KR102342310B1 - Method for preparing graphite sheet - Google Patents

Abstract

The present invention relates to a method for manufacturing a graphite sheet, and more particularly, a three-dimensional fiber substrate such as paper containing fibers having a carbon fraction of 50% or more using a precursor, and carbonization, graphitization, and rolling process are performed to conduct heat Also, it is possible to manufacture a graphite sheet having improved thermal conductivity in the vertical direction.

Description

Manufacturing method of graphite sheet {METHOD FOR PREPARING GRAPHITE SHEET}

The present invention relates to a method for manufacturing a graphite sheet.

In light of the recent trend of electronic devices becoming highly functional, highly integrated, and lightweight, it is essential to effectively dissipate the heat generated during operation of electronic devices. To this end, various heat dissipation materials are being developed and applied in the form of heat dissipation pads, heat dissipation sheets, and heat dissipation paints. Among them, the heat dissipation sheet is produced in the form of graphite sheet, polymer-ceramic composite sheet, and multi-layer coated metal thin film sheet. In addition to chemical properties and high thermal conductivity, in particular, thermal conductivity is much higher than that of copper, so it is widely used in various electronic devices.

As an example of the manufacturing method of a graphite sheet, there exists a method called "the expanded (expanded) graphite method." In this method, artificial graphite is prepared by immersing natural graphite in a mixed solution of concentrated sulfuric acid and concentrated nitric acid and then rapidly heating it. Then, the expanded graphite is removed from acid by washing, and processed into a film shape by a high-pressure press or roll. However, the graphite sheet manufactured through the above method has problems such as weak strength, poor other physical properties, and concerns about the influence of residual acids.

In order to solve this problem, a polymer graphitization method in which a polymer film is directly heat-treated to graphitize has been developed. Specifically, the polymer graphitization method is a process of carbonizing a polymer film, which is a precursor for a graphite sheet, usually at a temperature of 1,200 to 1,400 ℃, and a process of graphitizing a precursor for a graphite sheet that has been carbonized at a temperature of up to 2,800 ℃. A method for manufacturing a graphite sheet. Examples of the polymer film used at this time include polyoxadiazole, polyimide, polyphenylenevinylene, polybenzoimidazole, polybenzoxazole, polythiazole, and polyamide films.

This polymer graphitization method is a much simpler method compared to the conventional expanded graphite method, is a method that essentially does not cause mixing of impurities such as acid, and has the characteristics of obtaining excellent thermal and electrical conductivity close to that of single crystal graphite. .

However, the graphite sheet produced by such a polymer graphitization method has high thermal conductivity (thermal diffusivity) in the horizontal direction, but low thermal conductivity in the vertical direction. There are disadvantages.

The low vertical thermal conductivity of the graphite sheet cannot secure sufficient performance when applied as a heat dissipation material, and various technologies have been proposed to improve it.

As an example, Korean Patent Laid-Open No. 2017-0081874 discloses that by using a polyimide film including a thermally conductive material such as carbon nanotubes and boron nitride as a precursor of a graphite sheet, the thermal conductivity in the vertical direction of the graphite sheet can be improved. is starting

In addition, Korean Patent No. 1855281 discloses a method for manufacturing a heat dissipation sheet with excellent horizontal and vertical thermal conductivity. After perforating a graphite sheet manufactured by heat-treating a substrate coated with a coating solution containing a polymer, a carbonized polymer, or graphite, , discloses a method comprising the step of coating one or both sides thereof with a metal.

These patents improve the thermal conductivity of the graphite sheet in the vertical direction to some extent by adding a material having excellent thermal conductivity or forming a coating layer using the same, but the effect is not sufficient. In addition, the methods presented in these patents have a problem in that manufacturing costs are high because expensive polyimide films are used or the process is complicated. Therefore, there is a need for further development of a method for manufacturing a graphite sheet capable of economically manufacturing a graphite sheet having excellent thermal conductivity in both horizontal and vertical directions.

Republic of Korea Patent Publication No. 2017-0081874 Republic of Korea Patent No. 1855281

Accordingly, the present inventors have conducted research from various angles to solve the above problem. As a result, a fiber base is used as a precursor in the manufacture of a graphite sheet, the fiber base is impregnated with a thermally conductive interface material, and rolled before and after carbonization and graphitization. In the case of performing the process, it was confirmed that the thermal conductivity in the vertical direction of the finally manufactured graphite sheet was improved, and the flexibility was improved, thereby completing the present invention.

Accordingly, it is an object of the present invention to provide a method for manufacturing a graphite sheet that can easily and economically manufacture a graphite sheet having improved thermal conductivity, in particular, thermal conductivity in a vertical direction.

In order to achieve the above object, the present invention comprises the steps of (S1) preparing a fiber base using a short fiber; (S2) preparing a composite substrate by impregnating the fiber substrate obtained in step (S1) with a thermally conductive interface material; (S3) heat-treating the composite substrate obtained in step (S2) to carbonize and graphitize to prepare a graphite sheet; And (S4) provides a method of manufacturing a graphite sheet comprising the step of rolling to improve the thermal conductivity of the graphite sheet obtained in step (S3).

In the method for manufacturing a graphite sheet according to the present invention, a graphite sheet having excellent vertical and horizontal thermal conductivity can be manufactured by using a high-density fiber substrate as a precursor and performing a rolling process after carbonization and graphitization. In addition, since an expensive polyimide polymer film is not used as a precursor, the manufacturing cost is reduced, and thus the economic feasibility and productivity of the manufacturing process can be improved.

1 is a scanning electron microscope (SEM) image of the surface of a fiber substrate according to Example 1 of the present invention.
2 is a scanning electron microscope (SEM) image of a cross-section of a fiber substrate according to Example 1 of the present invention.
3 is a scanning electron microscope (SEM) image before and after rolling of a cross section of a fiber substrate according to Experimental Example 2 of the present invention.
4 is a scanning electron microscope (SEM) image of a cross-section of a composite substrate according to Experimental Example 3 of the present invention.
5 is a scanning electron microscope (SEM) image of a cross-section of a composite substrate according to Experimental Example 4 of the present invention after rolling.
6 is a scanning electron microscope (SEM) image of the surface of the graphite sheet according to carbonization and graphitization in Experimental Example 5 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, terms such as 'comprising' or 'having' are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, and one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

The term “horizontal thermal conductivity (thermal diffusivity)” of the graphite sheet used in the present invention refers to both the thermal conductivity of the graphite sheet in the longitudinal direction and the width direction on a plane.

The term “vertical thermal conductivity (thermal diffusivity)” of the graphite sheet as used in the present invention refers to the thickness direction (height direction) of the graphite sheet perpendicular to the longitudinal and/or width directions on the plane of the graphite sheet. Of course, it means both the thickness direction (height direction) of the graphite sheet forming an inclination angle with the longitudinal direction of the graphite sheet in the plane of the thermal conductivity.

Recently, electronic devices are required to emit heat due to an increase in thermal density due to light, thin, compact, highly functional, and high integration.

Recently, with the spread of electric vehicles and renewable energy vehicles, the use of electronic components is increasing, and since batteries with high heat generation are used as the main power source, measures against heat generation are essential. In particular, autonomous vehicles are an integral part of all electric and electronic industries such as mobile communication technology, lighting, cameras, displays, and batteries, and there are limits to development and dissemination unless the heat problem is solved.

In addition, as the weight reduction and slimming of various electronic devices including portable electronic devices and communication devices progress, heat control is continuously raised as a problem due to an increase in thermal density due to high integration of electronic devices. In the electrical and electronic industry, unless a superconductor (resistance = 0) is used, there is inevitably a heat problem, and this heat issue is closely related to reliability and lifespan as well as the performance of electronic devices. The demand for next-generation heat dissipation materials capable of efficiently discharging is rapidly increasing.

For this purpose, in the prior art, a graphite sheet prepared by heat-treating a polymer film such as polyimide at a high temperature is used. The film-based graphite sheet prepared by this polymer graphitization method has a structure in which the graphene layer is arranged in a 2D direction and has a thermal conductivity of 1,000 W/m·K or more in the horizontal direction, but a maximum of 20 W in the vertical direction. Although it has been reported up to /m·K, it usually has a lower thermal conductivity compared to the horizontal direction of 5 W/m·K or less. This heat conduction characteristic has no problem in dissipating heat generated in a hot spot area where a specific part of the electronic device locally rises to a high temperature. However, as described above, as the use of high-performance and small-sized components integrated in electronic devices increases in recent years, the low vertical thermal conductivity of the conventional graphite sheet has a limit in effectively dissipating the generated heat.

Accordingly, the present invention provides a method of manufacturing a graphite sheet using a fiber type as a precursor of the graphite sheet in order to improve the thermal conductivity in the vertical direction of the graphite sheet, which has been pointed out as a limitation of the existing heat dissipation material.

Specifically, the manufacturing method of the graphite sheet according to the present invention comprises the steps of (S1) preparing a fiber base using short fibers; (S2) preparing a composite substrate by impregnating the fiber substrate obtained in step (S1) with a thermally conductive interface material; (S3) heat-treating the composite substrate obtained in step (S2) to carbonize and graphitize to prepare a graphite sheet; and (S4) rolling the graphite sheet obtained in step (S4).

(S1) step

In step (S1), a fiber base is prepared using short fibers.

In the present invention, the fiber base includes short fibers (chopped 　 fibers) oriented in a three-dimensional form as a precursor of the graphite sheet. In particular, in the case of the present invention, since it has a three-dimensional crystal structure by using a fiber base including short fibers as a precursor of the graphite sheet, compared to the conventional graphite sheet using a polymer film having only a crystal structure in the horizontal direction as a precursor It is possible to manufacture a graphite sheet with improved thermal conductivity in the vertical direction. In addition, the polymer film used in the polymer graphitization method, which is a method of manufacturing a conventional graphite sheet, specifically, instead of an expensive polyimide film, a fiber substrate containing relatively inexpensive short fibers is used, thereby lowering the manufacturing cost and improving economic efficiency and productivity. have an advantage

The short fiber means a long fiber cut to a predetermined length, and the length is not particularly limited, but may be, for example, in the range of 3 to 56 mm.

The short fibers are meta-aramid (m-aramid), para aramid (aramid) such as aramid (aramid); polyimides (polyimide, PI) such as poly(amideimide), PAI) and polyetherimide (PEI); polyamide (PA); Polystyrene, PS), polyethylene (polyethylene, PE), polyethylene terephthalate (poly(ethyleneterephthalate), PET), polyvinyl chloride (poly(vinyl chloride), PVC), polyvinylidene chloride (poly(vinylidene chloride), PVDC ), polypropylene (PP), polysulfone, polyetheretherketone (poly(etheretherketone)), poly(phenylene sulfide), polycarbonate (polycarbonate, PC), polyaryletherketone (poly(aryletherketone)), acrylonitrile-butadiene-styrene polymer (ABS) and acrylate-styrene-acrylonitrile polymer (acrylonitrile styrene acrylate, ASA); and epoxy; Thermoset polymers such as (epoxy), phenol, unsaturated polyester, polyurethane (PU), melamine, urea; and polyacrylonitrile; PAN), pitch, and may be at least one selected from the group consisting of cellulose-derived carbon fibers Preferably, the short fibers are selected from the group consisting of aramid, polyimide and thermosetting polymer It may include more than one species.

In the fiber base, the above-mentioned short fibers are oriented in a three-dimensional form, and when a single fiber is used, the single fiber itself is usually drawn at a level of 1.5 to 20 times compared to the initial discharge rate, and the draw ratio is lead-free with a draw ratio of less than 1.5 times. It is formed in a highly oriented structure compared to the polyimide polymer film made of new material, and thus high thermal conductivity can be realized through the graphitization process. In addition, when the fiber base is used as a raw material for forming a graphite sheet, it has a three-dimensional isotropic structure, so that the difference in thermal conductivity in the horizontal and vertical directions is relatively low compared to the polymer film having a two-dimensional structure. It is effective in improving the thermal conductivity in the vertical direction.

The fiber base is a three-dimensional porous structure including pores therein, and may be in the form of a sheet, a fabric, or a web.

Accordingly, the fiber base material may be paper, nonwoven, woven, knit, felt, mat, prepreg or nano web, etc. have.

The manufacturing method of the fiber base is not particularly limited, and various methods known by those skilled in the art or various methods for modifying it can be used. For example, methods such as dry laid, wet-laid, spinning, air-laid, melt-blown, and lamination stretching methods may be used. have.

The fiber base may further include a material commonly used in addition to the short fibers. For example, it may further include a binder fiber, a surfactant, a dispersant, a thickener, etc. for bonding the short fibers constituting the fiber base and making the fiber base strong.

Here, in order to increase the strength of the fiber substrate to facilitate processing in a subsequent step, and to minimize the voids present inside the fiber substrate, the three-dimensional porous structure includes voids inside, that is, between the short fibers, and the bulk density In the initial fiber base having a (bulk density) of 10 to 60% of the inherent density, air contained in the voids present inside the fiber base acts as a resistance in heat conduction, so through rolling By removing this and increasing the bulk density of the fiber substrate, it is possible to secure the effect of improving the thermal conductivity of the finally manufactured graphite sheet, in particular, the thermal conductivity in the vertical direction.

The rolling may be performed according to a conventional method known in the art. The temperature and pressure of rolling may vary depending on the fiber base or the short fibers included therein. For example, the rolling can be performed at a temperature of 80 to 200 ° C and a pressure of 30 to 200 kgf / cm in the case of a continuous production method, and in the case of a sheet rolling method, it can be adjusted to a level similar to the linear pressure effect of the continuous production method have.

The thickness of the fiber base after the rolling is preferably 40 to 80% of the thickness of the fiber base before performing the rolling to improve thermal conductivity and other physical properties of the graphite sheet as a final product. The air permeability of the fiber base after the rolling is preferably 0.1 to 45% of the air permeability of the fiber base before performing the rolling to improve the thermal conductivity and other physical properties of the graphite sheet as a final product.

(S2) step

In step (S2), a composite substrate is prepared by impregnating the fiber substrate obtained in step (S1) with a thermally conductive interface material (TIM).

In the present invention, the composite substrate completely removes air by filling the pores of the fiber substrate prepared in the step (S1) through impregnation with a thermally conductive interface material, and increases the interfacial contact between the short fibers. It is possible to improve the thermal conductivity of the sheet in the horizontal and vertical directions.

The thermally conductive interface material is not limited to a type as long as a polymer having a carbon component fraction of 50% or more in terms of molecular structure. For example, the thermally conductive interface material is a chemical such as polyimide (PI), lignin, aramid, poly(amideimide, PAI), and polypropylene (polypropylne, PP). It may be at least one selected from the group consisting of a cured thermoplastic resin and a phenol resin, and preferably, the thermally conductive interface material has a relatively high carbon component fraction and is made of a resin with easy viscosity control. It may include one or more selected from.

The composite substrate may be obtained by impregnating the fiber substrate obtained in step (S1) in a varnish composition including the thermally conductive interface material.

Examples of the impregnation method include a method of immersing the fiber substrate in the varnish composition containing the thermally conductive interface material, and applying a varnish composition containing a thermally conductive interface material to the fiber substrate by various coating machines. There is a method of infiltrating the varnish composition containing the thermally conductive interface material into the fiber substrate by spraying, but is not limited thereto. Among them, the method of immersing the fiber base in the varnish composition containing the thermally conductive interface material is preferable because it can improve the impregnability of the varnish composition to the fiber base.

The content of the thermally conductive interface material in the varnish composition may be 10 to 80% by weight, preferably 30 to 60% by weight, based on 100% by weight of the total varnish composition. If the content of the thermally conductive interface material is less than the above range, the voids in the substrate cannot be sufficiently filled, so there is a limit to increasing the density, which may cause a problem of increasing resistance. It is preferable to determine the appropriate content within the above-mentioned range because the properties may be lowered.

A composite substrate is prepared by curing and drying the fiber substrate impregnated with the varnish composition to form a composite. In this case, the curing and drying conditions may vary depending on the type of material used.

Accordingly, the content of the thermally conductive interface material in the composite substrate may be 40 to 80% by weight based on 100% by weight of the composite substrate.

The composite substrate may further include a filler to improve thermal conductivity.

The filler may be a ceramic-based or polymer-based material, and in the case of a polymer-based material, may be the same material as the short fibers constituting the fiber substrate. In addition, the filler is preferably in the form of particles or powder, not in the form of chops or fibers, in that it is intended to fill the voids inside the fiber substrate.

The filler is a single-well carbon nanotube (SWCNT), multi-wall carbon nanotube (multi-well carbon nanotube, MWCNT), such as carbon nanotube (carbon nanotube, CNT), graphene (graphene), It may include at least one selected from the group consisting of graphite powder, conductive carbon black (carbon black), and boron nitride nanotube (BNNT).

The carbon nanotubes may have a diameter of 4 to 50 nm and a length of 1 to 500 μm.

The boron nitride nanotubes may have a diameter of 0.01 to 3 μm, preferably 0.1 to 1.0 μm.

When the diameter and length of the carbon nanotube and the diameter of the boron nitride nanotube are out of the above ranges, the effect of improving the vertical thermal conductivity of the finally manufactured graphite sheet may be weak or a problem may occur in the process.

The filler may be included in the varnish composition as described above and impregnated into the fiber substrate.

In addition, the content of the filler in the composite substrate is preferably 10% by weight or less based on 100% by weight of the composite substrate.

The composite substrate prepared in step (S2) has a three-dimensional porous structure, that is, includes pores between short fibers, and has a bulk density of 10 to 60% of the inherent density. In the carbonization graphitization process, which is a subsequent step, many components except carbon are thermally volatilized to reduce weight. Therefore, in order to facilitate processing, the strength of the composite substrate should be increased and voids present inside the fiber substrate should be minimized.

In addition, since air contained in the pores existing inside the composite substrate acts as a resistance in heat conduction, it is removed through rolling to increase the bulk density of the composite substrate to increase the thermal conductivity properties of the finally manufactured graphite sheet, especially in the vertical direction. It is possible to secure the effect of improving the thermal conductivity.

The temperature and pressure of the rolling may vary depending on the fiber base or the varnish composition. For example, the rolling can be performed at a temperature of 100 to 350 ° C and a pressure of 30 to 250 kgf / cm in the case of a continuous production method, and in the case of a sheet rolling method, it can be adjusted to a level similar to the linear pressure effect of the continuous production method have.

The thickness of the composite substrate subjected to the rolling is preferably 95% or less of the thickness of the fiber substrate before performing the rolling to improve thermal conductivity and other physical properties of the graphite sheet as a final product.

The increase rate of bulk density by the rolling is preferably 40 to 95% of the average density of the fiber substrate and the thermally conductive interface material. When the increase rate of the bulk density is less than the above range, too many pores are formed after the subsequent carbonization and graphitization process, so that the heat dissipation effect is reduced. do.

(S3) step

In the step (S3), the composite substrate obtained in the step (S2) is heat-treated to carbonize and graphitize to prepare a graphite sheet.

The heat treatment is to increase the thermal properties of the composite substrate, and is not particularly limited as long as it is a method for carbonizing and graphitizing polymers and/or fibers in general, and may be performed according to a conventional method known in the art.

For example, the carbonization temperature may be 800 to 1,500 °C, preferably 900 to 1,400 °C. In addition, the graphitization may be performed at a temperature of 2,600 to 3,000 °C, preferably 2,700 to 2,900 °C.

The carbonization and graphitization are preferably performed in an inert atmosphere so that the composite substrate is not oxidized by reaction with air. The medium used for maintaining the inert atmosphere is not particularly limited, and nitrogen or argon may be used.

In addition, the carbonization and graphitization times may be adjusted according to the materials constituting the composite substrate.

(S4) step

In step (S4), the graphite sheet obtained in step (S3) is rolled.

In the present invention, the rolling is to increase the bulk density and flexibility of the expanded graphite sheet due to the gas generated during the heat treatment in step (S3), and to further improve the thermal conductivity in the horizontal and vertical directions.

The rolling may be performed according to a conventional method known in the art.

The rolling pressure may vary depending on the physical properties of the produced graphite sheet. For example, the rolling may be performed at a pressure of 10 to 300 kgf / cm.

According to the manufacturing method of the graphite sheet of the present invention, by using a fiber substrate as a precursor of the graphite sheet, impregnating the fiber substrate with a thermally conductive interface material, and performing a rolling process before and after carbonization and graphitization, heat conduction in the horizontal direction It is possible to manufacture a graphite sheet having excellent thermal conductivity in the vertical direction as well as the degree of heat transfer. In addition, the manufacturing method of the graphite sheet can economically manufacture a graphite sheet having excellent horizontal and vertical thermal conductivity in a simple process without using an expensive polymer film as a precursor.

The graphite sheet manufactured by the manufacturing method as described above has a thermal conductivity of 1,000 to 2,000 W/m·K in the horizontal direction, a thermal conductivity of 10 to 40 W/m·K in the vertical direction, and an average thickness It may be 10 to 200 μm.

In particular, the graphite sheet according to the present invention exhibits thermal conductivity in the vertical direction greater than or equal to the limit value of the vertical thermal conductivity of the conventional graphite sheet, and is useful as a heat dissipation sheet for various electronic devices due to improved flexibility.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

[Example 1]

A fiber base was prepared using a wet method by mixing aramid short fibers having a length of 6 mm, aramid pulp, and polyvinyl alcohol having a length of 3 mm as binder fibers in a weight ratio of 25:72:3.

The fibrous substrate was rolled at a temperature of 120° C. and a pressure of 148 kgf/cm.

Then, the rolled fiber base in a padder mangle was impregnated with a varnish composition containing 10% by weight of polyimide, dried at 130° C., and cured at 350° C. to prepare a composite substrate.

The composite substrate was rolled at a temperature of 200° C. and a pressure of 200 kgf/cm.

The rolled composite substrate was carbonized in a nitrogen atmosphere at 1,200 °C.

Then, the carbonized composite substrate was graphitized in an argon atmosphere at 2,800° C., and then rolled at a pressure of 30 kgf/cm to prepare a graphite sheet.

[Example 2]

A graphite sheet was prepared in the same manner as in Example 1, except that a varnish composition containing 20% by weight of polyimide was used to prepare the composite substrate.

[Example 3]

A graphite sheet was prepared in the same manner as in Example 1, except that short fibers, pulp, and binder fibers were used in a weight ratio of 50:47:3 when preparing the fiber base.

[Example 4]

In the manufacture of the fiber base, short fibers, pulp, and binder fibers were used in a weight ratio of 50:47:3, and in the manufacture of the composite base, a varnish composition containing 20 wt% of polyimide was used. A graphite sheet was prepared in the same manner.

[Example 5]

A graphite sheet was prepared in the same manner as in Example 1, except that short fibers, pulp, and binder fibers were used in a weight ratio of 60:37:3 during the manufacture of the fiber base material.

[Example 6]

In the manufacture of the fiber base, short fibers, pulp, and binder fibers were used in a weight ratio of 60:37:3, and in the manufacture of the composite base, a varnish composition containing 20 wt% of polyimide was used, except that A graphite sheet was prepared in the same manner.

[Example 7]

A graphite sheet was prepared in the same manner as in Example 1, except that short fibers, pulp, and binder fibers were used in a weight ratio of 70:27:3 when preparing the fiber base.

[Example 8]

In the manufacture of the fiber base, short fibers, pulp, and binder fibers were used in a weight ratio of 70:27:3, and in the manufacture of the composite base, a varnish composition containing 20 wt% of polyimide was used, except that A graphite sheet was prepared in the same manner.

[Comparative Example 1]

A polyimide film having a thickness of 75 μm was carbonized and graphitized to prepare a graphite sheet. At this time, carbonization was carried out at 900 °C and graphitization was performed at 2,800 °C.

Experimental Example 1. Evaluation of physical properties of fiber substrates and analysis by scanning electron microscopy

The weight per unit area, thickness, and air permeability of the fiber substrates prepared in Examples 1, 3, 5, and 7 were measured. At this time, the air permeability was measured using an air permeability tester (FX3300, manufactured by Textest Instruments).

In addition, the surface and cross-section of the fiber substrate prepared in Example 1 were observed with a scanning electron microscope (SEM). As a scanning electron microscope, Hitachi's S-4800 was used.

The results obtained at this time are shown in Table 1, FIGS. 1 and 2 .

Weight per unit area (g/m2) Thickness (㎛) air permeability Example 1 30.0 126 5.53 Example 3 34.5 140 22.7 Example 5 32.0 123 17.0 Example 7 42.1 210 63.2

Referring to Figure 1, it can be confirmed that the fibrous substrate of the three-dimensional porous structure composed of short aramid fibers and having pores formed therein was prepared.

Experimental Example 2. Evaluation of the physical properties of the fiber base according to rolling and scanning electron microscopy analysis

After rolling the fiber substrates prepared in Examples 1, 3, 5, and 7, the weight per unit area, the thickness, and the air permeability were measured. At this time, the air permeability was measured through an air permeability tester (FX3300, manufactured by Textest Instruments).

In addition, cross-sections before and after rolling of the fiber substrate prepared in Example 1 were observed with a scanning electron microscope (SEM). As a scanning electron microscope, Hitachi's S-4800 was used.

The results obtained at this time are shown in Table 2 and FIG. 3 .

Weight per unit area (g/m2) Thickness (㎛) air permeability Example 1 30.0 52 0.927 Example 3 34.5 79 5.95 Example 5 32.0 69 3.89 Example 7 42.1 84 14.0

Referring to FIG. 3 and Table 2, it can be seen that the thickness and air permeability of the fiber substrate are reduced by rolling.

Experimental Example 3. Evaluation of the physical properties of the composite substrate and analysis by scanning electron microscopy

The cross-section of the composite substrate prepared in Example 1 was observed with a scanning electron microscope (SEM). As a scanning electron microscope, Hitachi's S-4800 was used.

The results obtained at this time are shown in FIG. 4 .

Referring to FIG. 4 , it can be seen that the varnish composition is uniformly impregnated in the fiber base.

Experimental Example 4. Evaluation of the physical properties of the composite substrate according to rolling and scanning electron microscopy analysis

For the composite substrates prepared in Examples 1 to 8, the weight after rolling and the thickness before and after rolling were measured.

In addition, the cross-section of the composite substrate prepared in Example 1 after rolling was observed with a scanning electron microscope (SEM). As a scanning electron microscope, Hitachi's S-4800 was used.

The results obtained at this time are shown in Table 3 and FIG. 5 .

Concentration of thermally conductive interfacial material (wt%) Weight (g) before rolling after rolling Thickness (㎛) Example 1 10 0.398 58 46 Example 2 20 0.471 64 54 Example 3 10 0.629 122 83 Example 4 20 0.778 128 89 Example 5 10 0.392 72 52 Example 6 20 0.460 78 55 Example 7 10 0.586 130 85 Example 8 20 0.799 139 99

Referring to FIG. 5 and Table 3, it can be seen that the thickness of the composite substrate is reduced by rolling.

Experimental Example 5. Evaluation and Scanning Electron Microscopy Analysis of Physical Properties of Graphite Sheets

For the graphite sheets prepared in Examples 1 to 8, the weight and yield according to carbonization and graphitization were measured.

In addition, the surface of the graphite sheet following carbonization and graphitization of the composite substrate prepared in Example 1 was observed with a scanning electron microscope (SEM). As a scanning electron microscope, Hitachi's S-4800 was used.

The results obtained at this time are shown in Table 4 and FIG. 6 .

carbonization graphitization Total yield (%) Weight (g) transference number(%) Weight (g) transference number(%) Example 1 0.183 46.0 0.122 66.7 30.7 Example 2 0.241 51.2 0.183 75.9 38.9 Example 3 0.286 45.5 0.229 80.1 36.4 Example 4 0.385 49.5 0.315 81.8 40.5 Example 5 0.191 48.7 0.139 72.8 35.5 Example 6 0.218 47.4 0.172 78.9 37.4 Example 7 0.283 48.3 0.217 76.7 37.0 Example 8 0.405 50.7 0.320 79.0 40.1

It can be seen from FIG. 6 that the color of the composite substrate changes to black after carbonization and silver after graphitization.

In addition, it can be seen from Table 4 that the carbonization yield of the composite substrate is 45 to 51%, the graphitization yield is 66 to 81%, and the total yield is 30 to 40%.

Experimental Example 6. Measurement of thermal conductivity of graphite sheet

For the graphite sheets prepared in Example 1 and Comparative Example 1, the thermal conductivity in the horizontal and vertical directions was measured. At this time, the thermal conductivity in the horizontal and vertical directions was measured using a thermal diffusivity measuring device (“LFA447 Nanoflash” manufactured by Netsch Co., Ltd.) for the graphite sheets prepared in Example 1 and Comparative Example 1 at a temperature of 25° C., respectively. It was measured at least 5 times and expressed as an average value. The results obtained at this time are shown in Table 5.

Horizontal thermal conductivity
(W/m K) vertical thermal conductivity
(W/m K) Example 1 800 23 Comparative Example 1 1,200 5

Referring to Table 5, it can be seen that the thermal conductivity of the graphite sheet according to Example 1 is higher than that of Comparative Example 1, and in particular, it can be confirmed that the thermal conductivity in the vertical direction is significantly improved compared to Comparative Example 1.

Claims (10)

(S1) forming a short fiber containing a polymer into a highly oriented three-dimensional porous structure and then rolling to prepare a fiber base;
(S2) applying a thermally conductive interface material to the fiber substrate obtained in step (S1), followed by rolling to prepare a composite substrate;
(S3) heat-treating the rolled composite substrate obtained in step (S2) to carbonize and graphitize to prepare a graphite sheet; and
(S4) comprising the step of rolling the graphite sheet obtained in step (S3),
The polymer is aramid or polyimide,
The thickness of the fiber base after the rolling in the step (S1) is 40 to 80% of the thickness of the fiber base before performing the rolling, and the air permeability of the fiber base after the rolling in the step (S1) is to perform the rolling 0.1 to 45% of the air permeability of the former fiber base,
The thickness of the composite substrate subjected to the rolling in step (S2) is 95% or less of the thickness of the fiber substrate before performing the rolling, and the rate of increase in bulk density by the rolling in step (S1) is the fiber substrate and the thermoelectric A method for producing a graphite sheet having 40 to 95% of the average density of the conductive interfacial material. delete According to claim 1,
Thermal conductivity in the vertical direction of the graphite sheet is 10 to 40 W / m · K, a method of manufacturing a graphite sheet. According to claim 1,
The method for producing a graphite sheet, wherein the fiber base is in the form of a sheet, a fabric or a web. According to claim 1,
The method for producing a graphite sheet, wherein the thermally conductive interface material includes at least one selected from the group consisting of polyimide, lignin, aramid, polyamideimide, polypropylene, and phenol. According to claim 1,
The composite substrate further comprises a filler, a method for producing a graphite sheet. 7. The method of claim 6,
The method for producing a graphite sheet, wherein the filler includes at least one selected from the group consisting of carbon nanotubes, graphene, graphite powder, conductive carbon black, and boron nitride nanotubes. According to claim 1,
The carbonization is performed at a temperature of 800 to 1,500 ℃, a method for producing a graphite sheet. According to claim 1,
The graphitization is performed at a temperature of 2,600 to 3,000 ℃, a method for producing a graphite sheet. According to claim 1,
The carbonization and graphitization are performed in an inert atmosphere, a method for producing a graphite sheet.

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