JP2016029003A - Flaky graphite, electrode material and flaky graphite-resin composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flaky graphite having excellent dispersibility in resin and capable of effectively improving the mechanical strength of the resin.SOLUTION: The present invention provides a flaky graphite wherein, in Raman spectra obtained by Raman spectroscopy, with a peak intensity ratio between D band and G band defined as D/G ratio, a change rate of the D/G ratio, when heated at 200°C for one hour, expressed by the formula (1), is a negative value, where formula (1) represents {(D/G ratio after heating-D/G ratio before heating)/(D/G ratio before heating)}×100.SELECTED DRAWING: None

Description

  The present invention relates to exfoliated graphite that can effectively improve the physical properties of a resin, an electrode material containing the exfoliated graphite, and an exfoliated graphite-resin composite material.

  Conventionally, exfoliated graphite has attracted attention because it can effectively improve the mechanical properties and the like of a resin with a small addition amount. An example of a method for producing such exfoliated graphite is disclosed in Patent Document 1 below. In the method for producing exfoliated graphite described in Patent Document 1, graphite is immersed in a strongly acidic aqueous solution such as nitric acid and heated. Acidic ions such as nitrate ions are intercalated between graphene graphene. By heating the graphite intercalated with nitrate ions, it is possible to peel the graphite and obtain exfoliated graphite having a smaller number of graphene stacks.

  Non-Patent Document 1 below discloses a method for producing oxidized exfoliated graphite by the Hammers method.

Special table 2009-511415 gazette

J. et al. Chem. Soc. W. S. Hummers et. al. 1958, 80, 1339

  However, exfoliated graphite obtained by the production methods of Patent Document 1 and Non-Patent Document 1 is oxidized. Therefore, the exfoliated graphite of Patent Document 1 and Non-Patent Document 1 is not sufficiently dispersible in the resin, and the mechanical strength of the obtained composite material may not be sufficiently increased.

  An object of the present invention is to provide exfoliated graphite that is excellent in dispersibility in a resin and can effectively increase the mechanical strength of the resin. Another object of the present invention is to provide an electrode material containing the exfoliated graphite and a exfoliated graphite-resin composite material.

  The exfoliated graphite according to the first invention of the present application is a Raman spectrum obtained by Raman spectroscopy. When the peak intensity ratio between the D band and the G band is D / G ratio, the exfoliated graphite is 200 ° C. for 1 hour. The rate of change of the D / G ratio represented by the following formula (1) when heated under conditions is a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

  In the exfoliated graphite according to the first invention of the present application, preferably, the rate of change of the D / G ratio is smaller than 0% and larger than −20%.

  In the exfoliated graphite according to the first invention of the present application, it is preferable that the shortest distance between both ends facing each other with a maximum distance is A, and the distance between the both ends is B. The degree of bending is 0.7 or more and 1.0 or less.

  In the exfoliated graphite according to the first invention of the present application, preferably, the thickness is 0.5 μm or less, and the maximum dimension in the laminated surface direction is 3.0 μm or more and 1000 μm or less.

  The exfoliated graphite according to the first invention of the present application preferably has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed in isopropyl alcohol at a concentration of 1% by weight.

  In the exfoliated graphite according to the first invention of the present application, the resistance value at a temperature of 25 ° C. when dispersed in a weight of 0.128 g in 10 g of isopropyl alcohol is preferably less than 1 MΩ.

  In the exfoliated graphite according to the first invention of the present application, the thickness is preferably 6 nm or more and 400 nm or less.

  In the exfoliated graphite according to the first invention of the present application, the aspect ratio is preferably in the range of 5 or more and 600 or less.

  The exfoliated graphite according to the second invention of the present application has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed in isopropyl alcohol at a concentration of 1% by weight.

  In the exfoliated graphite according to the second invention of the present application, preferably, in the Raman spectrum obtained by Raman spectroscopy, when the peak intensity ratio between the D band and the G band is defined as the D / G ratio, The rate of change of the D / G ratio represented by the following formula (1) when heated under the condition of 1 hour is a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

  In the exfoliated graphite according to the second invention of the present application, preferably, the rate of change of the D / G ratio is smaller than 0% and not lower than -20%.

  In the exfoliated graphite according to the second invention of the present application, preferably, when A is the shortest distance between both ends facing each other with a maximum distance, and B is the distance between both ends, A / B The degree of bending represented is 0.7 or more and 1.0 or less.

  In the exfoliated graphite according to the second invention of the present application, preferably, the thickness is 0.5 μm or less, and the maximum dimension in the laminated surface direction is 3.0 μm or more and 1000 μm or less.

  In the exfoliated graphite according to the third invention of the present application, the resistance value at a temperature of 25 ° C. when dispersed in 10 g of isopropyl alcohol at a weight of 0.128 g is smaller than 1 MΩ.

  In the exfoliated graphite according to the third invention of the present application, preferably, in the Raman spectrum obtained by Raman spectroscopy, when the peak intensity ratio between the D band and the G band is defined as the D / G ratio, The rate of change of the D / G ratio represented by the following formula (1) when heated under the condition of 1 hour is a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

  In the exfoliated graphite according to the third invention of the present application, the thickness is preferably 6 nm or more and 400 nm or less.

  In the exfoliated graphite according to the third invention of the present application, the aspect ratio is preferably in the range of 5 or more and 600 or less.

  Hereinafter, the first to third inventions may be collectively referred to as the present invention.

  The electrode material according to the present invention includes exfoliated graphite configured according to the present invention and a binder resin. Preferably, the binder resin is a fluororesin. Preferably, the fluororesin is polyvinylidene fluoride.

  The exfoliated graphite-resin composite material according to the present invention includes exfoliated graphite configured in accordance with the present invention and a resin. Preferably, the resin is a thermoplastic resin. Preferably, the thermoplastic resin is a polyolefin. Preferably, the polyolefin is polypropylene.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide exfoliated graphite which is excellent in the dispersibility in resin and can improve the mechanical strength of resin effectively.

  Details of the present invention will be described below.

(First invention)
The exfoliated graphite according to the first aspect of the present invention is a Raman spectrum obtained by Raman spectroscopy, wherein the peak intensity ratio between the D band and the G band is D / G ratio, at 200 ° C. for 1 hour. The rate of change of the D / G ratio represented by the following formula (1) when heated is a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

Exfoliated graphite;
In the present specification, exfoliated graphite is obtained by exfoliating a carbon material having a graphene laminated structure, and means a laminate of graphene sheets thinner than the original carbon material.

  As the carbon material having a graphene stacked structure, a carbon material having a structure in which a plurality of graphene such as graphite is stacked can be used. Further, as the graphite raw material, thermally expandable graphite obtained by subjecting graphite to acid treatment or expanded graphite obtained by heating and expanding the thermally expandable graphite may be used. Note that primary exfoliated graphite having a smaller number of graphene layers than natural graphite may be used as the carbon material.

  The number of graphene sheets laminated in exfoliated graphite should be less than the original carbon material, but is usually several layers to several thousand layers. From the viewpoint of effectively increasing the mechanical strength such as the tensile modulus of the resin, the number of laminated layers is preferably 500 layers or less, and more preferably 300 layers or less.

  As described above, exfoliated graphite has a structure in which thin graphene sheets are laminated. In particular, in the first invention, the exfoliated graphite preferably has a thickness of 0.5 μm or less. If the exfoliated graphite is too thick, the mechanical strength of the resin may not be sufficiently increased. From the viewpoint of further increasing the mechanical strength of the resin, the thickness of exfoliated graphite is more preferably 6 nm or more and 400 nm or less.

  The maximum dimension of the exfoliated graphite in the direction of the laminated surface is preferably 3.0 μm or more and 1000 μm or less. If the maximum dimension in the direction of the laminated surface is too small, the mechanical strength of the resin may not be sufficiently increased. On the other hand, if the maximum dimension in the direction of the laminated surface is too large, the effect is saturated and a further reinforcing effect may not be expected.

  The ratio of the maximum dimension in the laminate surface direction of exfoliated graphite to the thickness of exfoliated graphite is represented by the aspect ratio. If the aspect ratio of exfoliated graphite is too low, the reinforcing effect against external force applied in the direction intersecting the laminated surface may not be sufficient. If the aspect ratio of exfoliated graphite is too high, the effect may be saturated and a further reinforcing effect may not be expected. Therefore, the preferable lower limit of the aspect ratio of exfoliated graphite is about 5, and the preferable upper limit is about 600. More preferably, the aspect ratio is in the range of 5 or more and 100 or less.

  Exfoliated graphite is rigid and difficult to bend. In particular, in the first invention, when the shortest distance between both ends facing each other with a maximum distance is A, and the distance between the both ends is B, the bending degree represented by A / B is: It is preferable that it is 0.7 or more and 1.0 or less. When the bending degree of exfoliated graphite is within the above range, the mechanical strength of the resin can be further effectively increased by adding a small amount of exfoliated graphite.

  The exfoliated graphite preferably has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed in isopropyl alcohol at a concentration of 1% by weight. In this case, the dispersibility of exfoliated graphite in the resin can be further improved, and the mechanical properties of the resin can be further effectively improved.

  The viscosity can be measured by the following method. First, isopropyl alcohol and exfoliated graphite are measured in a screw tube so that the concentration of exfoliated graphite becomes 1% by weight. Then, an ultrasonic wave is irradiated for 1 minute at 28 kHz, and exfoliated graphite is fully disperse | distributed. The viscosity of the dispersion is measured using a rotary viscometer (manufactured by Toki Sangyo Co., Ltd.). The measurement is started, and the value at the time when the viscosity does not change in a steady state is evaluated as the viscosity of the dispersion.

  The exfoliated graphite preferably has a resistance value of less than 1 MΩ at a temperature of 25 ° C. when dispersed in 10 g of isopropyl alcohol at a weight of 0.128 g. In this case, the dispersibility of exfoliated graphite in the resin can be further increased, and the conductivity can be increased. The resistance value can be measured by the following method.

  First, 10 g of isopropyl alcohol and 0.128 g of exfoliated graphite are placed in a 20 ml container, and a dispersion is obtained by applying ultrasonic waves at 28 kHz for 1 minute. The temperature of the obtained dispersion is 25 ° C., and a tester is inserted while stirring with a stirrer. The data 2 minutes after the insertion was read as the resistance value at a temperature of 25 ° C. Note that the positive terminal and the negative terminal of the tester are inserted into the dispersion at a distance of 2 cm between the terminals and at a depth of 1 cm from the liquid surface.

  The exfoliated graphite according to the first invention is grafted with a compound having a short molecular chain. Therefore, in the present specification, exfoliated graphite to which the above compound is grafted is also generically called exfoliated graphite. A compound having a short molecular chain refers to a compound having a weight average molecular weight in the range of 50 to 1,000. From the viewpoint of further increasing the dispersibility in the resin, the weight average molecular weight of the compound grafted on the exfoliated graphite is preferably in the range of 90 to 500, and more preferably in the range of 90 to 200.

  The compound to be grafted on exfoliated graphite is not particularly limited, and examples thereof include Diels-Alder reactive compounds, Friedel-Crafts reactive compounds, radical reactive compounds, and cyclopentadienyl complex compounds. Among these, since a compound having a shorter molecular chain is grafted, a Diels-Alder reactive compound or a Friedel-Crafts reactive compound is preferable.

  As the Diels-Alder reactive compound, any general diene and parent diene can be used. For example, maleic acids such as maleic anhydride, dimethyl maleate, maleimide; tetracyanoethylene, dimethyl fumarate Alkenes such as dimethyl acetylenedicarboxylate; Cyclic dienes such as benzoquinone, anthraquinone, quinodimethane, cyclopentadiene, cyclohexene, and parent dienes; acenes such as anthracene; Furans such as furfuryl alcohol and furfural Butadienes such as 2,3-dimethyl-1,3-butadiene; aligns such as benzyne; imines such as benzylideneaniline; styrene and derivatives thereof.

  As the Friedel-Crafts reactive compound, any of general halides, carboxylic acid halides, acid anhydrides and the like can be used. For example, alkyl halogen such as N-chlorooctane and N-octanoyl chloride, Aliphatic acid halides; benzoic acid halides such as benzoyl chloride, or acid anhydrides such as succinic anhydride, phthalic anhydride, and propionic anhydride can be used.

  Examples of the radical reactive compound include compounds having (meth) acryl group, vinyl group, vinyl ether group, glycidyl group, thiol group, halogen group and the like.

  Examples of the cyclopentadienyl complex compound include ferrocene, nickelocene, titanocene, zirconocene and derivatives thereof. That is, as long as another compound is grafted on exfoliated graphite, the form of grafting is not particularly limited, and the compound may be bonded to exfoliated graphite by a coordinate bond using a cyclopentadienyl complex compound. In the case of a bond using a cyclopentadienyl complex compound, the compound can be removed by washing after slicing or the like, which is preferable.

  Such a compound grafted on exfoliated graphite has an effect of preventing re-lamination and agglomeration of once peeled graphene, and is excellent in solvent and resin dispersibility. Therefore, the graft amount of the compound is preferably 0.5 to 100 parts by weight with respect to 100 parts by weight of the exfoliated graphite obtained.

  The grafted compound can be detected by a known analysis method such as NMR, IR, or thermogravimetry. The detection method is not limited to a specific analysis method, but thermogravimetry is usually used from the viewpoint of simplicity and quantification. In this thermogravimetry, when the compound is grafted on exfoliated graphite, the decomposition temperature is generally detected on the higher temperature side than the normal decomposition temperature. Moreover, you may combine MS measurement etc. for the purpose of the structural analysis of this thermal decomposition product.

D / G ratio;
In this specification, the D / G ratio means a peak intensity ratio between the D band and the G band (D band peak intensity / G band peak intensity) in a Raman spectrum obtained by Raman spectroscopy. .

The D band in the Raman spectrum is a peak derived from the defect structure. In exfoliated graphite, the D band is usually observed in the vicinity of 1349 to 1353 cm ^{−1 of} the Raman spectrum.

On the other hand, the G band in the Raman spectrum is a peak derived from in-plane stretching vibration of a six-membered ring structure of carbon atoms. In exfoliated graphite, the G band is usually observed in the vicinity of 1578 to 1592 cm ^{−1 of} the Raman spectrum.

  The D / G ratio, which is the peak intensity ratio between the D band and the G band, indicates the degree of crystallinity of exfoliated graphite. The higher the D / G ratio, the greater the disorder of the structure and the higher the crystallinity. It is judged to be low.

  The D / G ratio of the exfoliated graphite according to the first invention is preferably in the range of 0.1 to 0.3. More preferably, it exists in the range of 0.1-0.25, More preferably, it exists in the range of 0.1-0.2. When the D / G ratio of exfoliated graphite is within the above range, the mechanical strength of the resin can be improved more effectively.

  In the first invention, the change rate (%) of the D / G ratio represented by the following formula (1) when heat-treated at 200 ° C. for 1 hour is a negative value. Note that the heat treatment is performed in air.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

  Thus, in the first invention, the reason why the change rate of the D / G ratio is a negative value is explained as follows.

  Usually, since the carbon material which has a graphene laminated structure is oxidized by heating in air, D / G ratio is raised by heating. On the other hand, in the first invention, as described above, a compound having a short molecular chain is grafted on the exfoliated graphite surface, and this graft molecule is easily detached by heating. When the graft molecules are detached, the crystallinity of exfoliated graphite is increased, and the D / G is lowered. That is, the change rate of the D / G ratio of exfoliated graphite becomes a negative value.

  Thus, in the exfoliated graphite according to the first invention, since the D / G ratio change rate is a negative value, that is, a compound having a short molecular chain is grafted, the dispersibility in the resin is effectively enhanced. Therefore, the mechanical strength of the resin can be dramatically increased. Alternatively, the mechanical strength of the resin can be increased by adding a smaller amount of exfoliated graphite.

  In the first invention, the change rate of the D / G ratio is preferably smaller than 0% and larger than -20%. When the change rate of the D / G ratio is −20% or less, flaking graphite is likely to aggregate or stack. Therefore, the dispersibility of exfoliated graphite in the resin is lowered, and it may be difficult to increase the mechanical strength of the resin.

  The exfoliated graphite according to the first invention can be manufactured by, for example, a manufacturing method described in the column of the manufacturing method described later.

(Second invention)
The exfoliated graphite according to the second invention has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed in isopropyl alcohol at a concentration of 1% by weight. Therefore, exfoliated graphite according to the second invention is excellent in dispersibility in the resin, and can effectively increase the mechanical properties of the resin such as the elastic modulus.

Exfoliated graphite;
In the present specification, exfoliated graphite is obtained by exfoliating a carbon material having a graphene laminated structure, and means a laminate of graphene sheets thinner than the original carbon material.

  As the carbon material having a graphene stacked structure, a carbon material having a structure in which a plurality of graphene such as graphite is stacked can be used. Further, as the graphite raw material, thermally expandable graphite obtained by subjecting graphite to acid treatment or expanded graphite obtained by heating and expanding the thermally expandable graphite may be used. Note that primary exfoliated graphite having a smaller number of graphene layers than natural graphite may be used as the carbon material.

  The number of graphene sheets laminated in exfoliated graphite should be less than the original carbon material, but is usually several layers to several thousand layers. From the viewpoint of effectively increasing the mechanical strength such as the tensile modulus of the resin, the number of laminated layers is preferably 500 layers or less, and more preferably 300 layers or less.

  As described above, exfoliated graphite has a structure in which thin graphene sheets are laminated. In particular, in the second invention, the exfoliated graphite preferably has a thickness of 0.5 μm or less. If the exfoliated graphite is too thick, the mechanical strength of the resin may not be sufficiently increased. From the viewpoint of further increasing the mechanical strength of the resin, the thickness of exfoliated graphite is more preferably 6 nm or more and 400 nm or less.

  The maximum dimension of the exfoliated graphite in the direction of the laminated surface is preferably 3.0 μm or more and 1000 μm or less. If the maximum dimension in the direction of the laminated surface is too small, the mechanical strength of the resin may not be sufficiently increased. On the other hand, if the maximum dimension in the direction of the laminated surface is too large, the effect is saturated and a further reinforcing effect may not be expected.

  The ratio of the maximum dimension in the laminate surface direction of exfoliated graphite to the thickness of exfoliated graphite is represented by the aspect ratio. If the aspect ratio of exfoliated graphite is too low, the reinforcing effect against external force applied in the direction intersecting the laminated surface may not be sufficient. If the aspect ratio of exfoliated graphite is too high, the effect may be saturated and a further reinforcing effect may not be expected. Therefore, the preferable lower limit of the aspect ratio of exfoliated graphite is about 5, and the preferable upper limit is about 600. More preferably, the aspect ratio is in the range of 5 or more and 100 or less.

  Exfoliated graphite is rigid and difficult to bend. In particular, in the second invention, when the shortest distance between both ends facing each other at the maximum distance is A and the distance between the both ends is B, the degree of bending represented by A / B is: It is preferable that it is 0.7 or more and 1.0 or less. When the degree of bending of exfoliated graphite is within the above range, the mechanical strength of the resin can be effectively increased by adding a smaller amount of exfoliated graphite.

  The exfoliated graphite preferably has a resistance value of less than 1 MΩ at a temperature of 25 ° C. when dispersed in 10 g of isopropyl alcohol at a weight of 0.128 g. In this case, the dispersibility of exfoliated graphite in the resin can be further increased, and the conductivity can be increased. The resistance value can be measured by the following method.

  First, 10 g of isopropyl alcohol and 0.128 g of exfoliated graphite are placed in a 20 ml container, and a dispersion is obtained by applying ultrasonic waves at 28 kHz for 1 minute. The temperature of the obtained dispersion is 25 ° C., and a tester is inserted while stirring with a stirrer. The data 2 minutes after the insertion was read as the resistance value at a temperature of 25 ° C. Note that the positive terminal and the negative terminal of the tester are inserted into the dispersion at a distance of 2 cm between the terminals and at a depth of 1 cm from the liquid surface.

  The exfoliated graphite according to the second invention is grafted with a compound. Preferably, a compound having a short molecular chain is grafted. In the present specification, exfoliated graphite to which the above compound is grafted is also generically called exfoliated graphite. A compound having a short molecular chain refers to a compound having a weight average molecular weight in the range of 50 to 1,000. From the viewpoint of further increasing the dispersibility in the resin, the weight average molecular weight of the compound grafted on the exfoliated graphite is preferably in the range of 90 to 500, and more preferably in the range of 90 to 200.

  The compound to be grafted on exfoliated graphite is not particularly limited, and examples thereof include Diels-Alder reactive compounds, Friedel-Crafts reactive compounds, radical reactive compounds, and cyclopentadienyl complex compounds. Among these, since a compound having a shorter molecular chain is grafted, a Diels-Alder reactive compound or a Friedel-Crafts reactive compound is preferable.

  As the Diels-Alder reactive compound, any general diene and parent diene can be used. For example, maleic acids such as maleic anhydride, dimethyl maleate, maleimide; tetracyanoethylene, dimethyl fumarate Alkenes such as dimethyl acetylenedicarboxylate; Cyclic dienes such as benzoquinone, anthraquinone, quinodimethane, cyclopentadiene, cyclohexene, and parent dienes; acenes such as anthracene; Furans such as furfuryl alcohol and furfural Butadienes such as 2,3-dimethyl-1,3-butadiene; aligns such as benzyne; imines such as benzylideneaniline; styrene and derivatives thereof.

  As the Friedel-Crafts reactive compound, any of general halides, carboxylic acid halides, acid anhydrides and the like can be used. For example, alkyl halogen such as N-chlorooctane and N-octanoyl chloride, Aliphatic acid halides; benzoic acid halides such as benzoyl chloride, or acid anhydrides such as succinic anhydride, phthalic anhydride, and propionic anhydride can be used.

  Examples of the radical reactive compound include compounds having a (meth) acryl group, a vinyl group, a vinyl ether group, a glycidyl group, a thiol group, a halogen group, and the like.

  Examples of the cyclopentadienyl complex compound include ferrocene, nickelocene, titanocene, zirconocene and derivatives thereof. That is, as long as another compound is grafted on exfoliated graphite, the form of grafting is not particularly limited, and the compound may be bonded to exfoliated graphite by a coordinate bond using a cyclopentadienyl complex compound. In the case of a bond using a cyclopentadienyl complex compound, the compound can be removed by washing after slicing or the like, which is preferable.

  Such a compound grafted on exfoliated graphite has an effect of preventing re-lamination and agglomeration of once peeled graphene, and is excellent in solvent and resin dispersibility. Therefore, the graft amount of the compound is preferably 0.5 to 100% by weight with respect to 100% by weight of the exfoliated graphite obtained.

  The grafted compound can be detected by a known analysis method such as NMR, IR, or thermogravimetry. The detection method is not limited to a specific analysis method, but thermogravimetry is usually used from the viewpoint of simplicity and quantification. In this thermogravimetry, when the compound is grafted on exfoliated graphite, the decomposition temperature is generally detected on the higher temperature side than the normal decomposition temperature. Moreover, you may combine MS measurement etc. for the purpose of the structural analysis of this thermal decomposition product.

viscosity;
In the second invention, the viscosity can be measured by the following method. First, isopropyl alcohol and exfoliated graphite are measured in a screw tube so that the concentration of exfoliated graphite becomes 1% by weight. Then, an ultrasonic wave is irradiated for 1 minute at 28 kHz, and exfoliated graphite is fully disperse | distributed. The viscosity of the dispersion is measured using a rotary viscometer (manufactured by Toki Sangyo Co., Ltd.). The measurement is started, and the value at the time when the viscosity is no longer changed in the steady state is evaluated as the viscosity of the dispersion.

  In the exfoliated graphite according to the second invention, the viscosity measured by such a method is 4.0 mPa · s or more, and the viscosity is high. Therefore, exfoliated graphite according to the second invention can increase the elastic modulus of the resin. The reason for this will be explained as follows.

  When a compound is grafted on ordinary exfoliated graphite, the compound is grafted on the edge portion of graphene. On the other hand, in the exfoliated graphite of the second invention, the compound is partially grafted even between the graphene layers, and the layers are open. Therefore, in the organic solvent, the organic solvent penetrates between the graphene layers, the exfoliated graphite swells, and the free movement of the organic solvent molecules is restricted. As a result, the viscosity of the solvent in which exfoliated graphite is dispersed is improved.

  In the exfoliated graphite according to the second invention, since the compound is grafted also between the graphene layers as described above, the resin also penetrates between the graphene layers when added to the resin. Since the resin is constrained between the graphene layers, the elastic modulus of the obtained composite material can be more effectively increased.

  As described above, in the second invention, since the exfoliated graphite has a high viscosity, that is, the compound is grafted between the graphene layers and the layers are opened, so that the elastic modulus of the resin is effectively increased. Can do.

  Furthermore, in the second invention, the exfoliated graphite preferably has a viscosity of 4.5 mPa · s or more, and more preferably 5.0 mPa · s or more. When it exists in the said range, the elasticity modulus of resin can be raised further. Further, the viscosity of exfoliated graphite is preferably 100 mPa · s or less, more preferably 10 mPa · s or less, and further preferably 6 mPa · s or less.

D / G ratio;
In the exfoliated graphite according to the second invention, in the Raman spectrum obtained by Raman spectroscopy, the peak intensity ratio between the D band and the G band is the D / G ratio (D band peak intensity / G band peak intensity). The rate of change in the D / G ratio represented by the following formula (1) when heated at 200 ° C. for 1 hour is preferably a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

The D band in the Raman spectrum is a peak derived from the defect structure. In exfoliated graphite, the D band is usually observed in the vicinity of 1349 to 1353 cm ^{−1 of} the Raman spectrum.

On the other hand, the G band in the Raman spectrum is a peak derived from in-plane stretching vibration of a six-membered ring structure of carbon atoms. In exfoliated graphite, the G band is usually observed in the vicinity of 1578 to 1592 cm ^{−1 of} the Raman spectrum.

  The D / G ratio, which is the peak intensity ratio between the D band and the G band, indicates the proportion of the irregular structure of exfoliated graphite, and it is determined that the higher the D / G ratio, the greater the disorder of the structure. Is done.

  The D / G ratio of exfoliated graphite according to the second invention is preferably in the range of 0.1 to 0.3. More preferably, it exists in the range of 0.1-0.25, More preferably, it exists in the range of 0.1-0.2. When the D / G ratio of exfoliated graphite is within the above range, the elastic modulus of the resin can be improved more effectively.

  In 2nd invention, it is preferable that the change rate (%) of D / G ratio represented by the said Formula (1) at the time of heat-processing on 200 degreeC and 1 hour conditions is a negative value. In this case, the dispersibility in the resin is further increased, and the elastic modulus of the resin is further effectively increased. Alternatively, the mechanical strength of the resin can be increased by adding a smaller amount of exfoliated graphite.

In the second invention, the change rate of the D / G ratio is preferably less than 0% and not less than -20%. When the rate of change in the D / G ratio is less than −20%, the sp ² defect structure of exfoliated graphite may increase, and the physical properties of exfoliated graphite may deteriorate. Therefore, it becomes difficult to improve physical properties when a composite material is used.

  The exfoliated graphite according to the second invention can be manufactured by, for example, a manufacturing method described in the column of manufacturing method described later.

(Third invention)
The exfoliated graphite according to the third invention has a resistance value less than 1 MΩ at a temperature of 25 ° C. when dispersed in 10 g of isopropyl alcohol at a weight of 0.128 g. Therefore, exfoliated graphite according to the third invention has high dispersibility in the resin and is excellent in conductivity. Moreover, since the exfoliated graphite has high dispersibility in the resin, the mechanical strength of the resin can be effectively increased.

Exfoliated graphite;
In the present specification, exfoliated graphite is obtained by exfoliating a carbon material having a graphene laminated structure, and means a laminate of graphene sheets thinner than the original carbon material.

  As the carbon material having a graphene stacked structure, a carbon material having a structure in which a plurality of graphene such as graphite is stacked can be used. Further, as the graphite raw material, thermally expandable graphite obtained by subjecting graphite to acid treatment or expanded graphite obtained by heating and expanding the thermally expandable graphite may be used. Note that primary exfoliated graphite having a smaller number of graphene layers than natural graphite may be used as the carbon material.

  The number of graphene sheets laminated in exfoliated graphite should be less than the original carbon material, but is usually several layers to several thousand layers. From the viewpoint of effectively increasing the mechanical strength such as the tensile elastic modulus of the resin, the number of laminated layers is preferably 600 layers or less, and more preferably 400 layers or less.

  As described above, exfoliated graphite has a structure in which thin graphene sheets are laminated. In particular, in the third invention, the thickness of exfoliated graphite is preferably 6 nm or more and 400 nm or less, more preferably 6 nm or more and 300 nm or less, and further preferably 6 nm or more and 200 nm or less. . If the exfoliated graphite is too thick, it may not be sufficiently dispersed in the resin.

  The maximum dimension of the exfoliated graphite in the laminated surface direction is preferably 3.0 μm or more and 1000 μm or less. If the maximum dimension in the direction of the laminated surface is too small, the mechanical strength of the resin may not be sufficiently increased. On the other hand, if the maximum dimension in the direction of the laminated surface is too large, the effect is saturated and a further reinforcing effect may not be expected.

  Further, the exfoliated graphite according to the third invention preferably has an aspect ratio in the range of 5 or more and 600 or less, more preferably in the range of 5 or more and 400 or less, and more preferably 5 or more and 200 or less. Is more preferably in the range of 5 or more and 100 or less. In the third invention, the aspect ratio refers to the ratio of the maximum dimension in the laminated surface direction of exfoliated graphite to the thickness of exfoliated graphite.

  If the aspect ratio of exfoliated graphite is too low, the reinforcing effect against external force applied in the direction intersecting the laminated surface may not be sufficient. If the aspect ratio of exfoliated graphite is too high, the effect may be saturated and a further reinforcing effect may not be expected.

  The exfoliated graphite preferably has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed in isopropyl alcohol at a concentration of 1% by weight. In this case, the dispersibility of exfoliated graphite in the resin can be further improved, and the mechanical properties of the resin can be further effectively improved.

  The viscosity can be measured by the following method. First, isopropyl alcohol and exfoliated graphite are measured in a screw tube so that the concentration of exfoliated graphite becomes 1% by weight. Then, an ultrasonic wave is irradiated for 1 minute at 28 kHz, and exfoliated graphite is fully disperse | distributed. The viscosity of the dispersion is measured using a rotary viscometer (manufactured by Toki Sangyo Co., Ltd.). The measurement is started, and the value at the time when the viscosity does not change in a steady state is evaluated as the viscosity of the dispersion.

  The exfoliated graphite according to the third invention is desirably grafted with a compound. Preferably, a compound having a short molecular chain is grafted. In the present specification, exfoliated graphite to which the above compound is grafted is also generically called exfoliated graphite. A compound having a short molecular chain refers to a compound having a molecular weight in the range of 30 to 1,000.

  When the compound is grafted on exfoliated graphite, exfoliated graphite is less likely to aggregate in the dispersion and restacking is difficult. In this case, the dispersibility of exfoliated graphite in the dispersion can be further improved, and the interparticle distance can be further reduced. Therefore, the resistance value of exfoliated graphite can be further reduced. Moreover, when the compound is grafted on exfoliated graphite, the dispersibility in the resin can be further enhanced.

  From the viewpoint of further enhancing the dispersibility in the dispersion or resin, the molecular weight of the compound grafted on the exfoliated graphite is preferably in the range of 40 to 600, more preferably in the range of 50 to 400. preferable.

  The compound to be grafted on exfoliated graphite is not particularly limited, and examples thereof include Diels-Alder reactive compounds, Friedel-Crafts reactive compounds, radical reactive compounds, and cyclopentadienyl complex compounds. Among these, since a compound having a shorter molecular chain is grafted, a Diels-Alder reactive compound or a Friedel-Crafts reactive compound is preferable.

  As the Diels-Alder reactive compound, any general diene and parent diene can be used. For example, maleic acids such as maleic anhydride, dimethyl maleate, maleimide; tetracyanoethylene, dimethyl fumarate Alkenes such as dimethyl acetylenedicarboxylate; Cyclic dienes such as benzoquinone, anthraquinone, quinodimethane, cyclopentadiene, cyclohexene, and parent dienes; acenes such as anthracene; Furans such as furfuryl alcohol and furfural Butadienes such as 2,3-dimethyl-1,3-butadiene; aligns such as benzyne; imines such as benzylideneaniline; styrene and derivatives thereof.

  As the Friedel-Crafts reactive compound, any of general halides, carboxylic acid halides, acid anhydrides and the like can be used. For example, alkyl halogen such as N-chlorooctane and N-octanoyl chloride, Aliphatic acid halides; benzoic acid halides such as benzoyl chloride, or acid anhydrides such as succinic anhydride, phthalic anhydride, and propionic anhydride can be used.

  Examples of the radical reactive compound include compounds having (meth) acryl group, vinyl group, vinyl ether group, glycidyl group, thiol group, halogen group and the like.

  Examples of the cyclopentadienyl complex compound include ferrocene, nickelocene, titanocene, zirconocene and derivatives thereof. That is, as long as another compound is grafted on exfoliated graphite, the form of grafting is not particularly limited, and the compound may be bonded to exfoliated graphite by a coordinate bond using a cyclopentadienyl complex compound. In the case of a bond using a cyclopentadienyl complex compound, the compound can be removed by washing after slicing or the like, which is preferable.

  Such a compound grafted on exfoliated graphite has an effect of preventing re-lamination and agglomeration of once peeled graphene, and is excellent in solvent and resin dispersibility. Therefore, the graft amount of the compound is preferably 0.5 to 100 parts by weight with respect to 100 parts by weight of the exfoliated graphite obtained.

  The grafted compound can be detected by a known analysis method such as NMR, IR, or thermogravimetry. The detection method is not limited to a specific analysis method, but thermogravimetry is usually used from the viewpoint of simplicity and quantification. In this thermogravimetry, when the compound is grafted on exfoliated graphite, the decomposition temperature is generally detected on the higher temperature side than the normal decomposition temperature. Moreover, you may combine MS measurement etc. for the purpose of the structural analysis of this thermal decomposition product.

Resistance value;
In the third invention, the resistance value can be measured by the following method.

  First, 10 g of isopropyl alcohol and 0.128 g of exfoliated graphite are placed in a 20 ml container, and a dispersion is obtained by applying ultrasonic waves at 28 kHz for 1 minute. The temperature of the obtained dispersion is 25 ° C., and a tester is inserted while stirring with a stirrer. The data 2 minutes after the insertion was read as the resistance value at a temperature of 25 ° C. Note that the positive terminal and the negative terminal of the tester are inserted into the dispersion at a distance of 2 cm between the terminals and at a depth of 1 cm from the liquid surface.

  In the third invention, the resistance value of the dispersion measured by the above method is smaller than 1 MΩ. Therefore, exfoliated graphite according to the third invention is excellent in conductivity and dispersibility in the resin is enhanced. The resistance value of exfoliated graphite can be lowered by, for example, producing by a production method that does not include an oxidation process, or by grafting a compound to exfoliated graphite.

  Furthermore, in the third invention, the resistance value of exfoliated graphite is preferably in the range of 1Ω to 1MΩ, more preferably in the range of 100Ω to 0.5MΩ, more preferably 100Ω to 0 More preferably, it is in the range of 3 MΩ or less. When it exists in the said range, electroconductivity and the dispersibility in resin can be improved further.

D / G ratio;
In the exfoliated graphite according to the third invention, in the Raman spectrum obtained by Raman spectroscopy, the peak intensity ratio between the D band and the G band is the D / G ratio (D band peak intensity / G band peak intensity). The rate of change (%) in the D / G ratio expressed by the following formula (1) when heated at 200 ° C. for 1 hour is preferably a negative value.

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

  In this specification, the D / G ratio means a peak intensity ratio between the D band and the G band in a Raman spectrum obtained by Raman spectroscopy.

The D band in the Raman spectrum is a peak derived from the defect structure. In exfoliated graphite, the D band is usually observed in the vicinity of 1349 to 1353 cm ^{−1 of} the Raman spectrum.

On the other hand, the G band in the Raman spectrum is a peak derived from in-plane stretching vibration of a six-membered ring structure of carbon atoms. In exfoliated graphite, the G band is usually observed in the vicinity of 1578 to 1592 cm ^{−1 of} the Raman spectrum.

  The D / G ratio, which is the peak intensity ratio between the D band and the G band, indicates the degree of crystallinity of exfoliated graphite. The higher the D / G ratio, the greater the disorder of the structure and the higher the crystallinity. It is judged to be low.

  The D / G ratio of exfoliated graphite according to the third invention is preferably in the range of 0.1 to 0.3. More preferably, it exists in the range of 0.1-0.25, More preferably, it exists in the range of 0.1-0.2. When the D / G ratio of exfoliated graphite is within the above range, the dispersibility in the resin can be more effectively increased.

  In 3rd invention, it is preferable that the change rate (%) of D / G ratio represented by the said Formula (1) at the time of heat-processing on 200 degreeC and 1 hour conditions is a negative value. In this case, dispersibility in the resin and conductivity can be further improved. In addition, since the dispersibility in the resin is improved, the elastic modulus of the resin can be further increased.

  In the third invention, the change rate of the D / G ratio is preferably -5% or less. Further, the change rate of the D / G ratio is preferably larger than −20%, and more preferably larger than −10%. When the change rate of the D / G ratio is within the above range, the graft chain can further prevent flaking graphite from agglomerating and restacking, and the dispersibility in the resin can be further enhanced. . Therefore, the tensile elastic modulus of the resin can be further increased.

  The exfoliated graphite according to the third invention can be manufactured by, for example, a manufacturing method described in the column of manufacturing method described later.

  Hereinafter, a method for producing exfoliated graphite, an electrode material, and an exfoliated graphite-resin composite material according to the first to third inventions (hereinafter, the first to third inventions are collectively referred to as the present invention) Further details will be described.

(Method for producing exfoliated graphite)
The method for producing exfoliated graphite according to the present invention is not particularly limited. For example, it can be produced by the following method.

  First, the carbon material having the graphene laminated structure described above is immersed in a liquid containing a liquid material having a surface tension at 20 ° C. of 50 mN / m or less. Thereafter, the carbon material is irradiated with electromagnetic waves and heated at a temperature lower than the boiling point of the liquid. Thereby, the carbon material is exfoliated without vaporizing the liquid in contact with the carbon material, and exfoliated graphite is obtained. The thinning of the carbon material can be more reliably performed by chemically bonding a compound to the carbon material.

  As the carbon material having a graphene stacked structure, a carbon material having a structure in which a plurality of graphene such as graphite is stacked can be used. Further, as the graphite raw material, thermally expandable graphite obtained by subjecting graphite to acid treatment or expanded graphite obtained by heating and expanding the thermally expandable graphite may be used. Note that primary exfoliated graphite having a smaller number of graphene layers than natural graphite may be used as the carbon material.

  In this specification, the liquid means a liquid material having a surface tension at 20 ° C. of 50 mN / m or less, or at least one liquid mixture containing a liquid material having a surface tension at 20 ° C. of 50 mN / m or less. Say. Regarding the mixture of the liquid materials, the mixture itself may have a surface tension of 50 mN / m or less, and if it contains at least one liquid material having a surface tension at 20 ° C. of 50 mN / m or less, the mixture itself The surface tension may not be 50 mN / m or less.

  For example, a compound that can be chemically bonded to the carbon material can be used as the liquid in which the carbon material is immersed. Moreover, you may use the mixture of the compound which can couple | bond with a solvent and a carbon material.

  The compound to be grafted (chemically bonded) to the carbon material is not particularly limited, and examples thereof include Diels-Alder reactive compounds, Friedel-Crafts reactive compounds, radical reactive compounds, and cyclopentadienyl complex compounds. It is done. Especially, since a compound with a shorter molecular chain is grafted, it is preferably a Diels-Alder reactive compound or a Friedel-Crafts reactive compound.

  As the Diels-Alder reactive compound, any general diene and parent diene can be used. For example, maleic acid such as maleic anhydride, dimethyl maleate, maleimide, tetracyanoethylene, dimethyl fumarate, etc. , Alkenes such as acrolein, alkynes such as dimethyl acetylenedicarboxylate, cyclic dienes such as benzoquinone, anthraquinone, quinodimethane, cyclopentadiene, cyclohexene, acenes such as the parent diene, anthracene, and furans such as furfuryl alcohol and furfural Butadienes such as 2,3-dimethyl-1,3-butadiene, alignments such as benzyne, imines such as benzylideneaniline, styrene and derivatives thereof.

  As the Friedel-Crafts reactive compound, any of general halides, carboxylic acid halides, acid anhydrides and the like can be used. For example, alkyl halogen such as N-chlorooctane and N-octanoyl chloride, Aliphatic acid halides, benzoic acid halides such as benzoyl chloride, or acid anhydrides such as succinic anhydride, phthalic anhydride, and propionic anhydride can be used.

  Examples of the radical reactive compound include compounds having (meth) acryl group, vinyl group, vinyl ether group, glycidyl group, thiol group, halogen group and the like.

  Examples of the cyclopentadienyl complex compound include ferrocene, nickelocene, titanocene, zirconocene and derivatives thereof. That is, the form of chemical bonding is not particularly limited as long as another compound is grafted on exfoliated graphite, and the compound may be bonded to exfoliated graphite by a coordinate bond using a cyclopentadienyl complex compound. In the case of a chemical bond using a cyclopentadienyl complex compound, the compound can be removed by washing after thinning, etc., which is preferable.

  The solvent is not particularly limited, but alcohols having 8 or less carbon atoms such as methanol, ethanol, isopropyl alcohol, toluene, xylene, chlorobenzene, dichlorobenzene, bromobenzene, dibromobenzene, benzylamine, methylbenzylamine, N- Examples include methyl pyrrolidone and N, N-dimethylformamide. Preferably, it is selected from the group consisting of alcohols having 8 or less carbon atoms, toluene, xylene, chlorobenzene, dichlorobenzene, bromobenzene, dibromobenzene, benzylamine, methylbenzylamine, N-methylpyrrolidone and N, N-dimethylformamide. Including at least one species. Only 1 type may be used for a solvent and 2 or more types of mixed solvents may be sufficient as it. Further, in addition to the above preferred solvent, another solvent such as water may be added.

  As described above, in this manufacturing method, the carbon material immersed in the liquid is irradiated with electromagnetic waves. The electromagnetic wave in this case is not particularly limited, and an electromagnetic wave having a wavelength of about 5 kHz to 100 GHz can be used. Therefore, the electromagnetic wave may be a microwave.

  About the apparatus which irradiates the said electromagnetic wave, a suitable electromagnetic wave generator can be used as long as an electromagnetic wave can be irradiated. Moreover, you may use a commercially available microwave oven for cooking as an electromagnetic wave irradiation apparatus. In that case, a carbon material immersed in the liquid may be placed in a cooking microwave and irradiated with electromagnetic waves.

  In order to irradiate electromagnetic waves such as microwaves more efficiently, for example, an apparatus including a flow reactor, an electromagnetic wave generator that generates electromagnetic waves, and a waveguide that transmits electromagnetic waves may be used. As the above flow type reactor, a horizontal reactor having a plurality of chambers continuous in series can be used.

  In the flow type reactor, the mixture of the carbon material and the liquid is transported with a space left above. Further, the electromagnetic wave is transmitted to the space by the waveguide. When such a flow type reactor is used, exfoliated graphite can be continuously produced.

  Further, the flow type reactor may be divided into a plurality of chambers by a partition plate, and may have a stirring means for stirring the contents in the reactor. The waveguide may be provided at the position of the partition plate. When such an irradiation device is used, the carbon material can be irradiated with electromagnetic waves more reliably.

  The amount of electromagnetic wave irradiation is not particularly limited as long as the exfoliated graphite can be obtained by heating the carbon material.

  The carbon material immersed in the liquid is heated by the electromagnetic wave irradiation. The carbon material is heated at a temperature lower than the boiling point of the liquid. Therefore, the compound is efficiently grafted onto the carbon material without vaporizing the liquid. Thereby, the π bond between the graphenes is weakened, and the compound is grafted not only to the end of the graphene stacked structure but also to the inside. As a result, the graphene is separated, and the carbon material is considered to be thinned.

  As a heating method other than electromagnetic wave irradiation, overall heating using a heater or the like is possible, but in this case, thinning of the carbon material does not proceed sufficiently. The reason is considered as follows.

  When the whole is heated by a heater or the like, side reactions are likely to occur, and the efficiency of the compound binding reaction to the carbon material is low. Therefore, it is considered that the compound graft occurs only at the end of the carbon material and does not proceed to the inside. On the other hand, heating by irradiation with electromagnetic waves directly heats the carbon material, so that the surface of the carbon material locally becomes high temperature, and the compound is likely to be bonded.

  The heating rate of heating by electromagnetic wave irradiation is not particularly limited. However, the higher the heating rate, the easier the local heating of the carbon material occurs, so that exfoliated graphite is easily obtained. Therefore, it is difficult to directly measure the rate of temperature rise of the carbon material heated by the irradiation of electromagnetic waves, but the rate of temperature rise as the temperature of the liquid in which the carbon material is immersed is preferably 15 ° C./min or more. More preferably, it is 100 ° C./min or more, and further preferably 500 ° C./min or more. However, if the rate of temperature rise is too high, the amount of electromagnetic wave irradiation becomes enormous, and therefore the rate of temperature rise as the temperature of the liquid in which the carbon material is immersed is preferably 1000 ° C./min or less.

  In this production method, heating by a heater or the like may be used in addition to heating by electromagnetic wave irradiation. For example, the amount of electromagnetic wave irradiation can be reduced by preheating to a temperature lower than the boiling point of the liquid using a heater or the like. As a result, the electromagnetic energy and the load on the apparatus can be reduced.

  In the present production method, exfoliated graphite is obtained by vaporizing the liquid in contact with the carbon material in the step of heating the carbon material by irradiation with electromagnetic waves as described above. Therefore, in detail, an exfoliated graphite dispersion in which exfoliated graphite is dispersed in a liquid is obtained. Exfoliated graphite can be recovered by removing the liquid from the exfoliated graphite dispersion.

  In recovering the exfoliated graphite from the exfoliated graphite dispersion, known methods such as filtration, centrifugation, gravity sedimentation, solvent separation, aggregating agent or adsorbent can be used. In that case, it is desirable to separate impurities such as unreacted compounds using a solvent or the like.

  As described above, in this production method, exfoliated graphite is produced without undergoing an oxidation process. Therefore, the exfoliated graphite obtained is excellent in conductivity.

(Exfoliated graphite-resin composite material)
The exfoliated graphite-resin composite material according to the first invention includes the exfoliated graphite according to the first invention described above and a resin. The exfoliated graphite-resin composite material can be obtained by mixing exfoliated graphite and a resin. The exfoliated graphite is excellent in dispersibility in the resin because the D / G ratio change rate is negative, that is, a compound having a short molecular chain is grafted. Therefore, the mechanical strength of the exfoliated graphite-resin composite material according to the first invention is dramatically increased.

  The exfoliated graphite-resin composite material according to the second invention includes the exfoliated graphite according to the second invention described above and a resin. The exfoliated graphite-resin composite material can be obtained by mixing exfoliated graphite and a resin.

  The exfoliated graphite has a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more. Therefore, the exfoliated graphite-resin composite material according to the second invention is excellent in mechanical strength such as elastic modulus.

  Further, when the exfoliated graphite has a negative D / G ratio change rate, that is, when a compound having a short molecular chain is grafted, the dispersibility into the resin is further enhanced. Therefore, in the exfoliated graphite-resin composite material in which such exfoliated graphite is dispersed in the resin, the elastic modulus is further increased.

  The exfoliated graphite-resin composite material according to the third invention includes the exfoliated graphite according to the third invention described above and a resin. The exfoliated graphite-resin composite material can be obtained by mixing exfoliated graphite and a resin.

  The resistance value of the exfoliated graphite at a temperature of 25 ° C. is smaller than 1 MΩ. Therefore, the resin composite material according to the third invention is excellent in conductivity. Further, since the exfoliated graphite is excellent in dispersibility in the resin, the resin composite material according to the third invention is also excellent in mechanical strength such as elastic modulus.

  Further, when the exfoliated graphite has a negative D / G ratio change rate, that is, when a compound having a short molecular chain is grafted, the dispersibility in the thermoplastic resin is further enhanced. Therefore, the elastic modulus is further increased in the resin composite material in which such exfoliated graphite is dispersed.

  Moreover, in this invention, the dispersibility of exfoliated graphite in resin can be improved further by using a compound with high affinity with desired resin as a compound grafted to a carbon material. Accordingly, the resin is not particularly limited, and various known resins can be used. Only one type of resin may be used, or two or more types may be used in combination.

  Especially, it is preferable that a thermoplastic resin is used as resin. In the exfoliated graphite-resin composite material using a thermoplastic resin, various molded products can be easily formed by using various molding methods under heating.

  Examples of the thermoplastic resin include polyethylene, polypropylene, polystyrene, polyacrylate, polyacrylonitrile, polyester, polyamide, polyurethane, polyethersulfone, polyetherketone, polyimide, polydimethylsiloxane, and copolymers thereof.

  Preferably, polyolefin can be used as the resin. Polyolefin is inexpensive and easy to mold under heating. Therefore, by using polyolefin as the thermoplastic resin, the cost of the exfoliated graphite-resin composite material can be reduced, and the exfoliated graphite-resin composite material can be more easily molded.

  The polyolefin is not particularly limited. For example, polyethylene, polypropylene, ethylene homopolymer, ethylene-α-olefin copolymer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid ester copolymer Polypropylene resins, such as polymers, ethylene-vinyl acetate copolymers, propylene homopolymers, propylene-α-olefin copolymers, propylene-ethylene random copolymers, propylene-ethylene block copolymers, Examples include butene homopolymers, homopolymers or copolymers of conjugated dienes such as butadiene and isoprene. Preferably, less expensive polypropylene is used. The polyolefin may be modified with maleic acid or the like.

  The blending ratio of exfoliated graphite and resin is not particularly limited, but preferably exfoliated graphite is in the range of 0.1 to 50 parts by mass with respect to 100 parts by mass of resin. By setting the blending ratio in such a range, mechanical strength such as tensile elastic modulus of the exfoliated graphite-resin composite material of the present invention can be effectively increased.

  When the blending ratio of exfoliated graphite is less than 0.1 parts by mass, the mechanical strength of the exfoliated graphite-resin composite material may not be sufficiently increased. When the mixing ratio of exfoliated graphite exceeds 50 parts by mass, the exfoliated graphite-resin composite material becomes brittle and may be easily broken.

  The exfoliated graphite-resin composite material of the present invention may contain various additives as long as the object of the present invention is not impaired. Such additives include phenol, phosphorus, amine or sulfur antioxidants; UV absorbers such as benzotriazole and hydroxyphenyl triazine; metal hazard inhibitors; hexabromobiphenyl ether or deca Halogenated flame retardants such as bromodiphenyl ether; flame retardants such as ammonium polyphosphate or trimethyl phosphate; various fillers; antistatic agents; stabilizers;

  The method for mixing exfoliated graphite and resin is not particularly limited. For example, a twin screw kneader such as a plast mill, a single screw extruder, a twin screw extruder, a Banbury mixer, a kneading apparatus such as a roll is used. And kneading under heating. Among these, the method of melt-kneading using a plast mill is mentioned.

  Furthermore, the exfoliated graphite-resin composite material obtained by the present invention can be formed into various shapes using an appropriate shaping method. As such a shaping method, a molding method such as press working, injection molding, or extrusion molding can be suitably used. Further, it may be shaped by a melt coating method. Using the shaping method as described above, a desired shape such as a sheet shape can be obtained.

(Electrode material)
The electrode material according to the present invention includes the exfoliated graphite described above and a binder resin. The electrode material is obtained by mixing exfoliated graphite and a binder resin. Since exfoliated graphite of the present invention is produced without undergoing an oxidation process, an electrode material in which exfoliated graphite is dispersed in a binder resin is excellent in conductivity. In particular, it is preferable that the exfoliated graphite has a resistance value smaller than 1 MΩ because the conductivity of the electrode material can be further increased.

  Therefore, the electrode material of the present invention can be suitably used for applications such as a positive electrode auxiliary material, a negative electrode material, and a capacitor electrode material for lithium ion secondary batteries.

  It does not specifically limit as binder resin, A water-based binder resin may be used and a non-aqueous binder resin may be used. As the aqueous binder resin, the styrene butadiene rubber (SBR) or carboxymethyl cellulose (CMC) can be used. As the non-aqueous binder resin, polyvinylidene fluoride (PVDF), polyimide resin, acrylic resin, butyral resin, or the like can be used.

  Preferably, a fluorine resin such as polyvinylidene fluoride (PVDF) is used as the binder resin. In that case, the wettability to the electrolytic solution can be further improved without inhibiting the conductivity of exfoliated graphite.

  Hereinafter, the present invention will be clarified by giving specific examples and comparative examples of the present invention. In addition, this invention is not limited to a following example.

[Examples 1 to 4 and Comparative Examples 1 to 4]
Example 1
As a carbon material in a 60 ml polytetrafluoroethylene container, 0.5 g of thermally expandable graphite (manufactured by Toyo Tanso Co., Ltd., product number: PF-8) and N-methylpyrrolidone (boiling point = 202 ° C., surface tension at 20 ° C. = (41 mN / m) 19.5 g was added to obtain a dispersion obtained by sufficiently infiltrating N-methylpyrrolidone into thermally expandable graphite. To this dispersion, 0.5 g of maleic anhydride was added and stirred sufficiently. Thereafter, with the opening of the polytetrafluoroethylene container being opened, heating to 190 ° C. at a temperature rising rate of 60 ° C./min using a microwave generator (manufactured by Actac, product number: Speed Wave 2) for 30 minutes After holding, it was naturally cooled to room temperature. This heating-cooling operation was repeated three times. The obtained dispersion was filtered, thoroughly washed with acetone, and dried to obtain exfoliated graphite.

  In addition, 10 parts by mass of the exfoliated graphite obtained, 90 parts by mass of a polypropylene resin (manufactured by Prime Polymer, trade name “J-721GR”), and a maleic acid-modified polypropylene resin (manufactured by Mitsui Chemicals, trade name “ Admer QE800 ") 10 parts by mass is supplied to an extruder, melted and kneaded, extruded from a T-die attached to the tip of the extruder, and formed into a sheet with a cooling roll, thereby a composite material sheet having a smooth surface thickness of 0.5 mm Got.

(Example 2)
As a carbon material in a 60 ml polytetrafluoroethylene container, 0.5 g of thermally expandable graphite (product number: PF-8, manufactured by Toyo Tanso Co., Ltd.) and furfuryl alcohol (boiling point = 170 ° C., surface tension at 20 ° C. = 38 mN) / M) 20 g was added, and a dispersion obtained by sufficiently infiltrating furfuryl alcohol into thermally expandable graphite was obtained. The dispersion is heated to 160 ° C. at a heating rate of 50 ° C./min using a microwave generator (actac product, product number: Speed Wave 2) with the opening of the polytetrafluoroethylene container opened. After holding for 30 minutes, it was naturally cooled to room temperature. This heating-cooling operation was repeated three times. The obtained dispersion was filtered, thoroughly washed with acetone, and dried to obtain exfoliated graphite.

  In addition, 10 parts by mass of the exfoliated graphite obtained, 90 parts by mass of a polypropylene resin (manufactured by Prime Polymer, trade name “J-721GR”), and a maleic acid-modified polypropylene resin (manufactured by Mitsui Chemicals, trade name “ Admer QE800 ") 10 parts by mass is supplied to an extruder, melted and kneaded, extruded from a T-die attached to the tip of the extruder, and formed into a sheet with a cooling roll, thereby a composite material sheet having a smooth surface thickness of 0.5 mm Got.

(Example 3)
Exfoliated graphite and composite material sheet in the same manner as in Example 2 except that commercially available natural graphite (product number: SRP-150, manufactured by Ito Graphite Industries Co., Ltd.) was used instead of thermally expandable graphite as the carbon material. Got.

Example 4
Exfoliated graphite and a composite material sheet were obtained in the same manner as in Example 1 except that natural graphite (Ito Graphite Industries, Ltd., product number: SG-BH8) was used as the carbon material instead of thermally expandable graphite. Obtained.

(Comparative Example 1)
In place of the exfoliated graphite obtained in Example 1, commercially available expandable graphite (manufactured by Toyo Tanso Co., Ltd., product number: PF-8) was used in the same manner as in Example 1 to prepare a composite material sheet. Obtained.

(Comparative Example 2)
Instead of the exfoliated graphite obtained in Example 1, a composite sheet was obtained in the same manner as in Example 1 except that commercially available natural graphite (product number: SRP-150, manufactured by Ito Graphite Industries Co., Ltd.) was used. Obtained.

(Comparative Example 3)
A composite sheet was obtained in the same manner as in Example 1 except that commercially available exfoliated graphite (manufactured by Asbury, product number: graphene Nano27) was used instead of exfoliated graphite obtained in Example 1.

(Comparative Example 4)
Instead of the exfoliated graphite obtained in Example 1, an oxidation with an oxygen content of 32% by weight prepared by the Hammers method (J. Chem. Soc. W. S. Hummers et. Al. 1958, 80, 1339) A composite material sheet was obtained in the same manner as in Example 1 except that graphite was used.

(Evaluation)
The rate of change in the D / G ratio of exfoliated graphite, expandable graphite, natural graphite and oxidized graphite of Examples 1 to 4 and Comparative Examples 1 to 4, the tensile modulus of elasticity and the bending degree of the composite material sheet are as follows. It was measured.

(1) Rate of change of D / G ratio First, using a microscopic laser Raman measuring apparatus (manufactured by Thermo Scientific, product number: NICORET ALMEGA XR), exfoliated graphite, expandable graphite, natural graphite, and The Raman spectrum of graphite oxide was measured.

Measurement condition;
Laser wavelength: 532 nm
Laser output: 25%
Slit: 25 μm hole Integration count: 32 times

  The Raman spectrum was measured for exfoliated graphite, expandable graphite, natural graphite and graphite oxide which were heat-treated in air at 200 ° C. for 1 hour and those which were not heat-treated.

The D / G ratio is determined by taking the maximum peak intensity in the range of 1300 cm ^{−1 to} 1400 cm ⁻¹ of the obtained Raman spectrum as the D band peak intensity, and the maximum peak intensity of 1540 cm ^{−1 to} 1640 cm ⁻¹ as G. It was determined by taking the peak intensity of the band.

  Using the D / G ratio before and after heating thus obtained, the change rate (%) of D / G was calculated from the following formula (1).

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

(2) Flexibility A sample was obtained by cutting the composite material sheets obtained in Examples and Comparative Examples with a cross-section sample preparation device (trade name “IB-09010CP” manufactured by JEOL). The cross section of the obtained sample was observed using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, trade name “S-3400N”). Thirty or more pieces of exfoliated graphite, expandable graphite, natural graphite or graphite oxide in the sample cross section were randomly selected and the degree of bending was measured. Specifically, the degree of bending was calculated as A / B where A is the shortest distance between both ends facing each other with a maximum distance, and B is the distance between both ends.

(3) Tensile Elastic Modulus The tensile elastic modulus of the composite material sheets obtained in Examples and Comparative Examples was measured according to JIS K6767.

Criteria for tensile modulus of elasticity;
◎: 2.1 GPa or more ○: 1.8 GPa or more, less than 2.1 GPa ×: less than 1.8 GPa

  The results are shown in Table 1 below.

[Examples 5 and 6 and Comparative Examples 5 and 6]
(Example 5)
As a carbon material in a 200 ml glass bottle, 0.5 g of thermally expandable graphite (product number: PF-8, manufactured by Toyo Tanso Co., Ltd.) and N-methylpyrrolidone (boiling point = 202 ° C., surface tension at 20 ° C. = 41 mN / m) 19.5 g was added, and a dispersion obtained by sufficiently infiltrating N-methylpyrrolidone into thermally expandable graphite was obtained. To this dispersion, 0.5 g of maleic anhydride was added and stirred sufficiently. Thereafter, with the opening of the glass bottle opened, using a microwave generator (manufactured by Actac Co., product number: Speed Wave 2), heated to 190 ° C. at a temperature rising rate of 60 ° C./min, held at room temperature for 30 minutes. Naturally cooled until. This heating-cooling operation was repeated three times. The obtained dispersion was filtered, thoroughly washed with acetone, and dried to obtain exfoliated graphite.

  Further, 10 parts by mass of the exfoliated graphite obtained and 100 parts by mass of a polypropylene resin (manufactured by Prime Polymer Co., Ltd., product number: J-721GR) were supplied to an extruder, melted and kneaded, and T attached to the tip of the extruder A composite sheet with a smooth surface and a thickness of 0.5 mm was obtained by extruding from a die and forming a sheet with a cooling roll.

(Example 6)
Exfoliated graphite was obtained in the same manner as in Example 5 except that natural graphite (manufactured by SEC Carbon, product number: SNO15) was used as the carbon material instead of thermally expandable graphite.

  Further, 10 parts by weight of the exfoliated graphite obtained and 100 parts by weight of the polypropylene resin were supplied to an extruder, and a composite material sheet was prepared in the same manner as in Example 5.

(Comparative Example 5)
Instead of exfoliated graphite, the heat-expandable graphite (product number: PF-8, manufactured by Toyo Tanso Co., Ltd.), which is the original carbon material of Example 5, was used as it was. 10 parts by weight of the thermally expandable graphite and 100 parts by weight of the polypropylene resin were supplied to an extruder, and a composite material sheet was prepared in the same manner as in Example 5.

(Comparative Example 6)
Instead of exfoliated graphite, natural graphite (product number: SNO15, manufactured by SEC Carbon Co.), which is the original carbon material of Example 6, was used as it was. 10 parts by weight of the natural graphite and 100 parts by weight of the polypropylene resin were supplied to an extruder, and a composite material sheet was prepared in the same manner as in Example 5.

(Evaluation)
The viscosity of exfoliated graphite of Examples 5 and 6 and Comparative Examples 5 and 6, the change rate of the D / G ratio, and the tensile modulus of the composite material sheet were measured in the following manner.

(1) Viscosity First, isopropyl alcohol and exfoliated graphite are measured in a screw tube so that the concentration of exfoliated graphite becomes 1% by weight. Then, an ultrasonic wave is irradiated for 1 minute at 28 kHz, and exfoliated graphite is fully disperse | distributed. The viscosity of the dispersion is measured using a rotary viscometer (manufactured by Toki Sangyo Co., Ltd.). The measurement was started, and the value at the time when the viscosity did not change after reaching a steady state was evaluated as the viscosity of the dispersion.

(2) Rate of change in D / G ratio First, using a microscopic laser Raman measuring apparatus (manufactured by Thermo Scientific, product number: NICORET ALMEGA XR), exfoliated graphite, expandable graphite, natural graphite or The Raman spectrum of graphite oxide was measured.

Measurement condition;
Laser wavelength: 532 nm
Laser output: 25%
Slit: 25 μm hole Integration count: 32 times

  The Raman spectrum was measured for exfoliated graphite, thermally expandable graphite, and natural graphite that were heat-treated in air at 200 ° C. for 1 hour and those that were not heat-treated.

The D / G ratio is determined by taking the maximum peak intensity in the range of 1300 cm ^{−1 to} 1400 cm ⁻¹ of the obtained Raman spectrum as the D band peak intensity, and the maximum peak intensity of 1540 cm ^{−1 to} 1640 cm ⁻¹ as G. It was determined by taking the peak intensity of the band.

  Using the D / G ratio before and after heating thus obtained, the change rate (%) of D / G was calculated from the following formula (1).

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

(3) Tensile Elastic Modulus The tensile elastic modulus of the composite material sheets obtained in Examples 5 and 6 and Comparative Examples 5 and 6 was measured according to JIS K7113.

Criteria for tensile modulus of elasticity;
◎: 2.1 GPa or more ○: 1.8 GPa or more, less than 2.1 GPa ×: less than 1.8 GPa

  The results are shown in Table 2 below.

[Examples 7 and 8 and Comparative Examples 7 to 11]
(Example 7)
As a carbon material in a 50 ml glass container, 0.5 g of thermally expandable graphite (Toyo Tanso Co., Ltd., product number: PF-8) and N-methylpyrrolidone (boiling point = 202 ° C., surface tension at 20 ° C. = 41 mN / m) 37 g was added, and a dispersion obtained by sufficiently infiltrating N-methylpyrrolidone into thermally expandable graphite was obtained. To this dispersion is added 3 g of maleic anhydride, and ultrasonic waves are applied at 28 kHz for 10 minutes. After that, after being transferred to a dedicated fluorine container and sealed, it was heated to 170 ° C. at a temperature rising rate of 60 ° C./min using a microwave generator (Actac Corp., product number: Speed Wave 2) and held for 30 minutes. Naturally cooled to room temperature. This heating-cooling operation was repeated three times. The obtained dispersion was filtered, sufficiently washed with acetone, and dried to obtain exfoliated graphite (the number of graphene sheets laminated: 302 layers, thickness: 101 nm, surface size: 1.82 μm).

Further, 10 parts by weight of the exfoliated graphite obtained and 100 parts by weight of homopolypropylene (manufactured by Nippon Polypro Co., Ltd., product number: EA9) were combined with Labo Plast Mill (manufactured by Toyo Seiki Co., Ltd., product number: R-100).
To obtain a composite material. Thereafter, a composite material sheet having a thickness of 0.5 mm was obtained by a heating press.

(Example 8)
As a carbon material in a 50 ml glass container, 0.5 g of thermally expandable graphite (Toyo Tanso Co., Ltd., product number: PF-8) and furfuryl alcohol (boiling point = 170 ° C., surface tension at 20 ° C. = 38 mN / m) 40 g was added, and a dispersion obtained by sufficiently infiltrating furfuryl alcohol into thermally expandable graphite was obtained. An ultrasonic wave is applied to this dispersion under conditions of 28 kHz and 10 minutes. After that, after being transferred to a dedicated fluorine container and sealed, it was heated to 160 ° C. at a temperature rising rate of 50 ° C./min using a microwave generator (Actac Corp., product number: Speed Wave 2) and held for 30 minutes. Naturally cooled to room temperature. This heating-cooling operation was repeated three times. The obtained dispersion was filtered, sufficiently washed with acetone, and dried to obtain exfoliated graphite (the number of graphene sheets laminated: 522 layers, thickness: 175 nm, surface size: 1.93 μm).

  Further, 10 parts by weight of the exfoliated graphite obtained and 100 parts by weight of homopolypropylene (manufactured by Nippon Polypro Co., Ltd., product number: EA9) were melt-kneaded by a Laboplast mill (manufactured by Toyo Seiki Co., Ltd., product number: R-100). A composite material was obtained. Thereafter, a composite material sheet having a thickness of 0.5 mm was obtained by a heating press.

(Comparative Example 7)
Instead of exfoliated graphite obtained in Example 7, commercially available exfoliated graphite (manufactured by Incubation Alliance, trade name: graphene flower, number of graphene sheets laminated: 10 layers, thickness: 3 nm, BET value: 1000 m ² / g, Surface size: 1 to 10 μm) was used. Other than that was carried out similarly to Example 7, and obtained the composite material sheet of thickness 5mm.

(Comparative Example 8)
Instead of exfoliated graphite obtained in Example 7, commercially available exfoliated graphite (manufactured by XGscience, trade name: xGnP-M5, graphene sheet lamination number: 1200 layers, thickness 420 nm, BET value: 140 m ² / g, surface Size: 5 μm). Other than that was carried out similarly to Example 7, and obtained the composite material sheet of thickness 5mm.

(Comparative Example 9)
Instead of exfoliated graphite obtained in Example 7, commercially available exfoliated graphite (manufactured by XGscience, trade name: xGnP-C750, number of graphene sheets laminated: 840 layers, thickness 280 nm, BET value: 700 m ² / g, surface Size: 1 μm) was used. Other than that was carried out similarly to Example 7, and obtained the composite material sheet of thickness 5mm.

(Comparative Example 10)
Instead of exfoliated graphite obtained in Example 7, commercially available natural graphite (manufactured by SEC Carbon, product number: SNO-5, number of graphene sheets laminated: 1500 layers, thickness 500 nm, BET value: 12 m ² / g, surface size : 5 μm). Other than that was carried out similarly to Example 7, and obtained the composite material sheet.

(Comparative Example 11)
Instead of exfoliated graphite obtained in Example 7, commercially available thermally expandable graphite (manufactured by Toyo Tanso Co., Ltd., product number: PF-8, number of graphene sheets laminated: 1100 layers, thickness 380 nm, BET value: 22 m ² / g, Surface size: 6 μm) was used. Other than that was carried out similarly to Example 7, and obtained the composite material sheet.

(Evaluation)
The resistance values, the D / G ratio change rate, the aspect ratio, and the tensile modulus of the composite sheet of Examples 7 and 8 and Comparative Examples 7 to 11 were as follows. Measured with

(1) Resistance value First, 10 g of isopropyl alcohol and 0.128 g of a sample for measurement of resistance value are placed in a 20 ml container (sample bottle snap cup No. 30 φ30 × 45), and subjected to ultrasonic waves at 28 kHz for 1 minute. Was applied to obtain a dispersion. The temperature of the obtained dispersion was 25 ° C., and a tester was inserted while stirring with a stirrer. The data 2 minutes after the insertion was read as the resistance value at a temperature of 25 ° C. The tester plus terminal and minus terminal were inserted into the dispersion at a distance of 2 cm between the terminals and a depth of 1 cm from the liquid surface. The resistance value of isopropyl alcohol itself was 9.05 MΩ.

(2) Rate of change of D / G ratio First, using a microscopic laser Raman measuring apparatus (manufactured by Thermo Scientific, product number: NICORET ALMEGA XR), exfoliated graphite, thermally expandable graphite, or natural The Raman spectrum of graphite was measured.

Measurement condition;
Laser wavelength: 532 nm
Laser output: 25%
Slit: 25 μm hole Integration count: 32 times

  The Raman spectrum was measured for exfoliated graphite, expandable graphite, and natural graphite that were heat-treated in air at 200 ° C. for 1 hour and those that were not heat-treated.

The D / G ratio is determined by taking the maximum peak intensity in the range of 1300 cm ^{−1 to} 1400 cm ⁻¹ of the obtained Raman spectrum as the D band peak intensity, and the maximum peak intensity of 1540 cm ^{−1 to} 1640 cm ⁻¹ as G. It was determined by taking the peak intensity of the band.

  Using the D / G ratio before and after heating thus obtained, the change rate (%) of D / G was calculated from the following formula (1).

Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100

(3) Shape 0.1 g of the sample for which the aspect ratio was determined was dispersed in 10 g of THF by applying ultrasonic waves at 28 kHz for 1 minute. To the obtained dispersion, 1 g of polystyrene was further added to dissolve the polystyrene. The resulting solution was placed in a vat and THF was evaporated in an oven. Thereafter, a sheet having a thickness of 0.5 mm and a sample concentration of 10% by weight for obtaining an aspect ratio was produced by a heating press. Next, the cross section of the graphene sheet was polished with a cross polisher and carbon was deposited. Next, SEM observation of the sheet cross section at a magnification of 3000 times was performed, and by image analysis, the maximum dimensions in the thickness and the laminated surface direction were obtained, and the aspect ratio was calculated.

(4) Tensile Elastic Modulus The tensile elastic modulus of the composite material sheets obtained in Examples and Comparative Examples was measured according to JIS K6767.

Criteria for tensile modulus of elasticity;
◎: 2.1 GPa or more ○: 1.8 GPa or more, less than 2.1 GPa ×: less than 1.8 GPa

  The results are shown in Table 3 below.

  In addition, the commercially available exfoliated graphite of Comparative Example 7 is produced by the CVD method, and the compound is not grafted. Moreover, the commercially available exfoliated graphite of Comparative Examples 8 and 9 is produced by the GIC method, and an oxidation process is included in the production process.

  From Table 3, the exfoliated graphite of Examples 7 and 8 has a low resistance value and excellent conductivity compared to the exfoliated graphite, natural graphite and thermally expandable graphite of Comparative Examples 7 to 11. Moreover, since exfoliated graphite of Examples 7 and 8 has improved dispersibility in the resin, it was confirmed that the tensile elastic modulus was increased.

Claims (32)

In the Raman spectrum obtained by Raman spectroscopy, when the peak intensity ratio between the D band and the G band is the D / G ratio, it is expressed by the following formula (1) when heated at 200 ° C. for 1 hour. Exfoliated graphite having a negative change rate of the D / G ratio.
Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100   The exfoliated graphite according to claim 1, wherein a change rate of the D / G ratio is smaller than 0% and larger than -20%.   When the shortest distance between both ends facing each other at the maximum distance is A and the distance between both ends is B, the degree of bending represented by A / B is 0.7 or more and 1.0 or less. The exfoliated graphite according to claim 1 or 2, wherein   The exfoliated graphite according to any one of claims 1 to 3, which has a thickness of 0.5 µm or less and a maximum dimension in the direction of the laminated surface of 3.0 µm or more and 1000 µm or less.   The exfoliated graphite according to any one of claims 1 to 4, wherein a viscosity at a temperature of 23 ° C when dispersed in isopropyl alcohol at a concentration of 1% by weight is 4.0 mPa · s or more.   The exfoliated graphite according to any one of claims 1 to 5, wherein a resistance value at a temperature of 25 ° C is less than 1 MΩ when dispersed in 10 g of isopropyl alcohol at a weight of 0.128 g.   The exfoliated graphite according to any one of claims 1 to 6, wherein the thickness is 6 nm or more and 400 nm or less.   The exfoliated graphite according to any one of claims 1 to 7, wherein the aspect ratio is in the range of 5 or more and 600 or less.   The electrode material containing the exfoliated graphite of any one of Claims 1-8, and binder resin.   The exfoliated graphite-resin composite material containing exfoliated graphite of any one of Claims 1-8, and resin.   The exfoliated graphite-resin composite material according to claim 10, wherein the resin is a thermoplastic resin.   The exfoliated graphite-resin composite material according to claim 11, wherein the thermoplastic resin is a polyolefin.   The exfoliated graphite-resin composite material according to claim 12, wherein the polyolefin is polypropylene.   Exfoliated graphite having a viscosity at a temperature of 23 ° C. of 4.0 mPa · s or more when dispersed at a concentration of 1% by weight in isopropyl alcohol. In the Raman spectrum obtained by Raman spectroscopy, when the peak intensity ratio between the D band and the G band is the D / G ratio, it is expressed by the following formula (1) when heated at 200 ° C. for 1 hour. The exfoliated graphite according to claim 14, wherein the change rate of the D / G ratio is a negative value.
Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100   The exfoliated graphite according to claim 14 or 15, wherein a change rate of the D / G ratio is less than 0% and -20% or more.   When the shortest distance between both ends facing each other at the maximum distance is A and the distance between both ends is B, the degree of bending represented by A / B is 0.7 or more and 1.0 or less. The exfoliated graphite according to any one of claims 14 to 16, which is   The exfoliated graphite according to any one of claims 14 to 17, having a thickness of 0.5 µm or less and a maximum dimension in the direction of the laminated surface of 3.0 µm or more and 1000 µm or less.   The electrode material containing the exfoliated graphite of any one of Claims 14-18, and binder resin.   The exfoliated graphite-resin composite material containing exfoliated graphite of any one of Claims 14-18, and resin.   The exfoliated graphite-resin composite material according to claim 20, wherein the resin is a thermoplastic resin.   The exfoliated graphite-resin composite material according to claim 21, wherein the thermoplastic resin is a polyolefin.   The exfoliated graphite-resin composite material according to claim 22, wherein the polyolefin is polypropylene.   Exfoliated graphite having a resistance of less than 1 MΩ at a temperature of 25 ° C. when dispersed at a weight of 0.128 g in 10 g of isopropyl alcohol. In the Raman spectrum obtained by Raman spectroscopy, when the peak intensity ratio between the D band and the G band is the D / G ratio, it is expressed by the following formula (1) when heated at 200 ° C. for 1 hour. The exfoliated graphite according to claim 24, wherein the change rate of the D / G ratio is a negative value.
Formula (1)
{(D / G ratio after heating−D / G ratio before heating) / (D / G ratio before heating)} × 100   The exfoliated graphite according to claim 24 or 25, wherein the thickness is 6 nm or more and 400 nm or less.   The exfoliated graphite according to any one of claims 24 to 26, wherein the aspect ratio is in the range of 5 or more and 600 or less.   An electrode material comprising exfoliated graphite according to any one of claims 24 to 27 and a binder resin.   The electrode material according to claim 28, wherein the binder resin is a fluororesin.   30. The electrode material according to claim 29, wherein the fluororesin is polyvinylidene fluoride.   The exfoliated graphite-resin composite material containing exfoliated graphite of any one of Claims 24-27, and resin.   The exfoliated graphite-resin composite material according to claim 31, wherein the resin is a polyolefin.