KR102229179B1 - 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

The carbon nanotube-coated graphite powder manufacturing method according to the present invention,
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: and
And a third step of mixing graphite with a functional group and carbon nanotubes with a cationic surfactant, and coating the carbon nanotubes with the cationic surfactant on the surface of the graphite with the functional group. .

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 carbon nanotube-coated graphite powder manufacturing method and a thermally conductive composite material including the carbon nanotube-coated graphite powder.

Graphite powder is known as a material having high thermal conductivity while having an inexpensive price, and is therefore used as a main filler for components requiring thermal conductivity and heat dissipation or heat dissipation composite materials.

However, graphite has anisotropic characteristics (horizontal: ~2,000W/mK, vertical: ~5W/mK) in which the thermal conductivity varies greatly depending on the stacking direction, so the thermal conductivity of the graphite-polymer heat dissipating composite material is mixed. It tends to be very low compared to the thermal conductivity of the composite, which can be expected by the law of mixture.

In order to solve such anisotropic thermal conductivity, attempts have been made to coat graphite with a metal such as copper, nickel, tin, aluminum, etc. having a thermal conductivity higher than that of graphite in the vertical direction.

For this, electrochemical, physical and thermal methods are used.

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

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

In order to solve this problem, attempts have been made to use carbon nanotubes having excellent thermal conductivity together with graphite as a filler for a thermally conductive composite material. However, in this case, the dispersion of the carbon nanotubes is not good, the interface contact force between 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 carbon nanotube-coated graphite powder manufacturing method and a thermally conductive composite material including the carbon nanotube-coated graphite powder capable of solving all of the above-described problems.

The 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;

The second step of attaching a cationic surfactant to the surface of the carbon nanotubes: and

And a third step of mixing graphite with a functional group and carbon nanotubes with a cationic surfactant, and coating the carbon nanotubes with the cationic surfactant on the surface of the graphite with the functional group. .

In addition, the above purpose,

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 carbon nanotubes

A third step of mixing graphite to which a functional group is attached and 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; And

It is achieved by the carbon nanotube-coated graphite powder manufacturing method comprising 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 including graphite powder coated with carbon nanotubes manufactured by the above-described methods.

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

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

1 is a flow chart showing a method of manufacturing graphite powder coated with carbon nanotubes according to a first embodiment of the present invention.
FIG. 2 is an electron micrograph taken by magnifying a sample before and after coating carbon nanotubes on graphite by 50,000 times. FIG. 2(a) is an electron micrograph taken of graphite before and after the carbon nanotubes were coated, and FIG. 2(b) ) Is an electron micrograph of graphite coated with carbon nanotubes according to Example 1, and FIG. 2(c) is an electron micrograph of graphite coated with carbon nanotubes according to Example 2, and FIG. 2 (d) is an electron micrograph taken of a state in which carbon nanotubes are coated on graphite according to Example 3.
3 is a flowchart showing a method of manufacturing graphite powder coated with carbon nanotubes according to a second embodiment of the present invention.
4 is a table comparing the thermal conductivity of thermally conductive composites manufactured according to Examples and Comparative Examples of the present invention.

Hereinafter, a method of manufacturing 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 (S12) of attaching a cationic surfactant to the surface of the carbon nanotubes;

It consists of a third step (S13) of mixing graphite to which a functional group is attached and 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.

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

Hereinafter, the first step (S11) will be described.

Graphite is immersed in a solution capable of attaching a functional group of 500 degrees or more to oxidize the surface of the graphite, and the functional group is attached to the surface of the graphite.

The solution is a substance capable of reacting with graphite and attaching functional groups to the graphite surface.

The solution may be one or more selected from the group consisting of pure water, basic aqueous solution, acidic aqueous solution, alcohol including ethanol, methanol, and a solution in which a compound including oxygen capable of oxidizing graphite is dissolved. Of course, it is not limited thereto.

Hereinafter, the second step (S12) will be described.

Cationic surfactants are substances that can be attached to carbon nanotubes in the tail and the middle while the head is ionized to +.

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

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

Hereinafter, the third step (S13) will be described.

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

The carbon nanotubes 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 based on the weight part of graphite to which the functional group is attached. Of course, it is not limited thereto.

[Example 1]

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

Carbon nanotubes have a diameter of 10-20 nm, and graphite is in the form of a powder with a size of 40 μm.

Put 40g of carbon nanotubes and 3.5L distilled water in a 5L bucket, disperse for 2 hours at 6000 RPM using a homogenizer, and filter.

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

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

50 g of oxidized graphite and 1000 ml of water are placed in a 5 L bucket, 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, 1.5 g of carbon nanotubes and 1000 ml of distilled water containing 1.5 g of cetyltrimethylammonium bromide (CTAB), a cationic surfactant, are 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 for 12 hours at 120 degrees. Then, the carbon nanotubes are coated on the graphite shown in FIG. 2(a), and graphite powder coated with carbon nanotubes having a carbon nanotube content of 3% compared to the graphite shown in FIG. 2(b) is prepared.

[Example 2]

In 1000 ml of an aqueous solution in which 50 g of oxidized graphite is dispersed so that the weight ratio of the graphite coated on the carbon nanotubes is 6:100 (the content of carbon nanotubes relative to graphite is 6%), 3 g of carbon nanotubes and CTAB (cetyltrimethylammonium), a cationic surfactant. Bromide) 3g of distilled water containing 2000ml is mixed. Then, the carbon nanotubes are coated on the graphite shown in FIG. 2(a), and graphite powder coated with carbon nanotubes having a content of 6% carbon nanotubes compared to the graphite shown in FIG. 2(c) is prepared. Other procedures are the same as in Example 1.

[Example 3]

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

Hereinafter, a method of manufacturing 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 (S22) of attaching a cationic surfactant to the surface of the carbon nanotubes;

A third step (S23) of mixing graphite to which a functional group is attached and 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;

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

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

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

Hereinafter, the fourth step (S24) will be described.

Metals having a thermal conductivity of 50 W/mK or more, such as copper, nickel, iron, and aluminum, are electrolessly plated on the carbon nanotube-coated graphite powder.

[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 graphite powder coated with carbon nanotubes is added to 250 ml of a plating solution in which a 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°C for 120 minutes, filtering and washing, and then drying at 120°C for 12 hours. Then, it is possible to obtain graphite powder coated with copper-plated carbon nanotubes.

[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 graphite powder coated with carbon nanotubes is added to 250 ml of a plating solution in which a 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°C for 240 minutes, filtering and washing, and then drying at 120°C for 12 hours. Then, it is possible to obtain graphite powder coated with copper-plated carbon nanotubes.

Hereinafter, the thermal conductivity of the composite material including the carbon nanotube-coated graphite powder manufactured by the method of the first and second embodiments of the present invention will be described. To this end, a thermally conductive composite specimen 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 according to Example 1, a composite specimen in which the weight of the carbon nanotube-coated graphite powder is 60% of the total weight of the composite material. To manufacture.

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

Carbon nanotube-coated graphite powder is added to the polyamide ethanol solution, mixed with a magnetic stirrer for 30 minutes, and then put in cold water to harden.

After drying, it is compression molded to 800kgf at 170°C using a hot press.

As shown in FIG. 4, the thermal conductivity of the composite specimen prepared by the method of Example 6 was 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 according to Example 2, a composite sample in which the weight of the carbon nanotube-coated graphite powder is 60% of the total weight of the composite material. To manufacture. The method of manufacturing the composite specimen is the same as in Example 6.

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

[Example 8]

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

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

[Example 9]

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

As shown in FIG. 4, the thermal conductivity of the composite specimen prepared by the method of Example 9 was 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 according to Example 5, a composite sample in which the weight of the carbon nanotube-coated graphite powder is 60% of the total weight of the composite material. 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 10 was found to be 9.15 W / mK.

[Comparative Example 1] A composite specimen containing no carbon nanotubes and only graphite powder in different sizes

Composite specimens for measuring thermal conductivity were prepared with graphite having a powder size of 5 μm, 10 μm, and 20 μm to which no carbon nanotubes were added, and the content of graphite powder was 60 wt%. To this end, a 10% polyamide ethanol solution is first prepared using polyamide (Elvamide-8602, DuPont) soluble in ethanol. Here, graphite powder is mixed with a magnetic stirrer for 30 minutes so that it becomes 40%, 50%, and 60% of the total weight of the composite material, and then put in cold water to harden. After drying, it is compression molded to 800kgf at 170°C using a hot press.

According to the graphite powder size, three composite specimens for measuring thermal conductivity are made.

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

As shown in FIG. 4, the thermal conductivity of the composite specimen containing graphite having a powder size of 5 μm to which no carbon nanotubes were 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 to which no carbon nanotubes were 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 to which no carbon nanotubes were added was 2.13 W/mK.

[Comparative Example 2] A composite specimen containing no carbon nanotubes and only graphite powder with different contents

Composite specimens for measuring thermal conductivity of 40 wt%, 50 wt%, and 60 wt% of graphite powder were prepared with graphite having a powder size of 40 μm to which no carbon nanotubes were added. The manufacturing method is the same as in Comparative Example 1.

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

As shown in FIG. 4, the thermal conductivity of the composite specimen containing 40wt% of graphite having a powder size of 40um to which no carbon nanotubes were added was 1.98W/mK.

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

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

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

Carbon nanotubes and graphite powder are each 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 10-20 nm, and graphite is in the form of a powder with a size of 40 μm.

Put 40g of carbon nanotubes and 3.5L of distilled water into a 5L bucket, pulverize for 2 hours at 6000 RPM using a homogenizer, and then filter. 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 (700W, bar-type).

50g of oxidized graphite and 1000ml of water were put in a 5L bucket, and mixed at 500 RPM with a homogeneous disperser.

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 nanotubes: graphite = 3:100), 2000 ml (carbon nanotubes: graphite = 6:100), 3000ml (carbon nanotubes: graphite = 9:100) was added, mixed for about 30 minutes, filtered, and dried at 120 degrees for 12 hours.

A composite specimen was prepared to measure the thermal conductivity of a simple mixture of carbon nanotubes and graphite. A 10% polyamide ethanol solution was prepared using ethanol-soluble polyamide (Elvamide-8602, DuPont). The graphite powder was mixed with a magnetic stirrer for 30 minutes so that the total weight of the composite material was 60%, and then put in cold water to harden. After drying, it is compression molded to 800kgf at 170°C using a hot press.

According to the content of carbon nanotubes compared to graphite, three composite specimens for measuring thermal conductivity are made.

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

As shown in FIG. 4, the thermal conductivity of the composite specimen obtained by simply mixing 3% carbon nanotubes compared to graphite and 60 wt% of 40 μm graphite was found to be 3.41 W/mK.

As shown in FIG. 4, the thermal conductivity of the composite specimen obtained by simply mixing 6% carbon nanotubes compared to graphite and 60 wt% of 40 μm graphite was found to be 3.63 W/mK.

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

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

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

Claims (6)

delete delete delete delete To a solution capable of attaching one or more functional groups selected from the group consisting of a solution in which an alcohol containing pure water, a basic aqueous solution, an acidic aqueous solution, ethanol, methanol, and a compound containing oxygen capable of oxidizing graphite is dissolved, A first step of soaking the graphite powder, oxidizing the surface of the graphite powder, and attaching a functional group to the surface of the graphite powder;
In the group of aliphatic amine salts and quaternary ammonium salts including compounds such as primary amine salts (DDAC), secondary and tertiary amine salts, quaternary ammonium salts (EQ), imidazole salts, polyoxyethylenealkylamines and pyridinium-type compounds A second step of attaching the selected cationic surfactant to the surface of the carbon nanotubes;
Graphite powder with functional groups attached to the surface and carbon nanotubes with cationic surfactant attached to the surface are mixed with a physical homogenizer, mixed with an ultrasonic mixer, dried after filtering, or spray dried, A third step of mixing by filtering a rotary drum to coat the surface of the graphite powder having a functional group attached thereto, and coating a carbon nanotube having a cationic surfactant attached thereto; And
A method for producing carbon nanotube-coated graphite powder comprising a fourth step of electroless plating a metal having a thermal conductivity of 50 W/mK or more on the carbon nanotube-coated graphite powder. delete

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