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{DESCRIPTION}
{Title of Invention}
GRAPHITE-BASED CARBON MATERIAL USEFUL AS GRAPHENE PRECURSOR,
AS WELL AS METHOD OF PRODUCING THE SAME
{Technical Field}
{0001}
The present invention relates to a graphite-based carbon
material useful as a graphene precursor which makes it possible
to obtain graphene by a simple method, as well as a method of
producing the same.
{Background Art}
{0002}
In recent years, addition of various nanomaterials has
been studied for purposes of downsizing and weight saving in
various fields. In particular, for problems of environments
or resources, carbon materials such as graphene, CNT (carbon
nanotube) and fullerene have attracted attention as nonmetal
nanomaterials.
For example, although carbon black has been used as a
conductive assistant for lithium-ion batteries and the like,
carbon nanofiber VGCF (registered trademark) manufactured by
Showa Denko K.K., etc. have been studied in recent years to
further secure conductivity (Patent Literature 1).
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Among them, graphene is superior to other carbon
materials in aspect of mass productivity, handleability, etc.,
as well as performance, and expectations have been placed on
graphene in various fields.
{0003}
In order to obtain high-quality graphene which, for
example, has fewer graphite layers, a method in which weak
ultrasonic waves are applied to natural graphite in a solvent
(NMP) for a long time (7-10 hours), large agglomerates which
deposit on the bottom are then removed, and the supernatant is
then centrifuged to concentrate it, thereby obtaining a
graphene dispersion in which 20% or more of flakes of a single
layer, 40% or more of flakes of double or triple layers, and
less than 40% of flakes of 10 layers or more of a graphite
material are dispersed at about 0.5 g/L, has been considered
(Patent Literature 2).
{Citation List}
{Patent Literature}
{0004}
PTL 1: JP-A-2013-77475 (Paragraph 0023)
PTL 2: WO 2014/064432 (lines 4-9 on page 19)
{Non Patent Literature}
{0005}
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NPL 1: Structural Change of Graphite with Griding;
authors: Michio INAGAKI, Hisae MUGISHIMA, and Kenji HOSOKAWA;
February 1st, 1973 (Received)
NPL 2: Changes of Probabilities Pl, PABA, PABC with Heat
Treatment of Carbons; authors: Tokiti NODA, Masaaki IWATSUKI,
and Michio INAGAKI; September 16th, 1966 (Received)
NPL 3: Spectroscopic and X-ray diffraction studies on
fluid deposited rhombohedral graphite from the Eastern Ghats
Mobile Belt, India; G.Parthasarathy, Current Science, Vol.90,
No. 7, 10 April 2006
NPL 4: 'Classification of solid carbon materials and their
structural characteristics; Nagoya Institute of Technology;
Shinji KAWASAKI
{Summary of Invention}
{Technical Problem}
{0006}
However, even when the graphite material (20% or more of
flakes of a single layer, 40% or more of flakes of double or
triple layers, and less than 40% of flakes of 10 layers or more)
obtained by the method disclosed in Patent Literature 2 was
mixed into a solvent, the amount of graphene dispersed in the
solvent was small, and only a dilute graphene dispersion could
be obtained. Additionally, although it is considered that a
supernatant is collected and concentrated, it takes along time
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for treatments to repeat the steps of collecting and
concentrating the supernatant, and there is a problem of
inferior production efficiency of a graphene dispersion. As
disclosed in Patent Literature 2, even by subjecting natural
graphite to an ultrasonic treatment for a long time, only weak
parts of the surface are exfoliated, other large parts do not
contribute to the exfoliation, and it is considered as a problem
that the amount of exfoliated graphene is small.
{00071
The invention was completed focusing on such problem
points, and a graphite-based carbon material, from which
graphene is easily exfoliated by carrying out predetermined
treatments to natural graphite, and which makes it possible to
disperse graphene at a high concentration or to a high degree
is called a graphene precursor. Then, an object of the
invention is to provide a graphite-based carbon material useful
as such a graphene precursor, as well as a method of producing
the same.
{Solution to Problem}
{0008}
In order to solve the above-described problems, the
graphite-based carbon material useful as a graphene precursor
of the invention is characterized by having a rhombohedral
graphite layer (3R) and a hexagonal graphite layer (2H), wherein
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a Rate (3R) of the rhombohedral graphite layer (3R) and the
hexagonal graphite layer (2H), based on an X-ray diffraction
method, which is defined by following Equation 1 is 31% or more:
Rate (3R) = P3/(P3+P4)x100 Equation 1
wherein
P3 is a peak intensity of a (101) plane of the rhombohedral
graphite layer (3R) based on the X-ray diffraction method, and
P4 is a peak intensity of a (101) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method.
According to the features, since a large amount of the
rhombohedral graphite layer (3R) from which a layer is easily
exfoliated is included therein, a graphite-based carbon
material useful as a graphene precursor, from which graphene
is easily exfoliated when the graphite-based carbon material
is useful as a precursor, and which makes it possible to disperse
graphene at a high concentration or to a high degree can be
obtained.
{0009}
The graphite-based carbon material useful as a graphene
precursor of the invention is characterized in that the Rate
(3R) is 40% or more.
According to the feature, as long as the Rate (3R) is 40%
or more, a graphite-based carbon material useful as a graphene
precursor from which graphene is more easily exfoliated,
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compared with cases where the Rate (3R) is 31% or more and less
than 40%, can easily be obtained.
{0010}
The graphite-based carbon material useful as a graphene
precursor of the invention is characterized in that the Rate
(3R) is 50% or more.
According to the feature, as long as the Rate (3R) is 50%
or more, a graphite-based carbon material useful as a graphene
precursor from which graphene is more easily exfoliated,
compared with cases where the Rate (3R) is 40% or more and less
than 50%, can easily be obtained.
{0011}
The graphite-based carbon material useful as a graphene
precursor of the invention is characterized in that an intensity
ratio P1/P2 of the hexagonal graphite layer (2H) based on the
X-ray diffraction method is 0.01 or more, wherein
P1 is a peak intensity of a (100) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method, and
P2 is a peak intensity of a (002) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method.
According to the feature, when the intensity ratio P1/P2
of the hexagonal graphite layer (2H) is made 0.01 or more, the
orientation disorder of crystal structure of carbon material
will be higher, graphene is easily exfoliated, and the
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graphite-based carbon material can be made to more effectively
function as the precursor.
{0012}
The above-described graphite-based carbon material
useful as a graphene precursor is characterized in that the
graphite-based carbon material is produced by carrying out a
radiowave-force-based treatment and a physical-force-based
treatment in a vacuum or in the air.
According to the feature, by combining a treatment based
on a radiowave force by microwaves, millimeter waves, plasma,
electromagnetic induction heating (Ili), magnetic fields or the
like, and a treatment based on a physical force by a ball mill,
jet mill, centrifugal force, supercriticality or the like, to
a natural graphite material in a vacuum or in the air, a
graphite-based carbon material including more rhombohedral
graphite layers (3R) is obtained. In addition, since the
treatments are carried out in a vacuum or in the air,
aftertreatments are simple.
{C)013}
A method of producing a graphite-based carbon material
useful as a graphene precursor of the invention is characterized
- by including: carrying out a radiowave-force-based treatment
and a physical-force-based treatment to a natural graphite
material in a vacuum or in the air.
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According to the feature, by combining a treatment based
on a radiowave force by microwaves, millimeter waves, plasma,
electromagnetic induction heating (IH), magnetic fields or the
like, and a treatment based on a physical force by a ball mill,
a jet mill, a centrifugal force, supercriticality or the like,
a graphite-based carbon material useful as a graphene precursor,
which more easily separates into graphene, compared with use
of either one of the treatments, can be obtained in a short time.
{00141
A method of producing a graphite-based carbon material
useful as a graphene precursor of the invention is characterized
in that the above-described natural graphite material has at
least a hexagonal graphite layer (2H), and an intensity ratio
Pl/P2 of the hexagonal graphite layer (2H) based on the X-ray
diffraction method is less than 0.01, wherein
P1 is a peak intensity of a (100) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method, and
P2 is a peak intensity of a (002) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method.
According to the features, the carbon material can be
produced from easily-available natural graphite of which the
orientation disorder of crystal structure of carbon material
is lower and general.
{0015}
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The graphite-based carbon material of the invention is
characterized by having a rhombohedral graphite layer (3R) and
a hexagonal graphite layer (2H), wherein a Rate (3R) of the
rhombohedral graphite layer (3R) and the hexagonal graphite
layer (2H), based on an X-ray diffraction method, which is
defined by following Equation 1 is 31% or more:
Rate (3R) = P3/(P3+P4)x100 Equation I
wherein
P3 is a peak intensity of a (101) plane of the rhombohedral
graphite layer (3R) based on the X-ray diffraction method, and
P4 is a peak intensity of a (101) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method.
According to the features, a large amount of the
rhombohedral graphite layer (3R) which is easily exfoliated to
layers can be obtained.
Furthermore other aspects are following.
A graphene dispersion is characterized in that the
graphene dispersion is obtained by carrying out a
radiowave-force-based treatment and a physical-force-based
treatment to the above-described graphite-based carbon
material useful as a graphene precursor in a liquid.
According to the feature, in a liquid such as a solvent,
heat acts on the graphite-based carbon material due to the
radiowave force by microwaves, millimeter waves, plasma,
electromagnetic induction heating (IH), magnetic fields or the
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like, and a physical force further acts thereon by a ball mill,
a jet mill, a centrifugal force, supercriticality or the like.
Therefore, by combining the radiowave-force-based treatment
and the physical-force-based treatment, a large amount of
graphene is easily exfoliated in a short time, a graphite-based
carbon material from which graphene is not exfoliated and which
remains in the liquid as a solvent is less, and graphene is highly
dispersed therein. Consequently, a large amount of graphene
can be dispersed in the liquid such as a solvent, and a
concentrated graphene dispersion is obtained.
The graphene dispersion is characterized by containing
at least 0.01 or more parts by weight of graphene.
According to this feature, when at least 0.01 or more
parts by weight of graphene is present, the graphene has high
dispersibility, and therefore, functions caused by dispersions
of the graphene can sufficiently be exerted.
A graphene composite is characterized in that the
graphene composite is obtained by mixing the above-described
graphite-based carbon material useful as a graphene precursor
or the above-described graphene dispersion with a composite
base material, followed by kneading them while applying a
shearing force to them.
According to the feature, the above-described
graphite-based carbon material or the above-described graphene
dispersion and the composite base material are kneaded while
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applying a sharing force to them, and therefore, graphene is
easily exfoliated therefrom, and exfoliated graphene is highly
dispersed therein. Consequently, a graphene composite, which
can disperse a large amount of graphene in a composite base
material such as monomers, polymers, other carbon materials,
ceramics, wood, cements, or metals, is obtained.
The graphene composite is characterized in that a
compatibilizer is used in kneading the graphene precursor or
the graphene dispersion with the composite base material.
According to the feature, due to effects of the
compatibilizer, graphene is more easily exfoliated.
{0016}
The graphene dispersion is characterized in that, when
0.1 part by weight of the above-described graphite-based carbon
material useful as a graphene precursor is mixed with
N-methylpyrrolidone (NMP), and an ultrasonic wave with an
output of 100 W and with a frequency of 20 kHz is applied to
the resulting mixture for 3 hours to thereby disperse graphene,
50% or more of an amount of graphene each having 10 layers or
less are exposed relative to a total amount of all graphene and
graphene precursors.
According to the i'eature, by only carrying out the
above-described treatments to 0.1 part by weight of the
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graphite-based carbon material useful as a graphene precursor,
a graphene dispersion in which graphene is dispersed at a high
concentration or to a high degree, such that the amount of
graphene each having 10 layers or less is 50% or more relative
to a total amount of all graphene and graphene precursors, can
be obtained.
{0017}
A graphite-based carbon material useful as a graphene
precursor is characterized in that the graphite-based carbon
material used with kneading a composite base material.
According to the feature, a sharing force is applied to
the graphite-based carbon material with kneading them, and
therefore, graphene is easily exfoliated therefrom, and
exfoliated graphene is highly dispersed therein. Consequently,
a graphene composite, which can disperse a large amount of
graphene in a composite base material such as monomers, polymers,
other carbon materials, ceramics, wood, cements, or metals, is
obtained.
{00181
The graphene in a composite base material is
characterized in that the composite base material is a resin.
According to the feature, a resin molded article having
a high degree dispersed graphene can be obtained. For example,
a resin molded article having an excellent elastic modulus can
be obtained.
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{Brief Description of Drawings}
{0019}
{Fig. 1} Fig. 1 is a figure which shows a crystal structure of
graphite, where (a) refers to a crystal structure of hexagonal
crystals, and (b) refers to a crystal structure of rhombohedral
crystals.
{Fig. 2} Fig. 2 is a diagram which shows an X-ray diffraction
profile of general natural graphite.
{Fig. 3} Fig. 3 is a diagram which illustrates a production
apparatus A using a jet mill and plasma of Example 1.
{Fig. 4} Fig. 4 is a figure which illustrates a production
apparatus B using a ball mill and magnetron of Example 1, where
(a) is a diagram which illustrates a pulverizing state, and (b)
is a diagram which illustrates a state where graphite-based
carbon materials (precursors) are collected.
{Fig. 5} Fig. 5 is a diagram which shows an X-ray diffraction
profile of a graphite-based carbon material of Sample 5 produced
by the production apparatus B according to Example 1.
{Fig. 61 Fig. 6 is a diagram which shows an X-ray diffraction
profile of a graphite-based carbon material of Sample 6 produced
by the production apparatus A according to Example 1.
{Fig. 7} Fig. 7 is a diagram which shows an X-ray diffraction
profile of a graphite-based carbon material of Sample 1
indicating a comparative example.
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{Fig. 8} Fig. 8 is a diagram which shows a dispersion-producing
apparatus which produces a dispersion using a graphite-based
carbon material as a precursor.
{Fig. 9} Fig. 9 is a diagram which shows dispersing states of
dispersions produced by using graphite-based carbon materials
of Sample 1 indicating a comparative example, and Sample 5
produced by the production apparatus B of Example 1.
{Fig. 101 Fig. 10 is a TEM image of a graphite-based carbon
material (graphene) dispersed in a dispersion.
{Fig. 11} Fig. 11 is a figure which shows distribution states
of a graphite-based carbon material dispersed in a dispersion
which was produced using a graphite-based carbon material
(precursor) of Sample 5, where (a) is a diagram which shows an
average size distribution, while (b) is a diagram which shows
a distribution of the number of layers.
{Fig. 12} Fig. 12 is a figure which shows a distribution state
of a graphite-based carbon material dispersed in a dispersion
which was produced using a graphite-based carbon material of
Sample 1 indicating the comparative example, where (a) is a
diagram showing an average size distribution, and (b) is a
diagram showing a distribution of the number of layers.
{Fig. 13} Fig. 13 is a diagram which shows distributions of the
number of layers of graphite-based carbon materials each
dispersed in dispersions that were produced using Samples 1 to
7 as precursors.
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{Fig. 14} Fig. 14 is a diagram which shows proportions of
graphene having 10 layers or less to a content of rhombohedral
crystals dispersed in a dispersion.
{Fig. 15} Fig. 15 is a figure which shows a distribution state
of graphite when varying conditions for producing a dispersion
using a graphite-based carbon material (precursor) of Sample
according to Example 2, where (a) is a diagram showing a
distribution in a case where an ultrasonic treatment and a
microwave treatment were combined, while (b) is a diagram
showing a distribution of the number of layers in a case where
an ultrasonic treatment was conducted.
{Fig. 16} Fig. 16 is a diagram which shows a resistance value
when a graphite-based carbon material of Example 3 was dispersed
in a conductive ink.
{Fig. 17} Fig. 17 is a diagram which shows a tensile strength
when a graphite-based carbon material of Example 4 was kneaded
with a resin.
{Fig. 18} Fig. 18 is a diagram which shows a tensile strength
when a graphite-based carbon material of Example 5 was kneaded
with a resin.
{Fig. 19} Fig. 19 is a diagram which shows dispersing states
of graphite-based carbon materials of dispersions for
describing dispersing states of Example 5 supplementary, where
(a) is a dispersing state of sample 12, and (b) is a dispersing
state of sample 2.
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{Description of Embodiments}
{0020}
The invention focuses on a crystal structure of graphite,
and, at first, matters relating to the crystal structure will
be explained. It has been known that natural graphite is
classified into three types of crystal structures, namely
hexagonal crystals, rhombohedral crystals and disordered
crystals, depending on an overlapping manner of layers. As
shown in Fig. 1, hexagonal crystals have a crystal structure
in which layers are arranged in the order of ABABAB.., while
rhombohedral crystals have a crystal structure in which layers
are arranged in the order of ABCABCABC...
{0021}
In natural graphite, there are almost no rhombohedral
crystals in a stage where natural graphite is excavated.
However, about 14% of rhombohedral crystals exist in general
natural graphite-based carbon materials because pulverization
or the like is carried out in a purification stage. In addition,
it has been known that a proportion of rhombohedral crystals
converges on about 30% even when pulverization is carried out
during purification for a long time (Non-Patent Literatures 1
and 2).
Moreover, a method in which graphite is expanded by
heating, rather than with physical forces such as pulverization,
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thereby flaking the graphite. However, even when graphite is
treated with a heat of 1600 K (about 1,300 C), a proportion of
rhombohedral crystals is about 25% (Non-Patent Literature 3).
Furthermore, the proportion is up to about 30% even when heat
of an extremely high temperature of 3000 C is applied thereto
(Non-Patent Literature 2).
Thus, although it is possible to increase a proportion
of rhombohedral crystals by treating natural graphite with
physical forces or heat, the upper limit is about 30%.
{0022}
Hexagonal crystals (2H), which are included in natural
graphite at a high level, are very stable, and an interlayer
van der Waals' force between their graphene layers is shown by
Equation 3 (Patent Literature 2). By applying an energy
exceeding this force, graphene is exfoliated. An energy
required for the exfoliation is inversely proportional to the
cube of the thickness. Therefore, in a thick state where
numerous layers are overlapped, graphene is exfoliated by a weak
physical force such as by very feeble ultrasonic waves. However,
in a case where graphene is exfoliated from somewhat thin
graphite, a very large energy is required. In other words, even
if graphite is treated for a long time, only weak parts of the
surface are exfoliated, and large parts remain not exfoliated.
100231
Fvdw = H.A/(6n.t3) Equation 3
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Fvdw: Van der Waals' force
H: Hamaker constant
A: Surface area of graphite or graphene
t: Thickness of graphite or graphene
{00241
The present inventors succeeded in increasing a
proportion of rhombohedral crystals (3R), which had been
increased to only about 30% by treatments of pulverization or
heating to an extremely high temperature, to 30% or more by
carrying out predetermined treatments, as shown below, to
natural graphite. The following findings were obtained as
results of experiments and studies. That is, when a content
of rhombohedral crystals (3R) in a graphite-based carbon
material is higher, particularly when the content is 31
% or more, there is a tendency that graphene is easily exfoliated
by use of such a graphite-based carbon material as a precursor,
thereby easily obtaining a highly concentrated and dispersed
graphene dispersion or the like. For the reason, it is
considered that, when a shear force or the like is applied to
rhombohedral crystals (3R), a deformation occurs between layers,
i.e. a deformation in the entire structure of the graphite
becomes large, and graphene is easily exfoliated independently
of the van der Waals' force. Accordingly, in the invention,
a graphite-based carbon material, from which graphene is easily
exfoliated by carrying out predetermined treatments to natural
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graphite, and which makes it possible to disperse graphene at
a high concentration or to a high degree, is called a graphene
precursor. Hereinafter, a method of producing a graphene
precursor showing predetermined treatments, a crystal
structure of the graphene precursor, and a graphene dispersion
using the graphene precursor will be described in that order
in examples below.
{00251
Here, in the specification, a graphene refers to a
flake-like or sheet-like graphene which is a crystal of a mean
size of 100 nm or more but which is not a fine crystal of a mean
size of several nanometers to tens of nanometers, and which has
layers or less.
Additionally, since graphene is a crystal with a mean size
of 100 nm or more, when artificial graphite and carbon black,
which are amorphous (microcrystal) carbon materials other than
natural graphite, are even treated, graphene cannot be obtained
(Non-Patent Literature 4) .
Further, in the specification, a graphene composite means
a composite which is produced by using the graphite-based carbon
material useful as a graphene precursor according to the
invention, i.e. a graphite-based carbon material having a Rate
(3R) of 31
% or more (e.g. Samples 2-7 of Example 1, samples 21, of
Example 5 described below) .
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{0026}
Hereinafter, examples for carrying out the
graphite-based carbon material useful as a graphene precursor
according to the invention, as well as the method of producing
the same will be described.
{Example 1}
{00271
<As to production of a graphite-based carbon material useful
as a graphene precursor>
A method for obtaining a graphite-based carbon material
useful as a graphene precursor by a production apparatus A using
a jet mill and plasma shown in Fig. 3 will be explained. As
an example, the production apparatus P, refers to a case in which
plasma is applied for the radiowave-force-based treatment and
in which the jet mill is used for the physical-force-based
treatment.
{0028}
In Fig. 3, the symbol 1 refers to a particle of 5 mm or
less of a natural graphite material (flaky graphite ACB-50
manufactured by Nippon Graphite Industries, ltd.); the symbol
2 refers to a hopper which stores the natural graphite material
1; the symbol 3 refers to a Venturi nozzle which discharges the
natural graphite material 1 from the hopper 2; the symbol 4
refers to a jet mill which jets the air which has been pumped
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from a compressor 5, while being divided into eight places, to
thereby allow the natural graphite material to collide against
the inside of a chamber by a jet blast; and the symbol 7 refers
to a plasma generator which sprays a gas 9, such as oxygen, argon,
nitrogen or hydrogen, through a nozzle 8 from a tank 6 and which
applies a voltage to a coil 11, wound around the outer periphery
of the nozzle 8, from a high-voltage power supply 10, thereby
generating plasma inside the chamber of the jet mill 4, and the
plasma generator is provided in each of four places inside the
chamber. The symbol 13 refers to a pipe which connects the jet
mill 4 and a dust collector 14 to one another; the symbol 14
refers to a dust collector; the symbol 15 refers to a collection
container; the symbol 16 refers to a graphite-based carbon
material (graphene precursor); and the symbol 17 refers to a
blower.
{0029}
Next, the production method will be explained.
Conditions for the jet mill and plasma are as follows.
The conditions for the jet mill are as follows.
Pressure: 0.5 MPa
Air volume: 2.8 m3/min
Nozzle inner Diameter: 12 mm
Flow rate: about 410 m/s
The conditions for plasma are as follows.
Output: 15 W
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Voltage: 8 kV
Gas species: Ar (purity 99.999 vol%)
Gas flow rate: 5 L/min
{00301
It is considered that the natural graphite materials 1,
which have been charged into the chamber of the jet mill 4 from
the Venturi nozzle 3, are accelerated to the sonic velocity or
higher inside the chamber, and are pulverized by impact between
the natural graphite materials 1 or by impact of them against
the wall, and that, simultaneously, the plasma 12 discharges
an electric current or excites the natural graphite materials
1, acts directly on atoms (electrons), and increases
deformations of crystals, thereby promoting the pulverization.
When the natural graphite materials 1 turn into fine particles
of a certain particle diameter (about 1 to 10 pm), their mass
is reduced, the centrifugal force is weakened, and,
consequently, the natural graphite materials 1 are pumped out
from the pipe 13 which is connected to the center of the chamber.
{0031}
A gas including graphite-based carbon materials
(graphene precursors), which have been flowed from the pipe 13
into a cylindrical container of the chamber of the dust
collector 14, forms a spiral flow, and drops the graphite-based
carbon materials 16, which collide with the internal wall of
the container, to a collection container 15 below, while an
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ascending air current generates in the center of the chamber
due to a tapered container part of the downside of the chamber,
and the gas is emitted from the blower 17 (so-called cyclone
effects). According to the production apparatus A in this
example, about 800 g of a graphene precursor from 1 kg of the
raw materials, i.e. natural graphite materials 1, is used. The
graphite-based carbon material (graphene precursors) 16 was
obtained (recovery efficiency: about 80%).
00321
Next, based on the production apparatus B using a ball
mill and microwaves shown in Fig. 4, a method for obtaining a
graphite-based carbon material useful as a graphene precursor
will be described. The apparatus B refers to, as an example,
a case where microwaves are applied as the
radiowave-force-based treatment and where a ball mill is used
for the physical-force-based treatment.
{0033}
In Fig. 4 (a) and (b), the symbol 20 refers to the ball
mill; the symbol 21 refers to a microwave generator (magnetron) ;
the symbol 22 refers to a wave guide; the symbol 23 refers to
a microwave inlet; the symbol 24 refers to a media; the symbol
25 refers to particles of 5 mm or less of a natural graphite
material (flaky graphite ACB-50 manufactured by Nippon Graphite
Industries, ltd.); the symbol 26 refers to a collection
container; the symbol 27 refers to a filter; and the symbol 28
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refers to graphite-based carbon material (graphene
precursors).
100341
Next, the production method will be explained.
Conditions for the ball mill and microwaves are as follows.
The conditions for the ball mill are as follows.
Rotational speed: 30 rpm
Media size: p5 mm
Media species: zirconia balls
Pulverization time: 3 hours
The conditions for the microwave generator (magnetron)
are as follows.
Output: 300 W
Frequency: 2.45 GHz
Irradiation method: Intermittent
{00351
1 kg of natural graphite carbon raw materials 25 and 800
g of media 24 are charged into the chamber of the ball mill 20,
the chamber is closed, and the mixture is treated at a rotational
speed of 30rpm for 3 hours. During the treatment, microwaves
are irradiated intermittently (for 20 seconds every 10 minutes)
to the chamber. It is considered that the microwave irradiation
acts directly on atoms (electrons) of the raw materials, thus
increasing deformations of the crystals. After the treatment,
media 24 are removed by the filter 27, and thus, powder of about
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pm of graphite-based carbon materials (precursors) 28 can
be collected in the collection container 26.
{00361
<As to an X-ray diffraction profile of graphite-based carbon
materials (graphene precursors) >
With reference to Figs. 5 to 7, X-ray diffraction profiles
and crystal structures will be described with respect to
graphite-based natural materials (Samples 6 and 5) produced by
the production apparatuses A and B, and the powder of about 10
pm of graphite-based natural materials (Sample 1: a comparative
example) obtained by using only the ball mill of the production
apparatus B.
The measurement conditions for the X-ray diffraction apparatus
are as follows.
Source : Cu Ka ray
Scanning speed : 20 / min
Tube voltage : 4 0 kV
Tube current : 30mA
According to the X-ray diffraction method
(horizontal-sample-mounting-model multi-purpose X-ray
diffractometer Ultima IV manufactured by Rigaku Corporation) ,
each sample shows peak intensities Pl, P2, P3 and P4 in the planes
(100) , (002) and (101) of hexagonal crystals 2H and in the plane
(101) of rhombohedral crystals 3R. Therefore, these peak
intensities will be explained.
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Here, the measurements of X-ray diffraction profile have
been used the so-called standardized values at home and abroad
in recent years. This horizontal-sample-mounting-model
multi-purpose X-ray diffractometer Ultima IV manufactured by
Rigaku Corporation is an apparatus which can measure X-ray
diffraction profile in accordance with JIS R 7651:2007
"Measurement of lattice parameters and crystallite sizes of
carbon materials". In addition, Rate (3R) is the ratio of the
diffraction intensity obtained by the Rate (3R) = P3 / (P3 +
P4)x 100, even if the value of the diffraction intensity is
changed, the value of Rate (3R) is not changes. Means that the
ratio of the diffraction intensity is standardized, it is
commonly used to avoid performing the identification of the
absolute value substance and its value does not depend on
measurement devices.
10037}
As shown in Fig. 5 and Table 1, Sample 5 produced by the
production apparatus B, which applies a treatment with a ball
mill and a microwave treatment, had high rates of peak
intensities P3 and Pl, and a Rate (3R) defined by Equation 1
showing a rate of P3 to a sum of P3 and P4 was 46%. Additionally,
the intensity ratio Pl/P2 was 0.012.
Rate (3R) = P3/(P3+P4)x100 Equation 1
wherein
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P1 is a peak intensity of a (100) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method,
P2 is a peak intensity of a (002) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method,
P3 is a peak intensity of a (101) plane of the rhombohedral
graphite layer (3R) based on the X-ray diffraction method, and
P4 is a peak intensity of a (101) plane of the hexagonal
graphite layer (2H) based on the X-ray diffraction method.
{0038}
{Table 1}
Peak intensities [counts.deg]
(20[ ])
Hexagonal crystals 2H (100) 162
[Pl] (42.33)
Hexagonal crystals 2H (002) 13157
[P2] (26.50)
Rhombohedral crystals 3R (101) 396
[P3] (43.34)
Hexagonal crystals 2H (101) 466
[P4] (44.57)
{0039}
In the same manner, as shown in Fig. 6 and Table 2, Sample
6 produced by the production apparatus A, which applies a
treatment based on the jet mill and a treatment based on plasma,
had high rates of peak intensities P3 and Pl, and the Rate (3R)
was 51%. In addition, the intensity ratio P1/P2 was 0.014.
{0040}
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{Table 2}
Peak intensities [counts.deg]
(20[ ])
Hexagonal crystals 2H (100) 66
[Pl] (42.43)
Hexagonal crystals 2H (002) 4,675
[P2] (26.49)
Rhombohedral crystals 3R (101) 170
[P3] (43.37)
Hexagonal crystals 2H (101) 162
[P4] (44.63)
{00411
Furthermore, as shown in Fig. 7 and Table 3, Sample 1
indicating a comparative example produced with only the ball
mill had a small rate of a peak intensity P3, compared with
Samples 5 and 6, and the Rate (3R) was 23%. In addition, the
intensity ratio P1/P2 was 0 .008.
{00421
{Table 3}
Peak intensities [counts.deg]
(20[ ])
Hexagonal crystals 2H (100) 120
[Pl] (42.4)
Hexagonal crystals 2H (002) 15,000
[P2] (26.5)
Rhombohedral crystals 3R (101) 50
[P3] (43.3)
Hexagonal crystals 2H (101) 160
[P4] (44.5)
{0043}
Thus, Sample 5 produced by the production apparatus B of
Example 1, and Sample 6 produced by the production apparatus
A of Example 1 had Rates (3R) of 46% and 51%, respectively, and
it was shown that their Rates (3R) were 40% or more, or 50% or
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more, compared with the natural graphite shown in Fig. 2 and
Sample 1 indicating a comparative example.
Next, graphene dispersions were produced using the
above-produced graphene precursors, and their easiness in
exfoliation of graphene was evaluated.
{00441
<As to graphene dispersions>
A method for producing a graphene dispersion will be
explained with reference to Fig. 8. Fig. 8 shows, as an example,
a case where an ultrasonic treatment and a microwave treatment
are combined in a liquid when a graphene dispersion is produced.
(1) 0 .2 g of a graphite-based carbon material useful as a
graphene precursor and 200 ml of N-methylpyrrolidone (NMP)
which serves as dispersing medium are charged to a beaker 40.
(2) The beaker 40 is put into a chamber 42 of a microwave
generator 43, and an ultrasonic trembler 44A of an ultrasonic
horn 44 is inserted into dispersing medium 41 from the upper
direction.
(3) The ultrasonic horn 44 is activated, and ultrasonic waves
of 20 kHz (100W) are continuously applied thereto for 3 hours.
(4) While the above ultrasonic horn 44 is actuated, the
microwave generator 43 is activated to apply microwaves of 2.45
GHz (300 W) intermittently (irradiation for 10 seconds every
minutes) thereto.
{00451
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Fig. 9 refers to appearances of graphene dispersions
produced in the above-described way when 24 hours had passed.
Although a portion of the graphene dispersion 30 using
Sample 5 produced by the production apparatus B was deposited,
a product entirely showing a black color was observed. For this,
it is considered that a large portion of the graphite-based
carbon materials used as graphene precursors are dispersed in
a state where graphene is exfoliated from them.
In the dispersion 31 using Sample 1 indicating a
comparative example, most of the graphite-based carbon
materials were deposited, and it was confirmed that a portion
thereof floated as a supernatant. From the facts, it is
considered that graphene was exfoliated from a small portion
thereof and that they floated as the supernatant.
{0046}
Furthermore, the graphene dispersion produced in the
above-described way was diluted to an observable concentration,
was coated onto a sample stage (TEM grid) , and the grid was dried.
Thus, the size and the number of layers of graphene was observed
in the captured image of a transmission electron microscope
(TEM), as shown in Fig. 10. In addition, the grid coated with
the diluted supernatant was used for Sample 1. For example,
in the case of Fig. 10, the size corresponds to a maximum length
L of a flake 33, which was 600 nm, based on Fig. 10 (a). As
for the number of layers, the end face of the flake 33 was
=
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observed in Fig. 10 (b), and overlapping graphene layers were
counted, thereby calculating the number of layers as 6 layers
(a portion indicated by the symbol 34). In this way, the size
and the number of layers were measured with respect to each flake,
and the numbers of graphene layers and the sizes shown in Figs.
11 and 12 were obtained.
{0047}
With reference to Fig. 11 (a), a particle size
distribution (distribution of sizes) of thin flakes included
in the graphene dispersion of Sample 5 (Rate (R3) of 46%)
produced by the production apparatus B of Example 1 was a
distribution having a peak of 0.5 pm. In addition, in Fig. 11
(b), as to the number of layers, a distribution which had a peak
in 3 layers and in which graphene having 10 layers or less were
68% was observed.
With reference to Fig. 12, a particle size distribution
(distribution of sizes) of thin flakes included in the
dispersion of Sample 1 (Rate (R3) of 23%) of the comparative
example was a distribution having a peak of 0.9 pm. In addition,
as for the number of layers, a distribution in which those having
30 layers or more occupied the greater portion and in which
graphene having 10 layers or less were 10% was observed.
From the results, it was revealed that, when the product
of Sample 5 produced by the production apparatus B was used as
a graphene precursor, a highly-concentrated graphene
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dispersion which contains plenty of graphene of 10 layers or
less and which has excellent dispersibility of graphene can be
obtained.
C00481
Next, with reference to Fig. 13, a relation between the
Rate (3R) of the graphene precursor and the number of layers
in the graphene dispersion will be described. Samples 1, 5 and
6in Fig. 13 are those described above. Samples 2, 3 and 4 were
produced by the production apparatus B which carried out a
treatment based on a ball mill and a microwave treatment, and
were graphene dispersions produced using graphene precursors
which had been produced by making the irradiating time of
microwaves shorter than that for Sample 5. In addition, Sample
7 was produced by the production apparatus A which carried out
a treatment based on a jet mill and a plasma treatment, and was
a graphene dispersion produced by using a graphene precursor
which had been produced by applying plasma of a higher output
than that for Sample 6.
{0049}
From Fig. 13,as to Samples 2 and 3 showing Rates (3R) of
31% and 38%, respectively, the distributions of the number of
layers have peaks at around 13 as the number of layers; that
is, the shapes of the distributions are close to that of a normal
distribution (dispersions using Samples 2 and 3) . As to Samples
4 to 7 showing Rates (3R) of 40% or more, the distributions of
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the number of layers have peaks at several as the number of layers
(thin graphene); that is, the shapes of the distributions are
those of a so-called lognormal distribution. On the other hand,
as to Sample 1 having a Rate (3R) of 23%, the distribution thereof
has a peak at 30 or more as the number of layers (a dispersion
using Sample 1). That is, it is understood as follows: there
is a tendency that, in cases where the Rate (3R) reaches 31%
or more, the shapes of the layer number distributions differ
from those for cases where the Rate (3R) is less than 31%; and
further, in cases where the Rate (3R) reaches 40% or more, the
shapes of the layer number distributions clearly differ from
those for cases where the Rate (3R) is less than 40%. In
addition, it can be understood that, as to proportions of
graphene of 10 layers or less, the Rate (3R) of the dispersion
using Sample 3 is 38%, while the Rate (3R) of the dispersion
using Sample 4 is 62%, and that, when the Rate (3R) reaches 40%
or more, a proportion of graphene of 10 layers or less rapidly
increases.
{00501
From these facts, it can be considered that graphene of
layers or less are easily exfoliated in cases where the Rate
(3R) is 31% or more, and that, as the Rate (3R) increases to
40%, 50% and 60%, graphene of 10 layers or less are more easily
exfoliated. However, it can be further considered that, to the
contrary, graphene of 10 layers or less are hard to exfoliate
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in cases where the Rate (3R) is less than 40%. In addition,
focusing on the intensity ratio P1 /P2 , Samples 2 to 7 show values
within a comparatively narrow range of 0.012 to 0.016, and any
of them are preferable because they exceed 0.01 where it is
considered that graphene is easily exfoliated since crystal
structures will be deformed.
100511
Furthermore, results obtained by comparing Rates (3R) and
proportions of graphene of 10 layers or less included therein
are shown in Fig. 14. With reference to Fig. 14, it was revealed
that, when the Rate (3R) reached around 31%, graphene of 10
layers or less started to increase (showing an ever-increasing
slope). Further, it was revealed that, around 40%, graphene
of 10 layers or less rapidly increased (as to proportions of
graphene of 10 layers or less, whereas the Rate (3R) of the
dispersion using Sample 3 was 38%, the Rate (3R) of the
dispersion using Sample 4 was 62%, and the proportion of
graphene of 10 layers or less rapidly increased by 24% as the
Rate (3R) increased by 4%), and that a percentage of graphene
of 10 layers or less against the total graphene was 50% or more.
In addition, the points of black squares in Fig. 14 each
correspond to different samples, and above-described Samples
1 to 7 and other samples are included therein.
100521
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From the facts, when a sample showing a Rate (3R) of 31%
or more is used as a graphene precursor to produce a graphene
dispersion, the proportion of distributed graphene of 10 layers
or less starts increasing; further, when a sample showing a Rate
(3R) of 40% or more is used as a graphene precursor to produce
a graphene dispersion, 50% or more of graphene of 10 layers or
less are produced. In other words, a graphene dispersion in
which graphene is highly concentrated and highly dispersed can
be obtained. Furthermore, because almost no graphite-based
carbon materials (precursors) included in the dispersion
deposit as described above, a concentrated graphene dispersion
can easily be obtained. According to this method, even a
graphene dispersion whose graphene concentration exceeded 10%
can be produced without concentrating it. Particularly, the
Rate (3R) is preferably 40% or more from a view point that the
proportion of dispersed graphene of 10 layers or less sharply
increases to 50% or more.
{0053}
The above description clarifies the following: when the
Rate (3R) is 31% or more, preferably 40% or more, and further
preferably 50% or more, separation into graphene of 10 layers
or less and thin graphite-based carbon materials of around 10
layers occurs in a greater proportion in many cases; and in the
case where these graphite-based carbon materials are used as
graphene precursors, a highly-concentrated graphene
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dispersion that has excellent dispersibility of graphene can
be obtained. Still further, Example 5 to be described below
clarifies that, in the case where the Rate (3R) is 31% or more,
graphite-based carbon materials are useful as a graphene
precursor.
{00541
Furthermore, an upper limit for the Rate (3R) is
considered that the upper limit is not particularly defined.
However, it is preferable that the upper limit is defined such
that the intensity ratio P1/P2 simultaneously satisfies 0.01
or more, because graphene precursors are easily exfoliated when
a dispersion or the like is produced. In addition, in cases
of production methods using production apparatuses A and B, the
upper limit is about 70%, from a viewpoint that graphene is
easily produced. Also, a method combining a treatment based
on the jet mill of the production apparatus A and a plasma
treatment is more preferable, because a graphene precursor
having a higher Rate (3R) can easily be obtained. Additionally,
the Rate (3R) as long as it reaches 31% or more by combining
the physical-force-based treatment and the
radiowave-force-based treatment.
{Example 2}
{0055}
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In Example 1, a case where the ultrasonic treatment and
the microwave treatment were combined for obtaining a graphene
dispersion is explained. In Example 2, only an ultrasonic
treatment was carried out while a microwave treatment was not
carried out, and other conditions were the same as those for
Example 1.
Fig. 15 (b) shows a distribution of a number of layers
with respect to a graphene dispersion which was obtained by
carrying out an ultrasonic treatment using the graphene
precursor of Sample 5 (Rate (3R) = 46%) produced by the
production apparatus B. In addition, Fig. 15 (a) is the same
as the distribution shown in Fig. 11 (b) of Sample 5 produced
by the production apparatus B of Example 1.
As a result, alth-:ugh the tendency of the distribution
of the number of layers was almost similar, a proportion of
graphene of 10 layers or less was 64%, and-was slightly decreased,
compared with 68% of Example 1. From the fact, it was revealed
that it was more effective to simultaneously carry out two of
the treatments based on a physical force and a radiowave force
for producing a graphene dispersion.
{Example 3}
{0056}
In Example 3, an example used for a conductive ink will
be described.
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Sample 1 (Rate (3R) = 23%), Sample 3 (Rate (3R) = 38%),
Sample 5 (Rate (3R) = 46%) and Sample 6 (Rate (3R) = 51%) of
Example 1 were used as graphene precursors in mixture solution
of water and an alcohol of the carbon number of 3 or less, which
severed as a conductivity-imparting agent, at concentrations
adopted for conductive inks, thus producing INK1, INK3, INKS
and INK6, and their resistance values were compared. Based on
the results, as the Rates (3R) became higher, the resistance
values were lower.
{Example 4}
{0057}
In Example 4, an example in which a graphene precursor
was kneaded with a resin will be explained.
When a resin sheet, in which graphene was dispersed, was
produced, the tensile strength was very superior although glass
fibers were added thereto. Therefore, a factor for this was
studied, and, consequently, a finding that a compatibilizer
added simultaneously with the glass fibers contributed to
formation of graphene from the precursor could be obtained.
Therefore, products obtained by mixing dispersing agents and
a compatibilizer into a resin were studied.
1 wt% of Sample 5 (Rate (3R) =46%) of Example 1 was added
as a precursor directly to LLDPE (polyethylene), and the mixture
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was kneaded while applying shear (a shearing force) thereto with
a kneader, two-shaft kneader (extruder) or the like.
It has been publicly known that, when a graphite-based
carbon materials turned into graphene, being highly dispersed
in a resin, the tensile strength increases. Therefore, by
measuring a tensile strength of the resin, degrees of
exfoliating into graphene and dispersion can relatively be
estimated. The tensile strength was measured with an exact
tabletop general-purpose testing machine (AUTOGRAPH AGS-J)
manufactured by Shimadzu Corporation under a condition of test
speed of 500 mm/min.
{00581
In addition, in order to compare degree of exfoliating
into graphene and dispersibility depending on the presence or
absence of additives, the following comparisons of three types
of (a), (b) and (c) were carried out.
(a) No additives
(b) a general dispersing agent (zinc stearate)
(c) a compatibilizer (a graft-modified polymer)
{0059}
With reference to Fig. 17 showing the measurement results,
the results will be explained. In addition, in Fig. 17, circles
refer to resin materials using Sample 1 of the comparative
example, and squares refer to resin materials using Sample 5
of Example 1.
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In case (a) where no additive was added, a difference of
the tensile strengths was small.
In case (b) where the dispersing agent was added, it was
revealed that formation of graphene was promoted to a certain
degree in the graphene precursor of Sample 5.
In case (c) where the compatibilizer was added, it was
revealed that that formation of graphene was significantly
promoted in the graphene precursor of Sample 5. This is because
it is considered that, besides effects to disperse graphene,
the compatibilizer binds the graphene layer-bound bodies and
the resin, and acts on them such that the graphene layer-bound
bodies are stripped therefrom, when applying shear in that state.
100601
Zinc stearate is explained above as an example of the
dispersing agent. However, those suited for compounds may be
selected. As examples of the dispersing agent, anionic (anion)
surfactants, cationic (cation) surfactants, zwitterionic
surfactants, and nonionic surfactants can be mentioned. In
particular, anion surfactants and nonionic surfactants are
preferable for graphene. Nonionic surfactants are more
preferable. Since nonionic surfactants are surfactants which
do not dissociate into ions and which show hydrophilic
properties by hydrogen bonds with water, as observed in
oxyethylene groups, hydroxyl groups, carbohydrate chains such
as glucoside, and the like, there is a merit that they can be
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used in nonpolar solvents, although they do not have a strength
of hydrophilicity as high as ionic surfactants. Further, this
is because, by varying chain lengths of their hydrophilic groups,
their properties can freely be changed from lipophilic
properties to hydrophilic properties. As anionic surfactants,
X acid salts (as for the X acid, for example, cholic acid, and
deoxycholic acid), for example, SDC: sodium deoxycholate, and
phosphate esters, are preferable. Furthermore, as nonionic
surfactants, glycerol fatty acid esters, sorbitan fatty acid
esters, fatty alcohol ethoxylates, polyoxyethylene alkyl
phenyl ether, alkyl glycosides, and the like are preferable.
00601
In above Examples 1 to 4, the production apparatus A using
a jet mill and plasma, and the production apparatus B using a
ball mill and microwaves are described as production
apparatuses which produce a graphene precursor. However, when
a treatment based on a radiowave force such as by microwaves,
millimeter waves, plasma, electromagnetic induction heating
(IH), and magnetic fields, and a treatment based on a physical
force such as by a ball mill, a jet mill, centrifugal force,
and supercriticality are combined, a precursor having a high
Rate (R3) can be obtained. Therefore, such combination of the
treatments is preferable. Additionally, as long as combining
the physical-force-based treatment and the
radiowave-force-based treatment, any specific treatments for
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the physical-force-based treatment and the
radiowave-force-based treatment can be adopted. In particular,
as seen in the production apparatuses A and B, it is preferable
that effects based on a radiowave force and a physical force
are simultaneously directed thereto. However, a radiowave
force and a physical force may alternately be directed thereto
at predetermined intervals. Moreover, as for the radiowave
force, different radiowave forces, such as treatments based on
microwaves and plasma, may alternately be applied thereto, and,
parallel with the treatments, treatments based on one or more
physical forces may be carried out. Furthermore, also as for
the physical force, different physical forces, such as
treatments based on a jet mill and supercriticality, may
alternately be applied thereto, and, parallel with the
treatments, treatments based on one or more radiowave forces
may be carried out.
{Example 5}
{00611
In order to further verify that those obtained when the
Rate (3R) is 31% or more are beneficial as graphene precursors,
which is described above in Example 1, an example in which a
graphene precursor was kneaded with a resin will be further
explained in Example 5. The following explains elastic moduli
of resin molded articles in which graphite-based carbon
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materials containing Samples 1 to 7 in Example 1, having Rates
(3R) plotted in Fig. 14, were used as precursors.
{0062}
(1) Using the above-described graphite-based carbon
material as a precursor, 5wt% of LLDPE (polyethylene: 20201J
produced by Prime Polymer Co., Ltd.) and lwt% of a dispersant
(nonionic surfactant) were mixed in an ion-exchanged water, and
the above-described device illustrated in Fig. 8 was actuated
under the same conditions, whereby graphene dispersions
containing 5wt% of graphene and graphite-based carbon materials
were obtained.
(2) 0.6 kg of the graphene dispersion obtained in (1) was
immediately kneaded into a resin of 5.4 kg using a kneader
(pressing-type kneader WDS7-30 produced by Moriyama Co . , Ltd.),
whereby pellets were produced. The kneading conditions are to
be described below. It should be noted that the mixing ratio
between the resin and the dispersion was selected so that the
amount of the graphene and graphite-based carbon materials
mixed therein was eventually 0.5wt%.
(3) The pellets produced in (2) were formed into a test
piece according to JIS K7161 lA (length: 165 mm, width: 20 mm,
thickness: 4 mm) by an injection molding machine.
(4) The elastic modulus (Mpa) of the test piece produced
in (3) was measured under a condition of a test speed of 500
ram/min according to JIS K7161 by a table-top type precision
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universal tester produced by Shimadzu Corporation (AUTOGRAPH
AGS-J).
{0063}
The kneading conditions were as follows.
Kneading temperature: 135 C
Rotor rotation speed: 30 rpm
Kneading time: 15 minutes
Pressurization in furnace: applying 0.3 MPa for 10
minutes after start, and depressurizing to atmospheric pressure
after the 10 minutes elapsed
{0064}
Here, the dispersion of the above-described graphene
dispersion into a resin is considered as follows. As the
melting point of a resin is generally 100 C or higher, water
evaporates in atmosphere, but in a pressing-type kneader, the
inside of a furnace can be pressurized. In the inside of the
furnace, the boiling point of water is raised so that the
dispersion is kept in a liquid form, whereby an emulsion of the
dispersion and the resin can be obtained. After applying
pressure for a predetermined time, the inside is gradually
depressurized, which causes the boiling point of water to
decrease, thereby allowing water to evaporate. Here, graphene
confined in water are left in the resin. This causes graphene
and graphite-based carbon materials to be dispersed at a high
concentration in the resin.
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Further, since the graphene and graphite-based carbon
materials tend to precipitate in the graphene dispersion as time
elapses, the graphene dispersion is kneaded into the resin
preferably immediately after the graphene dispersion is
obtained.
{0065}
It should be noted that the following may be used as the
means for obtaining the emulsion of the dispersion and the resin,
other than the pressing kneader: a chemical thruster; a vortex
mixer; a homomixer; a high-pressure homogenizer; a hydroshear;
a flow jet mixer; a wet jet mill; and an ultrasonic generator.
Further, the following may be used as a solvent for the
dispersion, other than water: 2-propanol (IPA); acetone;
toluene; N-methylpyrrolidone (NMP); and N,N-dimethyl
formamide (DMF).
{0066}
Table 4 illustrates the relationship between the Rates
(3R) of around 30% and the elastic moduli of resin molded
articles. It should be noted that Sample 00 in Table 4 is a
blank Sample in which no precursor was kneaded, Samples 11 and
12 have Rates (3R) between that of Sample 1 and that of Sample
2, and Sample 21 has a Rate (3R) between that of Sample 2 and
that of Sample 3.
{0067}
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{Table 4}
Sample No. 00 1 11 12 2 21 3 4
P3/(P3+P4) 23% 25% 28% 31% 35% 38% 42%
Elastic
modulus (MPa)
175 197 196 199 231 249 263 272
(Average in 5
times)
Difference 12.4 12.0 13.9 31.7 42.1 50.0 55.6
from blank
Under-10
layers upon
dispersion in 10% 12% 25% 25% 30% 38% 62%
NMP
(Reference)
{00681
Fig. 18 and Table 4 prove that the difference of the elastic
modulus with respect to that of sample 00 (blank) (increase
ratio of the elastic modulus) is approximately uniform around
10% until the Rate (3R) reaches 31%; after the Rate (3R) reaches
31%, the difference sharply increases to 32%; while the Rate
(3R) increases from 31% to 42%, the difference monotonously
increases to 50%; and after the Rate (3R) reaches 42%, the
difference slightly increases and converges to around 60%. In
this way, when the Rate (3R) is 31% or more, a resin molded
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article having an excellent elastic modulus can be obtained.
Further, since the amount of graphene and graphite-based carbon
materials contained in a resin molded article is 0.5wt%, which
is small, influence on properties that the resin originally
possesses is small.
{0069}
It is considered that this tendency attributes to a sharp
increase in a thin graphite-based carbon material containing
graphene having 10 or less layers in contact with a resin after
the Rate (3R) reaches 31%. Here, in Example 5, it is impossible
to determine the number of layers of graphene by observation
with TEM due to influences of a dispersant used for dispersion
in water. Then, only for reference, the reason for the sharp
increase described above is considered based on the
distribution of the numbers of layers of the graphite-based
carbon material illustrated in Table 4 upon dispersion in NMP.
Sample 12 and Sample 2 are compared with each other, and it is
found that both of the proportions of graphene (the number of
layers are 10 or less) were 25%. On the other hand, as
illustrated in Fig. 19, as to Sample 2, the proportion of thin
ones having less than 15 layers was greater as compared with
Sample 12; in other words, the graphite-based carbon material
dispersed as a precursor hada larger surface area, which means
that the area thereof in contact with the resin sharply
increased.
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In this way, Example 5 clearly indicates that when the
Rate (3R) is 31% or more, a graphite-based carbon material used
as a graphene precursor tends to be separated into graphene
having 10 or less layers and a thin graphite-based carbon
material.
{0070}
Moreover, in above-described examples, the production
apparatus using microwaves and ultrasonic waves is described
as a production apparatus for obtaining a graphene dispersion
using a precursor. However, when a treatment based on a
radiowave force such as by microwaves, millimeter waves, plasma,
electromagnetic induction heating (IH) and magnetic fields, and
a treatment based on a physical force such as by ultrasonic waves,
a ball mill, a jet mill, centrifugal force, and supercriticality
are combined, a graphene dispersion having a high graphene
concentration can be obtained. Therefore, such combination of
the treatments is preferable. In particular, as seen in the
production apparatus, it is preferable that effects based on
a radiowave force and a physical force are simultaneously
directed thereto. However, a radiowave force and a physical
force may alternately be directed thereto at predetermined
intervals.
{0071}
Moreover, in above-described examples, the production
apparatus using microwaves and ultrasonic waves is described
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as a production apparatus for obtaining a graphene dispersion
using a precursor. However, when a treatment based on a
radiowave force such as by microwaves, millimeter waves, plasma,
electromagnetic induction heating (IH) and magnetic fields, and
a treatment based on a physical force such as by ultrasonic waves,
a ball mill, a jet mill, centrifugal force, and supercriticality
are combined, a graphene dispersion having a high graphene
concentration can be obtained. Therefore, such combination of
the treatments is preferable. In particular, as seen in the
production apparatus, it is preferable that effects based on
a radiowave force and a physical force are simultaneously
directed thereto. However, a radiowave force and a physical
force may alternately be directed thereto at predetermined
intervals.
{0072}
Furthermore, in the above-described examples, graphene
dispersions, conductive inks and resin molded articles are
described as applications using precursors. However, also, by
mixing, as base materials, precursors into composite base
materials such as monomers, polymers, other carbon materials,
ceramics, woods, cements or metals, graphene composite may be
obtained. That is, in the present specification, a graphene
composite means products encompassing the above-described
graphene dispersions, conductive inks and resin molded articles.
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Additionally, a graphene dispersion encompasses paste products
with high viscosities.
{0073}
As examples of liquids or base materials for dispersing
precursors, the following materials can be mentioned. Resins
includes polyethylene (PE), polypropylene (PP), polystyrene
(PS), polyvinyl chloride (PVC), ABS resins (ABS), acrylic
resins (PMMA), polyamide/nylon (PA), polyacetal (PON),
polycarbonate (PC), polyethylene terephthalate (PET), cyclic
polyolefins (COP), polyphenylene sulfide (PPS),
polytetrafluoroethylene (PTFE), polysulfones (PSF),
polyamide-imide (PAI), thermoplastic polyimide (PI),
polyether ether ketone (PEEK), and liquid-crystal polymers
(LCP). In addition, among synthetic resins, as thermosetting
resins, thermoplastic resins such as epoxy resins (EP),
phenolic resins (PF), melamine resins (ME'), polyurethanes (PUR)
and unsaturated polyester resins (UP) can be mentioned; fibrous
nylon, and fibers of polyester, acryl, vinylon, polyolefin,
polyurethane, rayon or the like canbementioned; as elastomers,
isoprene rubbers (IR), butadiene rubbers (BR),
styrene/butadiene rubbers (SBR), chloroprene rubbers (CR),
nitrile rubbers (NBR), polyisobutylene rubbers/butyl rubbers
(IIR), ethylene propylene rubbers (EPM/EPDM),
chlorosulfonated polyethylene (CSM), acrylic rubbers (ACM),
epichlorohydrin rubbers (CO/ECO), and the like can be
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mentioned; as thermosetting resin-based elastomers, some
urethane rubbers (U), silicone rubbers (Q),
fluorine-containing rubbers (FKM), and the like can be
mentioned; and, as thermoplastic elastomers, elastomers based
on styrene, olefin, polyvinyl chloride, urethane, or amide can
be mentioned.
{00741
Moreover, as mineral oils, lubricating oils, and greases
can be mentioned, and, as compounded oils for rubbers,
paraffin-based mineral oils, naphthenic mineral oil, aromatic
mineral oils, and the like can be mentioned.
Furthermore, as nonpolar products, hexane, benzene,
toluene, chloroform, ethyl acetate, and the like can be
mentioned; as polar aprotic products, acetone,
N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP),
acetonitrile, and the like can be mentioned; and, as polar
protic products, acetic acid, ethanol, methanol, water,
1-butanol, 2-propanol, formic acid, and the like can be
mentioned.
{00751
In addition, as an example of natural graphite for
producing a graphite-based carbon material useful as a graphene
precursor, particles of 5 mm or less of a natural graphite
material (flaky graphite ACB-50 manufactured by Nippon Graphite
Industries, ltd.) is described above. However, as for the
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natural graphite, products which are flaky graphite, being
pulverized into 5 mm or less, and which have a Rate (3R) of less
than 25% and an intensity ratio Pl/P2 of less than 0.01 are
preferable, from a viewpoint that they are easily-available.
Industrial Applicability
100761
The following can be mentioned as products for attempting
functionalization according to graphene by adding the precursor
to objects.
= Additives for polymer materials such as resins, rubbers, or
coatings
= Additives for heat radiation sheets, conductive sheets, heat
radiation tapes, or conductive tapes
= Sintered metallurgy obtained by adding the precursor to metal
powder, followed by sintering
= Additives for ceramics such as lithium oxide or nanoclay
= Additives for nonmetals such as concrete, or non-polymer
materials
{0077}
The following can be mentioned as products using graphene
dispersions.
= Electrode agents, conductive auxiliaries, discharge
capacity-improving agents, charge/discharge
efficiency-improving agents for lithium-ion batteries
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= Electrodes or electrolyte solutions for capacitor products
= Conductive agents for conductive inks
Reference Signs List
{00781
1 a natural graphite material
4 a jet mill
7 a plasma generator
16 a graphite-based carbon material useful as a graphene
precursor
20 a ball mill
21 a microwave generator
24 a media
25 a natural graphite material
28 a graphite-based carbon material useful as a graphene
precursor
30 a graphene dispersion using Sample 5
31 a graphene dispersion using Sample 1
33 a flake
40 a beaker
41 a graphene dispersion
43 a microwave generator
44 an ultrasonic wave generator
53
