WO2018061830A1 - Graphite molded article production method - Google Patents

Graphite molded article production method Download PDF

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Publication number
WO2018061830A1
WO2018061830A1 PCT/JP2017/033495 JP2017033495W WO2018061830A1 WO 2018061830 A1 WO2018061830 A1 WO 2018061830A1 JP 2017033495 W JP2017033495 W JP 2017033495W WO 2018061830 A1 WO2018061830 A1 WO 2018061830A1
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Prior art keywords
graphite
graphene oxide
sheet
molded body
producing
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PCT/JP2017/033495
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French (fr)
Japanese (ja)
Inventor
祥 大澤
幸仁 中澤
宏佳 木内
寛人 伊藤
北　弘志
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コニカミノルタ株式会社
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Publication of WO2018061830A1 publication Critical patent/WO2018061830A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/198—Graphene oxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/205—Preparation

Definitions

  • the present invention relates to a method for producing a graphite molded body, and more particularly, to a method for producing a graphite molded body for efficiently producing a graphite molded body having high thermal conductivity.
  • Graphite contains real hydrogen having a structure in which carbon atoms are stacked in a two-dimensional network molecule (graphene) with a thickness of 1 atom in which hexagonal lattices are formed by covalent bonds of sp 2 hybrid orbitals. There are no or few crystals.
  • Graphene and graphite have unique properties such as electrical conductivity due to ⁇ electrons existing in the plane, high thermal conductivity derived from covalent crystals in which light carbon atoms are firmly bonded to each other, and high elastic modulus in the in-plane direction.
  • a processed molded body having physical properties derived from covalent crystals in the in-plane direction of the graphite is very valuable in industry.
  • An isotropic graphite compact is well known as a processed graphite compact.
  • Isotropic graphite molded bodies are manufactured from coke of petroleum and coal raw materials. Powders obtained by pulverizing raw coke and coal tar pitch obtained as a by-product during coke production are combined as a binder. A pulverized material of several tens to several hundreds ⁇ m called a kneaded product is used as a forming raw material.
  • This molding raw material can be molded by cold isostatic pressing (CIP), extrusion molding, mold molding, etc. to obtain a molded product, and then the molded product is sintered at a temperature around 1000 ° C. Then, the coke and the binder are integrated while the volatile components are evaporated.
  • CIP cold isostatic pressing
  • An isotropic graphite molded body can be obtained by performing calcination and crystallization at a temperature in the vicinity of ° C.
  • an isotropic graphite molded body composed of graphite can be obtained, but this is because only coke powder having a small anisotropy is simply spread when making a molded product.
  • Each graphite crystal inside the finished compact is oriented in various directions and becomes isotropic when the compact is viewed macroscopically and is therefore referred to as “isotropic” graphite.
  • a certain degree of anisotropy can be produced by extrusion molding or mold molding, but it is far from the state in which graphite crystals are regularly arranged.
  • isotropic graphite is greatly reflected in the properties of graphite crystals with anisotropy, in which covalent bonds are formed in a network form in the direction of the graphene plane and laminated by van der Waals force in the direction perpendicular to the graphene plane. I don't mean.
  • the thermal conductivity which is a physical property that greatly depends on the crystal structure, is as high as about 2000 W / (m ⁇ K) for a graphite single crystal, whereas isotropic graphite has several hundred W / ( m ⁇ K).
  • a graphite compact having highly oriented graphite crystals there is highly oriented pyrolytic graphite that can be produced from a polymer.
  • Highly oriented pyrolytic graphite produced from a polymer compared to isotropic graphite produced by simply pulverizing a raw material and carbonizing and graphitizing it, is made from a polymer film whose orientation is controlled, such as polyimide, as a raw material.
  • a highly oriented graphite molded body can be produced.
  • graphite is highly oriented in the in-plane direction, and its thermal conductivity approaches the performance of single crystal graphite.
  • the conventional graphite molded body can be molded relatively freely, but the isotropic graphite that does not sufficiently bring out the physical properties derived from the graphite crystal structure and the high-orientation raw material polymer It is difficult to control the initial orientation, and highly oriented pyrolytic graphite, which cannot be freely molded, has become the mainstream.
  • graphite crystals are constructed from graphene molecules that make up graphite, and highly oriented graphite compacts can be produced, there are many steps to use petroleum and coal raw materials with many impurities.
  • Graphene is a layered compound that is ideally separated from graphite one by one.
  • the graphene particles including one to several tens of layers are referred to as graphene particles. Since mere graphene particles have no affinity for solvents and the like, they can be dispersed only at a very low concentration without a dispersant, and the dispersibility in solvents is extremely low. An amount of solvent is required and is not practical. If the solvent to be used is reduced, the graphene particles are agglomerated quickly, resulting in an agglomerated material in which the orientation is significantly deteriorated. Also, if a large amount of dispersant is used, they naturally become impurities, and it is not possible to exhibit the performance specific to graphite.
  • graphene oxide is one of the most promising graphene materials for producing a graphite molded body from graphene molecules.
  • Graphene oxide imparts a hydrophilic oxygen-containing group such as a hydroxy group, an epoxy group, a carbonyl group, or a carboxy group in the plane of graphene, so that the dispersibility in water and some organic solvents is remarkably improved. For this reason, graphene oxide can be dispersed in a solvent in a state of being laminated from a single molecular layer to several tens of layers without using a dispersant that can be an impurity when producing a graphite crystal.
  • a molded product can be produced by molding this graphene oxide dispersion and removing the solvent.
  • the thickness of the dispersed graphene oxide particles is 1 nm or less to several nm
  • the diameter in the in-plane direction of the graphene oxide is several ⁇ m
  • the aspect ratio of the particle diameter in the thickness direction to the in-plane direction is Since it reaches 10,000, it can be laminated in the thickness direction, and a molded product having excellent orientation can be obtained by removing the solvent.
  • Non-Patent Document 1 heat treatment is performed at 1600 to 2850 ° C. for 30 minutes for reduction and crystallization.
  • the produced graphite has the highest thermal conductivity of 1434 W / (m ⁇ K), the same level as the highly oriented pyrolytic graphite, and a highly oriented graphite compact can be produced.
  • the graphite compact actually produced from this graphene oxide is similar to the highly oriented pyrolytic graphite produced from the same highly oriented graphite compact.
  • the heat treatment at around 3000 ° C. is performed from the outside, and it is still a manufacturing method with a large industrial load.
  • the present invention has been made in view of the above-described problems and situations, and its solution is to provide a method for producing a graphite molded body that efficiently produces a graphite molded body having high thermal conductivity from graphene oxide. is there.
  • the present inventor in the process of examining the cause of the above-mentioned problem, makes the heating method a resistance heating method by energization and further increases the pressure from graphene oxide by using a manufacturing method having a pressurizing step.
  • the inventors have found that an oriented graphite molded body can be produced efficiently and have reached the present invention.
  • a method for producing a graphite molded body using graphene oxide as a raw material comprising a step of resistance heating by energization and a step of pressing.
  • the orientation of the graphite crystal is further increased. It is considered that the thermal conductivity of the formed graphite compact can be significantly increased because the graphite density can be increased and the density of graphite can be increased.
  • the method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and includes a resistance heating step by energization and a pressurizing step. This feature is a technical feature common to or corresponding to the claimed invention.
  • the step of resistance heating by energization and the step of pressurization are performed simultaneously.
  • the process of resistance heating by the said electricity supply and the said pressurization process are performed separately.
  • the pressure applied to the graphene oxide in the pressurizing step is preferably 50 MPa or more, and more preferably 100 MPa or more. Thereby, the effect which improves the orientation of a graphite crystal is acquired.
  • the thermal conductivity of the graphite compact is preferably 1000 W / (m ⁇ K) or more, and more preferably 1500 W / (m ⁇ K) or more.
  • the graphite compact is preferably a graphite sheet.
  • ⁇ is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
  • the method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and includes a step of resistance heating by energization and a step of pressing.
  • the graphene oxide may be formed into a desired shape.
  • a graphene oxide solvent dispersion in which graphene oxide prepared by oxidizing graphite with a strong oxidizing agent is dispersed in a solvent is prepared, and then the graphene oxide solvent dispersion is molded using a mold having a desired shape, and then the solvent By removing the graphene, a graphene oxide molded product can be produced.
  • a graphite molded body having a high thermal conductivity can be produced in a short time and in a simple manner through a process of resistance heating by energization and a process of pressurization.
  • graphene oxide refers to graphene modified with an oxygen-containing group such as a carboxy group, a carbonyl group, a hydroxy group, and an epoxy group.
  • the graphene oxide used in the present invention is not particularly limited, but the oxygen content ratio (atomic%) of graphene oxide having an oxygen-containing group such as a carboxy group, a carbonyl group, a hydroxy group, or an epoxy group is in the range of 24 to 50 atomic%. It is preferable to be within.
  • the oxygen content ratio (atomic%) of graphene oxide can be measured by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS), and is represented by O / (C + O) atomic%. It is.
  • XPS X-ray photoelectron spectroscopy
  • the oxygen content ratio of graphene oxide can be measured using a Quantera SXM manufactured by ULVAC-PHI CORPORATION.
  • a monochromatic Al—K ⁇ ray is used as an X-ray source, and the spectroscope has a half-width of 0.5 eV or less when the Ag3d 5/2 peak of purified silver is measured.
  • Graphene oxide is a layered particle in which graphene constituting graphite is peeled off and oxidized by oxidizing graphite.
  • a larger diameter in the plane direction of the layered particle is preferable from the viewpoint of physical properties such as electrical conductivity, thermal conductivity, elastic modulus and strength.
  • the diameter in the plane direction of the layer is preferably 1 ⁇ m or more, more preferably 5 ⁇ m or more, and further preferably 10 ⁇ m or more as long as no trouble occurs in the dispersion state of the graphene oxide solvent dispersion.
  • Graphene oxide is a layered particle in which graphene constituting graphite is exfoliated and oxidized by oxidizing graphite, and its thickness is about 0.34 nm to several nm, and all of them are exfoliated to a single layer. There is no need, and depending on the application, a dispersed state of several to several tens of layers may be used as long as the orientation is not hindered.
  • Graphene oxide is obtained by oxidizing graphite or multilayer graphene with a strong oxidizing agent to give oxygen-containing groups such as epoxy groups, hydroxy groups, carbonyl groups, and carboxy groups to the surface and edges of graphene particles, and to the solvent. Can be dispersed. It is well dispersed in water, and organic solvents are compatible with solvents with hydrophilic groups, such as methanol, ethanol, tetrahydrofuran (THF), etc., and do not interfere with moldability and orientation depending on the application. Thus, the dispersion can be prepared with other organic solvents such as acetone, methyl ethyl ketone (MEK), and dichloromethane.
  • MEK methyl ethyl ketone
  • the graphene oxide solvent dispersion is a Hummers method or a modified modified version thereof.
  • the Hummers method can be used based on known literature.
  • Known documents for producing graphene oxide include W.W. S. Hummers. , Journal of American Chemistry (1958) 1339, M .; Hirata. , Carbon 42 (2004) 2929, and the like.
  • graphene oxide moldings By removing the solvent from the graphene oxide dispersion, graphene oxide molded products having various shapes can be produced.
  • a graphene oxide sheet can be produced by applying to a substrate and removing the solvent.
  • a thin film having a thickness of several nm is also possible.
  • the graphene oxide fiber can be produced by ejecting from a thin tube of the nozzle and removing the solvent.
  • it can also shape
  • the reduction of graphene oxide refers to a reaction in which oxygen-containing groups in graphene oxide are desorbed as water, oxygen, carbon monoxide, carbon dioxide, or carbonic acid.
  • the electrical resistivity decreases.
  • the graphene oxide molded product may be reduced, and the electrical resistivity may be adjusted depending on the application. By adjusting the electrical resistivity, conditions such as the amount of current to flow and the heating temperature can be adjusted in the step of resistance heating by energization.
  • the reduction reaction proceeds at a temperature of about 1000 ° C. or lower, a temperature of about 1000 ° C. or higher, usually 2000 ° C. or higher is required for the crystallization (graphitization) reaction to proceed. That is, the reaction rate of the reduction reaction is very fast compared to the crystallization (graphitization) reaction. For this reason, the reduction reaction may be performed in advance under mild conditions for the purpose of suppressing expansion during energization heating.
  • a conventionally known method for obtaining graphene oxide reduced product from graphene oxide can be used.
  • a method of reducing graphene oxide by heating thermal reduction
  • a method of reducing using a reducing agent such as hydrazine or ascorbic acid chemical reduction
  • a method of reducing graphene oxide by irradiating light photoreduction
  • a method of electrolyzing and reducing graphene oxide in an aqueous electrolyte solution electrolyzing and reducing graphene oxide in an aqueous electrolyte solution.
  • a current can be passed and self-heated by Joule heat generated by the resistance of the graphene oxide.
  • the direction of the flowing current is not particularly limited, and may be a direct current or an alternating current, and may be a steady current or a pulse current.
  • the magnitude of the current and voltage to flow varies depending on the size and resistance of the sheet, but the current is preferably passed so that the graphene oxide is heated to 1000 ° C. or higher, and is heated to 2000 ° C. or higher, more preferably 2500 ° C. or higher. It is preferable to pass an electric current.
  • current density 100000A / m 2 or more preferably 1000000A / m 2 or more, more preferably 10000000A / m 2 or more, and particularly preferably it is preferred to flow a current so that 100000000A / m 2 or more.
  • the current can be passed in a range not exceeding the limit of the current value derived from the electron density of graphite or the vicinity of 3600 ° C., which is the sublimation point of carbon.
  • the thermal conductivity of the formed graphite compact can be greatly increased by combining the step of pressurizing the graphene oxide. This is considered to be because not only high orientation graphite can be obtained by heating, but also pressurization can further enhance the orientation of graphene in the graphite and increase the density of graphite. .
  • Pressurization may be performed simultaneously with energization, or may be performed separately, that is, before or after energization. From the viewpoint of manifesting the effects of the present invention, the pressurization is preferably performed simultaneously with energization or after heating. Furthermore, the pressurization is preferably performed simultaneously with energization.
  • the efficiency of the covalent bond formation between the graphene oxide molecules is improved by energizing the graphene oxide molecules in a state where the graphene oxide molecules are pressure-bonded by pressure.
  • pressurization before energization can improve the adhesion between graphene oxide molecules and increase the efficiency of forming covalent bonds between graphene oxide molecules.
  • pressure after energization the orientation of graphene oxide molecules can be remarkably improved, and physical properties peculiar to highly oriented graphite can be expressed.
  • the pressurizing device may be added by surface contact using a press or the like, or may be sandwiched between rolls and added by line contact. If a desired pressure is applied, the shape is not limited. Moreover, the pressurizing direction may be applied uniaxially or from all directions.
  • the pressure applied to the graphene oxide in the pressurizing step is preferably 1 MPa or more, more preferably 10 MPa or more, further preferably 50 MPa or more, and particularly preferably 100 MPa or more.
  • the upper limit of the applied pressure is about 1000 MPa in the capacity of a general-purpose press device.
  • the energization time in the step of resistance heating by energization is preferably 60 seconds or less, more preferably 10 seconds or less, from the viewpoint of producing a graphite molded body in a short time. More preferably, it is less than a second.
  • the lower limit of the energization time may be a short current application such as a pulse as long as the crystallinity of graphite is improved and there is no hindrance to the performance characteristic of graphite.
  • a discharge plasma sintering apparatus may be used as a general-purpose apparatus capable of performing energization and pressurization simultaneously.
  • electrodes can be arranged on the upper and lower sides of the compact and pressure can be applied while energizing.
  • a sheet-like material can be sandwiched between electrodes, and pressure can be applied while flowing current in the thickness direction to cause self-heating. If the sheets are stacked and energized and pressed, a thick film sheet or a block body in which the sheets are pressure-bonded and bonded can be easily produced.
  • a cold isostatic pressurizing device (CIP) or a hot isostatic pressurizing device (HIP) may be used as a device that can apply pressure in all directions before or after energization heating. Since pressure can be applied from all directions, it is effective for improving the orientation of the molded body.
  • crystallization of graphene oxide can be promoted and graphitization can be promoted by self-heating and pressurization by Joule heat.
  • Graphitization means repairing the sp 2 covalent bond of graphene oxide, which was broken by an oxygen-containing group, making the layer spacing between graphenes 0.34 nm, which is the same as that of graphite crystals, and improving the orientation. It is.
  • physical properties close to those of a graphite single crystal can be expressed in the molded body.
  • Conventionally for example, compared with the case where a sheet-like highly oriented graphite is produced by externally heating polyimide, for example, it can be produced in a much shorter time, that is, efficiently.
  • the graphite molded body can be manufactured by a manufacturing method including a step of resistance-heating a graphene oxide molded product molded into a desired shape by energization and a step of pressing.
  • the shape can be preferably applied to a sheet shape, a fiber shape, a housing shape, a thin film shape, and the like.
  • a graphite sheet is mentioned as a sheet-like molded object.
  • Graphite is a structure in which a plurality of graphenes are stacked, and the layers are bonded together by a weak van der Waals force.
  • Graphene is a one-atom-thick two-dimensional network compound formed by covalently bonding carbon atoms in a hexagonal lattice. Strictly speaking, graphite is composed of only sp 2 carbon atoms, but actually has defects such as sp 3 carbon atoms, vacancies, and hetero atoms, and those containing these defects are also called graphite.
  • the graphite sheet represents a sheet-like object composed of graphite.
  • Thermal diffusion sheet can be used as a highly oriented graphite sheet.
  • CPU central processing unit
  • the highly oriented graphite sheet has a thermal conductivity that is several times that of copper (401 W / (m ⁇ K)), which exhibits the best performance among general-purpose metals, and has high industrial value.
  • the manufacturing method of the graphite sheet currently widely used industrially is only the highly oriented pyrolytic graphite produced from the polyimide described above, and still uses a process with a large industrial load. If the manufacturing method of this invention is used, a highly heat conductive graphite sheet can be produced cheaply and it is very valuable industrially.
  • a carbon fiber can be produced by applying the production method of the present invention to a graphene oxide formed into a fiber shape.
  • the conventional carbon fiber manufacturing process is as follows: 1) a process of making a fiber precursor made from a polymer or petroleum raw material flame-resistant / infusible by heat treatment at 200 to 300 ° C., 2) a fiber precursor made flame-resistant There is a carbonization process in which heat treatment is performed at around 1500 ° C, 3) a graphitization process in which the carbonized fiber is heat-treated at a temperature of 2000 ° C to 3000 ° C, and then a surface treatment, a polymer coating, and the like.
  • Carbon fibers made from fiber precursors spun from polyacrylonitrile, which is a conventional polymer, or pitch derived from petroleum raw materials, are first gradually heated to be able to withstand high-temperature heat treatment, called flameproofing and infusibilization processes. A process of sintering is required.
  • the precursor is melted if it is suddenly subjected to a high temperature treatment, and therefore, it is sintered over a relatively long time of several tens of minutes in the flameproofing / infusible process.
  • a fiber precursor made of graphene oxide when used, it does not melt like a polymer, so that high-temperature treatment exceeding 2000 ° C. can be performed suddenly.
  • the carbon fiber has no defects in its structure, it becomes a very high-strength material.
  • the carbon fiber breaks brittlely from that point.
  • ⁇ Graphite heat sink> By the method for producing a graphite molded body of the present invention, a heat sink composed of graphite can be efficiently produced. If necessary, a small heat sink or the like can be produced by a 3D printer or the like.
  • a transparent conductive film can be produced by forming a graphene oxide sheet with a nano-order thickness, reducing, and crystallizing.
  • the film surface is disturbed by the generated gas only by energization heating, and a desired highly crystalline transparent conductive film cannot be produced.
  • the currently used transparent conductive film is indium tin oxide (ITO), but there is a strong demand for alternative materials due to the fact that indium is a rare metal.
  • the thin film graphite (graphene) sheet can also be used as a gas barrier sheet.
  • graphene oxide vacancies and the like are generated in the surface due to oxidation reaction, and sp 2 covalent bond is formed by crystallization by current heating according to the present invention, the vacancies are repaired, and the orientation is improved by pressurization.
  • a gas barrier sheet having a very low gas permeability can be efficiently produced.
  • the graphene oxide sheet can be produced by applying a graphene oxide solvent dispersion with a certain thickness and drying the solvent. Any coating method may be used as long as the film quality is not affected as long as it can be applied and dried at a constant thickness. Examples include cast film formation, filtration film formation, dip coating, spin coating, and spray coating. Further, the graphene oxide sheet can be peeled off by applying it to a glass substrate or a resin base material. Any material may be used for the substrate and the substrate as long as the graphene oxide sheet can be peeled off.
  • a graphite sheet can be produced by reducing and crystallizing a graphene oxide sheet using a process of heating by heating and a process of applying pressure.
  • a voltage may be applied while being sandwiched between press machines, and it is sandwiched between two rolls, and by applying voltage to the rolls, pressure is applied by line contact while conveying the thickness direction.
  • An electric current may be passed through.
  • voltage may be applied to both ends of the sample to cause electricity to flow, and pressure may be applied to the energizing portion from the thickness direction using a press and a spacer. It is also possible to prepare another pair of separated rolls while sandwiching and conveying the sheet between the two rolls, applying a voltage between the separated rolls, and conveying the sheet while energizing the sheet in the in-plane direction. It is also possible to apply pressure to the energizing portion using another pair of rolls while energizing the sheet in the in-plane direction.
  • the pressure may be applied simultaneously with energization, or may be performed separately, that is, before or after energization.
  • Thermal conductivity (W / (m ⁇ K)) is represented by the product of thermal diffusivity (m 2 / s), specific heat capacity (J / kg ⁇ K), and density (kg / m 3 ). The thermal conductivity can be calculated by measuring the thermal diffusivity, specific heat capacity, and density.
  • ⁇ Thermal conductivity of graphite compact> A general-purpose metal having the highest thermal conductivity is copper, and its thermal conductivity is 401 W / (m ⁇ K). Therefore, the manufacturing method which has the thermal conductivity exceeding copper and produces a graphite molded object simply has industrial value. Furthermore, among the means for providing a graphite molded body having a thermal conductivity of 1000 W / (m ⁇ K) or more, at present, only an externally heated graphite sheet near about 3000 ° C. has been industrialized. A manufacturing method for producing a graphite molded body having a thermal conductivity of 1000 W / (m ⁇ K) or more is very industrially valuable.
  • the performance is close to the thermal conductivity of single crystal graphite, which is particularly valuable in industry.
  • the upper limit is not particularly limited because the higher the thermal conductivity is, the theoretical value of the thermal conductivity of the graphite single crystal is about 2000 W / (m ⁇ K).
  • the graphite molded body is a graphite sheet because of industrial versatility such as a thermal diffusion sheet.
  • Example 1 ⁇ Preparation of graphene oxide aqueous dispersion 1> 10 g of graphene nanoplatelets (thickness 6-8 nm, width 5 ⁇ m) of Tokyo Chemical Industry Co., Ltd. and 7.5 g of sodium nitrate were placed in a flask, and 621 g of concentrated sulfuric acid was added thereto. The flask was placed in an ice bath and 45 g of potassium permanganate was added in small portions while stirring so that the solution temperature did not exceed 20 ° C. Then, after returning to room temperature and stirring for 14 days, 1 L of 5 mass% sulfuric acid was added there, and it stirred for 1 hour.
  • the graphene oxide aqueous dispersion 1 was applied on a 25 ⁇ m PET (polyethylene terephthalate) film adhered to a glass substrate with an applicator adjusted to a gap of 1.5 mm. After drying at 50 ° C. for 10 hours, the film was peeled from the PET film to obtain graphene oxide sheet 1 (thickness: 44 ⁇ m).
  • the oxygen content ratio of the graphene oxide sheet 1 was 49 atomic%. The oxygen content ratio (atomic%) was measured by XPS described above.
  • thermal conductivity was represented by the following formula, and was calculated by measuring the thermal diffusivity, specific heat capacity, and density.
  • Thermal conductivity thermal diffusivity ⁇ specific heat capacity ⁇ density
  • the thermal diffusivity is Laser Pit of Advance Riko Co., Ltd.
  • the specific heat capacity is a differential scanning calorimeter (DSC 6220: manufactured by Hitachi High-Technologies Corporation)
  • the density is a sheet. The mass and volume were measured, and the thermal conductivity at a temperature of 23 ° C. of each of the prepared graphite sheets was calculated. The results are shown in Table 1.
  • the graphite sheet which is the sheet-like graphite molded body of the present invention has a higher thermal conductivity than that of the comparative example, and can be efficiently produced in a short time.
  • the present invention uses a graphene oxide solvent dispersion ability and an orientation ability with a high aspect ratio at the time of molding to produce a highly oriented graphite compact that is very valuable industrially. It is based on the idea that it can be produced efficiently. In order to efficiently produce a highly oriented graphite compact from graphene oxide, a simple electric heating and pressurizing process is essential at first glance. Excellent physical properties can be expressed. It can be said that the present invention is a production method that satisfies all the moldability, orientation and production efficiency of materials necessary for producing a highly oriented graphite compact, and is very valuable industrially. It can be said.
  • the method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and it is possible to produce a graphite molded body having high thermal conductivity from graphene oxide in a short time and with a simple method. It is possible to provide a method for producing a graphite molded body.

Abstract

The present invention addresses the problem of providing a graphite molded article production method for efficiently producing, from graphene oxide, a graphite molded article having high heat conductivity. This graphite molded article production method is for producing a graphite molded article by using graphene oxide as the starting material, wherein the method is characterized by comprising a step for resistance heating by current application and a step for pressurization.

Description

グラファイト成形体の製造方法Method for producing graphite compact
　本発明は、グラファイト成形体の製造方法に関し、より詳しくは、効率的に熱伝導率が高いグラファイト成形体を製造するグラファイト成形体の製造方法に関する。 The present invention relates to a method for producing a graphite molded body, and more particularly, to a method for producing a graphite molded body for efficiently producing a graphite molded body having high thermal conductivity.
　グラファイト（黒鉛）は、炭素原子がｓｐ２混成軌道の共有結合によって六方系格子状に形成された１原子厚さの２次元ネットワーク分子（グラフェン）が、積層された構造を有する実質水素が含まれない、又は少ない結晶体である。グラフェンやグラファイトは、その面状に存在するπ電子による電気伝導性や、軽い炭素原子同士が強固に結合された共有結合結晶に由来する高い熱伝導性、面内方向の高弾性率など、特異な物性を有しており、特にグラファイト面内方向の共有結合結晶に由来した物性を有する加工成形体は、産業上非常に価値がある。 Graphite (graphite) contains real hydrogen having a structure in which carbon atoms are stacked in a two-dimensional network molecule (graphene) with a thickness of 1 atom in which hexagonal lattices are formed by covalent bonds of sp 2 hybrid orbitals. There are no or few crystals. Graphene and graphite have unique properties such as electrical conductivity due to π electrons existing in the plane, high thermal conductivity derived from covalent crystals in which light carbon atoms are firmly bonded to each other, and high elastic modulus in the in-plane direction. In particular, a processed molded body having physical properties derived from covalent crystals in the in-plane direction of the graphite is very valuable in industry.
　グラファイトの加工成形体としては、等方性黒鉛成形体がよく知られている。等方性黒鉛成形体は、石油、石炭原料のコークスから製造されており、原料コークスを粉砕した粉末と、コークス製造時に副生成物として得られるコールタールピッチなどを結合剤として、それらを混合し、混捏品と呼ばれる数十～数百μｍの粉砕物を成形原料として用いている。この成形原料を、冷間等方圧加圧法（ＣＩＰ）や押出し成形法、型込め成形法などで成形し、成形物を得ることができ、その後、成形物を１０００℃付近の温度で焼結し、揮発分を蒸発させながら、コークスと結合剤を一体化させる。この焼成で抜けた揮発分によって空孔が生じるため、コールタールピッチで含浸し、再度焼成し、炭素化をし、さらにこの炭素化した成形物に通電することで、ジュール加熱を発生させ、３０００℃付近の温度で焼成、結晶化を行い、等方性黒鉛成形体を得ることができる。 An isotropic graphite compact is well known as a processed graphite compact. Isotropic graphite molded bodies are manufactured from coke of petroleum and coal raw materials. Powders obtained by pulverizing raw coke and coal tar pitch obtained as a by-product during coke production are combined as a binder. A pulverized material of several tens to several hundreds μm called a kneaded product is used as a forming raw material. This molding raw material can be molded by cold isostatic pressing (CIP), extrusion molding, mold molding, etc. to obtain a molded product, and then the molded product is sintered at a temperature around 1000 ° C. Then, the coke and the binder are integrated while the volatile components are evaporated. Since vacancies are generated by the volatile matter removed by this firing, it is impregnated with coal tar pitch, fired again, carbonized, and the carbonized molded product is energized to generate Joule heating. An isotropic graphite molded body can be obtained by performing calcination and crystallization at a temperature in the vicinity of ° C.
　以上のようなプロセスを経て、グラファイトで構成される等方性黒鉛成形体を得ることができるが、これは成形物を作る際に異方性が小さいコークス粉末を単に敷き詰めるだけであることから、出来上がった成形体内部の一つ一つのグラファイト結晶はいろいろな方向を向いており、成形体をマクロで見ると等方的となり、ゆえに“等方性”黒鉛と呼ばれている。押出し成形や型込め成形法で、ある程度の異方性を出すことはできるが、グラファイト結晶が整然と配向している状態とは程遠い。 Through the process as described above, an isotropic graphite molded body composed of graphite can be obtained, but this is because only coke powder having a small anisotropy is simply spread when making a molded product. Each graphite crystal inside the finished compact is oriented in various directions and becomes isotropic when the compact is viewed macroscopically and is therefore referred to as “isotropic” graphite. A certain degree of anisotropy can be produced by extrusion molding or mold molding, but it is far from the state in which graphite crystals are regularly arranged.
　したがって、等方性黒鉛は、グラフェン面方向に共有結合がネットワーク状で形成され、グラフェン面と垂直方向にファンデルワールス力で積層された、異方性を有するグラファイト結晶の性質が大きく反映されているわけではない。実際、結晶構造に大きく依存する物性である熱伝導性は、グラファイト単結晶が約２０００Ｗ／（ｍ・Ｋ）と超高熱伝導性を有するのに対して、等方性黒鉛は数百Ｗ／（ｍ・Ｋ）程度である。 Therefore, isotropic graphite is greatly reflected in the properties of graphite crystals with anisotropy, in which covalent bonds are formed in a network form in the direction of the graphene plane and laminated by van der Waals force in the direction perpendicular to the graphene plane. I don't mean. In fact, the thermal conductivity, which is a physical property that greatly depends on the crystal structure, is as high as about 2000 W / (m · K) for a graphite single crystal, whereas isotropic graphite has several hundred W / ( m · K).
　それに対して、高配向のグラファイト結晶を有する黒鉛成形体として、高分子から作製することができる高配向性熱分解黒鉛がある。単に原料粉砕物を敷き詰めて炭化、黒鉛化して製造する等方性黒鉛に対して、高分子から作製される高配向性熱分解黒鉛は、ポリイミドなどの配向制御した高分子フィルムを原料として、ポリイミド成形物を１５００℃付近で炭化、３０００℃付近で黒鉛化することで、高度に配向したグラファイト成形体を作製できる。例えばシート状の高配向性熱分解黒鉛成形体は、面内方向に高度にグラファイトが配向しており、その熱伝導率は、単結晶グラファイトの性能に近づいている。 On the other hand, as a graphite compact having highly oriented graphite crystals, there is highly oriented pyrolytic graphite that can be produced from a polymer. Highly oriented pyrolytic graphite produced from a polymer, compared to isotropic graphite produced by simply pulverizing a raw material and carbonizing and graphitizing it, is made from a polymer film whose orientation is controlled, such as polyimide, as a raw material. By carbonizing the molded product at around 1500 ° C. and graphitizing at around 3000 ° C., a highly oriented graphite molded body can be produced. For example, in a sheet-like highly oriented pyrolytic graphite molded body, graphite is highly oriented in the in-plane direction, and its thermal conductivity approaches the performance of single crystal graphite.
　ただし、高配向性グラファイトを作製するためには、ポリイミドの初期配向をコントロールする必要があり、実際にポリイミドで配向を制御し、グラファイト成形体として実現されているのは、数十μｍの厚さのポリイミドフィルムから作製されるグラファイトシートか、それの積層品のみであり、この製法から高配向性のグラファイトを自在に成形できるわけではない。 However, in order to produce highly oriented graphite, it is necessary to control the initial orientation of polyimide. Actually, the orientation is controlled by polyimide, and it is realized as a graphite compact with a thickness of several tens of μm. It is only a graphite sheet produced from the polyimide film or a laminate thereof, and highly oriented graphite cannot be freely molded by this production method.
　このように、従来の黒鉛成形体においては、比較的自由に成形できるが、グラファイト結晶構造に由来する物性を十分に引き出せているわけではない等方性黒鉛と、高配向ではあるが原料高分子の初期配向を制御することが難しく、自在に成形することができない高配向性熱分解黒鉛とが主流となっている。これら従来のグラファイト成形体の製法に対して、グラファイトを構成するグラフェン分子からグラファイト結晶を構築し、配向性の高いグラファイト成形体を作製できれば、わざわざ不純物の多い石油、石炭原料を使い、多くの工程を要する等方性黒鉛の製法や、出来上がったグラファイト成形体の配向性を担保するため、炭素材料ではないポリイミドフィルムを原料とする高配向性熱分解黒鉛の製法を使用する必要がなく、理想的なグラファイト成形体の製造方法となるはずである。 As described above, the conventional graphite molded body can be molded relatively freely, but the isotropic graphite that does not sufficiently bring out the physical properties derived from the graphite crystal structure and the high-orientation raw material polymer It is difficult to control the initial orientation, and highly oriented pyrolytic graphite, which cannot be freely molded, has become the mainstream. Compared to these conventional methods for producing graphite compacts, if graphite crystals are constructed from graphene molecules that make up graphite, and highly oriented graphite compacts can be produced, there are many steps to use petroleum and coal raw materials with many impurities. Is not necessary to use a highly oriented pyrolytic graphite production method that uses a polyimide film that is not a carbon material as a raw material to ensure the orientation of the isotropic graphite and the orientation of the finished graphite compact. It should be a method for producing a simple graphite molded body.
　グラフェンとは、グラファイトから理想的には一層ずつ剥離させた層状化合物のことをいう。ここでは、一層から数十層のものも含めてグラフェン粒子と呼ぶ。単なるグラフェン粒子は、溶媒などに親和性がないため、分散剤なしでは、非常に低濃度でしか分散できず、溶媒への分散性が著しく低いため、成形体を作製するためには、膨大な量の溶媒が必要となり現実的ではない。使用する溶媒を減らせば、グラフェン粒子同士がたちまち凝集し、配向性が著しく劣化した凝集物となる。また分散剤を多量に使ってしまえば、当然それらが不純物となり、グラファイト特有の性能を発揮させることはできない。 Graphene is a layered compound that is ideally separated from graphite one by one. Here, the graphene particles including one to several tens of layers are referred to as graphene particles. Since mere graphene particles have no affinity for solvents and the like, they can be dispersed only at a very low concentration without a dispersant, and the dispersibility in solvents is extremely low. An amount of solvent is required and is not practical. If the solvent to be used is reduced, the graphene particles are agglomerated quickly, resulting in an agglomerated material in which the orientation is significantly deteriorated. Also, if a large amount of dispersant is used, they naturally become impurities, and it is not possible to exhibit the performance specific to graphite.
　そこで、グラファイト成形体をグラフェン分子から作製するための最も有望なグラフェン材料として酸化グラフェンが挙げられる。酸化グラフェンは、グラフェンの面内にヒドロキシ基、エポキシ基、カルボニル基又はカルボキシ基などの親水性の酸素含有基を付与することで、水や一部の有機溶媒への分散性が著しく向上する。このため、グラファイト結晶を作製する際に不純物となり得る分散剤などを使用せず、酸化グラフェンを一分子層から数十層まで積層した状態で溶媒に分散させることができる。この酸化グラフェン分散体を成形し、溶媒を除去することで、成形物を作製することができる。 Therefore, graphene oxide is one of the most promising graphene materials for producing a graphite molded body from graphene molecules. Graphene oxide imparts a hydrophilic oxygen-containing group such as a hydroxy group, an epoxy group, a carbonyl group, or a carboxy group in the plane of graphene, so that the dispersibility in water and some organic solvents is remarkably improved. For this reason, graphene oxide can be dispersed in a solvent in a state of being laminated from a single molecular layer to several tens of layers without using a dispersant that can be an impurity when producing a graphite crystal. A molded product can be produced by molding this graphene oxide dispersion and removing the solvent.
　さらに、分散した状態の酸化グラフェン粒子の厚さが、１ｎｍ以下～数ｎｍとなる一方、酸化グラフェン面内方向の径は数μｍともなり、厚さ方向と面内方向の粒子径のアスペクト比が、１万にも達するため、厚さ方向へ整然と積層され、溶媒を除去することで配向性に非常に優れる成形物が得られる。 Further, while the thickness of the dispersed graphene oxide particles is 1 nm or less to several nm, the diameter in the in-plane direction of the graphene oxide is several μm, and the aspect ratio of the particle diameter in the thickness direction to the in-plane direction is Since it reaches 10,000, it can be laminated in the thickness direction, and a molded product having excellent orientation can be obtained by removing the solvent.
　ただし、酸化グラフェンの面内の結晶性は、酸素含有基が付与されたことで失われており、グラファイトへと還元、結晶化させる必要がある。例えば、非特許文献１では、還元、結晶化させるため、１６００～２８５０℃で３０分間熱処理を行っている。また、生成したグラファイトの熱伝導性は、記載された一番高いもので１４３４Ｗ／（ｍ・Ｋ）であり、高配向性熱分解黒鉛と同等水準であり、高配向性のグラファイト成形体ができていることがわかる。 However, the in-plane crystallinity of graphene oxide is lost due to the addition of oxygen-containing groups, and it is necessary to reduce and crystallize it into graphite. For example, in Non-Patent Document 1, heat treatment is performed at 1600 to 2850 ° C. for 30 minutes for reduction and crystallization. The produced graphite has the highest thermal conductivity of 1434 W / (m · K), the same level as the highly oriented pyrolytic graphite, and a highly oriented graphite compact can be produced. You can see that
　しかしながら、実際にこの酸化グラフェンから作製するグラファイト成形体は、高配向性の高い物性を達成するために、同じ高配向性のグラファイト成形体であるポリイミドから作製される高配向性熱分解黒鉛と同様の、３０００℃付近の熱処理を外部から行っており、依然として、工業的負荷が大きい製法となっている。 However, in order to achieve high physical properties with high orientation, the graphite compact actually produced from this graphene oxide is similar to the highly oriented pyrolytic graphite produced from the same highly oriented graphite compact. The heat treatment at around 3000 ° C. is performed from the outside, and it is still a manufacturing method with a large industrial load.
　そこで、よりエネルギー的負荷を少なくして、酸化グラフェン成形体を還元・結晶化し、グラファイト成形体を作製する方法として、等方性黒鉛の黒鉛化工程で使用されている、内部から加熱する自己発熱方式である、通電により抵抗加熱（通電加熱ともいう。）する方法が有望である。酸化グラフェンは、酸素含有基が導入されたことによって、そのπ電子共役系が破壊されているため、グラフェンに比べて、電気抵抗が著しく高いが、高分子やゴムなどの一般的な絶縁材料よりは電気抵抗が低いため、ある程度の電圧を印加することで電流を流すことができ、その高い電気抵抗によって、瞬時に超高温に発熱させることができる。非特許文献２では、酸化グラフェンに電気を流すことで、１分以内に還元と結晶化が可能であることが開示されている。 Therefore, self-heating by heating from the inside, which is used in the graphitization process of isotropic graphite, is a method of reducing and crystallizing graphene oxide compacts and producing graphite compacts with less energy load. A method of resistance heating by energization (also referred to as energization heating) is promising. Graphene oxide has a significantly higher electrical resistance than graphene because its π-electron conjugated system is destroyed due to the introduction of oxygen-containing groups. Since the electric resistance is low, a current can be passed by applying a certain voltage, and the high electric resistance can instantly generate heat to an extremely high temperature. Non-Patent Document 2 discloses that reduction and crystallization can be performed within one minute by passing electricity through graphene oxide.
　しかしながら、このような直接電気を流し、ジュール加熱によって急激に高温状態にできることは、焼結プロセスを短縮化し効率的にグラファイト成形体を形成できるメリットはあるが、グラファイト結晶の性質を反映した高配向性のグラファイト成形物を酸化グラフェンから作製する観点からは、十分ではなかった。 However, the fact that such direct electricity can be passed and the temperature can be rapidly increased by Joule heating has the advantage of shortening the sintering process and forming a graphite compact efficiently, but it has a high orientation reflecting the properties of graphite crystals. From the viewpoint of producing an excellent graphite molded product from graphene oxide, it was not sufficient.
　本発明は、上記問題・状況に鑑みてなされたものであり、その解決課題は、酸化グラフェンから効率的に熱伝導率が高いグラファイト成形体を製造するグラファイト成形体の製造方法を提供することである。 The present invention has been made in view of the above-described problems and situations, and its solution is to provide a method for producing a graphite molded body that efficiently produces a graphite molded body having high thermal conductivity from graphene oxide. is there.
　本発明者は、上記課題を解決すべく、上記問題の原因等について検討する過程において、加熱方法を通電による抵抗加熱方法とし、さらに加圧する工程を有する製造方法とすることにより、酸化グラフェンから高配向性のグラファイト成形体を効率的に作製できることを見いだし本発明に至った。 In order to solve the above-mentioned problems, the present inventor, in the process of examining the cause of the above-mentioned problem, makes the heating method a resistance heating method by energization and further increases the pressure from graphene oxide by using a manufacturing method having a pressurizing step. The inventors have found that an oriented graphite molded body can be produced efficiently and have reached the present invention.
　すなわち、本発明に係る上記課題は、以下の手段により解決される。 That is, the above-mentioned problem according to the present invention is solved by the following means.
　１．酸化グラフェンを原料とするグラファイト成形体の製造方法であって、通電により抵抗加熱する工程と、加圧する工程とを含むことを特徴とするグラファイト成形体の製造方法。 1. A method for producing a graphite molded body using graphene oxide as a raw material, comprising a step of resistance heating by energization and a step of pressing.
　２．前記通電により抵抗加熱する工程と前記加圧する工程とが、同時に行われることを特徴とする第１項に記載のグラファイト成形体の製造方法。 2. 2. The method for producing a graphite molded body according to claim 1, wherein the resistance heating step and the pressurizing step are performed simultaneously.
　３．前記通電により抵抗加熱する工程と前記加圧する工程とが、別々に行われることを特徴とする第１項に記載のグラファイト成形体の製造方法。 3. The method for producing a graphite molded body according to item 1, wherein the step of resistance heating by energization and the step of pressurizing are performed separately.
　４．前記加圧する工程における酸化グラフェンへの印加圧力が、５０ＭＰａ以上であることを特徴とする第１項から第３項までのいずれか一項に記載のグラファイト成形体の製造方法。 4. The method for producing a graphite molded body according to any one of claims 1 to 3, wherein an applied pressure to the graphene oxide in the pressurizing step is 50 MPa or more.
　５．前記加圧する工程における酸化グラフェンへの印加圧力が、１００ＭＰａ以上であることを特徴とする第１項から第４項までのいずれか一項に記載のグラファイト成形体の製造方法。 5. The method for producing a graphite molded body according to any one of claims 1 to 4, wherein an applied pressure to the graphene oxide in the pressurizing step is 100 MPa or more.
　６．熱伝導率が、１０００Ｗ／（ｍ・Ｋ）以上であることを特徴とする第１項から第５項までのいずれか一項に記載のグラファイト成形体の製造方法。 6. The method for producing a graphite molded body according to any one of items 1 to 5, wherein the thermal conductivity is 1000 W / (m · K) or more.
　７．熱伝導率が、１５００Ｗ／（ｍ・Ｋ）以上であることを特徴とする第１項から第６項までのいずれか一項に記載のグラファイト成形体の製造方法。 7. The method for producing a graphite molded article according to any one of items 1 to 6, wherein the thermal conductivity is 1500 W / (m · K) or more.
　８．前記グラファイト成形体が、グラファイトシートであることを特徴とする第１項から第７項までのいずれか一項に記載のグラファイト成形体の製造方法。 8. The method for producing a graphite molded body according to any one of claims 1 to 7, wherein the graphite molded body is a graphite sheet.
　本発明の上記手段により、酸化グラフェンから効率的に熱伝導率が高いグラファイト成形体を製造するグラファイト成形体の製造方法を提供することができる。 By the above means of the present invention, it is possible to provide a method for producing a graphite molded body that efficiently produces a graphite molded body having high thermal conductivity from graphene oxide.
　本発明の効果の発現機構ないし作用機構については、明確にはなっていないが、以下のように推察している。 The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.
　酸化グラフェンに通電加熱すると、短時間でグラファイト成形体を作製できるが、ジュール加熱による急激な温度上昇により、酸化グラフェンの還元時に放出される酸素含有基由来の水分子や、酸素、ＣＯ、ＣＯ２などのガスによる急激な膨張によって、酸化グラフェンの膜面や、酸化グラフェン分子自体の配向が乱れてしまうことが推定された。このため、結局、グラファイト結晶の性質を反映した高配向性のグラファイト成形物を酸化グラフェンから作製することはできていないと考えられる。 When graphene oxide is energized and heated, a graphite molded body can be produced in a short time. However, due to a rapid temperature rise caused by Joule heating, water molecules derived from oxygen-containing groups released during the reduction of graphene oxide, oxygen, CO, CO 2 It has been estimated that the film surface of graphene oxide and the orientation of the graphene oxide molecules themselves are disturbed by the rapid expansion caused by such gases. For this reason, after all, it is considered that a highly oriented graphite molded product reflecting the properties of graphite crystals cannot be produced from graphene oxide.
　本発明においては、通電により抵抗加熱する工程に加えて、酸化グラフェンを加圧する工程と組み合わせて、上記高配向性のグラファイト成形物を阻害する要因を取り除いたことにより、グラファイト結晶の配向性をさらに高め、また、グラファイトの密度を高くすることができるため生成するグラファイト成形体の熱伝導率を大幅に高くすることができるものと考えられる。 In the present invention, in addition to the step of resistance heating by energization, in combination with the step of pressurizing the graphene oxide, by removing the factor that inhibits the highly oriented graphite molded product, the orientation of the graphite crystal is further increased. It is considered that the thermal conductivity of the formed graphite compact can be significantly increased because the graphite density can be increased and the density of graphite can be increased.
　本発明のグラファイト成形体の製造方法は、酸化グラフェンを原料とするグラファイト成形体の製造方法であって、通電により抵抗加熱する工程と、加圧する工程とを含むことを特徴とする。この特徴は、各請求項に係る発明に共通する又は対応する技術的特徴である。 The method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and includes a resistance heating step by energization and a pressurizing step. This feature is a technical feature common to or corresponding to the claimed invention.
　本発明の実施態様としては、酸化グラフェン分子間の共有結合形成の効率性が向上する観点から、前記通電により抵抗加熱する工程と前記加圧する工程とが、同時に行われることが好ましい。また、前記通電により抵抗加熱する工程と前記加圧する工程とが、別々に行われることも、本発明の効果発現の観点から好ましい。 As an embodiment of the present invention, from the viewpoint of improving the efficiency of covalent bond formation between graphene oxide molecules, it is preferable that the step of resistance heating by energization and the step of pressurization are performed simultaneously. Moreover, it is also preferable from a viewpoint of the effect expression of this invention that the process of resistance heating by the said electricity supply and the said pressurization process are performed separately.
　さらに、本発明においては、前記加圧する工程における酸化グラフェンへの印加圧力が、５０ＭＰａ以上であることが好ましく、１００ＭＰａ以上であることが、より好ましい。これにより、グラファイト結晶の配向性を高める効果が得られる。 Furthermore, in the present invention, the pressure applied to the graphene oxide in the pressurizing step is preferably 50 MPa or more, and more preferably 100 MPa or more. Thereby, the effect which improves the orientation of a graphite crystal is acquired.
　また、本発明においては、グラファイト成形体の熱伝導率が、１０００Ｗ／（ｍ・Ｋ）以上であることが好ましく、１５００Ｗ／（ｍ・Ｋ）以上であることがよりに好ましい。 In the present invention, the thermal conductivity of the graphite compact is preferably 1000 W / (m · K) or more, and more preferably 1500 W / (m · K) or more.
　本発明の実施態様としては、グラファイト成形体が、グラファイトシートであることが好ましい。 As an embodiment of the present invention, the graphite compact is preferably a graphite sheet.
　以下、本発明とその構成要素、及び本発明を実施するための形態・態様について詳細な説明をする。なお、本願において、「～」は、その前後に記載される数値を下限値及び上限値として含む意味で使用する。 Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
　以下、本発明とその構成要素、及び本発明を実施するための形態・態様について詳細な説明をする。 Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail.
　《グラファイト成形体の製造方法》
　本発明のグラファイト成形体の製造方法は、酸化グラフェンを原料とするグラファイト成形体の製造方法であって、通電により抵抗加熱する工程と、加圧する工程とを含むことを特徴とする。 <Method for producing graphite molded body>
The method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and includes a step of resistance heating by energization and a step of pressing.
　酸化グラフェンは、所望の形状に成形されたものであっても良い。例えば、グラファイトを強酸化剤で酸化して作製した酸化グラフェンを溶媒中に分散させた酸化グラフェン溶媒分散物を作製し、その後酸化グラフェン溶媒分散物を所望の形状の型を用い成形し、その後溶媒を除去することにより酸化グラフェンの成形物を作製することができる。本発明では、これを通電により抵抗加熱する工程と、加圧する工程を経て高い熱伝導率を有するグラファイト成形体を短時間かつ簡便な方法で製造することができる。 The graphene oxide may be formed into a desired shape. For example, a graphene oxide solvent dispersion in which graphene oxide prepared by oxidizing graphite with a strong oxidizing agent is dispersed in a solvent is prepared, and then the graphene oxide solvent dispersion is molded using a mold having a desired shape, and then the solvent By removing the graphene, a graphene oxide molded product can be produced. In the present invention, a graphite molded body having a high thermal conductivity can be produced in a short time and in a simple manner through a process of resistance heating by energization and a process of pressurization.
　＜酸化グラフェン＞
　本発明において、酸化グラフェンとは、グラフェンに、カルボキシ基、カルボニル基、ヒドロキシ基、及びエポキシ基等の酸素含有基が修飾されたものを指す。本発明に用いる酸化グラフェンについては特に限定されないが、カルボキシ基、カルボニル基、ヒドロキシ基又はエポキシ基等の酸素含有基を有する酸化グラフェンの酸素含有比率（原子％）は、２４～５０原子％の範囲内であることが好ましい。２４原子％以上であると、溶媒分散性の観点から好ましく、また、上述の酸素含有基が特定量以上結合することでπ共役が切断され、酸化グラフェンの電気抵抗が高くなるため好ましい。また、５０原子％以下であると還元・結晶化の効率性の観点から好ましい。 <Graphene oxide>
In the present invention, graphene oxide refers to graphene modified with an oxygen-containing group such as a carboxy group, a carbonyl group, a hydroxy group, and an epoxy group. The graphene oxide used in the present invention is not particularly limited, but the oxygen content ratio (atomic%) of graphene oxide having an oxygen-containing group such as a carboxy group, a carbonyl group, a hydroxy group, or an epoxy group is in the range of 24 to 50 atomic%. It is preferable to be within. It is preferable from the viewpoint of solvent dispersibility to be 24 atomic% or more, and it is preferable because the above-described oxygen-containing group is bonded to a specific amount or more, so that π-conjugation is cut and the electric resistance of graphene oxide is increased. Moreover, it is preferable from a viewpoint of the efficiency of reduction | restoration and crystallization that it is 50 atomic% or less.
　（酸素含有比率の測定方法）
　酸化グラフェンの酸素含有比率（原子％）は、Ｘ線光電子分光法（Ｘ－ｒａｙ　Ｐｈｏｔｏｅｌｅｃｔｒｏｎ　Ｓｐｅｃｔｒｏｓｃｏｐｙ（以下、ＸＰＳともいう））で測定することができ、Ｏ／（Ｃ＋Ｏ）原子％で表される値である。ＸＰＳ測定条件は以下のとおりである。 (Measurement method of oxygen content ratio)
The oxygen content ratio (atomic%) of graphene oxide can be measured by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS), and is represented by O / (C + O) atomic%. It is. The XPS measurement conditions are as follows.
　酸化グラフェンの酸素含有比率は、アルバック・ファイ株式会社製のＱｕａｎｔｅｒａＳＸＭを用いて測定できる。測定条件としてはＸ線源として、単色化したＡｌ－Ｋα線を用い、分光器は清浄化した銀のＡｇ３ｄ５／２ピークを測定した際のピークの半値幅が０．５ｅＶ以下となるような条件で設定し、測定する。分光器の較正はＩＳＯ１５４７２に従って行う。 The oxygen content ratio of graphene oxide can be measured using a Quantera SXM manufactured by ULVAC-PHI CORPORATION. As measurement conditions, a monochromatic Al—Kα ray is used as an X-ray source, and the spectroscope has a half-width of 0.5 eV or less when the Ag3d 5/2 peak of purified silver is measured. Set and measure under conditions. Spectrometer calibration is performed according to ISO 15472.
　＜酸化グラフェンの面方向の径＞
　酸化グラフェンは、グラファイトを酸化処理することで、グラファイトを構成するグラフェンが剥離、酸化された、層状粒子である。この層状粒子の面方向の径が大きいほど、電気伝導性や、熱伝導性、弾性率や強度などの物性の観点から好ましい。層の面方向の径が、１μｍ以上あることが好ましく、５μｍ以上がより好ましく、酸化グラフェン溶媒分散体の分散状態に不具合が生じない範囲で、１０μｍ以上あることがさらに好ましい。 <Diameter of graphene oxide in the surface direction>
Graphene oxide is a layered particle in which graphene constituting graphite is peeled off and oxidized by oxidizing graphite. A larger diameter in the plane direction of the layered particle is preferable from the viewpoint of physical properties such as electrical conductivity, thermal conductivity, elastic modulus and strength. The diameter in the plane direction of the layer is preferably 1 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more as long as no trouble occurs in the dispersion state of the graphene oxide solvent dispersion.
　＜酸化グラフェンの厚さ＞
　酸化グラフェンは、グラファイトを酸化処理することで、グラファイトを構成するグラフェンが剥離、酸化された、層状粒子であり、その厚さは約０．３４ｎｍ～数ｎｍで、必ずしもすべてを単層まで剥離する必要はなく、用途に応じて、配向性に支障性をきたさない範囲で、数層～数十層の分散状態にしてもよい。 <Thickness of graphene oxide>
Graphene oxide is a layered particle in which graphene constituting graphite is exfoliated and oxidized by oxidizing graphite, and its thickness is about 0.34 nm to several nm, and all of them are exfoliated to a single layer. There is no need, and depending on the application, a dispersed state of several to several tens of layers may be used as long as the orientation is not hindered.
　＜酸化グラフェン溶媒分散体＞
　酸化グラフェンは、グラファイト、又は多層グラフェンを強酸化剤で酸化することによって、グラフェン粒子の面上や縁にエポキシ基やヒドロキシ基、カルボニル基や、カルボキシ基などの酸素含有基を付与され、溶媒に分散させることができる。水によく分散し、有機溶媒においても、メタノールやエタノール、テトラヒドロフラン（ＴＨＦ）などの、親水基を有する溶媒とは親和性があり、用途に応じて、成形性や配向性に支障が生じない範囲で、アセトンやメチルエチルケトン（ＭＥＫ）、ジクロロメタンなど、その他の有機溶媒でも分散体を作製することができる。 <Graphene oxide solvent dispersion>
Graphene oxide is obtained by oxidizing graphite or multilayer graphene with a strong oxidizing agent to give oxygen-containing groups such as epoxy groups, hydroxy groups, carbonyl groups, and carboxy groups to the surface and edges of graphene particles, and to the solvent. Can be dispersed. It is well dispersed in water, and organic solvents are compatible with solvents with hydrophilic groups, such as methanol, ethanol, tetrahydrofuran (THF), etc., and do not interfere with moldability and orientation depending on the application. Thus, the dispersion can be prepared with other organic solvents such as acetone, methyl ethyl ketone (MEK), and dichloromethane.
　酸化グラフェン溶媒分散物はＨｕｍｍｅｒｓ法、又はそれを改良したＭｏｄｉｆｉｅｄ
　Ｈｕｍｍｅｒｓ法で、公知の文献に基づいて作製することができる。酸化グラフェン作製の公知文献としては、例えば、Ｗ．Ｓ．Ｈｕｍｍｅｒｓ．，Ｊｏｕｒｎａｌ　ｏｆ　Ａｍｅｒｉｃａｎ　Ｃｈｅｍｉｓｔｒｙ（１９５８）１３３９、Ｍ．Ｈｉｒａｔａ．、Ｃａｒｂｏｎ　４２（２００４）２９２９などが挙げられる。 The graphene oxide solvent dispersion is a Hummers method or a modified modified version thereof.
The Hummers method can be used based on known literature. Known documents for producing graphene oxide include W.W. S. Hummers. , Journal of American Chemistry (1958) 1339, M .; Hirata. , Carbon 42 (2004) 2929, and the like.
　＜酸化グラフェン成形物＞
　酸化グラフェン分散体から、溶媒を除去することによって、さまざまな形状の酸化グラフェン成形物を作製することができる。例えば、シート状であれば、基材に塗布し、溶媒を除去することで、酸化グラフェンシートを作製できる。数ｎｍの厚さの薄膜形状のものも可能である。繊維状であれば、ノズルの細管から噴出させて、溶媒を除去することで、酸化グラフェン繊維を作製することができる。また、金型を用いて、成形しながら、溶媒を除去することで、所望の形に成形することもでき、３Ｄプリンターなどで所望の成形体を作製することもできる。 <Graphene oxide moldings>
By removing the solvent from the graphene oxide dispersion, graphene oxide molded products having various shapes can be produced. For example, in the case of a sheet shape, a graphene oxide sheet can be produced by applying to a substrate and removing the solvent. A thin film having a thickness of several nm is also possible. If it is fibrous, the graphene oxide fiber can be produced by ejecting from a thin tube of the nozzle and removing the solvent. Moreover, it can also shape | mold into a desired shape by removing a solvent, shape | molding using a metal mold | die, and can also produce a desired molded object with 3D printer etc.
　＜酸化グラフェン成形物の事前還元＞
　酸化グラフェンの還元とは、酸化グラフェン中にある酸素含有基が、水や酸素、一酸化炭素、二酸化炭素、炭酸として脱離していく反応のことをいう。酸化グラフェンシートを還元すると電気抵抗率が減少していく。酸化グラフェン成形物を還元処理し、用途によっては、電気抵抗率を調整してもよい。電気抵抗率の調整により、通電により抵抗加熱する工程において、流す電流量や、加熱温度等の条件を調整することができる。 <Pre-reduction of graphene oxide moldings>
The reduction of graphene oxide refers to a reaction in which oxygen-containing groups in graphene oxide are desorbed as water, oxygen, carbon monoxide, carbon dioxide, or carbonic acid. When the graphene oxide sheet is reduced, the electrical resistivity decreases. The graphene oxide molded product may be reduced, and the electrical resistivity may be adjusted depending on the application. By adjusting the electrical resistivity, conditions such as the amount of current to flow and the heating temperature can be adjusted in the step of resistance heating by energization.
　また、還元反応は約１０００℃以下の温度で進行するのに対し、結晶化（グラファイト化）反応を進行させるには約１０００℃以上、通常は２０００℃以上の温度を必要とする。つまり、結晶化（グラファイト化）反応に対して還元反応は反応速度が非常に速い。このため通電加熱時の膨張を抑える目的で、事前に温和な条件で還元反応を行ってもよい。 Further, while the reduction reaction proceeds at a temperature of about 1000 ° C. or lower, a temperature of about 1000 ° C. or higher, usually 2000 ° C. or higher is required for the crystallization (graphitization) reaction to proceed. That is, the reaction rate of the reduction reaction is very fast compared to the crystallization (graphitization) reaction. For this reason, the reduction reaction may be performed in advance under mild conditions for the purpose of suppressing expansion during energization heating.
　事前還元の方法は特に制限がなく、酸化グラフェンから酸化グラフェン還元物を得る従来公知の方法を用いることができる。例えば、酸化グラフェンを加熱して還元する方法（熱還元）、ヒドラジンやアスコルビン酸などの還元剤を用いて還元する方法（化学還元）、酸化グラフェンに光を照射して還元する方法（光還元）、電解質水溶液中で酸化グラフェンを電気分解して還元する方法（電気化学還元）などが挙げられる。酸化グラフェン還元物作製の公知文献としては、例えば、Ｃａｒｂｏｎ　５０（２０１２）３２１０などが挙げられる。 There is no particular limitation on the pre-reduction method, and a conventionally known method for obtaining graphene oxide reduced product from graphene oxide can be used. For example, a method of reducing graphene oxide by heating (thermal reduction), a method of reducing using a reducing agent such as hydrazine or ascorbic acid (chemical reduction), a method of reducing graphene oxide by irradiating light (photoreduction) And a method of electrolyzing and reducing graphene oxide in an aqueous electrolyte solution (electrochemical reduction). As publicly known literature for preparing graphene oxide reduced products, for example, Carbon 50 (2012) 3210 can be cited.
　《通電により抵抗加熱する工程》
　酸化グラフェンに電圧をかけることによって電流を流し、酸化グラフェンの抵抗によって発生するジュール熱によって自己発熱させることができる。流す電流の方向に特に限定はなく、直流であっても交流であってもよく、定常電流であってもパルス電流であってもよい。流す電流や電圧の大きさは、シートの大きさや抵抗によって変動するが、酸化グラフェンが１０００℃以上に加熱されるように電流を流すことが好ましく、２０００℃以上、より好ましくは２５００℃以上に加熱されるように電流を流すことが好ましい。例えば、電流密度が１０００００Ａ／ｍ２以上、好ましくは１００００００Ａ／ｍ２以上、より好ましくは１０００００００Ａ／ｍ２以上、特に好ましくは１００００００００Ａ／ｍ２以上になるように電流を流すことが好ましい。グラファイトの電子密度に由来する電流値の限界、又は、炭素の昇華点である３６００℃付近を超えない範囲で電流を流すことができる。 《Process of resistance heating by energization》
By applying a voltage to the graphene oxide, a current can be passed and self-heated by Joule heat generated by the resistance of the graphene oxide. The direction of the flowing current is not particularly limited, and may be a direct current or an alternating current, and may be a steady current or a pulse current. The magnitude of the current and voltage to flow varies depending on the size and resistance of the sheet, but the current is preferably passed so that the graphene oxide is heated to 1000 ° C. or higher, and is heated to 2000 ° C. or higher, more preferably 2500 ° C. or higher. It is preferable to pass an electric current. For example, current density 100000A / m 2 or more, preferably 1000000A / m 2 or more, more preferably 10000000A / m 2 or more, and particularly preferably it is preferred to flow a current so that 100000000A / m 2 or more. The current can be passed in a range not exceeding the limit of the current value derived from the electron density of graphite or the vicinity of 3600 ° C., which is the sublimation point of carbon.
　《加圧する工程》
　本発明においては、酸化グラフェンに通電加熱する工程に加えて、酸化グラフェンを加圧する工程を組み合わせることにより、生成するグラファイト成形体の熱伝導率を大幅に高くすることができる。これは、加熱により配向性の高いグラファイトが得られるだけでなく、加圧することにより、グラファイト中のグラフェンの配向性をさらに高め、また、グラファイトの密度を高くすることができるためであると考えられる。 《Pressurizing process》
In the present invention, in addition to the step of energizing and heating the graphene oxide, the thermal conductivity of the formed graphite compact can be greatly increased by combining the step of pressurizing the graphene oxide. This is considered to be because not only high orientation graphite can be obtained by heating, but also pressurization can further enhance the orientation of graphene in the graphite and increase the density of graphite. .
　加圧は、通電と同時に行っても良いし、別々に、つまり通電の前、又は後に行ってもよい。本発明の効果発現の観点からは、加圧は、通電と同時または加熱後に行うことが好ましい。さらに、加圧は、通電と同時に行うことが好ましい。 Pressurization may be performed simultaneously with energization, or may be performed separately, that is, before or after energization. From the viewpoint of manifesting the effects of the present invention, the pressurization is preferably performed simultaneously with energization or after heating. Furthermore, the pressurization is preferably performed simultaneously with energization.
　加圧を通電と同時に行うと、酸化グラフェン分子同士が圧力によって圧着した状態で通電することで、酸化グラフェン分子間の共有結合形成の効率性が向上する。 When the pressurization is performed simultaneously with the energization, the efficiency of the covalent bond formation between the graphene oxide molecules is improved by energizing the graphene oxide molecules in a state where the graphene oxide molecules are pressure-bonded by pressure.
　また、通電前に加圧し、酸化グラフェン分子同士の密着性を向上させ、酸化グラフェン分子間の共有結合形成の効率性を上げることができる。通電後に、加圧することで、酸化グラフェン分子の配向性を著しく改善させることができ、高配向性黒鉛特有の物性を発現させることができる。 In addition, pressurization before energization can improve the adhesion between graphene oxide molecules and increase the efficiency of forming covalent bonds between graphene oxide molecules. By applying pressure after energization, the orientation of graphene oxide molecules can be remarkably improved, and physical properties peculiar to highly oriented graphite can be expressed.
　加圧装置は、プレス機などを用いて、面接触で加えてもよいし、ロールで挟み、線接触で加えてもよく。所望の圧力が加われば、形状に制限はない。また、加圧方向は、一軸で加えてもよいし、全方位から加えてもよい。 The pressurizing device may be added by surface contact using a press or the like, or may be sandwiched between rolls and added by line contact. If a desired pressure is applied, the shape is not limited. Moreover, the pressurizing direction may be applied uniaxially or from all directions.
　加圧する工程における酸化グラフェンへの印加圧力は、１ＭＰａ以上であることが好ましく、１０ＭＰａ以上であることがより好ましく、５０ＭＰａ以上であることがさらに好ましく、１００ＭＰａ以上であることが特に好ましい。印加圧力の上限は汎用的なプレス装置の能力においては、１０００ＭＰａ程度である。 The pressure applied to the graphene oxide in the pressurizing step is preferably 1 MPa or more, more preferably 10 MPa or more, further preferably 50 MPa or more, and particularly preferably 100 MPa or more. The upper limit of the applied pressure is about 1000 MPa in the capacity of a general-purpose press device.
　さらに、本発明においては、前記通電により抵抗加熱する工程における通電時間が、グラファイト成形体を短時間に製造する観点から６０秒以下であることが好ましく、１０秒以下であることがより好ましく、３秒以下であることがさらに好ましい。通電時間の下限は、グラファイトの結晶性が向上し、グラファイト特有の性能発現に支障がない範囲であれば、パルスのような短い電流印加でもよい。 Furthermore, in the present invention, the energization time in the step of resistance heating by energization is preferably 60 seconds or less, more preferably 10 seconds or less, from the viewpoint of producing a graphite molded body in a short time. More preferably, it is less than a second. The lower limit of the energization time may be a short current application such as a pulse as long as the crystallinity of graphite is improved and there is no hindrance to the performance characteristic of graphite.
　通電と加圧を同時に行える汎用的な装置として放電プラズマ焼結装置を用いてもよい。放電プラズマ焼結装置では、成形体の上下に電極を配置し、通電しながら、加圧を行うことができる。例えば、シート状のものを電極で挟み、厚み方向に電流を流し自己発熱させながら、加圧することができる。シートを積層して通電、加圧すれば、シート同士が圧着、接着した厚膜シートや、ブロック体を簡便に作製することができる。 A discharge plasma sintering apparatus may be used as a general-purpose apparatus capable of performing energization and pressurization simultaneously. In the discharge plasma sintering apparatus, electrodes can be arranged on the upper and lower sides of the compact and pressure can be applied while energizing. For example, a sheet-like material can be sandwiched between electrodes, and pressure can be applied while flowing current in the thickness direction to cause self-heating. If the sheets are stacked and energized and pressed, a thick film sheet or a block body in which the sheets are pressure-bonded and bonded can be easily produced.
　通電加熱前、もしくは後に、全方位に圧力を加えられる装置として、冷間等方圧加圧装置（ＣＩＰ）、熱間等方圧加圧装置（ＨＩＰ）を用いてもよい。全方位から圧力を印加できるため、成形体の配向性向上に効果的である。 A cold isostatic pressurizing device (CIP) or a hot isostatic pressurizing device (HIP) may be used as a device that can apply pressure in all directions before or after energization heating. Since pressure can be applied from all directions, it is effective for improving the orientation of the molded body.
　本発明によれば、ジュール熱による自己発熱と加圧により、酸化グラフェンの結晶化を促進し、グラファイト化を進行させることができる。グラファイト化とは、酸素含有基で破壊された、酸化グラフェンのｓｐ２共有結合を修復すると共に、グラフェン同士の層間隔をグラファイト結晶と同程度の０．３４ｎｍにし、また、配向性を向上させることである。このグラファイト化によって、グラファイト単結晶と近い物性を成形体に発現させることができる。従来、例えばポリイミドを外部加熱してシート状の高配向性グラファイトを製造する場合に比べて、格段に短時間でかつ簡便につまり効率的に製造することが可能である。 According to the present invention, crystallization of graphene oxide can be promoted and graphitization can be promoted by self-heating and pressurization by Joule heat. Graphitization means repairing the sp 2 covalent bond of graphene oxide, which was broken by an oxygen-containing group, making the layer spacing between graphenes 0.34 nm, which is the same as that of graphite crystals, and improving the orientation. It is. By this graphitization, physical properties close to those of a graphite single crystal can be expressed in the molded body. Conventionally, for example, compared with the case where a sheet-like highly oriented graphite is produced by externally heating polyimide, for example, it can be produced in a much shorter time, that is, efficiently.
　＜グラファイト成形体の形状＞
　グラファイト成形体は、所望の形状に成形された酸化グラフェン成形物を、通電により抵抗加熱する工程と、加圧する工程とを含む製造方法により製造することができる。形状としては、シート状、繊維状、筐体形状及び薄膜形状等に好ましく適用することができる。 <Shape of graphite compact>
The graphite molded body can be manufactured by a manufacturing method including a step of resistance-heating a graphene oxide molded product molded into a desired shape by energization and a step of pressing. The shape can be preferably applied to a sheet shape, a fiber shape, a housing shape, a thin film shape, and the like.
　＜シート状グラファイト成形体＞
　シート状成形体として、グラファイトシートが挙げられる。グラファイトとは、複数のグラフェンが積層した構造であり、層間は弱いファンデルワールス力で結合している。グラフェンとは、六方系格子状に炭素原子が共有結合して形成された１原子厚さの２次元ネットワーク化合物である。厳密にはグラファイトはｓｐ２炭素原子のみから構成されるが、実際にはｓｐ３炭素原子や空孔、ヘテロ原子などの欠陥を有しており、これらの欠陥を含むものもグラファイトと呼ぶ。本発明において、グラファイトシートとは、グラファイトから構成されるシート状の物体を表す。 <Sheet graphite compact>
A graphite sheet is mentioned as a sheet-like molded object. Graphite is a structure in which a plurality of graphenes are stacked, and the layers are bonded together by a weak van der Waals force. Graphene is a one-atom-thick two-dimensional network compound formed by covalently bonding carbon atoms in a hexagonal lattice. Strictly speaking, graphite is composed of only sp 2 carbon atoms, but actually has defects such as sp 3 carbon atoms, vacancies, and hetero atoms, and those containing these defects are also called graphite. In the present invention, the graphite sheet represents a sheet-like object composed of graphite.
　高配向性グラファイトシートの用途として、熱拡散シートが挙げられる。スマートフォンやタブレット、ノートパソコン内のセントラルプロセッシングユニット（ＣＰＵ）の高性能化、マルチコア化に伴って、発熱量が増大しており、電子部品の故障を防ぐここと、ユーザーの高温による不快感を軽減するため、薄型のデバイスで十分な放熱スペースがない中、電子部品から発生した熱を速やかにシート面内方向に拡散できる、超高熱伝導性を有するシート部材が必要とされている。高配向性グラファイトシートは、汎用金属で最高の性能を示す、銅（４０１Ｗ／（ｍ・Ｋ））の数倍にもなる熱伝導性を有しており、産業上価値が高い。ただし、現状工業的に広く使用されているグラファイトシートの製法は、前述したポリイミドから作製される高配向性熱分解黒鉛のみで、依然として、工業的に負荷の大きいプロセスを用いている。本発明の製造方法を用いれば、安価に高熱伝導性のグラファイトシートを作製することができ、産業上非常に価値がある。 用途 Thermal diffusion sheet can be used as a highly oriented graphite sheet. As the central processing unit (CPU) in smartphones, tablets, and notebook computers becomes more sophisticated and multi-core, the amount of heat generation is increasing, which prevents electronic components from being damaged, and the user's discomfort due to high temperatures is reduced. Therefore, there is a need for a sheet member having ultrahigh thermal conductivity that can quickly diffuse the heat generated from the electronic component in the in-plane direction of the sheet while the thin device does not have sufficient heat dissipation space. The highly oriented graphite sheet has a thermal conductivity that is several times that of copper (401 W / (m · K)), which exhibits the best performance among general-purpose metals, and has high industrial value. However, the manufacturing method of the graphite sheet currently widely used industrially is only the highly oriented pyrolytic graphite produced from the polyimide described above, and still uses a process with a large industrial load. If the manufacturing method of this invention is used, a highly heat conductive graphite sheet can be produced cheaply and it is very valuable industrially.
　＜繊維状グラファイト成形体＞
　酸化グラフェンを繊維状に成形したものに、本発明の製造方法を適用することで、炭素繊維を作製することができる。従来の炭素繊維の製造プロセスは、１）高分子又は石油原料から作製される繊維前駆体を、２００～３００℃の熱処理で、耐炎化・不融化する工程、２）耐炎化した繊維前駆体を１５００℃付近で熱処理する炭素化工程、３）さらに炭素化した繊維を、２０００℃から３０００℃の温度で熱処理する黒鉛化工程、その後、表面処理や、ポリマーコーティングなどの工程があり、酸化グラフェンを原料とした酸化グラフェン繊維を炭素繊維製造の前駆体とすることで、耐炎化・不融化工程を経ずに、炭化・黒鉛化工程に移行することができ、黒鉛化工程でも、効率的に結晶化反応を行うことができる。従来の高分子であるポリアクリロニトリルや石油原料由来のピッチから紡糸された繊維前駆体から作製する炭素繊維では、まず高温熱処理に耐えられるように、耐炎化、不融化工程と呼ばれる、徐々に加温焼結していくプロセスが必要となっている。 <Fibrous graphite compact>
A carbon fiber can be produced by applying the production method of the present invention to a graphene oxide formed into a fiber shape. The conventional carbon fiber manufacturing process is as follows: 1) a process of making a fiber precursor made from a polymer or petroleum raw material flame-resistant / infusible by heat treatment at 200 to 300 ° C., 2) a fiber precursor made flame-resistant There is a carbonization process in which heat treatment is performed at around 1500 ° C, 3) a graphitization process in which the carbonized fiber is heat-treated at a temperature of 2000 ° C to 3000 ° C, and then a surface treatment, a polymer coating, and the like. By using the graphene oxide fiber used as a raw material as a precursor for carbon fiber production, it is possible to move to the carbonization / graphitization process without going through the flameproofing / infusibilization process. The reaction can be carried out. Carbon fibers made from fiber precursors spun from polyacrylonitrile, which is a conventional polymer, or pitch derived from petroleum raw materials, are first gradually heated to be able to withstand high-temperature heat treatment, called flameproofing and infusibilization processes. A process of sintering is required.
　この従来の工程では、いきなり高温処理をしてしまうと前駆体が融解してしまうため、耐炎化・不融化工程で、数十分の比較的長い時間をかけて焼結している。しかしながら、本発明の好ましい態様として、酸化グラフェンから作製した繊維前駆体を用いれば、高分子のように融解することがないため、いきなり２０００℃を超えるような高温処理を行うこともできる。また、炭素繊維は、その構造体内に欠陥がなければ、非常に高強度な材料になる反面、空隙や隙間などの欠陥が存在すると、そこを起点に脆性破壊してしまうため、本発明に係る通電により抵抗加熱する工程と加圧する工程を適用することで、効率的に黒鉛化反応を進行させつつ、空隙の生成などを抑制でき、産業上非常に価値がある。 In this conventional process, the precursor is melted if it is suddenly subjected to a high temperature treatment, and therefore, it is sintered over a relatively long time of several tens of minutes in the flameproofing / infusible process. However, as a preferred embodiment of the present invention, when a fiber precursor made of graphene oxide is used, it does not melt like a polymer, so that high-temperature treatment exceeding 2000 ° C. can be performed suddenly. Further, if the carbon fiber has no defects in its structure, it becomes a very high-strength material. On the other hand, if there are defects such as voids and gaps, the carbon fiber breaks brittlely from that point. By applying a resistance heating step and a pressurizing step by energization, it is possible to suppress the formation of voids and the like while efficiently advancing the graphitization reaction, which is very valuable industrially.
　＜グラファイト筐体＞
　酸化グラフェンは、溶媒に完全には溶解しないまでも、一分子層～数十層の状態で分散した溶液を作製できるため、所望の形の型を使いながら、溶媒を蒸発させることで、比較的自在に成形することができる。さらに作製した成形体に本発明のプロセスを用いることで、非常に高強度、高熱伝導などの高配向性黒鉛特有の性質を有する成形体を作製することができ、各種筐体、成形体に応用でき、産業上非常に価値がある。 <Graphite casing>
Since graphene oxide can produce a solution dispersed in a single molecular layer to several tens of layers even if it is not completely dissolved in the solvent, it is relatively easy to evaporate the solvent while using a mold of the desired shape. It can be molded freely. Furthermore, by using the process of the present invention for the produced molded body, it is possible to produce molded bodies having properties that are unique to highly oriented graphite, such as extremely high strength and high thermal conductivity, and can be applied to various cases and molded bodies. Can and is very valuable in industry.
　＜グラファイトヒートシンク＞
　本発明のグラファイト成形体の製造方法により、グラファイトで構成されたヒートシンクを効率的に作製することができる。必要に応じて３Ｄプリンターなどで小さいヒートシンクなども作製することができる。 <Graphite heat sink>
By the method for producing a graphite molded body of the present invention, a heat sink composed of graphite can be efficiently produced. If necessary, a small heat sink or the like can be produced by a 3D printer or the like.
　＜薄膜グラファイト（グラフェン）シート成形体＞
　本発明のグラファイト成形体の製造方法は薄膜形状のグラファイトに対しても適用できる。例えば、酸化グラフェンシートをナノオーダーの厚さで製膜し、還元、結晶化することで、透明導電膜を作製することもできる。ただし、ここでも、通電加熱しただけでは、発生するガスにより膜面が乱れ、所望の高結晶な透明導電膜を作製することはできない。本発明の製造方法を適用することで、非常に導電性の高い、平滑で透明な膜を作製することができる。現在使用されている透明導電膜は酸化インジウムスズ（ＩＴＯ）であるが、インジウムがレアメタルあることなどにより、代替材料が強く求められている。 <Thin graphite (graphene) sheet compact>
The method for producing a graphite molded body of the present invention can also be applied to thin-film graphite. For example, a transparent conductive film can be produced by forming a graphene oxide sheet with a nano-order thickness, reducing, and crystallizing. However, here, the film surface is disturbed by the generated gas only by energization heating, and a desired highly crystalline transparent conductive film cannot be produced. By applying the production method of the present invention, it is possible to produce a smooth and transparent film with very high conductivity. The currently used transparent conductive film is indium tin oxide (ITO), but there is a strong demand for alternative materials due to the fact that indium is a rare metal.
　酸化グラフェンであれば、原料は、黒鉛であり、地球上に存在する。そのため、グラフェンナノシートの透明導電膜の開発が活発に行われているが、結晶性の高いグラフェンを得る目的から化学気相蒸着（ＣＶＤ）によるグラフェン合成が主流である。本発明に係る通電により抵抗加熱する工程と加圧する工程を適用すれば、簡便な塗布製膜した酸化グラフェンシートから、短時間で簡便にグラフェン透明導電膜としてグラフェンシートを作製することができ、産業上非常に価値がある。 In the case of graphene oxide, the raw material is graphite and exists on the earth. Therefore, the development of a transparent conductive film of graphene nanosheets has been actively carried out, but for the purpose of obtaining graphene with high crystallinity, graphene synthesis by chemical vapor deposition (CVD) is the mainstream. By applying the resistance heating step and the pressurizing step according to the present invention, a graphene sheet can be easily produced as a graphene transparent conductive film in a short time from a simple coated and formed graphene oxide sheet. Very worthy on.
　また、薄膜グラファイト（グラフェン）シートは、ガスバリアシートとしても利用することができる。酸化グラフェンは、酸化反応によって、面内に空孔などが生じており、本発明の通電加熱による結晶化でｓｐ２共有結合が形成、空孔が修復されると共に、加圧による配向性の向上で、ガス透過性が非常に低いガスバリアシートを効率的に作製することができる。 Further, the thin film graphite (graphene) sheet can also be used as a gas barrier sheet. In graphene oxide, vacancies and the like are generated in the surface due to oxidation reaction, and sp 2 covalent bond is formed by crystallization by current heating according to the present invention, the vacancies are repaired, and the orientation is improved by pressurization. Thus, a gas barrier sheet having a very low gas permeability can be efficiently produced.
　＜酸化グラフェンシートの作製＞
　酸化グラフェンシートは、酸化グラフェン溶媒分散体をある一定の厚さで塗布し、溶媒を乾燥させることで作製することができる。一定の厚さで塗布し、乾燥させることができれば、膜質に不具合が生じない範囲でいかなる塗布方法を用いてもよい。例えば、キャスト製膜、濾過製膜、ディップコート、スピンコート、スプレー塗布などがある。また、酸化グラフェンシートはガラス基板や樹脂基材に塗布することで剥離することができる。酸化グラフェンシートが剥離できる範囲で、基板や基材にはいかなる材料を用いてもよい。 <Production of graphene oxide sheet>
The graphene oxide sheet can be produced by applying a graphene oxide solvent dispersion with a certain thickness and drying the solvent. Any coating method may be used as long as the film quality is not affected as long as it can be applied and dried at a constant thickness. Examples include cast film formation, filtration film formation, dip coating, spin coating, and spray coating. Further, the graphene oxide sheet can be peeled off by applying it to a glass substrate or a resin base material. Any material may be used for the substrate and the substrate as long as the graphene oxide sheet can be peeled off.
　＜酸化グラフェンシートの還元、結晶化＞
　通電加熱する工程及び加圧する工程を用いて酸化グラフェンシートの還元、結晶化を行ってグラファイトシートを作製することができる。厚さ方向に通電加熱する方法としてはプレス機で挟みながら、電圧をかけてもよく、二つのロールで挟み、ロールに電圧をかけることで、線接触で圧力をかけ搬送しながら、厚さ方向に電流を流してもよい。また、圧力をかけながら通電することができる放電プラズマ焼結装置などを用いてもよい。面内方向に通電して、加圧する場合は、サンプルの両端に電圧をかけて、電気を流し、通電部に厚さ方向からプレス機とスペーサーなどを用いて、圧力をかけてもよい。二つのロールでシートを挟み搬送しながら、離れたもう一対のロールを用意し、離れたロール間に電圧をかけ、シート面内方向に通電しながら、シートを搬送することもできる。シート面内方向に通電させながら、別の一対のロールを使って、通電部に圧力を加えることもできる。 <Reduction and crystallization of graphene oxide sheet>
A graphite sheet can be produced by reducing and crystallizing a graphene oxide sheet using a process of heating by heating and a process of applying pressure. As a method of energizing heating in the thickness direction, a voltage may be applied while being sandwiched between press machines, and it is sandwiched between two rolls, and by applying voltage to the rolls, pressure is applied by line contact while conveying the thickness direction. An electric current may be passed through. Moreover, you may use the discharge plasma sintering apparatus etc. which can supply with electricity, applying a pressure. When energizing and pressurizing in the in-plane direction, voltage may be applied to both ends of the sample to cause electricity to flow, and pressure may be applied to the energizing portion from the thickness direction using a press and a spacer. It is also possible to prepare another pair of separated rolls while sandwiching and conveying the sheet between the two rolls, applying a voltage between the separated rolls, and conveying the sheet while energizing the sheet in the in-plane direction. It is also possible to apply pressure to the energizing portion using another pair of rolls while energizing the sheet in the in-plane direction.
　圧力は、通電と同時に加えてもよく、別々に、つまり通電前、又は後に行ってもよい。
　《グラファイト成形体の物性》
　＜熱伝導率＞
　伝熱性能を表す物理量として熱伝導率がある。熱伝導率（Ｗ／（ｍ・Ｋ））は熱拡散率（ｍ２／ｓ）、比熱容量（Ｊ／ｋｇ・Ｋ）、密度（ｋｇ／ｍ３）の積で表される。熱拡散率、比熱容量、密度をそれぞれ測定することで、熱伝導率を算出できる。 The pressure may be applied simultaneously with energization, or may be performed separately, that is, before or after energization.
<Physical properties of graphite compact>
<Thermal conductivity>
There is a thermal conductivity as a physical quantity representing the heat transfer performance. Thermal conductivity (W / (m · K)) is represented by the product of thermal diffusivity (m 2 / s), specific heat capacity (J / kg · K), and density (kg / m 3 ). The thermal conductivity can be calculated by measuring the thermal diffusivity, specific heat capacity, and density.
　＜グラファイト成形体の熱伝導率＞
　汎用金属で最も高い熱伝導率を有するものは銅で、その熱伝導率は４０１Ｗ／（ｍ・Ｋ）である。したがって、銅を超える熱伝導率を有しグラファイト成形体を簡便に作製する製造方法は、産業上価値がある。さらに、１０００Ｗ／（ｍ・Ｋ）以上の熱伝導率を有するグラファイト成形体を提供する手段の中で、現状、約３０００℃付近の外部加熱したグラファイトシートのみが工業化されており、本発明の、１０００Ｗ／（ｍ・Ｋ）以上の熱伝導率を有するグラファイト成形体を作製する製造方法は、産業上非常に価値がある。また、１５００Ｗ／（ｍ・Ｋ）以上であると、単結晶グラファイトの熱伝導率に近い性能となり、産業上特に価値がある。熱伝導率は高いほど好ましいため特に上限に制限はないが、グラファイト単結晶の熱伝導率の理論値は、約２０００Ｗ／（ｍ・Ｋ）程度である。 <Thermal conductivity of graphite compact>
A general-purpose metal having the highest thermal conductivity is copper, and its thermal conductivity is 401 W / (m · K). Therefore, the manufacturing method which has the thermal conductivity exceeding copper and produces a graphite molded object simply has industrial value. Furthermore, among the means for providing a graphite molded body having a thermal conductivity of 1000 W / (m · K) or more, at present, only an externally heated graphite sheet near about 3000 ° C. has been industrialized. A manufacturing method for producing a graphite molded body having a thermal conductivity of 1000 W / (m · K) or more is very industrially valuable. Further, if it is 1500 W / (m · K) or more, the performance is close to the thermal conductivity of single crystal graphite, which is particularly valuable in industry. The upper limit is not particularly limited because the higher the thermal conductivity is, the theoretical value of the thermal conductivity of the graphite single crystal is about 2000 W / (m · K).
　また、グラファイト成形体が、グラファイトシートであることが、熱拡散シートなど産業上汎用性があることから好ましい。 Further, it is preferable that the graphite molded body is a graphite sheet because of industrial versatility such as a thermal diffusion sheet.
　以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれらに限定されるものではない。なお、実施例において「部」又は「％」の表示を用いるが、特に断りがない限り「質量部」又は「質量％」を表す。 Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "mass part" or "mass%" is represented.
　〔実施例１〕
　＜酸化グラフェン水分散体１の調製＞
　東京化成工業（株）のグラフェンナノプレートレット（厚さ６～８ｎｍ、幅５μｍ）１０ｇ、硝酸ナトリウム７．５ｇをフラスコに入れ、そこに濃硫酸６２１ｇを加えた。フラスコを氷浴につけ、撹拌しながら、過マンガン酸カリウム４５ｇを溶液温度が２０℃を超えないように少量ずつ加えた。その後、室温に戻し、１４日間撹拌した後、そこに、１Ｌの５質量％硫酸を加え１時間撹拌した。さらに、そこに３０質量％の過酸化水素水３０ｇを加え、１時間撹拌した。硫酸の濃度が３質量％、過酸化水素水の濃度が０．５質量％となるように調整した混合溶液１Ｌを加え希釈した。この溶液を、遠心分離（５０００ｒｐｍ、１５分）し、上澄みを除去、同様の混合溶液を加え、遠心分離を繰り返し１０回行った。同様の遠心分離を純水で１０回行い、１０回目で上澄みを捨てた後、２５０ｍＬの純水を加え酸化グラフェン水分散体１を作製した。 [Example 1]
<Preparation of graphene oxide aqueous dispersion 1>
10 g of graphene nanoplatelets (thickness 6-8 nm, width 5 μm) of Tokyo Chemical Industry Co., Ltd. and 7.5 g of sodium nitrate were placed in a flask, and 621 g of concentrated sulfuric acid was added thereto. The flask was placed in an ice bath and 45 g of potassium permanganate was added in small portions while stirring so that the solution temperature did not exceed 20 ° C. Then, after returning to room temperature and stirring for 14 days, 1 L of 5 mass% sulfuric acid was added there, and it stirred for 1 hour. Furthermore, 30 g of 30% by mass hydrogen peroxide water was added thereto and stirred for 1 hour. The mixture was diluted by adding 1 L of a mixed solution adjusted so that the concentration of sulfuric acid was 3% by mass and the concentration of hydrogen peroxide water was 0.5% by mass. This solution was centrifuged (5000 rpm, 15 minutes), the supernatant was removed, the same mixed solution was added, and the centrifugation was repeated 10 times. The same centrifugation was performed 10 times with pure water, and the supernatant was discarded at the 10th time. Then, 250 mL of pure water was added to prepare graphene oxide aqueous dispersion 1.
　＜酸化グラフェンシート１の作製＞
　酸化グラフェン水分散体１をガラス基板に貼付けた２５μｍのＰＥＴ（ポリエチレンテレフタレート）フィルム上に１．５ｍｍのギャップに調整したアプリケーターで塗布した。５０℃で１０時間乾燥させた後、ＰＥＴフィルムから剥離し、酸化グラフェンシート１（厚さ４４μｍ）を得た。酸化グラフェンシート１の酸素含有比率は４９原子％であった。酸素含有比率（原子％）は、前述したＸＰＳで測定した。 <Preparation of graphene oxide sheet 1>
The graphene oxide aqueous dispersion 1 was applied on a 25 μm PET (polyethylene terephthalate) film adhered to a glass substrate with an applicator adjusted to a gap of 1.5 mm. After drying at 50 ° C. for 10 hours, the film was peeled from the PET film to obtain graphene oxide sheet 1 (thickness: 44 μm). The oxygen content ratio of the graphene oxide sheet 1 was 49 atomic%. The oxygen content ratio (atomic%) was measured by XPS described above.
　＜グラファイトシート１の作製＞
　アルゴンフロー下、幅５ｍｍ、長さ５０ｍｍに切り出した酸化グラフェンシート１の中央部の長さ３０ｍｍの領域に、スペーサーを介して、プレス機を用いて１０ＭＰａの圧力を加えた。圧力を加えた状態で、酸化グラフェンの両端部に電圧を印加し、１５Ａで３０秒間電流を流し、グラファイト成形体としてシート状のグラファイトシート１を作製した。 <Preparation of graphite sheet 1>
Under an argon flow, a pressure of 10 MPa was applied to the region of 30 mm in the center of the graphene oxide sheet 1 cut out to a width of 5 mm and a length of 50 mm using a press through a spacer. In a state where pressure was applied, a voltage was applied to both ends of the graphene oxide, and a current was applied at 15 A for 30 seconds to produce a sheet-like graphite sheet 1 as a graphite compact.
　＜グラファイトシート２～４の作製＞
　グラファイトシート１の作製において、加圧する工程における圧力を表１のように変更した以外は、グラファイトシート１の作製と同様に作製し、グラファイトシート２～４を得た。 <Production of graphite sheets 2 to 4>
In the production of the graphite sheet 1, except that the pressure in the pressurizing step was changed as shown in Table 1, it was produced in the same manner as the production of the graphite sheet 1, and graphite sheets 2 to 4 were obtained.
　＜グラファイトシート５の作製＞
　アルゴンフロー下、幅５ｍｍ、長さ５０ｍｍに切り出した酸化グラフェンシート１の両端部に電圧を印加し、１５Ａで３０秒間電流を流した後、プレス機を用いて室温、１０ＭＰａで３０分間圧力を加え、グラファイト成形体としてシート状のグラファイトシート５を得た。 <Preparation of graphite sheet 5>
Under an argon flow, a voltage was applied to both ends of the graphene oxide sheet 1 cut into a width of 5 mm and a length of 50 mm, and a current was applied at 15 A for 30 seconds. As a graphite molded body, a sheet-like graphite sheet 5 was obtained.
　＜グラファイトシート６～８の作製＞
　グラファイトシート５の作製において、加圧する工程における圧力を表１のように変更した以外は、グラファイトシート５の作製と同様に作製し、グラファイトシート６～８を得た。 <Production of graphite sheets 6 to 8>
In the production of the graphite sheet 5, except that the pressure in the pressurizing step was changed as shown in Table 1, it was produced in the same manner as the production of the graphite sheet 5, and graphite sheets 6 to 8 were obtained.
　＜グラファイトシート９の作製＞
　アルゴンフロー下、幅５ｍｍ、長さ５０ｍｍに切り出した酸化グラフェンシート１の両端部に電圧を印加し、１５Ａの電流を３０秒間通電させたものを、グラファイトシート９とし、比較例とした。 <Production of graphite sheet 9>
Under the argon flow, a voltage was applied to both end portions of the graphene oxide sheet 1 cut out to a width of 5 mm and a length of 50 mm, and a current of 15 A was applied for 30 seconds to obtain a graphite sheet 9 as a comparative example.
　＜グラファイトシート１０の作製＞
　アルゴンフロー下、酸化グラフェンシート１を加熱炉で２５００℃に昇温した後、３０分間保持した。降温後、室温でプレス機を用いて２００ＭＰａで３０分間圧力を加えたものを、グラファイトシート１０とし、比較例とした。 <Production of Graphite Sheet 10>
Under an argon flow, the graphene oxide sheet 1 was heated to 2500 ° C. in a heating furnace and then held for 30 minutes. After lowering the temperature, a pressure applied at 200 MPa for 30 minutes at room temperature using a press machine was used as a graphite sheet 10 as a comparative example.
　《グラファイトシートの評価》
　〈熱伝導率の測定〉
　熱伝導率は以下の式で表され、熱拡散率、比熱容量、密度をそれぞれ測定することで算出した。 <Evaluation of graphite sheet>
<Measurement of thermal conductivity>
The thermal conductivity was represented by the following formula, and was calculated by measuring the thermal diffusivity, specific heat capacity, and density.
　＜通電加熱時の温度＞
　通電加熱条件でのグラファイトシート番号１～９の温度を、放射温度計で測定したところ、２０００℃以上の温度になっていることを確認した。具体的には２０００～３０００℃の温度範囲内であった。 <Temperature during energization heating>
When the temperature of graphite sheets Nos. 1 to 9 under the current heating condition was measured with a radiation thermometer, it was confirmed that the temperature was 2000 ° C. or higher. Specifically, it was within a temperature range of 2000 to 3000 ° C.
　　熱伝導率＝熱拡散率×比熱容量×密度
　熱拡散率は、アドバンス理工（株）のＬａｓｅｒ　Ｐｉｔ、比熱容量は、示差走査熱量計（ＤＳＣ６２２０：（株）日立ハイテクノロジーズ製）、密度は、シートの質量と体積を測定し、上記作製した各グラファイトシートの温度２３℃における熱伝導率を算出した。結果を表１に示す。 Thermal conductivity = thermal diffusivity × specific heat capacity × density The thermal diffusivity is Laser Pit of Advance Riko Co., Ltd., the specific heat capacity is a differential scanning calorimeter (DSC 6220: manufactured by Hitachi High-Technologies Corporation), and the density is a sheet. The mass and volume were measured, and the thermal conductivity at a temperature of 23 ° C. of each of the prepared graphite sheets was calculated. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１より、本発明のシート状のグラファイト成形体であるグラファイトシートは、比較例に比べ、熱伝導率が高く、かつ短時間で効率的に製造することができる。 From Table 1, the graphite sheet which is the sheet-like graphite molded body of the present invention has a higher thermal conductivity than that of the comparative example, and can be efficiently produced in a short time.
　本発明では、酸化グラフェンを出発原料とし、通電加熱によってｓｐ２共有結合を成形体全体に効率的に形成、かつ加圧によって配向性を向上させることで、従来実現されていなかった、グラフェン材料からビルドアップ的に高配向性のグラファイト成形体を効率的に作製することができ、このことは、酸化グラフェンの原料である、地球上に豊富に存在するグラファイトを、結晶本来の性質を損なうことなく、用途に応じて様々な形態に加工することが可能になることを意味している。 In the present invention, by using graphene oxide as a starting material, sp 2 covalent bonds are efficiently formed on the entire molded body by energization heating, and the orientation is improved by pressurization. It is possible to efficiently produce highly oriented graphite compacts in a build-up manner, which means that graphite, which is a raw material for graphene oxide, is abundant on the earth without damaging the original properties of crystals. This means that it can be processed into various forms depending on the application.
　従来から、酸化グラフェンに関しては、数多くの報告や特許文献が存在するが、そのほとんどが、２００４年に発見された単層グラフェンの優れた物性を目指すというものであった。本発明は、この大きな流れとは異なり、酸化グラフェンの溶媒分散能や、成形時、高アスペクト比による配向能力を利用することで、工業的に非常に価値がある高配向性のグラファイト成形体を、効率的に作製できるのではないかという発想に基づいたものである。酸化グラフェンから、効率的に高配向性のグラファイト成形体を作製するためには、一見、単純な通電加熱と加圧プロセスが必須で、かつこれを用いることで初めて高配向性のグラファイト成形体の優れた物性を発現させることができる。本発明は、高配向性グラファイト成形体を作製するために必要である、材料の成形性や配向性、製造の効率性の全てを満たす製造方法であるといえ、産業上非常に価値があるものといえる。 Conventionally, there have been many reports and patent literatures regarding graphene oxide, but most of them aimed at excellent physical properties of single-layer graphene discovered in 2004. In contrast to this large flow, the present invention uses a graphene oxide solvent dispersion ability and an orientation ability with a high aspect ratio at the time of molding to produce a highly oriented graphite compact that is very valuable industrially. It is based on the idea that it can be produced efficiently. In order to efficiently produce a highly oriented graphite compact from graphene oxide, a simple electric heating and pressurizing process is essential at first glance. Excellent physical properties can be expressed. It can be said that the present invention is a production method that satisfies all the moldability, orientation and production efficiency of materials necessary for producing a highly oriented graphite compact, and is very valuable industrially. It can be said.
　本発明のグラファイト成形体の製造方法は、酸化グラフェンを原料とするグラファイト成形体の製造方法であって、酸化グラフェンから短時間かつ簡便な方法で熱伝導率が高いグラファイト成形体を製造することができるグラファイト成形体の製造方法を提供することができる。 The method for producing a graphite molded body of the present invention is a method for producing a graphite molded body using graphene oxide as a raw material, and it is possible to produce a graphite molded body having high thermal conductivity from graphene oxide in a short time and with a simple method. It is possible to provide a method for producing a graphite molded body.

Claims (8)

  1. 　酸化グラフェンを原料とするグラファイト成形体の製造方法であって、通電により抵抗加熱する工程と、加圧する工程とを含むことを特徴とするグラファイト成形体の製造方法。 A method for producing a graphite molded body comprising graphene oxide as a raw material, the method comprising a step of resistance heating by energization and a step of pressing.
  2. 　前記通電により抵抗加熱する工程と前記加圧する工程とが、同時に行われることを特徴とする請求項１に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to claim 1, wherein the resistance heating step by the energization and the pressurizing step are performed simultaneously.
  3. 　前記通電により抵抗加熱する工程と前記加圧する工程とが、別々に行われることを特徴とする請求項１に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to claim 1, wherein the resistance heating step by the energization and the pressurizing step are performed separately.
  4. 　前記加圧する工程における酸化グラフェンへの印加圧力が、５０ＭＰａ以上であることを特徴とする請求項１から請求項３までのいずれか一項に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to any one of claims 1 to 3, wherein an applied pressure to the graphene oxide in the pressurizing step is 50 MPa or more.
  5. 　前記加圧する工程における酸化グラフェンへの印加圧力が、１００ＭＰａ以上であることを特徴とする請求項１から請求項４までのいずれか一項に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to any one of claims 1 to 4, wherein an applied pressure to the graphene oxide in the pressurizing step is 100 MPa or more.
  6. 　熱伝導率が、１０００Ｗ／（ｍ・Ｋ）以上であることを特徴とする請求項１から請求項５までのいずれか一項に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to any one of claims 1 to 5, wherein the thermal conductivity is 1000 W / (m · K) or more.
  7. 　熱伝導率が、１５００Ｗ／（ｍ・Ｋ）以上であることを特徴とする請求項１から請求項６までのいずれか一項に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to any one of claims 1 to 6, wherein the thermal conductivity is 1500 W / (m · K) or more.
  8. 　前記グラファイト成形体が、グラファイトシートであることを特徴とする請求項１から請求項７までのいずれか一項に記載のグラファイト成形体の製造方法。 The method for producing a graphite molded body according to any one of claims 1 to 7, wherein the graphite molded body is a graphite sheet.
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