JP2005089235A - Orientational graphite powder and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the graphite powder maintaining various characteristics of graphite and having high orientation and to provide a manufacturing method capable of manufacturing the powder by only a temperature process. <P>SOLUTION: The powder is formed by using a fiber material consisting of an aromatic polymer such as a polyamide as a starting raw material and only by the temperature process in which the starting raw material is fired in a prescribed atmosphere in accordance with a prescribed temperature profile. Concretely, the powder is formed by a step of preparing the aromatic polymer fiber material, a step of prefiring the fiber material at a prescribed temperature selected from a temperature range of 300-1,400°C and a step of subjecting again the fiber material to final firing at a temperature from normal temperature to a prescribed temperature near 3,000°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an oriented graphite powder that can be used in various fields such as a cathode material and a hydrogen storage material, and a method for producing the same.

Graphite made of carbon (C) occupies an important position as an industrial material because it has outstanding heat resistance, chemical resistance, high conductivity and high heat conductivity. Naturally produced graphite is used as such graphite. However, since the production amount is limited, artificially produced graphite is generally used. For example, in recent years, it has been industrially attempted to produce sheet-like graphite by using an aromatic polymer such as polyimide as a starting material and firing it. Examples of applications of this artificial graphite include products such as X-ray optical parts, high thermal conductive sheets, and diaphragms having excellent high frequency characteristics. About the manufacturing method etc., it is disclosed by patent document 1, etc., for example. However, these are all plate-shaped, sheet-shaped and block-shaped.
Japanese Patent Laid-Open No. 04-084600

  As described above, conventionally, only sheet-like or plate-like graphite produced through a firing process has been disclosed, and a method for artificially producing powdery graphite having a uniform size has not been known.

  Further, there is a method of pulverizing conventional plate-like and block-like graphite, but there is a problem that it is difficult to obtain fine powder because graphite has high lubricity.

  The present invention has been made in view of the above problems of the prior art, and an object thereof is to obtain an oriented graphite powder having a desired size by a relatively easy method.

  Specifically, for example, using a temperature process step, directly from an aromatic polymer (starting raw material) such as polyamide or polyimide, a method for producing a highly uniform graphite powder having a uniform size is provided. The obtained oriented graphite powder can be applied as an electron emission material, a hydrogen storage material, or the like.

  The first oriented graphite powder of the present invention is an oriented graphite powder whose main composition is carbon (C), and is characterized in that a void region is included in the powder. This functions as an oriented graphite powder suitable for applications such as electron emission and hydrogen storage. In particular, since the surface area of the voids can be substantially increased, it is particularly preferable when considering applications such as hydrogen storage.

In the first oriented graphite powder, the graphite powder density is preferably in the range of 0.60 to 1.60 g / cm ³ . More preferably, the powder density is in the range of 0.80 to 1.20 g / cm ³ .

  In the first oriented graphite powder, the graphite powder composition may include at least one or more of phosphorus (P), calcium (Ca), silicon (Si), aluminum (Al), and magnesium (Mg). preferable.

  In the first oriented graphite powder, it is preferable that a planar structure (graphene structure) having a six-membered carbon structure is laminated in a layered manner with a correlation. Thereby, various characteristics of graphite can be maintained even in a powder state.

  In the first oriented graphite powder, the crystallite size constituting the graphite powder is preferably 100 nm or more.

  The first method for producing an oriented graphite powder of the present invention comprises a step of preparing an aromatic polymer fiber body as a starting material, and a step of firing the starting material in a predetermined atmosphere according to a predetermined temperature profile. It is a feature. This makes it possible to directly obtain oriented graphite powder with a certain degree of particle size by controlling the diameter of the fibrous material that is the starting material, and to apply oriented graphite powder with excellent characteristics to various applications. It becomes easy.

  Further, the second method for producing an oriented graphite powder of the present invention comprises a step of preparing an aromatic polymer foam as a starting material and a step of firing the starting material in a predetermined atmosphere according to a predetermined temperature profile. It is characterized by this. This makes it possible to directly obtain oriented graphite powder with a certain degree of particle size by controlling the foaming degree of the starting foam, and to apply oriented graphite powder with excellent properties to various applications. Easy to do.

  In the method for producing an oriented graphite powder of the present invention, the starting material is polyamide, polyimide, polyphenylene terephthalamide (PPTA), polyphenylene oxasdiazo (POD), polybenzothiazole (PBT), polybenzobisthiazole (PBBO), It is preferably selected from polyphenylenebenzimidazole (PBI), polyphenylenebenzobisimidazole (PPBI), polythiazole (PT), and polyparaphenylenevinylene (PPV). Thereby, powdery oriented graphite can be easily obtained by controlling the temperature profile of the firing step. In particular, polyimide is preferable in terms of controllability.

  Moreover, in the manufacturing method of the oriented graphite powder of this invention, it is preferable that the said starting material is a woven fabric shape woven with the said aromatic polymer fiber body. Thereby, handling becomes easy and a raw material filling rate can be raised.

  Further, in the method for producing oriented graphite powder of the present invention, the temperature process of the firing step is a pre-baking step at a predetermined temperature selected from a temperature range of 300 ° C. to 1400 ° C., and a predetermined temperature again from room temperature to around 3000 ° C. It is preferable to consist of the process of carrying out this baking. Thereby, it is possible to directly obtain a graphite powder having a high orientation and a substantially uniform particle size.

  Further, in the method for producing an oriented graphite powder of the present invention, the pre-baking step is a condition of heating at 1200 ° C. within 3 hours after increasing the temperature from 400 ° C. to 1200 ° C. at a temperature rising rate of 10 ° C./min or less. It is preferable. This is preferable because the degree of orientation of the obtained graphite powder is increased.

  In the method for producing an oriented graphite powder of the present invention, the pre-baking atmosphere is preferably either argon or nitrogen or a mixed atmosphere thereof. Thereby, an atmosphere suitable for pulverization is obtained. In particular, when the starting material is polyimide, it is preferable in terms of pulverization that the pre-baking atmosphere is nitrogen.

  In the method for producing an oriented graphite powder of the present invention, the main firing step is selected from a temperature range of 2500 ° C. to 3200 ° C., and the temperature from normal temperature to the main firing temperature is increased at a rate of temperature increase of 10 ° C./min or less. After that, it is preferable that the heating temperature is within 3 hours at the main firing temperature. Thereby, the degree of orientation of the obtained graphite powder is increased, and the oriented graphite is directly powdered, which is preferable. In particular, the main baking temperature is preferably around 2700 ° C.

  Further, the method for producing an oriented graphite powder of the present invention preferably includes a step of producing the oriented graphite powder by the above-described method and a step of further adjusting the particle size by a general grinding method such as a jet mill. . As a result, it is possible to selectively align to a finer arbitrary particle size, so that the stability of performance can be enhanced.

  Moreover, the 1st electron emission material of this invention can obtain the thing excellent in the electron emission characteristic than before by using the above-mentioned orientation graphite powder. That is, it can be used mainly as a cold cathode material such as an electron emission device.

  Moreover, the 1st hydrogen storage material of this invention can occlude more hydrogen than before by using the above-mentioned orientation graphite powder. That is, it can be used mainly for constituent materials such as hydrogen storage tanks.

  In addition, the first battery negative electrode material of the present invention can be less deteriorated than before by using the oriented graphite powder described above. That is, it can be used mainly as a negative electrode material for secondary batteries such as nickel metal hydride.

  The first acoustic diaphragm of the present invention can form an acoustic member having excellent high frequency characteristics by using the oriented graphite powder described above. That is, it can be used mainly as a molding material for an acoustic diaphragm in a speaker.

  Moreover, the 1st heat radiation material of this invention can form the heat radiation material excellent in the heat conductive characteristic by using the orientation graphite powder described above. That is, it can be used mainly as a molding material such as a heat sink.

  By subjecting the aromatic polymer fiber body and the foam to a firing treatment, an oriented graphite powder having a uniform particle diameter can be easily obtained. Furthermore, by using the powder, there is a possibility that a wide range of application fields such as cold cathodes such as electron-emitting devices, hydrogen storage, and batteries may be expanded. Furthermore, the development of new composite materials combined with this is also possible.

  The basic process for forming a powdered product having an oriented graphite structure by heat-treating a fiber or foam of an aromatic polymer material such as polyamide or polyimide in an inert gas or the like is a known sheet or This is almost the same as the case of producing plate-like graphite.

  In the case of the formation of sheet-shaped graphite, it is important to control the firing conditions to maintain the sheet shape, but in order to obtain the powdery graphite of this embodiment, the layering of graphite in a high-temperature firing region of 2000 ° C. or higher By optimizing the process temperature / time, etc., on which orientation proceeds, oriented graphite powder having a desired shape can be obtained directly.

  More specifically, by using an aromatic polymer material fiber / foam as the starting material, an intermediate holding step (usually 1 hour) which is held at a constant temperature in a temperature range of about 2000 ° C., which has been required conventionally. The oriented graphite powder can be produced without going through the above. In order to obtain a higher quality product, it is also important to precisely control the firing temperature profile and firing atmosphere including the preliminary firing step.

  Hereinafter, the present invention will be described more specifically with reference to embodiments.

(First embodiment)
First, an example in which an oriented graphite powder was produced using a polyamide fiber body (trade name: KEVLAR (registered trademark) manufactured by Toray DuPont) having a thickness of about 15 μm as a starting material will be described.

  KEVLAR® is a para-type wholly aromatic amide fiber. First, the prepared amide fiber body was pre-fired in a pre-baking furnace. First, from room temperature to 1200 ° C. was heated at a rate of temperature increase of 3 ° C./min, and then pre-baked at 1200 ° C. for 3 hours. The heating rate during heating is desirably in the range of 10 ° C./min or less. Generally, the heating rate is determined in consideration of the molecular formula of the sample.

  The gas used is either an argon or nitrogen inert gas, and in some cases a mixture of both is also used. As a general tendency, data has been obtained that makes it easier to obtain powdered graphite with better quality of nitrogen gas than argon. In this embodiment, nitrogen gas is used.

  Subsequently, after pre-baking at 1200 ° C./3 hours, the temperature was lowered to room temperature. In this embodiment, the descending speed is 5 ° C./min. Although it is not necessary to control the descending speed at the time of cooling as strictly as the temperature rising speed, it is generally preferably 10 ° C./min or less.

  In this pre-baking step, the starting material is thermally decomposed, nitrogen and oxygen are released, and the weight ratio changes from 50% to 60% of the starting material and changes to the graphite precursor. This step is intended to promote graphitization in the main firing.

  Further, the pre-baked sample was transferred to an ultra-high temperature furnace, and baked according to the temperature program example of the main baking shown in FIG. 2 (b). In the present embodiment, the heating rate is 10 ° C./min up to 1000 ° C., and then 5 ° C./min up to 2700 ° C. The main baking temperature is 2700 ° C., and the holding time is 1 hour. Although the particle size of the powder obtained can be controlled by controlling the holding time, the time is determined in the present embodiment in consideration of the type of sample and the like.

  Cooling after the main firing was performed at a descending rate of 10 ° C./min up to 2200 ° C., and then 20 ° C./min up to 1300 ° C. Furthermore, cooling to room temperature is only 20 ° C / min with only water cooling.

  The particle size distribution of the oriented graphite powder obtained through the above steps was about 5 to 10 μm, and the fiber starting material could be directly powdered by configuring the temperature profile as described above. Further, when the obtained oriented graphite powder was examined, many pore regions existed inside the powder. Although the formation mechanism is not clear, it is considered to be caused by the present firing program, and as a result, it has an advantageous effect on various applications. As a result of evaluating the degree of orientation of the graphite powder obtained by X-ray diffraction or the like, it was confirmed that the crystallite size was 100 nm or more and the graphene structure was laminated in layers.

  In order to obtain an arbitrary finer particle size, when using a general pulverizer such as a jet mill, homogeneous oriented graphite powder of 5 μm or less could be obtained.

(Second Embodiment)
Although the starting material used in the above embodiment is an amide fiber body, in this embodiment, the amide fiber body in a woven fabric is used as the starting material. This is preferable because the handling becomes easy and the raw material filling rate can be increased.

  As a result of converting the amide woven fabric into powder graphite using the same temperature profile as in the first embodiment, an oriented graphite powder having a substantially uniform particle size was obtained as in the first embodiment.

(Third embodiment)
Although the starting material used in the first embodiment was an amide fiber body, it was confirmed that other polymer fiber materials could be pulverized by the same production method as described above. Specifically, although the temperature profiles are slightly different, polyimide, polyphenylene terephthalamide (PPTA), polyphenylene oxazadiazo (POD), polybenzothiazole (PBT), polybenzobisthiazole (PBBO), polyphenylene benzimidazole (PBI) ), Polyphenylenebenzobisimidazole (PPBI), polythiazole (PT), polyparaphenylene vinylene (PPV), etc., and oriented graphite powder was obtained.

(Fourth embodiment)
Although the starting material used in the first embodiment is a fibrous body, a polyimide foam is used as a starting material in this embodiment. This is a so-called sponge-like structure that is made porous by foaming a polymer film or the like. The thickness of the solid skeleton part of the used polyimide foam was several μm to several tens of μm. In this case as well, the handling becomes easier and the filling rate of the raw material can be increased as compared with the case of using the fiber body alone as the starting raw material.

  As a result of graphitizing the polyimide foam using the same temperature profile as in the first embodiment, the porous structure is decomposed and, as in the first embodiment, an oriented graphite powder having a substantially uniform particle size is obtained. I was able to.

(Fifth embodiment)
The electron emission characteristics of the oriented graphite powder obtained in the first embodiment were examined. For comparison, ordinary graphite powder was used. In either case, the same amount of powder was applied to a conductive substrate and placed in a vacuum apparatus to measure the field emission characteristics.

  As a result, it was confirmed that the oriented graphite powder obtained in the present embodiment emits 10% or more electrons compared to the conventional graphite powder.

(Sixth embodiment)
The hydrogen storage characteristics of the oriented graphite powder obtained in the first embodiment were also examined. As in the previous example, ordinary graphite powder was used for comparison.

  As a result, it was confirmed that the oriented graphite powder obtained in the present embodiment occludes about 1.5 times more hydrogen by weight ratio than the conventional graphite powder.

(Seventh embodiment)
The deterioration characteristics when the oriented graphite powder obtained in the first embodiment was used as a negative electrode material for a secondary battery were also examined. As a comparison, the case of ordinary graphite powder was also examined as in the previous example.

  As a result, it was confirmed that the oriented graphite powder obtained in the present embodiment is less about 10% of the battery output deterioration than the conventional graphite powder.

(Eighth embodiment)
The oriented graphite powder obtained in the first embodiment was molded to produce a loudspeaker diaphragm, and its high frequency characteristics were examined. For comparison, a graphite sheet prepared by the same heat treatment process was prepared.

  As a result, the diaphragm formed from the sheet-like graphite exhibited better characteristics than those formed from the oriented graphite powder obtained in the present embodiment because of the excellent degree of orientation in the plane direction. However, it is generally more difficult to produce a sheet-like material than to form a particle shape, which is disadvantageous in view of cost and area increase. From this point of view, when the diaphragm formed by processing oriented graphite powder is evaluated, it is slightly inferior to that of sheet-like graphite, but is superior to the case of using other materials. It was confirmed that it is suitable as an acoustic diaphragm material in terms of cost / freedom of production.

(Ninth embodiment)
The oriented graphite powder obtained in the first embodiment was molded to produce a heat sink, and the thermal conductivity was examined.

  As a result, although it does not reach the thermal conductivity of sheet-like graphite, it has a thermal conductivity of about 1.5 times that of copper and is suitable as a heat radiation material in terms of mass productivity, low cost, and freedom of production. I confirmed that there was.

  By subjecting the aromatic polymer fiber body and the foam to a firing treatment, an oriented graphite powder having a uniform particle size can be easily obtained. Furthermore, by using the powder, there is a possibility that a wide variety of application fields such as cold cathodes such as electron-emitting devices, hydrogen storage, and batteries may be expanded. Furthermore, it is possible to develop new composite materials combined with this.

Claims (19)

An orientational graphite powder having a main composition composed of carbon (C),
Oriented graphite powder containing pore regions inside the powder. In the oriented graphite powder according to claim 1,
An oriented graphite powder having a density of the graphite powder in the range of 0.60 to 1.60 g / cm ³ . In the oriented graphite powder according to claim 1,
Oriented graphite powder wherein the graphite powder composition contains at least one or more of phosphorus (P), calcium (Ca), silicon (Si), aluminum (Al), magnesium (Mg). In the oriented graphite powder according to claim 1,
Oriented graphite powder in which a planar structure (graphene structure) consisting of a six-membered carbon structure is layered in a correlated manner. In the oriented graphite powder according to claim 1,
The oriented graphite powder according to claim 1, wherein a crystallite size constituting the graphite powder is 100 nm or more. A method for producing oriented graphite powder, comprising: preparing an aromatic polymer fiber as a starting material; and firing the starting material in a predetermined atmosphere according to a predetermined temperature profile Method. A method for producing oriented graphite powder, comprising: preparing an aromatic polymer foam as a starting material; and firing the starting material in a predetermined atmosphere according to a predetermined temperature profile Method. In the manufacturing method of the oriented graphite powder of Claim 6 or 7,
The starting material is polyamide, polyimide, polyphenylene terephthalamide (PPTA), polyphenylene oxazadiazo (POD), polybenzothiazole (PBT), polybenzobisthiazole (PBBO), polyphenylene benzimidazole (PBI), polyphenylene benzobisimidazole A method for producing an oriented graphite powder selected from (PPBI), polythiazole (PT), and polyparaphenylene vinylene (PPV). In the manufacturing method of the orientation graphite powder of Claim 6,
A method for producing oriented graphite powder, wherein the starting material is in the form of a woven fabric woven with the aromatic polymer fiber body. In the manufacturing method of the oriented graphite of Claim 6 or 7,
A temperature process of the firing step is a process of pre-baking at a predetermined temperature selected from a temperature range of 300 ° C. to 1400 ° C., and a step of main firing again at a predetermined temperature from room temperature to around 3000 ° C. Production method. In the manufacturing method of the orientation graphite of Claim 10,
The method for producing oriented graphite powder, wherein the pre-baking step is a condition of heating at 400 ° C. to 1200 ° C. at a temperature increase rate of 10 ° C./min or less and then heating at 1200 ° C. for 3 hours. In the manufacturing method of the orientation graphite of Claim 10,
A method for producing oriented graphite powder, wherein the pre-firing atmosphere is either argon (Ar) or nitrogen (N ₂ ), or a mixed atmosphere thereof. In the manufacturing method of the oriented graphite of Claim 6 or 7,
The main baking step is selected from a temperature range of 2500 ° C. to 3200 ° C., and the temperature is increased from room temperature to the main baking temperature at a heating rate of 10 ° C./min. A method for producing an oriented graphite powder, which is a condition to perform. A method for producing an oriented graphite powder, comprising a step of producing an oriented graphite powder by the method according to claim 6 and a step of obtaining an arbitrary particle size by a general grinding method such as a jet mill. An electron emission material using the oriented graphite powder according to claim 1. A hydrogen storage material using the oriented graphite powder according to claim 1. A battery negative electrode material using the oriented graphite powder according to claim 1. An acoustic diaphragm using the oriented graphite powder according to claim 1. A heat radiation material using the oriented graphite powder according to claim 1.