KR20160131660A - Method for preparation of graphene - Google Patents

Abstract

The present invention relates to a preparation method of graphene using high pressure homogenization process. According to the present invention, graphene having a large area can be prepared with excellent efficiency. The preparation method of graphene comprises a step of passing a feed solution including graphite through a high pressure homogenizer including an inlet part, an outlet part, and a microchannel which connects the inlet part and the outlet part, and having a micrometer-scale diameter. The feed solution is injected to the inlet part of the high pressure homogenizer under the pressure of 400-2000 bar, and passes through the microchannel.

Description

Method for preparation of graphene [0002]

The present invention relates to a method for producing graphene using a high pressure homogenization process.

Graphene is a semimetallic material with a thickness corresponding to the carbon atomic layer, with the carbon atoms forming a hexagonally connected arrangement in two dimensions on the sp2 bond. Recently, evaluation of the characteristics of a graphene sheet having a carbon atom layer of one layer has revealed that the electron mobility is about 50,000 cm 2 / Vs or more and can exhibit very excellent electric conductivity.

Graphene also has structural, chemical stability and excellent thermal conductivity characteristics. In addition, it is easy to process one- or two-dimensional nanopatterns composed of carbon, which is a relatively light element. Graphene is expected to replace silicon-based semiconductor technology and transparent electrodes due to its electrical, structural, chemical, and economic properties, and it is expected to be applicable to flexible electronic devices due to its excellent mechanical properties.

Due to the many advantages and excellent properties of such graphenes, various methods have been proposed or studied to more effectively produce graphene from carbon-based materials such as graphite. Particularly, there have been various studies on a method for easily producing a graphene sheet or flake having a thinner thickness and a larger area so that excellent characteristics of graphene can be more dramatically developed. Such conventional methods of producing graphene include the following.

First, a method of peeling a graphene sheet from graphite by a physical method such as using a tape is known. However, this method is not suitable for mass production methods, and the peeling yield is also very low.

There is known a method for obtaining graphene or an oxide thereof which is peeled off from an intercalation compound in which an acid, a base, a metal or the like is interposed between carbon layers of graphite, or by peeling by a chemical method such as oxidizing graphite.

However, in the former method, a large number of defects may be generated on the finally produced graphene in the process of oxidizing the graphite to proceed the exfoliation and reducing the graphene oxide obtained therefrom to obtain graphene again. This may adversely affect the properties of the final produced graphene. In addition, the latter method requires additional processes such as using and treating an intercalation compound, which may complicate the overall process, resulting in a low yield and a low cost. Further, in this method, it is not easy to obtain a large-area graphene sheet or flake.

Recently, a method of producing graphene by separating carbon layers contained in graphite by ultrasonic irradiation or a milling method using a ball mill or the like has been applied most recently in the state where graphite or the like is dispersed in a liquid state. However, these methods have also been problematic in that it is difficult to obtain graphene having a sufficiently thin thickness and a large area, a large number of defects are formed on the graphene in the peeling process, or the yield of peeling is insufficient. Recently, studies have been reported on the preparation of few-layer graphene by stripping graphite using a high-speed homogenizer (HSH), but the HSH method still has problems in terms of dispersion, peel stability and mass-productivity.

As a result, there is a continuing need for a manufacturing method capable of easily producing a graphene sheet or flake having a thinner thickness and a larger area with higher yield. Particularly, a uniform large-area graphene sheet is very advantageous for manifesting graphene-specific characteristics by reducing the contact resistance between graphenes. Such graphenes can be re-dispersed in various solvents and can be used for various applications such as conductive paste compositions, conductive ink compositions, compositions for forming heat radiation substrates, electroconductive composites, composites for EMI containers, conductive materials for batteries, or slurries.

As a graphite peeling method, graphene having an average thickness of 10 to 20 nm in a single process through an impact generated by applying a controlled high pressure to a μ-channel structure and a strong shear force generated in a μ-channel (HPH), which is capable of producing graphite, is considered to be an effective graphite peeling method.

Accordingly, the inventors of the present invention have conducted intensive studies to increase the efficiency of peeling of graphite by HPH.

The present invention is to provide a method for producing graphene capable of producing graphene having a large area with excellent efficiency by using high pressure homogenization.

In order to solve the above problems, the present invention provides a feed solution containing graphite, comprising an inlet, an outlet, and a high-pressure homogenizer including a microchannel having a micrometer scale diameter and connecting between the inlet and outlet, Wherein the feed solution flows into the inlet portion of the high pressure homogenizer under a pressure of 400 to 2000 bar and passes through the microfluidic channel.

Hereinafter, the present invention will be described in detail.

Graphite

The term "graphite" used in the present invention refers to a material which is also called graphite or talc and belongs to a hexagonal system having a crystal structure such as quartz, and is a material having a black color and metallic luster. The graphite has a plate-like structure. A single layer of graphite is called "graphene" to be produced in the present invention, and thus graphite becomes the main raw material for the production of graphene.

In order to peel off graphene from the graphite, it is necessary to apply energy to overcome the pi-pi interaction between the stacked graphenes. In the present invention, the high-pressure homogenization method is used as described later. On the other hand, in order to improve the peeling efficiency of the high-pressure homogenization, it is preferable that the interlayer spacing of graphite is wider than that of pure graphite. Expansion graphite can be used for this purpose in the present invention.

As used herein, the term " expanding graphite " refers to graphite having a wider spacing than the interlayer spacing of pure graphite. Examples of the expanded graphite include thermally expanded graphite, modified graphite in which an intercalation compound is inserted between carbon layers, partially oxidized graphite, and edge functionalized graphene. Also, the expanded graphite has a tap density of 0.01 to 0.5 g / cm 3 and a BET (surface area) of 5 to 50 m 2 / g. The degree of expansion is obtained by putting a certain amount of powder sample into a graduated cylinder, inputting the number of taps, operating the cylinder, reading the scale of the cylinder, and dividing the mass of the powder by the final apparent volume of the powder when the volume change is within 2% Can be measured. In addition, BET can measure the surface area by measuring the amount of nitrogen gas adsorbed by adsorbing nitrogen gas on the powder surface and calculating by BET equation. At this time, the adsorption amount of the nitrogen gas can be measured by changing the pressure of the vacuum chamber while changing the pressure of the nitrogen gas at a given temperature.

Feed  solution

The term " feed solution " used in the present invention means a solution containing the graphite, which is introduced into a high-pressure homogenizer to be described later.

The concentration of the graphite in the feed solution is preferably 0.5 to 5 wt%. If the amount is less than 0.5% by weight, the concentration is too low to deteriorate the graphene peeling efficiency. If the amount is more than 5% by weight, the concentration may be excessively high, thereby blocking the flow path of the high-pressure homogenizer.

Further, a dispersant may be used to increase the degree of dispersion of the graphite in the feed solution. The dispersants act to maintain their dispersed state mediated by hydrophobic graphite, delaminated graphite or graphene due to their amphiphilic nature, and are also referred to as surfactants in other terms. As the dispersing agent, any dispersant may be used as long as it is used for graphene peeling, and an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. Specific examples thereof include pyrene-based low molecular weight derivatives; Cellulosic polymers; Cationic surfactants; Anionic surfactants; Gum arabic; n-Dodecyl bD-maltoside; Amphoteric surfactants; Polyvinylpyrrolidone type polymers; Polyethylene oxide type polymers; Ethylene oxide-propylene oxide copolymer; Tannic acid; Or a mixture of plural kinds of polyaromatic hydrocarbon oxides, which contains a polyaromatic hydrocarbon oxide having a molecular weight of 300 to 1000 in an amount of 60 wt% or more.

The weight ratio of the graphite and the dispersant is preferably 2.5 to 20. When the content is less than 2.5, the content of graphite is too low to detach the peeling efficiency. When the content exceeds 20, the content of the dispersing agent is too low and the effect of dispersing graphite deteriorates. More preferably, the weight ratio of the graphite and the dispersant is 2.5 to 5. [

The solvent of the feed solution can be selected from the group consisting of water, N-methyl-2-pyrrolidone, acetone, N, N-dimethylformamide, DMSO, CHP, N-dodecyl-pyrrolidone ), Benzyl benzoate, N-octyl-pyrrolidone, dimethyl-imidazolidinone, cyclohexanone, dimethylacetamide, NMF (N-Methyl Formamide), bromobenzene, chloroform, chlorobenzene, benzonitrile , Quinoline, benzyl ether, ethanol, isopropyl alcohol, methanol, butanol, 2-ethoxyethanol, 2-butoxyethanol, 2-methoxypropanol, tetrahydrofuran (THF), ethylene glycol, , Methyl ethyl ketone (butanone), alpha-terpineol, formic acid, ethyl acetate and acrylonitrile may be used.

High pressure Homogenization

Homogenizing the feed solution at high pressure to peel the graphene from the graphite in the feed solution.

The term 'high pressure homogenization' means applying a high pressure to a micro-channel having a micrometer scale diameter to apply a strong shear force to the material passing through it. Typically, high pressure homogenization is performed using a high pressure homogenizer including an inlet, an outlet, and a microchannel connecting between the inlet and outlet and having a micrometer scale diameter.

Particularly, in the present invention, the graphene produced has an average particle size of 1 to 20 mu m, preferably 2 to 10 mu m, and the feed solution is applied at a pressure of 400 to 2000 bar, preferably 600 to 1600 bar Pressure homogenizer and passes the microfluidic channel through the inlet of the high-pressure homogenizer under pressure. Above 2000 bar there is a problem that the average particle size of graphene becomes too small and below 400 bar the average particle size of graphene becomes too large and the particle size among graphene particles is not uniform.

Further, it is preferable that the fine flow path has a diameter of 10 to 800 탆.

Further, the feed solution that has passed through the microchannel can be reintroduced into the inlet of the high-pressure homogenizer, so that the graphene can be further peeled off.

The recycling process may be repeated 2 to 20 times. The reintroduction process can be carried out repeatedly using the high-pressure homogenizer used or using a plurality of high-pressure homogenizers. In addition, the re-inputting process may be performed separately or sequentially. Preferably, it is preferable to repeat the process until the average particle size of the graphene is 1 to 20 mu m, preferably 2 to 10 mu m. Here, the 'laterial size' of the graphene is defined as the longest distance among straight lines connecting two arbitrary points on the plane of each particle when each particle of the graphene is viewed on a plane having the widest area can do.

On the other hand, a step of recovering and drying graphene from the graphene dispersion recovered in the outlet may be further included. The recovering step may be carried out by centrifugation, vacuum filtration or pressure filtration. The drying step may be performed by vacuum drying at a temperature of about 30 to 200 ° C.

The graphene thus prepared may be redispersed in various solvents and used for various purposes. The graphene can be applied to a conventional paste such as a conductive paste composition, a conductive ink composition, a composition for forming a heat dissipation substrate, an electroconductive composite, an EMI chassis composite, a conductive material for a battery, or a slurry.

The present invention is characterized in that graphene having a large area can be produced with excellent efficiency by using high pressure homogenization.

Figure 1 shows an SEM image of graphene in a graphene dispersion prepared in an embodiment of the present invention.
Figure 2 shows an SEM image of graphene in a graphene dispersion prepared in an embodiment of the present invention.
Figure 3 shows a TEM image of graphene in a graphene dispersion prepared in an embodiment of the present invention.
FIG. 4 shows the result of analyzing the particle size of graphene in the graphene dispersion prepared in one embodiment of the present invention.
FIG. 5 shows the results of analyzing the particle size of graphene in the graphene dispersion prepared in one embodiment of the present invention.
Figure 6 shows the sheet resistance results of the film according to the graphene particle size of the graphene dispersion prepared in one embodiment of the present invention.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments are shown to facilitate understanding of the present invention. However, the following examples are intended to illustrate the present invention without limiting it thereto.

Example  One

One) Example  1-1

2.5 g of graphite (BNB90: expanded graphite (more pressed)) and 1 g of PVP58k (polyvinylpyrrolidone, weight average molecular weight: 58 k) as a dispersant were mixed with 500 g of distilled water to prepare a feed solution.

The feed solution was fed to the inlet of the high pressure homogenizer. The high pressure homogenizer has a structure including an inlet portion of the raw material, an outlet portion of the peeled product, and a microchannel connecting the inlet portion and the outlet portion and having a micrometer scale diameter.

A high pressure of 400 bar was applied through the inlet to feed the feed solution and a high shear force was applied while passing a fine flow path having a diameter of 75 mu m. The feed solution recovered to the outlet was reintroduced into the inlet of the high pressure homogenizer and the high pressure homogenization process was repeated. The graphene dispersion was repeated until the high pressure homogenization process was repeated 15 times.

2) Example  1-2 to 1-5

The pressure in the high pressure homogenizer was changed from 600 bar (Example 1-2), 800 bar (Example 1-3), 1200 bar (Examples 1-4 ) And 1600 bar (Examples 1-5), a graphene dispersion was prepared.

3) SEM  Image observation

The graphene grains in the graphene dispersions prepared in Examples 1-1 to 1-5 were observed with an SEM image, and the results are shown in FIG.

1 (b) to 1 (f) are graphs showing the graphite homogenization process without performing the high-pressure homogenization process. FIG. 1 (a) 1 (g) and 1 (h) show graphene prepared by performing the high-pressure homogenization process 15 times in each of Examples 1-1 and 1-2, respectively.

As shown in Figs. 1 (a) to 1 (f), it was observed that the particle size of graphene became smaller as the high-pressure homogenization pressure was increased. However, the surface roughness of graphene was slightly higher at low pressures (400 and 600 bar), but it was confirmed that the surface roughness was improved when the high pressure homogenization process was performed 10 times (FIGS. 1 (g) and 1 (h)).

Example  2

One) Example  2-1

2.5 g of graphite (C-therm011: expanded graphite (less pressed)) and 1 g of PVP58k (polyvinylpyrrolidone, weight average molecular weight: 58 k) as a dispersant were mixed with 500 g of distilled water to prepare a feed solution.

The feed solution was fed to the inlet of the high pressure homogenizer. The high pressure homogenizer has a structure including an inlet portion of the raw material, an outlet portion of the peeled product, and a microchannel connecting the inlet portion and the outlet portion and having a micrometer scale diameter.

A high pressure of 600 bar was applied through the inlet to feed the feed solution and a high shear force was applied while passing a fine flow path having a diameter of 75 mu m. The feed solution recovered to the outlet was reintroduced into the inlet of the high pressure homogenizer and the high pressure homogenization process was repeated. The graphene dispersion was repeated until the high pressure homogenization process was repeated 20 times in total.

2) Example  2-2 to 2-3

Except that the pressure in the high-pressure homogenizer was changed from 1100 bar (Example 2-2) to 1600 bar (Example 2-3) instead of 600 bar to prepare a graphene dispersion .

3) Example  2-4

The graphene dispersion was prepared in the same manner as in Example 2-1, except that EXP-60M (thermally expanded graphite) was used as the graphite.

4) Example  2-5

The graphene dispersion was prepared in the same manner as in Example 2-1, except that G50 (artificial graphite) was used as the graphite.

5) SEM  Image observation

The graphenes in the graphene dispersions prepared in Examples 2-1 to 2-5 were observed with an SEM image and the results are shown in Fig.

2 (a) and 2 (d) are graphs showing the graphite without the high-pressure homogenization process in Example 2-1, and FIGS. 2 (b) And the graphene produced by performing the process 10 times in total.

2 (e) shows the graphite without the high-pressure homogenization process in Example 2-4, and Figs. 2 (f) to 2 (h) (Fig. 2 (f)), 15 (Fig. 2 (g)) and 20 (Fig. 2 (h)).

2 (i) and 2 (k) show the graphite without the high-pressure homogenization process in Example 2-5, and the high-pressure homogenization process in Example 2-5 was performed 10 times 2 (j)) and 20 (Fig. 2 (k)).

As shown in Fig. 2, well-separated graphene was observed regardless of the type of graphite and the high-pressure homogenization pressure as a whole.

Example  3

In Examples 1-1 to 1-5, Example 2-1, Example 2-4, and Example 2-5, graphene obtained by performing high pressure homogenization process 10 times in total was observed with a TEM image, The results are shown in Fig.

As shown in Fig. 3, graphene that was well peeled in all the examples could be observed.

Example  4

In Examples 1-1 to 1-5, graphene particle size of the graphene dispersion prepared by performing the high-pressure homogenization process 10 times in total was analyzed, and the results are shown in FIG.

As shown in FIG. 4, the graphene particle size generally tends to decrease as the high-pressure homogenization pressure increases. In addition, the average particle size of graphene was similar to that of 600 bar and 800 bar, but it was confirmed that more uniform graphene was produced at 600 bar.

Example  5

In Examples 1-1 and 1-2, the graphene particle size of each of the prepared graphene dispersions was analyzed while performing the high-pressure homogenization process up to a total of 20 times. The results are shown in FIG.

As shown in FIG. 5, even when the total pressure of the homogenization process was 10 or more, the grains had an average grain size of 2 μm or more, and the grain size difference between graphenes was not large.

Example  6

In Examples 1-1 and 1-2, the sheet resistance of the graphene dispersion prepared according to the graphene particle size was shown in FIG.

As shown in FIG. 6, as the HPH driving pressure is lower, the size of the graphene flakes peeled is relatively large, which indicates that the use of the graphene flakes peeled leads to a decrease in sheet resistance during the production of the film.

Claims (10)

Passing a feed solution comprising graphite through an inlet, an outlet, and a high pressure homogenizer comprising a microchannel connecting between the inlet and outlet and having a micrometer scale diameter,
Wherein the feed solution flows into the inlet portion of the high-pressure homogenizer under pressure of 400 to 2000 bar and passes through the microchannel.
Graphene.
Wherein the graphite in the feed solution is peeled while passing through the fine flow path under application of a shear force to produce graphene.
Gt;
The method according to claim 1,
Characterized in that the concentration of graphite in the feed solution is from 0.5 to 5%
Gt;
The method according to claim 1,
Characterized in that the microchannel has a diameter of 10 to 800 mu m.
Gt;
The method according to claim 1,
Characterized in that the feed solution comprises a dispersing agent.
Gt;
The method according to claim 1,
The dispersant may be a pyrene-based low molecular weight material; Cellulosic polymers; Cationic surfactants; Anionic surfactants; Gum arabic; n-Dodecyl bD-maltoside; Amphoteric surfactants; Polyvinylpyrrolidone type polymers; Polyethylene oxide type polymers; Ethylene oxide-propylene oxide copolymer; Tannic acid; Or a mixture of plural kinds of polyaromatic hydrocarbon oxides, wherein the mixture contains a polyaromatic hydrocarbon oxide having a molecular weight of 300 to 1000 in an amount of not less than 60% by weight,
Gt;
6. The method of claim 5,
Wherein the content of the dispersing agent in the feed solution is 2 to 50% by weight based on the weight of the graphite.
Gt;
The method according to claim 1,
The solvent of the feed solution can be selected from the group consisting of water, N-methyl-2-pyrrolidone, acetone, N, N-dimethylformamide, DMSO, CHP, N-dodecyl-pyrrolidone ), Benzyl benzoate, N-octyl-pyrrolidone, dimethyl-imidazolidinone, cyclohexanone, dimethylacetamide, NMF (N-Methyl Formamide), bromobenzene, chloroform, chlorobenzene, benzonitrile , Quinoline, benzyl ether, ethanol, isopropyl alcohol, methanol, butanol, 2-ethoxyethanol, 2-butoxyethanol, 2-methoxypropanol, tetrahydrofuran (THF), ethylene glycol, , Methyl ethyl ketone (butanone), alpha-terpineol, formic acid, ethyl acetate and acrylonitrile.
Gt;
The method according to claim 1,
And the step of passing the recovered material recovered from the outlet to the high-pressure homogenizer is repeatedly performed one to 19 times.
Gt;
The method according to claim 1,
Characterized in that the graphene produced has a laterial size of from 1 to 20 mu m.
Gt;

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