KR20200076173A - Method for manufacturing the graphite powders coated by carbon nanotube and thermal conducting composite materials containing the graphite powders coated by carbon nanotube - Google Patents

Abstract

A method for manufacturing graphite powders coated with carbon nanotubes according to the present invention includes: a first step of attaching a functional group to the surface of graphite; a second step of attaching a cationic surfactant to the surface of carbon nanotubes; and a third step of mixing graphite to which a functional group is attached and the carbon nanotubes to which a cationic surfactant is attached, and coating the carbon nanotubes to which the cationic surfactant is attached to the surface of the graphite to which the functional group is attached.

Description

Method for manufacturing the graphite powders coated by carbon nanotube and thermal conducting composite materials containing the graphite powders coated by carbon nanotube}

The present invention relates to a method for manufacturing a graphite powder coated with carbon nanotubes and a thermally conductive composite material including a graphite powder coated with carbon nanotubes.

Graphite powder is known as a material having low cost and high thermal conductivity, and has been used as a main filler for components requiring heat conductivity and heat dissipation or heat dissipation composite materials.

However, graphite has anisotropic characteristics (horizontal: ~2,000W/mK, vertical: ~5W/mK) where the thermal conductivity is significantly different depending on the stacked direction, and the thermal conductivity of the graphite-polymer heat dissipation composite material is mixed. It shows a tendency to appear very low compared to the thermal conductivity of the composites, which can be expected by (law of mixture).

To solve this anisotropic thermal conductivity, attempts have been made to coat graphite with metals such as copper, nickel, tin, aluminum, etc., which have higher thermal conductivity than the vertical thermal conductivity of graphite.

To this end, electrochemical, physical and thermal methods are used.

The electrochemical method can achieve uniform coating and mass production, but has the disadvantage of generating high thermal resistance between polymer and graphite due to low interfacial wettability with metal-graphite.

On the other hand, the coating by methods such as physical (sputter, etc.) and thermal (thermal evaporator, etc.) has high interfacial adhesion with metal-graphite, but it is difficult to produce uniform coating and mass production, and has a high manufacturing cost.

In order to solve this problem, attempts have been made to use carbon nanotubes having excellent thermal conductivity as a thermally conductive composite filler with graphite. However, in this case, the dispersion of the carbon nanotubes is poor, and the interface contact force between the graphite and the carbon nanotubes and the interface contact force between the carbon nanotubes are very low, so it is difficult to expect an improvement in the thermal conductivity of the composite material.

Korean Registered Patent (10-1274441)

An object of the present invention is to provide a thermally conductive composite material including a carbon nanotube coated graphite powder manufacturing method and a carbon nanotube coated graphite powder that can solve all the above-mentioned problems.

Carbon nanotube-coated graphite powder manufacturing method for achieving the above object,

A first step of attaching a functional group to the surface of graphite;

A second step of attaching a cationic surfactant to the surface of the carbon nanotube: and

And a third step of mixing the functionalized graphite and the carbon nanotube to which the cationic surfactant is attached, and coating the carbon nanotube to which the cationic surfactant is attached to the graphite surface to which the functional group is attached. .

In addition, the above object,

A first step of attaching a functional group to the surface of graphite;

The second step of attaching a cationic surfactant to the surface of the carbon nanotube

A third step of mixing the functionalized graphite and the carbon nanotube to which the cationic surfactant is attached, and coating the carbon nanotube to which the cationic surfactant is attached to the graphite surface to which the functional group is attached; And

It is achieved by a carbon nanotube-coated graphite powder manufacturing method, characterized in that it comprises a fourth step of electroless plating a metal having a thermal conductivity of 50 W/mK or more on the carbon nanotube-coated graphite.

In addition, the above object is achieved by a thermally conductive composite material comprising graphite powder coated with carbon nanotubes prepared by the above-described methods.

In the present invention, carbon nanotubes are attached to the surface of graphite by coulomb interaction to prepare graphite coated with carbon nanotubes. Here, a metal having a thermal conductivity of 50 W/mK or more may be electroless plated.

When the composite is made by including the carbon nanotube-coated graphite in this way, the thermal conductivity of graphite in the composite in the vertical direction of the plate is improved. For this reason, the thermal interface resistance and the electrical contact resistance between graphite materials are reduced, and both the thermal conductivity and electrical conductivity of the composite material are improved.

1 is a flowchart illustrating a method for manufacturing a graphite powder coated with carbon nanotubes according to a first embodiment of the present invention.
Figure 2 is an electron micrograph of the sample before and after coating the carbon nanotubes on graphite magnified 50,000 times, Figure 2 (a) is an electron micrograph of graphite before the carbon nanotubes are coated, Figure 2 (b ) Is an electron micrograph of carbon nanotubes coated on graphite according to Example 1, FIG. 2(c) is an electron micrograph of carbon nanotubes coated on graphite according to Example 2, FIG. 2 (d) is an electron micrograph of carbon nanotubes coated with graphite according to Example 3.
3 is a flow chart showing a method for manufacturing a graphite powder coated with carbon nanotubes according to a second embodiment of the present invention.
Figure 4 is a table comparing the thermal conductivity of the thermally conductive composite prepared according to Examples and Comparative Examples of the present invention.

Hereinafter, a method for manufacturing a graphite powder coated with carbon nanotubes according to a first embodiment of the present invention will be described in detail.

As shown in Figure 1, the carbon nanotube coated graphite powder manufacturing method according to the first embodiment of the present invention,

A first step of attaching a functional group to the surface of graphite (S11);

A second step of attaching a cationic surfactant to the surface of the carbon nanotube (S12);

It is composed of a third step (S13) of mixing the functionalized graphite and the cationic surfactant-attached carbon nanotube and coating the functionalized graphite surface with the cationic surfactant-attached carbon nanotube.

Of course, the order of the first step (S11) and the second step (S12) can be changed.

Hereinafter, the first step S11 will be described.

The graphite is immersed in a solution capable of attaching a functional group of 500 degrees or more, and the surface of the graphite is oxidized to attach the functional group to the surface of the graphite.

The solution is a substance that can react with graphite and attach functional groups to the graphite surface.

The solution may be one or two or more selected from the group consisting of a solution containing a pure water, a basic aqueous solution, an acidic aqueous solution, an alcohol containing ethanol, methanol, and a compound containing oxygen capable of oxidizing graphite. Of course, it is not limited to this.

Hereinafter, the second step S12 will be described.

The cationic surfactant is a material that can be attached to the carbon nanotubes at the tail and the middle while the head is ionized with +.

The cationic surfactant may be added in an amount of 10 to 200 parts by weight based on parts by weight of carbon nanotubes.

Cationic surfactants include aliphatic amine salts including compounds such as primary amine salts (DDAC), secondary third/third amine salts, quaternary ammonium salts (EQ), imidazole salts, polyoxyethylenealkylamines, pyridinium types, and the like. It may be one or more selected from the group of quaternary ammonium salts. Of course, it is not limited to this.

The third step (S13) will be described below.

The functionalized graphite and the carbon nanotubes to which the cationic surfactant is attached are mixed with a physical homogenizer, mixed with an ultrasonic mixer, filtered and dried, spray dried, or rotary drum filtering. Thereby, the carbon nanotube to which the cationic surfactant is attached is coated on the surface of the graphite with a functional group attached.

The carbon nanotube to which the cationic surfactant is attached may be 0.1 to 50 parts by weight, 0.5 to 20 parts by weight, and 1 to 10 parts by weight relative to the weight part of graphite with a functional group attached. Of course, it is not limited to this.

[Example 1]

The graphite is coated with carbon nanotubes in the following order so that the weight ratio of the graphite coated on the carbon nanotubes is 3:100 (carbon nanotube content 3% compared to graphite).

Carbon nanotubes have a diameter of 10 to 20 nm, and graphite is a powder with a size of 40 um.

After placing the carbon nanotubes in 40 g and 3.5 L distilled water in a 5 L container, and dispersing for 2 hours at 6000 RPM using a homogenizer, filter.

After filtering, 1.5 g of carbon nanotubes and 1.5 g of cationic surfactant CTAB (cetyltrimethylammonium bromide) are mixed in 1000 ml of distilled water, and then dispersed with an ultrasonic disperser (700 W, bar-type) for 1 hour.

100 g of the graphite powder is oxidized for 30 minutes by CVD (chemical vapor deposition) at 650 degrees to recover about 97 g.

50 g of oxidized graphite and 1000 ml of water were placed in a 5 L container, and mixed at 500 RPM with a homogeneous disperser to obtain a dispersed aqueous solution.

To 1000 ml of an aqueous solution in which 50 g of oxidized graphite is dispersed, 1000 ml of distilled water containing 1.5 g of carbon nanotubes and 1.5 g of cationic surfactant CTAB (cetyltrimethylammonium bromide) is mixed. (Hereinafter referred to as “carbon nanotube solution”)

The carbon nanotube solution is further mixed for about 30 minutes with a homogenizer, filtered and dried at 120 degrees for 12 hours. Then, the carbon nanotubes are coated on the graphite shown in FIG. 2(a), and the graphite powder coated with the carbon nanotubes having a content of 3% of the carbon nanotubes compared to the graphite shown in FIG. 2(b) is prepared.

[Example 2]

To 1000 ml of an aqueous solution of 50 g of oxidized graphite dispersed so that the weight ratio of graphite coated on carbon nanotubes is 6:100 (6% of carbon nanotubes compared to graphite), 3 g of carbon nanotubes and cationic surfactant CTAB (cetyltrimethylammonium) bromide) Mix 2000 ml of distilled water containing 3 g. Then, the carbon nanotubes are coated on the graphite shown in FIG. 2(a), thereby preparing a graphite powder coated with carbon nanotubes having a content of 6% of the carbon nanotubes compared to the graphite shown in FIG. 2(c). The rest of the procedure is the same as in Example 1.

[Example 3]

To 1000 ml of an aqueous solution of 50 g of oxidized graphite dispersed so that the weight ratio of the graphite coated on the carbon nanotubes was 9:100 (9% of the carbon nanotubes compared to graphite), 4.5 g of carbon nanotubes and CTAB (cationic surfactant) cetyltrimethylammonium bromide) Mix 3000ml of distilled water containing 4.5g. Then, the carbon nanotubes are coated on the graphite shown in FIG. 2(a), and a graphite powder coated with the carbon nanotubes having a carbon nanotube content of 9% compared to the graphite shown in FIG. 2(d) is prepared. The rest of the procedure is the same as in Example 1.

Hereinafter, a method for manufacturing a graphite powder coated with carbon nanotubes according to a second embodiment of the present invention will be described in detail.

As shown in Figure 3, the carbon nanotube-coated graphite powder manufacturing method according to the second embodiment of the present invention,

A first step of attaching a functional group to the surface of graphite (S21);

A second step of attaching a cationic surfactant to the surface of the carbon nanotube (S22);

A third step of mixing the functionalized graphite and the cationic surfactant-attached carbon nanotube to coat the functionalized graphite surface with the cationic surfactant-attached carbon nanotube (S23);

It is composed of a fourth step (S24) of electroless plating a metal having a thermal conductivity of 50 W/mK or more on graphite coated with a carbon nanotube.

Of course, the order of the first step (S21) and the second step (S22) may be changed.

The first step (S21), the second step (S22), the third step (S23) in the carbon nanotube-coated graphite powder manufacturing method according to the second embodiment of the present invention is the first embodiment of the present invention. The carbon nanotube according to the first step (S11), the second step (S12), and the third step (S13) of the graphite powder manufacturing method are the same, so the description thereof will be omitted.

The fourth step (S24) will be described below.

The carbon nanotube coated graphite powder is electrolessly plated with a metal having a thermal conductivity of 50 W/mK or more, such as copper, nickel, iron, and aluminum.

[Example 4]

Copper coating was performed on the graphite powder coated with carbon nanotubes according to Example 2 by an electroless coating method. To this end, 20 g of the carbon nanotube-coated graphite powder is added to 250 ml of a plating solution in which copper metal salt is dissolved, and after mixing for 20 minutes, 200 ml of a plating solution containing a reducing agent is added. After mixing at 60 degrees for 120 minutes, filtering and washing, and drying at 120 degrees for 12 hours. Then, a graphite powder coated with copper-coated carbon nanotubes can be obtained.

[Example 5]

Copper coating was performed on the graphite powder coated with carbon nanotubes according to Example 2 by an electroless coating method. To this end, 20 g of the carbon nanotube-coated graphite powder is added to 250 ml of a plating solution in which copper metal salt is dissolved, and after mixing for 20 minutes, 200 ml of a plating solution containing a reducing agent is added. After mixing at 60 degrees for 240 minutes, filtering and washing, and drying at 120 degrees for 12 hours. Then, a graphite powder coated with copper-coated carbon nanotubes can be obtained.

Hereinafter, the thermal conductivity of the composite material including the graphite powder coated with the carbon nanotubes prepared by the method of the first and second embodiments of the present invention will be described. To this end, a sample of a thermally conductive composite material capable of measuring thermal conductivity is prepared.

[Example 6]

In order to measure the thermal conductivity of the thermally conductive composite material containing the carbon nanotube-coated graphite powder prepared in Example 1, a composite specimen having a carbon nanotube-coated graphite powder having a weight of 60% of the total weight of the composite material was prepared. To manufacture.

To this end, a 10% polyamide ethanol solution is prepared using polyamide (Elvamide-8602, DuPont) that is soluble in ethanol.

Carbon nanotube-coated graphite powder was added to the polyamide ethanol solution, and each was mixed for 30 minutes with a magnetic stirrer and then hardened by putting it in cold water.

After drying, compression molding is performed at 170 degrees to 800 kgf using a hot press.

As shown in Figure 4, the thermal conductivity of the composite specimen prepared by the method of Example 6 was found to be 5.51W / mK.

[Example 7]

In order to measure the thermal conductivity of the thermally conductive composite material containing the carbon nanotube-coated graphite powder prepared in Example 2, a composite specimen having a carbon nanotube-coated graphite powder weight of 60% of the total weight of the composite material was prepared. To manufacture. The method of manufacturing the composite specimen is the same as in Example 6.

As shown in Figure 4, the thermal conductivity of the composite specimen prepared by the method of Example 7 was found to be 7.12W / mK.

[Example 8]

In order to measure the thermal conductivity of the thermally conductive composite material containing the graphite powder coated with carbon nanotubes prepared in Example 3, a composite specimen having a carbon nanotube coated graphite powder having a weight of 60% of the total weight of the composite material was prepared. To manufacture. The method of manufacturing the composite specimen is the same as in Example 6.

4, the thermal conductivity of the composite specimen prepared by the method of Example 8 was 5.68 W/mK.

[Example 9]

In order to measure the thermal conductivity of the thermally conductive composite material containing the carbon nanotube-coated graphite powder prepared in Example 4, a composite specimen having a carbon nanotube-coated graphite powder weight of 60% of the total weight of the composite material was prepared. To manufacture. The method of manufacturing the composite specimen is the same as in Example 6.

As shown in Figure 4, the thermal conductivity of the composite specimen prepared by the method of Example 9 was found to be 8.62W / mK.

[Example 10]

In order to measure the thermal conductivity of the thermally conductive composite material containing the carbon nanotube-coated graphite powder prepared in Example 5, a composite specimen having a carbon nanotube-coated graphite powder weight of 60% of the total weight of the composite material was prepared. To manufacture. The method of manufacturing the composite specimen is the same as in Example 6.

4, the thermal conductivity of the composite specimen prepared by the method of Example 10 was 9.15 W/mK.

[Comparative Example 1] The carbon nanotubes are not mixed at all, and only the graphite powder is contained in different sized composite specimens.

Graphite having a powder size of 5 um, 10 um, and 20 um with no carbon nanotubes added at all, to prepare a composite specimen for measuring thermal conductivity with a graphite powder content of 60 wt%, respectively. To this end, a 10% polyamide ethanol solution is first prepared by using polyamide (Elvamide-8602, DuPont) soluble in ethanol. Here, the graphite powder is mixed with a magnetic stirrer for 30 minutes so as to be 40%, 50%, and 60% of the total weight of the composite material, and then hardened by putting it in cold water. After drying, compression molding is performed at 170 degrees to 800 kgf using a hot press.

Three composite specimens for thermal conductivity measurement are made according to the size of the graphite powder.

In accordance with the ASTM D5470 measurement standard, the vertical thermal conductivity of the composite specimen is measured.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing graphite having a powder size of 5 μm with no carbon nanotubes added was 1.46 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing graphite having a powder size of 10 μm with no carbon nanotubes added was 1.83 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing graphite having a powder size of 20 μm with no carbon nanotubes added was 2.13 W/mK.

[Comparative Example 2] The carbon nanotubes are not mixed at all, and only the graphite powder is contained in different contents.

Carbon nanotubes are not added at all, and graphite powder having a powder size of 40 μm is prepared, respectively, to prepare a composite specimen for measuring thermal conductivity with graphite powder content of 40 wt%, 50 wt%, and 60 wt%. The manufacturing method is the same as Comparative Example 1.

In accordance with the ASTM D5470 measurement standard, the vertical thermal conductivity of the composite specimen is measured.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing 40 wt% of graphite having a powder size of 40 μm without any addition of carbon nanotubes was 1.98 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing 50 wt% of graphite having a powder size of 40 μm with no carbon nanotubes added was 2.21 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen containing 60 wt% of graphite having a powder size of 40 μm with no carbon nanotubes added was 3.28 W/mK.

[Comparative Example 3] Carbon nanotubes and graphite powder, simply added composite specimens with different contents of carbon nanotubes

Carbon nanotubes and graphite powder are mixed in the following order so that the ratio of carbon nanotubes and graphite is 3:100, 6:100, and 9:100 by weight. Carbon nanotubes have a diameter of 10 to 20 nm, and graphite is a powder with a size of 40 um.

40 g of carbon nanotubes and 3.5 L of distilled water are placed in a 5 L container, crushed at 6000 RPM for 2 hours using a homogenizer, and filtered. Thereafter, 1.5 g of carbon nanotubes and 1.5 g of anionic surfactant NaDDBS were mixed with 1000 ml of water, respectively, and then dispersed for 2 hours using an ultrasonic disperser (700 W, bar-type).

50 g of oxidized graphite in a 5 L container and 1000 ml of water were added and mixed at 500 RPM with a homogenizer.

Here, an aqueous solution in which 1.5 g of carbon nanotubes and 1.5 g of anionic surfactant NaDDBS (anionic surfactant sodium dodecyl benzene sulfonate) are dispersed, 1000 ml (carbon nanotube: graphite = 3:100), 2000 ml (carbon nanotube: graphite = 6:100), 3000ml (carbon nanotube:graphite=9:100), mixed for about 30 minutes, filtered and dried at 120 degrees for 12 hours.

A composite specimen is prepared to measure the thermal conductivity of a composite in which carbon nanotubes and graphite are simply mixed. A 10% polyamide ethanol solution is prepared using soluble polyamide (Elvamide-8602, DuPont). Here, the graphite powder was mixed with a magnetic stirrer for 30 minutes so as to be 60% of the total weight of the composite material, and then hardened by putting it in cold water. After drying, compression molding is performed at 170 degrees to 800 kgf using a hot press.

Three composite specimens for thermal conductivity measurement are made according to the content of carbon nanotubes compared to graphite.

In accordance with the ASTM D5470 measurement standard, the vertical thermal conductivity of the composite specimen is measured.

As shown in FIG. 4, the thermal conductivity of the composite specimen in which 60 wt% of graphite with 3% of carbon nanotubes compared to graphite and 60 wt% of graphite was simply mixed was found to be 3.41 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen in which 60 wt% of graphite with 6% carbon nanotubes compared to graphite and 60 wt% of graphite was simply mixed was found to be 3.63 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen in which 60 wt% of graphite with 9% of carbon nanotubes compared to graphite and 60 wt% of 40 μm was simply mixed was found to be 3.57 W/mK.

Looking at Examples 6,7,8,9,10 and Comparative Examples 1,2,3 described above, the graphite coated with the carbon nanotubes is not compared with the case where the carbon nanotubes are not added or the carbon nanotubes are simply added. If included, it can be seen that the thermal conductivity of the composite material is high. Thermal conductivity is measured in Example 7 up to 7.12 Wm/K.

Furthermore, it can be seen that when the metal having high conductivity is plated on the graphite coated with carbon nanotubes, the thermal conductivity is higher. Thermal conductivity is measured in Example 10 up to 9.15 Wm/K.

Claims (6)

A first step of attaching a functional group to the surface of graphite;
A second step of attaching a cationic surfactant to the surface of the carbon nanotube: and
And mixing the functionalized graphite and the cationic surfactant-attached carbon nanotube, and coating the functionalized graphite surface with the cationic surfactant-attached carbon nanotube. Method for manufacturing graphite powder coated with carbon nanotubes. According to claim 1, In the first step,
The graphite is immersed in a solution capable of attaching a functional group of 500 degrees or more, oxidizes the surface of the graphite, and attaches the functional group to the surface of the graphite,
The solution is a material that can react with graphite to attach functional groups to the graphite surface,
Carbon nanotubes coated with one or two or more selected from the group consisting of a solution containing a pure water, a basic aqueous solution, an acidic aqueous solution, an alcohol containing ethanol, methanol and a compound containing oxygen capable of oxidizing graphite. Graphite powder manufacturing method. According to claim 1, In the second step,
The cationic surfactant, while the head is ionized to +, the tail and the middle portion is carbon nanotube coated graphite powder production method characterized in that the material that can be attached to the carbon nanotubes. According to claim 1, In the third step,
The functionalized graphite and the carbon nanotube to which the cationic surfactant is attached are mixed with a physical mixer, mixed with an ultrasonic mixer, filtered and dried, spray dried, or rotary drum filtering. By, the carbon nanotubes coated graphite powder manufacturing method, characterized in that for coating the carbon nanotubes with the cationic surfactant attached to the surface of the functional group attached graphite. A first step of attaching a functional group to the surface of graphite;
The second step of attaching a cationic surfactant to the surface of the carbon nanotube
A third step of mixing the functionalized graphite and the carbon nanotube to which the cationic surfactant is attached, and coating the carbon nanotube to which the cationic surfactant is attached to the graphite surface to which the functional group is attached; And
A method of manufacturing a graphite powder coated with carbon nanotubes, comprising the step of electrolessly plating a metal having a thermal conductivity of 50 W/mK or more onto graphite coated with carbon nanotubes. A thermally conductive composite material comprising graphite powder coated with carbon nanotubes prepared by the method of claim 1 or 5.

Images