KR20220148418A - Thermal conductive polymer composite and preparation method thereof - Google Patents

Abstract

The present invention relates to a thermally conductive polymer composite and to a manufacturing method thereof, and more specifically, to a thermally conductive polymer composite, which contains: a polymer resin; and a thermally conductive filler oriented in one direction within the polymer resin, wherein the thermally conductive filler may contain: graphite flakes having a functional group containing oxygen; and a magnetic coating layer formed on the surface of the graphite flakes.

Description

Thermal conductive polymer composite and preparation method thereof

The present invention relates to a thermally conductive polymer composite and a method for preparing the same.

Due to the recent technological development, electronic devices are gradually becoming lighter, thinner, smaller, and higher in performance. As electronic devices become highly direct, more heat is generated. There are various factors that cause failure of electronic devices. Among them, temperature failure is the most frequent. In the integrated device, resistance increases according to driving, and a rapid increase in thermal density occurs. The emitted heat generated by this causes not only the deterioration of the function of the electronic device, but also the malfunction of the peripheral device, the deterioration of the substrate, and the like. The most important factor affecting the lifespan and reliability of electronic components is efficient heat dissipation and dissipation. Research interest in a technology for controlling the emitted heat, which uses a lightweight material to effectively dissipate heat, is increasing.

Fields that require lightweight heat dissipation components include smartphones, tablet PCs, laptops, TVs, LEDs, and electric vehicles. Currently, in the case of smartphones, graphite film is used inside the device to solve the heat problem of the battery, and in the case of laptops, the central processing unit (CPU) generates the most heat, so the boron film is placed on the central processing unit (CPU). A motor that circulates the excess heat is installed to solve the heat problem. And in the case of the LED, the problem is solved by using a heat sink, which is a heat sink attached to a semiconductor device or the like to prevent temperature rise. In the case of electric vehicles, as various parts including batteries are installed, the weight of the vehicle increases, and technology development is underway to solve the heat generated by this. As described above, various methods and materials are used to solve the problem of heat generated by electronic devices, but various methods and materials are used to solve the heat problem, but it is difficult to completely solve the heat problem. Even now, the demand for lightweight and high heat dissipation materials in the automotive and electric/electronic industries is steadily increasing. Accordingly, the need for related research and technology development to prepare for the rapid growth of the lightweight and high heat dissipation material market is growing.

Meanwhile, in order to be used as a heat radiation source material for electronic devices, it should have a value of about 1 to 30 W/mK. Therefore, heat dissipation parts up to recently have mainly used metal and ceramic materials having excellent thermal conductivity, but have disadvantages in that formability is poor, weight is high, and manufacturing cost is high. The need for a light heat dissipation material with good formability that can compensate for these shortcomings is being raised. Heat-dissipating polymer composites are attracting attention as materials for heat-dissipating parts due to their advantages such as high moldability and low manufacturing cost.

Heat-dissipating polymer composite materials can improve thermal conductivity through the complexation of various types of thermally conductive fillers and polymer resins. Types of thermally conductive fillers include metals, ceramics, carbon-based fillers, and the like.

Although the metallic filler has high thermal conductivity, it is difficult to apply in a field requiring lightness, and problems such as thermal expansion occur. Ceramic-based fillers are currently commercially available, but have relatively low thermal conductivity compared to carbon-based fillers. Carbon-based fillers have a disadvantage in that they have poor insulation properties and are difficult to commercialize when used alone. However, these disadvantages can be overcome through complexation with polymers. In addition, due to the advantages of high thermal conductivity and light weight, it is attracting attention as a thermally conductive filler of a lightweight heat dissipation material.

As a related art, Korean Patent Laid-Open Publication No. 10-2018-0054223 discloses a method for manufacturing a graphene composite heat dissipation sheet, wherein graphene oxide flakes are added to a mixed solution containing a magnetic filler and a thermally conductive filler and stirred to produce graphene oxide. By preparing a fin solution, the heat dissipation property is improved by the magnetic filler and the heat dissipation sheet of the graphene composite material improved in heat conduction property by the heat conductive filler is provided.

The present inventors are a polymer composite containing graphite flakes as a thermally conductive filler, and by introducing a functional group containing oxygen partially at the edge of the graphite flakes to improve dispersibility without lowering thermal conductivity, and to the graphite flakes By coating magnetic particles and arranging them in one direction through the application of a magnetic field, a polymer composite capable of designing and adjusting a heat transfer path by improving heat dissipation and controlling the orientation to suit the purpose of use was developed and completed the present invention.

Republic of Korea Patent Publication No. 10-2018-0054223

In one aspect, the purpose

An object of the present invention is to provide a thermally conductive polymer composite and a method for manufacturing the same.

In order to achieve the above object,

In one aspect,

polymer resin; and

Including; a thermally conductive filler oriented in one direction in the polymer resin;

The thermally conductive filler,

graphite flakes having a functional group containing oxygen; and

A thermally conductive polymer composite comprising; a magnetic coating layer formed on the surface of the graphite flake is provided.

The graphite flake has an oxygen-containing functional group at an edge thereof.

The graphite flakes contain 30 to 40 atomic% oxygen.

The graphite flakes are electrochemically exfoliated graphite flakes having a thickness of 1 μm to 100 μm.

The magnetic coating layer may be made of a metal oxide having a magnetism, and the metal oxide having the magnetic property is Fe, Ni, Co, Al, Cr, Mo, Na, Ti, Cu, AuAg, Zn and their It may include one selected from the group consisting of combinations.

The polymer resin is polyacrylate, polymethacrylate, polystyrene, polyester, polyolefin, polyamide resin, polyimide, polyphenylene oxide, silicone resin, phenolic resin, epoxy resin, polyurethane, polyester resin, polyether -Ether ketone, polyphenylene sulfide, fluorine-containing polymer, polyvinyl chloride resin, PVB (polyvinyl butyral), PVA (polyvinyl alcohol), ethyl hydroxyethyl cellulose, polyaniline, polypyrrole, polyacetylene, polythiophene, It may be one selected from the group consisting of PEDOT (poly(3,4-ethylenedioxythiophene)) and combinations thereof.

As the polymer resin, it may be more preferable to use a hydrophilic polymer resin.

The thermally conductive polymer composite may include the graphite flakes and the polymer resin in a weight ratio of 1: 1 to 1: 20.

In another aspect,

forming a thermally conductive filler; and

and dispersing the thermally conductive filler in a mixed solution containing a polymer resin and then applying a magnetic field to orient the thermally conductive filler in one direction;

The step of forming the thermally conductive filler,

forming a functional group containing oxygen in the graphite flake; and

Forming a magnetic coating layer on the surface of the graphite flakes formed with the functional group containing oxygen;

The step of forming a functional group containing oxygen in the graphite flake,

The oxygen-containing functional group is partially formed at the edge of the graphite flake.

The step of forming a functional group containing oxygen in the graphite flake,

dispersing the graphite flakes in a sulfuric acid solution;

adding potassium permanganate to the sulfuric acid solution; and

It may include; adding hydrogen peroxide to the sulfuric acid solution to which potassium permanganate is added.

The step of forming the magnetic coating layer,

It may include; mixing the graphite flakes in which the functional group containing oxygen is formed in the solution with a metal oxide having magnetism or a precursor material of the metal oxide.

The step of orienting the thermally conductive filler in one direction may further include a curing step.

In another aspect,

A heat dissipation sheet comprising the thermally conductive polymer composite is provided.

In another aspect,

There is provided a method of manufacturing a heat dissipation sheet comprising; coating the thermally conductive polymer composite on a substrate.

The thermally conductive polymer composite according to one aspect includes thermally conductive fillers arranged in one direction, has remarkably excellent thermal conductivity, and can be manufactured at a low cost, and thus has high economic efficiency.

In addition, the thermally conductive polymer composite according to one aspect has an advantage in that the thermally conductive filler is disposed inside the polymer resin, so that it has excellent thermal conductivity and excellent insulation, adhesion, and moldability.

Accordingly, the thermally conductive polymer composite according to one aspect may be applied to various electronic devices requiring heat dissipation characteristics, such as notebooks, mobiles, TVs, and LEDs.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a schematic diagram schematically showing a method for manufacturing a thermally conductive polymer composite according to an embodiment;
2 is a schematic diagram schematically showing the step of forming the thermally conductive filler,
3 and 4 are particle size distribution diagrams of exfoliated graphite (EEG) and graphite oxide (GO) prepared by Preparation Example 1,
5 is a graph of XRD results of exfoliated graphite (EEG);
6 is a graph comparing the XRD results of exfoliated graphite (EEG) and graphite oxide (GO) prepared by Preparation Example 1,
7 and 8 are I _D /I _G intensity ratio distribution graphs obtained from Raman analysis of exfoliated graphite (EEG) and graphite oxide (GO) prepared by Preparation Example 1,
9 is a photograph observed by SEM of graphite (EEG) and graphite oxide (GO) prepared by Preparation Example 1,
10 is a graph showing the results of XPS analysis of graphite (EEG) and graphite oxide (GO) prepared in Preparation Example 1;
11 is a graph showing the results of TGA analysis of graphite (EEG) and graphite oxide (GO) prepared in Preparation Example 1;
12 is a photograph observing the magnetic properties of the graphite oxide (GO) prepared in Preparation Example 1 and the graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (mEEG) prepared in Preparation Example 2;
13 is a graph of XRD analysis results of graphite oxide (GO) prepared in Preparation Example 1 and graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (mEEG) prepared in Preparation Example 2;
14 is a photograph observed by SEM of the graphite oxide (GO) prepared in Preparation Example 1 and the graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (mEEG) prepared in Preparation Example 2;
15 is a graph showing the results of TGA analysis of the graphite oxide (GO) prepared in Preparation Example 1 and the graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (mEEG) prepared in Preparation Example 2;
16 is a schematic view schematically showing the orientation degree evaluation method of the polymer composite prepared in Example 1 and Comparative Example 1,
17 is a Raman analysis result graph of the polymer composite prepared in Example 1 and Comparative Example 1,
18 is a photograph observed by FIB-SEM of the internal structure of a polymer resin (neat epoxy) that is not mixed with a thermally conductive filler,
19 is a photograph observed by FIB-SEM of the internal structure of the polymer composite prepared in Example 1;
20 is a graph evaluating the thermal conductivity according to the thermally conductive filler content of the polymer composites prepared in Example 1, Comparative Example 1, and Comparative Example 2;

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the following examples are provided in order to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for a clearer description, and elements indicated by the same reference numerals in the drawings are the same elements. In addition, the same reference numerals are used throughout the drawings for parts having similar functions and functions. In addition, "including" a certain element throughout the specification means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

In one aspect,

polymer resin; and

Including; a thermally conductive filler oriented in one direction in the polymer resin;

The thermally conductive filler,

graphite flakes having a functional group containing oxygen; and

A thermally conductive polymer composite comprising; a magnetic coating layer formed on the surface of the graphite flake is provided.

Hereinafter, a thermally conductive polymer composite according to an embodiment will be described in detail.

The thermally conductive polymer composite according to an embodiment includes a polymer resin.

The thermally conductive polymer composite according to an embodiment includes a thermally conductive filler in the polymer resin, and at the same time has thermal conductivity, adhesiveness and moldability, and can have insulating properties, so it can be prepared in various forms, and insulating properties. It can be used as a heat dissipation material that must have

The polymer resin may be any material having electrical insulation or conductivity.

For example, the polymer resin is polyacrylate, polymethacrylate, polystyrene, polyester, polyolefin, polyamide resin, polyimide, polyphenylene oxide, silicone resin, phenol resin, epoxy resin, polyurethane, polyester resin. , polyether-ether ketone, polyphenylene sulfide, fluorine-containing polymer, polyvinyl chloride resin, PVB (polyvinyl butyral), PVA (polyvinyl alcohol), polyvinyl alcohol (PVA), ethyl hydroxyethyl cellulose, etc. and may include a polymer resin having conductivity, such as polyaniline, polypyrrole, polyacetylene, polythiophene, and PEDOT (poly(3,4-ethylenedioxythiophene)).

Preferably, in order to increase the dispersibility of graphite flakes having a hydrophilic functional group, a hydrophilic polymer may be used.

The thermally conductive polymer composite according to an embodiment includes a thermally conductive filler oriented in one direction in the polymer resin.

The thermally conductive polymer composite according to an embodiment may exhibit remarkably excellent thermal conductivity through the thermally conductive filler oriented in one direction in the polymer resin.

The thermally conductive filler is

graphite flakes having a functional group containing oxygen; and

and a magnetic coating layer formed on the surface of the graphite flakes.

The thermally conductive filler includes graphite flakes having a functional group including oxygen.

The graphite flakes are graphite flakes, preferably graphite flakes having a thickness of 1 μm to 100 μm obtained by electrochemically exfoliating natural graphite or expanded graphite.

The graphite flakes having a functional group containing oxygen are preferably oxidized only on the surface of the graphite flakes having a thickness of 1 μm to 100 μm, so that ultimately only the edges are oxidized and the base plane is not oxidized. It is a graphite flake having a functional group containing oxygen in part.

Accordingly, the graphite flakes having a functional group containing oxygen may contain oxygen in an amount of 50% or less, more preferably 30 to 40 atomic%, more preferably 33 to 38 atomic%, and the oxygen is the graphite flakes. is selectively coupled to the edge of

The oxygen content is higher than the amount of oxygen contained in graphite (about 9 at%) that has not been pretreated such as natural graphite or expanded graphite, and oxygen in the edge and base plane prepared by methods such as hummers. It is a lower value than graphite oxide (FGO) (about 64.2 at%) in which a functional group containing

The oxygen-containing functional group may be an epoxy group, a carbonyl group, a carboxyl group, or the like.

The functional group containing oxygen may increase the dispersibility of the graphite flakes in the process of manufacturing the thermally conductive polymer composite, and through this, the uniformity of physical and chemical properties of the thermally conductive polymer composite according to an embodiment can be further improved. .

In addition, the graphite flake has an advantage in that it has excellent thermal conductivity compared to the graphite oxide because there are significantly fewer defect regions compared to graphite oxide in which both edges and base planes are oxidized in the related art.

The thermally conductive filler includes a magnetic coating layer formed on the surface of the graphite flakes.

The magnetic coating layer may be made of a metal oxide having a magnetism, and the metal oxide having a magnetism is from the group consisting of Fe, Ni, Co, Al, Cr, Mo, Na, Ti, Cu, AuAg, Zn, and combinations thereof. It may include one selected type.

For example, the metal oxide having the magnetic properties may be Fe ₃ O ₄ .

The magnetic coating layer may increase the orientation of the thermally conductive filler during the manufacturing process of the thermally conductive polymer composite.

Specifically, by applying a magnetic field after mixing a thermally conductive filler including graphite flakes with the magnetic coating layer formed thereon with a polymer resin, the thermally conductive filler can be oriented in one direction, and then cured by curing the oriented in one direction A thermally conductive polymer composite including a thermally conductive filler may be prepared.

The thermally conductive polymer composite according to an embodiment may significantly improve heat dissipation properties compared to the thermally conductive polymer composite including the randomly arranged thermally conductive fillers.

The thermally conductive polymer composite according to an embodiment may include the graphite flakes and the polymer resin in a weight ratio of 1: 1 to 1: 20.

If, compared to the graphite flakes, when the polymer resin is included in less than the weight ratio, the structure of the thermally conductive polymer composite is unstable, so that it may be difficult to fix the graphite flakes in a specific direction in the polymer resin, and the weight ratio If it exceeds, a problem in that the heat dissipation property is lowered by the polymer resin may occur.

The shape of the thermally conductive polymer composite according to an embodiment is not limited and may have various shapes.

In another aspect,

forming a thermally conductive filler; and

and dispersing the thermally conductive filler in a mixed solution containing a polymer resin and then applying a magnetic field to orient the thermally conductive filler in one direction;

The step of forming the thermally conductive filler,

forming a functional group containing oxygen in the graphite flake; and

Forming a magnetic coating layer on the surface of the graphite flakes formed with the functional group containing oxygen;

Hereinafter, a method of manufacturing a thermally conductive polymer composite according to an embodiment will be described in detail with reference to the drawings.

1 is a schematic diagram schematically showing a method of manufacturing a thermally conductive polymer composite according to an embodiment, and FIG. 2 is a schematic diagram schematically illustrating a step of forming the thermally conductive filler.

The method of manufacturing the thermally conductive polymer composite 100 according to an embodiment includes forming a thermally conductive filler 30;

The step of forming the thermally conductive filler 30,

forming a functional group containing oxygen in the graphite flake 10; and

and forming a magnetic coating layer on the surface of the graphite flake 20 on which the oxygen-containing functional group is formed.

The step of forming a functional group containing oxygen in the graphite flake 10 is a step of forming the graphite flake 20 having a functional group containing oxygen by oxidizing the graphite flake.

In this case, the graphite flakes 10 may be graphite in the form of electrochemically exfoliated flakes having a thickness of preferably 1 μm to 100 μm.

The step of forming a functional group containing oxygen in the graphite flake 10 controls the oxidation of the graphite flake, selectively oxidizing the surface, and ultimately partially forming the functional group containing oxygen at the edge make it

Through the above step, the edge of the graphite flake 10 is oxidized, but the basal plane is prevented from being oxidized or minimized to increase the dispersibility of the graphite flake in aqueous solution and reduce the defect area in the graphite. It can prevent the thermal conductivity from falling.

The graphite flakes 20 having a functional group containing oxygen prepared through the above steps have excellent crystallinity compared to graphite oxide prepared by treatment with a strong acid by a conventional hummer's method, etc., and thus have excellent thermal conductivity. There are remarkably excellent advantages.

The step of forming a functional group containing oxygen in the graphite flake 10 is

dispersing the graphite flakes 10 in a sulfuric acid solution;

adding potassium permanganate to the sulfuric acid solution; and

It may include; adding hydrogen peroxide to the sulfuric acid solution to which potassium permanganate is added.

By adding distilled water in the above step, Mn0 ₇ /MnO ³⁺ acting as an oxidizing agent on the basal plane is changed to MnO ^4- , so that functional groups containing oxygen, such as epoxy group, carbonyl group, carboxyl group, etc., are at the ends of the graphite flakes. (edge) can be partially bound.

The graphite flakes 20 prepared through the above steps may contain 30 to 40 atomic% oxygen.

The forming of the thermally conductive filler 30 may further include washing and drying the graphite flakes formed with the oxygen-containing functional group prepared through the above steps.

For example, the graphite flakes are separated and recovered from the solution to which potassium permanganate, sulfuric acid and hydrogen peroxide are added, washed with hydrochloric acid, etc. The washing and drying method is not limited thereto.

The step of forming the thermally conductive filler,

and forming a magnetic coating layer on the surface of the graphite flake on which the oxygen-containing functional group is formed.

The step is a step of magnetizing the thermally conductive filler to orient the thermally conductive filler in one direction through the application of a magnetic field.

The step may include mixing the graphite flakes in which the functional group containing oxygen is formed in a solution and a metal oxide having magnetism or a precursor material of the metal oxide.

In this case, the metal oxide having the magnetic properties and the precursor material of the metal oxide are 1 selected from the group consisting of Fe, Ni, Co, Al, Cr, Mo, Na, Ti, Cu, Au, Ag, Zn, and combinations thereof. It may include a species, and the precursor material may be one selected from the group consisting of alkoxides, chlorides, hydroxides, oxyhydroxides, nitrates, carbonates, acetates, oxalates, and mixtures thereof including the metal, but is not limited thereto. .

The solvent contained in the solution is water, methanol, ethanol, propanol, isopropanol, butanol, ethyl acetate, butyl acetate, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), toluene, xylene, hexane, heptane, octane, and the like.

For example, the washed and dried graphite flakes with functional groups containing oxygen are dispersed in distilled water and mixed with a Fe ₃ O ₄ solution to form a magnetic coating layer of Fe ₃ O ₄ on the surface through wet coating or FeCl ₂ ·4H ₂ O, FeCl ₃ ·6H ₂ O can be mixed with the Fe ₃ O ₄ precursor solution to form a Fe ₃ O ₄ coating layer on the surface

The step of forming the thermally conductive filler 30 may further include washing and drying the thermally conductive filler 30 having a magnetic coating layer formed on the surface of the graphite flake manufactured through the above step.

For example, after washing the thermally conductive filler 30 with distilled water, etc., it may be obtained using a centrifuge, etc., and may be dried by a freeze-drying method, but the washing and drying method is not limited thereto.

In the method of manufacturing the thermally conductive polymer composite 100 according to an embodiment, the thermally conductive filler 30 is dispersed in a mixed solution containing the polymer resin 40 and then a magnetic field is applied to move the thermally conductive filler in one direction. Orienting; includes.

In this case, the magnetic field application may be performed by applying a magnetic field in the vertical direction of the mixed solution using a neodymium magnet or the like.

The step of orienting the thermally conductive filler in one direction further includes a curing step.

The curing step is a curing method for curing the polymer resin 40, and may be performed by various known methods such as photo curing or thermal curing. For the curing, the mixed solution is optionally used for the polymer resin 40 ) may further include a curing agent for curing, and may further include additives such as a catalyst, an auxiliary curing agent, an initiator, a surfactant, a plasticizer, a thickener, a diluent, and the like.

The method for manufacturing the thermally conductive polymer composite 100 according to an embodiment may further include a step of removing gas in the mixed solution (degassing step) before performing the curing step, and the thermal conductivity produced through this The heat dissipation characteristics of the polymer composite 100 may be further improved.

The step of removing the gas may be performed by a method of depressurizing the mixed solution, for example, may be performed using a vacuum oven.

The method of manufacturing the thermally conductive polymer composite 100 according to an embodiment may further include a step of molding before performing the curing step, and the thermally conductive polymer composite 100 manufactured through this may be formed in various shapes. can do.

In another aspect,

A heat dissipation sheet comprising the thermally conductive polymer composite is provided.

The heat dissipation sheet may have a form in which the thermally conductive polymer composite is formed on a substrate.

The heat dissipation sheet may include a substrate and a coating layer including the thermally conductive polymer composite.

In this case, the type of the substrate is not limited as long as it is a thin film on which the thermally conductive polymer composite can be coated.

The substrate may have adhesiveness, and through this, it may be easily attached to an electronic device or the like.

In addition, the substrate may have flexibility and thus may be formed on various types of electronic devices.

For example, the substrate may include acrylic resin, silicone resin, rubber resin, polyurethane resin, vinyl acetate resin, epoxy resin, polyethylene, polypropylene, polyethylene terephthalate, polyethylene terephthalate glycol, polycarbonate, polystyrene, polyamide. , polybutylene terephthalate, polymethyl pentene, polyvinyl chloride, nylon and copolymers thereof may be selected from the group consisting of, but not limited thereto, and substrates of various materials that can be used in conventional heat dissipation sheets may be applied. have.

In another aspect,

There is provided a method of manufacturing a heat dissipation sheet comprising; coating the thermally conductive polymer composite on a substrate.

In this case, the coating may be performed using a solution process such as doctor blading, bar coating, spin coating, dip coating, micro gravure coating, imprinting, inkjet printing, spraying, but is not limited thereto.

Hereinafter, the present invention will be described in detail through Examples and Experimental Examples.

However, the following examples and experimental examples are only to illustrate the present invention, the content of the present invention is not limited by the following examples.

<Preparation Example 1> Preparation of graphite oxide (GO)

1.0 g of electrochemically exfoliated graphite (EEG) flakes were dispersed in 46 ml of sulfuric acid (H ₂ SO ₄ ) cooled to 0°C. 6.0 g of potassium permanganate was previously stirred in 100 ml of distilled water to prepare an aqueous solution, and an aqueous solution of potassium permanganate was slowly added to the sulfuric acid (H ₂ SO ₄ ) to prevent temperature rise. The reaction mixture was then mechanically stirred at 90° C. for 4 hours. After the stirring process, 20 ml of hydrogen peroxide (H ₂ O ₂ ) was added to complete the reaction to prepare graphite oxide (GO) in which a functional group containing oxygen was formed at the edge.

<Preparation Example 2> Preparation of graphite oxide (GO)/Fe ₃ O ₄ (mEEG)

Step 1: Graphite oxide (GO) was prepared by the method of Preparation Example 1.

Step 2: Centrifugation was repeated 3 times and 5 times, respectively, at 13000 rpm using 3.4% hydrochloric acid (HCl) and distilled water to wash the graphite oxide (GO). The completely neutralized mixture was dried under vacuum for 3 days using freeze drying.

Step 3: The graphite oxide (GO) prepared in steps 1 and 2 was put in 800 ml of distilled water and uniformly dispersed by ultrasonic waves, and a magnetic fluid EMG-605 solution (Fe ₃ O ₄ containing aqueous solution) 0.8 in 200 ml of the dispersion. ml was added in several portions. Then, the magnetic fluid was uniformly dispersed by using a physical force. After reacting for 1 hour, centrifugation was performed at 13000 rpm. The obtained precipitate was dried under vacuum for 1 day using freeze-drying to prepare graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (hereinafter, mEEG).

<Example 1> Polymer composite including GO-Fe ₃ O ₄ thermally conductive filler (A_mEEG) oriented in one direction

Step 1: A thermally conductive filler was prepared by the method of Preparation Example 2.

Step 2: The thermally conductive filler was added to a polymer mixture in which bisphenol A-based EPOKUCKDO YD-128 was mixed with a polymer resin, a curing agent, and an accelerator in a weight ratio of 10:6:0.1, followed by uniform stirring. Afterwards, in order to remove pores in the polymer mixture, a defoaming process was performed at 25° C. for 1 hour and 40° C. for 2 hours under vacuum.

Step 3: After completion of defoaming, in order to vertically align the thermally conductive filler in the polymer, a polymer mixture to which the thermally conductive filler is added is placed in a magnetic field region using a magnet to orient the thermally conductive filler in one direction, and then at 80° C. 1 A polymer composite including a thermally conductive filler oriented in one direction was prepared by curing at 100° C. for 2 hours, and at 120° C. for 1 hour.

<Comparative Example 1> Exfoliated graphite Polymer Composite Containing Thermally Conductive Filler

A polymer composite including exfoliated graphite as a thermally conductive filler was prepared in the same manner as in Example 1, except that in step 1 of Example 1, exfoliated graphite was used as the thermally conductive filler.

<Comparative Example 2> Polymer composite including randomly oriented GO-Fe ₃ O ₄ thermally conductive filler (R_mEEG)

Randomly arranged thermally conductive fillers were included in the same manner as in Example 1, except that in the curing process of Step 3 of Example 1, the process of orienting the thermally conductive filler in one direction was not performed. A polymer composite was prepared.

<Comparative Example 3> Polymer composite including graphene-Fe ₃ O ₄ thermally conductive filler oriented in one direction

The same method as in Example 1 was performed, except that in step 1 of Example 1, graphene was used instead of graphite oxide (GO).

<Comparative Example 4> Polymer composite including FGO-Fe ₃ O ₄ thermally conductive filler oriented in one direction

In step 1 of Example 1, instead of graphite oxide (GO) having a functional group containing oxygen formed at the edge, graphite flakes were treated with a strong acid to produce oxygen at the edge and the base plane. The same method as in Example 1 was performed except that graphite oxide (FGO) having a functional group formed thereon was used.

<Experimental Example 1> Characterization of graphite oxide (GO)

The properties of the electrochemically exfoliated graphite flakes (hereinafter, exfoliated graphite (EEG)) and the graphite oxide (GO) prepared in Preparation Example 1 were comparatively analyzed by the following method.

(1) particle size analysis

Particle size analysis (PSA; Mastersizer 2000) was used to confirm the particle size distribution, and the results are shown in FIGS. 3 and 4 .

3 is a particle size distribution of exfoliated graphite (EEG), and FIG. 4 is a particle size distribution of graphite oxide (GO).

As shown in FIG. 3 , exfoliated graphite (EEG) had an average particle size of about 16.92 μm, and as shown in FIG. 4 , it was confirmed that graphite oxide (GO) had an average particle size of about 10.59 μm.

Through this, it can be seen that, in Preparation Example 1, the graphite flake size was reduced as well as the particle size distribution became uniform.

(2) XRD analysis

In order to understand the physical properties of exfoliated graphite (EEG), the results of analysis using XRD (X-ray diffraction; EUROPE600) for four regions of exfoliated graphite (EEG) are shown in FIG. was analyzed. In addition, the result of comparison with the analysis result using XRD for the graphite oxide (GO) obtained in Preparation Example 1 is shown in FIG. 6 .

As a result of analysis through FIG. 5 , it was confirmed that the average particle diameter of exfoliated graphite (EEG) was about 2.1 to 2.9 nm.

In addition, as shown in FIG. 6 , in the case of exfoliated graphite (EEG), the (002) peak representing the d-spacing of graphite was observed at about 26.6°, whereas graphite oxide (GO) was observed at about 25.3°. and the interplanar distance was confirmed to be about 2.92 nm.

From the above results, it can be seen that graphite flakes including a functional group containing a small amount of oxygen were synthesized in Preparation Example 1.

(3) Raman spectroscopic analysis

In order to confirm the defect degree of exfoliated graphite (EEG) and graphite oxide (GO) prepared in Preparation Example 1, it was analyzed by Raman spectroscopy (RAMANtouch), and the I _D /I _G intensity ratio distribution of 400 samples was calculated. The results are shown in FIGS. 7 and 8 .

As a result of Raman spectroscopy, the Raman spectrum of exfoliated graphite (EEG) showed a broad D peak (about 1358 cm ^-1 ) and a sharp G peak (about 1583 cm ^-1 ). The G peak means the in-plane bond stretching mode of the sp ² C atom pair. D peaks are caused by defects such as structural edges, functional groups, or structural disturbances. On the other hand, in graphite oxide (GO), a functional group containing oxygen was introduced by edge selective oxidation, so that the intensity of the D peak was strongly observed overall.

7 is a result for exfoliated graphite (EEG), as shown in FIG. 7 , it can be seen that the I _D /I _G strength ratio of exfoliated graphite (EEG) has a wide range of values of about 0.3 to 1.2. That is, the I _D /I _G intensity ratio distribution of exfoliated graphite (EEG) is non-uniform, and it can be seen that exfoliated graphite (EEG) has non-uniform properties.

FIG. 8 is a result for graphite oxide (GO), and as shown in FIG. 8 , it can be seen that the I _D /I _G intensity ratio of graphite oxide (GO) has a narrow range of about 0.65 to 0.8. That is, the graphite oxide (GO) prepared in Preparation Example 1 has a uniform I _D /I _G intensity ratio distribution, and it can be seen that the graphite oxide (GO) has more uniform properties compared to the exfoliated graphite (EEG). have.

(4) SEM analysis

The surface structures of the exfoliated graphite (EEG) and graphite oxide (GO) were analyzed through a scanning electron microscope (S-4300), and the results are shown in FIG. 9 .

The upper photograph of FIG. 9 is a photograph of exfoliated graphite (EEG) observed by SEM, and as in the upper photograph of FIG. It can be seen that the μm is relatively large.

The lower photograph of FIG. 9 is a photograph of graphite oxide (GO) observed by SEM. As in the lower photograph of FIG. 9, in the case of graphite oxide (GO), aggregation of graphite particles during the introduction of functional groups containing oxygen It can be seen that this is reduced and synthesized as graphite oxide having a relatively smooth structure.

(5) XPS analysis

By using X-ray photoelectron spectroscopy (XPS, X-ray photoelectron spectroscopy; K-Alpha), the chemical properties of the surface components of the exfoliated graphite (EEG) and graphite oxide (GO) and the bonding state of the molecules were analyzed. 10 is shown.

The upper graph of FIG. 10 is an analysis result of exfoliated graphite (EEG), and as shown in the upper graph of FIG. 10 , it can be seen that exfoliated graphite (EEG) contains about 9.23 at% oxygen. This can be expected to occur through oxidation of graphite by hydroxide ions during the electrochemical exfoliation process. In addition, small amounts of nitrogen and sulfur were detected in exfoliated graphite. This can be expected to be doped during the electrochemical exfoliation process.

The lower graph of FIG. 10 is an analysis result of graphite oxide (GO). As shown in the lower graph of FIG. 10, the graphite oxide (GO) surface-modified through edge selective oxidation contains about 35.98 at% oxygen. Able to know.

The graphite oxide (GO) showed greater peak intensities of carboxyl and carbonyl groups than exfoliated graphite (EEG), indicating that surface oxidation was increased.

From the above results, it can be seen that a large amount of carboxyl and carbonyl groups were induced in the edge portion of the graphite flake through step 1 of Example 1.

(6) TGA analysis

Thermogravimetric analysis (TGA) was used to analyze the thermal stability of exfoliated graphite (EEG) and graphite oxide (GO).

For the analysis, the exfoliated graphite (EEG) and graphite oxide (GO) were heat-treated by raising the temperature to 900° C. at a rate of 10° C. per minute in an oxygen atmosphere, and the results obtained through this process are shown in FIG. 11 .

As shown in FIG. 11 , in the case of exfoliated graphite (EEG), there was almost no mass loss before 700° C., and complete oxidation and decomposition occurred after 800° C. It can be seen that the exfoliated graphite (EEG) had a high level of thermal stability.

On the other hand, in the case of graphite oxide (GO), mass loss begins to occur at temperatures below 100°C. This is expected to be due to the separation of moisture and adsorbed oxygen atoms. In addition, a significant mass loss is observed near about 200°C, which may be attributed to the decomposition of oxygen functional groups in graphite oxide (GO). It can be seen that the complete decomposition of graphite oxide (GO) occurred around 700°C, 200°C lower than that of exfoliated graphite (EEG).

<Experimental Example 2> Characterization of thermally conductive filler

The characteristics of the graphite oxide (GO) prepared in Preparation Example 1 and the graphite oxide (GO)/Fe ₃ O ₄ thermally conductive filler (mEEG) prepared in Preparation Example 2 were compared and analyzed by the following method.

(1) Magnetic Characterization Analysis

The magnetic properties of the thermally conductive filler according to the presence of the magnetic coating layer were confirmed through the formation of an external magnetic field, and the results are shown in FIG. 12 .

The left photograph of FIG. 12 is the graphite oxide (GO) prepared in Preparation Example 1, and the right photograph is the thermally conductive filler (mEEG) prepared in Preparation Example 2.

As shown in FIG. 12 , it can be seen that the thermally conductive filler (mEEG) prepared in Preparation Example 2 has magnetism and responds to an external magnetic field.

(2) Crystal structure analysis

XRD analysis was performed on the graphite oxide (GO) prepared in Preparation Example 1 and the thermally conductive filler (mEEG) prepared in Preparation Example 2, and the results are shown in FIG. 13 .

As shown in FIG. 13 , in graphite oxide (GO), a peak due to Fe ₃ O ₄ is not observed, whereas in the thermally conductive filler (mEEG), Fe ₃ O ₄ at about 30.6°, 35.9°, 57.4°, and 63° Diffraction peaks by (220), (311), (511), (440) were observed.

Through this, it can be confirmed that Fe ₃ O ₄ having magnetism is present together with exfoliated graphite in the thermally conductive filler (mEEG).

(3) Surface structure and thermal analysis

The results of observation by SEM of the graphite oxide (GO) prepared in Preparation Example 1 and the thermally conductive filler (mEEG) prepared in Preparation Example 2 are shown in FIG. 14, and the results of analysis by a thermogravimetric analyzer (TGA) are shown in FIG. 15 indicated. During thermogravimetric analysis, heat treatment was performed by increasing the temperature at a rate of 10° C. per minute in an oxygen atmosphere.

The upper photograph of FIG. 14 is a photograph of the graphite oxide (GO) prepared in Preparation Example 1, and the lower photograph is a photograph of observing the thermally conductive filler (mEEG) prepared in Preparation Example 2. As shown in FIG. 14 , it was confirmed that Fe ₃ O ₄ particles having a size of about 25 nm were formed on the surface of the thermally conductive filler (mEEG) prepared in Preparation Example 2 through SEM.

In addition, as shown in FIG. 15 , in the case of graphite oxide (GO), complete decomposition occurred near 700 ° C, and significant mass loss could be observed, and in the case of thermally conductive filler (mEEG), mass loss occurred before 700 ° C. However, complete decomposition did not occur in the presence of Fe ₃ O ₄ . After 721°C, no mass loss was observed, and it was confirmed that about 16% of iron oxide was present in the filler.

<Experimental Example 3> Characterization of polymer composites

The properties of the polymer composites prepared in Example 1 and Comparative Example 1 were comparatively analyzed by the following method.

(1) Analysis of orientation

Raman spectroscopic analysis was performed on the polymer composites prepared in Example 1 and Comparative Example 1 to measure the degree of orientation of the thermally conductive filler by the following method.

In the case of a two-dimensional carbon material, the shape according to the location of the sample can be predicted through the Raman spectrum. In particular, in the case of exfoliated graphite of two-dimensional flakes, the intensity of the G peak appears high in the plane direction, and the intensity of the D peak is measured at the edge due to the edge exposure of graphene. Using this principle, the polymer composite including the randomly arranged thermally conductive filler (R_mEEG) of Comparative Example 1 and the polymer composite including the thermally conductive filler (A_mEEG) oriented in one direction of Example 1 in FIG. 16 The results of Raman spectroscopy analysis in the same manner as shown in FIG. 17 are shown, and the orientation of the filler in the polymer resin was evaluated by comparing the I _D /I _G intensity ratio using Equation 1 below.

<Equation 1>

As a result of the calculation, the I _D / I _G intensity ratio of the polymer composite including the randomly arranged thermally conductive filler (R_mEEG) of Comparative Example 1 was about 0.40, and the thermally conductive filler (A_mEEG) oriented in one direction of Example 1 was The I _D /I _G intensity ratio of the polymer composite containing it has a value of about 0.72. From these results, it can be seen that the polymer composite aligned in one direction through the application of a magnetic field has an orientation degree of about 1.8.

(2) Internal structure analysis

The internal structure of the thermally conductive composite prepared in Example 1 was observed using a FIB-SEM (Focused ion beam-scanning electron microscope; Helios G4) to minimize surface irregularities generated during the etching process.

In order to identify the filler in the polymer composite, the polymer composite of Example 1 was compared and analyzed with a polymer resin (neat epoxy) not mixed with a thermally conductive filler.

18 is an internal image of the neat epoxy. As shown in FIG. 18, it can be seen that the neat epoxy does not have a filler inside and has a smooth cross-section.

19 is an internal image of the thermally conductive polymer composite of Example 1, through which it can be confirmed that the thermally conductive filler exists in the form of flakes in the polymer matrix. In addition, as indicated by the arrow, it can be confirmed that the heat transfer path in the vertical direction is formed in the polymer matrix.

(3) Heat conduction performance evaluation

The thermal conductivity of the thermally conductive polymer composite (A_mEEG) of Example 1 and the thermally conductive composite of Comparative Examples 1 to 4 was analyzed using a thermal conductivity analyzer (TCi), and the results are shown in FIG. 20 and Table 1. . The thermal conductivity analyzer (TCi) was measured without additional calibration or pre-processing using MTPS (Modified transient plane source) technology to analyze the thermal conductivity and efficiency of the material.

Thermal Conductivity (W/mK) Example 1 1.0 Comparative Example 3 0.6 Comparative Example 4 0.4

As shown in FIG. 20 , the thermal conductivity values of the thermally conductive composites of Comparative Example 1 (EEG) and Comparative Example 2 (R_mEEG) were similar, and the thermally conductive composite of Example 1 was compared with Comparative Example 1 and Comparative Example 2 It can be seen that a remarkably excellent value is exhibited. Specifically, in the case of Example 1 in which the thermally conductive fillers are arranged in one direction compared to Comparative Example 2 in which they are randomly arranged, it can be seen that the thermal conductivity is increased by about 200%.

Through this, it can be seen that aligning the thermally conductive filler in one direction helps to form a heat transfer path. In addition, it can be seen that through the alignment of the pillars through the application of a magnetic field, it is possible to design an appropriate path for the target and control the direction.

In addition, as shown in FIG. 20 , as a result of analyzing the thermal conductivity value of the polymer composite according to the content of the thermally conductive filler, the thermal conductivity value increases as the filler content increases, regardless of the type of filler and whether or not a magnetic field is applied. Able to know.

This can be considered because as the content of the thermally conductive filler increases, the possibility of adjacent fillers in the polymer resin increases, thereby making continuous network formation advantageous.

Table 1 compares the thermal conductivity when the thermally conductive filler is contained in the same content. As shown in Table 1, the polymer composite of Example 1 is a polymer using graphene of Comparative Example 3 as a thermally conductive filler. Polymer of Comparative Example 4 using, as a thermally conductive filler, a composite and graphite flakes of Comparative Example 4, prepared by treating the graphite flakes with a strong acid, in which functional groups containing oxygen were formed on edges and base planes It can be seen that the thermal conductivity value is significantly superior to that of the composite.

10: exfoliated graphite
20: exfoliated graphite having a functional group containing oxygen
30: thermally conductive filler
40: polymer resin
100: thermally conductive polymer composite

Claims (15)

polymer resin; and
Including; a thermally conductive filler oriented in one direction in the polymer resin;
The thermally conductive filler,
graphite flakes having a functional group containing oxygen; and
A thermally conductive polymer composite comprising; a magnetic coating layer formed on the surface of the graphite flake.
According to claim 1,
The graphite flake is a graphite flake having a functional group partially containing oxygen at an edge thereof, a thermally conductive polymer composite.
According to claim 1,
The graphite flakes contain 30 atomic% to 40 atomic% oxygen, a thermally conductive polymer composite.
According to claim 1,
The graphite flakes are electrochemically exfoliated exfoliated graphite flakes having a thickness of 1 μm to 100 μm, a thermally conductive polymer composite.
According to claim 1,
The magnetic coating layer is made of a metal oxide having a magnetic, thermally conductive polymer composite.
6. The method of claim 5,
The magnetic metal oxide is
Fe, Ni, Co, Al, Cr, Mo, Na, Ti, Cu, AuAg, Zn, and a thermally conductive polymer composite comprising one selected from the group consisting of combinations thereof.
According to claim 1,
The polymer resin is polyacrylate, polymethacrylate, polystyrene, polyester, polyolefin, polyamide resin, polyimide, polyphenylene oxide, silicone resin, phenolic resin, epoxy resin, polyurethane, polyester resin, polyether -Ether ketone, polyphenylene sulfide, fluorine-containing polymer, polyvinyl chloride resin, PVB (polyvinyl butyral), PVA (polyvinyl alcohol), ethyl hydroxyethyl cellulose, polyaniline, polypyrrole, polyacetylene, polythiophene, One selected from the group consisting of PEDOT (poly (3,4-ethylenedioxythiophene)) and combinations thereof, a thermally conductive polymer composite.
According to claim 1,
The thermally conductive polymer composite includes the graphite flakes and the polymer resin in a weight ratio of 1: 1 to 1: 20, the thermally conductive polymer composite.
forming a thermally conductive filler; and
and dispersing the thermally conductive filler in a mixed solution containing a polymer resin and then applying a magnetic field to orient the thermally conductive filler in one direction;
The step of forming the thermally conductive filler,
forming a functional group containing oxygen in the graphite flake; and
Forming a magnetic coating layer on the surface of the graphite flakes formed with the oxygen-containing functional group; comprising, a method for producing a thermally conductive polymer composite.
10. The method of claim 9,
The method for producing a thermally conductive polymer composite, wherein the oxygen-containing functional group is partially formed at an edge of the graphite flake.
10. The method of claim 9,
The step of forming a functional group containing oxygen in the graphite flake,
dispersing the graphite flakes in a sulfuric acid solution;
adding potassium permanganate to the sulfuric acid solution; and
Adding hydrogen peroxide to the sulfuric acid solution to which the potassium permanganate is added; including, a method for producing a thermally conductive polymer composite.
10. The method of claim 9,
The step of forming the magnetic coating layer,
A method of manufacturing a thermally conductive polymer composite, comprising a; mixing the graphite flakes in which the functional group containing oxygen is formed in a solution and a metal oxide having a magnetism or a precursor of the metal oxide.
10. The method of claim 9,
Orienting the thermally conductive filler in one direction is a curing step; the method of manufacturing a thermally conductive polymer composite further comprising a.
A heat dissipation sheet comprising the thermally conductive polymer composite of claim 1.
A method of manufacturing a heat dissipation sheet comprising; coating the substrate with the thermally conductive polymer composite of claim 1 .

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