JP2008050245A - Manufacturing method of artificial graphite powder and artificial graphite fine powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an artificial graphite fine powder with excellent characteristics having a particle diameter of about 1-3 μm, a low ratio of long diameter to short diameter, a satisfactory bulk density, a low oil absorption amount and a low specific surface area, and also to provide a manufacturing method of the powder. <P>SOLUTION: The method of manufacturing the artificial graphite powder comprises dry crushing a carbon precursor, wet crushing, drying the resulting fine powder and graphitizing. The artificial graphite fine powder is manufactured by the above method and has an average particle diameter of at most 1±0.5 μm and a maximum particle diameter of 7 μm, comprises a primary particle having a ratio of long diameter to short diameter of at most 2, and has a crystallite size d<SB>002</SB>of at most 3.37 Å, a DBP oil absorption is at most 70 ml/100 g, a specific surface area of at most 20 m<SP>2</SP>/g and a bulk density of at least 0.3 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to artificial graphite fine powder and a method for producing the same, and relates to an artificial graphite fine powder having an average particle size of about 1 μm or less or 3 μm or less, which is effective for use in batteries, conductive assistants for capacitors, various conductive filler materials, and the like. And a manufacturing method.

Conventionally, powders of carbon materials and graphite materials have been used for various applications taking advantage of properties such as electrical conductivity, thermal conductivity, and slidability.
Typical examples of these include carbon black, natural graphite powder, and artificial graphite powder. Recently, vapor grown carbon fiber (VGCF), carbon nanotube, and the like are also known.

  Carbon black is generated by incomplete combustion of hydrocarbons such as petroleum and natural gas, or pyrolysis, and the resulting particles are agglomerated with very fine nano-micron primary particles, that is, a plurality of primary particles. It constitutes secondary particles called connected structures.

When wet measurement is performed with a laser-diffraction type particle size distribution analyzer, an average particle size measurement value of submicron order is obtained, but only secondary particles or aggregates of these are measured. Absent.
In reality, there is no carbon black having primary particles of 1 μm or less.

  Main applications of carbon black include conductive additives and rubber additives. Particularly in the field of conductive assistants, the above-mentioned structure is effectively used to contribute to improving the conductivity of the additive, but there is no example of use by breaking it into primary particles.

Among the carbon blacks currently in use, Ketjen Black, which is particularly excellent in conductivity, has a primary particle size of 30 nm, an oil absorption of 360-500 ml / 100 g, and a specific surface area of 800-1050 m ² / g, both of which have a high oil absorption. , High specific surface area.
For this reason, a large amount of solvent is required when dispersed in a solvent, and there is a problem in terms of work, such as the possibility of dripping at the edges when forming a coating film using this.
Moreover, when it is used in a dry process, it remains agglomerated, and it is difficult to uniformly disperse, and there are disadvantages that characteristics such as conductivity cannot be sufficiently provided.

Among other conductive carbon blacks, carbon black made by Mitsubishi Chemical has a particle size of 20-50 nm, oil absorption of 130-175 ml / 100 g, carbon black made by Tokai Carbon has a particle size of 18-70 nm, oil absorption 60-130 ml / 100 g, all have a particle size of several tens of nm or less, and the oil absorption exceeds 100 ml / 100 g.

Conventional carbon black production methods are basically not suitable methods for obtaining micron-order primary particles, and there are many cases where combustion is insufficient and there is a risk of having carcinogenicity. There is also.
Furthermore, since it is an agglomerate, the bulk density is low. For example, a lithium ion battery negative electrode material, a large amount of powder in a predetermined volume is required for improving the characteristics, and the dispersion medium used in combination. When the amount is limited to a small amount, it is not a suitable material.

  Carbon black having a particle size of about 1 μm and low oil absorption and specific surface area to such a degree that the above-mentioned drawbacks can be eliminated has not been obtained.

  Other than carbon black, there are graphite fine powders obtained by pulverizing and classifying natural graphite and artificial graphite.

Natural graphite is highly crystallized graphite and exhibits high charge / discharge capacity when used as a negative electrode material for lithium ion batteries.
For example, Japanese Patent Laid-Open No. 2000-200606 describes a powder obtained by pulverizing natural graphite with a jet mill and heat-treating it at a temperature of 900 ° C. or more as a graphite powder for a lithium secondary battery negative electrode material. (Patent Document 1)

  JP2000-200466A

However, when highly crystallized natural graphite is pulverized to a fine powder, it tends to be flaky and the ratio of the major axis to the minor axis increases.
When the ratio of the major axis to the minor axis is high, orientation is easy and anisotropy tends to occur in the characteristics.

  For example, when used as a negative electrode material for lithium ion secondary batteries, the cycle characteristics due to charge and discharge are reduced by orientation, and even in coating films for other electronic applications, it is oriented in the plane direction, so isotropic conductivity is obtained. If required, there are disadvantages such as inappropriateness.

For example, natural graphite fine powder FS-4 (manufactured by Qingdao Koyu Shishiki) made in China has an average particle size of 3.6 μm, and the ratio of major axis to minor axis is about 2.8.
No other natural graphite powder having a particle diameter of about 1 μm and a ratio of the major axis to the minor axis is comparable.
The average particle diameter is about 3 to 4 μm even in the case of a commercially available product and a fine-grained product.

In addition, HOP series (manufactured by Nippon Graphite Industry Co., Ltd., average particle diameter of 4 μm) is obtained by pulverizing earth graphite as a kind of natural graphite, but its bulk density is as low as 0.15 g / cm ³ .

  The method for producing artificial graphite is a method obtained by firing and graphitizing a carbon precursor such as coke, coke and binder-pitch mixed molded body, and mesophase pitch.

Artificial graphite is easier to control the ratio of the major axis to the minor axis than natural graphite, and includes the following.
Artificial graphite UF-J5 (manufactured by Showa Denko) has an average particle diameter of 3.0 μm and a bulk density of 0.2 g / cm ³ , and artificial graphite SG series (manufactured by SSC) has an average particle diameter of 1 μm and a specific surface area of 16 ˜25 m ² / g, oil absorption 70-120 ml / 100 g, bulk density 0.2 g / cm ³ or average particle size 3 μm, specific surface area 5-20 m ² / g, oil absorption 40-120 ml / 100 g, bulk specific gravity 0 There are 2 g / cm ³ .
Artificial graphite KS6 (manufactured by TIMCAL) has an average particle diameter of 3 μm, a specific surface area of 20 m ² / g, d ₀₀₂ 3.357 mm, and artificial graphite CX-10000 (manufactured by Chuetsu Graphite Industries) has an average particle diameter of 3 μm.

  These are all obtained by cutting or pulverizing artificial graphite blocks and particles, and further sizing them, so that the bulk density is not sufficient, and the oil absorption and specific surface area are the same as in the above carbon black. There are high drawbacks.

  Vapor grown carbon fibers (VGCF) and carbon nanotubes have a large ratio of major axis to minor axis and are excellent in terms of improving electrical conductivity, but are expensive and have limited uses. In addition, since the ratio of the major axis to the minor axis is large and the bulk density is low, a device for dispersion and mixing is required.

In addition to those described above, carbon / graphite powders are utilized in various fields and methods in various fields and methods, taking advantage of their respective particle sizes, shapes, and other characteristics.
However, the fine powder of carbon material and graphite material has a particle size of about 1 μm to 3 μm, a small ratio of the major axis to the minor axis, a low specific surface area, a relatively small oil absorption, and a high bulk density. Nothing has been obtained.

  In view of the situation as described above, the present invention is a fine powder having a particle size of about 1 μm to 3 μm, a ratio of the major axis to the minor axis is low, has a sufficient bulk density, and has a low oil absorption and specific surface area. An artificial graphite fine powder having the above characteristics and a method for producing the same are provided.

In order to solve the above problems, the present invention proposes primary particles having an average particle size of 1 μm ± 0.5 μm or less, a maximum particle size of 7 μm or less, and a ratio of major axis to minor axis of 2 or less. And an artificial graphite fine powder having a crystallite size d ₀₀₂ of 3.37 mm or less, a DBP oil absorption of 70 ml / 100 g or less, a specific surface area of 20 m ² / g or less, and a bulk density of 0.3 g / cm ³ or more. is there.
This production method was obtained by subjecting carbon precursors such as coke, raw coke, and meso-face pitch to the same or after firing as necessary, followed by dry grinding and further wet grinding and drying as necessary. The fine powder is graphitized.
The present invention is described in detail below.

  As the carbon precursor used as the raw material of the present invention, various cokes, meso face pitches, meso carbon micro beads and the like are used.

In coke, calcine coke and raw coke can be directly pulverized, but calcine coke is hard and difficult to grind.
In addition, when raw coke is finely pulverized (wet) to 1 μm, deformation, aggregation, granulation, etc. may occur, and a powder having a desired particle size may not be obtained.
For this reason, in order to perform a grinding | pulverization appropriately, what baked raw coke at 800-1200 degreeC is preferable.

As the coke structure, those having a flow structure and a mosaic structure are suitable.
This structure changes the ratio of the major axis to the minor axis after graphitization after pulverization, so if a graphite powder with a smaller ratio of major axis to minor axis is required, use a mosaic or fine mosaic structure. Is preferred. Specifically, when a graphite powder having a smaller ratio of the major axis to the minor axis is required from those having an expansion coefficient of 2 × 10 ⁻⁶ / ° C. or more when graphitized, it is 5 × 10 ⁻⁶ / ° C. or more. It is preferable to choose from those.

In order to obtain the target graphite fine powder, the above carbon precursor is first pulverized.
This pulverization is slightly different depending on whether the target powder has a particle size of 1 μm or 3 μm.
In the case of a 3 μm product, it is possible only by dry pulverization using various pulverizers. However, in the case of a 1 μm product, wet pulverization using a bead mill is required following dry pulverization.
The pulverization is gradually and finely pulverized into coarse particles, medium particles, fine particles, and ultrafine powders according to the particle size of the raw material to obtain a desired particle size.

The pulverizer used in the dry pulverization is appropriately selected according to the size and hardness of the raw material.
Large lumps with a particle size of several centimeters are high torque type Orient Mill (made by Orient Co., Ltd.), Rotoplex, Feather Mill (made by Hosokawa Micron Co., Ltd.) and Cutter Mill (Tokyo Atomizer Co., Ltd.). Medium crushing is performed by a crusher such as a roll crusher (Makino Co., Ltd.).
Next, in order to pulverize more finely, or if it is a raw material of several mm, from the beginning Pulverizer (-Dalton, Tokyo Atomizer, etc.), Hammer Mill, ACM Pulverizer, Victory Mill, Coroplex, Ultraplex (Hosokawa Micron Co., Ltd.), Tabo Mill (Tabo Industries Co., Ltd.), Impeller Mill (Seisin Enterprise Co., Ltd.), Vibrating Mill (Chuo Kako Co., Ltd.), etc. Do.
Alternatively, in order to further reduce the particle size, dry pulverization is performed to a particle size as fine as possible with a jet crusher (for example, Seisin Co., Ltd., Hosokawa Micron Co., Ltd., Nippon Numatic Kogyo Co., Ltd., etc.). .

  Thereafter, if necessary, wet grinding is performed with a bead mill (Shinmaru Enterprises, Ashizawa Finetech Co., Ltd., Nihon Eirich Co., Ltd., etc.) until the average particle size is 3 μm or less and 1 μm or less.

  In the case of producing a 1 μm product, it is difficult to reach the target particle size only by the dry pulverization method, and therefore, wet pulverization with a bead mill is necessary following dry pulverization. Although the dispersion medium for wet pulverization is not specified, it is preferable to use water because it is inexpensive in consideration of the price of the dispersion medium, safety, wastewater treatment costs, and the like.

  The maximum particle size of the pulverized product is set to 13 μm or less and 7 μm or less for the 3 μm product and the 1 μm product, respectively, considering aggregation during firing / graphitization and drying.

    In the case of wet pulverization, subsequent drying is necessary. However, the drying method is not particularly limited as long as it does not cause aggregation after drying.

    As dryers, hot air circulation dryers that are simply dried with hot air, vibration dryers, fluidized bed dryers, spray dryers, air dryers that are sprayed and dispersed while applying air currents to a slurry, and freezers There are dryers.

  Among these, the air dryer is preferable because it can be dried while being dispersed so as not to aggregate. However, among the air-flow dryers, the flash jet dryer has the drawbacks that internal adhesion is likely to occur during operation, and the spray dryer is easy to granulate, so it is necessary to select the operation conditions. Particularly preferred is a micro mist dryer, which can be dried without generating aggregates even after wet crushing.

  Other dryers, i.e., hot-air circulating dryers, vibration dryers, etc., are not preferred because they tend to agglomerate during drying and require a crushing step after drying. If graphitization is performed with the agglomeration remaining, strong agglomeration will be generated, the particle size will become too large, or if aggregates or granules are mixed in the drying after the last wet pulverization, there will be a quality problem There are drawbacks such as

After pulverization, firing is performed as necessary.
In the case of wet pulverization, it is appropriate to pulverize and dry after firing.

Firing is performed when there is a large amount of volatile matter and it is necessary to make it very small. When the heat history of 800 ° C. or higher is already received, it is possible to proceed directly to graphitization in the next step.
The firing conditions are suitably performed at a firing temperature of 800 to 1200 ° C. in a non-oxidizing atmosphere, and may be slightly higher or lower than this as long as the volatile components become a very small amount. However, the treatment at about 1300 to 1400 ° C. is generally a place where the hardness of the carbon material is the highest, so if there is a pulverization step thereafter, it will be difficult to pulverize, which is not preferable.

  In general, the generation of volatile components by pyrolysis of the carbon precursor is most often 600 to 800 ° C. If graphitization is performed with a large amount of volatile matter, troubles may occur in the operation of the furnace due to the generation of a large amount of volatile matter, or agglomeration due to the volatile matter may occur. Baking is preferably performed at a reduced temperature.

  After firing, it is graphitized in an inert gas or reducing atmosphere in an Atchison furnace or the like. The graphitization temperature is preferably 2800 to 3200 ° C. Below 2800 ° C, the conductivity of the powder obtained due to insufficient crystallization is low, and when it exceeds 3200 ° C, it cannot be substantially graphitized.

  The artificial graphite fine powder of the present invention is obtained as described above.

The characteristics of the artificial graphite fine powder obtained as described above are as follows. In the 1 μm product, the ratio of the major axis to the minor axis is 2 or less, the crystallite size d ₀₀₂ is 3.37 mm or less, the DBP oil absorption is 70 ml / 100 g or less, The specific surface area is 20 m ² / g or less and the bulk density is 0.3 g / cm ³ or more.
The 3 μm product has a major axis / minor axis ratio of 2 or less, a crystallite size d ₀₀₂ of 3.37 mm or less, a DBP oil absorption of 35 ml / 100 g or less, a specific surface area of 5 m ² / g or less, and a bulk density of 0.9 g / cm ³ or more. It is.

Applications of the artificial graphite fine powder of the present invention are as follows.
Conductive aid for batteries, capacitors and fuel cells.
Filler or structural member for imparting conductivity to resin, rubber, ink, ceramics, metal, carbonaceous carbon, composite material, etc., or for controlling electric characteristics such as resistance and charge amount.
Filler for controlling hydrophilicity and lipophilicity of resins, rubbers, inks, ceramics, metals, carbonaceous carbon, composite materials, etc.
Filler for controlling the hardness of resin, rubber, ink, ceramics, metal, carbonaceous carbon, composite material, etc.
Filler for controlling mechanical properties such as strength, fracture energy, friction coefficient, etc. of resin, rubber, ink, ceramics, metal, carbonaceous carbon, composite material, etc.
Coating carrier such as CVD and plating.

    In the present invention, a fine powder having excellent characteristics with a small ratio of major axis to minor axis, a sufficient bulk density, low oil absorption, and low specific surface area can be obtained for graphite fine powder having a particle diameter of about 1 μm.

Examples and comparative examples

    Next, embodiments of the present invention will be described in the following examples.

After coarsely pulverizing coal-based pitch raw coke having a mosaic structure and a thermal expansion coefficient of 5.7 × 10 ⁻⁶ / ° C. to an average particle size of about 40 to 60 μm using Orient Mill (manufactured by Orient) The powder was pulverized with a jet mill STJ-400 (manufactured by Seishin Enterprise Co., Ltd.) to obtain a powder of about 4 μm.
Next, this 4 μm powder was fired at 1000 ° C. in a nitrogen atmosphere.
After firing, water is used as a dispersion medium by a beads mill (manufactured by Shinmaru Enterprises), a small amount of surfactant is added, and the mixture is dispersed and processed repeatedly, with an average particle size of 0.8 μm, maximum Wet grinding was performed until the particle size became 7 μm or less.
Thereafter, the powder obtained by drying with an airflow type dryer flash jet dryer was graphitized at 3000 ° C. in an Atchison furnace.
Thereafter, water was used as a dispersion medium again by the above bead mill, and wet crushing was performed by repeatedly passing through the bead mill twice in a state where a small amount of surfactant was added and mixed and dispersed. Finally, it was dried by an airflow type dryer flash jet dryer to obtain fine graphite powder.
The resulting graphite powder had a mean particle size of 1 μm and a maximum particle size of 6.5 μm. Further, when each characteristic was measured, the specific surface area was 16 m ² / g, the oil absorption was 59 ml / 100 g, the crystallite size d ₀₀₂ was 3.364 Å, the bulk density was 0.3 g / cm ³ , and the ratio of the major axis to the minor axis was 1.7.

Coarse raw coke having a mosaic structure and a thermal expansion coefficient of 2 × 10 ⁻⁶ / ° C. is coarsely pulverized to an average particle size of about 40 to 60 μm with an Orient mill (manufactured by Orient), and further vibrated. The powder was pulverized with a mill (manufactured by Chuo Kakoki Co., Ltd. and then with a jet mill SJT-400 (manufactured by Seishin Enterprise Co., Ltd.)) to obtain a powder of about 4 μm.
Next, this powder was fired at 1000 ° C. in a nitrogen atmosphere.
Thereafter, a graphite fine powder was obtained in the same manner as in Example 1 except that a micro mist dryer (Fujisaki Electric Co., Ltd.) was used in two drying steps.
The obtained graphite fine powder had an average particle size of 1.1 μm and a maximum particle size of 6.5 μm. When measuring each characteristic, the specific surface area was 15 m ² / g, the oil absorption was 65 ml / 100 g, the crystallite size d ₀₀₂ was 3.363 mm, the bulk density was 0.3 g / cm ³ , and the ratio of the major axis to the minor axis was 1. It was 9.

The raw coke used in Example 1 was dry pulverized in the same manner as in Example 1 and fired at 900 ° C.
Next, wet pulverization was performed with a bead mill (manufactured by Ashizawa Finetech Co., Ltd.) using water as a dispersion medium, and pulverization was performed until the average particle size became 0.8 μm and the maximum particle size became 7 μm.
The slurry was thinly spread on a bat and dried at 110 ° C. with a hot air dryer (manufactured by ESPEC).
The obtained powder was graphitized at 3000 ° C. in an Atchison furnace, and then wet pulverized in the same manner as in Example 1, followed by final drying using an airflow dryer Micromist dryer (manufactured by Fujisaki Electric Co., Ltd.). A fine graphite powder was obtained.
The obtained powder had an average particle size of 1.1 μm and a maximum particle size of 6.8 μm. When measuring each characteristic, the specific surface area was 15 m ² / g, the oil absorption was 66 ml / 100 g, the crystallite size d ₀₀₂ was 3.364 Å, the bulk density was 0.3 g / cm ³ , and the ratio of the major axis to the minor axis was 1. .75.

After insolubilizing a mesophase pitch with a softening point of 350 ° C., dry grinding using an orientation mill and a jet mill in the same manner as in Example 1 to obtain an average particle size of 3.5 μm, and then gradually raising the temperature in air Then, it was infusibilized by treatment at a maximum of 320 ° C. for 30 minutes.
This was fired at 900 ° C. in a nitrogen stream, and then graphitized at 3000 ° C. in an Atchison furnace.
The obtained powder was classified with an airflow classifier, and the fine particle side was passed through a sieve having an opening of 25 m with an ultrasonic vibration sieve to obtain a fine graphite powder.
The obtained powder had an average particle size of 3.0 μm and a maximum particle size of 12 μm. When each characteristic was measured, the specific surface area was 4.9 m ² / g, the oil absorption was 33 ml / 100 g, the crystallite size d ₀₀₂ was 3.364 mm, the bulk density was 0.9 g / cm ³ , and the ratio of the major axis to the minor axis Was 1.75.
(Comparative Example 1)

Coal pitch-based coke having a mosaic structure and a thermal expansion coefficient of 5.7 × 10 ⁻⁶ / ° C. is coarsely pulverized to an average particle size of about 40 to 60 μm with an orient mill, and then further pulverized with a dead mill. The particle size was 4 μm.
This powder was fired at 1000 ° C. in a nitrogen atmosphere. Using a bead mill, water is used as a dispersion medium, a small amount of surfactant is added, mixed and dispersed, and repeatedly treated. Wet grinding until an average particle size of 0.8 μm and a maximum particle size of 7 μm or less is achieved. did. The obtained slurry was transferred to a vat and dried in a hot air dryer. After drying, it was crushed with an orient mill, then transferred to a graphite crucible and graphitized at 3000 ° C. However, the hard aggregate of several mm that could not be crushed by duplication replicated, and the desired graphite fine powder could not be obtained. It was.
(Comparative Example 2)

  The daily coke was dry pulverized with an orientation mill and an impeller mill, and then wet pulverized with a bead mill (manufactured by Ashizawa Finetech Co., Ltd.). However, although the average particle size becomes 0.6 to 1.1 μm even if the treatment is continued for a long time, the maximum particle size is conversely increased with the lapse of time, and a particle size of less than 7 μm could not be obtained.

Claims (6)

  A process for producing artificial graphite fine powder, characterized in that a fine powder obtained by dry pulverizing a carbon precursor and further wet pulverizing is dried and graphitized.   A process for producing artificial graphite fine powder, characterized in that a fine powder obtained by dry pulverizing and firing a carbon precursor and further wet pulverizing is dried and graphitized.   A method for producing artificial graphite fine powder, characterized by graphitizing fine powder obtained by dry-pulverizing a carbon precursor.   A method for producing artificial graphite fine powder, characterized in that fine powder obtained by dry-grinding a carbon precursor is calcined and graphitized. An artificial graphite fine powder produced by the production method according to any one of claims 1 to 4, wherein the average particle size is 1 µm ± 0.5 µm or less, the maximum particle size is 7 µm or less, and the ratio of the major axis to the minor axis is 2 or less primary particles having a crystallite size d ₀₀₂ of 3.37 cm or less, a DBP oil absorption of 70 ml / 100 g or less, a specific surface area of 20 m ² / g or less, and a bulk density of 0.3 g / cm ³ or more. Artificial graphite fine powder. An artificial graphite fine powder produced by the production method according to claim 1, wherein the average particle size is 3 μm ± 0.5 μm or less, the maximum particle size is 12 μm or less, and the ratio of major axis to minor axis is 2 or less primary particles having a crystallite size d ₀₀₂ of 3.37 mm or less, a DBP oil absorption of 35 ml / 100 g or less, a specific surface area of 5 m ² / g or less, and a bulk density of 0.9 g / cm ³ or more. Artificial graphite fine powder.