, and the manufacturing cost can be reduced. In addition, the separator formed by the pelletized product according to the present invention is excellent in power conversion efficiency, mechanical properties and gas impermeability because a highly conductive carbon material is uniformly dispersed, and is reliable in miniaturization. And a fuel cell with a high level of
[Brief description of the drawings]
FIG. 1 is an enlarged view showing a carbon mixture before being put into a heat kneader. FIG. 2 is an enlarged view of a carbon mixture showing a state where a thermoplastic resin is melted. FIG. 3 is an enlarged view showing an internal cross section of a pelletized product according to the present invention. [Explanation of symbols]
(1) Carbon material (artificial graphite, carbon black), (2) Thermoplastic resin (liquid crystal polyester, polyvinyl chloride), (3) Body pigment (silica, barium sulfate), (4) ·Carbon fiber,

Claims (8)

Carbon black, 70 to 95 parts by weight of one or more fine carbon materials selected from artificial graphite and natural graphite,
One or two selected from polyvinyl acetate, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polycarbonate, polyester resin, polystyrene, polyvinyl butyral, styrene acrylic, liquid crystal polyester (LCP) and polyphenylene sulfide 5 to 30 parts by weight of at least one kind of thermoplastic resin,
Silica, barium sulfate, calcium carbonate, kaolin, bentonite, and 0.1 to 5 parts by weight of one or more kinds of fine particulate extender pigments selected from aluminum hydroxide,
A pelletized material characterized in that the finely divided carbon material and the finely divided extender are uniformly dispersed in a pellet structure and are firmly bound by a thermoplastic resin. 2. The pelletized product according to claim 1, wherein a large number of short fiber (filament) carbon fibers having a length of 15 mm or less are uniformly dispersed in a pellet structure. 3. The average particle size of the carbon material is 0.05 to 200 μm, the average particle size of the thermoplastic resin is 10 to 200 μm, and the average particle size of the extender is 0.01 to 10 μm. Pelletized material. A pellet is formed from the pelletized product according to any one of claims 1 to 3 and has a specific resistance of 1 × 10 ⁻³ to 10 × 10 ⁻³ Ωcm, a tensile strength of 10 to 20 MPa and a bending strength of 10 to 250 MPa. A separator for a fuel cell, comprising: While keeping the heat kneader controllable at a high temperature range between a high temperature region higher than the melting point of the thermoplastic resin and a low temperature region lower than the softening point of the thermoplastic resin, a fine-grained carbon material in the heat kneader, A step of kneading a carbon mixture containing a fine-grained thermoplastic resin and a fine-grained extender,
A step of solidifying the thermoplastic resin while controlling the temperature of the heat kneader to a low temperature range, and forming a molded body of the carbon mixture,
Forming a compact of the carbon mixture into a pellet. The method for producing a pelletized product according to claim 5, further comprising a step of kneading the carbon mixture in a high temperature range, and further kneading the carbon mixture by controlling a heat kneader in a middle temperature range higher than the softening point of the thermoplastic resin. In the kneading process, the carbon mixture is kneaded by a heat kneader of an interlocking twin-screw rudder, and the temperature of the interlocking twin-screw rudder is controlled along a flow of the carbon mixture into three temperature ranges of a high temperature region, a medium temperature region and a low temperature region. The method for producing a pelletized product according to claim 6, comprising a step of carrying out. The step of forming into a pellet form includes a step of forming a formed body of the carbon mixture into a linear form, and a step of cutting the linear formed body into a predetermined length to form a pellet form. 8. The method for producing a pelletized product according to any one of items 7 to 7.

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