TW202120775A - Method for preparing graphite sheet - Google Patents

Abstract

The present invention relates to a method for manufacturing a graphite sheet and, more specifically, can manufacture a graphite sheet with improved thermal conductivity, particularly, improved vertical thermal conductivity by using, as a precursor, a three-dimensional fiber substrate such as paper that comprises a fiber having a carbon fraction of 50% or more, and performing carbonization, graphitization and rolling.

Description

Manufacturing method of graphite sheet

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

With the recent development trend of electronic equipment towards high functionality, high integration, lighter, thinner, shorter and smaller size, it must be able to effectively dissipate the heat generated when the electronic equipment is driven. To this end, various heat dissipation materials are actively being developed and used in the form of heat sinks, heat sinks, and heat dissipation paints. Among them, the heat sink can be made into shapes such as graphite sheet, polymer ceramic composite sheet, multilayer coated metal film sheet, etc., and graphite sheet has characteristics such as light weight, slim, and heat-resistant. It has the advantages of excellent chemical resistance and high thermal conductivity, especially because of its better thermal conductivity than copper, it is widely used in various electronic devices.

As a method of manufacturing the graphite sheet, a method called "expanded graphite method" can be adopted. In the above method, artificial graphite is produced by rapidly heating the natural graphite after immersing it in a mixed solution of concentrated sulfuric acid and concentrated nitric acid. Next, the expanded graphite is washed to remove the acid, and then processed into a film shape by high-pressure punching or rolling. However, the graphite flakes manufactured by the method described above have problems such as weak strength, poor other physical properties, and are easily affected by residual acid.

In order to solve the above-mentioned problems, a polymer graphitization method in which graphitization is performed by direct heat treatment of a polymer film has been developed. Specifically, the polymer graphitization method is a process of sequentially carbonizing a polymer film as a precursor for graphite sheets, usually at a temperature of 1,200 ~ 1,400°C, and a process of carbonizing at a temperature of up to 2,8000°C. The graphite flakes are made of graphite flakes by the process of graphitizing the graphite flakes with the precursor. As the polymer film used at this time, it can include, for example, polyoxadiazole, polyimide, polyphenylene vinylene, polybenzimidazole, polybenzoxazole, polythiazole, and polyamide film.

The polymer graphitization method as described above is a very simple method compared with the existing expanded graphite method. It is a method that does not essentially cause impurities to be mixed in. It also has excellent thermal conductivity close to that of single crystal graphite. Characteristics of conductivity.

However, although the graphite sheet manufactured by the above-mentioned polymer graphitization method has high thermal conductivity (thermal diffusivity) in the horizontal direction, the thermal conductivity in the vertical direction is low, and because it is a polymer The film uses an expensive polyimide film, so there is a problem of high manufacturing cost.

The lower thermal conductivity of the graphite sheet in the vertical direction as described above cannot fully guarantee the performance when used as a heat dissipation material, so many new technologies for improving it have been proposed.

As an example, the Republic of Korea Patent No. 2017-0081874 discloses a graphite sheet precursor using a polyimide film containing thermally conductive materials such as carbon nanotubes and boron nitride to improve the vertical orientation of the graphite sheet. The direction of thermal conductivity technology.

In addition, in the Republic of Korea Registered Patent No. 1855281, as a method for manufacturing a heat sink with excellent thermal conductivity in the horizontal and vertical directions, it is disclosed that the method involves the use of a coating solution containing polymer, carbonized polymer, or graphite. The substrate is heat-treated to produce a graphite sheet and perforated, after which one side or both sides are coated with metal.

Although the above-mentioned patent improves the thermal conductivity of the graphite sheet in the vertical direction to a certain extent by adding a substance with excellent thermal conductivity or using it to form a coating, its effect is not sufficient. Moreover, the method disclosed in the above-mentioned patent may also cause the problem of increased manufacturing cost due to the use of expensive polyimide film or the excessively complicated engineering. Therefore, there is an urgent need to develop a graphite sheet manufacturing method that can manufacture graphite sheets with excellent thermal conductivity in both horizontal and vertical directions in a more economical manner. [Advanced Technical Literature] Republic of Korea Published Patent No. 2017-0081874 Registered Patent No. 1855281 in the Republic of Korea

In view of this, the inventors of the present invention have conducted extensive studies in various aspects in order to solve the above-mentioned existing problems. The material is rolled before and after carbonization and graphitization, which can enhance the vertical thermal conductivity of the finally manufactured graphite sheet and improve its flexibility, thereby completing the present invention.

Therefore, the object of the present invention is to provide a graphite sheet manufacturing method capable of simply and economically manufacturing a graphite sheet with improved thermal conductivity, especially thermal conductivity in the vertical direction.

In order to achieve the above-mentioned object, the present invention provides a method for manufacturing a graphite sheet, including: (S1) a step of manufacturing a fiber base material using short fibers; (S2) by adding the fiber base obtained in the above step (S1) The step of manufacturing a composite substrate by impregnating the material with a thermally conductive interface material; (S3) the step of carbonizing and graphitizing the composite substrate obtained in the above step (S2) by heat treatment, and thereby manufacturing a graphite sheet; And, (S4) a step of rolling in order to improve the thermal conductivity of the graphite sheet obtained in the above step (S3).

The graphite sheet manufacturing method to which the present invention is applied can manufacture graphite sheets with excellent thermal conductivity in the vertical and horizontal directions by using a high-density fiber substrate as a precursor and performing a rolling process after carbonization and graphitization. In addition, there is no need to use an expensive polyimide polymer film as a precursor, so the manufacturing cost can be saved and the economy and productivity of the manufacturing process can be improved thereby.

Next, the present invention will be explained in more detail.

The terms or words used in this specification and claims should not be limited to general meanings or dictionary meanings to be interpreted, but should be properly interpreted so that the inventor can use the best method to interpret his own invention. On the basis of the principle of defining the concept of terminology, an explanation is made in accordance with the meaning and concept of 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. Unless there is a clear meaning to the contrary in the context, singular sentences also include plural meanings. In the present invention, terms such as "including" or "having" are only used to specify the existence of the features, numbers, steps, actions, constituent elements, components, or combinations of the above described in the specification, and should not be understood as pre-excluded The possibility that one or more other features, numbers, steps, actions, constituent elements, components, or combinations of the foregoing may exist or be added.

The term "thermal conductivity (thermal diffusivity) of the graphite sheet in the horizontal direction" used in the present invention refers to the thermal conductivity of the graphite sheet in the length direction and width direction of a plane.

The term "thermal conductivity (thermal diffusivity) of the graphite sheet in the vertical direction" used in the present invention not only refers to the thickness direction of the graphite sheet at right angles to the length and/or width direction of the graphite sheet plane ( The thermal conductivity in the height direction also refers to the thermal conductivity in the thickness direction (height direction) of the graphite sheet at an oblique angle to the longitudinal direction of the graphite sheet plane.

In recent years, the lighter, thinner, shorter, smaller, more functional, and highly integrated electronic devices have led to an increase in heat density and therefore require better heat dissipation performance. The heat dissipation characteristics described above are not only closely related to the performance of electronic devices, but also their reliability. Sex and longevity are closely related.

In addition, with the recent popularity of electric vehicles and renewable energy vehicles, more and more electronic components are used, and because batteries with a large amount of heat are used as the main power source, reliable measures must be taken to deal with heat generation problems. . In particular, self-driving cars are an aggregate of all electrical and electronic industries such as mobile communication technology, lighting, cameras, displays, and batteries. Therefore, if they cannot effectively solve the heat generation problem, it will be difficult to successfully develop and become popular.

In addition, as various electronic devices, including portable electronic devices and communication devices, have become lighter and thinner, electronic components have become more integrated and their heat density has become higher and higher, so heat generation control has always been It is a problem that needs to be solved urgently. Unless a superconductor (resistance=0) is used in the electrical and electronic industry, it will inevitably lead to heat generation problems. The heat generation problems described above are not only closely related to the performance of electronic devices, but also closely related to their reliability and life. Therefore, development is urgently needed A new generation of heat dissipation material that can effectively dissipate the heat generated in electronic equipment has been developed.

For this reason, a graphite sheet manufactured by heat-treating a polymer film such as polyimide at a high temperature is used in the prior art. The thin-film graphite sheet manufactured by the above-mentioned polymer graphitization method has a graphene layer (graphene layer) arranged along the 2D direction on its structure, and the thermal conductivity in the horizontal direction can reach 1,000 W/m·K. Above, but the thermal conductivity in the vertical direction can only reach up to 20 W/m·K, usually only below 5 W/m·K, which is much lower than the thermal conductivity in the horizontal direction. Through the above-mentioned thermal conductivity characteristics, it is possible to dissipate heat generated in a hot spot area where a specific part of the electronic device is locally heated to a higher temperature. However, as mentioned above, with the recent increase in integrated high performance and small components used in electronic equipment, the existing graphite sheet has a low thermal conductivity in the vertical direction, making it difficult to effectively dissipate the generated heat. .

Therefore, in the present invention, in order to improve the thermal conductivity of the graphite sheet in the vertical direction, which is the limit existing in the existing heat dissipation materials, a graphite sheet using a fiber material (fiber type) as the precursor of the graphite sheet is provided. The manufacturing method of the film.

Specifically, the method for manufacturing a graphite sheet to which the present invention is applied includes: (S1) a step of manufacturing a fibrous base material from short fibers; (S2) by impregnating the fibrous base material obtained in the above step (S1) with thermal conductivity The step of manufacturing a composite substrate by using an interface substance; (S3) a step of carbonizing and graphitizing the composite substrate obtained in the above step (S2) by heat treatment, thereby manufacturing a graphite sheet; and, (S4) ) A step of rolling the graphite sheet obtained in the above step (S4). Step ( S1 )

In step (S1), short fibers are used to produce a fibrous base material.

In the present invention, the above-mentioned fiber substrate as a precursor of the graphite sheet includes chopped fibers arranged in a three-dimensional form. In particular, in the present invention, a fibrous substrate containing short fibers is used as the precursor of the graphite sheet, and it has a three-dimensional crystal structure. Therefore, it is possible to manufacture a polymer film with only a horizontal crystal structure as the precursor. Compared with the conventional graphite sheet used in the body, the thermal conductivity in the vertical direction is improved. In addition, by replacing the polymer film used in the existing graphite sheet manufacturing method, that is, the polymer graphitization method, with a fibrous substrate containing relatively inexpensive short fibers, specifically, it can replace the expensive polyimide film. Reduce manufacturing costs and thereby improve its economy and productivity.

The aforementioned short fiber refers to a product obtained by cutting long fiber into a certain length, and the length is not particularly limited, and can be in the range of 3 to 56 mm, for example.

The above-mentioned short fibers can be made from aramid such as m-aramid and p-aramid; such as poly(amideimide, PAI), Polyimide (PI) such as poly(etherimide, PEI); such as polyamide (PA); polystyrene (PS), polyethylene (PE) , Polyethylene terephthalate (poly(ethyleneterephthalate), PET), poly(vinyl chloride) (PVC), poly(vinylidene chloride) (PVDC), polypropylene ( polypropylene, PP), polysulfone, poly(etheretherketone), poly(phenylene sulfide), polycarbonate (PC), poly(etheretherketone) aryletherketone), acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA) and other thermoplastic polymers; Such as epoxy, phenol, unsaturated polyester, polyurethane (PU), melamine, urea and other thermoset polymers; and thermoset polymers derived from poly One or more selected from the group consisting of polyacrylonitrile (PAN), pitch (pitch), and cellulose (cellulose) carbon fibers. Preferably, the aforementioned short fiber may include one or more selected from the group consisting of aramid, polyimide, and thermosetting polymer.

The above-mentioned fibrous base material is made up of short fibers as described above arranged in a three-dimensional form, and when short fibers are used, the short fibers themselves can usually be stretched 1.5 to 20 times compared with the initial discharge speed. The polyimide polymer film produced in an unstretched state is less than 1.5 times larger than that formed with a higher oriented structure, so that higher thermal conductivity can be achieved through the graphitization process. In addition, when the above-mentioned fiber substrate is used as a raw material for forming a graphite sheet, because it has a 3-dimensional isotropic structure, the difference in thermal conductivity in the horizontal and vertical directions is relatively lower than that of a 2-dimensional polymer film. , Which can effectively improve the thermal conductivity of the graphite sheet in the vertical direction.

The fibrous base material is a three-dimensional porous structure containing pores inside, and may be in the form of a sheet, a fabric, or a mesh.

Therefore, the above-mentioned fiber substrate can be, for example, paper, nonwoven, woven, knit, felt, mat, prepreg or Nano web and so on.

The manufacturing method of the said fibrous base material is not specifically limited, The method well-known to a general technician or various methods which deform|transform it can be utilized. For example, dry laid, wet-laid, spinning, air-laid, melt-blown, laminated Stretching method and other methods.

The fibrous base material can contain commonly used substances in addition to the short fibers. As an example, it is possible to include binder fibers, surfactants, dispersants, thickeners, etc. for bonding the short fibers constituting the fibrous base material and reinforcing the fibrous base material.

Among them, in order to make the processing in the subsequent steps easier by increasing the strength of the fiber base material and minimize the pores existing in the fiber base material, the three-dimensional porous structure contains pores between the short fibers. And the bulk density (bulk density) is about 10 to 60% of the inherent density (inherent density) of the initial fibrous base material, the air eventually contained in the pores inside the fibrous base material will hinder heat conduction, so by using rolling The manufacturing method removes air and increases the bulk density of the fiber substrate, which can ensure the thermal conductivity of the finally manufactured graphite sheet, especially the improvement effect of the thermal conductivity in the vertical direction.

The above-mentioned rolling can be performed by a general method known in the industry. The rolling temperature and pressure can be adjusted according to the above-mentioned fibrous base material or the short fibers contained therein. For example, the above-mentioned rolling can be performed with a pressure of 30 to 200 ㎏f/㎝ in the case of continuous production at a temperature of 80 to 200 ℃, while in the sheet rolling method, it can be set to the spinning effect of the continuous production method. Similar level.

In order to better improve the thermal conductivity and other physical properties of the final product, that is, the graphite sheet, the thickness of the fibrous substrate after rolling is preferably 40 to 80% of the thickness of the fibrous substrate before rolling. In order to better improve the thermal conductivity and other physical properties of the final product, that is, the graphite sheet, the air permeability of the fibrous substrate after rolling is preferably 0.1 to 45% of the air permeability of the fibrous substrate before rolling. Step ( S2 )

In the above step (S2), a composite substrate is manufactured by impregnating the fiber substrate obtained in the above step (S1) with a thermal interface material (TIM).

In the present invention, the composite substrate can be impregnated to fill the pores of the fibrous substrate manufactured in the above step (S1) with a thermally conductive interface material and completely remove air, thereby increasing the interface contact between short fibers and This improves the thermal conductivity of the final graphite sheet in the horizontal and vertical directions.

The type of the aforementioned thermally conductive interface material is not particularly limited, as long as it is a polymer with a carbon component of 50% or more. For example, the aforementioned thermally conductive interface material can be made of polyimide (PI), lignin, aramid, poly(amideimide, PAI), polyimide One or more selected from the group consisting of chemically cured thermoplastic resins such as polypropylene (PP) and phenol resins. Preferably, the above-mentioned thermally conductive interface substance can include a component composed of carbon elements. One or more selected from the group consisting of high and relatively easy-to-control viscosity resins.

The composite substrate can be obtained by impregnating the fibrous substrate obtained in the step (S1) in a varnish composition containing the thermally conductive interface material.

As an example of the above-mentioned impregnation method, a method of impregnating the above-mentioned fibrous substrate in a varnish composition containing the above-mentioned thermally conductive interface substance, and coating the above-mentioned varnish composition containing the above-mentioned thermally conductive interface substance by various coating machines are included. The method of fiber base material, the method of infiltrating the varnish composition containing the said thermally conductive interface substance into the said fiber base material using a spray, etc. are not limited to this. Preferably, the method of impregnating the fibrous substrate in the varnish composition containing the thermally conductive interface substance can improve the impregnation of the fibrous substrate in the varnish composition.

The content of the thermally conductive interface substance in the varnish composition can be 10 to 80% by weight, preferably 30 to 60% by weight based on 100% by weight of the entire varnish composition. When the content of the above-mentioned thermally conductive interface substance is lower than the above-mentioned range, the increase in density is limited because the pores in the substrate cannot be fully filled, and therefore the resistance increases. On the contrary, when the number of rows exceeds the range, it may be caused by If the viscosity is too high, the uniformity of impregnation will decrease. Therefore, it is better to determine an appropriate content within the above-mentioned range.

The composite substrate is manufactured by curing and drying the fibrous substrate impregnated with the varnish composition. At this time, the above-mentioned curing and drying conditions can be adjusted according to the type of substance used.

Therefore, the content of the thermally conductive interface substance in the composite substrate can be 40 to 80% by weight based on 100% by weight of the composite substrate.

In order to achieve the effect of improving thermal conductivity, the composite substrate may further include a filler.

The filler can be a ceramic or polymer material, and the polymer material can be the same material as the short fibers constituting the fiber base material. In addition, in order to achieve the purpose of filling the pores inside the fibrous base material, the form of the filler is preferably in the form of particles or powder instead of chop or fiber.

The above-mentioned fillers can include carbon nanotubes (CNT), graphene (single-well carbon nanotube, SWCNT), multi-well carbon nanotube (MWCNT) and other carbon nanotubes (CNT), graphene (single-well carbon nanotube, SWCNT), etc. Graphene), graphite powder (graphite powder), conductive carbon black (carbon black), and boron nitride nanotube (BNNT) selected from one or more types.

The diameter of the above-mentioned carbon nanotubes can be 4 to 50 ㎚, and the length can be 1 to 500 ㎛.

The diameter of the above-mentioned boron nitride nanotubes can be 0.01 to 3 ㎛, preferably 0.1 to 1.0 ㎛.

When the diameter and length of the carbon nanotubes and the diameter of the boron nitride nanotubes exceed the above ranges, it may lead to a slight or engineering problem in which the effect of improving the thermal conductivity of the finally manufactured graphite sheet in the vertical direction is negligible.

The filler can be impregnated into the fibrous base material by being included in the varnish composition as described above.

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 manufactured through the above step (S2) has a three-dimensional porous structure, which contains pores between short fibers, and its bulk density is about 10 to 60% of the inherent density. . Because in the subsequent step, carbonization and graphitization, many components other than carbon will be thermally volatilized and cause weight loss. Therefore, in order to make the processing easier, the strength of the composite substrate needs to be increased and will exist on the fiber substrate. The internal voids are minimized.

In addition, the air contained in the pores inside the composite substrate will hinder heat conduction. Therefore, by removing the air by rolling and increasing the bulk density of the composite substrate, the thermal conductivity of the final graphite sheet can be ensured. Especially the improvement effect of the thermal conductivity in the vertical direction.

The temperature and pressure of the rolling can be adjusted according to the fiber substrate or the varnish composition. For example, the above-mentioned rolling can be performed with a pressure of 30 to 250 ㎏f/cm in the case of continuous production at a temperature of 100 to 350°C, while in the sheet rolling method, it can be set to the spinning effect of the continuous production method. Similar level.

In order to better improve the thermal conductivity and other physical properties of the final product, that is, the graphite sheet, the thickness of the composite substrate after the rolling is preferably 95% of the thickness of the fibrous substrate before the rolling.

The increase rate of the bulk density after the rolling is preferably 40 to 95% of the average density of the fibrous base material and the thermally conductive cross-sectional material. When the increase rate of the above-mentioned bulk density is less than the above-mentioned range, excessive pores will be formed after the subsequent carbonization and graphitization work, which will lead to the reduction of the heat dissipation effect. On the contrary, when the above-mentioned range is exceeded, the final product, namely the graphite sheet Decreased flexibility leads to fragile problems. Step ( S3 )

In the above step (S3), carbonization and graphitization are performed by heat treatment of the composite base material obtained in the above step (S2), thereby manufacturing a graphite sheet.

The purpose of the above heat treatment is to improve the thermal properties of the composite substrate, and is not particularly limited, as long as it is a general method for carbonization and graphitization of polymers and/or fibers, and it can use general methods known in the industry. The method is executed.

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

In order to avoid the oxidation reaction between the composite substrate and air, the carbonization and graphitization are preferably performed in an inert gas environment. The medium used to maintain the above-mentioned inert gas environment is not particularly limited, and nitrogen or argon can be used.

In addition, the above-mentioned carbonization and graphitization time can be adjusted according to the material constituting the above-mentioned composite substrate. Step ( S4 )

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

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

The above-mentioned rolling can be performed by a general method known in the industry.

The above-mentioned rolling pressure can be adjusted according to the physical properties of the produced graphite flakes. For example, the aforementioned rolling can be performed under a pressure of 10 to 300 ㎏f/cm.

The graphite sheet manufacturing method of the present invention can be manufactured by using a fibrous substrate as a precursor of the graphite sheet, impregnating the fibrous substrate with a thermally conductive interface substance, and performing a rolling process before and after carbonization and graphitization. Graphite sheet with excellent thermal conductivity in the vertical direction and thermal conductivity in the vertical direction. In addition, the above-mentioned graphite sheet manufacturing method does not require the use of an expensive polymer film as a precursor, and it is possible to more economically manufacture a graphite sheet with excellent thermal conductivity in the horizontal and vertical directions through a simple process.

The thermal conductivity of the graphite sheet manufactured by the above method in the horizontal direction can be 1,000 to 2,000 W/m·K, the thermal conductivity in the vertical direction can be 10 to 40 W/m·K, and the average thickness can be It is 10 to 200㎛.

In particular, the vertical thermal conductivity of the graphite sheet to which the present invention is applied can reach the limit of the thermal conductivity of the existing graphite sheet in the vertical direction, and because its flexibility is improved, it can be used as a heat sink for various electronic devices. Wait for use.

Next, in order to facilitate the understanding of the present invention, preferred embodiments are introduced, but the following embodiments are only used to illustrate the present invention, and relevant practitioners should be able to understand that the present invention can be carried out within its scope and the scope of technical ideas. Various changes and modifications, as described above, are all included in the scope of the appended claims. [Examples and Comparative Examples] [Example 1]

Aramid staple fiber with a length of 6 mm, aramid pulp, and polyvinyl alcohol with a length of 3 mm as a binder fiber are mixed in a weight ratio of 25:72:3, and the method is wet-laid. Manufacture a fibrous base material.

The above-mentioned fibrous base material was rolled at a temperature of 120°C and a pressure of 148 ㎏f/cm.

Next, the rolled fibrous base material is impregnated in a varnish composition containing 10% by weight of polyimide in a padder mangle, and then dried at 130°C and cured at 350°C , Thereby manufacturing a composite substrate.

The above-mentioned composite base material was rolled at a temperature of 200°C and a pressure of 200 ㎏f/cm.

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

Next, the carbonized composite substrate was graphitized in an argon atmosphere at 2,800°C, and then rolled under a pressure of 30 ㎏f/cm to produce graphite flakes. [Example 2]

Except that a varnish composition containing 20% by weight of polyimide was used in the production of the composite substrate, graphite flakes were produced in the same manner as in Example 1 above. [Example 3]

Except that short fibers, pulp, and binder fibers were used in a weight ratio of 50:47:3 when manufacturing the fibrous base material, graphite sheets were manufactured in the same manner as in Example 1 above. [Example 4]

In addition to the use of short fibers, pulp, and binder fibers in a weight ratio of 50:47:3 when manufacturing the fiber substrate, and the use of a varnish composition containing 20% by weight of polyimide when manufacturing the composite substrate Otherwise, a graphite sheet was produced in the same manner as in Example 1 above. [Example 5]

Except that short fibers, pulp, and binder fibers were used in a weight ratio of 60:37:3 when manufacturing the fibrous base material, graphite sheets were manufactured in the same manner as in Example 1 above. [Example 6]

In addition to the use of short fibers, pulp, and binder fibers in a weight ratio of 60:37:3 when manufacturing the fibrous substrate, and the use of a varnish composition containing 20% by weight of polyimide when manufacturing the composite substrate Otherwise, a graphite sheet was produced in the same manner as in Example 1 above. [Example 7]

Except that short fibers, pulp, and binder fibers were used in a weight ratio of 70:27:3 when manufacturing the fibrous base material, graphite sheets were manufactured in the same manner as in Example 1 above. [Example 8]

In addition to the use of short fibers, pulp, and binder fibers in a weight ratio of 70:27:3 when manufacturing the fibrous substrate, and the use of a varnish composition containing 20% by weight of polyimide when manufacturing the composite substrate Otherwise, a graphite sheet was produced in the same manner as in Example 1 above. [Comparative Example 1]

Graphite sheets are manufactured by carbonizing and graphitizing a polyimide film with a thickness of 75 mm. At this time, carbonization is performed at 900°C, and graphitization is performed at 2,800°C. Test Example 1. Physical property evaluation and scanning electron microscope analysis of fibrous base material

The weight, thickness, and air permeability of the fiber base materials manufactured in Examples 1, 3, 5, and 7 were measured. At this time, the air permeability was measured with an Air Permeability Tester (FX3300, manufactured by Textest Instruments).

In addition, the surface and cross section of the fibrous base material manufactured in Example 1 were observed with a scanning electron microscope (SEM). As the scanning electron microscope, Hitachi S-4800 was used.

The results obtained at this time are shown in Table 1, Figure 1 and Figure 2. [Table 1] Weight per unit area (g/㎡) Thickness (㎛) Breathability 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 Fig. 1, it can be confirmed that a fibrous substrate with a three-dimensional porous structure composed of aramid short fibers and having pores formed therein was manufactured. Test Example 2. Physical property evaluation and scanning electron microscope analysis of fibrous base material after rolling

The weight per unit area, thickness, and air permeability of the fibrous base materials produced in Examples 1, 3, 5, and 7 after rolling were measured. At this time, the air permeability was measured with an air permeability tester (FX3300, manufactured by Textest Instruments).

In addition, a scanning electron microscope (SEM) was used to observe the surface and cross section of the fibrous base material manufactured in Example 1 before and after rolling. As the scanning electron microscope, Hitachi S-4800 was used.

The results obtained at this time are shown in Table 2 and Figure 3. [Table 2] Weight per unit area (g/㎡) Thickness (㎛) Breathability 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 above, it can be confirmed that the thickness and air permeability of the fibrous base material can be reduced by rolling. Test example 3. Physical property evaluation and scanning electron microscope analysis of composite substrate

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

The result obtained at this time is shown in Figure 4.

Referring to Fig. 4, it can be confirmed that the varnish composition is uniformly impregnated into the fiber substrate. Test Example 4. Physical property evaluation and scanning electron microscope analysis of the composite substrate after rolling

The weights of the composite substrates produced in Examples 1 to 8 after rolling and the thicknesses before and after rolling were measured.

In addition, a scanning electron microscope (SEM) was used to observe the surface and cross-section of the composite substrate manufactured in Example 1 after rolling. As the scanning electron microscope, Hitachi S-4800 was used.

The results obtained at this time are shown in Table 3 and Figure 5. [table 3] Concentration of thermally conductive interface 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 above, it can be confirmed that the thickness of the composite substrate can be reduced by rolling. Test Example 5. Physical property evaluation and scanning electron microscope analysis of graphite sheet

The weight and yield of the graphite flakes produced in Examples 1 to 8 were measured when carbonization and graphitization were performed.

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

The results obtained at this time are shown in Table 4 and Figure 6. [Table 4] Carbonization Graphitization Total yield (%) Weight (g) Yield (%) Weight (g) Yield (%) 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

Referring to Figure 6, it can be confirmed that the color of the composite substrate turned black after carbonization, and turned silver after graphitization.

In addition, referring to Table 4 above, it can be confirmed 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%. Test Example 6. Thermal conductivity measurement of graphite sheet

The horizontal and vertical thermal conductivity of the graphite sheets manufactured in Example 1 and Comparative Example 1 were measured. At this time, the thermal conductivity in the horizontal and vertical directions is measured by using the graphite sheets manufactured in Example 1 and Comparative Example 1 with a thermal diffusivity measuring device based on the light exchange method (product of Netsch Corporation [LFA447 Nanoflash]) The measurement was performed 5 times or more at a temperature of 25°C and the average value was calculated. The results obtained at this time are shown in Table 5. [table 5] Horizontal thermal conductivity (W/m·K) Thermal conductivity in vertical direction (W/m·K) Example 1 800 twenty three Comparative example 1 1,200 5

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

no

Fig. 1 is a scanning electron microscope (SEM) photograph of the surface of a fiber substrate to which Example 1 of the present invention is applied. Fig. 2 is a scanning electron microscope (SEM) photograph of a cross-section of a fiber substrate of Example 1 to which the present invention is applied. Fig. 3 is a scanning electron microscope (SEM) photograph of a cross section of a fiber substrate of Example 2 to which the present invention is applied before and after rolling. Fig. 4 is a scanning electron microscope (SEM) photograph of a cross-section of a composite substrate according to Example 3 of the present invention. Fig. 5 is a scanning electron microscope (SEM) photograph of a cross section of a composite substrate according to Example 4 of the present invention after rolling. Fig. 6 is a scanning electron microscope (SEM) photograph of the carbonized and graphitized graphite sheet surface according to Example 5 of the present invention.

Claims (10)

A method for manufacturing a graphite sheet, which is characterized in that it comprises: (S1) Steps to use short fibers to make a fibrous base material; (S2) A step of manufacturing a composite substrate by impregnating the fibrous substrate obtained in this step (S1) with a thermally conductive interface substance; (S3) A step of carbonizing and graphitizing the composite substrate obtained in this step (S2) by heat treatment, thereby manufacturing a graphite sheet; and, (S4) A step of rolling the graphite sheet obtained in this step (S3). The method for manufacturing a graphite sheet according to claim 1, characterized in that: The short fiber includes one or more selected from the group consisting of aramid, polyimide, thermoplastic polymer, heat-fixing polymer, and carbon fiber. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The fibrous base material is a three-dimensional porous structure. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The fiber substrate is in the shape of a sheet, a fabric or a net. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The thermally conductive cross-sectional material includes one or more selected from the group consisting of polyimide, lignin, aramid, polyimide, polypropylene, and phenol. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The composite substrate also contains fillers. The method for manufacturing a graphite sheet according to claim 6, characterized in that: The filler includes one or more selected from the group consisting of carbon nanotubes, graphene, graphite powder, conductive carbon black, and boron nitride nanotubes. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The carbonization is performed at a temperature of 800 to 1,500°C. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The graphitization is performed at a temperature of 2,600 to 3,000°C. The method for manufacturing a graphite sheet according to claim 1, characterized in that: The carbonization and graphitization are performed in an inert gas environment.

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