TW201538424A - Method of producing flaked graphite, flaked graphite, and flaked graphite-resin composite material - Google Patents

Abstract

Provided is a method of producing flaked graphite, which makes it possible to efficiently mass-produce flaked graphite of superior dispersibility into a resin. The method of producing flaked graphite comprises a step for inserting a catalyst between graphite layers, and a step for subjecting the graphite to a release treatment by chemically bonding a reactive compound to the graphite using the catalyst, thereby obtaining flaked graphite.

Description

Method for producing exfoliated graphite, exfoliated graphite and exfoliated graphite-resin composite material

The present invention relates to a method for producing exfoliated graphite using GIC (Graphite Intercalation Compound) and exfoliated graphite obtained by the method for producing exfoliated graphite. Further, the present invention relates to a exfoliated graphite-resin composite obtained by mixing the exfoliated graphite and a resin.

Graphene is excellent in toughness, electrical conductivity, thermal conductivity, and heat resistance. Therefore, various methods for producing exfoliated graphite having a smaller number of graphene or graphene layers than the original raw material graphite have been proposed.

As a method of mass-produced graphene or exfoliated graphite, a method of producing GIC (Graphite Intercalation Compound) from graphite and stripping between the obtained GIC graphene is known. As a method for obtaining such a GIC, 1) a two-bulb method, 2) a liquid phase contact reaction method (mixing method), 3) a solid phase pressing method, 4) a solvent method, and 5) an electrochemical method are proposed. Wait.

Patent Document 1 listed below discloses an example of such a manufacturing method. Here, a method of producing graphene or exfoliated graphite by mechanically dispersing GIC using an alkali metal in a specific solvent is disclosed.

On the other hand, in the following Non-Patent Document 1, it is disclosed that a metal halide such as ferric chloride or aluminum chloride which acts as an acceptor for an aromatic compound is dissolved in a solvent such as nitromethane or sulfoxide. The method of graphite impregnation. According to this method, it can be produced by a solvent method Receptor type GIC.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-535690

[Non-patent literature]

[Non-Patent Document 1] D. Ginderow, R. Setton, C. R. Acad. Sci. Palis 257, 687 (1963)

As shown in Patent Document 1, in the conventional method of producing graphene or exfoliated graphite by the so-called donor type GIC, it is necessary to use a special device which avoids reaction with moisture or oxygen in the air. In addition, there is a problem that dangerous solvents are used or the risk of process control is high. Therefore, graphene or exfoliated graphite cannot be mass-produced safely and efficiently by GIC.

On the other hand, in Non-Patent Document 1, although a method of obtaining an acceptor type GIC by a solvent method is reported, a method of producing graphene or exfoliated graphite from an acceptor type GIC is not shown.

An object of the present invention is to provide a method for producing exfoliated graphite which is capable of efficiently mass-producing exfoliated graphite excellent in resin dispersibility.

Further, another object of the present invention is to provide a exfoliated graphite obtained by the above method for producing exfoliated graphite and a exfoliated graphite-resin composite material containing the exfoliated graphite.

The method for producing exfoliated graphite of the present invention comprises the steps of: inserting a catalyst into a graphite layer; and performing a stripping treatment on the graphite by chemically bonding the reactive compound with graphite using the above-mentioned catalyst to obtain a thinned graphite. The above reactive compound is preferably a Diels-Alder reactive compound. Further, the above reactive compound is preferably Fu- Frid-Crafts reactive compound.

In the method for producing exfoliated graphite of the present invention, it is preferred that the catalyst be a compound which acts as a charge acceptor for an aromatic compound. More preferably, the above catalyst is a metal halogen compound.

In the method for producing exfoliated graphite of the present invention, the step of inserting a catalyst between the graphite layers may be carried out in a solvent.

In the method for producing exfoliated graphite of the present invention, the step of inserting a catalyst between the graphite layers may be carried out in the presence of a supercritical fluid.

In the method for producing exfoliated graphite of the present invention, in the step of inserting a catalyst into the graphite layer, a gas-state catalyst may be inserted between the graphite layers.

In the method for producing exfoliated graphite of the present invention, the step of subjecting the graphite to a stripping treatment may be carried out in the presence of a supercritical fluid.

In the method for producing exfoliated graphite according to the present invention, in the step of subjecting the graphite to a stripping treatment, the reactive compound may be chemically bonded to the graphite by bringing the reactive compound in a gaseous state into contact with the graphite.

In the method for producing exfoliated graphite according to the present invention, it is preferred that the catalyst is a compound which acts as a charge acceptor for an aromatic compound, and in the solvent, the catalyst forms a complex with the solvent. The ligand of the above complex is preferably an electron-donating compound. The ligand of the above complex is preferably a compound having an aromatic ring. Further, the ligand of the above complex is preferably a compound having an isolated electron pair.

In the method for producing exfoliated graphite of the present invention, it is preferred that the solvent has a solubility parameter of 10 or less.

The exfoliated graphite of the present invention can be obtained by the above-described method for producing exfoliated graphite. The exfoliated graphite of the present invention is preferably chemically bonded to a Diels-Alder reactive compound. Further, it is preferably chemically bonded to a Fridel-Crafts reactive compound.

The exfoliated graphite-resin composite material of the present invention contains the exfoliated graphite of the present invention, And resin.

According to the method for producing exfoliated graphite of the present invention, exfoliated graphite excellent in dispersibility to a resin can be mass-produced efficiently. Further, the exfoliated graphite-resin composite material of the present invention contains the exfoliated graphite described above. Therefore, according to the present invention, it is possible to provide a exfoliated graphite-resin composite material which is excellent in mechanical strength.

1‧‧‧reactor

2, 3‧‧‧1st and 2nd raw material containers

4‧‧‧1st on-off valve

5‧‧‧1st carbon dioxide gas cylinder

6‧‧‧2nd on-off valve

7‧‧‧3rd on-off valve

8‧‧‧2nd carbon dioxide gas cylinder

9‧‧‧4th on-off valve

10, 11‧‧‧1st and 2nd reaction zones

12‧‧‧Vacuum pump

Fig. 1 is a graph showing XRD (X ray diffraction) spectra of samples obtained in Examples 1 to 5 and Comparative Example 1 and raw material graphite.

Fig. 2 is a view showing a schematic view of a reaction apparatus used in Example 4.

Fig. 3 is a view showing a schematic view of a reaction apparatus used in Example 5.

Hereinafter, the details of the present invention will be described.

In order to achieve the above problems, the inventors of the present invention have diligently studied and found that after the catalyst is inserted between the graphite layers, the reactive compound is chemically bonded to the graphite by using the catalyst, whereby the exfoliated graphite can be easily obtained. this invention.

The method for producing exfoliated graphite of the present invention comprises: a first step of inserting a catalyst into a graphite layer; and performing a stripping treatment on the graphite by chemically bonding the reactive compound to the graphite by using the catalyst to obtain exfoliated graphite The second step.

(Step 1)

In the first step, a catalyst is inserted between the graphite layers of the raw material graphite to obtain expanded graphite. Here, the expanded graphite is a GIC in which a catalyst as an intercalation material is interposed between the graphene layers, or a graphite compound in a state in which the GIC layer is highly opened. In the present invention, since the intercalation material is interposed between the graphene layers, the distance between the graphene layers is widened.

Examples of the raw material graphite include natural graphite, artificial graphite, and heat-expandable graphite. HOPG and so on. Further, HOPG (Highly Oriented Pyrolytic Graphite) means a highly aligning graphite crystal produced by vapor-phase growth of a hydrocarbon gas. The heat-expandable graphite means graphite which has a certain degree of acid by intercalating a graphene layer of graphite by an acid, and the acid is volatilized by heat treatment, thereby having the ability to expand. Such thermally expandable graphite can be obtained from AIR WATER Co., Ltd. or Suzuki Chemical Co., Ltd., and the like. Further, a fibrous material having a graphene structure such as carbon fiber can also be used as the raw material graphite. That is, the form of the raw material graphite is not particularly limited.

Further, in the present invention, the exfoliated graphite is a laminate of graphene sheets or a single layer of graphene sheets. The exfoliated graphite is obtained by subjecting graphite to a stripping treatment. That is, the exfoliated graphite is a laminate of graphene sheets or a single layer of graphene sheets which are thinner than the original graphite.

The number of layers of the graphene sheets in the exfoliated graphite is 1 or more. The number of layers of the graphene sheets is preferably 1,000 or less, and more preferably 150 or less, from the viewpoint of further effectively increasing the mechanical strength such as the tensile modulus of the resin.

The exfoliated graphite has a structure in which a thin graphene sheet is laminated. Thereby, the aspect ratio of the exfoliated graphite is relatively large. Further, the aspect ratio of the exfoliated graphite in the present invention means the ratio of the maximum dimension in the direction of the layered direction of the exfoliated graphite to the thickness of the exfoliated graphite.

When the aspect ratio of the exfoliated graphite is too low, there is a case where the reinforcing effect applied to the external force in the direction intersecting the above-mentioned accumulation layer is insufficient. If the aspect ratio of the exfoliated graphite is too high, the effect is saturated, and the above-described reinforcing effect cannot be expected. Therefore, the preferred lower limit of the aspect ratio of the exfoliated graphite is about 50, and the upper limit is preferably about 5,000.

The catalyst is not particularly limited, and is preferably a compound which acts as a charge acceptor for an aromatic compound. For example, the following metal halides represented by (1) MXn (wherein M is a metal of Groups 2 to 7 of the periodic table, X is a halogen, n is an integer of 2 to 5), and (2) is represented by MAX. Compound salt, (3) complex represented by ML or MLX, (4) package A charge acceptor containing an organic compound or (5) a trivalent phosphorus compound or the like.

(1) Metal halides represented by MXn:

M is a Group 2 to Group 7 metal of the periodic law table. Examples of such a metal include ruthenium, boron, magnesium, aluminum, lanthanum, calcium, strontium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, gallium, lanthanum, cerium, zirconium, hafnium, molybdenum,鎝, 钌, 铑, palladium, silver, cadmium, indium, tin, antimony, bismuth, antimony, tungsten, antimony, bismuth, antimony, platinum, gold, mercury, antimony, lead, antimony, etc.

The above X is a halogen and is fluorine, chlorine, bromine or iodine. The above n is an integer corresponding to 2 to 5 of the valence of the metal.

Among the above MXn, as a preferred metal halide, X is chlorine, and examples thereof include copper chloride, iron chloride, zinc chloride or aluminum chloride. The above metal chloride is low in price and relatively low in toxicity, so that it is preferred.

Further, the metal halide represented by MXn may be a metal halide containing a plurality of halogens as in the case of MX ₁ X ₂ . In this case, X ₁ and X ₂ are different halogen elements.

(2) Compound salt represented by MAX:

When A is set to an acid, it is a composite salt of an acid, a halogen, and a metal represented by MAX. As described above, M is a Group 2 to Group 7 metal element of the periodic table. A is an acid. The acid may be an inorganic acid such as sulfuric acid, nitric acid, phosphoric acid or boric acid, or may be an organic acid. X is the above halogen.

(3) the complex represented by ML or MLX

M is a metal element of Group 2 to Group 7. L is a compound which functions as a ligand such as acetamidineacetone, ethylenediamine, phthalocyanine, ammonia, carbon monoxide or cyano group. X is the above halogen.

(4) Charge receptors containing organic compounds

As the organic compound which functions as the above-mentioned charge acceptor, for example, it can be used with p-benzoquinone, 2,3,5,6-tetramethyl-p-benzoquinone, 2-methyl-1,4-naphthoquinone, or tetra. An organic compound capable of forming a charge transporting complex (CT complex) of an aromatic compound such as fluorine-1,4-benzoquinone, 7,7,8,8-tetracyanoquinolodimethane or 2-cyanopyridine Compound.

(5) Trivalent phosphorus compounds

Examples of the trivalent phosphorus compound include triphenyl phosphite and a trialkyl phosphite.

In the first step, the method of inserting the catalyst into the graphite layer is not particularly limited. For example, a method of inserting a catalyst into a graphite layer by a solvent method using a solvent can be mentioned. Further, the catalyst may be inserted between the graphite layers in the presence of a supercritical fluid, or a catalyst in a gaseous state may be inserted between the graphite layers.

Regarding a method of inserting a catalyst into a graphite layer by a solvent method, first, a solvent and a complex compound of a compound which acts as a charge acceptor for graphite are formed in a solvent. Next, by bringing the formed complex into contact with the raw material graphite, the catalyst is inserted between the graphite layers to expand the graphite.

As the solvent to be used in the first step, a solvent capable of forming a charge transporting complex (CT complex) with a compound which acts as a charge acceptor for the above aromatic compound is preferably used. Further, in the case where the solvent forms a complex with the compound, the solvent becomes a ligand of the above complex.

Whether or not a CT complex is formed with the compound which functions as a charge acceptor described above can be confirmed by light absorption spectroscopy. That is, whether the specific absorption of the CT complex called the CT band at the time of mixing occurs in the long wavelength region can qualitatively determine whether or not the CT complex is formed.

Examples of the solvent in which the solvent itself forms a CT complex with the compound which functions as a charge acceptor include a solvent containing an aromatic compound such as benzene, toluene, xylene or tetrahydronaphthalene, or a derivative or a mixture thereof. .

The solvent which can form a CT complex with the compound which functions as a charge acceptor mentioned above can also be a solvent containing the aromatic compound, such as N-methyl pyrrolidone or pyridine.

Further, a solvent having an isolated electron pair such as methyl ethyl ketone or diethyl ether can also be used. Such a solvent has a low CT complex forming ability but is electron-donating, and thus can be used in the present invention.

Further, as the solvent, a mixed solvent of a solvent which forms a CT complex and a solvent which does not have a CT complex formation ability with the compound which functions as a charge acceptor can also be used. Examples of the other solvent having no CT complex formation ability include a normal alkane or a cycloalkane. Further, as the other solvent, an organic halogen-based solvent such as chloroform, chloromethyl, dichloromethyl, dichloroethane, diiodomethane or dibromoethane can also be used.

The dissolution parameter of the above solvent is preferably 10 or less, more preferably 9.5 or less. The solvent having a dissolution parameter of 10 or less is exemplified by various literatures: benzene, toluene, ethylbenzene, xylene, methyl ethyl ketone, diethyl ketone, benzaldehyde, di-n-butyl phosphate, ortho-benzene. Dibutyl diformate and the like.

Further, the solubility parameter of tetrahydrofuran (THF) was 9.1, which was low, and it was not preferable because the ratio of the hydrogen bonding component of the dissolution parameter was high. In this case, even if the above-mentioned compound which functions as a charge acceptor is added to THF, the CT band does not appear to be confirmed by the light absorption spectrum.

As the above solvent, it is also possible to use a limonene, a terpene, a decene, a decene, a butadiene, a part of an alkane or a cycloalkane which is a double bond. An unsaturated hydrocarbon such as an alkene or a hydrazine.

As another embodiment of the solvent which can be used in the first step, a solution obtained by dissolving a compound which forms a CT complex with the compound which functions as a charge acceptor in a solvent can be mentioned. In this case, the compound forming the above CT complex becomes a ligand. Further, the solvent is not particularly limited, and an inert solvent may be used, or a solvent in which the solvent itself and a compound acting as a charge acceptor form a CT complex may be used.

The compound having the ability to form a CT complex can also be a compound constituting a solvent having its own ability to form a CT complex. Further, it may be an aromatic compound such as naphthalene, biphenyl, anthracene, phenanthrene or anthracene in a solid state.

Examples of the inert solvent include a cycloalkane, an n-alkane, a halogenated carbon-based solvent, and the like.

Further, as the solvent used in the first step, it is necessary to dissolve the compound which functions as a charge acceptor, and therefore it is desirable to have a solvent having a certain degree of interaction with the compound which functions as a charge acceptor. Jiawei does not have strong ionic interactions.

When a hydrophobic solvent having a strong interaction such as a hydrogen bond or an ionic bond is used, the ligand of the formed complex is difficult to be substituted with the aromatic bond having an SP2 bond between the graphene layers. The situation of the reaction. Therefore, the formation of GIC, that is, the formation of expanded graphite cannot be performed. Therefore, it is desirable that the above solvent be a strong ionic interaction with a compound that functions as a charge acceptor.

As described above, in the case of using the solvent method, the above-mentioned compound which functions as a charge acceptor and graphite are mixed in the above solvent. By this operation, the compound functioning as a charge acceptor forms a complex in a solvent, and the complex is contacted with the raw material graphite. Further, the raw material graphite may be brought into contact with the complex after the formation of the complex compound. That is, after the complex compound of the above-described compound acting as a charge acceptor is formed in a solvent, the raw material graphite may be introduced into a solvent to bring the complex into contact with the raw material graphite.

In addition, the raw material graphite may be introduced while the compound functioning as a charge acceptor is introduced into the solvent, and the compound which functions as a charge acceptor may be charged and then input into the raw material graphite.

When the complex compound is brought into contact with the raw material graphite, it is preferred to carry out heating. By heating, the above-described compound acting as a charge acceptor further promotes the intercalation between the graphene layers of the raw material graphite. That is, the speed of embedding can be increased.

Further, as for the heating temperature, it is preferred that the boiling point of the solvent is not reached. However, from the viewpoint of further increasing the speed of embedding, it is preferred that the heating temperature is high, and it is desirable to have a temperature higher than normal temperature.

In the solvent method, in the first step, a compound which functions as a charge acceptor is inserted into a layer of graphene. Thus, the expanded graphite is formed in a solvent. However, regarding the expanded graphite obtained in the first step, the layers of graphene are not so enlarged. This aspect will be explained later.

The expanded graphite obtained in the first step can be separated from the above solvent by filtration or centrifugation by a solvent method. In the case of having a sheet shape or a three-dimensional shape, the above expanded graphite may be directly taken out from the solvent. Further, it is desirable that the compound which functions as a charge acceptor and the other ligand compound which are not inserted into the graphite are removed by washing.

Further, as described above, in the present invention, the catalyst may be inserted between the graphite layers in the presence of a supercritical fluid to obtain expanded graphite. The supercritical fluid is not particularly limited, and supercritical carbon dioxide, supercritical water or the like can be used.

In the case of using a supercritical fluid, the catalyst is supplied to the reaction vessel only by the amount necessary for chemical equilibrium via supercritical carbon dioxide, so that the loss of the raw material can be reduced.

Further, in the present invention, the catalyst in a gaseous state may be brought into contact with the raw material graphite, whereby the catalyst may be inserted between the graphite layers to obtain expanded graphite.

In the case of using a catalyst in a gaseous state, only a necessary amount accompanying chemical equilibrium is supplied to the reaction vessel by volatilization of the catalyst, so that loss of the raw material can be reduced.

When the XRD spectrum of the expanded graphite obtained in the first step was measured, it was found that the distance between the graphene layers was not sufficiently enlarged. However, by performing the second step described below, exfoliated graphite which is sufficiently enlarged between the graphene layers can be obtained.

(Step 2)

In the present invention, the second step is performed after the first step, and the expanded graphite obtained in the first step is brought into contact with the reactive compound. In other words, the raw material graphite that is in contact with the catalyst, that is, the graphite in which the compound functioning as a charge acceptor is brought into contact with the reactive compound, reacts to form a chemical bond. Therefore, between the graphite layers, the above-mentioned reactive compound which is larger than the compound which originally functions as a charge acceptor is inserted. Thereby, the graphite layers are enlarged and the graphite is peeled off, and exfoliated graphite can be obtained.

Thus, in the second step, the reactive compound and the graphite are chemically bonded to each other. Stripping treatment is easy. The amount of the reactive compound chemically bonded in the second step is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, still more preferably 3.0% by weight, and still more preferably 100% by weight based on the raw material graphite. 5.0% by weight or more. Further, the amount of the reactive compound chemically bonded in the second step is preferably 200% by weight or less based on 100% by weight of the raw material graphite.

The reactive compound used in the second step is not particularly limited as long as it is a known reactive organic compound chemically bonded to a graphite raw material, and examples thereof include a Diels-Alder reactive compound and a Fridel-Crafts reactive compound. Or a radical reactive compound or the like.

Examples of the Diels-Alder-reactive compound include maleic anhydride derivatives such as maleic anhydride and dimethyl maleate, and N-phenyl maleimide and the like. A quinone imine, a furfural derivative such as furfural, decyl alcohol, mercaptoamine, 5-methyl-2-furaldehyde, mercapto mercaptan or 2-furopyryl chloride, 2-methylfuran, 2-ethyl Furan derivatives such as furan, 2-methoxyfuran and 2-cyanofuran, vinyl modified solvents such as vinyl acetate, p-chlorostyrene, N-vinyl-2-pyrrolidone or phenylimidazoline Amines, etc. These compounds may be used alone or in combination of two or more.

The Fridell-Crafts reactive compound can be used as long as it is a normal halide, a carboxylic acid halide, an acid anhydride or the like, and for example, 1-chlorododecane, N-chlorooctane or N-octyl chloride can be used. An alkyl halide or an aliphatic acid halide, a benzoic acid halide such as benzamidine chloride, an anhydride such as succinic anhydride or phthalic anhydride or propionic anhydride, or the like. These compounds may be used alone or in combination of two or more.

Examples of the radical-reactive compound include a compound having a radically reactive functional group, and examples thereof include a compound selected from the group consisting of a (meth) acrylonitrile group, a vinyl group, a vinyl ether group, a glycidyl group, and a thiol group. a compound of at least one of a group consisting of a halogen group, a carbonyl group, a carboxyl group, a sulfo group, an amine group, a hydroxyl group, a decyl group, a nitrile group, an isocyanate group, a decyl group, and a derivative thereof.

The reaction using the reactive compounds can be carried out in a solvent or in the presence of a supercritical fluid. Further, treatment such as heating may be performed as needed. Further, the reactive compound in a gaseous state may be brought into contact with graphite.

When a Lewis acidic compound such as a metal halogen compound is used as the compound which functions as a charge acceptor by using the above Diels-Alder reactive compound, the compound which functions as a charge acceptor also functions as a reaction catalyst, and thus It does not require heating and reacts at room temperature, so productivity is extremely high.

In the case where a Lewis-Crafts-reactive compound is used and a Lewis acidic compound such as a metal halogen compound is used as the compound which functions as a charge acceptor, the compound which functions as a charge acceptor functions as a reaction catalyst, and thus Extremely productive.

These reactive compounds can be expected to have a surface modification effect by bonding with exfoliated graphite. As the surface modification effect, hydrophilization, hydrophobization, or imparting of an organic reactive functional group may be selected as needed. In the Fridel-Crafts reaction, alkylation of the exfoliated right ink can be achieved using a chlorinated alkyl group as the reactive compound. Since the alkylated modified exfoliated graphite is excellent in compatibility with a resin, it is advantageous in the following resin composite.

In the second step, the graphene layer is further expanded by the bonding of the terminal portion of the graphene or the reactive compound between the layers to cause peeling. After the second step, mechanical peeling treatment such as ultrasonic treatment or mechanical shear treatment may be performed as needed. In this case, exfoliated graphite having a higher peeling degree can be obtained. Further, by repeating the series of operations of the first step and the second step described herein, the degree of peeling can be further improved.

In the method for producing exfoliated graphite according to the present invention, the first step and the second step can be carried out by using the same solvent, and a single apparatus, continuous equipment, or the like can be realized, and thus productivity is excellent. However, the expanded graphite may be taken out after the first step, and the peeling treatment may be performed using another solvent in the second step. In this case, a solvent suitable for the bonding reaction of the reactive compound in the second step can be selected, so that the reactive compound can be widely selected.

In the method for producing exfoliated graphite of the present invention, exfoliated graphite can be obtained by using, for example, a compound which functions as a charge acceptor, a solvent, a reactive organic compound or the like in place of a dangerous compound such as an alkali metal. Therefore, it is possible to mass-produce the exfoliated graphite more safely.

Further, the reactive compound in the second step may be added to the expanded graphite solvent dispersion after the first step, and the exfoliated graphite can be produced substantially by a single apparatus or a continuous apparatus. In this case, high productivity and low cost can be further achieved.

Further, in the production method of the present invention, high-temperature heating, vacuum treatment, or the like is not necessarily required. Therefore, in this case, scale enlargement becomes easy, and mass productivity of exfoliated graphite can be improved more effectively.

In the present invention, either of the first step and the second step may be carried out in the presence of the supercritical fluid, or both the first step and the second step may be carried out in the presence of a supercritical fluid. However, it is preferred that both the first step and the second step be carried out in the presence of a supercritical fluid.

In this case, the steps of filtration, washing, drying, and the like may be omitted. Further, in this case, the catalyst or the reactive compound is supplied to the reaction container only by the amount necessary for the chemical equilibrium via the supercritical carbon dioxide, so that the loss of each raw material can be further reduced. Further, after the exfoliated graphite is recovered, the raw material graphite is introduced into the reaction container, whereby the expansion and flaking treatment can be repeated.

Further, as described above, in the present invention, the first step can be carried out using a catalyst in a gaseous state, or the second step can be carried out using a reactive compound in a gaseous state. Preferably, the first step is carried out using a catalyst in a gaseous state, and the second step is carried out using a reactive compound in a gaseous state.

In this case, the filtration and washing steps can be omitted. Further, in this case, the catalyst or the reactive compound is supplied to the reaction container only by the necessity of volatilization, so that the loss of each raw material can be further reduced. Further, after recovering the exfoliated graphite, The raw material graphite is charged into the reaction vessel, whereby the expansion and flaking treatment can be repeated.

(thinned graphite)

The exfoliated graphite of the present invention is produced in accordance with the above-described method for producing exfoliated graphite. Therefore, exfoliated graphite which is sufficiently enlarged between graphene layers or exfoliated graphite which is a single layer of graphene sheets can be obtained.

Further, in the present invention, the exfoliated graphite is a laminate of graphene sheets or a single layer of graphene sheets. As described above, the exfoliated graphite is obtained by subjecting graphite to a peeling treatment. That is, the exfoliated graphite is thinner than the original graphite, and is a laminate of graphene sheets or a single layer of graphene sheets.

The number of layers of the graphene sheets in the exfoliated graphite is 1 or more. The number of layers of the graphene sheets is preferably 1,000 or less, and more preferably 150 or less, from the viewpoint of more effectively increasing the mechanical strength such as the tensile modulus of the resin.

The exfoliated graphite has a structure in which a thinner graphene sheet is laminated. Therefore, the aspect ratio of exfoliated graphite is relatively large. Further, the aspect ratio of the exfoliated graphite in the present invention means the ratio of the maximum dimension in the direction of the layered direction of the exfoliated graphite to the thickness of the exfoliated graphite.

When the aspect ratio of the exfoliated graphite is too low, there is a case where the reinforcing effect applied to the external force in the direction intersecting the above-mentioned accumulation layer is insufficient. If the aspect ratio of the exfoliated graphite is too high, the effect is saturated, and the above-described reinforcing effect cannot be expected. Therefore, the preferred lower limit of the aspect ratio of the exfoliated graphite is about 50, and the upper limit is preferably about 5,000.

Specifically, according to the production method of the invention, exfoliated graphite having a BET specific surface area after drying of 30 m ² /g or more can be provided. In such exfoliated graphite, since the BET specific surface area is large, the mechanical strength and the like of the resin can be sufficiently improved even by adding a small amount of the resin.

Further, exfoliated graphite having a specific surface area larger than 2000 m ² /g is actually difficult to manufacture. Therefore, the BET specific surface area after drying of the exfoliated graphite of the present invention is preferably 30 m ² /g or more, more preferably 300 m ² /g or more. Further, the BET specific surface area after drying is preferably a theoretical surface area of graphene of 2,800 m ² /g or less.

The exfoliated graphite in the present invention is a composite of a reactive compound and exfoliated graphite. Therefore, the compatibility with the resin is better than that of the exfoliated graphite in which the reactive compound is not bonded. As the above reactive compound, a Fridell-Crafts reactive compound such as a chlorinated alkyl group is preferably used. In the case of using a Fridel-Crafts reactive compound, the compatibility with the obtained exfoliated graphite resin can be further improved.

With respect to the above reactive compound, it is preferably 0.5 to 1000 parts by weight, more preferably 1.0 to 500 parts by weight, chemically bonded to 100 parts by weight of the exfoliated graphite, and more preferably 3.0 to 100 parts by weight for chemical bonding. Knot.

When the amount of the reactive compound is too large, the reactive compound forms a layer between the exfoliated graphite and the composite resin, and phase separation occurs. If the amount is too small, the effect of dissolving the exfoliated graphite and the composite resin becomes low. The situation.

Regarding the exfoliated graphite of the present invention, it is preferred that the peak derived from the graphite layer between 26.4 degrees in the XRD spectrum is small or substantially absent. That is, in the exfoliated graphite of the present invention, the peak intensity of 26.4 degrees from the graphite layer in the XRD spectrum is preferably 30% or less, more preferably 15% or less, more preferably 15% or less, more preferably 15% or less. 5% or less. Preferably, a peak of substantially 26.4 degrees does not exist. In this case, the graphene becomes sufficiently enlarged to have a larger specific surface area.

The exfoliated graphite obtained by the production method of the present invention is substantially not oxidized. Therefore, in the present invention, exfoliated graphite excellent in conductivity or thermal conductivity can be obtained. Further, by combining the exfoliated graphite with the resin, it is also easy to provide a composite material having a high modulus of elasticity and being strong.

Further, in the present invention, the above-mentioned compound which functions as a charge acceptor may remain on the surface of the graphite. In this case, it is also possible to improve the solvent dispersibility by selecting the compound which functions as a charge acceptor.

The exfoliated graphite obtained in the present invention as described above is excellent in dispersibility with a polar solvent such as water. Moreover, surface treatment by a reactive compound is also easy. Therefore, it becomes preferable to use as a filler added to a resin. Thereby, the improvement of the mechanical strength or the elastic modulus of the resin can be easily achieved.

(Slice flake graphite-resin composite)

A thinned graphite-resin composite material can be obtained by combining the above exfoliated graphite with a resin. The obtained composite material can be used for electrochemical materials such as conduction, heat conduction, dielectric, electromagnetic wave absorption or sensor materials, or mechanical strength materials such as rigidity, heat resistance and dimensional stability.

As the resin, various known synthetic resins can be used. As the synthetic resin, for example, a thermoplastic resin can be used. Regarding the resin composite material using a thermoplastic resin, various molding methods can be easily obtained by using various molding methods under heating.

Examples of the thermoplastic resin include polyethylenes such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, and polypropylenes such as homopolypropylene, block polypropylene, and atactic polypropylene. Polyolefin, drop a cyclic polyolefin such as a olefin resin; a vinyl acetate copolymer such as polyvinyl acetate or ethylene-vinyl acetate; or a polyvinyl acetate derivative such as polyvinyl alcohol or polyvinyl butyral; and PET (polyethylene terephthalate). Polyethylene terephthalate), polyesters such as polycarbonate and polylactic acid, polyether resins such as polyethylene oxide, polyphenylene ether and polyetheretherketone, PMMA (polymethyl methacrylate) Acrylic resin such as methyl ester), fluorene resin such as polyfluorene or polyether oxime, fluorinated resin such as PTFE (polytetrafluoroethylene) or PVDF (polyvinylidene fluoride), nylon Polyurethane resin, halogenated resin such as polyvinyl chloride or vinylidene chloride, polystyrene, polyacrylonitrile or the like. It is especially preferred that it is a low-priced polyolefin which is easy to form under heating.

Further, a thermosetting resin can also be used as the above synthetic resin. About using hot hard The resin composite material of the resin is obtained by a three-dimensional bond structure of the resin after the heat curing, so that a molded article excellent in heat resistance and chemical resistance can be obtained.

Examples of the thermosetting resin include a phenol resin, an epoxy resin, a melamine resin, a urea resin, a urethane resin, an acrylic resin, a furan resin, an ester resin, and an oxime. Resin, etc. The above synthetic resin may be used alone or in combination of two or more.

In the present invention, the exfoliated graphite is preferably contained in an amount of from 0.3 to 100 parts by mass, more preferably from 0.5 to 30 parts by mass, per 100 parts by mass of the resin composite material. The reason for this is that if the amount of exfoliated graphite is too small, a sufficient effect of addition may not be obtained, and if it is too large, the effect of addition may be saturated, and the physical properties may be adversely affected.

Further, as described above, the exfoliated graphite of the present invention is a composite of chemically bonded exfoliated graphite and a reactive compound. Therefore, since the interaction with the resin can be designed, the obtained composite material is particularly excellent as an electrochemical and mechanical material.

(Examples and Comparative Examples)

Hereinafter, the present invention will be clarified by enumerating specific examples and comparative examples of the invention. Furthermore, the invention is not limited to the following examples.

(Example 1)

40 g of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), 0.4 g of a compound which functions as a charge acceptor (manufactured by Wako Pure Chemical Industries, Ltd.), and 0.4 g of graphite raw material (manufactured by Toyo Carbon Co., Ltd.) 0.5 g of the product name "PF powder 8" was stirred at room temperature for 7 days with a stirrer to obtain expanded graphite. Next, 0.5 g of maleic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.), which is a Diels-Alder reactive monomer, was dissolved in 30 g of toluene, and added dropwise to expanded graphite. Then, the contents were filtered and washed, and exfoliated graphite was obtained by vacuum drying.

(Example 2)

Exfoliated graphite was obtained in the same manner as in Example 1 except that 1-chlorododecane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the Friedel-Crafts reactive monomer instead of the Diels-Alder reactive monomer.

(Example 3)

Exfoliated graphite was obtained in the same manner as in Example 1 except that vinyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the Diels-Alder reactive monomer.

(Example 4)

Fig. 2 is a schematic view showing a reaction apparatus used in Example 4. In the reactor 1, 1.0 g of a graphite raw material (manufactured by Toyo Carbon Co., Ltd., trade name "PF powder 8") was charged, and iron chloride (III) which is a compound which functions as a charge acceptor was introduced into the first raw material container 2 1.7 g (manufactured by Wako Pure Chemical Industries, Ltd.), 1.5 g of maleic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) was placed in the second raw material container 3 as a Diels-Alder reactive monomer.

Then, the first switching valve 4 is opened, and the first raw material container 2 and the first carbon dioxide storage cylinder 5 are connected, and then the second switching valve 6 is opened, and the temperature and pressure of the first reaction zone 10 are set to 60 ° C and 11 MPa.

Next, the first on-off valve 4 was closed and left for 10 days, whereby iron (III) chloride was brought into contact with the graphite raw material via supercritical carbon dioxide to obtain expanded graphite. Then, the second on-off valve 6 is closed, the third on-off valve 7 is opened, the second raw material container 3 and the second carbon dioxide cylinder 8 are connected, and the fourth on-off valve 9 is opened to set the temperature and pressure of the second reaction zone 11 It is set to 60 ° C and 11 MPa. Next, the third on-off valve 7 was closed and left for 2 days, whereby maleic anhydride was brought into contact with the expanded graphite via supercritical carbon dioxide to obtain exfoliated graphite. Further, the obtained exfoliated graphite was opened by closing the fourth on-off valve 9 and opening the reactor 1.

(Example 5)

Fig. 3 is a schematic view showing a reaction apparatus used in Example 5. 0.5 g of a graphite raw material (manufactured by Toyo Carbon Co., Ltd., trade name "PF powder 8") was introduced into the reactor 1, and iron (III) chloride as a charge acceptor type compound was introduced into the first raw material container 2 (Wako Pure Chemical Co., Ltd.) Company system Into the second raw material container 3, 3.5 g of vinyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.) as a Diels-Alder reactive monomer was placed in the second raw material container 3.

Next, the first and second switching valves 4 and 6 are opened, and the reactor 1 and the first raw material container 2 are vacuumed by the vacuum pump 12. Then, the first on-off valve 4 was closed, and the reactor 1 and the first raw material container 2 were heated at 360 ° C for 12 hours to bring the iron (III) chloride into contact with the graphite raw material to obtain expanded graphite.

After the reactor 1 and the first raw material container 2 were left to cool at room temperature, the second on-off valve 6 was closed, and the fourth on-off valve 9 was opened, and the reactor 1 was set to 80 ° C, and the second raw material container 3 was set to 65 ° C. After heating for 6 hours, vinyl acetate was volatilized and brought into contact with the expanded graphite, whereby exfoliated graphite was obtained. In the obtained exfoliated graphite, by closing the fourth on-off valve 9, the first and second on-off valves 4 and 6 are opened again to be vacuumed, and excess vinyl acetate is dried and recovered.

(Comparative Example 1)

A sample was obtained in the same manner as in Example 1 except that the Diels-Alder reactive monomer was added.

(Evaluation)

Thermal analysis:

The grafting rate was measured by the weight reduction caused by heating using a thermal analysis device (TG/DTA6300) manufactured by Sii Corporation. With respect to the evaluation conditions, the temperature was raised from room temperature at 5 ° C /min to 550 ° C, and the graft ratio was calculated by the following formula. The results are shown in Table 1 below.

Grafting rate (% by weight) = (weight at 150 ° C - weight at 500 ° C) / weight at 150 ° C) × 100

XRD measurement;

X-ray diffraction measurement was performed using an X-ray diffraction device SmartLab manufactured by RIGAKU. The tube voltage was set to 40 kV, the tube current was set to 200 mA, and diffraction was obtained by the 2θ-θ method. Regarding the scanning speed, it is scanned at a speed of 4 degrees per minute. The sample was placed in such a manner that the depressed portion of the sample stage for the powder was flat, and the reinforcement was pressed to perform XRD measurement. Further, according to the production method of the present invention, in the X-ray diffraction measurement, the peak located at 26.4 degrees of the layer crystal from the graphite as the raw material becomes smaller as the peeling, that is, the progress of the flaking. This principle is used as a standard for the degree of peeling of graphite. The results are shown in Fig. 1. 1 is a raw material graphite, B is a comparative example 1, C is a first embodiment, D is a second embodiment, E is a third embodiment, F is a fourth embodiment, and G is a fifth embodiment. XRD spectroscopy.

According to the XRD spectrum of Fig. 1, it was confirmed that in the samples of Examples 1 to 5, the graphite was further peeled off compared with Comparative Example 1, and the flaking was sufficiently advanced.

Claims (19)

A method for producing exfoliated graphite, comprising: a step of inserting a catalyst into a graphite layer; and a step of performing a stripping treatment on the graphite by chemically bonding the reactive compound to the graphite by using the catalyst to obtain exfoliated graphite. The method for producing exfoliated graphite according to claim 1, wherein the reactive compound is a Diels-Alder reactive compound. The method for producing exfoliated graphite according to claim 1, wherein the reactive compound is a Fridel-Crafts reactive compound. The method for producing exfoliated graphite according to any one of claims 1 to 3, wherein the catalyst is a compound which acts as a charge acceptor for an aromatic compound. The method for producing exfoliated graphite according to claim 4, wherein the catalyst is a metal halogen compound. The method for producing exfoliated graphite according to any one of claims 1 to 5, wherein the step of inserting the catalyst between the graphite layers is carried out in a solvent. The method for producing exfoliated graphite according to any one of claims 1 to 5, wherein the step of inserting the catalyst between the graphite layers is carried out in the presence of a supercritical fluid. The method for producing exfoliated graphite according to any one of claims 1 to 5, wherein in the step of inserting the catalyst into the graphite layer, a gas-state catalyst is interposed between the graphite layers. The method for producing exfoliated graphite according to any one of claims 1 to 8, wherein the step of subjecting the graphite to a stripping treatment is carried out in the presence of a supercritical fluid. The method for producing exfoliated graphite according to any one of claims 1 to 8, wherein in the step of subjecting the graphite to a stripping treatment, the reactive compound and the graphite are chemically bonded by contacting the reactive compound in a gaseous state with graphite. Knot. The method for producing exfoliated graphite according to claim 6, wherein the catalyst is a compound which acts as a charge acceptor for an aromatic compound, and in the solvent, the catalyst forms a complex with the solvent. The method for producing exfoliated graphite according to claim 11, wherein the ligand of the complex is an electron-donating compound. The method for producing exfoliated graphite according to claim 11 or 12, wherein the ligand of the above complex is a compound having an aromatic ring. The method for producing exfoliated graphite according to any one of claims 11 to 13, wherein the ligand of the above complex is a compound having an isolated electron pair. The method for producing exfoliated graphite according to any one of claims 6 to 11, wherein the solvent has a solubility parameter of 10 or less. A exfoliated graphite obtained by the method for producing exfoliated graphite according to any one of claims 1 to 15. The exfoliated graphite of claim 16 is chemically bonded to a Diels-Alder reactive compound. The exfoliated graphite of claim 16 is chemically bonded to a Fridel-Crafts reactive compound. A exfoliated graphite-resin composite material comprising the exfoliated graphite according to any one of claims 16 to 18, and a resin.