KR20120074694A - Manufacturing method of high thermal conductivity expanded graphite sheet by hybrid high thermal-conductivity fine particle - Google Patents

Abstract

PURPOSE: A heat spreader and a method for manufacturing the same are provided to effectively control heat generated from electronic devices and to reduce the sizes of the electronic devices. CONSTITUTION: A method for manufacturing a heat spreader includes the following: natural graphite is oxidized and expanded; highly thermal conductive nano-sized carbide and nitride such as C, SiC, Bn, and AlN are dispersed in horizontal interlayer pores to be vacuum-filled without coagulation; a compressive molding process is implemented using a roller or a press; and the resultant product is in the form of a sheet or a plate. Ammonium polycarboxylate, sodium polycarboxylate, sodium dodecylsulfate, and ethylene glycol are further added into the product as a dispersing agent.

Description

High thermal conductivity expanded graphite sheet incorporating high thermal conductivity fine particles and its manufacturing method {MANUFACTURING METHOD OF HIGH THERMAL CONDUCTIVITY EXPANDED GRAPHITE SHEET BY HYBRID HIGH THERMAL-CONDUCTIVITY FINE PARTICLE}

In order to compensate for the disadvantage of graphite having excellent thermal conductivity in the horizontal direction but low thermal conductivity in the vertical direction, the graphite is expanded to densely fill high conductive particles in the pores of the expanded anisotropic layer to develop a high thermal conductivity composite material. It is the technical field about the construction method.

In recent years, all the electronic devices such as light emitting diode (LED), light emitting diode television (LED TV), liquid crystal display (LCD), notebook, plasma display panel (PDP), mobile display, etc. As a large amount of heat is generated in a small area, there is a problem of degrading the performance of the product, such as damage to parts or circuits. In other words, as the performance improvement of high efficiency, high functionality, and light and small components is socially demanded, it is becoming an important issue to generate heat generated from sets, modules, and parts of electronic products.

The technology to date has been used in the form of sheets or gaskets by compression molding natural graphite having an anisotropic layer since the 1960s. However, graphite has an anisotropic arrangement even when compressed according to the anisotropy, and its thermal conductivity is 150W / mk or more in the horizontal direction and 3-4W / mk or less in the vertical direction, depending on the degree of compression. Has been using electromagnetic products.

In the case of heat dissipating materials, thermal conductivity is excellent, hot spots do not occur, and economical heat dissipating materials have been constantly raised and active development is underway.

Moreover, the air layer existing in the conventional graphite sheet was a cause of the thermal conductivity fall to a horizontal direction and a vertical direction at thermal conductivity 0.025 W / mk.

Therefore, to solve the above problems, there is a conventional method of impregnating resin and pyrolysis in an inert gas after compression molding in order to transfer heat in the vertical direction, but the process is complicated and the generation of toxic gas and additional thermal energy consumption There are disadvantages in economic efficiency due to problems and rising manufacturing costs.

On the other hand, while conventionally used as a thermal heat dissipation system using aluminum, copper, etc., the hot spot of the heat sink was inevitable due to the thermal isotropy of the metal material.

Therefore, in the present invention, the patent for preparing the heat dissipating material by filling the amorphous carbon fine particles, which is a prior art (graphite heat dissipating material including amorphous carbon fine particles and its manufacturing method) of Patent 10-0971780, may be further improved. In other words, by first treating the expanded graphite with acid to make high purity, impurities that lower the thermal conductivity characteristics were removed, and then the thermal conductivity was improved through the filling of carbides and nitrides, which have high thermal conductivity, and the vacuum filling method, a new filling method. By using the invention was invented to produce an effective heat dissipation material that can significantly improve the thermal conductivity in the vertical direction.

Therefore, the technical problem to be achieved by the present invention is to increase the horizontal expansion of the natural graphite to the maximum, heat treatment to high purity after the high-temperature conductivity in the particulate carbon, ammonium nitride, boron nitride, silicon carbide having high thermal conductivity It is to provide a method of manufacturing a heat dissipating material having excellent thermal conductivity in the horizontal and vertical direction by filling.

More specifically, the technical problem to be achieved by the present invention is not only to increase the thermal conductivity and the heat diffusion efficiency in the horizontal direction of the graphite from the surface in contact with the heat source, but also to significantly improve the heat dissipation in the vertical direction, which is used in heat sinks of electronic products. It is to provide a method for producing an efficient heat insulating material that can improve the performance and durability.

In order to achieve the above technical problem, the present invention is highly expanded natural graphite and remove impurities contained in the expanded natural graphite (filled) and then filled with high thermal conductivity fine particles (carbon, AlN, BN, SiC) in the horizontal interlayer pores It provides a method of manufacturing a high thermal conductivity heat insulating material characterized in that the expanded graphite plate or sheet structure is compression molded to have a high density.

Until now, natural graphite (graphite) is crushed into particles of a certain size, oxidized, intercalated at about 80 ° C-150 ° C, washed and dried. Intercalation refers to the insertion of an intercalation material between the graphite (carbon) layer and the layer. In the sulfuric acid-graphite intercalation, oxidizing agents such as chromium oxide (CrO ₃ ), potassium permanganate (KMnO ₄ ), and nitric acid (HNO ₃ ) are used to oxidize the carbon layer. The intercalated graphite starts to expand above 160 ° C, especially when expanded in an expansion furnace of 600-1,000 ° C, which causes the particles of graphite to expand at least 80-350 times in the direction of the C axis, that is, perpendicular to the crystal plane of the graphite particles. do. In the present invention, conventional natural graphite refers to a powder having a particle size of 30 to 80 mesh.

Typically, graphite sheet production is used by roller compression molding using graphite having an expansion volume of about 180-350 ml / g with a compression ratio of 30% or more. The density of the sheet after roller compression molding can be up to 0.8-1.25 g / cm 3 and can be adjusted by the pressure applied to the particles of expanded graphite and the roller, and the thickness can be produced up to 0.1-6.0 mm. Due to the roller compression molding of expanded graphite, the thermal anisotropy increases as the thermal conductivity in the vertical direction with respect to the thermal conductivity in the horizontal direction increases as the compression rate increases (the larger the density becomes). The heat spreading rate and conductivity of the electronic component to the vertical plane are low, and the heat dissipation load on the edge surface increases. This means that the heat dissipation to the back of the sheet having a large area becomes more difficult, and the higher the density, the better the heat spreader of the graphite sheet is, but in the vertical direction, the heat dissipation is caused by convection with air. The heat dissipation performance in the back is bound to be low.

A void exists in the compression-expanded graphite, and the air present in the void causes the thermal conductivity to decrease in the vertical direction and the horizontal direction with a thermal conductivity of 0.025 W / mk. In addition, electron micrographs, as shown in FIG. 1, it can be seen that they are long in the horizontal plane and short in the vertical direction.

Therefore, the present invention is filled with high thermal conductivity fine particles (carbon, AlN, BN, SIC) in the pores of the graphite sheet, the thermal anisotropy is large by improving the cooling performance by the convection with air in the vertical plane and the thermal conductivity in the horizontal direction The heat dissipation to the vertical plane is greatly increased. The theoretical density of ordinary graphite is about 2.28 g / cm 3, and the density of the sheet produced by the conventional roller using the graphite is 0.8-1.25 g / cm 3, so that approximately 45-65 of the theoretical density of ordinary graphite is used. As much as% voids remain in the graphite sheet.

When the high thermal conductivity particles are filled in the pores of the natural expanded graphite, it is possible to improve the thermal diffusion and thermal conductivity by increasing the density of the molded body. Amorphous carbon fine particles can reduce the presence of the 45-65% void of the theoretical density to as small as 15-55% and control the thermal conductivity performance according to the density.

It is possible to think of a method of mixing metal (Al, Cu, etc.) particles, which are thermally isotropic materials, for the heat dissipation to the vertical plane of the natural expanded graphite sheet, but the method of mixing metals has many difficulties in atomizing the metal particles. It is stable because there is no reaction, but Al reacts rapidly and has foamability. In addition, there is a problem in that it is uneconomical in terms of price and relatively increases the weight of the seat.

In the present invention, the carbide and nitride fine particles filled in the pores of the expanded graphite are (pitch, coke, natural gas, tar, etc.) from the group consisting of aluminum nitride (AlN), boron nitride (BN), and silicon carbide (SiC). It can be used with one or more materials selected.

In the isotropic molding of graphite, the thermal conductivity is 80W / mk at 1.75g / cm3 and 160W / mk at 1.85g / cm3, and isotropic graphite has good thermal conductivity as compared to the horizontal axis of the anisotropic graphite sheet. It can be seen. In the case of aluminum nitride (AlN) and silicon carbide (SiC), which are used as filling materials, the thermal conductivity in the horizontal and vertical directions is 140 to 180 W / mk and 120 W / mk, respectively, and the boron nitride (BN) is horizontal. The thermal conductivity of 71 W / mk in the vertical direction and 121 W / mk in the vertical direction improves the thermal conductivity in the vertical direction when intercalating the expanded graphite.

In the case of expanded graphite expanded 200-500 times, it has 5 ~ 15 sized interlayer voids. For the material filled between these interlayer voids, it is appropriate to insert materials with particle size of less than 5 nm and particle size less than 5 Do. 1 to 5% by weight of dispersants such as polycarboxylate ammonium salt (5468-cf), polycarboxylate sodium salt (44-cf), sodium dodecyl sulfate (SDS), ethylene glycol (EG) It is added to and dispersed to use.

The heat dissipation effect can be maximized when the nitride and carbide fine particles are filled in this range, and the filling method includes immersion method and vacuum filling method, but the filling particles easily penetrate between the interlayer pores of the expanded graphite during the manufacturing using the vacuum filling method. Can be compounded. In the present invention, the content of the material inserted between the interlayer pores of the expanded graphite is preferably 30% of the total weight.

In case of less than 5%, the filling effect is insignificant, and in case of 30% or more, the filling effect may be insufficient. In case of inserting within 30%, the thermal conductivity in the horizontal and vertical directions is greatly improved. Will be imported.

Therefore, in order to achieve the above object, the present invention uses calcium fluoride (HF), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl) as impurities in natural graphite to obtain calcium oxide (CaO), iron oxide (Fe ₂ O ₃ ), After removing sodium oxide (Na ₂ O), intercalation and heat treatment at high temperature to expand 200-500 times to produce expanded graphite, and then vacuum-filled carbide and nitride fine particles having high thermal conductivity to form a composite sheet Manufacture. This sheet is a novel manufacturing method for improving the thermal properties of conventional anisotropic sheets and isotropic sheets.

The high thermal conductivity sheet composited by high expansion of natural graphite and vacuum-filled high thermal conductivity particulates is applied to the heat generated from the top of various integrated circuits of electronic circuit boards, light sources of display devices, etc. Direct or indirect contact provides a heat spreading and heat dissipation solution.

The present invention can be applied to various applications as a thermal diffusion and heat dissipation material that can effectively control the heat generated from electronic devices composed of electronic circuits in view of the latest electronic products, displays, and lighting development trends requiring ultra-thin and ultra-thin products. And it can maximize the efficiency more than four times than the existing heat dissipation method. This heat dissipation material, along with economics, can reduce the weight of applied product sets and have a profound effect on slimmer electronics. In addition, it can be applied to a method for preparing a composite having new physical properties and properties by filling the microparticles of different characteristics in the porous powder using the vacuum filling method used in the production of the composite.

1 is a SEM (scanning electron microscope) photograph before and after filling of carbon fine particles in expanded graphite of a composite powder prepared by vacuum immersion method
2 is a thermal conductivity data according to the filling rate of the intercalation material
3 is a graph showing the thermal conductivity when the vacuum filling using a dispersant
4 is a graph showing the vertical thermal conductivity when carbon fine particles, nitrides and carbide fine particles are added between interlayer voids of expanded graphite;

Natural graphite powders with particle size of 30 to 80 mesh (HF), sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl) are used to produce composite sheets of natural graphite and carbide or nitride fine particles. Acid treatment to prepare high-purity natural graphite powder, followed by oxidation treatment with sulfuric acid, intercalation, and rapid thermal treatment at 600 ~ 1,000 ℃ for 1 ~ 5 minutes for expansion with expansion rate of 200 ~ 500ml / g Graphite was prepared. Group consisting of carbide or nitride fine particles, ie, carbon (pitch, coke, natural gas, tar, etc.), aluminum nitride (AlN), boron nitride (BN), and silicon carbide (SiC) One or more materials selected from were vacuum filled. At this time, the vacuum filling was mixed with fine particles in a predetermined amount of solvent, and then a dispersion was prepared using polycarboxylate ammonium salt, polycarboxylate sodium salt, sodium dodecyl sulfate, and ethylene glycol as a dispersant, and the prepared dispersion was immersed in expanded graphite powder. After that, the vacuum was maintained at a pressure of about 0.1 to 2 Mpa or more for 1 to 30 minutes to remove the air in the voids between the layers of the graphite particles. At the same time, the fine particles in the dispersion were forced to penetrate into the pores and complexed.

(Example 1)

The natural graphite used in the present invention had a particle size of 50-80 mesh, purity was 94.6%, quartz (SiO ₂ ) 2.79%, iron oxide (Fe ₂ O ₃ ) 0.91%, aluminum oxide (Al ₂ O) as impurities. ₃ ) 0.61%, calcium oxide (CaO) 0.4%, and magnesium oxide (MgO) 0.38%. Inclusion of such impurities leads to deterioration of the thermal conductivity, so that the acid treatment is performed using hydrofluoric acid (HF), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl) to remove impurities as shown in Table 1, followed by 99.88%. Natural graphite having a purity of was used in the experiment. In the case of acid treated graphite, the amount of impurities is reduced to 0.06% of quartz (SiO ₂ ), 0.02% of iron oxide (Fe ₂ O ₃ ), 0.02% of aluminum oxide (Al ₂ O ₃ ), and 0.01% of magnesium oxide (MgO). It was.

Impurity control of graphite through acid treatment Na ₂ O MgO K ₂ O CaO Fe ₂ O ₃ Al ₂ O ₃ TiO ₂ MnO SiO ₂ Ignition loss Natural graphite 0.009 0.38 0.09 0.40 0.91 0.61 0.04 0.02 2.79 94.6 Acid treated graphite - 0.01 - - 0.02 0.02 0.01 - 0.06 99.88

(unit %)

High purity natural graphite, complete with acid treatment using hydrofluoric acid (HF), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl), uses sulfuric acid (H ₂ SO ₄ ) as an insert material, and chromium oxide (CrO ₃ ), Oxidative treatment was performed using an intercalation process using potassium permanganate (KMnO ₄ ), nitric acid (HNO ₃ ), etc., and then 200-500 ml / g using a quartz crucible at 600-900 ° C. for 1-5 minutes. Expanded graphite with high expansion volume was used to prevent thermal degradation caused by unexpanded graphite, and polycarboxylate of nitride and carbide fine particles (carbon, AlN, BN, SiC) having sizes of several tens of nm to 5 μm or less Dispersion was made by using ammonium salt, polycarboxylate sodium salt, sodium dodecyl sulfate, and ethylene glycol to prepare a dispersion, and then mixed in a predetermined amount to make a composite using the vacuum filling method shown above, and pressurized at 400 to 1.5 ton / cm ² . After molding, through 3 ~ 5 rollers at room temperature In this case, the time was prepared by a roller compaction for about 1-3 minutes having a shrinkage of 30% or more and a density of 1.5 ~ 2.0 g / cm ³ . As shown in FIG. 3, the thermal conductivity of polycarboxylate ammonium salt, polycarboxylate sodium salt, sodium dodecyl sulfate, and ethylene glycol in the case of not using a dispersant and vacuum-filled using the dispersant was 2.0 and 7.9 w / mk, respectively. It was increased about 4 times with dispersant.

Natural graphite used in the present invention is used to expand the thermal properties due to unexpanded graphite by using expanded graphite having a high expansion volume of 300-500 ml / g, and mixed a certain amount of amorphous carbon fine particles of 10 ~ 110nm and the vacuum shown above The composite was made by dipping and a sheet having a shrinkage of 30% or more and a density of 1-2 g / cm 3 was produced by the compression molding method. Table 2 shows the expanded graphite and the content of amorphous carbon fine particles, carbides and nitrides.

additive Nitride and Carbide Fines
(weight%) Vertical thermal conductivity
(W / mk) Carbon black (20nm) 0 4.0 5 4.2 10 5.5 Carbon black (4㎛) 3 9.7 SiC 3 6.2 BN 3 7.4 AlN 3 10.9 High Purity Secondary Purification 0 12.0

(Example 2)

Example 2 was prepared by using a composite powder of expanded graphite and amorphous particulate carbon, carbides and nitrides prepared in Example 1 each to a thickness of 1mm, compression ratio of 30% or more, pressure 500 ~ 700kg / cm ² , The thermal conductivity measurement data in the vertical direction is shown.

As shown in Table 2 and FIG. 4, when 0, 5, or 10 weight percent of carbon fine particles were added between the interlayer pores of the expanded graphite, the thermal conductivity in the vertical direction increased to 4.0, 4.2, and 5.55 w / mk, respectively. However, when the carbon fine particles, nitride and carbide fine particles (SiC, BN, AlN) of FIG. 4 were filled in 3 weight percent, the thermal conductivity in the vertical direction increased 1.5 to 2.5 times to 9.7, 6.2, 7.4, and 10.9 W / mk, respectively. In addition, when the high-purity purification was performed at 12.0W / mk when the second-purification of the natural graphite was used, the thermal conductivity was greatly improved.

Claims (4)

After natural graphite is swelled and expanded, nano-sized carbides and nitrides (C, SiC, BN, and AlN) having high thermal conductivity are dispersed without aggregation in a horizontal interlayer void without vacuum packing to roller or press. A heat dissipating material characterized in that it is produced in a sheet (sheet) or plate after compression molding.
The method of claim 1,
When high purity expanded graphite is prepared using hydrofluoric acid (HF), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl) to remove impurities contained in and on the matrix surface of the expanded graphite, A heat dissipating material characterized by having high thermal conductivity by filling conductive fine particles in interlayer voids.
The method of claim 1,
The content of carbides and nitrides (C, SiC, BN, AlN) is less than 30% by weight relative to the total weight of the expanded graphite and the packed fine particles, polycarboxylate ammonium salt as a dispersant to avoid agglomeration to less than 1 particle size, A heat dissipating material comprising polycarboxylate sodium salt, sodium dodecyl sulfate, and ethylene glycol in an amount of 1 to 5 percent by weight to uniformly disperse and fill the interlayer voids.
The method of claim 3, wherein
A heat dissipation material comprising the step of manufacturing a heat dissipation sheet by compression molding the mixture with a roller or a press, including the step of preparing by filling with vacuum when the high thermal conductivity fine particles are filled. Manufacturing method.

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