JP2016056080A - Graphite-based carbon material used as graphene precursor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graphite-based carbon material from which graphene is easily peeled off when used as a precursor, with which a graphene dispersion with high concentration is easily obtained, and which is used as a graphene precursor.SOLUTION: A graphite-based carbon material, used as a graphene precursor, has Rate(3R), a rate defined by following (formula 1) according to the X-ray diffraction method, of 31% or more. Rate(3R)=P3/(P3+P4)×100 (formula 1). Here, P3 is a peak intensity of a (101) plane of a rhombohedral graphite layer (3R) according to the X-ray diffraction method, and P4 is a peak intensity of the (101) plane of a hexagonal graphite layer (2H) according to the X-ray diffraction method.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a graphite-based carbon material used as a graphene precursor capable of obtaining graphene by a simple method.

In recent years, the addition of various nanomaterials has been studied for the purpose of reducing the size and weight in various fields. In particular, due to environmental and resource problems, carbon materials such as graphene, CNT (carbon nanotube), and fullerene are attracting attention as non-metallic nanomaterials.
For example, carbon black has been used as a conductive aid for lithium ion batteries and the like, but in recent years, carbon nanofiber VGCF (registered trademark) manufactured by Showa Denko Co., Ltd. has been studied in order to further ensure conductivity ( Patent Document 1).
Among them, graphene is superior to other carbon materials in terms of performance as well as mass production and handling, and is expected in various fields.

  In order to obtain high-quality graphene with a small number of graphite layers, natural graphite is given a weak ultrasonic wave in a solvent (NMP) for a long time (7 to 10 hours), and then a large lump precipitated on the bottom is removed. Thereafter, the supernatant is centrifuged and concentrated, so that a graphite material having a single-layer flake of 20% or more, a double-layer or three-layer flake of 40% or more, and a 10-layer or more of flakes of less than 40% is reduced to 0.0. A method for obtaining a graphene dispersion in which about 5 g / L is dispersed has been studied (Patent Document 2).

JP2013-77475A (paragraph 0023) International Publication No. 2014/064432 (Page 19, Line 4-Line 9)

Structural changes accompanying polishing of graphite; Author: Michio Inagaki, Hisae Mugishima, Kenji Hosokawa; February 1, 1973 (accepted) Changes in probability P1, PABA, and PABC associated with carbon heat treatment; Authors: Inayoshi Noda, Masaaki Iwatsuki, Michio Inagaki; September 16, 1966 (accepted) 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 Classification of solid carbon materials and their structural characteristics; Nagoya Institute of Technology Junji Kawasaki

  However, the graphite material obtained by the method disclosed in Patent Document 2 (single-layer flakes are 20% or more, 2-layer or 3-layer flakes is 40% or more, and 10-layer or more flakes are less than 40%) is a solvent. In addition, the amount of graphene dispersed in the solvent was small and only a thin graphene dispersion was obtained. Further, it is conceivable to collect and concentrate the supernatant, but repeating the step of collecting and concentrating the supernatant has a problem that it takes time to process and the production efficiency of the graphene dispersion is poor. As disclosed in Patent Document 2, even when natural graphite is subjected to ultrasonic treatment for a long time, only a weak portion of the surface peels off, and most of the other does not contribute to peeling, and the amount of graphene to be peeled is Less is considered a problem.

  The present invention has been made by paying attention to such problems, and a graphite-based carbon material that can be easily peeled off by applying a predetermined treatment to natural graphite, and can graphene be highly concentrated or highly dispersed. It is called a graphene precursor and an object is to provide a graphite-based carbon material used as the graphene precursor.

In order to solve the above problems, the graphite-based carbon material used as the graphene precursor of the present invention,
It has a rhombohedral graphite layer (3R) and a hexagonal graphite layer (2H), and an X-ray diffraction method of the rhombohedral graphite layer (3R) and the hexagonal graphite layer (2H). The graphene precursor is characterized in that the ratio Rate (3R) defined by the following (formula 1) is 31% or more.
Rate (3R) = P3 / (P3 + P4) × 100 (Equation 1)
here,
P3 is the peak intensity of the (101) plane of the rhombohedral graphite layer (3R) by X-ray diffraction method P4 is the peak intensity of the (101) plane of the hexagonal graphite layer (2H) by X-ray diffraction method.
According to this feature, since the rhombohedral graphite layer (3R) is easy to peel off, the graphene can be easily peeled off when used as a precursor, and the graphene can be highly concentrated or dispersed. A graphite-based carbon material used as a precursor is obtained.

In addition, the graphite-based carbon material used as the graphene precursor is
It has a rhombohedral graphite layer (3R) and a hexagonal graphite layer (2H), and an X-ray diffraction method of the rhombohedral graphite layer (3R) and the hexagonal graphite layer (2H). The ratio Rate (3R) defined by the following (Formula 1) is 40% or more.
Rate (3R) = P3 / (P3 + P4) × 100 (Equation 1)
here,
P3 is the peak intensity of the (101) plane of the rhombohedral graphite layer (3R) by X-ray diffraction method P4 is the peak intensity of the (101) plane of the hexagonal graphite layer (2H) by X-ray diffraction method.
According to this feature, since the rhombohedral graphite layer (3R) is easy to peel off, the graphene can be easily peeled off when used as a precursor, and the graphene can be highly concentrated or dispersed. A graphite-based carbon material used as a precursor is obtained.
In addition, the graphite-based carbon material used as the graphene precursor is
The ratio Rate (3R) is 50% or more.
According to this feature, when the rate Rate (3R) is 50% or more, it is possible to easily obtain a graphite-based carbon material used as a graphene precursor from which graphene is more easily peeled than when it is 40% or more and less than 50%. it can.

In addition, the graphite-based carbon material used as the graphene precursor is
The hexagonal graphite layer (2H) is characterized in that an intensity ratio P1 / P2 by an X-ray diffraction method is 0.01 or more.
here,
P1 is the peak intensity of the (100) plane of the hexagonal graphite layer (2H) by the X-ray diffraction method P2 is the peak intensity of the (002) plane of the hexagonal graphite layer (2H) by the X-ray diffraction method.
According to this feature, if the strength ratio P1 / P2 of the hexagonal graphite layer (2H) is 0.01 or more, the orientational disorder of the crystal structure of the carbon material is high, and the graphene is easily peeled off. It can function as a precursor more effectively.

The graphite-based carbon material used as the graphene precursor described above is characterized in that it is produced by applying a treatment with a radio wave force and a treatment with a physical force in a vacuum or in the air.
According to this feature, natural graphite materials in vacuum or in the air are treated with radio waves such as microwave, millimeter wave, plasma, electromagnetic induction heating (IH), magnetic field and ball mill, jet mill, centrifugal force, supercritical, etc. By combining the treatment with the physical force, a graphite-based carbon material containing more rhombohedral graphite layer (3R) can be obtained. Further, since the treatment is performed in a vacuum or in the air, post-treatment is easy.

In addition, the graphene dispersion is characterized by being obtained by subjecting the graphite-based carbon material used as the graphene precursor described above to a treatment by radio wave force and a treatment by physical force in the liquid. Yes.
According to this feature, heat is applied to the graphite-based carbon material in a liquid such as a solvent, and microwaves, millimeter waves, plasma, electromagnetic induction heating (IH), a magnetic force such as a magnetic field, and ultrasonic waves. , Physical force such as ball mill, jet mill, centrifugal force, supercritical, etc. will be applied, and by combining treatment with radio wave force and treatment with physical force, it will be peeled off in a large amount of graphene in a short time It is easy, and because there is little graphite carbon material remaining in the solvent and other liquids without being separated from the graphene, and graphene is highly dispersed, it is possible to disperse a large amount of graphene in the solvent and other liquids. A liquid is obtained.

In addition, the graphene dispersion contains at least 0.01 parts by weight of graphene.
According to this feature, if the graphene is at least 0.01 parts by weight or more, the graphene has a high dispersibility, so that the function due to the graphene dispersion is sufficiently exhibited.

In addition, the graphene composite is kneaded while mixing the graphite-based carbon material used as the graphene precursor described above or the graphene dispersion described above with the composite matrix and applying shear force. It is characterized by what was obtained.
According to this feature, it is kneaded while applying shearing force, easily peeled off by graphene, and the peeled graphene is highly dispersed, so monomers, polymers, other carbon materials, ceramics, wood, cement, metal Thus, it is possible to obtain a graphene composite in which a large amount of graphene can be dispersed in the composite matrix.

In addition, graphene complex
A compatibilizer is used when kneading the base material.
According to this feature, the graphene is more easily peeled off by the action of the compatibilizing agent.

Also, a method for producing a graphite-based carbon material used as a graphene precursor, characterized in that a natural graphite material is subjected to treatment by radio wave force and treatment by physical force in a vacuum or in the air. Yes.
According to this feature, natural graphite materials are treated with radio wave forces such as microwave, millimeter wave, plasma, electromagnetic induction heating (IH) and magnetic field, and physical forces such as ball mill, jet mill, centrifugal force and supercritical force. By using together with the treatment by, it is possible to obtain a graphite-based carbon material used as a graphene precursor that is more easily separated into graphene than the treatment with either one.

In addition, a method for producing a graphite-based carbon material used as a graphene precursor,
The natural graphite material described above has at least a hexagonal graphite layer (2H), and the intensity ratio P1 / P2 of the hexagonal graphite layer (2H) by X-ray diffraction is less than 0.01. It is characterized by being.
here,
P1 is the peak intensity of the (100) plane of the hexagonal graphite layer (2H) by the X-ray diffraction method P2 is the peak intensity of the (002) plane of the hexagonal graphite layer (2H) by the X-ray diffraction method.
According to this feature, the graphite-based carbon material can be produced from general readily available natural graphite having a low orientation disorder of the crystal structure of the carbon material.

The graphene dispersion is
The graphite-based carbon material 0.1 parts by weight used as the graphene precursor described above is mixed with N-methylpyrrolidone (NMP), and an ultrasonic wave with an output of 100 W and a frequency of 20 kHz is applied for 3 hours, When graphene is dispersed, the number of graphenes having 10 or less layers is expressed by 50% or more with respect to the total number of all graphenes and graphene precursors.
According to this feature, the number of layers with respect to the total number of graphenes and the total number of graphite as graphene precursors is 10 by simply performing the above-described treatment on 0.1 part by weight of the graphite-based carbon material used as the graphene precursor. A graphene dispersion liquid in which graphene is highly concentrated or highly dispersed such that the number of graphenes below the layer is 50% or more can be obtained.

It is a figure which shows the crystal structure of graphite, (a) is a hexagonal crystal, (b) is a rhombohedral crystal structure. It is a figure which shows the X-ray-diffraction profile of general natural graphite. It is a figure explaining the manufacturing apparatus A using the jet mill and plasma of Example 1. FIG. It is a figure explaining the manufacturing apparatus B using the ball mill and magnetron of Example 1, (a) is a figure explaining the state grind | pulverized, (b) is the state which collects a graphite-type carbon raw material (precursor). It is a figure explaining. It is a figure which shows the X-ray-diffraction profile of the graphite-type carbon raw material of the sample 5 manufactured by the manufacturing apparatus B of Example 1. FIG. 6 is a diagram showing an X-ray diffraction profile of a graphite-based carbon material of Sample 6 manufactured by the manufacturing apparatus A of Example 1. FIG. It is a figure which shows the X-ray-diffraction profile of the graphite-type carbon raw material of the sample 1 which shows a comparative example. It is a figure which shows the dispersion liquid preparation apparatus which produces a dispersion liquid using a graphite-type carbon raw material as a precursor. It is a figure which shows the dispersion | distribution state of the dispersion liquid produced using the graphite-type carbon raw material of the sample 1 manufactured by the sample 1 which shows the comparative example, and the manufacturing apparatus B of Example 1. FIG. It is a TEM imaging figure of the graphite type carbon material (graphene) dispersed in the dispersion. It is a figure which shows the distribution state of the graphite type | system | group carbon material disperse | distributed to the dispersion liquid produced using the graphite type carbon material (precursor) of the sample 5, (a) is distribution of average size, (b) is the number of layers. FIG. It is a figure which shows the distribution state of the graphite type | system | group carbon material disperse | distributed to the dispersion liquid created using the graphite type | system | group carbon material of the sample 1 which shows a comparative example, (a) is distribution of average size, (b) is the number of layers. FIG. It is a figure which shows distribution of the number of layers of the graphite-type carbon raw material disperse | distributed to the dispersion liquid created using the sample 1-7 as a precursor. It is a figure which shows the ratio of the graphene of 10 layers or less with respect to the content rate of the rhombohedral crystal | crystallization dispersed in the dispersion liquid. It is a figure which shows the distribution state of the graphite at the time of changing the conditions which produce a dispersion liquid using the graphite-type carbon raw material (precursor) of the sample 5 of Example 2, (a) is an ultrasonic treatment and a microwave treatment. (B) is a figure which shows distribution of the number of layers at the time of carrying out an ultrasonic treatment. It is a figure which shows resistance value when the graphite-type carbon raw material of Example 3 is disperse | distributed to conductive ink. It is a figure which shows the tensile strength when the graphite-type carbon raw material of Example 4 is knead | mixed with resin.

  The present invention focuses on the crystal structure of graphite, and matters relating to this crystal structure will be described first. It is known that natural graphite is classified into three types of crystal structures, hexagonal, rhombohedral and disordered, depending on how the layers overlap. As shown in FIG. 1, the hexagonal crystal has a crystal structure in which layers are stacked in the order of ABABAB ··, and the rhombohedral crystal has a crystal structure in which layers are stacked in the order of ABCABCABC ···.

Natural graphite has almost no rhombohedral crystals at the stage of excavation, but is crushed and the like at the purification stage. Therefore, about 14% of rhombohedral crystals are present in a general natural graphite-based carbon material. In addition, it is known that the rhombohedral crystal ratio converges at about 30% even when crushing during purification is performed for a long time (Non-Patent Documents 1 and 2).
In addition to the physical force such as crushing, there is known a method in which graphite is expanded by heating to make a flake, but even if the graphite is heated to 1600 K (about 1300 degrees Celsius), the rhombohedral crystal is used. The ratio is about 25%. (Non-Patent Document 3). Furthermore, even when an extremely high temperature of 3000 degrees Celsius is applied, the temperature is about 30% (Non-patent Document 2).
Thus, it is possible to increase the ratio of rhombohedral crystals by treating natural graphite with physical force or heat, but the upper limit is about 30%.

  Hexagonal crystal (2H), which is abundant in natural graphite, is very stable, and the van der Waals force between the graphene layers is represented by (Equation 3) (Patent Document 2). By applying energy exceeding this force, graphene peels off. The energy required for exfoliation is inversely proportional to the cube of the thickness, so graphene exfoliates with weak physical force such as ultrasonic waves in a very thin state where the layers are infinitely thick. To do so, a very large amount of energy is required. In other words, even if the graphite is treated for a long time, only the weak part of the surface peels off, and the majority remains unpeeled.

Fvdw = H · A / (6π · t3) (Equation 3)
Fvdw: Van der Waals force
H: Hamaker constant
A: Surface area of graphite or graphene
t: Graphite or graphene thickness

  The inventors of the present application give a ratio of rhombohedral crystals (3R) that is increased only to about 30% by pulverization or heating to an ultra-high temperature by performing a predetermined treatment as shown below on natural graphite. We succeeded in increasing to more than%. When the content of rhombohedral crystals (3R) of the graphite-based carbon material is increased, particularly when the content is 40% or more, the use of this graphite-based carbon material as a precursor tends to cause exfoliation to graphene. As a result of experiments and research, it was obtained as a knowledge that graphene solutions with high concentration and high dispersion can be easily obtained. This is because when a rhombohedral crystal (3R) is subjected to a shearing force, distortion occurs between the layers, that is, the distortion of the entire graphite structure increases, and it does not depend on the van der Waals force and easily peels off. It is thought that it is to become. For this reason, in the present invention, graphene is easily exfoliated by applying a predetermined treatment to natural graphite, and a graphite-based carbon material capable of highly dispersing or dispersing graphene is referred to as a graphene precursor. In Examples, a graphene precursor manufacturing method showing a predetermined treatment, a graphene precursor crystal structure, and a graphene dispersion using the graphene precursor will be described in this order.

Here, in this specification, graphene is a crystal having an average size of 100 nm or more, is not a microcrystal having an average size of several nm to several tens of nm, and is a flaky or sheet-shaped graphene having 10 or less layers Say.
Since graphene is a crystal having an average size of 100 nm or more, artificial graphite and carbon black, which are amorphous (microcrystalline) carbon materials other than natural graphite, do not yield graphene even when they are processed ( Non-patent document 4).
Further, in this specification, the graphene composite is a graphite-based carbon material used as the graphene precursor according to the present invention, that is, a graphite-based carbon material having a Rate (3R) of 40% or more (for example, a sample of Example 1 described later) 4-7) means the composite prepared.

  Hereinafter, examples for carrying out a graphite-based carbon material used as a graphene precursor according to the present invention and a method for producing the same will be described.

<About the production of graphite-based carbon materials used as graphene precursors>
A method for obtaining a graphitic carbon material used as a graphene precursor by the manufacturing apparatus A using a jet mill and plasma shown in FIG. 3 will be described. The manufacturing apparatus A exemplifies a case where plasma is applied as a process by radio wave force and a jet mill is used as a process by physical force.

  In FIG. 3, reference numeral 1 denotes a natural graphite material having a particle size of 5 mm or less (scale graphite ACB-50 manufactured by Nippon Graphite Industry), 2 a hopper containing the natural graphite material 1, and 3 a natural graphite material 1 injected from the hopper 2 Venturi nozzle 4, jet mill for injecting air pumped from the compressor 5 into 8 locations and causing the natural graphite material to collide with the chamber by jet jet, 7 for oxygen, argon, nitrogen, hydrogen, etc. from the tank 6 Is a plasma generator that generates a plasma in the chamber of the jet mill 4 by injecting a gas 9 from the nozzle 8 and applying a voltage from a high voltage power source 10 to a coil 11 wound around the outer periphery of the nozzle 8. There are 4 places inside. 13 is a pipe connecting the jet mill 4 and the dust collector 14, 14 is a dust collector, 15 is a collecting container, 16 is a graphite-based carbon material (graphene precursor), and 17 is a blower.

Next, a manufacturing method will be described. The conditions of the jet mill and the plasma are as follows.
The conditions of the jet mill are as follows.
Pressure: 0.5 MPa
Air volume: 2.8m3 / min
Nozzle inner diameter: 12mm
Flow velocity: about 410m / s
The plasma conditions are as follows.
Output: 15W
Voltage: 8kV
Gas type: Ar (purity 99.999 Vol%)
Gas flow rate: 5L / min

  The natural graphite material 1 put into the chamber of the jet mill 4 from the venturi nozzle 3 is accelerated in the chamber at a speed higher than the speed of sound, and is pulverized by the impact of hitting the natural graphite materials 1 and the walls, and at the same time, the plasma 12 is natural. By discharging or exciting the graphite material 1, it is considered that it directly acts on atoms (electrons), increases the distortion of the crystal and promotes pulverization. When the natural graphite material 1 becomes a fine powder to a certain particle size (about 1 to 10 μm), the mass is reduced and the centrifugal force is weakened, so that the natural graphite material 1 is sucked out from the pipe 13 connected to the center of the chamber.

  The gas mixed with the graphite-based carbon material (graphene precursor) flowing into the cylindrical container of the chamber of the dust collector 14 from the pipe 13 becomes a swirling flow, and the graphite-based carbon material 16 colliding with the inner wall of the container is collected below. While being dropped into the container 15, an upward air flow is generated at the center of the chamber by the tapered container portion below the chamber, and the gas is exhausted from the blower 17 (so-called cyclone action). According to the manufacturing apparatus A in this example, a graphite-based carbon material (graphene precursor) 16 used as a graphene precursor of about 800 g was obtained from 1 kg of natural graphite material 1 as a raw material (recovery efficiency: about 80%) ).

  Next, a method for obtaining a graphite-based carbon material used as a graphene precursor by the manufacturing apparatus B using the ball mill and the microwave shown in FIG. 4 will be described. The manufacturing apparatus B uses a case where a microwave is applied as a process using radio wave force and a ball mill is used as a process using physical force.

  4 (a) and 4 (b), reference numeral 20 is a ball mill, 21 is a microwave generator (magnetron), 22 is a waveguide, 23 is a microwave inlet, 24 is a medium, and 25 is a particle of 5 mm or less. Natural graphite material (scale graphite ACB-50 manufactured by Nippon Graphite Industries Co., Ltd.), 26 is a collection container, 27 is a filter, and 28 is a graphite-based carbon material (graphene precursor).

Next, a manufacturing method will be described. The conditions of the ball mill and the microwave generator are as follows.
The conditions of the ball mill are as follows.
Rotation speed: 30rpm
Media size: φ5mm
Media type: Zirconia balls Grinding time: 3 hours The conditions of the microwave generator (magnetron) are as follows.
Output: 300W
Frequency: 2.45 GHz
Irradiation method: Intermittent

  1 kg of natural graphite-based carbon raw material 25 and 800 g of media 24 are put into the chamber of the ball mill 20, the chamber is closed, and the treatment is performed at a rotation speed of 30 rpm for 3 hours. During this process, the chamber is irradiated with microwaves intermittently (20 seconds every 10 minutes). It is considered that this microwave irradiation directly acts on the raw material atoms (electrons) to increase crystal distortion. After the treatment, the media 24 is removed by the filter 27, whereby the graphite-based carbon material (precursor) 28 having a powder size of about 10 μm can be collected in the collection container 26.

<X-ray diffraction profile of graphite-based carbon material (precursor)>
Referring to FIGS. 5 to 7, a graphite-based natural graphite material (sample 6, sample 5) manufactured by manufacturing apparatuses A and B and a graphite system of about 10 μm powder obtained using only the ball mill of manufacturing apparatus B The X-ray diffraction profile and crystal structure of a natural material (Sample 1: Comparative Example) will be described. According to the X-ray diffractometry (sample horizontal multipurpose X-ray diffractometer Ultima IV, manufactured by Rigaku Corporation), each sample is composed of hexagonal crystal 2H face (100), face (002), face (101), and rhombohedron, respectively. Since the peak intensities P1, P2, P3, and P4 are shown on the surface (101) of the crystal 3R, these will be described.

As shown in FIG. 5 and Table 1, the sample 5 manufactured by the manufacturing apparatus B that performs the processing by the ball mill and the microwave processing has a high ratio of the peak intensity P3 and the peak intensity P1, and P3 and P4 of P3. The Rate (3R) defined by (Equation 1) indicating the ratio to the sum of is 46%. The intensity ratio P1 / P2 was 0.012.
Rate (3R) = P3 / (P3 + P4) × 100 (Equation 1)
here,
P1 is peak intensity of (100) plane of hexagonal graphite layer (2H) by X-ray diffraction method P2 is peak intensity of (002) plane of hexagonal graphite layer (2H) by X-ray diffraction method P3 is rhomboid (4) is the peak intensity of the (101) plane of the hexagonal graphite layer (2H) by the X-ray diffraction method.

  Similarly, the sample 6 manufactured by the manufacturing apparatus A that performs the processing by the jet mill and the processing by the plasma has a high ratio of the peak intensity P3 and the peak intensity P1, as shown in FIG. (3R) was 51%. The intensity ratio P1 / P2 was 0.014.

  Further, as shown in FIG. 7 and Table 3, the sample 1 showing the comparative example manufactured only by the ball mill has a smaller peak intensity P3 than the samples 5 and 6, and the rate (3R) is 23. %Met. The intensity ratio P1 / P2 was 0.008.

Thus, in Sample 5 manufactured by the manufacturing apparatus B of Example 1 and Sample 6 manufactured by the manufacturing apparatus A of Example 1, Rate (3R) is 46% and 51%, which are shown in FIG. It was shown to be 40% or more or 50% or more compared with natural graphite or Sample 1 showing a comparative example.
Next, using the graphene precursor produced above, a graphene dispersion was prepared, and the ease of peeling of the graphene was compared.

<About graphene dispersion>
A method for preparing the graphene dispersion will be described with reference to FIG. FIG. 8 shows an example in which ultrasonic treatment and microwave treatment are used in combination when preparing a graphene dispersion.
(1) 0.2 g of graphite-based carbon material used as a graphene precursor and 200 ml of N-methylpyrrolidone (NMP) which is a dispersion are put into a beaker 40.
(2) The beaker 40 is put into the chamber 42 of the microwave generator 43, and the ultrasonic transducer 44A of the ultrasonic horn 44 is inserted into the dispersion 41 from above.
(3) The ultrasonic horn 44 is operated and 20 kHz (100 W) ultrasonic waves are continuously applied for 3 hours.
(4) While the ultrasonic horn 44 is operated, the microwave generator 43 is operated to apply microwave 2.45 GHz (300 W) intermittently (irradiation every 5 minutes for 10 seconds).

FIG. 9 shows that the graphene dispersion prepared as described above has passed 24 hours.
It was confirmed that the graphene dispersion 30 using the sample 5 manufactured by the manufacturing apparatus B was partially precipitated but the whole was black. This is considered that many of the graphite-based carbon materials used as the graphene precursor are dispersed in a state of being separated from the graphene.
It was confirmed that in the dispersion liquid 31 using the sample 1 showing the comparative example, most of the graphite-based carbon material is precipitated, and a part thereof is floating as a supernatant liquid. From this, it is considered that a small part peels off to graphene and floats as a supernatant.

  In addition, the graphene dispersion prepared as described above is diluted and applied to an observable concentration on a data base (TEM grid), dried, and shown in FIG. 10 of a transmission electron microscope (TEM). The size and number of layers of graphene were observed from various captured images. In addition, about the sample 1, what diluted and apply | coated the supernatant liquid was used. For example, in the case of FIG. 10, the size is about 600 nm, which is the maximum length L of the flake 33 from FIG. 10A, and the number of layers from FIG. 10B is the number of layers by observing the end face of the flake 33 and counting the overlap of the graphene layers 6 layers (region indicated by reference numeral 34). In this way, the size and the number of layers of each flake (the number of flakes is N) were measured, and the number and size of the graphene layers shown in FIGS. 11 and 12 were obtained.

Referring to FIG. 11A, the particle size distribution (size distribution) of flaky flakes contained in the graphene dispersion of sample 5 (Rate (R3) is 46%) manufactured by the manufacturing apparatus B of Example 1 ) Was a distribution having a peak at 0.5 μm. Moreover, in FIG.11 (b), the number of layers was distribution with the peak of 3 layers and graphene of 10 layers or less becoming 68%.
Referring to FIG. 12, the particle size distribution (size distribution) of flaky flakes contained in the dispersion of Sample 1 of Comparative Example (Rate (R3) is 23%) is a distribution having a peak at 0.9 μm. Met. Further, the number of layers was a distribution in which most of the layers were 30 layers or more, and the graphene of 10 layers or less was 10%.
From this result, when the sample 5 manufactured by the manufacturing apparatus B is used as a graphene precursor, there are many graphenes of 10 layers or less, excellent dispersibility of graphene, and high concentration graphene dispersion. I found that it was obtained.

  Next, with reference to FIG. 13, the relationship between the ratio Rate (3R) of the graphene precursor and the number of layers in the graphene dispersion will be described. Samples 1, 5, and 6 in FIG. 13 are as described above. Samples 2, 3, and 4 are manufactured by a manufacturing apparatus B that performs processing by a ball mill and microwave processing, and graphene using a graphene precursor that is manufactured with a shorter microwave irradiation time than Sample 5 is used. A dispersion is prepared. Sample 7 was manufactured by a manufacturing apparatus A that performs processing by a jet mill and plasma processing, and a graphene dispersion was prepared using a graphene precursor that was manufactured by applying plasma with a higher output than sample 6. Is.

  From FIG. 13, Sample 4-7 in which Rate (3R) is 40% or more has a so-called log-normal distribution shape in which the shape of the layer number distribution has a peak at a portion of several layers (thin graphene). On the other hand, Sample 1-3 having a Rate (3R) of less than 40% has a shape having a peak at a portion where the number of layers is 30 or more (dispersed liquid using Sample 1) or a shape close to a normal distribution (Samples 2, 3). Using a dispersion liquid). That is, it can be seen that when the Rate (3R) is 40% or more, the shape of the distribution of the number of layers tends to be clearly different from less than 40%. The ratio of graphene in 10 layers or less is 38% for the rate (3R) of the dispersion using the sample 3, whereas the rate (3R) for the dispersion using the sample 4 is 62%. It can be seen that when the Rate (3R) is 40% or more, the proportion of graphene in 10 layers or less is rapidly increasing.

  From these facts, when Rate (3R) is 40% or more, it becomes easy to peel off to graphene of 10 layers or less, and further, as Rate (3R) increases to 50% and 60%, graphene of 10 layers or less Furthermore, it becomes easier to peel off, and conversely, if it is less than 40%, it is considered difficult to peel off to 10 layers or less of graphene. Further, when focusing on the intensity ratio P1 / P2, Sample 2 to Sample 7 have values within a relatively narrow range of 0.012 to 0.016, and the crystal structure is distorted and easily peeled off from graphene. Since it exceeds 0.01 considered, all are preferable.

  Further, FIG. 14 shows the result of comparison between Rate (3R) and the ratio of containing 10 layers or less of graphene. Referring to FIG. 14, when the rate (3R) is 25% or more, the graphene of 10 layers or less begins to increase (inclined to the right), and the graphene of 10 layers or less rapidly increases around 40% ( The ratio of graphene in 10 layers or less is 38% for the rate (3R) of the dispersion using the sample 3, whereas the rate (3R) for the dispersion using the sample 4 is 62%. 3R) increased by 4%, the proportion of graphene in 10 layers or less rapidly increased so as to increase by 24%), and it was found that 10% or less of graphene accounted for 50% or more of the total. Note that the black square points in FIG. 14 are different samples, and the above-described sample 1-7 and other samples are also included.

  From this, when a graphene dispersion is prepared using a sample having a Rate (3R) of 40% or more as a graphene precursor, 10% or less of graphene is produced by 50% or more. That is, a graphene dispersion with a high concentration and high dispersion of graphene can be obtained. Further, as described above, since the graphite-based carbon material (precursor) contained in this dispersion hardly precipitates, a dark graphene dispersion can be easily obtained. By this method, a graphene dispersion having a graphene concentration exceeding 10% could be prepared without concentration. Although the rate of dispersion of graphene of 10 layers or less is small, less than 50%, the rate (3R) of 25% or more and less than 40% is preferable from the viewpoint of increasing the rate of dispersion of graphene of 10 layers or less. .

  In addition, the upper limit of Rate (3R) is 40% or more, and it is not necessary to define it in particular. However, when creating a dispersion liquid or the like, the strength ratio R1 / R2 should satisfy 0.01 or more at the same time. It is preferable because it is easily separated into graphene. In addition, in the case of the manufacturing method using the manufacturing apparatuses A and B, the upper limit is about 70% from the viewpoint that the graphene precursor is easily manufactured. In addition, the method using the treatment with the jet mill of the manufacturing apparatus A and the plasma treatment in combination is more preferable because a product having a high Rate (3R) can be easily obtained. Note that it is only necessary that the rate (3R) is 40% or more by combining the processing by physical force and the processing by radio wave force.

In Example 1, the case of using ultrasonic treatment and microwave treatment in combination when obtaining the graphene dispersion was described. However, in Example 2, only ultrasonic treatment was performed and microwave treatment was not performed. Other conditions are the same as in the first embodiment.
FIG. 15B shows the distribution of the number of layers of the graphene dispersion obtained by subjecting the graphene precursor of Sample 5 (Rate (3R) = 46%) manufactured by the manufacturing apparatus B to ultrasonic treatment. 15A is the same as the distribution shown in FIG. 11B of the sample 5 manufactured by the manufacturing apparatus B of the first embodiment.
As a result, the distribution tendency of the number of layers is almost the same, but the proportion of graphene of 10 layers or less is 64%, which is a little lower than that of 68% in Example 1. From this, it has been found that it is more effective to perform two processes of physical force and radio wave force simultaneously when preparing the graphene dispersion.

In Example 3, an example used for conductive ink will be described.
Sample 1 of Example 1 (Rate (3R) = 23%), Sample 3 (Rate (3R) = 38%), Sample 5 (Rate (3R) = 46%), Sample 6 (Rate (3R) = 51%) ) Is a graphene precursor, and INK1, INK3, INK5, and INK6 are prepared in a mixed solution of water and an alcohol having a carbon number of 3 or less, which is a conductivity-imparting agent, and the respective resistance values are set. Compared. From this result, as the Rate (3R) becomes higher, the resistance value becomes lower.

In Example 4, an example of kneading into a resin will be described.
When creating a resin sheet in which graphene was dispersed, the tensile strength of the glass fiber added was very good, and the cause was investigated. The compatibilizer added simultaneously with the glass fiber was converted into graphene precursor. It was found as a finding that it contributes to Then, what mixed the dispersing agent and the compatibilizing agent with resin was examined.
Sample 1 of Example 1 (Rate (3R) = 46%) was added as a precursor to 1 wt% directly to LLDPE (polyethylene), and a share (stepping force) was applied using a kneader or a twin-screw kneader (extruder). While kneading.
Since it is known that the tensile strength increases when graphitic carbon material is graphenized and highly dispersed in the resin, the degree of grapheneization and dispersion can be inferred relatively by measuring the tensile strength of the resin. Can do. The tensile strength was measured with a desktop precision universal testing machine (AUTOGRAPH AGS-J) manufactured by Shimadzu Corporation under the condition of a test speed of 500 mm / min.

In addition, in order to compare grapheneization and dispersibility with and without additives, the following three types (a), (b), and (c) were compared.
(A) No additive (b) General dispersant (zinc stearate)
(C) Compatibilizer (graft-modified polymer)

A result is demonstrated with reference to FIG. 17 which shows a measurement result. In FIG. 17, the circle marks are resin materials using the sample 1 of the comparative example, and the square marks are resin materials using the sample 5 of the first embodiment.
When the additive (a) was not added, the difference in tensile strength was small.
It can be seen that when the dispersant (b) is added, the graphene precursor of Sample 5 is accelerated to some extent by graphene.
When the compatibilizer (c) is added, the graphene precursor of Sample 5 is found to be considerably accelerated in graphene formation. This is because it is considered that the compatibilizer acts to peel off the graphene layer combination when the graphene layer combination and the resin are combined and the shear is added in that state in addition to the effect of dispersing graphene. .

  Although zinc stearate has been described as an example of the dispersing agent, it is preferable to select one having properties suitable for the compound. For example, examples of the dispersant include an anionic (anionic) surfactant, a cationic (cationic) surfactant, a zwitterionic surfactant, and a nonionic (nonionic) surfactant. Particularly for graphene, anionic surfactants and nonionic surfactants are preferred. More preferably, it is a nonionic surfactant. Nonionic surfactants are surfactants that do not dissociate into ions, such as sugar chains such as oxyethylene groups, hydroxyl groups, and glucosides, and are hydrophilic by hydrogen bonding with water. However, there is a merit that it can be used in a nonpolar solvent. Then, by changing the hydrophilic group chain length, the property can be freely changed from lipophilic to hydrophilic. As the anionic surfactant, an X acid salt (X acid is, for example, cholic acid or deoxycholic acid), for example, SDC: sodium deoxycholate, phosphate ester, or the like is preferable. Further, as the nonionic surfactant, glycerin fatty acid ester, sorbitan fatty acid ester, fatty alcohol ethoxylate, polyoxyethylene alkylphenyl ether, alkyl glycoside and the like are preferable.

  In the above-described Example 1-4, the manufacturing apparatus A that uses a jet mill and plasma and the manufacturing apparatus B that uses a ball mill and a microwave have been described as manufacturing apparatuses that manufacture the graphene precursor. Precursor with a high ratio Rate (R3) when combined with treatments using electromagnetic forces such as plasma, electromagnetic induction heating (IH), and magnetic fields, and treatments using physical forces such as ball mill, jet mill, centrifugal force, and supercritical force Is preferable. In addition, the process by physical force and the process by radio wave force are used together, and the type of individual process of the process by physical force and the process by radio wave force does not matter. In particular, as in the manufacturing apparatuses A and B, it is preferable that the action due to the radio wave force and the physical force is simultaneously applied, but the radio wave force and the physical force are alternately applied at predetermined intervals. Also good. Further, regarding the radio wave force, for example, different radio wave forces such as a process using microwaves and plasma may be alternately applied, and in parallel therewith, a process using one or more physical forces may be performed. As for physical force, for example, different physical forces such as jet mill and supercritical processing may be alternately applied, and in parallel therewith, processing by one or two or more radio forces may be performed.

  In the above-described embodiments, the preparation apparatus using microwaves and ultrasonic waves has been described as the preparation apparatus for obtaining the graphene dispersion using the precursor. However, microwaves, millimeter waves, plasma, electromagnetic induction heating (IH) It is preferable to use a combination of a treatment with a radio wave force such as a magnetic field and a treatment with a physical force such as an ultrasonic wave, a ball mill, a jet mill, a centrifugal force, or a supercritical force because a graphene dispersion with a high graphene concentration can be obtained. In particular, it is preferable that the action of the radio wave force and the physical force be applied simultaneously as in the creation device, but the radio wave force and the physical force may be applied alternately at predetermined intervals.

  In the above-described examples, the graphene dispersion, the conductive ink, and the resin molded product have been described as applications using the precursor, but as a base material, a monomer, a polymer, another carbon material, ceramics, wood, cement, You may obtain a graphene composite by mixing a precursor in composite base materials, such as a metal. That is, in this specification, a graphene composite means what includes the graphene dispersion liquid, conductive ink, and resin molding which were mentioned above. Further, the graphene dispersion includes a paste having a high viscosity.

For example, the following are mentioned as a liquid and a base material which disperse | distribute a precursor.
As resins, polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), ABS resin (ABS), acrylic resin (PMMA), polyamide / nylon (PA), polyacetal (POM), polycarbonate (PC), polyethylene terephthalate (PET), cyclic polyolefin (COP), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyamideimide (PAI), thermoplastic polyimide (PI), Examples include polyetheretherketone (PEEK) and liquid crystal polymer (LCP). Among the synthetic resins, thermoplastic resins such as epoxy resin (EP), phenol resin (PF), melamine resin (MF), polyurethane (PUR), unsaturated polyester resin (UP), and the like are used as thermosetting resins. Nylon, polyester, acrylic, vinylon, polyolefin, polyurethane, rayon and other fibers, and isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR) as elastomers Thermosetting resin-based elastomers such as polyisobutylene rubber / butyl rubber (IIR), ethylene propylene rubber (EPM / EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), epichlorohydrin rubber (CO / ECO), etc. one Urethane rubber (U), silicone rubber (Q), and fluorine rubber (FKM), thermal styrenic as thermoplastic elastomers, olefin-based, vinyl chloride-based, urethane-based, elastomers amide.

Examples of mineral oils include lubricating oils and greases, and examples of rubber compounding oils include paraffinic mineral oils, naphthenic mineral oils, and aromatic mineral oils.
Furthermore, as nonpolar sources, hexane, benzene, toluene, chloroform, ethyl acetate, etc., polar aprotic compounds such as acetone, N, N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), Examples of polar protic compounds such as acetonitrile include acetic acid, ethanol, methanol, water, 1-butanol, 2-propanol, and formic acid.

  In addition, as a natural graphite for producing a graphitic carbon material used as a graphene precursor, a natural graphite material having a particle size of 5 mm or less (scale graphite ACB-50 manufactured by Nippon Graphite Industry Co., Ltd.) has been described as an example. Graphite is flaky graphite and is pulverized to 5 mm or less, and is preferable from the viewpoint that a rate (3R) of less than 25% and a strength ratio P1 / P2 of less than 0.01 are easily available.

The following can be cited as examples of functionalization with graphene by adding a precursor to an object.
・ Additives for polymer materials such as resin, rubber and paint ・ Additives for heat dissipation sheets, conductive sheets, heat dissipation tapes and conductive tapes ・ Sintered metallurgy added to metal powder and sintered ・ Ceramics such as lithium oxide and nanoclay Additives ・ Additives for non-metallic and non-polymeric materials such as concrete

Examples of the graphene dispersion liquid include the following.
・ Lithium-ion battery electrode agent, conductive auxiliary agent, discharge capacity improver, charge / discharge efficiency improver ・ Electrode for capacitor products, conductive agent for electrolyte and conductive ink

DESCRIPTION OF SYMBOLS 1 Natural graphite material 4 Jet mill 7 Plasma generator 16 Graphite type carbon material 20 used as a graphene precursor 20 Ball mill 21 Microwave generator 24 Media 25 Natural graphite material 28 Graphite type carbon material 30 used as a graphene precursor Graphene dispersion 31 used Graphene dispersion 33 using document 1 Flakes 40 Beaker 41 Graphene dispersion 43 Microwave generator 44 Ultrasonic generator

Claims (1)

It has a rhombohedral graphite layer (3R) and a hexagonal graphite layer (2H), and an X-ray diffraction method of the rhombohedral graphite layer (3R) and the hexagonal graphite layer (2H). A graphite-based carbon material used as a graphene precursor, wherein a rate Rate (3R) defined by the following (formula 1) is 31% or more.
Rate (3R) = P3 / (P3 + P4) × 100 (Equation 1)
here,
P3 is the peak intensity of the (101) plane of the rhombohedral graphite layer (3R) by X-ray diffraction method P4 is the peak intensity of the (101) plane of the hexagonal graphite layer (2H) by X-ray diffraction method.